Stainless Steel: Types, Grades and Finishes.

Choosing the right type of stainless steel isn’t always obvious. Different families, grades and finishes behave very differently in service depending on your application and project needs. Knowing what to consider when selecting your precision components is crucial.

This guide gives you a fast, practical route to material specification for your engineering projects: a simple A2 vs A4 selector, a clear stainless steel grades chart that maps common material naming to ISO/AISI/EN/UNS, side‑by‑side comparisons like 304 vs 316 and a compact overview of the five types of stainless steel material available more broadly and their grades.
Once you have a strong overview of your desired grade of stainless steel for your application, you will be able to specify your fasteners correctly the first time, every time.

Contents:

• The 5 Types of Stainless Steel.
• Crystalline Structure and Why It Matters.
• Magnetic vs Non‑Magnetic Stainless Steel.
• The most common Stainless Steel Grades Chart.
  (Stainless Steel Grades Explained)
• Austentic Stainless Steel Grades.
• Austentic Stainless Steel Comparisons.
• Ferritic Stainless Steel Grades.
• Martensitic Stainless Steel Grades.
• Duplex Stainless Steel Grades.
• Precipitation Hardening Stainless Steel Grades.
• Stainless Steel Finishes (Fastener‑Relevant).
• How to Specify Stainless Steel For Your Projects.

 

The 5 Types of Stainless Steel.

Austenitic Stainless Steel.

The most common family for fasteners and general fabrications. It offers excellent corrosion resistance with very good formability and high toughness, even at low temperatures. 
In the annealed state, it’s generally non-magnetic, although heavy cold-work can induce some magnetism. These grades aren’t hardenable by heat treatment, but they will work-harden quickly, so thread forming, deep-draw and spinning often need staged operations. Weldability is good; use low-carbon or stabilised variants for thick sections to reduce sensitisation.

Typical grades: 304 (A2) and 316/316L (A4).
Uses: general assemblies, food equipment, architectural fixings, marine components (A4).

Ferritic Stainless Steel.

Ferritics have a body-centred cubic (BCC) structure and are magnetic. They’re typically lower cost than austenitics and bring decent scaling resistance, moderate corrosion resistance and very good resistance to stress-corrosion cracking. Strength and toughness are lower than austenitics, especially at sub-zero temperatures, but thermal expansion is lower too, which can help in cyclic-heat applications with tight tolerances. They are not hardenable by heat treatment (except minor strengthening by cold-work), and weldability varies with grade, with stabilised types performing best.

Example grades: 430, 446 (EN 1.4016, 1.4762).
Uses: automotive exhausts, industrial equipment, and appliances.

Martensitic Stainless Steel.

Martensitics possess a body-centred tetragonal (BCT) structure after hardening. They are heat treatable to achieve high hardness and wear resistance and are magnetic in all conditions. Corrosion resistance sits below austenitics and ferritics, so surface finish and correct tempering matter; free-machining variants trade more corrosion resistance for productivity. Preheat, controlled cooling and tempering are important to avoid cracking in thick or highly constrained parts.
Example grades: 410, 420, 440C (EN 1.4006, 1.4021, 1.4125).
Uses: tools, knives, and certain high‑strength fasteners.

Duplex Stainless Steel.

Duplex steels have a mixed austenitic/ferritic microstructure, delivering high yield strength (roughly double that of 304/316) with excellent resistance to pitting, crevice attack and chloride stress-corrosion cracking. They are magnetic due to the ferritic phase and are not hardenable by heat treatment, though they do work-harden under forming. Welding requires control of heat input to preserve phase balance when done correctly. They provide robust performance from splash zones to immersed service.

Example grades: 2205 (EN 1.4462), 2304 (EN 1.4362), 2507 (EN 1.4410), S32760/Zeron 100 (EN 1.4501).
Uses: chemical processing, offshore/marine, high‑load structures, duplex stainless steel fasteners.

 

Precipitation Hardening (PH) Stainless Steel.

PH grades are strengthened by ageing heat treatment to deliver very high tensile properties with useful corrosion resistance. Most are magnetic (martensitic or semi-austenitic matrices), and they’re supplied solution-treated then aged to the specified condition (e.g. H900/H1025). They machine and fabricate well in the solution state, with final ageing applied after forming or machining to lock in strength. Corrosion resistance typically sits between 304 and 410, so avoid tight crevices in chloride-rich service.

Examples: 17‑4PH (EN 1.4542), 15‑5PH (EN 1.4545), 17‑7PH (EN 1.4568).
Uses: aerospace and high‑performance components.

 

Crystalline Structure and Why It Matters.

Crystal structure underpins how stainless steels behave in service.
It explains why some grades bend and form easily, why others harden with heat, and why magnetism appears in one family but not another.

Understanding FCC, BCC and BCT makes selection faster. You’ll know when to choose 316L for welded hygienic equipment, when a martensitic grade delivers the clamp load you need, and when duplex pays off in chlorides. This section links the structure to properties so you can scan the various grades of stainless steel chart and A2/A4 selector with confidence.
Use it as a quick technical refresher before finalising material and finish.

Austenitic (FCC) steels such as 304/316 offer toughness and ductility with reliable corrosion resistance; they’re generally non‑magnetic when annealed and aren’t hardenable by heat treatment.

Ferritic (BCC) steels such as 430/446 are magnetic and less ductile; they resist stress‑corrosion cracking better than austenitics in certain media such as hot chloride enviroments, hypochlorite streams and refinery conditions.

Martensitic (BCT) steels such as 410/420/440C are magnetic and hardenable by heat treatment, giving high strength and wear resistance but reduced corrosion performance compared to austenitic stainless steels.

Duplex grade steels such as 2205/2507 comprise roughly 50/50 austenite and ferrite, delivering high yield strength (about twice that of 304/316) plus strong resistance to chloride pitting, crevice attack and stress-corrosion cracking. They’re slightly magnetic and remain weldable, but need controlled heat input to keep the phase balance. Use duplex where you need higher clamp load and chloride resilience.


Precipitation-hardening (PH) stainless steels such as 17-4PH and 15-5PH, gain strength from a two-step heat treatment: solution treat, then age treatment. Ageing at 480–620 °C creates fine precipitates (Cu-rich in 17-4PH) that pin dislocations, delivering very high proof/tensile strength while retaining stainless corrosion resistance.

Magnetic vs Non‑Magnetic Stainless Steel.

The material's crystal structure drives magnetism: FCC (austenitic) is typically non‑magnetic when annealed, BCC/BCT (ferritic/martensitic) are magnetic, while duplex sits between being only slightly magnetic. It's also worth remembering that cold work can shift behaviour, turning austenitic grades slightly magnetic over time. The table below shows the different types of stainless steel and their magnetic properties by family.

When is magnetism desirable?

Where components interact with electromagnetic devices (EMI shielding, motors, sensors), controlled magnetism may be required. For food, medical or architectural uses, magnetism is rarely a performance requirement; corrosion resistance and hygiene are the priority.

The Most Common Stainless Steel Grades Chart. (Stainless Steel Grades Explained) 

Use this ss grades chart to translate between the most common standard material names and common standards of the different grades of stainless steel (ISO 3506, AISI/SAE, EN and UNS). Start with the left column, then cross‑check the adjacent standards and notes.

Can't find the specific steel you are looking for in this table?
The further sections in this article extensively cover all stainless steel grades within the five families as laid out previously. Use the grid at the article introduction for quick navigation to your desired material. 

Austentic Stainless Steel Grades.

301 Stainless Steel.

Overview:
High work-hardening 18/8 for springs and formed steel strip; strong after cold-working.

Also known as:
AISI 301; EN 1.4310 (X10CrNi18-8); UNS S30100.

Typical uses:
Clips, springs, hose clamps, architectural strip steel.

Notes & limitations:
Becomes magnetic when heavily cold-worked; use 304/305 for deep-draw.

Magnetism:
Non-magnetic in annealed condition; becomes clearly magnetic after cold-work.

Hardness, hardenability & temperature limits:
Annealed HB 150–200 (approx. HRC 10–20); work-hardens to HB 250–380 depending on reduction. Not hardenable by heat treatment. Usable to 870 °C in dry air; good toughness to cryogenic temperatures.

Standards & certification:
Typical: sheet/plate EN 10088 / ASTM A240; bar A276/A479; tube A213/A269. MTRs to EN 10204 3.1 as standard, 3.2 by agreement.

Fasteners & markings:
Not a standard ISO 3506 fastener family; use A2/A4 where property class marking is required.

302 Stainless Steel.

Overview:
Close to 304 but slightly higher carbon; a touch stronger, a touch less weld-forgiving.

Also known as:
AISI 302; UNS S30200.

Typical uses:
Wire, springs, fastener wire.

Notes & limitations:
Higher carbon can reduce corrosion resistance if sensitised; consider 304L when welding.

Magnetism:
Non-magnetic annealed; becomes mildly magnetic after cold-work.

Hardness, hardenability & temperature limits:
Annealed HB 150–190; work-hardened wire is significantly higher. Not heat-treatable. Similar service limits to 304: up to 870 °C (dry air); good cryogenic toughness.

Standards & certification:
A240 (plate), A276/A479 (bar), A313 (spring wire). EN 10204 3.1 standard; 3.2 on request.

Fasteners & markings:
Not a designated ISO 3506 fastener family; select A2/A4.

303 (A1) Stainless Steel.

Overview:
Free-machining 18/8 Stainless Steel with sulphur for easy turning; corrosion resistance lower than 304.

Also known as:
A1 fastener family; AISI 303; EN 1.4305 (X8CrNiS18-9); UNS S30300.

Typical uses:
Turned parts, spacers, precision-machined screws, fittings.

Notes & limitations:
Avoid marine/chloride service; sulphides reduce pitting resistance.

Magnetism:
Generally non-magnetic annealed; can show slight magnetism after heavy cold-work.

Hardness, hardenability & temperature limits:
Annealed HB 170–200. Not heat-treat hardenable; work-hardens modestly. Service to 870 °C in dry air; good cryogenic toughness but choose 304/316 for best corrosion.

Standards & certification:
Bar A582/A276; EN 10088 bars. EN 10204 3.1 standard; 3.2 by agreement.

Fasteners & markings:
Available as A1 under ISO 3506 with low property classes for dry, non-corrosive interiors. Markings show A1-50/55 and other A1 codes. Avoid for wet/chloride use.

304 (A2) family Stainless Steels (includes 304L / 304H) - “18/8/ 18/10”.

Overview:
Workhorse 18/8 for general corrosion resistance, fabrication, hygiene. 304L: low-carbon for welding. 304H: high-carbon for creep strength at temperature. “18/8” and “18/10” are common composition labels within 304.

Also known as:
A2 (ISO 3506 fasteners); AISI 304/304L/304H; EN 1.4301 / 1.4307 / 1.4948; UNS S30400 / S30403 / S30409.

Typical uses:
A2-70 bolts/screws, food equipment, enclosures, sinks and structural fabrications.

Notes & limitations:
Not for chlorides or coastal splash; consider 316/A4.

Magnetism:
Non-magnetic annealed; becomes slightly magnetic after cold-work (fastener threads/heads may attract a magnet).

Hardness, hardenability & temperature limits:
Annealed HB 150–190. Not heat-treat hardenable; work-hardens during forming/fastening. 304H supports improved creep strength in 500–700 °C service with strong oxidation resistance up to 870 °C. Excellent cryogenic toughness to liquid-nitrogen temperatures.

Standards & certification:
Sheet/plate A240; bar A276/A479; pipe A312; tube A213/A269; fasteners ISO 3506-1/-2. EN 10204 3.1 standard; 3.2 on request.

Fasteners & markings:
A2-70 / A2-80 common. Heads marked A2 plus the property class and maker’s mark (e.g., A2-70). Use lubrication/anti-seize to reduce galling.

305 Stainless Steel.

Overview:
High-nickel 18/8 Stainless steel with low work-hardening; optimised for deep-draw without intermediate anneals.

Also known as:
AISI 305; UNS S30500.

Typical uses:
Pressings, deep-drawn housings, battery cans.

Notes & limitations:
Strength lower than 301 after forming; corrosion roughly 304-like.

Magnetism:
Non-magnetic annealed; remains largely non-magnetic after deep drawing.

Hardness, hardenability & temperature limits:
Annealed HB 140–180. Not heat-treat hardenable; minimal work-hardening. Service to 870 °C; excellent cryogenic toughness.

Standards & certification:
A240 (sheet/plate), A666 (sheet/strip). EN 10204 3.1/3.2 as above.

Fasteners & markings:
Not an ISO 3506 fastener family.

309 Stainless Steel.

Overview:
Heat-resistant Cr-Ni for oxidation resistance to 1,000–1,090 °C; better than 304 in hot atmospheres.

Also known as:
AISI 309/309S; UNS S30900/S30908; EN 1.4828.

Typical uses:
Furnace parts, heat shields, boiler baffles.

Notes & limitations:
Not for strongly carburising atmospheres; the 310 family performs better at the top end.

Magnetism:
Non-magnetic annealed; slight magnetism possible after cold-work.

Hardness, hardenability & temperature limits:
Annealed HB 160–200. Not heat-treatable. Oxidation resistance to 1,000+°C; fair cryogenic toughness, though usually chosen for high temperature applications.

Standards & certification:
A240 (plate), A276/A479 (bar), A312 (pipe). EN 10204 3.1 / 3.2.

Fasteners & markings:
Not used for ISO 3506 fasteners.

310 / 310S family Stainless steels.

Overview:
High Cr/Ni heat-resistant austenitic; oxidation resistant to 1,050–1,150 °C. 310S is low-carbon for welded service.

Also known as:
AISI 310/310S/310H; UNS S31000/S31008/S31009; EN 1.4841 / 1.4845.

Typical uses:
Furnace furniture, radiant tubes, kilns, heat exchangers.

Notes & limitations:
Moderate resistance to carburisation; select carefully for cycling/nitriding.

Magnetism:
Non-magnetic annealed; may become slightly magnetic after heavy cold-work.

Hardness, hardenability & temperature limits:
Annealed HB 160–200. Not hardenable by heat treatment. Continuous service commonly up to 1,050 °C (environment dependent). Austenitic toughness is retained at low temperatures.

Standards & certification:
A240, A276/A479, A312. EN 10204 3.1 standard; 3.2 on request.

Fasteners & markings:
Not typically an ISO 3506 fastener family material.

316 (A4) family Stainless Steels (includes 316L / 316Ti) - “marine grade”.

Overview:
Molybdenum-bearing 18/10 Stainless Steel for improved chloride pitting/crevice resistance; 316L for welding; 316Ti stabilised for high-temp/welded service. A4 fasteners are 316-based; “-70” ≈ 700 MPa class.

Also known as:
A4 (ISO 3506 fasteners); AISI 316/316L/316Ti; EN 1.4401 / 1.4404 / 1.4571; UNS S31600 / S31603 / S31635.

Typical uses:
Marine fixings, pumps/valves, pharma/food kit, A4-70 bolts/screws.

Notes & limitations:
Warm, stagnant chloride crevices still risky; for severe chlorides, consider 317L/6Mo/duplex.

Magnetism:
Non-magnetic annealed; may become mildly magnetic after cold-work or heading.

Hardness, hardenability & temperature limits:
Annealed HB 150–200. Not heat-treat hardenable; work-hardens during forming/assembly. Oxidation to 870 °C; good creep strength for 316Ti in mid-temperatures; excellent cryogenic toughness.

Standards & certification:
A240, A276/A479, A312/A213. EN 10204 3.1 standard; 3.2 by agreement.

Fasteners & markings:
A4-70 / A4-80 common. Heads marked A4-70 etc. Use anti-seize to prevent galling; consider A4-80 for higher strength.

317L Stainless Steel.

Overview:
Higher-Mo austenitic with stronger resistance to localised attack than 316L; low-carbon for welds.

Also known as:
AISI 317L; UNS S31703; EN 1.4438.

Typical uses
Chemical process equipment, pulp & paper, flue-gas scrubbers.

Notes & limitations:
Costlier than 316; for extreme chlorides, move to 6% Mo (e.g., 254 SMO).

Magnetism:
Non-magnetic annealed; slight magnetism after heavy cold-work.

Hardness, hardenability & temperature limits:
Annealed HB 160–200. Not heat-treatable. Service to 870 °C; excellent cryogenic toughness.

Standards & certification:
A240, A276/A479, A312/A213. MTR 3.1 standard; 3.2 on request.

Fasteners & markings:
Not a designated ISO 3506 fastener family (use A4).

321 Stainless Steel.

Overview:
Ti-stabilised 304-type for resistance to sensitisation (weld HAZ); suited to 540–815 °C service.

Also known as:
AISI 321/321H; EN 1.4541 / 1.4878; UNS S32100 / S32109.

Typical uses:
Exhaust manifolds, expansion joints, stack liners.

Notes & limitations:
Polishing response is limited by Ti, not a pitting upgrade over 304.

Magnetism:
Non-magnetic annealed; slight magnetism after cold-work.

Hardness, hardenability & temperature limits:
Annealed HB 150–190. Not heat-treatable. Better resistance to intergranular attack at 500–800 °C than 304; good cryogenic toughness.

Standards & certification:
A240, A276/A479, A312. EN 10204 3.1/3.2.

Fasteners & markings:
Not an ISO 3506 fastener family.

347 Stainless Steel.

Overview:
Nb-stabilised 304-type; resists intergranular attack after exposure to 427–899 °C; weld-friendly.

Also known as:
AISI 347/347H; EN 1.4550 / 1.4961; UNS S34700 / S34709.

Typical uses:
Boiler tubes, exhaust stacks, chemical process piping.

Notes & limitations:
Corrosion resistance 304; not a chloride upgrade.

Magnetism:
Non-magnetic annealed; may become slightly magnetic after cold-work.

Hardness, hardenability & temperature limits:
Annealed HB 150–190. Not heat-treatable. Designed for service 540–870 °C; good cryogenic toughness.

Standards & certification:
A240, A276/A479, A312/A213. EN 10204 3.1/3.2.

Fasteners & markings:
Not an ISO 3506 fastener family.

201 Stainless Steel.

Overview:
Low-nickel 200-series austenitic (Cr-Mn-N) with higher work-hardening; economical 301/304 alternative in mild environments.

Also known as:
AISI 201; EN 1.4372; UNS S20100.

Typical uses:
Appliance trim, catering interiors, decorative sheet.

Notes & limitations:
Lower chloride resistance than 304; can become magnetic when cold-worked.

Magnetism:
Non-magnetic annealed; becomes magnetic after significant cold-work.

Hardness, hardenability & temperature limits:
Annealed HB 150–190. Not heat-treat hardenable; work-hardens readily. Service to 870 °C; fair cryogenic toughness.

Standards & certification:
A240, A666. EN 10204 3.1.

Fasteners & markings:
Not an ISO 3506 fastener family.

202 Stainless Steel.

Overview:
Cr-Ni-Mn austenitic as a cost-reduced 300-series substitute; decent toughness, moderate corrosion resistance.

Also known as:
AISI 202; UNS S20200.

Typical uses:
Kitchenware, automotive trim, building components.

Notes & limitations:
Not for coastal/marine service; chloride pitting risk vs 304/316.

Magnetism:
Non-magnetic annealed; becomes magnetic after heavy cold-work.

Hardness, hardenability & temperature limits:
Annealed HB 150–190. Not heat-treatable. Service to 870 °C; fair cryogenic toughness.

Standards & certification:
A240, A666. EN 10204 3.1.

Fasteners & markings:
Not an ISO 3506 fastener family.

904L Stainless Steel.

Overview:
Super-austenitic with high Ni/Cr + Cu; strong resistance to reducing acids (e.g. sulphuric) and chlorides.

Also known as:
Alloy 904L; EN 1.4539; UNS N08904.

Typical uses:
Pharma/chemical plant, fertiliser equipment, marine fittings.

Notes & limitations:
More difficult to machine; higher cost than standard 300-series.

Magnetism:
Non-magnetic annealed; may show slight magnetism after heavy cold-work.

Hardness, hardenability & temperature limits:
Annealed HB 160–200. Not heat-treatable. Service to 870 °C; good cryogenic toughness.

Standards & certification:
A240, A276/A479, A312. EN 10204 3.1/3.2.

Fasteners & markings:
Not an ISO 3506 fastener family.

254 SMO Stainless Steel (6% Mo)

Overview:
6 Mo super-austenitic with very high pitting/crevice resistance; chloride-rich service specialist.

Also known as:
EN 1.4547; UNS S31254; 254 SMO.

Typical uses:
Seawater heat exchangers, offshore, pulp & paper bleach plant.

Notes & limitations:
Work-hardens quickly; powerful tooling and lubrication are needed.

Magnetism:
Non-magnetic annealed; slight magnetism possible after severe cold-work.

Hardness, hardenability & temperature limits:
Annealed HB 170–210. Not heat-treatable. Continuous service is usually limited to 450–500 °C to preserve corrosion resistance, excellent toughness at low temperatures.

Standards & certification:
A240, A276, A312/A213. EN 10204 3.1/3.2.

Fasteners & markings:
Not an ISO 3506 fastener family; use A4 for standard marine fasteners.

Nitronic 50

Overview:
High-strength, corrosion-resistant austenitic; roughly twice the yield of 304/316; non-magnetic even when cold-worked.

Also known as:
XM-19; UNS S20910; EN 1.3964.

Typical uses:
Marine shafts, pumps, fasteners, cryogenic equipment.

Notes & limitations:
Machinability lower than 304; select condition (annealed/high strength) to suit.

Magnetism:
Essentially non-magnetic in all conditions.

Hardness, hardenability & temperature limits:
Annealed HB 190–240; strain-hardened higher. Not hardenable by heat treatment. Good to cryogenic temperatures; hot service typically below 550 °C for best properties.

Standards & certification:
Commonly to ASTM A276/A479 (bar), A182 (forgings). EN 10204 3.1.

Fasteners & markings:
Used for anti-galling fasteners but not covered by ISO 3506 property classes; heads show grade/mark as specified.

Nitronic 60

Overview:
Wear/galling-resistant austenitic; corrosion roughly 304-like with much better self-mated wear.

Also known as:
Alloy 218; UNS S21800.

Typical uses:
Valve stems, bushes, fasteners where galling is an issue.

Notes & limitations:
Not a 316-level pitting performer; prioritise for tribology.

Magnetism:
Typically non-magnetic.

Hardness, hardenability & temperature limits:
Annealed HB 180–240; work-hardened higher. Not heat-treatable. Service typically <600 °C; good low-temperature toughness.

Standards & certification:
ASTM A276/A479 (bar), A182 (forgings). EN 10204 3.1.

Fasteners & markings:
Often specified where anti-galling is critical; not ISO 3506 property-classed.

Higher‑Strength Austenitic Options (Bumax 88 / Bumax 109)

Bumax 88 and Bumax 109 are proprietary austenitic fasteners offering significantly higher proof strength than standard A2/A4 classes while retaining stainless corrosion performance.

Availability: Non‑standard items may require custom ordering via Accu’s Screw Builder or custom procurement facilities.

Austentic Stainless Steel Comparisons.

304 vs 316 Stainless Steel 

304 vs 316: 304 (A2) is versatile and cost‑effective. 316 (A4) adds molybdenum for better resistance in chloride‑bearing settings. If the environment is coastal or chemical, choose 316/316L; otherwise, 304 often suffices where cost is a consideration.

A2 vs A4 Stainless Steels (304 vs 316 When to Choose Which)

Rule of thumb: Use A2 (304) for indoor and mild outdoor exposure. Step up to A4 (316/316L) wherever chlorides, sea air or chemicals are present. For higher loads, choose the matching High Tensile class; for inspection‑driven requirements, select the 200HV variants.

 

 

303 vs 304 Stainless Steel (When to Choose Which)

Rule of thumb: Choose 303 when precision turning speed and thread quality are the priority in mild environments. Choose 304 (A2) when corrosion resistance, weldability or hygiene matter.

When to specify 303.

• High‑speed machining of small, intricate parts where cycle time matters.

• Threads that must be clean with minimal burrs, in non‑marine settings.

When to specify 304 (A2).

• General‑purpose fasteners and fabrications, especially where welds or washdown exist.

• Any risk of chlorides or occasional outdoor exposure (non‑coastal).

Caveats:

• If machining is critical and corrosion is a concern, consider 304 bar with optimised tooling or a modified‑sulphur 304 only where standards allow. For coastal/chemical, step up to 316/316L (A4).

Ferritic Stainless Steel Grades.

409 / 409L Stainless Steels.

Overview:
Low-cost, Ti-stabilised ferritic for high-temp oxidation; common exhaust grade. 409L is low-carbon for weldability.

Also known as:
EN 1.4512; AISI 409/409L; UNS S40900/S40910.

Typical uses:
Automotive exhausts, heat shields, burner parts.

Notes & limitations:
Modest corrosion resistance-protects from road salt crevices.

Magnetism:
Strongly magnetic (ferritic).

Hardness, hardenability & temperature limits:
Annealed HB 150–190. Not hardenable by heat treatment. Oxidation resistance to 675–750 °C, depending on the environment. Poor cryogenic toughness (avoid sub-zero impact).

Standards & certification:
A240 (sheet/plate), A268 (ferritic tube). EN 10204 3.1.

Fasteners & markings:
Not used for ISO 3506 fasteners.

410S Stainless Steel.

Overview:
Low-carbon, soft-martensite/ferritic variant for improved weldability vs 410; oxidation-resistant.

Also known as:
AISI 410S; UNS S41008.

Typical uses:
Heat exchangers, annealing covers, automotive manifolds.

Notes & limitations:
Not hardenable; moderate corrosion resistance-keep out of chlorides.

Magnetism:
Magnetic (ferritic/martensitic matrix).

Hardness, hardenability & temperature limits:
Annealed HB 150–190; cannot be hardened by quench/temper. Service to 600–700 °C. Limited low-temperature toughness.

Standards & certification:
A240, A268. EN 10204 3.1.

Fasteners & markings:
Not used for ISO 3506 fasteners.

430 / 430F Stainless Steel.

Overview:
430: 17% Cr general-purpose ferritic with good formability and finish.
430F: free-machining sulphurised variant for turned parts (reduced corrosion vs 430).

Also known as:
EN 1.4016 (430); EN 1.4105/1.4104 (430F); AISI 430/430F, 18/0 Stainless Steel.

Typical uses:
Appliances, decorative trim; 430F for screws, fittings.

Notes & limitations:
Magnetic; avoid marine/chloride crevices; 430F not for corrosive service.

Magnetism:
Strongly magnetic (ferritic). 430F also magnetic.

Hardness, hardenability & temperature limits:
Annealed HB 150–190. Not heat-treatable. Service up to 815 °C (oxidation). Poor cryogenic toughness.

Standards & certification:
A240 (sheet/plate), A582/A276 (bar). EN 10204 3.1.

Fasteners & markings:
430F may be used for free-machined screws, but not ISO 3506 property-classed for corrosion service.

 

434 Stainless Steel.

Overview:
Mo-alloyed 430 for better pitting/oxidation resistance (to 816 °C).

Also known as:
EN 1.4113; AISI 434.

Typical uses:
Exhaust components, hot-water tanks, heat-resistant trim.

Notes & limitations:
Formability below 430; consider 436 for improved forming.

Magnetism:
Magnetic (ferritic).

Hardness, hardenability & temperature limits:
Annealed HB 160–200. Not heat-treatable. Limited low-temperature toughness.

Standards & certification:
A240, A268. EN 10204 3.1.

Fasteners & markings:
Not used for ISO 3506 fasteners.

 

436 Stainless Steel.

Overview:
Nb-stabilised modification of 434; reduced ridging during stretch-form; good hot oxidation.

Also known as:
EN 1.4513; AISI 436; UNS S43600.

Typical uses:
Automotive trim/exhaust, formed housings.

Notes & limitations:
Not a chloride-resistant grade; pick 444 for wet chloride service.

Magnetism:
Magnetic (ferritic).

Hardness, hardenability & temperature limits:
Annealed HB 160–200. Not heat-treatable. Limited cryogenic toughness.

Standards & certification:
A240, A268. EN 10204 3.1.

Fasteners & markings:
Not ISO 3506 certified for fasteners. 

 

439 Stainless Steel.

Overview:
Ti-stabilised 18% Cr ferritic with improved weldability/formability vs 430.

Also known as:
EN 1.4510; AISI 439; SUS 430LX.

Typical uses:
Automotive exhausts, heat exchangers, and catering equipment.

Notes & limitations:
Corrosion is roughly 304-like in mild atmospheres, but not a marine grade.

Magnetism:
Magnetic (ferritic).

Hardness, hardenability & temperature limits:
Annealed HB 150–190. Not heat-treatable. Poor cryogenic impact toughness.

Standards & certification:
A240, A268. EN 10204 3.1.

Fasteners & markings:
Not ISO 3506 compliant for fastener use.

 

441 Stainless steel.

Overview:
Nb-stabilised 18% Cr ferritic with better high-temp strength than 409/439; good surface finish.

Also known as:
EN 1.4509; AISI 441; UNS S44100.

Typical uses:
Boilers, gas appliance parts, and catering equipment.

Notes & limitations:
Oxidation resistance to 950 °C; still magnetic; not for chloride splash.

Magnetism:
Magnetic (ferritic).

Hardness, hardenability & temperature limits:
Annealed HB 160–200. Not heat-treatable. Limited sub-zero toughness.

Standards & certification:
A240, A268. EN 10204 3.1.

Fasteners & markings:
Not ISO 3506 certified for fastener use.

 

444 Stainless Steel.

Overview:
Mo-alloyed, Ti/Nb-stabilised ferritic with very good chloride pitting resistance; “ferritic answer” to 316L in many wet services.

Also known as:
EN 1.4521 (X2CrMoTi18-2); AISI 444; UNS S44400.

Typical uses
Hot-water tanks, heat-exchangers, coastal architectural sheet.

Notes & limitations:
Lower toughness than austenitics; avoid tight radii in deep draw applications.

Magnetism:
Magnetic (ferritic).

Hardness, hardenability & temperature limits:
Annealed HB 170–210. Not heat-treatable. Service to 300–350 °C is recommended to preserve corrosion resistance; poor cryogenic toughness.

Standards & certification:
A240, A268. EN 10204 3.1.

Fasteners & markings:
Not ISO 3506 certified for fastener use.

 

446 Stainless Steel.

Overview:
Very high-chromium ferritic for hot oxidation/sulphidation resistance.

Also known as:
EN 1.4762; AISI 446.

Typical uses:
Furnace parts, incineration, high-temp ducts.

Notes & limitations:
Low high-temperature strength; poor formability vs 430/444.

Magnetism:
Magnetic (ferritic).

Hardness, hardenability & temperature limits:
Annealed HB 180–220. Not heat-treatable. Oxidation resistance up to 1,100 °C; very poor cryogenic toughness.

Standards & certification:
A240, A268. EN 10204 3.1.

Fasteners & markings:
Not ISO 3506 certified for fastener use.

 

447 Stainless Steel (super-ferritic).

Overview:
29% Cr, 4% Mo ferritic with seawater-level pitting resistance; used in condenser/desalination service (AL 29-4/29-4C family).

Also known as:
UNS S44700/S44735 (29-4/29-4C).

Typical uses:
Power-plant condensers, desalination, brine coolers.

Notes & limitations:
Specialist fabrication; use qualified weld procedures; keep surfaces clean and pickled.

Magnetism:
Magnetic (ferritic).

Hardness, hardenability & temperature limits:
Annealed HB 200–230. Not heat-treatable. Service usually <300 °C to preserve corrosion resistance; poor cryogenic impact strength.

Standards & certification:
Typically to proprietary/ASTM condenser specifications. EN 10204 3.1 by agreement.

Fasteners & markings:
Not ISO 3506 certified for fastener use. 

Martensitic Stainless Steel Grades.

403 Stainless Steel.

Overview:
12% Cr martensitic; higher toughness vs 410; hardenable.

Also known as:
AISI 403; UNS S40300.

Typical uses:
Turbine parts, forgings.

Notes & limitations:
Lower corrosion resistance than 410/420; protect in chlorides.

Magnetism:
Magnetic in all conditions (martensitic).

Hardness, hardenability & temperature limits:
Annealed HB 160–200; oil-quenched and tempered typically up to HRC 35–42 depending on section. Service to 450 °C; limited cryogenic toughness (avoid sub-zero impacts).

Standards & certification:
A276 (bar), A473 (forgings). EN 10204 3.1.

Fasteners & markings:
Not ISO 3506 standard; where used, heads show grade/spec rather than A-class property values.

 

410 Stainless Steel.

Overview:
General-purpose 12% Cr hardenable martensitic; good strength after heat treatment.

Also known as:
AISI 410; EN 1.4006; UNS S41000.

Typical uses:
Cutlery, turbine blades, fasteners, pump/valve parts.

Notes & limitations:
Not for seawater; preheat/temper to avoid cracking.

Magnetism:
Magnetic (martensitic).

Hardness, hardenability & temperature limits:
Annealed HB 160–200; quenched and tempered HRC 35–45 typical. Service generally <425–500 °C. Poor cryogenic toughness.

Standards & certification:
A240 (plate), A276/A479 (bar), A182 (forgings). EN 10204 3.1.

Fasteners & markings:
Occasionally used for hard fasteners (non-ISO 3506). Mark with grade/spec; apply lubrication to reduce galling.

 

416 Stainless Steel.

Overview:
Free-machining martensitic (S-added) for high productivity; hardenable; always magnetic.

Also known as:
AISI 416; UNS S41600.

Typical uses:
Shafts, fasteners, gears, turned parts.

Notes & limitations:
Reduced corrosion vs 410; poor weldability.

Magnetism:
Magnetic.

Hardness, hardenability & temperature limits:
Annealed HB 170–200; quenched and tempered typically to HRC 28–38 (lower than 410/420 due to S). Not for cryogenic service; hot service typically <400 °C.

Standards & certification:
A582/A276 (bar). EN 10204 3.1.

Fasteners & markings:
Used for free-machined screws; not ISO 3506 property-classed for corrosion service.

 

420 (A/B/C) & 420F Stainless Steels.

Overview:
High-carbon martensitic for very high hardness; polishable. 420C is the highest-carbon variant; 420F is free-machining.

Also known as:
AISI 420 / 420C / 420F; UNS S42000.

Typical uses:
Knife blades, surgical grade stainless steel, shear blades, gauges and fasteners.

Notes & limitations:
Corrosion resistance depends on hardness and finish; avoid >427 °C in service.

Magnetism:
Magnetic (martensitic).

Hardness, hardenability & temperature limits:

• 420A/B: typically HRC 45–52
  
  

• 420C: typically HRC 50–56
  
  

• 420F: lower achievable hardness due to S inclusions
  Limited cryogenic toughness; hot service generally <400 °C.
  
  All as annealed HB 180–220; hardened/tempered.

Standards & certification:
A276/A479 (bar), A580 (wire), A484 (general req.). EN 10204 3.1.

Fasteners & markings:
Used where high hardness is needed; not ISO 3506 classed; heads marked per grade/spec.

 

431 Stainless Steel.

Overview:
16% Cr with Ni for higher toughness/strength; hardenable; better corrosion than 410/420.

Also known as:
AISI 431; EN 1.4057 (X17CrNi16-2); UNS S43100.

Typical uses:
Pump shafts, piston rods, marine shafts (non-splash).

Notes & limitations:
Still not “marine grade”; protect from stagnant chlorides.

Magnetism:
Magnetic (martensitic).

Hardness, hardenability & temperature limits:
Annealed HB 180–220; quenched and tempered, typically HRC 35–45. Limited sub-zero toughness; hot service <450 °C.

Standards & certification:
A276/A479 (bar), A182 (forgings). EN 10204 3.1.

Fasteners & markings:
Occasional high-strength fasteners (non-ISO 3506).

 

440 (A/B/C) & 440F Stainless Steels.

Overview:
High-carbon 16–18% Cr martensitic; 440C gives the highest hardness/wear; 440F is free-machining.

Also known as:
AISI 440A/B/C; UNS S44002/S44003/S44004; 440F.

Typical uses:
Bearings, valves, cutting instruments, knives and tools

Notes & limitations:
Needs full hardening + temper; corrosion is only moderate once tempered.

Magnetism:
Magnetic (martensitic).

Hardness, hardenability & temperature limits:
Annealed HB 200–.

Fasteners & markings:
Occasional high-strength fasteners (non-ISO 3506).

 

Duplex Stainless Steel Grades.

2101 Stainless Steel (lean duplex).

Overview:
Lean duplex (Cr-Mn-N) with duplex-typical strength and SCC resistance; cost-effective versus 304/316.

Also known as:
LDX 2101; EN 1.4162; UNS S32101.

Typical uses:
Structural plate, tanks, bridges, marine scrubbers.

Notes & limitations:
Not a 6% Mo substitute; check PREN against the environment.

Magnetism:
Duplex steel structure is magnetic.

Hardness & hardenability:
Typically 190–240 HB in solution-annealed condition. Not hardenable by heat treatment; work-hardens under cold-forming.

Temperature limits & toughness:
Best for continuous service up to 250 °C; avoid prolonged exposure above 300 °C to limit embrittlement. Good low-temperature toughness down to around −40 to −50 °C (verify per spec).

Standards & certification:
Common specs: ASTM A240 (plate), A789/A790 (tube/pipe), A182 (forgings); EN 10088 for products. EN 10204 3.1/3.2 MTRs typically available.

Fasteners:
When supplied as Duplex Fasteners, property classes are usually 70/80 under ISO 3506 (duplex “D” family). Head markings show the steel family letter and property class.

 

2304 Stainless Steel (lean duplex).

Overview
23% Cr, 4% Ni duplex; corrosion roughly 316L with 2× the yield strength.

Also known as
EN 1.4362; UNS S32304.

Typical uses
Pressure vessels, process piping, structural components.

Notes & limitations
Avoid prolonged exposure above 300 °C.

Magnetism
Magnetic (duplex).

Hardness & hardenability
190–240 HB solution-annealed. Not heat-hardenable; work-hardens with cold-work.

Temperature limits & toughness
Continuous service 250 °C; limit long holds at higher temperatures. Good toughness to roughly −50 °C depending on product form.

Standards & certification
ASTM A240, A789/A790, A182; EN 10088. EN 10204 3.1/3.2 available.

Fasteners:
Duplex Fasteners are typically class 70/80; ISO 3506 “D” family identification on head markings.

 

2003 Stainless Steel (lean duplex).

Overview:
Mo-enhanced lean duplex bridging 316 and 2205; good SCC resistance; lower sigma-phase risk than 2205.

Also known as:
ATI 2003; UNS S32003.

Typical uses:
Process piping, marine service, welded tube.

Notes & limitations:
Proprietary grade-check availability and equivalence.

Magnetism:
Magnetic (duplex).

Hardness & hardenability:
Typically, 200–240 HB solution-annealed. Not heat-hardenable; work-hardens under cold-forming.

Temperature limits & toughness:
Recommended continuous use up to 250 °C. Toughness at low temperature is generally good to around −40 °C; confirm per fastener data sheet.

Standards & certification:
Usually ordered to ASTM A240/A789/A790 or equivalent; EN 10088, where applicable. EN 10204 3.1/3.2 standard.

Fasteners:
Where available as Duplex Fasteners, expect ISO 3506 duplex family with 70/80 classes; head marks show family + class.

 

2205 Stainless Steel (standard duplex).

Overview:
Workhorse duplex (22% Cr, 3% Mo); high strength with excellent SCC and pitting resistance; prefer S32205 over S31803.

Also known as:
UNS S32205 (preferred) / S31803; EN 1.4462.

Typical uses:
Chemical process vessels, oil & gas pipework, FGD systems.

Notes & limitations:
Control heat input during welding to avoid embrittling phases.

Magnetism:
Magnetic (duplex).

Hardness & hardenability:
240–290 HB solution-annealed. Not heat-hardenable; work-hardens with cold-work.

Temperature limits & toughness:
Best up to 250 °C in continuous service; prolonged exposure above 300 °C risks sigma-phase embrittlement. Usually tough to −50 °C; verify for thick sections.

Standards & certification:
ASTM A240 (plate), A789/A790 (tube/pipe), A182 (forgings), A479 (bar); EN 10088. EN 10204 3.1/3.2 available.

Fasteners:
Duplex Fasteners are commonly supplied to ISO 3506 “D” grades in property classes 70/80; head markings indicate family and class.

 

2507 Stainless Steel (super duplex).

Overview:
25% Cr super duplex with very high pitting/crevice resistance and strength; excellent in chloride service.

Also known as:
UNS S32750; EN 1.4410.

Typical uses:
Seawater systems, desalination, offshore risers/valves.

Notes & limitations:
Welding needs tight control; avoid continuous service above 250 °C.

Magnetism:
Magnetic (duplex).

Hardness & hardenability:
270–310 HB solution-annealed. Not heat-hardenable; work-hardens under cold-forming.

Temperature limits & toughness:
Continuous up to 250 °C; prolonged exposure above 300 °C risks embrittlement. Low-temperature toughness is good, but can reduce below −40 °C; check per spec.

Standards & certification:
ASTM A240, A789/A790, A182, A479; EN 10088. EN 10204 3.1/3.2 available.

Fasteners:
Where specified as Duplex Fasteners, supplied under ISO 3506 duplex family (typically class 80). Head markings show family and class.

 

ZERON 100 Stainless Steel (super duplex).

Overview:
Highly alloyed super duplex (Cu-bearing) with strength above 2205 and excellent acid/chloride resistance.

Also known as:
UNS S32760.

Typical uses:
Subsea pipework, FGD, desalination, high-chloride processing.

Notes & limitations:
Qualified welding procedures are essential; verify impact toughness at low temperatures per fastener specification sheets.

Magnetism:
Magnetic (duplex).

Hardness & hardenability:
270–320 HB solution-annealed. Not heat-hardenable; work-hardens with cold-work.

Temperature limits & toughness:
Continuous service typically capped at 250 °C; limit time above 300 °C. Low-temperature toughness acceptable in many forms to around −40 °C (confirm on MTR).

Standards & certification:
ASTM A240, A790, A182, A479; EN 10088. EN 10204 3.1/3.2 MTRs standard.

Fasteners:
Duplex Fastener rules apply; property class usually 80; head marking shows “D” family plus class.

 

255 Stainless Steel (super duplex family).

Overview:
High-strength duplex with excellent pitting/crevice resistance; often referenced as Ferralium 255.

Also known as:
UNS S32550 (J93370/J32550 variants), Ferralium 255.

Typical uses:
Marine shafts, pumps, chemical plant.

Notes & limitations:
Check specification variant (cast/wrought) and chloride limits.

Magnetism:
Magnetic (duplex).

Hardness & hardenability:
260–320 HB solution-annealed. Not heat-hardenable; can work-harden.

Temperature limits & toughness:
Use up to 250 °C in continuous service; avoid long exposure above 300 °C. Low-temperature performance depends on product; −40 °C is a typical qualification point-verify.

Standards & certification:
ASTM A240/A790/A182, A479; EN 10088. EN 10204 3.1/3.2 available.

Fasteners:
Duplex Fasteners typically ISO 3506 duplex family, class 80; head marks indicate family and class.

 

Precipitation Hardening Stainless Steel Grades.

7-4PH Stainless Steel.

Overview:
Martensitic PH stainless; high strength up to 300 °C with good corrosion resistance; widely available (H900–H1150 conditions).

Also known as:
Type 630; EN 1.4542; UNS S17400; SUS630.

Typical uses:
Aerospace fittings, pump shafts, marine hardware (non-crevice).

Notes & limitations:
Avoid prolonged 370–480 °C (embrittlement/stress-corrosion susceptibility).

Magnetism:
Magnetic (martensitic matrix).

Hardness & hardenability:
Age-hardening alloy. Typical hardness: HRC 42–46 in H900; HRC 28–35 in H1025–H1150. Hardenable by precipitation ageing after solution treatment.

Temperature limits & toughness:
Good properties to 300 °C. Toughness decreases at sub-zero temperatures; not a cryogenic grade.

Standards & certification:
ASTM A564 (bar), A693 (plate), A705 (forgings). EN 10088-3/-2 equivalents. EN 10204 3.1/3.2 MTRs common.

Fasteners:
PH fasteners are usually specified by grade and heat-treat condition rather than ISO property classes; head markings follow manufacturer/condition codes.

 

15-5PH Stainless Steel.

Overview:
Cleaner, tougher evolution of 17-4 with improved transverse properties; single low-temperature age.

Also known as:
UNS S15500; XM-12.

Typical uses:
Aerospace components, high-load shafts, valves.

Notes & limitations:
Comparable corrosion to 17-4; select a condition for section size.

Magnetism:
Magnetic (martensitic).

Hardness & hardenability:
Age-hardening. Typical hardness: HRC 40–45 (H900-type ages), HRC 30–36 (higher-temperature ages).

Temperature limits & toughness:
Useful to 300 °C. Sub-zero toughness better than 17-4 in many forms, but still not a cryogenic alloy-confirm per fastener spec.

Standards & certification:
ASTM A564/A693/A705. EN 10088 where applicable. EN 10204 3.1/3.2 available.

Fasteners:
PH fastenersare usually specified by grade and heat-treat condition rather than ISO property classes; head markings follow manufacturer/condition codes.

 

13-8Mo Stainless Steel.

Overview:
High-strength martensitic PH with excellent toughness and SCC resistance in large sections.

Also known as:
UNS S13800.

Typical uses:
Aerospace structural parts, landing-gear components, high-load shafts.

Notes & limitations:
Often, VIM/VAR melted; specify the melt route for critical aerospace use.

Magnetism:
Magnetic (martensitic).

Hardness & hardenability:
Age-hardening. Typical hardness: HRC 38–46 depending on ageing condition (e.g., H950/H1000).

Temperature limits & toughness:
Good strength to 315 °C. Retains toughness better than 17-4/15-5; sub-zero performance is still limited versus austenitic grades.

Standards & certification:
ASTM A564/A693 (where listed) and aerospace AMS specs (e.g., AMS bars/forgings). EN 10204 3.1/3.2 available from aerospace mills.

Fasteners:
PH fasteners are usually specified by grade and heat-treat condition rather than ISO property classes; head markings follow manufacturer/condition codes.

 

17-7PH Stainless Steel.

Overview:
Semi-austenitic PH stainless for spring applications; high strength, good fatigue, moderate corrosion.

Also known as:
UNS S17700; EN 1.4568.

Typical uses:
Springs, diaphragms, bellows.

Notes & limitations:
Comparable corrosion profile to 304; not for marine enviroments.

Magnetism:
Becomes magnetic after conditioning (RH/CH spring tempers).

Hardness & hardenability:
Age-hardening after conditioning. Typical hardness in spring tempers: HRC 38–47 (condition dependent).

Temperature limits & toughness:
Useful for springs to 315 °C in appropriate tempers. Not suitable for cryogenic service.

Standards & certification:
ASTM A693 (plate/strip), A313 (spring wire), where applicable. EN 10204 3.1/3.2 available.

Fasteners:
Rare in use in PH fasteners, usually specified by grade and heat-treat condition rather than ISO property classes; head markings follow manufacturer/condition codes.

 

15-7Mo Stainless Steel.

Overview:
Semi-austenitic PH with Mo for higher room/elevated-temperature strength than 17-7.

Also known as:
UNS S15700.

Typical uses:
High-strength springs, diaphragms, clips (CH900 condition).

Notes & limitations:
Limited ductility in CH900; form in the annealed state, then age.

Magnetism:
Magnetic after conditioning/ageing.

Hardness & hardenability:
Age-hardened spring tempers around HRC 40–48 depending on process (e.g., CH900).

Temperature limits & toughness:
Good spring properties to 315 °C. Not recommended for cryogenic use.

Standards & certification:
ASTM A693 (strip/plate) and relevant spring wire specs. EN 10204 3.1/3.2 available.

Fasteners:
PH fasteners are usually specified by grade and heat-treat condition rather than ISO property classes; head markings follow manufacturer/condition codes.

 

A286 (Alloy 660) Stainless Steel.

Overview:
Precipitation-hardened austenitic iron-nickel alloy; high strength to 700 °C with useful corrosion resistance.

Also known as:
UNS S66286; ASTM Grade 660.

Typical uses:
High-temperature stainless steel bolt grades, turbine/engine hardware.

Notes & limitations:
Not a seawater alloy; protects against crevice attack at standard operating temperatures.

Magnetism:
Essentially non-magnetic (austenitic), with slight magnetism possible after cold-work.

Hardness & hardenability:
Age-hardened. Typical hardness HRC 26–36, depending on ageing/section size.

Temperature limits & toughness:
Maintains strength to 700 °C. Not intended for cryogenic service; for sub-zero duties, use austenitic stainless grades instead.

Standards & certification:
ASTM A453 Grade 660 (bolting), A638 (forgings), A713 (investment castings) and others per product. EN 10204 3.1/3.2 MTRs standard.

Fasteners:
PH fasteners fpr A286 are ordered to A453 Gr. 660 classes (A/B/C/D) rather than ISO 3506 property classes; head markings show grade/class per standard.

 

Fastener‑Relevant Stainless Steel Finishes.

Finish alters surface condition, appearance and cleanability. The base alloy still governs inherent corrosion resistance, but certain finishes can enhance it by removing contaminants, lowering roughness or sealing the surface. Others are mainly cosmetic or functional for handling and torque control.

Passivated – Restores the chromium-rich passive film on the material.

What is Passivated Stainless Steel?: Chemical treatment (typically nitric or citric systems) that removes free iron and shop contamination after forming or machining.

Benefits: Functional. Improves resistance to tea-staining and general corrosion by renewing the passive layer; essential after machining, blasting or heat tint removal. No dimensional change.

Notes: Specify to ISO/ASTM passivation standards where required; rinsing and drying quality affect the outcome.

Self colour (as-formed) – Standard, unpolished stainless appearance.

What is Self Coloured Stainless Steel?: The natural finish from cold forming/heading with a light manufacturing sheen.

Benefits: Mostly cosmetic/economic. No added processing cost; retains material properties.

Notes: Surface may carry minor tool marks or lubricant residues; passivation is recommended for best corrosion performance, especially for coastal or wash-down service.

Brushed / Polished – Mechanically refined surface (e.g., No.4 brushed; No.8 mirror)

What it is: Abrasive finishing to reduce roughness and create a directional (brushed) or mirror (polished) look.

Benefits: Both cosmetic and functional. Smoother surfaces trap fewer contaminants and are easier to clean; edges are deburred. Mirror polish can reduce initiation sites for pitting.

Notes: Always passivate after mechanical finishing to remove smeared iron. State the required roughness (e.g., Ra ≤ 0.8 μm for hygiene-critical areas).

Bead-blasted – Uniform matte texture.

What it is: Non-metallic media blasting to create a low-glare, even surface.

Benefits: Mainly cosmetic/handling. Reduces glare and visually hides minor forming marks; improves grip during assembly.

Notes: Slightly increases surface area and roughness, which can raise tea-staining risk in coastal or chloride-rich environments. Follow with passivation; consider electropolish for harsh sites instead.

Electropolished – Smooth, cleanable, corrosion-enhanced surface

What it is: Controlled anodic dissolution that levels peaks and removes inclusions and heat tint.

Benefits: Strongly functional. Improves cleanability and biofilm resistance, and can measurably improve pitting/crevice performance versus mechanically polished-only parts. Aids inspection and aesthetics.

Notes: Ideal for food, pharma, and coastal fixtures. Specify target roughness and visual standard if critical.

AccuBlack (Chemical blacking for stainless steels) – Low-build, uniform black oxide finish

What it is: Accu’s chemical blacking process for stainless fasteners, producing a deep black, low-reflectivity surface without altering dimensions.

Benefits: Primarily cosmetic and handling. Glare reduction for visible assemblies and optics; minimal effect on thread fit. With appropriate post-treatment (oil/wax), it offers light corrosion assistance compared with self-colour, but it is not a substitute for specifying the correct marine grade of material in the onset.

Notes: Blackened stainless steels should still be passivated prior to blacking, where appropriate. If torque-tension consistency is critical, specify lubrication/thread locker as part of the finish system.

 

How to Specify Stainless Steel For Your Projects.

When a drawing says only material: stainless steel, it leaves room for error. A clear specification locks in performance, compliance and cost control. It also speeds procurement because the buyer can source to a known standard without queries or substitutions.

What’s the industry standard?

For fasteners, the common naming standard is:
Steel family/grade → Property class > Finish/treatment > Standards & certification.

• Grades: A2 = 304; A4 = 316; duplex fasteners use the D family; PH and special grades are stated explicitly.
  
  

• Property classes: A2-70, A2-80, A4-70, A4-80 (per ISO 3506).
  
  

• Finishes/treatments: Passivated, pickled, electropolished, lubricated/anti-seize, cleanroom packed etc as required.
  
  

• Standards: ISO 3506 (fasteners), product standards (e.g., ISO 4017 hex bolts), and EN 10204 3.1/3.2 for MTRs.
  For plate, bar and tube, cite EN steel numbers (e.g., 1.4301/1.4404) or UNS, plus product specs (e.g., ASTM A240, EN 10088).

What’s the benefit of specifying like this?

• Predictable performance: The right grade, strength class and finish match the environment and load case, reducing corrosion risk, galling and premature failure.
  
  

• Fewer site issues: Clear details avoid mixed batches, wrong head markings, or unsuitable finishes.
  
  

• Clean documentation: Auditable against recognised standards (ISO/EN/ASTM) and MTRs, which keeps projects moving through QA.
  
  

Non‑standard supply:

If you need tight hardness control (e.g., 200 HV max), unusual sizes, or higher-strength austenitics (e.g., Bumax 88/109) and speciality anti-galling options (e.g., Nitronic 60), state it explicitly. 

Accu can quote through Screw Builder or custom ordering, matching the grade, property class, finish and certification so the parts arrive “right-first-time”.

 

FAQs

Q: Are A2 stainless steel Screws OK outdoors?

A: Yes. A2 suits outdoor, non‑coastal environments. For coastal or chloride exposure, use A4.

Q: Is A4 stainless steel marine grade?

A: Yes. A4 aligns with 316 and is widely known as marine-grade stainless steel.

Q: Which is better for coastal areas, A2 or A4?

A: A4. It offers better resistance to pitting and crevice corrosion in chloride‑rich atmospheres.

Q: What’s the difference between A4‑70 and A4‑80?

A: Both are 316‑family fasteners. A4‑80 has a higher proof stress, so choose it for higher clamp loads.

Q: Is 316L food-grade stainless steel?

A: 316L is widely used in hygienic service due to its low carbon content and strong corrosion resistance in many food processing environments.

Q: Is stainless steel magnetic?

A: Austenitic grades (e.g., 304/316) are generally non‑magnetic when annealed but can become slightly magnetic after cold work. Ferritic, martensitic and PH grades are magnetic; duplex is slightly magnetic.

Q: What type of drill bit is best for stainless steel?

A: Use cobalt HSS or carbide drill bits, slow speed, high feed and cutting fluid. For work‑hardened austenitics, keep the bit sharp and avoid rubbing.

Q: How many types of stainless steel are there?

A: Five primary families: austenitic, ferritic, martensitic, duplex and precipitation hardening.