Stainless steel fastener grades refer to standardized classifications that define the material composition, mechanical properties, corrosion resistance, and suitable applications of stainless steel fasteners such as bolts, nuts, and screws. These grades help ensure that the correct material is selected for various industrial uses.
A stainless steel fastener grade may be identified using several systems:
| System | Description |
| SAE / AISI (U.S. Standards) | Grades like 304, 316, 410, and 17-4PH refer to different stainless steel types (austenitic, martensitic, precipitation-hardened, etc.) |
| UNS (Unified Numbering System) | Global identifiers like S30400 or S31603 |
| EN / DIN (European Standards) | European material numbers such as 1.4301 or 1.4401 |
| ASTM Standards | Standards such as ASTM A193 or A320 define performance and service conditions for fasteners |
Stainless Steel Fastener Grades Comparison Table
| SAE Grade | EN/DIN (Steel #) | EN Name | UNS Number | Remarks |
| 440A | 1.4109 | X65CrMo14 | S44002 | High hardness, lower corrosion |
| 440B | 1.4112 | X90CrMoV18 | S44003 | Mid carbon, higher hardness |
| 440C | 1.4125 | X105CrMo17 | S44004 | Very high hardness, tool-grade |
| 440F | – | – | S44020 | Free-machining variant |
| 430 | 1.4016 | X6Cr17 | S43000 | Ferritic, magnetic |
| 316 | 1.4408 | G-X 6 CrNiMo 18-10 | S31600 | Cast stainless steel |
| 409 | 1.4512 | X6CrTi12 | S40900 | Ferritic, automotive exhaust |
| 410 | – | – | S41000 | Martensitic, hardened |
| 301 | 1.431 | X10CrNi18-8 | S30100 | High strength, work hardenable |
| 301LN | 1.4318 | X2CrNiN18-7 | – | Nitrogen-added for strength |
| 304L | 1.4307 | X2CrNi18-9 | S30403 | Low carbon, better weldability |
| 304L | 1.4306 | X2CrNi19-11 | S30403 | Variant of 304L |
| 304LN | 1.4311 | X2CrNiN18-10 | S30453 | Nitrogen-added for strength |
| 304 | 1.4301 | X5CrNi18-10 | S30400 | General-purpose austenitic |
| 304H | 1.4948 | X6CrNi18-11 | S30409 | High temp, high carbon version |
| 305 | 1.4303 | X5CrNi18-12 | S30500 | Better cold forming |
| 312 | – | X5CrNi30-9 | – | High heat and oxidation resistance |
| 310 | 1.4841 | X22CrNi2520 | S31000 | High temp, oxidation resistant |
| 310S | 1.4845 | X5CrNi2520 | S31008 | Low carbon 310 |
| 321 | 1.4541 | X6CrNiTi18-10 | S32100 | Ti stabilized, for welding |
| 321H | 1.4878 | X12CrNiTi18-9 | S32109 | High carbon version |
| 316L | 1.4404 | X2CrNiMo17-12-2 | S31603 | Low carbon version of 316 |
| 316 | 1.4401 | X5CrNiMo17-12-2 | S31600 | Marine-grade, chloride resistance |
| 316LN | 1.4406 | X2CrNiMoN17-12-2 | S31653 | N-enhanced version of 316L |
| 316L | 1.4432 | X2CrNiMo17-12-3 | S31603 | Variant of 316L |
| 316L | 1.4435 | X2CrNiMo18-14-3 | S31603 | Higher molybdenum variant |
| 316 | 1.4436 | X3CrNiMo17-13-3 | S31600 | Higher corrosion resistance |
| 316Ti | 1.4571 | X6CrNiMoTi17-12-2 | S31635 | Ti stabilized, weld protection |
| 316LN | 1.4429 | X2CrNiMoN17-13-3 | S31653 | Stronger variant of 316L |
| 317L | 1.4438 | X2CrNiMo18-15-4 | S31703 | Higher Mo, more corrosion-resistant |
| 2304 | 1.4362 | X2CrNi23-4 | S32304 | Duplex SS, good strength |
| 2205 | 1.4462 | X2CrNiMoN22-5-3 | S31803 / S32205 | Duplex, high strength/corrosion |
| J405 | 1.4501 | X2CrNiMoCuWN25-7-4 | S32760 | Super duplex, seawater resistance |
| 904L | 1.4539 | X1NiCrMoCu25-20-5 | N08904 | Super austenitic, high corrosion |
| – | 1.4529 | X1NiCrMoCuN25-20-7 | N08926 | Super austenitic |
| 254SMO | 1.4547 | X1CrNiMoCuN20-18-7 | S31254 | High-end stainless, seawater use |
Why Are Stainless Steel Fasteners Classified by Grade?
- Different strength requirements: Structural steel vs. precision components
- Different corrosion environments: Dry indoor vs. saltwater or acidic media
- Different weldability and machinability
- Varying performance at high or low temperatures
Stainless Steel Fasteners: Strength Grades and Markings
Stainless steel fasteners are classified by strength grades and markings to indicate their mechanical properties (such as tensile strength, yield strength) and material types. This system helps engineers and buyers select the appropriate fastener for specific industrial applications.
Stainless Steel Fastener Strength Grades
| Marking | Standard | Type | Tensile Strength (MPa) | Description |
| A1-50 / A2-50 / A4-50 | ISO 3506 | Austenitic | ≥ 500 | For general corrosion-resistant environments with lower strength demands |
| A2-70 / A4-70 | ISO 3506 | Austenitic | ≥ 700 | Most commonly used; good strength for construction and machinery |
| A2-80 / A4-80 | ISO 3506 | Austenitic | ≥ 800 | High-strength, strain-hardened austenitic stainless steel |
| C1-70 / C4-70 | ISO 3506 | Martensitic | ≥ 700 | Heat-treatable stainless steel with high strength |
| B8 / B8M Class 1 / 2 | ASTM A193 | Austenitic | ~515–860 | Used in high-temperature or pressure piping systems |
| B6 / B7 / B8C | ASTM A193 | Martensitic / PH | ≥ 860 | Suitable for flange joints, high-strength bolts |
ISO 3506 Stainless Steel Marking System (A2 / A4, etc.)
| Code | Material Type | Equivalent Steel | Recommended Environment |
| A1 | Cold-worked Austenitic | Similar to 304 | General use, non-welded parts |
| A2 | Standard Austenitic | 304 / 304L | Indoor and mildly corrosive environments |
| A3 | Acid-resistant Austenitic | Similar to 316 | More aggressive corrosion exposure |
| A4 | Molybdenum-bearing Austenitic | 316 / 316L | Marine and chemical environments |
| A5 | Heat-resistant Austenitic | 316Ti | High-temperature, acidic environments |
| C1 / C4 | Martensitic | 410, etc. | High strength, lower corrosion resistance |
| F1 | Ferritic | 430 | Mildly corrosive conditions, lower cost |
Example Marking Interpretations
- A2-70
- A2: Austenitic stainless steel (304 grade)
- 70: Minimum tensile strength of 700 MPa
- Typical Use: Machinery, kitchenware, hardware
- A4-80
- A4: Austenitic stainless steel (316 grade with Mo)
- 80: Minimum tensile strength of 800 MPa
- Typical Use: Marine environments, chemical equipment
Contact MT.BOLTS
MT.BOLTS specializes in the manufacturing and supply of 17-4 PH Stainless Steel fasteners including screws, bolts, nuts, and washers. Our products conform to international standards (ANSI / ASTM / DIN / ISO / JIS) and are available in various materials, dimensions, and surface finishes.
Contact us today to learn more about fasteners and to procure high-quality products. Our technical team is ready to provide expert support and custom selection solutions.
