Introduction to the GB/T 3098.25-2020 Standard
GB/T 3098.25-2020 is a critical national standard in China that provides a comprehensive guideline for the selection of stainless steel and nickel alloy fasteners based on their mechanical performance characteristics. This standard is part of the broader GB/T 3098 series, which addresses mechanical properties of fasteners, and it specifically focuses on materials like austenitic, martensitic, ferritic, duplex stainless steels, and nickel alloys. Its primary purpose is to assist engineers, designers, and manufacturers in choosing appropriate fasteners for applications requiring high corrosion resistance, strength, and durability under various environmental conditions, such as marine, chemical processing, and high-temperature environments.
The scope of this standard includes detailed chemical composition tables that outline the mass fractions of key elements like carbon (C), silicon (Si), manganese (Mn), phosphorus (P), sulfur (S), chromium (Cr), molybdenum (Mo), nickel (Ni), copper (Cu), nitrogen (N), niobium (Nb), and titanium (Ti). These compositions are cross-referenced with ISO codes, corresponding fastener groups, and related standards to ensure compatibility and reliability. For instance, it draws from GB/T 3098.6 for bolts, screws, and studs made of stainless steel, GB/T 3098.15 for nuts, and others for specialized applications.
In practical terms, this guide helps mitigate risks associated with material failure by specifying compositions that enhance properties like tensile strength, yield strength, and resistance to intergranular corrosion. It also includes notes on avoiding unintended element additions during manufacturing to preserve quenchability, mechanical properties, and applicability. Professionals in mechanical engineering rely on this standard to optimize fastener selection, ensuring compliance with international equivalents like ISO 3506 and EN standards.
Key benefits include improved safety in structural assemblies, cost-effectiveness through appropriate material choices, and enhanced performance in aggressive environments. For example, austenitic grades are favored for their non-magnetic properties and formability, while duplex grades offer a balance of strength and corrosion resistance. This standard promotes best practices in material science, emphasizing the importance of precise alloying to achieve desired mechanical outcomes. By adhering to these guidelines, industries can reduce downtime and maintenance costs associated with fastener degradation.
Chemical Compositions of Austenitic Stainless Steels
Table 1 from GB/T 3098.25-2020 details the chemical compositions of austenitic stainless steels, referencing GB/T 3098.6, GB/T 3098.15, GB/T 3098.16, and GB/T 3098.21. These compositions are crucial for determining the mechanical properties and corrosion resistance of fasteners. Values are given as mass fractions in percent, with most being maximum limits unless specified as ranges or minimums. Austenitic steels are known for their excellent formability, weldability, and resistance to oxidation, making them ideal for fasteners in corrosive environments.
The table lists ISO codes alongside elemental compositions, including C, Si, Mn, P, S, Cr, Mo, Ni, Cu, N, Nb, and Ti, and assigns corresponding fastener groups like A1, A2, A2L, A3, A4, A4L, A5, and A8. For example, ISO 4305-303-00-I (group A1) has C up to 0.12, Cr 17.0-19.0, and S ≥0.15 for improved machinability. These specifications ensure consistency in performance, such as maintaining austenitic structure for non-magnetic properties.
Notes emphasize that unspecified elements should not be added without buyer consent, except for refining, and precautions must be taken against contaminants affecting properties. The groups align closely but not identically with other GB/T standards. This data aids in selecting materials for specific loads and temperatures, preventing issues like stress corrosion cracking.
| ISO Code | C | Si | Mn | P | S | Cr | Mo | Ni | Cu | N | Nb | Ti | Groupe |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 4305-303-00-I | 0.12 | 1 | 2 | 0.06 | ≥0.15 | 17.0~19.0 | – | 8.0~10.0 | 1 | 0.1 | – | – | A1 |
| 4301-304-00-I | 0.07 | 1 | 2 | 0.045 | 0.03 | 17.5~19.5 | – | 8.0~10.5 | – | 0.1 | – | – | A2 |
| 4307-304-03-I | 0.03 | 1 | 2 | 0.045 | 0.03 | 17.5~19.5 | – | 8.0~10.5 | – | 0.1 | – | – | A2L |
| 4311-304-53-I | 0.03 | 1 | 2 | 0.045 | 0.03 | 17.5~19.5 | – | 8.0~11.0 | – | 0.12~0.22 | – | – | A2L |
| 4567-304-98-X | 0.08 | 1 | 2 | 0.045 | 0.03 | 17.0~19.0 | – | 8.0~10.5 | 1.0~3.0 | – | – | – | A2 |
| 4567-304-30-I | 0.04 | 1 | 2 | 0.045 | 0.03 | 17.0~19.0 | – | 8.0~10.5 | 3.0~4.0 | 0.1 | – | – | A3 |
| 4541-321-00-I | 0.08 | 1 | 2 | 0.045 | 0.03 | 17.0~19.0 | – | 9.0~12.0 | – | – | – | 5×C~0.70 | A3 |
| 4550-347-00-I | 0.08 | 1 | 2 | 0.045 | 0.03 | 17.0~19.0 | – | 9.0~12.0 | – | – | 10×C~1.00 | – | A3 |
| 4401-316-00-I | 0.08 | 1 | 2 | 0.045 | 0.03 | 16.0~18.0 | 2.00~3.00 | 10.0~13.0 | – | 0.1 | – | – | A4 |
| 4404-316-03-I | 0.03 | 1 | 2 | 0.045 | 0.03 | 16.5~18.5 | 2.00~3.00 | 10.0~13.0 | – | 0.1 | – | – | A4L |
| 4406-316-53-I | 0.03 | 1 | 2 | 0.045 | 0.03 | 16.5~18.5 | 2.00~3.00 | 10.0~12.5 | – | 0.12~0.22 | – | – | A4L |
| 4578-316-76-E | 0.04 | 1 | 2 | 0.045 | 0.015 | 16.5~17.5 | 2.00~2.50 | 10.0~11.0 | 3.0~3.5 | 0.1 | – | – | A4 |
| 4571-316-35-I | 0.08 | 1 | 2 | 0.045 | 0.03 | 16.5~18.5 | 2.00~2.50 | 10.5~13.5 | – | – | – | 5×C~0.70 | A5 |
| 4529-089-26-I | 0.02 | 0.75 | 2 | 0.035 | 0.015 | 19.0~21.0 | 6.0~7.0 | 24.0~26.0 | 0.5~1.5 | 0.15~0.25 | – | – | A8 |
| 4547-312-54-I | 0.02 | 0.7 | 1 | 0.035 | 0.015 | 19.5~20.5 | 6.0~7.0 | 17.5~18.5 | 0.50~1.00 | 0.18~0.25 | – | – | A8 |
| 4478-083-67-U | 0.03 | 1 | 2 | 0.04 | 0.03 | 20.0~22.0 | 6.0~7.0 | 23.5~25.5 | 0.75 | 0.18~0.25 | – | – | A8 |
Chemical Compositions of Martensitic, Ferritic, and Duplex Steels
Table 2 outlines the chemical compositions for martensitic, ferritic, and duplex stainless steels, essential for fasteners requiring high strength and moderate corrosion resistance. Martensitic steels offer hardenability through heat treatment, ferritic provide good ductility, and duplex combine austenitic and ferritic phases for superior strength and pitting resistance.
ISO codes are linked to elements and groups like C1, C3, C4, F1, D2, D4, D6, and D8. For martensitic, ISO 4006-410-00-I (C1) has C 0.08~0.15 and Cr 11.5~13.5. Duplex examples include ISO 4462-318-03-I (D6) with Cr 21.0~23.0 and Mo 2.5~3.5. Notes include tungsten requirements for certain codes and PREN calculations for duplex recognition.
| ISO Code | C | Si | Mn | P | S | Cr | Mo | Ni | Cu | N | Nb | Ti | Groupe |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Martensitic Stainless Steels | |||||||||||||
| 4006-410-00-I | 0.08~0.15 | 1 | 1.5 | 0.04 | 0.03 | 11.5~13.5 | – | 0.75 | – | – | – | – | C1 |
| 4021-420-00-I | 0.16~0.25 | 1 | 1.5 | 0.04 | 0.03 | 12.0~14.0 | – | – | – | – | – | – | C1 |
| 4028-420-00-I | 0.26~0.35 | 1 | 1.5 | 0.04 | 0.03 | 12.0~14.0 | – | – | – | – | – | – | C1 |
| 4057-431-00-X | 0.12~0.22 | 1 | 1.5 | 0.04 | 0.03 | 15.0~17.0 | – | 1.50~2.50 | – | – | – | – | C3 |
| 4005-416-00-I | 0.08~0.15 | 1 | 1.5 | 0.04 | ≥0.15 | 12.0~14.0 | 0.6 | – | – | – | – | – | C4 |
| Ferritic Stainless Steels | |||||||||||||
| 4016-430-00-I | 0.08 | 1 | 1 | 0.04 | 0.03 | 16.0~18.0 | – | – | – | – | – | – | F1 |
| Duplex Stainless Steels | |||||||||||||
| 4482-320-01-X | 0.03 | 1 | 4.0~6.0 | 0.035 | 0.03 | 19.5~21.5 | 0.10~0.60 | 1.50~3.50 | 1 | 0.05~0.20 | – | – | D2 |
| 4362-323-04-I | 0.03 | 1 | 2 | 0.035 | 0.015 | 22.0~24.5 | 0.10~0.60 | 3.5~5.5 | 0.10~0.60 | 0.05~0.20 | – | – | D2 |
| 4062-322-02-U | 0.03 | 1 | 2 | 0.04 | 0.01 | 21.5~24.0 | 0.45 | 1.00~2.90 | – | 0.16~0.28 | – | – | D4 |
| 4162-321-01-E | 0.04 | 1 | 4.0~6.0 | 0.04 | 0.015 | 21.0~22.0 | 0.10~0.80 | 1.35~1.90 | 0.10~0.80 | 0.20~0.25 | – | – | D4 |
| 4662-824-41-X | 0.03 | 0.7 | 2.50~4.0 | 0.035 | 0.005 | 23.0~25.0 | 1.00~2.00 | 3.0~4.5 | 0.10~0.80 | 0.20~0.30 | – | – | D4 |
| 4462-318-03-I | 0.03 | 1 | 2 | 0.035 | 0.015 | 21.0~23.0 | 2.5~3.5 | 4.5~6.5 | – | 0.10~0.22 | – | – | D6 |
| 4481-312-60-J | 0.03 | 1 | 1.5 | 0.04 | 0.03 | 24.0~26.0 | 2.5~3.5 | 5.5~7.5 | – | 0.08~0.30 | – | – | D6 |
| 4410-327-50-E | 0.03 | 1 | 2 | 0.035 | 0.015 | 24.0~26.0 | 3.0~4.5 | 6.0~8.0 | – | 0.24~0.35 | – | – | D8 |
| 4501-327-60-I | 0.03 | 1 | 1 | 0.03 | 0.01 | 24.0~26.0 | 3.0~4.0 | 6.0~8.0 | 0.5~1.0 | 0.20~0.30 | – | – | D8 |
| 4507-325-20-I | 0.03 | 0.7 | 2 | 0.035 | 0.015 | 24.0~26.0 | 3.0~4.0 | 6.0~8.0 | 1.0~2.5 | 0.20~0.30 | – | – | D8 |
Chemical Compositions of High-Temperature Stainless Steels and Nickel Alloys
Table 3 covers compositions for high-temperature applications, including martensitic steels and austenitic precipitation-hardening types with nickel alloys. These materials are designed for elevated temperatures, offering creep resistance and oxidation protection.
Groups include CH0, CH1, CH2, V or VH, VW, SD, SB, and 718. For nickel alloy 2.4668 (718), C is 0.02~0.08, with high Ni (50.00~55.00) and Mo (2.80~3.30). Notes detail additional elements like V, Al, B, Co, Fe, and Nb for specific codes.
| ISO Code | C | Si | Mn | P | S | Cr | Mo | Ni | Cu | N | Nb | Ti | Groupe |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Martensitic Stainless Steels | |||||||||||||
| 4021-420-00-I | 0.16~0.25 | 1 | 1.5 | 0.04 | 0.03 | 12.0~14.0 | – | – | – | – | – | – | CH0 |
| 4028-420-00-I | 0.26~0.35 | 1 | 1.5 | 0.04 | 0.03 | 12.0~14.0 | – | – | – | – | – | – | CH1 |
| 4057-431-00-X | 0.12~0.22 | 1 | 1.5 | 0.04 | 0.03 | 15.0~17.0 | – | 1.50~2.5 | – | – | – | – | CH2 |
| 4923-422-77-E | 0.18~0.24 | 0.5 | 0.40~0.90 | 0.025 | 0.015 | 11.0~12.5 | 0.8~1.2 | 0.30~0.80 | – | – | – | – | V or VH |
| 1.4913 | 0.17~0.23 | 0.5 | 0.40~0.90 | 0.025 | 0.015 | 10.0~11.5 | 0.50~0.80 | 0.20~0.60 | – | 0.05~0.10 | 0.25~0.55 | – | VW |
| Austenitic Precipitation Hardening Stainless Steels and Nickel Alloys | |||||||||||||
| 4980-662-86-X | 0.08 | 1 | 2 | 0.04 | 0.03 | 13.5~16.0 | 1.0~1.5 | 24.0~27.0 | – | – | – | 1.90~2.35 | SD |
| 2.4952 | 0.04~0.10 | 1 | 1 | 0.02 | 0.015 | 18.0~21.0 | – | ≥65 | 0.2 | – | – | 1.80~2.70 | SB |
| 2.4668 | 0.02~0.08 | 0.035 | 0.035 | 0.015 | 0.015 | 17.0~21.0 | 2.80~3.30 | 50.00~55.00 | 0.3 | – | – | 0.60~1.20 | 718 |
Common Grades for Cold-Heading Fasteners – Austenitic
Table A.1 lists common austenitic grades for cold-heading fasteners, cross-referencing categories, groups, ISO codes, European designations, ASTM codes, US common names, GB/T positions, GB/T 20878 codes, and related standards. This aids in selecting materials for high-volume production of screws and bolts.
| Catégorie | Groupe | ISO Code | European Code | European Grade | ASTM Code | US Name | GB/T Position | GB/T 20878 Code | Related Standards |
|---|---|---|---|---|---|---|---|---|---|
| Sulfurized Austenitic | A1 | 4305-303-00-I | 1.4305 | X8CrNiS18-9 | S30300 | 303 | Chapter 5, Table 1 | S30317 | ASTM A959, EN 10088-3 |
| A1 | 4570-303-31-I | 1.457 | X6CrNiCuS18-9-2 | S30331 | 303Cu | GB/T 3098.6 GB/T 3098.15 | – | EN 10088-3 | |
| General Purpose Austenitic | A2L | 4307-304-03-I | 1.4307 | X2CrNi18-9 | S30403 | 304L | Chapter 5, Table 1 | S30403 | ASTM A959, EN 10088-3, EN 10263-5, EN 10269 |
