Introduction to the GB/T 3098.16 Standard
This standard specifies the mechanical properties of stainless steel set screws and similar non-tensile fasteners, focusing on austenitic grades. It ensures reliability in corrosive environments, such as marine or chemical applications, by defining chemical compositions and performance criteria. Compliance with GB/T 3098.16-2014 guarantees fasteners withstand operational stresses without failure.
Engineers should reference this for selecting materials that balance corrosion resistance and mechanical strength, preventing issues like intergranular corrosion through appropriate alloy choices.
Chemical Composition
The chemical composition for austenitic stainless steel groups used in set screws is outlined in Table 2, consistent with GB/T 3098.6-2014. Manufacturers select within specified ranges unless otherwise agreed. For intergranular corrosion-prone applications, test per GB/T 4334 and prefer stabilized A3/A5 or low-carbon (≤0.03%) A2/A4 groups.
- Compositions maximize corrosion resistance while maintaining formability.
- Adjustments like sulfur substitution with selenium enhance machinability in A1 group.
- Stabilization with titanium or niobium prevents carbide precipitation.
| 类型 | Group | Chemical Composition (mass fraction) / %一个 | Note | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| C | Si | Mn | P | S | Cr | Mo | Ni | Cu | |||
| Austenitic | A1 | 0.12 | 1 | 6.5 | 0.2 | 0.15～0.35 | 16～19 | 0.7 | 5～10 | 1.75～2.25 | b, c, d |
| A2 | 0.1 | 1 | 2 | 0.05 | 0.03 | 15～20 | —e | 8～19 | 4 | f, g | |
| A3 | 0.08 | 1 | 2 | 0.045 | 0.03 | 17～19 | —e | 9～12 | 1 | h | |
| A4 | 0.08 | 1 | 2 | 0.045 | 0.03 | 16～18.5 | 2～3 | 10～15 | 4 | g, i | |
| A5 | 0.08 | 1 | 2 | 0.045 | 0.03 | 16～18.5 | 2～3 | 10.5～14 | 1 | h, i | |
一个 Maximum values unless stated otherwise.
b Sulfur may be replaced by selenium.
c If nickel content is below 8%, minimum manganese content shall be 5%.
d If nickel content exceeds 8%, no minimum copper content is specified.
e Molybdenum content may be added at manufacturer’s discretion; specify limits if needed.
f If chromium content is below 17%, minimum nickel content shall be 12%.
克 For stainless steel with maximum carbon 0.03%, nitrogen may reach 0.22%.
h For stabilization, titanium ≥ (5×C%) to 0.8%, or niobium/tantalum ≥ (10×C%) to 1.0%.
我 For larger diameters, carbon may increase to 0.12% to achieve properties.
Mechanical Properties
General Requirements
Set screws must meet values in Tables 3 and 4 for acceptance. These properties ensure durability under torque and hardness demands in assembly applications.
- Verify via specified tests for consistent performance.
- Applicable to hardness classes 12H and 21H.
Guaranteed Torque for Socket Set Screws
Socket set screws comply with minimum torque in Table 3, tested at specified lengths to simulate real-world use.
| Nominal Thread Diameter d | Minimum Test Length一个 / mm | Hardness Class | ||||
|---|---|---|---|---|---|---|
| Flat Point | Cone Point | Dog Point | Cup Point | 12H | 21H | |
| 1.6 | 2.5 | 3 | 3 | 2.5 | 0.03 | 0.05 |
| 2 | 4 | 4 | 4 | 3 | 0.06 | 0.1 |
| 2.5 | 4 | 4 | 5 | 4 | 0.18 | 0.3 |
| 3 | 4 | 5 | 6 | 5 | 0.25 | 0.42 |
| 4 | 5 | 6 | 8 | 6 | 0.8 | 1.4 |
| 5 | 6 | 8 | 8 | 6 | 1.7 | 2.8 |
| 6 | 8 | 8 | 10 | 8 | 3 | 5 |
| 8 | 10 | 10 | 12 | 10 | 7 | 12 |
| 10 | 12 | 12 | 16 | 12 | 14 | 24 |
| 12 | 16 | 16 | 20 | 16 | 25 | 42 |
| 16 | 20 | 20 | 25 | 20 | 63 | 105 |
| 20 | 25 | 25 | 30 | 25 | 126 | 210 |
| 24 | 30 | 30 | 35 | 30 | 200 | 332 |
一个 Minimum length corresponds to at least one full socket depth as per product standards.
Hardness Requirements
Set screws must achieve hardness levels in Table 4, critical for wear resistance and load-bearing capacity.
| Hardness | Hardness Class | |
|---|---|---|
| 12H | 21H | |
| Vickers Hardness HV | 125～209 | ≥210 |
| Brinell Hardness HB | 123～213 | ≥214 |
| Rockwell Hardness HRB | 70～95 | ≥96 |
Hardness Testing
Conduct tests per GB/T 231.1 (HB), GB/T 230.1 (HRB), or GB/T 4340.1 (HV). In disputes, use Vickers as basis. Follow procedures from GB/T 3098.3 for accuracy.
- Ensure surface preparation avoids altering results.
- Test multiple points for uniformity in production batches.
Appendices
Appendix B: Austenitic Stainless Steel Compositions (from ISO 683-13:1986)
This informative appendix provides detailed compositions for austenitic steels, aiding in material selection for specific environments.
| Steel Type一个 | Chemical Compositionb (mass fraction) / % | Group Designationd | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| C | Si max | Mn max | P max | S | N | Cr | Mo | Nb | Nic | Se min | Ti | Cu | ||
| 10 | 0.030 max | 1 | 2 | 0.045 | 0.030 max | — | 17.0～19.0 | — | — | 9.0～12.0 | — | — | — | A2e |
| 19aN | 0.030 max | 1 | 2 | 0.045 | 0.030 max | 0.12～0.22 | 16.5～18.5 | 2.5～3.0 | — | 11.5～14.5 | — | — | — | A4e |
Notes from appendix: Type numbers are provisional; no additions of unlisted elements without agreement; prevent scrap contamination.
Appendix C: Austenitic Stainless Steels for Cold Heading and Extruding (from ISO 4954:1993)
This appendix lists compositions optimized for cold forming processes, ensuring workability without compromising strength.
| Steel Type Designation一个 | Chemical Compositionb (mass fraction) / % | Group Designationc | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| No. | Name | ISO 4954:1979 | C | Si max | Mn max | P max | S max | Cr | Mo | Ni | Others | |
| 78 | X 2 CrNi 18 10 E | D20 | ≤0.030 | 1 | 2 | 0.045 | 0.03 | 17.0～19.0 | — | 9.0～12.0 | — | A2d |
| 88 | X 3 CrNiCu 18 9 3 E | D32 | ≤0.04 | 1 | 2 | 0.045 | 0.03 | 17.0～19.0 | — | 8.5～10.5 | Cu:3.00～4.00 | A2 |
Notes: Designations include sequential numbers and ISO names; no unlisted element additions; prevent contamination for optimal properties.
Appendix E: Relative Magnetic Permeability of Austenitic Stainless Steels
For magnetic-sensitive applications, consult metallurgists. Austenitic steels are non-magnetic in solution-annealed state but may become magnetic after cold working. Relative permeability μr measures magnetization; values near 1 indicate low permeability.
- Example: A2: μr ≈1.8
- A4: μr ≈1.015
- A4L: μr ≈1.005
- F1: μr ≈5
Use in electronics or medical devices where low magnetism is essential.
常问问题
What stainless steel group is recommended for intergranular corrosion resistance?
Prefer stabilized A3 or A5 groups, or low-carbon A2/A4 with ≤0.03% carbon. Test per GB/T 4334 to confirm suitability in aggressive environments.
How does cold working affect magnetic properties of set screws?
Cold deformation can induce magnetism in austenitic steels. Select low-permeability grades like A4L for applications requiring non-magnetic fasteners.
What if hardness test results fall outside Table 4 ranges?
Reject the batch as it may indicate improper heat treatment. Retest using Vickers method as the arbiter and investigate manufacturing processes.
Can chemical compositions be adjusted beyond Table 2?
Only by agreement between buyer and manufacturer. Unauthorized changes risk compromising corrosion resistance or mechanical integrity.
Why specify minimum test lengths for torque testing?
To ensure full socket engagement, simulating actual use and preventing premature failure due to inadequate grip during installation.
How to choose between 12H and 21H hardness classes?
12H for general corrosion-resistant applications; 21H for higher strength needs, like vibration-prone assemblies, balancing toughness and hardness.
