ASTM A194 Grade 6 (410 Stainless)
The 410 stainless heavy hex nut for A193 B6 studs — hardened and tempered, 20 to 28 HRC, for valve and steam service.
What A194 6 is.
ASTM A194 Grade 6 is a hardened-and-tempered nut in Type 410 martensitic stainless, the companion to A193 B6 studs. It is heat treated to 20 to 28 HRC, and Grade 6F is the same nut in free-machining Type 416.
Grade 6 is used on valve bonnets, steam equipment and pumps where a magnetic, hardenable stainless is wanted. We machine it to order from certified 410 or 416 bar.
Chemical composition.
| Element | Symbol | Min % | Max % |
|---|---|---|---|
| Carbon | C | 0.08 | 0.15 |
| Manganese | Mn | — | 1.00 |
| Phosphorus | P | — | 0.040 |
| Sulfur | S | — | 0.030 |
| Silicon | Si | — | 1.00 |
| Chromium | Cr | 11.5 | 13.5 |
Values per ASTM A194/A194M-24, Tables 1, 2 and 5 (verified against the specification). Confirm the edition called out on your purchase order with our estimating team.
Mechanical properties.
| Nut style and size (in.) | Proof load stress (ksi) | Hardness, min | Hardness, max |
|---|---|---|---|
| Heavy hex, all sizes | 150 | 228 HBW / 20 HRC | 271 HBW / 28 HRC |
| Hex (finished pattern), all sizes | 135 | 228 HBW / 20 HRC | 271 HBW / 28 HRC |
Values per ASTM A194/A194M-24, Tables 1, 2 and 5 (verified against the specification). Confirm the edition called out on your purchase order with our estimating team. Grade 6F (Type 416 / 416Se) has the same mechanical requirements. Tempered for at least 1 h. Grade 6F chemistry per Table 1: C 0.15 max, Mn 1.25 max, P 0.060 max, S 0.15 min (416) or S 0.060 max with Se 0.15 min (416Se), Si 1.00 max, Cr 12.0–14.0.
Specifications that apply.
How A194 6 ships from Houston.
- Heavy hex nuts (the default for pressure bolting)
- Finished hex nuts
- Jam nuts
- Custom and special nuts to drawing
A194 6 fasteners we make.
Every item is manufactured to your drawing or standard in A194 6, imperial or metric, with an EN 10204 3.1 certificate.
What is ASTM A194 Grade 6?
Grade 6 is A194's martensitic stainless nut. Type 410 hardens by quenching, so the nut is heat treated to a 20 to 28 HRC window rather than solution annealed. The lower hardness ceiling compared with 2H reflects the need to keep the martensite tough. Grade 6F substitutes Type 416, which contains sulfur for machinability and is otherwise equivalent; it is the common choice for high-volume production.
Matching the stud
Use Grade 6 with A193 B6 studs. For sour service to NACE MR0175 / ISO 15156, specify nuts that meet the 22 HRC limit the standard sets for 410-type martensitic material; the 20 to 28 HRC window of Grade 6 overlaps it, so ask for nuts selected below 26 HRC on the certificate.
Testing, certification and marking
- Hardness tested per lot; proof-load tested on request or where the specification requires it
- Grade symbol 6, or 6B on nuts machined from bar (ASTM A194 Table 7), and manufacturer's identification on one face of every nut
- EN 10204 3.1 material test report with heat number and chemistry; 3.2 witness available
- Oversize tapping for coated studs and PTFE / zinc / hot-dip galvanized finishes available
ASTM A193 Grade B6 (410 Stainless)
Hardenable 410 stainless bolting — 110 ksi with corrosion resistance B7 lacks, for valve trim, steam and mildly corrosive service.
ASTM A194 / ASME SA-194ASTM A194 Grade 8 (304 Stainless)
304 stainless heavy hex nut for A193 and A320 B8 studs — solution treated, 80 ksi proof load, corrosion resistant from cryogenic to 1500 °F.
ASTM A194 / ASME SA-194ASTM A194 Grade 2H
The standard heavy hex nut for A193 B7 studs — quenched and tempered carbon steel, 175 ksi proof load, 24 to 35 HRC.