ASTM A194 Grade 7
The Cr-Mo heavy hex nut — same 4140 steel as a B7 stud, rated for elevated temperature and the usual match for B16 and L7.
What A194 7 is.
ASTM A194 Grade 7 is a quenched-and-tempered chromium-molybdenum steel heavy hex nut made from the same AISI 4140 family as A193 B7. With 24 to 35 HRC hardness and a 175 ksi proof load it matches 2H in strength, and its alloy content keeps that strength at the temperatures where carbon steel begins to soften.
Grade 7 is the specified nut for B16 studs in steam service and for A320 L7 studs at low temperature (marked 7L when impact tested, or 7BL on nuts machined from bar). We machine it from certified 4140 bar, with oversize tapping and coatings to suit the stud.
Chemical composition.
| Element | Symbol | Min % | Max % |
|---|---|---|---|
| Carbon | C | 0.38 | 0.48 |
| Manganese | Mn | 0.75 | 1.00 |
| Phosphorus | P | — | 0.035 |
| Sulfur | S | — | 0.040 |
| Silicon | Si | 0.15 | 0.35 |
| Chromium | Cr | 0.80 | 1.10 |
| Molybdenum | Mo | 0.15 | 0.25 |
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 | 175 | 248 HBW / 24 HRC | 327 HBW / 35 HRC |
| Hex (finished pattern), all sizes | 150 | 248 HBW / 24 HRC | 327 HBW / 35 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.
Specifications that apply.
How A194 7 ships from Houston.
- Heavy hex nuts (the default for pressure bolting)
- Finished hex nuts
- Jam nuts
- Custom and special nuts to drawing
A194 7 fasteners we make.
Every item is manufactured to your drawing or standard in A194 7, imperial or metric, with an EN 10204 3.1 certificate.
What is ASTM A194 Grade 7?
Grade 7 is the chromium-molybdenum heavy hex nut in ASTM A194. Its chemistry is the same 0.38 to 0.48 percent carbon, 0.80 to 1.10 percent chromium, 0.15 to 0.25 percent molybdenum steel used for A193 B7 studs, and it is heat treated to the same hardness window as 2H. The alloy content is what separates it from 2H in service: at elevated temperature the Cr-Mo nut holds its hardness and proof load longer than plain carbon steel.
Grade 7, 7L and 7M
- Grade 7: standard elevated-temperature Cr-Mo nut; pairs with B7 and B16.
- Grade 7L: Grade 7 Charpy impact tested at −150 °F under A320 S3; pairs with A320 L7.
- Grade 7M: Grade 7 tempered to 235 HBW maximum for NACE sour service; pairs with B7M and L7M.
Testing, certification and marking
- Hardness tested per lot; proof-load tested on request or where the specification requires it
- Grade symbol 7, or 7B 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
Recent A194 7 jobs.
ASTM A193 Grade B16
Vanadium-strengthened Cr-Mo bolting that holds its strength where B7 starts to relax — steam turbines, HP steam flanges and hot valve bonnets.
ASTM A320 / ASME SA-320ASTM A320 Grade L7
The low-temperature twin of B7 — same 4140 Cr-Mo steel, same 125 ksi strength, but impact tested at −150 °F for cryogenic and cold-climate service.
ASTM A194 / ASME SA-194ASTM A194 Grade 7M
Controlled-hardness Cr-Mo nut for sour service at temperature — 235 HBW max, NACE MR0175, for B7M and L7M studs.