ASTM A194 Grade 7M
Controlled-hardness Cr-Mo nut for sour service at temperature — 235 HBW max, NACE MR0175, for B7M and L7M studs.
What A194 7M is.
ASTM A194 Grade 7M is Grade 7 tempered to a maximum of 235 HBW for hydrogen sulfide service. It keeps the chromium-molybdenum chemistry that resists softening at temperature while meeting the 22 HRC ceiling of NACE MR0175 / ISO 15156, and it is hardness tested on every piece.
7M is the alloy-steel alternative to 2HM for sour lines that also run hot. We machine it from certified 4140 bar, test 100 percent and certify it with the matching B7M or L7M studs.
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 | 150 | 159 HBW / 84 HRB | 235 HBW / 99 HRB |
| Hex (finished pattern), all sizes | 135 | 159 HBW / 84 HRB | 235 HBW / 99 HRB |
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. 100 percent hardness testing; final stress relief after machining at not less than 50 °F below the original tempering temperature (1200 °F minimum in a furnace after an induction temper above 1300 °F).
Specifications that apply.
How A194 7M ships from Houston.
- Heavy hex nuts (the default for pressure bolting)
- Finished hex nuts
- Jam nuts
- Custom and special nuts to drawing
A194 7M fasteners we make.
Every item is manufactured to your drawing or standard in A194 7M, imperial or metric, with an EN 10204 3.1 certificate.
What is ASTM A194 Grade 7M?
7M takes the Cr-Mo Grade 7 nut and tempers it further, to a 159 to 235 HBW window, so it can be used where wet hydrogen sulfide is present. Proof load falls to 150 ksi to match the softer B7M stud. Because every piece must be hardness tested, 7M carries a 100 percent inspection record on its certificate rather than a lot sample.
7M or 2HM?
Both meet the same NACE hardness limit and proof load. 2HM is plain carbon steel and is the more common, lower-cost choice for ambient sour service. 7M's chromium-moly chemistry gives it better property retention at elevated temperature, so it is preferred on hot sour lines and wherever the piping specification calls for an alloy nut.
Testing, certification and marking
- Every nut hardness tested (100 percent, A194 clause 8.1.3.1); proof-load tested per lot
- Grade symbol 7M, or 7MB 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 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.
ASTM A193 / ASME SA-193ASTM A193 Grade B7M
B7 tempered to 22 HRC max for sour service — the NACE MR0175 bolting grade for wellheads, sour gas and H₂S process piping.
ASTM A194 / ASME SA-194ASTM A194 Grade 2HM
The sour-service heavy hex nut — 2H tempered to 235 HBW max for NACE MR0175, matched to A193 B7M and A320 L7M studs.