ASTM A194 Grade 4
A carbon-molybdenum nut grade withdrawn from ASTM A194 — kept here for legacy drawings; Grade 7 is the current alloy-steel nut for B7 and L7 studs.
What A194 4 is.
ASTM A194 Grade 4 was a carbon-molybdenum (AISI 4037-type) heavy hex nut grade for elevated-temperature service. It has been removed from the specification and does not appear in A194/A194M-24, so it can no longer be certified to a current edition. Drawings and old purchase specifications still call for it, and this page records what it was.
For new work we supply Grade 7 (chromium-molybdenum, 1100 °F temper) with B7 and L7 studs, or Grade 2H where the joint does not need alloy nuts. Where a legacy drawing insists on Grade 4, we will quote a Grade 7 nut marked and certified to the current edition and note the substitution.
Chemical composition.
| Element | Symbol | Min % | Max % |
|---|---|---|---|
| Carbon | C | 0.40 | 0.50 |
| Manganese | Mn | 0.70 | 0.90 |
| Phosphorus | P | — | 0.035 |
| Sulfur | S | — | 0.040 |
| Silicon | Si | 0.15 | 0.35 |
| Molybdenum | Mo | 0.20 | 0.30 |
Grade 4 (carbon-molybdenum) has been withdrawn from ASTM A194; it does not appear in A194/A194M-24. The values shown are from the last edition that listed the grade and cannot be verified against the current specification. Order Grade 7 for new work.
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 |
Grade 4 (carbon-molybdenum) has been withdrawn from ASTM A194; it does not appear in A194/A194M-24. The values shown are from the last edition that listed the grade and cannot be verified against the current specification. Order Grade 7 for new work.
Specifications that apply.
How A194 4 ships from Houston.
- Heavy hex nuts (the default for pressure bolting)
- Finished hex nuts
- Jam nuts
- Custom and special nuts to drawing
A194 4 fasteners we make.
Every item is manufactured to your drawing or standard in A194 4, imperial or metric, with an EN 10204 3.1 certificate.
Why Grade 4 is no longer on the certificate
ASTM A194 has trimmed its ferritic grade list over the years, and Grade 4 was one of the grades removed. A194/A194M-24 lists Grades 1, 2, 2H, 2HM, 3, 6, 6F, 7, 7M, 43 and 16 for the ferritic side. A nut cannot be certified to a grade the current edition does not contain, so an order for Grade 4 is filled with Grade 7, which is the chromium-molybdenum nut used with A193 B7 and A320 L7 studs, or with the nut grade the stud specification requires.
Testing, certification and marking
- Not certifiable to A194/A194M-24; Grade 7 supplied and marked 7 (or 7L when impact tested under A320)
- EN 10204 3.1 material test report with heat number and chemistry for the supplied grade
- Substitution noted on the certificate and the packing list
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 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.