ASTM A194 Grade 3
The 5 Cr-Mo heavy hex nut for A193 B5 studs — matched corrosion behaviour on hot, sulfur-bearing refinery lines.
What A194 3 is.
ASTM A194 Grade 3 is a quenched-and-tempered nut in AISI 501, the same 5 percent chromium, half percent molybdenum steel as A193 B5. It is heat treated to 24 to 35 HRC with a 175 ksi proof load for heavy hex nuts, so it matches 2H and 7 in strength while sharing B5's resistance to oxidation and sulfidation at temperature.
Grade 3 is specified with B5 studs on 5 Cr piping and furnace hardware in refineries. We machine it to order from certified bar.
Chemical composition.
| Element | Symbol | Min % | Max % |
|---|---|---|---|
| Carbon | C | 0.10 | — |
| Manganese | Mn | — | 1.00 |
| Phosphorus | P | — | 0.040 |
| Sulfur | S | — | 0.030 |
| Silicon | Si | — | 1.00 |
| Chromium | Cr | 4.0 | 6.0 |
| Molybdenum | Mo | 0.40 | 0.65 |
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 3 ships from Houston.
- Heavy hex nuts (the default for pressure bolting)
- Finished hex nuts
- Jam nuts
- Custom and special nuts to drawing
A194 3 fasteners we make.
Every item is manufactured to your drawing or standard in A194 3, imperial or metric, with an EN 10204 3.1 certificate.
What is ASTM A194 Grade 3?
Grade 3 is the 5 Cr-Mo nut in A194, produced from the same AISI 501 steel as A193 B5 studs and quenched and tempered at 1050 °F minimum. The proof load and hardness window are the same as Grade 2H and Grade 7, so the joint is as strong as a B7/2H set; the difference is corrosion behaviour in hot sulfur-bearing streams, where the 5 percent chromium of both stud and nut resists sulfidation that would attack carbon or low-alloy steel.
Testing, certification and marking
- Hardness tested per lot; proof-load tested on request or where the specification requires it
- Grade symbol 3, or 3B 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 B5
5 Cr-½ Mo bolting for hot, sulfur-bearing refinery service — the grade that matches P5 piping and furnace hardware.
ASTM A194 / ASME SA-194ASTM 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 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.