AISI 4140 Alloy Steel (UNS G41400)
The workhorse Cr-Mo steel behind B7, L7 and Grade 7 — the bar stock for studs, shafts, couplings and any part that needs 100 to 150 ksi and good toughness.
What 4140 is.
AISI 4140 is a 0.40 percent carbon chromium-molybdenum steel and the most widely used alloy steel in the fastener and oil-tool industries. It hardens through in sections to about 2½ inches, tempers to a wide range of strengths and machines well in the annealed or pre-hardened condition. It is the base steel for ASTM A193 B7, A320 L7 and A194 Grade 7.
ASTM A322 governs the chemistry of hot-wrought bar and ASTM A434 the mechanical classes of quenched-and-tempered bar. We stock certified 4140 and 4142 bar for machined components and non-ASTM-grade fasteners.
Chemical composition.
| Element | Symbol | Min % | Max % |
|---|---|---|---|
| Carbon | C | 0.38 | 0.43 |
| 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 A322-13(2018) Table 1 (verified against the specification). Confirm the edition called out on your purchase order with our estimating team. 4142 (G41420): carbon 0.40–0.45 %, otherwise identical.
Mechanical properties.
| Diameter (in.) | Yield strength, min (ksi) | Tensile strength, min (ksi) | Elongation, min (%) | Reduction of area, min (%) |
|---|---|---|---|---|
| 1½ and under | 110 | 130 | 16 | 50 |
| Over 1½ to 2½ | 105 | 125 | 16 | 50 |
| Over 2½ to 4 | 95 | 115 | 16 | 45 |
| Over 4 to 7 | 85 | 110 | 16 | 45 |
| Over 7 to 10 | 80 | 105 | 15 | 40 |
Values per ASTM A434/A434M-18 Table 1 (verified against the specification). Confirm the edition called out on your purchase order with our estimating team.
| Diameter (in.) | Yield strength, min (ksi) | Tensile strength, min (ksi) | Elongation, min (%) | Reduction of area, min (%) |
|---|---|---|---|---|
| 1½ and under | 90 | 110 | 20 | 50 |
| Over 1½ to 2½ | 80 | 105 | 20 | 50 |
| Over 2½ to 4 | 75 | 100 | 20 | 50 |
| Over 4 to 7 | 75 | 95 | 20 | 50 |
| Over 7 to 10 | 65 | 90 | 18 | 40 |
Values per ASTM A434/A434M-18 Table 1 (verified against the specification). Confirm the edition called out on your purchase order with our estimating team.
| Diameter (in.) | Yield strength, min (ksi) | Tensile strength, min (ksi) | Elongation, min (%) | Reduction of area, min (%) |
|---|---|---|---|---|
| 1½ and under | 130 | 155 | 14 | 35 |
| Over 1½ to 2½ | 120 | 150 | 14 | 35 |
| Over 2½ to 4 | 110 | 140 | 14 | 35 |
| Over 4 to 7 | 105 | 135 | 14 | 35 |
| Over 7 to 10 | 100 | 130 | 14 | 35 |
Values per ASTM A434/A434M-18 Table 1 (verified against the specification). Confirm the edition called out on your purchase order with our estimating team.
Specifications that apply.
How 4140 ships from Houston.
- Studs, bolts and threaded rod machined from bar
- Shafts, pins, couplings and machined components
- Certified A322 bar, annealed, normalised or quenched and tempered to A434
4140 fasteners we make.
Every item is manufactured to your drawing or standard in 4140, imperial or metric, with an EN 10204 3.1 certificate.
4140 as bar versus 4140 as B7
The same 4140 bar can become an A434 Class BC shaft or an A193 B7 stud; the difference is which specification governs the heat treatment and testing. A434 classes are strength levels for bar with tensile and yield minimums by diameter. A193 B7 adds a minimum tempering temperature, a hardness cap of 35 HRC, per-lot testing and grade marking. When a drawing simply says 4140 with a hardness or strength, we treat and certify to A434 or to the drawing; when it says B7 we certify to A193.
Choosing a class
- Class BB: 110 ksi tensile, the general machining and shafting level.
- Class BC: 130 ksi, the usual pre-hardened condition for pump shafts, couplings and non-ASTM studs.
- Class BD: 155 ksi, the high-strength level for pins, tooling and heavily loaded components; toughness drops, so specify it with care in cold service.
Testing, certification and marking
- Tensile and hardness tested per lot on the finished product
- Grade or alloy marking by grade, class and heat on the certificate and manufacturer's identification on every piece
- EN 10204 3.1 material test report with heat number and chemistry; 3.2 witness available
Recent 4140 jobs.
ASTM A193 Grade B7
The workhorse alloy-steel bolting grade for flanges, valves and pressure equipment — 125 ksi tensile, quenched and tempered 4140.
ASTM A322 bar · ASTM A434 Q&T barAISI 4340 Alloy Steel (UNS G43400)
The deep-hardening high-strength steel — 4340 reaches 155 ksi and beyond in large sections — for crankshafts, drilling tools, aircraft parts and A320 L43 bolting.
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.