4142 Alloy Steel (UNS G41420)
4140's higher-carbon sibling: the same chromium-molybdenum steel with 0.40 to 0.45 percent carbon for a little more hardenability and strength in large sections — quenched and tempered to A434 Class BB, BC or BD.
What 4142 is.
4142 is a chromium-molybdenum alloy steel identical to 4140 except that its carbon range is shifted up by 0.02 percent. That small change improves hardenability, so larger sections reach full hardness on quenching and the steel holds strength better in heavy bar. It is quenched and tempered to the same ASTM A434 classes as 4140 and used for the same shafts, studs, gears and machinery parts, and it is often what a mill supplies against a 4140 order.
We machine 4142 from certified A322 bar, quenched and tempered to A434 Class BB, BC or BD, or to a hardness range on the drawing. For pressure bolting the closely related chemistry is ASTM A193 B7.
Chemical composition.
| Element | Symbol | Min % | Max % |
|---|---|---|---|
| Carbon | C | 0.40 | 0.45 |
| 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).
Mechanical properties.
| Condition and nominal diameter (in.) | Tensile strength, min (ksi) | Yield strength 0.2% offset, min (ksi) | Elongation, min (%) | Reduction of area, min (%) | Hardness |
|---|---|---|---|---|---|
| Class BB — 1½ and under | 110 | 90 | 20 | 50 | — |
| Class BB — over 1½ to 2½ | 105 | 80 | 20 | 50 | — |
| Class BB — over 2½ to 4 | 100 | 75 | 20 | 50 | — |
| Class BB — over 4 to 7 | 95 | 75 | 20 | 50 | — |
| Class BB — over 7 to 10 | 90 | 65 | 18 | 40 | — |
| Class BC — 1½ and under | 130 | 110 | 16 | 50 | — |
| Class BC — over 1½ to 2½ | 125 | 105 | 16 | 50 | — |
| Class BC — over 2½ to 4 | 115 | 95 | 16 | 45 | — |
| Class BC — over 4 to 7 | 110 | 85 | 16 | 45 | — |
| Class BC — over 7 to 10 | 105 | 80 | 15 | 40 | — |
| Class BD — 1½ and under | 155 | 130 | 14 | 35 | — |
| Class BD — over 1½ to 2½ | 150 | 120 | 14 | 35 | — |
| Class BD — over 2½ to 4 | 140 | 110 | 14 | 35 | — |
| Class BD — over 4 to 7 | 135 | 105 | 14 | 35 | — |
| Class BD — over 7 to 10 | 130 | 100 | 14 | 35 | — |
Values per ASTM A434/A434M-18 Table 1 for the 4100 series, quenched and tempered (verified against the specification). Yield is 0.2 % offset; elongation in 2 in.
Specifications that apply.
How 4142 ships from Houston.
- Machined components from certified bar
- Studs, threaded rod and U-bolts
- Hex bolts and cap screws
- Nuts, washers and spacers
- Pins, shafts and bushings
4142 fasteners we make.
Every item is manufactured to your drawing or standard in 4142, imperial or metric, with an EN 10204 3.1 certificate.
What is 4142 steel?
4142 is a 0.42 percent carbon chromium-molybdenum steel, one step up the 41xx series from 4140. The extra carbon raises hardenability and as-quenched hardness, which helps large diameters reach the specified strength through the section. In everything else, machinability, weldability with preheat, response to nitriding and induction hardening, it matches 4140, and the two are frequently supplied interchangeably against the A434 classes.
Choosing the A434 class
- Class BB, 110 ksi: general shafts and studs, easiest to machine after heat treatment.
- Class BC, 130 ksi: high-strength studs, gears and tooling; the most common order.
- Class BD, 155 ksi: maximum strength for small and medium sections; check toughness for impact service.
- For pressure-boundary bolting, order to A193 B7 so the testing and marking match the code.
Testing, certification and marking
- Tensile and hardness tested per heat-treat lot
- Manufacturer's identification and heat number on every piece
- EN 10204 3.1 material test report with heat number and chemistry; 3.2 witness available
- PMI and magnetic particle inspection on request
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.
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 A193 / ASME SA-193ASTM A193 Grade B7
The workhorse alloy-steel bolting grade for flanges, valves and pressure equipment — 125 ksi tensile, quenched and tempered 4140.