AISI 4140 and H11 are very similar in carbon content — both are around 0.40% carbon. Even so, they belong to different classes: 4140 is a quenched and tempered steel, while H11 is a hot work tool steel. The element that separates them is chromium.
1% chromium against 5% chromium
In AISI 4140 chromium is 1.00% and molybdenum 0.25%. In H11 chromium rises to 5.00%, molybdenum rises to 1.30%, and 0.50% vanadium is added to the composition. Silicon also rises from 0.25% to 0.90%.
That composition gives H11 its resistance to tempering: the part does not lose its hardness while working at high temperature. 4140, by contrast, softens as it heats up. Even at room temperature the difference is large — according to our datasheets, H11 gives a tensile strength of 1793 MPa when hardened and tempered, while AISI 4140 is at 930 MPa in a 50 mm section.
Comparison in numbers
| PROPERTY | AISI 4140 | H11 |
|---|---|---|
| Carbon (C) | 0.40% | 0.40% |
| Chromium (Cr) | 1.00% | 5.00% |
| Molybdenum (Mo) | 0.25% | 1.30% |
| Vanadium (V) | — | 0.50% |
| Silicon (Si) | 0.25% | 0.90% |
| Manganese (Mn) | 0.85% | 0.30% |
| Tensile strength Rm | 930 MPa (50 mm section) | 1793 MPa |
| Yield strength Rp0.2 | 770 MPa (50 mm section) | 1482 MPa |
| Elongation | 17% (50 mm section) | 8% |
| Reduction of area | — | 30% |
| UNS | G41400 | — |
| AMS | 6349 · 6382 | 6485 · 6487 |
Values are taken from our product datasheets; section thickness and the applied heat treatment regime change the result.
Which one, and when?
AISI 4140 is preferred — shafts, gear bodies, fasteners, hydraulic components, general machine manufacturing. It is the first steel that comes to mind wherever moderate strength is required at room temperature; it is easy to source and easy to machine.
H11 is required — hot forging dies, extrusion dies, die casting components and aerospace parts carrying load at high temperature. If the specification calls out AMS 6485 or AMS 6487, the grade being asked for is H11; 4140 is not an acceptable substitute.
Neighbouring alloys
For the step above 4140, see our AISI 4140 – AISI 4340 comparison; for much higher strength at room temperature, see the 300M and AerMet 100 pages.
Technical datasheets
AISI 4140 — chemical composition, mechanical values, standard equivalents
H11 — chemical composition, mechanical values, standard equivalents
Both grades are supplied to order in round bar, flat bar, plate, sheet, pipe and forged forms. Contact us for a quotation.