Quenched & tempered steel grades
3 quenched & tempered steel grades from 2 designation systems, each with a full data sheet. Sorted by system; the yield and tensile values are the first line of each grade's mechanical table.
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AISI / SAE
| Grade | No. | Type | C % | Yield MPa | Tensile MPa | Equivalents |
|---|---|---|---|---|---|---|
| 4140 | G41400 | Chromium-molybdenum low-alloy steel (chromoly) | 0.38 – 0.43 | ≈ 415 | ≈ 655 | 42CrMo4, SCM440, 42CrMo |
| 4340 | G43400 | Nickel-chromium-molybdenum low-alloy steel, deep hardening | 0.38 – 0.43 | ≈ 470 | ≈ 745 | 34CrNiMo6, 36CrNiMo4, SNCM439 |
EN (European)
| Grade | No. | Type | C % | Yield MPa | Tensile MPa | Equivalents |
|---|---|---|---|---|---|---|
| 42CrMo4 | 1.7225 | Chromium-molybdenum steel for quenching and tempering | 0.38 – 0.45 | 900 | 1100–1300 | 4140, 4142, SCM440 |
The heat treatment is the grade
Quenched-and-tempered steels are sold on the properties the heat treatment produces, not on chemistry alone. S690QL guarantees 690 MPa yield after quenching and tempering; the same analysis in the as-rolled condition would deliver less than half of that.
The practical consequence is that the condition must be on the order. A certificate that names a grade without naming +QT tells you nothing useful about strength, and a thickness must be stated too — guaranteed yield falls as section thickness rises, because a thick section cools more slowly and hardens less.
Welding without destroying what you bought
Every welding pass re-heats the steel next to it, and in a quenched-and-tempered grade that means locally undoing the temper. The heat-affected zone can end up both harder and more brittle than the parent, or softer, depending on the heat input.
The controls are specific: preheat according to thickness and carbon equivalent, limit the heat input to the range the mill recommends, use low-hydrogen consumables and keep the interpass temperature inside a defined window. These grades are welded routinely in crane booms and excavator arms — but by procedure, not by improvisation.
Abrasion grades are a separate conversation
Wear plate — AR400, AR450, AR500 and the branded equivalents — is quenched and tempered too, but it is specified by surface hardness rather than by yield. AR500 at roughly 500 HBW resists abrasion far better than S690QL, and bends far less willingly.
Using a wear grade as a structural member, or a structural QT grade as a liner, both waste money. The question to answer first is whether the part is loaded or worn.
faq.h
What does QL mean in S690QL?
Q for quenched and tempered, L for guaranteed impact toughness at low temperature — −40 °C for QL and −60 °C for QL1. The 690 is the guaranteed yield in MPa for the thinnest thickness band.
Can S690QL be welded?
Yes, routinely, but by procedure: preheat set by thickness and carbon equivalent, controlled heat input within the mill's recommended range, low-hydrogen consumables and a defined interpass temperature window. Uncontrolled welding softens or embrittles the heat-affected zone.
What is the difference between AR400 and S690QL?
What they guarantee. AR400 is specified by surface hardness, around 400 HBW, for abrasion resistance. S690QL is specified by yield strength for load carrying. A wear plate is not a structural plate and vice versa.
Does guaranteed yield change with thickness?
Yes, and substantially. Thick sections cool more slowly during quenching and harden less, so the standard publishes lower guaranteed yield for thicker bands. A grade name without a thickness is an incomplete specification.
Is Hardox the same as AR500?
Hardox is a brand of quenched-and-tempered wear plate, and its 500 grade sits in the same hardness range as generic AR500. They are comparable in hardness but not identical in toughness, flatness or bendability guarantees, which is part of what the brand sells.