GlossaryKind of term: Manufacturing term42CrMo4
What is 42CrMo4?
42CrMo4 (1.7225) is a chromium-molybdenum quench and temper steel for shafts and heavily loaded parts; its delivery condition, +A or +QT, sets the route.
42CrMo4, material number 1.7225, is a low-alloy chromium-molybdenum steel for parts that must be strong and tough: shafts, gears, bolts, cranks and hydraulic components. The closest US grade is 4140. It is usually supplied soft annealed (+A) or quenched and tempered (+QT); in +QT it has been hardened and tempered before delivery, to a strength that depends on diameter or thickness. The faces that wear can afterwards be induction hardened or nitrided.
What does the standard say about 42CrMo4?
42CrMo4 is covered by EN ISO 683-2, the successor to EN 10083-3, with composition and mechanical properties per delivery condition and size range. Because the strength achievable after quenching and tempering falls with diameter, a strength or hardness requirement is only unambiguous with condition and size attached. A drawing that says only 42CrMo4, with no condition or strength, is missing a requirement. The variant with controlled sulphur, 42CrMoS4 (1.7227), is in the same standard.
How does 42CrMo4 behave in the shop?
The condition drives the route. In +QT you machine straight to size, at lower cutting data and with more wear than in the soft state, but with no heat treater involved. In +A it machines more easily; if quenched and tempered strength is needed, it then goes out for quenching and tempering, usually to a heat treater, and comes back for finishing, with allowance for distortion and any scale. If a bearing seat is induction hardened after roughing, it usually needs a grinding allowance followed by grinding or hard turning, depending on tolerance, roughness and distortion. Each step is its own item: machining, the subcontracted heat treatment, and finishing in a further setup. Which route is cheapest depends on quantity, size, tolerances and lead time.
What is 42CrMo4 often confused with?
42CrMo4 is not 42CrMoS4, which has a controlled sulphur content for better chip breaking. And quenched and tempered is not through hardened to a high hardness: 42CrMo4+QT is strong and tough and machines with standard cutting tool materials, while a part hardened to a high HRC afterwards calls for hard turning with CBN or grinding.
Frequently asked questions
What does +QT after 42CrMo4 mean?
Quenched and tempered: hardened and then tempered. The steel is stronger and tougher than in the soft annealed condition and still machines straight to size, at lower cutting data and with more tool wear.
Is 42CrMo4 the same as 4140?
They are close and often listed as equivalents, but the standards differ in composition limits and delivery conditions. Order to the designation and condition on the drawing, and have the certificate state that standard.