42CrMo4: Steel Technical Specifications

0142CrMo4 steel: key characteristics and properties

42CrMo4 steel (material number 1.7225) is a chromium-molybdenum quenched and tempered alloy steel classified according to EN ISO 683-2:2018 (formerly EN 10083-3), roughly equivalent to AISI/SAE 4140. It is among the most widely used engineering alloys for mechanical parts subjected to fatigue and torsion, thanks to the high hardenability imparted by chromium and molybdenum, the high mechanical properties after quenching and tempering, and good machinability. The combination of these characteristics makes it the benchmark grade when a non-alloy steel such as C45 cannot guarantee sufficient depth of hardening in the required sections.

The composition, defined by EN ISO 683-2:2018 (formerly EN 10083-3), comprises carbon 0.38-0.45%, chromium 0.90-1.20% and molybdenum 0.15-0.30%; molybdenum also reduces the susceptibility to temper embrittlement. After quenching and tempering (+QT), 42CrMo4 reaches tensile strengths, depending on the diameter, between approximately 800 and 1300 MPa, with typical hardness values of 280-320 HBW. It is supplied mainly in the quenched and tempered condition, as well as annealed or hot-rolled for subsequent processing.

Typical applications range from drive shafts, gears, pins and connecting rods in the automotive sector and heavy machinery, to components for oil&gas and equipment subjected to high dynamic loads.

02Chemical composition of 42CrMo4 steel

The chemical composition of 42CrMo4 is defined by EN ISO 683-2:2018 (formerly EN 10083-3) and forms the basis of the mechanical properties obtainable after quenching and tempering. Carbon (0.38-0.45%) determines the hardness achievable after hardening; chromium (0.90-1.20%) increases hardenability and promotes the formation of stable carbides; molybdenum (0.15-0.30%) improves temper resistance and counteracts temper embrittlement, a critical aspect for safety-critical components. Manganese (0.60-0.90%) and silicon (≤0.40%) complete deoxidation and contribute to hardenability and structural refinement.

Phosphorus (≤0.025%) and sulphur (≤0.035%) contents are kept low to limit brittleness and ensure machinability. The improved-machinability variant 42CrMoS4 (material number 1.7227) features controlled sulphur in the range 0.020-0.040%, while keeping the other compositional characteristics unchanged. On request, supply with calcium treatment for inclusion control is available, benefiting toughness and transverse fatigue strength.

03Mechanical properties of 42CrMo4 steel

The mechanical properties of 42CrMo4 depend on the delivery condition and, after quenching and tempering (+QT), on the reference diameter of the piece: the material's hardenability allows high values to be maintained even on medium-to-large sections. EN ISO 683-2:2018 (formerly EN 10083-3) prescribes the ranges by dimensional class listed below; the yield strength Rp0.2 decreases from approximately 900 MPa for small sections to approximately 550 MPa for diameters of 100-160 mm.

Hardness after quenching and tempering typically ranges between 280 and 320 HBW, corresponding to approximately 29-34 HRC. Percentage elongation increases from 10% for small sections up to 13-14% for larger diameters, confirming good ductility despite the high strength. The KV impact toughness remains at values on the order of 35 J for most sections, an important requirement for components subjected to dynamic and impact loads. The elastic modulus is approximately 210 GPa. The rotating-bending fatigue limit is on the order of 370 MPa.

04Physical characteristics of 42CrMo4 steel

The physical characteristics of 42CrMo4 are those typical of quenched and tempered alloy steels and are used for the thermomechanical dimensioning of components. The density is approximately 7.85 g/cm³. The modulus of elasticity (Young's modulus) is approximately 210 GPa at room temperature, with a slight reduction as temperature increases (approximately 205 GPa at 100 °C). Poisson's ratio is 0.27-0.30.

Specific heat (460-470 J/(kg·K)) and thermal conductivity (42.6-46 W/(m·K)) are useful parameters for calculating heat-treatment cycles. The coefficient of linear thermal expansion (about 12.2 μm/(m·K) over the 20-100 °C range) must be taken into account when calculating tolerances on components subject to thermal cycling. Electrical resistivity is of the order of 0.2 Ω·mm²/m. These values are physical properties of the material and do not constitute normative requirements of EN ISO 683-2:2018 (formerly EN 10083-3).

05Heat treatments of 42CrMo4 steel

The reference treatment for 42CrMo4 is quenching and tempering, consisting of hardening followed by tempering. Hardening involves austenitising at about 840-870 °C followed by oil quenching; water quenching is reserved for large sections where oil does not provide sufficient quench severity. Oil quenching is preferable for complex geometries and crack-sensitive parts, as it limits internal stresses and the risk of cracking; water quenching increases quench severity but raises the risk of distortion and cracking.

Tempering is carried out between 540 and 680 °C and is the parameter that balances strength and toughness: lower temperatures favour tensile strength, while higher temperatures favour toughness and impact toughness. Hardness in the as-quenched state (martensitic, before tempering) reaches about 55-58 HRC, consistent with a carbon content of ~0.42%. Among the preliminary treatments, normalising (840-880 °C, air cooling) refines the structure; soft annealing (680-720 °C) and spheroidise annealing (740-770 °C) reduce hardness to facilitate chip removal.

42CrMo4 can also undergo surface treatments: induction surface hardening makes it possible to exceed 53 HRC at the surface while maintaining a tough quenched and tempered core; nitriding is common on shafts and gears to increase surface hardness, wear resistance and fatigue strength.

06Industrial applications of 42CrMo4 steel

42CrMo4 is used in sectors requiring strength, toughness and hardenability in medium-to-large sections. In the automotive and commercial vehicle sector it is used for half-shafts, drive shafts, gears, pins and steering tie rods, where fatigue strength and toughness matter. In heavy machinery it is used for gears (quenched and tempered, and nitrided), connecting rods, spindles and hydraulic cylinders, taking advantage of good machinability combined with high hardenability.

In the oil&gas sector it is used for drill pipe and plant components, for its wear resistance and toughness in harsh environments. It is also used in the railway sector (axles and suspension components) and in certain structural components where strength and toughness are required; for the most critical aerospace applications, such as high-strength landing gear, higher-toughness/higher-strength grades are typically used (e.g. 34CrNiMo6, 4340/300M), while 42CrMo4 covers less-stressed components. Its versatility stems from the ability to modulate surface hardness and core toughness through heat treatments.

07Frequently asked questions about 42CrMo4 steel

7.1What is the difference between 42CrMo4 and 4140?

42CrMo4 (EN ISO 683-2:2018 (formerly EN 10083-3), 1.7225) and AISI/SAE 4140 (ASTM A29) are very close grades, considered approximate equivalents. The main difference is in manganese: 0.60-0.90% in 42CrMo4 versus 0.75-1.00% in 4140. The carbon, chromium and molybdenum ranges are practically identical, so mechanical strength and hardenability are comparable. They remain grades from different standards: the equivalence is indicative, not an identity.

7.2What are the standard delivery conditions?

42CrMo4 is supplied mainly in the quenched and tempered condition (+QT), ready for structural use. Also available are the annealed condition, for applications requiring low hardness and excellent machinability, and the hot-rolled/as-rolled condition, when there are no specific hardness requirements prior to machining.

7.3How is machinability optimised?

Machinability is improved by annealing: soft annealing at 680-720 °C, or spheroidise annealing at 740-770 °C, brings hardness below 241 HBW (and below 200 HBW in the spheroidise case). The 42CrMoS4 variant (sulphur 0.020-0.040%) offers superior machinability with otherwise equivalent properties.

7.4What are the international equivalents?

In addition to AISI/SAE 4140, 42CrMo4 has approximate equivalents in GB/T 3077 42CrMo (China) and JIS SCM440 (Japan), the latter with slight differences in manganese and silicon content. These are indicative equivalents, useful for procurement but not a perfect identity between standards.

7.5When should you choose 42CrMo4 over other grades?

42CrMo4 is the typical choice when a balance is needed between strength (Rm ~900-1300 MPa depending on section), toughness (KV ≥35 J) and hardenability in medium-to-large sections, performance not achievable with a non-alloy steel such as C45. When greater hardenability or toughness is required in even larger sections, nickel-chromium-molybdenum grades such as 39NiCrMo3 or 34CrNiMo6 are considered.

08Siderticino 42CrMo4 steel

Siderticino supplies certified-quality 42CrMo4 steel in accordance with EN ISO 683-2:2018 (formerly EN 10083-3), with material traceability and EN 10204 inspection documents (type 2.1 as standard, type 3.1 on request). The range includes round bars and plate blocks, mainly in the quenched and tempered condition, with custom cutting and third-party heat treatments.

For available sizes, finishes, delivery conditions and to request a quote, see the product page: 42CrMo4 steel products. For related grades, see the technical datasheets for 39NiCrMo3 and C45; for the category, quenched and tempered steels. To estimate the weight of semi-finished products, the steel bar weight calculator tool is available.

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