42CrMo4: Steel Technical Specifications

1. 42CrMo4 steel: fundamental characteristics and properties

The 42CrMo4 steel (material number 1.7225) is a chromium-molybdenum alloy quenched and tempered steel classified according to standard EN 10083-3, an indicative equivalent of AISI/SAE 4140. It is among the most widely used construction alloys for mechanical components subjected to fatigue and torsion stresses, thanks to the high hardenability provided by chromium and molybdenum, the high mechanical properties after quenching and tempering, and good machinability on machine tools. The combination of these characteristics makes it the reference standard when a non-alloy steel such as C45 does not guarantee sufficient hardening penetration on the required sections.

The composition, defined by EN 10083-3, provides for carbon 0.38-0.45%, chromium 0.90-1.20% and molybdenum 0.15-0.30%; molybdenum also reduces sensitivity to temper brittleness. After quenching and tempering (+QT), 42CrMo4 achieves tensile strengths ranging, depending on diameter, between about 800 and 1300 MPa, with typical hardness of 280-320 HBW. It is mainly supplied in the quenched and tempered condition, as well as annealed or hot-rolled for subsequent processing.

Typical applications range from transmission shafts, gears, pins and connecting rods in the automotive and heavy mechanical engineering sectors, to components for oil&gas and equipment subject to high dynamic stresses.

2. Chemical composition of 42CrMo4 steel

The chemical composition of 42CrMo4 is defined by standard 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 quenching; chromium (0.90-1.20%) increases hardenability and promotes the formation of stable carbides; molybdenum (0.15-0.30%) improves tempering resistance and counteracts temper brittleness, a critical aspect for high-responsibility components. Manganese (0.60-0.90%) and silicon (≤0.40%) complete deoxidation and contribute to hardenability and structural refinement.

Phosphorus (≤0.025%) and sulfur (≤0.035%) contents are limited to reduce brittleness and ensure machinability. The improved-machinability variant 42CrMoS4 (material number 1.7227) has controlled sulfur in the range 0.020-0.040%, while keeping the other compositional characteristics unchanged. Supply with calcium treatment for inclusion control is available on request, benefiting toughness and transverse fatigue resistance.

3. Mechanical 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 part: the material’s hardenability allows high values to be maintained even on medium-to-large section thicknesses. Standard EN 10083-3 prescribes the ranges by size class shown below; the yield strength Rp0.2 decreases from about 900 MPa for small sections to about 550 MPa for diameters 100-160 mm.

Hardness after quenching and tempering typically ranges between 280 and 320 HBW, corresponding to about 29-34 HRC. Elongation percentage increases from 10% for small sections up to 13-14% for larger diameters, confirming good ductility despite the high strength. Impact energy KV remains at values in the order of 35 J for most sections, an important requirement for components subject to dynamic loads and impact. The elastic modulus is about 210 GPa. The rotating bending fatigue limit is in the order of 370 MPa [TO BE VERIFIED: indicative value, depends on surface condition, section and finish].

4. Physical characteristics of 42CrMo4 steel

The physical characteristics of 42CrMo4 are typical of quenched and tempered alloy steels and are used for the thermomechanical sizing of components. Density is about 7.85 g/cm³. The modulus of elasticity (Young’s modulus) is about 210 GPa at room temperature, with a slight reduction as temperature increases (about 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 linear thermal expansion coefficient (about 12.2 µm/(m·K) in the 20-100 °C range) should be considered when calculating tolerances on components subject to thermal cycles. Electrical resistivity is in the order of 0.2 Ω·mm²/m. These values are physical properties of the material and do not constitute regulatory requirements under EN 10083-3.

5. Heat treatments of 42CrMo4 steel

The reference treatment for 42CrMo4 is quenching and tempering, consisting of quenching followed by tempering. Quenching involves austenitizing at about 840-870 °C with cooling in oil (or water for smaller sections). Oil cooling is preferable for complex geometries and large sections, as it limits internal stresses and the risk of cracks; water cooling increases quenching severity but increases the risk of distortion and cracks.

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

Surface treatments are also applicable to 42CrMo4: induction surface quenching allows exceeding 53 HRC on the surface while maintaining a tough quenched and tempered core; nitriding is common on shafts and gears to increase surface hardness and resistance to wear and fatigue.

6. Industrial applications of 42CrMo4 steel

42CrMo4 is used in sectors requiring strength, toughness and hardenability on medium-to-large sections. In the automotive and industrial vehicle sector, it is used for half-shafts, transmission shafts, gears, pins and steering tie rods, where fatigue resistance and toughness matter. In heavy mechanical engineering, it is used for gears (quenched-tempered and nitrided), connecting rods, spindles and hydraulic cylinders, exploiting good machinability combined with high hardenability.

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

7. Frequently asked questions about 42CrMo4 steel

7.1. What is the difference between 42CrMo4 and 4140?

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

7.2. What are the standard delivery conditions?

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

7.3. How is machinability optimized?

Machinability is improved through annealing: soft annealing at 680-720 °C, or spheroidize annealing at 740-770 °C, brings hardness below 241 HBW (and below 200 HBW in the spheroidized case). The 42CrMoS4 variant (sulfur 0.020-0.040%) offers superior machinability while keeping other properties unchanged.

7.4. What are the international equivalents?

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

7.5. When to 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 on medium-to-large section thicknesses, performance not achievable with a non-alloy steel such as C45. When greater hardenability or toughness is needed on even larger sections, nickel-chromium-molybdenum grades such as 39NiCrMo3 or 34CrNiMo6 are considered.

8. 42CrMo4 steel from Siderticino

Siderticino supplies certified quality 42CrMo4 steel in compliance with EN 10083-3, with material traceability and EN 10204 inspection certification (2.1 as standard, 3.1 on request). The range includes round bars and plate blocks, mainly in the quenched and tempered condition, with cutting to size and subcontracted heat treatments.

For available sizes, executions, delivery conditions and quote requests, see the product page: 42CrMo4 steel products. For related grades, see the technical data sheets 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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