39NiCrMo3: Steel Technical Specifications

0139NiCrMo3 steel: general characteristics

39NiCrMo3 steel (material number 1.6510, EN ISO 683-2:2018 (formerly EN 10083-3)) is a nickel-chromium-molybdenum alloy steel for quenching and tempering, used in the quenched and tempered condition (+QT) for mechanical components subjected to fatigue and torsional loading: transmission shafts, crankshafts, gears, pins and connecting rods. 

The alloy - C 0.35-0.43%, Ni 0.70-1.00%, Cr 0.60-1.00%, Mo 0.15-0.25% - offers good hardenability and a balanced combination of strength and toughness: after quenching and tempering it reaches Rm 980-1180 MPa for sections up to 16 mm, with values decreasing as the diameter increases. Compared with a non-alloy quenched and tempered steel such as C45, it maintains more uniform properties across medium-to-large sections. However, it exhibits limited weldability and susceptibility to temper embrittlement, to be managed during heat-treatment cycles. It is standardised under EN ISO 683-2:2018 (formerly EN 10083-3) (hot-rolled) and EN ISO 683-7:2024 (formerly EN 10277:2018) (cold-finished products).

The balance between carbon and alloying elements makes 39NiCrMo3 the typical choice when a C45 does not guarantee sufficient hardenability across the section, but the alloy contents of a 42CrMo4 are not required. It belongs to the family of quenched and tempered steels and is available in the +N, +A and +QT conditions. For the size range, processing and quotation: 39NiCrMo3 - products and quote request.

02Chemical composition of 39NiCrMo3

The chemical composition of 39NiCrMo3 is defined by EN ISO 683-2:2018 (formerly EN 10083-3) for material number 1.6510. It is a medium-carbon Ni-Cr-Mo alloy steel: carbon provides the hardening capability and the hardness after tempering, while nickel, chromium and molybdenum govern its hardenability and toughness.

2.1Chemical composition table

The contents prescribed by EN ISO 683-2:2018 (formerly EN 10083-3) (heat analysis) are given in the table below.

2.2Role of the alloying elements

Nickel increases toughness and lowers the ductile-to-brittle transition temperature. Chromium increases hardenability and wear resistance. Molybdenum improves temper stability and counteracts - without fully eliminating it - the temper embrittlement typical of this family of steels. Manganese, besides its deoxidizing function, binds sulphur as manganese sulphide (MnS), limiting hot shortness, while silicon acts as a deoxidizer and contributes to strength. On request the grade is available with calcium treatment (Ca) to improve transverse properties, or in the enhanced-machinability variants with lead (Pb 0.15-0.35%) or controlled sulphur (S 0.020-0.040%).

2.3Control of residual elements

EN ISO 683-2:2018 (formerly EN 10083-3) limits harmful elements in order to preserve toughness: phosphorus does not exceed 0.025% (preventing cold shortness and segregation), sulphur 0.035% (controlling the inclusions that reduce transverse toughness). In the enhanced-machinability variants, sulphur is instead deliberately raised within a controlled window (0.020-0.040%) to promote machinability (chip formation). The choice between the "clean" variant and the controlled-sulphur variant depends on the required trade-off between transverse toughness and machinability.

2.4Permissible deviations on the product analysis

EN ISO 683-2:2018 (formerly EN 10083-3) permits deviations of the product analysis from the heat analysis: indicatively C ±0.02%, Mn ±0.04%, Cr ±0.05%, Ni ±0.05%, Mo ±0.03%. These are not the steelworks' process tolerances, but the standard's limits within which the analysis on the finished product may differ from the heat analysis. It is a relevant parameter for the conformity of the mill test certificate (MTC) issued in accordance with EN 10204 (certificate 2.1 or 3.1).

03Mechanical properties of 39NiCrMo3 in the quenched and tempered condition (+QT)

The mechanical properties of 39NiCrMo3 depend on the size class: the values prescribed by EN ISO 683-2:2018 (formerly EN 10083-3) apply to the reference section indicated and decrease as the diameter or thickness increases, owing to the lower quenching severity at the core. The values refer to a longitudinal specimen, at 20 °C, in the +QT condition.

3.1Mechanical properties by size class

Note: the values apply to hot-rolled +QT products according to EN ISO 683-2:2018 (formerly EN 10083-3), up to the reference section of 250 mm. For larger sections (forged) the available data are only indicative (ref. UNI 7874) and must be agreed at the time of order. EN ISO 683-2:2018 (formerly EN 10083-3) specifies for the +QT condition the values of Rm, Rp0.2, A, Z and KV; Brinell hardness is not a requirement of +QT (it is instead prescribed as a maximum value for the annealed condition +A). The HB values in the table are indicative correlations derived from Rm.

3.2Hardness and elastic moduli

In the annealed condition (+A) the hardness is limited to a maximum value prescribed by the standard (of the order of about 248 HB). In the quenched and tempered condition the hardness follows the dimensional class according to the correlation with Rm given in the previous table. The modulus of elasticity is E ≈ 210 GPa and the shear modulus G ≈ 80 GPa; the density is ≈ 7.85 kg/dm³ (= 7.85 g/cm³), a typical value for Ni-Cr-Mo alloy steels. These parameters ensure rigidity and dimensional stability suited to loaded components.

3.3Fatigue strength and toughness

The combination of deep hardenability and toughness makes 39NiCrMo3 suitable for components subject to cyclic stresses. The prescribed KV impact toughness is ≥ 35-40 J (longitudinal specimen, at 20 °C) for sections over 16 mm. Actual fatigue behaviour, however, does not depend on the material alone: surface finish, residual stresses and the tempering temperature adopted have a decisive influence and must be referred to the individual component. A high tempering temperature (≥ 550 °C) favours toughness; a lower one favours strength.

04Physical characteristics of 39NiCrMo3

Physical data are design parameters for calculating thermal expansion, stiffness and thermal cycles. Unless otherwise indicated, they are typical values for Ni-Cr-Mo alloy steels, to be confirmed on the datasheet of the supplying steelworks in the case of critical calculations.

4.1Density and elastic moduli

The combination of typical density and high moduli offers good rigidity for a given section, useful in the design of shafts and parts subject to bending and torsion.

4.2Thermal properties and expansion

The linear thermal expansion coefficient (≈ 11.2 × 10⁻⁶/K) is the key parameter for calculating tolerances on components subject to thermal cycles. The thermal conductivity of Ni-Cr-Mo alloy steels is generally lower than that of carbon steels: this results in longer equalization times during heating, an aspect to be considered in the treatment cycles of heavy-section parts in order to avoid thermal gradients and stresses. Dimensional stability after quenching and tempering favours repeatability in series treatments.

4.3Electrical and magnetic properties

39NiCrMo3 is a ferromagnetic steel; the electrical and magnetic properties do not constitute selection criteria for its typical mechanical applications and are not prescribed by EN ISO 683-2:2018 (formerly EN 10083-3). The presence of nickel, chromium and molybdenum modifies the resistivity compared to base carbon steels, but for specific electromechanical applications reference must be made to data certified by the supplier, not to generic literature values.

05Heat treatments of 39NiCrMo3

5.1Overview of treatments

The heat treatments of 39NiCrMo3 according to EN ISO 683-2:2018 (formerly EN 10083-3) include normalising, soft annealing and - as the final treatment for the service condition - quenching and tempering (hardening followed by tempering). Correct management of the cycles, in particular the tempering temperature, determines the final compromise between strength and toughness and is essential to avoid the temper embrittlement to which the grade is sensitive.

5.2Critical temperatures and quenching and tempering

Indicative transformation points: Ac1 ≈ 740 °C, Ac3 ≈ 790 °C, Ms ≈ 330 °C, Mf ≈ 110 °C (values sensitive to the actual composition of the batch). Quenching and tempering involves:

• Austenitising and quenching: ≈ 840-850 °C. The standard medium for this alloy steel is oil or polymer; water quenching (≈ 840 °C), although permitted by some steelworks datasheets, increases the risk of cracks and distortions - also because of the known sensitivity of 39NiCrMo3 to flakes (white spots) - and must be assessed case by case, not assumed as standard practice for thin sections.
• Tempering: 550-650 °C, with adequate holding time and controlled cooling past the temper embrittlement range; the temperature is selected according to the target strength/toughness.

The following table shows the typical evolution of the properties as a function of the tempering temperature, on a Ø 10 mm specimen oil-quenched at 850 °C. These are indicative values from a steelworks datasheet, not a substitute for the +QT requirements in the table at §3.1, which refer to the actual section of the product.

The minimum impact toughness in the range ≈ 250-450 °C and its recovery above 500 °C reflect temper embrittlement: to achieve high toughness, tempering is carried out at high temperature with rapid cooling through the critical zone.

5.3Normalising and annealing

Normalising is performed at ≈ 860 °C with air cooling, to refine the grain and homogenise the structure before machining or as a pre-treatment for quenching and tempering. Soft annealing involves slow furnace cooling to reduce hardness ahead of machining, with the resulting hardness limited to the maximum prescribed by the standard (approximately 248 HB). The choice of the initial condition affects the time and quality of machining.

5.4Hardenability (Jominy) and welding

EN ISO 683-2:2018 (formerly EN 10083-3) specifies a Jominy hardenability band for the +H variant (grain size ≥ 5). At 1.5 mm from the quenched end the hardness is between 52 and 60 HRC; at 30 mm between 34 and 51 HRC. Maintaining high hardness at considerable distances from the end confirms the ability to obtain predominantly martensitic structures at the core on medium-to-large sections, within the limits imposed by the alloy content.

Weldability is limited (high carbon equivalent). When welding is unavoidable, preheating (on the order of 300 °C) and post-weld stress relieving (approximately 550 °C) are adopted, to be defined by a dedicated procedure (WPS) according to thickness and heat input, in order to limit the risk of hydrogen-induced cold cracking. As this is a steel used in the quenched and tempered condition, welding is not the typical service condition and must be entrusted to qualified personnel.

06Applications of 39NiCrMo3

39NiCrMo3 is used in the quenched and tempered condition for mechanical components subjected to fatigue and torsion, where strength combined with toughness is required on medium sections with sufficiently uniform through-hardening.

6.1Automotive and power transmission

In the power transmission sector, 39NiCrMo3 is used for drive shafts, crankshafts, half-shafts, camshafts, gears and connecting rods: components subjected to dynamic stresses and prolonged fatigue cycles, where the combination of strength and toughness after quenching and tempering is the decisive requirement. Hardenability ensures uniform performance even on sections on the order of a hundred millimetres.

6.2Industrial machinery and machine tools

In general and heavy engineering, the grade is used for spindles, press shafts, pins, tie rods and components subjected to bending, torsion and tension under severe conditions. It is also used in earthmoving and construction machinery, for axles and structural parts that must withstand high loads while maintaining dimensional stability. Machinability is adequate and can be further improved with the controlled-sulphur or leaded variants.

6.3Oil & Gas and energy

In the oil & gas sector, 39NiCrMo3 is used for supports, equipment frames and mechanical components of drilling and extraction equipment. In the energy sector it is used for transmission components and mechanical parts subjected to cyclic loading. In these fields, the final grade selection must always be verified against the specific service requirements (temperature, environment, criticality), which may require more highly alloyed grades.

6.4Application limits and alternative grades

39NiCrMo3 has lower hardenability than more highly alloyed Ni-Cr-Mo grades: on very large sections or for high core strength it may not be sufficient. It is also susceptible to temper embrittlement and to flakes, with limited weldability. For higher-responsibility applications - large sections, aerospace or defence structural requirements - grades such as 42CrMo4, 34CrNiMo6 or 36NiCrMo16 (a class close to AISI 4340/300M) are typically used. Specifying 39NiCrMo3 in such fields without a specific component qualification is not correct.

07Frequently asked questions about 39NiCrMo3

7.1What are the equivalents of 39NiCrMo3?

Material number 1.6510. Under the same designation it appears in the historical Italian standard UNI 7845 (39NiCrMo3) and in NF A35-552 (France). Indicative equivalent, not an identity: AISI/SAE ~9840 (USA), approximate owing to composition differences. Equivalence with BS 970 817M40 (UK) and JIS SNCM439 should be avoided, as both have a markedly higher nickel content (close to AISI 4340) and do not correspond to 39NiCrMo3.

7.2How do dimensions affect the mechanical properties?

The +QT properties decrease as the section increases: from Rm 980-1180 MPa with Rp0.2 ≥ 785 MPa for d ≤ 16 mm, down to Rm 740-880 MPa with Rp0.2 ≥ 540 MPa for 160 < d ≤ 250 mm, while maintaining elongation ≥ 11-13% (see the table in §3.1). Properties must always be referred to the dimensional class of the semi-finished product.

7.3Can 39NiCrMo3 steel be welded?

Weldability is limited. When required, welding calls for preheating and post-weld stress relieving defined by a qualified procedure, in order to prevent hydrogen-induced cold cracking. This is not the typical service condition of the grade, which operates in the quenched and tempered condition.

7.4Which heat treatment is applied to 39NiCrMo3?

The standard heat treatment for service is quenching and tempering: hardening at ≈ 840-850 °C in oil or polymer, followed by tempering at 550-650 °C, calibrated to the required strength/toughness trade-off. Water quenching is permitted but riskier in terms of cracking and distortion.

7.539NiCrMo3 or C45: what are the differences?

C45 is a non-alloy quenched and tempered steel (EN ISO 683-1:2018 (formerly EN 10083-2)) with modest hardenability: its properties fall off rapidly on thick sections. 39NiCrMo3, being alloyed, maintains more uniform strength and toughness as the diameter increases, at a higher cost. The numerical comparison must be made at the same dimensional class and delivery condition.

7.639NiCrMo3 or 42CrMo4: how to choose?

Both are alloy quenched and tempered steels (EN ISO 683-2:2018 (formerly EN 10083-3)). 42CrMo4 (Cr-Mo, no. 1.7225) generally offers higher hardenability and core strength on large sections; 39NiCrMo3 (Ni-Cr-Mo) favours toughness thanks to nickel. The choice depends on section, strength/toughness requirements and availability: for large sections and high strength the tendency is towards 42CrMo4, for components where toughness matters towards 39NiCrMo3.

7.7What are the dimensional tolerances?

Nominal dimensions and form tolerances are to be agreed at the time of order in accordance with EN ISO 683-2:2018 (formerly EN 10083-3). For cold-finished products (cold-drawn, peeled), the tolerances of EN ISO 683-7:2024 (formerly EN 10277:2018) apply. Machining tolerances typically follow the general classes of ISO 2768-1 (fine "f" or medium "m"), while for forgings the reference is EN 10243-1. The class must be selected according to the functional requirements of the component and the cost-performance trade-off.

0839NiCrMo3 supply: conditions, certifications and standards

8.1Delivery conditions and certification

Siderticino supplies 39NiCrMo3 in the normalised (+N), annealed (+A) and quenched and tempered (+QT) conditions, in round and square bars, flat bars and forgings. Every supply is accompanied by an EN 10204 type 2.1 declaration of compliance or, on request, a type 3.1 inspection certificate, with traceability of chemical composition and mechanical properties. The choice of delivery condition optimises the customer's machining lead times: +A for machinability, +QT for immediate mechanical performance, +N as an intermediate condition or pre-treatment.

8.2Reference standards and technical support

Reference standards: EN ISO 683-2:2018 (formerly EN 10083-3) (alloy quenched and tempered steels, hot-rolled products) and EN ISO 683-7:2024 (formerly EN 10277:2018) (cold-finished products); certification in accordance with EN 10204. In addition to supplying the material, Siderticino offers the related processing services: custom steel cutting on 39NiCrMo3 bars and support in defining the delivery condition, the quenching and tempering parameters and the finishes. For preliminary sizing of semi-finished products, the steel bar weight calculator is available.

→ For the diameter range, processing options and a quote, see the product page: Request a 39NiCrMo3 quote.