39NiCrMo3: Steel Technical Specifications

1. 39NiCrMo3 steel: general characteristics

The 39NiCrMo3 steel (material number 1.6510, EN 10083-3) is a nickel-chromium-molybdenum alloy quenched and tempered steel, used in the quenched and tempered condition (+QT) for mechanical components subject to fatigue and torsional stress: 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 decreasing values as the diameter increases. Compared to a non-alloy quenched and tempered steel such as C45, it maintains more uniform properties on medium-to-large sections. However, it has limited weldability and sensitivity to temper embrittlement, which must be managed during heat treatment cycles. It is governed by EN 10083-3 (hot-rolled products) and EN 10277-5 (cold-finished products).

The balance between carbon and alloying elements makes 39NiCrMo3 the typical choice when a C45 does not guarantee sufficient hardenability on the section, but the alloy content of a 42CrMo4 is not required. It belongs to the family of quenched and tempered steels and can be supplied in the +N, +A and +QT conditions. For size range, machining and a quote: 39NiCrMo3 – products and quote request.

2. Chemical composition of 39NiCrMo3

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

2.1. Chemical composition table

The contents prescribed by EN 10083-3 (cast analysis) are shown in the table below.

2.2. Role of the alloying elements

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

2.3. Control of residual elements

EN 10083-3 limits harmful elements to preserve toughness: phosphorus does not exceed 0.025% (preventing cold brittleness and segregation), sulfur does not exceed 0.035% (controlling inclusions that reduce transverse toughness). In improved-machinability variants, sulfur is instead deliberately raised within a controlled range (0.020-0.040%) to promote chip formation. The choice between the “clean” variant and the controlled-sulfur variant depends on the required compromise between transverse toughness and machine-tool machinability.

2.4. Permitted deviations on product analysis

EN 10083-3 allows deviations of the product analysis from the cast analysis: approximately C ±0.02%, Mn ±0.04%, Cr ±0.05%, Ni ±0.05%, Mo ±0.03%. These are not steel mill process tolerances, but the regulatory limits within which the analysis of the finished product may differ from the cast analysis. This is a relevant parameter for the conformity of the mill test certificate (MTC) issued according to EN 10204 (certificate 2.1 or 3.1).

3. Mechanical 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 10083-3 apply to the indicated reference section and decrease as diameter or thickness increases, due to the lower quenching severity at the core. The values refer to a longitudinal test piece, at 20 °C, in the +QT condition.

3.1. Mechanical properties by size class

Note: the values apply to hot-rolled +QT products according to EN 10083-3, up to the reference section of 250 mm. For larger sections (forgings) the available data are indicative only (ref. UNI 7874) and must be agreed upon at the time of order. 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 the +QT condition (it is instead prescribed as a maximum value for the annealed +A condition). The HB values in the table are indicative correlations derived from Rm.

3.2. Hardness and elastic moduli

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

3.3. Fatigue resistance and toughness

The combination of deep hardenability and toughness makes 39NiCrMo3 suitable for components subject to cyclic loading. The prescribed impact energy KV is ≥ 35-40 J (longitudinal test piece, at 20 °C) for sections over 16 mm. Actual fatigue behavior, however, does not depend on the material alone: surface finish, residual stresses and the tempering temperature used have a decisive effect and must be assessed for the specific component. A high tempering temperature (≥ 550 °C) favors toughness, while a lower one favors strength.

4. Physical properties of 39NiCrMo3

Physical data are design parameters for calculating expansion, stiffness and heat treatment cycles. Unless otherwise stated, these are typical values for Ni-Cr-Mo alloy steels, to be confirmed on the supplying mill’s datasheet in the case of critical calculations.

4.1. Density and elastic moduli

The combination of typical density and high moduli provides good stiffness for a given section, useful in the design of shafts and components subject to bending and torsional stress.

4.2. Thermal properties and expansion

The coefficient of linear thermal expansion (≈ 11.2 × 10⁻⁶ K⁻¹) 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 heating equalization times, an aspect to consider in heat treatment cycles for thick-walled parts, in order to avoid thermal gradients and stresses. Dimensional stability after quenching and tempering favors repeatability in batch treatments.

4.3. Electrical and magnetic properties

39NiCrMo3 is a ferromagnetic steel; electrical and magnetic properties are not selection criteria for its typical mechanical applications and are not prescribed by EN 10083-3. The presence of nickel, chromium and molybdenum alters 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.

5. Heat treatments of 39NiCrMo3

5.1. Overview of treatments

The heat treatments of 39NiCrMo3 according to EN 10083-3 include normalizing, soft annealing and – as the treatment for use – quenching and tempering (quenching 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.

5.2. Critical 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 heat). Quenching and tempering involves:

• Austenitizing and quenching: ≈ 840-850 °C. The standard medium for this alloy steel is oil or polymer; water quenching (≈ 840 °C), although permitted by some mill datasheets, increases the risk of cracking and distortion – also due to the known sensitivity of 39NiCrMo3 to flakes (white points) – 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 through the temper embrittlement range; the temperature is selected according to the target strength/toughness balance.

The table below shows the typical evolution of properties as a function of tempering temperature, on a Ø10 mm test piece oil-quenched at 850 °C. These are indicative values from mill datasheets, not a substitute for the +QT requirements in the table in §3.1, which refer to the actual section of the product.

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

5.3. Normalizing and annealing

Normalizing is carried out at ≈ 860 °C with air cooling, to refine the grain and homogenize the structure before machining or as a pre-treatment for quenching and tempering. Soft annealing involves slow furnace cooling to reduce hardness in preparation for machine-tool machining, with the resulting hardness limited to the maximum value prescribed by the standard (approximately 248 HB). The choice of starting condition affects machining time and quality.

5.4. Hardenability (Jominy) and welding

EN 10083-3 prescribes a Jominy hardenability band for the +H variant (grain size ≥ 5). At 1.5 mm from the quenched end, 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 (in the order of 300 °C) and post-weld stress relieving (approximately 550 °C) are adopted, to be defined with a specific procedure (WPS) depending on thickness and heat input, to limit the risk of hydrogen cold cracking. Since 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.

6. Applications of 39NiCrMo3

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

6.1. Automotive and power transmission

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

6.2. Industrial mechanics and machine tools

In general and heavy mechanical engineering, the grade is used for spindles, press shafts, pins, tie rods and components subject to bending, torsion and tension under demanding 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-sulfur or leaded variants.

6.3. Oil & 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 subject to cyclic loading. In these fields, the final selection of the grade must always be verified against specific service requirements (temperature, environment, criticality), which may require grades with a higher alloy content.

6.4. Application 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 requirements, it may not be sufficient. It is also sensitive to temper embrittlement and flaking, with limited weldability. For higher-responsibility applications – large sections, aerospace or defense 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.

7. Frequently asked questions about 39NiCrMo3

7.1. What are the equivalents of 39NiCrMo3?

Material number 1.6510. It appears with the same designation in the historical DIN 17200 and UNI 7845 standards (39NiCrMo3) and in NF A35-552 (France). Indicative equivalents, not identities: BS 970 817M40 (UK) and AISI/SAE ~9840 (USA), both approximate due to compositional deviations. Equivalence with JIS SNCM439 should be avoided, as it has a significantly higher nickel content (close to AISI 4340) and does not correspond to 39NiCrMo3.

7.2. How does size affect mechanical properties?

+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, maintaining elongation ≥ 11-13% (see table in §3.1). Properties must always be referred to the size class of the semi-finished product.

7.3. Can 39NiCrMo3 steel be welded?

Weldability is limited. When necessary, welding requires preheating and post-weld stress relieving defined by a qualified procedure, to prevent hydrogen cold cracking. This is not the grade’s typical service condition, as it is used in the quenched and tempered condition.

7.4. What heat treatment is applied to 39NiCrMo3?

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

7.5. 39NiCrMo3 or C45: what are the differences?

C45 is a non-alloy quenched and tempered steel (EN 10083-2), with modest hardenability: properties decay rapidly on thick sections. 39NiCrMo3, being alloyed, maintains more uniform strength and toughness as diameter increases, at a higher cost. The numerical comparison should be made at the same size class and delivery condition.

7.6. 39NiCrMo3 or 42CrMo4: how to choose?

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

7.7. What are the dimensional tolerances?

Nominal dimensions and shape tolerances are to be agreed upon at the time of order according to EN 10083-3. For cold-finished products (cold-drawn, peeled), the tolerances of EN 10277-5 apply. Machining tolerances typically follow the general ISO 2768-1 classes (fine “f” or medium “m”), while for forgings reference is made to EN 10243-1. The class must be selected according to the functional requirements of the component and the cost-performance compromise.

8. 39NiCrMo3 supply: conditions, certifications and standards

8.1. Delivery conditions and certification

Siderticino supplies 39NiCrMo3 in the normalized (+N), annealed (+A) and quenched and tempered (+QT) conditions, in round, square and flat bars and forgings. Each supply is accompanied by a 2.1 inspection certificate or, on request, a 3.1 certificate according to EN 10204, with traceability of chemical composition and mechanical properties. The choice of delivery condition optimizes the customer’s machining time: +A for machinability, +QT for immediate mechanical performance, +N as an intermediate condition or pre-treatment.

8.2. Reference standards and technical support

Reference standards: EN 10083-3 (alloy quenched and tempered steels, hot-rolled products) and EN 10277-5 (cold-finished products); certification according to EN 10204. In addition to supplying the material, Siderticino offers related machining services: cutting steel to size on 39NiCrMo3 bars and support in defining the delivery condition, quenching and tempering parameters and finishes. For preliminary sizing of semi-finished products, the steel bar weight calculation tool is available.

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