42CrMo Steel Bar

42CrMo Steel Bar

42CrMo steel (approximately US grade AISI-4140) belongs to low-alloy medium carbon steel and also belongs to ultra-high-strength steel.

42Cr2Mo steel is a super high strength steel with high strength and toughness, good hardenability, no obvious temper brittleness, small deformation during quenching, high fatigue limit and multiple impact resistance after quenching and tempering, good impact toughness at low temperature, high creep strength and endurance strength at high temperature. Surface hardening after quenching and tempering is usually used as heat treatment scheme for this steel. Suitable for manufacturing large and medium-sized plastic moulds requiring certain strength and toughness.

1. 42CrMo Equivalent World Steel Grade:

  • China Standard: GB/T 3077-1999
  • ISO Standard: 42CrMo4
  • CET Steel Standard: 42CrMo4
  • Japanese Standard: SCM440
  • German Standard: 42CrMo4 or 1.7225
  • American Standard: 4140 or G41400

2. Chemical composition:

  • Carbon C:  0.38-0.45%
  • Silicon Si:  0.17-0.37%
  • Mn: 0.50-0.80%
  • Sulfur S: < 0.035%
  • Phosphorus P:  < 0.035%
  • Chromium: 0.90-1.20%
  • Nickel:  < 0.030%
  • Copper: < 0.030%
  • Molybdenum: 0.15-0.25%

3. Physical properties:

  1. Critical point temperature (approximate value): Ac1 = 730 C, Ac3 = 800 C, Ms = 310 C.
  2. Linear expansion coefficient: temperature 20-100 degrees C/20-200 degrees C/20-300 degrees C/20-400 degrees C/20-500 degrees C/20-600 degrees C, linear expansion coefficient: 11.1 x 10K/12.1 x 10K/12.9 x 10K/13.5 x 10K/13.9 x 10K/13.9 x 10K 14.1 x 10K.
  3. Elastic modulus: temperature 20 degree C/300 degree C/400 degree C/500 degree C/600 degree C, elastic touch 210000MPa/185000MPa/175000MPa/165000MPa/15500oMPa
  4. 42CrMo allowable stress 42CrMo allowable stress 186-310/MPa, yield point 930s/MPa, 42CrMo strength, hardenability, good toughness, small deformation during quenching, high creep strength and endurance strength at high temperature.

3. Mechanical properties:

  • Tensile strength_b (MPa): > 1080 (110)
  • Yield strength_s (MPa): > 930 (95)
  • Elongation rate (%): > 12
  • Section shrinkage(%): > 45
  • Impact energy Akv (J): > 63
  • Impact toughness value alpha kV (J/cm2): > 78 (8)
  • Hardness: <217HB

4. Heat treatment:

Annealing annealing No.1 “annealing at 760 + 10 C, furnace cooling to 400 air cooling. HB220-230
Normalize No. 4 860 (+10 C) and discharge air-cooled.
Quenching quenching + tempering No. 5 840 (+10 (+10 (+10), (depending on the complexity of product shape), tempering 680-700 degrees. HB<217
Quenching at quenching + tempering No. 6 840 (+10) and tempering at 470. HRC41-45
Quenching at quenching + tempering No. 7 840 (+10) and tempering at 480. HRC35-45
Quenching at quenching + tempering No. 8 850 C and tempering at 510 degrees. HRC38-42
Quenching at quenching + tempering No. 9 850 C and tempering at 500 degrees. HRC40-43
Quenching at quenching + tempering No. 10 850 (?) and tempering at 510 (?) HRC36-42
Quenching at quenching + tempering No. 11 850 (?) and tempering at 560 (?) HRC32-36
Quenching at quenching + tempering No. 12 860 (?) and tempering at 390 (?) HRC48-52

Do you wish to know the difference between 42CrMo4 and 42CrMo?

The main difference is 42CrMo4 is EN standard, 42CrMo is China GB standard. P, V and S element is a little different each other, machinery property is similar.

42CrMo4 is from European standard-EN10083, 42CrMo4 is a kind of alloy steel with high hardenability, good toughness and small deformation during quenching. It has high creep strength and endurance strength at high temperature.

42CrMo is from China GB/T standard steel grade, it is a medium carbon alloy structural steel with good mechanical properties, good hardenability and wide application. In the machinery industry, it is often used to manufacture gears, connecting rods, high strength bolts and other important parts. China factory create 42CrMo follow SAE 4140 steel standard.The difference is below:

  1. Based on the standard:

42CrMo4 is from EN10083 standard, which come from different standards, 42CrMo is from China GB/T 3077 alloy structural steel standard.

  1. Chemical composition:

The chemical constituents of 42CrMo4 and 42CrMo are shown in Table 1 and Table 2.

Table 1:

Tips: touch the table(form) and scroll left and right to see the whole table(form) on phone screen.

42CrMo40.38-0.45 ≤0.40  0.6-0.9 ≤0.035 ≤0.035 0.15-0.300.90-1.20  ≤0.40

Table 2:

Tips: touch the table(form) and scroll left and right to see the whole table(form) on phone screen.

Normal Quality0.38-0.450.17-0.450.5-0.8≤0.035≤0.0350.15-0.250.90-1.20
High Quality0.38-0.450.17-0.450.5-0.8≤0.025≤0.0250.15-0.250.90-1.20
Extra High Quality0.38-0.450.17-0.450.5-0.8≤0.015≤0.0250.15-0.250.90-1.20

Table 1: Chemical composition compare of 42CrMo4 and 42CrMo

Table 2: GB/T 30772015 Standard seperate 42CrMo for different quality level, higher quality live with lowwer composition of P and S element.

Normal quality steel:        P< 0.035  S< 0.035
High quality steel:            P< 0.025  S< 0.025
Extra high quality steel:   P< 0.025 S< 0.015

It can also be seen from the above table that the contents of Si, Mn and Mo are different. The GB/T 3077 of P and S content is classified into three grades. The standard value of EN10083 limits the maximum content. The P and S contents of medium and high quality steel in GB/T 3077 standard are similar to those in EN10083 standard. The content range of Si and Mo in GB/T 3077 standard is narrower than EN10083 standard. If only chemical composition is considered, 42CrMo can meet the requirement of 42CrMo4 in EN10083 by choosing high quality steel with attention to Mn content.

3. Hardenability:

The hardening bandwidth is given in EN standard, which is divided into three grades: H, HL and HH. It can be used for reference when ordering, and it also provides standard information for designers to choose.

  1. Mechanical properties:

Regarding the location and method of sampling, according to GB/T 2975 , when the diameter of bar is d > 50mm, the distance from outside diameter of bar is d/4 as the center, and the diameter of test bar is 25mm. The sample is tempered according to the standard heat treatment process, and then the tensile sample and impact sample are made for testing.

According to EN standard, the rod is tempered according to the recommended heat treatment process, and then sampled on the rod. The diameter of the rod is d > 25 mm, and the sampling position is 12.5 mm away from the outside diameter of the rod. The rod is made into tensile and impact samples for testing.

For impact test standard specimens, GB standard uses Charpy U-notched specimens, while EN standard uses Charpy U-notched specimens. The notched depth of the two specimens is the same, but the radius of the notched bottom is different. U-type is lmm, V-type is 0.25mm, and V-notched stress is relatively concentrated. When the specimens are impacted, it appears more sensitive. In the past, U-notched specimens were mainly used in China.

In order to meet the needs of some enterprises, the impact test method of GB/T 12778-2008 metal Shapi (v-notched) was promulgated in China, which can be used for steel with special requirements. In both standards, the corresponding heat treatment specifications and mechanical properties are required.

  1. Low magnification and non-metallic inclusions:

For low magnification structure, the corresponding requirement of low magnification structure is given according to the quality grade of steel in GB3077, while the requirement of low magnification structure is not given in EN standard.

For non-metallic inclusions, there is no requirement and recommended value in GB3077, only the supply and demand sides are required to negotiate, while in EN 10083, the relevant requirements and testing methods for non-metallic inclusions are put forward, which is convenient for both sides to negotiate.

  1. Grain size:

In GB3077, grain size is proposed as a special requirement. After consultation between supplier and demander, it can be indicated in the contract that fine grain steels of grade 5 or less are required. In EN10083, the grain size is required to be smaller than or equal to grade 5, and the corresponding detection methods and heat treatment and quenching conditions are given for selection.

  1. Delivery status:

In GB3077, steel is usually delivered in hot rolling or forging. If the buyer requires delivery in heat treatment (annealing, normalizing or high temperature tempering), it needs to be specified in the contract. But five deliveries are given in EN10083.

The states are selected as non-heat treatment, heat treatment to improve cutting performance, softening annealing, quenching and high temperature tempering and other heat treatment states.

In summary, through the discussion of chemical composition, hardenability, mechanical properties, low magnification and non-metallic inclusions, grain size and delivery status of 42CrMo steel by the two standards, the following conclusions are drawn:

7.1 EN 10083 standard is more strict, while GB3077 standard is relatively simple and loose.

7.2 The testing requirements of mechanical properties in EN 10083 standard directly reflect the material properties of steel in practical application, which is convenient for designers to check and calculate.

7.3 EN10083 standard specifies the relevant requirements of hardenability. When 42CrMo4 steel is selected as gear workpiece, it is convenient to choose this standard for ordering.

7.4 When enterprises need batch production, it is more convenient to choose EN-10083 standard supply, and GB3077 standard supply when enterprises produce single or small batches.

7.5 The emergence of standards and the development of national machinery manufacturing industry are complementary. In European countries, most metallurgical enterprises will equip corresponding heat treatment equipment to meet the different order requirements of mechanical enterprises.
In China, the heat treatment equipment of mechanical enterprises is more complete than that of metallurgical enterprises, so most of our customers do not require heat treatment for the delivery status of steel, but complete it by themselves.