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What is the difference between 42CrMo and 42CrMo4?

42CrMo is a medium carbon alloy structural steel with good comprehensive properties and hardenability. It is often used in manufacturing gear, connecting rod, high strength bolts and other important parts in the processing process.
They come from different standards in different countries. 42CrMo is the material of Chinese standard GB / T 3077 and the specification of alloy structural steel. The material of 42CrMo4 belongs to EN 10083 series, Quenched and tempered steel.

1. Differences in chemical composition. As shown in the figure below, there is a slight difference in the content of element Si, and the content of Si in 42CrMo is less than that in 42CrMo4. In addition, according to gb3077, P and s contents can be divided into three grades, while 42CrMo4 only limits its maximum content.

2. Different Hardenability Requirements. The hardenability of 42CrMo has no specific value of quenching bandwidth. If there are special requirements, the buyer and the supplier can discuss the solution by themselves. The specific value of hardening bandwidth is specified in 42CrMo4. 42CrMo4 is divided into three grades h, HL and HH for reference when ordering.

3. Different delivery conditions. 42CrMo pipes are usually delivered in hot rolling and hot forging conditions. If the customer needs heat treatment conditions (annealing, normal goods, high temperature tempering), it should be indicated in the contract. For en1008342crmo4 pipe, there are five delivery conditions to choose from: no heat treatment, heat treatment, softening annealing, quenching and high temperature tempering.

4. Differences in impact test requirements. When the impact test is carried out according to GB / t2975, 42CrMo sample is taken at 1 / 4 of the outer diameter of the rod as the center of the rod with diameter greater than 50 mm. When the diameter of the sample bar is 25 mm, it should be modulated according to the requirements of heat treatment process, and then the tensile sample should be tested. In en10083 standard, bars are tempered according to the recommended heat treatment. When the sampling diameter is greater than 25 mm, the sampling position should be centered 12 mm around the outer diameter of the rod. In addition, 42CrMo uses Charpy u-notch toughness, while 42CrMo4 uses Charpy V-notch toughness. The two notches have the same depth, but the radii at the bottom of the notches are different (U-shaped 1 mm, V-shaped 0.25 mm).

What’s 42CrMo4 steel

42CrMo4 steel belongs to ultra-high strength steel, with high strength and toughness, good hardenability, high fatigue limit and multiple impact resistance after quenching and tempering treatment, and good low temperature impact toughness. The steel is suitable for manufacturing large and medium-sized plastic molds that require certain strength and toughness.

Equivalent steel standard

Application

High hardenability, high strength, good toughness, small deformation during quenching, high creep strength and lasting strength at high temperature. Used to manufacture forgings that require higher strength, such as large gears for locomotive traction, turbocharger transmission gears, pressure vessel gears, rear axles, connecting rods and spring clamps that are heavily loaded, and can also be used for deep well drilling under 2000m Rod joints and fishing tools, and can be used for molds of bending machines, etc.

Chemical composition

C: 0.38～0.45%

Si: 0.17～0.37%

Mn: 0.50～0.80%

S: allowable residual content ≤0.035%

P: allowable residual content ≤0.035%

Cr: 0.90～1.20%

Ni: allowable residual content ≤0.030%

Cu: allowable residual content ≤0.030%

Mo: 0.15～0.25%

Mechanical properties

Tensile strength σb (MPa): ≥1080

Yield strength σs (MPa): ≥930

Elongation δ5 (%): ≥12

Reduction of area ψ (%): ≥45

Impact work Akv (J): ≥63

Impact toughness value αkv (J/cm2): ≥78

Hardness: ≤217HB

*42CrMo4 steel forging heat treatment process

1.42CrMo4 steel forgings require quenching and tempering treatment after forging. Due to the large difference in cross-section size, the tendency of water quenching to crack is greater, the quenching hardness of the large cross-section after oil quenching is lower, and the metallographic structure and mechanical properties are often unqualified, which directly affects the fatigue strength and service life of the crankshaft .

2. With high strength and high yield point, the comprehensive mechanical properties are better than 40Cr. The cold deformation plasticity and machinability are both moderate, and the overheating sensitivity is small, but there is a tendency to temper brittleness and white spot sensitivity. Generally used in quenched and tempered state.

3. The forging process adopts the water-soluble quenching medium quenching process. In order to ensure the normal use of quenching liquid, the temperature of the quenching liquid must be strictly controlled. The inverse melting point of the quenching medium is 70℃, and the best use temperature is (30～60)℃. The temperature of the quenching liquid must always be controlled within the range required by the process.