42CrMo Steel Round Bar

42CrMo Overview

42CrMo steel belongs to ultra-high-strength steel , with high strength and toughness, good hardenability, no obvious temper brittleness, high fatigue limit and multiple impact resistance after quenching and tempering, and good low-temperature impact toughness. 42CrMo steel is suitable for manufacturing large and medium-sized plastic molds that require certain strength and toughness .

42CrMo Chemical Composition

• Carbon C: 0.38~0.45%
• Silicon Si: 0.17~0.37%
• Manganese Mn: 0.50~0.80%
• Sulfur S: allowable residual content ≤0.035%
• Phosphorus P: allowable residual content ≤0.035%
• Chromium Cr: 0.90~1.20%
• Nickel Ni: allowable residual content ≤0.30%
• Copper Cu: allowable residual content ≤0.30%
• Molybdenum Mo: 0.15~0.25%

42CrMo Mechanical Properties

• Hardness: Annealed, 147~241HB, 42CrMo
• Mechanical properties of 42CrMo:
• Tensile strength σb (MPa): ≥1080(110)
• Yield strength σs (MPa): ≥930(95)
• Elongation δ5 (%): ≥12
• Reduction of area ψ (%): ≥45
• Impact energy Akv (J): ≥63
• Impact toughness value αkv (J/cm2): ≥78(8)
• Hardness: ≤217HB

In order to increase the mold life to more than 800,000 mold times, the hardening method of quenching and low temperature tempering can be implemented on the pre-hardened steel. When quenching, preheat at 500-600°C for 2-4 hours, and then keep it at 850-880°C for a certain period of time (at least 2 hours), then put it in oil and cool to 50-100°C and air cooling, the hardness can reach 50 after quench -52HRC, in order to prevent cracking, 200°C low temperature tempering treatment should be carried out immediately. After tempering, the hardness can be maintained above 48HRC.

Salt bath vanadium infiltration treatment

The neutral salt bath vanadium treatment process of 42CrMo steel, and the carbide layer can be obtained by the neutral salt bath vanadium treatment of 42CrMo steel.

1. Carbon vanadium compound, the infiltration layer has uniform structure, good continuity and compactness, uniform thickness, compact structure, high microhardness and high wear resistance, surface hardness, wear resistance and resistance Performance such as adhesion is greatly improved.

2. The solubility of VC in austenite is higher than that in the ferrite body. As the temperature decreases, VC precipitates from the ferrite body, strengthening the alloy and refining the grains, and the compound layer shows higher hardness .

42CrMo steel belongs to high carbon and high chromium ledeburite steel, with a high content of carbides, accounting for about 20%, and it is often unevenly distributed in bands or nets, with serious segregation, and it is difficult for conventional heat treatment to change the situation of carbide segregation. It seriously affected the mechanical properties of steel and the service life of the mold. The shape and size of carbides also have a great impact on the performance of steel, especially the large-shaped sharp-angled carbides have a relatively large splitting effect on the steel matrix, and they often become the source of fatigue fracture. For this reason, the raw material rolled steel must be processed. The forging is changed to fully crush the eutectic carbides to make them small and uniformly distributed. The fiber structure is distributed around the cavity or non-directionally, thereby improving the transverse mechanical properties of the steel.

During forging, the billet is upset and drawn several times from different directions, and the “two light and one heavy” method is used for forging, that is, the billet should be lightly hit at the beginning of forging to prevent breakage. It can be hit hard at the intermediate temperature of 980 to 1020°C In order to ensure the crushing of carbides, 42CrMo steel has not been forged, it adopts solid solution double refinement treatment, that is, two-stage preheating at about 500°C and 800°C, solution treatment at 1100~1150°C, quenching into hot oil or austempering , High-temperature tempering at 750°C, heating and oil cooling at 960°C after machining, and final heat treatment, which can also refine carbide, rounded edges, and refined grains.

42CrMo Tempering

Recommended tempering specification for 42CrMo steel

42CrMo steel

Program	Quenching temperature/°C	Temper
Use	Heating temperature/°C	Medium	Hardness HRC
(1) (2) (3)	1020~1040	Stress relief Remove stress and reduce hardness Remove stress and reduce hardness	150~170 200~275 400~425	Oil or nitrate — —	61~63 57~59 55~57
(4) (5) (6)	1115~1130	Removal of stress and formation of secondary hardening Removal of stress and formation of secondary hardening Removal of stress and formation of secondary hardening	510~520°C multiple tempering -78°C cold treatment Temper at 510~520°C once -78°C cold treatment plus 510~520°C tempering once, then -78°C cold treatment	— — —	60~61 60~61 61~6

42CrMo Quenching

42CrMo Steel

Program	First preheating/°C	Second preheating/°C	Quenching temperature/°C	cool down	Cool in the medium	Medium temperature/°C	medium	hardness (HRC)
(1) (2) (3) (4) (5)	550~660	840~860	950~1000 1020~1040 1020~1040 1115~1130 1115~1130	oil oil Molten Nitrate oil Molten Nitrate	20~60 20~60 400~550 20~60 400~450	To room temperature To oil temperature 5~10min To oil temperature 5~10min	Air cooling Air cooling Air cooling Air cooling Air cooling	58~62 62~63 62~63 42~50 42~50

Corresponding Grade

1. Russia ГOCT 38XM,
2. American AISI 4140/4142,
3. British BS 708M40/708A42/709M40,
4. French NF 40CD4/42CD4,
5. German DIN 41CrMo4/42CrMo4,
6. Japan JIS SCM4,
7. International ISO 683/1 3

Quenching specification

General quenching and tempering specifications: quenching temperature 1000~1050°C, quenching oil or quenching gas, hardness ≥60HRC; tempering temperature 160~180°C, tempering time 2h, or tempering temperature 325~375°C, tempering times 2 ~3 times.

Physical properties

1. Critical point temperature (approximate value): Ac1=730°C, Ac3=800°C, Ms=310°C.
2. Linear expansion coefficient: temperature 20~100°C/20~200°C/20~300°C/20~400°C/20~500°C/20~600°C,
3. Linear expansion coefficient: 11.1×10K/12.1×10K/12.9×10K/13.5×10K/13.9×10K14.1×10K.
4. Elastic modulus: temperature 20°C/300°C/400°C/500°C/600°C,
5. Elastic modulus 210000MPa/185000MPa/ 175000MPa/165000MPa/15500oMPa

Process Specification

Hot working specification

The heating temperature is 1150 ~1200°C, the starting temperature is 1130 ~1180°C, and the ending temperature is> 850°C, when φ> 50mm, slow cooling.

Normalizing norms

The normalizing temperature is 850~900°C, and the furnace is air-cooled.

High temperature tempering specification

The tempering temperature is 680~700°C, and the furnace is air-cooled.

Quenching and tempering specifications

Preheating temperature is 680~700°C, quenching temperature is 840~880°C, oil cooling, tempering temperature is 580°C, water cooling or oil cooling, hardness ≤217HBW.

Specification for sub-temperature quenching strengthening and toughening treatment

Quenching temperature 900°C, tempering temperature 560°C, hardness (37±1) HRC

Specification for induction hardening and tempering

The quenching temperature is 900°C, the tempering temperature is 150~180°C, and the hardness is 54~60HRC.

Typical Application Examples

It is suitable for making large and medium-sized plastic molds that require certain strength and toughness.