A Comprehensive Guide to 42CrMo4 Steel

What is 42CrMo4 steel?

42CrMo4 is a commonly used alloy structural
steel with high strength, good toughness, and hardenability, which is suitable
for manufacturing large and medium-sized mechanical parts and various
engineering components.

The density of 42CrMo4 is 7.85 g/cm³, the thermal conductivity is 42.7 W/mK, the linear expansion coefficient is 11.7 × 10 ^ -6 / °C, and the specific heat capacity is 0.46 kJ / ( kg·K ).

Representation method of brand 42CrMo4

The ’42’ in 42CrMo4 represents its average
carbon content of 0.42 %. This is the same as the last two ’40’ in the US brand
4140, representing a carbon content of 0.4 %. The final number, 4, indicates
that the average content of Cr is 4/ 4 = 1 %, and the Mo content is not
mentioned.

Characteristics of 42CrMo4 steel

42CrMo4 has high strength, high
hardenability, good toughness, small deformation during quenching, high creep
strength, and lasting strength at high temperatures.

42CrMo4 steel is an improved variety of
AISI standard 4140 steel. The steel has good machinability, easy polishing,
easy to bite, and can be electroplated.

Equivalent grades of steel 42CrMo4 (1.7225)

Chemical Composition of 42CrMo4 steel

Standard	Steel grade
	Chemical Composition %
	C:	Mn:	Si:	P:	S:	Cr:	Ni:	Mo:
EN	42CrMo4 – 1.7225
	0.38-0.45	0.6-0.9	<0.40	<0.025	<0.035	0.9-1.2	–	0.15-0.30
PN	40HM
	0.38-0.45	0.40-0.70	0.17-0.37	<0.035	<0.035	0.9-1.2	<0.30	0.15-0.25
EN	42CrMoS4 – 1.7227
	0.38-0.45	0.60-0.90	0.10-0.40	<0.035	0.020-0.035	0.9-1.20	–	0.15-0.30
ASTM	AISI 4140 – UNS G41400
	0.38-0.43	0.75-1.00	0.20-0.35	<0.035	<0.040	0.8-1.1	–	0.15-0.25
AISI	AISI 4145 – UNS G41450
	0.43-0.48	0.75-1.00	0.15-0.35	<0.035	<0.040	0.8-1.1	–	0.15-0.25
EN	37CrMo4
	0.35-0.40	0.6-0.9	<0.3	<0.025	<0.025	0.9-1.2	–	0.15-0.30
EN	43CrMo4
	0.40-0.46	0.6-0.9	<0.4	<0.025	<0.030	0.9-1.2	–	0.15-0.30
NF	42CD4
	0.39-0.45	0.6-0.9	0.1-0.4	<0.035	<0.035	0.9-1.2	–	0.15-0.25
NF	40CD4
	0.39-0.45	0.5-0.8	0.2-0.5	<0.030	<0.025	0.95-1.30	–	0.15-0.30
BS	708M40
	0.36-0.44	0.7-1.0	–	<0.035	<0.035	0.9-1.2	<0.4	0.15-0.25
BS	709M40
	0.36-0.44	0.7-1.0	–	<0.035	0.02-0.04	0.9-1.2	<0.4	0.15-0.25
GOST	38ChM – 38ХМ
	0.35-0.42	0.35-0.65	0.17-0.37	<0.035	<0.035	0.9-1.3	<0.3	0.2-0.3
GOST	38ChMA – 38ХМА
	0.35-0.42	0.35-0.65	0.17-0.37	<0.025	<0.025	0.9-1.3	<0.3	0.2-0.3
JIS	SCM4
	0.38-0.43	0.60-0.85	0.15-0.35	<0.030	<0.030	0.9-1.2	<0.25	0.15-0.30
STAS	41MoCr11
	0.38-0.45	0.40-0.80	0.17-0.37	<0.035	<0.035	0.9-1.3	<0.30	0.15-0.30

Mechanical Properties of 42CrMo4 steel

• Tensile strength σ_b (MPa): ≥ 1080 (110)
• Yield strength σ_s (MPa): ≥ 930 (95)
• Elongation δ₅ (%): ≥ 12 
• Reduction of area ψ (%): ≥ 45 
• Impact energy A_kv (J): ≥ 63 
• Impact toughness value a_kv (J/cm²): ≥ 78 (8)
• Hardness: ≤ 217HB 
• Sample size: The sample blank size is 25 mm.

Mechanical properties of 42CrMo4 alloy when quenched and tempered (+QT):

• Round bars:
  • General:
    • Hardness HRC: 35,0 – 48,5
    • Hardness HV: 340-490
    • Density: 7,82 g/cm³
  • Diameter D: < 16 mm
    • Yield strength Re: > 900 MPa
    • Tensile strength Rm: 1100-1300 MPa
    • Elongation A: > 10 %
    • Percent reduction of area Z: > 40 %
  • Diameter D: 16-40 mm
    • Yield strength Re: > 750 MPa
    • Tensile strength Rm: 1000-1200 MPa
    • Elongation A: > 11 %
    • Percent reduction of area Z: > 45 %
    • Impact energy KV: > 35 J
  • Diameter D: 40-100 mm
    • Yield strength Re: > 650 MPa
    • Tensile strength Rm: 900-1000 MPa
    • Elongation A: > 12 %
    • Percent reduction of area Z: > 50 %
    • Impact energy KV: > 35 J
  • Diameter D: 100-160 mm
    • Yield strength Re: > 550 MPa
    • Tensile strength Rm: 800-950 MPa
    • Elongation A: > 13 %
    • Percent reduction of area Z: > 50 %
    • Impact energy KV: > 35 J
  • Diameter D: > 160 mm
    • Yield strength Re: > 500 MPa
    • Tensile strength Rm: 750-900 MPa
    • Elongation A: > 14 %
    • Percent reduction of area Z: > 550 %
    • Impact energy KV: > 35 J
• Flat bars:
  • Thickness: < 8 mm
    • Yield strength Re: > 900 MPa
    • Tensile strength Rm: 1100-1300 MPa
    • Elongation A: > 10 %
    • Percent reduction of area Z: > 40 %
  • Thickness: 8-20 mm
    • Yield strength Re: > 750 MPa
    • Tensile strength Rm: 1000-1200 MPa
    • Elongation A: > 11 %
    • Percent reduction of area Z: > 45 %
    • Impact energy KV: > 35 J
  • Thickness: 20-60 mm
    • Yield strength Re: > 650 MPa
    • Tensile strength Rm: 900-1000 MPa
    • Elongation A: > 12 %
    • Percent reduction of area Z: > 50 %
    • Impact energy KV: > 35 J
  • Thickness: > 100 mm
    • Yield strength Re: > 500 MPa
    • Tensile strength Rm: 750-900 MPa
    • Elongation A: > 14 %
    • Percent reduction of area Z: > 55 %
    • Impact energy KV: > 35 J

Mechanical properties of 42CrMo4 alloy when quenched, tempered and cold-drawn (+QT+C):

• Round bars:
  • Diameter D: 5-10 mm
    • Yield strength Re: > 770 MPa
    • Tensile strength Rm: 1000-1200 MPa
    • Elongation A: > 8 %
  • Diameter D: 10-16 mm
    • Yield strength Re: > 750 MPa
    • Tensile strength Rm: 1000-1200 MPa
    • Elongation A: > 8 %
  • Diameter D: 16-40 mm
    • Yield strength Re: > 720 MPa
    • Tensile strength Rm: 1000-1200 MPa
    • Elongation A: > 9 %
  • Diameter D: 40-100 mm
    • Yield strength Re: > 650 MPa
    • Tensile strength Rm: 900-1100 MPa
    • Elongation A: > 10 %

Mechanical properties of 42CrMo4 alloy when quenched, tempered, peeled, then cold-drawn and quenched and tempered again (+QT+SH / +C+QT):

• Round bars:
  • Diameter D: 16-40 mm
    • Yield strength Re: > 750 MPa
    • Tensile strength Rm: 1000-1200 MPa
    • Elongation A: > 11 %
    • Impact energy KV: > 35 J
  • Diameter D: 40-100 mm
    • Yield strength Re: > 650 MPa
    • Tensile strength Rm: 900-1100 MPa
    • Elongation A: > 12 %
    • Impact energy KV: > 35 J

Mechanical properties when spheroidized, cold drawn and heat treated again (+AC+C+AC)

• Diameter D: 2-5 mm
  • Yield strength Re: < 620 MPa
  • Percent reduction of area Z: > 60 %
• Diameter D: 5-40 mm
  • Yield strength Re: < 610 MPa
  • Percent reduction of area Z: > 60 %

Physical and mechanical properties when spheroidized, cold drawn, spheroidized again and skin passed (+AC+C+AC+LC)

• Diameter D: 2-5 mm
  • Tensile strength Rm: < 660 MPa
  • Percent reduction of area Z: > 58 %
• Diameter D: 5-40 mm
  • Tensile strength Rm: < 650 MPa
  • Percent reduction of area Z: > 58 %

Heat treatment specification and metallographic structure 

• Heat treatment specification: quenching 850 °C, oil cooling; tempering 560 °C, water-cooled, oil-cooled. 
• Metallographic structure: tempered sorbite.

Variant	Condition	Format	Dimension [mm]	Yield strength min [MPa]	Tensile strength [MPa]	Elongation A5 [%]	Reduction of area Zmin [%]	Hardness	Impact (ISO-V) strengthmin
Rp0.2 * Reh, ** Rel
42CrMo4 M (6082), MoC 410 M	+AR	Round bar	25 < 160	–	–	–	–	350 HB typical	–
	+A	Round bar	25 < 160	–	–	–	–	241 HB typical	–
	+QT	Round bar	25 < 40	750**	1000-1200	11	45	300-350 HB	20 °C 35 J (long)
		Round bar	40 < 100	650**	900-1100	12	50	270-320 HB	20 °C 35 J (long)
		Round bar	100 < 160	550**	800-950	13	50	240-280 HB	20 °C 35 J (long)

Uses of 42CrMo4 Steel

It has good processability, easy polishing,
easy biting, and electroplating. It has good strength and toughness, high
hardenability, small deformation during quenching, high creep strength, and
lasting strength at high temperatures. It can manufacture forgings with higher
strength and larger quenched and tempered sections than 35CrMo steel, such as
large gears for locomotive traction, turbocharger transmission gears, rear
axles, connecting rods, and spring clips with great load. It can also be used
for drill pipe joints and fishing tools for oil deep wells below 2000 m. Our 42CrMo4 steel is used in various applications, such as:
1. Fasteners: Unyielding Connections
42CrMo4 steel is widely used to produce fasteners, such as bolts, nuts, and screws, that are essential for creating unyielding connections in various structures and machinery. The exceptional tensile strength and resilience of this steel make it a preferred choice for fastening applications, ensuring safety and reliability.
2. Shafts: Transmitting Torque with Precision
In mechanical engineering, shafts are pivotal in transmitting torque and rotational motion. 42CrMo4 steel’s high fatigue strength and excellent wear resistance make it a go-to material for crafting robust and reliable shafts. These shafts can withstand tremendous stresses while maintaining dimensional stability over extended periods, ensuring efficient and smooth machinery operation.
3. Crankshaft: Enduring Power and Performance
Crankshafts are the heart of internal combustion engines, converting linear motion into rotational power. The demands placed upon crankshafts necessitate a material with exceptional properties. 42CrMo4 steel’s high yield strength and toughness make it an ideal choice for crafting crankshafts that endure cyclic loading, ensuring long-lasting power and performance.
4. Machinery Parts: Precision Engineering at Its Finest
Precision machinery requires equally precise components. 42CrMo4 steel, with its excellent machinability and high dimensional stability, is often the material of choice for crafting intricate machinery parts. From gears and bearings to connecting rods and hydraulic components, this steel’s superior mechanical properties ensure optimal performance and longevity.
5. Gears: Smooth Transmission, Minimal Wear
Gears are the backbone of various industrial systems, ensuring smooth power transmission. The wear resistance, high surface hardness, and fatigue strength of 42CrMo4 steel ensure minimal wear and tear, allowing gears to function flawlessly under heavy loads and extreme conditions.
6. Steel Collets: Firm Gripping Power
Steel collets are vital in applications where a firm grip on tools or workpieces is essential. The combination of toughness and excellent grip retention makes 42CrMo4 steel an excellent choice for crafting durable and reliable collets used in machining, woodworking, and other precision applications.
7. Conveyors and Rolls: Reliability in Material Handling
Conveyors and rolls are integral components in material handling systems across various industries. 42CrMo4 steel’s resistance to wear and impact, coupled with its high load-bearing capacity, ensures the reliability and efficiency of conveyors and rolls, reducing downtime and maintenance costs.
8. Steel Couplings: Uniting Components Seamlessly
Steel couplings are crucial for connecting rotating shafts in machinery, ensuring seamless power transmission. The exceptional strength, fatigue resistance, and torsional strength of 42CrMo4 steel make it an ideal choice for crafting reliable and durable steel couplings that withstand the rigors of demanding applications.
9. Drill Collars: Steadfast Drilling Performance
In the oil and gas industry, drill collars are essential for drilling. 42CrMo4 steel’s high strength, resistance to torsional stresses, and exceptional fatigue performance make it a reliable choice for crafting drill collars that endure the demanding conditions of drilling operations.
10. Steel Piston Rods: Precision and Stability
Piston rods are critical in hydraulic and pneumatic systems, converting fluid pressure into linear motion. 42CrMo4 steel’s high yield strength and hardness ensure precision and stability, making it an excellent material for crafting durable and reliable steel piston rods.
11. Steel Ejector: Ensuring Efficiency in Ejection Systems
In industrial manufacturing, ejector systems remove finished products or waste materials from molds or machines. The superior toughness, wear resistance, and corrosion resistance of 42CrMo4 steel ensure efficient and reliable performance in steel ejectors, reducing downtime and improving productivity.
In conclusion, the versatility of 42CrMo4 steel is unmatched, making it a go-to material in various industries and applications. Its exceptional mechanical properties, including high strength, toughness, and wear resistance, ensure outstanding performance and durability for critical components.

Machinability of 42CrMo4 alloy steel

42CrMo4 alloy steel has good machinability in the annealed condition.

Forming of 42CrMo4 alloy steel

42CrMo4 alloy steel has high ductility. It can be formed using conventional techniques in the annealed condition. It requires more pressure or force for forming because it is tougher than plain carbon steels.

Welding of 42CrMo4 alloy steel

42CrMo4 can be welded using all conventional techniques. However, the mechanical properties of this steel will be affected if it is welded in the heat treated condition, and post weld heat treatment should be performed.

Heat Treatment of 42CrMo4 alloy steel

42CrMo4 bars are heated at 845°C followed by quenching in oil. Before hardening, it can be normalized by heating at 913°C for a long period of time followed by air cooling.

Forging of 42CrMo4 alloy steel

42CrMo4 is forged at 926 to 1205°C.

Hot Working of 42CrMo4 alloy steel

42CrMo4 steel can be hot worked at 816 to 1038°C.

Cold Working of 42CrMo4 alloy steel

42CrMo4 alloy steel can be cold worked using conventional methods in the annealed condition.

Annealing of 42CrMo4 alloy steel

42CrMo4 steel is annealed at 872°C  followed by slowly cooling in the furnace.

Tempering of 42CrMo4 alloy steel

42CrMo4 alloy steel can be tempered at 205 to 649°C depending upon the desired hardness level. The hardness of the steel can be increased if it has lower tempering temperature. For example, tensile strength of 225 ksi can be achieved by tempering at 316°C (600°F), and a tensile strength of 130 ksi can be achieved by tempering at 538°C (1000°F).

Hardening of 42CrMo4 alloy steel

42CrMo4 alloy steel can be hardened by cold working, or heating and quenching.

How to manufacture 42CRMO4 steel?

Manufacturing high-quality 42CrMo4 steel is a strict quality control process, and each connection step requires sufficient experience and strict quality control. From the following figure, we can roughly see a production process diagram.

Below, we will mainly discuss the following key points in manufacturing 42CrMo4 steel.
Casting Technology
There are two mainstream methods for smelting and casting 42CrMo4. One is electric arc furnace smelting, secondary refining, and vacuum degassing; the other is the converter steelmaking and continuous casting technology used by large steel mills.
The difference is that electric arc furnace steelmaking is suitable for small-scale production, and the composition of molten steel is greatly affected by scrap steel. And converter steelmaking is suitable for mass production, with high purity of molten steel. Compared with electric arc furnace steelmaking, the smelting cycle is shorter, and the electricity consumption is lower.
Hot working method
Corresponding to smelting and casting processes, the 42CrMo4 steel ingots produced by EAL+LF+VD are mainly used for hot forging, including free and die forging.
The 42CrMo4 steel billets produced using the converter + continuous casting process are usually used as hot-rolled products, producing extremely high production efficiency.
Finally, it should be noted that they can be applied to each other but must match the size of the billet to ensure a sufficient compression ratio.

Preliminary heat treatment process selection

42CrMo4 steel is usually delivered without heat treatment after hot rolling or forging. However, considering the material’s machinability, 42CrMo4 steel is usually selected for softening and annealing treatment.
The choice of normalizing 42CrMo4 is often to improve processing performance, eliminate internal stress, and prepare a good metallographic structure for final heat treatment.
What is the gas content of 42CRMO4 steel?
Gas in steel is a general term for gases such as oxygen, nitrogen, and hydrogen absorbed by the medium during smelting, welding, or chemical or electrochemical reactions on the steel surface. Gas in steel has adverse effects on its performance, and its content should be strictly controlled.
Oxygen in steel
Steelmaking itself is an oxidation process. Although Oxygen scavengers such as ferromanganese, ferrosilicon, and aluminum are added in the later stage of steelmaking, some oxygen is still dissolved in the steel.
Oxygen is generally dissolved in ferrite or forms oxides such as FeO, SiO₂, MnO, and Al₂O₃ (i.e., non-metallic inclusions in steel), which reduces the tensile strength, plasticity, and toughness of 42CrMo4 steel. Especially when inclusions exist, the fatigue strength of 42CrMo4 steel decreases, and the cold and hot workability worsens.
Therefore, it is necessary to strictly adopt VD deoxidation and other oxygen control technologies to make the oxygen content of 42CrMo4 steel lower than 20ppm or even lower.
Nitrogen in Steel
During steelmaking, molten steel absorbs nitrogen from the air. Some dissolve in ferrite, and some become non-metallic inclusions. When 42CrMo4 steel does not contain elements such as Al, Ti, Zr, etc., most nitrogen forms a needle-like compound Fe₄N with iron. Although the presence of Fe₄N improves the strength of 42CrMo4 steel, it greatly reduces its plasticity and toughness.
By preventing LF nitrogen absorption technology and increasing the VD denitrification rate, these two methods can effectively reduce and control nitrogen content below 90 ppm.
Hydrogen in Steel
The solubility of hydrogen in steel significantly decreases with the decrease in temperature. When hydrogen exists in an atomic state, it dissolves into the voids of iron. When the dissolved hydrogen in steel exceeds 3 milliliters per 100 grams, it will exist in a molecular state, and hairlike cracks appear on the internal cross-section of the steel ingot or forging, called cracking. They look like elliptical silver-white spots, also known as white dots.
White spots cause hydrogen embrittlement in steel. Low-carbon steel is not easy to form white spots. Still, medium carbon alloy steel (such as AISI 1045 steel, C55 steel), especially medium carbon nickel chromium molybdenum steel (such as 34CrNiMo6 steel, 30CrNiMo8 steel, AISI 4340 steel), is most sensitive to hydrogen embrittlement. For 42CrMo4 steel, it is also easy to form white spots, leading to material cracking.
VD vacuum degassing technology can effectively remove hydrogen gas. To avoid embrittlement, 42CrMo4 steel can also be annealed at about 650 ℃ to diffuse hydrogen from the steel, eliminate Supersaturation, and achieve the purpose of hydrogen removal. Generally, the hydrogen content can be controlled below 2.0ppm
42CRMO4/DIN 1.7225 Heat Treatment

Normalization and annealing of 42CrMo4/DIN 1.7225 steel

When 42CrMo4 steel needs to improve its comprehensive properties, it is usually achieved through heat treatment. Before the final heat treatment, we first consider the preliminary heat treatment, and the conventional methods include normalizing and annealing. Let’s talk about the differences and characteristics of 42CrMo4, annealing and normalizing, to help us choose when facing different requirements.
Different effects and purposes
The main purpose of normalizing 42CrMo4 is to refine the grains, homogenize the structure, and prepare the structure for final heat treatment. The annealing time of 42CrMo4 steel is generally arranged after forging, hot rolling, and welding, mainly to reduce the internal stress of the structure. Material, softening structure, improving turning performance.

Comparison of different processes	42CrM04 normalized	42CrM04 annealing
Temperature, ° C	850-900	800-850
Cooling	Air cooling	Furnace cooling
Cooling rate	Faster	Slow down
Crystal grain size	Okay	Ordinary
Machinability	Ordinary	Okay
Deformation	Big ones	Smaller
Heat treatment cycle	Short time	Long time
Surface hardness, HBW	200-250	≤ 229

Heat treatment process improvement of 42CrMo4 wind power spindle

The low temperature impact toughness of the 42CrMo4 wind power spindle cannot meet the requirements after conventional heat treatment. The improved cooling quenching process is used to reduce the quenching temperature from 860 °C to 810 °C, and the water quenching and oil cooling method is used to make the product fully meet the technical requirements.

Wind power spindle

A wind power spindle is one of the key components of the wind power generator. Our company has manufactured a batch of Indian 1.25 MW wind power spindles. The material is 42CrMo4, the size is Ø1402mm/Ø642mm × 2978mm (inner hole diameter Ø = 108mm), and the weight is 8.466 t. technical conditions: Rm ≥ 500MPa, 750MPa ≤ Re ≤ 900MPa, A5 ≥ 14 %, Z ≥ 35 %, AKV ≥ 27J (-20 °C), single value ≥ 24.3J. The chemical composition of the main axis is shown in Table 1.
Table.1 Chemical composition of 142CrMo4 wind turbine spindle (mass fraction, %)

C	Mn	Si	P	S	Cr	Mo
0.38–0.45	0.60–0.9	≤0.40	≤0.035	≤0.035	0.90–1.2	0.20–0.3

Improvement of heat treatment process parameters of wind power spindle

The conventional heat treatment process of 42CrMo4 material is shown in Figure 1.
The main shaft of the wind turbine spindle with furnace number 063-2333 is taken for heat treatment according to the process shown in Figure 1. The chemical composition of the main shaft is shown in Table 2. The test results of mechanical properties after heat treatment are shown in Table 3.
It can be seen from Table 3 that the low temperature impact toughness of the spindle is much lower than the technical requirements. For this reason, we have improved the heat treatment process of the wind power spindle. The improved heat treatment process is shown in Fig.2. Similarly, a spindle is taken from the wind turbine spindle with furnace number 063-2333 for heat treatment according to the process shown in Figure 2. The mechanical properties test results after heat treatment are shown in Table 4.

Analysis and discussion

The comprehensive performance requirements of the 42CrMo4 wind power spindle are high, especially the low temperature impact toughness, which cannot meet the requirements according to the conventional process. After calculation, this steel’s carbon equivalent [C] is 0.63, which belongs to a kind of steel that can be quenched by water, but special care is needed. Therefore, cooling quenching is adopted in the improved process, and good results are obtained. The reasons are as follows.
Firstly, the quenching temperature is reduced to 810 °C to ensure the complete austenitizing temperature of the steel. After calculation, the material Ac3 is about 758 °C, and Ar3 is 700 °C, which is lower than 810 °C. At this temperature, quenching meets the quenching requirements, and no phase transformation occurs before quenching. Reducing the surface temperature of the product to 810 °C before quenching can reduce thermal stress and greatly reduce the cracking tendency.
Secondly, according to the supercooled austenite transformation curve of this kind of steel, the lower bainite structure can be obtained at a certain distance from the surface by water quenching and oil quenching, thus greatly improving the comprehensive mechanical properties of this part. The water cooling time is determined according to the sampling position, and the product’s sampling position must be 30 mm from the surface. The water cooling time during water quenching is calculated to ensure that the entire product is still in the plastic + elastic-plastic state and has been converted to slower oil cooling to avoid quenching cracks.

Fig.1 Conventional heat treatment process of 42CrMo4 metal material
Table.2 Spindle chemical composition (mass fraction, %) of furnace number 063 – 2333)

C	Si	Mn	P	S	Cr	Ni	Mo	Cu	Nb	Al
0.42	0.28	0.72	0.008	0.006	1.16	0.49	0.27	0.15	0.043	0.03

Fig.2 Improved heat treatment process of 42CrMo4 wind power spindle
Table.3 Mechanical properties of spindle after heat treatment according to the conventional process

Re/MPa	Rm/MPa	A5(%)	Z(%)	AKV (-20 ℃)/J
635	820	17	54	9, 8, 11

Table.4 Mechanical properties of the spindle after heat treatment according to the new process

Re/MPa	Rm/MPa	A5(%)	Z(%)	AKV (-20 ℃)/J
639	815	17	55	24.5, 31, 63

Finally, the improved tempering temperature is based on the tempering temperature of the traditional process. Experience shows that for forgings of this kind of size and steel grade, the strength of water quenching and oil quenching is slightly higher than that of pure oil quenching, so the tempering temperature of the improved process is slightly higher than that of the traditional process, thus further improving the impact toughness of the product.

Conclusion

• (1) The improved cooling and quenching process of the 42CrMo4 wind power spindle can meet the corresponding technical requirements.
• (2) The improved new process can avoid quenching cracks.

Author: Liu Guoping

FAQ:

Question 1: Why should the carbon content of 42CrMo4 alloy structural steel be controlled between 0.38 % and 0.45 %?

Explanation 1: Controlling the range of carbon content can provide good toughness and hardenability while ensuring the high strength and hardness of the material. Lower carbon content can reduce the tendency of brittleness, while higher carbon content can increase the hardness of the material. Therefore, the balance between excellent mechanical properties and processability of 42CrMo4 steel can be achieved by controlling the carbon content between 0.38 % and 0.45 %.

Question 2: Why do 42CrMo4 alloy structural steel contain chromium and molybdenum?

Explanation 2: Chromium and molybdenum are key alloying elements in 42CrMo4 alloy structural steel. The addition of chromium can improve the hardness, strength and corrosion resistance of the steel, while the addition of molybdenum can significantly improve the hardenability and strength of the steel, and improve its high temperature resistance and thermal fatigue performance. The appropriate content of chromium and molybdenum in 42CrMo4 steel can make it have excellent high temperature strength, durability and wear resistance, which is suitable for engineering applications requiring high strength and toughness.

Question 3: What are the delivery status of 42CrMo4 alloy structural steel?

The delivery status of 3: 42CrMo4 alloy structural steel mainly includes heat treatment status and annealing status. Specifically, according to different processing and application requirements, steel can be delivered in heat treatment or annealing state.
Heat treatment status: Hot rolled steel is usually provided in heat treatment status upon delivery. Heat treatment can change the microstructure and properties of steel by controlling the heating temperature and cooling rate. In the heat treatment state, 42CrMo4 steel is subjected to appropriate heating, heat preservation and cooling processes to obtain the required mechanical properties and microstructure.
Anneal state: Cold rolled steel and cold drawn steel are usually supplied in anneal state upon delivery. Annealing is performed by heating the steel to a certain temperature and then slowly cooling to room temperature to eliminate internal stress and improve the plasticity and toughness of the steel. The annealed steel has a more uniform structure and better processing performance.
According to the specific application requirements, suppliers and users can choose the appropriate delivery status according to the contract agreement to ensure that the steel can meet the requirements during use.
In general, 42CrMo4 alloy structural steel is widely used in the manufacture of large and medium-sized mechanical parts requiring high strength and toughness, as well as various engineering components due to its excellent properties. Whether in mechanical engineering, automobile manufacturing or energy industry, 42CrMo4 steel plays an important role in providing reliable material solutions for various application scenarios.

The difference between 42CrMo and 42CrMo4

The differences between 42CrMo and 42CrMo4 are described from the aspects of chemical composition, mechanical properties, and hardenability so that our mechanical designers and mechanical technicians can understand their similarities and differences and choose two brands according to the specific application.
42CrMo is a medium carbon alloy structural steel with good comprehensive mechanical properties, hardenability, and wide application. In the machinery industry, it is often used to manufacture important parts such as gears, connecting rods, and high-strength bolts. In production and manufacturing, we often encounter drawings of European countries that mention 42CrMo4 material. However, in the national standard for 42CrMo, these two brands are universal; what are the differences, and what are their respective characteristics? Given the above problems, we discuss them in detail as follows.

Based on the standard

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

Chemical constituents

The chemical compositions of 42CrMo4 and 42CrMo are shown in Table 1 and Table 2.
Table.1 Chemical Composition of GB3077 Standard 42CrMo

	C	Si	Mn	S	P	Mo	Cr	Cu
42CrMo4	0.38-0.45	≤0.40	0.6-0.9	≤0.035	≤0.035	0.15-0.30	0.90-1.20	≤0.40
42CrMo	0.38-0.45	0.17-0.45	0.5-0.8	≤0.04	≤0.035	0.15-0.25	0.90-1.20	–

Table.2 P and S Content of 42CrMo in GB3077 Standard

	C	Si	Mn	S	P	Mo	Cr	Cu
42CrMo	0.38-0.45	0.17-0.45	0.5-0.8	≤0.04	≤0.035	0.15-0.25	0.90-1.20	–
Normal quality 42CrMo	0.38-0.45	0.17-0.45	0.5-0.8	≤0.035	≤0.035	0.15-0.25	0.90-1.20	–
High quality 42CrMo	0.38-0.45	0.17-0.45	0.5-0.8	≤0.025	≤0.025	0.15-0.25	0.90-1.20	–
Ultra High Quality 42CrMo	0.38-0.45	0.17-0.45	0.5-0.8	≤0.015	≤0.025	0.15-0.25	0.90-1.20	–

• Ordinary 42CrMo steel: P < 0.035; S <
  0.035.
• High quality 42CrMo steel: P < 0.025; S
  < 0.025.
• Extra-high quality 42CrMo steel: P < 0.025;
  S < 0.015.

It can also be seen from the above table
that the content of Si, Mn, and Mo is different. GB/ T3077P and S content is
divided into three grades. The standard value of EN10083 limits the maximum
content. The P and S content of high-quality steel in GB/T3077 standard is
similar to that in EN10083. The content range of Si and Mo in GB/T3077 standard
is narrower than in EN10083 standard. If only considering the chemical
composition, 42CrMo can choose high-quality steel and pay attention to the Mn
content to meet the requirements of 42CrMo4 in EN10083.

Hardenability

The hardening bandwidth is given in the EN standard, divided into three grades: H, HL, and HH. It can be used for reference when ordering and also provides standard information for designers to choose from.
Mechanical properties
The sampling position and method are according to GB/T2975. When the bar diameter d>50mm, the distance centered on the bar’s outer diameter is d/4, and the diameter of the test bar is 25mm. The samples were tempered according to the standard heat treatment process, and then the tensile samples and impact samples were made for testing.
According to the EN standard, the bar is tempered according to the recommended heat treatment process and then sampled on the bar. The diameter of the bar is d>25mm, and the sampling position is 12.5mm away from the bar’s outer diameter. The rod was made into tensile and impact specimens for testing.
The GB standard uses the Charpy U-notched sample for the impact test standard sample, and the EN standard uses the Charpy U-notched sample. The notch depth of the two specimens is the same, but the radius of the notch bottom is different. The U-shaped is 1 mm, the V-shaped is 0.25mm, and the notch stress is relatively concentrated. When the sample is impacted, it appears more sensitive. In the past, U-notched specimens were mainly used in China.
To meet the needs of some enterprises, GB/T 12778-2008 impact test method metal sand (V-notch) was promulgated in China, which can be used for special steel requirements. In both standards, the corresponding heat treatment specifications and mechanical properties are required.
Low magnification and non-metallic inclusions
For macrostructure, GB3077 gives the corresponding macrostructure requirements according to the quality grade of steel, while the EN standard does not give the requirements of the macrostructure.
For non-metallic inclusions, there is no requirement and recommended value in GB3077, and only the supply and demand sides need to negotiate. In EN 10083, the relevant requirements and detection methods of non-metallic inclusions are put forward to facilitate the negotiation between the two sides.
Granularity
Grain size is proposed as a special requirement in GB3077. After negotiation between the supply and demand sides, it can be indicated in the contract that fine-grain steel below grade 5 is needed. In EN 10083, the grain size must be less than or equal to grade 5, and the corresponding detection method and heat treatment quenching conditions are given for selection.
Delivery status
In GB3077, steel is usually delivered by hot rolling or forging. If the demand side requires heat treatment (annealing, normalizing, or high-temperature tempering) delivery, it should be noted in the contract. However, five deliveries are given in EN 10083. 
The heat treatment state is selected as non-heat treatment, heat treatment to improve cutting performance, softening annealing, quenching, and high temperature tempering.
Through the discussion of the two standards on the chemical composition, hardenability, mechanical properties, low magnification and non-metallic inclusions, grain size, and delivery status of 42CrMo steel, the following conclusions are drawn:
The EN 10083 standard is relatively strict, while the GB3077 standard is relatively simple and loose.
The testing requirements of the EN 10083 standard for mechanical properties directly reflect the material properties of steel in practical applications, which is convenient for designers to check and calculate.
EN 10083 standard specifies the relevant requirements of hardenability. When 42CrMo4 steel is selected for the gear workpiece, it is more convenient to select this standard order.
When enterprises need mass production, it is more convenient to choose EN-10083 standard supply and GB3077 standard supply for single-piece or small batch production.
The emergence of standards and the development of the national machinery manufacturing industry complement each other. In European countries, most metallurgical enterprises will be equipped with corresponding heat treatment equipment to meet the different ordering requirements of mechanical enterprises.