40CrNiMoA, 4340, and SNCM439 are all types of high-strength alloy steel that contain similar chemical compositions, making them somewhat interchangeable for certain applications.
Chrome-Moly low alloy steel series contains 0.5% – 9% Cr and 0.5% – 1% Mo and lower than 0.20% carbon. 40CrNiMoA, 4340 and SNCM439 are the low alloy chromoly steel materials from the different standards. 40CrNiMoA steel is a Chinese standard chromium-molybdenum high strength steel with good hardenability and toughness. 4340 and SNCM439 are standards from American and Japanese respectively. In most situation they can be alternative materials, unless there is a special note or used for special purpose. Their differences are mainly existed in chemical elements, details showed as follows:
| Standards | GB | AISI | JIS |
| Material | 40CrNiMoA | 4340 | SNCM439（SNCM8） |
| C | 0.37~0.44 | 0.38~0.43 | 0.36~0.43 |
| Si | 0.17~0.37 | 0.15~0.35 | 0.15~0.35 |
| Mn | 0.50~0.80 | 0.60~0.80 | 0.60~0.90 |
| P | ≤0.025 | ≤0.035 | ≤0.030 |
| S | ≤0.025 | ≤0.040 | ≤0.030 |
| Cr | 0.60~0.90 | 0.70~0.90 | 0.60~1.00 |
| Ni | 1.25~1.65 | 1.65~2.00 | 1.60~2.00 |
| Mo | 0.15~0.25 | 0.20~0.30 | 0.15~0.30 |
It was used where require high tensile and good wear-resistance property parts such as heavy-duty axles, shafts, heavy-duty gears, spindles, pins, studs, bolts, couplings, sprockets, pinions, torsion bars, connecting rods. These high tensile alloy steel has been widely used in the areas such as petrol chemical industry, automotive, steam power equipment and other high temperature services.
| C(％) | Si(％) | Mn(％) | P(％) | S(％) | Cr(％) | Ni(％) | Cu(％) | Mo(％) |
| 0.37～0.4 | 0.17 ~ 0.37 | 0.50 ~ 0.80 | ≤0.025 | ≤0.025 | 0.60～0.90 | 1.25 ~ 1.65 | ≤0.25 | 0.15 ~ 0.25 |
| Yield Strength Rp0.2(MPa) |
Tensile Strength Rm(MPa) |
Impact Energy AKV(J) |
Elongation A(%) |
Impact toughness | Reduction of area ψ (%): |
Hardness |
| ≥ 835(85) | ≥ 980(100) | ≥ 78 | ≥ 12 | ≥ 98(10) | ≥ 55 | ≤ 269 HBW |
40CrNiMoA is a type of alloy steel that contains chromium, nickel, and molybdenum as its major alloying elements. It is a low-alloy steel with high strength, toughness, and hardenability, making it suitable for use in heavy-duty machinery and equipment.
40CrNiMoA is commonly used in components such as gears, shafts, and bolts, where high strength and durability are required. It has excellent fatigue resistance and improved wear resistance due to the presence of nickel, molybdenum, and chromium.
The mechanical properties of 40CrNiMoA can be improved through heat treatment, such as quenching and tempering. This process helps to improve its hardness, toughness, and strength, making it suitable for use in high-stress applications.
Compared to other types of steel, 40CrNiMoA offers superior mechanical performance at higher temperatures, making it an ideal material for use in high-temperature applications.
Overall, 40CrNiMoA is a highly versatile and durable alloy steel that is widely used in various industries, including automotive, aerospace, marine, and construction. Its high strength, toughness, and hardenability make it an excellent choice for heavy-duty applications that require reliable and long-lasting components.
SNCM439 is a type of chromium-nickel-molybdenum (Cr-Ni-Mo) alloy steel grade. It is similar to 40CrNiMoA steel grade and has similar chemical composition, with slight differences in the content of some elements.
The chemical composition of SNCM439 is as follows:
SNCM439 has excellent hardenability, and it can be heat-treated to achieve high hardness and strength. It is commonly used in the manufacturing of gears, shafts, and other components where high strength and resistance to wear and fatigue are required.
Compared to other types of steel, SNCM439 offers superior mechanical performance at higher temperatures, making it an ideal material for use in high-temperature applications.
Overall, SNCM439 is a highly durable and versatile alloy steel that is widely used in various industries, including automotive, aerospace, marine, and construction.
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