Knowledge

35CrMo and 40Cr, as common alloy structural steels, although widely used in mechanical manufacturing and engineering applications, each exhibit their unique characteristics and advantages in terms of chemical composition, mechanical properties, and specific application scenarios.

 

Properties:	35CrMo	40Cr
Carbon content	Medium carbon (about 0.35%)	Medium-high carbon (about 0.40%)
Alloy elements	Cr (0.8 - 1.1%)	Cr (0.8 - 1.1%)
	Mo（0.15-0.25%）
Strength and toughness	Higher strength, excellent toughness and fatigue resistance	Strength slightly lower, medium toughness
Quenching property	Better (molybdenum improves quenching property)	Good (chromium enhances quenching property)
High-temperature performance	Better (molybdenum delays temper brittleness)	General
Processing performance	Slight poorer cutting performance, requires tempering optimization for improvement	Better cutting performance

 

Firstly, from the perspective of chemical composition, the carbon content of 35CrMo ranges from 0.32% to 0.40%, silicon content is 0.17% to 0.37%, manganese content is 0.40% to 0.70%, chromium content is 0.80% to 1.10%, and it particularly contains 0.15% to 0.25% of molybdenum. The addition of molybdenum significantly enhances the material's heat resistance and creep resistance. In contrast, 40Cr has a slightly higher carbon content, ranging from 0.37% to 0.44%, silicon and manganese contents are 0.17% to 0.37% and 0.50% to 0.80% respectively, and chromium content is similar to 35CrMo, at 0.80% to 1.10%, but it does not contain molybdenum. These minor differences in composition largely determine the performance differences between the two materials.

In terms of mechanical properties, 35CrMo is renowned for its outstanding static strength, impact toughness and fatigue limit. Its hardenability is significantly better than that of 40Cr, meaning that during heat treatment, 35CrMo can achieve a deeper hardened layer, thereby enhancing overall strength. More importantly, 35CrMo can maintain relatively high creep strength and endurance strength at high temperatures, with a long-term working temperature up to 500℃, which enables it to operate stably under high-temperature conditions. However, 35CrMo has a medium plasticity during cold deformation and relatively poor weldability, requiring special welding techniques. In contrast, after quenching and tempering treatment, 40Cr, although its comprehensive mechanical properties are slightly inferior to 35CrMo, still shows good low-temperature impact toughness and notch sensitivity, making it suitable for most mechanical manufacturing fields. Although the hardenability of 40Cr is not as good as that of 35CrMo, it is sufficient to meet most practical needs in actual applications. Additionally, 40Cr has medium plasticity during cold deformation and fair machinability, but its weldability is also poor, which requires special attention in practical applications.

In terms of application scenarios, 35CrMo is often used to manufacture key mechanical parts that need to withstand high impact, high bending and torsion, and high loads due to its excellent high-temperature performance and hardenability. For instance, core components such as herringbone gears, crankshafts, and connecting rods in steel rolling mills often require 35CrMo to ensure long-term stable operation. Additionally, 35CrMo is widely used in the manufacturing of fasteners and conduits that operate at high temperatures, ensuring structural stability and safety in high-temperature environments. On the other hand, 40Cr, with its good comprehensive performance, is widely used in the manufacturing of important parts that bear alternating loads, medium speeds, and medium loads. For example, components such as steering knuckles, rear half shafts in automobiles, and gears in machine tools need to have good wear resistance and fatigue resistance during use, and 40Cr can well meet these requirements. Moreover, 40Cr is also suitable for making medium-sized plastic molds due to its good machinability, which can improve the manufacturing efficiency and precision of molds.

To sum up, 35CrMo and 40Cr each have their own advantages in terms of chemical composition, mechanical properties, and application scenarios. 35CrMo, with its excellent high-temperature performance and hardenability, is suitable for high-temperature and high-load working conditions; while 40Cr, with its good comprehensive performance and wide application range, is a commonly used material in the mechanical manufacturing field. The choice of which material to use should be based on specific usage requirements and working conditions for comprehensive consideration to ensure the performance and reliability of the final product.