40Cr is China's GB standard steel grade. 40Cr steel is one of the most widely used steel types in the machinery manufacturing industry. After quenching and tempering treatment, it has good comprehensive mechanical properties, good low-temperature impact toughness and low notch sensitivity. Steel has good hardenability. It can be hardened to Ф28~60mm during water quenching and to Ф15~40mm during oil quenching. In addition to quenching and tempering treatment, this steel is also suitable for cyanidation and high-frequency quenching treatment.
The characteristics of 40Cr steel are mainly reflected in the following aspects. High strength and hardness: Due to the addition of appropriate amounts of alloy elements, 40Cr steel has high strength and hardness, which can meet some engineering applications that require higher material strength. Good wear resistance: Its wear resistance is due to its high hardness and the addition of alloy elements, which makes its surface have a certain degree of wear resistance, so it is suitable for some occasions with high wear resistance requirements. Good heat treatment performance and weldability: 40Cr steel can obtain a certain hardness after heat treatment, and is suitable for surface and quenching treatments such as high-frequency quenching and flame quenching. At the same time, it also has good solderability. Good toughness and plasticity: As a medium carbon quenched and tempered steel, 40Cr steel shows good toughness and plasticity during processing and use.
Weldability of 40Cr steel: It is easy to segregate during crystallization and is sensitive to crystallization cracks. During welding, arc craters and weld grooves are prone to cracks. The carbon content is high and it is easy to obtain a hardened structure that is sensitive to cold cracking during rapid cooling. When the cooling rate in the overheated zone is high, hard and brittle high-carbon martensite is easily formed, making the overheated zone embrittled.
The key points of the 40Cr steel welding process are: generally welding is performed in the annealed state; the welding method is not restricted; larger linear energy is used and the preheating temperature is appropriately increased. Generally, the preheating temperature and interlayer temperature can be controlled between 250 and 300°C; the welding materials should ensure that the composition of the deposited metal is basically the same as the base metal; quenching and tempering heat treatment should be carried out in time after welding. If it is difficult to quench and temper in time, intermediate annealing can be performed or kept at a temperature higher than preheating for a period of time to eliminate diffusible hydrogen and soften the tissue. For products with complex structures and many welds, intermediate annealing can be performed after a certain number of welds are welded.
40Cr steel contains elements that are beneficial to nitriding. 40Cr can obtain higher surface hardness after nitriding treatment. After quenching and tempering treatment, the nitriding hardness of 40Cr can reach 72~78HRA, and the core hardness can reach 43~55HRC.
40Cr steel nitriding process route: forging - annealing - rough machining - quenching and tempering - finishing - stress relief - rough grinding - nitriding - fine grinding or grinding.Because the nitride layer is thin and brittle, a stronger core structure is required. Therefore, it is necessary to perform quenching and tempering heat treatment to obtain tempered sorbite to improve the mechanical properties of the core and the quality of the nitride layer.
40Cr steel has excellent mechanical properties and wear resistance and is widely used in many fields. Mold industry: In mold manufacturing, 40Cr steel is commonly used for mold frames, templates, mold rods, mold blanks and other components. Its high strength and durability make it an excellent material for mold making.Bearing manufacturing: Because 40Cr steel plate has good wear resistance and high hardness, it is often used to manufacture various types of bearings to meet the bearing performance requirements of mechanical equipment.Auto parts: In automobile manufacturing, 40Cr steel is often used to manufacture important mechanical parts, such as steering knuckles, crankshafts, connecting rods, etc. These parts need to withstand large loads and friction, and the performance of 40Cr can just meet these requirements. Mechanical parts: 40Cr steel is also a commonly used material for key parts in various mechanical equipment, such as gears, shafts, etc. Their high strength and good toughness enable these parts to maintain stable performance in complex working environments.
It should be noted that although 40Cr has the above advantages and a wide range of applications, factors such as the working conditions, usage requirements and processing technology of the parts need to be comprehensively considered in specific applications to ensure that the selection and use of materials can meet actual requirements.
