What is 40Cr steel? What are the characteristics of 40Cr steel?

40Cr steel is a medium-carbon modulated steel. Normalizing can promote spheroidization of the structure and improve the cutting performance of blanks with a hardness less than 160HBS. Tempered at a temperature of 550~570℃, the steel has the best comprehensive mechanical properties. The hardenability of this steel is higher than that of 45 steel, and it is suitable for surface hardening treatments such as high-frequency quenching and flame quenching. Medium carbon quenched and tempered steel, cold heading mold steel. The steel is moderately priced and easy to process. It can obtain certain toughness, plasticity and wear resistance after appropriate heat treatment.

The normalizing section promotes tissue spheroidization and is suitable for surface hardening treatments such as high-frequency quenching and flame quenching. After quenching and tempering, it is used to manufacture mechanical parts that bear medium loads and work at medium speeds, such as steering knuckles, rear axles of automobiles, and gears, shafts, worms, spline shafts, center sleeves, etc. on machine tools; after quenching and medium temperature tempering After quenching, it is used to manufacture parts that can withstand high load, impact and medium-speed operation, such as gears, spindles, oil pump rotors, sliders, collars, etc.; after quenching and low-temperature tempering, it is used to manufacture parts that can withstand heavy load, low impact and have Wear resistance, parts with a physical thickness of less than 25mm on the cross-section, such as worms, spindles, shafts, collars, etc.; after quenching and tempering and high-frequency surface quenching, they are used to manufacture parts with high surface hardness and wear resistance without significant Impact parts, such as gears, sleeves, shafts, spindles, crankshafts, spindles, pins, connecting rods, screws, nuts, intake valves, etc. In addition, this kind of steel is suitable for manufacturing various transmission parts that undergo carbonitriding treatment, such as gears and shafts with larger diameters and good low-temperature toughness. Elastic modulus E (20℃) /MPa 200000～211700, shear modulus G (20℃) 80800, quenched at 850℃, oil cooling; tempered at 520℃, water cooling, oil cooling. The surface quenching hardness of 40Cr is HRC52-60, and the flame quenching can reach HRC48-55. 40Cr steel is a nitridable steel, and the elements it contains are conducive to nitriding. 40Cr can obtain higher surface hardness after nitriding treatment. The highest hardness of 40Cr after nitriding treatment can reach HRA72~78, that is, HRC43~55. ​

Nitriding workpiece process route: forging – annealing – rough machining – quenching and tempering – finishing – stress removal – rough grinding – nitriding – fine grinding or grinding.

Since the nitride layer is thin and brittle, it requires a higher-strength core structure. Therefore, quenching and tempering heat treatment must be performed first to obtain tempered sorbite to improve the mechanical properties of the core and the quality of the nitride layer. Soft nitriding is active nitriding. Pay attention to preheating before welding 40Cr steel to prevent internal chilling and quenching cracks in the weld due to heat dissipation from the matrix. It is best to add normalizing after welding and before tempering. It is easy to segregate during crystallization and is sensitive to crystallization cracks (a type of thermal crack). It is easy to crack in arc craters and concave parts of the weld during welding. The cnc milling carbon fiber content is high, and it is easy to obtain a hardened structure (martensite structure) that is sensitive to cold cracks during rapid cooling. When the cooling rate in the overheated zone is high, it is easy to form hard and brittle high-carbon martensite and embrittle the overheated zone. Sample blank size (mm): 25 Heat treatment: First quenching heating temperature (℃): 850; Coolant: Oil Second quenching heating temperature (℃): – Tempering heating temperature (℃): 520; Coolant : Water and oil tensile strength (σb/MPa): ≥980 Yield point (σs/MPa): ≥785 Elongation after break (δ5/%): ≥9 Area shrinkage (ψ/%): ≥45 Impact absorption Work (Aku2/J): ≥47 Brinell hardness (HBS100/3000) (annealed or high temperature tempering state): ≤2071, generally welded in the annealed (normalized) state.

2. Welding methods are not restricted

3. Use larger linear energy and increase the preheating temperature appropriately. Generally, the preheating temperature and interlayer temperature can be controlled between 250 and 300°C.

4. Welding materials should ensure that the composition of the deposited custom metal fabrication is basically the same as that of the base metal, such as J107-Cr5. Quenching and tempering heat treatment should be carried out promptly after welding. If it is difficult to perform quenching and tempering 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, an intermediate annealing can be performed after a certain number of welds are welded. The delivery status of 40Cr is heat treatment (normalizing, annealing or high temperature tempering) or non-heat treatment. The delivery status should be specified in the contract.