45# steel belongs to GB699 "(high quality) carbon structural steel", and 40Cr belongs to GB3077 "alloy structural steel". The difference is after heat treatment. The main role of Cr in heat treatment is to improve the hardenability of steel. Due to the increase in hardenability, the mechanical properties of 40Cr alloy after quenching (or quenching and tempering) are significantly higher than those of 45 #steel, such as strength, hardness, and impact toughness. However, due to the strong hardenability, the internal stress of 40Cr steel during quenching is also higher than that of 45# steel. 45# steel is large, and under the same conditions, the cracking tendency of 40Cr material is greater than that of 45# steel. Therefore, in order to avoid the cracking of the workpiece, the oil with lower thermal conductivity is mostly used as the quenching medium during the quenching of 40Cr (sometimes the double liquid quenching method is also used, as the saying goes, water quenching oil cooling), while the 45 steel uses water with higher thermal conductivity as the quenching medium. medium.
40Cr alloy plate characteristics: medium carbon modulation steel, cold heading die steel. 40cr alloy steel is easy to process, and certain toughness, plasticity and wear resistance can be obtained after proper heat treatment. Normalizing can promote the spheroidization of the structure and improve the cutting performance of the blank with a hardness less than 160HBS. Tempering at a temperature of 550~570℃, 40cr alloy steel has excellent comprehensive mechanical properties. The hardenability of 40cr alloy steel is higher than that of 45 steel, which is suitable for surface hardening treatments such as high frequency quenching and flame quenching.
After quenching and low temperature tempering, the 40cr alloy plate is used to manufacture parts with heavy load, low impact and wear resistance, and the solid thickness of the cross section is below 25mm, such as worms, spindles, shafts, collars, etc.; after quenching and tempering After high-frequency surface hardening, it is used to manufacture parts with high surface hardness and wear resistance without great impact, such as gears, sleeves, shafts, main shafts, crankshafts, spindles, pins, connecting rods, screws, nuts , Intake valve, 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.
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