Study On Double Frequency Induction Hardening Process Of Forged Cold-rollers Of Cr3 And Cr5 Steels

With the rapid development of automobile and home appliance industries,the demand for cold-rolled plate is increasing rapidly.In the production of cold-rolled plate,the high quality cold roller is an important essential to ensure the quality of rolling material and improve the production efficiency.It is of great significance to develop cold-roller with high hardness,deep hardened layer and good microstructure.In this paper,the?440 cold rollers were made of Cr3 and Cr5 steel through smelting,forging,quenching and tempering,50/250Hz double frequency induction quenching and so on.The microstructure and properties of each stage were tested and analyzed.The microstructure and hardness of the finished cold rollers were tested and analyzed after quantitative layer by layer grinding.CR3 and Cr5 materials are smelted by DC electric arc furnace+ladle refining+vacuum degassing,and electroslag remelting.The chemical composition meets the requirements.After forging and normalizing,the spot segregation,non-metallic inclusion,carbide network and grain size meet the requirements.After rough machining and quenched-tempered heat treatment,the microstructure of the roller is mainly tempered sorbite and uniformly distributed fine carbide particles.The tensile strength of Cr3 is 1073 MPa,the elongation is 42.3%,and the impact energy is 23.7J/cm~2;the tensile strength of Cr5 test piece is 1088 MPa,the elongation is 44.0%,and the impact energy is 33.0 J/cm~2.The final heat treatment of the roller was carried out by using 50/250Hz double frequency induction hardening process,and the hardness test and microstructure analysis of the roller layer by layer within 35mm depth were carried out.The results show that the depth of the hardened layer(hardness higher than HSD90)is the largest when the descending speed of Cr3 sample is 0.7mm/s,reaching 17.5mm.The hardness within 35mm depth are higher than HSD90 when Cr5 sample descend at 0.5mm/s,0.7mm/s and 1.0mm/s,and the overall hardness is the highest when the roll body falls at 0.7mm/s,and the hardness decreases slowly before the layer depth is 32.5mm.At the shallow layer,the microstructure is mainly indistinguishable cryptocrystalline martensite,a small amount of fine granular carbide and a small amount of retained austenite;with the increase of the layer depth,bainite,tempered martensite and lath martensite appear in the microstructure.Under the condition of fixed other process parameters,the best descending speed of 50/250Hz double frequency induction quenching process for CR3 and Cr5 samples is 0.7mm/s.With this double frequency induction quenching,excellent microstructure and properties of Cr3 and Cr5?440 cold rollers can be obtained.