关键词: 40Cr钢, 横向开裂, 夹渣, 表层硬化, 保护渣,

Abstract: In view of the transverse cracking of Φ75 mm 40Cr round steel, the samples are analyzed by direct reading spectrometer, metallographic microscope, SEM, EDS and microhardness. The results show that the cracks are mainly caused by slag inclusion in steel, and the surface defects are formed by burned in grinding to form a hardened layer of martensite, which reduces plasticity and eventually leads to cracking under the action of shearing force. Through process improvement, the amount of lime is adjusted from 2. 5 kg/t to 4. 2 kg/t, the slagging agent is adjusted from 0.45 kg/t to 0. 85 kg/t, the Ca/Al ratio is adjusted from 0. 05 to 0. 07, and the nozzle penetration depth is adjusted from 95 mm to 105 mm, mold flux alkalinity is adjusted from 0. 78 to 0. 86, viscosity is adjusted from 0. 34 pa • s to 0.45 pa • s, reducing continuous casting speed fluctuations, etc., it is effectively to avoid the defects of casting slag inclusion, and the surface defect rate of rolling materials decreases from 0. 35% to 0. 08% , ensuring the quality of round steel products.