冷却时间对U75V 60kg/m重轨热处理硬化层的影响

Effect of cooling time on hardened layer of U75V 60 kg/m heavy rail after heat treatment

将U75V 60 kg/m重轨试样加热至900℃,保温50 min后,用压缩空气对轨头表面进行强制冷却50~90 s,研究U75V 60 kg/m重轨热处理硬化层与冷却时间之间的关系。研究结果表明：热处理过程中,冷却时间大于80 s时,轨头中心表面自回火温度低于在该冷却速率下珠光体转变终止温度,珠光体相变完成;重轨热处理后硬化层组织为细珠光体,随着冷却时间的增加,珠光体平均片层间距减小,但趋势放缓,当冷却时间为90 s,离轨头中心表面3 mm处珠光体平均片层间距约为83 nm;随着冷却时间的增加,硬化层厚度增大,硬度、抗拉强度、伸长率及冲击韧性提高,当冷却时间大于80 s时,性能趋于稳定。

The U75V 60 kg/m heavy rail samples were heated to 900 ℃ for a fixed duration of 50 min.After that,rail head surface were cooled forcedly by jetting compressed air for 50-90 s,the relationship between hardened layer of U75V heavy rail after heat treatment and cooling time was studied.The results show that during heat treatment,the self-tempering temperature at the centre surface of rail head is lower than finishing temperature of pearlite transformation at same cooling rate when cooling time is more than 80 s.Under this condition,pearlite transformation is finished;the hardened layer structure of rail head after heat treatment is fine pearlite,and with the increase of cooling time,the average pearlite interlamellar spacing of hardened layer at the center of rail head decreases,but tends to be stable.The average pearlite interlamellar spacing 3 mm to the surface is about 83 nm when cooling time reaches 90 s;with the increase of cooling time,the thickness of hardened layer,hardness,tensile strength,elongation and impact toughness increase,and these properties tend to be stable when cooling time is more than 80 s.