热处理对U76CrRE稀土重轨钢夹杂物和微观组织的影响

选取U76CrRE钢坯进行1100、1200、1300 ℃分别保温1、2、3 h的热处理,使用FEI-QUANTA400型扫描电镜对夹杂物进行了观察,利用Axiovert型蔡司光学显微镜对微观组织进行观察,使用Qness-Q10A+全自动显微硬度计进行硬度测试。结果表明,热处理对U76CrRE稀土重轨钢中夹杂物的作用明显,使夹杂物形状与尺寸都有明显改善,随着加热温度的升高,可以进一步优化MnS和复合夹杂物的形貌和尺寸。在1100 ℃加热时,MnS与复合夹杂物尺寸随着保温时间的增加而减小,形状得到明显改善;在1200 ℃加热时,随着保温时间的增加,MnS尺寸减小,复合夹杂尺寸变大。U76CrRE稀土重轨钢的晶粒随着加热温度的升高明显增大,硬度呈现先减后增的趋势,随着保温时间的增加逐渐减小。在1100 ℃加热时,试验钢中组织皆为马氏体、贝氏体和残留奥氏体,且晶界均不明显;在1200 ℃与1300 ℃保温超过1 h后,试验钢中网状渗碳体明显;在1300 ℃保温1 h时,晶界积碳严重,碳化物未得到有效溶解。在1200 ℃保温1 h时,试验钢中晶粒均匀,晶界明显,组织主要为残留奥氏体与珠光体,组织均匀。

Effect of heat treatment on inclusions and microstructure of U76CrRE rare earth heavy rail steel

U76CrRE billets were heat treated at 1100 ℃, 1200 ℃ and 1300 ℃ for 1 h, 2 h and 3 h, respectively. The inclusions were observed by FEI-QUANTA400 scanning electron microscope, the microstructure and hardness were observed and tested by means of Axiovert Zeiss optical microscope and Qness-Q10A+automatic microhardness tester. The results show that the heat treatment has obvious effect on the inclusions in the U76CrRE rare earth heavy rail steel, and the shape and size of inclusions are significantly improved. With the increase of heating temperature, the morphology and size of MnS and compound inclusions can be further optimized. When heated at 1100 ℃, the size of MnS and compound inclusions decreases with the increase of holding time, and the shape is obviously improved. When heated at 1200 ℃, the size of MnS decreases and the size of compound inclusions increases with the increase of holding time. The grain size of the U76CrRE rare earth heavy rail steel increases obviously with the increase of heating temperature, and the hardness shows a trend of first decreasing and then increasing, while decreases gradually with the extension of holding time. When heated at 1100 ℃, the microstructure of the tested steel is martensite, bainite and retained austenite, and the grain boundary is not obvious. After holding at 1200 ℃ and 1300 ℃ for more than 1 h, the network cementite in the tested steel is obvious. When heat treated at 1300 ℃ for 1 h, the carbon deposition at the grain boundary is serious and the carbides are not effectively dissolved. When held at 1200 ℃ for 1 h, the grains of the tested steel are uniform, the grain boundaries are obvious, the microstructure is mainly retained austenite and pearlite, and the microstructure is uniform.