摘要
采用热膨胀仪和差示扫描量热仪(DSC)研究了过共析钢在连续加热条件下奥氏体化过程,测定了不同阶段的临界温度点,通过Thermo-Calc与Dictra软件进行了理论计算,并且研究了加热速率、初始组织以及含C量对其的影响.结果表明,整个连续加热过程可以分为5个阶段,临界温度点的实验结果与计算结果基本吻合.提高加热速率可以提高逆共析转变的起始和终了温度,增大逆共析转变温度区间,残余渗碳体溶解终了温度不变,奥氏体均匀化终了温度升高.粗大的珠光体初始组织使得逆共析转变起始和终了温度提高,增大了逆共析转变的温度区间,残余渗碳体溶解和奥氏体均匀化阶段的终了温度也有所提高.增大含C量对逆共析转变几乎没有影响,但是会明显提高残余渗碳体和奥氏体均匀化阶段终了的温度.
Cold-drawn pearlitic steel wires exhibit ultrahigh strength and have important applications where high strength and wear resistance are required.The hypereutectoid compositions present a promising potential for increasing the mechanical properties,especially the strength.The austenitization process strongly influences the following pearlitic microstructure and thus the mechanical properties.Continuous heating is always used in the industrial processing.However,the austenitization of pearlite in hypereutectoid steels during continuous heating has not been investigated systematically.In this work,the dilatometer and DSC were employed to investigate the austenitization kinetics of hypereutectoid steels during continuous heating.Microstructure evolution was observed with SEM and EBSD.The dilatometer and DSC curves were analyzed with derivative method.The whole austenitization can be divided into five stages：initial microstructure,reverse eutectoid transformation,retained cementite dissolution,homogenization and homogeneous austenite.Tangent method was used for measuring the critical temperatures of different stages.Experimental determination of transformed fraction was obtained through the lever method.Calculation with Thermo-Calc and Dictra software was carried out for the austenitization and considered to be a reasonable result by comparing with the experimental data.There is a turning point for the reduction rate of cementite and formation of austenite at the finishing temperature of reverse eutectoid transformation,which is similar with the austenitization in low carbon steel and spheroidal pearlite of hypereutectoid steel.Effects of heating rates,initial microstructure and carbon content were studied by varying the relevant parameters.Higher heating rate increases the starting and finishing temperatures of reverse eutectoid transformation and widens the temperature range,has no effect on the finishing temperature of retained cementite dissolution,increases the finishing temperature of homogenization.Coarser initial pearlitic microstructure increases the starting and finishing temperatures,widens the temperature range for reverse eutectoid transformation,increases the finishing temperature for retained cementite dissolution and homogenization.Enhancement of carbon content has little effect on the reverse eutectoid transformation,but increases the finishing temperature for retained cementite dissolution and homogenization.The effects mentioned above on the austenitization kinetics were discussed for mechanism analysis and compared with the observations of relevant systems provided by other research.
出处
《金属学报》
SCIE
EI
CAS
CSCD
北大核心
2014年第10期1179-1188,共10页
Acta Metallurgica Sinica
关键词
连续加热
过共析钢
奥氏体化
加热速率
初始组织
含C量
continuous heating, hypereutectoid steel, austenitization, heating rate, initial microstructure,carbon content
