低温临界区退火时间对22MnB5钢组织和性能的影响

为了研究22MnB5钢在退火过程中的组织演变规律,细化热冲压成形后马氏体板条束,通过扫描电镜(SEM)、能谱分析、电子背散射衍射(EBSD)分析技术和拉伸实验等方法,研究了不同低温临界区退火时间对22MnB5钢显微组织和力学性能的影响,并阐述了不均匀奥氏体在退火过程中的转变机制及合金元素对粒状珠光体形成的影响.研究表明,经低温临界区不同退火时间保温及随后等温处理后,得到不同的珠光体形态,在770℃保温0.5 h,并在700℃等温处理后,得到铁素体基体上分布颗粒状碳化物的粒状珠光体组织;随着临界区保温时间的延长,奥氏体转变逐渐均匀,使部分奥氏体在随后的等温过程中发生共析转变,得到多边形铁素体+片层状珠光体组织.粒状珠光体组织有利于细化淬火后的马氏体板条束,提高综合力学性能.

Effect of low-temperature intercritical annealing time on microstructure and properties of 22MnB5 steel

To investigate the microstructure evolution of 22MnB5 steel in annealing process and refine the lath martensite after hot stamping,the effect of low-temperature intercritical annealing time on microstructure and mechanical properties of 22MnB5 steel was studied by scanning electron microscopy(SEM),energy spectrum analysis,electron backscattered diffraction(EBSD) analysis technology and tensile test.The mechanism of nonhomogeneous austenite transformation during annealing process and the effect of alloy elements on the granular pearlite formation were also described.The results showed that different morphology of pearlite was obtained by different low-temperature intercritical annealing time and isothermal process subsequently.When the annealing time was 0.5 h at 770 ℃,the granular pearlite with granular carbide was distributed on the ferrite matrix was obtained during isothermal process at 700 ℃ subsequently.With the intercritical annealing time increased,the austenitic transformation was homogenized gradually;so that some austenite occurred eutectoid transformation during isothermal process subsequently,the polygonal ferrite and lamellar pearlite was formed.Granular pearlite is beneficial to refine lath martensite after quenching,which improves the mechanical properties.