轧制-退火工艺制备超细晶D6A钢的微观组织与织构

Microstructures and textures of ultrafine grained D6A steel by using rolling and annealing

对D6A钢热轧板进行了两相区轧制及退火处理,获得超细晶D6A合金钢样品,微观结构特征为纳米尺寸的球粒状渗碳体弥散分布于亚微米尺寸的铁素体组织中。实验结果表明:随着退火温度由550℃升高至650℃,铁素体晶粒被拉长现象逐渐减弱直至消失,晶粒尺寸呈现先减小后增大的趋势,在550℃时达到最小尺寸400nm;同时渗碳体尺寸逐渐由70增加至140nm,其质量分数分数由9.6%降低至3.6%;随着退火温度升高,实验钢沿α和γ取向线分布的{112}<110>、{111}<112>和{001}<110>织构强度逐渐减弱,600℃退火后消失,{110}<001>与{112}<111>织构逐渐增强,硬度随退火温度升高由472HV逐渐减小至423HV。细晶强化、纳米尺寸渗碳体的析出强化,以及织构强化的共同作用是超细晶D6A钢的主要强化机制。

Ultrafine-grained D6A steels were achieved by intercritical rolling and annealing, and the microstructure features show that nanoscale spherical cementite depressively distributes in ferrite matrix. Experiment results show that ferrite lath gradually became granular and large with increasing annealing temperature from 550 ℃ to 650 ℃. After annealing at 550 ℃ for 300 s, the grain size reaches the smallest size of 400 nm. The size of spherical cementite increases from 70 to 140 nm with annealing temperature increasing from 550 to 650 ℃, and the mass fraction decreases from 9.6% to 3.6%. Meanwhile, the texture components along α and γ orientation distribution lines such as{ll2}〈l10〉, {111}〈112〉 and {001}〈110〉 gradualy weaken and disappear after annealing at 650 ℃ for 300 s. However, { 110}〈001〉 and { 112}〈111〉 misorientations gradually enhance concurrently. Micro- hardness of the steel decreases from 472 HV to 423 HV with the increase of annealing temperature. Ultrafine-grained let- rite, nanoscale spherical cementite and special textures are important factors in strengthening D6A steel.