采用不同超声冲击参数处理SMA490BW钢,研究了冲击后试样在低、高倍下的微观组织特征、残余应力及硬度分布等表面完整性能的变化.实验结果表明,经过超声冲击表面处理后,样品表面层晶粒细化为纳米晶,平均晶粒尺寸约为30nm;并在试样表层引入残余压应力,数值最大约为255.5MPa;超声冲击对SMA490BW钢表面能够起到明显的强化作用,与未经处理的试样相比,处理后试样表面硬度最大提高了约66.7％.超声冲击强化处理改善SMA490BW钢的表面完整性的效果与冲击电流、冲击时间之间的关系不遵循单调变化规律,超声冲击参数为20min/1.5A时,试样具有较好的表面完整性,冲击影响层深度约为320μm.
Ultrasonic impact trcatment (UIT) on the surface of SMA490BW steel was carried out under different parameters conditions.Influence of different impact parameters on the surface integrity including the feature of microstructure under low and high magnification,residual stress and hardness of the samples,was observed and analyzed.Experimental results indicate that after the UIT,the size of the grains is in the nmsized range (＜100nm) in the surface layer,mean grain size is about 30 nm;residual compressive stress is induced in the surface layer after UIT,the maximum is approximately 255.5MPa;the surface strength of SMA490BW steel can be improved evidently by UIT,compared to the sample without treatment,treated surface hardness is increased by 66.7％.Surface integrity of SMA490BW steel improved by UIT is not a simple monotonic variation with UIT current and time,the optimal surface integrity is obtained by UIT with the current/1.5A and time/20min and the thickness of affected layer is about 320μm.
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