超纯净高强度双相钢的超高周疲劳行为

Very High Cycle Fatigue Behavior of Super Clean Dual Phase High Strength Steels

利用超声加载疲劳试验方法(加载频率为20 kHz),对采用真空感应冶炼(VIM)和电渣重熔冶炼(ESR)两种工艺生产的贝氏体-马氏体双相高强钢的超高周疲劳行为进行了研究,并利用扫描电子显微镜对疲劳断口进行了分析。研究结果表明,在109循环周次内,两种双相钢的超高周疲劳S-N曲线为连续下降型,在107循环周次以后,疲劳断裂由表面起裂转变为内部起裂。VIM工艺双相钢内部疲劳断裂主要由非金属夹杂物引起,而超纯净的ESR工艺双相钢很少发生内部疲劳断裂,仅有少量试样的疲劳裂纹萌生于内部软相贝氏体组织。经过ESR工艺处理后,贝氏体-马氏体双相钢的超高周疲劳强度比VIM工艺提高了95 MPa,抗疲劳性能明显增加。

Bainite-martensite dual phase steels were manufactured by two different processes of vacuum induction melting(VIM)and electroslag remelting(ESR).Very high cycle fatigue behavior of two dual phase high strength steels was investigated using an ultrasonic fatigue testing method with a loading frequency of 20 kHz,and fatigue fractures were observed using SEM.The results indicate that S-N curves of two bainite-martensite dual phase steels decline continuously within 109 cycles.Fatigue crack initiates from sample surface when cycles to failure are less than 107.However,a significant change in the slope of the S-N curve is observed accompanying the transition from surface to internal crack initiation when cycles to failure are between 107 and 109.The internal fatigue failure of VIM dual phase steel initiates from the nonmetallic inclusions.However,only two samples of ESR dual phase steel exhibit the internal fatigue failure between 107 and 109 cycles,and two internal fatigue fractures initiate from the large soft bainite microstructure.Therefore,fatigue strength of ESR steel is enhanced by about 95 MPa compared with that of VIM steel in 109 cycles,and the reliability of very high cycle fatigue is improved greatly.