铁素体-珠光体型非调质钢的高周疲劳破坏行为

研究了三种碳和钒含量不同的铁素体-珠光型非调质钢的高周疲劳破坏行为,并与调质钢进行了对比.结果表明,铁素体-珠光体型非调质钢的高周疲劳性能与其微观组织特征有关.提高铁素体相硬度,其疲劳极限及疲劳极限比均提高,疲劳极限比最高可达0.60,远高于调质钢的0.50;热轧态粗大的网状铁素体-珠光体组织的疲劳性能较差,低于同等强度水平的高温回火马氏体组织。铁素体-珠光体型非调质钢疲劳破坏机制不同于调质钢,其疲劳裂纹基本上萌生于试样表面的铁素体/珠光体边界,并优先沿着铁素体/珠光体边界扩展;对于同等强度水平的调质钢,不存在像铁素体那样的软相,因而易在试样表层粗大的夹杂物处萌生疲劳裂纹.

High–cycle fatigue fracture behavior of ferrite–pearlite type microalloyed steels

High-cycle fatigue fracture behaviors of three ferrite-pearlite type microalloyed steels with different carbon and vanadium content and one quenched and tempered(QT) low alloy steel 40Cr for comparison were investigated by rotating bending fatigue test.The results show that microstructure has a significant effect on the fatigue properties of the microalloyed forging steels.Both fatigue limit and fatigue limit ratio increase with increasing the hardness of ferrite and the fatigue limit ratio of 22MnVS steel is as high as 0.60,which is much higher than that of QT steel 40Cr.The formation of film-like ferrite along coarse prior austenite grain boundary deteriorates the fatigue properties of medium-carbon steels 38MnVS and 48MnS in as-rolled condition,which is lower than that of QT steel 40Cr.The fatigue fracture mechanism of rnicroalloyed steels is different from that of QT steel.For the microalloyed steels,almost all the fatigue cracks initiated mainly along the boundary between ferrite and pearlite and propagated preferentially along that boundary,whereas for QT steel with same strength level,which does not possess soft phase of ferrite,the fatigue cracks easily initiated at coarse subsurface inclusions.