硫化物变性处理45MnVS非调质钢的高周疲劳性能

 长条状的硫化物夹杂往往会导致热轧/锻造含硫钢的力学性能呈现出明显的各向异性。为了明确硫化物变性处理铁素体-珠光体型非调质钢的疲劳性能各向异性,采用轴向力控制高频疲劳试验机(应力比R=-1)研究了工业生产的45MnVS非调质钢锻态及调质态的高周疲劳断裂行为。结果表明,试验料纵向样中的MnS夹杂分布较为均匀,多呈短棒状或纺锤形,平均长宽比为3.4±1.7。与未变性处理的含硫非调质钢相比,试验料塑性和韧性的各向异性得到显著降低。锻态与调质态横向样的疲劳性能略低于纵向样,调质态样的疲劳极限比(0.52~0.54)明显高于锻态样(0.46)。在ΔK值大于约35 MPa·m1/2时,横向样的疲劳裂纹扩展速率略大于纵向样。疲劳断口分析表明,2种状态横向样的疲劳裂纹均主要起源于钢中条棒状MnS夹杂,且调质态样受影响的程度更大。上述结果表明,试验钢硫化物变性处理后的疲劳性能各向异性很小,锻态组织的各向异性程度略低于调质态组织,但后者具有更为优异的疲劳性能。

High-cycle fatigue properties of microalloyed medium-carbon forging steel 45MnVS with modified sulfide

The elongated sulfide inclusion is primarily responsible for the mechanical properties anisotropy of hot-rolled and forged sulfur-containing structural steels. In order to explore the fatigue anisotropy of microalloyed ferritic-pearlitic forging steel with modified sulfide,high-cycle fatigue properties of a commercial microalloyed forging steel 45MnVS with as-forged and quenched and tempered (QT) microstructures was studied by using axial-force-controlled fatigue testing with a stress ratio of -1. The results show that the sulfides are primarily short rod-like or slightly elongated with an average length to width ratio of 3.4±1.7 and relatively uniformly distributed in the steel. Although there are still ductility and toughness anisotropy in the tested steel,this anisotropy is significantly lowered than that of other microalloyed medium-carbon forging steels which did not subjected to sulfide modification. The fatigue properties of the as-forged and QT samples in the transversal direction are slightly lower than those in the longitudinal direction,and the fatigue limit ratio of the QT samples (0.52-0.54) is notably higher than those of the as-forged samples (0.46). The transversal sample exhibits a slightly higher fatigue crack growth rate than the longitudinal sample only when the stress intensity factor range is higher than about 35 MPa·m1/2. Further fatigue fracture surface investigation revealed that the fatigue fractures are primarily initiated at short rod-like sulfides for both the as-forged and QT samples,and this influence is more notably for the QT sample. It is thus concluded that the fatigue anisotropy of the tested steel with modified sulfide is rather small and the anisotropy degree of the as-forged sample is slightly lower than of the QT sample,although the latter exhibits more superior fatigue properties than the former.