15Cr14Co12Mo5Ni2齿轮钢的扭转疲劳特性及裂纹扩展行为

 通过扭转疲劳试验，研究了15Cr14Co12Mo5Ni2钢的扭转疲劳断裂的裂纹扩展行为和夹杂物尺寸与扭转疲劳寿命之间的关系。得到了钢的扭转疲劳极限强度和τ-N]曲线，15Cr14Co12Mo5Ni2钢的扭转疲劳极限强度为350 MPa，扭转疲劳寿命分散度较大。通过断口观察，发现15Cr14Co12Mo5Ni2钢的疲劳破坏模式以表面破坏和近表面破坏为主，主要由氧化物夹杂引起。通过计算应力强度因子ΔK]和裂纹扩展门槛值ΔKth]分析15Cr14Co12Mo5Ni2钢的疲劳裂纹扩展的断裂力学条件，试验钢在断裂过程中受载荷情况为，II型载荷—I型载荷—II型载荷—I＋II型载荷，分别对应起裂源区、纤维区、疲劳裂纹扩展区和瞬断区；当有大裂纹产生时，则不会产生纤维区，受载荷情况则为：II型载荷—I＋II型载荷。通过公式推导和数据拟合得到夹杂物尺寸和15Cr14Co12Mo5Ni2钢扭转疲劳寿命的关系，发现随着夹杂物尺寸减小，钢的τ-N]曲线向高寿命区移动。当引起裂纹萌生的夹杂物尺寸小于5 μm时，在350 MPa应力下，15Cr14Co12Mo5Ni2钢的扭转疲劳寿命超过107循环周次。

Torsion fatigue characteristics and crackpropagation behavior of 15Cr14Co12Mo5Ni2 gear steel

The crack propagation behavior oftorsion fatigue fracture and the relationship between inclusions size and tor-sion fatigue lifeof 15Cr14Co12Mo5Ni2 steel were researchedthroughtorsion fatigue test. Torsional fatigue limit strength and τ-N cure was obtained,and the value of 15Cr14Co12Mo5Ni2 steel was 350 MPa,whosedispersion was large. Through observed fractures,the surface failure mode and subsurface failure mode as the main failure mode of the test steel,and the fracture mainly resulting from oxide inclusions were found. Thefracture mechanics conditions of fatigue crack propagation of 15Cr14Co12Mo5Ni2 steel were analyzed by calculating stress strength factorΔK and crack propa-gation threshold valueΔKth. The load process of test steel in fracture was:type II load,type I load,type II load,and type I+II load,which corresponded to crack sourcezone,fiber zone,fatigue crack propagation zone and instantaneous fracture zone. When the large crack formed,fiber zone would not appear,andthe load process was type II load,andtype I+II load. The relationship between the size of the inclusions and the torsional fatigue life of the 15Cr14Co12Mo5Ni2 steel was obtained by eliciting formulas and fitting dates. It wasfound thatτ-N cure of the test steel moved toward the high life zone,andwhen the size of inclusion in crack initiation was less than 5 μm,torsional fatigue life of 15Cr14Co12Mo5Ni2 steel would be more than 107 cycles with 350 MPa stress.