冷拉拔珠光体钢丝的力学性能各向异性研究

Study on Anisotropic Mechanical Properties of Cold Drawn Pearlitic Steel Wire

利用拉伸试验机、SEM和TEM研究了冷拉拔珠光体钢丝力学性能的各向异性。结果表明,原始盘条(应变e=0)中,各向抗拉强度相近;随着钢丝应变的增加,钢丝各向抗拉强度的差异逐渐明显。其中,平行于拉伸轴方向(P样品)和与拉伸轴呈45°方向(I样品)符合应变强化规律;垂直于拉伸轴方向(V样品)抗拉强度稳定在1320 MPa左右。形变钢丝中,平行方向抗拉强度最高,45°方向次之,垂直方向抗拉强度最低。原始盘条中,各向均发生穿晶断裂;形变钢丝中,平行方向的断裂机制为微孔聚集型,45°方向和垂直方向发生穿晶断裂或沿晶断裂。拉伸断口纵截面TEM像表明,平行方向上,位错均匀分布在铁素体片层中,各片层协调形变;垂直方向上,位错在铁素体/渗碳体界面处塞积缠结,产生应力集中直至断裂。表现出明显的各向异性。

Cold drawn pearlitic steel wires with ultra-high strength are widely applied in industrial fields such as bridge cables, automobile tire and springs rope. In recent years, the strengthening mechanism and microstructure evolution have been profoundly studied. In order to investigate the influence of microstructure evolution on mechanical properties, the anisotropic mechanical properties of cold drawn pearlitic steel wires were investigated by tensile test, SEM and TEM. Results indicated that the distinctions of tensile strength between three directions（parallel to the tensile axis, inclined to the tensile axis（45°）, vertical to the tensile axis） were amplified with increasing strain. The effect of strain strengthening was observed in parallel and inclined directions while the vertical direction remained strength stability in1320 MPa. The wire rod was isotropic and the fracture mode was transgranular fracture; After cold drawing, the tensile strength reached peaks in parallel direction and valleys in vertical direction. The fracture mechanism of inclined and vertical directions remained transgranular or intergranular fracture while the fracture mechanism of parallel direction was converted into microvoid accumulation fracture. In TEM, the phenomenon was discovered that due to non-homogeneous distribution in vertical direction, dislocations piled up at the boundaries resulting in stress concentration. On the contrary, the dislocations were uniformly distributed which led to homogeneous transformation in parallel direction.