中文摘要：

使用旋转弯曲疲劳试验机在室温空气中测试LZ50车轴钢的S-N曲线以获得其在超长寿命区域的疲劳性能。结果显示,材料在弯曲5×10^6-10^9次时达到疲劳极限;在高于疲劳极限的应力范围,材料的S-N曲线满足三参数方程。对材料表面及断口的观察表明,疲劳裂纹始于材料表面铁素体组织,裂纹起始位置的断口上没有夹杂物等材料缺陷存在。上述结果与既有文献报道的研究结果不同,既有文献认为夹杂物在超长寿命区引起疲劳破坏。为了阐明LZ50车轴钢中夹杂物是否会引起材料在超长寿命区的疲劳破坏,使用测定的裂纹扩展门槛值和断裂力学理论分析了夹杂物引起车轴钢疲劳裂纹扩展的临界尺寸。

英文摘要：

The S-N curve in the gigacycle regime was obtained from cantilever-type rotary bending fatigue tests using hourglass-shaped specimens of LZ50 axle steel for railway vehicles in an open environment at the room temperature. The results show that the material has the fatigue limit at 5×10^6-10^9 cycles and the S-N curve in the range tigue cracks the reported of stresses over the fatigue limit fits the three parameter equation. Observations indicate that fainitiate from ferrite at the surface of the material. This experimental result is different from that of literature in which an inclusion inside LZ50 axle steel was considered to induce fatigue fractures in the gigacycle regime. In order to examine whether an inclusion inside LZ50 axle steel can induce fatigue fractures or not in the gigacycle regime, the critical size of an inclusion liable to fatigue crack propagation was estimated by using the threshold stress in the intensity factor range, △Kth.