初始损伤对不同钢组织延性起裂韧性的影响

对两种钢热处理后得到的3种材料组织的缺口试样,在常温下进行了不同预加载荷的4点弯曲正反弯实验.在缺口前引入不同的微孔洞损伤量,而后通过高温回火处理消除残余应力和加工硬化.随后在室温下进行4点弯曲加载和不同载荷下的卸载实验,通过力学参数测量和微观观察就初始损伤对不同钢组织缺口试样延性起裂韧性的影响进行了实验研究.结果表明:当预加载荷比Po/Pgy小于0.86时,材料A的延性起裂韧性Pi/Pgy随Po/Pgy的增加缓慢下降,材料B和C的Pi/Pgy基本不变;当Po/Pgy大于0.86后,随着Po/Pgy的增加,3种材料的延性起裂韧性Pi/Pgy很快下降.延性起裂韧性的降低是由于材料在预加载中产生的初始损伤所引起的.初始损伤的量越大,延性起裂韧性降低的程度越大.细晶粒材料A的延性起裂韧性Pi/Pgy低于粗晶粒材料C.夹杂物含量较高,尺寸较大的材料C的延性起裂韧性Pi/Pgy低于夹杂物量少,尺寸小的材料B.对产生这些结果的原因进行了分析.

Effect of initial damage on ductile fracture initiation toughness of different microstructures of steels

In this paper, a series of four point normal and reverse bending experiments were carried out on the three heat-treat microstructures of two steels, which introduce different levels of microcavity damage. The residual stress and work hardening were removed by tempering the specimens at high temperature. Then the specimens were loaded by four point bending and unloaded at different loads. By measurement of mechanical parameters and microscopic observation, we have experimentally investigated the effects of initial damage on the ductile fracture initiation toughness of notched specimens with different microstructures of steels. The experimental results show that when the pre-load ratio Po/Pgy is less than 0.86, the ductile fracture initiation toughness Pi/ Pgy of material A decreases slowly with the increase of the Po/Pgy , and the Pi/Pgr of material B and C does not almost change with the Po/Pgy. However, when the Po/Pgy is larger than 0.86, the Pi/Pgy of the three materials would decrease quickly with the increase of the Po/Pgy. The decrease of the ductile fracture initiation toughness is caused by the initial damage induced by the pre-load. The larger the amount of the initial damage is, the more obvious the decrease of toughness will be. The ductile fracture initiation toughness Pi/Pgy of the material A with fine grain is less than that of the material C with coarse grain. The ductile fracture initiation toughness of material C with high content and larger size of inclusion will be less than that of the material B with low content and small size of inclusion. The paper has also analyzed the causes leading to such results.