超强钢18NiC250在不同加载速率下的断裂韧性

为了揭示国产超强钢18NiC250的强度、断裂韧性随加载速率的变化规律，利用电子万能试验机和Hopkinson压杆，测试其在0.001～2 000 s-1的塑性流动应力应变曲线及在10-1~106 MPam1/2/s的断裂韧性，同时对断裂破坏机理进行了微观分析。结果表明:该材料的强度对加载速率不敏感，即流动应力基本保持在1.9 GPa；而断裂韧性很敏感，当加载速率由10-1 MPam1/2/s增大到106 MPam1/2/s时，断裂韧性降低了38.2%，断裂模式由韧窝断裂转变为解理断裂。

Fracture toughness of ultra-strength steel 18NiC250 at different loading rates

To reveal the sensitivity of strength and fracture toughness to loading rate for ultra-strength steel 18NiC250, the plastic flow stress-strain curves of 18NiC250 were measured in the strain-rate range from 0.001 s^-1 to 2 000 s^-1 and its fracture toughness was obtained in the loading-rate range from 10^-1 MPa·m^1/2/s to 10⁶ MPa·m^1/2/s by using a CSS4410 test machine and a SHPB system. And the fracture failure mechanism of 18NiC250 was discussed by fractography and Taylor experiment. Results show that the flow stress of 18NiC250 is not sensitive to loading rate and it can remain 1.9 GPa. But the fracture toughness of 18NiC250 is quite sensitive to loading rate, it decreases by 38.2% when the loading rate increases from 10^-1 MPa·m^1/2/s to 10⁶ MPa·m^1/2/s, and the corresponding fracture mode changes from ductile dimple to cleavage.