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在镍铬钼铜低合金高强度铸钢的生产中经常因出现异常断口而降低铸件的塑性和韧性。这种断口缺陷无法用热处理办法消除。作为一种冶金缺陷,探讨其产生的原因和消除办法是生产急待解决的问题。本文以扫描电镜为主要工具,对这种断口的性质、特征和产生的原因作了初步探讨。 实验的结果认为:铬镍钼铜低合金高强度铸钢中的异常断口为贝壳状断口。它的宏断形貌是淡灰色无金属光泽的碎石状粗晶组织,微观形貌是大小不等的韧窝,属于韧性晶界断裂。 产生贝壳状断口的原因是第二类硫化物和氮化钛的沿晶分布,它降低了晶间结合力并作为裂纹的核心,促使晶间断裂的产生和发展。 加入稀土和硅钙可以控制硫化物形态和消除贝壳状断口。
In the production of nickel-chromium-molybdenum-copper low-alloy high-strength cast steel often due to abnormal fracture and reduce the plasticity and toughness of the casting. This fracture failure can not be eliminated by heat treatment. As a kind of metallurgy defect, it is an urgent issue to explore the causes of production and its elimination. In this paper, scanning electron microscopy as the main tool for the fracture of the nature, characteristics and the reasons for the initial made a discussion. The result of the experiment shows that the abnormal fracture in the Cr-Ni-Mo-Cu low-alloy high-strength cast steel is the shell-shaped fracture. Its macroscopic appearance is light gray metallic gravel grained coarse-grained microstructure with dimples of unequal sizes, belonging to the ductile grain boundary fracture. The reason for the conchoidal fracture is the second type of sulfide and titanium nitride along the crystal distribution, which reduces the intergranular binding force and as the core of the crack, prompting the generation and development of intergranular fracture. Adding rare earth and calcium silicate can control sulfide morphology and eliminate conchoidal fracture.