热处理对Q460钢冷挤压内螺纹表层组织与性能的影响

Effect of heat treatment on microstructure and properties of cold extruded internal thread of Q460 steel

根据内螺纹的成形过程,研究经热处理前后冷挤压加工内螺纹的表层显微组织结构及其力学性能。结果表明,热处理试样挤压成形后螺纹表层的条形纤维组织中裂纹的数量以及裂纹的宽度和长度都减小了,增加了纤维的流线密集程度,晶粒破碎和细化程度更高。热处理试样挤压成形后螺纹牙顶、牙侧与牙根部分显微硬度有较大程度的提高,各位置硬化层深度略有降低,显微硬度曲线变化梯度较低,其抗拉强度也有较大程度的提高,能够承受的最大拉力为202.68 kN,提高了9.24%。

Microstructure and mechanical properties of the surface layer in cold-extruded internal thread of Q460 steel before and after heat treatment were investigated by means of FE-SEM,microhardness and tensile tests.The results show that the number and the width of the cracks formed along the elongated fibrous structure of the surface layer in the internal thread after heat treatment were all reduced,and the intensity of fiber streamline is increased and the grains are refined.Microhardness at crest,flank and root of the cold-extruded internal thread after heat treatment is improved evidently with slight decrease of the depth of hardened layer.The gradient of the microhardness curve in the hardened layer is decreased and its tensile strength is also improved evidently for the cold-extruded internal thread after heat treatment.The sustained maximum pulling force of the internal thread after heat treatment reaches to 202.68 kN,and increasing 9.24% compared with that before treatment.