工程科学学报2025，Vol.47Issue(10)：1989-2001,13.DOI:10.13374/j.issn2095-9389.2025.01.03.003
低温形变热处理对高强度螺栓钢氢致延迟断裂行为的影响
Effect of low-temperature ausforming on hydrogen-induced delayed fracture of high-strength bolt steel
摘要
Abstract
High-strength bolts are widely used in construction machinery,steel structures,bridges,automobiles,and other industrial sectors owing to their high load-bearing capacity and connection efficiency.With the advancement of modern industry,there is a growing demand to further enhance the strength of high-strength bolt steel without significantly compromising its resistance to hydrogen embrittlement or hydrogen-induced delayed fracture(HIDF).To investigate the potential of microstructural control in improving the HIDF resistance of high-strength bolt steel,a V+Nb-microalloyed Cr-Ni-Mo high-strength bolt steel was subjected to low-temperature ausforming(i.e.,controlled forging starting at～950℃and finishing at～625℃),followed by direct water quenching and tempering at 450℃for 2 h.The HIDF behavior was evaluated using slow strain rate tensile(SSRT)tests on pre-electrochemically hydrogen-charged notched round bar tensile specimens,along with hydrogen thermal analysis.The microstructural features were examined and their influence on HIDF was discussed.For comparison,the same steel was also processed by conventional forging(starting at～1170℃and finishing above 900℃,followed by air cooling),quenching,and tempering(austenitized at 945℃,oil-quenched,and tempered at 450℃for 2 h,air-cooled).The results show that low-temperature-controlled forging produced a fine-banded microstructure with pronounced grain elongation along the forging direction and a grain size reduction of～53%.The prior austenite grain boundaries were serrated and lacked coarse cementite film precipitation,while～7.7%polygonal ferrite formed along these boundaries.Both the smooth and notched tensile strengths of the low-temperature-controlled forged samples increased by approximately 5.6%and 9.1%,respectively,compared to those of the conventionally forged samples.Notably,despite the increase in strength,the low-temperature ausformed sample exhibited excellent HIDF resistance.The notch tensile strength(indicating HIDF resistance)increased by 62.1%,and the hydrogen embrittlement sensitivity index(measured by the relative notch tensile strength loss rate)decreased by 27.6%after low-temperature-controlled forging.The fracture mechanism transitioned from brittle intergranular fracture along prior austenite grain boundaries(in conventionally forged samples)to transgranular quasi-cleavage fracture in low-temperature ausformed samples.The brittle zone area on the fracture surface was significantly reduced,from～38%in the former to～20%in the latter,despite nearly identical diffusible hydrogen content.The enhanced HIDF resistance is mainly attributed to the fine banded structure,formation of polygonal ferrite,and changes in cementite morphology along the prior austenite grain boundaries.Therefore,tailoring the microstructure and grain boundary characteristics through low-temperature deformation is an effective strategy to further improve the HIDF resistance of high-strength bolt steels.关键词
高强度螺栓钢/形变热处理/控制锻造/氢致延迟断裂/氢脆/微观组织Key words
high-strength bolt steel/ausforming/controlled forging/hydrogen-induced delayed fracture/hydrogen embrittlement/microstructure分类
矿业与冶金引用本文复制引用
徐亿选,惠卫军,方博洋,华卓,张永健,赵晓丽..低温形变热处理对高强度螺栓钢氢致延迟断裂行为的影响[J].工程科学学报,2025,47(10):1989-2001,13.基金项目
国家自然科学基金(面上项目)资助项目(52071010) （面上项目）
