【作者】 刘浩然；

【导师】 王青峰；

【作者基本信息】 燕山大学 ， 材料学， 2018， 硕士

【摘要】 本文采用自行设计的耐候高强螺栓钢NHL10为试验钢,通过对试验钢进行不同热处理工艺,获得了不同的淬火与回火组织,以及不同的力学性能。同时采用光学显微镜、场发射型电子扫描显微镜与透射电子显微镜对马氏体组织的Packet、Block、Lath以及析出相结构进行了表征,同时对各结构的形态数量进行了统计分析。通过室温拉伸、冲击试验和洛氏硬度试验,测试了回火态试验钢的力学性能;通过周期浸润加速试验和恒载荷缺口拉伸试验,测试了试制NHL10钢典型热处理态的耐候性能与抗延迟断裂性能。结果表明,随着淬火温度的升高,试验钢原奥氏体晶粒及马氏体Packet/Block结构的尺寸均明显长大,而Lath结构尺寸未发生明显变化,同时析出相数量减少,原奥晶粒尺寸与淬火马氏体Packet、Bock结构尺寸呈线性相关。随着回火温度上升,Packet、Block等微结构略有长大;晶界处析出相数量显著上升,同时聚集球化,尺寸增大,使拉伸强度下降;回火马氏体Packet结构尺寸与屈服强度之间的关系符合经典Hall-Petch公式;随着回火温度升高,马氏体大角度晶界所占比例提高,阻碍了裂纹扩展,导致冲击性能提高。基于以上研究,试验钢优化的调质处理工艺是:875℃淬火+500℃回火。根据上述结果,进行了 NHL10钢的工业试制,试制产品力学性能、耐候性能及抗延迟断裂性能均满足技术要求。更多还原

【Abstract】 In this paper;weathering and high-strength bolt steel NHL10,designed by ourselves,is used as test steel.The different quenching and tempering structures and mechanical properties of the test steels were obtained through different heat treatment processes.Meanwhile,the structure of Packet,Block,Lath and precipitate phase of martensite were characterized by optical microscope,filed emission type election scanning microscope and transmission electron microscope,and statistical analysis is made for the number and shape of each structure.The mechanical properties of tempered steel were tested by room temperature tensile test,impact test and Rockwell hardness test;The weathering resistance and delayed fracture resistance of NHL 10 steel were tested by cyclic infiltration accelerated test and constant load notched tensile test.The results show that,with the increase of quenching temperature,the size of original austenite grain and martensite Packet/Block structure of test steel grew obviously,but the size of Lath structure did not change obviously,and the number of precipitation phase decreased.The size of original austenite grain was linearly related to the Packet and Bock structure size of quenched martensite.With the rise of tempering temperature,the micro structure of Packet and Block grew slightly,the number of precipitates at the grain boundary increased significantly,and the spheroidization,size increased,and the tensile strength decreased,and the relationship between the Packet structure size and yield strength of tempered martensite conforms to the classical Hall-Petch.In addition,the ratio of large angle grain boundaries of martensite increased,which hindered the expansion of cracks and led to the improvement of impact properties.Based on the above research,the optimized quenching and tempering process of the test steel is:quenching at 875 ℃,tempering at +500℃.According to the above results,the trial production of NHL10 steel is carried out.The mechanical properties,weathering resistance and delayed fracture resistance of the products are all met the technical requirements.更多还原