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利用热膨胀试验研究了9Cr钢随冷却速度变化的相变行为,设定奥氏体化温度分别为860和1000℃,利用OM、SEM、TEM、XRD和室温拉伸对比研究不同热处理温度下9Cr钢的显微组织及力学性能。研究表明:随着冷却速度增加,9Cr钢发生铁素体/珠光体相变、贝氏体相变和马氏体相变,其中马氏体相变临界冷速为1.6℃/s;860℃热处理后9Cr钢的显微组织为板条贝氏体/马氏体和少量等轴铁素体,并有4%的残余奥氏体;奥氏体化温度升至1000℃后,奥氏体晶粒尺寸增加,9Cr钢中铁素体几乎消失,板条特征更加明显,力学性能与860℃热处理后基本相同,均达到HL级抽油杆钢的要求,说明9Cr钢具有较宽的工艺窗口。
The phase transformation behavior of 9Cr steel with cooling rate was studied by means of thermal expansion test. The austenitizing temperatures were set at 860 and 1000 ℃, respectively. Comparing the results of OM, SEM, TEM, XRD and room temperature tensile tests, The microstructure and mechanical properties. The results show that as the cooling rate increases, the ferrite / pearlite transformation, bainite transformation and martensitic transformation occur in 9Cr steel. The critical cooling rate of martensitic transformation is 1.6 ℃ / s and the temperature is 860 ℃ After heat treatment, the microstructure of 9Cr steel was lath bainite / martensite and a small amount of equiaxed ferrite with 4% retained austenite. After the austenitizing temperature rose to 1000 ℃, the austenite The grain size increases, the ferrite almost disappears in 9Cr steel, and the slab characteristics are more obvious. The mechanical properties are basically the same after 860 ℃ heat treatment, reaching the requirements of HL grade sucker rod steel, which shows that 9Cr steel has a wide process window.