热处理工艺对9Cr钢组织与力学性能的影响

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,9 Cr 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.

Effect of heat treatment process on microstructures and mechanical properties of 9Cr steel

The phase transformation behaviors of 9Cr steel with the change of cooling rates were studied by thermal expansion test.The microstructures and mechanical properties of 9Cr steel with heat treatment at 860 and 1 000℃were observed by OM,SEM,TEM,XRD and measured by tensile test at room temperature.The results show that the ferrite/pearlite,bainite and martensite phase transitions take place in order with increasing the cooling rate.The critical cooling rate of martensite phase transformation is 1.6℃/s.After the heat treatment at 860℃, the microstructures of 9Cr steel are polygonal ferrite and lath martensite/bainite and 4% of retained austenite.Af-ter austenitizing at 1 000℃,the grain size increases and the ferrite almost disappears.The character of lath be-comes obvious.Compared with 9Cr steel austenitized at 860℃,the mechanical properties meet the mechanical prop-erty requirement of HL level of sucker rod steel which shows that 9Cr steel has a wide processing window.