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用热模拟试验机研究了C-Mn-Mo-Nb针状铁素体钢的相变特性,采用拉伸和压缩方法检测了试验钢在奥氏体化加热后冷却至不同温度时的屈服应力和弹性模量,采用高温拉伸试验机对比检测了加热至奥氏体化以下,试验温度时钢的屈服应力和弹性模量。结果表明：在奥氏体化后冷却过程中,钢的屈服应力在650～500℃相变温度范围内从约75 MPa提高至约450 MPa,但弹性模量在针状铁素体相变温度区间（600℃左右）出现谷值。在550℃以上,从室温加热至试验温度拉伸方法获得钢的屈服应力和弹性模量较奥氏体化加热法的高。相变过程中,晶体结构转变及位错密度增加是弹性模量波谷产生的主要原因;晶体结构转变、位错密度增加和析出使屈服应力急剧增加。而相同组织状态下,钢的屈服强度和弹性模量主要受温度影响。不同测试方法所得数据的差异,主要是由不同的组织结构转变而非测试方法造成。

Phase transformation of C-Mn-Mo-Nb acicular ferrite steel was analyzed and high temperature yield stress and Young＇s modulus of the tested steel after austenization and during cooling were examined by tension and compression tests on a Gleeble3500 simulator.For comparsion,yield stress and elastic modulus of the steel reheated to different temperatures below austenizing temperature were measured by tension test.The results show that the yield strength increases from 75 MPa to 450 MPa at the temperatures from 650 ℃ to 500 ℃ during cooling after austenization.But the valley value of the Young＇s modulus is observed at the temperature of acicular ferrite transformation（about 600 ℃）.Above 550 ℃,the yield stress and Young＇s modulus of the steel treated by reheating is higher than that of by austenization and then cooling to the same temperature.The crystal lattice transition and dislocation density increase due to phase transformation results in the valley value of Young＇s modulus,and the crystal lattice transition,dislocation density increase and precipitation causes the yield stress increasing rapidly.The difference of yield stress and Young＇s modulus measured at high temperature for the steel between austenized and then cooled and the reheated to the same temperature is due to different microstructure,but not the test methods.