热处理工艺对AFA耐热钢组织和力学性能的影响

Effect of heat treatment process on microstructure and mechanical properties of AFA heat-resistant steel

为考察热处理工艺对AFA耐热钢组织和力学性能的影响,本文利用光学显微镜、扫描电镜、X射线衍射等技术,研究了新型含铝奥氏体耐热钢(AFA)在不同保温温度和冷却方式下的组织演变规律及力学性能的变化。结果表明:加热温度和冷却方式对试样的显微组织均产生影响。随着保温温度的升高,晶粒的平均尺寸逐渐增大。在1150和1200℃保温冷却后,空冷试样的晶粒尺寸略大于炉冷试样。不同温度下保温冷却后,析出相在晶内和晶界均有分布,晶内析出相形状变为圆形或颗粒状,晶界处变为长条状,但种类并未发生改变。析出相的平均尺寸随着保温温度的升高而增大。在1200℃下炉冷后,析出相的平均尺寸、面密度和晶界覆盖率均高于空冷,此时炉冷试样的硬度值达到170 HV,高于空冷,但抗拉强度和延伸率较低,分别为680 MPa和13.04%。

The microstructure evolution and changes of mechanical properties of alumina-forming austenitic heat-resistant steel(AFA)under different cooling modes(air cooling and furnace cooling)after holding at different temperatures(950,1050,1150 and 1200℃)were investigated by optical microscope,scanning electron microscopy(SEM),X-ray diffraction(XRD),etc.The results show that both the heating temperatures and the types of cooling had effects on the microstructure of the samples.With the increase in temperature,the average size of grains gradually increased.After holding at 1150 and 1200℃followed by cooling,the average grain sizes in air-cooled samples were slightly bigger than that in furnace-cooled samples.After holding at different temperatures and cooling,the precipitated phases were distributed within the grains and their boundary.The shapes of precipitates within the grains became round or granular,and those in the grain boundaries became a long strip,nevertheless the kinds of precipitates did not change.The average size of precipitates also increased with the increase of holding temperatures.After furnace cooling at 1200°C,the average size,density and grain boundary coverage of precipitates were higher than that after air cooling.Therefore,under this condition,the hardness value of the furnace-cooled sample was also higher,which was 170 HV.But the tensile strength and elongation were lower,which were 680 MPa and 13.04%,respectively.