X70管线钢的应变时效行为

Strain Aging Behavior of X70 Pipeline Steel

采用扫描电子显微镜(SEM)、透射电子显微镜(TEM)等手段研究了时效温度和预应变量对X70管线钢的显微组织和力学性能的影响。结果表明,由于时效温度比较低(最高300℃),时效前后X70钢的组织都由粒状贝氏体+针状铁素体+M/A组成,没有明显的变化。时效前后抗拉强度的变化也不明显。随着时效温度的提高活化的间隙原子增多,钉扎的位错数量增加,屈服强度提高;当时效温度高于200℃时可供钉扎的位错开始大量回复,屈服强度逐渐降低。随着时效温度的提高柯氏气团及析出物的数量增加,使材料硬化,冲击韧性逐渐下降。随着预应变量的增大可被间隙原子钉扎的位错数量增加,屈服强度逐渐升高。随着预应变量的增大硬质相M/A边界处产生的应力集中不断增大,产生微裂纹的概率不断提高,使冲击韧性逐渐下降。

Effect of pre-strain and aging temperature on mechanical property and microstructure of X70 pipeline steel was investigated by means of scanning electron microscope（ SEM） and transmission electron microscope（ TEM）. The results indicate that the X70 steel shows a microstructure compopsed of granular bainite, acicular ferrite and M/A. The aging temperatures below 300℃, exhibit nearly no effect on the microstructure and the tensile strength of the steel. With the rising of aging temperature, the quantity of activated interstitial atoms, therewith, the pinning effect on dislocations increases, which leads to the gradual increase of the yield strength; However, when the temperature raises to above 200℃, the recovery of pinning effect occurs resulting in the decline of the yield strength. With the rising of aging temperature, the hardening of material induced by the increased cottrell atmosphere and precipitations leads to the decline of the impact toughness. With the increase of the pre-strain, the increment of dislocations may lead to the increase of yield strength, and the stress concentration will increase at boundries of the hard brittle phase M/A, therewith increase the probability of the formation micro-cracks, as a result, the impact toughness delines.