调质工艺对X80级管件钢性能与组织影响研究

Research on the influence of quenching-and-tempering process on the properties and microstructure of X80 grade pipe fitting steel

为研究调质工艺对X80级管件钢的性能和组织影响,通过力学性能检验、光学显微镜(OM)、透射电镜(TEM)、萃取复型及电子背散射衍射(EBSD)等手段,研究了同一温度淬火后,不同回火温度对X80级管件钢性能和组织的影响.结果表明,经940℃淬火后,在500~650℃范围内回火,试验钢的屈服强度和抗拉强度随回火温度的升高均先增加后降低.随回火温度的升高,试验钢由板条贝氏体铁素体(BF)和粒状贝氏体(GB)的混合组织转变为GB和准多边铁素体(QF)混合组织,M/A岛由细长条状变为颗粒状,并发生分解,BF中的板条亚结构逐渐弱化.在500~600℃范围内,组织中析出相随回火温度升高逐渐增多,600℃时析出相开始聚集长大,温度继续升高,析出相尺寸明显增大.回火过程中,试验钢屈服强度受基体组织软化和析出强化两方面的影响.试验钢的低温冲击韧性随回火温度升高逐渐增大,主要是大角度晶界比例增加所致.

In order to research the influence of quenching-and-tempering process on the properties and microstructure of X80 grade pipe fitting steel,the properties and microstructure of X80 grade pipe fitting steel quenched at the same temperature and tempered at different temperatures were studied by means of mechanical property tests,OM,TEM,extraction replica and EBSD and other means. The results indicated that after being quenched at 940 ℃ and tempered from 500 ℃ to 650 ℃,yield strength and tensile strength of the tested steel firstly increased and then decreased as the tempering temperature increased. With the increase of tempering temperature,the microstructure of tested steel changed from BF ＋ GB to GB ＋ QF and the bainite lath disappeared gradually. The M/A island changed from slenderbar to particle and part of it decomposed.Meanuhile the substructure of slate in BF quadually weakened. In the range of 500 ℃ to 600 ℃,amount of precipitated phase in microstructure increased with the increase of tempering temperature. The precipitated phase began to gather and grow from 600 ℃ and precipitated phase size grew significantly as the tempering temperature continued to increase from 600 ℃ The yield strength was affected by the softening of the matrix and precipitation strength in the tempering process. The low-temperature impact toughness of tested steel increased gradually with the increase of tempering temperature,mainly due to the inerease of the ration of large angle grain boundaries.