等温处理对高级别管线钢晶内铁素体形成的影响

Influence of Isothermal Treatment on Formation of Intra-granular Ferrite in Magnesium Treated High-grade Pipeline Steel

采用热模拟技术,研究700、650、600、550℃等温处理对管线钢晶内铁素体形成的影响以及600℃下钢的组织随等温时间的转变规律。测量不同等温温度处理后钢的维氏硬度,分析钢中诱导晶内铁素体析出的夹杂物的成分。结果表明,由700℃逐渐降低至550℃进行等温处理,钢的硬度先降低后升高,晶内铁素体的数量在650℃时最大;600℃时在原奥氏体晶粒内部,晶内针状铁素体与贝氏体存在竞争关系;由Mg、Al、Ti等元素构成的复合夹杂物可以诱导晶内铁素体形核。

The effect of isothermal treatment at temperatures in the range of 700,650,600 and 550 ℃, and that of isothermal holding time at 600 ℃ on formation of intra-granular ferrite （IGF） in Mg treated steel were studied by using thermal simulation. Vickers hardness test was also carried out for the steel isothermally treated at different temperatures, and the constituent of the inclusions that enhance the formation of intragranular ferrite was analyzed by EDAX. The results show that the amount of IGF reach to maximum at 650 ℃ and the hardness of the steel decreases at first and then increases, when the isothermal temperature decreases from 700 ℃ to 550 ℃. However, intra-granular ferrite disappears when the isothermal temperature decreases to 550 ℃. It is found that IGF and bainite competed to form in the austenite grains at 600 ℃. The further analysis indicates that inclusions consisting of Mg, AI and Ti could induce the IGF nucleation.