Tian Yong, Wang Hongtao, Xu Xiaoning, Wang Zhaodong, Misra R D K, Wang Guodong
State Key Laboratory of Rolling and Automation, Northeastern University, Shenyang 110819, China.
Laboratory for Excellence in Advanced Steel Research, Department of Metallurgical, Materials and Biomedical Engineering, University of Texas at El Paso, El Paso, TX 79968, USA.
Materials (Basel). 2020 Jan 31;13(3):634. doi: 10.3390/ma13030634.
Isothermal treatment affects the microstructural evolution and the precipitation behavior of high-strength low alloy (HSLA) steels. In this regard, thermal simulation of different isothermal treatment temperatures was adopted by using a thermomechanical simulator. The results showed that hardness reached the maximum value at 600 °C holding temperature, which was related to a finer grain structure and granular bainite. The strengthening effect of precipitates was remarkable due to the combination of small particle size and small interparticle spacing. It is presumed that the precipitation started after 600 s at 600 °C. Precipitation strengthening continued to exist, even though coarsening of ferrite grains led to softening phenomena when the specimen was isothermally held at 750 °C, which led to relatively high hardness. The precipitates were fcc (Ti, Nb) (N, C) particles, and belonged to MX-type precipitates. Average size of precipitates increased from 3.14 to 4.83 nm when the specimens were isothermally held between 600 °C and 800 °C. Interparticle spacing of precipitates also increased with increasing isothermal treatment temperatures. These led to a reduction in precipitation strengthening. At the same time the polygonal ferrite content increased and ferrite grain size got larger, such that the hardness decreased continuously.
等温处理会影响高强度低合金（HSLA）钢的微观组织演变和析出行为。在此方面，通过使用热机械模拟器对不同等温处理温度进行了热模拟。结果表明，在600℃保温温度下硬度达到最大值，这与更细小的晶粒组织和粒状贝氏体有关。由于小颗粒尺寸和小颗粒间距的组合，析出物的强化效果显著。据推测，在600℃时600秒后开始析出。即使当试样在750℃等温保温时铁素体晶粒粗化导致软化现象，但析出强化仍然存在，这导致硬度相对较高。析出物为面心立方（Ti，Nb）（N，C）颗粒，属于MX型析出物。当试样在600℃至800℃之间等温保温时，析出物的平均尺寸从3.14纳米增加到4.83纳米。析出物的颗粒间距也随着等温处理温度的升高而增加。这些导致析出强化降低。同时，多边形铁素体含量增加且铁素体晶粒尺寸变大，从而使硬度持续下降。
