Abstract: The effect of cooling rate 100-10 °C/min from 1150 °C to 500 °C on attribute of inclusions and behavior of inducing intragranular ferrite nucleation in 0.45C steel casting billet has been studied by using high temperature confocal superpower laser-beam microscope to control cooling rate combined with optical, scanning electron microscope and energy dispersive spectrometer. Results show that with decreasing cooling rate the high melting-point inclusions in steel basically no-change while the low melting-point inclusions size and amount in steel trend towards increasing, especially the amount of vanadium carbo-nitride increases obviously; with decreasing cooling rate the amount of precipitated intragranular ferrite increases ,the average grain size increases and the ferrite ratio first increases and afterwards decreases. As continuous cooling with 30 Y/min, the ratio of size of inclusions in steel less than 10 μm is up to 93% , the average size of ferrite is 9.2 μm and the dimensions ratio of ferrite is 30.2%.

Key words: 0.45C Steel, Casting Billet, Cooling Rate, Inclusions, Intragranular Ferrite, Structure

摘要： 借助控制冷却速度的高温激光共聚焦显微镜,结合光学显微镜和扫描电镜、能谱分析仪研究1150℃至500℃时,冷却速度100~10℃/min对0.45C钢铸坯中夹杂物的属性、诱发晶内铁素体形核行为的影响。结果表明,随冷却速度减小,高熔点夹杂物基本没有变化,低熔点夹杂物的数量和尺寸有增加的趋势,尤其是钒的碳氮化物数量增加明显;随冷却速度降低,析出的晶内铁素体的数量增加,平均粒径增大,铁素体比例先增加后减小。当30℃/min连续冷却时,钢中夹杂物尺寸小于10μm比例高达93%,铁素体平均粒径为9.2μm,铁素体面积比例达30.2%。

关键词: 0.45C钢, 铸坯, 冷却速度, 夹杂物, 晶内铁素体, 组织