T24钢过冷奥氏体连续冷却转变研究

来源期刊:中南大学学报(自然科学版)2014年第11期

论文作者:王晓峰 李红英 张尚青 李阳华

文章页码:3769 - 3778

关键词:T24钢;CCT图;连续冷却;相变

Key words:T24 steel? continuous cooling transformation diagram? continuous cooling? phase transformation

摘    要:利用Gleeble-1500 热模拟机测量T24钢以不同速度连续冷却时的膨胀曲线,结合差热分析法与金相-硬度法,确定临界点及相变温度点,绘制并对比分析T24钢的过冷奥氏体的连续冷却曲线(CCT 图),研究实验钢连续冷却时的奥氏体转变。研究结果表明:T24钢过冷奥氏体在高温区可能发生铁素体转变,中温区可能发生贝氏体转变,低温区可能发生马氏体转变;当冷却速度小于0.10 ℃/s 时,转变产物为铁素体和少量贝氏体的混合组织;当冷却速度分别为0.03,0.05和0.10 ℃/s时,过冷奥氏体先在高温区发生组织转变,转变量分别为49%,25%和22%,之后在中温区发生组织转变。在0.50~10.00 ℃/s的冷却速度范围内,转变产物为贝氏体。当冷却速度大于20.00 ℃/s时,转变产物为马氏体。合金元素Cr和Mo等能够推迟奥氏体分解,Mn对贝氏体转变有促进作用,对于T24钢,只有以低于0.10 ℃/s的速度冷却才会有先共析铁素体和碳化物生成,在0.50~10.00 ℃/s 的较宽冷却速度范围内连续冷却都会发生贝氏体转变。

Abstract: The dilatometric curves of T24 steel during continuous cooling process at different cooling rates were measured on Gleeble-1500 thermal mechanical simulator. According to DSC analysis and microstructure observation combined with hardness test, the critical temperatures and phase transformation temperatures were determined from the dilatometric curves, which were used to determine the continuous cooling transformation (CCT) diagram of T24 steel. The results show that ferrite can be formed in supercooled austenite of tested steel at higher temperature intervals, and bainite transformation and martensite transformation can occur in intermedium temperature and low temperature zones respectively. The transformation product consists of polygonal ferrite and a small amount of bainite at the cooling rates below 0.10 ℃/s. High temperature transformation occurs at first when the super-cooled austenite is cooled at the rates of 0.03, 0.05 and 0.10 ℃/s, and then middle temperature microstructure transformation begins to take place. The percentages of transformation product in high temperature ranges are 49%, 25% and 22% correspondingly and when the cooling rate ranges from 0.50 to 10.00 ℃/s, the product is mainly composed of bainite. When the cooling rate is higher than 20.00 ℃/s, martensite is the main transformation product. Because the alloy elements such as Cr and Mo can inhibit the decomposition of austenite, proeutectoid ferrite can be formed only at the condition of cooling rate below 0.10 ℃/s. Mn can accelerate the bainite transformation, and therefore bainite can be easily formed during the continuous cooling process for a large range of cooling rate (0.5-10.00 ℃/s).

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