XGTC300L搪瓷钢的连续冷却转变行为与析出规律

Continuous cooling transformation behavior and precipitation pattern of XGTC300L enamelled steel

采用Gleeble-3500热模拟试验机获得了XGTC300L搪瓷钢在不同冷却速度下的温度-膨胀量曲线,通过对不同冷速下试样的显微组织特征和硬度变化规律进行研究,绘制了钢的动态CCT曲线。结果显示,热变形后的XGTC300L搪瓷钢在0.2~50℃/s冷速区间冷却时,其基体组织均为铁素体,且随着冷速的增加铁素体晶粒尺寸逐渐减小。在0.2℃/s冷速下,钢的硬度值最低,约为96.6 HV0.1;在0.5~5℃/s的冷速区间内,钢的硬度值变化不大,约为110.0 HV0.1;在10~30℃/s的冷速区间内,钢的硬度值约为120.0 HV0.1;在50℃/s冷速下硬度值达到最高,约为137.9 HV0.1。在30℃/s的快冷速下,铁素体的基体和晶界处均发现了含硼碳化物析出,而在0.2℃/s的慢冷速下仅有条状渗碳体在晶界析出。在0.2~50℃/s冷速区间,随着冷速的增加,相转变开始温度由850℃降至810℃,相转变终了温度由840℃降至750℃,且转变时间逐渐缩短。动态CCT曲线中仅发现了铁素体相区,未发现贝氏体或马氏体转变相区。因此XGTC300L搪瓷钢的轧后控冷工艺应采取大于30℃/s的较高冷速,以获得较小的铁素体晶粒和一定量的含硼析出物,从而提高其综合性能。

Temperature-expansion curves of the XGTC300L enamelled steel at different cooling rates were obtained by a Gleeble-3500 thermal simulation test machine.The dynamic CCT curve of the steel was drawn by studying the microstructure characteristics and hardness variation of the specimens at different cooling rates.The results show that the matrix of the XGTC30OL enamelled steel after hot deformation consists of ferrite when cooled within the range of 0.2-50 ℃/s,and the ferrite grain size decreases with the increase of cooling rates.At the cooling rate of 0.2 C/s,the steel exhibits the lowest hardness value,about 96.6 Hv0.1.In the range of 0.5-5℃/s,the hardness value changes litle,about 110.0 HV0.1.In the range of 10-30 ℃/s,the hardness value is about 120.0 HV0.1.At the cooling rate of 50℃/s,the steel reaches its highest hardness value,about 137.9 Hv0.1.At the fast-cooling rate of 30 ℃/s,boron-containing carbides are found in the ferrite matrix and grain boundary,while only strip cementite precipitates at the grain boundary at the slow cooling rate of 0.2 ℃/s.In the range of 0.2-50℃/s,with the increase of cooling rate,the start temperature of transformation is decreased from 850℃to 810℃,the end temperature of transformation is decreased from 840℃to 750℃,and the transformation time decreases gradually.In the dynamic CCT curve,only the ferrite phase region is found,and the phase region of bainite or martensite is not found.Therefore,the controlled cooling process after rolling of the XGTC300L enamelled steel should adopt a higher cooling rate of more than 30 C/s to obtain smaller ferrite grains and a certain number of boron-containing precipitates,so as to improve its comprehensive performance.