工程科学学报2025，Vol.47Issue(11)：2213-2222,10.DOI:10.13374/j.issn2095-9389.2025.02.10.001
钛微合金钢连续冷却过程中纳米碳化物的析出控制
Control of nano-sized carbide precipitation during continuous cooling in titanium microalloyed steels
摘要
Abstract
Previous research on nano-sized carbides in Ti-microalloyed high-strength steels primarily focused on isothermal processes,specifically simulating the coiling process after laminar cooling of hot-rolled strips.This study investigated the phase transformation,precipitation behavior,and mechanical properties of titanium microalloyed steel under different cooling processes.A Gleeble-3800 thermal simulator,transmission electron microscopy(TEM),and microhardness testing were used for this analysis.To obtain more accurate performance data,the hardness value of a single sample was obtained from the average of fifty uniformly selected measurements.Each measurement ensures that the indentation is located within the matrix grain to avoid the influence of grain boundary stress on the data.Additionally,five typical bright field images,including over 100 precipitated particles,were selected for each sample.The size distribution of the precipitated phases was measured using Gatan Digital Micrograph(DM)software,while their crystal structure was analyzed using high-resolution transmission electron microscopy(HRTEM).The data obtained from these measurements are presented as average hardness±standard deviation,where the standard deviation reflects the degree of non-uniformity in the hardness distribution.The results indicate that after deformation at 900℃,the microhardness of the room-temperature microstructure generally increases with higher cooling rates.However,slow cooling facilitates γ→α phase transformation,which promotes the precipitation of nano-sized carbides.A hardness peak of 260±9.9 HV was observed at a cooling rate of 0.5℃·s-1,attributed to precipitation strengthening.A two-stage controlled cooling process is subsequently employed:rapid cooling at 20℃·s-1 to the phase transformation start temperature of 635℃,followed by slow cooling at 0.1℃·s-1.The resulting microstructure is mainly composed of quasi-polygonal ferrite,with an average particle size of 2.55nm and a microhardness of 275.5±11.3 HV.The precipitation strengthening effect produced is 293.4 MPa.When the partitioning temperature is set at 700℃,a ferrite structure is obtained at a cooling rate between 0.1-0.5℃·s-1,with a peak hardness of 260.6±8.1 HV observed at 0.5℃·s-1.The average size of precipitated particles was 6.73 nm.In contrast,a partitioning temperature of 600℃suppresses ferrite transformation,leading to lower overall hardness in the room-temperature microstructure.For the production of titanium microalloyed high-strength steel using medium-thick plate processes,and to fully promote the precipitation of nano-sized carbides and maximize their strengthening effect,the finish cooling temperature during laminar cooling should be controlled close to the phase transformation start temperature.Subsequent cooling rate reduction measures,such as stacking,slow cooling pits,or steam cooling,are also recommended.If air cooling is applied after laminar cooling,nano-sized carbides can still contribute to precipitation strengthening;however,a higher finish cooling temperature(e.g.,700℃)should be maintained.The results demonstrated that the coordination between the final cooling temperature during laminar cooling and the subsequent cooling rate is a critical process parameter for controlling the precipitation of nano-scale carbides in medium-thick plate production.These findings provide a theoretical basis for expanding the application of Ti-microalloyed high-strength steels in the production of medium-thick plates and even construction rebars.关键词
钛微合金钢/连续冷却/铁素体相变/析出动力学/强化机理Key words
titanium microalloyed steel/continuous cooling/ferrite transformation/precipitation kinetics/strengthening mechanism分类
矿业与冶金引用本文复制引用
霍向东,陈松军,吴浩,彭明天,李烈军,张鑫奎..钛微合金钢连续冷却过程中纳米碳化物的析出控制[J].工程科学学报,2025,47(11):2213-2222,10.基金项目
广西重点研发计划资助项目(2024AB08231) （2024AB08231）
