焊接热循环对Ti-Nb微合金钢中第二相粒子的影响
Effect of Weld Thermal Cycle on Second Phase Particles in Ti-Nb Micro-alloyed Steel
王 敏
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作者单位：山东山大产业集团有限公司， 山东 济南 250061
中文关键字：第二相粒子；微合金钢；焊接热循环
英文关键字：second phase particle； micro-alloyed steel； weld thermal cycle
中文摘要：利用焊接热模拟及碳萃取复型技术，对Ti-Nb微合金钢及其模拟焊接粗晶热影响区中第二相粒子的形态、数量及物相进行了研究。结果表明，母材中第二相粒子的形状不规则，粒子中Nb的相对含量wNb/(wNb+wTi)在0.25~0.82之间，尺寸较大的粒子含有较多Ti，形状接近方形；尺寸较小的粒子含有较多的Nb，形状接近球形。焊接热循环后，粒子的数量显著减少、平均尺寸增大，残留的粒子变为方形。t8/5从10 s增大到60 s时，粒子的平均尺寸进一步增大，粒子数量进一步减少，粒子中Nb的相对含量均在0.20~0.50之间。但t8/5再从60 s增大到120 s时，粒子的平均尺寸反而减小，粒子数量增大，又重新出现一些含Nb量较高的球形粒子。分析表明，焊接热循环加热过程中粒子的溶解具有较大的滞后效应，大约滞后于实际温度70 ℃，粒子的溶解持续到焊接热循环冷却过程的高温阶段；t8/5较大时，冷却过程中粒子不但能以残留的粒子为晶核析出，还能通过独立形核析出。利用建立的粒子沉淀热力学模型对不同温度时粒子的成分进行了计算，计算结果与试验值吻合良好。
英文摘要：By using carbon extraction replica technology and welding thermal simulation, the morphology, quantity and size distribution of second phase particle in Ti-Nb micro-alloyed steel was investigated. Experiment results show that the particles in the steel are irregular in shape, and exhibit a slight size-dependence in that the relative contents of Nb decrease with the increase of particle size. The Nb contents in the particles is in a wide range of 0.25~0.82. After weld thermal cycle, the shape of remaining particles in simulated CGHAZ changes from irregular shape to cubicle one, the particle number per unit area decreases, and the mean particle size increases. Furthermore, the particle mean size first increases with t8/5 (from 10 s to 60 s), and then decreases at 120 s, and the particle number per unit area first decreases with t8/5 (from 10 s to 60 s), and then increases at 120 s. It detectes two kinds of re-precipitation, on the surviving particles and re-precipitation by independent nucleation, the later occurre occurs only in case of large t8/5. The compositional change of particle, as a function of temperature is predicted using a equilibrium thermodynamic model. The calculated results are in good agreement with the measured ones.