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利用热模拟试验机、SEM、HRTEM及EDS研究了Ti-Mo和Ti-Mo-Nb低碳微合金钢的连续冷却转变规律,探讨了Nb对Ti-Mo微合金钢组织及性能的影响。结果表明:Nb元素能够提高钢的Ac1和Ac3温度,降低冷却过程中奥氏体的分解温度,缩小铁素体-珠光体相区,使贝氏体相区向左下方移动。此外,Nb的添加能够细化Ti-Mo-Nb微合金钢中的组织,提高硬度。利用HRTEM对冷速为50℃/s的样品进行分析,发现:Ti-Mo和Ti-Mo-Nb微合金钢中均存在少量应变诱导析出的碳化物,分别为(Ti,Mo)C和(Ti,Nb,Mo)C粒子,呈随机分布。2种析出物均为Na Cl型结构,其晶格常数分别为0.432和0.436 nm,平均粒径分别为12.11和8.69 nm。TiMo-Nb微合金钢中析出相体积分数更多,尺寸更小,是其组织细化、硬度提高的主要原因。
The continuous cooling transformation of Ti-Mo and Ti-Mo-Nb low-carbon microalloyed steels was studied by means of thermal simulator, SEM, HRTEM and EDS. The effects of Nb on microstructure and properties of Ti-Mo microalloyed steels were also discussed. The results show that Nb can increase the Ac1 and Ac3 temperatures of steel, decrease the decomposition temperature of austenite during the cooling process, reduce the ferrite - pearlite phase and move the bainite phase to the lower left. In addition, the addition of Nb can refine the microstructure of Ti-Mo-Nb microalloyed steel and increase the hardness. Using HRTEM to analyze samples with a cooling rate of 50 ℃ / s, it is found that a small amount of strain-induced carbides are present in Ti-Mo and Ti-Mo-Nb microalloyed steels, namely (Ti, Mo) C and Ti, Nb, Mo) C particles were randomly distributed. Both of the two precipitates are NaCl-type structures with lattice constants of 0.432 and 0.436 nm, respectively, with average particle sizes of 12.11 and 8.69 nm, respectively. TiMo-Nb microalloyed steel precipitated more phase volume fraction, smaller size, is the main reason for the refinement of its organization, the hardness increased.