Nb對(duì)Ti-Mo微合金鋼連續(xù)冷卻相變規(guī)律及組織性能的影響

Nb對(duì)Ti-Mo微合金鋼連續(xù)冷卻相變規(guī)律及組織性能的影響Effect of Nb on the Continuous Cooling Transformation Rule and Microstructure, Mechanical Properties of Ti-Mo Bearing Microalloyed Steel

利用熱模擬試驗(yàn)機(jī)、掃描電子顯微鏡(SEM)、高分辨透射電子顯微鏡（HRTEM）及能譜儀（EDS）研究了Ti-Mo和Ti-Mo-Nb低碳微合金鋼的連續(xù)冷卻轉(zhuǎn)變規(guī)律，探討了Nb對(duì)Ti-Mo微合金鋼組織及性能的影響。結(jié)果表明：Nb元素能夠提高鋼的Ac1和Ac3溫度，降低冷卻過程中奧氏體的分解溫度，縮小鐵素體-珠光體相區(qū)，使貝氏體相區(qū)向左下方移動(dòng)。此外，Nb的添加能夠細(xì)化Ti-Mo-Nb微合金鋼中的組織，提高硬度。利用HRTEM對(duì)冷速為50 ℃/s的樣品進(jìn)行分析，發(fā)現(xiàn)：Ti-Mo和Ti-Mo-Nb微合金鋼中均存在少量應(yīng)變誘導(dǎo)析出的碳化物，分別為(Ti, Mo)C和 (Ti, Nb, Mo)C粒子，呈隨機(jī)分布。兩種析出物均為NaCl型結(jié)構(gòu)，其晶格常數(shù)分別為0.432和0.436nm，平均粒徑分別為12.11 nm和8.69 nm。Ti-Mo-Nb微合金鋼中析出相體積分?jǐn)?shù)更多，尺寸更小，是其組織細(xì)化，硬度提高的主要原因。

In recent years, with the fast development of automotive industry, more and more attention has been focused on developing high strength automobile steels with excellent formability. The microalloying elements, such as Nb, Ti, Mo, which can facilitate grain refinement and precipitation hardening, were added into steels to achieve high strength and good formability. The Ti-Mo and Ti-Mo-Nb microalloyed high strength ferritic steel were developed. In this work, the continuous cooling transformation curves (CCT) of Ti-Mo and Ti-Mo-Nb steels were obtained. And the effect of Nb on the microstructure and mechanical properties of Ti-Mo low carbon microalloyed steel was investigated by means of SEM, HRTEM and EDS. The results showed that Nb could raise the Ac1 and Ac3 temperatures, and restrain the ferrite-pearlite and bainite transformation. Moreover, Nb could also refine the microstructure and harden the matrix of steel which attributed to the strain-induced precipitation of nano-sized (Ti, Nb, Mo)C particles identified by HRTEM and EDS. It was also found that the strain-induced precipitation of (Ti, Mo)C was existed in the Ti-Mo steel. And both of (Ti, Mo)C and (Ti, Nb, Mo)C particles were NaCl type structure. The lattice constants / the average particle sizes of (Ti, Mo)C and (Ti, Nb, Mo)C were 0.432 nm and 0.436 nm / 12.11 nm and 8.69 nm, respectively.

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