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采用0.07 wt%Ti和0.015 wt%Nb-0.07 wt%Ti微合金化的成分体系,通过控轧控冷和控轧控冷+回火工艺制备了厚度为30 mm的钢板。钢板在TMCP状态的形貌为贝氏体板条和沿贝氏体板条分布的马奥组元和析出物构成。回火后马奥组元分解,贝氏体板条界面弱化,在贝氏体板条中形成了大量细小的Ti的析出物。钢板中的析出物主要包括:粗大的TiN析出、TiC、Ti4 C2 S2析出和Nb-Ti的复合析出等。粗大方形TiN在钢中的Al2 O3、MgO或Ti2 O3的夹杂上形核长大,边长为5μm左右。在0.07 wt%Ti成分体系中,TMCP和TMCP+回火状态钢板中的析出物主要是100 nm以下的TiN、TiC和Ti4 C2 S2析出。在0.015wt%Nb-0.07 wt%Ti成分体系中,析出物主要是Ti和Nb的碳化物析出,尺寸300 nm以下。添加微量的Nb会导致0.07 wt%Ti钢板的强度和冲击功下降,其原因可能是由于Nb和Ti形成较大的复合析出物,降低了析出物对位错运动的抑制作用,导致钢板力学性能下降。
The micro-alloyed system of 0.07 wt% Ti and 0.015 wt% Nb-0.07 wt% Ti was prepared by controlled rolling and controlled rolling and controlled cooling and tempering process. The morphology of the steel plate in the TMCP state is composed of bainite laths and martensite and precipitates distributed along the bainite laths. After tempering MAO component decomposition, bainitic slab interface weakening, formed in the bainite lath a large number of small Ti precipitates. The precipitates in the steel plate mainly include coarse TiN precipitation, TiC, Ti4 C2 S2 precipitation and Nb-Ti composite precipitation. Thick square TiN in the steel Al2 O3, MgO or Ti2 O3 inclusions on the nucleus grew up, the side length of about 5μm. In the 0.07 wt% Ti component system, the precipitates in TMCP and TMCP + tempered steel are mainly TiN below 100 nm, TiC and Ti4 C2 S2 are precipitated. In the 0.015wt% Nb-0.07wt% Ti component system, precipitates mainly consist of carbides of Ti and Nb precipitates with a size of 300 nm or less. The addition of trace amount of Nb will result in the decrease of strength and impact energy of 0.07 wt% Ti steel. The reason may be that Nb and Ti form larger composite precipitates, reducing the inhibitory effect of precipitates on dislocation motion, resulting in the mechanical properties of steel sheet decline.