Evolution of Microstructure and Crystallographic Texture During Welding for 1.5 GPa Ultra-high Strength Steel Toughened by an Elongated Grain Structure With Intensive Texture

Abstract

The advanced microstructure of the elongated grain structure with intensive texture, which mainly consists of $\left\{ {112} \right\}\left\langle {110} \right\rangle_{\alpha } \,{\text{and}}\,\left\{ {332} \right\}\left\langle {113} \right\rangle_{\alpha }$ components, significantly improves the toughness of 1.5 GPa ultra-high strength steel by delamination toughening. The elongated grain structure with texture affects the microstructure evolution of heat affected zone (HAZ), resulting in the refinement of coarse-grained HAZ(CGHAZ), the separate distribution of granular bainite and lath martensite in fine-grained HAZ (FGHAZ) and the formation of clustered blocky martensite in intercritical HAZ (ICHAZ). In ICHAZ, the sharp $\left\{ {112} \right\}\left\langle {100} \right\rangle_{\alpha }$ of untransformed grains does not undergo reorientation for high thermal stability. For transformed grains, initial $\left\{ {112} \right\}\left\langle {110} \right\rangle_{\alpha } \,{\text{and}}\,\left\{ {332} \right\}\left\langle {113} \right\rangle_{\alpha }$ components are reproduced by texture heredity. However, with the increase of peak temperature, the heredity tendency of texture weakens, causing the reduction of texture intensity. In CGHAZ, the Goss and $\left\{ {112} \right\}\left\langle {110} \right\rangle_{\alpha }$ texture are obtained because of grains oriented growth. It is found that serious and heterogenous HAZ softening is a significant feature. FGHAZ becomes the weakest zone due to the massive formation of granular bainite. Due to the disappearance of $\,\left\{ {332} \right\}\left\langle {113} \right\rangle_{\alpha }$ and the formation of Goss texture, CGHAZ shows the least modulus.