Coarse Grained Heat-Affected Zone Microstructure and Brittleness of Ti-Nb-B Microalloyed High Toughness and Wear Resistant Steel

Abstract

The effects of B, Ti-Nb, and Ti-Nb-B microalloying on the microstructure and properties of the coarse grain heat affected zone (CGHAZ) of C-Mn-Si-Mo wear-resistant steel have been investigated by means of thermal simulation, mechanical property test, microstructure analysis, and theoretical formula calculation. The B, Ti-Nb, and Ti-Nb-B microalloyed C-Mn-Si-Mo wear-resistant steels prepared by a controlled rolling + direct quenching + low temperature (CR + DQ + T) process have martensite/bainite (M/B) dual-phase microstructure and fully-refined effective grain size, which make the base metal to have high hardness and impact toughness. At the heat input of 20 kJ/cm, the impact toughness of CGHAZ of three kinds of microalloyed wear-resistant steels decreased in varying degrees. The main reasons for brittleness were coarse grain embrittlement and microstructural embrittlement. Ti-Nb-B microalloying can effectively prevent grain growth in CGHAZ while avoiding the formation of pearlite, small lump ferrite, and large grain carbides at the grain boundaries, thereby reducing the embrittlement of coarse grain and microstructure.

Evaluation of the Properties and Microstructure of Thick-Walled Welded Joint of Wear Resistant Materials

“…In turn, the Authors of [ 5 ] indicate that the time of cooling in the range of 800–500 °C to ensure the proper toughness of the welded joint should not be less than 3 s. The fracture toughness of high-strength steel joints is also significantly affected by the heat input; its value greater than 20–30 kJ/cm results in a significant reduction in the impact energy of the produced test joint not only in room but also at a reduced temperature [ 5 ]. Similar conclusions were presented by the Authors of [ 40 ]. The presence of the micro-addition of boron in the test steel ( Table 2 ) can also contribute to the refinement and reduction in the size of martensitic packets and its refining effect on the grain/lath boundaries can improve the increase in the strength properties and fracture toughness [ 43 ].…”

“…The resulting microstructures of the welded base materials within HAZ were similar to those presented in the works on the issues relating to the welding of these construction materials, e.g. [ 5 , 11 , 14 , 16 , 18 , 40 , 46 ].…”

“…The studies carried out so far have shown that welding Hardox steels results in an increase in their embrittlement within the welded joint area [ 7 , 13 , 38 , 39 , 40 ]. The impact energy of metallic alloys depends not only on their structure, but also on the grain size or the precipitation processes at the grain boundaries.…”