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.
Highlights
The rapid development of industry requires long-lasting performance of wear-resistant steel.It is common to increase the carbon content and multi-alloying to increase the hardness but this results in poor solderability of the material [1]
Dudziński et al [2] reported that when the temperature peak is too high and the cooling rate is slow, the coarse-grained heat-affected zone (CGHAZ) stays in the high-temperature zone for a long time, which makes the austenite grain coarser
Through the controlled rolling (CR) + direct quenching (DQ) + T process, the effective grain size [4] can be refined to make the base material have high hardness and good impact toughness [5], which could be explored in further studies about the brittleness of wear-resistant steel welded CGHAZ
Summary
The rapid development of industry requires long-lasting performance of wear-resistant steel. Different regions of the base metal are subjected to different welding thermal cycles, resulting in uneven microstructure and mechanical properties of the weld heat affected zone (HAZ). After the phase transformation is completed, the grain in the region become coarser and the local embrittlement is severe, which results in the poor welding performance of high hardness and wear resistant steel. The research on CGHAZ of wear-resistant steel is mainly focused on welding heat input, only a few studies have focused on the influence of the composition and microstructure of the Metals 2019, 9, 289; doi:10.3390/met9030289 www.mdpi.com/journal/metals. In this paper, controlled rolling (CR) + direct quenching (DQ) + low temperature tempering (T) processes have been used to obtain high hardness and high toughness wear-resistant steels with different compositions of microalloying. The effect of microalloying composition on the brittleness of CGHAZ is studied under the condition of a large welding heat input
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