Effect of pre-deformation mode on the microstructures and mechanical properties of Hadfield steel
Introduction
Since its invention over 100 years ago, Hadfield steel has been a widely used wear-resistant material because of its excellent work hardening ability and combination of strength and ductility [1], [2]. However, Hadfield steel is vulnerable to severe plastic deformation at the initial stage of service, especially under high applied stress. This phenomenon can greatly reduce its service life [3], [4]. Therefore, various hardening methods have been conducted to improve the initial strength of Hadfield steel [5], [6], [7], [8].
Explosion hardening is a common method to harden Hadfield steel railway crossings to improve the wear resistance and service life [2], [9], [10]. Explosion hardening is essentially a kind of shock wave deformation [11]. Compared with the conventional mechanical deformation (e.g., rolling deformation and tensile deformation), the shock-wave deformation has two major features: namely, ultra-high strain rate and low plastic strain. The compressive residual stress distributed along the surface layer through shock-wave deformation can significantly improve the mechanical properties [12]. Shock-wave deformed materials display distinct characteristics, such as resistance to macro plastic deformation [9], deep residual stress layer [12], [13], [14], and different plastic deformation mechanisms [14]. Explosions can produce shock waves with high energy and short pulse duration, which directly affect the deformation feature characteristics developed in the microstructure [15]. The research to date has focused on the effect of explosion hardening on the microstructure and property of material [10], [16], but it is unclear how it differs from other deformation modes.
The current study aimed to investigate the role of deformation mode on the microstructure and mechanical properties of a Hadfield steel. Here, the steel was subjected to either explosion hardening treatment or cold rolling to obtain materials with similar hardness level. Subsequently, the microstructure and mechanical properties were thoroughly studied to understand the microstructure and property relationship.
Section snippets
Experimental procedure
The test steel used in the present study was a conventional Hadfield steel with a chemical composition of 1.14%C, 11.7%Mn, 0.42%Si, 0.001%P, 0.005%S, and balanced Fe (in wt%). The steel was smelted in a 50 kg vacuum induction furnace and forged into a 60 mm × 60 mm block. The steel was heat treated at 1050 °C for 1 h followed by water quenching. Plate-shaped specimens of 60 mm × 110 mm × 17 mm were prepared to conduct different deformations. Plastic sheet explosive was used for explosion
Results
The heat-treated microstructure consisted of equiaxed grains with an average size of 89 ± 11 µm, which contained a large fraction of coincidence site lattice (CSL) boundaries (i.e., ∑3 and ∑9, Fig. 2). ∑3 annealing twin boundaries with 60°/[111] misorientation had the highest fraction (~0.47) in the microstructure followed by ∑9 boundaries with 39°/[110] misorientation (~0.05, Fig. 3), which largely appeared at the intersection of two ∑3 boundaries (i.e., ∑3 + ∑3 = ∑9 [17], [18], Fig. 2a). The
Discussion
Generally, plastic strain taking place within a grain during monotonic deformations (e.g., compression [9] and tension [1] deformation modes) are irreversible. In cold rolling, two deformation modes are operating, namely shear and compression. The former is mostly observed at the surface, where the friction is maximum and becomes negligible at the mid thickness of the rolled sample [19]. Therefore, the material is largely subjected to compression deformation mode in the mid thickness of the
Conclusions
In the current study, a conventional Hadfield steel was subjected to different deformation modes, namely, explosion and cold rolling, to obtain a similar hardness level. However, the change in the deformation mode led to considerable alteration in the microstructure and tensile properties, as summarized below.
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After cold rolling, the grains were largely elongated along the rolling direction. However, the grains mostly maintained their equiaxed morphology in the exploded sample. The strain
Acknowledgements
The authors gratefully acknowledge the National Natural Science Youth Fund of China (No. 51501161). Deakin University's Advanced Characterization Facility is acknowledged for use of the EBSD instruments.
Data availability
The raw/processed data required to reproduce these findings cannot be shared at this time as the data also forms part of an ongoing study.
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These authors contributed equally to this work.