Influence of Heat Treatment on Residual Stress Formation in the Wear-Resistant Steel 60–Steel 15–Steel 60 Bimetal Materi
Introduction
The bimetal layer structure and properties of material have been extensively studied due to their special properties and applications. In particular, high wear-resistant steels 60 and 15 in bimetal form have been in use in many industries including energy, aeronautical and automotive. Despite the many studies conducted in the past, heat treatment has not been adequately studied and there is a lack of information in this field. The current study aims to investigate the effects of heat treatment on the residual stress formation in the wear-resistant steel 60-steel 15-steel 60 bimetal material. Heat treatments ranging from 1020 °C to 1090 °C and 5, 10, 20 and 40 minutes were selected, and residual stress over a Ni-based diffusion layer around the steel 15 insert were analyzed with X-ray diffraction.
Heat Treatment Process
The primary objective of this heat treatment process was to form a nickel-based diffusion layer around the, steel 15 insert and modify the characteristics of the bimetal material. The experimental samples were taken from a pre-welded wear-resistant steel 60-steel 15-steel 60 bimetal composed of one steel 15 insert in the middle. Prior to the heat treatment process, the samples were preheated to around 900 °C and then cooled down to room temperature. After this, different temperature and time conditions were applied to the samples to form the desired nickel-based diffusion layer.
Metal layer: The metal layers consist of the steel 60 and steel 15. Steel 60 is known for its superior mechanical properties, such as excellent wear and corrosion resistance, due to its specified compositions of chrome and molybdenum. Steel 15 has similar properties to steel 60 but is more wear resistant and has better meta-stability.
Carburization layer: The carburization layer forms around the steel 15 insert, which is formed by diffusion of carbon into the steel 15 and diffusion of nickel into the metal matrix of the steel 60.
Results and Discussion
Figure 1 and Figure 2 show the residual stress distributions using diffraction tests. The direct bonded interface did not show significant signs of residual stress, whereas the diffusion layer experienced a higher stress concentration in the middle of the diffusion layer, indicating that the heat treatment process formed a compressive stress center (Figure 1b). As the temperature increases, the diffraction peak width increases, indicating that the cost-rate of the diffusion layer increases.
Fig.1 Residual Stress Distribution with Diffraction Tests
As the heat treatment time increased, the depth of the Ni-rich layer increased. The Ni-rich layer increased the hardness of the material and improves wear performance. Additionally, the Ni-rich layer was found to increase the tensile strength and hardness of the material, which is attributed to the large rate of diffusion in the Ni-rich layer due to the different diffusion coefficients of the elements (Figure 2).
Fig.2 Effect of Heat Treatment Time on Length of Ni-Rich Layer
Conclusion
The effects of heat treatment on the wear-resistant steel 60-steel 15-steel 60 bimetal material were investigated in this study. The results showed that heat treatment can form a compressive stress center in the middle of the diffusion layer. The heat treatment process increased the rate of diffusion, resulting in increased hardness and tensile strength of the material. Additionally, the length of the Ni-rich layer increased with the increase in heat treatment time. The results of this study indicate that the heat treatment process can be used as a means of increasing wear resistance, tensile strength, and hardness of the bimetal material.
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