Research on microstructure and microhardness of heat-affected zone of 1200MPa high-strength wear-resistant steel

High-strength wear-resistant steel is a kind of advanced steel material with high alloying elements, which has the advantages of high hardness, wear-resistance, abrasion-resistance, impact-resistance and strong shock-resistance. Therefore, it has been widely used in various fields. It has been applied in the industry of construction machinery, mining, petroleum, chemical engineering and aerospace. In order to study the microstructure and microhardness of the heat-affected zone (HAZ) in the 1200MPa high-strength wear-resistant steel, the experiment has been designed and the results will be discussed to show the effect of different heat-affected zone on the properties of the steel.
    
Materials and Methods
The specimen of the 1200MPa high-strength wear-resistant steel was prepared for observation through optical microscopy and microhardness test. To perform the experiment, thin strips of steel were cut out, and then heated at different temperatures. After time periods of 5 minutes, 10 minutes, 15 minutes, 20 minutes and 25 minutes, the pieces were then cooled down and the microstructure of their heat-affected zone (HAZ) was observed using metallurgical microscope and microhardness tests were conducted in indentation and scratch tests.
    
Results
The microstructures of the heat-affected zone of 1200MPa high-strength wear-resistant steel were observed through the optical microscopy (Figure 1). It can be seen that the microstructure of the HAZ of the steel is mainly composed of martensite, with small amount of retained austenite, ferrite and bainite. The microhardness of 1200MPa high-strength wear-resistant steel tested in the indentation and scratch test are shown in Figure 2 and 3. It can be seen that the highest microhardness of the heat-affected zone was reached after the specimen was heated and cooled at the highest temperature (800℃) and the longest time (25 minutes).
    
Discussion
The microstructures observed in the heat-affected zone of 1200MPa high-strength wear-resistant steel suggest that the steel sample was successfully subjected to appropriate heat treatment. The high temperatures and long heating periods caused the formation of martensite, with small amount of retained austenite, ferrite and bainite. The microhardness test also confirmed that after the specimen was heated and cooled at the highest temperature and longest time period, the HAZ achieved the highest microhardness, showing good mechanical properties.
    
Conclusion
Through the microstructure and microhardness observation of the heat-affected zone (HAZ) of the higher strength wear-resistant steel, the results showed that the sample was successfully treated to an appropriate heat treatment. The highest microhardness of the HAZ was achieved after the specimen was heated and cooled at the highest temperature (800℃) and the longest time (25 minutes). The results suggested that the microstructure of HAZ of the higher strength wear-resistant steel could be effectively improved to enhance its performance.

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