Continuous Cooling Transformation and Microstructure Properties of 65MnCr Wear-resistant Steel
To investigate the consistency, the Continuous Cooling Transformation (CCT) curve of the 65MnCr wear-resistant steel has been studied. CCT experiments were carried out in a laboratory dilatometer, using samples in the form of circular discs with 25-mm diameters. Experiments were done in the temperature range of 700 to 900°C. The tests were series of 25-minute cooling from a 925-degree quenching temperature to room temperature in a heated steel box. The cooling rate representing the cooling curve for 65MnCr wear-resistant steel was about 25 ºC/min. The results of the cooling rate tests were carried out by an Infrared Thermometer (IRT) connected to the dilatometer.
The resultant CCT curves are shown in Figure 1. The CCT curve of 65MnCr wear-resistant steel was obtained by plotting the volume fraction of the ferrite, austenite and martensite against the temperature. The CCT curve shows the transformation of austenite to ferrite, pearlite and martensite with the cooling process. The transformation start temperature (onset temperature of ferrite), Ms temperature, Acm temperature and Mf temperature can easily be determined from the CCT curve.
Analysis of the CCT curve indicates that the Ms temperature was about 705 °C and the Acm temperature was about 605 °C. Furthermore, the transformation start temperature (onset temperature of ferrite) was about 740 °C and Mf temperature was about 500 °C. These results show that the 65MnCr wear-resistant steel exhibits a favorable combination of high wear-resistant and corrosion-resistant properties.
The microstructure of the 65MnCr wear-resistant steel obtained from the CCT curve is depicted in Figure 2. The microstructure consists of ferrite, austenite, pearlite and martensite. The ferrite and pearlite have good wear-resistant properties because they have high hardness and wear-resistance. The Martensite has superior hardness and superior wear-resistance due its high carbon and chromium contents.
The combination of the good wear-resistant and corrosion-resistant properties with the low cost of the 65MnCr wear-resistant steel make it the ideal material for many industrial applications, such as engine components, construction machinery, agricultural tools, and components for oil and gas extraction. Furthermore, the cooling conditions of 65MnCr wear-resistant steel can be adjusted as required to achieve an optimal microstructure for the desired service application.
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