Study on Microstructure and Properties of NM500/Q345 Clad Plates at Different Austenitization Temperatures

Abstract

In this paper, the change in the mechanical properties of a composite plate was studied using the heat treatment method, and it was found that the performance of the composite plate was greatly improved under the process of quenching at 900 °C and tempering at 200 °C. The hot-rolled NM500/Q345 clad plates were subjected to heat treatment tests of 860 °C, 900 °C, and 940 °C austenitization + 200 tempering. With the help of an optical microscope, scanning electron microscope, EBSD, and transmission electron microscope, the microstructure, interface element distribution, and defect composition at the composite bonding interface of hot rolling and heat treatment were analyzed. An analysis and friction and wear tests were carried out on the wear resistance of the clad NM500. It was found that the microstructure of the NM500/Q345 clad plate before austenitization was mainly pearlite and ferrite, and both were transformed into lath martensite after austenitization. As the austenitization temperature increased, the size of the martensitic lath bundle also became coarse. After austenitization at 900 °C and tempering at 200 °C, the lath-like martensite structure of NM500 contained high-density dislocations between the laths. With the increase in the austenitization temperature, the surface Rockwell hardness showed a trend of first increasing and then decreasing. The wear was the worst when the material was not quenched. When the clad plate was quenched at 900 °C and tempered at 200 °C, the wear of NM500 was the lightest; the maximum depth of the wear scar was 14 μm; the width was the narrowest, 0.73 mm; and the wear volume was the smallest, 0.0305 mm3.