Research On NM500/Q345/NM500 Three Layer Rolling Composite And Heat Treatment Process

Traditional wear-resistant materials such as high-manganese steel,wear-resistant cast iron and low-alloy wear-resistant steel have high wear resistance,and can withstand large impact and high stress,those metals are suitable for harsh conditions.Components manufactured by these materials can significantly improve the service life of mechanical equipments,but greatly increase the production cost,and these materials have some limitations in some applications.Therefore,this paper proposes the use of metal composite plate instead of the traditional single wear-resistant material.A wear-resistant composite plate is prepared by a vacuum hot rolling method,which use the relatively low price Q345 as base layer,with the low alloy steel NM500 as the clad layer.The appearance of the composite plate has greatly reduced the production cost.Composite plate has high wear resistance and hardness while ensuring good toughness and weldability.In this paper,a composite plate with a good plate shape was prepared through experiments,and then the composite plate was heat treated with quenching and low temperature tempering.The main research contents are as follows:1)By designing the rolling experiment process and parameters,welding composite billets and vacuuming them,composite plates were rolled out with good plate shape and no macro-layering.During the experiment,the method of group blanking is three-layer symmetry,that is,a layer of Q345 were covered with two layers of NM500.The thickness of Q345 were 6mm,8mm and 10 mm,respectively.Results demonstrated the feasibility of the experimental process.2)The microstructure of the composite plate after vacuum rolling was analyzed,and the impact of the different rolling reduction ratios and thickness of substrates on the microstructure of the composite plate interface was researched.Interface defects and inclusions were analyzed through the EDS.The tensile test was used to study the effect of reduction ratio on the tensile properties and elongation of the composite plate.Rockwell hardness of the NM500 was also measured.As the reduction rate increased,the variation of the thickness ratio of Q345 was analyzed and the change curve was plotted.Experiments show that when the reduction rate is 70% and the thickness of the substrate is 8mm,the microstructure of the composite plate at the interface is better,and the tensile strength and elongation are also the best.3)The composite plates were quenched at 860,900 and 940°C,respectively.The quenching medium was water.The effects of different quenching temperatures on the microstructure were investigated.The quenched composite plates were uniformly tempered at 200°C to analyze the changes of microstructure after tempering.The tensile tests and surface hardness measurements were performed on the heat-treated composite specimens,and the effect of the heat treatment temperatures on the mechanical properties was compared with that of the hot-rolled composite plates.The experiment shows the average tensile strength of composite plates after heat treatment exceeds 1250 MPa.After quenching at 900°C and tempering at 200°C,the microstructure and properties of the composite plate are the best.