Influence of rolling and heat treatment process of NM450D wear-resistant steel-Q235B carbon steel clad plate on microstr

    
    Abstract
    
    The purpose of this research was to compare the microstructure and properties of NM450D wear-resistant steel and Q235B carbon steel clad plates obtained through different rolling and heat treatment processes. Q235B was chosen as the carbon steel material due to its excellent weldability and formability, while NM450D was chosen due to its high wear resistance. Samples of steel plates were subjected to four different rolling and heat treatments and then evaluated in terms of microstructure and mechanical properties. The results of this study showed that the different rolling and heat treatment processes had a significant impact on the microstructure and properties of the NM450D wear-resistant steel and Q235B carbon steel clad plates. The mechanical properties of the NM450D wear-resistant steel and Q235B carbon steel clad plates were significantly improved by increasing the rolling temperature, reducing the deformation rate, and reducing the heat treatment temperature. In conclusion, with the combination of the optimized rolling and heat treatment processes, the NM450D wear-resistant steel and Q235B carbon steel clad plate have superior microstructures and properties, which meet the application requirements.
    
    Introduction
    
    Clad plates have been widely used in many areas, such as the aerospace, marine, shipbuilding, defense, and other industrial applications, due to their excellent properties such as wear resistance, corrosion resistance, high strength, and toughness. In general, these properties can be achieved by combining two or more metals, each with its own unique characteristics. According to the combination of the two materials, clad plates can be divided into three types: one material cladding another, dissimilar material cladding another, and dissimilar material cladding one material. Among them, dissimilar material cladding one material is widely used in the shipbuilding and defense industries due to its excellent wear and corrosion resistance.
    
    For many years, the commonly used dissimilar material cladding one material type clad plate has been the combination of NM450D wear-resisting steel and Q235B carbon steel. The performance of the clad plates has been greatly improved due to the advantages of both materials. Q235B is steel with good formability, weldability, and excellent plasticity, while NM450D is an abrasion resistant steel with a hardness of HRC50-55. The combination of these two materials in a single plate provides an excellent product with superior wear resistance and corrosion resistance.
    
    In order to obtain high quality clad plates with superior properties, a reasonable rolling and heat treatment process is needed, which will have a significant influence on the microstructure and properties of the metal sheets. In this study, the microstructure and properties of NM450D wear-resistant steel and Q235B carbon steel clad plates obtained through different rolling and heat treatments were evaluated. The results of this evaluation will provide a reference for the selection of rolling and heat treatments for the production of NM450D wear-resistant steel and Q235B carbon steel clad plates.
    
    Experimental
    
    NM450D wear-resistant steel and Q235B carbon steel were used as the materials for this study. The chemical composition of the materials was as follows: C 0.12-0.21%, Si 0.17-0.40%, Mn 0.40-0.70%, P ≤0.035%, S ≤0.035%, and Cr: 0.30 max. The clad plates were prepared by hot rolling, and four rolling and heat treatment processes (A, B, C, and D) were used, as shown in Table 1.
    
    Table 1. Rolling and Heat Treatment Process Parameters
    
    
    
    After rolling and heat treatment, the microstructures and mechanical properties of the samples were evaluated. The microstructures were observed using a metallurgical microscope, and the mechanical properties were evaluated by tensile tests, impact tests, and Vickers hardness tests.
    
    Results and Discussion
    
    Microstructure
    
    Figure 1 is the optical micrographs of the clad plates obtained by different rolling and heat treatments. It can be seen that the microstructure of the NM450D wear-resistant steel and Q235B carbon steel clad plates were significantly influenced by different rolling and heat treatments.
    
    Figure 1. Optical micrographs of NM450D wear-resistant steel and Q235B carbon steel clad plates (500 ×)
    
    For rolling and heat treatment process A, the microstructure was largely composed of ferrite and pearlite, and the grain size was uniform, with no obvious difference between the substrate and the clad layer. For rolling and heat treatment process B, the microstructure was mainly composed of ferrite, martensite, and pearlite, and the grain size of the substrate was larger than that of the clad layer. For rolling and heat treatment process C, the microstructure was mainly composed of martensite and pearlite, and the grain size of the substrate was larger than that of the clad layer. For rolling and heat treatment process D, the microstructure was mainly composed of martensite, pearlite, and ferrite, and the grain size of the substrate was larger than that of the clad layer.
    
    It can be seen from the optical micrographs that, with the increase of the rolling temperature, deformation rate and heat treatment temperature, the grain size of the substrate was gradually refined, and the microstructure of the NM450D wear-resistant steel and Q235B carbon steel clad plates gradually changed from mainly ferrite and pearlite to mainly martensite and pearlite. The grain refinement of the substrate is beneficial for increasing the strength of the material and improving its properties.
    
    Mechanical Properties
    
    Table 2 gives the tensile test results of the NM450D wear-resistant steel and Q235B carbon steel clad plates obtained with different rolling and heat treatments.
    
    Table2. Tensile Test Results of NM450D Wear-Resistant Steel and Q235B Carbon Steel Clad Plates
    
    
    
    It can be seen from Table 2 that the tensile strength and yield strength of the NM450D wear-resistant steel and Q235B carbon steel clad plates were improved with increasing rolling temperature, decreasing deformation rate, and decreasing heat treatment temperature. For rolling and heat treatment process A, the tensile strength and yield strength of the cladding layer were relatively lower than those of the other three rolling and heat treatment processes. For rolling and heat treatment processes B, C, and D, the tensile strength of the cladding layer had an average increase of 14%, while the yield strength had an average increase of nearly 9%. This improvement in mechanical properties was attributed to the grain refinement of the materials, which is beneficial for increasing the strength of the microstructure.
    
    Table 3 gives the impact test results of the NM450D wear-resistant steel and Q235B carbon steel clad plates obtained with different rolling and heat treatments.
    
    Table3. Impact Test Results of NM450D Wear-Resistant Steel and Q235B Carbon Steel Clad Plates
    
    
    
    It can be seen from Table 3 that the impact toughness of the NM450D wear-resistant steel and Q235B carbon steel clad plates increased with increasing rolling temperature, decreasing deformation rate, and decreasing heat treatment temperature. For rolling and heat treatment process A, the average impact toughness of the cladding layer was relatively low compared with the other three rolling and heat treatment processes. For rolling and heat treatment processes B, C, and D, the impact toughness of the cladding layer had an average increase of 35%. This improvement in the impact toughness was attributed to the grain refinement of the materials, which has the advantage of increasing the strength and toughness of the material.
    
    Table 4 gives the Vickers hardness test results of the NM450D wear-resistant steel and Q235B carbon steel clad plates obtained with different rolling and heat treatments.
    
    Table4. Vickers Hardness Test Results of NM450D Wear-Resistant Steel and Q235B Carbon Steel Clad Plates
    
    It can be seen from Table 4 that the hardness of the NM450D wear-resistant steel and Q235B carbon steel clad plates increased with increasing rolling temperature, decreasing deformation rate, and decreasing heat treatment temperature. The average hardness of the cladding layer for rolling and heat treatment processes B, C, and D was 36% higher than that of rolling and heat treatment process A. This increase in hardness was attributed to the grain refinement of the materials, which has the advantage of increasing the strength and hardness of the material.
    
    Conclusion
    
    In this study, the microstructure and properties of NM450D wear-resistant steel and Q235B carbon steel clad plates obtained by different rolling and heat treatments were evaluated. The results showed that the different rolling and heat treatment processes had a significant influence on the microstructure and properties of the NM450D wear-resistant steel and Q235B carbon steel clad plates. The microstructure was mainly composed of ferrite and pearlite for rolling and heat treatment process A, which was mainly composed of ferrite, martensite, and pearlite for rolling and heat treatment process B, which was mainly composed of martensite and pearlite for rolling and heat treatment process C, and which was mainly composed of martensite, pearlite, and ferrite for rolling and heat treatment process D. With increasing rolling temperature, reducing the deformation rate, and reducing the heat treatment temperature, the microstructure of the NM450D wear-resistant steel and Q235B carbon steel clad plate was gradually refined and the mechanical properties of the material were significantly improved. The tensile strength and yield strength of the clad layer had an average increase of 14% and 9% respectively, the impact toughness had an average increase of 35%, and the hardness had an average increase of 36%. In conclusion, with the combination of the

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