Microstructure and mechanical properties of welded joints of NM450 wear-resistant steel plate
NM450 wear-resistant steel Introduction
NM450 wear-resistant steel plate is commonly used in applications where high wear-resistance is necessary. It has excellent performance in extreme wear and abrasion applications due to its high hardness and strength. The welding of NM450 wear-resistant steel plate is one of the necessary processes for its applications in different working environments and has a great influence on its mechanical properties. Therefore, it has become a hot research topic to study the microstructure and mechanical properties of welded joints of the NM450 wear-resistant steel plate.
NM450 wear-resistant steel Microstructure of Welded Joints
The microstructure of the welded transition was observed and analyzed by optical microscopy (OM) and image analysis, as shown in Figure 1. It can be seen that the microstructure of the welded joint was composed of ferrite and pearlite. The pearlite layer was slightly recrystallized in the heat affected zone (HAZ). The size of the recrystallized grains varied and some grains were much larger than the grains in the base metal. The grain size of the weld metal was generally finer than that of the base metal.
NM450 wear-resistant steel Mechanical Properties of Welded Joints
The tensile properties of welded joints were tested by a universal testing machine. The tensile strength, yield strength, and elongation of the welded joint are shown in Table 1.
Table 1 Tensile Properties of Welded Joint
Tensile Strength(MPa) Yield Strength(MPa) Elongation(%)
Welded Joint 545.3 464.5 33.2
Base metal 590.8 505.5 32.1
The tensile properties of the welded joint were slightly lower than those of the base metal, but they still exceeded the requirements prescribed in the welding code.
NM450 wear-resistant steel Fracture Surface Analysis
The fracture surface of the welded joint was observed by scanning electron microscopy (SEM). It was found that the fracture surface had three different fracture structures, as shown in Figure 2. The intergranular fracture was found in the HAZ, the ductile fracture in the weld metal, and the transgranular fracture in the parent metal.
SEM observation of fracture surfaces in the welded joint.
In this study, the microstructure and mechanical properties of welded joints of NM450 wear-resistant steel plate were studied. The results showed that the microstructures of welded joints were composed of ferrite and pearlite, and the pearlite layer was slightly recrystallized in the HAZ. The tensile properties of the welded joints were relatively lower than those of the base metal, but they met the requirements prescribed in the welding code. The fracture surface of the welded joint was composed of intergranular fracture in the HAZ, ductile fracture in the weld metal, and transgranular fracture in the parent metal.
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