Quasi-brittle Deformation and Fracture Behaviors of NM450TP High-Strength Wear-Resistant Steel Plates during Twice Tensile Test

As the strength grade increases, the cold formability of high-strength steels (HSS) inevitably decreases and the brittleness tendency is obvious. However, in most existing studies on HSS forming the assumption of ductile material was commonly used, and the brittle properties of HSS were not clearly understood. In this paper, a deliberately designed uniaxial twice tensile test was employed to examine the quasi-brittle deformation and fracture behaviors of NM450TP wear-resistant steel plates. FEM models considering non-uniform mechanical properties were constructed, and DC04 plates characterized by typical ductile material were tested for comparison. The results showed that the brittle trend of NM450TP plates causes obvious localized strain during stretching, and the fracture is sensitive to the random initial imperfections. The deformation outside the necking zone is small and the deformation capacity is preserved; thus, it would be conservative to evaluate the formability of HSS by the conventional concept of percentage elongation. The non-uniform FEM models can reproduce the fracture mode of NM450TP plates during tensile tests. In comparison, the ductile DC04 specimens can “average” the mechanical properties before fracture within a wide range via large plastic deformation, and then the deformation is more uniform. The correction index n for conversion of elongation value of NM450TP plates in the Oliver formula was obtained. In the studied cases, n ranges from 0.685 to 0.752 for specimens with gauge length of 150 mm, while it ranges from 0.839 to 0.931 when the gauge length is 15 mm.