Abstract
High-strength, wear-resistant steel often suffers from delayed cracking after flame cutting. Delayed cracking can lead to extremely harmful sudden brittle fracture; therefore, it is necessary to study the formation of delayed cracking in high-strength steel. This work investigated the influence of TiN inclusions and segregation on the delayed cracking in NM450 wear-resistant steel by optical microscopy, scanning electron microscopy, X-ray diffraction, transmission electron microscopy and electron backscattered diffractometer methods. The results indicated that the delayed cracks originated from the segregation zones (SZs) containing multiple high-hardness segregation bands. The tensile strength of the SZ specimens was higher than that of non-segregation zone (NSZ) specimens, while the total elongation and reduction of area of the SZ specimens were relatively lower compared with the NSZ specimens. Therefore, the delayed cracking on the flame cutting surface of the NM450 steel plate was attributed to the existence of SZs that contain a high density of dislocations and considerable micro-sized TiN inclusions.
Highlights
With the development of heavy industry, the demand for high-strength steel has increased, and more high-strength steel has been developed [1]
High-strength wear-resistant steel often suffers from delayed cracking after flame cutting due to aggregation of residual hydrogen in the steel plate
In order to accurately prepare the tensile specimens from the segregation zones (SZs) and non-segregation zone (NSZ), the sheet was etched with 10 mL of nitric acid and 90 mL of ethanol until the macroscopic segregation was observed in the thickness direction, and the samples were cut by an electric spark wire cutting machine followed by further machining into tensile specimens
Summary
With the development of heavy industry, the demand for high-strength steel has increased, and more high-strength steel has been developed [1]. High-strength wear-resistant steel often suffers from delayed cracking after flame cutting due to aggregation of residual hydrogen in the steel plate. It is necessary to study the cause of delayed cracking in high-strength steel. NM450 wear-resistant steel is a low-alloy, high-strength martensitic steel widely used in the mechanical engineering field because of its low cost and excellent mechanical properties. Nb, are widely used to improve the strength, toughness and other mechanical properties of low-alloy, high-strength steel [1,7]. Delayed cracking in the NM450 steel plate often occurs in the flame cutting surface. In this work, delayed cracking was studied by a series of tensile tests performed on the segregation zones (SZs) and non-segregation zones (NSZs) of NM450 steel. The influence of TiN inclusions and segregation on delayed cracking was analyzed in detail
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