Economically alloyed high-strength steel for use in mine equipment

Zhong-yang

et al. 2022

Metals

NM550 wear-resistant steel is widely used in large-scale engineering and mining machinery under extremely harsh working conditions. In NM550 steel, the addition of Ti can cause the formation of micron-scale TiN and TiC inclusions, easily triggering cleavage fractures. The fracture behavior and precipitation rule of micron-scale TiN and TiC inclusions on the tensile process in NM550 steel was investigated by scanning electron microscopy, transmission electron microscopy, and energy spectrum analysis combined with thermodynamic theory. The TiN precipitated in the solid–liquid two-phase region at a precipitation temperature of 1710 K, whereas that of TiC was 1158 K along the austenite grain boundary. The sizes of the TiN precipitated in the liquid phase and the TiC precipitated in austenite were both at the micron scale, which is prone to cleavage fracture during the stretching process. Under tensile stress, microcracks were first initiated at the TiN inclusion, which were further separated forming a hole, whereas the TiC inclusion was divided into two sections with a long and narrow gap formed between the substrates. The sizes of the TiN and TiC were related to the cooling rate, Ti, and N contents. The larger the cooling rate and the lesser the Ti and N content, the smaller the TiN and TiC sizes.

Section: Fracture Behavior Of Micron-scale Tin and Tic Inclusionsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Study of the Fracture Behavior of TiN and TiC Inclusions in NM550 Wear-Resistant Steel during the Tensile Process

Zhong-yang

et al. 2022

Metals

“…Owing to the excellent combination of strength and wear resistance, thick NM550 wear-resistant steel is widely used in the mechanical equipment and engineering structures of mining, construction, metallurgy, and other industries [1]. However, delayed cracking in the flame cutting surface of the thick NM550 steel often happens after flame cutting, resulting in great harm with its subsequent use.…”

Section: Introductionmentioning

confidence: 99%

Influence of TiN Inclusions and Segregation Bands on the Mechanical Properties and Delayed Crack in Thick NM550 Wear-Resistant Steel

Sun,

Du,

Tong

et al. 2023

Materials

The formation mechanism of the delayed crack after flame cutting and mechanical properties in thick NM550 wear-resistant steel are studied by optical microscopy, scanning electron microscopy, energy dispersive spectroscopy, X-ray diffraction, and an electron backscattered diffractometer. The delayed crack is formed at the segregation zone (SZ) located in the center of the 65 mm thick steel plate. The strength of the non-segregation zone (NSZ) with a martensite microstructure is slightly higher than that of SZ with a mixture microstructure of martensite plus bainite, and the plasticity of NSZ is significantly better than that of SZ. There exists a more severe segregation in the SZ, and only a slight segregation in the NSZ. The average grain sizes of the segregation bands in the NSZ and SZ are 15.72 µm and 6.76 µm, respectively. The number density of TiN larger than 5 µm in the NSZ and SZ is 0.031 and 1.156 number/mm2, respectively. Therefore, a high hardness segregation band with fine grains and a high dislocation density, along with the large number of coarse TiN inclusions within it, results in delayed cracking. For TiN inclusions close to the crack, microvoids or microcracks around the TiN are formed, and the delayed crack will propagate along the edge of the TiN or through the TiN inclusions.

“…Low-alloy high-strength wear-resistant steels have numerous advantages such as low alloying content, simple manufacturing process, high toughness, and wear resistance (Jiang et al, 2011;Ojala et al, 2014;Ryabov et al, 2017). Currently, microalloying, and heat treatment have been widely adopted to improve the strength, toughness, and wear resistance of low-alloy high-strength steels, mainly through adding elements Ti, B, Nb, and V (Nikitin et al, 2016;Shi et al, 2016). Among these microalloying elements, Ti is typically used to form nanosized precipitates with excellent hightemperature stability, eventually inhibiting the growth of austenitic grains.…”

Section: Introductionmentioning

confidence: 99%

Correlation Between Microstructure and Fracture Behavior in Thick HARDOX 450 Wear-Resistant Steel With TiN Inclusions

Wang

et al. 2021

Front. Mater.

This work investigates the correlation between TiN inclusions and microstructural properties of HARDOX 450 steel using optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and electron backscattered diffractometer (EBSD) methods. Some amount of microsized TiN inclusions were formed in the temperature range of the solid–liquid zone; however, they exhibited fracture features of deep dimples rather than a cleavage plane, which is closely related to the ability of the microstructure to arrest cracks. Upon tensile loading, a single microcrack first appeared inside the microsized TiN inclusions, and then, multiple microcracks formed, parts of which widened in the direction of tensile stress. A schematic mechanism map was plotted to reveal the propagation behavior and fracture mechanism of the microcracks in the TiN inclusions.