Surface cracking mechanism of continuously cast low carbon low alloy steel slabs

Abstract

Surface cracking mechanism of continuously cast lovv carbon lovv alloy steel slabsThe present state of understanding of surface cracking in low C low alloy steel slabs in the continuous casting (CC) and direct rolling (DR) processes is outlined. Hot cracking of the CC slab surface can be explained in terms of carbide and/or nitride precipitation behaviour. In addition to'}' grain boundary precipitation, the matrix strengthening owing to dynamic precipitation and the existence of softer layers along the boundaries such as grain boundary allotriomorphs of ferrite or precipitate free zones play animportant role in intergranular ductile fracture. The origin of hot cracking during the DR process lies also in the precipitation of carbides and/or nitrides, and is not related to the severe embrittlement caused by a similar mechanism with dynamic precipitation of sulphides, which is observed usually in the high strain rate deformation after reheating at higher temperatures. Furthermore, a well known effect of C on hot cracking susceptibility in both CC and DR processes, attaining a maximum in the range 0·10-0·15 wt.-%C, isfound to arise mainlyfrom '}' grain growth during solidification in the mould. Some methods to prevent surface cracking are also discussed.MST/1226

Hot ductility of TWIP steels

“…The presence of microalloy precipitates can also reduce the strain to fracture by a number of possible mechanisms: precipitate free zones are often observed adjacent to austenite grain boundaries, and this may lead to strain concentration at the grain boundary; the particles (or groups of particles) at the grain boundaries may act as crack initiation sites; or general matrix precipitation can lead to an increase in strength, and an overall reduction in ductility [19][20][21]. The proposed mechanism for low ductility failures in the presence of Nb and V carbonitrides is illustrated in Fig.2.3(a)~(c) in this case it being precipitate free zones which allow strain concentration [19].…”

Effect of Thermal Cycle and Nitrogen Content on the Hot Ductility of Boron-bearing Steel

“…Therefore, defect-free slab surface is a prime requirement for the economic production of steel by HDR. [3][4][5] One approach to making slabs that are free of surface cracks is to add alloying elements to improve the steel's hot ductility. [6][7][8] Addition of B to plain carbon steel improves hot ductility in the austenite single-phase region because solute B atoms that segregate to grain boundaries can occupy vacancies and thus prevent formation and propagation of microcracks at grain boundaries.…”

Study on MnS Precipitation Thermodynamics of DL05 Cable Steel

“…Increasing the Mn content in the steel will increase the probability of the combination of sulfur and manganese, and the formula (1) in the equilibrium forward movement, which can hinder the formation of FeS and other low melting point compounds in the austenite grain boundaries. theoretically to achieve this goal, manganese sulfur ratio to reach 7 [3][4][5].…”