Effect of solidification path and contraction on the cracking susceptibility of carbon peritectic steels

In the continuous casting process, the shrinkage of the peritectic phase transition during the initial solidification process has an important influence on the surface quality of peritectic steel. The initial solidification process of 0.10C%, 0.14C%, and 0.16C% peritectic steels was observed in situ by a high temperature laser confocal microscope, and the contraction degree during initial solidification was characterized by surface roughness. The results showed that under the cooling rate of 20 °C/s, the surface roughness value Ra(δ/γ) of 0.10C% peritectic steel was 32 μm, the Ra(δ/γ) value of 0.14C% peritectic steel was 25 μm, and the Ra(δ/γ) value of 0.16C% peritectic steel was 17 μm. With increasing carbon content, the contraction degree of the δ→γ transformation decreased, and the value of the surface roughness Ra(δ/γ) declined. Therefore, surface roughness can characterize the contraction degree of the δ→γ transformation in the initial solidification process of peritectic steel under the condition of a large cooling rate.

Section: Surface Roughness Ra(δ/γ)mentioning

confidence: 99%

Study of the Effect of Carbon on the Contraction of Hypo-Peritectic Steels during Initial Solidification by Surface Roughness

Wen

et al. 2018

“…Peritectic reaction of steel is an important transformation mode of Fe-C alloy with a carbon content ranging from 0.10% to 0.53% in the initial stage of solidification [1][2][3][4]. When the primary high-temperature δ-ferrite reacts with the residual molten steel L to produce the γ-austenite, the difference in crystal structure between the δ phase (BCC structure) and the γ phase (FCC structure) results in a large volume contraction in the process of solidification, which causes uneven cooling of the primary shell in the mold, thus forming shells with different thicknesses and high cracking susceptibility [5][6][7][8][9][10]. This cause is considered as the main reason for the surface cracking of this type of steel.…”

Section: Introductionmentioning

confidence: 99%

Effect of Magnesium Treatment on the Hot Ductility of Ti-Bearing Peritectic Steel

Wang

et al. 2020

Surface cracking is a major defect in the production of continuous casting slabs of peritectic steel. The difference in crystal structure between δ phase (before peritectic transformation of steel) and γ phase (after peritectic transformation) results in volume contraction, which leads to uneven cooling of mold and thus forming slab shells with different thicknesses. Then, coupled with the concentration of local stress, surface cracking occurs on slabs. In this paper, the effect of magnesium treatment on the hot ductility of Ti-bearing peritectic steel was studied, and the characteristics of solidification structure and TiN particles were analyzed. Magnesium treatment for Ti-bearing peritectic steel could significantly improve the hot ductility of continuous casting slabs by refining the original austenite structure. After the magnesium treatment, the average grain size of the original austenite of peritectic steel decreased by about 18.7%, and the size of Mg-rich TiN particles decreased by about 41%. In addition, the minimum reduction of area at the third brittle zone after the magnesium treatment was higher than 60%, and the fracture appearance changed from intergranular fracture to ductile fracture after the treatment. The contents of Mg, Ti, O, and N in peritectic steel and the cooling conditions were adjusted reasonably to promote the formation of highly dispersed Mg-rich TiN particles with a sufficient number density and a proper size in the initial solidification stage of peritectic steel, so as to induce the high-temperature δ-ferrite nucleation. Based on the fine δ structure formed by peritectic transformation, through the use of structure heredity and the pinning effect of secondary-precipitated nano TiN particles on the austenite grain boundary, a fine and dense original austenite structure could be obtained to improve the hot ductility of peritectic steel. Industrial tests showed that through the magnesium treatment, the surface cracks of Ti-bearing peritectic steel were effectively restrained, and the corner cracks of slabs were basically eliminated.

“…Some alloys are susceptible to cracking during solidification, which has attracted the interest of many researchers. One of the most important examples in industrial practice is the production of peritectic steels in continuous casting, in which frequently occurring cracks are called hot tears, including surface longitudinal cracks and internal cracks [1][2][3][4][5][6][7][8]. Surface longitudinal crack formation is caused by the brittleness of the dendritic front, and all cracks observed originate and propagate along the interdendrites in the mushy zone [6,8].…”

Section: Introductionmentioning

confidence: 99%

“…Several models have been proposed for evaluating the tendency of solidification cracks. Various methods can be divided into three categories based on liquid feeding (non-mechanical methods) [12][13][14][15][16], stress and strain (mechanical methods) [4,6,17], and a combination of the two methods. A model of feeding behavior was first proposed by Feurer [12] to analyze the crack formation between dendrites, where two parameters, SPV (the maximum flow rate) and SRG (solidification shrinkage rate), were used and a crack occurs when SPV < SRG.…”

Section: Introductionmentioning

confidence: 99%

Influence of Alloy Elements on Cracking in the Steel Ingot during Its Solidification

Guo

Wen

2019

The average steepness of |dT/d(f s ) 1/2 | on the T − (f s ) 1/2 curve were calculated during peritectic solidification, which was used to investigate the effect of alloying elements on surface longitudinal cracks of peritectic steels in the solidification process. The value of |dT/d(f s ) 1/2 | indicates the liquid feeding capacity between interdendrites during solidification, where cracks can easily occur if there is poor capacity of liquid feeding, as in peritectic solidification shrinkage. The cracking tendency as a function of carbon content was well described by the |dT/d(f s ) 1/2 | at the cooling rates of 0.5, 5, and 10 • C/s, and the influences of other solute elements on |dT/d(f s ) 1/2 | were also calculated.The results indicate that the possibility of crack occurrence increased and the maximum average steepness |dT/d(f s ) 1/2 | changed from 496.75 • C located near 0.09C wt.% to 622.14 • C near 0.11C wt.% with increasing cooling rate. The value of |dT/d(f s ) 1/2 | on the T − (f s ) 1/2 curve during the peritectic solidification can be used to analyze the solidification crack for peritectic steels.