Mechanical reduction can mitigate most internal defects. However, internal cracks are more frequently observed in high-carbon steels than in low-carbon steels following the mechanical reduction process. This study presents theoretical calculations of the mechanical properties of low-carbon steel Q235 and high-carbon steels U71Mn and GCr15 to evaluate the mechanism of internal cracking in high-carbon steels. The calculations indicate that U71Mn and GCr15 exhibit lower critical strains and broader mushy zones compared to Q235, thereby increasing the crack sensitivity of high-carbon steels. The mechanism of internal cracking in high-carbon steels is further examined through microstructural analysis. The results reveal that internal cracks in U71Mn and GCr15 typically form in the columnar crystal zone. Elevated concentrations of carbon, phosphorus and sulphur are often found near the final solidification zone, which weakens the grain boundaries and promotes crack propagation along them.
YangEJJiangMHouZW, et al.Improvement of internal quality for continuous casting slab by heavy reduction at solidification endpoint. China Metall2020; 30: 23–28.
2.
ChenLSongBChenTM, et al.Control countermeasures of center porosity and shrinkage in 45 steel continuous casting bloom. Iron Steel2018; 53: 49–54.
3.
ZhaoXKZhangJMLeiSW, et al.The position study of heavy reduction process for improving centerline segregation or porosity with extra- thickness slabs. Steel Res Int2014; 85: 645–658.
4.
LiuYX. Reason of formation harmful effect and removal of band structure in low carbon alloy steel. Heat Treat Met2000; 000: 1–3.
5.
XingLDGuCLvZY, et al.High-temperature internal oxidation behavior of surface cracks in low alloy steel bloom. Corros Sci2022; 197: 110076.
6.
LuoSZhuMJiC. Theoretical model for determining optimum soft reduction zone of continuous casting steel. Ironmak Steelmak2014; 41: 233–240.
7.
ZhaoJPLiuLRaoJY. Effect of solidification reduction process on center compactness of continuous casting bloom. Iron Steel2018; 53: 30–36. 44.
8.
ByrneCTercelliC. Mechanical soft reduction in billet casting. Steel Times Int2002; 26: 33–35.
9.
HanZWChenDFFengK, et al.Development and application of dynamic soft-reduction control model to slab continuous casting process. ISIJ Int2010; 50: 1637–1643.
10.
JiCLuoSZhuMY. Analysis and application of soft reduction amount for bloom continuous casting process. ISIJ Int2014; 54: 504–510.
11.
ZhuGSWangXHYuHX, et al.Analysis on internal crack in continuous casting slab. J Iron Steel Res Int2004; 16: 43–46.
12.
MatsumiyaTItoMKajiokaH, et al.An evaluation of critical strain for internal crack formation in continuously cast slabs. Trans Iron Steel Inst Japan1986; 26: 540–546.
13.
WangBZhangJMXiaoC, et al.Analysis of internal cracks in continuous casting slabs with soft reduction. High Temp Mater Processes2016; 35: 269–274.
14.
HuPZhangHZhangXZ, et al.Application of a corner chamfer to steel billets to reduce risk of internal cracking during casting with soft reduction. ISIJ Int2014; 54: 2283–2287.
15.
WuHJLeiCXuCJ, et al.Effect of final electromagnetic stirring on internal thermal stress, strain and cracking of continuous casting bloom. ISIJ Int2023; 63: 1373–1382.
16.
ZongNFHuangJLiuJ, et al.Analysis of internal cracks in high carbon casting bloom induced by soft reduction process and its improvement using numerical simulations and industrial experiments. Metall Res Technol2020; 118: 02.
17.
ZongNFHuangJLiuY, et al.Controlling centre segregation and shrinkage cavities without internal crack in as-cast bloom of steel GCr15 induced by soft reduction technologies. Ironmak Steelmak2021; 48: 944–952.
18.
ZongNFZhangHLiuY, et al.Analysis on morphology and stress concentration in continuous casting bloom to learn the formation and propagation of internal cracks induced by soft reduction technology. Ironmak Steelmak2019; 46: 872–885.
19.
WonYMHanHNYeoTJ, et al.Analysis of solidification cracking using the specific crack susceptibility. ISIJ Int2000; 40: 129–136.
20.
ClyneTWWolfMKurzW. The effect of melt composition on solidification cracking of steel, with particular reference to continuous casting. Metall Trans B1982; 13: 259–266.
21.
WangPChenLTangQW, et al.Propagation form of internal cracks induced by continuous casting soft reduction and control strategy for internal quality. J Iron Steel Res Int2024; 31: 622–633.
22.
GaoYBBaoYPWangM, et al.Investigation on the effect of reduction process on internal quality of high carbon steel billet and its evolution in as-rolled wire rod. Metall Res Technol2024; 121: 06.
23.
GaoYBaoYPWangY, et al.Development of a novel strand reduction technology for the continuous casting of homogeneous high-carbon steel billet. Steel Res Int2023; 94: 94. DOI: https://doi.org/10.1002/srin.202200740
24.
JiangDQSunSJWuH, et al.Influence of mechanical reduction amount on internal quality of continuous casting billets by thermal and numerical simulation. J Iron Steel Res Int2023; 30: 1234–1243.
25.
WuGRChenTCChenHY, et al.The crack control strategy is influenced by the continuous casting process of Cr12MoV steel. Steel Res Int2024; 95: 95. DOI: https://doi.org/10.1002/srin.202400101
26.
KimK-hYeoT-JOhKH, et al.Effect of carbon and Sulfur in continuously cast strand on longitudinal surface cracks. ISIJ Int1996; 36: 284–289.
27.
LankfordWT. Some considerations of strength and ductility in the continuous-casting process. Metall Trans1972; 3: 1331–1357.
28.
WonYMYeoTJSeolDJ, et al.A new criterion for internal crack formation in continuously cast steels. Metall Mater Trans B2000; 31: 779–794.
29.
LiXBDingHTangZY, et al.Formation of internal cracks during soft reduction in rectangular bloom continuous casting. Int J Miner Metall Mater2012; 19: 21–29.
30.
ZongNFZhangHLiuY, et al.Analysis of the off-corner subsurface cracks of continuous casting blooms under the influence of soft reduction and controllable approaches by a chamfer technology. Metall Res Technol2019; 116: 10.
31.
LinQYJiangHJZhuMY. Analysis of reduction parameters of dynamic soft reduction in continuous casting. J Mater Metall2004; 3(4): 261–265.
32.
SuzukiKMiyamotoT. Study on the formation of “A” segregation in steel ingot. Trans Iron Steel Inst Japan1978; 18: 80–89.
33.
SuzukiKTakahashiKNishiT, et al.Mechanical properties of the slabbing mill roll materials at room and elevated temperatures. Tetsu-to-Hagane1975; 61: 371–387.
34.
ZhaoJLiuLFanJ, et al.Study and application of soft reduction technology in continuous casting. Cailiao Daobao/Mater Rev2016; 30: 57–61.
35.
SunZQXuQTTaoLQ, et al.Reagent and preparation method for low magnification test of solidification microstructure and dendrite corrosion of continuous casting billet. 2011.
36.
HH. Inner crack formation in continuous casting of steel: stress or strain criterion: Steelmaking Conference Proceeding. 1994.
