MFLT was done for the 12Cr1MoVG blank bar in accordance to standard GB/T 31212-2014,the detection results showed that the proportion of the long crack with the depth more than 0.30 mm was 15％around.The analysis showed that the corner crack of the billet was the main reason which caused the long crack of the blank bar surface.The problem was settled through increasing tundish molten steel overheat temperature from 15-30 ℃ to 35-45 ℃ and increasing casting speed from 0.85 m/min to 0.95 m/min and adopting weak cooling and uniform cooling of billet etc.The long crack proportion was reduced to below 3％after adopting the technology improvements.
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