The die steel 4Cr5MoSiV1 was produced with the path of hot metal + scrap→100 t EAF→double LF→ double VD→ round billet continuous casting (section Φ 500 mm)→ step reheating furnace→ 950 rolling mill

in the special steel division new district of Shandong Steel. There are defects in the detection of individual batches die steel 4Cr5MoSiV1. By using the ultrasonic testing to locate the defect location

and analyzing with the way of Metallographic analysis and scanning electron microscopy (SEM)

finally confirmed the center defect and the rolling compression ratio small are the main reasons of the testing substandard batch of steel 4Cr5MoSiV1

and the corresponding improved measures are put forward.