| 摘要 |
Pipe-swelling can be prevented by piercing-rolling a high-alloy steel billet heated to a temperature range from 900 to 1250° C. with a piercing mill equipped with main rolls having a surface roughness Rmax of 150 to 500μm. A ratio (the gap WG of guide rolls/the gap WR of the main rolls) is preferably at 1.10 to 1.20. The difference (θP−θR) is preferably set at 0 to 3.0°, whereθR is an angle between an exit-side face of each of the main rolls of the piercing mill and the pass line; andθP is an angle between a rolling face of the piercing plug and the pass line.
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