| 摘要 |
<p>A process for producing seamless steel pipes having performances at least equivalent to those of conventional seamless steel pipes produced by off-line heat treatment, which process permits pipe production and heat treatment to be conducted on one and the same production line. The process is characterized by using a billet of a low-alloy steel containing 0.15-0.50 % C, 0.1-1.5 % Cr, 0.1-1.5 % Mo, 0.005-0.50 % Al, 0.005-0.50 % Ti and 0.003-0.50 % Nb and also by comprising the following steps (1) to (5): (1) hot rolling the billet at a draft of 40 % or above in terms of cross-sectional compressibility, (2) finishing the hot rolling at 800-1,100 DEG C, (3) concurrently heating the rolled pipe immediately after the finishing under the temperature and time conditions satisfying the following relationship (a) in a concurrent heating unit: 23500 ≤ (T+273) x (21+log t) ≤ 26000...(a), wherein T represents a temperature ( DEG C) of 850 DEG C or above, and t represents a time (hr), (4) quenching the pipe immediately after being taken out of the concurrent heating unit, and (5) subjecting the quenched pipe to final tempering at a temperature of the Ac1 transformation point or below. It is acceptable to conduct intermediate heat treatment (quenching or a combination of quenching with tempering) between the steps (4 and 5).</p> |
