| 摘要 |
PURPOSE:To obtain a titled steel pipe by heating the steel pipe which is reheated during the course of hot rolling and is finally rolled to specific temp. prior to direct hardening thereby forming sufficient hardened structure even with the steel pipe of relatively low carbon equiv. CONSTITUTION:A steel pipe which is reheated during the course of hot rolling of a low alloy seamless steel pipe of 0.15-0.45% carbon equiv. and is finally rolled is again heated or held to or at the temp. in the austenite area and is then subjected to quench tempering heat treatments. Here, if the carbon equiv. given by the formula is below the lower limit, necessary strength cannot be obtained and in excess of the upper limit, weldability is degraded. In the stage of rolling such low-alloy steel ingot by a seamless pipe making method, the pipe is subjected to final rolling for the purpose of improving the out of roundess of the steel pipe, but if there are variations in the temp. in the part of the steel pipe, the accuracy of shape cannot be obtained; therefore, the steel pipe is reheated during hot rolling. In order to obtain sufficient hardened structure of the steel pipe in this stage, the pipe is reheated or held to or at the temp. in the austenite area. Thereafter, the steel pipe is subjected to direct hardening heat treatments. |
