| 摘要 |
A steel pipe with excellent expandability, comprising, by mass%, C: 0.1 to 0.45%, Si: 0.3 to 3.5%, Mn: 0.5 to 5%, P: less than or equal to 0.03%, S: less than or equal to 0.01%, soluble Al: 0.01 to 0.8% (more than or equal to 0.1 % in case Si content is less than 1.5%), N: less than or equal to 0.05%, O: less than or equal to 0.01%, and balance being Fe and impurities, having a tensile strength of more than or equal to 600MPa and a uniform elongation satisfying following formula (1). This steel pipe, having the above described chemical composition, can be obtained, for example, by being heated at temperatures from 700 to 790 °C, then being forced-cooled down to a temperature of lower than or equal to 100°C with the cooling rate of greater than or equal to 100°C/min at the temperature from 700 to 500°C. u - el ‰§ 28 - 0.0075 �¢ TS
wherein u-el means uniform elongation (%), and TS means tensile strength (MPa). |
