| 摘要 |
PROBLEM TO BE SOLVED: To provide a steel pipe for a machine structure which has improved machinability, in particular, an improved cutting machinability of the inner surface of the steel pipe, by controlling a metallographic structure without containing an expensive alloy, and to provide a manufacturing method therefor. SOLUTION: The steel pipe for the machine structure superior in machinability includes controllingα[%] defined by the expression:α=830-270C-90Mn-70Cr-83Mo to 580 to 640, wherein C, M, Cr and Mo represent respective contents of the elements; and has the metallographic structure which comprises tempered bainite of 20 to 70% by an area rate, ferrite of 25% or less (including 0%) by an area rate, and the balance tempered martensite. COPYRIGHT: (C)2008,JPO&INPIT
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