| 摘要 |
PROBLEM TO BE SOLVED: To produce a welded joint excellent in fatigue strength by specifying the chemical compsns. of a base metal and a weld metal and the welding conditions and limiting welding heat input. SOLUTION: By limiting the chemical compsns. of a base metal and a weld metal and welding heat input, the ferritic volume rates in the weld heat-affected zone and the weld metal heated to the temp. range of the Ac1 point to less than the m.p. are regulated to >=70%. Since ferrite is excellent in ductility (reduction of area), cracking generating resistance to the repetitions of local strains is also high, and, even in the case of the generation of fatigue cracking, it easily closes the cracking, thus its cracking propagating resistance is also high. Then, it has been found that the fatigue cracking propagating rate is slowest in the case of 30 to 300μm ferrite grain size. Moreover, the above welding heat input is limited to 3300 to 30000J/cm, and as the welding method, coating arc welding or gas shield arc welding is used.
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