| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide a weld joint capable of improving the fatigue crack occurrence resistance of a welding area without conducting special design or application, and exerting the resistance characteristic against fatigue crack extension in a base material part when fatigue crack goes thereinto. <P>SOLUTION: The weld joint has a chemical composition containing, by mass, 0.01-0.10% C, 0.04-0.60% Si, 0.50-2.00 Mn, ≤0.025% P, ≤0.020% S, 0.003-0.060% Al, 0.001-0.100% Ti, 0.0020-0.0120% N, 0.04-0.50% Mo, and the balance Fe with impurities. The weld joint has a mixed construction comprising the substrate of a hard part and a flexible part dispersed in the substrate, and is configured by welding the base material in which the hardness difference between the hard and flexible parts is 150 or more at Vickers hardness. The hardness of a weld heat-affected zone satisfies between each hardness of the base material and weld metal, an inequality (1): [Min(base material hardness, weld metal hardness)]×1.5≥(maximum value of HAZ hardness) äwherein Min(base material hardness, weld metal hardness) means a lower value in hardness values of the base material and weld metal; and the maximum value of HAZ hardness means the maximum value of hardness in the weld heat-affected zone}. Further, the weld joint is characterized in that the ratio, (rotation-bending fatigue strength)/(tensile strength) in the weld heat-affected zone is 0.45 or more. <P>COPYRIGHT: (C)2012,JPO&INPIT |
