Abstract: A case hardening steel for warm forging at a forging temperature of 850° C. to 1100° C. The case hardening steel has a chemical composition including: C: 0.15 to 0.23%; Si: 0.60 to 0.95%; Mn: 0.60 to 1.20%; P: 0.035% or less; S: 0.035% or less; Cr: 1.50% or less (excluding 0%); Al: 0.050% or less; Ti: 0.01 to 0.05%; B: 0.0005 to 0.0050%; N: 0.0020 to 0.0200%; Mo: 0.20% or less as an optional element; Nb: 0.01 to 0.05% as an optional element; and Fe, and satisfies Formulae 1 and 2: Formula 1: 90??120*C+20.1*Si?5.3*Mn?8.5*Mo+96?80, Formula 2: 160?40*Si+39*Mn+10*Cr+30*Mo+84?145.

Abstract: A method for producing a resin part includes: preparing an intermediate body comprising a first member and a second member, the first member containing a resin; and welding the first member with the second member by performing scanning of the intermediate body with a first laser beam and a second laser beam. In the welding of the first member with the second member, the scanning with the first laser beam and the second laser beam is performed in a state in which a center of a second spot is located on a rear side in a direction of the scanning with the first laser beam and the second laser beam as compared to a center of a first spot while at least a part of the first spot and at least a part of the second spot overlap with each other.