PURPOSE: To obtain the titled insert with superior oxidation resistance and thermal fatigue resistance by using a heat resistant steel for forging having a martensite structure contg. a little ferrite and a specified composition consisting of C, Si, Mn, Ni, Cr, Mo and Fe.

CONSTITUTION: This insert for a precombustion chamber with superior oxidation resistance and thermal fatigue resistance is made of a heat resistant steel for forging having a martensite structure contg. a little ferrite and a chemical composition consisting of 0.25W0.4% C, 0.5W1.5% Si, ≤1% Mn, 0.2W1% Ni, 15W18% Cr, 0.5W1.5% Mo and the balance Fe with impurities. The insert is hardly cracked even when it undergoes repeated heating at ≤ about 850°C during use, so the service life can be remarkably prolonged.