PURPOSE: To improve the durability of an insert by providing the peripheral part of a nozzle hole bored in the bottom wall of this insert with an alloy layer excellent in machinability and thermal fatigue resistance.

CONSTITUTION: The main body 5 of the insert is formed of a heat-resistant steel. The whole area of the peripheral part of at least one side of a nozzle hole 7 bores in the bottom wall which closes one side of a cylindrical part is provided with a heat resistant alloy layer having machinability and heat resistance more excellent that those of the main body 5 of the insert. The compsn. of the heat-resistant alloy layer is preferably regulated to the one constituted of, by weight, ≤0.5% C, ≤1.0% Si, ≤2.0% Mn, 5 to 15% Ni, 10 to 30% Cr, 10 to 20% W, 5 to 25% Fe and the balance Co with inevitable impurities. The heat-resistant alloy layer is formed by cladding by welding 10 or the like. In this way, its thermal fatigue resistance is improved, so that it can withstand use as an insert for a high load swirl chamber type Diesel engine.