GRATE BAR FOR SINTERING MACHINE

PROBLEM TO BE SOLVED: To decrease the reduced thickness due to corrosion and increase life by providing a chromium and iron carbide layer of high chromium concentration on a surface. SOLUTION: A chromium and iron carbide layer of high chromium concentration is provided on the surface of the grate bar 1 of a sintering machine made of high chromium cast iron. In order to form such a layer, a chromium cementing process which is generally called a chromising process is carried out. On performing this process, a metallic semi-closed container is first filled with a cementing agent having a prescribed composition. A material to be processed, such as the grate bar 1 with a prescribed shape made of an iron steel material such as a high chromium cast iron of a prescribed composition is embedded in the cementing agent. Then, when the grate bar 1 is heated for a prescribed time at a prescribed temperature while inactive gas such as argon, reducing gas is supplied to the container, a very hard chromium/iron carbide layer having prescribed surface chromium concentration, layer thickness and surface hardness is formed. The reason why the semi-closed container is used is that the thermal decomposition gas of air and ammonium chloride in the container is released outside.