The influence of cooling rate on the structure of martensite nickel-chromium cast iron

摘要

The objective of this work was to evaluate the influences of the mould material and mould construction on microstructural characteristics and casting hardness of mill balls made of martensite nickel-chromium iron. This work is part of the investigations on the production of grinding bodies (balls) made of martensite white iron, type Ni-hard, that were aimed at improving the technological process by introducing combined moulds (metal-shell like core). The basic intention of using a combined mould was to achieve faster cooling of the metal in the cavities where the balls are formed than in a charging system. The use of a sand coating around the charging system, produced by the shell method enables a sand casting, without the inner faults that appear as the result of metal shrinkage. Since the thermo-physical properties of the mould have a significant influence during the crystallization and solidification of the cast product, through their inflence on metal cooling rate, one of the problems was the choice of the optimum material for the mould. Our choice, based on all techno-economic parameters, was a mould with insertions made of stell, grey cast iron and copper, enabling the cheaper replacement of the part exposed to the influences of casting.