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Effect of the cooling rate on the mottled cast iron microstructure designed for the mill rolls

Krawczyk J., Pacyna J.

Metallurgy and Foundry Engineering

2009

Vol. 35, no. 2

101-110

The influence of the cooling rate changes on the mottled cast iron microstructure was described in the paper. The investigated material constituted mottled cast iron, spheroidal, chromium-nickel. This cast iron, according to currently binding standards was marked GJS-HV300(SiCrNi2-3). The microstructure was described both qualitatively and quantitatively. The discussion of the formation mechanisms and their influence on the morphology of structural components and phases was conducted. The heat treatment was performed in such a way as to obtain either a pearlitic or a bainitic matrix as well as a different morphology of lederburitic cementite and graphite precipitates for the same matrix.

W pracy opisano wpływ zmian w szybkości chłodzenia na mikrostrukturę żeliwa połowicznego. Badanym materiałem było żeliwo połowiczne, sferoidalne, chromowo-niklowe. Żeliwo to wg obecnie obowiązujących norm oznaczono GJS-HV300(SiCrNi2-3). Mikrostruktura została opisana jakościowo i ilościowo. Przeprowadzono dyskusję mechanizmów tworzenia się oraz ich wpływu na morfologię składników strukturalnych i faz. Obróbkę cieplną wykonano tak, aby w mikrostrukturze uzyskać osnowę perlityczną lub bainityczną oraz dla takiej samej osnowy różną morfologię wydzieleń cementytu ledeburytycznego i grafitu.

Effect of the microstructure on tribological phenomena occurring on the surface of a mill roll made of SA5T cast iron (GJSL-HV600 - GJSL-330NiMoCr12-8-3)

Krawczyk J.

Archives of Foundry Engineering

2008

Vol. 8, iss. 2

170-174

This paper deals with the role of the microstructure in the tribological wear processes occurring in a cast iron mill roll. For this purpose, a piece of a broken roll, made in Italy, was collected. Its microstructure consisted of modular graphite, transformed ledeburite and a matrix composed of bainite and martensite. Metallographic investigations were performed on the roll working surface in conjunction with metallographic tests effected within its surface layer. There was established the relation between the microstructure of the roll and the process of its tribological wear. The following was ascertained: micro-shrinkages or graphite precipitations nearby the working area cause cracks between those places and the working area; in the surface layer, cracks occur usually in the zone of ledeburitic cementite. At places of considerable precipitations of ledeburitic cementite, the tribological wear intensity of the roll is lower. A banded layout of precipitations of ledeburitic cementite facilitates a selective spalling of some parts of the roll material. The results of this study allow broadening the data base related to the effect of the microstructure on tribological wear of mill rolls, which in future will permit one to design their proper microstructure of cast iron mill rolls.