Effect of chromium on the thixoformability of hypoeutectic cast iron

Author(s)

Davi Munhoz Benati

• Document type: Doctoral Thesis
• Press: Campinas, SP.
• Institution: Universidade Estadual de Campinas (UNICAMP). Faculdade de Engenharia Mecânica
• Defense date: 2016-03-02

Examining board members

Eugênio José Zoqui; Andréa Madeira Kliauga; Conrado Ramos Moreira Afonso; Maria Helena Robert; Paulo Roberto Mei

• Advisor: Eugênio José Zoqui

Abstract

This work investigated the effects of chromium in the thixoformability of the Fe¿2.5%C¿1.5%Si hypoeutectic cast iron aiming to develop new semisolid alloys with low viscosity and morphological stability at the semisolid state. Fe¿2.5%C¿x%Cr¿1.5%Si alloys (x equal to 0, 3, 5 e 7%Cr) were produced by sand casting at the IMBIL company without any particular semisolid production method. The experimental procedure consisted in heating samples to the semisolid state at 50% of liquid phase (temperatures for each alloy were determined by Thermo-Calc software), held them at this temperature for 0, 30, 60 and 90s and then: 1) cool them to the room temperature to analyze the morphological stability (microstructural characterization, grain size, contiguity, chromium profile); 2) subject them to a hot compression test to analyze the rheological behaviour (maximum stress and maximum viscosity during the semisolid processing). Mechanical properties were evaluated by means of hardness tests and three point bending tests for both as cast and thixoformed samples. SEM/EDS and XRD analysis were conducted to evaluate the carbides presented in the microstructure of chromium alloyed alloys. In situ heating experiments using a Laser Scanning Confocal Microscope were conducted to evaluate the solid-to-liquid transition. Results pointed to a great stability for all alloys with minimum variations of microstructure with the increasing of holding time from 0 to 90s ¿ similar microstructures and mechanical properties were found for all samples. Rheological behaviour pointed to maximum stress in the order of 5MPa and maximum viscosity in the order of 105Pa.s, similar to the behaviour of Al-Si alloys during semisolid processing. Also, the addition of chromium has been proved to be an efficient route to improve hardness for Fe¿2.5%C¿1.5%Si hypoeutectic cast iron with no significant losses in terms of semisolid behaviour (AU)

• FAPESP's process: 11/19997-0 - Effect of chromium in the thixoformability of hipoeutetic cast iron
• Grantee: Davi Munhoz Benati
• Support Opportunities: Scholarships in Brazil - Doctorate