Abstrakt
The paper describes influence of rare earth metals (REMs) on G20Mn5 cast steel microstructure and mechanical properties. The cerium
mixture of the following composition was used to modify cast steel: 49.8% Ce, 21.8% La, 17.1% Nd, 5,5% Pr and 5.35% of REMs. Cast
steel was melted in industrial conditions. Two melts of non-modified and modified cast steel were made. Test ingots were subject to heat
treatment by hardening (920°C/water) and tempering (720°C/air). Heat treatment processes were also performed in industrial conditions.
After cutting flashes off samples of cast steel were collected with purpose to analyze chemical composition, a tensile test and impact
toughness tests were conducted and microstructure was subject to observations. Modification with use of mischmetal did not cause
significant changes in cast steel tensile strength and yield strength, while higher values were detected for fractures in the Charpy impact
test, as they were twice as high as values for the data included in the PN-EN 10213:2008 standard. Observations performed by means of
light and scanning microscopy proved occurrence of significant differences in grain dimensions and morphology of non-metallic
inclusions. Adding REMs resulted in grain fragmentation and transformed inclusion shapes to rounded ones. Chemical composition
analyses indicated that round inclusions in modified cast steel were generally oxysulphides containing cerium and lanthanum. In the paper
the author proved positive influence of modification on G20Mn5 cast steel mechanical properties.
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