Microstructure and Fatigue of G20Mn5 Cast Steel
Cast steels, commonly used in structural and safety parts for different applications (e.g. trains, building machines or excavators), undergo severe cyclic loadings. Cast microstructures exhibit a variety of defects depending on the foundry process and the particular component geometry. Present work analyzes the relation between post casting heat treatment and fatigue life of G20Mn5 cast steel.
G20Mn5 steel grade ingots (300x100x100 mm) were cast at Castmetal Feurs foundry (Loire – France). These ingot dimensions allow for a significant microstructure gradient. Ingots were submitted to two post casting heat treatements: normalization or quenching and tempering.
First, the microstructure was characterized by optical light and SEM observations for both heat treatments. The variation of the microstructure within the ingot volume has been quantified. Mechanical test samples (monotonic and fatigue) were cut in the center and the outer area of the ingots.
Shrinkage porosity controls fatigue life at the first order for both heat treatments. The variation of this porosity in the ingot volume was quantified for both heat treatments. The porosity increases from the ingot surface to the center. The correlation between void volume fraction and fatigue life was determined for both heat treatments.