Effect of Silicon Content on Intergranular Embrittlement of Ferritic Spheroidal Graphite Cast Iron Suffered from Cyclic Heating

Abstract

The effect of silicon content on intergranular embrittlement of ferritic spheroidal graphite cast irons after suffer a certain number of thermal cycles is investigated. The tensile elongation tends to increase with the number of thermal cycles, and increased silicon content leads to eventual embrittlement. The fracture surface of a 2.9Si specimen changes from dimple pattern feature to intergranular fracture, whereas the fracture surfaces of both 4.0Si and 4.3Si specimens change from the brittle cleavage to intergranular fracture that following with increasing the number of thermal cycles. The intergranular cracking path will initiate and propagate through the eutectic cell boundaries due to the presence of micro-segregated inclusions that clustered in the eutectic cell boundary region. These inclusions are oxides that mainly contain magnesium, phosphorus and cerium. Experimental analysis detected that the magnesium elements not only segregated in the vicinity of eutectic cell boundaries, but also the annealed ferritic grain boundaries. However the embrittlement resulted from cyclic heating is strongly dependent on the morphology of clustered inclusions and is pertaining to the variation of silicon content. The observed magnesium-containing inclusions located in the central region of the matrix may profoundly affect the overall tensile fracture behavior of heat resistant used SG cast irons.