Effects of Micro-Alloying Elements on Microstructure, Element Distribution and Mechanical Properties in Gray Irons

Abstract

This paper elucidates the effects of micro-alloying (Cr, Mo, rare earth and Ag) on the microstructure, element distribution and mechanical properties including Brinell hardness and tensile strength in cast gray irons. Experimental results show that the morphology of main graphite transforms from type C to type A and is refined obviously in the modified gray iron after micro-alloying. The pearlite content is also reduced, and the pearlite interlamellar spacing is smaller in the modified gray iron. The distribution and segregation of micro-alloying elements have determined the change of microstructure. More Cr and Mo atoms are tended to dissolve in pearlite and are likely to replace Fe atoms to form M3P in final solidified phosphorus eutectic regions. Meanwhile, segregation of rare earth metals toward boundaries should be considered into roles in refining graphite and pearlite interlamellar spacing. No obvious enrichment of Ag is found in matrix or at grain boundaries from experimental EPMA results. Multiple micro-alloying in gray irons improves the hardness and tensile strength at room temperature and at 700 °C by modifying the microstructure as well. Finer graphite and smaller pearlite interlamellar spacing results in better hardness, tensile strength and elongation in modified gray irons.