Effect of boron in cast iron

Boron, mostly considered a residual element, has started to cause issues in the cast iron foundries by causing a decrease in the strength of pearlitic gray and ductile iron castings. Because of the increase in the use of boron-added steel scrap from automotive steel and a lack of agreement on the critical levels of boron in cast iron, foundries are facing difficulties in controlling the microstructure of gray iron castings when boron is present. The current investigation was designed to analyze the effects of boron in cast irons and predict a mechanism to understand its effects with a vision of finding ways to mitigate and/or control the amount and effect of boron in cast iron. Initially, an experimental study was performed to understand the effect of boron in gray cast iron at four different levels of boron and two carbon equivalents. The study showed that boron acts as a strong carbide stabilizer and ferrite promoting element. The effect of boron on mechanical properties however was seen to vary with carbon equivalent. The experiment was then modified to understand the mutual effect of boron with nitrogen, titanium, and tin to search for a way to mitigate the boron effects. It was observed that nitrogen can help mitigate the effect of boron in gray iron whereas, titanium addition can enhance it. A parallel study to understand the effect of boron in ductile iron was also performed. Boron in ductile iron degrades the graphite sphericity making it into compacted graphite, which led to a deterioration in mechanical properties and significant carbide precipitation, even in casting section sizes as thick as 30mm. The results from the studies indicate that the effect of boron on spherical graphite in ductile iron can be much more severe than in gray iron --Abstract, page iv