Effect of phosphorus on intermediate temperature embrittlement of high silicon

Spheroidal graphite cast irons can be susceptible to intermediate temperature embrittlement at temperatures between 350°C and 500°C. It has been reported that the corresponding loss of ductility increases with the sulphur and magnesium content of the alloy, but can be eliminated by a sufficiently low ratio of magnesium to phosphorus content.

Using a low-sulphur, low-phosphorus alloy, previous work clarified the role of magnesium and suggested that small MgO precipitates developing at grain boundaries due to diffusion of oxygen from the atmosphere contributed to the generation of brittleness. The present work aimed to clarify how the addition of phosphorus could effect this process and make spheroidal graphite cast irons immune to brittleness at intermediate temperatures.