Distribution of Phosphorus in Fe-P-C-Cu-Mo Sintered Alloy and its Effect on Propesties

In order to obtain the strengthening effect of sintered steel phosphorus is used as one of the alloying elements.In present work the distribution of phosphorus in Fe-P-C-Cu-Mo alloy containing 0.6%P and its effect on properties were studied by means of Auger electron spectroscopy, scanning electron microscopy,mechanical properties test machine etc.lt is found that when the above alloy,is sintered at 1080-1200℃ the concentration of phosphorus at grain boundaries is higher than that at intracrystalline.At above sintering temperature range the lower the sintering temperature is,the higher the concentration of phosphorus at grain boundaries will be. The effect of grain boundary segregation of phosphorus on the impact toughness is concealed by the structure of as-sintered alloy which contains a large amount of ferrite.The fracture surface of alloys sintered at 1080-1240℃ is of intracrystalline. In addition, it was found that after tempering the effect of distribution of phosphorus on the way of fracture and the mechanical properties is very great. The specimens were tempered at 200℃ the dissolved molybdenum will inhibit phosphorus segregation towards the grain boundaries and the fracture surface is of transgranular. Tempering at 400℃ decreases the impact toughness and causes intergranular fracture because during tempering at 400℃ molybdenum is in the form of molybdenum carbde (Mo₂c) and phosphorus dominantly segregates into grain boundaries. During tempering at 600℃ the trend of phosphorus segregation towards the grain boundaries decreases and phosphorus mainly precipitates on the internal pore surfaces. The specimens tempered at 600℃ will have high impact toughness and the fracture surfaces of above specimens are dimpled ductile fracture.