PHOSPHORUS is usually added with sulphur to improve machinability. The Phosphorus present in Austenitic stainless steels increases strength. However, it has a detrimental effect on corrosion resistance and increases the tendency of the material to crack during welding.In most of cast iron will contain between 0.10 and 0.90 percent phosphorus originating from the iron ore.
Most of the phosphorus combines with the iron to form iron phosphide (Fe3P). This iron phosphide forms a ternary eutectic with cementite and austenite (pearlite at room temperature). The ternary eutectic is known as steadite and is a normal feature in the microstructure of cast irons. Steadite is relatively brittle, and with high phosphorus content, the steadite areas tend to form a continuous network outlining the primary austenite dendrites.
The condition reduces toughness and makes the cast iron brittle, so that the phophorus content must be carefully controlled to obtain optimum mechanical properties. Phosphorus increases fluidity and extends the range of eutectic freezing, thus increasing primary graphitization when the silicon content is high and phosphorus content is low. It is therefore useful in very thin casting where a less fluid iron may not take a perfect impression of the mold. If the silicon, sulphur, manganese and phosphorus contents are controlled at proper level, the only remaining variable affecting the strength of a pearlitic gray iron is the graphite flakes. Since graphite is extremely soft and weak, its size, shape, and distribution will determine the mechanical properties of the cast iron. It is the reduction of the size of the graphite flakes and the increase in their distribution that have accounted for the improvement in the quality of gray cast iron.
ORIGIN: CHINA
ADVANTAGE:
• High Recovery
• Consistent Quality
|
