Steady
A steadite (or phosphite eutectic ) is a ternary eutectic consisting of the three elements iron , phosphorus and carbon (90.71% Fe + 6.89% P + 2.4% C at 950 ° C). As a rule, steadite is regarded as a structural defect in cast iron .
Emergence
The steadite is formed directly from the melt. If this is cooled down, γ mixed crystal (γ MK) separates out first . The remaining melt is now enriched with carbon and when the binary eutectic composition of iron and carbon is reached, ledeburite (γ-MK + Fe 3 C) begins to precipitate . The temperature of this reaction is shifted to lower temperatures with increasing phosphorus content (0% P = 1147 ° C). The ternary-eutectic point is reached at 950 ° C and the residual melt solidifies with the formation of the ternary eutectic, consisting of Fe 3 C + Fe 3 P + γ-MK. With further cooling, the γ-MK's ability to dissolve carbon and phosphorus decreases. At 745 ° C, the γ-MK disintegrates into pearlite (α-MK + Fe 3 C).
scope of application
Steadite is sometimes a desired structural component, as it represents a very hard phase with a hardness of 700 HBW to 800 HBW . In comparison, perlite has a hardness between 250 HBW and 350 HBW. In order to achieve an increase in wear resistance through Steadit, it must form a cohesive phosphide network.
literature
- H. Schumann, H. Oettel (Ed.): Metallography 14th edition. Wiley-Vch, Weinheim 2005, ISBN 3-527-30679-X