Rheological Behavior of Semisolid Hypoeutectic Cast Iron Alloyed to Chromium

摘要

This paper proposes and tests new Fe-2.6wt%C-2.8wt%Cr-1.8wt%Si specially designed for thixoforming processing. Samples were heated to the semisolid state at 1195 ℃ and held at this temperature for 0,30, 60 and 90s, and then subjected to compression tests. Two-platen compression tests were carried out in order to determine the semisolid behavior. The holding time in the semisolid range simulates the industrial heating process that is time-controlled rather than temperature controlled. Morphological characterization pointed to an as cast microstructure composed by pearlite matrix plus chromium based carbides and nodular graphite and heated conditions composed by pearlitic matrix plus chromium based carbides without free graphite. The semisolid behavior indicated that at 1195 ℃ the thixoforming procedure requires a maximum stress of 2.5 MPa and maximum apparent viscosity of 4.8x10~5 Pa.s for the Os soaking time condition, 2.0 MPa and 4.6xl05 Pa.s for 30 s,1.7 MPa and 3.7xl05 Pa.s for 60 s and 1.2MPa and 3.3x10~5 Pa.s for 90 s of holding time, best condition achieved.