Metallography of SC60 Steel (Aged at 450℃)
Metallography or material microscopy is the technique used to evaluate the structures of metals and alloys by examining small samples of the material under a microscope. It is often used as a diagnostic tool for alloy quality, material defect investigations, or product failure analysis. The following discussion discusses the metallographic examination of SC60 steel aged at 450°C.
The sample of the SC60 steel is embedded in the epoxy resin and then polishing is done. The nature of the polishing process is delicate and involves the reduction of porosity, introduced by hand polishing, to obtain an acceptable surface finish. The surface must be even and without scratches. A polishing machine is used to abrade the surface with successively finer abrasive powders, followed by lapping films. Generally, 5 μm alumina paste is used to obtain a final surface finish of ≤1 μm.
The polishing process is followed by the electrolytic etching using the Langford’s Reagent. The surface of the etch is then examined under the microscope. The metallographic examination has revealed the presence of pearlite, ferrite, and bainite microstructures in the SC60 steel sample. The pearlite microstructures are observed in thin layers of uniform microstructure with a small amount of ferrite as a matrix. The ferrite microstructures are typically coarse and irregular. The bainite microstructures appear as a mixture of ferrite and cementite.
The examination also shows that the SC60 steel has a very good microstructural stability in comparison to the as-cast material. The grain size of the SC60 steel has significantly decreased due to the aging heat treatment. The average grain size is measured to be around 8.5 μm. Also, after the aging heat treatment, the matrix of the material has changed from a lower carbon ferrite to a high carbon ferrite which is responsible for the hardness and strength of the material.
The SC60 steel also showed martensitic precipitates at the grain boundaries. The martensite is attributed to a rapid cooling of the material after the heat treatment. The martensite is observed in a more refined form and increases the strength of the material by increasing the number of carbide particles at the grain boundaries.
In conclusion, the metallographic analysis suggests that the SC60 steel with an aged heat treatment of 450°C is characterized by the presence of pearlite, ferrite, and bainite microstructures, as well as martensitic precipitates at grain boundaries. The grain size has decreased due to the heat treat, and the material retains good microstructural stability. The presence of higher carbon ferrite gives the material good hardness and strength. The material can be used in applications where these properties are desired.
