Annealing is an umbrella term used in heat treating, which refers to the process of raising the temperature and controlled cooling of a material to make it more ductile, reduce its hardness and generally make it more amenable to machine. The annealing technique is applied to castings primarily to improve machinability by softening the material. This heat-treating process is used to turn pearlite into ferrite. Whereas the annealing of steel only coalesces lamellar pearlite into granular pearlite, the annealing of cast iron results in a completely ferrite base structure. The annealing temperature in this case is just above the eutectoid interval at around 720°C. Annealing heat treatment is carried out for the following grades:
Stress relieving heat treatment is a process that is used to reduce internal stresses in the structure of material during further machining to applications with high precision requirements and narrow tolerances. It is not practically possible to manufacture a cast product without internal stresses owing to different rates of cooling within the product. The size and direction of these internal stresses are dependent on the geometry of the cast components, their design, and the processes conditions during casting. Stress relieving heat treatment is done at temperature between 500-550°C, which are below the area of eutectoid transformation, so an unwanted change in structure and therefore a change in the mechanical properties during the heat treatment process is avoided.
Stress relieving can be carried out for GJS- and GJL-grades upon request.