The production of ADI
The material ADI gains ist strength from a special form of heat-treatment. This heat-treatment process is shown in the following diagram: A-B: Heating stage to 840-950° C
B-C: Austenitizing phase - soaking stage for the saturation of carbon by the austenite
C-D: Quick transfer to a salt bath
D-H: Ausferritizing by isothermal soaking between 250 - 400° Celsius after H: Cooling to room temperature.
the following diagram shows the hardening property of the material which is dependant upon temperature plotted against time:
The cooling time can be extended for thicker components through the alloying with Cu, Ni and Mo, thus pushing the perlite peak to the right.
A sufficiently long soaking time in the ausferrite areas must be maintained so that the austenite can stabilize.
Requirements for the safe production of cast parts from ADI:
- The alloy composition must be matched to the quenching conditions in the hardening shop - the most important influencing factor on this is the competence of the annealing shop and is command over the process!
- he decisive element for the establishment of the hardening parameters (e.g. its duration) is always the slowest area of a part to cool down. N.B.: Usually, but not always, also the thickest part.
- A separate test bar is only of limited significance. Evidence of grain structure and properties (such as hardness or ductility) should be gained from the component itself.
- The founder must adhere to his prescribed analysis.