This documentation describes the development of a prototype expert system that gives advice on the material to be selected for an application if the service condition of hardenability is given as input to the system. Some features of the system and system design and implementation in G2 are presented. We conclude that the expert system can be extended with knowledge on more service conditions.
Materials for any process construction (i.e. pipelines, high pressure distillation columns etc.) need specific properties such as strength, toughness and corrosion resistance, etc. to satisfy service requirements. For example. the materials used for building a gas pipeline system must have enough strength to withstand a high pressure of 1,000-3000 psi. If the gas contains H2S and/or CO2. it should also have corrosion resistant properties. The design or selection of material for a specific application involves searching for a material having the optimum properties required for the application. This task is usually done by an expert in the field. However it can be performed by a non-expert if a good decision support system is available. We have built such an intelligent advisory prototype expert system for material design using G2
One of the classes of materials which is extensively used for a variety of applications is steel. Basically steel is an alloy of iron (Fe) and carbon (C) along with other elements like manganese (Mn). chromium (Cr). molybdenum (Mo). silicon (Si). nickel (Ni). etc. Alloying elements in steels enhance the properties of steels depending on their type and proportion in the steel. Steel is generally classified on the different amounts of alloying elements in it.
Steels arc prepared by melting different raw materials in furnaces and then refining to obtain steel of the proper grade containing the specified quantities of alloying elements. The molten steel is then cast to a solid state. The as-cast steel is normally not useful for direct service applications due to non-homogeneity and high thermal stresses developed during solidification. Instead it is usually given a combination of heating and cooling operations, timed and applied in the solid state in a way that will produce desired properties.
The first step in the heat-treatment of steel is to heat the material to some temperature above the critical range of 750 °C to 850 °C and then cooled in a desired method such as air cooling oil quenching water quenching. etc. The properties obtained in the material depend on the cooling rate. Now since the center of the material component geometry has the slowest cooling rate, the choice of the cooling medium should result in a cooling rate at the center above the critical cooling rate in order to produce the required properties at the center [Avner 1987].
For example, the hardness (which is directly related to cooling rate) of the heat-treated component will be minimum at the center because of the minimum cooling rate at this point.