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Metal Casting Technologies : September 2007
74 www.metals.rala.com.au TECHNICAL FEATURE in austenite-liquid region, where a1=0.057 and a2=0.11 and T represents the temperature given as input and 0.17 and 0.53 are the starting values, which also varies according to the region. A looping structure has been developed which makes use of this formula and assigns X1 and X2 values for different temperatures. From X1 and X2 values, composition percentage can be calculated for the given input using lever rule. This method is applicable for all the curves in the phase diagram provided their carbon content variation (i.e. a1 and a2) differs. Similarly the role of temperature for change in composition has been computerized. For this a simple mathematical approach has been carried out, which can be illustrated with the same diagram (Fig.1). It is known that for a given temperature X1 and X2 values are manipulated by the system using the logical approach. Here at temperature 1300°C X1=1.253 and X2=2.62. This temperature acts as the maximum temperature for both these carbon contents. Similarly the maximum temperature for the carbon content given as input can be calculated by the formula developed. This maximum temperature is calculated for the given carbon content for both left and right hand side curves as shown in the Fig. 2. Max T=1490-((carbon content-0.17)/0.057)*10; [left curve] [Eq.3] Max T=1490-((carbon content-0.53)/0.11)*10; [right curve] [Eq.4] Taking the maximum temperature into account, the system compares the input temperature with it and gives the corresponding composition percentage. Let us consider an example from the above austenite-liquid curve Fig. 2. With the given input, the maximum temperature for it is calculated using the equation 3 and 4. Here 0.85 is the carbon content and 1400°C is the temperature given as input. From Fig. 3, it is clear that maximum temperature corresponding to the input carbon content is 1370°C and 1460°C. So if the input temperature is between these temperatures it represents a composition of austenite and liquid [Fig.4]. Figure 2. X1 and X2 values for the given temperature Figure 3. Maximum temperature for given input Figure 4. Flowchart for the role of temperature in determining the composition Figure 5. Carbon content variation in Ferrite and Austenite region