TABLE OF CONTENTS Steels are useful materials because of their sophistication and low cost. The many phase transformations and processing variables associated with them can be exploited to achieve a very large range of desirable properties. For example, there are reliable commercial alloys available for the whole range of strength from 250 up to 5500 MN m ?2 The very complexity which makes steels so useful also makes their design difficult. This chapter illustrates how the design process can be enhanced using models, which can be of many different kinds. Blind procedures, such as regression analysis, are one type which deal with the recognition of patterns in experimental data. Models based on firm physical principles have predictive capabilities. A practically useful model is always one which is a compromise between these two extremes.
The general method for constructing a model is summarized in the flow chart presented in Fig. 14.1. The first stage consists of an identification of the problem and a consideration of the likely physical mechanisms involved. A model should be constructed using the most advanced theory available and after making a thorough assessment of the published literature. This usually identifies areas where adequate knowledge does not exist, in which case approximations must be made in order to progress. The lack of theory or data can be investigated further as resources become available, but need not unduly hinder the formulation of a model. In practice, this means that the target precision has to be chosen to suit the...
