The Relationship Between CCT And TTT Curves Of Structural Steel

The CCT curve and TTT curve play an important role in the heat treatment of steel.They are still obtained by tedious experiments at present. The theoretical study of thesetwo curves has decades of history, but so far the systematic and complete theoreticalsystem is still not idea one.All studies mensioned can be divided into three parts. The first is the classicadditivity rule which is used in converting TTT curve into CCT curve. This result is notaccurate, so that the modified additivity rule was proposed by adding a nonlinearfunction. The generic function which is fitted using the carbon content (plain carbonsteel) or carbon equivalent (low-carbon alloy steel) of the structural steels is obtained,and thus the accurate theory model of turning TTT curve to CCT curve can be abtained.Finally, according to the experimental results, these modified models have goodaccuracy.The second is the common theory of changing CCT curve to TTT curve. A moremature theory has been choosee. We find that the deviation which is obtained bycomparing with the theoretical calculation data and the experimental results is justopposite to the first portion. Whereby, with adding the nonlinear function to normalfunction, then the calculated time of TTT curve is corrected. The general functionrelation for calculating nonlinear function coefficient is got via a similar method of thefirst portion. By verified with the experimental results, the accurate theory model ofconverting CCT curves to TTT curve is obtained, so as to, the prediction of the TTTcurve from the CCT curve of the material can be realized. These results can providetheoretical references for actual productions.