This chapter discusses the processes involved in the calculation of cooling and heating curves and the estimation of austenitizing time. The chapter discusses the transformation of austenite, describing nucleation and growth rates. The chapter examines the calculation of the amount of martensite and retained austenite, and hardenability calculations. It reviews models for tempering of steels, estimation of mechanical properties, the hardness of martensite, and factors to consider to be able to calculate the residual stresses. It provides information on Kirkaldy’s model used for calculating Jominy curves. Tables for calculating the temperature distribution in steels as a function of time...