Jominy end quench test theory

EXPERIMENT6 HEAT TREATMENT OF STEEL final microstructure, (2) thermal strain remaining in the steel after the cooling step and (3) the final grain size of the steel. (1) Microstructure: Referring to the Continuous Cooling Transformation (CCT) curve for a 1080 steel (cf. Figure 28), note that all possible cooling rates have been divided into three separate ranges. In the .Yast" range are included all rates from the extremely fast rate (almost a vertical line) to the cooling rate labeled CR which is a line tangent to the curve representing the start of the eutectoid reaction. Since all rates in this range enter directly into the martensite region without first going through the eutectoid region, 100% martensite is produced (assuming that the steels are quenched through M). In the slow range, the range bounded by the extremely slow rate (almost a horizontal line) and the cooling rate labeled CRP, the tangent to the curve for the finish of the eutectoid or reaction, belong all rates that cause the formation of 100% pearlite. Note that all of these rates pass completely through the region of the CCT curve representing the eutectoid reaction. The intermediate range, bounded by CRw and CRp includes all cooling rates that produce mixtures of pearlite and martensite, the relative amount of each depending on how close the particular cooling rate approaches either CR or FAST SLOW RATE OF COOLING Figure 29. Hardenability Curve The sequence of resulting microstructures as one passes from the very fast to the very slow rates, namely, pure martensite, a martensite-pearlite mixture, and then pure pearlite, is nicely demonstrated in Figure 29, a graph of the stee's final 68