Abstract
For the purpose of improving the processes of rapid heating and quenching of carbon steel, time-temperature-austenitization diagrams (T-T-A diagrams) were plotted for hypereutectoid steels (with carbon contents: 0.92, 1.28%). The dimension of specimen, preheat-treatments and experimental procedure were the same as in a previous report on hypoeutectoid steels. The experimental results are as follows:
(1) Periods of time required for starting and finishing of austenitization are almost the same and short in duration for fine-pearlite (F.P.) and spheroidized cementite (S.C.), while it takes a longer time for coarse pearlite (C.P.). S.C. structure of 0.92% carbon steel has a coarser spheroidized structure than 1.28% carbon steel, so that the finishing of its austenitization would take a much longer time than other structures.
(2) Compared with T-T-A diagrams of carbon steel (carbon contents: 0.20, 0.40, 0.69, 0.92 and 1.28%), the time required for starting of austenitization is almost the same, unrelated with carbon contents. The time required for finishing of austenitization becomes shorter with increase in the carbon content of hypoeutectoid steels, while it is almost identical in hypereutectoid steels.
(3) The austenitizing reaction is very rapid in carbon steels than generally considered. On quenching of carbon steels at a specified temperature, a very short holding time is sufficient for quenching and thereby the S.C. structure seems to be effective.
