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Tempering is controlled by diffusion and transformation depends not only on temperature also depends on the time. Than temperature is the first time is the second, but does not look down upon the effects of time, because conflict transformation occurs under certain conditions. Some changes occur to a certain temperature, such as residual austenite decomposes above 200 ℃, Fe3C carbides to 400 deg, recrystallization of ferrite in more than 600 c, and so on, all indicate that the decisive influence of tempering temperature. But all tempering can occur in a certain temperature range, in the context of the low temperature long time transformation and high temperature short time may have the same effect, which provides the basis for high instead of low temperatures back. Tempered carbon steel and low alloy steel is often divided into low temperature, temperature and tempering in three categories. Tempering temperature above Ac1 tempering law low, medium and high temperatures. The selection principle is short-time high-temperature tempering and long time microstructure and mechanical properties of low temperature tempering to achieve phase. Figure 1 is T8Mn steel quenching Hou different tempered temperature, and tempered time on hardness of relationship figure, time to logarithmic coordinates said, in most time range within hardness changes close hand line, steel of tempered time in 10s within Shi, tempered Hou of hardness that occurred fast changes, in 1~10min Shi, hardness changes relative more slow, but changes still is big, and in 1~2H within changes smaller.
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