Die steel annealing process of complete annealing

Add Date: 2017/7/19    Clicks: 235

Complete annealing of die steel is the heating of sub-eutectoidal steel to above AC3. It is kept warm for a sufficient time to completely convert to austenite and to homogenise (or essentially homogenise) the austenite, followed by slow cooling.

The purpose of complete annealing of die steel is: to soften the die steel for later machining or plastic deformation processing; to refine the grain of the die steel and eliminate internal stresses and to prepare a suitable organisation for quenching.

In order to achieve the above purpose, the heating temperature of the complete annealing of the mould steel (highly recommended download: mould steel and mould price estimation method) is usually specified as 20~30℃ above AC3. But the die steel contains strong carbide forming elements, such as W, Cr, molybdenum and vanadium, its austenitising temperature should be appropriately increased some. This can make them form carbide can be faster into the austenite.

Die steel annealing heating and holding should be sufficient time to make austenite homogenization. The cooling rate after holding should be decided according to the purpose to be achieved. Generally mould steels take longer to fully anneal. In order to shorten the time of the process, after the insulation can be as soon as possible to the steel Cong annealing heating temperature down to slightly below the lower critical temperature. Thereafter, the choice of appropriate cooling rate slow cooling, so that the pearlite transformation temperature range into the required metallurgical organization and performance.

Sub-eutectoid steel is completely annealed and the normal organization is ferrite and pearlite. However, due to the different cooling rates, the shape, distribution and amount (%) of ferrite and pearlite are not the same. The percentage of pearlite in steel varies due to different cooling rates and the carbon content of pearlite is generally different. Because after complete or incomplete annealing of sub-eutectoid or eutectoid steels, the vast majority of carbon is present in the pearlite (the carbon content of ferrite is only 0.008% at room temperature). After annealing pearlite more, the carbon content of pearlite is low; pearlite less, its carbon content is high. Therefore, care should be taken during metallographic examination. Unless after a good complete annealing (close to the equilibrium state) of the steel, can not only rely on the number of pearlite in the field of view to compare with the steel of eutectic composition (after complete annealing for 100% pearlite), to make the style contains a number of carbon judgment.