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How to Prevent Reticulated Ferrite and Reticulated Cementite

Hypereutectoid carbon steel, high-carbon alloy tool steel heating temperature is too high during annealing heat treatment, cooling rate is too slow, will precipitate network cementite (carbide) along the austenite grain boundary. The initial forging temperature of the blank is too high, and the cooling rate after forging is too slow, and network carbides will appear. In the current production, the heating temperature and cooling rate should be strictly controlled. If the network structure appears, it can be heated to above Accm to keep it warm, and then normalized after air cooling. If the grains are still coarse after normalizing, spheroidizing annealing should be carried out. It can also be re-annealed after quenching and tempering.

Hypoeutectoid steel mesh ferrite is also formed due to the high heating temperature and precipitation at the grain boundary during slow cooling. When 45 steel is fully annealed, if the temperature is high and the time is too long, the ferrite will be distributed along the grain boundary, and at the same time, needle-like or massive ferrite will be distributed into the grain boundary to form a network structure in the Widmanstatten state. In addition to technological measures, it can also be eliminated by complete annealing. Due to improper annealing process of 08 steel raw materials, during slow cooling, three-time network cementite precipitates on the ferrite grain boundary, which causes the steel to become brittle and stamping cracks, which can be eliminated by normalizing. 15MnB steel is normalized at 950℃, the ferrite produced is distributed along the grain boundary, and the grains are coarse. As manganese reduces the Ac1 point, the steel is overheated seriously and the crystal grains increase sharply. The B element can promote the acicular distribution of ferrite, and at the same time, it does not solid-solution strengthen ferrite. B will also reduce the temperature of pearlite to ferrite transformation, so the normalizing temperature should be strictly controlled. It can be eliminated by spheroidizing annealing heat treatment. Too high normalizing temperature of 40Cr steel will also cause the ferrite to be distributed in a network.