1, spring sheet brittleness
Brittleness is one of the common defects of reeds. It can be divided into two types: heat treatment brittleness and hydrogen embrittlement after galvanizing. Microscopically, the fractures of hydrogen embrittlement were found to be along the crystal, dimples, secondary cracks, etc., and hairline and hydrogen micropores were observed on the fracture surface.
1) Heat treatment brittleness
Spring steel has a tendency of heat sensitivity and temper brittleness, and its tempering temperature is often in the first type of temper brittleness and the second type of temper brittleness. If it cannot be tempered, insulated and cooled in time, it will make the spring The sheet is brittle.
Solution: Control the tempering temperature and timely temper, heat and cool.
2) Hydrogen embrittlement
Hot-dip galvanizing tends to increase fragility of the reed. This is because prior to galvanizing, pickling must be performed to remove the scale, which causes a part of hydrogen to penetrate into the coating and the base metal, weakening the bond between the metal crystal atoms at the grain boundary. Force and generate internal stress to make the reeds brittle.
Solution: Control the pickling time and temperature, standardize the galvanizing process, and after galvanizing, hold the hydrogen removal process at 180 °C for several hours, thus reducing the brittleness of the plating and structure of the reed.
2, heat treatment crack
The heat treatment generally causes a small probability of reed crack defects. If cracks occur, the causes are: improper heat treatment process, improper tooling, and operator error. Improper heat treatment process means that the reed heating temperature is too high and the holding time is too long, so that the austenite grains in the reed structure are coarsened, and the martensite needles are coarsened after quenching, resulting in an increase in internal stress and brittleness of the reed. A heat treatment crack is formed.
Solution: Use the mesh belt furnace to process the reed, control the heating temperature to 790 °C, control the holding time, direct oil quenching, and timely tempering after cleaning, which can effectively solve the heat treatment crack defects generated by the reed.
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