1. Brittleness is one of the common defects of reeds, which can be divided into heat treatment brittleness and hydrogen embrittlement after galvanizing. It is found that the hydrogen embrittlement fractures are intergranular, dimples and secondary cracks, and hairlines and hydrogen micropores can also be observed on the fractures.
1) Heat treatment brittleness
Spring steel has a tendency of heat sensitivity and temper brittleness, and its tempering temperature is often just at the junction of the first type of temper brittleness and the second type of temper brittleness. If it is not tempered, kept warm, and cooled in time, the reed will become brittle.
Solution: Control the tempering temperature, temper, keep warm and cool down in time.
2) Hydrogen embrittlement
After hot-dip galvanizing, the brittleness of the reed tends to increase. This is because pickling must be carried out before galvanizing to remove scale, which will cause a part of hydrogen to penetrate into the coating and the base metal, weaken the bonding force between metal crystal atoms on the grain boundary, generate internal stress, and make the reed brittle, that is, "hydrogen embrittlement" ".
Solution: Control the pickling time and temperature, standardize the galvanizing process, keep the temperature at 180°C for several hours after galvanizing and before the dehydrogenation process, which can reduce the brittleness of the reed coating and structure.
2. Heat treatment cracks
Generally, the probability of crack defects caused by heat treatment is very small. If cracks appear, the reasons are: improper heat treatment process, improper debugging of tooling, operator error, etc. Improper heat treatment means that the heating temperature of the reed is too high and the holding time is too long, which will coarsen the austenite grains in the reed structure, and the martensite needles will be coarse after quenching, resulting in increased internal stress and brittleness of the reed, thus forming Heat treatment cracks.
Solution: Use a mesh belt furnace to process the reed, control the heating temperature to 790°C, control the holding time, and directly oil quench and temper in time after cleaning, which can effectively solve the crack defect of the reed heat treatment.
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