The control measures of spring steel reed brittleness and heat treatment crack defects

1. Brittleness is one of the common defects of reeds, which can be divided into heat treatment brittleness and hydrogen embrittlement after galvanizing. Microscopically, hydrogen embrittlement fractures have intergranular, dimples, secondary cracks, etc., and hair lines and hydrogen micropores can also be observed on the fracture surface.
1) Heat treatment brittleness

Spring steel has a tendency to heat sensitivity and temper brittleness, and its tempering temperature is often just right at the junction of the first type of temper brittleness and the second type of temper brittleness. If it cannot be tempered, kept warm and cooled in time, it will cause the spring The flakes are brittle.

Solution: Control the tempering temperature, and timely temper, heat preservation and cooling.

2) Hydrogen embrittlement

After hot-dip galvanizing, it is easy to increase the brittleness of the reed. This is because before galvanizing, pickling must be carried out to remove the oxide scale, which will cause a part of hydrogen to penetrate into the coating and the base metal, weakening the bond between the metal crystal atoms on the grain boundary Force and generate internal stress, making the reed brittle, that is, “hydrogen embrittlement.”

Solution: Control the pickling time and temperature, standardize the galvanizing process, and after galvanizing, keep it at 180°C for several hours before proceeding with the hydrogen removal process, which can reduce the brittleness of the coating and structure of the reed.

2. Heat treatment cracks

Heat treatment generally has a relatively small probability of crack defects in the reed. If cracks occur, the reasons are: improper heat treatment process, improper adjustment of tooling, and operator error. Improper heat treatment process means that the heating temperature of the reed is too high and the holding time is too long, which causes the austenite grains in the reed structure to be coarsened. After quenching, the martensite needles are coarse, resulting in the increase of internal stress and brittleness of the reed. Form heat treatment cracks.

Solution: Use a mesh belt furnace to process the reeds, control the heating temperature to 790℃, control the holding time, direct oil quenching, and temper in time after cleaning, which can effectively solve the heat treatment crack defects of the reeds.