Causes of abnormal hardness of spring steel spring

The hardness of spring steel spring leaf is insufficient or too high, or the hardness of spring steel spring leaf in the same batch is different, some of which are high or some are low. The main reasons are as follows:
The hardness of spring steel spring is insufficient after quenching

1) The heating temperature of spring is low or the holding time is insufficient. In this state, the content of carbon and alloy elements in austenite is not enough, and even there are some untransformed pearlite or undissolved ferrite in the spring structure, which leads to the hardness of the spring after quenching.

2) If the heating temperature is too high or the holding time is too long, the surface of the spring will be decarburized and the hardness will be reduced.
2. The hardness of spring steel spring is low after tempering
1) The hardness of the spring is too low after quenching, which leads to the low hardness.
2) The higher tempering temperature and longer holding time lead to lower hardness.

3. The hardness of spring steel spring is high. The main reason is lower tempering temperature or shorter holding time.

4. The hardness of spring steel spring is different in the same batch, the main reasons are as follows
The same batch of reed some hardness is insufficient, some high, in addition to technological reasons, heat treatment equipment is also a key factor. Due to the fact that the reeds are mostly heat treated in box type resistance furnace, the reeds are often packed in bulk in metal baskets, and the heating is very uneven, which is one of the important reasons for the uneven hardness of the same batch of reeds.

Solution: reasonable control of heating temperature and holding time, and corresponding inspection after quenching to prevent tempering hardness. In addition, the box type resistance furnace is mesh belt furnace, which can solve the problem of uneven hardness of the same batch of reeds.