Heat treatment defects of precision seamless steel tubes

Precision seamless steel tubes generally have quality defects after heat treatment. Of course, this has a lot to do with technical operation. Let's take a look at what causes the defects of precision seamless steel tubes:

1. Overheating:

Overheating of the microstructure after quenching can be observed from the rough mouth of the precision seamless steel pipe. If coarse needle-shaped martensite is present in the quenched structure of the precision seamless steel pipe, it is quenched and superheated. The reason for the next year is that the quenching heating temperature is too high or the heating and holding time is too long to cause overheating of the cotton; or because the original structure of the banded carbide is serious, a local martensite needle is formed in the low carbon region between the two belts. Large, causing local overheating. The retained austenite increases in the superheated structure, and the dimensional stability decreases. Due to the overheating of the quenched structure, the coarse crystal of the steel causes the nuclear bondability of the high-pressure alloy tube to decrease, the impact resistance is lowered, and the life of the high-pressure alloy tube is also lowered. Excessive heat can even cause quenching cracks.

2. Quenching crack:

During the quenching and cooling process, the precision seamless steel tube is called the quenching crack due to the internal stress and the crack formed by the tensile strength of the material at this position. The causes of such cracks are: due to excessive heating temperature of quenching or too rapid cooling, the microstructure stress of the thermal stress and metal mass volume is greater than the fracture strength of the steel; the original defects of the working surface form stress concentration during quenching; Severe surface decarburization and carbide segregation; insufficient tempering or quenching in time after quenching of the parts; excessive cold stress caused by the previous process, forged folding sauce, deep turning tool marks, sharp edges and corners of oil grooves, etc. In short, the cause of quenching crack may be one or more of the above factors, and the existence of internal stress is the main reason for the formation of quenching cracks. The quenching crack is deep and slender, the fracture is straight, and the fractured surface has no oxidation color. It tends to be longitudinally cracked or ring-shaped on the bearing ring; the shape on the bearing steel ball is S-shaped, T-shaped or ring-shaped. The microstructure characteristic of the quenching crack is that there is no decarburization on both sides of the crack, which is obviously different from the forging crack and the material crack.

3. Heat treatment deformation:

In the heat treatment of precision seamless steel tubes, there are thermal stresses and microstructure stresses. These internal stresses can overlap or partially cancel each other. It is complex and variable because it can follow heating temperature, heating speed, cooling method, cooling rate, The shape and size of the part and the way of loading the furnace change, so the heat treatment deformation is inevitable. Knowing and mastering its changing cracks can make the deformation of bearing parts in a controllable range, which is conducive to the normal production. Of course, the mechanical collision during the heat treatment will also deform the part, but this deformation can be reduced and avoided by improving the operation and the like.

In the heat treatment of precision seamless steel tubes, there are many factors that affect the production of precision seamless steel tubes, which requires the skilled workers to be quite skilled and continue to carry out in the subsequent operations to sum up.