The bright heat treatment of seamless tubes
does not have to be a vacuum furnace. It is heated in a protective atmosphere, which is what we often call a continuous bright quenching furnace. The protective gas is pure hydrogen or a mixture of nitrogen and hydrogen, which can also decompose ammonia into gas. There is another kind, quenching in bright quenching medium is also possible.
The vacuum heat treatment refers specifically to the treatment in a vacuum environment, but there are many treatments in a vacuum environment: quenching, tempering, annealing, and some include sintering and brazing. It should be noted that vacuum heat treatment will not necessarily be bright, but it can be done if required.
The difference between seamless tube quenching and vacuum heat treatment:
Vacuum heat treatment is a heat treatment under the isolation of air, which can avoid oxidation and decarburization of the surface of the workpiece to the greatest extent, and quenching is only one way of heat treatment, which is to heat the steel to the austenitizing temperature and keep it for a certain period of time, and then use Cooling at a rate greater than the critical cooling rate to obtain a non-diffusion-type transformation structure, quenching can be performed by vacuum heating, or by other relatively simple and inexpensive heating methods.
When people often say vacuum, they do not refer to the specific vacuum degree. Materials have different performances under different vacuum degrees and temperatures. The vacuum degree is low and the temperature is low. It is oxidizing, and it is in a high temperature and high vacuum state. Reductive properties. Even if the vacuum heat treatment is under the same vacuum degree, some materials are oxidized, and some materials are not oxidized, the performance is that some come out bright, and some are not bright. Vacuum heating is only a condition. If the vacuum air quenching furnace is cooled, the gas is not pure, such as water in the oil of the vacuum oil quenching furnace or incomplete degassing, which will cause the workpiece to not be bright, and inert gases such as nitrogen and argon will also have difference.
Therefore, in vacuum heat treatment, it will be bright if the right process is used, rather than general vacuum heat treatment should be bright.
In fact, it is a problem of the oxygen content of the atmosphere, or the content of the oxidizing atmosphere.
Vacuum treatment is to remove the air and reheat it. The air contains 21% oxygen. If you pump the furnace to a very low pressure, the number of oxygen molecules will become PPM level, but the environment below 1 atmosphere can be said to be In a vacuum, if you only pump 0.5 atmospheres, the oxygen molecules will only be half less than in the atmosphere, and the oxidation reaction will occur with steel at high temperature.
Atmospheric heat treatment can also reduce the oxygen content to a very low level, so that no oxidation reaction occurs on the surface of the part, but the principle is to use a reducing gas to react and take away the oxygen in the atmosphere.