The heat treatment process of seamless steel pipe

Annealing is to heat the cold-rolled precision bright seamless steel pipe to an appropriate temperature, use different holding times according to the material and workpiece size, and then slowly cool it. The purpose is to make the internal structure of the metal reach or approach a state of equilibrium, obtain good process performance and performance, or prepare for further quenching.

Normalizing is to heat the cold-rolled precision bright steel pipe to an appropriate temperature and then cool it in the air. The effect of normalizing is similar to annealing, but the obtained structure is finer. It is often used to improve the cutting performance of the material and sometimes used as the final heat treatment for some parts with low requirements.

Quenching is to heat and keep the cold-rolled precision bright steel pipe, and then quickly cool it in a quenching medium such as water, oil, or other inorganic salts, or organic aqueous solutions. After quenching, the cold-rolled precision bright steel pipe becomes hard, but also brittle.

To reduce the brittleness of the cold-rolled precision bright steel pipe, the cold-rolled precision bright steel pipe after quenching is kept warm for a long time at an appropriate temperature above room temperature and below 650℃ and then cooled. This process is called tempering.

Annealing, normalizing, quenching, and tempering are the "four fires" in the overall heat treatment, among which quenching and tempering are closely related and are often used together. They are indispensable.

The "four fires" have evolved into different heat treatment processes with different heating temperatures and cooling methods. To obtain a certain strength and toughness, the process of combining quenching and high-temperature tempering is called tempering. After some alloys are quenched to form a supersaturated solid solution, they are placed at room temperature or a slightly higher appropriate temperature for a long time to improve the hardness, strength, or electrical and magnetic properties of the alloy. Such a heat treatment process is called aging treatment.

The method of combining pressure processing deformation with heat treatment effectively and closely to obtain a good strength and toughness combination for cold-rolled precision bright steel pipes is called deformation heat treatment; heat treatment in a negative pressure atmosphere or vacuum is called vacuum heat treatment, which can not only prevent oxidation and decarburization of cold-rolled precision bright steel pipes, keep the surface of cold-rolled precision bright steel pipes smooth after treatment, and improve the performance of the workpiece, but also pass penetrants for chemical heat treatment.

Surface heat treatment is a metal heat treatment process that only heats the surface of cold-rolled precision bright steel tubes to change the mechanical properties of the surface. To heat only the surface of cold-rolled precision bright steel tubes without transferring too much heat into the interior of the workpiece, the heat source used must have a high energy density, that is, a large amount of heat energy is given to the unit area of cold-rolled precision bright steel tubes so that the surface or local part of the cold-rolled precision bright steel tube can reach high temperature in a short time or instantaneously. The main methods of surface heat treatment are flame quenching and induction heating heat treatment. Commonly used heat sources include flames such as oxyacetylene or oxypropane, induced current, laser, and electron beam.

Chemical heat treatment is a metal heat treatment process that changes the chemical composition, structure, and properties of the surface of cold-rolled precision bright steel tubes. The difference between chemical heat treatment and surface heat treatment is that the latter changes the chemical composition of the surface of the workpiece. Chemical heat treatment is to heat the workpiece in a medium (gas, liquid, solid) containing carbon, nitrogen, or other alloy elements and keep it warm for a long time so that elements such as carbon, nitrogen, boron, and chromium can penetrate the surface of the workpiece. After the elements are infiltrated, other heat treatment processes such as quenching and tempering are sometimes required. The main methods of chemical heat treatment are carburizing, nitriding, and metalizing.

Heat treatment is one of the important processes in the manufacturing process of mechanical parts tools and molds. Generally speaking, it can guarantee and improve the various properties of cold-rolled precision bright steel pipes, such as wear resistance and corrosion resistance. It can also improve the organization and stress state of the blank to facilitate various cold and hot processing.

For example, white cast iron can be obtained through long-term annealing to obtain forgeable cast iron and improve plasticity; gears can be used with the correct heat treatment process. The service life can be doubled or dozens of times longer than that of gears that have not been heat treated; in addition, cheap carbon steel has some expensive alloy steel properties by infiltrating certain alloy elements, which can replace some heat-resistant steel and stainless steel; almost all tools and molds need to be heat treated before they can be used.