Heat treatment of steel pipe Part 1
Created date: 2021-11-12

Traditionally, people think that there is no heat treatment process in pipe rolling plant, but in fact, controlled rolling and controlled cooling, on-line normalization and mandrel bright annealing can be considered to belong to the category of heat treatment. In addition, most companies set the heat treatment line in the pipe rolling plant.

Controlled rolling and controlled cooling is a new process since 1980s, which is widely used in plate production. It mainly improves the strength and toughness index by controlling the rolling temperature (in most cases, it needs to combine V, Nb, Ti and other refined grain elements) and the cooling rate after rolling.


On line normalization refers to normalizing (normalizing) heat treatment on the rolling line, that is, heating the raw pipe to austenization and air cooling on the large cooling bed by the sizing machine to improve the strength. The most common steel grades in pipe rolling plant are N80 class I and K55 coupling materials. At present, our company is still developing P110 class casing of on-line quasi quenched quasi bainite.


Definition and significance of heat treatment

Heat treatment of steel pipe is a process method to change the internal structure of steel pipe through the operation of heating, insulation and cooling of steel in solid state, so as to obtain the required properties. Generally, according to the purpose requirements, the heat treatment process of steel can be divided into: annealing, quenching + tempering, quenching and tempering treatment, and surface treatment.

Heat treatment can give full play to the potential of steel pipe, improve the service performance of workpiece (steel pipe), reduce the weight of workpiece (steel pipe), save materials, reduce costs and prolong service life. On the other hand, the heat treatment process can also improve the processing performance, improve the processing quality and reduce tool wear. At the same time, some physical and chemical indexes can be obtained only after heat treatment. Such as: high H2S stress corrosion resistance, strengthening of stainless steel pipe, etc.

For our company, whether it is pipe rolling plant or pipe processing plant, the heat treatment process improves the physical and chemical indexes such as strength and toughness of steel pipe, so as to meet the requirements of users and improve economic benefits. In the pipe rolling plant, the on-line normalization process significantly simplifies the process flow and reduces the production cost; In the pipe processing plant, high value-added steel pipes are mainly produced through quenching and tempering treatment, especially TP series non API petroleum special pipes with corrosion resistance, collapse resistance, both corrosion and collapse resistance and ultra-high strength.


Basic principle of heat treatment


The internal structure of metals and alloys is changed by heating, heat preservation and cooling to obtain the structure required by the service performance of workpieces. This technology is called heat treatment process. The same material can obtain different properties after different heat treatment. The change of properties is due to the change of microstructure. Therefore, understanding the structural change of steel during heat treatment is the basis for correct heat treatment.

Like other natural sciences, metal heat treatment technology develops with the development of productivity and is closely related to the development of other science and technology. Heat treatment is the result of the development of ancient metallurgical technology. As a part of metallurgical technology, it has gradually developed into a discipline.

In Chinas history, heat treatment technology appeared in the iron age, accompanied by the emergence of cast iron. Steel making in ancient times was carried out by decarburization annealing and repeated forging of cast iron, that is, the so-called hundred refining into steel. With the development of steelmaking technology, heat treatment technology has also been developed. Since the Han Dynasty, Chinas heat treatment technology has been recorded in writing, including general quenching technology, quenching medium and carburizing process, almost involving all aspects of heat treatment technology. For example, fire and hydration are quenchedis contained in the historical records and heavenly palace book. According to the separate biography of Pu Yuan, Pu Yuan made 3000 swords for Zhuge Liang in the inclined valley around Meixian County, Shaanxi Province. He said: the water in Hanzhong is dull and weak and does not quench; Shu water is cool and strong , so he sent someone to Chengdu to get water. Quench it is really sharp. From the textual research of unearthed cultural relics and some written records, it can be clearly seen that Chinas heat treatment technology has a long history and superb skills, which was inferior to that of other countries at that time.