Seamless Steel Tube Annealing Type

1. Seamless annealing and isothermal annealing of seamless steel pipes, also known as recrystallization annealing, generally referred to as annealing, which is mainly used for casting, forging and hot-rolled profiles of various carbon steels and alloy steels with sub-eutectoid composition. Sometimes used for welding structures. It is often used as a final heat treatment for some non-heavy workpieces or as a pre-heat treatment for certain workpieces.

1. Spheroidizing annealing Spheroidizing annealing is mainly used for hypereutectoid carbon steel and alloy tool steel (such as steel cutting tools, measuring tools, and steels used in molds). Its main purpose is to reduce hardness, improve machinability, and prepare for later quenching.
2. Stress-relieving annealing Stress-relieving annealing, also known as low-temperature annealing (or high-temperature tempering), is mainly used to eliminate residual stresses in castings, forgings, welded parts, hot-rolled parts, and cold-drawn parts. If these stresses are not eliminated, it will cause deformation or cracking of the steel after a certain period of time or during subsequent cutting operations.

Annealing and normalizing1. Annealing of steel The steel is heated to a certain temperature and kept for a while, then it is slowly cooled, called annealing. Annealing of steel is a heat treatment method in which steel is heated to a temperature at which a phase change or a partial phase change occurs, and is slowly cooled after being kept warm. The purpose of annealing is to eliminate tissue defects, improve the structure to homogenize the components and refine the grains, improve the mechanical properties of the steel, reduce the residual stress, and at the same time reduce the hardness, improve the plasticity and toughness, and improve the cutting performance.

Therefore, in order to eliminate and improve the structural defects and internal stress left in the previous process, and to prepare for the subsequent process, the annealing is a semi-finished heat treatment, also known as pre-heat treatment.

2. Normalizing normalizing of steel is a heat treatment method in which the steel is heated above the critical temperature to completely transform the steel into uniform austenite and then naturally cool in the air. It can eliminate the network cementite of hypereutectoid steel. It can be used to refine the crystal lattice of hypoeutectoid steel and improve the comprehensive mechanical properties. It is economical to replace the annealing process with the normalized fire for the less demanding parts.

Complete annealing treatment Complete annealing treatment heating the hypoeutectoid steel to 30~50 °C above Ac3 temperature, heating the hypereutectoid steel to a temperature range of about 50 °C above Ac1 temperature, and maintaining sufficient temperature at this temperature to become Vostian After the single-phase structure (hypo-eutectoid steel) or the Worth field body and the snow-bearing carbon mixed structure, the steel is softened by furnace cooling to obtain the best ductility and fine grain structure of the steel.

The annealing process of spiral submerged arc welded steel pipe and seamless steel pipe is very different. Nearly all castings of cast iron will generate thermal stress during the cooling process. During the heat treatment process, special normalization treatment and annealing treatment will be completed. The main reason for the occurrence of internal stress and internal stress is that the internal flesh thickness of the casting is different. Due to the difference in heat drop during the rapid cooling process, the difference in flesh thickness will cause each inconsistent contraction to be different, thus causing the so-called internal stress.

The cold part has a higher latent length, and the hot part has a lower length, so the hot part will form a hot spot to cause partial deformation after the cold part is contracted, and the strength of the deformed part, along with the deformation degree Increase and increase, and finally can not be further deformed, the formation of some kind of elastic stress inside the casting, even plastic strain, that is, internal stress, this stress can be almost as high as the tensile strength, and for any external reasons When the local stress exceeds the tensile strength, such castings are easy to cause cracking, and heat treatment is the most important way to eliminate internal stress. The main program is a temperature rise, so that all cast built in a very uniform and slow, the heating and cooling.

The annealing temperature of the steel pipe depends mainly on the components of the casting and the amount of strength that must be removed. Even the possible changes in the structure must be considered. The most suitable annealing temperature can be roughly summarized as follows: For non-alloyed cast iron, Between 500 and 575 ° C, for low-strength cast iron, between 550 ~ 600 ° C, for high-alloy cast iron between 600 ~ 650 ° C, the temperature distribution in the furnace must be Uniformity is possible to avoid the presence of temperature gradients.

In any case, the flame or hot gas used for annealing cannot be sprayed directly onto the casting to avoid the thin wall portion causing thermal stress and increasing residual stress during heating. The amount of existence, which in turn causes cracking, will be eliminated in the first hour after reaching the annealing temperature, depending on the thickness of the casting. In general, the annealing time must be increased by one hour for every 25 mm increase in casting thickness..

A worker from a steel pipe company, which is located in China.