Seamless steel pipe is an economical section. Originally produced and exported abroad, China introduced the advanced technology of the former Soviet Union in the 1950s and produced the first seamless steel pipe. Seamless steel tubes are mainly used in the fields of crude oil exploitation and processing, pipeline transportation, mechanical processing, large-scale stadium construction, and boiler manufacturing. Different application areas have different requirements for the performance of steel. In terms of crude oil extraction, the seamless pipe is used in the oil well pipe, so the seamless steel pipe used for the oil well pipe must be subjected to a quenching and tempering treatment.
There are three methods for water quenching outside the tank, namely, water spray on the outside of the steel pipe, water spray on the inner surface of the steel pipe, and water spray on the inner and outer surfaces of the steel pipe; the water quenching process in the tank has the following methods: 1. Dip quenching, It is the easiest method, but this method tends to bend the tube and the surface may form a vapor film. 2. Dip quenching and axial injection of water in the steel pipe, but the method has certain requirements on the length of the steel pipe, and the quenching performance exceeding a certain length is not good. 3. Dip quenching and axial injection and outer spray water in the steel pipe. The structure of the quenching device is complicated, and the control is not good, so that the nozzle is blocked by pollutants. 4. Dip quenching and axially spraying water inside and outside the steel pipe. The device of the method is controlled by computer and has good quenching performance.
The purpose of quenching heating is to heat the steel above the critical point and heat it at a suitable temperature to completely transform the microstructure into austenite, so that the alloy compound and carbide are sufficiently dissolved and uniformly dispersed in the austenite. In the case of rapid heat treatment by induction heating, in order to accomplish the above quenching heating, the first condition is to determine the quenching heating temperature according to various factors as follows.
(1) Effect of rapid heating on critical point of steel. The critical points Ac1 and Ac3 of steel change with the increase of heating heating rate, and the variation range depends on the chemical composition of steel. Normally, Ac1 and Ac3 increase as the heating rate increases. Therefore, the quenching heating temperature must be adjusted according to the chemical composition of the steel and the heating rate of the induction heating. Instead of using the quenching heating temperature used in the conventional heat treatment, a higher quenching heating temperature is used to ensure complete austenitization of the steel structure.
(2) Effect of rapid heating on the dissolution of alloying elements and their compounds. Quenching requires that the alloying elements in the steel and the compounds and carbides formed in the steel can be dissolved into austenite to form a solid solution to facilitate the strengthening of the steel after the post-heat treatment. Induction heating and quenching heating time is very short, which is unfavorable for the dissolution of alloying elements and their compounds. For this reason, only measures to increase the temperature are used to promote dissolution.
(3) Effect of rapid heating on austenite homogenization. Quenching heating temperature is an important condition for homogenizing carbon distribution in primary austenite. The uniformity of austenite is directly related to the structural characteristics of the quenched structure and the microstructure and properties of the steel after tempering. Therefore, quenching such as hot temperature should meet the requirements of austenite homogenization.
In summary, the above requirements should be considered when determining the quenching heating temperature under rapid heating conditions. At the same time, it is necessary to consider the short-lived characteristics of rapid heating and quenching insulation to develop the quenching heating temperature. The traditional quenching heating temperature is usually at a critical temperature above Ac1 and Ac3, wherein the hypoeutectoid low alloy steel is Ac3+ (30~50°C), and the eutectoid and hypereutectoid low alloy steel is Ac1+ (30~50°C). The quenching heating temperature of some induction heating rapid heat treatment steels is shown in the following table. From the comparison data of the quenching heating temperature of the hypoeutectoid steel in the table, it can be considered that the induction heating quenching temperature is 50~100 °C higher than the traditional heating quenching temperature. This is only a summary of the data, and should be adjusted according to the actual situation. For more, visit:https://www.hu-steel.com/product85_1000.html
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