Seamless square tube controlled cooling technology
By tonywuphotography from Pixabay
Controlled cooling technology is very important in the production of rolling a technology that by controlling the temperature and cooling rate after rolling the steel to improve the organization and performance of steel and, ultimately, good mechanical properties. With the development of control cooling technology, which has been applied to more mature sheet, strip, wire and other fields.
For high-quality carbon steel pipe, the test process using air cooling after rolling to produce a more uniform equiaxed ferrite and pearlite structure; when using mist cooling after rolling process, although in subsequent air cooling the steel temperature slightly rise, due to the steel surface by alternating the role of aerosol cooling and subsequent air cooling, the surface temperature is reduced after the first rise, while the middle and inner temperature changes relatively slowly diffuse. Such diversification of pipe wall thickness direction of the organization is bound to appear. In the steel surface generated bainite 0.9mm thickness and 0.9mm to 35mm thickness of the transition zone composite tissue. Because usually acicular ferrite dislocation density higher than equiaxed ferrite dislocation density, therefore, from the point of view of dislocation strengthening, acicular ferrite corresponding yield strength greater than equiaxed ferrite corresponding yield strength . In addition, after the rolling mist cooling tube structure point of view, it equiaxed ferrite grain size is significantly smaller than the equiaxed ferrite grains by air cooling obtained from fine-grain strengthening perspective, significantly improved mechanical properties
Seamless square tube in order to control the cooling after rolling to better promote and apply to seamless production of low C low Mn seamless steel rolling surface for rapid cooling to obtain high-strength, high toughness of acicular ferrite tissue and sorbite, grain refinement significantly, the overall mechanical properties of steel greatly improved; for carbon structural steel and alloy steel pipe, after rolling the use of appropriate rapid cooling process, can be rapidly cooled and steel in Under their dual role tempering heat, get the surface with high strength, high toughness sorbite, acicular ferrite, lower bainite and other organizations, at the same time, the degree of internal ferrite mesh reduced grain refinement, mechanical properties such as strength and toughness of steel as a whole at the same time improve and impact toughness in the case of elongation is not reduced significantly improve, improve the state-rolled low impact toughness. Allow rapid cooling after rolling process rectangular steel composite thickness direction of the organization, help improve overall performance overall seamless square tube. In order to study the results of the initial applied to production practice, jointly developed a controlled cooling after rolling hot rolled seamless system to improve the overall performance improvement of the product.
Rolled steel after the main heat by radiation, conduction and convection in three ways. Seamless square tube which convective heat transfer between the steel surface and the cooling medium is the main form of heat. Using a mixture of water and air as a cooling medium, called “mist cooling.” When air-cooled, the cooling rate than the steel surface of the steel pipe itself is much slower thermal conductivity, relatively uniform thickness direction of the steel pipe temperature; when mist cooling, cooling pipe surface speed greatly improved, there is a certain temperature gradient in the vicinity of the surface of the steel pipe in the thickness direction. Hot rolled seamless pipe by the finish rolling temperature was lowered to room temperature in about 950 process, depending on the cooling conditions, the austenite decomposed into different tissue types of product. Therefore, when the temperature difference between mist cooling pipe near the surface in the thickness direction, will inevitably lead to diversification pipe thickness direction of the organization; because of the internal pipe rely on heat conduction heat transfer, it is continuous throughout the temperature change, and therefore, even if the formation of different organizations, also the presence of a transition zone between the organization, namely: between the different microstructures of a mixing zone coexist, like steel from different types of tissue layers of composite. Organizational diversity so that the mechanical properties of the steel pipe is changed, the new exhibit mechanical properties such as strength and toughness combination; organizational continuity between the pipe so that the different types of tissue in close connection with the “transition zone”, does not occur “layered” phenomenon; complex organization makes steel in different thicknesses at different mechanical properties exhibit, demonstrate the features and advantages of the composite material.