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.. commercial air cleaner