In order to control cooling after rolling technology to better promote and applied to the production of seamless steel tube, seamless steel tubes for rapid cooling after rolling to get the surface of high strength, high toughness acicular ferrite microstructure and tempering sorbite organizations, significant grain refinement, the overall mechanical properties of steel greatly improved; For carbon structural steel and alloy structural steel, rolled after the adoption of appropriate rapid cooling process in the dual role of rapid cooling and heat tempered steel themselves, get surface with high strength, high toughness tempered sorbite, acicular ferrite, bainite and other organizations, while the internal network to reduce the degree of ferrite grain refinement, the overall strength and Efficiency Heating
Coolingtoughness of steel and other mechanical while improving performance and, in the case of elongation does not decrease greatly improved toughness, improve the state-rolled low impact toughness. Allow rapid cooling process after rolling thick-walled seamless composite thickness direction of the organization, the overall benefit of improved overall performance. Cooling the hot-rolled steel mainly by radiation, conduction and convection in three ways. Among them, the convective heat transfer between the pipe surface and the cooling medium is the main way of cooling. Using a mixture of water and air as a cooling medium, called “mist cooling.” When air-cooled, steel pipe surface heat faster than their thermal conductivity is much slower, more uniform thickness direction of the steel pipe temperature; when mist cooling, heat pipe surface speed greatly improved, there is a certain temperature gradient near the surface of the steel pipe thickness direction. Finishing the hot-rolled seamless process reaches room temperature in about 950 , depending on the cooling conditions, the austenite decomposition product of different tissue types. Therefore, when the temperature difference between the mist cooling pipe near the surface in the thickness direction, the thickness direction of the steel tube will inevitably lead to diverse organizations; pipe due to internal heat conduction heat transfer relies, the temperature throughout the continuously changing, so that even the formation of different tissues is also present in the transition region between organizations, namely: the type of microstructure between a mixing zone coexist, if different types of pipe tissue layers composite. Organizational diversity so that the mechanical properties of the steel pipe is changed, a new exhibit mechanical properties such as strength and toughness combination; tissue continuity between the pipe so that different types of organizations closely integrated through the “transition zone” does not happen “layered” phenomenon; complex organization with different thickness of the steel pipe in place, showing the different mechanical properties, demonstrate the features and advantages of the composite material. As we all know, steel composite material has many unique advantages, such as: steel surface grain refinement can improve the overall fatigue resistance, in the construction sector, the steel surface fine grain refinement compared with the full-face eve