ONLINE-CONTROLLED SEAMLESS STEEL TUBE COOLING PROCESS AND SEAMLESS STEEL TUBE MANUFACTURING METHOD WITH EFFECTIVE GRAIN REFINEMENT

摘要

An online-control cooling process for seamless steel tube for effectively refining grains, comprising the following steps: when the temperature of a crude tube is higher than Ar3, evenly spraying water along the circumferential direction of the tube so as to continuously cool the tube to T1°C∼T2°C, the cooling rate being controlled to be N1°C/s∼N2°C/s, wherein T1=810-360C-80(Mn+Cr)-37Ni-83Mo, T2=T1+115°C, N1=55-80×C, N2=168*(0.8-C), and C, Mn, Cr, Ni and Mo in the equations each represent the mass percentage of corresponding elements in the seamless steel tube; then, cooling to the room temperature at cooling rate no more than 10°C/s. Correspondingly, also provided are a method for manufacturing seamless steel tube for effectively refining grains, and a seamless steel tube. The online-control seamless steel tube cooling process does not require adding too many alloying elements, which is simple and can yield seamless steel tubes with good grain refinement and better toughness.