Abstract: A method of heating a long metal product to a desired temperature by an induction heating coil while continuously moving the long metal product longitudinally. The long metal product thus heated attains a uniform temperature throughout its entire length. For this purpose, the space enclosed by the induction heating coil is hypothetically divided into a plurality of sections in the direction in which the long metal product travels. The temperature of the long metal product in each hypothetically divided section is estimated by calculation from the temperature of the long metal product at the inlet of the induction heating coil. Based on the estimated temperatures, the power supplied to the induction heating coil is controlled so that the temperature of the long metal product agrees with the desired temperature at the outlet of the induction heating coil.

Abstract: An immersion cooling apparatus includes a mechanism for immersing a hot metal pipe with the axis thereof directed horizontally in a cooling tank containing cooling liquid, and a mechanism for locking the immersed pipe in position in the cooling tank. While the locking mechanism is preventing the pipe from moving, a nozzle extending toward the interior of the pipe in the direction of the pipe axis injects cooling liquid into the pipe. The cooling liquid thus injected flows completely through the pipe so that the pipe being cooled is not injured or bent.

Abstract: A molten steel, which may optionally contain boron to increase hardenability is poured into ingot molds, bloomed and primary hot worked to a mother tube of intermediate cross-section. Before being cooled down to below about 800.degree. C, the mother tube is reheated to about 930.degree. C, scale from the outside surface thereof is removed, and it is secondary hot worked to a pipe of final dimensions with a reduction, measured in terms of equivalent strain as expressed by the following formula, of not less than .epsilon. = 0.02 for the removal of scale from the inside surface of the pipe. It is then directly quenched to produce a finished seamless steel pipe having far better shape at a higher heat efficiency than in the conventional process. Better toughness is effected when the degree of secondary hot work is not smaller than .epsilon. = 0.20..epsilon. = .sqroot.2/3 .sqroot.(.epsilon..sub.1 - .epsilon..sub.2).sup.2 + (.epsilon..sub.2 - .epsilon..sub.3).sup.2 + (.epsilon..sub.3 - .epsilon..sub.1).sup.