PROCESS FOR PRODUCTION OF HIGH ALLOY STEEL TUBES

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A process by which high alloy steel tubes having not only corrosion resistance requisite to oil well pipes but also desired strength can be produced by selecting cold working conditions without excessive addition of alloying components. Specifically, a process for producing high alloy steel tubes which comprises producing a high alloy steel tube stock having a chemical composition containing by mass C : 0.03% or below, Si : 0.5% or below, Mn : 0.3 to 1.0%, Ni : 25 to 40%, Cr : 20 to 30%, Mo : 0 to 4%, Cu : 0 to 3% and N : 0.05 to 0.30% with the balance consisting of Fe and impurities through hot working and, if necessary, solid solution heat treatment and then cold-drawing the tube stock, characterized in that the cold drawing is conducted under such conditions that the reduction ratio (Rd) of the final cold drawing step in terms of reduction in area falls with the range of 10 to 40% and satisfies the relationship (1) : Rd(%) > (MYS-83)/11-(1.3ŒCr+Mo+90ŒN) ... (1) [wherein Rd and MYS are reduction ratio (%) in terms of reduction in area and target yield strength (MPa) respectively; and Cr, Mo and N are their respective contents (% by mass)]. The steel tubes may contain Ca, Mg and/or rare earth elements.