Process for producing seamless stainless steel pipe

Abstract

A process for producing seamless pipes which comprises conducting a piercing rolling step, a elongating rolling step using a mandrel bar, and a sizing rolling step and subsequently conducting a product heat treatment. In the process, when the carbon-equivalent weight, namely the sum of the weight of graphite in the lubricant and the carbon content in the organic binder, per unit area of the lubricant adhering to the mandrel bar surface in the above-mentioned step of elongating rolling is expressed by C (g/m) or the maximum extent of carburization in the inner surface of the pipe to be heat-treated but prior to the heat treatment is expressed by ΔC (% by mass), the heating temperature for the pipe to be heat-treated is expressed by T (° C.), and the time during which a decarburizing gas is blown into the inside of the pipe to be heat-treated is expressed by tor t(seconds), and further, the blowing time calculated taking into account the wall thickness reduction in the step of cold working is expressed by tor t(seconds), a predetermined relation is satisfied and the actual decarburizing gas blowing time in the heat treatment is longer than the time t, t, tor t(seconds), whereby seamless stainless steel pipes reduced in carburized layer formation can be produced even when the carbon adhesion to the pipe inner surface is caused in, for example, mandrel mill rolling.