The present invention relates to a process for hardening the interior surface of a long, thin-walled, small inside diameter, tubular member, such as a tube which would be used to form a downhole pump barrel. More particularly, it relates to a process involving progressive heating with an internally positioned, electro-magnetic induction coil, followed by immediate quenching with a quench ring assembly, to develop a martensitic case on the inner surface of the tube. The invention further extends to the apparatus utilized in conducting the process, and to the product tube itself.