Study of ion-plasma nitriding of welded seam of bimetallic pipe liner made of 08Kh17Т steel

The research is focused on nitriding of bimetallic tubes produced by cold radial forging with a 08Kh17Т steel welded tube as an inner liner. Bimetallic cylinders are used in submersible plunger pumps for oil wells. Continuous operation, effects of mechanical particles and corrosion result inthe inner layer wear, hence a need to improve the equipment lifetime requires special attention. One way of increasing the product reliability is to apply ion-plasma nitriding on the liner. Cold radial forging has proved not to alter the welding pool area but to change the grain shape and orientation.The hardness distribution along the weld remains virtually the same, which guarantees the quality of the nitrided layer formed by the subsequent surface treatment. The study concerned the influence of the composition of the ion-plasma nitriding medium (with the same technological and energy parameters of the process) on the nitriding features at the weld zones. The structure and properties of the obtained layers were studied. It was found that during nitriding in the medium of dissociated ammonia, the hardness of the nitrided layer in the centre of the weld is significantly higher than that of the nitrided layers of other weld zones. This ‘spotty’ hardness negatively affects the product characteristics. To reduce the brittleness of nitrided layers, saturation was carried out in nitrogen–hydrogen media with different argon content and methane additives. The study allowed to determine the composition of the mediumat which a uniform hardened layer, including the weld zone, was obtained on the whole inner surface of the liner.The study was carried out with the financial support of the Government of Perm Territory within the framework of scientific project No. C 26/513.