Microstructural and wear resistance characterization of superficial oxidized piercing plugs applied to the rolling of seamless steel pipes

Seamless steel pipes are primarily used to extract and transport oil and gas. One of the main cost drivers in its production process is related to the tooling used in the process, like the piercing plugs. Besides the impact on cost, the mechanical and wear resistance of those plugs is essential to ensure a good quality of the pipes being produced. The piercing plugs are manufactured using steel designed for tooling and usually pass through an oxidation heat treatment at high temperatures before being used in the rolling process to ensure appropriate tribological properties. This work aimed to characterize the evolution of the oxides layers formed on the oxidation heat treatment of piercing plugs and its wear performance. With this purpose, the oxides layers were analyzed by confocal optical microscopy, scanning electric microscopy, X-ray and backscattered electron diffraction in samples submitted to two heat treatment routes: i) Single cycle and II) Double cycle. Besides these tests, tribological analyses were also carried out to measure wear rates. Based on the obtained results, this paper concluded that an effective double cycle oxidation heat treatment provides an oxide layer with low porosity, appropriate thickness, reduced hematite fraction and mainly formed by wustite and magnetite that provided lower wear rate; 205% lower than the measured for the single cycle. It was concluded that the use of the double cycle oxidation improve the component wear behavior and, consequently contributes to the increase of tool service-life. (author)