Abstract
The aim of this work was to study the micro-abrasive wear resistance of an API 5L X-70 microalloyed steel plasma nitrided under different conditions of time and temperature. Pulsed DC plasma nitriding experiments were performed under a treatment atmosphere of 10%N2 + 90%H2, at temperatures of 410, 440 and 470 °C and for nitriding times of 1, 3 and 5h. The results show that plasma nitriding performed at 440 °C and 1h led to the formation of a compound layer constituted mainly of ε-Fe2-3N nitride and a diffusion zone with large needle-like nitride, offering the highest wear resistance. The amount of γ’- Fe4N phase was found to increase with the plasma nitriding time, decreasing the wear resistance of the material.
Highlights
The American Petroleum Institute (API) classifies the steels used in the oil industry according to their application, chemical composition and mechanical strength
Microalloyed steels can be applied in the ore-conveying pipelines; the inner wall of the pipe is characterized by a poor wear resistance, when in contact with slurries containinghard abrasive particles, such as hematiteand silica
Sputter cleaning on the surface of the samples was carried out at 200-250oC under an argon atmosphere at a pressure of 100 Pa for about 15 min, and plasma nitriding experiments were performed at temperatures of 410, 440 and 470 °C using different nitriding times, under 533 Pa of pressure and volumetric flow-rate of the gas mixture of 400 cm3/min, which was strictly controlled by blending the pure gases in the required composition of 10% N2 and 90% H2
Summary
The American Petroleum Institute (API) classifies the steels used in the oil industry according to their application, chemical composition and mechanical strength. Those steels used in the transmission lines (transfer and transport of oil and natural gas) are designated as API 5L1. The microalloyed steels fulfill these requirements due to the effects of hardening and strengthening promoted by precipitation, solid-solution, and grain refinement that can occur during their thermomechanical processing[2,3]. Due to a good control over the processing variables, such as temperature of deformation, strain rate and degree of strain, the controlled rolling allows improvement of the mechanical properties of the microalloyed steels[4,5]. Microalloyed steels can be applied in the ore-conveying pipelines; the inner wall of the pipe is characterized by a poor wear resistance, when in contact with slurries containinghard abrasive particles, such as hematiteand silica
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