Nitriding of X-52 Carbon Steel: Mechanical Characterization

Carbon steel is the most cost effective material that being used in oil and gas
industry. Although it is widely used, it has some limitation particularly in terms of
corrosion resistance. Improving the surface properties can be beneficial to reduce the
corrosion rate. Nitriding is one of the methods to improve the surface properties of
carbon steel typically done at 495-595°C for 70 hours. Since corrosion resistance is
related to the metal surface interaction with the corrosive environment, improving
surface by nitriding could increase corrosion resistance of carbon steel. However,
typical length of nitriding which is 70 hours is not economical. Only thin nitride
layer required to improved carbon steel corrosion resistance. Thus, objective of this
research is to conduct nitriding at 450°C, 480°C, and 520°C for 8 hours only.
Metallography characterization, surface hardness measurement, and XRD
characterization after the treatment were performed to examine the result of the
treatment The surface hardness of nitriding at 8 hours is similar with the surface
hardness of nitriding at 70 hours. Higher nitriding temperature produces higher
surface hardness. Nitriding at 450°C produced surface hardness of302HV. Surface
hardness of 344HV is produced when nitriding at 480°C. Nitriding at 520°C
produced the highest surface hardness which is 398HV. The only different is the
case depth. 70 hours of nitriding can produced case depth around 25 ~m. Nitriding
for 8 hours can only produced case depth of3~m to 6~m. Phase transformation does
not occur at the core metal due to low temperature heat treatment. X-ray diffraction
pattern shows that alloying nitride is form due to nitrogen diffusion. The presence of
alloying nitride increases the surface hardness. The conclusion of this project is
nitriding is successful at shorter duration of 8 hours but lower nitriding thickness of
3-6 ~m. The mechanical characteristic of the nitriding layer is comparable to the
nitriding at 70 hours.