The Effect of Welding Parameters on the Corrosion Resistance of Austenitic Stainless Steel

Electricity produced in power plants is essential in our everyday life. In general, the energy transfer takes place after processing the energy source in boilers or steam generators. Steam is generated through this process, that operates the turbines and they generate electricity through the generators. As such equipment operates in a high pressure, corrosive and high temperature environment, these circumstances may damage the tubes in the heat exchangers. Our research examines the potential of corrosion of heat exchanger tubes after welding. The typical corrosion process is pitting. The corrosion resistance of stainless steel depends on a protective, passive film formed on the surface of the steel exposed to the service environment. The use of fusion welding for fabrication leads to local variations in the chemical composition inside the material, which may significantly alter the stability of the passive layer and hence the corrosion behavior. The impact of welding parameters (shielding gas, amperage) was examined on corrosion resistance of X6CrNiTi18-10 austenitic stainless steel. The corrosion test was performed according to ASTM G48 standard. The weight loss was measured in Fe(III)-chloride solution by the first corrosion test. The results showed that the corrosion resistance of stainless steel was better at 50 A and 10 l/min welding parameters. During the second test, a potentiodynamic corrosion test was made, and the potentiodynamic curve was measured in 9% saline solution. In this solution, the stainless steel had a better corrosion property because it was measured in a less aggressive medium

Effects of Thermochemical Surface Treatments on the Industrially Important Properties of X2CrNiMo 17-12-2 Austenitic Stainless Steel

Austenitic stainless steels have low corrosion resistance in applications where strong acids and vapors attack the surface, typically in food and chemical industries. This drawback can be improved by surface treatments. Salt bath, gaseous or plasma-based surface treatments are a diffusion process for improving the hardness of the surface layer of stainless steels without significantly affecting their corrosion resistance. Low temperature nitriding and carburizing process can form a diffusion zone or/and compound phase. The corrosion-wear resistance of austenitic stainless steels can also improve with low temperature plasma nitriding and carburizing. The effect of these treatments on hardness and corrosion resistance was investigated in this research. Optical microscopy and Vickers hardness test were used for the characterization of the surface and potentiodynamic tests were performed to determine the corrosion rate. The results show that the hardness of the kolsterised sample is higher compared to the plasma nitride one. Beside this property, the corrosion rate is similar, but pitting corrosion was observed on the surface, due to the Cr2N formation

Effect of different active screen hole sizes on the surface characteristic of plasma nitrided steel

Active screen plasma nitriding (ASPN) was performed on tempered 42CrMo4 low alloy steel samples. The effects of two technological parameters, namely 1) the hole size of the screen and 2) the open area ratio were investigated on the properties of the developed nitride layer. Scanning electron microscopy (SEM), atomic force microscopy (AFM) and Vickers microhardness testing were used for the characterization of the surface. The thickness of the nitride layer, the microhardness and the length of the nitride diffusion zone and surface areal parameters like surface roughness, skewness, grain diameter and area were measured and correlated with the screen hole size and open area ratio. It was found that these two major technological parameters influence different aspects of the developed nitride layer. The layer thickness and surface skewness (connected to either a balanced surface with zero skewness or the appearance of hill-like complex structures with positive skewness) is more sensitive to the open area ratio, while the surface roughness is primarily a function of the hole size. The maximum surface hardness, the length of the nitride diffusion zone or the size (diameter and surface area) of the nitride grains did not show a strong correlation with either of these two parameters. Keywords: Active screen plasma nitriding, Hole size, Surface characterisation, AF

Az aktív ernyő anyagának szerepe a plazmanitridálás során

A kutatás során az aktív ernyő anyagának szerepét vizsgáltuk plazmanitridálás során. 42CrMo4 típusú acélt nitridáltunk ötvözetlen acélból és titánból készített, valamint nikkelbevonatos aktív ernyővel. A plazmanitridálás 490 és 510 °C-on, 4 órán keresztül 75% N2 + 25% H2 gázkeverékkel történt. A vizsgálatokhoz pásztázó elektronmikroszkópot, energiadiszperzív röntgenspektrometriát és röntgenfotoelektron-spektrometriát alkalmaztunk. A vizsgálatok kimutatták, hogy a nikkelbevonatos ernyővel vas-nitrid nem képződött a felületen, továbbá a nitrogén többnyire molekuláris (N2) formában van jelen a képződött rétegben

The Role of the Material of Active Screen During the Plasma Nitriding Process

In this research the effect of the active screen’s material was investigated. 42CrMo4 steel was plasma nitrided with unalloyed steel, titanium and nickel active screen at 490 and 510 °C for 4h in 75 % N2 + 25 % H2 gas mixture. Scanning electron microscopy (SEM), energy dispersive spectrometry (EDS) and X-ray photoelectron spectroscopy (XPS) were used for the characterisation of the surface properties. Iron-nitride was not formed on the surface with nickel screen. The evaluation of examination results showed that most of the detected nitrogen was molecular (N2) in the formed layer