Steel nitriding optimization through multi-objective and FEM analysis☆

Abstract Steel nitriding is a thermo-chemical process leading to surface hardening and improvement in fatigue properties. The process is strongly influenced by many different variables such as steel composition, nitrogen potential, temperature, time, and quenching media. In the present study, the influence of such parameters affecting physic-chemical and mechanical properties of nitride steels was evaluated. The aim was to streamline the process by numerical–experimental analysis allowing defining the optimal conditions for the success of the process. Input parameters–output results correlations were calculated through the employment of a multi-objective optimization software, modeFRONTIER (Esteco). The mechanical and microstructural results belonging to the nitriding process, performed with different processing conditions for various steels, are presented. The data were employed to obtain the analytical equations describing nitriding behavior as a function of nitriding parameters and steel composition. The obtained model was validated, through control designs, and optimized by taking into account physical and processing conditions. Highlights The paper shows the development of a model based on very broad experimental activity. The data were employed to provide a provisional tool for nitrided steel mechanical and microstructural behavior. A very good experimental–numerical correlation was found

Multi-objective optimization of steel nitriding

Steel nitriding is a thermo-chemical process largely employed in the machine components production to solve mainly wear and fatigue damage in materials. The process is strongly influenced by many different variables such as steel composition, nitrogen potential (range 0.8–35), temperature (range 350–1200 °C), time (range 2–180 hours). In the present study, the influence of such parameters affecting the nitriding layers' thickness, hardness, composition and residual stress was evaluated. The aim was to streamline the process by numerical–experimental analysis allowing to define the optimal conditions for the success of the process. The optimization software that was used is modeFRONTIER (Esteco), through which was defined a set of input parameters (steel composition, nitrogen potential, nitriding time, etc.) evaluated on the basis of an optimization algorithm carefully chosen for the multi-objective analysis. The mechanical and microstructural results belonging to the nitriding process, performed with different processing conditions for various steels, are presented. The data were employed to obtain the analytical equations describing nitriding behavior as a function of nitriding parameters and steel composition. The obtained model was validated through control designs and optimized by taking into account physical and processing conditions

Water Electrolysis for the Production of Hydrogen to Be Employed in the Ironmaking and Steelmaking Industry

The way to decarbonization will be characterized by the huge production of hydrogen through sustainable routes. Thus, the basic production way is water electrolysis sustained by renewable energy sources allowing for obtaining "green hydrogen". The present paper reviews the main available technologies for the water electrolysis finalized to the hydrogen production. We describe the fundamental of water electrolysis and the problems related to purification and/or desalinization of water before electrolysis. As a matter of fact, we describe the energy efficiency issues with particular attention to the potential application in the steel industry. The fundamental aspects related to the choice of high-temperature or low-temperature technologies are analyzed. Keywords: water electrolysis; ironmaking; steelmaking;

Integration of Open Slag Bath Furnace with Direct Reduction Reactors for New-Generation Steelmaking

The present paper illustrates an innovative steel processing route developed by employing hydrogen direct reduced pellets and an open slag bath furnace. The paper illustrates the direct reduction reactor employing hydrogen as reductant on an industrial scale. The solution allows for the production of steel from blast furnace pellets transformed in the direct reduction reactor. The reduced pellets are then melted in open slag bath furnaces, allowing carburization for further refining. The proposed solution is clean for the decarbonization of the steel industry. The kinetic, chemical and thermodynamic issues are detailed with particular attention paid to the slag conditions. The proposed solution is also supported by the economic evaluation compared to traditional routes

Integration of Open Slag Bath Furnace with Direct Reduction Reactors for New‐Generation Steelmaking

The present paper illustrates an innovative steel processing route developed by employing hydrogen direct reduced pellets and an open slag bath furnace. The paper illustrates the direct reduction reactor employing hydrogen as reductant on an industrial scale. The solution allows for the production of steel from blast furnace pellets transformed in the direct reduction reactor. The reduced pellets are then melted in open slag bath furnaces, allowing carburization for further refining. The proposed solution is clean for the decarbonization of the steel industry. The kinetic, chemical and thermodynamic issues are detailed with particular attention paid to the slag conditions. The proposed solution is also supported by the economic evaluation compared to traditional route

Microstructural, Mechanical and Wear Properties of Atmospheric Plasma-Sprayed and High-Velocity Oxy-Fuel AlCoCrFeNi Equiatomic High-Entropy Alloys (HEAs) Coatings

In this investigation, atmospheric plasma spray (APS) and high-velocity oxy-fuel (HVOF) techniques were used to produce AlCoCrFeNi coatings. High-entropy alloys (HEAs), due to their mechanical, chemical, and physical properties are capturing the attention of the international scientific community. Starting feedstock powders were characterized in terms of size, phase, and size, and corrosion test in NaCl, ball on disk, rubber wheel, and jet erosion tests was carried out on the obtained coatings. The results of the tribological investigation show that in the case of APS coatings, corrosion and wear behavior depend on the microstructure phases of the coating, as well as the amount of oxides. In particular, the wear morphology of APS surfaces is characterized by brittle fracture, with the presence of pores, cracks, and grooves. For HVOF coatings, further investigations on process parameters are needed because of the poor adhesion strength between the coating and the substrate. Anyway, the obtained corrosion resistance of HVOF coating is greater than that of the C steel substrate used to benchmark the results, and in addition, it ensures better performances in rubber wheel and jet erosion tests, but its wear resistance in the ball-ondisk test is worse because of the debris remaining in the wear track

Improving the Wear and Corrosion Resistance of Maraging Part Obtained by Cold Gas Spray Additive Manufacturing

The use of the cold gas spray (CGS) process as a metal additive manufacturing (MAM) technique for metallic part production has been deeply studied recently, mainly due to its advantages over other MAM techniques. CGS MAM is a high-productivity technique with a very low level of particle oxidation, microstructural changes, phase transformations, or deleterious residual thermal stresses in the part. The use of CGS MAM to produce maraging parts represents a gain for the industry by saving machining time and preventing raw material waste. Its wear resistance and corrosion behavior were evaluated in this work and were compared with cermet coatings deposited by high-velocity oxy-fuel (HVOF) on the CGS MAM maraging. This work presents the innovative and effective combination of different thermal spraying processes and materials to obtain MAM maraging parts with higher wear resistance, evaluating abrasion, sliding, and water erosion wear type

The influence of the powder characteristics on 316L stainless steel coatings sprayed by cold gas spray

Thermally sprayed 316L stainless steel coatings are commonly used on metallic structures due to their corrosion and wear resistance when compared to carbon steel. Cold Gas Spray (CGS) is a convenient thermal spray process to deposit 316L coatings, producing thick and very dense coatings, with almost no deleterious changes on the feedstock properties to the coating condition. The powder characteristics have influence on the microstructure of the coating, such as porosity and oxide contents, which alter its corrosion and wear behavior. CGS is an efficient technique to reduce the problems associated with material melting commonly found in other conventional thermal spray methods. In this work, different 316L powders, produced by different manufacturers, were deposited by CGS, applying the same equipment and parameters, with the objective to evaluate the relation between the powders' characteristics and coating properties. Their microstructure, adherence, hardness, as well as the performance on corrosion and wear testing were evaluated. The water atomized powders presented in general better results than gas atomized powders

A comparison of cold spray, atmospheric plasma spray and high velocity oxy fuel processes for WC-Co coatings deposition through LCA and LCCA

In this study, an environmental and economic assessment of WC-Co coatings deposited by Cold Gas Spray (CGS), Atmospheric Plasma Spray (APS) and High Velocity Oxy Fuel (HVOF) spray technologies is carried out. Using SimaPro LCA software, several environmental impact categories are analyzed to compare their environmental performance. The economic analysis includes capital and operating expenditures. The results have highlighted that all three processes exhibit low environmental impact in terms of CO2 emissions but the performance of the CGS process is heavily influenced by the low deformability of WC-Co, while the APS process is affected by high electricity consumption. In terms of economic analysis, the HVOF process exhibits the best performance, while the CGS process requires most time to deposit the coating, and consequently, it is the process where the workforce component is most significant. These results depend on the fact that CGS might not be the most suitable deposition technique for fabricating WC-Co coatings