Austenitic stainless steels are extensively used in a wide variety of industries including the chemical industry due to their good combination of corrosion resistance and weldability.

In high-temperature treatment of stainless steels, M₂₃C₆ and chromium carbide are formed along grain boundaries of austenite, causing preferential depletion of Cr along the grain boundary and, consequently, an increased rate of corrosion.

Therefore, many researches have been conducted on the effects of the main factors such as temperature, concentration, microstructure, welding process parameters and pH value on the corrosion characteristics of a 316 L stainless-steel welded joint in different corrosion media. To the best of our knowledge, little research has focused on the investigation of the relationship between the corrosion behaviour and microstructure of a 316 L stainless-steel welded joint in nutrient fertilizer solutions.

In our country, the recent increase in the number of greenhouses for vegetables necessitates production processes of nutrient fertilizer including Ca(NO₃)₂, KNO₃, KH₂PO₄. Concentrator vessels used in these processes are made of 316 L stainless steel by welding, which requires a great wealth of information concerning the corrosion resistance of the 316 L parent material and weld metal against nutrient fertilizer solutions.

Pang Il Jin, a researcher at the Faculty of Material Science and Technology, quantitatively evaluated the corrosion resistance of 316 L weld metal and parent material, and clearly illustrated their corrosion mechanisms for the methodology of corrosion protection under the service conditions of concentrator vessels.

The test results showed that corrosion potentials of the weld were clearly lower than those of the parent material due to the heterogeneity of the microstructure in the welds.

You can find more information in his paper “A comparative study on corrosion resistance of 316 L stainless-steel welds in nutrient fertilizer solutions such as Ca(NO₃)₂, KNO₃, KH₂PO₄” in “The Canadian Journal of Chemical Engineering” (SCI).

Water is one of the most important natural resources for all living organisms including humans, animals, plants and other organisms. High-quality water is a major factor for human health, environment protection and sustainable development.

There are many WQE methods, and the results from different methods may differ from one another. Therefore, it is necessary to decide which is better.

Yang Won Chol, a researcher at the Faculty of Material Science and Technology, has proposed a novel integrated WQE approach combined with other various WQE methods, and illustrated and compared the effectiveness by applying it to two WQE cases.

First, he developed a novel integrated WQE approach combined with multiple WQE methods based on the weighted membership degree. It consists of the following steps: determining the WQGs of evaluation objects using multiple WQE methods, determining the priority weights of the individual methods, calculating the weighted membership degrees that evaluate objects in every grade/rank, and calculating final WQG indices of objects.

He applied it to two application cases. The results showed that the proposed approach had the maximum correlation and the minimum deviation, compared to other methods, which illustrated the validity of the proposed approach.

For more information, please refer to his paper “A New Integrated Water Quality Evaluation Approach Combined with Different Evaluation Methods Based on Weighted Membership Degree” in “Water Resources Management” (SCI).

Since high carbon steel has high tensile strength and hardness and good wear resistance, and is cheaper than alloy steels, it has been widely used for manufacturing cutting tools, formers, springs, rails, etc. However, it is recommended to avoid welding of high carbon steel with poor weldability as much as possible because the weld zones of this steel can be easily cracked by high hardenability.

Nevertheless, there are many cases in practice that need inevitable welding. Especially, welding high carbon steel with good wear resistance and high impact strength such as 75Mn steel is one of the challenges in practice: butt-joint welding of track rails of 75Mn steel, for example.

Various welding methods were used to join high carbon steel such as rails, and in these methods, enough preheating and post-weld heat treatment were performed in order to prevent cracking. However, there may be cases where preheating or post-heating cannot be applied but should be avoided. If preheating and post-weld heat treatment of welding zones are not conducted, additional oxidation and deformation of weld zones can be prevented and welding costs can be saved.

Jon Yong Il, a researcher at the Faculty of Material Science and Technology, investigated an arc welding process for a long butt joint of high carbon 75Mn steel plates without preheating to ensure the quality of weld and high productivity.

The analysis of microstructures and mechanical properties of weld showed that the metal inert gas (MIG) welding process is a dominant one among various welding methods.

You can find the details in his paper “Application possibility of arc welding processes for long butt joint of 75Mn steel plates without preheating” in “The Journal of Engineering” (SCI).