Heat-Affected Zone Characterization of X2CrNiN22-2 Lean Duplex Stainless Steel by Metallographic and Electrochemical Techniques

Abstract

This research aimed to investigate the heat-affected zone of lean duplex stainless steel grade X2CrNiN22-2. Different heat-affected zone microstructures and grain morphologies were developed by Gleeble simulations. The governing microstructures were evaluated by metallographic techniques and electrochemical corrosion measurements. It was found that the 1200-800 °C cooling time significantly affects the microstructure, austenite content, and corrosion properties. The average austenite content in the case of 1 s cooling time is 30.7 ± 1%, which increased with the longer cooling times up to 38.6 ± 0.9%. The rapid cooling times resulted in a more ferritic microstructure, which promoted nitride precipitation in the ferrite grains. The nitride precipitations acted as nucleation sites for pitting initiation in 3.5 wt.% NaCl solution. The lowest pitting potential was measured in the case of the most rapidly cooled sample: 573 ± 31 mV, while the balanced, annealed microstructure had much better pitting corrosion resistance, showing a pitting potential of 1308 ± 62 mV vs. the Ag/AgCl (KCl sat.) reference electrode. The results of this research can be used in designing welding parameters for the welding of the X2CrNiN22-2 lean duplex stainless steel. Graphical Abstract

Kinetics of Intermetallic Phase Precipitation in Manual Metal Arc Welded Duplex Stainless Steels

“…In work [3], Varbai showed the results of welding simulation tests using the Gleeble device, indicating a strong correlation between cooling conditions and the microstructural morphology and corrosion resistance of LD X2CrNiN22-2 steel specimens. Specifically, the author reported that the HAZ of the 2202 steel grade shows excellent weldability as, even at shorter cooling times (lower heat inputs), the austenite content remains above 30% on average.…”

“…Difficult operating conditions of devices and working structures, e.g., in the energy, food, chemical, paper, and marine industries, require the use of materials that are resistant to environmental impacts and, at the same time, are characterized by high durability [1,2]. A common choice of designers in such situations are chromium-nickel corrosion-resistant steels with a two-phase structure (ferritic-austenitic), which demonstrate good corrosion resistance and higher mechanical properties than standard austenitic steels [3]. Typically, these steels are used in contact with aqueous solutions of chlorides and as a substitute for austenitic steels.…”

“…The development of this group of steels, forced by the need to reduce costs and ensure an equilibrium structure and appropriate weldability, has led to the development of many types of duplex steels, which are currently divided into lean duplex (LD), duplex, super duplex, and hyper duplex. All species from these groups are characterized by a balanced structure of approximately 50% ferrite and the main classification criterion in this case is the chemical composition [3,4]. The welding of elements from this group of high-alloy steels with a complex structure requires meeting certain procedural conditions that reduce the risk to their weldability.…”

“…The welding of elements from this group of high-alloy steels with a complex structure requires meeting certain procedural conditions that reduce the risk to their weldability. The basic problems of weldability of duplex steels include the risk of loss of mechanical and corrosion properties resulting from the increase in the volume fraction of ferrite due to the impact of short welding thermal cycles and the tendency to form cold cracks (and other manifestations of hydrogen embrittlement) and hot cracks as well as precipitations of intermetallic phases, e.g., the sigma (σ) phase [2,3,5,6].…”

“…Duplex steels can be successfully joined using various arc processes (SMAW, MAG, FCAW, GTAW, and SAW) as well as laser, resistance, and friction processes [1][2][3][4]8,10,11]. Very good results are also reported in the case of making dissimilar joints of duplex steel with other iron alloys and even with non-ferrous metal alloys [10,12].…”