Lean Duplex Stainless Steel Research Articles

Shear behavior of stiffened single perforated lean duplex stainless steel (LDSS) rectangular hollow beams

This paper presents the study on shear behavior of stiffened single perforated LDSS rectangular hollow beam, considering various orientations / patterns viz., inclined (IS), vertical (VS), horizontal (HS) and ring (RS); and effect of various cross-sections i.e. flat, angular and semi-circular (considering same material consumption). Based on the study, it has been found that in general, inclined stiffener (with flat cross-section) is relatively most effective in enhancing the shear capacity of perforated beams. For the inclined stiffeners, it is observed that the rate of increase in shear capacity (Vu/Vy) increases (in a non linear trend) with increasing stiffener length for higher stiffener thicknesses. In the case of vertical and horizontal stiffeners, there appears to have no/little significant improvement in shear capacity for both the variation in length, width and thickness. For the ring stiffeners, it is found that, shear capacity increases with increase in both breadth and thickness of the stiffeners. Comparison made between angular and semi-circular sections (keeping the same cross sectional area) showed that both the sections predicted similar behavior of shear capacity.

Computer prediction of α/γ phase fraction in multi-pass weld of duplex stainless steel and microstructural improvement welding process

A computer simulation of the α/γ phase transformation in a multi-pass weld of duplex stainless steel (DSS) was made to predict the distribution of the γ phase fraction in the heat-affected zone (HAZ). The kinetic equations including rate constants of the dissolution behavior as well as the precipitation behavior of the γ phase were determined by an isothermal heat treatment test. Based on the kinetic equations determined, the distribution of the γ phase fraction in a multi-pass weld of lean DSS was calculated by applying the incremental method combined with a heat conduction analysis of the welding process. The γ phase fraction was reduced in the higher temperature HAZ; however, that in the reheated HAZ was increased and recovered to the base metal level. Microstructural analysis revealed that the calculated results of the γ phase fraction in the multi-pass weld were consistent with experimental ones. Based on the computer prediction, the microstructural improvement welding (“reheat bead welding”) process, an analogous concept to the temper bead welding technique, is newly proposed for recovering the γ phase fraction in the weld just as in the as-welded situation.

Corrosion Fatigue Numerical Model for Austenitic and Lean-Duplex Stainless-Steel Rebars Exposed to Marine Environments

Steel rebars of structures exposed to cyclic loadings and marine environments suffer an accelerated deterioration process by corrosion fatigue, causing catastrophic failure before service life ends. Hence, stainless steel rebars have been emerging as a way of mitigating pitting corrosion contribution to fatigue, despite the increased cost. The present study proposes a corrosion fatigue semiempirical model. Different samples of rebars made of carbon steel, 304L austenitic (ASS), 316L ASS, 2205 duplex (DSS), 2304 lean duplex stainless steels (LDSS), and 2001 LDSS have been embedded in concrete and exposed to a tidal marine environment for 6 months. Corrosion rates of each steel rebar have been obtained from direct measurement and, considering rebar standard requirements for fatigue and fracture mechanics, an iterative numerical model has been developed to derive the cycles to failure for each stress range level. The model resulted in a corrosion pushing factor for each material, able to be used as an accelerating coefficient for the Palmgren-Miner linear rule and as a performance indicator. Carbon steel showed the worst performance, while 2001 LDSS performed 1.5 times better with the best cost-performance ratio, and finally 2205 DSS performed 1.5 times better than 2001 LDSS.

Metallographic screening of duplex stainless steel weld microstructure with a bipolar electrochemistry technique

A novel bipolar electrochemistry screening method to reveal corrosion susceptibility of weld microstructures is introduced. This metallographic method is applied to characterise the weld microstructure of a lean duplex stainless steel. The corrosion behaviour of the Fusion Zone (FZ), Heat Affected Zone (HAZ) and Base Metal (BM) was revealed, with the most severe etch response found at the interface between Fusion Zone (FZ) – Heat Affected Zone (HAZ). Transpassive and crevice corrosion were more significant in the FZ, with the highest corrosion resistance observed in the BM. The observed behaviour was linked to differences in local element distributions and the ferrite-to-austenite phase fraction. Corrosion pits formed via preferential dissolution of the ferrite, with the austenite preferentially dissolving in the transpassive region.

Microstructure Evolution during Annealing at Different Temperatures and Hot Deformation Behavior of Lean Duplex Stainless Steel 2101

Herein, the microstructure evolutions and mechanical properties of lean duplex stainless steel 2101 (LDX2101) are evaluated at different temperatures and a strain rate of 1 s−1. The experimental results show that the ratio of ferrite to austenite (α/γ) is increased between 950 and 1250 °C in total, but a turning temperature range occurs at 1000–1050 °C due to dissolution of the Cr2N precipitates along the phase boundaries. In LDX2101, high number density of Cr2N precipitates exist below 1000 °C and above 1100 °C, respectively. The morphologies of Cr2N precipitates change from massive to acicular with increasing temperatures. In addition, the excess strain is concentrated in α, and therefore strain is difficult to transfer to the adjacent γ. The aforementioned factors may lead to greater stress concentration along the phase boundaries (α/γ) and grain boundaries or grains (α), which causes edge cracking and surface cracking. With increase in deformation temperatures, the reduction of area increases and tensile strength decreases, but a turning temperature range occurs at 1000–1050 °C. The optimum hot deformation zone is in the temperature range of 1000–1100 °C by considering the precipitation temperature range of Cr2N precipitates. The formation mechanisms of Cr2N precipitates at different annealing temperatures are investigated.

Structural response to axial testing of cold-formed stainless steel angle columns

In this paper, the structural stability and compressive capacity of pin-ended cold-formed stainless steel angle columns with different slenderness were experimentally investigated. The experimental programme was performed on press-braked lean duplex stainless steel equal-leg angle sections with nominal dimensions of 80 × 80 × 4 mm, and involved material testing, initial imperfection measurements and 11 column tests. The test setup and procedure, together with the key experimental results, axial load vs. lateral deflections, axial load vs. torsional rotations and characterised failure modes, were fully reported and analysed. The experimental observations reveal that the failure mode type, including local/torsional, flexural-torsional and flexural effects, is highly dependent on the column's slenderness and initial imperfections. The measured compressive strengths were compared with the resistance predictions determined according to European and Australia/New Zealand codified design procedures. It was found that experimentally obtained ultimate capacities are significantly higher than those calculated according to the specifications. However, the database of test results is still quite limited, and a further research is needed to amplify the data needed to enable a more precise assessment of the codified procedures.

Effect of cold rolling on phase separation in 2202 lean duplex stainless steel

The effect of plastic deformation (cold rolling) on the thermal aging of a lean 2202 duplex stainless steel at intermediate temperatures (280 °C–450 °C) was studied using a combination of atom probe tomography and thermoelectric power measurements. In the undeformed condition, spinodal decomposition of ferrite was shown to be the prime aging process with an activation energy of 206 kJ/mol. Plastic deformation enhanced the aging and the austenite partly transformed into martensite. When no precipitation or phase transformation was observed in austenite, both ferrite and martensite decomposed. The spinodal decomposition kinetics of ferrite increased with increasing deformation rate. The FeCr-rich martensite also decomposed at 450 °C, via a nucleation and growth process, owing to a decrease of the Cr content in the matrix. Chromium nitrides, G-Phase, and Cu-rich precipitates were observed in the decomposed martensite.

Ultimate strength of lean duplex stainless steel single-shear bolted connections with four bolts

The recently developed lean duplex stainless steel (STS329FLD, KS) offers higher strength, greater corrosion resistance and lower cost compared with austenitic stainless steel (STS304 and STS316, KS) due to reduced nickel content. However, stainless steels are not included under structural materials in Korean Design Standards (KDS), and the corresponding design specifications are not regulated. In this paper, the structural behaviour of lean duplex stainless steel (STS329FLD) four-bolted connections were investigated through a parametric finite element analysis. The effectiveness of the analysis model was verified through a comparison of the test results. The main variables are end distance parallel to the direction of applied force and edge distance perpendicular to the direction of applied force. Curling (Out-of-plane deformation in the plate thickness) occurred in both test and analysis. It is found that curling reduced ultimate strength by up to 29%. Conditions of end distance and edge distance for lean duplex stainless steel bolted connection with a strength reduction effect caused by curling were investigated. Strengths according to current design specifications and equations proposed in previous studies were compared with analysis strengths. A modified equation was suggested that considers both actual fracture mode at ultimate state and the effect on strength caused by curling.

Initial Deformation Behaviors in Lean Duplex Stainless Steel

The deformation behaviors of the austenite phase in lean duplex stainless steels were investigated through uniaxial tension tests with different amounts of deformation. Microstructural analysis showed that in the initial deformation stage the deformation in austenite grains had a predominant effect on the strain hardening behavior of the LDX-2101 steel. The initial deformation in the austenite grains was found to be mainly accommodated by the formation of stacking faults. As the deformation increased further, mechanical twins were generated by the initial stacking faults and sequentially interacted with dislocations to accommodate the strain. The analysis of dislocation behavior revealed that the deformation twinning process followed the three-layer twin formation mechanism.

Structural Performance of Innovative Lean Duplex Stainless Steel Built-UP Columns under Various Loading

Structural Performance of Innovative Lean Duplex Stainless Steel Built-UP Columns under Various Loading - written by Hima M S , Samithamol Salim published on 2020/07/06 download full article with reference data and citations

Improvement of the Corrosion Resistance by Addition of Ni in Lean Duplex Stainless Steels

On newly developed Febalance-18Cr-7Mn-3Mo-3W-0.4N-(0.03, 0.57)Ni (in wt%) lean duplex stainless steels, the microstructure, element partitioning behavior, and resistance to pitting corrosion were investigated. After solution treatments, the two alloys were found to have similar microstructures in terms of phase fraction and grain size, and have a precipitation-free matrix. The polarization tests revealed that the addition of Ni was beneficial to improve the resistance to pitting corrosion, which was confirmed by the rise in pitting and repassivation potentials. The uniform corrosion behavior and galvanic corrosion rate of the matrix were investigated to explain the improved pitting corrosion resistance of the Ni-added lean duplex stainless steel. As a result, it was found that the addition of Ni enhanced the resistance to uniform corrosion by reducing the galvanic corrosion rate between the ferrite and austenite phases in the lean duplex stainless steel; thus, the pit growth rate was decreased, leading to improvement of the resistance to pitting corrosion.

Early stage of marine biofilm formation on duplex stainless steel.

The aim of this work was to investigate the bacteria-surface interactions occurring during the first hour of adhesion of marine Pseudoalteromonas NCIMB 2021 at the surface of 2304 lean duplex stainless steel in artificial seawater. A complete characterization of the biofilm and the passive film was performed coupling epifluorescence microscopy, scanning electron microscopy (SEM), x-ray photoelectron spectroscopy (XPS), and time of flight secondary ion mass spectrometry (ToF-SIMS). The coupling of XPS and ToF-SIMS analyses revealed that (1) protein and polysaccharide contents in the biofilm are similar in the presence or absence of nutrients, (2) the biofilm is mainly composed of proteins and the protein content is similar to the one of Tightly Bound EPS, (3) increased bacterial activity due to nutrients leads to chromium enrichment in the passive film in close vicinity to the bacteria.

Autogenous Fiber Laser Welding of 316L Austenitic and 2304 Lean Duplex Stainless Steels.

This study presents results of experimental tests on quality of dissimilar welded joints between 316L austenitic and 2304 lean duplex stainless steels, welded without ceramic backing. Fiber laser welded butt joints at a thickness of 8 mm were subjected to non-destructive testing (visual and penetrant), destructive testing (static tensile test, bending test, and microhardness measurements) and structure observations (macro- and microscopic examinations, SEM, element distribution characteristics, and ferrite content measurements). Non-destructive tests and metallographic examinations showed that the welded joints meet the acceptance criteria for B level in accordance with EN ISO 13919–1 standard. Also the results of the destructive tests confirmed the high quality of the joints: specimens were fractured in base material with lower strength—316L austenitic stainless steel and a 180° bending angle was obtained confirming the high plasticity of the joints. Microscopic examination, SEM and EDS analysis showed the distribution of alloying elements in joints. The microhardness of the autogenous weld metal was higher by about 20 HV0.2 than that of the lean duplex steel. Ferrite content in the root was about 37% higher than in the face of the weld. The Schaeffler phase diagram was used to predict the phase composition of the welded joints and sufficient compliance with the magnetic method was found. The presented procedure can be used for welding of 316L–2304 stainless steels dissimilar welded joints of 8 mm thickness without ceramic backing.

Cover Picture: Materials and Corrosion. 7/2020

Cover:Correlation of electron work function to crystallographic orientation and local misorientation of LDX 2101 20% cold deformed by scanning Kelvin probe force microscopy and scanning electron microscope–electron backscattered diffraction.More detailed information can be found in: Nuria Fuertes, Rachel Pettersson, Effect of cold rolling on microstructure, corrosion and electrochemical response of the lean duplex stainless steel LDX 2101® by a correlative EBSD–SKPFM investigation, Materials and Corrosion 2020, 71, 1052.

Finite element Analysis on Buckling Strength of Stainless Steel Circular Hollow Section Columns Under Concentric Axial Compression

Stainless steel has superior corrosion resistance, fire resistance, and maintenance compared to carbon steel as a structural material. Although austenitic stainless steel (STS304) has mainly been used as structural steel material, lean duplex stainless steel, STS329FLD with lower nickel component (reduced to 0.5–1.0% in KS) has recently been developed as a substitute for austenitic stainless steel. Since duplex stainless steel is less costly and has excellent corrosion resistance compared with austenitic stainless steel, its use is expected to increase in the field of industry and infrastructure. However, there have been little data to apply this duplex stainless steel member to structural use. This paper presents an experimental and numerical investigation on the structural behaviors of austenitic stainless steel (STS304 TKC) and lean duplex stainless steel (STS329FLD TKC) circular columns subjected to concentrically axial compression. Test specimens were fabricated with four types of column lengths and slender ratios and were tested with both fixed ends. Duplex stainless steel (STS329FLD TKC) material showed higher yield stress and tensile strength than those of austenitic stainless steel (STS304 TKC). The results such as buckling shapes (local and global buckling) and ultimate strengths through additional parametric analysis were investigated and were compared with those predicted by current design codes [American Society of Civil Engineers (ASCE) and Eurocode (EC 3)] and by design equations of previous studies. Modified buckling equations were recommended considering the initial imperfection factor and limiting slenderness of two types of stainless steel circular columns and the accuracy of buckling strength prediction was improved.

Damage mechanisms and failure analysis of high-strength eutectoid and duplex stainless steel wires subjected to static and cyclic axial tension loading under transverse compressive loads

Multi-wire strands used in a wide range of structural applications are designed to withstand high axial and cyclic tensile loads, but they can also be subjected to permanent or accidental transverse loads that might alter their tensile and fatigue behavior. In this context, the paper presents, respectively, a comparative experimental analysis involving two types of high-strength cold-drawn wires made of conventional eutectoid steel and an advanced lean duplex stainless steel. The same empirical fracture criterion was found to predict the tensile bearing capacity as a function of the applied transverse load in the two wires. The fatigue endurance required by the standards in force for prestressing steel wires when free from transverse loads are satisfied by the two wire types even under transverse loads as high as 40% of their tensile strength. The analysis of the failure mechanisms reveals consistent macroscopic and microscopic differences between the wires, which result from the local biaxiality of stress state and from the microstructural alteration induced by the transverse load when large plastic deformation occurs.

Data on the comparative assessment of corrosion resistance of 2101 duplex and 410 martensitic stainless steel for application in petrochemical crude distillation system

The corrosion resistance of 2101 lean duplex stainless steel and 410 martensitic stainless steel were studied and compared in 1M – 6M H2SO4 solution by coupon measurement for application in extreme process environments. Data obtained showed 2101 duplex steel is significantly more resistant to corrosion at lower concentrations (1M and 2 M H2SO4 solution) of the acid solution with final corrosion rate values of 0.000010 mm/y and 0.00028 mm/y compared to the values obtained for 410 martensitic steel at 0.0019 mm/y and 0.0738 mm/y. H2SO4 concentration at 4M - 6M narrowed the margin between the corrosion rates of both steel with final values of 0.0235 mm/y, 0.0326 mm/y and 0.0459 mm/y for 2101 duplex steel, and 0.0479 mm/y, 0.0482 mm/y and 0.0511 mm/y for 410 martensitic steel which signifies the corrosion resistance of both steels are comparable and generally similar at higher concentrations of SO4 2− anions. Statistical analysis through analysis of variance shows H2SO4 concentration strongly influence the corrosion rate value of both steel compared to exposure time which has limited influence.

Structural behaviour of hybrid stainless steel stub columns under axial compression

Numerical study on structural performance of hybrid stainless steel stub columns are provided in this paper by utilizing finite element (FE) software, Abaqus. Two novel stainless steel grades were used viz., Lean duplex stainless steel (LDSS) and Duplex stainless steel (DSS) for hybrid stainless steel stub columns. The current investigation on hybrid stub columns consist of two configurations: (1) Hybrid stainless steel (HSS) stub column adopting DSS on the flanges and LDSS on the web; and (2) Hybrid stainless steel (HSSa) stub column using DSS and LDSS on the web and flanges respectively. The numerical results are presented in terms of column capacity (Pu) and failure modes. As observed from the investigation, both flange thickness (tf) and flange width (bf) have more influence on the column capacity for HSS stub column as compared to HSSa stub column. On the other hand, increase in web thickness (tw) is found to provide an enhancement in column capacity for HSSa compared to HSS stub column, in contrast to the effect of tf and bf. In general, EN 1993-1-4 Class 3 limit for internal web is observed to be reliable for all stainless steel stub columns. Based on the FE results, new DSM formulation for HSS and HSSa stub columns was proposed based on modified DSM equation for carbon steel.

Numerical Investigation on Torsional Behaviour of Lean Duplex Stainless Steel Semi-elliptical Hollow Section Members

A systematic parametric study has been conducted to investigate the behaviour of lean duplex stainless steel semi-elliptical hollow section members subjected to torsion, using finite element software, Abaqus. The finite element models were initially validated with reliable experimental results; upon which parametric study was conducted. Effects of various key parameters such as aspect ratio, curve length, size and thickness of cross-section were studied. Based on the finite element study, sections of higher aspect ratio, curve length, larger size, and higher thickness were found to have more torque carrying capacity. Available design equations for plates under shear loading were checked for their applicability to the design of semi-elliptical hollow sections subjected to torsion. An attempt has also been made to develop design equations for lean duplex stainless steel semi-elliptical hollow section under torsion, based on EN 1993-1-4: 2006 + A1. Additionally, design equations based on deformation based method (in line with continuous strength method) were also proposed. The proposed equations were found to give reliable results for design of lean duplex stainless steel semi-elliptical hollow section members under torsion.

Effect of Ce on thermo-plasticity of lean duplex stainless steel

ABSTRACT The effect of Ce on the hot-working ability of lean duplex stainless steel (LDSS) was investigated in this paper. A hot tensile test was performed by GLEEBLE 3500 to compare the high-temperature deformation behaviour of materials containing 0.01% Ce and no rare earth added. The results show that Ce significantly promoted LDSS recrystallization at a strain rate of = 1 × 10−3 s−1, softening austenite phase in the duplex material, reducing the strength difference between ferrite and austenite. With the strain rate increases, the ferrite phase recrystallized obviously and the recrystallization of ferrite enlarged the hardness difference between two phases aggravating the deformation incompatibility of the austenite and ferrite, which is not conducive to the high-temperature deformation performance of the material. Meanwhile, the increase of strain rate inhibited austenite recrystallization behaviour. Besides, LDSS containing Ce exhibits an improved deformation performance under high temperature due to the size and number of inclusions reducing significantly after the rare earth added.