Duplex Stainless Steel Research Articles

Optimization approach of DED process to fulfil the requirements on material properties and component performance of waterjet impeller

Directed energy deposition (DED) processes have a great potential for ship building industry to reduce the lead time of ship part supply. However, ship parts such as propellers and impellers have critical requirements on material’s properties and component’s performance. To ensure the exploitation of DED manufacturing for critical parts, an optimization approach of DED process was developed and demonstrated on waterjet impeller made of duplex stainless steel. The developed approach is based on the understanding of the effects of DED process and heat treatment on the material microstructure, and the effects of the microstructure on the material properties, all optimized to fulfil the requirements on the component. The manufacturing and qualification testing were planned based on the requirements in accordance with the current standard guidance. The assessments by standard testing methods, including tensile, Charpy impact, and bending tests demonstrates that the DED material with an optimized heat treatment fulfil the standard requirements. Corrosion and cavitation tests were also performed and demonstrates the high resistances of DED material to cavitation erosion.

Effect of Coating Damage on the Micro Area Corrosion Performance of HDR Duplex Stainless Steel

In order to determine the effect of damaged insulating enamel on the corrosion of high-chromium (H), duplex (D), and corrosion-resistant (R) duplex stainless steel, the corrosion characteristics of HDR duplex stainless steel in 3.5% NaCl solution were studied by means of local electrochemical impedance spectroscopy (LEIS) and micro-morphology analysis. It was shown that the LEIS impedance was stable at about 7.0 × 103 Ω within 10 days when the HDR duplex stainless steel was not coated. The minimum LEIS impedance of exposed HDR at the damaged area fluctuated around 6.5 × 103 Ω within 15 days when the coating of the self-control insulating enamel damaged area was 1 mm × 10 mm. The coating-damaged area from 1 mm × 10 mm reduced to a circular hole with a diameter of φ1 mm, and the LEIS impedance of the exposed HDR increased at the damaged coating. When extending along the damaged coating to the intact coating area, the impedance rapidly increased, and the further the distance from the damage, the greater the increase in impedance. The impedance of coated HDR increased with the prolongation of immersion time and ultimately stabilized. The thicker the coating, the longer the impedance took to reach a stable state. The stabilized coating had a better effect on improving the corrosion resistance of HDR duplex stainless steel. Within 15 days, the HDR ferrite structure at different areas of coating damage prioritized corrosion. Cl− mainly comes from the solution, and Si and S elements mainly come from elements of the collective itself, with Cl− adsorption, S, and Si element inclusion being the main factors influencing the corrosion of the ferrite structure.

Research on mechanical properties of duplex stainless steel S22053 at elevated temperature and after fire

Stainless steel has advantages such as corrosion resistance, durability and esthetic appearance, with extensive application prospects in the field of construction engineering. In order to investigate the mechanical properties of duplex stainless steel S22053 at elevated temperature and after fire, 58 standard coupons were fabricated, with 4 coupons for tensile tests at ambient temperature, 18 coupons for steady-state tests at elevated temperatures, and 36 coupons for tensile tests after fire. The temperatures were set at 100 °C, 200 °C, 300 °C, 400 °C, 500 °C, 600 °C, 700 °C, 800 °C and 900 °C, in total of 9 temperature levels. Two cooling methods, water cooling and air cooling, were employed for the postfire coupons. Based on the test results, the expressions of stress-strain relations for duplex stainless steel S22053 under two fire conditions were proposed, and comparisons were made with existing models. The reduction formulas for 6 major mechanical parameters (E0, σ0.05, σ0.2, σ1.0, σ2.0 and σu) of duplex stainless steel S22053 under two fire conditions were obtained through data fitting. Reliability analysis was performed on the mechanical property parameters, and corresponding standard values were proposed.

Microstructural and mechanical properties of electron beam welded super duplex stainless steel

The electron beam welding of super duplex stainless steels is associated with challenges due to the concentrated heat input and the nitrogen loss that result in a predominantly ferritic structure after the solidification. This study presents an approach to overcome this issue by feeding nickel-based filler wire into the melt pool in welding of 2507 super duplex stainless steel. Results showed that the high-frequency beam oscillation combined with a multi-beam technique led a good mixing between the base metal and the filler wire, even at a large depth-to-width ratio. Additionally, the weld geometry was characterized by near-parallel fusion lines and a narrow heat-affected zone. The nickel addition resulted in a balanced microstructure in the weld metal with ferrite fractions of 35–55 %, despite a significant nitrogen loss, consequently leading to impact energy values of 215 ± 15 J and hardness values of 285 ± 15 HV. The findings of this investigation allow fabricators to effectively design electron beam welding processes for producing thick-walled super duplex stainless steel components.

Distribution and Characteristics of Residual Stresses in Super Duplex Stainless Steel Pipe Weld

This paper explores the distribution and features of residual stresses formed by super duplex stainless steel pipe welding. Experimental investigations, which encompass an elevated temperature tensile test and metallographic observation along with a hardness test and residual stress measurement, were first conducted to obtain the mechanical properties at high base metal temperatures and to confirm whether or not the duplex stainless steel undergoes martensitic phase development during the welding process. Finally, experiments were performed to scrutinize the residual stress evolution through the metallurgical phase transformation in the weld region and its vicinity. A sequentially coupled 3D thermal, mechanical and metallurgical finite element (FE) model capable of incorporating the experimental consequences was established next. A 3D FE simulation of the girth welding process was conducted, and the axial and hoop residual stress profiles along the girth were evaluated. The results substantiate that martensitic phase evolution occurs in the process of cooling during the welding of super duplex stainless steel, and they also highlight the significance of taking the metallurgical phase transformation into account in the numerical reproduction of the girth welding process for the accurate expression of weld-induced residual stresses, which is especially important for precisely predicting hoop residual stresses.

Analysis of coated samples containing hydroxyapatite/multiwalled carbon nanotubes on 2205 DSS substrate

For biomedical applications, hydroxyapatite and carbon nanotubes are currently being applied over duplex stainless steel (DSS) alone in order to increase corrosion resistance and biocompatibility. A composite of hydroxyapatite and multi-walled carbon nanotubes was used to improve biocompatibility, osseointegration, and corrosion resistance on 2205 DSS using electrophoretic deposition. The study investigates the effects of potential and time on the properties of the deposited layer in order to determine electrophoretic deposition factor values that are appropriate. The coating properties and effective groups of the phase resulting from this process are determined by Fourier transform infrared spectroscopy and X-ray diffraction. The antibacterial properties of E. coli bacterial strains are investigated for the coated layer. The adhesion between the hydroxyapatite and multi-walled carbon nanotube layers on the 2205 duplex stainless steel substrate was qualitatively evaluated using the adhesive tape test. It was found that the optimal suspension, which consists of 65 weight percent hydrogen acetate and 35 weight percent multi-walled carbon nanotubes, had a homogeneous morphology, a thick structure, and no cracks when coated at 50 V for two minutes.

A stochastic study of the effect of the phase ratio on the corrosion resistance of duplex stainless steel

The effect of the phase ratio of austenite and ferrite on the pitting potential (Epit) and passive current density of ASTM A890 grade 3A duplex stainless steel (DSS) was investigated using a stochastic method. The cumulative probability of the Epit value of DSS at different potential sweep velocities was linear, indicating that the pitting potential obeyed a normal distribution. In addition, the relationship between the pitting potential and the potential sweep velocity at various phase ratios was fitted by Epit ∝ log(v). The increase in ferrite promoted the sensitivity of the DSS to the potential sweep velocity. When the phase ratio of austenite and ferrite was 1:1, it showed better corrosion resistance. The phase ratio affected the passive current density more significantly than pitting potential.

Development of a duplex stainless steel for dry storage canister with improved chloride-induced stress corrosion cracking resistance

The chloride-induced stress corrosion cracking (CISCC) is one of the major integrity concerns in dry storage canisters made of austenitic stainless steels (ASSs). In this study, an advanced duplex stainless steel (DSS) with a composition of Fe–19Cr–4Ni-2.5Mo-4.5Mn (ADCS) was developed and its performance was compared with that of commercial ASS and DSS alloys. The chemical composition of ADCS was determined to obtain greater pitting and CISCC resistance as well as a proper combination of strength and ductility. Then, the thermomechanical processing (TMP) condition was applied, which resulted in higher strength than ASSs (304L SS and 316L SS) and better ductility than DSSs (2101 LDSS and 2205 DSS). The potentiodynamic polarization and electrochemical impedance spectra (EIS) results represented the better pitting corrosion resistance of ADCS compared to 304L SS and 316L SS by forming a better passive layer. The CISCC tests using four-point loaded specimens showed that cracks were initiated at 24 h for 304L SS and 144 h for 316L SS, while crack was not found until 1008 h for ADCS. Overall, the developed alloy, ADCS, showed better combination of CISCC resistance and mechanical properties as dry storage canister materials than commercial alloys.

Investigation of Spinodal Decomposition in Isothermally Heat Treated LDX 2101 type Duplex Stainless Steel at 475 °C

Spinodal decomposition of the ferritic phase, a thermally induced phase transformation process is studied in an LDX 2101 type lean-duplex stainless steel by different examination methods. This phase transformation in duplex stainless steels has special importance because it is responsible for the so called "475 °C embrittlement". This deterioration process causes a decrease in toughness and corrosion resistance. Fe-Cr alloys, thus several stainless steels, are susceptible to the spinodal decomposition at intermediate and low temperatures (<600 °C). Therefore, it is important to study this phenomenon in novel lean-duplex stainless steels as well. Our results revealed that spinodal decomposition occurs to a lesser extent in the studied type of lean-duplex stainless steel but its effect is not negligible in applications.

Numerical modeling of the temperature distribution and melt flow in dissimilar fiber laser welding of duplex stainless steel 2205 and low alloy steel

The research outlined in this paper pertains to the computational modeling and experimental investigation of laser keyhole welding between duplex stainless steel 2205 and low carbon steel (A516). A crucial aspect of keyhole welding entails predicting the phase transition behavior of the materials involved. The vaporized metal generates a recoil pressure and distorts the interface between the liquid and vapor phases, thus forming a vapor capillary. A multiphysics model employing the finite volume method was proposed to achieve a highly accurate simulation of the temperature and velocity fields. The findings demonstrate that the resulting weld bead relies heavily on the keyhole's structural characteristics. Additionally, analysis of the temperature distribution at a specific temporal and spatial point reveals that duplex stainless steel exhibits elevated temperatures owing to low thermal penetration at a distance of 5 mm from the juncture of the two components compared to A516. The numerical simulation results were in good agreement with experimental results for prediction of temperature filed and melt flow that have impact on weld bead and melt pool geometry. The weld bead width changes according to variation of welding speed and laser power has been in good agreement with the temperature distribution at upper surface of the workpiece extracted from simulation results. The melt pool geometry predicted from the simulation results (melt flow and temperature field) has been in good agreement with the melt pool geometry of the experiment. The temperature distribution from simulation results has a good correlation with the microstructural changes of the melt pool region according to the melting, solidification and temperature gradient at the melt pool region and adjacent HAZ of base metals.

Dissimilar joining of duplex AISI 2304 stainless steel/austenitic AISI 321 stainless steel using resistance spot welding technique: Microstructural evolutions, tensile-shear properties, and fracture analysis

In this work, microstructural characteristics and mechanical performance of spot weld joints of AISI 321 austenitic stainless steel (ASS)/AISI 2304 duplex stainless steel (DSS) were experimentally assessed. The welding current and time were varied to determine their effects on the failure load/energy and mechanism of dissimilar welds. The weld metal (WM)’s microstructure had a ferritic matrix as well as a distribution of grain boundary, Widmanstätten, and transgranular austenite. Some precipitates were found in the weld. The heat-affected zone (HAZ) of the AISI 321 ASS did not experience extensive phase evolutions and only grain coarsening occurred. This led to the HAZ softening. While extensive phase transformations were identified in the HAZ of the AISI 2304 DSS. Its microstructure contained a ferrite matrix with Widmanstätten and grain boundary-type austenite. Such microstructure resulted in the HAZ strengthening. Alteration of the welding condition from 1 kA – 2 s to 3 kA – 2 s raised peak load (tensile-shear strength) from 9.7± 0.8 to 16± 1 kN and energy absorbed to fracture from 15.52 ±1 to 51.2± 2 J. Enhanced WM size was responsible for them. Finally, as welding condition reached 4 kA – 2 s, they would decrease to 14.4±1 kN and 41.76± 3 J, respectively. It arises from surface splash. Once the welding condition varied from 3 kA – 1 s to 3 kA – 3 s, the weld performance was promoted i.e., improvement of peak load from 13± 1 to 19.6± 0.5 kN and energy absorbed to fracture from 23.4±2 to 49±3 J. It results from the WM enlarged. Ultimately, welding condition of 3 kA – 4 s causes a degradation in the weld performance i.e., drop of peak load to 15.8±1 kN and energy absorbed to fracture to 33.18± 2 J. This was on account of surface splash. With reference to the fracture analysis, interfacial, single pull-out, and double pull-out fracture modes were characterized.

Microstructural and Hall–Petch Analysis of Additively Manufactured Ferritic Alloy Using 2507 Duplex Stainless Steel Powder

The powder bed fusion–laser beam (PBF-LB) process, a method of additive manufacturing (AM), was used to print duplex stainless steel (DSS) using commercial-grade 2507 powders. While conventionally processed DSS has a two-phase microstructure consisting of 50% austenite and 50% ferrite, the PBF-LB-printed 2507 alloy was nearly 100% ferrite. Optimal processing conditions that minimized porosity were determined to be 290 W laser power and 1000 mm/s scan speed, and grain size, texture, and phases were characterized as a function of laser power and scan speed. Grain size increased with increasing laser power but decreased with increasing scan speed. A <100> texture diminished with increasing scan speed from 1000 mm/s to 1400 mm/s. No austenite phase was detected. Transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM) characterization revealed nanoscale chromium nitride precipitates in the ferritic matrix (incoherent hexagonal close-packed (HCP) precipitates at grain boundaries and coherent body-centered cubic (BCC) precipitates within the grains) and a high density of tangled dislocations. Tensile tests of as-printed alloys showed a yield strength of 570 MPa, an ultimate tensile strength of 756 MPa, and an elongation to failure of 10%. The tensile properties were analyzed based on the observed microstructure considering grain size, nanoscale precipitates, and the high density of dislocations.

Fatigue life of super duplex stainless steel sheets (UNS S32750) as influenced by micro plasma arc welding parameters: an investigation using the surface response method

Fatigue life of super duplex stainless steel sheets (UNS S32750) as influenced by micro plasma arc welding parameters: an investigation using the surface response method

Microstructural characteristics of different heat-affected zones in welded joints of UNS S32304 duplex stainless steel using the GMAW process: analysis of the pitting corrosion resistance

Abstract The influence of specific microstructural characteristics on the properties of single-pass welding joints was assessed by optical processed images, transmission electron microscopy, microhardness measurements and corrosion tests conducted in various regions of the heat-affected zone (HAZ) in a lean duplex stainless steel. The welded joints were obtained with heat inputs of 1.5 and 2.5 kJ/mm using a gas metal arc welding (GMAW) process with a shielding gas enriched in Ar. Three selected regions in the HAZ showed different ferrite grain sizes and austenite fractions. The place in the welded joint where the HAZ was narrowest, and therefore experiences the highest cooling rate, is most prone to the formation of cubic CrN metastable nitrides. Conversely, the place where the HAZ was wider promotes the precipitation of stable Cr2N nitrides with more coalesced intragranular austenite (IGA) particles, where presumably random interfaces predominate. The HAZ region where the cooling rate was the highest presented more pitting corrosion resistance.

Quantification of the Post-Fire Strength Retention Factors for Selected Standard Duplex and Lean Duplex Stainless Steel Grades.

The experimental quantification of retention factors related to the post-fire strength as well as the post-fire ductility of intentionally selected stainless steel grades applied in construction is the objective of the research presented here. These steel grades are characterized by a two-phase austenitic-ferritic microstructure of the duplex type. In this context, two mutually corresponding chromium-nickel-molybdenum steel grades are subjected to analysis, namely X2CrNiMoN22-5-3 steel belonging to the standard duplex group (DSS 22% Cr) and X2CrMnNiN21-5-1 steel belonging to the lean duplex group (LDSS). The similarities and differences in the mechanical properties exhibited by these steel grades after effective cooling, following more or less prolonged simulated fire action conforming to several development scenarios, are identified and indicated. The resistance of a given steel grade to permanent structural changes induced by the heating program proved to be the critical factor determining these properties and resulting in many cases in increased susceptibility to brittle fracture. The results obtained experimentally seem to confirm the quantitative estimates of post-fire retention factors forecast by Molkens and his team, specified for the steels exhibiting a duplex-type structure and tested by us. However, several of these estimates might be considered somewhat risky. Nevertheless, our results do not confirm the significant post-fire strengthening of steel grades belonging to the LDSS group following prior heating at a sufficiently high temperature, as reported earlier by Huang Yuner and B. Young.

Effect of Ball to Powder Ratios on the Phase Transformation of Austenite and Ferrite During Ball Milling of SAF-2507 Super Duplex Stainless Steel Powders

Effect of Ball to Powder Ratios on the Phase Transformation of Austenite and Ferrite During Ball Milling of SAF-2507 Super Duplex Stainless Steel Powders

Deformation Behavior and Texture Evolution of Ferrite and Austenite Phases in Lean Duplex Stainless Steel

To avoid cracks during hot rolling, a short process of direct cold rolling following solution treatment of the casting billet for preparing lean duplex stainless steel plates is proposed. The effect of cold rolling reduction on the microstructure, texture, and mechanical properties of UNS S32101 is investigated. The results show that dislocation slip is the main character in ferrite, which leads to dislocation tangles, dislocation cells, high‐density dislocation walls, and deformed microbands. However, twinning and strain‐induced martensite transformation (SIMT) occur in austenite, and the SIMT mechanism of austenite follows the classical model γ → ε → α′ and γ → α′, with the orientation relationship of Kurdjumov–Sachs ( and ) and Nishyama–Wassermann (N–W) ( and ). Meanwhile, at 50%, there is a transition from Cu texture to Brass texture in the austenite phase. At 12.5%, the yield strength is 344 MPa higher than that of the traditional hot rolling process, and the elongation remains about 35%. With the increasing cold rolling reduction, the elongation decreases while the strength rises significantly. Strengthening dislocations, fine‐tuning grains, and SIMT are the primary contributors to the improvement in strength.

Optimization of mechanical and surface properties of friction stir welded dissimilar joint of 2507 SDSS and 317L ASS by controlling process parameters

Stainless steel welding has been widely used in industrial manufacturing, and friction stir welding has been recognized to reduce production costs significantly. To fully utilize the different properties of 2507 super duplex stainless steel (SDSS) and 317L austenitic stainless steel (ASS), the mechanical and surface properties of 2507 SDSS and 317L ASS dissimilar stainless steel joints were improved using the friction stir welding (FSW) method. The influence of rotation speed on the microstructural characteristics, mechanical properties, and corrosion behavior of the weld joints was investigated by welding at a constant speed of 20 mm/min within the range of 300–600 rpm. Specifically, at 400 rpm, a welded joint with optimal performance was obtained. When the rotation speed is 400 rpm, the yield strength (YS) and ultimate tensile strength (UTS) of the welding joint are 493 and 692 MPa, respectively, and the elongation (EL) is 32 %. The tensile strength is higher than 317L ASS but lower than 2507 SDSS, the EL is lower than those of 317L ASS and 2507 SDSS, and the friction coefficient of the welded joint is 0.93, which is between 317L ASS and 2507 SDSS. Notably, the refinement of grains in the stirred zone significantly improved the corrosion resistance of the welded joint, considerably exceeding that of the 317L ASS but still lower than the 2507 SDSS. This work can provide a process reference for studying the mechanical and corrosion properties of dissimilar stainless steel FSW.

Behaviour and design of duplex stainless steel bolted connections failing in block shear

Duplex stainless steel (DSS) is an emerging construction material for structural engineering, which is featured with high mechanical strength and superior corrosion resistance. Compared with considerable research on DSS structural members, available research is relatively limited for structural joints/connections between these members. In line with this concern, this paper presents a comprehensive experimental and numerical study of duplex stainless steel bolted connections (DSSBCs), focusing on the behaviour and design related to block shear failure. Eleven specimens are tested to investigate the effect of different bolt arrangements on the block shear behaviour. Furthermore, a detailed numerical study was performed as a supplement to the experimental tests, where the anisotropic mechanical properties of DSS are considered in the finite element modelling. Based on the test and analysis results, it is found that the block shear failure mode of DSSBCs resembles that of carbon steel bolted connections, which can be characterised as necking of the tensile section and yielding of the shear sections. Using the experimental and numerical data obtained in this and previous studies, the applicability of various block shear design methods to stainless steel bolted connections is assessed. An updated design method is proposed for predicting the block shear capacity of duplex and austenitic stainless steel bolted connections. A proper partial safety factor/resistance factor is suggested for the proposed method based on the results of reliability analyses.

Rotary friction welding of X70 steel to duplex stainless steel

The objective of this research work is to present the mechanism of rotary friction welding of two dissimilar steels (X70 steel and duplex stainless steel). The selected rotational speed was maintained during the welding process. The welded sample was characterized by optical microscopy and hardness measurements. The welding sequence was presented. The duration and the mechanism of different welding stages have been determined. Optical observation revealed distinct zones in the welded joint. The Vickers hardness profile showed the difference in hardness across the welded joint.