Tensile and Impact Properties of Shielded Metal Arc Welded AISI 409M Ferritic Stainless Steel Joints

The present study is concerned with the effect of filler metals such as austenitic stainless steel, ferritic stainless steel and duplex stainless steel on tensile and impact properties of the ferritic stainless steel conforming to AISI 409M grade. Rolled plates of 4 mm thickness were used as the base material for preparing single pass butt welded joints. Tensile and impact properties, microhardness, microstructure and fracture surface morphology of the joints fabricated by austenitic stainless steel, ferritic stainless steel and duplex stainless steel filler metals were evaluated and the results were reported. From this investigation, it is found that the joints fabricated by duplex stainless steel filler metal showed higher tensile strength and hardness compared to the joints fabricated by austenitic and ferritic stainless steel filler metals. Joints fabricated by austenitic stainless steel filler metal exhibited higher ductility and impact toughness compared with the joints fabricated by ferritic stainless steel and duplex stainless steel filler metals.     

Study of Formation and Reversion of the Martensitic Phase Induced by Deformation of Lean Duplex Stainless Steel

Lean duplex stainless steels consist of a low percentage of nickel and molybdenum, presenting twice as much resistance compared to austenitic stainless steel and their cost is about twice as low. However, this class of steels has microstructural instabilities, such as the formation of martensite induced by austenite deformation by cold rolling. This feature can significantly alter the properties of interest of this steel. The formation of the martensitic structure, as well as its reversion, is little studied in the steels of the austenitic–ferritic structure. The process of formation and reversal of the martensitic structure in cold rolled stainless steel duplex UNS S32304 was investigated through magnetic measurements, microhardness and X-ray diffraction analyzes. The deformation process allowed the formation of the -martensite phase from the austenite phase with an increase in the values of saturation magnetization, coercive field and micro-hardness values as well as a change in the intensity of the X-ray diffraction peaks. The heat treatment performed at \(650\,^\circ \hbox {C}\) showed an increase in the peak intensity of the austenitic phase and a decrease in the saturation magnetization values, demonstrating a possible reversal of the martensitic structure. The SEM observations after annealing the Beraha’s etched samples revealed the possibility of a martensite transformation and reversion in a Lean duplex stainless steels.     

Potentiodynamic Polarization Behavior and Pitting Corrosion Analysis of 2101 Duplex and 301 Austenitic Stainless Steel in Sulfuric Acid Concentrations

The corrosion behavior of 2101 duplex and 301 austenitic stainless steel in the presence of sulfate (SO₄ ^2?) anion concentrations was investigated through polarization techniques, weight loss and optical microscopy analysis. The corrosion rates of the steels were comparable after 3M H₂SO₄. Results confirm that the duplex steel displayed a higher resistance to pitting corrosion than the austenitic steel. Experimental observation shows that its pitting potential depends on the concentration of the SO₄ ^2? ions in the acid solution due to adsorption of anions at the metal-film interface. The duplex steel underwent stable pitting at relatively higher potentials and significantly higher corrosion current than the austenitic steel. The duplex steel exhibited lower corrosion potential values thus less likely to polarize in the acid solution. Solution concentration had a limited influence on the polarization behavior of the austenitic steel and hence its reaction to SO₄ ^2? ion penetration from analysis of the pitting potentials and observation of its narrower polarization scans compared to the duplex steel which showed wide scatter over the potential domain with changes in concentration.     

Effect of Temperature and Chloride Ion Concentration on the Electrochemical Behaviour of Stainless Steel

The effect of temperature and chlorideion concentration on the electrochemical behaviourof austenitic-ferritic duplex stainless steelCOR 25 in an aqueous solution of 60%H_3PO_4+4%H_2SO_4is studied in this paper.The experiments show that the anodic activepeak current on potentiodynamic polarizationincreases by an order of magnitude with an in-crease of temperature from 50℃ and with anincrease of chloride ion from<1 mg/1 to 1500mg/1.Compared with the other materials tested,the austenitic-ferritic duplex stainless steelshows favourable corrosion characteristics inelectrochemical tests,being comparable to thefully austenitic alloy Sanicro 28,which hasa higher chromium and nickel content,and ismuch better than GX3CrNiMo2010.Corrosion ofthe duplex material is normally phase selec-tive,with phase boundary attack after unfavour-able heat treatments.     

Impact behavior of different stainless steel weldments at low temperatures

A comparative study was made of the fracture behavior of austenitic and duplex stainless steel weldments at cryogenic temperatures by impact testing. The investigated materials were two austenitic (304L and 316L) and one duplex (2505) stainless steel weldments. Shielded metal arc welding (SMAW) and tungsten inert gas welding (TIG) were employed as joining techniques. Instrumented impact testing was performed between room and liquid nitrogen (?196 °C) test temperatures. The results showed a slight decrease in the impact energy of the 304L and 316L base metals with decreasing test temperature. However, their corresponding SMAW and TIG weld metals displayed much greater drop in their impact energy values. A remarkable decrease (higher than 95%) was observed for the duplex stainless steel base and weld metals impact energy with apparent ductile to brittle transition behavior. Examination of fracture surface of tested specimens revealed complete ductile fracture morphology for the austenitic base and weld metals characterized by wide and narrow deep and shallow dimples. On the contrary, the duplex stainless steel base and weld metals fracture surface displayed complete brittle fracture morphology with extended large and small stepped cleavage facets. The ductile and brittle fracture behavior of both austenitic and duplex stainless steels was supplemented by the instrumented load–time traces. The distinct variation in the behavior of the two stainless steel categories was discussed in light of the main parameters that control the deformation mechanisms of stainless steels at low temperatures; stacking fault energy, strain induced martensite transformation and delta ferrite phase deformation.     

Characterization of Weld Solidification Cracking in a Duplex Stainless Steel

Weld solidification cracking in the duplex stainless steel SAF 2205 has been investigated and compared with that of alternate duplex and austenitic stainless steels. Varestraint weld-ability testing showed SAF 2205 to exhibit a lower cracking susceptibility than that of the duplex stainless steel Ferralium 255 but greater than that of a Type 304 austenitic stainless steel which solidified as ferrite and exhibited Ferrite Number 8 (FN 8) in the weld fusion zone. The high augmented strain levels required to induce cracking in these three alloys during Varestraint testing indicated a high resistance to solidification cracking at strain levels normally encountered in structural weldments. Cracking susceptibilities of the duplex and Type 304/FN-8 stainless steels were appreciably lower than that of a Type 304L stainless steel which solidified entirely to austenite and exhibited less than FN 1 in the weld fusion zone.

Microstructural characterization of SAF 2205 using conventional black-and-white and two different color metallography techniques showed solidification cracks to be associated with ferrite grain boundaries. Color metallography was also effective in revealing the fusion zone solidification structure and delineating second phases, including inter- and intragranular austenite and fine Cr₂N precipitates. Fractographic analysis of solidification crack surfaces from SAF 2205 Varestraint samples revealed dendritic and flat topographies, and confirmed a solidification versus solid-state cracking mechanism.     

Effect of δ-ferrite co-existence on hot deformation and recrystallization of austenite

This work evaluates the effect of co-existence of a large volume fraction of δ-ferrite on the hot deformation and dynamic recrystallization (DRX) of austenite using comparative hot torsion tests on AISI 304 austenitic and 2205 duplex stainless steels. The comparison was performed under similar deformation conditions (i.e. temperature and strain rate) and also under similar Zener-Hollomon, Z, values. The torsion data were combined with electron backscatter diffraction (EBSD) analysis to study the microstructure development. The results imply a considerable difference between DRX mechanisms, austenite grain sizes and also DRX kinetics of two steels. Whereas austenitic stainless steel shows the start of DRX at very low strains and then development of that microstructure based on the necklace structure, the DRX phenomena in the austenite phase of duplex structure does not proceed to a very high fraction. Also, the DRX kinetics in the austenitic steel are much higher than the austenite phase of the duplex steel. The results suggest that at a similar deformation condition the DRX grain size of austenitic steel is almost three times larger than the DRX grains of austenite phase in duplex steel. Similarly, the ratio of DRX grain size in the austenitic to the duplex structure at the same Z values is about 1.5.     

The properties of a wrought biomedical cobalt-chromium alloy

Two wrought biomedical cobalt-chromium alloys have been developed, and their mechanical properties and corrosion resistance determined by means of tensile and hardness tests and by electrochemical potential-time curves for isolated specimens in a 6.0 wt% NaCl solution at room temperature. In comparison with a current dental alloy, SC-H, and the basic type 18-8 austenitic stainless steel, it is shown that alloy II (chemical composition in wt%:0.11 C, 22.07 Cr, 15.20 Ni, 3.75 Mo, 9.30 W, balance Co) has superior properties. The alloy has a high strength together with a good ductility which permits adequate workability. Also, both cobalt-chromium alloys show a passive behaviour in 6.0 wt% NaCl solution, whereas the basic type 18-8 austenitic stainless steel shows a fluctuating potential and is thus susceptible to pitting, making it unsuitable for surgical implants.     

马氏体相变对孔蚀闭塞区化学和电化学行为的影响

采用模拟闭塞电池法和模拟闭塞溶液法研究了奥氏体304不锈钢形变诱发马氏体相变对孔蚀闭塞区化学和电化学行为的影响。为了模拟闭塞区内外间的电偶电流，对试件通入电流进行阳极极化。结果表明，与未形变的304不锈钢的试验结果相比，随着马氏体含量的增加，闭塞区溶液pH值下降，Cl^-迁入闭塞区的量更多。马氏体相的存在增强了材料的电化学活性，使其在模拟闭塞溶液中的自腐蚀电位负移，维钝电流密度增加，加速了闭塞区金属阳极溶解，促进了孔蚀的发展。     

Interaction between austein-ferrite phases on passive performance of 2205 duplex stainless steel

The passive behavior of 2205 duplex stainless steel (DSS) and its individual phases (α-phase, γ-phase) in neutral 3.5% NaCl solution was investigated by various electrochemical methods. The results indicated that galvanic effect between α and γ phases cannot deteriorate local corrosion, but favors the enhancement of the passive film. Under the galvanic effect, the diffusion of the dissolved passive cations would be promoted in a short distance between α and γ zones, leading to modifications of the chemical composition and semiconductive property of the passive film and therefore the enhancement of the corrosion resistance of DSS 2205.     

高强度奥氏体不锈钢的发展

工程应用对奥氏体不锈钢的强度、韧性、低磁性和耐蚀性的要求不断提高。本文综述了高强度奥氏体不锈钢(RP0.2≥400MPa)的发展趋势,以及几种高强度奥氏体钢的化学成分和力学性能。     

奥氏体铸体和18—8不锈钢在烧碱中的腐蚀行为

用失重法和电化学方法研究了奥氏体铸铁的１８－８不锈钢在高温烧碱中的腐蚀行为。用扫描电镜观察了两种材料泵件表面的腐蚀形貌,分析了奥氏体铸铁耐碱腐蚀性能优于１８－８不锈钢的原因。     

A new etching route for revealing the austenite grain boundaries in an 11.4% Cr precipitation hardening semi-austenitic stainless steel

A detailed metallographic characterization of a precipitation hardening semi-austenitic stainless steel is described. A new etching procedure based on the Lichtenegger and Blöch color etching solution, which is frequently used in duplex stainless steels to differentiate delta ferrite from austenite, has been used to differentiate martensite, austenite and the Chi-phase in this stainless steel. By changing the etching conditions, this etchant now reveals the austenite grain boundaries when the steel is in the austenitic state. Moreover, this solution is able to reveal also the prior austenite grain boundaries when the steel is in its martensitic state. This etching procedure represents a great advantage because it reveals, at the same time, different features of the microstructure.     

Microstructure and Corrosion Resistance of Dissimilar Weld-Joints between Duplex Stainless Steel 2205 and Austenitic Stainless Steel 316L

The microstructure and corrosion resistance of dissimilar weld-joints between stainless steel SAF 2205 and stainless steel AISI 316 L were investigated. Welding was accomplished by different types of welding wires AWS ER 347, AWS ER 316 L and AWS ER 309 L. To verify soundness of welded samples, nondestructive tests were performed. Metallographic samples were prepared from cross-section areas of weldjoints to investigate microstructure of different regions of weld-joints by optical microscopy and scanning electron microscopy. Corrosion resistance of weld-joints was evaluated in NaCl solution by potentiodynamic polarization and electrochemical impedance techniques. In the weld metal AWS ER 347, the brittle sigma phase was created, resulting in the decrease of weld-joint corrosion resistance. According to the results of metallurgical investigations and corrosion tests, welding wire AWS ER 309 L was suitable for welding duplex stainless steel(SAF 2205) to austenitic stainless steel(AISI 316L) by gas tungsten arc welding(GTAW)process.     

粉末冶金316L不锈钢抗腐蚀性能及其合金元素Si的作用

研究表明,添加4wt%Si 的粉末冶金316L 不锈钢由单相奥氏体转变为奥氏体+铁素体双相组织,烧结密度和体积收缩率分别提高12%和230%,疏松和孔隙明显减少,从而显著提高抗 Cl~-离子腐蚀性能,接近冶炼316L 不锈钢的水平。     

Synergistic effect of erosion and hydrogen on properties of passive film on 2205 duplex stainless steel

Stainless steels have shown great potential in the application of offshore oil and gas industry.However,the internal surface of stainless steel pipeline may simultaneously suffer erosion from the fluid media inside the pipeline and the damage of hydrogen that is generated from the external activities such as cathodic protection.The synergistic effect of erosion and hydrogen on the properties of passive film on 2205 duplex stainless steel was studied for the first time in a loop system coupled with a hydrogen-charging cell.The components,protective performance and semiconductive structure as well as properties of the passive film under different conditions were investigated using in-situ electrochemical techniques,surface characterization and computational fluid dynamics simulation.The results show that the combination of erosion and hydrogen could greatly thin the passive film,furthermore,the Fe³⁺/Fe²⁺ratio and O₂^-/OH^-ratio in the passive film also decrease dramatically under such a condition.Therefore,the hydration degree of the passive film greatly increases,resulting in an increase in active sites and a decrease in the stability of the passive film.Erosion could destroy the passive film through the impact of sand particles and accelerate the mass transfer process of electrochemical reaction.While hydrogen can not only enhance the charge transfer process,but also make the passive film highly defective.Under the combination of erosion and hydrogen condition,erosion could enhance the hydrogen damage and simultaneously hydrogen could also enhance erosion.Therefore,the synergistic effect of erosion and hydrogen could dramatically change the passive film component,decrease the protective performance,and increase the susceptibility of pitting corrosion of 2205 stainless steel in Cl-containing environment.     

粉末冶金多孔高氮奥氏体不锈钢的制备及性能

采用粉末冶金方法制备了多孔高氮奥氏体不锈钢并研究其力学性能和耐腐蚀性能。结果表明,高温气固渗氮能促进双相不锈钢向奥氏体不锈钢的转变,在其显微组织中出现了细条状和颗粒状CrN相析出物。随着造孔剂含量的提高孔隙率随之提高,而力学性能和耐腐蚀性能降低。与普通的多孔不锈钢相比,这种多孔高氮奥氏体不锈钢的力学性能更加优越,源于N的固溶强化和CrN等析出物的强化机制。随着孔隙率的提高多孔高氮奥氏体不锈钢的腐蚀倾向和腐蚀速率逐渐增大,造孔剂含量(质量分数)为10%的试样具有最佳的耐腐蚀性能。提高烧结温度有利于烧结块体的致密化,使腐蚀速率明显下降。     

Effect of cold rolling on microstructure and magnetic properties in a metastable lean duplex stainless steel

Microstructural and magnetic properties changes of a metastable ferritic–austenitic stainless steel due to cold rolling were studied together with the possibility to develop a new ferritic–martensitic stainless steel. In order to reduce costs low-Ni content was maintained in the lean duplex stainless steel considered, making it more susceptible to strain-induced martensitic transformation. In this study a practically complete γ → α′ transformation was found for 80% of thickness reduction, resulting a new two-phase ferritic–α′ martensitic stainless steel. To investigate the structural evolution different values of thickness reduction were applied. Light optical and scanning electron microscopy were performed to characterize the morphology and grain refining of the structure after each rolling step. Martensitic transformation and work hardening were detected and analyzed by studying of magnetic properties (saturation magnetic polarization, relative magnetic permeability, coercivity). Additionally, hardness tests were performed. The results highlighted a strong grain refining and increase in martensitic phase and hardness with increasing cold deformation. A direct relationship between microstructure and magnetic properties was revealed. In particular the reciprocal of relative magnetic permeability and the coercivity increased with martensite content and the amount of cold deformation. Therefore, the possible application of magnetic measurements as non-destructive tests to study microstructural evolution during cold rolling was shown for the steel considered.     

Laser Shock Processing of an Austenitic Stainless Steel and a Nickel-base Superalloy

An austenitic stainless steel 1Cr18Ni9Ti and a solid solution-strengthened Ni-base superalloy GH30 were shock processed using a Q-switched pulsed Nd-glass laser. Microstructure, hardness and residual stress of the laser shock processed surface were investigated as functions of laser processing parameters. Results show that high density of dislocations and fine deformation twins are produced in the laser shock processed surface layers in both the austenitic stainless steel and the nickel-base superalloy.Extensive strain-induced martensite was also observed in the laser shock processed zone of the austenitic steel. The hardness of the laser shock processed surface was significantly enhanced and compressive stress as high as 400 MPa was produced in the laser shock processed surface.     

Electrochemical polarization and pitting behaviour of Fe-Al-Mn alloys in chloride solutions

The electrochemical polarization behaviour of the austenitic Fe-8.25 Al-29.95 Mn-0.85 C and Fe-9.33 AI-25.94 Mn-1.45 C alloys, either solution-annealed and/or age-treated, was investigated in 3.5 wt% NaCl solution. Potentiodynamic polarization tests showed that these alloys passivated with difficulty and had much higher anodic passive current densities than that of the conventional austenitic 316 stainless steel (SS). The susceptibility to pitting corrosion of these alloys under open-circuit potential conditions was also studied in 6% FeCl₃ solution. Metallographical examination indicated that pitting and general corrosion occurred on the specimen surfaces. The corrosion rates of these alloys were about one order of magnitude higher than that of the AlSl 316 SS. In general, the corrosion resistances of the Fe-Al-Mn alloys studied were inferior to that of the conventional stainless steel.[/p]