Delta Ferrite Content Research Articles

Influence of heat input on the microstructure and mechanical properties of CLAM steel multilayer butt-welded joints

Tungsten inert gas (TIG) welding was considered as one of the candidate technologies to achieve the box structure of test blanket module (TBM). In this paper, the effects of heat input on the microstructure and mechanical properties of multilayer TIG butt-welded China Low Activation Martensitic (CLAM) steel were investigated by microstructure observations, Vickers hardness, tensile and Charpy impact tests. The results showed that the microstructure of the weld metal (WM) were coarse quenched martensite and residual delta-ferrite. When the heat input value increased from 1.73 kJ/mm to 2.41 kJ/mm, the width of martensite laths increased slightly and the delta-ferrite content decreased firstly then increased. Moreover, the increasing heat input resulted in remarkable tempering effect on the previous layer of the WM by the following deposited layers. The transverse hardness distribution of the joints showed that softening occurred in the heat-affected zone (HAZ), and the hardness of WM decreased slightly as the heat input increased. The ultimate tensile strength values of the joints with various heat input were all higher than 630 MPa, and the rupture position located at the HAZ. Charpy impact toughness of the as-welded joints met the toughness criteria for the welded joint (≥27 J) of creep resistant 9Cr steel according to the standard of ISO-3580.

Effect of Welding Processes on the Microstructure and Mechanical Properties of Duplex Stainless Steel Weld Joints

Abstract The objective of the present investigation involves studying the microstructure and mechanical properties of duplex stainless steel (DSS) alloy 2205 and super DSS (SDSS) alloy 2507 weld joints fabricated by tungsten inert gas (TIG) welding and its variant, activated TIG (A-TIG) welding. Square butt weld joints were fabricated from 10-mm-thick plates of DSS and SDSS using single pass A-TIG and multi-pass TIG welding processes. The filler wire ER2209 was used for multi-pass TIG welding of DSS 2205, and ER2594 filler wire was used for multi-pass TIG welding of SDSS 2507. The microstructure in the A-TIG weld metals was found to be coarser, which was caused by high peak temperatures during A-TIG welding. The microstructures exhibited different forms of austenite, including grain boundary allotriomorphs, Widmanstätten side plates, and intragranular precipitates in the weld metal. In the A-TIG weld metals, the microstructure exhibited a balanced ferrite-to-austenite ratio. The hardness values of multi-pass TIG weld joints were higher compared to A-TIG weld joints. The tensile and yield strengths of multi-pass TIG weld joints were higher compared to A-TIG weld joints, which was mainly due to higher delta ferrite content and finer microstructure. The toughness values obtained by Charpy impact testing were higher in A-TIG weld joints compared with multi-pass TIG weld joints at room temperature, which was mainly due to the balanced ferrite-to-austenite ratio in the weld microstructure. However, at subzero temperatures, the A-TIG weld joints exhibit lower impact toughness because of their coarser weld metal structure.

Microstructural and Mechanical Properties Evolution of Bimetallic Cr-Ni and Cr-Mn-Ni Stainless Steel Joints

In the present work, the replacement feasibility of AISI 304 (Cr-Ni) with low nickel AISI 201 (Cr-Mn-N-Ni) stainless steel has been studied by employing dissimilar welding. Three different welding speeds were selected for gas tungsten arc welding process. The solidification mode and delta-ferrite content were predicted using WRC-1992 diagram, and conventional ferritescope was also used to calculate delta-ferrite. The microstructural analysis of weldments revealed the presence of lathy ferrite morphology dominated by vermicular ferrite for high and medium welding speed specimens, whereas low welding speed specimen depicts only vermicular morphology of ferrite in the weldments. Further, SEM–EDS analysis of weldments was carried out on weldments and indicated for the precipitation at fusion boundary. The tensile strength and microhardness was evaluated to establish structure–property correlation. It was observed that the weldments with higher welding speed depicted better mechanical properties. Failure of the tensile specimens took place in the fusion zone of AISI 201 side (adjacent to fusion boundary) in all three weldments. XRD analysis of fractured surfaces confirmed the formation of intermetallic compounds as Cr23C6 and martensite (small amount), which were responsible for deterioration of mechanical properties and failure of weld joints in fusion zone. Fractographic investigation of fractured surfaces revealed the presence of dimple-like morphology which leads to ductile fracture.

Effect of sulfate on the pitting potential of austenitic stainless steels 18Cr8Ni and 17Cr6Mn5Ni in chloride media

Abstract Pitting corrosion resistance of two austenitic stainless steels, 18Cr8Ni (Type 304L or UNS S30403 stainless steel) and 17Cr6Mn5Ni, was evaluated in three electrolytic solutions containing a fixed concentration of 0.6M sodium chloride and different additions of sodium sulfate, 0.06M, 0.15M or 0.6M. Cyclic potentiodynamic polarization tests were performed on as-received samples and on specimens annealed at 1010°C, 1040°C, 1070°C or 1100°C. The best pitting corrosion resistance was presented by the 17Cr6Mn5Ni steel annealed at 1070°C or 1100°C, with lower delta ferrite contents, in the electrolyte with the highest sulfate concentration. It can be found that the addition of sodium sulfate inhibits pitting corrosion and has a better inhibitor effect in the high manganese steel.

High-temperature oxidation of the dissimilar weld between AISI 304L and Fe-15.6Cr-8.5Mn using Ar and Ar-4%N2 shielding gas

Purpose The dissimilar welds between AISI 304L and Fe-15.6Cr-8.5Mn were investigated on oxidation at 700°C with the effects of dissolved nitrogen in the welds. This paper aims to clarify the oxidation behaviors to expand the range of application for Fe-Cr-Mn stainless steel. Design/methodology/approach Dissimilar welds between AISI 304L and Fe-15.6Cr-8.5Mn were fabricated using gas tungsten arc welding to investigate the oxidation behavior of the welds at 700°C. Pure Ar and Ar-4%N2 shielding gases were used to evaluate the effects of nitrogen gas. The welds were introduced to the cyclic oxidation test. In each cycle, the furnace was heated up to 700°C, and the temperature was kept at 700°C for 8 h, then the mass gain because of oxidation was examined. The scales after oxidation test were investigated by using scanning electron microscopy with EDX and X-ray diffraction analysis. Findings Addition of 4 per cent nitrogen to Ar shielding gas reduced delta-ferrite content in the weld. Ar-4%N2 shielding gas resulted in dissolved nitrogen which helped increase the diffusivities of chromium or oxygen vacancies in the oxide to facilitate the chromia formation at the inner part near the steel substrate. This protective layer can help reduce the Fe outward diffusion, thus reducing mass gain because of iron oxide formation. Originality/value The oxidation behavior of dissimilar welds between AISI 304L and Fe-15.6Cr-8.5Mn were investigated at 700°C. The evaluation is beneficial for expanding the range of application of Fe-Cr-Mn stainless steel at high temperature.

Effect of the H2 content in shielding gas on the microstructure and oxidation resistance of Fe−15.7 wt.% Cr−8.5 wt.% Mn steel GTA welds

The mixing of hydrogen in Ar-N2 shielding gas could produce a Fe-15.7 wt.% Cr-8.5 wt.% Mn steel weld bead shape in accordance with ISO 5817 quality level B at the welding speed of 5.4 mm s–1. At this speed the acceptable weld bead shape could not be obtained when using Ar-N2 as the shielding gas. The beneficial role of hydrogen could improve the welding productivity. At the same welding speed, the addition of hydrogen in the Ar-N2 shielding gas reduced the concentration of nitrogen dissolved in the weld, thus reducing the austenite stabilising effect due to nitrogen and increasing the delta ferrite content in the weld. Mixing hydrogen in the Ar-N2 shielding gas considerably reduced the weld oxidation rate, possibly from the hydrogen dissolved in the oxide.

Effect of oxide fluxes on activated TIG welding of AISI 316L austenitic stainless steel

In this work, activated TIG (A-TIG) welding on 8 mm thick plates of AISI 316L stainless steel was carried out. The effect of various single component fluxes and a multi-component flux on weld bead geometries was analysed. The multi-component flux mixture resulted in though thickness penetration in a single pass. Metallography of different zones was observed and weld zone was found to exhibit austenitic-ferritic microstructure. Delta ferrite content was measured with Ferritoscope and increase in delta ferrite content was observed in A-TIG weld zones as compared to base metal. From microhardness measurements, weld zone was found to be harder than the base metal due to increase in delta ferrite fraction.

Uvođenje novog termina - Gustina feritnog broja (FND) za merenje feritnog broja zavarenih spojeva na tankim limovima od nerđajućeg čelika serije 300

Delta-ferrite content in austenitic steel welds is a crucial parameter to control, since a number of properties depend on this. A FeritScope® is commonly used commercially to measure the Ferrite Number (FN) of the welds which takes advantage of the fact that the retained delta-ferrite phase at room temperature is magnetic whereas austenite is not. However, the readings obtained from the FeritScope® are influenced by a number of constraints such as sheet thickness, weld clad thickness, etc. Although some correction factors have been introduced by the FeritScope® manufacturer to account for these influential conditions, some other geometrical features of the welds were also found to influence the measured FN; for example, despite being a major influential parameter, there is no factor introduced to correct the measurement inconsistencies associated with smaller weld crown widths. In addition, the results obtained on measuring the FN using a FeritScope® contradicted the trends that were expected considering the literature. This research introduces a term called Ferrite Number Density (FND) to represent the ferrite content, in which the measured FN is further proportioned with the cross-sectional area of the weld bead, thus eliminating its dependency on the geometrical size of the weld. It has been established from this research that for welds completed on sheets thicker than 2.4 mm, the FN can be directly used as an indicator of the ferrite content in the weld; however, for thinner sheets, the FND must be used to indicate the ferrite content of the weld, if a FeritScope® with an apportioned size probe is used, e.g. in this case an FGAB1.3-Fe probe. Use of FND eliminated all the contradictions obtained between experimental data and literature for thin sheet welds.

Effect of Low-Temperature Sensitization on the Corrosion Behavior of AISI Type 304L SS Weld Metal in Simulated Groundwater

The manuscript presents the investigations carried out on the effect of low-temperature sensitization (LTS) of 304L SS weld metal on its corrosion behavior in simulated groundwater, for its application as a canister material for long-term storage of nuclear vitrified high-level waste in geological repositories. AISI type 304L SS weld pad was fabricated by multipass gas tungsten arc welding process using 308L SS filler wire. The as-welded specimens were subsequently subjected to carbide nucleation and further to LTS at 500 °C for 11 days to simulate a temperature of 300 °C for 100-year life of the canister in geological repositories. Delta ferrite (δ-ferrite) content of the 304L SS weld metal substantially decreased on carbide nucleation treatment and further only a marginal decrease occurred on LTS treatment. The microstructure of the as-welded consisted of δ-ferrite as a minor phase distributed in austenite matrix. The δ-ferrite appeared fragmented in the carbide-nucleated and LTS-treated weld metal. The degree of sensitization measured by double-loop electrochemical potentokinetic reactivation method indicated an increase in carbide nucleation treatment when compared to the as-welded specimens, and further increase occurred on LTS treatment. Potentiodynamic anodic polarization investigations in simulated groundwater indicated a substantial decrease in the localized corrosion resistance of the carbide-nucleated and LTS 304L SS weld metals, when compared to the as-welded specimens. Post-experimental micrographs indicated pitting as the primary mode of attack in the as-welded, while pitting and intergranular corrosion (IGC) occurred in the carbide-nucleated weld metal. LTS-treated weld metal predominantly underwent IGC attack. The decrease in the localized corrosion resistance of the weld metal after LTS treatment was found to have a direct correlation with the degree of sensitization and the weld microstructure. The results are detailed in the manuscript.

Low Temperature Embrittlement studies on Stainless Steel 304 LN TIG Welds

Austenitic stainless steel 304LN (SS 304LN) is widely used in nuclear industry. TIG welding is selected here to weld the stainless steel plates because it offers the possibility of producing high quality and porosity free welds. However, weld metal experiences hot cracks during welding of austenitic stainless steels. Due to this, austenitic stainless steel welds are designed to have 3-8% delta ferrite in the weld metal to avoid hot cracks during solidification. With the presence of delta ferrite, when these materials are exposed to elevated temperature (300 - 500°C) the weld transforms into embrittlement phases such as iron rich α and chromium rich α, G phase and M23C6. These embrittlement phases deteriorate the mechanical properties of the weld. In this study, an attempt is made to study the low temperature embrittlement on SS 304LN TIG Welds. The low temperature embrittlement behaviour on aged samples at (300, 350, 400°C) was evaluated for 10000 hours by mechanical property testing and micro structural examination. Mechanical testing involves Hardness test and Impact test. Delta ferrite measurement was done to see any transformation of delta ferrite. Fracture surfaces were characterized using SEM. Increase in hardness with increase in aging temperature and decrease in delta ferrite content at 350°C and 400 °C clearly indicate that aging temperature affects kinetics of transformation of delta ferrite. Scanning Electron Microscopy did not show any transformation of delta ferrite. It was found that aging treatment has a strong influence on impact toughness. Decreases in impact toughness value especially at sub – zero temperatures indicate kinetics of transformation of delta ferrite is affected by aging temperature during low temperature aging.

Correlation between microstructure and intergranular corrosion behavior of low delta-ferrite content AISI 316L aged in the range 550–700 °C

Abstract The microstructure and the phase identification of austenitic stainless steel AISI 316L with low δ-ferrite content (δ ≤ 1%) and aged for up to 80 000 h at temperatures ranging from 550 to 700 °C were investigated by using an optical microscope (OM), a scanning electron microscope (SEM) and a transmission electron microscope (TEM). Local changes of chromium content, resulting from nucleation and growth of chromium-rich phases during aging, were quantitatively assessed by energy dispersive X-ray spectroscopy (EDX) in the scanning transmission electron microscope (STEM). The intergranular corrosion behavior (IGC) of annealed and aged specimens was evaluated using the double loop electrochemical potentiokinetic reactivation (DL-EPR) and completed by IGC morphologies according to the ASTM A262 practice A standard. The results showed that δ-ferrite decomposed gradually into M 23 C 6 at 550 °C and decomposed totally into intermetallic phases (σ, η, χ, and R) and into secondary austenite (γ r ) at temperatures equal to or higher than 650 °C. Similarly γ-austenite decomposed into M 23 C 6 carbide at 550 °C and into intermetallic phases such as η and σ in addition to carbide, at higher temperatures. The time-temperature-sensitization diagram (TTS) was established and used to calculate the critical cooling rate (CCR) that prevents IGC sensitization. The analysis of IGC results leads to the conclusion that sensitization-desensitization is still controlled by the characteristics of chromium-depleted area surrounding austenite grain boundary regions. No significant effect of remained δ-ferrite and derived components on the corrosion behavior of AISI 316 L containing 1% of δ-ferrite.

Optimization of Welding Parameters, Influence of Activating Flux and Investigation on the Mechanical and Metallurgical Properties of Activated TIG Weldments of AISI 316 L Stainless Steel

This research investigation articulates the joining of AISI 316 L austenitic stainless steel plates of thickness 5 mm by activated tungsten inert gas (A-TIG) welding. Prior to the welding, the optimization of process parameters and the selection of suitable flux have been carried out to join the plates in a single pass welding. The experimental results show that the complete weld penetration can be achieved by using activating flux. The microscopic study divulges the presence of delta ferrite, sigma phase and various forms of austenite in the weld zone. Fischer Feritscope result indicates that the delta ferrite content in the weld is higher (7.8 FN) than the base metal (1.3 FN) which results in superior mechanical properties of the weld. Field Emission-Scanning Electron Microscope (FE-SEM) fractography reveals that the failure of weldments occurs in ductile mode. 180° bend test study reveals the good ductility of the joint.

Microstructure and Corrosion Behavior of Laser Melted 304L SS Weldment in Nitric Acid Medium

The manuscript presents the effect of laser surface melting on the corrosion property of 304L SS weldment in nitric acid medium. 304L SS weldment was prepared by gas tungsten arc welding process and subsequently laser surface melted using Nd:YAG laser. The microstructure and corrosion resistance of laser surface melted 304L SS weldment was evaluated and compared with that of 304L SS as-weldment and 304L SS base. Microstructural evaluation was carried out using optical and scanning electron microscopes attached with energy-dispersive x-ray spectroscopy. Corrosion investigations were carried out in 4 and 8 M nitric acid by potentiodynamic polarization technique. From the results, it was found that laser surface melting of the weldment led to chemical and microstructural homogeneities, accompanied by a substantial decrease in delta ferrite content, that enhanced the corrosion resistance of the weldment in 4 and 8 M nitric acid. However, the enhancement in the corrosion resistance was not substantial. The presence of small amount of delta ferrite (2-4 wt.%) in the laser surface melted specimens was found to be detrimental in nitric acid. X-ray photoelectron spectroscopy studies were carried out to investigate the composition of the passive film.

Investigations on Design and Formulation of Buttering Layer Electrode Coatings for Bimetallic Welds

The bimetallic welds (BMWs) between ferritic low alloy steels and austenitic stainless steel are used widely in steam generators of the power plants. The adoption of these welds in wide industrial applications provides feasible solutions for the flexible design of the products by using each material efficiently and economically. The present paper is an effort towards studying the development of austenitic stainless steel buttering filler material for bimetallic weld joint. The work aims at the design and development of buttering layer electrode coatings for shielded metal arc welding process using extreme vertices design methodology suggested by McLean and Anderson to study the effect of electrode coating ingredients on the buttering layer metal composition and delta ferrite content to prevent solidification cracking.

Study on surface appearance, geometry size, and delta-ferrite content of ZrO2-aided TIG welding of AISI 316LN stainless steel

This study investigated the influence of oxide with a more negative Gibbs free energy (ΔG) on the surface appearance, geometry size, and delta-ferrite (δ-Fe) content of AISI 316LN stainless steel subjected to flux-aided tungsten inert gas (TIG) welding. Powdered ZrO2 of various particle sizes mixed with 80 % water/20 % acetone solution was used as flux. The potential advantages of ZrO2-aided TIG welding were also demonstrated. The results show that nanoscale ZrO2 flux produces a TIG weld with a slag-free surface, but it did not significantly increase the depth-to-width ratio of the weld. The present work also found that ZrO2 flux slag influences the δ-Fe content of AISI 316LN stainless steel weld. ZrO2-aided TIG welding has low tendency to form undercut ting and allows high-speed welding. The potential advantages of the ceramic slag created by the ZrO2 flux are a small tem-perature difference between the center and edges of welding pool surface, a low solidified rate of liquid metal at the rear of the welding pool, as well as alleviation of the arc pressure at the front of the welding pool.

Effects of nitrogen and hydrogen in argon shielding gas on bead profile, delta-ferrite and nitrogen contents of the pulsed GTAW welds of AISI 316L stainless steel

AbstractThe general effects of 1, 2, 3 and 4 vol.-% nitrogen and 1, 5 and 10 vol.-% hydrogen in argon shielding gas on weld bead profile (depth/width ratio: D/W) and the δ-ferrite content of AISI 316L pulsed GTAW welds were investigated. The limits for imperfections for the quality levels of welds were based on ISO 5817 B. The plates with a thickness of 6 mm were welded at the flat position and the bead on plate. Increasing hydrogen content in argon shielding gas increases the D/W ratio. Excessive hydrogen addition to argon shielding gas will result in incompletely filled groove and excessive penetration of weld. Increasing welding speed decreases the weld-metal volume and the D/W ratios. Nitrogen addition to argon shielding gas has no effect on the D/W ratio. The addition of a mixture of nitrogen and hydrogen to argon shielding gas on the D/W ratio does not show any interaction between them. An effect on the D/W ratio can be exclusively observed as a function of hydrogen content. Increasing hydrogen content in argon shielding gas increases the δ-ferrite content of weld metal. Increasing either nitrogen content in shielding gas or welding speed decreases the δ-ferrite content of weld metal. The nitrogen addition increases the weld metal nitrogen content, however, the hydrogen addition leads to a decrease of weld metal nitrogen content.

Corrosion Resistance Studies of Austenitic Stainless Steel Grades in Molten Zinc-Aluminum Alloy Galvanizing Bath

The corrosion inhibition performance and mechanical behavior of galvanized and heat-treated four newly developed austenitic stainless steel grades and type 316L austenitic stainless steel for application as sink rolls in galvanizing baths of 0.14–0.21 wt.% aluminum was investigated and compared through immersion corrosion test to determine the weight loss between 168 and 504 h, tensile test, and Charpy impact test. The delta ferrite content of the test samples was observed and estimated through optical microscopy, feritscope, and ONRL diagram. Scanning electron microscopy and energy dispersive spectroscopy were used to characterize the surface microstructure, morphology, and chemical composition of the galvanized coating of the steel samples. Result showed that only two of the newly developed stainless steel compositions were selected for use in fabrication of galvanizing hardware based on the comparisons of corrosion and mechanical performances of tested alloys.

Creep Deformation and Rupture Behavior of Single- and Dual-Pass 316LN Stainless-Steel-Activated TIG Weld Joints

Creep deformation and rupture behavior of single-pass and dual-pass 316LN stainless steel (SS) weld joints fabricated by an autogenous activated tungsten inert gas welding process have been assessed by performing metallography, hardness, and conventional and impression creep tests. The fusion zone of the single-pass joint consisted of columnar zones adjacent to base metals with a central equiaxed zone, which have been modified extensively by the thermal cycle of the second pass in the dual-pass joint. The equiaxed zone in the single-pass joint, as well as in the second pass of the dual-pass joint, displayed the lowest hardness in the joints. In the dual-pass joint, the equiaxed zone of the first pass had hardness comparable to the columnar zone. The hardness variations in the joints influenced the creep deformation. The equiaxed and columnar zone in the first pass of the dual-pass joint was more creep resistant than that of the second pass. Both joints possessed lower creep rupture life than the base metal. However, the creep rupture life of the dual-pass joint was about twofolds more than that of the single-pass joint. Creep failure in the single-pass joint occurred in the central equiaxed fusion zone, whereas creep cavitation that originated in the second pass was blocked at the weld pass interface. The additional interface and strength variation between two passes in the dual-pass joint provides more restraint to creep deformation and crack propagation in the fusion zone, resulting in an increase in the creep rupture life of the dual-pass joint over the single-pass joint. Furthermore, the differences in content, morphology, and distribution of delta ferrite in the fusion zone of the joints favors more creep cavitation resistance in the dual-pass joint over the single-pass joint with the enhancement of creep rupture life.

Technology of Welding Joints Mixed with Duplex Steel

Results of the examinations of sample plates of mixed joints with the duplex steel were discussed. Examinations were taken on the sample plates of mixed joints of sheet plates type P355NL1 and X2CrNiMoN22-5-3 welded by the flux-cored wire DW-329A by the Kobelco company of the following category T 22 9 3 NL RC/M3 in the gas shroud M21 (Ar+18%CO2) (plate no.1), and nickel covered electrodes E Ni 6082 by the Böhler company (plate no. 2). Results of the side bend test of welded joint, transverse tensile test, stretching of the weld metal, impact strength, micro and macroscopic metallographic examinations, and measurements of the delta ferrite content were presented.

Metallurgical evaluation of austenitic stainless surfacing welding on SAE 4130 steel

The objective of this study was to make a metallurgical evaluation of the austenitic stainless surfacing welding on the sealing area of the riser tubes made of SAE 4130 steel. The study was divided into two steps. The first step aims to determine the dilution rate and deposition rate for the minimum and maximum levels of heat input according to the welding procedure specification (WPS) for TIG and SMAW processes, followed by analysis and study on the Schaeffler diagram in order to identify the welding consumable best-suited to attend the established quality criteria. This study identified the electrode 312 as the filler material for the first layer, and the electrodes 309 and 308 for the second layer, both using the maximum heat input of the WPS and the SMAW process, with benefits to productivity. The second step has as its objective the validation of the empirical results found in the 1st step, with the execution of surfacing welds with two layers each, and the metallurgical characterization of the welded joints by mechanical testing and microstructural analysis by optical and electronic microscopy. The results of mechanical testing and microstructure were considered satisfactory, filling the adopted quality criteria. An austenitic-ferritic microstructure with delta ferrite content between 10 and 15% was observed for both layers of the surfacing. The electrode 312 assumed a prominent position in the application of the first layer of the surfacing weld on the SAE 4130 steel, according to its higher content of delta ferrite and chromium, avoiding hot cracks formation. For the second layer, both the 309 and 308 may be used. All welds were made with high heat input, ensuring increased productivity, without significant change in the physical and mechanical characteristics.