Microstructure Of Weld Metal Research Articles

Improvement of the toughness and ductility of the weld beads by inducing growth of acicular ferrite with TiO2-nanoparticles during submerged arc welding

This work was focused to relate the mechanical properties of weld beads with size and superficial density of the acicular ferrite (AF) needles changing by impregnating two different sizes of TiO2-nanoparticles at the bevel before the SAW process. Microstructure of weld metal with addition of TiO2-nanoparticles with 21 and 127 nm sizes, respectively, shows an increase of the density (61.3 and 75.4%) and length of AF needles formed (156.4 and 68.8%), in comparison to the weld metal without TiO2-nanoparticles, namely the WB-0. Moreover, chemical analyses at weld metal and inclusions of weld beads with TiO2-nanoparticles reveal and increase on their Ti contents respect to those in the WB-0. Tensile and yield strength of the weld bead fabricated with the smallest TiO2-nanoparticles diminished in comparison to other weld beads. Besides, it was found that the average Vickers microhardness of weld metal decreased by adding TiO2-nanoparticles. On the other hand, their Charpy V-notch toughness values were found to be 30.1 and 102.6% bigger respect to those of the WB-0, by adding TiO2-nanoparticles with 21 and 127 nm sizes, respectively. In general, it was found that by adding TiO2-nanoparticles before the SAW process, the density and dimensions of the AF needles increase, which could be associated with the improvement of toughness and ductility of weld beads.

Investigations on Impact Toughness and Microstructure Characteristics of Gas Metal Arc Welded HY-80 Steel Plate

HY-80 is the high yield steel that commonly used for naval ship and submarine. Arc welding operations are critical stage in fabrication of this steel. During welding, the problem may occur in the heat affected zone due to the high temperature makes the microstructure suddenly changes. Coarse grain heat affected zone (CGHAZ) develops close to the fusion line, steel become brittle and the impact toughness decrease. This research investigated the microstructure of HY-80 weldment, impact toughness at sub-zero temperatures, and hardness distribution along cross-section of the welded joint. ER100S welding wire, Ar+10%CO2 shielding gas mixture and single V-groove butt joint with an angle of 60° were selected prior to welding. 12 mm thick of HY-80 steel plate that used in this experiment was multipass welded by gas metal arc welding (GMAW). Impact toughness at sub-zero temperature, hardness and microstructure evolutions of base metal (BM), heat affected zone (HAZ) and weld metal (WM) were observed. The result shows at a temperature of-80 °C, the lowest impact toughness was measured at WM (61 J) as compared to fusion line (101 J) and BM (217 J). The hardness measurement shows the maximum hardness was measured in CGHAZ followed WM and BM. Vickers hardness test result of weld joint at bottom area are higher than top area. It may caused of the low heat input of back weld compared to other passes. The lower heat input, cooling rate increased and initiate the formation of hard phase. The microstructure of WM shows acicular ferrites and non-metallic inclusions, these inclusions may deteriorate the impact toughness.

Pulsed Nd:YAG laser welding of 17-4 PH stainless steel: Microstructure, mechanical properties, and weldability investigation

Pulsed Nd:YAG laser welding of 17-4 martensitic precipitation hardening (PH) stainless steel (SS) is investigated. In order to achieve optimum laser welding parameters, bead on plate (BOP) welding was conducted on 17-4 PH SS. No crack was detected in the weldments, and microstructure of weld metal was δ-ferrite in the martensite matrix. Resistance to cracking of weldment was correlated to the presence of δ-ferrite in the weld metal, and using pulsed Nd:YAG laser as a low heat input welding method. Four HAZs were distinguished and microstructure evaluation in each zone is discussed. In the second part of this research, pulsed Nd:YAG laser welding of similar 17-4 PH SS in butt joint configuration was performed. Microstructure characterization and mechanical properties of weldment in as-welded and aged in 550 °C for 30 min conditions were investigated and compared. Aging caused precipitation of copper-rich clusters and increasing hardness of weld metal and homogenizing the hardness in HAZ. Tensile test results demonstrated that the failure occurred in the base metal and showed features of ductile fracture.

Effects of the welding processes and consumables on the fatigue and fracture performances for 3.5 wt.% nickel steels

Ethylene based on ethane gas in petrochemical products has a great economic advantage. Ethane gas can typically be liquefied by cooling to − 95 °C for more efficient transportation. To ensure the structural integrity of very large ethane gas carriers, ethane gas storage tanks are fabricated using materials that exhibit excellent fatigue and fracture performances at cryogenic temperatures, such as SUS304L, Invar alloys, Al 5083-O, high-manganese steels, and nickel steels. This study compared the fatigue and fracture performances of 3.5-wt.% nickel steels considering the welding processes and consumables. To compare the fatigue and fracture performances of 3.5-wt.% nickel steels, three different welding consumables were used for the weld metals with flux core arc welding and flux core arc welding + submerged arc welding. Fatigue and fracture tests with various nickel alloy steels were conducted according to ASTM E647 and ISO 12135, respectively. The mechanical properties with flux core arc welding + submerged arc welding were higher than those with flux core arc welding. In the case of the fracture toughness, the crack tip opening displacement values with flux core arc welding were approximately 45 and 18% lower than those with flux core arc welding + submerged arc welding at room and low temperatures (173 K), respectively. With a fixed slope of 3.0 and a material constant, C, the associated fatigue crack growth rate of the heat-affected zone with flux core arc welding was higher than that in the weld metal. In addition, the fatigue crack growth threshold values of the weld metal were higher than those of the heat-affected zone. The fatigue and fracture performance of various nickel alloy steels was explained in terms of the microstructure of weld metals.

The influence of Ti and Nb on solidification cracking of ferritic stainless steels, as determined using self-restrained samples

The susceptibility to solidification cracking of ferritic stainless steels was studied using the self-restrained method. The unstabilised steel was compared with mono and dual stabilised (Ti and/or Nb) steels. Autogenous gas tungsten arc welding at a speed of 6 mm/s, 3 mm/s, and 1 mm/s was done. All the specimens cracked at a welding speed of 6 mm/s. The weld metal of both the unstabilised and the stabilised steels contained a mixture of columnar and equiaxed grains. At a welding speed of 3 mm/s, all the specimens except the unstabilised grade cracked. The weld metal microstructures were mostly columnar, and the dual stabilised grades showed equiaxed grains. At a welding speed of 1 mm/s, the Nb stabilised and the dual stabilised steel containing Mo cracked whilst the other alloys did not crack. At a welding speed of 1 mm/s, the weld metal was dominated by columnar grains. The cracks were interdendritic. The crack surfaces were enriched in Nb, Ti, Mn, Si, Al, Mn, and Mo. The unstabilised ferritic stainless steel was resistant to solidification cracking whilst the stabilised steels were not. Low melting point eutectic phases associated with Ti and Nb might have contributed to solidification cracking.

Effect of cold metal transfer process parameters on microstructural evolution and mechanical properties of AISI 316L tailor welded blanks

Annealed austenitic stainless steel AISI 316L sheets of 1.6-mm and 2-mm thickness respectively was successfully joined by cold metal transfer (CMT) process at two different heat inputs of 0.125 to 0.236 kJ/mm. The process parameters such as welding current and welding speed were optimized to get defect free joints with full penetration depth. The geometry of the weld bead and microstructure of AISI 316L tailor welded blanks using ER308L filler wire are evaluated. Weld metal microstructure inspection by optical microscopy (OM) revealed that higher heat input used to melt the material led to equiaxed grains in the center of weld metal (WM). Due to the lower heat input, the microstructure at the heat-affected zone (HAZ) was similar to base metal (BM). Tailor welded blank’s (TWBs) were formed by designing L9 orthogonal array for 1.6 mm, 2 mm, and dissimilar thickness joint (1.6 mm and 2 mm) wherein the joints exhibited higher tensile strength and hardness as compared to base metal. The increase in tensile strength is corroborated to the increase in δ-ferrite and content of the alloying elements and the grain size in the WM. The microstructure refinement and the δ-ferrite presence contributed to the increase in hardness at the WM compared to HAZ and BM. Bend test revealed quality and soundness of the TWBs with no cracks or openings. The X-ray diffraction plots exhibited an increase in ferrite in WM and the ferrite number has been quantified at an average of 6.36 FN for TWBs and less than 0.5 FN for BM using Fischer Feritscope, which results in better mechanical properties. Fractography examinations indicated that samples failed as a result of the presence of dimples and microvoids resulting in ductile mode fracture at the welded joints.

GMAW Cold Wire Technology for Adjusting the Ferrite–Austenite Ratio of Wire and Arc Additive Manufactured Duplex Stainless Steel Components

The use of commercially available filler metals for wire and arc additive manufacturing (WAAM) of duplex stainless steel components results in a microstructure with a very low ferrite content. The ferrite–austenite ratio in the duplex stainless steel weld metal depends on both the cooling rate and particularly on the chemical composition. However, the research and testing of special filler metals for additive deposition welding using wire and arc processes is time-consuming and expensive. This paper describes a method that uses an additional cold wire feed in the gas metal arc welding (GMAW) process to selectively vary the alloy composition and thus the microstructure of duplex stainless steel weld metal. By mixing different filler metals, a reduction of the nickel equivalent and hence an increase in the ferrite content in additively manufactured duplex stainless steel specimens was achieved. The homogeneous mixing of electrode and cold wire was verified by energy dispersive spectroscopy (EDS). Furthermore, the addition of cold wire resulted in a significant increase in sample height while the sample width remained approximately the same.

Solidification Behavior of Duplex Stainless Steel (UNS S32205) Welds as a Function of WRC–1992 Diagram Equivalents and Cooling Rate

Duplex stainless steels solidify as 100 % Ferrite, however solidification of Duplex Stainless steel welds is a function of Chromium equivalent and Nickel equivalent alloying elements, filler metal and base metal composition and associated weld thermal cycle. Resultant solidification mode behavior and hence final weld metal microstructure is always a matter of interest among researcher because mechanical properties and corrosion properties are depending on weld metal ferrite content. The present research is to investigate the solidification mode behavior of duplex stainless steel welds with varying Chromium equivalent and Nickel equivalent ratios and associated weld cooling rate. In order to meet this objective, weld coupon were prepared using experimental Low Nickel, Medium Nickel and High Nickel electrodes using SMAW process, step wise increased in Nickel content from commercially available standard 09 weight percentage Nickel in E2209 design. WRC-1992 Diagram has been used to calculate Chromium Equivalent and Nickel equivalent and predict Ferrite Number using compositions of Base metal and Nickel enriched experimental electrodes. Microstructure characterization of all weld coupons is carried out using ASTM A 923 Method. Calculated values were correlated with the different microstructures developed. According to the findings of the studies, weld produced with higher Nickel content electrode, when cooled with maximum rate approximately 100.8 °C/ Sec , considered under study, exhibited FA-mode of solidification with as low as 1.71 Cr eq /Ni eq ratio and there was no noteworthy presence of intermetallic phases and precipitations in as-weld microstructures at approximate retained ferrite level of 15 Ferrite Number.

Microstructure and strain rate sensitivity behavior of SM490 structural steel weld zone investigated using indentation

In this study, a series of optical microscope examinations, constant loading rate indentation (CLR), and creep indentation (CI) tests were performed on room temperature to investigate the strain rate sensitivity behavior of the SM490 structural steel weld zone. Microstructures of weld metal (WM), fine-grain heat-affected zone (HAZ), and base metal (BM) in the weld zone were observed using optical microscopy. Numerous CLR tests were performed at a wide range of strain rate indentation from 0.02 s−1 to 0.2 s−1 in the middle regions of WM, fine-grain HAZ, and BM across the weld zone, and as a result strain rate indentation effects on both indentation hardness and yield strength were investigated. The results showed that both yield strength and indentation hardness of WM, fine-grain HAZ, and BM exhibit the strain rate-dependent behavior, in which yield strength and indentation hardness tend to increase with increasing strain rate indentation. Strain rate sensitivity (SRS) values of WM, fine-grain HAZ, and BM were determined by using three different models: indentation hardness, yield strength, and creep indentation models. The SRS behavior of SM490 structural steel weld zone was investigated. The results indicated that, while both yield strength and indentation hardness of BM are lower than those when compared with HAZ and WM, BM has the highest SRS value than does fine-grain HAZ and WM. Furthermore, WM has the lowest SRS value compared with the SRS values of other components in the weld zone. The results of this study were used to assess and understand the strain rate sensitivity behavior of SM490 structural steel weld zone.

Effects of phosphorus impurity on the microstructure and impact toughness of weld joint for the 12Cr2Mo1R heat resistant steel

A shielded metal arc welding (SMAW) process was used to join the 12Cr2Mo1R heat resistant steel plates in a butt configuration with R407C welding electrode. The microstructure of weld metal was examined by using the optical microscope, the morphology of the cracking and the propagation zones of the impact fracture surface were observed by the scanning electron microscopy. The small island-like M-A phases were found on the ferrite matrix, which composed by martensite and retained austenite with irregular shapes. With the increase of phosphorus impurity, the brittleness of weld metal increased and the impact toughness was sensitive to phosphorus impurity. The phosphorus impurity in the R407C welding electrode can change the fracture morphology of the weld joint.

Microstructure Evolution and Distribution of Mechanical Properties in Shielded Metal Arc Welded Dissimilar DSS 2205 and HY80 Joints

Dissimilar welding is a unique and complex process because in each zone in the different welding area have unique structures and characteristics. The modified structure may have a significant effect on weld metal properties. In this research, the primary objective is to investigate the microstructure evolution and hardness distribution mode of a different joint HY80 steel plate and Duplex type 2205 welded by using thick weld or shielded metal arc weld (SMAW). The microstructure of weld metal zones was observed. The test plates were welded in both butt joint and fillet joint by using E309L filler metal. It was found that the 309L electrode provides the equilibrium between austenite and ferrite phase in the different weld metal zones of DSS 2205 and HY80 steel joint. The results show that hardness distribution of different joint of both butt weld and fillet weld presents sinusoidal trend, where hardness in HAZ is highest. The peak value of hardness appeared in HY 80 base metal near the fusion line. The microstructure of base metal DSS 2205 shows fine grains of ferrite and austenite grains with dark and light shades respectively. The microstructure of weld metal shows coarse grains of austenite along with some slag inclusions as dark spots. The Heat Affected Zone of HY80 steel plate shows coarse grains of austenite and ferrite, while the heat affected zone of DSS 2205 shows thin fusion line with coarse grains of ferrite as dark zones and coarse grains of austenite as light zones. There is, a degree of variation in weld metal ferrite content was observed. Keywords: Duplex Stainless Steel, HY80, SMAW, Dissimilar Joint, Hardness, and Impact Toughness.

Effect of Nickel on the Microstructure, Hardness and Impact Toughness of SM570-TMC Weld Metals

SM570-TMC steel was applied in the various fields of steel construction where higher strength is required than conventional mild steel. This steel is commonly fabricated by fusion welding where flux-cored arc welding (FCAW) is preferred due to efficiency consideration. In this study, 14 mm thickness of SM570-TMC steel was butt weld by FCAW using three electrode wires with different nickel content (0% Ni, 1% Ni, 1.5% Ni). The microstructure of weldments was studied using an optical microscope. The hardness distribution tests were performed in the heat affected zone, parent metal and weld metal. And impact toughness of weld metals were measured at temperatures of 25 °C, 0 °C and -20 °C. The results show the steel plate welded using welding wire containing 1% Ni provides more superior impact toughness in the weld metal than welding wire 0% Ni, while the impact toughness of the sample which welded using welding wire containing 1.5% tend to decrease. Nickel element which deposited to weld metal by using welding wires containing 1% Ni has improved the impact toughness, but 1.5% Ni may too high which deteriorate impact toughness.

A Comparative Study on Direct and Pulsed Current Micro-plasma Arc Welding of Alloy Ti–6Al–4V

In this project, the sheet of Ti–6Al–4V alloy (annealed) with a thickness of 1 mm was welded with butt joints by means of pulsed current micro-plasma arc welding without using a filler metal. The purpose of this study is to optimize parameters in the event of increasing tensile strength by using pulse current and its comparison with the pulse-free system. Optical microscope and scanning electron microscope were used to investigate the type of phases, microstructure of weld metal, base metal and heat-affected zone. Results illustrated that due to the low thickness of the sheet, the non-use of filler metal in the welding process and the lower heat input of this process, all contributed to a higher cooling rate of the molten pool.

Study of Microstructure 304L Austenitic Stainless Steel Weld Deposited by GTAW for Root Pass and SMAW for Filler Passes

In the present experimentation, a 10mm thick austenitic stainless steel plate type 304L is welded using single V-joint configuration and approaching the joint from one side. Back purging has been employed to protect the rear side of the root pass weld metal against oxidation. The root pass has been deposited by gas tungsten arc welding (GTAW) process. The filler passes are deposited by shielding metal arc welding (SMAW) process at 90A and 120A welding currents giving heat inputs of the order of 0.679 and 0.933 kJ/mm respectively while the speed of weld deposition was kept practically constant. The results of experimentation show that the micro-hardness of weld metal and heat affected zone (HAZ) of weldments produced at lower heat input is higher whereas impact toughness value of weld metal and HAZ is lower than that of joints produced at higher heat input. The microstructure of weld metal and heat affected zone developed at lower weld heat input has been observed finer in comparison to that resulted at higher heat input. This has primarily happened due to a higher rate of cooling at low heat input.

The comparative evaluation of AISI 316/A387-Gr.91 steels dissimilar weld metal produced by CCGTAW and PCGTAW processes

The mechanical properties (impact toughness and hardness profile) and the microstructure of dissimilar weld metal of AISI 316 and A387-Gr.91 steels produced by constant and pulsed currents GTAW were studied. The microstructural studies showed that the pulsed current application leads to finer and equiaxed dendrites in the weld metal central region, as well as to the expansion of this region. In addition, the pulsed current produces finer secondary phases with more uniform distribution. The chemical analysis of the dendritic and interdendritic zones revealed that the segregation of alloy elements takes place in the entire weld metals and that it is more intensive with the constant current. The segregation is recognized as the main agent in forming the secondary phases, such as MC carbides ((Nb, Ti) C) and intermetallic compounds. Moreover, the microstructure images and map analysis of the weld metal near the fusion line indicated that a filler-deficient zone, including beaches, peninsulas and islands with a chemical composition similar to the base metal is developed. It was disclosed that the zone scope is decreased by the pulsed current. It was observed that the use of the pulsed current increases the weld metal fracture toughness and hardness simultaneously.

A new constitution diagram for dissimilar metal welds of high-manganese steels

When dissimilar metal welding of high-manganese (Fe-Mn) steels with low-alloyed steels, martensite may form in the weld metal. Current constitution diagrams for weld metal microstructure prediction cannot be used for Fe-Mn steels since the influence of the high manganese content in those steels is not sufficiently considered in the Ni equivalent. This paper concentrates on the development of a new constitution diagram for reliable weld metal microstructure prediction when dissimilar metal welding of Fe-Mn steels with low-alloyed ferritic and martensitic steel grades. For developing the constitution diagram a specially designed arc melting technique was used to experimentally simulate dissimilar weld metals in different dilutions and compositions. The resulting samples were evaluated regarding the type and quantity of the microstructural phases by means of hardness and ferrite number measurements as well as light-optical microscopy. Using this dataset it was possible to determine functional correlations between the chemical composition and the weld metal microstructures. By means of statistical analysis, a new constitution diagram was developed. Actual GMAW welds of different material combinations were performed to validate the applicability of the diagram. The new constitution diagram has a very high prediction accuracy and also distinguishes between the different types of martensite (e and α’).

Effects of Ti addition on the microstructure and mechanical properties of multi-pass E6010 high-cellulosic electrode weld metal

The aim of the present research was investigating the effects of Ti addition on the microstructure and mechanical properties of the E6010 high cellulosic electrode weld metal. Different concentrations of ferrotitanium were added to the electrode coating. Then, the effects of recovered Ti on the microstructure, tensile strength, hardness and impact strength of the weld metal were explored. Results showed that the recovery percent of Ti was below 10%. However, the Ti added to the melt altered the microstructural constituents and different ferrite morphologies including acicular ferrite, Widmanstatten ferrite, polygonal ferrite, and ferrite with secondary phase aligned along with the bainitic microstructure were developed at various Ti concentrations. Also, the addition of Ti improved hardness, tensile strength and yield strength while it deteriorated elongation and impact strength of the weld deposit. Finally, it was postulated that the Ti concentration in the weld metal should be lower than 0.065 wt% to achieve a deposit satisfying AWS A5.1 standard requirements.

Effect of aging treatment on the microstructures and mechanical properties evolution of 25Cr-20Ni austenitic stainless steel weldments with different Nb contents

The microstructure evolutions and the mechanical properties of the 25Cr-20Ni austenitic stainless steel weld metals with different Nb contents were investigated during the long term aging treatment at 700 °C. M23C6, Nb(C, N), α-Cr phase and Nb-nitride phase (Z phase) were observed in the microstructures of the aged weld metals. The results showed that the α-Cr phase precipitated in the interdendritic regions of the weld metals after being exposed to 700 °C for 500 h and the element Nb accelerated the precipitation of the α-Cr phase significantly. The density of the α-Cr phase decreased with the increase of the distance away from the primary Nb(C, N). Additionally, the α-Cr phase showed a crystallographic relationship with the austenitic matrix, [11¯1¯]α-Cr // [11¯0]γ and (011¯)α-Cr // (1¯1¯1)γ. It was observed that the Z phase precipitated in the periphery of the Nb(C, N) and may replace the Nb(C, N) after long term exposure to high temperature. The transformation of the Nb(C, N) into Z phase suggested that the Z phase had a higher stability than the Nb(C, N) particles at 700 °C for long term aging. The tensile strength of the Nb-bearing weld metal showed a continuous decrease at the initial stage of the aging treatment and then went up slightly with the prolonged aging time. However, the elongations and the impact energies of the weld metals decreased monotonously with the increase of the aging time.

Assessment of yield strength mismatch in X80 pipeline steel welds using instrumented indentation

Strain-based design (SBD) of pipelines allows stress owing to displacement-controlled loads originating from landslides, seismic motions, or frost heaves, to exceed yield stress. In such cases, the distribution of the strain over a large area (pipe) rather than local area (weld) is preferred. Accordingly, in SBD, yield strength of the circumferential girth weld is over matched when compared to the base metal. In this work, API-X80 pipeline steel sections were joined together using the robotic Gas-Metal Arc Welding (GMAW) process; filler metals and shielding gases were varied to achieve three different levels of strength (even, over and under match) between the weld and base metal. Weld metal and HAZ cross-section microstructures were investigated and correlated with micro-hardness maps to ensure that different mismatch levels were achieved. Yield strengths of the welds in the hoop direction were measured using both instrumented indentation and conventional tensile testing. The instrumented indentation technique used a 100-μm diameter nearly-flat indenter to estimate yield strengths for the welds and heat-affected zones from the load-displacement response for each zone. The measured yield strengths were compared with 0.2% offset tensile yield strength obtained through conventional tensile testing of all-weld and base metal specimens. Strength measurements, in the hoop direction, for weld metal from both of the techniques agreed to within 4.6%. The results showed that the nearly-flat tip indentation method can be used as a tool to directly estimate strength mismatch of pipeline girth welds. Measurements of yield strength for narrow coarse and fine grained heat-affected zones, which cannot be measured through any other method, can also be assessed using the techniques described herein.

Effects of dilution on alloy content and microstructure in multi-pass steel welds

Dilution represents the contribution from base material to weld metal and its important effects are complicated for multi-pass steel welds. In this study, the dilution was determined for each bead in a 3-pass gas tungsten arc (GTA) weld and a corresponding submerged arc (SA) weld. Different filler materials were used with each process, but both cases involved the deposition of filler wires into grooves in low-alloy (SA508) ferritic steel plates. Martensite and bainite were observed in the heat-affected zone (HAZ) of the base material in both cases. Acicular ferrite dominated the SA weld metal, while this phase was mixed with martensite and bainite in the GTA weld metal. Thermal-metallurgical modelling was performed and it correctly predicted the microstructures in the base-material HAZ for both the GTA and SA weldments. It also captured the GTA weld metal microstructure, when transformations from austenite to acicular ferrite and bainite were treated as being equivalent. However, this approximation led to overestimation of the martensite volume fraction in the SA weld metal. The modelling revealed that increases in dilution favour martensite formation but suppress bainite/ferrite transformations, owing to the melting of greater quantities of the base material, which has a relatively high hardenability.