Hardness In HAZ Research Articles

Effect of precipitate evolution on galvanic corrosion behavior of friction stir welded AA6061-T6 joint after post-weld aging

The microstructural transformation of FSW AA6061-T6 joint after post-weld T6 and its effects on the mechanical properties and corrosion behavior was investigated through electrochemical tests, immersion experiments and transmission electron microscopy (TEM) observation. The research results show that the joint efficiency and strength can be enhanced by post-welding aging. The hardness of SZ is recovered to a level close to that of matrix due to the sufficient precipitation of the effective strengthening phase β''. The main β' precipitate in over-aged HAZ coarsens during post-weld aging and cannot effectively restore strength, resulting in the lowest hardness in HAZ and limited tensile strength of the joint. The presence of macro-galvanic effects in the whole joint was confirmed. In SZ, the highest level of aging characteristics is caused by the highest aging drive due to fully solidified atoms, and is confirmed by the continuous grain boundary precipitates (GBPs) and dense matrix precipitates, which lead to the most positive potentials. Whereas, in HAZ, discrete GBPs and coarsened matrix precipitates indicate over-aged features, which lead to the most negative potentials. The potential difference between SZ and HAZ results in a macro-galvanic effect in the joint, where SZ is protected as the cathode and HAZ is corroded faster as the anode.

Dissimilar welding of Inconel 713 superalloy and AISI 4140 steel using Nd:YAG pulse laser: An investigation on the microstructure and mechanical properties

In the present research, welding of Inconel 713 superalloy and high strength AISI 4140 steel was successfully implemented by using pulsed Nd:YAG laser. The effect of heat input on the microstructural and mechanical properties of the weld was studied to find the best conditions for achieving a high quality weld. The microstructure characteristics of different weld regions including weld metal and heat affected zone were examined using the optical and scanning electron microscopies. It was observed that a columnar dendritic structure was formed at the edge of weld metal due to higher gradient temperature, while the reduction of gradient at the center of weld metal produced a cellular dendritic structure. The increase of heat input encouraged the formation of coarse dendritic structure which resulted in a reduction in the hardness of weld metal. The HAZ of 4140 steel side showed the maximum hardness for different values of heat inputs due to formation of martensitic microstructure, while the hardness in HAZ of Inconel 713 side was not showed a significant change. The higher value of heat input led to the segregation of Nb, Mo and Ti elements in the inter-dendritic regions and formation of brittle laves phase which resulted in a reduction in the tensile strength. However, the weld joint indicated a maximum tensile strength of 1068 MPa at lower heat input (1875 J/mm). The fracture surface of the tensile specimens showed a brittle fracture in the weld metal at different heat inputs.

Effects of Cooling Conditions on Mechanical Properties and Wear Performance of JIS S45C Steel Coated by Wire Arc Spray

The study of the effects of cooling conditions on mechanical properties and wear performance by coating AISI S45C steel with Chrome Nickel Amorphous wire arc spray showed that the average surface hardness of specimens under different cooling conditions such as SCCW, SCCO, SCCS and SCCNT was 601.6 HV, while the surface hardness of HAZ of SCCS and SCCW specimens decreased to 80-90 HV. The tensile test revealed that the average ultimate tensile strength of coated specimens was 706 MPa which was slightly higher than that of uncoated specimens. This result is consistent with Tukey’s one-way ANOVA method, which found a significant difference in tensile strength values at 0.05 and 0.01 levels. For wear resistance, coated specimens showed higher wear resistance compared to uncoated specimens. Overall, the results of this study showed that wire arc spray coating could increase the strength and stress and decrease %elongation of the specimens. Therefore, this technique is suitable for maintenance work to increase the strength of steel in the industry.

Effect of Repeated Weld Repairs on Microstructure and Mechanical Properties of Heat-Affected Zone in CA6NM Stainless Steel

The low-carbon martensitic stainless steel CA6NM is widely used in the impellers of hydroelectric and nuclear power units due to its advantages of high hardness, corrosion fatigue strength, and good fracture toughness. In order to analyze the number of repair welding times on the properties of heat-affected zone (HAZ, the most unstable area of welded joint property) in CA6NM, the microstructure and mechanical properties of HAZ with once-repaired welds (1R) and twice-repaired welds (2R) were tested. Through data analysis, the following conclusions are drawn for welded joints: (1) the grain size of HAZ with a different number of repair welding processes is smaller than that of the base material; (2) the density of texture concentration is reduced and the directionality is not obvious; (3) the density of twins and dislocations are increased; (4) the hardness and impact energy of HAZ of the 1R and 2R specimens are higher than that of the base material.

Problems encountered in underwater welding and remedies- a review

Wet underwater welding has proved to be the most suitable solution for underwater repairs and fabrication works. However, number of difficulties are faced that are specifically depicted in the testing and analysis of welds obtained while welded underwater. Major issues that are faced include immediate contact of workpiece with water leading to severe quenching effect, hydrogen diffusion due to dissociation of water which causes hydrogen induced cracking, arc instability, porosity in welds due to infused gases, loss of alloying elements leading to degradation of mechanical properties and microstructure of weld metal, increased hardness of HAZ and associated cracking. Since its inception during world war I, number of researchers have worked on finding the way out to control the harmful effects due to problems encountered during underwater welding. This paper discusses the experimental works conducted for detailing the problems encountered and the solutions suggested by researchers to overcome them. Controlling the input parameters during welding, addition of alloying elements into the electrode coating and multipass welding are the suggested solutions for obtaining desired characteristics in the welds.

Experimental investigation of tensile properties and microstructure of TIG welded dissimilar joints of Al6061/Al5083 Aluminum alloy

The welding of aluminium alloys especially in dissimilar combination is challenging owing to numerous problems. The present study focuses to optimize processes parameters for dissimilar welding of 6 mm thick dissimilar Al-6061 and Al-5083, using Tungsten Inert Gas welding as well as to investigate the influence of the process parameters on tensile properties and microstructure of developed welds. A single V-butt joint configuration (bevel angle 60 and root gap 2 mm) ̊ of plates was used for welding. Three levels of input parameters viz. voltage, current and welding speed were selected for performing experiments as per L9 orthogonal array. The hardness and tensile strength were taken as output parameters or performance characteristic in the study. The optimum parameter settings for highest heat affected zone hardness and ultimate tensile strength of dissimilar welds have been suggested by using S/N ratio. The result predicted by optimization has an error of 2-3%. Finally, the effects of voltage, current and welding speed on m icro structure, hardness and tensile strength of welds have been investigated. Welding speed and current were the most influencing process parameter for controlling the hardness of HAZ and tensile strength of the welds.

Performance of weld bead profile during A-TIG welding on nitrogen alloyed stainless steel

Austenitic stainless steel (ASS) is widely fabricated by tungsten inert gas (TIG) welding for aesthetic look and superior mechanical properties while compared to other arc welding process. Hitherto, the limitation of this process is low depth of penetration and less productivity. To overcome this problem activated tungsten inert gas (A-TIG) welding process is employed as an alternative. In this investigation the welding performance of conventional TIG welding is compared with A-TIG process using TiO2 and SiO2 flux with respect to weld bead geometry. The experimental investigation on A-TIG welding of ASS-201 grade shows TiO2 flux helps in achieve higher penetration as compared to SiO2 flux. While welding with SiO2 the hardness in HAZ and weld region higher than that of TIG welding process.

Investigation of arc stability, microstructure evolution and corrosion resistance in underwater wet FCAW of duplex stainless steel

Underwater wet flux-cored arc welding (FCAW) process was used to join 2205 duplex stainless steel using Ni-based filler under three different heat inputs of 16.9 kJ/cm, 23.5 kJ/cm and 32 kJ/cm. The arc stability, microstructure and corrosion resistance with different heat inputs were studied. The results showed that the welding process at the heat input of 23.5 kJ/cm was stable with less spatter and good weld appearance. The weld width, weld penetration and dilution ratio increased with increasing heat input. A single-phase austenitic microstructure was obtained for all welds with varied parameters. The heat-affected zone consisted of coarse ferrite and austenite in grain boundary. The grain size of weld zone and heat-affected zone coarsened as the heat input rose. Compared with the base 2205 base metal, the hardness of HAZ increased about 15% while the weld metal changed little. Electrochemical test in 3.5% NaCl solution indicated that the corrosion resistance of the weld metal under high heat input was better, but its corrosion resistance was inferior to that of base materials. Weld metal obtained at 23.5 kJ/cm possessed comprehensive properties in terms of arc stability and corrosion resistance. These results are helpful to promote the application of duplex stainless steel in the fields of nuclear power fields.

Bead-on-Plate Underwater Wet Welding on S700MC Steel

The participation of high strength steels in marine and offshore structures is increasing, which makes it necessary to develop recommendations for underwater repair welding works. The article presents the results of bead-on-plate welded specimens made of S700MC high strength steel in underwater wet welding conditions by covered elec- trodes. Three specimens with heat input values in the range 0.91-1.05 kJ/mm were made. The specimens were sub- jected to visual, metallographic, macro- and microscopic tests as well as hardness measurements using the Vickers method. It was found that the higher heat input leads to formation of mixed bainite-martensite microstructure in the heat-affected zone (HAZ). Lower heat input value results in presence of martensite in HAZ. It was shown that in the scope of the performed tests, the maximum hardness of HAZ did not exceed the critical value for the material group, and the increase in heat input caused the decrease of hardness by about 25 HV10 to a level 250-260 HV10.

Effect of post weld heat treatment on mechanical properties of MIG welded mild steel

ABSTRACT In railway locomotive, fabricated bogie frame structures are susceptible to crack when made up of un-heat-treated and heat-treated structure. Therefore, variation in behaviour of the samples made of the same material in both the conditions, that is, PWHT and un-heat-treated is important to quantify and analyse. In the present work, specimens from IS 2062 E410 are prepared as per standard weld procedure specification using MIG welding and half of the welded samples are heat-treated following a predefined heat treatment procedure. The samples are tested to find out their mechanical properties like hardness, toughness, tensile strength and microstructure of HAZ. Refined grain structure and significant improvement in mechanical properties of the specimen are observed in the samples undergone post-weld heat treatment.

Failure analysis of cracked 2.25Cr–1.0Mo steel tubes of an oil refinery boiler

After failure of a refinery boiler, some cracks were detected in its tubes made of 2.25Cr-1Mo steel. The tubes were in the boiler superheater section. To determine causes of the cracking, samples were taken from the tubes, and different microscopical and analytical techniques such as scanning electron microscopy (SEM) and mechanical tests were used. Furthermore, finite element analysis (FEA) was used to evaluate the stress conditions in one of the cracked tubes. The results of analysis showed that the tube material was in accordance with the ASTM A213 chemical composition requirement however based on the calculated J-factor, the material was susceptible to temper embrittlement. The FEA results showed tensile residual stress formed at welding zone due to non-alignment before tubes welding. Considering the intergranular propagation of the cracks, the hardness of HAZ and other findings, it was concluded that stress corrosion cracking was the major damage mechanism.

Proširena primena sistema za predviñanje tvrdoće kod zavarivanja čelika A533B za razne niskolegirane čelike

Temper bead welding is one of effective repair welding methods in case that post weld heat treatment is not easily applied. In order to evaluate the effectiveness of temper bead welding, hardness in HAZ becomes important factor. The neural network-based hardness prediction system of HAZ in temper bead welding for A533B low-alloy steel has been constructed by the authors in the previous study. However, for HAZ hardness prediction of other steels, it is necessary to obtain hardness database for each steel which is time-cost consuming, if the same method is used. The present study has been conducted to develop the generalized hardness prediction method applicable for other steels by utilizing the hardness data-base of A533B steel assuming that the hardness in HAZ of steels after tempering have a linear relationship with LMP (Larson-Miller parameter). By using the newly proposed extended method, only a few hardness data-base for the other steels is needed to obtain. Hardness distribution in HAZ of temper bead welding for other steels was calculated by using the extended hardness prediction system. The thermal cycles used for calculation were numerically obtained by a finite element method. The experimental results have shown that the predicted hardness is in good accordance with the measured one for steels without secondary hardening. It follows that the currently proposed extended method is effective for estimating the tempering effect during temper bead welding for the steels without secondary hardening.

Study on Corrosion Resistance and Welding Properties of High Strength, Tough Bainite Steel CB10

In order to gain the high strength and toughness bainite steel, author reported on their own developed CB10 steel. The CB10 steel was heat treated at different tempering temperatures to control the microstructure and mechanical capabilities, and further its variation regular pattern were explored. The results showed that bainite, ferrite and M/A island could be engendered when CB10 steel was tempering at 250℃, 450℃, 600℃ and 670℃, respectively. With the increase of tempering temperature, lath-type bainite was obviously began to merge and coarsen, as well as polygonal ferrite was appeared. When the tempering temperature was above 600℃, recovery and re-crystallization were occurred in some regions. In particular, the mechanical properties of CB10 steel were the best at 450℃ tempering temperature, among them its tensile strength was 632 MPa, the yield strength was 487MPa, the elongation was 25%, and the Charpy absorbed energy was greater than 140J. As following, anti-HIC and weldability of CB10 steel were tested. The results indicated that there was no cracks on the surface of sample, displaying excellent anti-HIC and weldability performance. Moreover, the maximum hardness of HAZ was 231Hv, the maximum Charpy absorbed energy was 285.0J, and fracture morphology all belonged to ductile fracture when the impact temperature was above -60℃.

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.

Investigation of Early Cracking of Dissimilar Metal Welds in a 1000-MW Ultra-supercritical Power Plant Close to the Sea

The early cracking of dissimilar metal welds (DMWs) between T91 martensitic steel and austenitic steel in a 1000-MW ultra-supercritical power plant was investigated in this article. Optical microscopy and scanning electron microscopy were used to characterize the microstructures of DMWs. The result shows that the breakdown of DMWs was brittle rupture along the prior austenite crystal boundary. The crack extended from T91 heat-affected zone to T91 base metal. Compared with the spare DMWs, its tensile strength and bending properties met the standard for DMWs. Hardness of T91 HAZ from failed DMWs was much higher than that of spare DMWs. Some pitting was observed at the T91 HAZ. Associating the high hardness of DMWs and particular service environment, it is concluded that the failure of DMWs was caused by the stress-corrosion crack.

Resistance spot welding of AISI-316L SS and 2205 DSS for predicting parametric influences on weld strength – Experimental and FEM approach

The present study reports the effects of RSW process parameters like heating cycle, welding current and electrode tip diameter on the tensile shear strength and nugget size of dissimilar metal welding of 2205 duplex stainless steel (DSS) and AISI-316L stainless steel sheets. Tensile shear tests were conducted to access the tensile shear strength and associated physical variations of the nugget formed. Finite element (FE) simulation of the tensile–shear test was performed using ABAQUS explicit FE software. The finite element results were compared with experimental results through the aid of graphical representation by comparing the obtained stress–strain values for validation. The resistance spot welds are subjected to Vickers microhardness test and identified that hardness of HAZ is less for AISI-316L and high in DSS-2205 as compared to respective base metal, moreover heterogeneous hardness values obtained in the weld metal zone (WMZ) exhibits higher hardness in ASS-316L and low hardness in DSS-2205 side as compared with base metal. Furthermore, SEM fractography indicates that the failure of tensile shear spot welded specimen occurs in the ductile mode of fracture.

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.

Extended Application of Hardness Prediction System for Temper Bead Welding of A533B Steel to Various Low-Alloy Steels

Temper bead welding is one of effective repair welding methods in case that post weld heat treatment is not easily applied. In order to evaluate the effectiveness of temper bead welding, hardness in HAZ becomes important factor. The neural network-based hardness prediction system of HAZ in temper bead welding for A533B low-alloy steel has been constructed by the authors in the previous study. However, for HAZ hardness prediction of other steels, it is necessary to obtain hardness database for each steel which is time-cost consuming, if the same method is used. The present study has been conducted to develop the generalized hardness prediction method applicable for other steels by utilizing the hardness data-base of A533B steel assuming that the hardness in HAZ of steels after tempering have a linear relationship with LMP (Larson-Miller parameter). On using the newly proposed extended method, only a few hardness data-base for the other steels is needed to obtain. Hardness distribution in HAZ of temper bead welding for other steels was calculated by using the extended hardness prediction system. The thermal cycles used for calculation were numerically obtained by a finite element method. The experimental results have shown that the predicted hardness is in good accordance with the measured one for steels without secondary hardening. It follows that the currently proposed extended method is effective for estimating the tempering effect during temper bead welding for the steels without secondary hardening.

Microstructures and Hardness of the Experimental 57Fe15Cr25Ni Steel Around TIG Weld-Joints for Reactor Structure Materials

The microstructures and hardness of tungsten inert gas (TIG) welded experimental 57Fe15Cr25Ni steel were investigated through optical–scanning electron microscopy analyses and with a hardness tester, respectively. The welding process restructured the constituent atoms into regular and irregular crystal lattices. Rapid cooling of the weld metal allowed the formation of a dendritic (columnar) structure, with porous grains. By contrast, slow cooling influenced HAZ and led to the formation of grain structures. The crystal lattice became more organized and larger than other zones. Meanwhile, the base metal formed circular nets that covered large area inside thick and thin grain boundaries. The diffraction patterns revealed texturing in the weld metal. The crystallite orientation changed from (111) to (200) and (220) planes. The weld metal profile broadened (amorphous) and had full width at half maximum (fwhm) value larger than those in HAZ and the base metal. The weld metal possessed hardness of 121 HV, which is slightly lower than the hardness of the base metal (130 HV). HAZ exhibited the highest hardness value (152 HV). Hardening was influenced by carbon and outer oxygen migration to the grain boundaries, which formed colonies, i.e., chromium carbide, aluminum carbide, aluminum oxide, silicone oxide, and silicon carbide (precipitation hardening). Welding (heat) may change the microstructure and hardness of HAZ and the weld metal region, which would be brittle and very critical in responding to applied loads.

Hardness analysis on carburized steel weld joint by SMAW using different welding current

Low-cost weld joint on wear-resist gear train component was introduced for replacing conventional bolted connection to avoid its additional material and holes requirement. This study was concerned on the hardness analysis of carburized steel weld joint generated from SMAW with different welding currents, namely 80, 100, and 120 A. The results indicated that the hardness is decreased at HAZ and subsequently increased at weld metal for all samples. On the other hand, the highest welding current applied during welding shows the highest hardness curve among the other currents up to 226.5±2 HV at weld metal. By micro-and macrostructural analyses, phases evolution during thermal cycle on welding process played the crucial role to determine the hardness of HAZ, while the weld metal hardness was dominantly driven by the carbon-rich element distribution.