Weld Metal Zone Research Articles

Microstructural Analysis of Ballistic Tests on Welded Armor Steel Joints

The deformation and fracture behavior of welded joints made from quenched and tempered steel closely conforming to AISI 4340 were investigated. Due to weld thermal cycles and under matching fillers, the welded armor steel joints showed poor ballistic performance compared with the base metal (BM). The problems encountered in the past were reduced by depositing a soft austenitic stainless-steel buttering layer in between the BM and the hardfaced layer. This method showed enhancement in ballistic performance and good weld integrity. In this investigation, an attempt is made to investigate the microstructure after ballistic testing on the weld metal zone consisting of the hardfaced interlayer. The results reveal the microstructural characteristics before and after ballistic testing of armor steel welds fabricated using the shielded metal arc welding (SMAW) process.

The Characteristics of Weld Metal Zone Welded with Various Filler Metals

Recently, the fuel oil of diesel engines of marine ships is being changed to heavy oil of low quality as the oil price is getting higher and higher. Therefore, the wear and corrosion in all parts of the engine, such as cylinder liner, piston crown, and spindle and seat ring of exhaust valves has predominantly increased. Thus, the repair welding of the piston crown is a unique method to prolong its life in a economical point of view. In this case, filler metals with a high corrosion and wear resistance are mainly being used for repair welding. However, the piston crown on the ships job site is often actually being welded with mild filler metals. Therefore, in this study, mild filler metals, such as E4301, E431316, and E4316, were welded to the SS401 steel as the base metal, and the corrosion properties of their weld metals with and without post weld heat treatment were investigated with some electrochemical methods in 0.1% H2SO4 solution. The weld metal welded with E4301 filler metal exhibited the best corrosion resistance among the filler metals in the case of no heat treatment, however, its resistance was considerably decreased due to the post weld heat treatment (annealing:625°C, 2hr). In particular, the weld metal of E4316 exhibited relatively a good corrosion resistance by the post weld heat treatment.

Weldability of dissimilar joint between F82H and SUS316L under fiber laser welding

As one of the high beam quality heat sources, 4kW fiber laser was applied for joining between reduced activation ferritic/martensitic steel, F82H and SUS316L austenitic stainless steel, and the microstructural analyses and Vickers hardness measurements were carried out before and after post-weld heat treatment (PWHT). The microstructure of joint can be divided into four regions which are base metal of F82H, heat affected zone (HAZ) in F82H, weld metal (WM) and base metal of SUS316L. Also, it is revealed that the high-power fiber laser can be employed for constructing butt joint between F82H and SUS316L by applying PWHT and shifting the laser beam position to SUS316L, where the distance between the contact face and beam should be set as a range from radius to diameter of laser beam.

Combined Effect of Resistance Spot Welding and Post-Welding Sensitization on the Pitting Corrosion Behavior of AISI 304 Stainless Steel

This work studies the combined effect of resistance spot welding and post-welding sensitization on the pitting corrosion behavior of AISI 304 (UNS S30400) by using cyclic potentiodynamic polarization tests. The combined effect of welding and post-welding sensitization give rise to worse pit nucleation resistances and better repassivation capacities than those of the state without prior welding. This behavior is caused by the weld metal zone, a cast dendritic microstructure with δ-ferrite in interdendritic regions, whose microstructural regeneration kinetics is faster than that of HAZ and that of the parent metal and where the chromium-rich phases are more homogeneously distributed than in the parent metal.

Numerical Simulation of Gradient Heat Treatment Process of Cylinder Welding Component of 30Si2MnCrMoV Steel

The finite element analysis method was applied to simulate the gradient field heat treatment process of a cylinder welding component of 30Si2MnCrMoV steel by software ANSYS. In the heat treatment process，the distribution of temperature field, the variation curve of residual stress with time，the distribution of residual stress along the axial direction of cylinder, and the axial and radial deformation of the specimen were calculated and the influences of partial heating area on the distribution of temperature and residual stress were analyzed. The calculating results show that the temperature in the weld metal zone and heat affected zone of welding specimens may exceed the phase transformation points during the gradient heat temperature. The residual stress and the radial deformation in the weld metal zone were greater than those in the matrix zone. The final deformation of specimen was along the axial direction. With the increase of partial heating area, the phase transformation area was increased and the residual stress was reduced effectively.

Evaluation of Effect of Welding Methods to Corrosion and Hardness Characteristics of Welded Zone

Recently a fuel oil of the diesel engine in the merchant ship has been changed with heavy oil of low quality as the oil price is getting higher and higher .Therefore, the wear and corrosion against all parts of the engine are significantly increased with using of heavy oil of low quality. In particular, the degree of wear and corrosion in between spindle and seat ring of exhaust valve are more serious compared to the other parts of the engine due to severe environment such as the high temperature of exhaust gas and repeating impact. Thus, repair welding is a unique method to prolong their lifetime in an economical point of view. In this study, an effect of welding methods to corrosion and mechanical properties of both weld and base metal zone was investigated with some electrochemical methods such as measurement of corrosion potential, cathodic and anodic polarization curves, cyclic voltammogram and AC impedance etc. in. The hardness of the weld metal zones exhibited comparatively higher values than that of the base metal zone. And their corrosion resistances were also increased compared to the base metal. The weld metal zone of P1F( plasma welding with 1 pass) showed a relatively good corrosion resistance as well as the hardness compared to the other welding methods. Consequently, it is considered that plasma welding method is a desirable method compared to other welding methods for both better corrosion and hardness properties.

Characteristics Evaluation of Weld Metal Zone Welded with Various Repair Welding Filler Metals

Recently, the fuel oil of diesel engine of marine ships has been changed with heavy oil of low quality as the oil price is getting higher and higher. Therefore, the wear and corrosion against all parts of the engine, such as cylinder liner, piston crown, and spindle and seat ring of exhaust valves has predominantly increased due to its consumption. Thus, the repair welding of the piston crown is a unique method to prolong its life in a economical point of view. In this case, filler metals having a better corrosion and wear resistance are mainly being used for repair welding. However, the piston crown on the ship’s job site is often actually being welded with mild filler metals. Therefore, in this study, the mild filler metals, such as E5016, E1216, and E2316, were welded to the SS401 steel as the base metal, and the corrosion properties of their weld metal zones with and without post weld heat treatment were investigated with some electrochemical methods in 0.1% H2SO4 solution. The weld metal zone welded with E1216 filler metal exhibited the best corrosion resistance among the filler metals with irrespective of heat treatment, however, its corrosion resistance was somewhat decreased due to the post weld heat treatment(annealing:625oC, 2hr). In particular, the weld metal of E2316 exhibited relatively a good corrosion resistances by the post weld heat treatment.

ホットワイヤを用いたCO<sub>2</sub>ガスシールドアーク溶接金属部の微細組織とその機械的性質に及ぼす効果

New welding method (F-MAG) based on CO2 gas-shielded arc welding method (MAG) was developed to increase deposition rate of weld metal. In F-MAG, filler wire (hot-wire) heated using direct-current was put into rear part of weld-pool formed with main electrode used in MAG.Multi-layered weld metals were prepared using both F-MAG and MAG. Microstructures of both as-weld and reheated zones in uppermost layer of the multi-layered weld metals were examined and the effects of microstructures on mechanical properties were analyzed. Both the as-weld and reheated zones of weld metal formed with F-MAG consisted of acicular ferrite (AF) and/or equiaxed ferrite and so on. Both strength and elongation in as-weld and reheated zones formed with F-MAG were superior compared with those formed with MAG. It could be suggested that strength increased by refinement of AF due to increase in the concentration of alloy elements being contained in hot-wire. Larger elongation of weld metal in F-MAG compared with that in MAG could be analyzed in terms of the aggregate of AFs with almost parallel slip systems between neighboring AFs, hereafter referred as to ALPS. The number of AFs contained in an ALPS formed in weld metal formed with F-MAG is larger than that with MAG, in spite of the sizes of ALPSs in weld metals formed with MAG and F-MAG being almost same between them. Deformation occurs over a lot of AFs in the case of finer AF through the rotation of tensile test piece during deformation.

CO<sub>2</sub>ガスシールドアーク溶接金属部の微細組織と機械的性質に及ぼすホットワイヤの効果

The new welding method called as F-MAG, which has been developed based on CO2 gas-shielded arc welding method (MAG) increase deposition rate of weld metal. F-MAG welding method is combined with hot-wire, as having been used in TIG arc- and laser-welding methods. F-MAG is performed using hot-wire which is inserted into the rear part of weld pool made with leading electrode. Hot-wire melts by both electrical heating of itself and heat of weld pool.Multi-layered weld metals were prepared using F-MAG and MAG. Microstructures and mechanical properties of both as-weld and reheated zones in uppermost layer of the multi-layered weld metals formed with F-MAG and MAG were examined and the effects of hot-wire on microstructures and mechanical properties were analyzed.Both the as-weld and reheated zones of weld metal formed with F-MAG consisted of acicular ferrite (AF), equiaxed ferrite and so on. Both strength and elongation in as-weld and reheated zones formed with F-MAG were superior compared with those formed with MAG. It could be suggested that strength increased by refinement of AF due to increase in the concentration of alloying elements being contained in hot-wire. Larger elongation of weld metal in F-MAG compared with that in MAG could be analyzed in terms of the Aggregate of acicular ferrite Laths with nearly Parallel Slip systems between neighboring acicular ferrite laths (ALPS). The number of AFs contained in an ALPS formed with F-MAG is larger than that with MAG, in spite of the sizes of ALPSs formed with MAG and F-MAG being almost same. Deformation occurs over a lot of AFs in the case of finer AF formed with F-MAG through the rotation of tensile test piece during deformation, resulting in the larger elongation.

Effect of modes of metal transfer and microstructure on corrosion behavior of welded modified ferritic stainless steel in acidic environments

The effects of modes of metal transfer, i.e., short-circuit (SC) and spray (S) modes in single-pass gas metal arc welding of modified ferritic stainless steel using two types of austenitic stainless steel filler metals on microstructure as well as corrosion behavior of weld metal and high-temperature heat-affected zone (HTHAZ), were investigated. The results show that primary solidification modes (PSM) of the welds were exclusively dependent upon the Creq/Nieq ratio of the respective welds. However, the amount of grain boundary austenite and martensite transformation in the welds were solely dependent upon the mode of metal transfer and the extent of cooling rate. Regarding the corrosion mechanism, grain boundary corrosion (GBC) behavior of welds and HTHAZ relied on the microstructural changes along the grain boundary due to the variation in mode of metal transfer. The results show that S-mode resisted grain boundary corrosion of the welds and both GBC as well as pitting corrosion of the HTHAZ. On the other hand, SC-mode improved only pitting corrosion resistance of the welds. Between the filler wires used, 316L welds, in general, provided better corrosion resistance compared with 308L welds.

Characteristics of Surface Microstructures for Welded Joint of 7A52 Aluminum Alloy before and after Surface Nanocrystallization

The surface nanocrystallization process by high energy shot peening (HESP) was carried out on the TANDEM MIG welded joints surface of 7A52 aluminum alloy after artificial aging. The microstructure features of welded joints surface layer were systematically characterized by using optical microscopy (OM) ,transmission electron microscopy (TEM) observations and X-ray diffraction (XRD) analysis. Based on the experimental observation, the banded texture of 7A52 aluminum alloy base metal was eliminated after HESP. After 50min of HESP processing, the thickness of deformed layer in the base metal (BM), weld metal zone (WM) and heat affected zone (HAZ) was 50μm, 70μm and 60μm separately. Obtained from the TEM micrographs, the average grain size of surface layer in the base metal, weld metal zone and HAZ was about 20nm, 26nm and 32nm respectively. The size of grain in the weld metal zone and HAZ was larger than the base metal. Moreover, the distribution of nanocrystalline in the weld metal zone and HAZ was uneven compared with the base metal.

Corrosion Characteristics of Welding Zone by Types of Repair Welding Filler Metals and Post Weld Heat Treatment

Recently, the fuel using in the diesel engines of marine ships has been changed to a low quality of heavy oil because of the steady increase in the price of oil. Therefore, the wear and corrosion in all parts of the engine such as the cylinder liner, piston crown, and spindle and seat ring of exhaust valves has correspondingly increased. The repair welding of a piston crown is a unique method for prolonging its lifetime from an economic point of view. In this case, filler metals with a high corrosion and wear resistance are mainly being used for repair welding. However, often at a job site on a ship, a piston crown is actually welded with mild filler metals. Therefore, in this study, mild filler metals such as CSF350H, E8000B2, and 435 were welded to SS401 steel as the base metal, and the corrosion properties of the weld metals with and without post weld heat treatment were investigated using some electrochemical methods in a 0.1% <TEX>$H_2SO_4$</TEX> solution. The weld metal welded with CSF350H filler metal exhibited the best corrosion resistance among these filler metals, irrespective of the heat treatment. However, the weld metal zones of the E8000B2 and 435 filler metals exhibited better and worse corrosion resistance with the heat treatment, respectively. As a result, it is suggested that in the case of repair welding with CSF350H and 435 filler metals, no heat treatment is advisable, while heat treatment is desirable if E8000B2filler metal is used with repair welding.

Evaluation of fracture behavior of the reheated weld zone in API 2W Gr. 50 steel weld metals

In this study the effect of martensite-austenite (M-A) constituents on the fracture behaviour of the reheated weld zone formed by subsequent weld passes in API 2W Gr. 50 steel welds was evaluated. For the weld thermal cycle simulation process with the Geeble thermal simulator, the actual single-pass weldment was used rather than the base metal. The reheated weld zone in the weld metal was categorized into four typical areas according to the peak temperature. The test results indicated that toughness is closely related to the fraction of the martensite-austenite constituents.In particular, the intercritical reheated weld zone with a high fraction of M-A as well as a coarse-grained reheated zone can be considered as local brittle zones of weld metal.

Homology Applied to Characterization of Welded Grain Structures in Low Carbon Steel

In the present work, organization of grains within the weld zone in SS400 low carbon steel is investigated. A classification method based on the concept of topological quantity is proposed to investigate the heat affected zone (HAZ) and the center of the weld metal zone (WMZ). The image of each area includes various grains. By using the conventional image analysis techniques, we can analyze the distribution of its size. However, it is difficult to capture the structure of each. In addition, analyzing each grain does not mean the elucidation of the whole. By calculating the average amount of homology of the grains, we make a distinction in these areas quantitatively.

Microstructure and Corrosion Resistance of Dissimilar Welded Joints between Duplex Stainless Steel and Austenitic Stainless Steel

The dissimilar metals components of duplex stainless steels are more and more used in engineering fields recently. But the welding of dissimilar metals is more a challenge than that of similar metals. The joints of dissimilar metals between 2205 duplex stainless steel and 304 austenitic stainless steel were produced by tungsten inert gas arc welding (GTAW) with welding wire ER2209 and ER309, respectively. The microstructural characterization of welded joints is systematically analyzed by using optical microscope and X-ray diffractometer. The pitting corrosion resistance of the joints is evaluated by electrochemical test. Results show that the microstructure of joint consists of austenite and ferrite, and no detrimental phases precipitate in the weldment. The biphase ratio of austenite (γ) / ferrite (α) is adequate both in weld metal and heat-affected zone (HAZ), which is advantageous to the performance of welded joints. The weld metals have relatively lower pitting corrosion resistance compared with the 2205 base metal, and the pitting corrosion resistance of the joint produced with ER2209 is better than that of the joint with ER309 in chloride solution.

Laser 용접한 스테인리스강의 용접부위의 부식특성에 관한 평가

*Department of Marine Equipment Engineering, Korea Maritime Uni versity, Pusan, Korea**Department of Marine System Engineering, Korea Maritime Unive rsity, Pusan, Korea***Education and Research Division, Korea Institute of Maritime and Fisheries Technology. Pusan, KoreaKEY WORDS: Laser welding 레이저용접, Intergranular corrosion 입계부식, Weld metal 용접금속, Heat affected zone 열영향부, Corrosion current density 부식전류밀도, Chromium depletion 크롬결핍ABSTRACT: Laser welding was carried out on austenitic 304 (STS 304) and 2 2 APU stainless steels. In this case, the differences between t he corrosion characteristics of the welding zones of the two stain less steels were investigated using electrochemical methods. Th e Vickers hardness values of the weld metal (WM) zones in both cases, the STS 304 and 22 APU stainless steels, showed relatively higher values th an those of other welding zones. The corrosion current densities of the heat affe cted zone (HAZ) of the 22 APU and the base metal (BM) zone of t he STS 304 exhibited the highest values compared to the other welding zone s. It is generally accepted that when STS 304 stainless steel i s welded using a general welding method, intergranular corrosion is often observ ed at the grain boundary because of its chromium depletion area . However, when laser welding was performed on both the STS 304 and 22 APU stai nless steels, no intergranular corrosion was observed at any of the welding zones. Consequently, it is considered that the intergranular co rrosion of stainless steel can be controlled with the application of laser welding.교신저자 김진경: 부산광역시 영도구 동삼동 1125번지, 051-620-5791, jg21kim@naver.com

Intergranular precipitation and corrosion in weld of low Cr ferritic stainless steel

In the present research, intergranular precipitation and corrosion in the weld of low Cr ferritic stainless steel was investigated. Free-exposure and double loop electrochemical potentiokinetic reactivation corrosion test results revealed that IGC occurred in both the weld metal and heat-affected zone of the welds aged for more than 1 h at 500 °C. Intergranular Cr segregation was observed around the TiC precipitation of the weld in which IGC developed during the corrosion tests. This observation is subsequently discussed in the experimental results.

Investigation of the localized corrosion associated with phase transformation of tube-to-tube sheet welds of hyper duplex stainless steel in acidified chloride environments

The localized corrosion associated with phase transformation of tube-to-tube sheet welds of hyper duplex stainless steel (HDSS) was investigated in acidified chloride environments. The localized corrosion resistance of the HDSS tube-to-tube sheet welded with an Ar shielding gas supplemented with N2 increased greatly due to a decrease in the α-phase fraction and Cr2N, and a decrease in the pitting resistance equivalent number (PREN) difference between the α-phase and γ-phase in the weld metal and heat-affected zone. It was found that the HDSS tube-to-tube sheet welds showed significantly better localized corrosion resistance than a costly super austenitic grade (S32050) welds.

Study on the Microstructure in Weld Metal of Cr-Ni Stainless Steel under Different Welding Technology

According to Cr-Ni stainless steel, three different welding technology and the appropriate welding process parameters were selected. Three welded joints of Cr-Ni stainless steel were prepared. The microstructure in weld metal zone of Cr-Ni stainless steel under different welding methods was studied by X-fluorescent chemical composition analysis and microstructure analysis. The results show that alloy composition of the weld metal are different and distribute unequally under different welding methods, microstructure morphology and grain size of the weld layer are quite different. the structure of bottom is small amount of γ phase and a little δ phase are combined together and cover is γ phase and Cu-wealthy phases in the welds under TIG-MAG welding. the structure of bottom is coarse columnar crystal and cover is typical cellular dendrite in the welds under TIG- TIG welding. the structure of bottom is tiny equiaxial dendrites and columnar crystal and cover is some γ phase and a little δ phase are combined together in the welds under TIG-SMAW welding.

The effect of microstructures on fatigue crack growth in Q345 steel welded joint

ABSTRACTIt is a traditional that the fatigue crack growth behavior is sensitive to microstructure in threshold regime, while it is sensitive to R‐ratio in Paris regime. Fatigue test is carried out for welded joints of a Q345 steel where the compact tension specimens with 3.8 and 12.5 mm thickness are used, and comparisons of fatigue crack growth behavior between base metal and a few different locations in the welded joint are considered in Paris regime. Welding residual stresses are removed by heat treatment to focus the study on the microstructural effect. It is shown that fatigue crack growth rate (FCGR) in the base metal is not sensitive to R‐ratio, but the FCGR increases in the overheated zone, the fusion zone and the weld metal zone with R‐ratio increasing. To the low R‐ratio, FCGR in the three zones is smaller than that in the base metal, but they approximate the same with base metal under the high R‐ratio. The mechanism of fatigue crack growth is analyzed through crack path in microstructures and SEM fractograph. The coarse‐grained ferrite in the base metal is of benefit to relaxation of the average stress at the crack tip, and the fatigue crack growth predicts branching and deflection within above different locations in the welded joint. These tortuous crack paths with crack branching and deflection will promote crack closure as well as crack‐tip stress shielding and then resulted in higher crack growth resistance.