Grain Size In Heat Affected Zone Research Articles

Near-threshold fatigue crack growth behavior of the weld metal and heat-affected zone in an ex-service CrMoV steel joint

Threshold value (ΔKth) and fatigue crack growth behavior at different temperatures and stress ratios were investigated in weld metal (WM) and heat-affected zone (HAZ) of an ex-service CrMoV steel joint. Compared with the ΔKth at 25 ℃, the ΔKth at 500 ℃ and 540 ℃ were still high, because significant oxide-induced crack closure (OICC) occurred in WM and HAZ during high-temperature tests. The high-temperature ΔKth of HAZ were higher than those of WM, due to their more severe oxidation and more significant OICC. This was owing to the lower Si and Cr content and smaller grain size in HAZ.

Effect of Different Ultrasonic Power on the Properties of RHA Steel Welded Joints

Based on the changes of microhardness, tensile strength, and impact resistance caused by the difference of macroscopic morphology and microstructure of welded joints, this paper studied the effect of different ultrasonic power on the properties of welded joints during the welding of homogeneous armor steel. It is experimentally found that the macroscopic morphology of those joints is very different. Compared with conventional welding, ultrasonic welding can increase the weld depth and the width of the heat-affected zone (HAZ) on either side of the weld. However, only the ultrasonic wave at an appropriate power level can increase the weld width. In addition, appropriate ultrasonic power can significantly improve the grain state of the weld. With the increase of ultrasonic power, the grain size in HAZ will decrease. The microhardness of the weld will first increase and then decrease, while the microhardness of the HAZ will increase. This is basically consistent with the changing trend of impact resistance. An ultrasonic wave can also increase the tensile strength of a welded joint up to 802 MPa, 12.4% higher than that in conventional welding. However, a high-power ultrasonic wave will bring down the tensile strength. This study provides guidance for the selection of ultrasonic-assisted regulation power to achieve the different properties of homogeneous armor steel joints.

Rotary Friction Welding and Dissimilar Metal Joining of Aluminium and Stainless Steel Alloys

Friction welding (FW) is cost-effective, efficient, occupational safer and also eco-friendly in the absence of pollution, smoke, fume, and IR radiation during welding than conventional welding technologies. In this paper, the joining of aluminium AA6063 and steel SS304 dissimilar metal is explained with different faying surfaces and their SEM images of weld interface (WI), joint quality, tensile and yield strength, and the axial shortening are evaluated and compared. The joint quality factor of the experiment faying surface modification ‘E3’ was the maximum and about >100% with 236 MPa strength. The axial shortening was also less than 27 mm. The joint with hemispherical faying surface showed ‘U’ shaped WI and the joint with taper faying surface showed ‘V’ shape WI. So, the cross-sectional area of WI can be increased and the strength also increased. FW yields very high strength, low-stress weld with no weld defects such as porosity, voids etc. Here, in most cases, the joint strength is equal to base metal strength and it can avoid fastening to join two metals. FW has a minimal and narrow heat-affected zone (HAZ) of few microns size that differentiates FW from other welding techniques. The grain size of HAZ is directly proportional to the heat input during welding. During fusion welding of dissimilar materials, a lot of intermetallic compounds are formed at the weld interface and that will lead to poor strength of the welding because they have different chemical and mechanical qualities; therefore FW is a good choice for joining dissimilar metal rods as the intermetallic compounds can be reduced by FW.

Basic Microstructural Characterization of Second Phases in Homogeneous Weld Joint Made of X6CrNiNbN25-20 Steel After Long-Term Exposure Time at 973 K

Abstract New blocks of fossil fuel power plants designed for steam temperatures above 873 K require advanced stainless steels as material for superheater or reheater systems. Weld joints are critical parts in fossil power units. Great attention is paid to the exploitation of new steel grades with higher material properties. In the austenitic steels family, the superior grade is undoubtedly HR3C steel (X6CrNiNbN25-20). A detailed knowledge on stability and microstructure composition during thermal exposure of the weld joints made from HR3C is necessary in order to use them in fossil fuel power plants with ultrasupercritical (USC) and new advanced ultrasupercritical (A-USC) steam parameters. The aim of the paper is to identify critical minor phases in HR3C steel, which allow acceleration of creep damage. The σ-phase and rough carbides M23C6 type is considered as such a phases in this steel. In this study, the σ-phase is identified and studied in more detail in relation to the development of creep damage at 973 K. Experimental material of the homogeneous HR3C weld joints in two states: in the as-welded state (AW) and after the postweld heat treatment (PWHT). Weld joints were manufactured by orbital welding using the gas tungsten arc welding (GTAW) method, heat input Qs = 1600 J/mm, interpass 423 K, three beads. Nickel-base alloy UTP A6170 Co (equivalent to Thermanit 617) was used as a filler material. The PWHT was carried out at the temperature of 1503 K for 15 min. Stress rupture tests were performed on the cross-weld (CW) joints of tubes ø 38 × 6.3 mm at 973 K with times to rupture up to nearly 22,000 h. The polished surface of the longitudinal sections was subjected to color etching in Murakami (30 g K3(Fe(CN)6), 30 g KOH, 60 ml H2O) in order to highlight the σ-phase. Several microscopic techniques were used for the study. The results were supplemented by creep, grain size, and microhardness data hardness vickers (HV) 0.5. The PWHT specimens exhibited an average σ-phase size of approximately 5 μm as well as AW specimens in specimens with short time to rupture (tr). However, tr such as 20,000 h, the average σ-phase size already reached dangerous border 10 μm. The AW specimens as opposed to the PWHT specimens did not show a noticeable growth of austenitic grains in the heat-affected zone (HAZ). In specimens after PWHT, the average grain size in HAZ was more than twice that of the body material (BM). It is worth noting that creep ductility values of specimens in the state after PWHT are very low, which is the result of coarse-grained structure in the HAZ and accelerated precipitation of σ-phase particles along grain boundaries during creep at 973 K.

Analysis of weld characteristics of micro plasma arc welded thin stainless steel 306 L sheet

Abstract This work demonstrates joining of thin steel sheet using micro plasma arc welding (MPAW) process. A series of welding experiments are carried out by applying full factorial design of experiment. The process parameters considered are welding current, welding speed and stand-off distance. A sufficient number of trial experiments are conducted to find suitable process window for MPAW of 500 μm thick SS-316 L sheets. Seven weld bead geometry characteristics (viz., area of fusion zone, top bead width, bottom bead width, bead height or penetration, reinforcement, width of left side of heat affected zone (HAZ) and width of right side HAZ), three tensile properties (ultimate tensile strength, yield strength and percentage elongation), micro-hardness and grain size of HAZ are considered as weld quality parameters. Various outlier tests are applied first time in welding for detection of extreme data from the tensile data set. The effects of heat input and process parameters on the measured weld quality parameters are studied. Analysis of variance (ANOVA) is also applied to estimate the relative importance of individual parameter and their interaction on the total variability. Finally, regression models are developed for representing the input and output relationship of the MPAW process.

Microstructure and Mechanical Properties of Fiber Laser Welded GH3535 Superalloy

As a primary material of the thorium molten salt reactor (TMSR) that is a suitable candidate reactor of the Generation IV nuclear reactors, GH3535 superalloy was successfully welded. The effect of laser beam welding (LBW) on microstructure evolution of fusion zone (FZ) and heat affected zone (HAZ), such as element segregation, precipitate behavior and grain evolution, was investigated. The microhardness and tensile properties were tested and discussed. The results of microstructure evolution showed that a number of fine M6C-γ eutectic phases precipitated at solidification grain boundaries and interdendritic region in FZ. Compared to base metal zone (BMZ), the grain size of HAZ has no obvious change. While a few of M6C-γ eutectic phases were observed in partially melted zone (PMZ) of HAZ. The results of microhardness indicated that the hardness of FZ was higher than that of HAZ and BMZ. The results of tensile test showed that the ultimate tensile strength of joints at room temperature, 650 and 700 °C were 98%, 97% and 99% of that of BM, respectively. All the tensile specimens of joints failed in BMZ rather than in PMZ where M6C carbides had been transformed into M6C-γ eutectic phases.

The effects of welding parameters on the small scale resistance spot weldability of Ti-1Al-1Mn thin foils

The present paper primarily investigates the effects of key welding parameters, including ramp time, holding time, welding time, welding current and electrode force, on small scale resistance spot weldability of Ti-1Al-1Mn thin foils with thickness of 0.05mm. A single lap joint is performed to estimate mechanical properties of welded joint by tensile-shear test, together with weld morphology, microstructure, microhardness and element distribution examines. Weld morphology examine results demonstrate that diameter and thickness of surface indentation stabilize around 365μm, 8μm respectively. The variations of weld morphology with welding parameters differ significantly from large scale resistance spot welding (LSRSW). Microhardness examine results reveal that weld nugget has the highest microhardness value, and softening phenomenon is observed in heat affected zone (HAZ) with respect to base material, which is attributed to pronounced grain growth. Additionally, grain size effect becomes significantly as T/dg (sheet thickness to average grain size in HAZ) ratio below a critical value around 7. In light of obtained results, it could be validated that peak load of welded joint is mainly determined by weld nugget size, failure mode and average grain size of HAZ.

Ways of Numerical Prediction of Austenitic Grain Size in Heat-Affected Zone of Welds

In the present time there is a clear effort to achieve the most exact mathematical description of the behaviour of “Hi-tech” materials when exposed to temperature and stress loading. Besides the common numerically predicted values such as temperature, deformation and stress fields, or as the case may be structure changes during phase transformations, demands for prediction of the austenitic grain size in HAZ of welds become more and more frequent. That is why the present submission deals with the analysis of the determination of the grain size and grain growth kinetics of HR3C single-phase austenitic steel using the Monte Carlo Potts method. The procedure of obtaining the input data for numerical simulations will be demonstrated on HR3C steel, including the determination of grain growth kinetics and definition of all the parameters needed for a computational model. Results from the numerical simulation in Sysweld program will be then compared against the real experiment for a multi-layered weld made on HR3C tube.

Study the effect of shielded metal arc welding process parameters, cryo-treatment and preheating on welding characteristics and modelling by an artificial neural network

Depth of heat affected zone (HAZ), depth of penetration and bead geometry (bead height and bead width) are most important characteristics of a weldment. In addition to weld process parameters welding conditions like preheating and cryo-treatment greatly affect the weldment characteristics. It is possible to get good bead geometry with cryo-treatment and preheating for some range of current, voltage and arc travel rate for which bead formation may not be possible in normal welding condition. In SMAW (shielded metal arc welding) process, selecting appropriate values for process variables is essential in order to control weldment characteristics. Also, conditions must be selected that will ensure a predictable and reproducible weld bead. In this investigation the effects of cryo-treatment and preheating on various metallurgical aspect, namely, the depth of HAZ, weld interface, grain growth and grain refinement regions have been studied. While cryo-treatment before welding decreased the grain size in HAZ and preheating increased the grain size and cryo-treatment after welding did not significantly increase the grain size. The process was modelled using an artificial neural network. Supervised mode of learning was used while training the neural networks. The test cases showed good convergence with the measured experimental values.

Welding of Fe-Al Intermetallic Compound and Steel by SPS Technology

The welding between Fe-Al intermetallic compound and high-strength steel was done via SPS technology. Microstructure, elements concentration and micro-hardness of welding joint were examined. The results indicated that there was no obvious welding heat-affected zone in both Fe-Al intermetallic compound and high-strength steel. The HAZ microstructures of high-strength steel were mainly martensite. In Fe-Al intermetallic compound, the grain size of heat-affected zone was larger than that of base metal and the density of heat-affected zone was lower than that of base metal. Besides, the grains of base metal had deformation phenomena. The welding joint had steady performance and the connection was reliable. Under the influence of chemical potential differences, unidirectional impulses discharge current and axial pressure, elements diffused perfectly in a short period of time.

EH36-TM강의 대입열 EGW 용접부 저온 인성에 미치는 미세 조직의 영향

The characteristics of high heat input (342kJ/cm) EG (Electro Gas Arc) welded joint of EH36-TM steel has been investigated. The weld metal microstructure consisted of fine acicular ferrite (AF), a little volume of polygonal ferrite (PF) and grain boundary ferrite (GBF). Charpy impact test results of the weld metal and heat affected zone (HAZ) met the requirement of classification rule (Min. 34J at <TEX>$-20^{\circ}C$</TEX>). In order to evaluate the relationship between the impact toughness property and the grain size of HAZ, the austenite grain size of HAZ was measured. The prior austenite grain size in Fusion line (F.L+0.1 mm) was about <TEX>$350{\mu}m$</TEX>. The grain size in F.L+1.5 mm was measured to be less than <TEX>$30{\mu}m$</TEX> and this region was identified as being included in FGHAZ(Fine Grain HAZ). It is seen that as the austenite grain size decreases, the size of GBF, FSP (Ferrite Side Plate) become smaller and the impact toughness of HAZ increases. Therefore, the CGHAZ was considered to be area up to 1.3mm away from the fusion line. Results of TEM replica analysis for a welded joint implied that very small size (<TEX>$0.8\sim1.2{\mu}m$</TEX>) oxygen inclusions played a role of forming fine acicular ferrite in the weld metal. A large amount of (Ti, Mn, Al)xOy oxygen inclusions dispersed, and oxides density was measured to be 4,600-5,300 (ea/mm2). During the welding thermal cycle, the area near a fusion line was reheated to temperature exceeding <TEX>$1400^{\circ}C$</TEX>. However, the nitrides and carbides were not completely dissolved near the fusion line because of rapid heating and cooling rate. Instead, they might grow during the cooling process. TiC precipitates of about 50 ~ 100nm size dispersed near the fusion line.

Effect of heat-input on austenite grain size in the heat-affected zone of HSLA-100 steel

The prior-austenite grain size in the heat-affected zones of single-pass butt welded joints in thick HSLA-100 steel plates was evaluated. The grain size was related with the temporal history of the location, which was obtained using an existing thermal model based on Gaussian heat source distribution for two different heat-input conditions. For a heat-input of 10 kJ/cm the grain size in the coarse grain heat-affected zone was 80 μm corresponding to a peak temperature of 1450 °C, but falls sharply to 40 μm within a distance of 0.5 mm from the fusion line. At a higher heat-input of 40 kJ/cm the grain size is 130 μm for the same peak temperature and the coarse grain heat-affected zone is 1.1 mm wide. The austenite grain size significantly influences the microstructure and properties of the heat-affected zone.

Gas tungsten-arc filler welding of AZ31 magnesium alloy

Optical microscopy and scanning electron microscopy (SEM) were used to examine the microstructure and fracture of AZ31 magnesium alloy joint welded by automatic gas tungsten-arc filler (GTAF) welding process with AZ61 wire. More endeavors have been put on investigating the effect of filler wire on microstructure and performance of welded joint. The result showed that the grain size in heat-affected zone (HAZ) of GTAF welded joint holds significant variety compared with that of GTA welded joint (without filler wire). The modification of microstructure in HAZ has changed the fracture location as well as the ultimate tensile strength (UTS) of joint in tensile test.

Plunging method for Nd : YAG laser cladding with wire feeding

The effects of wire feeding direction and position, cladding time, and cladding speed on the quality of cladding layer for laser cladding with wire feeding are studied. Experiment results indicate that the wire feeding direction and position are important for wire laser cladding. By adopting the correct wire feeding direction and position, the wire can be plunged into the melt pool and can be melted by the heat of the molten metal. With the increase of cladding speed, the dilution of clad layer can be reduced and the growth of the grain size of heat-affected zone of the base metal can be limited. If proper cladding parameters are used, the clad layers will have a good surface shape, sound metallurgical bonding with base metal, low dilution, and the effect of heating on heat-affected zone metal can be limited. The hardness of the clad layer and heat-affected zone are checked. It indicates that with the increase of cladding speed, the hardness of the clad layer and heat-affected zone increases.

調質高張力鋼潜弧溶接熱影響部の切欠靱性と溶接軟化に関する研究(第2報)

Of the metallurgical factors influencing the notch toughness of submerged-arc weld heat-affected zone, study was made on the effect of pre-treatment of base metal on notch toughness of coarse grained heat-affected zone, especially for steel containing strong carbide or nitride forming elements.Also the effect of cooling rate and microstructure on the notch toughness of duplicated weld heat-affected zone was investigated with maximum heating temperature 1350°C.Notch toughness of duplicated weld heat-affected zone in solution-treated steel is lower in general. In steels containing niobium, vanadium and titanium, notch toughness of duplicated weld heat-affected zone is higher in rapidly cooled cycles, when the base metal is normalized or quenched, both followed by spheroidizing treatment. Austenite grain size in heat-affected zone is smaller, comparing to that of steel free from such elements.However, the effect was hardly observed in duplicated weld heat-affected zone cooled with slower rate of cooling, 7°C/sec at 540°C.In ferritic steels such as Steel AtoH, slower the cooling rate of duplicated weld heat-affected zone, the lower the notch toughness greatly. While low alloy high tensile steel such as Steel ItoL, cooling rate dependency of notch toughness is smaller, i.e., low alloy high strength steel with higher hardenability has superior notch toughness in weld heat-affected zone in case of large heat input welding.According to the results for quenched and tempered Steel I highest notch toughness is obtained, when the weld heat-affected zone is cooled, keeping up with the Cf' time of CCT diagram. Especially the peak of notch toughness is brought by mixed structure of lower bainite and martensite.