Grain Size Of Weld Metal Research Articles

A comparative study on the mechanical behavior of S355J2 steel repair-welded joints

The mechanical behavior of repair-welded joints was particularly important for the service safety of steel structures. The microstructure and mechanical behavior of S355J2 steel base metal, welded and repair-welded joints were investigated in this paper. The low cycle fatigue tests on S355J2 steel base metal, welded, and repair-welded joints were conducted fully reversed with strain amplitudes varying from ±0.2% to ±1.1%. The results found that the microhardness of repair-welded joints decreased by about 20 HV with the growth in grain size of weld metal and heat-affected zone. Both elongations of welded and repair-welded joints were reduced by about 25.1% compared with the base metal. Considering the cyclic loading behavior, S355J2 steel base metal, welded, and repair-welded joints exhibited continuously softened, while the repair-welded joints exhibited a greater amount of softening than welded joints. Based on the Coffin-Manson equation, the decreased ratio of permissible total strain amplitude of repair-welded joints was significantly higher for medium and high cycle fatigue (> 104) compared to low cycle fatigue (< 104). The low cycle fatigue fracture surface shows that the defects in the repair-welded joints were the fatigue crack initiation position, but the S355J2 steel base metal and welded joints were initiated on the surface of the specimen.

Effect of the Initial Grain Size on Laser Beam Weldability for High-Entropy Alloys

This study investigated the effect of the initial grain size on the laser beam weldability of CoCrFeMnNi high-entropy alloys (HEAs). Cold-rolled, annealed, and cast HEAs with different initial grain sizes exhibited clear differences in weldability. The cold-rolled, annealed, and cast HEAs exhibited grain sizes of 1.5, 8.1, and 1.1 mm, respectively. The grain size of the weld metal (WM) in cold-rolled/annealed HEAs was coarser than that of the base metal (BM), whereas the grain size of the WM in the cast HEA was finer than that of the BM. Shrinkage voids were present in the central region of all laser WMs. The cold-rolled and annealed HEA exhibited a tensile strength greater than 600 MPa owing to the grain size of the coarse WM and the presence of shrinkage voids; however, tensile fracture occurred in the central region of the WM. However, because the grain size of the cast HEA BM was finer than that of the WM, the tensile fracture occurred in the BM, and it had the same tensile properties as the BM. Therefore, the laser weldability of the HEA depended on the initial grain size, and the grain refinement of the WM was essential for improving the weldability.

Improvement of cryogenic toughness for 9% Ni steel keyhole TIG butt-welded joints with a Ni interlayer

The cryogenic (−196 °C) toughness of weld metal (WM) in 9 wt% nickel (9Ni) steel joints sharply decreases after welding compared with the tempered base metal. In this study, a novel deep penetration keyhole tungsten inert gas (K-TIG) welding technology was applied in 9Ni steel joint to improve the efficiency of backing welding. At the same time, the pure Ni plate and the molybdenum (Mo) wire were added to form the WM and improve the cryogenic impact toughness of the welded joints. The microstructure, mechanical properties, and fractography of joints were carefully investigated. The results show that adding appropriate amounts of Ni and trace Mo to the WM can improve the cryogenic toughness. The microstructure of WM after adding Ni mainly presents body-centered cubic structure martensite with Ni-rich grain boundaries. The grain size of martensite is refined by adding an appropriate Ni and Mo, which leads to the improvement of cryogenic impact toughness. After K-TIG welding, the tensile strength of WM in all joints is superior to the base metal. The maximum cryogenic impact absorbed energy of 97.3 J in WM was obtained by adding a 0.5 mm thick Ni plate. Besides, the grain size of WM and the cryogenic impact absorbed energy are in good agreement with the Hall-Petch relationship. Based on electron microfractography analysis, it is found that the WM without filler exhibits a brittle fracture mode at the impact test, while the WM filled with Ni exhibits a ductile fracture mode. Moreover, the heat affected zone (HAZ) in all joints demonstrates the mixed fracture mode. The results demonstrate that K-TIG welding can be applied to the backing welding, and the body-centered cubic martensitic WM with high cryogenic toughness can be achieved by adding appropriate Ni, which has great potential in the high-speed construction of industrial vessels.

Influence of Laser Power on Grain Size and Tensile Strength of 5A90 Al–Li Alloy T-joint Fabricated by Dual Laser-Beam Bilateral Synchronous Welding

Dual laser-beam bilateral synchronous welding is introduced to produce the 2.5 mm thick 5A90 Al–Li alloy T-joint. The grain morphology and grain size of weld metal (WM) in the T-joint are analyzed and calculated. The tensile experiment, scanning electron microscopy and energy disperse spectroscopy are respectively employed to study the tensile strength, fracture morphology and chemical composition of the T-joint. The results reveal that when the laser power is increased from 2500 to 3000 W, the grain sizes of fine-grained layers and columnar dendrites near the fusion line are significantly reduced. Conversely, that of equiaxed dendrites at the WM center is not sensitive to the variety of laser power. Moreover, the degree of elemental segregation in WM near the fusion line is also aggravated with the increasing of the laser power. The tensile strength of the T-joint with the laser power of 2500 W is significantly higher than that with the laser power of 3000 W. The tensile fracture locations are occurred in the weld toe with obvious pores, shear dimples and tear ridges, which are the typical characteristics of ductile fracture. Besides, the chemical compositions of the second phase particles in the WM are more sensitive to than the variation of laser power compared with that of the matrix.

Effect of aluminide coatings on penetration and microstructure of TIG welded 9Cr-1Mo steel for fusion blanket applications

Aluminide coatings with a top alumina layer on 9Cr steels are considered candidates for fusion blanket applications. One of the critical issues associated with such coating is the fabrication sequence. It is therefore important to investigate the effect of aluminide coating on weld properties of 9Cr steels. This work is a preliminary investigation of the weldability of aluminide coated 9Cr-1Mo steels using bead-on-plate welding experiments. Alumina coated GRADE 91 steel samples by hot dip aluminizing followed by normalizing and plasma tempering were generated. Bead-on-plate welding studies were conducted at different heat inputs by varying the weld speed (100,125,150 mm/min) and using a constant current of 200 A by autogenous tungsten inert gas (TIG) welding process. The effect of coating on the weld microstructure was investigated using X-ray diffraction (XRD), scanning electron microscopy with energy dispersive x-rays (SEM-EDX) and microhardness tests. It was observed that the presence of alumina (Al2O3) on the top of coated samples resulted in improved depth of penetration (DOP) due to arc constriction. The presence of Al rich inclusions (AlN) in the weld bead were also observed. The marginal increase in Al concentration of the weld bead appears to reduce the grain size of weld metal for coated sample and microhardness was enhanced compared to the uncoated 9Cr-1Mo steels.

TMF Influence on Weld Structure at the Welding of 12X18H9T

The transverse magnetic field (TMF) use allows to obtain follow effects: increasing the electrode melting coefficient, reducing the base metal penetration depth and grinding the weld metal structural components. The paper analyzed the existing literature data about the TMF influence on the refinement of the weld metal structure. It is experimentally shown that the alternating TMF influence of 6 Hz frequency reduces the grain size of weld metal is almost twice in comparison with the welding process without the TMF influence at submerged arc welding of plates of austenitic steel type 12X18H9T (X10CrNiTi18-9). The average grains size is 7-6 index, when welding without the TMF influence and the average grains size of the weld metal corresponds to 8 index, with separate inclusions of grains with 7 index when welding with the TMF influence. This is should increase the yield strength value of the weld metal in accordance with the data of Hall – Petch.

Characterization the contribution and limitation of the characteristic processing parameters in cold metal transfer deposition of an Al alloy

Cold metal transfer (CMT) depositing processes in aluminium alloy were conducted using various characteristic parameters which represent for the control of current output and wire motion. The effects of characteristic parameters on the energy input characteristic, metal transfer behavior, weld geometry, and microstructure of deposited weld metal were investigated. There were some limitations for characteristic parameters to achieve stable CMT process. For stable CMT process, the three distinct energy input periods of CMT cycle were controlled by characteristic parameters and thereby affect the features of deposited weld metal. The speed of wire feed motion affected not only burn phase duration but also short-circuiting duration. With the increased speed of wire feed motion, the whole energy input first increased and then decreased; the weld width and contact angle decreased, which was different from the effects of other characteristic parameters. An increment in short-circuiting current resulted in an increase in dilution ratio and grain size of weld metal although whole energy input was essentially constant. In conclusion, adjusting characteristic parameters can control the energy input process coupled with metal transfer behavior to design and optimize the weld properties for each special CMT application, which is suitable for additive manufacturing of aluminium alloy.

Effect of Grain Size on Solidification Cracking Susceptibility of Type 347 Stainless Steel during Laser Welding

In this study, the effect of grain size on solidification cracking susceptibility of Type 347 stainless steel was investigated by using U-type hot cracking test with developed in-situ observation method and the effect of grain size of the weld metal on critical strain for solidification cracking was evaluated quantitatively. The grain size of the weld metal varied from about 70 to 210μm by changing in the grain size of the base metal. Consequently, it was concluded that according to the measurement of CST (Critical Strain Temperature), solidification cracking susceptibility increased with an increase in grain size of weld metal. Moreover, the area of the grain boundary for each unit area decreased when the grain size increased, and then strain which was applied for grain boundary increased and then critical strain for solidification cracking of grain boundary decreased with grain size. Therefore, it was guessed that the solidification cracking susceptibility increased with an increase in grain size.

Ｚｒ添加試作Ａｌ‐高Ｍｇ溶接ワイヤと低周波パルスミグ溶接法の併用によるＡｌ‐Ｚｎ‐Ｍｇ３元系合金の溶接凝固割れ感受性の改善

Solidification crack susceptibility of GMA weld metal of Al-4.5%Zn-1.2%Mg A7N01 base metal has been successfully improved by combination of low frequency switching pulsed GMAW process and Zr added Al-7%Mg tentative wire. Close relationship between grain size of weld metal and crack susceptibility was observed and remarkable reduction in crack susceptibility was obtained in weld metal with fine equiaxed grains of 20 to 30 μm in diameter. This marked grain refinement can be obtained only by the combination of low frequency switching pulsed GMAW of 2.5 to 50 Hz and Zr added Al-7%Mg tentative wire. No considerable grain refinement was observed with Zr-free wire. Relationship between oscillation behavior of molten pool caused by current pulsation and grain refinement was discussed.

オーステナイトステンレス鋼溶接金属の凝固制御に関する研究 ＩＩ 電磁かくはん併用ティグ溶接による結晶粒の微細化

The effect of electromagnetic stirring on the microstructure of fully austenitic stainless steel weld metal was investigated. The parameters examined to achieve the grain refinement were magnetic field intensity, the frequency of alternately stirring and relative distance from an electrode to magnetic field center. Bead-on-plate TIG welds were made in the conditions that welding current was 60A and travel speed was 3 cm/min. A significant decrease in the grain size of weld metal could be achieved when the electrode was located 1 to 2 cm apart from the magnetic field center to welding direction and the stirring frequency was 0.5 to 1 Hz.It was the most likely that remelting of a primary dendrite arm by stirred molten metal played a main role of the grain refinement of weld metal, and both the existence of fragments separated from a primary dendrite arm and the increase in constitutional supercooling ahead of solid-liquid interface due to molten-metal stirring assisted the weld metal in grain-refining.