Temperature Of Base Metal Research Articles

Effect of low temperature on fatigue crack propagation behavior of QP980 steel and laser-welded joint

This paper aims to investigate the fatigue crack propagation behavior of quenching and partitioning 980 steel (as base metal) and its welded joint at low-temperature environments. The fatigue crack propagation tests are carried out at 25°C, −40°C and −80°C under R=0.1, 0.3 and 0.5. The results show that the fatigue crack propagation threshold value increases and fatigue crack propagation rate decrease of base metal, whereas welded joint behaved opposite results as the temperature decreases. The fatigue ductility to brittle transition temperature of base metal is lower than that of welded joint. Compared with the welded joint, the base metal has higher fatigue resistance.

Porosity suppression of nickel-based superalloy by modulated base temperature in laser welding and mechanism analysis

This paper investigates the distribution pattern of welding porosity defects in annular weld seams of superalloy during laser welding. The results reveal that the initial portion of the annular weld seam exhibits a higher density and larger size of porosity defects compared to the ending portion. At a laser power of P = 360 W, the numerical simulation combination showed that the A1 region's average cooling rate is 8.767 × 103 °C/s and the A2 region is 8.151 × 103 °C/s that the thermal conduction effect at the initial welding position leads to an elevation in the base metal temperature in the subsequent unwelded region, thereby reducing the solidification rate of the molten pool in the latter half of the weld seam and effectively decreasing the porosity rate at the weld seam. Furthermore, the study demonstrates that elevating the base metal temperature can effectively modify the cooling rate of the molten pool, thereby influencing the formation of porosity defects. At a laser power of P = 360 W, increasing the base metal temperature to 600 °C reduces the cooling rate of the molten pool from 8.767 × 103 °C/s at a base metal temperature of T = 20 °C to 7.451 × 103 °C/s, leading to a decrease in the porosity rate from 3.357% to 0.022%. At a laser power of P = 672 W, increasing the base metal temperature to 600 °C reduces the cooling rate of the molten pool from 6.781 × 103 °C/s at a base metal temperature of T = 20 °C to 5.056 × 103 °C/s, leading to a decrease in the porosity rate from 8.214% to 0.002%. The increase in laser power brings more heat input, so the solidification rate of the molten pool decreases, but the porosity increases significantly. However, increasing the base temperature can effectively suppress the porosity defects under different laser powers. The research further reveals the relationship between welding porosity rate and cooling conditions, providing a control strategy for achieving low porosity rate welds.

Use of Orthogonal Arrays in Design of a Fuzzy Logic Controller to Predict the Proof Stress for the TIG Welded Al-65032

Fuzzy logic controller (FLC) is well suited where there is a considerable amount of uncertainty in the process. The material properties of a weldment in TIG welding depend on welding parameters like shielding gas pressure, current, torch angle, Electrode size, electrode projection, arc length etc. It is also influenced by the joint parameters like groove angle, land, root gap, preheating temperature. But a lot of noise parameters like variation of base material properties, variation in quality of inert gas used, variation in ambient conditions, variation in workman ship etc introduce uncertainties in the into the process. To deal with such uncertainties an FLC is designed and validated. In the current work, four parameters namely inert gas pressure, current, groove angle of the joint and preheating temperature of base metal are considered as input variables and the influence of these variables on the 0.2% proof stress is studied. Three linguistic terms are used for each parameter. To minimise the number of experiments in designing data base an L-9 orthogonal array is chosen for experimentation. TIG welding is carried and data base with 9 rules are formulated. For the input and out variables Triangular membership function is selected and FLC is designed. The FLC is validated with 5 more experiments. Mamdani approach is used to develop the Fuzzy controller.

TIG 육성용접을 위한 모재 온도와 오실레이션에 따른 비드형성 특성에 관한 연구

오버레이 용접은 해양 플랜트 분야, 원자력 발전소 분야, 다양한 발전 설비, 중장비 및 대형 디젤엔진 등과 같은 많은 산업 분야에 적용되고 있다. 오버레이용접은 지속적으로 발전하고 있으며 그 수요 또한 계속해서 증가하고 있다. 따라서 높은 생산성과 고품질의 오버레이 용접이 요구되고 있다. 오버레이 용접에서 LF는 비드 겹침부에서 빈번히 발생하며 비드의 퍼짐성이 낮다는 것이 주요 원인이다. 비드퍼짐성이 좋지 않은 경우, 비드의 산골차가 커지는 외관결함의 문제와 LF와 같은 문제가 발생한다. 본 연구에서는 목적은 비드 퍼짐성의 특성을 파악하기 위해 C형 용가재를 이용한 TIG 용접으로 모재 온도와 오실레이션 증가에 따른 특성을 연구 하였다. 모재의 온도와 오실레이션 폭이 증가함에 따라 비드 폭은 비례하여 증가하는 결과를 나타내었다. 오실레이션의 폭의 특성에 따라 용입의 형태가 변하고 오실레이션폭이 커질수록 비드 퍼짐비는 1로 수렴하는 비드형성 특성의 결과를 확인하였다.

Investigation of Mechanical Properties for Hybrid Joint of Aluminium to Polymer using Friction Stir Welding (FSW)

This paper deals with investigating mechanical properties for friction stir welded hybrid joint (i.e. metal to polymer). The dissimilar joining of aluminium alloy (AA6061-T6) and polycarbonate with the plates of 3mm thickness was carried out by friction stir welding (FSW). The welding was done well below its melting temperature of base metal. This has come up with producing better weld joints. The influence of welding process parameters on strength of joint has been evaluated by means of tensile test. The tool rotational speeds were taken between 500 to 1400 rpm and tool traverse speeds were taken between 40 to 80 mm min–1. The joint welded at 500 rpm and 40 mm min-1 yielded a maximum tensile strength of 14.91MPa. The joint characteristics analyzed by means of microstructure testing in which weld zone revealed mechanical interlocking phenomenon between AA 6061 and PC. Microhardness measurement on the welding zone exhibited an irregular distribution of hardness at the welded joint.

Bending Fatigue of Thermal Barrier Coatings

Thermal barrier coatings (TBCs) are ceramic coatings used in gas turbines to lower the base metal temperature. During operation, the TBC may fail through, for example, fatigue. In this study, a TBC system deposited on a Ni-base alloy was tested in tensile bending fatigue. The TBC system was tested as-sprayed and oxidized, and two load levels were used. After interrupting the tests, at 10,000–50,000 cycles, the TBC tested at the lower load had extensive delamination damage, whereas the TBC tested at the higher load was relatively undamaged. At the higher load, the TBC formed vertical cracks which relieved the stresses in the TBC and retarded delamination damage. A finite element (FE) analysis was used to establish a likely vertical crack configuration (spacing and depth), and it could be confirmed that the corresponding stress drop in the TBC should prohibit delamination damage at the higher load.

Study on the microstructure and toughness of dissimilarly welded joints of advanced 9Cr/CrMoV

Abstract

Effect of initial temperature on joint of aluminum alloy to galvanized steel welded by MIG arc brazing-fusion welding process

The variation of initial temperature of the base metal is conducted by a preheat treatment process, and its effect on metal insert gas (MIG) arc dissimilar metal brazing-fusion joint of aluminum alloy (Al) to steel plate is studied. Results show that though increasing the initial temperature of base metal, the joint appearance improves and wetting ability of liquid Al on steel becomes better. Three different zones are observed at brazed interface in all the joints. Zn-rich zone at weld toe and Zn-rich zone at weld root are characterized by the existence of Zn, while central zone is identified due to the formation of intermetallic compounds (IMCs) layer. The IMCs layer becomes thicker with the rise of initial temperature because of the increased peak temperature. At the initial temperature of 100 °C, the joint achieves the highest tensile strength of 180 MPa, which is equivalent to 80 % of that of Al alloy base metal and fractures at heat affected zone on Al side. The initial temperature of base metal influences the mechanical properties and fracture position of the joint through governing the thickness of IMCs layer and wetting ability of liquid Al alloy on the surface of steel.

Determination of Thermal Barrier Coatings Average Surface Temperature After Engine Operation for Lifetime Validation

Assessment of ex-service parts is important for the power generation industry. It gives us the opportunity to correlate part conditions to specific operating conditions like fuel used, local atmospheric conditions, operating regime, and temperature load. For assessment of thermal barrier coatings, one of the most valuable pieces of information is the local thermal condition. A method has been developed in Alstom, allowing determination of a thermal barrier coating average surface temperature after engine operation. It is based on the analysis of the phase composition of the thermal barrier coating by the acquisition of an X-ray diffraction spectrum of the coating surface, and its analysis using Rietveld refinement. The method has been validated by comparing its outcome to thermal models and base metal temperature mapping data. It is used for assessment of combustor and turbine coatings with various purposes: Determination of remnant coating life, building of lifing models, or determination of the coating degradation mechanisms under some specific operating conditions. Examples will be presented showing applications of this method.

Stationary GMAW-P weld metal deposit spreading

Non-isothermal spreading of non-travelling pulsed gas metal arc weld (GMAW-P) deposits was studied by experiments and numerical simulation. After an initial transient period, metal from the melting welding wire was deposited as a regular stream of droplets into a molten weld pool whose spreading was enhanced by direct arc heating of the solid substrate and weld pool convection. Accurate predictions of the final weld cross-section and time histories of base metal temperature and weld pool radius were produced by this simulation, which included mass, energy and momentum of transferring filler metal droplets. Dimensional analysis showed that speed of weld pool spreading was initially dominated by the momentum of liquid droplets while thermal convection by surface tension-driven flow became important at intermediate times. Eventually, the rate of spreading was matched to the thermal diffusion rate in the liquid. Capillary forces were never important in weld pool spreading. The weld metal deposit shape was well-approximated as a spherical cap with increasing volume and constant contact angle.

溶接母材表面の仕上げに関する研究 ２ ブラシ掛け時のスパッタに作用する力とその除去限界

In the arc welding, spatters attached around the bead of base metal. The adhered spatters lower the surface quality of the welding product. Therefore, it is very important to remove the spatters from the welding product. In general, wire brushes of bevel type or cup type have been used to remove the spatters. However, the adherent force of spatters on base metal is not constant. Then, the removal force, which is needed to remove the adhered spatters, is not also constant. Moreover, spatters are scattered on the base metal. Therefore, in order to remove the spatters by the brush, it is very important to clear the relationship between brushing conditions and the removal behavior of spatters.In this study, the removal forces of the adhered spatters are measured by using the removal tool to which strain gages attached. The shapes of the adhered spatters are also measured. Moreover, the force that is applied to the spatter in the brushing has been measured by using a model spatter. The shape of the model spatter is very similar to that of the adhered spatter. A steel plate with scale is used as a base metal. In brushing the metal, the pushing force of the brush is 29.4 N and the holding angle, that is the angle between the brush and base metal, is 15, 20, 25, or 30 degrees.As the result, it is indicated that the applied force to the model spatter in the brushing increases with the height of model spatter proportionally. The holding angle of the wire brush has little influence on the applied force to the model spatter. When the temperature of base metal is less than about 450 K, most of the removal shear forces of spatters are less than about 50 N. In this case, all of the attached spatters can be removed by the brushing. However, when the temperature of the base metal become high, the removal shear force become large and it become hard to remove all of the adhered spatter.

スパッタの結合力とその影響因子 アーク溶接時に発生するスパッタに関する研究 （第２報）

In the CO2 gas shielded arc welding, spatters are scattered around and bonded to the surface of base metal, and it is still unclear what are the main factors of the difference of their bonding force.In this paper we examined the bonding force of spatters, which were bonded on the surface of base metal (SS400) in different conditions and temperatures in the CO2 gas shielded arc welding (using the solid wire of 1.2 mm in diameter).The conditions of the surface of base metal were as follows:(1) The surface has scale, (2) The scale of the surface was removed with the surface grinder (Rmax=0.6μm), (3) The ground surface was fumed, and(4) The scale of the surface was removed with the disc grinder (Rmax=7-16μm).The temperature of base metal was raised by the ceramic heating unit of 14 mm in diameter, which was set up at the back of base metal. The bonding force was measured through the shear force of the spatter. 400 spatters were examined on each surface. Most of the dimeters of the spatters were 0.4 to 1.4 mm.When the temperature of base metal was below about 450 K, spatters on the surface with scale was not hot enough to melt the base metal and could not bond there by melting the surface of base metal. Most of their shear stresses were below about 40 MPa, but as the temperature raised, the shear stress was increased up to nearly (300) MPa.The fume on the surface or the roughness of the surface did not affect the bonding force as directly as the scale on the surface. The temperature, however, affected the bonding force. When the temperature of base metal was below 450 K, the bonding force became a little smaller.When the spatter bonded on the surface, because of the heat transfer, the change of the microstructure and correspondingly hardening was found to occur. When the spatter and the heat-affected zones of base metal were examined, their Vickers hardnesses indicated a little higher value (some spatters had the value of 470 (Hv)) than the hardness of base metal (156-165 (Hv)), although it depended on the conditions of the surface and the temperature.

Factors affecting adhesion of spatter: Study of spatter occurring during arc welding (2nd Report)

Summary In CO2 gas-shielded arc welding, spatter is scattered and adheres to the base metal surface. The main factors affecting any difference in the bonding force remain obscure. This paper examines the bonding force of spatter adhering to the surface of SS400 base metal (rolled steel sheets) under different temperature conditions in CO2 gas-shielded arc welding using 1.2 mm dia. solid wire. The following four types of base metal surface condition were adopted: Type 1: As-received surface covered with an oxide film; Type 2: Ground surface machined with a plain grinder (Rmax = 0.6 μm); Type 3: Surface with fume adhering to the ground surface; Type 4: Free-ground surface machined with a disc grinder (Rmax = 7–16 μm). The base metal was heated by a 14 mm dia. x 600 mm ceramic heater arranged on the back of the base metal. The bonding force was measured as the shearing force of the spatter. Some 400 spatter particles on each surface were examined. The particles mostly have diameters ranging between 0.4–1.4 mm. At a base metal temperature below around 450 K, the spatter on the scaled surface is insufficiently hot to melt the base metal and cannot adhere by melting the base metal surface. The shear stress is mostly below around 40 MPa. Despite a rising base metal temperature, however, spatter removal is still possible at less than 300 MPa. Fume on the surface or the surface roughness do not affect the bonding force as directly as scale on the surface. The temperature, however, affects the bonding force. At a base metal temperature below around 450 K, the bonding force is slightly smaller. When spatter adheres to the surface, heat causes the microstructure to change with corresponding hardening. The spatter and HAZ of the base metal here show a slightly higher Vickers hardness value (some spatter particles having HV470) than the base metal hardness (HV156–165), although this depends on the surface conditions and temperature.

Ｔｉ系アモルファスろうによるＣＰＴｉ及びＴｉ‐６Ａｌ‐４Ｖろう付継手の組織と機械的性質

The microstructure and mechanical properties of commercial pure titanium (CPTi) and Ti-6Al-4V alloy joints brazed with newly developed Ti-base amorphous filler metals have been investigated by microscopy, electron probe microanalysis, tensile test, fatigue test and salt immersion test.The developed amorphous filler metals were three kinds of Ti-37.5Zr-15Cu-10Ni, Ti-35Zr-15Cu-15Ni and Ti-25Zr-50Cu. Their melting points were approximately 100°C lower than those of the conventional Ti-base brazing filler metals. With these filler metals, CPTi and Ti-6Al-4V alloy could be brazed at temperatures below α-β transformation (880°C) and β transus temperature (995°C), respectively.In brazing at temperature below α-β transformation or β transus temperature of base metal used, the original fine structure of the base metal was nearly preserved and a brazed zone was recognized to exist obviously. However, at temperature above these temperatures, the grains of the base metal were coarsened and in the brazed zone the fine acicular phases were observed.The tensile properties of the joints brazed at temperatures below these transformation temperatures, was compared with that of the base metal and then in brazing for a suitable brazing time, the joint was fractured in the base metal.From fatigue test results of the Ti-6Al-4V alloy brazed joint, in the joint brazed at temperature below β transus, the fatigue life indicated a fairly good value but all joints failed in the brazed zone. When brazed at 1000°C, joints showed low fatigue life considerably.The corrosion behavior of the brazed joints was quite equivalent to that of the base metal.

Mechanical aspects of high temperature coatings

High temperature coatings are used for two main functions, either to protect a base metal against corrosion or erosion or to minimize wear. A third function is to reduce the base metal temperature in the case of thermal barrier coatings; however, resistance to hot corrosion and oxidation is again mandatory. The main functions of such a coating can only be fulfilled when the coating has sufficient resistance to thermal strains and protects the base metal without deterioration. In this paper we describe the strains that arise during the application of a coating-mainly due to thermal expansion mismatch-and during service-due to diffusion, aging and chemical reactions with atmosphere, e.g. the formation of oxides. These strains cause cracks within a coating which reduce its ability to protect the base metal against a corrosion attack. In the second part of this paper the influence of the coating on the mechanical properties of the coated component is described. In general, a high temperature component is subjected to static loadings-the material undergoes creep-and to cyclic loadings-the component undergoes fatigue. In both cases a coating has some influence either through changes in the material properties due to a different heat treatment or through changes in the surface of a component due to the presence of the coating; hence a coating alters the conditions for crack initiation. From laboratory experience of high temperature coatings applied to gas turbine blades it can be shown that, depending on the type of coating and the method of application, the changes in materials might be positive, negative or negligible. For all applications it seems to be possible to select coatings without marked effects on the mechanical properties of the base metal. However, it is not always possible to choose the coatings best able to protect the base metal against corrosion or wear, because to achieve mechanical compatibility it is sometimes necessary to use coatings which are not stable for the required lifetimes. In-service examples from gas turbine experience are presented.

マンガンシリコン高張力鋼の熔接による脆化領域について

For mild steels it has been recognized that the V-notch Charpy Impact value or the weld heat affected embrittled zone, 10 to 14mm apart from the center of welded bead, is decreased from the value of base metal. This paper deals mainly the experimental study on the similarly embrittled zone in high tensile Mn-Si steels. Standard V-notch Charpy test was employed to evaluate the notch toughness in the embrittled zone in eight high tensile Mn-Si steels, namely N3, N6, K1, K4, M3, M6, Y4 and Y6.The main conclusions are as follows:—1. Al inear relationship was found between the degree of embrittlement and the transition temperature of base metal, the higher the embrittlement, the higher the transition temperature.2. The degree of. embrittlement and the transition temperatures of the tested high tensile Mn-Si steels were lower than that of ordinary mild steels.3. The maximum temperature attained in the embrittled zone was lower than the Al transformation point.