Strength Of Weld Metal Research Articles

Toward optimum friction stir welding tool shoulder diameter

Currently friction stir welding tools are designed by trial and error. Here we propose and test a criterion for the design of a tool shoulder diameter based on the principle of maximum utilization of supplied torque for traction. The optimum tool shoulder diameter computed from this principle using a numerical heat transfer and material flow model resulted in best weld metal strength in independent tests and peak temperatures that are well within the commonly encountered range.

Effect of Strength of Weld Metal on Plastic Deformation Capacity of the Beam

Effect of Strength of Weld Metal on Plastic Deformation Capacity of the Beam

Empirical Formulae Estimating Strength of Weld Metal Considering with Change of Chemical Composition of Weld Wire by Heat Input

Empirical Formulae Estimating Strength of Weld Metal Considering with Change of Chemical Composition of Weld Wire by Heat Input

高強度溶接金属の靭性に及ぼす酸化物の影響:高強度溶接金属の特性支配因子の検討(第二報)

高強度溶接金属の靭性に及ぼす酸化物の影響:高強度溶接金属の特性支配因子の検討(第二報)

Strengthening behavior analysis of weld metal of laser hybrid welding for microalloyed steel

The weld metal with high strength and good toughness was obtained for medium thickness microalloyed steel by using high power laser hybrid welding technology. Mechanical properties of weld metal were evaluated by using room temperature tensile test and low temperature three-side Charpy V-notch (CVN) impact test. The results show that the yield strength and ultimate tensile strength of weld metal are up to 713 MPa and 918 MPa, respectively. Both of them are almost 1.5 times higher than those of base metal. Under the strict three sides CVN condition, the −40 °C low temperature impact absorbed energy is up to 32 J and also higher than that of base metal. Weld metal predominately consists of granular bainite and carbon-free bainite. Both of them mainly contain lath morphology bainitic ferrite. The lath morphology bainitic ferrite with fine grain size plays an important role in higher strength. Dispersive carbide and high density dislocation are found in strengthening weld metal.

매설 가스 배관 이종금속 용접부의 강도 불일치가 잔류응력에 미치는 영향 고찰

본 연구에서는 실제 용접 과정을 모사하는 유한요소 해석을 이용하여 강도 불일치를 가지는 매설 천연가스 배관 용접부의 잔류응력 분포를 계산한다. 유한요소 해석 절차의 타당성을 검증하기 위해 온도 및 잔류응력 해석 결과들은 실제 용융부 형상과 API 579 적용 결과와 비교된다. 기계적 강도 차이, 용접 금속의 강도, 덧살 및 입열량 등과 같은 용접 및 재료 변수들이 잔류응력 분포에 미치는 영향을 평가하기 위해 Parametric Study가 수행된다. 최종적으로 Parametric Study 결과에 근거하여 용접 및 재료 변수들의 영향이 고찰된다. 특히, 모재들 사이의 강도 불일치는 잔류응력 분포에 미미한 영향을 미침을 확인하였다.

Effects of heat treatment process and niobium addition on the microstructure and mechanical properties of low carbon steel weld metal

The mechanical properties and microstructure were evaluated and analyzed by optical microscopy (OM) and transmission electron microscopy (TEM) for micro-alloy carbon steel weld metal with and without Nb addition, respectively, under different heat treatment processes including stress relief annealing, normalizing, and no treatment after welding. The strength and elongation of the weld metal without treatment after welding were improved with the addition of Nb element, and the impact toughness was not affected obviously with the Nb addition. After stress relief annealing, the strength decreased for the Nb-free weld metal, while the elongation and impact toughness increased. However, for the Nb-bearing weld metal, stress relief annealing improved the strength of the weld metal significantly, and deteriorated the elongation and impact toughness. In the case of normalizing treatment to the weld metal, it was shown that with the increase of the holding time at the normalizing temperature of 920 °C, for both the weld metals with and without Nb addition, the microstructure of the columnar grain zone (CGZ) was transformed from one of columnar grain into one of equiaxed grain. The grain size of the equiaxed grain zone (EGZ) increased initially, then remained almost unchanged with the prolonging of the holding time. The mechanical properties of the weld metal with and without Nb addition showed no obvious change with the increasing holding time. With the increase of the normalizing temperature, the strength of the Nb-bearing weld metal increased, while the elongation and impact toughness decreased significantly. OM and TEM analysis found that the fine NbC particles were precipitated at the normalizing temperature of 920 °C, which refined the grains of the weld metal and increased the impact toughness. With the increase of the normalizing temperature, the content of widmanstatten ferrite (WF) in the Nb-bearing weld metal increased, whereas the quantity of the NbC particles decreased, which improved the strength and lowered the impact toughness.

Microstructure and Toughness of 1000 MPa High Strength Weld Metal

Welding of 1000 MPa high strength alloy steel is difficult because of its welding cold cracking sensitivity and the difficulty in maintaining high joint toughness. In this paper the effects of alloy elements on welding cracking tendency are analyzed, and measures to prevent cold crack are proposed. Welding wires with high strength was deposited into weld metal and welded into joint. Tensile test, micro-hardness test and Charpy impact test were used to evaluate the strength and toughness of weld metal and heat affected zone. Optical microscope, transmission electron microscope and scanning electron microscope were used to analyze the microstructure. It is shown that the weld metal mainly consists of lath martensite, lath bainite, and residual austenite which exists between the laths. The strength of weld metal increases in a small degree with increasing carbon equivalent and its toughness and ductility are not related to carbon equivalent. The toughness and ductility are much sensitive to nonmetallic inclusions. The welded joint has tensile strength of higher than 1000 MPa when welded at heat input of 11 kJ/cm and 15 kJ/cm and the mechanical properties are little influenced by the amount of heat input in this range. The whole welded joint has good comprehensive properties.

Effect of Oxygen Content on Toughness in High Strength Weld Metal

The effect of oxygen content on toughness in the high strength weld metals with full martensitic microstructures was investigated for Gas Metal Arc Welding (GMAW) and Gas Tungsten Arc Welding (GTAW). Solid and Flux cored two types wires were examined for their influence on the resulting oxygen content in weld metals. It has succeeded in controlling the oxygen contents without changing welding processes. As expected, the increasing oxygen content obviously decreased the upper shelf energy (vEshelf). One of the primary reasons of this tendency is considered that the higher density of oxide makes dimples on the ductile fracture surface smaller. On the other hand, as unexpected, the oxygen content from 7 to 450 ppm had no impact on the fracture appearance transition temperature (FATT), and oxides at the brittle fracture initiation point have not been found. This result supports that the oxides in high strength full martensitic weld metals (Vickers hardness = 360 ~ 430) have no harmful effect on FATT.

高張力鋼継手の耐脆性破壊特性に及ぼす溶接継手軟質化の影響

Recently, high strength steel plate such as 950MPa class strength is focused as material of hydropower plant due to its effect on cost reduction and it has been already used to penstocks in Kanna-gawa and Omaru-gawa hydropower plants in Japan. However, it comes to issue that welding restrictions for preventing welding cracks and keeping strength are much severer than ordinary strength steel, for example, preheat condition or inter-pass-temperature range. If under-matching (lower strength in weld metal than base plate) is applied, it is possible that high strength steel plate becomes easier to use because restrictions in welding process may decrease by application of softer welding materials. By applying softer welding, it is assumed that mechanical performances of the structure changes due to existence of heterogeneous region. However, quantitative effect of application of under-matching for high strength steel on deformation behavior and fracture assessment is not certain.In this report, in order to evaluate the effect of under-matching design on brittle fracture behavior, standard CTOD tests and wide plate tests with through-thickness notch by the welded joint using actual combination of 950MPa steel plate for penstock and various welding materials (950-570MPa class), were performed. As a result, welded joint with softer welding materials showed higher resistance to brittle fracture. Furthermore, taking into consideration of allowable stress, sufficient load capacity was observed even in case of application of 570MPa class welding consumables.

Effects of Welding Positions on Mechanical Properties and Microstructure in Weld Metal of High Strength Steel

In this study the effects of two welding positions included in flat and upward vertical on the mechanical properties and microstructure of high strength weld metal deposited with shielded metal arc welding (SMAW) using an electrode of ASME SFA 5.5-96 E9018B3 type have been investigated. The aim of the present work is to study the effects of these two welding positions for a weld metal alloyed with 1%Mo, 2%Cr, 0.79%Mn, and 0.08% C in the stress relieved condition. For studying mechanical properties Tensile, Impact and hardness experiments have been conducted; meanwhile chemical analysis and microstructure studying have been carried out on specimens. The results show that welding position does not have any significant effect on tensile and hardness of the weld metal but in vertical position welding metal toughness is lower than toughness in flat position in all temperatures. Transition temperature of ductile fracture to brittle fracture is -50 °C for E9018B3 in welding of high strength micro alloyed steels.

Characterization of a High Strength Weld Metal for TRIP Steels Using EBSD and HAADF/STEM Imaging

Extended abstract of a paper presented at Microscopy and Microanalysis 2009 in Richmond, Virginia, USA, July 26 – July 30, 2009

Experimental study on method of estimating strength of weld metal in steel structure

We conducted the welding experiment using three kinds of test piece, actual size, diaphragm and butt joint. Then, we examined the influence on strength, cooling time and carbon equivalent of weld metal by welding conditions on the different test pieces. We calculated an estimate of cooling time and chemical components. Consequently, we concluded that the strength of weld metal can be estimated by heat input, interpass temperature, carbon equivarent of welding wire and shape of test piece.

Effect of mechanical mismatching on the ductile-to-brittle transition curve of welded joints

The effect of mechanical mismatching (ratio between the yield strength of base and weld metal) on the toughness of welded joints at different temperatures was analysed and the ductile-to-brittle transition curves of these welded joints were experimentally obtained. The filler metal of the joints was always the same, varying the base metal and the width of the welded zone. Two base metals were selected, one with a higher strength than the filler metal (undermatched joint) and the other with a lower strength than the filler metal (overmatched joint). In addition, the joints were made using two different weld widths, 20 and 10 mm. The fracture behaviour of the joints were determined at different temperatures using SE(B) specimens provided with short cracks ( a/ W = 0.22). Besides, long crack specimens ( a/ W = 0.5) were also used for comparison. In the case of overmatched joints, the J-values for ductile crack growth are larger than for the undermatched joints. In addition, the ductile-to-brittle transition curve is displaced towards lower-temperatures and higher-toughness values and the toughness for cleavage fracture is also larger for overmatching than for undermatching. All these effects are more significant as the weld width decreases and have been explained in terms of constraint modifications.

Pulse current treatment effect on the strength of reinforcing steel and its weld joint under impact loading

We present results of static and impact tension tests of as-received reinforcing steel specimens, specimens with weld joints in their test portion, as well as specimens pretreated by high-density pulse current. As test results demonstrate, an increased strain rate enhances strength, and the pulse current treatment greatly influences the strength and plasticity of a defect-containing weld metal under static and impact tension.

Microstructure, Mechanical and Corrosion Behaviour of Dissimilar Weldments between AISI 304 Stainless Steels and AISI 1020 Carbon Steels Produced by Gas Tungsten Arc Welding Using Different Consumables

Gas tungsten arc welding was applied to join AISI 304 stainless steel and AISI 1020 carbon steel sheets with three types of consumables – AISI 308L, AISI 309L and AISI 316L stainless steel wires. Weld metals produced by all consumables exhibited the identical hardness of ca. 350 HV. This value was higher than those of stainless steel and carbon steel base metals, indicating the relatively high strength of weld metals. The corrosive behaviour of weld metals was investigated by a potentiodynamic method. Specimens were tested in 3.5 wt% NaCl solution saturated by laboratory air at 27°C. A pitting potential of weld metal produced by the AISI 309L consumable was higher than those of weld metals produced by the AISI 308L and AISI 316L consumables respectively. The chemical compositions and microstructure of weld metals were also investigated. The pitting corrosion resistance of weld metals produced by different consumables is discussed in the paper in terms of the pitting resistance equivalent number (PREN) calculated from the chemical compositions and the content of delta ferrite in the austenite matrix of the weld metals.

Thermo-mechanical treatments of Sc- and Mg-modified Al–Cu alloy welds

High-strength heat-treatable aluminum alloy AA2219 finds application in aerospace industries. Though it has good weldability, with alternating current–tungsten inert gas welding, the joint efficiency obtained is only 40%, particularly in thicker plates. In the present study, an attempt has been made to improve the weld metal properties by modifying the chemistry of fusion zone and post-weld thermo-mechanical treatments. Fillers were made through casting route by melting conventional 2319 filler with Sc and Mg. Two levels of Sc (0.3% and 0.6%) and four levels of Mg (0.3% to 0.6%) were varied. Compressive deformation was done on the fusion zone of the weld to get three levels of percentage of reduction (4%, 8%, and 12%). As welded specimens and welds after compressive deformation, those were subjected to post-weld aging treatments at 190oC for different periods up to 100 h. Compressive deformation on the welds made with modified filler of 2319 with Sc and Mg resulted in significant improvement in the weld metal strength.

Effects of welding parameters on tensile strength of weld metal in flux cored arc welding

Effects of welding parameters such as welding current, voltage and travel speed on the tensile strength of weld metal in flux cored arc welding were studied. The results were interpreted in terms of chemical composition and microstructural change in the weld metal. When heat input was increased to 2˙1 kJ mm–1 by increasing welding current, the tensile strength of the weld metal increased. However, the tensile strength of the weld metal decreased when heat input was increased from 2˙1 to 4˙5 kJ mm–1 by reducing travel speed or by increasing voltage. It showed that when heat input is higher than 2˙1 kJ mm–1 the decrease in tensile strength was related with the microstructural change. However, when heat input is lower than 2˙1 kJ mm–1 the increase in tensile strength was hardly related with the microstructural change. As Pcm value in the weld metal increases in the heat input up to 2˙1 kJ mm–1, it is believed that Pcm value has more powerful effect than microstructure in the heat input range. It showed that variation of the welding parameter resulted in different recoveries of the alloying elements in the wire. The recoveries increased with an increase in welding current and/or travel speed, but they decreased with an increase in voltage. The effects of welding parameters on the recoveries were rationalised with the time available for the reaction with oxygen during welding.

Effect of Grain Boundary Ferrite on Susceptibility to Cold Cracking in High-strength Weld Metal

Due to the practical limitations of lowering the diffusible hydrogen content of flux-containing welding consumables, it is now felt that modification of the weld microstructure would alleviate the risk of weld metal cracking in multi-pass weld deposits. Thus, this study aimed to identify and evaluate the effect of the weld microstructure on the cold cracking susceptibility of FCAW weld metals and then to provide a basic guideline for designing new welding consumables from a microstructural point of view. In order to identify the parameter(s) that can quantify the microstructural susceptibility of multi-pass weld deposit, two sets of FCAW wires with tensile strength of about 600 MPa were prepared by controlling the Ni content to allow sufficient variation in the weld microstructure, but with little change in weld metal strength. The cold crack susceptibility of those two chemistries was evaluated by a multi-pass weld metal cracking test at various levels of diffusible hydrogen content. All of the cold cracks developed were Chevron-type, and the occurrence of such cracks depended upon the proportion of grain boundary ferrite (%GF) as well as the diffusible hydrogen (HD) content. In fact, at the same level of HD, higher Ni (1.5%Ni) wire showed better resistance to cold cracking than lower Ni (0%Ni) wire even though the latter was stronger and also higher in carbon equivalent. This result could be explained solely by the difference in grain boundary ferrite content between those two welds since Chevron cracking preferentially initiates at and propagates along grain boundary ferrite. Therefore, we propose the use of a value of %GF as a parameter to quantify the microstructural susceptibility of ferritic multipass weld deposit with a strength level of about 600 MPa. It was further suggested that, in addition to the hydrogen control approach, microstructural modification in the form of reducing the %GF can be pursued to develop welding consumables with improved resistance to cold cracking.

Effect of carbonate in electrode coating on the microstructure and mechanical properties of weld

Abstract In this study, various additions of carbonates, MgCO 3 , Na 2 CO 3 , K 2 CO 3 and BaCO 3 , respectively, were added in electrode coating to investigate microstructure and mechanical properties of weld metal. The results showed that α-Fe phase with bcc structure existed in each weld metal. The microstructure included of the primary ferrite (i.e. grain boundary ferrite and intragranular polygonal ferrite), the ferrite with second phase and acicular ferrite. When the addition of MgCO 3 and Na 2 CO 3 increased, the content of primary ferrite increased and acicular ferrite decreased. On the other hand, the addition of K 2 CO 3 and BaCO 3 promoted the content of primary ferrite reducing and acicular ferrite increasing. So far as mechanical properties were concerned, the addition of carbonates affected hardness, tensile strength and toughness of weld metal. MgCO 3 and Na 2 CO 3 diminished the mechanical properties due to the microstructure became coarser. Oppositely, K 2 CO 3 and BaCO 3 improved mechanical properties due to the microstructure became finer.