Fracture Toughness Of Weld Metal Research Articles

Study on fracture toughness of 617 Ni-based alloy welded joint under different elevated temperatures

Abstract

A Study on Fatigue Life Improvement of Welded Joints in All Positions and Fracture Toughness of Weld Metal for CO2 Gas Arc Elongated Bead Welding Method with Low Transformation Temperature Welding Material

A Study on Fatigue Life Improvement of Welded Joints in All Positions and Fracture Toughness of Weld Metal for CO₂ Gas Arc Elongated Bead Welding Method with Low Transformation Temperature Welding Material

Effect of Trace Element on Microstructure and Fracture Toughness of Weld Metal

The microstructure and fracture toughness of weld metal under Ti-free and Ti-containing different fluxes were investigated in this study. It was found that the trace element Ti of flux in submerged arc welding produced significant influence on the fracture toughness. The addition of 60 ppm Ti induced the sharp increase in J0.2 value from 232.78 to 364.08 kJ/m2. Microstructure characterization revealed that a large number of oxide inclusions prompted the nucleation of acicular ferrites and refined grains, which improved the fracture toughness of Ti-containing weld metal greatly. Moreover, the crack propagation path was more tortuous and bifurcated due to the small amount of carbide precipitations along grain boundaries and blocky martensite–austenite islands for Ti-containing weld metal. Meanwhile, the large-angle grain boundaries caused crack deflection and increased the resistance of crack propagation compared to Ti-free weld metal.

The comparative evaluation of AISI 316/A387-Gr.91 steels dissimilar weld metal produced by CCGTAW and PCGTAW processes

The mechanical properties (impact toughness and hardness profile) and the microstructure of dissimilar weld metal of AISI 316 and A387-Gr.91 steels produced by constant and pulsed currents GTAW were studied. The microstructural studies showed that the pulsed current application leads to finer and equiaxed dendrites in the weld metal central region, as well as to the expansion of this region. In addition, the pulsed current produces finer secondary phases with more uniform distribution. The chemical analysis of the dendritic and interdendritic zones revealed that the segregation of alloy elements takes place in the entire weld metals and that it is more intensive with the constant current. The segregation is recognized as the main agent in forming the secondary phases, such as MC carbides ((Nb, Ti) C) and intermetallic compounds. Moreover, the microstructure images and map analysis of the weld metal near the fusion line indicated that a filler-deficient zone, including beaches, peninsulas and islands with a chemical composition similar to the base metal is developed. It was disclosed that the zone scope is decreased by the pulsed current. It was observed that the use of the pulsed current increases the weld metal fracture toughness and hardness simultaneously.

Improvement of Weld Metal Fracture Toughness by Micro-Addition of Rare Earth Metal

Improvement of Weld Metal Fracture Toughness by Micro-Addition of Rare Earth Metal

The effects of functionally graded material structure on wear resistance and toughness of repaired weldments

To perform a long lasting, crack-free repair welding on ultrahigh strength steels, the filler metal must be chosen and applied properly. Avoiding several short-term repairs or replacements, the repaired weldment should reveal comparative characteristics such as wear resistance, toughness and hardness to base metal. In the present study, a novel functionally graded material have been introduced to obtain enhanced wear resistance and hardness at surface as well as improved fracture toughness at fusion line of repaired weldments. A comparative study of wear resistance of repaired weld metals has been carried out by pin-on-disk apparatus at 5 N normal load and 0.14 ms −1 sliding speed. Fracture toughness of weld metal was also evaluated by charpy absorbed fracture energy tests and scanning electron microscopy fractograghs. The results show that by employing functionally graded layers, toughness was enhanced significantly while retaining the surface wear resistance.

Fracture Toughness Evaluation of Laser Beam-Welded Joints of 780 MPa-Strength Class Steel

For fracture assessment of steel structures with laser beam-welded joints, it is significantly important to evaluate the fracture toughness of the weld metal. However, the fracture toughness of weld metal is often impossible to measure by standard Charpy impact testing in the brittle-to-ductile transition or upper-shelf temperature region, because of fracture path deviation (FPD) from the weld metal due to narrow weld bead and a high degree of overmatching in strength. In this work, evaluated fracture toughness of laser beam-welded joints of 780 MPa-strength class (HT780) steel is examined by Charpy impact testing and CTOD fracture toughness testing. The improved Charpy impact tests, using the specimen with three parallel welds or the side-groove specimen, are conducted in order to prevent FPD. The applicability and significance of the improved impact test methods to the laser beam-welded joints of high-strength steel are investigated by means of Weibull stress analysis. The Weibull stress analysis indicates that the 3-weld method could not necessarily prevent FPD in laser beam-welded joints of HT780 steel, since side beads are not as hard as main weld beads, due to reheating at the main weld. On the other hand, a side-groove specimen is effective for avoiding FPD, but intrinsic VE of the weld metal could not necessarily be obtained by using this specimen.

Fracture toughness of electron beam welded Ti6Al4V

Abstract Two pass and three pass bead-over-bead (BoB) electron beam weld technique was attempted on Ti6Al4V to improve its Charpy impact and fracture toughness of weld metal portion. Hardness and microstructural studies were also done to support the findings. The hardness values of the weld metals were found to be higher than their base metal counterpart. The weld metal hardness came down when deposited with bead-over-bead technique. Conventional stringer bead welding caused reduction in Charpy impact toughness compared to its base metal counterpart. Bead-over-bead technique improved the notch toughness of weld metals. The fracture toughness values of the weld metals were found to be superior to that of base metal. This is in contrast to the Charpy impact toughness values where the impact toughness of base metal was better than the stringer and bead-over-bead weld metals. The better fracture toughness of weld metals was related to the basket-weave structure compared to the equi-axed structure of base metal. Bead-over-bead technique was found to help in improving the fracture toughness of weld metal further. Overall, the study showed that the bead-over-bead technique improved both notch toughness and fracture toughness of Ti6Al4V electron beam weld metals.

Effect of laser beam welding on fracture toughness of a Ti-6.5Al-2Zr-1Mo-1V alloy sheet

Investigation of fracture toughness on Ti-6.5Al-2Zr-1Mo-1V alloy thin sheet and its laser-welded joints has been carried out. In the test compact tension (CT) specimens and single specimen technology were used. In addition, hardness distribution and microstructure of the welded joints were examined. Fracture test indicates that brittle unstable fracture occurs after slow crack propagation for all the specimens, except that one heat affected zone (HAZ) specimen is brittle crack initiation. It is found that rolling directions have no obvious effect on fracture toughness of base metal. Moreover, fracture toughness of weld metal is obviously decreased in comparison with base metal whatever in as-welded condition or in stress relief condition. Post-weld heat treatment (PWHT) leads to fracture toughness of the welds further decreasing. Fractography observation shows that the fracture mode is predominantly dimpled in base metal. However, there exists intergranular fracture in the weld metal. Thus, the transition of fracture mode from both base metal and HAZ to weld metal may lead to dramatic decrease in fracture toughness. Microstructure examination reveals that the microstructure of weld metal consists of large grains with fine acicular structure. The formation of fine α acicular structure is due to rapid cooling during laser welding. After PWHT, the acicular structure is coarsened.

Effect of nickel content on mechanical properties and fracture toughness of weld metal of WWER-1000 reactor vessel welded joints

Welding of WWER-1000 reactor vessel of steel 15X2HMΦA is performed using the C B-12X2H2MAA wire and Φ⨿-16 or Φ⨿-16A flux. Nickel content in the weld metal usually lays within the limits 1.2–1.9%. The experimental data is shown on the weld metal with the nickel contents 1.28–2.45% after irradiation with fluence up to 260.10 22n/m 2 at energy more than 0.5 MEV. The embrittlement was measured by shift of critical brittleness temperature. Has appeared, that the weld metal with the low nickel content is the least responsive to irradiation embrittlement. The mechanical properties and fracture toughness of the weld metal with the contents of a nickel less than 1.3% are studied. Specimens CT-1T are tested, the “master-curve”, and its confidence bounds with probability of destruction 5 and 95% is built. “Master-curve” in the specified confidence interval is affirmed by CT-4T specimens test data. Is shown, that the mechanical properties and fracture toughness of the weld metal with the contents of nickel less than 1.3% satisfy the normative requirements.

Critical issues in achieving ductile behaviour of welded moment connections

A comprehensive research program on large-size, welded moment connections conducted after the 1994 Northridge earthquake in California has identified three critical issues that could significantly affect the strength and ductility of the connections. They are: fracture toughness of weld metal, geometry and size of weld access hole, and control of panel zone deformation. Experimental and analytical studies on each of the issues have been performed at the Center for Advanced Technology for Large Structural Systems at Lehigh University. This paper presents brief descriptions of the studies, key results obtained and recommendations made to insure ductile performance of the connections.

Accuracy of Crack Size Measurement in Welded Joint by Advanced AUT System for Non Destructive Evaluation of Fracture Strength.

For non destructive estimation of brittle fracture strength at welded joint, fracture mechanics require to monitor fracture toughness of weld metal and two dimensional flaw sizes of length and height. Up to now, many methods have been proposed to measure both flaw length and height in laboratory. However, industrial inspection methods estimate only flaw length and other advanced methods proposed have several barriers for applying industrial problems. As the results, NDE measurement data have been used only for flaw detection, and strength has never been estimated non destructively for industral structures. In this paper, the authors applied the advanced automatic ultrasonic inspection system to measure not only flaw length but also flaw height for industrial welded structures. Using this system, 22 specimens with artificial inner and surface cracks in welded joint varying crack length and height were measured non destructively. After non destructive measurement, welded joint specimens were broken by tensile test in liquid nitrogen, and the crack size were measured by fractography. Comparing the crack size by fractography to the one by ultrasonics method, errors in non destructive sizing by the ultrasonic system were estimated accurately. Using the fracture mechanics procedures, effect of the error in non destructive flaw sizing on strength estimation was investigated.

The influence of weld strength mismatch on crack-tip constraint in single edge notch bend specimens

Previous work by Dodds and Anderson provides a framework to quantify finite size and crack depth effects on cleavage fracture toughness when failure occurs at deformation levels where J no longer uniquely describes the state of stresses and strains in the vicinity of the crack tip. Size effects on cleavage fracture are quantified by defining a value termed J SSY: the J to which an infinite body must be loaded to achieve the same likelihood of cleavage fracture as in a finite body. In weld metal fracture toughness testing, mismatch between weld metal and baseplate strength can alter deformation patterns, which complicate size and crack depth effects on cleavage fracture toughness. This study demonstrates that there is virtually no effect of ±20 percent mismatch on J SSYif the distance from the crack tip to the weld/plate interface (L min) exceeds 5 mm. At higher levels of overmatch (50 to 100%), it is no longer possible to parameterize the departure of J SSYfor a weldment from that for a homogeneous SE(B) based on L min alone. Weld geometry significantly influences the accuracy with which J SSYfor a welded SE(B) can be approximated by J SSYfor a homogeneous specimen at these extreme overmatch levels.

On the assessment of dynamic fracture characteristics of weld metal

The dynamic fracture toughness of weld metals was tested by using the dynamic specific energy, ⋎ pj , as a measure. The results show that this approach can be used to estimate the dynamic fracture toughness of different microstructural areas of weld metal. Depending on the microstructure, different values of ⋎ pj were observed. The dynamic fracture toughness J Id measured and calculated by using ⋎ pj lies within ±15%.

Fracture toughness of weld metals in steel piping for nuclear power plants

To determine toughness behaviour of dissimilar welds in steel piping and obtain data to evaluate Leak-Before-Break for these welds, an experimental study on fracture toughness was carried out. This paper provides Charpy impact properties and fracture toughness data of base and weld metals of dissimilar welds in nuclear piping.

Rosenhain Centenary Conference - 2. Design implications for materials selection 2.2 Design against brittle fracture

The paper assesses the current position and future trends in a complete definition of the problem of brittle fracture. It is concluded that there is a need for a more uniform approach to the specification of toughness requirements in present design standards, and ways of achieving this are indicated. The acceptance of the presence of defects leads to the use of fracture mechanics techniques in defining conditions for avoiding fracture initiation. A new treatment for a toe crack in a fillet weld is illustrated, as an example of this approach. Because of interpretation and experimental difficulties in assessing the fracture toughness of weld metals and heat affected zones, it is concluded that it would be inappropriate to use the c.o.d. test, on its own, to specify material toughness levels for National Standards. Some of these difficulties are illustrated and areas for future research are discussed, including the role of the physical metallurgist.

継手強度の見地からみた溶接金属と母材の適合性に関する―考察

In the welded joints, it becomes a common idea that the strength of weld metals is equal to or higher than it of base metal from the viewpoints of efficiency of welded joints. Otherwise, it is effective to use the weld metal whose strength is lower it of base metal in order to prevent the initiation of weld cracking. If welded joints having lower grade weld metal have larger strength than it required as the welded joints, it is one of the useful welding procedure to use the lower grade welding rod.In this report, the state tensile and brittle fracture behaviors of the welded joints having wled metal whose strength is lower than it of base metal—so called Soft Welded joints—are investigated. The example results of calculations about soft ratio and fracture toughness of weld metal required to guarantee the static tensile and brittle fracture strength which is almost equal to those of base metal were showed (Figs. 5, 11, 12, 15). In a case of production or selection the welding rod, a suggestion about tensile strength required as weld metals was made (Fig. 8).