A Study on Reducing Oxygen Content in Weld Metals for Narrow Groove GMA Welding  with a Local CO<sub>2</sub> Adding Nozzle

Three weld metals with different oxygen contents were developed. The influence of oxygen contents on the microstructure and impact toughness of weld metal was investigated through high heat input welding tests. The results showed that a large number of fine inclusions were formed and distributed randomly in the weld metal with oxygen content of 500 ppm under the heat input condition of 341 kJ/cm. Substantial cross interlocked acicular ferritic grains were induced to generate in the vicinity of the inclusions, primarily leading to the high impact toughness at low temperature for the weld metal. With the increase of oxygen content, the number of fine inclusions distributed in the weld metal increased and the grain size of intragranular acicular ferrites decreased, which enhanced the impact toughness of the weld metal. Nevertheless, a further increase of oxygen content would contribute to a great diminution of the austenitic grain size. Following that the fraction of grain boundary and the start temperature of transformation increased, which facilitated the abundant formation of pro-eutectoid ferrites and resulted in a deteriorative impact toughness of the weld metal.

Download Full-text

Hydrogen-Assisted Cracking in GMA Welding of High-Strength Structural Steel—A New Look into This Issue at Narrow Groove

Metals ◽

10.3390/met11060904 ◽

2021 ◽

Vol 11 (6) ◽

pp. 904

Author(s):

Thomas Schaupp ◽

Nina Schroeder ◽

Dirk Schroepfer ◽

Thomas Kannengiesser

Keyword(s):

Structural Steel ◽

Crack Formation ◽

Gma Welding ◽

Gas Metal Arc Welding ◽

High Strength ◽

Opening Angle ◽

Diffusible Hydrogen ◽

Weld Metals ◽

Metal Arc Welding ◽

Hydrogen Assisted Cracking

Modern arc processes, such as the modified spray arc (Mod. SA), have been developed for gas metal arc welding of high-strength structural steels with which even narrow weld seams can be welded. High-strength joints are subjected to increasingly stringent requirements in terms of welding processing and the resulting component performance. In the present work, this challenge is to be met by clarifying the influences on hydrogen-assisted cracking (HAC) in a high-strength structural steel S960QL. Adapted samples analogous to the self-restraint TEKKEN test are used and analyzed with respect to crack formation, microstructure, diffusible hydrogen concentration and residual stresses. The variation of the seam opening angle of the test seams is between 30° and 60°. To prevent HAC, the effectiveness of a dehydrogenation heat treatment (DHT) from the welding heat is investigated. As a result, the weld metals produced at reduced weld opening angle show slightly higher hydrogen concentrations on average. In addition, increased micro- as well as macro-crack formation can be observed on these weld metal samples. On all samples without DHT, cracks in the root notch occur due to HAC, which can be prevented by DHT immediately after welding.

Download Full-text

Effect of Oxygen Content on Toughness in High Strength Weld Metal

Materials Science Forum ◽

10.4028/www.scientific.net/msf.638-642.3687 ◽

2010 ◽

Vol 638-642 ◽

pp. 3687-3692 ◽

Cited By ~ 1

Author(s):

Shuichi Nakamura ◽

Toshiei Hasegawa ◽

Ryuuichi Shimura ◽

Isamu Kimoto

Keyword(s):

Oxygen Content ◽

Arc Welding ◽

Gas Metal Arc Welding ◽

Harmful Effect ◽

High Strength ◽

Fracture Initiation ◽

Initiation Point ◽

Weld Metals ◽

Effect Of Oxygen ◽

Welding Processes

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.

Download Full-text

Influence of Oxygen Content on Microstructure and Inclusion Characteristics of Bainitic Weld Metals

ISIJ International ◽

10.2355/isijinternational.53.279 ◽

2013 ◽

Vol 53 (2) ◽

pp. 279-285 ◽

Cited By ~ 9

Author(s):

Jun Seok Seo ◽

Changhee Lee ◽

Hee Jin Kim

Keyword(s):

Oxygen Content ◽

Weld Metals

Download Full-text

The stability of dislocation networks under various oxygen-doping conditions in superconducting Bi2Sr2CaCu2Oy single crystals and their influence on the flux pinning properties

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100171742 ◽

1994 ◽

Vol 52 ◽

pp. 802-803

Author(s):

Y. Feng ◽

X. Y. Cai ◽

R. J. Kelley ◽

D. C. Larbalestier

Keyword(s):

Single Crystals ◽

Oxygen Content ◽

Basal Plane ◽

Flux Pinning ◽

Pinning Centers ◽

Before And After ◽

Anomalous Peak ◽

Basal Plane Dislocation ◽

The Stability ◽

Further Development

The issue of strong flux pinning is crucial to the further development of high critical current density Bi-Sr-Ca-Cu-O (BSCCO) superconductors in conductor-like applications, yet the pinning mechanisms are still much debated. Anomalous peaks in the M-H (magnetization vs. magnetic field) loops are commonly observed in Bi2Sr2CaCu2Oy (Bi-2212) single crystals. Oxygen vacancies may be effective flux pinning centers in BSCCO, as has been found in YBCO. However, it has also been proposed that basal-plane dislocation networks also act as effective pinning centers. Yang et al. proposed that the characteristic scale of the basal-plane dislocation networksmay strongly depend on oxygen content and the anomalous peak in the M-H loop at ˜20-30K may be due tothe flux pinning of decoupled two-dimensional pancake vortices by the dislocation networks. In light of this, we have performed an insitu observation on the dislocation networks precisely at the same region before and after annealing in air, vacuumand oxygen, in order to verify whether the dislocation networks change with varying oxygen content Inall cases, we have not found any noticeable changes in dislocation structure, regardless of the drastic changes in Tc and the anomalous magnetization. Therefore, it does not appear that the anomalous peak in the M-H loops is controlled by the basal-plane dislocation networks.

Download Full-text

A study of oxygen and vacancy ordering in YBa2Cu3O7−x

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100152793 ◽

1989 ◽

Vol 47 ◽

pp. 164-165

Author(s):

Y. P. Lin ◽

A. H. O’Reilly ◽

J. E. Greedan ◽

M. Post

Keyword(s):

Electron Microscopy ◽

Neutron Diffraction ◽

Oxygen Content ◽

Carbon Film ◽

Nitrogen Atmosphere ◽

Vacancy Ordering ◽

Powder Samples ◽

Vacancy Chains ◽

Chain Ordering

In the basal planes of the orthorhombic YBa2Cu3O7-X compound with x=0.07, which has a Tc of around 90K, chains of copper-oxygen are formed along the [010] direction. Previous investigations on the variation of Tc with oxygen content have shown the existence of a plateau at Tc = 60K for x=0.3 to 0.4, suggesting the presence of a separate phase. This phase has also been identified to be orthorhombic, but with a 2x superlattice along [100] of the parent structure, and the superlattice has been attributed to the formation of alternating copper-oxygen and copper-vacancy chains. In our work, we have studied the chain ordering phenomenon by electron microscopy and neutron diffraction on samples with different oxygen contents. We report here some of our electron microscopy findings for samples with x=0.4.Powder samples of YBa2Cu3O7-X were prepared by controlled re-oxidation of previously reduced material. For electron microscopy, the sample was dry ground using a mortar and pestle in a dry nitrogen atmosphere without the use of any solvent and transferred dry onto holey carbon film for examination in a Philips CM12 microscope.

Download Full-text

The biochemistry of drugs and doping methods used to enhance aerobic sport performance

Essays in Biochemistry ◽

10.1042/bse0440063 ◽

2008 ◽

Vol 44 ◽

pp. 63-84 ◽

Cited By ~ 7

Author(s):

Chris E. Cooper

Keyword(s):

Oxygen Uptake ◽

Oxygen Content ◽

Oxygen Delivery ◽

Sport Performance ◽

Blood Substitutes ◽

Altitude Training ◽

Blood Oxygen ◽

Oxygen Carriers ◽

Sports Performance ◽

Blood Doping

Optimum performance in aerobic sports performance requires an efficient delivery to, and consumption of, oxygen by the exercising muscle. It is probable that maximal oxygen uptake in the athlete is multifactorial, being shared between cardiac output, blood oxygen content, muscle blood flow, oxygen diffusion from the blood to the cell and mitochondrial content. Of these, raising the blood oxygen content by raising the haematocrit is the simplest acute method to increase oxygen delivery and improve sport performance. Legal means of raising haematocrit include altitude training and hypoxic tents. Illegal means include blood doping and the administration of EPO (erythropoietin). The ability to make EPO by genetic means has resulted in an increase in its availability and use, although it is probable that recent testing methods may have had some impact. Less widely used illegal methods include the use of artificial blood oxygen carriers (the so-called ‘blood substitutes’). In principle these molecules could enhance aerobic sports performance; however, they would be readily detectable in urine and blood tests. An alternative to increasing the blood oxygen content is to increase the amount of oxygen that haemoglobin can deliver. It is possible to do this by using compounds that right-shift the haemoglobin dissociation curve (e.g. RSR13). There is a compromise between improving oxygen delivery at the muscle and losing oxygen uptake at the lung and it is unclear whether these reagents would enhance the performance of elite athletes. However, given the proven success of blood doping and EPO, attempts to manipulate these pathways are likely to lead to an ongoing battle between the athlete and the drug testers.

Download Full-text