Cracking Resistance Of Welded Joints Research Articles

Evaluation of crack resistance of welded joints with soft interlayers

Introduction. Welded joints in large-sized metal structures (e.g., in the structures of ship hulls) subject to low-cycle fatigue are considered. The characteristic appearance of soft interlayers, which are significantly plastically deformed under working loads, was noted. Deformation of the metal structure with damage, especially in the form of cracks, reduces the strength and reliability of structural elements and joints. Pre-deformation negatively affects plasticity; therefore, much depends on the residual plasticity of the cracking material. At the same time, with a decrease in residual plasticity, such an important reliability indicator as the resistance of the material to crack propagation — the fracture toughness – decreases. The paper is devoted to the development of a model that includes analytical dependences for assessing the crack resistance of metal structures and their welded joints with soft interlayers according to the crack resistance limit for all crack sizes.Materials and Methods. The theory and methods of linear mechanics of materials destruction, structural-mechanical approach are used. The calculation results were analyzed and compared to the experimental data and other analytical solutions. The numerical experiment was performed for the ferrite-perlite steel grades of 10, 50, 22K, St3sp, etc., widely used in industry, as well as for alloy steels hardened to medium and high strength of 30KhGSA, 37KhN3A, etc. Results. Analytical dependences are obtained for calculating the relative crack resistance limit according to three main known mechanical characteristics of the state of the material of the soft interlayer of the welded joint.Discussion and Conclusions. The results obtained can be used to assess the crack resistance of pre-deformed structural elements and welded joints (including those with soft interlayers) operating under a transverse load. The results of experimental data and analytical calculations are shown in dimensionless form, which enables to obtain invariant results with respect to the fracture toughness limit.

Crack resistance of welded joints of austenitic steel at cryogenic temperature

On the basis of experimental, numerical and analytical results, functional dependences of such crack resistance characteristics as critical opening of cracks in the temperature range from 300 K to 77 K and thickness of welded joints of the steels under study were obtained. The functional dependences of the parameters of the kinetic diagrams of low-cycle fracture on the mechanical properties of the material for a wide class of welded joints of austenitic stainless cyclically stable steels are given.

Analytical Evaluation of Strengthening, Local Internal Stresses and Microderformations in Welded Joint Metal during Wet Underwater Welding

Analysis of structural factor influence on local internal stresses and zones of deformation localization in upper and lower bainite structures in welded joints of low-alloy steel at wet underwater welding was performed. It is established that when welding joints under the water and applying an external electromagnetic field in the metal of the heat-affected zone (HAZ), a finer-grained substructure is formed with a general decrease in the dislocations density and with their uniform distribution. Estimates of the local internal stresses level considering the dislocation density distribution in the structural zones of their localization show that their maximum level is formed in the metal of the HAZ overheating region at welding without the external electromagnetic field along the upper bainite laths boundaries. The upper bainite structure is characterized by forming localized deformation zones, where the most significant dislocation density gradients are observed. This can lower the crack resistance of welded joints. Low values of local internal stresses are characteristic of welded joints obtained in the modes applying an external electromagnetic field. This is facilitated by the overall decrease in the dislocation density and their uniform distribution in the lower bainite structural components, which provides high crack resistance of welded joints.

Information and analytical tools for assessing the structural survivability and safety of technological equipment

The tasks of information and computational support for the analysis of the survivability and safety of power shells of technical objects are formulated, aimed at studying their properties taking into account damages and abnormal effects. To solve them, algorithms and computational tools have been developed, aimed at analyzing damage and assessing the risk of re-occurrence of accidents at technical objects, modeling the structural and mechanical heterogeneity of welded joints and calculating their crack resistance, parametric modeling of welded joints with defects, analyzing the sensitivity of structures to defects, damages, and off-design effects, and evaluating their survivability and safety. Information support has been developed, which contains a systematic list of factors reducing survivability and safety, the results of experimental studies of the crack resistance of welded joints and the survivability of shells with a developing macrocrack, as well as the accumulated results of solving model and applied problems on analyzing the properties of damaged shell structures, as reference data.

Evaluation of Vibration Treatment Effect on Mechanical Properties of Welded Joints of Steel Pipes 5CrMo16

In modern refining conditions associated with increasing requirements for the quality of products produced and ensuring the safety of processes, the operating conditions of the equipment are becoming more complicated, and the range of materials used is expanding. A significant part of the equipment, especially used to carry out high-temperature processing processes in hydrogen sulfide and oxidative sulfur-containing media, is made of heat-resistant chromomolybdenum steels of the type 5CrMo16, the welding process of which is quite complicated. In this work, studies of the mechanical properties of welded joints made of steel are presented 5CrMo16 under various modes of loading welded joints during welding, and new results on the crack resistance of welded joints during repeated heating are also experimentally obtained. Conclusions on the level of residual stresses in the samples, strength characteristics of the weld, as well as the fracture resistance of the weld metal of the examined samples were made.

Investigation of structure and properties of welded joints of pipe steels

The work is devoted to the study of microstructure and crack resistance of welded joints of pipe materials of main gas and oil pipelines for the Far North regions. Reliable operation of pipelines in harsh climatic conditions of such regions can be provided by the use of materials that have a combination of high values of strength, toughness, cold resistance and weld ability. The results of studies of samples from large diameter pipes with an operating pressure of up to 7.4 MPa at test temperatures of -10 and -20 °C. are presented. These pipes are made of hot-rolled low-carbon low-alloy steel. Various welding methods were used to produce welded joints: high-frequency induction welding, multi-arc automatic welding, laser and hybrid welding. This allowed us to evaluate the influence of the heating and cooling rate during welding on the characteristics of the structural States of the weld, the fusion line, and the overheating area in the zone of thermal influence. It was revealed that a rough needle structure of Vidmanshtett is formed in the zone of overheating of the longitudinal seam at a high cooling rate. Using a low cooling rate allows you to get the Vidmanshtett structure within 2-3 points. It is shown that the crack resistance of the base metal of the pipes practically does not change with a decrease in the test temperature. The values of crack resistance for the metal of the zone of thermal influence have a large spread, which may be due to the influence of technological features of cooling the pipe billet after welding.

Strength of welded joint sunder quasi -brittle fracture

In the study of the crack resistance of welded joints with constructive incomplete welds, which are regulated by welding GOSTs and have a wide practice of application, including for critical structures, it is necessary to keep in mind that these stress concentrators on the sharpness of their tops are significantly different from fatigue and operational cracks. Welding defects have the same difference: faulty welds, faulty fusions, undercuts. This paper shows that the strength of welded joints with structural faulty welds in addition to mechanical characteristics and the length of the faulty weld also depends on the radius at its top. Based on the ratios of fracture mechanics, a strain fracture criterion is proposed -the critical opening of the concentrator under consideration, depending on the radius at its top. At the same time, with the reduction of the radius at the top of the concentrator to a certain critical value, comparable to the radius at the top of the crack, the proposed criterion coincides with the material characteristic according to GOST 25.506-85 – the critical crack opening. Dependence for assessing the quasi-brittle strength of welded joints with faulty welds based on the critical disclosure of the concentrator under consideration satisfactorily corresponds to the experimental data on samples from the AMg6 alloy.

Effect of the structure on the mechanical properties and cracking resistance of welded joints of low-alloyed high-strength steels

Low-alloyed high-strength steels are widely used for the manufacture of welded metal structures in various branches of modern industry, including construction, agricultural, transport, engineering and defence. To produce joints of these metals mechanized or automatic welding in shielding gases are mostly used. Nowadays, such progressive technologies as laser and hybrid laser-arc welding implement, which allows obtaining welded joints at increased speed with much smaller dimensions of welds and heat-affected zones, to improve the quality of high-strength steel joints and the to raise productivity of their manufacture. In this work, we studied the influence of the structural-phase composition and specific parameters of the structure, which are formed in the weld metal and the heat-affected zone, on the strength and crack resistance of welded joints of low-alloyed high-strength steels. The structure and phase composition of welded joints of high-strength steels was investigated depending on the technological parameters of arc, laser and hybrid laser-arc welding. It is shown how the microstructure affects the operation properties of welded joints. The relationship between the phase composition, the parameters of the grain and fine structure of the metal (substructures, dislocation densities, sizes and distribution of carbides in the structural components of bainite, martensite, etc.) of welded joints, their mechanical properties, fracture toughness and the level of local internal stresses in various structural components is investigated. The most influencing structural factors shown to be the dispersion of the bainitic structure and substructure, the uniform distribution of the density of dislocations, and the absence of extended dislocation clusters − zones of nucleation and propagation of cracks.

Structure and Crack Resistance of N-A-XTRA-70 Steel Joints Manufactured by Hybrid Laser-Arc Welding

Crack resistance of welded joints is one of the most important indices of service reliability of critical designation structures. The purpose of the research is the establishment of the influence of technological modes, hybrid laser-arc welding of high strength steel NA-XTRA-70 on the formation of structure in the metal welded joints, as well as analysis of the influence of this structure on their crack resistances. For the experiments the laboratory setup has been developed on which the experiments were carried out in the technological scheme that provides the location of the consumable electrode arc at a certain distance in front of the laser beam in the welding direction. Nd: YAG-laser DY 044 of company ROFIN (Germany) was a laser radiation source. Power for consumable electrode arc was carried out by welding generator PSG-500. Investigations of structural-phase changes in weld metal and HAZ were carried out by means of optical microscopy (optical microscope Versamet-2 and Neophot-32), microhardness was measured using M-400 gage of Leco company at 0.98N loading. Fractographic investigations were carried out by scanning electron microscopy (scanning electron microscope SEM-515 of PHILIPS company, Netherlands) on fractured specimens of welded joints, made as a result of impact bend tests. An analysis of crack resistance of the welded joints was carried out under different conditions of test temperatures. It was based on experimental data, received by a quantitative fractography method. It is shown that metal of a welded joint produced by hybrid laser-arc welding at Vw = 72m/h rate has mainly failure of ductile nature after external loading. This indicates sufficient level of crack resistance and further working capacity under operation conditions.

Crack Resistance of Welded Joints of Pipe Steels of Strength Class K60 of Different Alloying Systems

The crack resistance of welded joints of pipe steels of strength class K60 and different alloying systems is studied. The parameter of the crack tip opening displacement (CTOD) is shown to be dependent on the size of the austenite grains and on the morphology of bainite in the superheated region of the heat-affected zone of the weld. The crack resistance is shown to be controllable due to optimization of the alloying system.

Effect of structural factors on mechanical properties and crack resistance of welded joints of metals, alloys and composite materials

Effect of structural factors on mechanical properties and crack resistance of welded joints of metals, alloys and composite materials

Crack Resistance and Structural Analysis on Thermit Welding

War-broken parts can be repaired quickly without electricity and gas in the wild by use of the thermit welding technology, so it is of great significance to study on welded quality of thermit welding parts for its military application. As the crack resistance of welded parts is an important target to estimate the welded performance, crack resistance test and microstructure analysis have been conducted on test specimens made of Q235 welded parts. Results showed that as the crack ratio was less than 20% in the Y-groove crack test, the crack propagation would not occur in the practical welding structure and that the crack resistance of welded joints could meet the welded demand.

Effects of electron beam local post-weld heat-treatment on the microstructure and properties of 30CrMnSiNi2A steel welded joints

To improve the microstructure and properties of electron beam welded joints, vacuum or furnace whole post-weld heat-treatment (FWPWHT) should usually be carried out. Electron beam local post-weld heat-treatment (EBLPWHT) is a quite new heat-treatment procedure that provides the advantages of high precision, flexibility and efficiency, energy saving, and higher productivity. In this paper, the microstructure, mechanical properties, fracture toughness and fatigue properties of electron beam welded joints of 30CrMnSiNi2A steel in the as-welded (AW) and EBLPWHT conditions have been investigated. The results show that the microstructures of different zones of joints in the AW condition are changed by the EBLPWHT procedure, in which the welds from coarse needle martensite are transformed into lath-shaped martensite; and the main structures of the heat-affected zones (HAZ) from lath-shaped martensite into lower bainite. The properties of the welded joints can be improved by EBLPWHT in some extent, especially the fracture toughness of the welds, and the fatigue crack resistance of welded joints can be improved significantly. However, more appropriate heat-treatment parameters of EBLPWHT have to be studied in order to improve the mechanical properties of the base metal near to the HAZ.

Influence of Microadditions on the Resistance to Brittle Fracture of Welded Joints of Oil Pipelines

On the basis of the results of testing of influence of modifying microadditions (Ce, Y, Ba, Ca, and Zr) on the characteristics of the resistance to brittle fracture of a weld metal of welded joints of oil-and-gas pipelines, their optimal content in welds is determined. We propose mathematical models for numerical prediction of the crack resistance of welded joints.

Decreasing the effect of sulphur and hydrogen on the cracking resistance of welded joints

Decreasing the effect of sulphur and hydrogen on the cracking resistance of welded joints

A method of calculating the hot cracking resistance of welded joints

A method of calculating the hot cracking resistance of welded joints

Hot cracking resistance of welded joints in austenitic steels produced by high-speed laser welding

(1997). Hot cracking resistance of welded joints in austenitic steels produced by high-speed laser welding. Welding International: Vol. 11, No. 2, pp. 149-151.

Effect of thermal conditions during welding on cracking resistance of welded joints in 15Kh1M1F steel under low‐cycle creep conditions

Effect of thermal conditions during welding on cracking resistance of welded joints in 15Kh1M1F steel under low‐cycle creep conditions

Low-temperature cyclic cracking resistance of welded joints in a martensitic-austenitic steel

Low-temperature cyclic cracking resistance of welded joints in a martensitic-austenitic steel

Characteristics of static and fatigue strength and of crack resistance of welded joints in structural steels at low temperatures. Communication 1

The article presents the results of experimental investigations of the effect of low temperatures (down to 77°K) on the resistance to static and low cycle deformation and rupture of steels 09G2S, 10KhSND, 06G2AF, 20KhGSA, 07Kh3GNMYuA, and ON6. It also presents the dependences of the theoretical characteristic of low cycle fatigue mTe of steels at low temperature under rigid loading on the index of ductility {ie022-01} under static loading and test temperatures down to 77°K.