Heat-affected Zone Of Welded Joints Research Articles

ВЛИЯНИЕ ТЕРМИЧЕСКОГО ЦИКЛА СВАРКИ НА СТРУКТУРУ И СВОЙСТВА ФЕРРИТО-АУСТЕНИТНЫХ СТАЛЕЙ 08Х22Н6Т И 08Х18Г8Н2Т

The results of researches on influence of thermal cycle of welding on structure and phase transformations in metal of heat-affected zone of welded joints of 08Cr22Ni6Ti and 08Cr18Mn8Ni2Ti steels are presented. It is shown, that at automatic submerged-arc welding of welded joints of ferrite-austenite steels the fall of plasticity is observed. It is established that the impact toughness of overheat section of heat affected zone at normal temperature has high values of impact toughness, and at test temperature of minus 20 oC values of impact toughness below 0.4 MJ/m2 were obtained.

Peculiarities of microstructure formation in the heat-affected zone of welded joints of pipes of x100 strength class

The features of the formation of the structure of coarse-grained heat-affected zone (CGHAZ) of a welded joint of pipe steel grade X100 are investigated depending on the cooling rate by simulating welding thermal cycles on thermo-mechanical Simulator – Gleeble 3800. As a result, a continuous cooling thermokinetic (CCT) diagram of austenite decomposition in the CGHAZ metal of pipe steel grade X100 was constructed, which makes it possible to study the structure and kinetics of phase transformations when the steel is exposed to the welding thermal cycle. It was found that the austenite decomposition is accompanied by bainitic and martensitic transformations in the range of cooling rates of 0.1–150 ºC/s. With an increase in the cooling rate, the bainite structure changes its morphology from a globular and coarse acicular to a dispersed acicular with a pronounced packet organization and a lath morphology, islands of the martensite-austenitic (MA)-constituents, which have an acute-angled shape and are distributed at the boundaries between laths, packets and inside them, are gradually transformed into thin layers. The martensite structure appears at a cooling rate of more than 15 ºC/s. Large blocks (crystals) of bainite with MA components can be observed in the structure despite an increase in the cooling rate. Hardness values change from 245–285 to 307–353 HV with the appearance and increase in the fraction of the martensite structure.

Effect of Ti/N Ratio on Impact Strength of High Strength Pipe Steel Welded Joint Heat-Affected Zone

Effect of Ti/N Ratio on Impact Strength of High Strength Pipe Steel Welded Joint Heat-Affected Zone

Microstructural Features of Low-Alloy Pipeline Steels that Determine Impact Strength of Welded Joint Heat-Affected Zone

Microstructural Features of Low-Alloy Pipeline Steels that Determine Impact Strength of Welded Joint Heat-Affected Zone

Analysis of Precipitates in Welded Joint of TP347H Stainless Steel

The precipitates in welded joint heat affected zone (HAZ) and base metal of TP347H stainless steel were observed and analyzed by SEM, TEM and EPMA. The results show that precipitate of NbC can be observed in welded joint HAZ in as-welded, and more NbC precipitate in high temperature service. The size of primary NbC in base metal ranges from tens of nanometers to hundreds of nanometers, but only tens of nanometers of the precipitated NbC. The fine precipitate of NbC is mainly distributed in the crystal, however, continuous distribution of NbC is also observed on the grain boundary of the service joint. Cr carbide precipitates at the grain boundary, and some of particles distribute continuously on the grain boundary after service. The fine NbC precipitated in the crystal strengthens the matrix, and the continuous distribution of Nb and Cr carbides on the grain boundary reduces the interfacial bonding strength, then both of which result decrease of the material plasticity.

Effects of rail flash-butt welding and post-weld heat treatment processes meeting different national standards on residual stresses of welded joints

AbstractThis study investigates residual stresses of the welded joint heat-affected zone for the processes that meet the Chinese and European standards of field rail welding. Furthermore, this study investigates the factory rail welding process and different normalizing methods in China. According to the residual stresses data and the Debye ring test result, the residual stresses distribution of the welded joint meets the Chinese standard and uses induction normalizing treatment resulting in the best service performance and an improvement in grain size uniformity. In the absence of a normalizing process, the ideal welding process that meets the Chinese standard is actually inferior to that which meets the European standard, with regard to a uniform distribution of the residual stresses of the welded joint.

Study of the Effect of Austenite Grain Inclination Towards Growth on Impact Strength of Low-Carbon Low-Alloy Steel Welded Joint Heat-Affected Zone

Kinetics of austenite grain growth in the heat affected zone (HAZ) in low-carbon low-alloy steels welded joints is studied. The effect of metal structure and phase composition of the metal section of the near weld region of the heat affected zone (NWR HAZ) on the change in hardness and to brittle failure resistance is evaluated. The maximum nominal austenite grain diameter that provides a standard impact strength value is determined.

ТЕРМИЧЕСКИЕ ЦИКЛЫ И ОСОБЕННОСТИ РАСПАДА АУСТЕНИТА ПРИ ЛАЗЕРНО-ГИБРИДНОЙ СВАРКЕ СТАЛЕЙ КЛАССА ПРОЧНОСТИ К52 И К60

Laser-hybrid welding (LHW) is an advanced high-performance technology for obtaining all-inone connections. Phase transformations, thermal welding cycle and microstructures of a welding seam and of a heat-affect zone (HAZ) influence on the quality of welding joint of LHW. This article defines experimentally the thermal cycles and shows the results of kinetics of austenite decomposition at the usage of technology of LHW combined with the multi-arc automatic welding under flux. There were defined cooling rates influencing the change of properties of heataffected zone of welded joints of steel in tube sorts with strength class K52 and K60. First part of the paper presents objects of investigations, chemical composition and technologies under which the welded joints were obtained. The second part of the article shows a method of investigation which reflects samples and operations with instruments, equipment with the help of which parameters of thermal cycles and cooling rates were fixed. The third part shows the peculiarities of formation of structure-phase composition of welded joints with the help of tables, diagrams and microstructures of heat-affected zones at various cooling rates. We found that in the result of LHW in HAZ the decomposition of austenite in the studied steels is 350–360 HV, which increases the probability of formation of hardening structures in welded joints and may lead to crack formation. It is revealed the normative value of hardness can be provided if the metal cooling rate at LHW do not exceed 20 °C/c.

The effect of cooling speed on the structure and properties of the heat affected zone in welded compounds of ferrite-austenitic steels

Such parameters as the maximum heating temperature, duration of stay at high temperatures, the rate of cooling influence greatly the structure and properties of the heat-affected zone of welded joints of steels and alloys. In the present work, the effect of different cooling speed upon the impact of the thermal cycle of welding on the structure, the fine structure and toughness of ferrite-austenitic steels is investigated. It is established that the cooling speed after welding has a great influence on the shock impact toughness, the phase composition and the structure of the zone of ferrite-austenitic steels.

Research into defectiveness of welded joints of steam pipes operated over a long time

The welded joints of steam pipelines of the power units of thermal power plants, which are operated for long periods under conditions of creep and low-cycle fatigue, are the most damaged elements of power units. By the attributes of cohesion, we presented the classification of the types in the defectiveness of the welded joints of steam pipelines, which is appropriate to use for refining the special features of physical-chemical processes and structural changes that occur in metal of the welded joints of steam pipelines. The represented types of damages are characteristic for the welded joints, which exhausted their base resource, including the prolonged one. We revealed the most characteristic places of defectiveness in metal of the welded joints and orienting of cracks towards the weld metal, as well as the metallographic attribute of defectiveness. The physical-chemical processes are examined, which specify structural changes in the long-operated welded joints of steam pipelines. We examined the process of slowing down the dislocations by the carbide precipitates, which coagulate lengthwise and, in the form of intermittent chains, are concentrated along the boundaries of grains of the α-phase. We established that the creep pores to the largest degree are formed in the places of contact between coagulating carbides and grains of the α-phase. It was revealed that the creep cracks are formed at the sections of incomplete recrystallization of the heat-affected zone of welded joints (about 75 %), the fusion (approximately 15 %), while the rest is at other sections of HAZ, as well as in the weld metal and in the base metal. It is demonstrated that the creep cracks developed by the brittle mechanism, which is contributed by the presence of segregations in the near-boundary zones of grains of the α-phase. We established that the fatigue cracks predominantly develop at the section of fusion, overheating and incomplete recrystallization of HAZ, as well as near the backing rings in the places of contact of the pipe elements with different thickness. Dependence is detected of the reduction in metal resistance of the long operated welded joints of steam pipelines to the formation of fatigue cracks on the level of degradation of their structure. Data of present study are necessary for obtaining welded joints with decreased defectiveness in the process of prolonged operation under conditions of creep and low-cycle fatigue.

Effect of Thermal Cycling Treatment on Structure and Properties of Ferritic-Austentic Steel Welded Joint Heat-Affected Zone Metal

Results are provided for a study of the effect of thermal cycling treatment on the structure and properties of ferritic-austenitic steel welded heat-affected zone metal. Optimum thermal cycling regimes are determined. It is shown that an increase in heat-affected zone impact strength with thermal cycling is due to fragmentation of structural components, redistribution of alloying elements between phases, and excess phase amount and morphology.

Microstructure and Toughness of Heat-affected Zone of Weld Joint for Pipeline Steels with High Deformability

Microstructure and Toughness of Heat-affected Zone of Weld Joint for Pipeline Steels with High Deformability

Prediction of the Properties of Heat-Affected Zone of Welded Joints of Sheets from Aluminum Alloys with Structured Surface

Welded joints of light structured sheets from aluminum alloy EN AW-6181-T4 (DIN EN 515) of the Al – Si – Mg system are studied. The welding is performed in an argon environment with a short arc by the method of cold metal transfer (CMT®). The results of the study are used in an amended Leblond model for describing the variation of the properties of the heat-affected zone of welded joints of structured sheets.

Effect of the Morphology of Structure on the Resistance of Welded Joints of High-Strength Pipe Steels to Brittle Fracture

The morphology of the structure of the near-weld region of the heat-affected zone of welded joints of high-strength pipe steels is studied and its effect on the resistance of the metal to brittle fracture is determined.

Specification of metal damageability mechanism of long-operated steam line welds

The features of metal damageability of welded joints of steam lines, long operated under creep conditions, made of steels 15H1M1F and 12H1MF were specified. Damageability classification, consisting of five stages was proposed. The formation mechanisms of creep pores and fatigue cracks were considered. It was found that creep pores are formed most intensively in the area of incomplete recrystallization of heat-affected zone of welded joints made of heat-resistant steels. It was revealed that the metal destruction of welded joints has predominantly brittle intergranular nature. In the destruction area, the body of α-phase grains is affected by individual or locally grouped creep pores. It was found that the origination and development of fatigue cracks on the inner surface of steam lines have locally grouped nature. Their development is characterized by the absence of branching. Specification of metal damageability features of long-operated welded joints of steam lines will allow to reduce the damageability intensity, which provides increased lifetime.

On the decomposition of austenite in the heat-affected zone upon welding of high-strength steels

The kinetics of the decomposition of austenite in the heat-affected zone of welded joints of low-carbon microalloyed high-strength steels has been investigated. A new approach to selecting the parameters of the thermal cycle of welding that ensure the service characteristics of welded joints on a level no lower than the normative requirements is suggested.

Investigation of creep damage in advanced martensitic chromium steel weldments using synchrotron X-ray micro-tomography and EBSD

In recent years, a design concept for the stabilisation of the microstructure by addition of boron and nitrogen was developed. This so called martensitic boron–nitrogen strengthened steel (MARBN) combines boron strengthening by solid solution with precipitation strengthening by finely dispersed nitrides. Welded joints of MARBN steels showed no formation of a uniform fine grained region in the heat affected zone (HAZ) which is in general highly susceptible to Type IV cracking. In this work, the crossweld creep strength of a newly developed MARBN steel was analysed and the evolution of damage was investigated using synchrotron microtomography supported by electron microscopy. Three-dimensional (3D) reconstructions of the tested samples together with electron backscatter diffraction investigations revealed an intense void formation in a restricted area along small grains at prior austenite grain boundaries in the HAZ as the main reason for premature creep failures in the HAZ of welded joints.

Optimization of the structure and properties of the heat-affected zone of welded joints in high-strength pipe steels

To determine methods for minimizing the detrimental effect of the welding cycle, investigations were carried out into the effect of the heat input in multi-arc submersion-arc welding and welding technology on the structure and properties of the heat-affected zone of welded joints in a high-strength pipe steel. The experimental results are analysed to determine the technological measures greatly reducing the microhardness of the welded joint and increasing the proportion of ductile failure on the fracture surface of impact specimens.

Modeling Heating Effects in the Heat-Affected Zone of High-Strength Pipe Steel K70 with Double-Pass Submerged Arc Welding

Simulation modeling is used in order to study metal structure in a heat-affected zone (HAZ) during submerged-arc welding. A correlation is established between low values of impact energy observed and features of HAZ structure formation during submerged-arc welding of low-alloy steel of strength category K70. It is shown that the appearance of brittle precipitates with an increase in content of the main alloying elements at large grain boundaries is a reason for low impact energy in the area of large HAZ grains during steel K70 welding. Development of these areas is connected with repeated heating (simulating a second pass during rolling) in a temperature range somewhat lower than the Ac 1 point. A reduction in cooling rate in the first heating cycle (which corresponds to an increase in linear energy during welding) facilitates precipitate enlargement over grain boundaries. Multipass welding and a reduction in pass linear energy are recommended in order to exclude the formation of these areas and to improve and stabilize impact energy in a welded joint HAZ.

Structure and ductility of the heat-affected zone of welded joints of a high-strength steel

Methods of optical microscopy and scanning and transmission electron microscopy have been used to study the structure of welded joints of a high-strength structural steel with different types of the weld metal. The impact toughness of the heat-affected zone (HAZ) has been determined at temperatures of +20 and −40°C. Based on the fractograph investigations of the character of the fracture of the welded joints after tests for impact bending, the regions that are the most dangerous for crack initiation have been determined. Structural factors that affect the brittleness of the near-weld zone of welded joints with the austenite metal of the weld are indicated, including the existence of an austenite-bainite structure and coarse carbides, as well as the specific distribution of hydrogen.