Influence of heat input on microstructure and fracture toughness property in different zones of X80 pipeline steel weldments (original) (raw)
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This study was focused on wear-resistant material prepared by CO 2 GMAW method to basically determine the alloys and hardfacing technology which could be employed into mining equipment. Three flux-cored wires with different chemical compositions, marked by DM-I, DM-II and DM-III were used in welding a martensitic steel for the comparison of the microstructures and mechanical properties of the welding metals and HAZ. The results show that DM-I weld metal contains martensite plus other reinforced phases, while both DM-II and DM-III alloys lead to mainly martensitic microstructures with little precipitates. Among all of the tested materials the DM-I alloy has the highest hardness and wear resistance but the lowest impact toughness among the experimental weld metals. Meanwhile, the hardness, impact toughness and wear resistance of the DM-II and DM-III alloys are close to those of the base metal but the DM-III is not as strong as DM-II. Dimples can be found on the impact fracture of the weld metals, but the steel fracture consists of both cleavage and dimples. Thus HAZ has less risk for cracking than the welds, and the DM-II wire which produces the weld having identical mechanical properties to the base metal is suitable for further application.
Influence of Heat Treatments on the Microstructure of Welded Api X70 Pipeline Steel
2017
Welding is one of the most important technological processes used in many branches of industry such us industrial engineering, shipbuilding, pipeline fabrication among others. Generally, welding is the preferred joining method and most common steel are weldable. This investigation is a contribution to some scientific works which have been done on welding of low carbon steel. This work, presents some heat treatments were used to alter the microstructure of base metal (BM), heat affected zone (HAZ) and weld metal (WM) in the welded pipe steel of grade API X70. It presents the microstructures obtained after three heat treatments at 200°C, 400°C and 600°C for 30 min. Scanning electron microscopy and X-ray diffraction have been used as characterization techniques to observe the WM microstructures, in addition the Vickers hardness test are also achieved. The results revealed that the isothermal heat treatment caused grain growth and coarsening reactions in the weld zone and the hardness o...
Brittle Fracture in Heat-Affected Zones of Girth Welds of Modern Line Pipe Steel (X100)
Fracture of Nano and Engineering Materials and Structures
Girth welds of modern line pipe steel, such as X100, issued from a pulsed automatic gas metal arc welding, were tested to check their performance in artic temperature conditions. It is shown that an impact specimen at-20 °C with a notch placed in the middle of the fusion line could break at low energy (<40 J). The brittle zone is located in the coarse-grained heat-affected zone of the weld. The reproduction of two heat-affected zones with a thermal-mechanical simulator, Gleeble 1500, allows to determine the mechanical behaviour of representative microstructures of the welded joint. Tension tests with or without notch and impact tests are performed between-196 °C and 20 °C. This experimental database is used to fit materials constitutive equations which are used in a finite element code to predict the fracture of the welded joint.
Effect of Heat Treatment on the Microstructural Evolution in Weld Region of 304L Pipeline Steel
Journal of Thermal Engineering, 2016
In this work, the effect of isothermal heat treatments at 300 °C on microstructure evolution after welding by Tungsten Inert Gas (TIG) welding technique of 304L pipeline steel have been studied. Microstructures of the weldments were investigated using scanning electron microscopy (SEM), X-ray diffraction analysis (XRD), and hardness measurements. Microstructural evolution in welded joint was identified. Results indicated that the microstructure of fusion zones exhibited dendritic structure. The applied heat treatments affected the microstructure of the welded joint. However some defects have been observed in weld joint.
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In this paper, the welding quality of API 5L X60 steel pipes was investigated after the application of three different welding scenarios by applying submerged arc welding (SMAW), tungsten inert gas (TIG) and hybrid (TIG + SMAW) welding methods with an average heat input of ca. 1 kJ mm −1 for all passes. For this purpose, the ultrasonic and radiographic tests were done to detect possible discontinuities such as crack and porosity in the welding zones. In addition, the macro and microstructures of weld zones were made to examine different zones in terms of weld quality and phases. Moreover, the hardness, impact toughness and tensile tests were carried out to determine the mechanical properties of the weldments. The tensile strength of the pipe weldments was recorded to be ∼603, 610 and 625 MPa after the welding of pipes by SMAW, TIG + SMAW and TIG welding, respectively. In addition, the impact toughness of the welds was obtained to be 48, 76 and 66 J, for these welding methods, successively. According to the experimental findings, all three welding plans were successfully applied to the steel pipes and found to be suitable regarding the relevant international standards.
The International Conference on Materials Science, Mechanical and Automotive Engineerings and Technology in Cappadocia (IMSMATEC 2019), 2019
In this work, various welding procedures including shielded metal arc welding and/or tungsten inert gas welding were applied to 24'' diameter API 5L X60 steel pipes used in natural gas and crude oil pipelines. The welding plans were considered to be 4 passes in total which were root pass, hot pass, fill pass and cap pass. The root and hot passes were made as one bead, whereas the fill and cap passes were implemented as two and three beads, respectively. After the welding applications, the welded samples were subjected to tensile, hardness and notch impact tests. Moreover, the macro and microstructural analyses were carried out to examine heat effected zone and grain morphology.
Materials Science and Engineering: A, 2018
In this study, the effect of different microstructures resulting from thermochemical processes of X65 pipeline steel on mechanical properties of welding in the presence of hydrogen was investigated. According to studies conducted, due to the charge of hydrogen, the hardness of base metal (BM) increased by 10% , the hardness of heat affected zone (HAZ) samples increased by about 13% , the yield strength of base metal increased by an average of 5% and the yield strength of HAZ increased by about 7%, indicating hardening. Elongation was reduced by 32-70% and the percentage of ductile fracture decreased by an average 46% which shows that the fracture of samples in the presence of hydrogen is brittle. In the study of hydrogen defect and concentration of hydrogen permeated to the material it was determined that, the ferrite-pearlite banded microstructure of base metal has a higher hydrogen defect sensitivity than HAZ with an acicular ferrite microstructure and hard phase. In base metal samples under various rolling conditions, the two-pass rolled and the final rolling temperature of 800 °C sample (2BM800), with a smaller grain microstructure and higher interface, had the most diffusive hydrogen content and therefore had the highest hydrogen defects. In the case of HAZ samples, the effect of hydrogen on the increase in hardness and strength properties is greater than that of the base metal samples due to the different microstructure (of the acicular ferrite) and the variable grain size (i.e. the presence of two coarse-grained and fine grained areas). Overall, the results of this study showed that the microstructure has a significant effect on mechanical properties, the amount of diffusive hydrogen and hydrogen defects in welds.
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2022
The microstructure and mechanical properties of welded joint of TMCP890 are studied by means of thermal simulation and gas metal arc welding. It is found that the heat-affected zone has high toughness after welding. After welding with 900-MPa grade filler wire, the weld metal has good toughness and the strength of welded joint is comparable to that of the steel. Two hundred fifty degrees celsius postweld heat treatment does not affect the strength and toughness of welded joint. After 480°C postweld heat treatment, the strength is a little lowered and toughness of weld metal and heat-affected zone is reduced remarkably. After 600°C postweld heat treatment, the strength and toughness of weld metal and heat-affected zone are damaged seriously. Light optical microscope, SEM, TEM, and EBSD are used to analyze the microstructure of experimental samples. It is found that filmy residual austenite and low quantity of M-A constitutes with small size contribute to the high toughness of heat-affected zone in a great deal. The adverse effect of high-temperature postweld heat treatment on toughness is because of the large-sized precipitated particles.
The structural integrity of high-strength welded pipeline steels: a review
International Journal of Structural Integrity, 2020
PurposeThe key purpose of conducting this review is to identify the issues that affect the structural integrity of pipeline structures. Heat affected zone (HAZ) has been identified as the weak zone in pipeline welds which is prone to have immature failuresDesign/methodology/approachIn the present work, literature review is conducted on key issues related to the structural integrity of pipeline steel welds. Mechanical and microstructural transformations that take place during welding have been systematically reviewed in the present review paper.FindingsKey findings of the present review underline the role of brittle microstructure phases, and hard secondary particles present in the matrix are responsible for intergranular and intragranular cracks.Research limitations/implicationsThe research limitations of the present review are new material characterization techniques that are not available in developing countries.Practical implicationsThe practical limitations are new test methodol...
INVESTIGATION OF THE MECHANICAL AND MICROSTRUCTURAL PROPERTIES OF WELDED API X70 PIPELINE STEEL
The mechanical properties of pipelines particularly those in marine environments are influenced by corrosion activity of seawater throughout their service lives. The degree to which these properties are influenced in seawater compared to those exposed to air needs to be better understood. In this study, the chemical composition of API X70 pipeline steel plate, microstructure and mechanical properties of the welded joints of same steel plates exposed to ambient air and seawater respectively were investigated. It was found that the base metal consisted of manganese (0.51wt% Mn), low carbon content (0.051 wt% C) and small quantities of alloying elements such as vanadium (0.021wt% V), molybdenum (0.118 wt% Mo), chromium (0.240 wt% Cr), copper (0.002 wt% Cu), and a carbon equivalent (CE IIW) of 0.38. Scanning Electron Microscope (SEM) showed that the microstructure of base metal sample has large grains formed in packets which have certain crystallographic orientation but contain submicron grains arranged in a chaotic interlocking manner. The tensile tests performed using a UNITED type universal testing machine confirmed that the yield strength of the base metal was 573.045MPa which conforms to API standard for X70 steel pipe. The manual metal arc (MMA) welding technique was applied to produce the welded joints. For the welded joints exposed to ambient air at room temperature, the yield strength was 680.624MPa while the compressive strength was 1500.2MPa, and the impact energy at-10°C was 112.68J. Air tests referred to tests conducted in the laboratory at room temperature. For the welded joints exposed to seawater for 12 weeks, the yield strength was 609.154MPa while the compressive strength was 1219.34MPa, and the impact energy at-10°C was 61.48J. The above results for air and seawater exposures were used to determine the environmental reduction factors of the two environments. Hardness tests conducted using Vickers hardness tester revealed variations in hardness across the base metal, the HAZ and the weld, with the weld having the highest average Vicker's hardness value (223.8HV) followed by the base metal (217.3HV) and the HAZ had the least (214.5HV)