Heat Affected Zone Of Steel Research Articles

Observation of inclusions and intra-granular ferrite evolutions at the HAZ of low-carbon steel with different thermal histories

This study investigated the formation and growth of intra-granular ferrite with inclusions (TiN, MnS) in the heat-affected zone (HAZ) of a welding joint in low-carbon steels. The relationship between the cooling rate and the density and size of inclusions was analyzed. An orientation relationship akin to the Baker–Nutting relationship was identified between TiN and ferrite, while the orientation relationship between MnS and ferrite approximated the Kurdjumov–Sachs relationship. At low cooling rates, in the absence of nucleation support from TiN and MnS inclusions, the microstructure in the HAZ comprised Widmanstätten ferrite. Additionally, the shape, size, and density of primary ferrites and Widmanstätten ferrite in steels were influenced by sulfur content.

Effects of Cr additions on Corrosion and Erosion-Corrosion Behaviors in the Weld Heat-Affected Zone of Hadfield Steel in Brine Environments

The corrosion and erosion-corrosion behaviors in the weld heat-affected zone (HAZ) of Hadfield steels with varying Cr contents (1, 2, and 3 wt%) were examined. Various experimental methods, including electrochemical polarization, impedance, and weight loss measurements, were utilized. Two types of isothermal heat treatments were conducted in a box furnace to simulate the intercritical HAZ, known to be the most vulnerable region in terms of mechanical properties and environmental stabilities, and large-scale samples for the erosion-corrosion experiment were fabricated. The results showed that increasing the Cr content improved the resistance to corrosion and erosion-corrosion, but there was an inflection point where adding more Cr had the opposite effect. Up to 2 wt%, a higher resistance was exhibited owing to the formation of a thin and protective oxide scale enriched with Cr that adhered to the steel surface. On the other hand, adding 3 wt% of Cr resulted in decreased resistance. This was due to the formation of coarse M<sub>7</sub>C<sub>3</sub> (M: Cr) precipitated along the grain boundary, which caused the development of a thick and unstable oxide scale that detached locally. Based on these findings, it is essential to optimize the Cr content to ensure a high resistance to corrosion and erosion-corrosion in the HAZ of Hadfield steel.

Effect of Ca Addition on Inclusions of Welding Heat-Affected Zone in Pressure Vessel Steels

Pressure vessel steels are used in the manufacture of tanks for the storage of gases, chemical materials and oil. To meet the increasing production demands, high-wire-energy welding is widely used in the manufacture of pressure vessel steels. This means that the weldability of pressure vessel steels needs to be improved. Therefore, in order to reveal the microalloying effect of Ca in pressure vessel steel, this study took a commonly used pressure vessel steel as the research object, and three groups of experimental steels with different Ca mass fractions were prepared using vacuum metallurgy, controlled rolling and controlled cooling. Welding heat simulation technology was used to simulate the welding heat of experimental steel and the welding heat-affected zone (HAZ) was investigated. The inclusions of the welding HAZ in the experimental steels were observed by using a metallographic microscope and scanning electron microscope (SEM). The mechanism of intragranular acicular ferrite (IAF) nucleation induced by the inclusions containing Ca elements in the welding HAZ of pressure vessel steels was also discussed. The research results show that the addition of Ca increased the number density of effective inclusions in the welding HAZ of the experimental steel up to 535.60 pieces/mm2. The addition of the Ca element was beneficial for producing more pinning inclusions in the experimental steel welding HAZ under the experimental conditions, and the inclusions were mainly elliptical oxide complex inclusions of Ca-Si with a size of about 2 μm. Meanwhile, Al2O3 and MnS were precipitated. After the addition of Ca elements, Mn-poor regions appeared around the inclusions containing Ca in the welding HAZ. IAF nucleation was mainly induced by the local compositional change mechanism and supplemented by the stress–strain energy mechanism and inert interface energy mechanism. This study provides a valuable reference for optimizing the welding process of pressure vessel steels and is of great importance for understanding the IAF nucleation mechanism of Ca-containing inclusions in the welding HAZ of pressure vessel steels.

Effect of high-frequency induction weld seam on the deformation of M1700 ultra-high strength steel shell structures considering residual tensile stress

The feasible cold forming procedure to massively manufacture ultra-high strength steel (UHSS) light-weighting profiles so far in industrial fields consists of roll forming, welding, cutting and bending. To reveal the role the high-frequency induction weld (HFIW) line plays in the subsequent plastic forming, a serials of deliberately designed collapse tests of the shell structures taken from M1700 roof rail pillar with a wall-thickness of 2 mm and triangle cross-section were conducted. Real geometries and inhomogeneous material properties of the weld seam and heat-affected zone (HAZ), together with the residual tensile stresses within the weld seam after HFIW, were fully considered in the numerical simulation. The Brozoo's modified CL damage model and Oyane damage model were employed and compared. The results show that the deformation resistance of the shell structures is modified by the material accumulation around the HFIW seams during the collapse tests. The cracks mainly occur within the critical HAZ outside the tube and the temper softening zone inside the tube under the action of softening effect in the HAZ of M1700 steel. The residual tensile stresses increase the crack probability of weld seams. The predicting accuracy of fracture location of the Oyane damage model is higher than that of the Brozoo's modified CL damage model.

Stress corrosion of HAZ subdivision of X80 pipeline steel in sterile high-sulfate soil

The welding heat affected zone (HAZ) is a high-risk region of corrosion, and influenced by multi-factors, such as stress, microbe and microstructure. Sulfate reducing bacteria (SRB) enhance the corrosion of the stressed HAZs, especially coarse-grained HAZ (CGHAZ). CGHAZ has least percentage of HAGBs, largest effective grain size, and highest volume fraction of MA island, which leads to the severer corrosion. SRB accelerate the localized corrosion of steel HAZs, and the maximum pitting depths of CGHAZ with and without SRB reach 9.97 and 7.65 μm, respectively. The elastic stress lowers the equilibrium potential and weakens the protective ability of film, which boosts the corrosion process, while SRB further enhance this accelerating effect of the stress on the corrosion.

The relative effect of boron and nitrogen concentrations on microstructure and creep resistance of weld simulated heat-affected zones of modified 9Cr-1Mo steel

To comprehend the combined impact of B and N concentrations on modified 9Cr-1Mo steel's heat affected zone (HAZ) creep resistance, five different steels with varying B (0-100 ppm) and N (20-500 ppm) concentrations were subjected to two types of weld thermal cycles (WTC), namely coarse-grained HAZ simulation and inter-critical HAZ simulation with peak temperatures of 1175 °C and 850 °C, respectively. Prior to and after creep testing (at 650 °C, 120 MPa stress), the microstructures and precipitates in the WTC simulated samples were studied using optical and electron microscopy, electron backscattered diffraction, and auger electron spectroscopy techniques. As expected, simulated HAZs of high B-containing steels (70-100 ppm B) showed superior creep resistance compared to low B steels (0-25 ppm B) due to the B stabilizing effect of M23C6 precipitates (primarily (Fe,Cr)23(B,C)6) though the rupture time for the simulated HAZs are lower than that of the base metals tested at the same test temperatures and stress levels. An interesting finding is that, despite the fact that 70 ppm B steel (with 108 ppm N) demonstrated the best creep resistance in normalized and tempered condition, 100 ppm B steel (with just 20 ppm N) obtained the best creep resistance of simulated HAZ. Large difference in the rupture lives between simulated ICHAZ and simulated CGHAZ specimens reveals the effect of triaxility in reducing the rupture lives in simulated CGHAZ specimens. This is also applicable to actual weld joints.

Fundamental study of blue wavelength laser for welding low thickness dissimilar Cu and steel materials

The present study reports on the application of blue wavelength (450 nm), continuous wave laser welding of Ni-coated copper to mild steel in lap joint configuration. The laser power was varied from 1 kW to 1.5 kW in incremental steps of 0.1 kW whilst the welding speed was kept constant at 6 m/min. Metallographic examination of the weld samples revealed that the weld penetration and width strongly correlated to the laser power, the characteristic of a stable welding process due to the high absorption of the blue wavelength laser. No substantial cracks or a large number of porosities were observed in the welds. The mechanical properties of the weld samples were characterized through tensile testing and microhardness measurements to establish the microstructure property relationship. The maximum tensile strength measured for specified weld geometries was 649 N with corresponding weld efficiency of 91%. The higher-strength welds showed a tensile fracture in the heat-affected zone (HAZ) of Cu, at the periphery of weld nuggets while lower-strength welds showed interfacial fracture due to the lack of fusion. In samples made with sufficient penetration the joint strength was controlled by the HAZ rather than the joint microstructure. A significant increase in the microhardness was measured inside the weld nugget compared to the parent materials, attributed to the formation of Cu-Fe composite microstructure owing to the inter-mixing of Cu and Fe during welding. The highest microhardness was observed in the HAZ of the mild steel due to martensitic microstructure formation in this region.

Microstructure and corrosion behavior of welded joint between 2507 super duplex stainless steel and E690 low alloy steel

Microstructure and corrosion behavior of welded joints between super duplex stainless steel 2507 and low alloy steel E690 were characterized herein. The joints are composed of base metal and heat affected zone (HAZ) of the two steels, weld metal, and dilution zone at the interface between weld metal and HAZ of E690 steel. Concentration gradients of Fe, Ni, Cr, and Mo exist between fusion boundary and Type-II boundary, and martensite band with a high hardness is formed. The changes of microstructure, element diffusion in different regions, and local acidification in E690 HAZ lead to heterogeneous corrosion attacks on the welded joints in artificial seawater. After long-term exposure, a corrosion groove is generated at the HAZ of E690 adjacent to the interface, where high stress corrosion cracking vulnerability is expected.

Stress corrosion cracking of X80 steel heat-affected zone in a near-neutral pH solution containing Bacillus cereus

Bacillus cereus (B. cereus) is observed to have varying effects on the stress corrosion cracking (SCC) sensitivity of different microstructures in the simulated heat-affected zone (HAZ) of X80 steel. At open circuit potential (OCP), the SCC sensitivity of different microstructures increased from 3.40–7.49% in an abiotic medium to 10.22–15.17% in a biotic medium. At −0.9 V (SCE), it increased from 22.81–26.51% to 35.76–39.60%. The increment in SCC sensitivity upon exposure to B. cereus was highest in the coarse-grained HAZ (7.68 and 16.79% at OCP and −0.9 V, respectively), followed by the intercritical and fine-grained HAZs. Owing to differences in the phase composition, grain boundary type, dislocation density, and surface volta potential, the initial adhesion number and position of B. cereus in the microstructure of the HAZ were differed, resulting in different sensitivities to SCC.

Characteristics of Cold Cracking in the Heat-Affected Zone of Carbon Steel

The effects of hydrogen and microstructure on the cold cracking susceptibility of the heat-affected zone (HAZ) of carbon steel were investigated. Various carbon steel plates with tensile strengths of 400- and 500-MPa grade were employed, and the cold cracking susceptibilities of the HAZs were evaluated using implant tests. To investigate the effects of hydrogen and microstructure, implant test assemblies were produced with two types of welding electrodes (low-hydrogen and cellulose) and two different welding conditions (low and high heat inputs). The results indicate that the microstructure was more important than hydrogen in determining the cold cracking susceptibility of the HAZ of carbon steel.

Research on hydrogen permeation in the X80 steel heat-affected zone with different heat inputs

Through electrochemical hydrogen permeation experiment at different hydrogen charging current densities, the hydrogen diffusion kinetic parameters such as penetration time tB , steady-state hydrogen permeation current density I ∞, hydrogen diffusion coefficient D, adsorbed hydrogen concentration C 0, hydrogen flux J, and hydrogen trap density NT in the heat-affected zone of X80 steel welding with different heat input were analyzed. The results show that the penetration time gradually decreases, and the I ∞ gradually increases with the increase of hydrogen charging current density. The penetration time of BM at the same hydrogen charging current density is the smallest, and the penetration times of CGHAZ specimens with different heat input conditions are relatively close. BM has the most significant hydrogen diffusion coefficient and negligible hydrogen trap density at the same hydrogen charging current densities. For CGHAZ, D significantly decreases and NT substantially increases, and there exists a threshold value that makes the lowest D in the CGHAZ with different heat inputs.

Microstructure evolution and microhardness of thermal-simulated HAZ in Fe–Mn–Al–C steel

The microstructure evolution and microhardness of Fe–Mn–Al–C steel heat-affected zone (HAZ) were investigated systematically using the weld thermal simulation technique. The results illustrated that the microstructure in HAZ with different peak temperatures (600, 800, 1000 and 1300°C) and heat inputs (10, 20 and 30 kJ cm–1) mainly consisted of ferrite and austenite. When the peak temperature was 1300°C, there are many high-angle grain boundaries which may inhibit crack propagation. With the increase in heat input, κappa carbide precipitation increased, the grain size became finer and microhardness increased. The microhardness was 438 HV when the peak temperature was 1300°C at 30 kJ cm–1. Highlights The welding of high carbon, high aluminium and low-density steel was simulated. The HAZ was composed of austenite and a small amount of high-temperature δ-ferrite. The proportion of high- and low-angle grain boundaries has a great influence on the mechanical properties. The welding heat input was 30 kJ cm–1, the grain size of the HAZ decreased and microhardness was the largest.

The Prediction of Ferrite Ratio in HAZ of EH36 Steel Electro‐Gas Welding Joints Based on Leblond Equation

A favorable microstructure is a perquisite for ensuring the quality of welding joints, but grain coarsing inevitably occurs in the heat‐affected zone (HAZ). Controlling the reduction of deterioration as much as possible is a key problem in welding engineering. Based on the welding experiment, a finite element model considering the contact heat transfer of water‐cooled sliders is constructed to obtain key information about the welding heat cycle, such as T8/5, and a prediction algorithm for the microstructure prediction of HAZ is developed based on the Leblond model. The results show that the proportion of ferrite gradually decreases with the increase in cooling rate. The evolution law of the model prediction is the same as that of the experimental results, and the maximum error is within 5%, indicating that the prediction is accurate and reliable. This observation has great significance for the optimization of the electro‐gas welding process.

Toughening and Hardening Limited Zone of High-Strength Steel through Geometrically Necessary Dislocation When Exposed to Electropulsing.

The enhancement of both low-temperature impact toughness and the hardness of a high strength steel heat-affected zone (HAZ) is investigated by using high-density electropulsing (EP). The athermal and thermal effects of EP on HAZ microstructure and resultant mechanical properties were examined based on physical metallurgy by electron backscattered diffraction and on tests of hardness and impact toughness at −60 °C, respectively. EP parameters were carefully determined to avoid electro-contraction and excessive pollution of the base metal by using numerical simulation. The EP results show that the mean impact toughness and hardness of HAZ are 2.1 times and 1.4 times improved, respectively. In addition to the contribution of microstructure evolution, geometrically necessary dislocation (GND) is also a contributor with an increase of 1.5 times, against the slight decrease in dislocation line density and dislocation density. The mechanisms behind this selective evolution of dislocation components were correlated with the localized thermal cycle EP, i.e., the competition among thermo- and electro-plasticity, and work-hardening due to local thermal expansion. The selective evolution enables the local thermal cycle EP tailor the martensitic substructure that is most favorable for toughness and less for hardness. This selective span was limited within 4 mm for a 5 mm thick sample. The local thermal cycle EP is confirmed to be capable of enhancing in both toughness and hardness within a millimeter-scale region.

Metallurgical Factors Affecting the Tensile Properties of Weld Heat-Affected Zone in Medium Mn Transformation-Induced Plasticity Steel

The role of retained austenite in the mechanical property changes in the medium Mn transformation-induced plasticity (TRIP) steel heat-affected zone (HAZ) was elucidated throug a comparison with conventional TRIP steel. The two steel grades had similar microstructures consisting of ferritic phases with a high fraction of retained austenite in the as-received state; however, the difference in properties after welding was significant. The microstructures of both steels were dramatically changed to a martensitic matrix in the coarse-grained HAZ region. The medium Mn TRIP steel HAZ can have a higher retained austenite fraction than the conventional one; hence, an excellent combination of tensile strength and elongation can be obtained. The decisive difference between the two steels was determined in terms of austenite stability and the initial grain size.

Effect of Nb Addition and Heat Input on Heat-Affected Zone Softening in High-Strength Low-Alloy Steel.

The effect of both Nb content and heat input on the softening phenomenon of the heat-affected zone (HAZ) of low-alloy high-strength steel was studied through welding thermal simulation experiments. The microstructure evolution, density variation of geometrically necessary dislocation, microhardness distribution and the second phase precipitation behavior in HAZ was characterized and analyzed by combining the optical microscope, scanning electron microscope, high-resolution transmission electron microscope with microhardness tests. The results showed that the softening appeared in the fine-grain HAZ (FGHAZ) of the low-alloy high-strength steel with the polygonal ferrite and bainite microstructure. With an increase in Nb content, the FGHAZ softening was inhibited even with high heat input; however, the hardness shows little variation. On the one hand, the increase in the Nb content increased the volume fraction of high-strength bainite in the FGHAZ. On the other hand, the remarkable strengthening was produced by the equally distributed precipitation nanoparticles. As a result, the two factors were the main reason for the solution of the FGHAZ softening problem in the low-alloyed high-strength steel with the mixed microstructure of ferrite and bainite.

Influence of ICCGHAZ on the Low-Temperature Toughness in HAZ of Heavy-Wall X80 Pipeline Steel

Low-temperature embrittlement in the heat-affected zone (HAZ) of heavy-wall X80 weld joints is a primary challenge for arctic oil & gas exploitation. In this paper, the influence of intercritically reheated coarse-grained HAZ (ICCGHAZ) on the low-temperature toughness of the weld joint in a 22 mm thick X80 spiral submerged arc welded pipe was studied through instrumented Charpy V-notch impact test at −80~20 °C and corresponding fracture surface characterization. The results indicated that the influence of ICCGHAZ on the overall toughness of the weld joint is related to temperature. At temperatures below −45 °C, individual and tiny martensite-austenite (MA) constituent debonding can trigger cleavage fracture–which was proved to be nucleation-controlled–and the probability of embrittlement of the ICCGHAZ increases. At temperatures higher than −45 °C, only relatively large or closely distributed MA constituent in ICCGHAZ satisfies the conditions to trigger propagation-controlled cleavage fractures, and the influence of ICCGHAZ on the overall toughness is not remarkable.

Eliminating the Brittleness Constituent to Enhance Toughness of the High-Strength Steel Weld Heat-Affected Zone Using Electropulsing.

The evolution of the martensite–austenite (MA) constituent in the heat-affected zone (HAZ) of high-strength steel FH690 welds when subjected to electropulsing (EP) treatment was investigated herein, with the aim of eliminating brittle MA to enhance toughness. The features induced by EPT were correlated with the microstructure and fractography through scanning electron microscopy and electron backscatter diffraction analyses, together constituting an impact property evaluation. The Charpy V-notch impact results showed EPT could improve toughness of the HAZ from 34.1 J to 51.8 J (the calibrated value was 46 J). Examinations of EP-treated microstructure showed a preferred Joule heating: at the site of the MA constituent, the cleavage fractography introduced by the MA constituent was substituted with ductile dimples with various sizes. Decreases in grain size of 40% and 47% for the matrix and the retained austenite, respectively, were achieved; while for regions without the MA constituent, microstructural modification was negligible. The temperature rise at sample surface was less than 60 °C. The mechanism behind this favorable Joule heating for the MA constituent was correlated with the electrical properties of the MA constituent in contrast with martensite matrix. The toughness enhancement of the HAZ was thus attributed to the elimination of the coarse MA constituent. The present investigation suggested that electropulsing, characterized as a narrow-duration current, is a promising method for preferred elimination of brittle factors and thus improving the toughness of HAZ of high-strength steel within a limited region with a width less than 2 mm.

Corrosion Behavior of X100 Steel Heat-affected Zone in Acidic Soil Solution

Corrosion Behavior of X100 Steel Heat-affected Zone in Acidic Soil Solution

Microstructure and Mechanical Properties of Welded Joints of 1.4462 Duplex Steel Made by the K-TIG Method.

K-TIG (Keyhole Tungsten Inert Gas) method is a new, emerging welding technology that offers a significant acceleration of the joining process, even for very thick plates. However, its potential for welding of certain materials is still unknown. Particularly challenging are duplex steels as this technology does not allow the use of a filler material, which is crucial for these steels and for weld joint microstructure adjustment. In order to demonstrate the suitability of this technology for single-pass welding of 1.4462 duplex steel detailed studies of the microstructure of the weld joints obtained for different linear energies were carried out and discussed with respect to their mechanical properties. According to the results obtained, the heat-affected zone (HAZ) shows a microstructure similar to the HAZ of duplex steel welded with the traditional TIG multi-pass methods. However, the weld, due to the lack of filler material, had a microstructure different to that typical for duplex steel welded joints and was also characterized by an increased content of ferrite. However, all joints, both in terms of microstructure and mechanical properties, met the requirements of the relevant standards. Moreover, the K-TIG process can be carried out in the linear energy range typical of duplex steel welding, although further optimization is needed.