Heat-affected Area Research Articles

Study on the Mechanical Response Behavior of X80 Pipeline Steel Welding Structure under Tensile Stress

Abstract The weld joint is composed of the weld area and the heat-affected area. The heterogeneity of the organizational structure will lead to local strain mismatch and affect its mechanical properties. This paper studies the strain distribution characteristics of the weld area and the heat-affected area under tensile stress, and reveals the respective strain response mechanism of the two regions. It is found that the weld area has lower yield strength and hardness, greater uniform elongation and strain hardening index. The plastic strain of the weld joint under tensile stress is highly heterogeneous, and the strain response mechanism is mainly based on the processing hardening effect. The strain response of the heat-affected area is weak and is affected by grain-oriented hardening. The research results provide a theoretical basis and experimental basis for the design of pipeline steel welding process and the safety evaluation under plastic deformation conditions.

Study on metal corrosion behavior of heat-affected zone of oil pipeline

Due to the influence of welding technology, a series of non-uniform and continuous heat-affected zones formed by welding seams is the weakest link of pipeline steel. Compared with the X70 steel, the heat-affected area is in the form of coarse acicular and massive ferrite, granular bainite, and a small amount of pearlite, with weak strength and corrosion resistance. Therefore, this paper simulated the heat-affected zone of the high-strength steel welding seam by the Gleeble 3500 thermal/force simulation testing machine for two heat cycles. Taking Shengli crude oil as the experimental medium, the metal corrosion morphology of heat-affected zones at different temperatures and transmission rates during hot oil transportation was analyzed through immersion experiment and corrosion morphology characterization. The results show that the increase in temperature and flow rate will increase the overall corrosion rate of the metal in the heat-affected area. In the range of 30∼50°C, pitting corrosion was the main corrosion feature of the metal, and in the range of 50∼70°C, the corrosion morphology of the metal changed from pitting corrosion characteristics to comprehensive corrosion characteristics. In the range of the flow rate studied (1∼4 m/s), the metal in the heat-affected area was mainly the overall corrosion rate, and the metal surface showed the erosion-corrosion characteristics along the flow rate direction.

Surface microstructural alterations and grain refinement mechanisms of tungsten heavy alloys by thermo-mechanical coupling: A laser-assisted milling case

Ultrafine-grained (UFG) tungsten heavy alloys possess potential applications in precision instruments and nuclear protection. In the present study, a comprehensive investigation of machined surface microstructural alterations and grain refinement mechanisms in laser-assisted milling (LAM) 95W-3.5Fe-1.5Ni alloy was demonstrated by recognizing its surface microstructures and mechanical properties under different combinations of the laser power and cutting depth. Graded microstructural characteristics along the surface degenerating layer and subsurface deformed layer of tungsten heavy alloy were identified for the first time, dramatically changing from workpiece bulk. Results showed that the adaptability between the thickness of the laser heat-affected layer and the depth of cut greatly influenced surface recrystallization layer microstructures regarding the thermal-mechanical coupling effect. An ordered, continuous, and equiaxed refined grains distribution layer was recognized when a particular machining condition was adopted, resulting in a substantial improvement of mechanical hardness. It could be indicated that a redundant heat-affected area would induce strain accumulation and promote recrystallization in LAM. Moreover, a dislocation density-based recrystallization model was applied to complement the experimental results considering the temporal transformation of grain refinement and recovery phenomena. Clarifying the above aspects is crucial to control the tungsten heavy alloys' surface microstructures and service performance during high-performance machining operations.

Investigation of NS-single-point laser ablation of bronze under different incidence angles and pulses

A fundamental understanding of ablation in different incidence angles is indispensable to expand the result to volume ablation where nonperpendicular irradiation exists. So far, no study with this orientation has been conducted in the category of volume laser machining. In this study, a nanosecond laser with different fluencies was utilized for single-point ablation experiments. The effect of incidence angles of 0°, 30°, and 60° on the ablation depth and the crater geometry was evaluated. Different laser pulse numbers are also considered. The results show that the ablation depth for 0° and 30° angles is almost in the same range for the initial pulses, but afterward, the ablation depth for the incidence 30° drops considerably. As the number of incident pulses increases, the ablation depth first develops approximately linearly and then grows exponentially. By changing the incident from 0° to 60°, the affecting area changes as well. The affecting area could be categorized into two distinct areas: (1) ablation area (A.A) where the crater ablation depth rapidly increases for the first 20 pulses and then, as more incident pulses arrive, it does not grow anymore and reaches a plateau due to the increase in the ablation depth. The second area (2) is the heat-affected area (H.A.A) of the crater where no further ablation occurs, but due to heat accumulation, it becomes constantly bigger when more incident pulses strike the crater. This heat-affected area tends to stay almost constant for the first incident pulses (up to 10) and, after a sharp increase, tends to enlarge steadily as the number of incident pulses rises to 70.

Performance recovery of locally buckled reduced beam section connections by attaching buckling-restrained components

Reduced beam section (RBS) connections are ductile connections that have been widely used in steel structures. Because of the reduction of web resistance, local buckling usually occurs under large deformations and is associated with decreased strength. In addition, the complex deformation of beams prevents determining the residual strength, hence posing a challenge in postearthquake repairs. In this study, a buckling-restrained system (BRS) including steel channels and a mortar was proposed for deformed RBS regions to provide lateral support on buckled plates so as to recover the connection strength. Two full-scale RBS connections with various cutting ratios were first tested, and then the connection was repaired with BRS loaded again. The test results indicated that the repaired connections were loaded at a drift angle of up to 4% without fracture or strength deterioration. The negative strength increased by approximately 18%, and the maximum strength was similar to that of the original connection, indicating that the column-to-beam flexural strength ratio of the connection did not change. The strain at the heat-affected area also did not increase and rather decreased because of the additional support of the restraint. The dissipated energy capacities of the repaired specimens were approximately 92% and 87% of the values of the original specimens. These results confirmed that BRS provided sufficient lateral resistance and helped recover the connection performance.

Analysis of Effect of Temperature Variation Preheat on SMAW Welding of Microstructures, and ST60 and SS400 Steel Hardness

Welding is a metal joining process by melting some base and filler metals. SMAW welding (Shielded Metal Arc Welding) is one of the industry's most widely used welding methods. SMAW welding requires preheating (preheating) to reduce residual stress, distortion, and cold cracking in the weld metal. Preheat also can affect the microstructure and hardness of the weld metal. This study aims to analyze variations preheating on SS400 and ST60 steel against micro tests by SMAW welding, namely electric arc welding with covered electrodes. Temperature variation preheating used in SS400 steel was 140°C, 170°C, 300°C and 400°C in ST 60 steel. The results showed that the higher the temperature preheat, the larger the grain size of the microstructure in the parent metal region, the heat-affected area, and the weld metal area. The higher temperature preheat also led to a decrease in violence in the three areas. ST60 steel has a larger microstructure grain size and lower hardness than SS400 steel at all temperature variations preheat.

Apparatus Design of One-Step Double-Side Friction Stir Welding for Aluminum Plates

Aluminum alloys emerged as one of the materials used in manufacturing automotive car bodies due to their advantageous properties such as high strength-to-weight ratio, relatively low cost, high ductility, and high corrosion resistance. However, joining aluminum alloys using fusion welding poses serious problems due to the high solubility of hydrogen gas, which causes porosity in welding metal. Subsequently, solid-state welding, such as friction stir welding (FSW), has been considered a porosity-free aluminum joining method. However, the method has limitations, such as low flexibility and the need for a complex clamping system. It is particularly problematic when welding plates. It causes the welding process to be carried out twice on opposite sides, resulting in longer production times. This study designed and assembled a one-step double-side FSW apparatus to address this challenge and conducted welding trials with various welding parameters. During the welding trial, the upper and lower tool rotation varied at 900/900 rpm and 1500/1500 rpm. As a result, one-step double-side FSW was successfully used for welding 6 mm aluminum without any porosity defects. Faster tool rotation results in a wider heat-affected area and higher tensile strength. In addition, the hard test showed that the one-step double-side FSW process had a lower hardness compared to the hardness of the base metal.

Investigation of thermal damage in continuous wave laser-induced nanowelding

Continuous wave (CW) laser-induced nanowelding holds great promise in micro-and nano-devices. However, because of the lengthy irradiation duration, the heat effect from CW laser irradiation may harm the manufactured devices. The simulation results show that an increase in irradiation duration will slightly improve the welding temperature but greatly expand the heat-affected area when the irradiation time exceeds 100 ms. Experimental results confirm that Cu nanowires irradiated for 20 ms are slightly oxidized. As the irradiation period is increased to 10,000 ms, the oxygen concentration in Cu nanowires significantly increases, and the color of Cu nanowires becomes first black, then green. The electrical property of the oxidized Cu-Au nanojunction shifts from ohmic contact to Schottky contact. Furthermore, the large heat-affected area will weaken the adhesion between the Au pad and the substrate due to the large difference in thermal expansion coefficient between the metal film and the insulating layer. Consequently, CW laser-induced thermal damage not only impairs the electrical properties of nanostructures but also their reliability.

Numerical simulation and experiment on morphology control of grooves processed by a picosecond laser on TC11 titanium alloy

The chief aim of this paper is to control groove morphology precisely. In this paper, a 2D temperature field model for ultrafast picosecond laser grooving was set up on the foundation of the two-temperature model coupled with the phase change model. Then, a series of simulations were executed to investigate the influence of laser parameters such as laser power, scanning speed and repetition rate on ultrafast picosecond laser grooving. Finally, a number of experiments were performed to verify the model. The results suggest that the laser power has an obvious influence on the groove width and depth because the heat-affected zone area and single-pulse laser energy increase when the laser power varies from 2 W to 5 W. Obvious impacts of scanning speed on the groove depth and quality are observed in the present simulation due to the variation of overlap between sequential pulses and pulse numbers. The groove width and quality depend on the repetition rate. This is because the increase in the repetition rate has a certain contribution to increasing the temperature of heat residue and pulse number. This research contributes to present theoretical guidance on laser grooving.

Study on the Application of the GTAW Process in Strengthening the Welding Quality of Short Duplex Stainless Pipe

This study focuses on the results of the welding process when the Taguchi method is added to the design of experimental welding parameters when creating the welding procedure for gas tungsten arc welding (GTAW) by ASME Code for duplex stainless steel (UNS31803). A Vickers hardness tester is employed to collect and convert the tensile strength data for each test piece (weld bead, base material, and heat-affected area). A ferritic rate meter can quickly determine the ferric contents, which affect corrosion resistance and susceptibility to cracking. The test data are entered into the Taguchi technique to analyze the influence of each component on the welding quality. The L9 (34) orthogonal table is used to design the parameters for the experiment. We fixed the same shielding gas and flow rate. Backing gas at root, workpiece clamping angle, heat input, and interlayer temperature are employed as control factors for the four essential variables of the GTAW process. The ideal set of quality analysis and optimization parameters can be found. The welding parameters could be used to improve the welding quality of thin and short duplex stainless steel pipe fittings during argon welding.

Research on the End-Face Distribution of Rotational Molding Heating Gun Based on Numerical Simulation Method

The distribution of heating gun ends plays a decisive role in the sidewall properties of finished rotomolded products. To obtain the optimal distribution of the end face of a rotational molding heating gun, the temperature response of the end-face mold under heating gun heating was investigated, and an analysis method based on numerical simulation is proposed. The FDS (fire dynamics simulator) was used to construct a heating model of the heating gun, simulate and obtain a heatmap of the temperature field distribution of a heating gun of Φ30–70 mm, and determine the optimal diameter and heating distance of the heating gun. ANSYS was used to establish the thermal response model of the heat-affected mold, which was combined with the mold structure and thermophysical properties of steel. A temperature field distribution on the inner wall surface of Φ30, Φ50, and Φ70 mm heating guns when heating at each diameter of the end face was obtained and the distribution position of the end face of each diameter heating gun was determined. ANSYS was used to establish the thermal response model of the end-face mold and obtain the temperature field distribution of the inner wall surface of the end-face mold. The size of the heat-affected area of each diameter heating gun was combined, the end-face heating gun distribution was optimized, and the optimal heating gun end-face distribution was obtained. An experimental platform was built, and a validation experiment was set up. Through the analysis and processing of the data of three experiments, the temperature variation curve of each diameter on the inner surface of the end-face mold was obtained. We compare and analyze the simulation and experimental results to determine the feasibility of the FDS + ANSYS method and the correctness and accuracy of the simulation model and the results.

MICRO-CRACK ANALYSIS IN THE STUDY OF FATIGUE FRACTURE IN THE HAZ IN THE HIGH YIELD STRENGTH MICRO-ALLOYED STEELS

Various applications have been described in the literature for the High-Strength and Low-Alloy steels (HSLA) industry, analysing their use both in industrial and marine equipment and machines and in structures that require appropriate resilience values and toughness at low temperatures. For successful operation under conditions as large structures under extreme service conditions, it is essential to ensure the proper toughness both in base metal (USITEN 355 0.5 Ni Grade I steel) and in the heat-affected area of the weld. (ZAC). This research carries out Crack Tip Opening Displacement (CTOD) tests, showing, in this article, the first part of the test corresponding to fatigue pre-cracking and a summary table of the results of fracture toughness, to guarantee that, under the conditions which exist in welding, both the fatigue fracture values and the fracture toughness are acceptable by the applicable standards. Keywords: SMAW, weld line, CTOD, stress intensity factor, input heat energy, crack growth rate, fatigue fracture, fracture toughness

The Study of Corrosion Behaviors of Carbon Steel Weldments and Their Inhibition in Simulated Pore Solution Using Multi-Electrode Array Technique

A multi-electrode array sensor was developed to study the corrosion behaviors of carbon steel weldments and the effectiveness of the NaNO2 inhibitor in carbonated pore solution. The sensor can simulate a complete weldment, and the measurement results can match well with the coupon immersion test. The galvanic corrosion between the weld area, heat-affected area, and base metal area, as well as the effect of nitrite corrosion inhibitor on the weld area, were observed by measuring the open circuit potential, coupling potential, and galvanic current. The results show that corrosion is likely to happen around the weld metal area and its adjacent heat-affected zone. The intensive galvanic currents can accelerate the localized corrosion, while NaNO2 can inhibit it.

고경도 장갑판재의 TACOM 규격 평가를 통한 다양한 용접재료의 특성분석에 관한 연구

A very thick single-armor material is generally used for bulletproof performance in combat vehicles; as a result, the combat capability is greatly reduced by the heavy weight. The armor plate of a combat vehicle is manufactured by applying a welding process to the joints of high-hardness steel. However, when applying the welding process to the high-hardness armor plate, the hardness decreases owing to hot softening in the heat-affected area, resulting in deterioration of the bulletproof performance. In this study, three different welding materials were selected, and their weld strengths were evaluated according to the TACOM standard. The mechanical properties and microstructures of the welded parts of the three materials were analyzed through tensile, bending, impact, and hardness tests. Finally, the most suitable welding material was selected for the high-hardness armor plate.

A numerical study on heat transfer performances of horizontal ground heat exchangers in ground-source heat pumps

Horizontal ground heat exchangers (HGHEs) have advantages such as convenient construction and low cost; however, their application and popularization are restricted owing to traditional linear HGHEs occupying large space and presenting low total heat transfer capacity. Spiral-coil and slinky-coil HGHEs have been proposed, but currently a comprehensive comparison and evaluation for these types of HGHEs are still needed. In this study, a three-dimensional heat transfer model of the three types of HGHEs for ground source heat pumps (GSHPs) was established. Based on the simulation results, the long-term heat transfer performances were investigated, including the temperature field of surrounding energy-storage soils, outlet working fluid temperature, coefficient of performance (COP) of units, and surplus temperature of the energy-storage soils. A new concept named heat transfer capacity per heat-affected area was proposed in this paper. It is found that the spiral-coil HGHEs have the best performances in terms of working-fluid outlet temperature, unit COP, total heat transfer capacity, heat transfer rate heat-affected area. The linear HGHEs shows the best performances in terms of mitigating heat imbalance risk and heat transfer rate per length. The results provide a reliable basis for selection of HGHE types in engineering practice and improvement guide in the future.

Fire Performance of Self-Tapping Screws in Tall Mass-Timber Buildings

Building elements are required to provide sufficient fire resistance based on requirements set forth in the National Building Code of Canada (NBCC). Annex B of the Canadian standard for wood engineering design (CSA O86-19) provides a design methodology to calculate the structural fire-resistance of large cross-section timber elements. However, it lacks at providing design provisions for connections. The objectives of this study are to understand the fire performance of modern mass timber fasteners such as self-tapping screws, namely to evaluate their thermo-mechanical behavior and to predict their structural fire-resistance for standard fire exposure up to two hours, as would be required for tall buildings in Canada. The results present the great fire performance of using self-tapping screws under a long time exposure on connections in mass timber construction. The smaller heated area of the exposed surface has limited thermal conduction along the fastener’s shanks and maintained their temperature profiles relatively low for two hours of exposure. Based on the heat-affected area, the study presents new design principles to determine the residual length of penetration that would provide adequate load-capacity of the fastener under fire conditions. It also allows determining safe fire-resistance values for unprotected fasteners in mass timber construction exposed up to two hours of standard fire exposure.

Effect of Microstructure on High-Strength Low-Alloy Steel Welded Joint Toughness with Simulation of Heat-Affected Zone Coarse-Grained Area

A simulated coarse-grained heat affected zone microstructure formation mechanism is established in high strength low alloy steels using electron backscatter diffraction (EBSD). The governing effect of dispersion and ratios between different types of ferritic structural constituents on variation in impact strength is demonstrated. It is assumed from results of simulating a heat affected zone coarse-grained area that a reduction in welding energy input leads to a shift in ductile-brittle transition temperature towards a lower temperature.

Influence of process parameters on the machinability of nickel aluminum bronze alloy by electrochemical micromachining process – A desirability analysis approach

The machining of Nickel Aluminum Bronze (NAB) via traditional machining methods creates many problems which include wear of the tool, the appalling surface of the finished product, large dimensional deviation, and excessive heat-affected area. These issues can be mitigated by non-traditional techniques such as electrochemical micromachining, electric discharge machining, laser beam machining, and plasma arc machining. Electrochemical micromachining (ECMM) works under the principle of anodic dissolution. Difficult to machine materials can be easily machined by ECMM technique. The micro-domain applications of NAB are found in perforated orifice and pharmaceutical industries. In this study, micro-drilling on NAB alloy was conducted using the ECMM process. The influence of two different electrolytes such as sodium chloride (non-passivating) and sodium nitrate (passivating) while micromachining NAB alloy was analyzed. The response surface methodology (RSM) approach was proposed to obtain the maximum material removal rate (MRR). The output response MRR was analyzed using desirability analysis. The NAB alloy machined with sodium chloride electrolyte was found to have 2.20 times higher MRR than the component machined with sodium nitrate solution.

Optimization of Parameters for the Cutting of Wood-Based Materials by a CO2 Laser

This article deals with the laser cutting of wood and wood composites. The laser cutting of wood and wood composites is widely accepted and used by the wood industry (due to its many advantages compared to, e.g., saw cutting). The goal of this research was to optimize the cutting parameters of spruce wood (Pices abies L.) by a low-power CO2 laser. The influence of three factors was investigated, namely, the effect of the laser power (100 and 150 W), cutting speed (3, 6, and 9 mm·s−1), and number of annual rings (3–11) on the width of the cutting kerf on the top board, on the width of the cutting kerf on the bottom board, on the ratio of the cutting kerf width on the top and bottom of the board, on the width of the heat-affected area on both sides of the cutting kerf (this applies to the top and bottom of the board), and on the degree of charring. Analysis of variance (ANOVA) and correlation and regression analysis were used for developing a linear regression model without interactions and a quadratic regression model with quadratic interactions. Based on the developed models, the optimization of parameter settings of the investigated process was performed in order to achieve the final kerf quality. The improvement in the quality of the part ranged from 3% to more than 30%. The results were compared with other research dealing with the laser cutting of wood and wood composites.

Investigating the mechanisms of shape distortion of the heat-affected region during electric-arc welding of oilfield pipelines

The article studies the issue of the influence of the most encountered in practice defects of welded joints of a one-piece joint, formed in the process of applying a weld when connecting oilfield pipelines to a joint by electric arc manual welding, on the strength characteristics of a welded joint by scrutinizing the condition of the pipe material close to the heat-affected zone. As a test sample, a butt welded joint with obvious defects was used. The geometric parameters of the welded joint were measured using standard means and the hardness of the heat-affected zone was determined by the Rockwell method in certain areas with justification of the welding process. The reason for softening is established. The change in the geometry of the heat-affected area is due to the accumulation of filler material during its melting on one side of the weld with a decrease in welding speed. Recommendations are given for the prevention of the destruction of welded structures and the occurrence of emergency situations in oilfield pipelines.