Local Heat Treatment Research Articles

The impact of deformation in the zone of welded joints on the force action of the rolling stock on the track

The causes of deformation in the zone of welded joints are considered. Authors experimentally studied changes in hardness on the rolling surface of the rail in the longitudinal and transverse profiles within the thermally affected zone of the welded joint. It is established that the hardness of the rolling surface of the rail in the longitudinal direction in the thermally affected zone of the joint is uneven and is determined by the structures arising from the effects of the thermal cycles of welding and the quality of the local heat treatment. In this case, two "low spots" are clearly traced with a decrease in hardness to 290...300 HB and with a higher hardness up to 350 HB right in the welded joint. Experimentally investigated the change in the depth of the welded joint from the implemented tonnage. At the same time with strain gauge method, using the force method developed by N. N. Kudryavtsev, continuous changes in vertical forces when the wheels move along the welded joint zone were recorded. Average values of vertical forces from loaded cars were established. Experimental distributions of vertical forces were approximated by theoretical laws according to the Kolmogorov — Smirnov matching criterion. Recommendations are given on minimizing the harmful impact of rolling stock on the track in areas of lowering welded joints.The following conclusions were made.1. Geometry of the joint irregularity is in the form of a W-shaped deformation with an influx of metal on the receiving rail and lowering on the directing rail. The width of the upper part of the deformation varies between 160...200 mm along the axis of the rail.2. Deformation zone of the welded joint is a source of increased dynamic impact from the wheels of the rolling stock on the elements of the upper track structure. According to the results of experimental studies it was found that the greatest increase in dynamic effects was observed from locomotive wheels up to 45.. . 70 kN, maximum values reached 180...210 kN, from the wheels of loaded freight cars the values of vertical forces increased by 35.. .45 kN, maximum values reached 145...170 kN, from the wheels of empty cars increase dynamic impacts amounted to 14...16 kN, maximum values reached 32...36 kN.

Local Heat Treatment for Suppressing Gastroduodenal Stent-Induced Tissue Hyperplasia Using Nanofunctionalized Self-Expandable Metallic Stent in Rat Gastric Outlet Model.

Despite the promising results from the placement of covered or uncovered self-expandable metallic stent (SEMS) as a nonsurgical therapeutic option for the malignant gastric outlet obstruction (GOO), the long patency of the stent is still limited because of stent-induced tissue hyperplasia. Here, a local heat treatment using a nanofunctionalized SEMS is proposed for suppressing stent-induced tissue hyperplasia during GOO treatment. Highly efficient photothermal gold nanoparticle (GNP) transducer-coated SEMSs (GNP-SEMSs) were prepared for local heat treatment in rat gastric outlet. The in vivo heating temperature in rat gastric outlet model was evaluated and compared with in vitro heating temperature. Three groups of our developed 45 rat gastric outlet models were used: group A, noncoated SEMS only; group B, GNP-SEMS plus local heating; and group C, GNP-SEMS only to investigate in vivo efficacy of GNP-SEMS mediated local heating. Ten rats per group were sacrificed for 4 weeks, and five rats per group were sacrificed immediately after local heat treatment. The in vivo heating temperature was found to be 10.8% lower than the in vitro heating temperatures. GNP-SEMSs were successfully placed through a percutaneous approach into the rat gastric outlet (n = 45). The therapeutic effects of GNP-SEMS were assessed by histologic examination including hematoxylin-eosin, Masson trichrome, immunohistochemistry (TUNEL and CD31), and immunofluorescence (Ki67), and the results showed significant prevention of tissue hyperplasia following stent placement without adjacent gastrointestinal tissue damage. GNP-SEMS-mediated local heating could be an alternative therapeutic option for the suppression of tissue hyperplasia following stent placement in benign and malignant GOOs.

Underwater In Situ Local Heat Treatment by Additional Stitches for Improving the Weldability of Steel

In this paper the influence of in situ local heat treatment performed by additional stitches on the weldability of high-strength low-alloy (HSLA) S355J2C+N steel was tested. The investigated steel is characterized by high susceptibility to cold cracking. It is necessary to find a method to improve the quality of welded joints. The local heat treatment was applied as an effect of bead-on plate welding made on the face of a Tekken test joint. The specimens were made by the use of covered electrodes in the water environment. For testing weldability, Tekken test specimens were made. Then, the different number of the pad welds with different overlapping were laid on the face of the tested welds. Non-destructive (NDT) visual and penetrant tests were undertaken. During the NDT, imperfections like shape mistakes and spatters were found. Then, metallographic macro- and microscopic testing were performed. The macroscopic observations proved that water environment can generate imperfections like cracking and pores. However, for specimens with additional stitches the number of imperfections decreased. Microscopic tests proved that the proposed technique affected the structure of the heat-affected zone (HAZ). The specimens without the application of additional stitches are characterized by brittle bainitic and martensitic structure. Specimens, in which the additional stitches were applied, contain tempered martensite, fine ferrite and fine pearlite in their HAZ. It was also observed that the number of cracks decreased for in situ local heat-treatment specimens. The final step was Vickers HV10 hardness measurement. These measurements confirmed previous results. The heat from additional stitches affected the steel by significantly decreasing the hardness by 80–100 HV10. The results of experiments showed that the heat from pad welds provided microstructural changes in heat-affected zones and a decrease in the susceptibility to cold cracking, which results in improvement in the weldability of HSLA steel in wet welding conditions.

Structure, Mechanical Properties, and Stressed State of Weld Joints of the Tial(Nb, Cr, Zr) Intermetallic System

Structural features, mechanical properties, and stressed state of welded joints of the TiAl system intermetallic compound (Nb, Cr, Zr) after electron-beam welding and subsequent electron-beam local heat treatment are determined. It was shown that stresses generated immediately after welding contributed to the appearance of cold cracks in the weld. Residual stresses in welded joints were determined using the technology and compact equipment based on the method of electronic speckle interferometry created at the Paton Electric Welding Institute of the National Academy of Sciences of Ukraine. It was found that after electron-beam welding, due to rapid cooling of the weld metal, phase transformations occurred, which deteriorated its mechanical characteristics. A method was developed for the local heat treatment of a welded joint by an electron beam immediately after the end of the welding process. Parameters of the local heat treatment process can significantly reduce the cooling rate, maintaining the temperature of the welded joint for 5 min at the level of 900°C. This can significantly reduce the level of residual stresses in the weld and contribute to the formation of a favorable three-component structure: γ-phase, (γ + α2)-phase and β-phase, which increases the weld ductility. A study of mechanical properties during the compression test of the weld showed that after local heat treatment, the yield strength of the weld was improved, while the tensile strength and degree of deformation under compression increased significantly. The proposed local heat treatment is effective and economically justified, which allows to reduce residual welding stresses by 30%, thus preventing the formation of cracks in welds, as well an improving structural and mechanical characteristics.

Development and Modeling of Differentially Heat-Strengthened Rail Welding: Welding and Local Heat Treatment Modeling

During the manufacturing of continuous welded rail track, the problem of the local hardened points in the welded joint during rail joint welding is resolved by using local heat treatment of the welded joint. As a result, the quenching structure formation is excluded. However, the appearance of new heat-affected zones with reduced hardness is possible. During operation, such rails are characterized by increased tread surface wear in these areas and rail flattening at the welded joint, which is the main reason for retiring the rails from service earlier than the guaranteed service life. A new technology based on the dependence of the structural component dispersion (primarily perlite and carbide particles formed in the process of rail butt welding) is proposed for the steel composition and cooling conditions. The cooling rate has a decisive influence on the dispersion degree of the ferrite-cementite structure formed during the austenite decomposition. During the welding rail process, the granular perlite formation is possible in a butt weld in areas with a temperature ranging within points Ac1 and Acm. To determine these critical temperatures, thermodynamic calculations were performed using the Thermo–Calc® software (TCFE database) allowing the chemical composition of the samples obtained by spectrometry. The iron–carbon state diagrams for rail steel 76KhSF with the minimum and maximum alloying element content according to GOST R 51685–2013 are modeled. To obtain the minimum number of sections with reduced hardness, it is possible to weld rails using shot discontinuous flash welding. In order to eliminate the formation of defective areas with a quenching structure, it is possible to control the cooling of the welded joint by contact heating. Temperature distribution measurement during welding according to given modes and controlled cooling confirms the theoretical conclusions.

Mechanical property and characterization of 7A04-T6 aluminum alloys bonded by friction stir welding

The 7A04-T6 aluminum (Al) alloys were bonded via a friction stir welding (FSW) technique. The tensile strength of this FSW joint was the highest when the welding speed was 120 mm/min and the rotation speed was 1000 r/min, which reached 77.93 % of that of the base material (BM). The nugget zone (NZ) consisted mainly of the fine grains; the grain boundary misorientation angle in NZ was about 15°, indicating that the propagation of micro-crack was hindered to a certain degree, improving the toughness of this joint. The S-N curve of this joint showed that the fatigue strength decreased with an enhancement of the fatigue life when N was below 105, also N was above 106. The fatigue limit (141 MPa) of the joint was calculated through an up-and-down test method, the fatigue fracture position occurred in HAZ, exhibiting the ductile fracture. Then a laser local heat treatment (LLHT) process was carried out on this weld seam, which refined the microstructure, strengthening the mechanical property of this FSW joint.

Experimental investigations for a postweld heat treatment on Ti-6Al-4V titanium welds with a defocused laser beam

The purpose of this study is to apply a local heat treatment (LHT), in-situ, on the weld bead, using a defocused Yb: YAG laser beam on a continuous regime, in order to reduce residual stresses and decompose the brittle a’ martensite, into a lamellae and fine β phase. Laser scan experiments were firstly performed on a commercially pure titanium grade 2, with a wide range of parameters, in order to provide a “heat treatment window” without titanium melting. After optimization of the processing parameters, to obtain a sufficient width and depth for the scanning zone, experiments have been performed on a β-treated, fully martensitic Ti-6Al-4V sheet. For each processing experiments, the decomposition of a’, was studied based on metallographic cross sections. A local heating with a minimum energy density at 700 J.cm-2, has a sufficient effect to destabilize a’, while for an energy density at 1000 J.cm-2 , a diffusional transformation take place, with the formation of Widmanstätten microstructure. Finally, these optimized conditions were applied on a full penetration Ti-6Al-4V welds. The results of the LHT will be described in terms of the microstructural changes observed in the welded zone and hardness evolution.

Experimental investigation of distortion behavior of laser heat treated blanks

Aluminum alloys fulfill the growing demands for lightweight applications and are completely recyclable. The use of high-strength aluminum alloys offers the opportunity to replace safety-relevant steel components. Currently, the use of these alloys is limited due to their low formability and high springback during forming at room temperature. The use of tailored blanks with locally adapted material properties is one opportunity to overcome these limitations. By local heat treatment, zones are locally softened and thus crack critical areas during forming can be avoided. At present, blanks with tailored properties are not used extensively. One reason for this is component distortion due to thermal stress, which makes handling the heat-treated sheets more difficult. Aim of this study is the identification and reduction of thermally caused component distortion. Therefore, in this paper the influence of the initial material condition, the sheet thickness as well as the laser spot size on the distortion behavior is investigated.

Experimental and Numerical Study on Cutting Performance of Coal Plow

Coal plow is one of the important equipment for thin seam mining, it is very important to improve the performance of plow for efficient coal mining. In order to study the cutting performance of the coal plow, the cutting test is carried out in National Energy Mining Equipment Research Center, and the forces of the plow bit with different cutting speeds and depths are obtained. According to the properties of simulated coal wall, the intrinsic parameters of coal wall material are determined, and the three-dimensional bond contact model of coal wall is established by EDEM software. The force information of coal plow, the distribution of coal particles and the residual state of the coal wall surface are obtained through the numerical simulation. The results show that the maximum error of the force obtained by DEM simulation and experiment is 7.849 %, and the error of the width the residual coal ridge is 6.5 %. The force distribution of the plow bit is analyzed by combining the discrete element method with the finite element method. The high dynamic stress area of the plow bit is mainly concentrated in the back of the body and the alloy head inlay position. In order to reduce the consumption of the plow bit, local heat treatment is carried out on the plow bit, which can improve the mechanical properties of the plow bit. The simulation results are verified by experiments and industrial production, which proves the accuracy and feasibility of using DEM to study the cutting performance of coal plow.

Enhancement of the Forming Limits for Orbital Formed Tailored Blanks by Local Short-term Heat Treatment

Nowadays, the manufacturing industry faces opposing challenges like a reduction of carbon dioxide on the one hand and on the other hand an increasing weight due to higher safety standards and additional functions. Concepts like lightweight design and functional integration are essential to ensure a sustainable and individual mobility. Gear systems consist of multi-functional parts with a varying sheet thickness and different geometric elements. Since conventional manufacturing processes like shearing are reaching their limits due to complexity and a lack in efficiency, the application of Tailored Blanks is a promising approach to meet these requirements. Manufactured by orbital forming, these process-adapted blanks dispose a high material efficiency. A tumbling motion of the upper punch enables the material distribution, realizing functional components with different material thickenings. The substitution of steel by aluminum is a common approach to meet the demands of lightweight construction. However, the use of aluminum results in a decreased formability at a constant level of strength. In order to enhance the local forming limits, a short-term heat treatment can be applied, reducing the materials’ strength, whereas the untreated areas still offer the initial properties. To transfer the results of fundamental research in Sheet-Bulk Metal Forming with conventional steel to the use of lightweight material, the precipitation hardenable aluminum alloy EN AW 6016 is investigated in an orbital forming process. Since the formability of aluminum is limited and the material flow during the process is three-dimensional, different heat treatment strategies are applied to a rotational-symmetric Tailored Blank and the resulting components are investigated regarding their geometry and mechanical properties. To increase the geometric complexity with regard to an industrial application, the transferability to a cyclic-symmetric layout is analyzed. To evaluate the potential of the heat treatment, the treated components are compared to Tailored Blanks manufactured without heat treatment.

Study of Tailor Heat Treated Blanks Using the Fourier-series-based VFM

In this work, the Virtual Fields Method (VFM) was used to identify the properties of tailor heat treated (THT) blanks, in terms of different hardening parameters. The spatial variation of the hardening parameters was described using the Fourier series approach. The chosen material is an aluminum alloy 5754 H111 that undergoes a localized heat treatment. From the blank sheet, dog-bone specimens were cut and treated using a laser in the central zone. Tensile tests were performed on the sample using Digital Image Correlation (DIC) to obtain the full-field deformation history. Finally, the F-VFM was applied to identify the spatial distribution of the hardening parameters. In order to compare the results with reference values, further tests were conducted on not treated specimens. Thus, the so-called Fourier-based VFM (F-VFM) was introduced for finite deformation plasticity problems; numerical data are used to validate the inverse approach, and, afterwards, the inverse identification process is applied on experimental data from THT specimens.

Effect of Internal Air Flow on Local Postweld Heat Treatment for Large Diameter ASME P92 Steel-Welded Pipes

Abstract Local postweld heat treatment (PWHT) is usually employed in field fabrication of large-sized ASME SA-335 Grade P92 steel pipes. Internal air flow in pipes that arise from field fabrication can result in considerable convection losses on the inside surface of the pipe when the pipe is not strictly sealed off. Welding and local PWHT experiments of a large diameter P92 steel pipe were conducted both with and without internal air flow, and temperature field of both sides of the pipe was measured. The conjugate heat transfer between the pipe and the internal air is simulated using computational fluid dynamics (CFD) method. The effect of internal air flow on temperature field was further investigated. Results indicate that temperature gradient along through-thickness direction and axial direction during local PWHT is significantly increased due to internal air flow. The increasing rate of temperature difference between inner and outer surface at weld centerline to internal air velocity is about 14.5 °C/(m s−1). The maximum temperature is no longer located at the weld centerline, which will lead to a risk of overheating. The temperature drop is severer in the air inlet side than air outlet side at same distance from weld centerline. For local PWHT to be successful, the internal air flow should be strictly limited during local PWHT; otherwise, the width of heated band (HB) should be extended.

Methods of elimination of rails increased damage in the area of weld joints

Rail weld joints from electric-contact welding in stationary and fi eld conditions, as well as those from aluminothermic welding are weak points on tracks that are easily damaged compared with rails outside the weld joints. Currently, these weak points are the defects connected with lack of penetration in the welding area, burns at the points of poor contact of the rail foot with the current-carrying contact tips, or with defects of the weld joint machining after welding, as well as the local hardness reduction in areas affected by heat after welding, and local heat treatment after welding. Elimination of wide areas of reduced hardness at the weld joint points producing saddles, cracks, and chipping, and promoting rails damage next to such joints is a major challenge for increasing the serviceability of weld joints. This study introduces three avenues for elimination of increased damage of rails at weld joints including:• Improvement of technology and equipment for electriccontact welding and local heat treatment after welding in the stationary and fi eld conditions.• Development of technology and equipment for induction welding in the stationary and fi eld conditions.• Development of technology and equipment for differentiated induction tempering of rails preliminary welded in strings 800 m long.

In Situ Structural Characterization of Functionally Graded Ni–Ti Shape Memory Alloy During Tensile Loading

A functionally graded NiTi shape memory alloy wire was investigated by in situ synchrotron radiation-based X-ray diffraction (SR-XRD) during cyclic tensile deformation. The transformation temperatures were determined by DSC and the thermomechanical behaviour was analysed by three-point bending test. The present study focussed on the localized heat treatment (Joule heat effect, reaching 300 °C, 350 and 400 °C pulses for 10 min) of NiTi wires, using an equipment that allows a large variety of graded conditions. Structural, mechanical and thermomechanical characterization is presented to get a perspective of the different types of graded functionality. A combination of two strategies has been used for the in situ analysis by SR-XRD of the tensile tests: (i) continuously following the structural evolution at one single point (at the center of the heat-treated segment) all long the load/unload cycle and (ii) scanning the full heat-treated segmentat previously defined discrete steps of the stress–strain curve. The combined information from both types of tests provided detailed information about the phase transformations taking place in different regions of the functionally graded segment, at different steps of the tensile load/unload cycle, giving a better understanding of the overall mechanical, namely the evidence of the sequence B2 ↔ R ↔ B19′ for the direct and reverse transformations.

Experimental investigation of the formability of ultrahigh-strength sheet material using local heat treatment

ABSTRACTIn this study, the effects of local heat treatment temperature on the V-bending formability of Martensitic 1200 steel, was investigated experimentally. In the first stage of the study, local heating temperatures were determined according to the stress-strain curves obtained as a result of the hot tensile test. Other experimental parameters included temperature (room temperature - RT/25, 300, 400 and 500°C), die-punch angle (30, 60, 90 and 120°) and punch holding time (0 and 10 s). The heating procedure in the bending operation was carried out locally only in the bending zone with the temperature controlled heating rod. The hardness values were found as 5.19% HV at the forming temperatures of RT–300°C, 2.31% HV at 300–400°C and 1.85% HV at 400–500°C. Due to the coarseness of the carbides in the microstructure, softening of the sheet material was observed up to 400°C. The slight increase in the flexure observed in the sheet materials bent at 500°C was caused by secondary precipitation hardening.

A Phenomenological Mechanical Material Model for Precipitation Hardening Aluminium Alloys

Age hardening aluminium alloys obtain their strength by forming precipitates. This precipitation-hardened state is often the initial condition for short-term heat treatments, like welding processes or local laser heat treatment to produce tailored heat-treated profiles (THTP). During these heat treatments, the strength-increasing precipitates are dissolved depending on the maximum temperature and the material is softened in these areas. Depending on the temperature path, the mechanical properties differ between heating and cooling at the same temperature. To model this behavior, a phenomenological material model was developed based on the dissolution characteristics and experimental flow curves were developed depending on the current temperature and the maximum temperature. The dissolution characteristics were analyzed by calorimetry. The mechanical properties at different temperatures and peak temperatures were recorded by thermomechanical analysis. The usual phase transformation equations in the Finite Element Method (FEM) code, which were developed for phase transformation in steels, were used to develop a phenomenological model for the mechanical properties as a function of the relevant heat treatment parameters. This material model was implemented for aluminium alloy 6060 T4 in the finite element software LS-DYNA (Livermore Software Technology Corporation).

Finite element analysis of residual stress in 2.25Cr-1Mo steel pipe during welding and heat treatment process

The circumferential butt-welded pipe was fabricated using 2.25Cr-1Mo steel and then subjected to local post-weld heat treatment (LPWHT) for releasing residual stress after multi-pass welding. The sectioning method was employed to measure residual stress. Based on SYSWELD software, a thermo-metallurgical-mechanical coupled computational approach was developed to analyses the residual stress distribution on 2.25Cr-1Mo welded pipe. A three-dimensional finite element model and moving heat source model were employed in simulation. The effects of solid-state phase transformation (SSPT), tempering as well as creep were considered simultaneously. The effectivity of computational approach was verified by experimental measurement. The simulation results showed that SSPT could induce an undulating stress profile and large stress gradient in welded zone. The stress gradient could be reduced during LPWHT while there were stress peaks at the edges of heated region. Tempering effect could decrease the residual stress at high-stress region by material softening and yielding. Creep caused a global transformation from elastic strain to plastic strain, which led to a macro-scale stress relaxation. It is necessary to consider SSTP, tempering as well as creep in material model for more accurate simulation results.

Properties of Longitudinal Welded Steel Pipes for Piled Foundations Built under Cryolithic Zone Conditions

The mechanical properties of the base metal and the welded joints are estimated during tension, impact bending, drop weight tearing, static bending, flattening tests, and the Vickers hardness and the residual tangential stresses in them are determined for the longitudinal welded pipes 219–1020 mm in diameter and 8–12 mm in wall thickness manufactured by the AO Vyksunskii Metallurgical Plant. The hardness distribution over the pipe perimeter and the cross section is uniform and the cracking resistance of the pipes at negative temperatures up to –60°C is high. Local heat treatment of the welded seam and high-temperature tempering of the entire pipe ensure a high strength and high cold resistance of the pipes. The longitudinal pipes subjected to local and bulk heat treatment can be used like seamless pipes and as piles for the bases of buildings and structures erected in the cryolithic zone.

Electron Beam Welding, Heat Treatment and Hardening of Beta-Titanium

Analysis of the electron beam welding and different modes of heat treatment such as local heat treatment, furnace annealing, slow speed cooling, water quenching and aging impact on the structure and mechanical properties of pseudo-β titanium alloy VT19 welded joints. Microstructure of obtained welded joints in the states after welding and heat treatment were investigated. Using welded joints microsections approximate amount of β-phase has been obtained. Mechanical properties of the welded joints were analyzed and dependency of tensile strength and amount of β-phase were build.

Possibilities of Using a Local Heat Treatment to Produce New Precision Alloys

The possibilities of using a local heat treatment to produce gradient materials, which differ from common alloys by the presence of two or more macroscopic areas with fundamentally different physical or mechanical properties, is discussed. The method to produce gradient materials representing a ferromagnetic matrix, in which the paramagnetic areas are distributed according to a preset law, is described. The fields of practical application of such materials are discussed.