Carbon Steel Joints Research Articles

Contribution to Structural Integrity: Fatigue and Fracture Related Full Scale Experimental Investigations Carried Out at CSIR-SERC

CSIR - Structural Engineering Research Centre (CSIR-SERC), Chennai, has state-of-the-art facilities and expertise for carrying out R&D studies in the areas related to fatigue and fracture behaviour of structural components and materials. In the last 25 years, the laboratory has efficiently utilised the facilities and expertise available in serving various institutions and industries related to energy sector, automobile applications, railways, aerospace applications, construction industry etc. Fatigue and fracture studies have been carried out on steel tubular joints of offshore jacket platforms, carbon steel and stainless steel piping components used in power plants, automobile components (connecting rods, air springs, air suspension systems, industrial and automobile chains, stabiliser legs, hub brackets, sub-frames, rubber bushes, parallel link brackets etc.), tyre curing press, alumino-thermit and flash-butt welded rail joints used in Indian Railways, reinforcing bars (thermo-mechanically treated bars, corrosion resistant steel etc.), and many other components and materials. This paper describes some of the important investigations carried out in the Fatigue and Fracture Laboratory (FFL) of CSIR-SERC and presents some salient test results.

Estimation of Cooling Rate and Its Effect on Temperature Dependent Properties in GTA Welded High Carbon Steel Joints

An elaborate study has been conducted in this article to estimate the cooling rate of the Gas Tungsten arc (GTA) welded steel butt joints of grade AISI 1090. The temperature dependent thermal parameters has been investigated in connection with developed rate of cooling. Experiment has been carried out ffto determine the thermal cycle formed along the longitudinal direction from weld bead. Implementing experimental temperatures, Adams empirical cooling rate correlation has incorporated to analyze rate of cooling. A correlation has been suggested in this study, derived from thick plate temperature distribution model. To find out the heat loss from the joint, Vinokurov’s empirical combined heat transfer coefficient has been utilized and with it has verified with conventional heat transfer coefficient based on convection and radiation. Cooling rate has been found out to be very rapid at z = 36mm to z = 108mm based on thick plate model and it has completely agreed with the variation of Adams correlation. At higher temperatures above 800ºC, heat loss due to radiation completely dominates the convection and lower temperatures convection heat loss influences much than radiation. Heat loss due to convection and radiation fully justified with the results produced based on cooling rate and rapid cooling near the fusion boundary exists only for 5s-10s.

Image analysis of cracks in the weld metal of a wet welded steel joint by three dimensional (3D) X-ray microtomography

Hydrogen is readily available in underwater wet welds due to the dissociation of water at high temperatures. Low weld metal toughness and thermal contraction during cooling can lead to the nucleation of cracks, which seriously affect the mechanical properties of the weld. In this paper, X-ray microtomography (μCT) and image analysis (IA) were employed to image and measure crack length and morphology in the weld metal of a wet welded low carbon steel joint. The images were corrected for noise and illumination. The cracks were segmented and post-processed to correct for artifacts. Size and shape parameters were measured and showed a large average value for the Feret diameter (385μm) compared to average crack thickness (18μm). Three dimensional (3D) renderings of the detected cracks revealed a spatial distribution in which densely cracked regions are separated by layers of crack-free material. The combination of μCT and IA proved to be a powerful tool to characterize a complex defect system in 3D, providing information that cannot be obtained with traditional 2D microscopy techniques.

An Experimental Investigation on Spot Weld Growth on Dissimilar Joints of 304L Austenitic Stainless Steel and Medium Carbon Steel (Part 1)

Carbon steels and stainless steels are more frequently welded joints than any other materials because of their weldability characteristics. So the spot welded joining characteristic of these two materials are discussed in this paper. The experiment was conducted on medium carbon steel and 304L austenitic stainless by varying the process controlling parameters; such as welding current, welding time and electrode pressing force. As such two sets of data were collected to characterize the formation of spot weld using pneumatic based 75kVA spot welder. The first set was made for the variation of welding time and current whereas the second was made for the variation of welding current and electrode force. The welded specimens are finally underwent the tensile test, hardness test and metallurgical test to characterize the weld growth. The weld nugget growth was noticed for the welding current and weld time increment except the electrode force. By increasing the electrode force, the process resistances were reduced and consequently the weld nugget was reduced. Moreover the effect of heat imbalance was clearly noticed in the weld nuggets due to different electrical and chemical properties.

An Experimental Investigation on Spot Weld Growth on Dissimilar Joints of 304L Austenitic Stainless Steel and Medium Carbon Steel (Part 1)

Carbon steels and stainless steels are more frequently welded joints than any other materials because of their weldability characteristics. So the spot welded joining characteristic of these two materials are discussed in this paper. The experiment was conducted on medium carbon steel and 304L austenitic stainless by varying the process controlling parameters; such as welding current, welding time and electrode pressing force. As such two sets of data were collected to characterize the formation of spot weld using pneumatic based 75kVA spot welder. The first set was made for the variation of welding time and current whereas the second was made for the variation of welding current and electrode force. The welded specimens are finally underwent the tensile test, hardness test and metallurgical test to characterize the weld growth. The weld nugget growth was noticed for the welding current and weld time increment except the electrode force. By increasing the electrode force, the process resistances were reduced and consequently the weld nugget was reduced. Moreover the effect of heat imbalance was clearly noticed in the weld nuggets due to different electrical and chemical properties.

Butt Joining of Aluminum to Steel by Arc Brazing Process

Butt joining of aluminum alloy to carbon steel and stainless steel was conducted by using gas tungsten arc welding process with Zn-15%Al and Al-12%Si flux-cored filler wires, respectively. The microstructure and mechanical properties of the as-welded and post-weld heat treated joints were examined. Presetting 1.5 mm-wide welding gap can promote the wetting ability of molten filler metal on the faying surfaces, and then significantly enhance the joint strength. During tensile testing, the specimens from 5A02 Al/Q235 carbon steel joint fractured in Al base metal, but those from 5A02 Al/304 stainless steel joint fractured in the weld or through the interfacial layer. Hardening effect was observed in the heat-affected zone (HAZ).

Mechanical properties of SPCC low carbon steel joints prepared by metal inert gas welding

To better understand the fatigue and tensile properties of SPCC steels welded by metal inert gas welding, the mechanical properties of the welded component in several localized regions, e.g., weld metal, heat affected zone (HAZ) and base metal, were investigated. The tensile and fatigue properties of the weld metals were high compared to the other areas (base metal and HAZ) due to the precipitated Ti containing oxide inclusions in acicular ferrite (bainite). Two typical microstructures were mainly observed in the heat affected zones (HAZ): (i) bainite in a ferrite matrix (HAZ-B) and (ii) a ferrite phase with low internal stress (HAZ-A). The hardness of HAZ-B was higher than HAZ-A because of the partially formed bainite structure and precipitated Ti containing oxide inclusions. The mechanical properties of the weld sample were further investigated using test specimens that included all regions, i.e., weld metal, HAZ and base metal (BHW). The tensile and fatigue properties of the BHW sample were found to be lower than those in all other regions, which was influenced by the high internal stress. The mechanical properties were analyzed using microstructural and crystal characteristics, as examined by TEM and EBSD analysis. In addition, the fatigue strength can be precisely evaluated using a modified Goodman diagram.

Joining of 1100 Al Alloy to AISI 1045 Carbon Steel by Friction Stir Welding

Joining of dissimilar materials like Al alloy to carbon steel is attractive for industrial applications such as automotive industry. In this research, Friction Stir Welding (FSW) has been used to joint between dissimilar materials like 1100 Al alloys to AISI 1045 carbon steel. In this paper, the effect of rotational speed, feedrate and offset of tool are investigated on mechanical and metallurgical properties of the welding. The joints were evaluated by mechanical testing and metallurgical analysis. Metallurgical properties carried out by optical microscopy and Scanning Electron Microscopy (SEM) and mechanical properties conducted by the joint strength. Finally, optimum value of tool rotational speed and feedrate were obtained 710 rpm and 28 mm/min respectively and the best offset value of the tool obtained 1.5 mm in the Al alloy. Tensile strength properties of Al1100/1045 carbon steel joints were found to be approximately 20% lower than that of the Al 1100-H14 alloy base metal

接合自己完了型摩擦圧接した黄銅挿入材と軟鋼との継手における挿入材形状の検討

This paper describes the examination of the insert piece shape for the joint of a low carbon steel (LCS) fixed specimens using a brass insert piece by an autocompleting friction welding method, that method was developed by authors. The weld faying surface of the LCS specimen had a 10mm diameter, and the joint was made with a friction speed of 27.5rps (1650rpm) and a friction pressure of 90MPa. Then, the effect of the thickness and that at the bottom of the grooves (groove bottom thickness) for the brass insert piece on the joining phenomena and joint properties were investigated. The joint, which was made with an insert piece thickness of 4mm and a groove diameter of 11mm, had the circumferential shear fracture during the friction process at the groove bottom thickness of 0.95mm or below. However, some joints did not have the circumferential shear fracture although other joints had its fracture at a groove bottom thickness of 1.15mm or above. The joint efficiency of those joint had scatter, although that increased with increasing the groove bottom thickness and one of the joint had 100% joint efficiency at 1.45mm. That is, the joint, which had reliably the circumferential shear fracture with the 100% joint efficiency, was not obtained at an insert piece thickness of 4mm. To reliably obtain the joint which had the circumferential shear fracture with the 100% joint efficiency, the effect of the insert piece thickness was investigated. The joint efficiency increased with increasing insert piece thickness, and the scatter of that was decreased. When the joint was made with an insert piece thickness of 8mm and a groove diameter of 11mm, those had reliably the circumferential shear fracture with the 100% joint efficiency at the groove bottom thickness of 0.70 and 0.75mm. Also, when the joint was made with an insert piece thickness of 6mm and a groove diameter of 12mm, the joint had also reliably the circumferential shear fracture at the groove bottom thickness of 0.70mm. Therefore, a joint with 100% joint efficiency, which was made with the LCS with the brass insert piece, should be made with opportune brass insert piece shape of that thickness, the groove diameter, and the groove bottom thickness. In conclusion, a dissimilar joint was able to make by an autocompleting friction welding method.

金属樹脂直接レーザ接合法による低炭素鋼とアルミニウム合金との異種金属継手に関する研究

Dissimilar material joining is a key process in manufacturing multimaterial products. The objectives of this research is to produce and evaluate dissimilar metal joints of SPCD low carbon steel and A5052 aluminium alloy with sandwiching polyethylene terephthalate (PET) plastic for both joint strength and galvanic corrosion. Laser-Assisted Metal and Plastic (LAMP) joining method could produce the sandwich structure, owing to availability of either metal-side or plastic-side laser irradiation. The maximum tensile shear load achieved 5500 N in the obtained dissimilar metal joints of 30 mm width, where both the metal sheets were elongated. Typical Transmission Electron Microscope (TEM) pictures of the jointed areas demonstrate that the steel or the aluminum was tightly bonded to PET through each metal-oxide film in nanoscale size. Moreover, it was reveled that aluminum galvanic corrosion of the obtained joints was drastically suppressed in an immersion test using salt agar, compared with conventional laser welds of carbon steel and aluminum alloy.

Numerical Simulation of Residual Stresses in Single Pass Butt-Weld of Dissimilar Pipe Joint during the Fusion Welding Process

Dissimilar metal welded joints are widely used in engineering structures nowadays. Among the various types of material combinations, dissimilar welded joints of carbon steel and austenitic stainless steel are very common in shipbuilding, nuclear and chemical industries. In this study the finite element software MSC.Marc is employed to calculate the welding residual stresses in dissimilar butt-welded Q235 steel and 304 stainless steel pipes with different welding currents. The calculation results indicate that the welding residual stresses present asymmetric distribution, peaks of residual stresses on inner surface tend to be in 304 stainless side which can be significant higher than the yield stresses of parent metals. Changing in welding current does not have a significant effect on the peak of stress in weld center line.

210304 炭素鋼摩擦圧接継手の機械的性質に及ぼす摩擦過程の影響(OS15 生産加工3,オーガナイズド・セッション)

The effect of friction process include of initial contact process on mechanical properties of friction welded S35C carbon steel joint using a brake type friction welder was investigated. The faying surface of works were machined to turning and sawing. The burr and the heat affected zone were increased with increasing of initial contact pressure and friction time. Microstructures of the weld interface showed fine structure than that of the base metal, but the effect of welding conditions were small. The hardness of weld interface showed higher value than the base metal. The tensile strength of joint with faying surface specimen showed as same as base metal.

Fatigue behaviour of friction welded medium carbon steel and austenitic stainless steel dissimilar joints

This paper reports the fatigue behaviour of friction welded medium carbon steel–austenitic stainless steel (MCS–ASS) dissimilar joints. Commercial grade medium carbon steel rods of 12mm diameter and AISI 304 grade austenitic stainless steel rods of 12mm diameter were used to fabricate the joints. A constant speed, continuous drive friction welding machine was used to fabricate the joints. Fatigue life of the joints was evaluated conducting the experiments using rotary bending fatigue testing machine (R=−1). Applied stress vs. number of cycles to failure (S–N) curve was plotted for unnotched and notched specimens. Basquin constants, fatigue strength, fatigue notch factor and notch sensitivity factor were evaluated for the dissimilar joints. Fatigue strength of the joints is correlated with microstructure, microhardness and tensile properties of the joints.

Influence of heating source position and dilution rate in achieving overmatched dissimilar welded joints

The investigation addresses the overall performance of black and white joints (BWJ) of low carbon steel (LCS) and stainless steel thin sheets achieved by laser hybrid welding. Assuming that the structural integrity is directly influenced by the processing temperature, a thermal simulation of BWJ of thin sheets was developed. Afterwards, the base metals apportionment at joint formation, namely their distinct dilution rate, was originally estimated from the top surface temperature variation. Defect-free laser hybrid dissimilar welds were experimentally obtained using the selected filler metal and the energetic input from the process simulation, even for a critical analysed case of heat source displacement from the weld gap centreline towards LCS. Detailed macro and microstructural examination of the BWJ and related microhardness analysis results are presented. The tensile tests results indicate that in the case of transversally loaded BWJ, the positive difference in yield between the weld metal and the base materials protects the weld metal from being plastically deformed; the flat transverse tensile specimens loading up to failure reveals large strains in LCS, far away from the weld.

Analysis Method of Friction Torque and Weld Interface Temperature during Friction Process of Steel Friction Welding

This paper describes an analysis method of the friction torque and weld interface temperature during the friction process for steel friction welding. The joining mechanism model of the friction welding for the wear and seizure stages was constructed from the actual joining phenomena that were obtained by the experiment. The non-steady two-dimensional heat transfer analysis for the friction process was carried out by calculation with FEM code ANSYS. The contact pressure, heat generation quantity, and friction torque during the wear stage were calculated using the coefficient of friction, which was considered as the constant value. The thermal stress was included in the contact pressure. On the other hand, those values during the seizure stage were calculated by introducing the coefficient of seizure, which depended on the seizure temperature. The relationship between the seizure temperature and the relative speed at the weld interface in the seizure stage was determined using the experimental results. In addition, the contact pressure and heat generation quantity, which depended on the relative speed of the weld interface, were solved by taking the friction pressure, the relative speed and the yield strength of the base material into the computational conditions. The calculated friction torque and weld interface temperatures of a low carbon steel joint were equal to the experimental results when friction pressures were 30 and 90 MPa, friction speed was 27.5 s-1, and weld interface diameter was 12 mm. The calculation results of the initial peak torque and the elapsed time for initial peak torque were also equal to the experimental results under the same conditions. Furthermore, the calculation results of the initial peak torque and the elapsed time for initial peak torque at various friction pressures were equal to the experimental results.

Laser-roll welding of a dissimilar metal joint of low carbon steel to aluminium alloy using 2 kW fibre laser

Recently, lightening, speed-up and decreasing vibration of the transport vehicles have been discussed for improving of environmental problems. As one solution, the material hybrid concept using aluminum alloys and high strength steels has been proposed. Therefore, new welding processes by which these dissimilar materials can be joined in high reliability and productivity are demanded. Laser roll welding was developed for joining of dissimilar metals by M. Kutsuna, M. Rathod and A. Tsuboi in 2002. Up to now, a CO2 laser has been used as a heat source. In the present work, laser roll welding of low carbon steel and aluminum alloy using a 2 kW fibre laser was investigated to improve the joint properties due to the effective heating characteristics. Effects of the process parameters were studied. Otherwise, the influences of process parameters on the weldability, the formation of intermetallic compound layer and the mechanical properties have been investigated. As a result, various types of intermetallic compound layer were confirmed at the laser roll welded joint interfaces. When intermetallic compound layer thickness was less than 10 μm, the specimen was a failure in the base metal of low carbon steel in the tensile shear test.

Dissimilar friction stir spot welding of low carbon steel and Al–Mg alloy by formation of IMCs

Dissimilar lap joints of low carbon steel and Al–Mg alloy were obtained by friction stir spot welding. Mechanically mixed layer between top and bottom plates was not formed at the weld nugget due to the limited tool penetration and the pin height of welding tool lower than the thickness of Al plate laid in top side. These welding conditions made it possible to weld steel plate using welding tools made out of a general tool steel. With increasing tool penetration depth (TPD), tensile shear force of joint increased and maximum value of 3·0 kN was obtained at the TPD of 0·5 mm, but excessive tool penetration beyond 0·5 mm was caused in a deformation of Al plate of top side. In the result of interface observation, interaction layer was formed between Fe and Al alloy, which was constituted by various intermetallic compounds (IMCs). Consequently, the size of strongly bonded area containing Fe3Al and Fe4Al13 IMCs increased with TPD, which resulted in the increase in joint strength under the limited TPD.

Comparative responses of welded joints to surface mechanical attrition treatment and shot peening

Responses of welded joint of carbon steel to surface mechanical attrition treatment (SMAT) and shot peening (SP) were investigated. Experimental evidences showed that the microstructure of treated surface in the welded joint by means of SMAT was characterised by nanometre grains of about 13·6 nm in size and that of SP was characterised by highly dense dislocation configuration. The similar microhardness profiles with different peak values in the top surface were observed for three typical zones of welded joints processed by SMAT and SP. Compared with as welded specimens, SMAT and SP processes have improved the fatigue strength by as much as 61 and 36·3% respectively based on fatigue life 2×106 cycles. The observed enhanced fatigue behaviours of the welded joint processed by SMAT and SP should be attributed to the combined influences of compressive residual stress, work hardening, nanostructure and elimination of microdiscontinuities in the vicinity of welded joints.

Mechanical Properties of Friction Stir Welded Carbon Steel Joints — Friction Stir Welding with and without Transformation

Low temperature friction stir welding (including below A1 point) was successful for three types of carbon steels with different carbon contents (IF steel, S12C, S35C). For all the carbon steels, the strength of the FSW joints increased when compared to that of the normal structure (ferrite + pearlite) of base metal. Compared with IF steel, the microstructures and mechanical properties of the carbon steel joints are significantly affected by the welding conditions due to the phase transformations. For the S12C steel, the welding produces a ferrite-pearlite structure, and the strength slightly increases with the increasing welding speed (decreasing the heat input) due to the refined microstructure. For the S35C steel, under the conditions exceeding the lower critical cooling rate, martensite was formed, resulting in a significantly increased joint strength; while under the conditions when martensite is not formed, the strength of the joint increased with the increasing welding speed (decreasing the heat input) due to the refined microstructures. Thus, friction stir welding enables us to control both the maximum temperature and the cooling rate in order to produce higher strength joints.

Investigation of the mechanical properties and microstructure of friction welded joints between AISI 4140 and AISI 1050 steels

Joining of dissimilar metals is one of the most essential needs of industries. Manufacturing with joint of alloy steel and normal carbon steel is used in production, because it decreases raw material cost. In this study, joining of AISI 4140 steel (medium carbon and low alloy steel) and AISI 1050 steel (medium carbon steel) was successfully achieved. Mechanical properties, macro and micro structural investigation of materials joined with this process were completed; joint strength was tested and optimum welding parameters were obtained. Moreover, temperature change of the weld zone was measured with an infrared temperature measurement device during welding; and the effects of the friction welding parameters on welding zone temperature were investigated. The highest tensile strength acquired in the welded specimens is 6% higher than parent AISI 1050 steel and the lowest tensile strength obtained was 1.9% lower than the parent AISI 1050 steel.