Strength Of Base Metal Research Articles

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Laser shrink fitting for shaft coupling was developed as application of laser forming. The coupling of the pipe of stainless steel and bar of carbon steel is made by laser shrink fitting. A bar is inserted into a pipe, and the pipe surface of the bar-inserted-part is irradiated and heated by 1kw class laser. Metallographic structure of the laser irradiated part of the pipe and bar is not changed. The fitted part of the pipe is shrunk in both circumferential and axial direction. The residual stress on the surface of the fitted pipe is a compressive one in the circumferential and axial direction. The tensile strength of the fitted part is nearly equal to the tensile strength of base metal of stainless steel pipe.

Determining Impact of Crack Width on the Repairing of Crack on the Surface of Carbon Steel by Welding Methods

If pipelines are damaged or fail to function normally, downstream units will stop operation, daily activities will be disrupted, or the process will shut down. Awareness of and knowing about the condition of pipelines in service as well as recognizing the cause of failure and then taking timely measures to makes appropriate changes can increase productivity. One of the appropriate measures is to repair the surface crack of steel pipelines using different welding methods. Two variables of crack width and crack depth are common in all the repair methods. In this research, the first variable is the crack width and other variables are considered the second variables. Thus, the effect of crack width on the repairing of steel surface crack is determined using two repairing methods including flame spraying fusion welding and magnetic induction diffusion welding. The test results of these two methods are analyzed and then compared using the Taguchi test design method with one factor at one level (one-factor ANOVA). Investigating and analysis of the results showed that the contribution of crack width variable in flame spraying fusion welding and magnetic induction diffusion welding methods is 10.14% and 18.37% to achieving the tensile strength of base metal and 66.20% and 51.94% to achieving relative elongation in the base metal, respectively. Thus, to achieve tensile strength in the base metal, studying the effect of crack width is not enough by itself in both methods; however, to achieve relative elongation of the base metal, the most effective variable is crack width.

Joint properties of ultra thin 430M2 ferritic stainless steel sheets by friction stir welding using pinless tool

In this study, friction stir butt welding of ultra thin 430M2 ferritic stainless steel sheets with satisfactory joint properties has been achieved using a pinless WC-Co tool. Friction stir welding was carried out at a tool rotational speed of 900rpm and a travel speed of 96mm/min. FSW joints were welded completely without any unwelded zone resulting from smooth material flow, despite of being adopted pinless tool. It was revealed that the maximum tensile strength of FSW welds was 468MPa, equivalent to the tensile strength of base metal. Notably, it was found that sigma phase formation in FSW welds is suppressed compared with that of arc welds, resulting in improving joint strength. These results suggest that the low input process of FSW is an effective substitute for the conventional fusion welding GTAW in ultra thin ferritic stainless steel plate.

High performance in base metal and CGHAZ for ferrite-pearlite steels

A method for improving mechanical properties of base metal and coarse-grained heat-affected zone (CGHAZ) in ferrite-pearlite steel was proposed. Two steels, with and without special addition of Ti, were fabricated for contrast experiments. Gleeble-3500 simulator was used to simulate CGHAZ. Microstructures were characterized by optical microscope (OM), scanning electron microscope (SEM) and transmission electron microscope (TEM). Tensile tests and Charpy impact tests were performed. Results show that nano-sized in-situ titanium oxides form in the melt. Compared with those of as-rolled steel without Ti addition, yield strength, elongation and toughness of as-rolled base metal with Ti addition are all promoted. During welding thermal simulation, the coarsened titanium oxides act as nucleation sites for acicular ferrite, which is favourable microstructure in CGHAZs. Toughness in CGHAZ of the steel with Ti addition is nearly ten times that in the CGHAZ of the contrast steel. Evolution of microstructures and mechanical properties was investigated and formation mechanism of titanium oxides was discussed.

Microstructural Evolution and Mechanical Properties of Simulated Heat-Affected Zones in Cast Precipitation-Hardened Stainless Steels 17-4 and 13-8+Mo

Cast precipitation-hardened (PH) stainless steels 17-4 and 13-8+Mo are used in applications that require a combination of high strength and moderate corrosion resistance. Many such applications require fabrication and/or casting repair by fusion welding. The purpose of this work is to develop an understanding of microstructural evolution and resultant mechanical properties of these materials when subjected to weld thermal cycles. Samples of each material were subjected to heat-affected zone (HAZ) thermal cycles in the solution-treated and aged condition (S-A-W condition) and solution-treated condition with a postweld thermal cycle age (S-W-A condition). Dilatometry was used to establish the onset of various phase transformation temperatures. Light optical microscopy (LOM), scanning electron microscopy (SEM), and energy dispersive spectrometry (EDS) were used to characterize the microstructures, and comparisons were made to gas metal arc welds that were heat treated in the same conditions. Tensile testing was also performed. MatCalc thermodynamic and kinetic modeling software was used to predict the evolution of copper (Cu)-rich body center cubic precipitates in 17-4 and β-NiAl precipitates in 13-8+Mo. The yield strength was lower in the simulated HAZ samples of both materials prepared in the S-A-W condition when compared to their respective base metals. Samples prepared in the S-W-A condition had higher and more uniform yield strengths for both materials. Significant changes were observed in the matrix microstructure of various HAZ regions depending on the peak temperature, and these microstructural changes were interpreted with the aid of dilatometry results, LOM, SEM, and EDS. Despite these significant changes to the matrix microstructure, the changes in mechanical properties appear to be governed primarily by the precipitation behavior. The decrease in strength in the HAZ samples prepared in the S-A-W condition was attributed to the dissolution of precipitates, which was supported by the MatCalc modeling results. MatCalc modeling results for samples in the S-W-A condition predicted uniform size of precipitates across all regions of the HAZ, and these predictions were supported by the observed trends in mechanical properties. Cross-weld tensile tests performed on GMA welds showed the same trends in mechanical behavior as the simulated HAZ samples. Welding in the S-W-A condition resulted in over 90 pct retention in yield strength when compared to base metal strengths. These findings indicate that welding these PH stainless steels in the solution-treated condition and using a postweld age will provide better and more uniform mechanical properties in the HAZ that are more consistent with the base metal properties.

Microstructural characteristics and mechanical properties of the dissimilar friction-stir butt welds between an Al–Mg alloy and A316L stainless steel

In this research, dissimilar butt joining of an Al–Mg alloy (AA5083) to austenitic stainless steel (A316L) by using friction-stir welding (FSW) process was examined. FSW parameters and joint design were optimized, owning to achieve the best joint strength. The processed FSWs at the optimized traverse speeds of 16, 20, and 25 mm/min with the sound surface appearance were considered for further cross-sectional investigations, microstructural characterizations, and mechanical testings. In situ reactions at the interface of Al–Mg alloy and stainless steel during FSW processes were studied by using field emission-scanning electron microscopy (FE-SEM) and line-scan energy-dispersive X-ray spectroscopy (EDS) analysis. As expected from the monitored thermal histories during FSW joining, the features indicating the formation of tunneling like defects were observed at low heat inputs (low w/v ratios). Moreover, some discontinuous thin intermetallic layers (with the thickness of ∼0.5 μm) were formed at the joint interface at the expressed processing conditions. Mechanical performances of the prepared dissimilar joints were assessed during transverse tensile loading and Vickers indentation micro-hardness testing. The joint strength ratio to the ultimate tensile strength (UTS) of the weakest base metal (BM) was improved up to ∼93 %, as all of the dissimilar FSWs failed from the Al–Mg base alloy, with a Vickers hardness enhancement of ∼460 % at the interface.

Upset Resistance Welding of Carbon Steel to Austenitic Stainless Steel Narrow Rods

Effects of welding current (at the range of 2-4 kA) on the microstructure and mechanical properties of upset resistance welds of AISI-1035 carbon steel to AISI-304L austenitic stainless steel rods were investigated. The results showed that the joint strength first increased by raising the welding current up to 3 kA and then decreased beyond it. Increasing trend was related to more plastic deformation, accelerated diffusion, reduction of defects and formation of mechanical locks at the joint interface. For currents more than 3 kA, decrease in the joint strength was mainly caused by formation of hot spots. Using the optimum welding current of 3 kA, tensile strength of the joint reached to ~76% of the carbon steel base metal strength. Microstructural observations and microhardness results confirmed that there was no hard phase, i.e., martensite or bainite, at the weld zone. Moreover, a fully austenitic transition layer related to carbon diffusion from carbon steel was observed at the weld interface.

Microstructural evolution and mechanical properties of Grades 23 and 24 creep strength enhanced ferritic steels

Grades 23 and 24 creep strength enhanced ferritic (CSEF) steels are relatively new materials that have been designed with improved high-temperature strength compared to conventional 2.25Cr–1Mo alloys. These new steels share alloying strategies that were used in the past for CrMo derivatives such as the CrMoV steels. Grades 23 and 24 are often grouped with similar CSEF steels in terms of mechanical properties and fabrication characteristics. However, recent experience indicates that these alloys require more unique care to ensure adequate properties for the intended service in both the base metal and welds. The differences in behaviour between these new steels and more conventional CrMo steels can be attributed to relatively minor variations in composition that lead to rather significant differences in microstructure. This review summarises technical information and practical experience on the manufacture and use of Grades 23 and 24 CSEF steels for power generation applications. Factors that influence the microstructure and strength of base metal are discussed for each alloy along with influences from common fabrication processes such as welding and bending. The results of this review provides manufacturers, fabricators and end users with information that can be applied to help ensure optimal performance of these steels in high-temperature applications associated with power generation.

Effect of welding parameters on the mechanical and microstructural properties of friction stir welded AA- 2014 joints

In this study, the effect of processing parameters on the mechanical and microstructural properties of aluminum AA2014-T6 joints produced by friction stir welding was analyzed. Friction stir welding was carried out on a milling machine. Different samples were produced by varying the tool rotational rates (700, 1000 rpm) and travel speeds (45-105 mm/min). Tensile tests performed at room temperature were used to evaluate the mechanical properties of the joints. In order to analyze the microstructural evolution of the material, the welds’ cross-sections were observed under optical microscope. The results shows that the resulting microstructure is free of defects and tensile strength of the welded joints is upto 75% of the base metal strength.

Evaluation on Fatigue Performance and Fracture Mechanism of Laser Welded TWIP Steel Joint Based on Evolution of Microstructure and Micromechanical Properties

The fatigue performance and fracture mechanism of laser welded twinning induced plasticity (TWIP.) steel joint were investigated experimentally based on the evolution of microstructure and micromechanical properties. The optical microscopy was used to analyze the evolution of microstructure. The variation of composition and phase structure of fusion zone were detected by energy dispersive X-ray and X-ray diffraction spectrometers. The micromechanical behaviors of the various zones were characterized using nanoindentation. The static tensile test and high cycle fatigue test were performed to evaluate the mechanical properties of welded joint and base metal. The microstructures, tensile properties and fatigue strength of base metal as well as welded metal were analyzed. The fatigue fracture surfaces of base metal and welded joint were observed by means of scanning electron microscopy, in order to identify fatigue crack initiation sites and propagation mechanisms. Moreover, the fatigue fracture characteristics and mechanisms for the laser welded TWIP steel joints were analyzed.

Progress in Creep-Resistant Steels for High Efficiency Coal-Fired Power Plants

Recent progress in creep-resistant bainitic, martensitic, and austenitic steels for high efficiency coal-fired power plants is comprehensively reviewed with emphasis on long-term creep strength and microstructure stability at grain boundaries (GBs). The creep strength enhanced ferritic (CSEF) steels, such as Grade 91 (9Cr–1Mo–0.2V–0.05Nb), Grade 92 (9Cr–0.5Mo–1.8W–VNb), and Grade 122 (11Cr–0.4Mo–2W–1CuVNb), can offer the highest potential to meet the required flexibility for ultra-supercritical (USC) power plants operating at around 600 °C, because of their smaller thermal expansion and larger thermal conductivity than austenitic steels and Ni base alloys. Further improvement of creep strength of martensitic 9 to 12Cr steels has been achieved by substituting a part or all of Mo with W and also by the addition of Co, V, Nb, and boron. A martensitic 9Cr–3W–3Co–VNb steel strengthened by boron and MX nitrides, designated MARBN, exhibits not only much higher creep strength of base metal than Grade 91, Grade 92, and Grade 122 but also substantially no degradation in creep strength due to type IV fracture in welded joints at 650 °C. High-strength bainitic 2.25 to 3Cr steels have been developed by enhancing solid solution hardening due to W and precipitation hardening due to (V,Nb)C carbides in bainitic microstructure. The improvement of creep strength of austenitic steels has been achieved by solid solution hardening due to the addition of Mo, W, and nitrogen and by precipitation hardening due to the formation of fine MX (M = Ti, Nb, X = C, N), NbCrN, M23C6, Cu phase, and Fe2(Mo,W) Laves phase. The boundary and sub-boundary hardening are shown to be the most important strengthening mechanism in creep of creep-resistant steels and is enhanced by fine dispersions of precipitates along boundaries.

Evaluation of the creep cavitation behavior in Grade 91 steels

Even in properly processed Grade 91 steel, the long term performance and creep rupture strength of base metal is below that predicted from a simple extrapolation of short term data. One of the mechanisms responsible for this reduction in strength is the development of creep voids. Importantly, nucleation, growth and inter linkage of voids under long term creep conditions also results in a significant loss of creep ductility. Thus, elongations to rupture of around 5% in 100,000 h are now considered normal for creep tests on many tempered martensitic steels. Similarly, creep damage development in the heat affected zones of welds results in low ductility cracking at times below the minimum expected life of base metal. In all cases, the relatively brittle behavior is directly a consequence of creep void development. Indeed, the results of component root cause analysis have shown that crack development in Grade 91 steel in-service components is also a result of the formation of creep voids. The present paper examines background on the nucleation and development of creep voids in 9%Cr type martensitic steels, presents information regarding methods which allow proper characterization of the creep voids and discusses factors affecting creep fracture behavior in tempered martensitic steels. It is apparent that the maximum zone of cavitation observed in Grade 91 steel welds occurred in a region in the heat affected zone which is ∼750 μm in width. This region corresponds to the band where the peak temperature during welding is in the range of ∼1150–920 °C.The cavity density in this band was over about 700 voids/mm2 at an estimated creep life fraction of ∼99%.

Microstructures and mechanical properties of flash butt welded high strength steel joints

Weld thermal cycles, microstructures and mechanical properties of flash butt welded RS590CL steel joints have been investigated. The results indicated that the weld thermal cycles are characterized by high peak temperatures and rapid heating and cooling rates, and the joints included the weld interface zone (WZ), coarse grain zone (CZ), fine grain zone (FZ) and partially recrystallized zone (PZ). The WZ and CZ consist mainly of coarsened upper bainite while the FZ has a fine equiaxed grain structure containing ferrite and pearlite with NbC precipitates. The WZ and CZ have higher hardness compared with the FZ, PZ and base metal. The joint strength (584-611MPa) can match the base metal strength (575–595MPa). The impact toughness of weld interface zone in the joints depends on welding parameters. The excessive flash allowance results in reducing the joint toughness. The reasons for the reduced joint toughness are related to the coarsened upper bainite, retained oxides and joining defects in the weld interface zone. The suitable combination of flash allowance (8–9mm), upset allowance (5.5–7.0mm) and upset pressure (123–160MPa) is beneficial for the improvement of joint toughness.

Joint properties of friction welded joint between 6061 Al alloy pipe and Al-Si12CuNi (AC8A) Al cast alloy pipe

This paper describes the joint properties of the friction welded joint between 6061 (AA6061) Al alloy pipe and Al-Si12CuNi (AC8A) Al cast alloy pipe. When joints were made with a friction pressure of 25 MPa, a friction speed of 27.5 rps, and a forge pressure of 30 MPa, the joint strength increased with increasing friction time, and it was approximately 40 % of the ultimate tensile strength of the AC8A base metal at a friction time of 2.0 s. However, all joints fractured at the weld interface between the AA6061 side and the AC8A side, which had an AC8A adhering to the weld interface on the AA6061 side (mixed-mode fracture). When joints were made at a friction time of 0.3 s with the same friction pressure and friction speed, the joint strength increased with increasing forge pressure, and it was approximately 60 % of the AC8A base metal at a forge pressure of 175 MPa. Many joints had the fracture at the AC8A side although one of the joints had at the mixed-mode fracture. On the other hand, when joints were made at friction times of 0.7 and 2.0 s, the joint strength was approximately 60 % of the AC8A base metal at a forge pressure of 75 MPa. Those joints fractured on the AC8A side, because the adjacent region of the weld interface was softened. In addition, the flash of the joint with a friction time of 0.7 s was fewer than that of 2.0 s. To obtain the joint with the fracture from the AC8A side, the joint should be made with the opportune friction time such as 0.7 s and the opportune forge pressure such as 75 MPa because this joint had no cracks at the weld interface.

Comparative Investigation of FSW and TIG Welded Joints of 7075-T6 Aluminum Alloy

The comparative microstructural and mechanical characteristics of fusion welds (Tungsten Inert Gas - TIG) and solid-state welds (Friction Stir Welding - FSW) of aluminum alloy 7075-T6 (AA7075-T6) are investigated in this paper. Microstructures of base metal and welded zones are analyzed by optical microscopy. The mechanical properties of welded joints are evaluated through hardness measurements and uniaxial tensile tests. The experimental results shown that the TIG welded joints are often cracked along the joins. The grain size grows in welded zone of TIG are dramatically coarser than that of FSW. Furthermore, comparison with the base metal, both the hardness and tensile strength in the welded TIG are reduced significantly in comparison with those in the FSW. Specifically, the tensile strength of the TIG and of the FSW welded joints is approximately 42% and 70% that of the base metal, respectively

Joining Mg alloys with Zn interlayer by novel ultrasonic-assisted transient liquid phase bonding method in air

A novel ultrasonic-assisted transient liquid phase bonding method was developed to joining magnesium alloys with Zn interlayer at 370°C in air. The influence of ultrasonic time on the microstructure and mechanical property of the joints was investigated. The introducing of ultrasonic into transient liquid phase bonding process showed benefit effects on inducing and promoting the eutectic reaction between Mg and Zn, and also accelerating the isothermal solidification process. The joint shear strength increased nonlinearly with the ultrasonic time lengthened and had a relationship with the thicknesses of the Mg51Zn20 and MgZn intermetallic compound layer, α-Mg(Zn) solid solution layer, and the total joint area. The highest average shear strength of the joints for 120s ultrasonic time reached to 106.4MPa, which was nearly equal to the strength of Mg base metal.

Microstructures and mechanical properties of metal inert-gas arc welded Mg–steel dissimilar joints

The joining of Mg alloy to steel was realized by metal inert-gas arc welding, and the weld thermal cycle characteristics and Mg–steel joints were investigated. The results show that the temperature distribution in the joints is uneven. Mg alloy welds present a fine equiaxed grain structure. There exists a transition layer consisting mainly of AlFe, AlFe3 and Mg(Fe, Al)2O4 phases at Mg/steel interface, and it is the weakest link in Mg–steel joints. The welding heat input and weld Al content have the significant effect on the joint strength. The joint strength increases with increasing the heat input from 1680 J/cm to 2093 J/cm, due to promoting Mg/steel interface reaction. When weld Al content is increased to 6.20%, the joint strength reaches 192 MPa, 80% of Mg alloy base metal strength. It is favorable to select the suitable welding heat input and weld Al content for improving joint strength.

Microstructural Properties and Four-Point Bend Fatigue Behavior of Ti-6.5Al-2Zr-1Mo-1V Welded Joints by Electron Beam Welding

Abstract With the help of a four-point-bend of fatigue rig, high-cycle fatigue tests were carried out on an Ti–6.5Al–2Zr-1Mo-1V titanium alloy at room temperature, 20 Hz and R = 0.1 in ambient air. The test results indicated that the fatigue strength of base metal, 888 MPa, is about 120% of yield strength. The fatigue strength of joints is 814 MPa. It is about 110% of yield strength of base metal. When the loading stress is higher, the fatigue failure region is located in middle weld zone of weld face, which the cracks are propagated along coarse β phase’s grain boundary. When the loading stress is lower, the fatigue failure region is located between the incomplete recrystallization zone and base metal. The crack nucleation resistance gradually increases from the WN to HAZ with the variable of loading stress and β phase (little α′ phases)→ α + β phase→ α phase.

Mechanical properties of TIG and EB weld joints of F82H

This work investigates mechanical properties of weld joints of a reduced activation ferritic/martensitic steel, F82H and effects of post weld heat treatment on the welds. Vickers hardness, tensile and Charpy impact tests were conducted on F82H weld joints prepared using tungsten-inert-gas and electron beam after various heat treatments. Although narrow groove tungsten-inert-gas welding reduced volume of weld bead, significant embrittlement was observed in a heat affected zone transformed due to heat input. Post weld heat treatment above 993K successfully moderated the brittle transformed region. The hardness of the brittle region strongly depends on the heat treatment temperature. Meanwhile, strength of base metal was slightly reduced by the treatment at temperature ranging from 993 to 1053K. Moreover, softening due to double welding was observed only in the weld metal, but negligible in base metal.

Joint properties of friction welded joint between pure magnesium and pure aluminium with post-weld heat treatment

Abstract The present paper described the investigation of the joint properties of friction welded joint between pure magnesium (CP-Mg) and pure aluminium (CP-Al) with post-weld heat treatment (PWHT). The joint in as-welded condition fractured from the adjacent region of the weld interface, although that had the same strength as the tensile strength of the CP-Al base metal. This joint had the intermediate layer (interlayer) consisting of intermetallic compound (IMC) on the weld interface, and its thickness was below approximately 1 μm. Most of joints subjected to PWHT autogenously fractured at IMC interlayer and that mainly occurred between Mg2Al3 and Mg17Al12 although those layers had a little each other at the fractured surfaces. The IMC interlayer grew to CP-Mg and CP-Al sides, and its thickness increased with increasing heating temperature and/or heating time. The main reasons for the autogenous fracture from the adjacent region of the weld interface of the joint were considered the growth of IMC interlayer of the joint during PWHT process. Furthermore, that fracture of the joint was thought the generating of the thermal stresses in the radial and/or circumferential directions during the cooling stage of PWHT process.