Microstructure Of Base Metal Research Articles

Investigations on metallurgical and mechanical properties of CO2 laser beam welded Alloy 825

ABSTRACTIn the research work, an attempt is made to join nickel-based alloy 825 by employing CO2 laser beam welding. Successful full penetration weld joint of a 5 mm thick plate is achieved with a very low heat input of 120 J-mm−1. Narrow weld bead width of 0.6 mm at the root and 1.6 mm at the cap is observed fusion zone; the interface and base metal microstructures have been examined using both optical and scanning electron microscopic techniques to understand the microstructural changes which have occurred due to laser welding. A range of tests of Vickers micro hardness, tensile and impact tests had been performed on the weldment to ascertain the mechanical properties of the joint. Tensile failure at the base metal and a 180° root bend test conducted on the weldment ascertain the soundness of the weld joint produced. An attempt is made to correlate the microstructure and mechanical properties of the weldment. Intermetallics TiN and Al4C3 observed in the SEM\\EDS analysis at the fusion zone are found to have improved the weld metal strength and hardness.

INFLUENCE OF HEAT TREATMENTS ON THE MICROSTRUCTURE OF WELDED API X70 PIPELINE STEEL

Welding is one of the most important technological processes used in many branches of industry such us industrial engineering, shipbuilding, pipeline fabrication among others. Generally, welding is the preferred joining method and most common steel are weldable. This investigation is a contribution to some scientific works which have been done on welding of low carbon steel. This work, presents some heat treatments were used to alter the microstructure of base metal (BM), heat affected zone (HAZ) and weld metal (WM) in the welded pipe steel of grade API X70. It presents the microstructures obtained after three heat treatments at 200°C, 400°C and 600°C for 30 min. Scanning electron microscopy and X-ray diffraction have been used as characterization techniques to observe the WM microstructures, in addition the Vickers hardness test are also achieved. The results revealed that the isothermal heat treatment caused grain growth and coarsening reactions in the weld zone and the hardness of weld joints decreased were the main transformations after increasing the temperature of the heat treatment.

Effect of heavy ion irradiation and α+β phase heat treatment on oxide of Zr-2.5Nb pressure tube material

Effect of heavy-ion irradiation on the crystalline phase transformation of oxide of Zr-2.5Nb alloys has been studied. The steam-autoclaved oxide of pressure tube is irradiated with 306 KeV Ar+9 ions at a dose of 3 × 1019 Ar+9/m2. The damage profile has been estimated using “Stopping and Range of Ions in Matter” computer program. The variation of the crystal structure along the depth of the irradiated oxide have been characterized non-destructively by Grazing Incidence X-ray Diffraction technique and compared with unirradiated-oxide. The effect of different base metal microstructures on the characteristic of oxide has also been studied. Base metal microstructure as well as the cross-sectional oxide have been characterized using transmission electron microscope. Heavy ion irradiation can significantly alter the distribution of phases in the oxide of the alloy. The difference in chemical state of alloying element has also been found between unirradiated-oxide with that of irradiated-oxide using X-ray photo electron spectroscopy. Chemical state of Nb in steam autoclaved oxide is also altered when the base metal is α + β heat treated.

An Experimental Study on Effect of T-Joint’s Root Gap on Welding Properties

The aimed of this research is to investigate the effect of T-Joint’s root gap on physical and mechanical properties of weld metal. Low carbon steel were joined in T-joint types using MIG (Metal Inert Gas) with variation of root gap. The root gap used were 0 mm, 3 mm and 6 mm. The physical properties examined with chemical composition, microstructure and corrosion using optical microscope. The mechanical properties were measured with respect to the strength and hardness using Universal testing machine and Vickers Microhardness. The results show that the highest value found in welds with a gap of 3 mm with a value of 163.57 MPa. Hardness value is directly proportional to the tensile strength of the material. The highest value found in welds with root gap of 3 mm, followed by root gap of 6 mm, and 0 mm Hardness values in the welding area is higher than the parent metal and HAZ because the number of Si, Mn and Cu elements in the welding metals are bigger than base metal. Weld with all variation of root gap have a good corrosion resistance because the corrosion rate in welds with various root gap have a value below 0.02 mmpy. Microstructure of weld metals were Accicular ferrite, Widmanstatten ferrite, and grain boundary ferrite, while microstructure of base metal and HAZ were ferrite and perlite.

Electron Beam Welding of High Strength Quenched and Tempered Steel

The paper deals with the investigation of microstructure and mechanical properties of electron beam welded joints of high strength steel grades S690QL and S960QL in quenched and tempered condition. The microstructure of base metal was composed of bainite and martensite mixture at hardness about 270HV10 and 340HV10 for the S690QL and S960QL steels, respectively. The weldment was composed of several characteristic subzones revealed on the transverse sections. The central region of the weldment consisted mainly of coarse columnar dendritic grains which perpendicular to the fusion zone boundary. The microstructure of the heataffected zone near the fusion line consisted mainly of martensite, however, in both steels the microstructure varied with the distance from the fusion line. The tensile strengths of welded joints were Rm=850 MPa (S690QL) and 1074MPa (S960QL) and corresponded the tensile strengths of the base materials.

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.

Oxidation behavior of binary Ti-xW (0 ≤ x ≤ 30, wt%) alloys at 650 °C as a function of W concentration

The role of composition on the oxidation behavior of the Ti-W system at 650°C was investigated utilizing a compositionally graded specimen, Ti-xW (0≤x≤30, all compositions in wt%). Microstructural evolution of the base material and thickness of the oxide layers were assessed as a function of composition. Some of the observations with regard to the evolved base metal microstructure, including: α lath and β rib/precipitates and lamellar structure, were found to be comparable to what is reported for Ti-Mo system. It was also shown that formation of a thinner oxide does not necessarily imply on the lower oxygen ingress.

Welding cooling rate effects on microstructure of an API 5l x100 steel

The aim of this work was to investigate the influence of five different cooling rates on properties of weld metal (WM) and heat affected zone (HAZ) of an API 5L X100 steel welded by GMAW. Bead on pipe (BOP) welds were made on 100x300 mm sections of a 15.8 mm thickness and 580 mm outside diameter API 5L X100 pipe, through five preheat temperatures (-30, 34, 100, 150 and 200 °C), aiming to obtain different cooling rates. Thermocouples were used to obtain the cooling time from 800 to 500 ºC (Δt8/5) during welding. The microstructures of base metal (BM) and HAZ were analyzed by light microscopy and scanning electron microscopy (SEM). Hardness measurements were made on the BOP welds in order to identify maximum and minimum values. As expected, due to the different cooling rates during welding, the distinct preheat temperatures have influenced the weld properties. Maximum and minimum HAZ microhardness, and weld metal hardness decrease as the preheat temperature increases. HAZ area, grain size of fine grained HAZ and coarse grained HAZ increase with increasing preheat temperature.

Effects of Root Opening on Physical and Mechanical Properties of the Double Side Welded of Ship Materials

The effects of root opening process parameters on the phisical and mechanical properties of mild steel specimens of grade LR Gr A having dimensions 200 mm× 100 mm× 12 mm, welded by gas metal arc welding were investigated. The variation of root opening that used were 3 mm, 5 mm and 7 mm. The physical properties examined with regard with microstructure, macrosructure, and corrosion using optical microscope and stereozoom. The measured of mechanical properties with regard to strength, hardness and toughness using, tensile test, Vickers hardness Test, and Charpy impact test. The test results show the base metal had a hardness of approximately 110 VHN and a maximum hardness of approximately 190 VHN that corellates with microstructure of weld metals. Microstructure of base metal and HAZ are ferite and perlite, while microstructure of weld zone are acicular ferrite and grain boundary ferrite. The corrosion rate of weld metals with various root opening categorized as materials having excellent corrosion resistance value. Welding joints with opening roots 3 mm and 5 mm can be used for construction. All welded specimens exhibited fracture at base metals

Microstructural Evolution and Wear Resistance of Friction Stir-Processed AISI 52100 Steel

Friction stir processing (FSP) was successfully applied on AISI 52100 steel. The influence of process parameters on the microstructure and mechanical properties of the material was evaluated. It was observed that the initial ferritic-pearlitic microstructure of the base metal is transformed to the martensitic microstructure with retained austenite in the stir zone. The results also showed that microhardness and wear resistance of the FSP samples are, respectively, at least 2 and 15 times higher than those of the base metal. The improvement of the mechanical properties of FSP samples was attributed to their microstructural characteristics. The mechanisms controlling the wear behavior of the base metal and FSP samples were also discussed.

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

Improving weldability of an advanced high strength steel by design of base metal microstructure

Cold rolled samples of a low carbon Mo–Ti–Nb microalloyed steel were subjected to simulated continuous annealing cycles using a Gleeble 3500 thermomechanical simulator to suitably optimize the base metal micro-constituents in order to improve weldability. The cycles, CR-1 and CR-2 were designed to assess the cooling rate effect (i) CR-1: 10°C/s–780°C(120s)–2°C/s-730°C–100°C/s, (ii) CR-2: 10°C/s–780°C(120s)–2°C/s–730°C–50°C/s], CR-1-T to assess the tempering effect [CR-1-T: 10°C/s–750°C(120s)–2°C/s–730°C–100°C/s–10°C/s–200°C/s (120s)–60°C/s] and B-1 and B-2, to assess the effect of bainite [B-1: 10°C/s–780°C(60s)–2°C/s–760°C–40°C/s–470°C/s (60s)–70°C/s and B-2: 10°C/s–780°C(120s)–2°C/s–760°C–20°C/s–470°C/s (60s)–10°C/s] on weldability of the steel. Dilatometric studies were conducted on a Gleeble 1500D to obtain the intercritical temperature regime (Ar1–Ar3) and the transformation temperatures for the low temperature transformation products. It was recorded that the cycle with 100°C/s cooling rate (CR-1) resulted in a weldment full of cracks at the (Mn–Fe)S interfaces. A cooling rate of 50°C/s (CR-2) caused cracks at the (Mn–Fe)S inclusions in the weld zone and the HAZ, and also softening of the heat affected zone (HAZ). The cracks generated by the CR-1 cycle could be completely avoided by introducing a short tempering cycle of 120s at 200°C to the CR-1 cycle (CR-1-T). CR-1-T cycle resulted in tempering of martensite (31% by volume) and precipitation of Ti–C in the ferrite that helped avoid the weldment cracks and retain the tensile properties close to that of the CR-1 cycle. B-1 cycle with a nominal presence of bainite in the ferritie-martensite structure resulted in cracks in the weldment. However, in B-2 cycle with the introduction of an optimized amount of bainite (37%) in a ferritic-martensitic matrix in association with Mo–C precipitation in ferrite, a crack-free weldment with improved tensile properties could be obtained. Among the studied thermal cycles, CR-1-T and B-2 manifested the best combination of weldability and tensile properties.

The effect of heat treatment on microstructure and tensile properties of cold spray Zr base metal glass/Cu composite

ZrCuAlNiTi metal glass (MG) powders were prepared by inert gas-atomization with a mean particle size of 40μm. Copper based composite with a 5% weight fraction of metallic glass powder were manufactured using cold spraying. Microhardness, tensile test (NOL ring samples) and tribology test were employed to characterize the corresponding deposits. The influence of the metallic glass particles (MG) addition and post heat treatment on the microstructure and mechanical properties of the composite was studied with a focus on the interaction between the matrix and the reinforcing particles. The composite exhibits higher tensile strength (about 366MPa) than pure copper in the as sprayed condition and also better elongation which increases from 3.0% to 6.6% following the addition of MG. A lower wear rate (0.62×10−5mm3/(N×m)) of the composite indicates that the MG particles allow improving the wear resistance.

Effects of Filler Compositions on Mechanical and Physical Properties of the Dissimilar Resistance Spot Welded between Aluminium Alloy and Carbon Steel

The resistance spot weld (RSW) of dissimilar materials betweeen steel and aluminium is generally more complex than that of similar materials due to the extreme differences in the mechanical, physical and chemical properties of the base metals. This study proposed the use of filler material to connect the differences of their properties. Al-Alloy 5083 with thickness of 4 mm and 1.2 mm thick carbon steel SS400 were joined in lap joint types using RSW with the filler materials. The filler materials were a mixture of steel and aluminium in which weight composition variations (Fe:Al) were 90:10; 70:30; 30:70 and 90:10 in percent. The physical properties were examined based on the microstructure using optical microscope while the mechanical properties were measured with respect to the strength and hardness using Universal Testing Machine and Vickers Microhardness respectively. Results showed that weld metals with filler composition of 70:30% had highest shear-strength. The microstructure examinations showed that Microstructure of base metal and HAZ carbon steel was ferrite and perlite while that of weld metal was bainite. There were no significant differences in the microstructures and the hardness of weld metal, HAZ, and the base metal of aluminium alloy-5083 due to nonheat-treatable material.

An Experimental Study of Microstructure and Mechanical Behavior of Alloy 625 Weld Overlay Deposited On ASTM A516 Grade 70

Background/Objectives: Surface modification for protection against corrosion is a critical field of research in the oil and gas industry. Alloy 625 is a superalloy with excellent resistance to pitting and corrosion. Methods/Statistical Analysis: Alloy 625 weld overlays were cladded through GTAW process on A516 carbon steel. The welding current ranging from 230 - 240 A the welding voltage 11 - 13 V; welding polarity EN (-). After welding, optical and SEM observations were conducted to determine the changes in the microstructure of base metal and clad. For examination of mechanical strength of claddings shear test was performed in accordance with ASTM A265 standard. Results: After Optical microscopy examinations, two different microstructures were observed in the HAZ zone. In the base metal, the grain size was reduced during the manufacturing process. The microstructure of weld metal was austenitic with dendritic structure. EDX observation showed that precipitates were mainly Niobium carbide (NbC). In the HAZ near the clad, microstructure included acicular ferrite, widmanstatten pattern, bainite, and pearlite. The tensile strength of a clad interface can be an important Consideration. For examination of mechanical strength of claddings shear test was performed in accordance with ASTM A265 standard. The minimum shear strength of different samples was 210 and 255 Mpa, which is higher than what it is stated in ASTM A265 standard. Conclusion/Application: The results showed that the manufacturing parameters in welding result in an appropriate mixing between base metal and clad material. The shear strength is higher than base metal and acceptable.

Research on Microstructure and Properties of Base Metal and Weld of Electron Beam Welding 0.30C-Cr-W Steel

Due to the difficulty of manufacturing complex small pieces ofthe new bearing steel0.30C-Cr-W with high-performance in the aviation industry, the electron beam welding process are usually used for preparing the complex parts.Thewelding performance of 0.30C-Cr-W steelwas calculated by theory and confirmedby actual experiments.The base metal was preheated,then welded and heattreated for weldments.The purpose of this work is to study the properties and the microstructure changes of base metal after heat treatment, weldments before heat treatment and weldments after heat treatment.The results show that the base metalafter heat treatment is sorbitic,weldzone of weldments after heat treatmentismartensite and austenite, theprecipitated M23C6 and M6C in latter (the weld zoneof weldmentsafter heat treatment) were more thanthe former (the base metalafter heat treatment), and the strengthof the latter is 23.4%lower than the former, theroom temperature impact absorbing energy and hardness of the latter increased 13.5% and 6.6%. It may be considered that0.30-C-Cr-W steel is not suitablefor welding by the theoretical calculations, but after reasonable preheat and post-weld heat treatment, the mechanical properties of the weld afterheat treatment can satisfy the requirements.

Nanoindentation for investigation of microstructural compositions in SM490 steel weld zone

Microstructural compositions in the weld zone of structural steel with 0.16wt.% C were investigated using optical microscopy and nanoindentation. Nine grid indentation experiments of 121 points were performed on different locations of three regions, base metal (BM), heat-affected zone (HAZ), and weld metal (WM) of the weld zone. The elastic modulus and hardness for each indenting point were then extracted from the nanoindentation results. Using the statistical analysis of 121 nanoindentation test results for each location, the microstructural compositions and the corresponding volume fractions of individual weld zone were investigated. Microstructures of BM, HAZ, and WM were observed using optical microscopy. The results showed that BM, HAZ, and WM are composed of three microstructural phases, low stiffness ferrite, high stiffness ferrite, and pearlite with different mechanical properties. The influence of the number of indenting points on the application of statistical analysis was also discussed.

Study on Welding-Seam Characteristics and Formation of Tailor-Welded Blanks with Big Unequal Thickness

170P1/DX54D+Z was a kind of laser-welding-tailored-blanks with unequal thickness. But it usually occurred poor welding seam especially when the thickness has an obvious difference. In this study, it was explored that the important influence factors of welding seam and formations based on the micro-hardness, microstructure testing and cupping experiment. The micro-hardness and microstructure of base metal，welding seam and heat affected zone (HAZ) has been observed. In addition, offset of welding seam and Erickson value was also measured. It was analyzed that the effect of the thickness difference and chemical compositions on welding seam and formation. It was stated that there were a great influence of thickness difference and chemical compositions on the properties of welding seam and formation.

Microstructural Changes Induced by Ultrashort Pulsed Lasers in Microdrilling of Fuel Nozzles

Microholes for gasoline direct injection (GDI) nozzles were obtained in martensitic stainless steel AISI 440C with conventional micro-EDM and two laser based processes: water-jet guided μs-laser and fs-laser. Since the analyzed drilling methods heavily differ for their thermal input on materials, the three processes were compared from the perspective of the microstructural changes induced in the bulk material after drilling. Moreover, the sharpness of the edges was taken into account as distinctive feature for a comparison among the three processes, being the spray atomization maximized by a cavitation process inside the microhole.A tailored procedure was optimized to prepare the samples for Scanning Electron Microscopy (SEM) and metallographic analyses. The cross sections of micro-EDM drilled samples revealed the presence of a recast (white) layer of 1-2μm in thickness even using the lowest spark energy in the tested range. Samples drilled by water-jet guided μs-laser are affected by the same phenomenon, with an even more pronounced effect. Moreover, they showed the extrusion of the melt material along the hole axis under the action of the water-jet conveying the beam. The extremely fast cooling of this layer also makes the machined surfaces prone to cracking. Conversely, metallographic analysis of cross sections of ultrashort pulsed laser drilled samples, showed no modification of the base metal microstructure in the sub-surface regions, thus testifying that the fs-pulsed laser drilling was an almost pure ablation process and not affected by a remarkable liquid phase as for the other two thermal processes. Periodicity and dimensions of laser induced periodic surface structures (LIPSS) generated by ultrashort pulsed laser were characterized by means of Scanning Electron Microscopy. SEM analysis of the microhole edges revealed burrs for the water-jet guided μs-laser while radii of 3-4μm for micro-EDM and less than 1μm for fs-lasers were measured.

Evolution of microstructure and mechanical properties of VVER-1000 RPV steels under re-irradiation

This is a comprehensive study of microstructure and mechanical properties evolution at re-irradiation after recovery annealing of VVER-1000 RPV weld and base metals as well as the effect of annealing on the microstructure and properties of base metal in the zone of the temperature gradient that is implemented during annealing using special heating device. It is shown that the level of radiation-induced microstructural changes under accelerated re-irradiation of weld and base metal is not higher than for the primary irradiation. Thus, we can predict that re-embrittlement of VVER-1000 RPV materials considering the flux effect will not exceed the typical embrittlement rate for the primary irradiation.