Study on the Compressive Stress Retention in Quenched Cam of 100Cr6 Steel Based on Coupled Thermomechanical and Metallurgical Modeling

The assembled camshaft has obvious advantages in material optimization and flexible manufacturing. As the most important surface modification technique, the heat treatment process is utilized in this work to promote the desired compressive residual stress on the near-surface of the 100Cr6 steel assembled cam. The Johnson-Mehl-Avrami equation and Koistinen-Marbuger law are integrated into the ABAQUS software via user subroutines to simulate the evolution of diffusional transformation and diffusionless transformation, respectively. The linear mixture law is used for describing the coupled thermomechanical and metallurgical behaviors in the quenching of steel cam. The influences of various quenchants and the probable maximum phase volume fractions on surface residual stress or hardness are analyzed. Results show that a greater amount of martensite volume fraction and a slower martensitic transformation rate are beneficial for the compressive stress retention. Compared with the conventional quenching oil, the fast oil quenched cam surface has higher final compressive stress and hardness.     

Optimization of Electron Beam Welding Joint of Water-Cooled Ceramic Breeder Blanket

The water-cooled ceramic breeder (WCCB) blanket is a component of the China Fusion Engineering Test Reactor (CFETR). The Reduced Activation Ferrite/Martensite (RAFM) steels are the preferred structural materials for WCCB blanket. As a kind of RAFM steels, China low activation martensitic (CLAM) steel was welded by electron beam welding (EBW), and then quenched-tempered treatment was carried out. The results show that at the welding state, the welding seam was composed of large martensite and δ ferrite and the organization of the heat-affected zone (HAZ) was changed slightly with the different heat input. Moreover, the hardness of welded joints was higher than that of base material (BM), but the impact toughness was very low. After quenched-tempered treatment, the δ ferrite in the weld was eliminated, the residual stress of the test plate decreased as a whole, and the mechanical properties were improved significantly.     

Controlling Welding Residual Stress and Distortion of High-Strength Aluminum Alloy Thin Plates by a Trailing Hybrid High-Speed Gas Fluid Field

This paper presents an investigation of the welding residual stress and distortion of LY12 high-strength aluminum alloy (6061) by improving the local welding thermal and mechanical fields. A trailing hybrid high-speed gas fluid method was proposed and applied to decrease the welding residual stress and distortion of 6061 aluminum alloy efficiently. Firstly, the temperature and stress fields were calculated using the finite element simulation method, considering a trailing hybrid high-speed gas fluid field. The distance between the aerodynamic load and the heat source action was a key factor determined by the simulation method. In addition, the reasonable effective range of gas pressure was obtained. Subsequently, welding and distortion tests were conducted on the self-developed device under conventional welding and high-speed gas fluid field conditions. The results showed that an aerodynamic load under 30 MPa of gas pressure was available near the area at a distance of 20–28 mm from the heat source for thin plate welding distortion. The peak longitudinal residual tensile stresses in the weld’s mid-length section decreased by 77.73%, the peak residual compressive stresses decreased by 69.23% compared with conventional welding, and the deflection distortion disappeared almost entirely. The maximum deflection of the distortion was only 1.79 mm, which was 83.76% lower than the 11.02 mm of the conventional welding distortion. This validates that the method can simultaneously and greatly eliminate the welding residual stress and distortion.     

Low-Energy Pulsed-Laser Welding as a Root Pass in a GMAW Joint: An Investigation on the Microstructure and Mechanical Properties

Root pass is a fundamental step in multi-pass welding. In gas metal arc welding (GMAW), the weld bead qualities depend on the process parameters, filler materials, and welder abilities. This work investigates the effect of a Nd: YAG pulsed laser as a first pass to reduce the welders’ reliance on the AH36 low-alloy steel with 5.5 mm thickness. This autogenous automatable process delivers reduced thermal impact due to the concentrated high-energy source, pulse overlap, and higher penetration depth-to-power ratio than continuous lasers. The outcomes indicate that the PL as a root welding generated a small HAZ compared to the GMAW condition. In addition, the subsequent arc passes positively affected the microstructure, reducing the hardness from around 500 to 230 HV. The PL + GMAW achieved similar strength results to the GMAW, although its Charpy impact values at −50 °C were around 15% lower than the arc condition.     

Prediction of HAZ Microstructure and Hardness for Q960E Joints Welded by Triple-Wire GMAW Based on Thermal and Numerical Simulation

Since heat affected zone (HAZ) is the weak area of welded joints, this article proposes a method to predict the HAZ microstructure and hardness for the triple-wire gas metal arc welding (GMAW) process of Q960E high strength steel. This method combines welding thermal simulation and numerical simulation. The microstructures and hardness of Q960E steel under different cooling rates were obtained by thermal simulation and presented in a simulated HAZ continuous cooling transformation (SH-CCT) diagram. The cooling rate in HAZ were obtained by numerical simulation with ANSYS software for the triple-wire welding of Q960E thick plates. By comparing the cooling rate with the SH-CCT diagram, the microstructure and hardness of the HAZ coarse-grained region were accurately predicted for multiple heat input conditions. Further, an ideal heat input was chosen by checking the prediction results. This prediction method not only helps us to optimize the welding parameters, but also leads to an overall understanding of the process-microstructure-performance for a complex welding process.     

The Effect of Shot Peening on Residual Stress and Surface Roughness of AMS 5504 Stainless Steel Joints Welded Using the TIG Method

This article presents the influence of the Shot Peening (SP) process on residual stress and surface roughness of AMS 5504 joints welded using the Tungsten Inert Gas (TIG) method. Thin-walled steel structures are widely used in the aviation and automotive industries, among others. Unfortunately, the fatigue properties become worse during the welding process. Samples of 1 mm-thick AMS 5504 steel plates were first prepared using TIG welding and then strengthened by the Shot Peening (SP) process. The technological parameters of the SP process were changed in the range of time t from 2 min to 4 min and of pressure p from 0.4 MPa to 0.6 Mpa. The residual stresses were measured by X-ray diffraction in three zones: fusion zone (FZ), heat-affected zone (HAZ) and base metal (BM). The results showed that SP introduced compressive residual stresses in all of the zones measured, especially in the FZ. The greatest value of compressive residual stresses σ = −609 MPa in the FZ was observed for the maximum parameters of SP (p = 0.6 MPa, t = 4 min). The increase in value of residual stress is about 580% when compared to welding specimens without treatment. As a result of shot peening in the FZ, the mean roughness value Ra decreased in range 63.07% to 77.67% in the FZ, while in the BM increased in range 236.87% to 352.78% in comparison to specimen without treatment. Selected surface roughness parameters in FZ and BM were analyzed using neural networks. In FZ, it was demonstrated that the most correlated parameters with residual stresses are Rt and Rsk. On the other hand, in the BM zone, the most correlated parameters were Rv, Rt and Rq. This enables the estimation of stresses in the welded joint after SP on the basis of selected roughness parameters.     

High-Power Fiber Laser Welding of High-Strength AA7075-T6 Aluminum Alloy Welds for Mechanical Properties Research

The results disclosed that both the microstructure and mechanical properties of AA7075-T6 laser welds are considerably influenced by the heat input. In comparison with high heat input (arc welding), a smaller weld fusion zone with a finer dendrite arm spacing, limited loss of alloying elements, less intergranular segregation, and reduced residual tensile stress was obtained using low heat input. This resulted in a lower tendency of porosity and hot cracking, which improved the welded metal’s soundness. Subsequently, higher hardness as well as higher tensile strength for the welded joint was obtained with lower heat input. A welded joint with better mechanical properties and less mechanical discrepancy is important for better productivity. The implemented high-power fiber laser has enabled the production of a low heat input welded joint using a high welding speed, which is of considerable importance for minimizing not only the fusion zone size but also the deterioration of its properties. In other words, high-power fiber laser welding is a viable solution for recovering the mechanical properties of the high-strength AA 7075-T6 welds. These results are encouraging to build upon for further improvement of the mechanical properties to be comparable with the base metal.     

Characteristics of Impulse Carburization LPC Process

In the present work, Pyrowear53 steel was subjected to the impulse carburizing LPC process. After carburation, the material was quenched and tempered. Postprocessing analyses included the measurement of hardness, carbon content, residual austenite, and residual stresses. The results revealed that the thermochemical treatment resulted in the formation of an approximately 1200 µm wide carburized layer. The results of hardness, carbon content, and residual austenite measurement showed a continuous gradient (drop) in the measured values within the carburized layer. However, the results of residual stresses revealed the existence of a local extremum, namely, a zone with higher compressive stresses at the depth between 600 and 1000 µm. This was explained by a different temperature for initiation of martensite transformation as a function of carbon content. This difference resulted in the occurrence of two martensite expansion fronts at two different depths, resulting in an increase in compressive stresses at the noted depth range. Moreover, it was concluded that this region was present for material containing between 0.8 and 0.4 wt% carbon for Pyrowear53.     

Effect of Laser Peening on Microstructural Changes in GTA-Welded 304L Stainless Steel

The introduction of tensile residual stress has led to the induction of damage such as fatigue, corrosion fatigue, and stress corrosion cracking (SCC) in stainless steel in association with the influence of environments, components, surface defects, and corrosive factors during its use. Compressive residual stress can be achieved through various techniques. Among several methods, laser peening can be more attractive as it creates regularity on the surface with a high-quality surface finish. However, there is very little research on heavily peened surface and cross-section of stainless steel with very deep compressive residual stress. This work focused on welding and laser peening and the influence of Al coating on the microstructural changes in 304L stainless steel. The specimen obtained by laser peening had a very deep compressive residual stress of over 1 mm and was evaluated based on microstructural and hardness analysis. Therefore, a model for microstructural change by laser peening on welded 304L stainless steel was proposed.     

Double Pulse Resistance Spot Welding of Dual Phase Steel: Parametric Study on Microstructure,Failure Mode and Low Dynamic Tensile Shear Properties

Resistance spot welding (RSW) of dual phase (DP) steels is a challenging task due to formation of brittle martensitic structure in the fusion zone (FZ), resulting in a low energy capacity of the joint during high-rate loading. In the present study, in situ postweld heat treatment (PWHT) was carried out by employing a double pulse welding scheme with the aim of improving the mechanical performance of DP590 steel resistance spot weld joint. Taguchi method was used to optimize in situ PWHT parameters to obtain maximum peak load and failure energy. Experiments were designed based on orthogonal array (OA) L16. Mechanical performance was evaluated in terms of peak load and failure energy after performing low dynamic tensile shear (TS) test. Microstructural characterization was carried out using a scanning electron microscope (SEM). The results show that improvements of 17 and 86% in peak load and failure energy, respectively, were achieved in double-pulse welding (DPW) at optimum conditions compared to traditional single-pulse welding (SPW). The improvement in mechanical performance resulted from (i) enlargement of the FZ and (ii) improved weld toughness due to tempering of martensite in the FZ and subcritical heat affected zone (SCHAZ). These factors are influenced by heat input, which in turn depends upon in situ PWHT parameters.     

Quantification of Residual Stress Relief by Heat Treatments in Austenitic Cladded Layers

The effect of the heat treatment on the residual stresses of welded cladded steel samples is analyzed in this study. The residual stresses across the plate’s square sections were determined using complementary methods; applying diffraction with neutron radiation and mechanically using the contour method. The analysis of the large coarse grain austenitic cladded layers, at the feasibility limits of diffraction methods, was only made possible by applying both methods. The samples are composed of steel plates, coated on one of the faces with stainless steel filler metals, this coating process, usually known as cladding, was carried out by submerged arc welding. After cladding, the samples were submitted to two different heat treatments with dissimilar parameters: one at a temperature of 620 °C maintained for 1 h and, the second at 540 °C, for ten hours. There was some difference in residual stresses measured by the two techniques along the surface of the coating in the as-welded state, although they are similar at the welding interface and in the heat-affected zone. The results also show that there is a residual stress relaxation for both heat-treated samples. The heat treatment carried out at a higher temperature showed sometimes more than 50% reduction in the initial residual stress values and has the advantage of being less time consuming, giving it an industrial advantage and making it more viable economically.     

Experimental Investigation and Parametric Optimization of the Tungsten Inert Gas Welding Process Parameters of Dissimilar Metals

Special attention is required when joining two materials with distinct chemical, physical and thermal properties in order to make the joint bond robust and rigid. The goal of this study was to see how significantly different tungsten inert gas (TIG) welding process parameters (welding current, gas flow rate, root gap, and filler materials) affect mechanical properties (tensile, hardness, and flexural strength), as well as the bead width and microstructural properties, of dissimilar welds In comparison to SS 316 and AISI 1020 low-carbon steel. TIG welding parameters were optimized in this study using a Taguchi-based desirability function analysis (DFA). From the experimental results, it was observed that welded samples employing ER-309L filler wires had a microstructure consisting of a delta ferrite network in an austenite matrix. The tensile strength experimental results revealed that welding current, followed by GFR, was a highly influential parameter on tensile strength. Weld metals had higher hardness and flexural strength than stainless steel and carbon steel base metals. This was supported by the fact that the results of our tests had hardness ratings greater than a base for the FZ and HAZ, and that no crack was observed in the weld metal following U-shape flexural bending. Welding current has a significant impact on the bead width of welded specimens, followed by root gap. Furthermore, the dissimilar welded sample responses were optimized with a composite desirability percentage improvement of 22.90% by using a parametric setting of (A2B4C4D2). Finally, the validation of the experiment was validated by our confirmation test results, which agreed with the predictive optimum parameter settings.     

Effective Range of FSSW Parameters for High Load-Carrying Capacity of Dissimilar Steel A283M-C/Brass CuZn40 Joints

In the current study, a 2 mm thick low-carbon steel sheet (A283M—Grade C) was joined with a brass sheet (CuZn40) of 1 mm thickness using friction stir spot welding (FSSW). Different welding parameters including rotational speeds of 1000, 1250, and 1500 rpm, and dwell times of 5, 10, 20, and 30 s were applied to explore the effective range of parameters to have FSSW joints with high load-carrying capacity. The joint quality of the friction stir spot-welded (FSSWed) dissimilar materials was evaluated via visual examination, tensile lap shear test, hardness test, and macro- and microstructural investigation using SEM. Moreover, EDS analysis was applied to examine the mixing at the interfaces of the dissimilar materials. Heat input calculation for the FSSW of steel–brass was found to be linearly proportional with the number of revolutions per spot joint, with maximum heat input obtained of 11 kJ at the number of revolutions of 500. The temperature measurement during FSSW showed agreement with the heat input dependence on the number of revolution. However, at the same revolutions of 500, it was found that the higher rotation speed of 1500 rpm resulted in higher temperature of 583 °C compared to 535 °C at rotation speed of 1000 rpm. This implies the significant effect for the rotation speed in the increase of temperature. The macro investigations of the friction stir spot-welded joints transverse sections showed sound joints at the different investigated parameters with significant joint ligament between the steel and brass. FSSW of steel/brass joints with a number of revolutions ranging between 250 to 500 revolutions per spot at appropriate tool speed range (1000–1500 rpm) produces joints with high load-carrying capacity from 4 kN to 7.5 kN. The hardness showed an increase in the carbon steel (lower sheet) with maximum of 248 HV and an increase of brass hardness at mixed interface between brass and steel with significant reduction in the stir zone hardness. Microstructural investigation of the joint zone showed mechanical mixing between steel and brass with the steel extruded from the lower sheet into the upper brass sheet.     

Mechanical Properties and Microstructural Characterization of Laser Welded S32520 Duplex Stainless Steel

This paper investigates an experimental design of laser butt welding of S32520 duplex stainless steel, which has been passed out with the help of a pulsed Nd: YAG laser supply. The intention of the present research is to learn the impact of beam diameter, welding speed, and laser power on the superiority of the butt weld. The individuality of butt joints has been characterized in terms of tensile properties, fractography, and hardness. It was noticed that unbalanced particle orientations indirectly produce a comparatively fragile quality in the laser welded joint. The outcome of varying process parameters and interaction effect of process parameters on ultimate tensile strength and micro hardness were studied through analysis of experimental data. With different process parameters, the heat energy delivered to the material was changed, which was reflected in tensile strength measurement for different welded samples. From this present research, it was shown that, up to a certain level, an increase in process parameters amplified the tensile strength, but after that, certain level tensile strength decreased with the increase in process parameters. When process parameters exceeded that certain level, the required amount of heat energy was not delivered to the material, resulting in low bead width and less penetration, thus producing less strength in the welded joint. Less strength leads to more ductile weld joints. Microhardness was higher in the weld zone than in the base region of welded samples. However, the heat affected zone had a high microhardness range.     

Experimental Study on Bead on Plate (BOP) Welding of 6 mm Thick 9% Nickel Steel by Fiber Laser Welding

Nine percent nickel steel has excellent properties in a cryogenic environment, so it has recently been used as a tank material for most LNG fuel-powered ships. However, 9% nickel steel causes arc deflection due to its tendency of magnetization during manual FCAW welding and the currently used filler metal is 10–25 times more expensive as a base metal compared to other materials, depending on manufacturers. Furthermore, the properties of its filler metal cause limitation in the welding position. To overcome these disadvantages, in this study, the tendency of penetration shape was analyzed through a fiber laser Bead on Plate (BOP) welding for 9% nickel steel with a thickness of 6 mm and a range of welding conditions for 1-pass laser butt welding of 6 mm thick 9% nickel steel with I-Groove were derived. Through this study, basic data capable of deriving optimal conditions for laser butt welding of 9% nickel steel with a thickness of 6 mm were obtained.     

Effect of Heat Input on the Ballistic Performance of Armor Steel Weldments

The purpose of this study is to examine the projectile penetration resistance of the base metal and heat-affected zones of armor steel weldments. To ensure the proper quality of armor steel welded joints and associated ballistic protection, it is important to find the optimum heat input for armor steel welding. A total of two armor steel weldments made at heat inputs of 1.29 kJ/mm and 1.55 kJ/mm were tested for ballistic protection performance. The GMAW welding carried out employing a robot-controlled process. Owing to a higher ballistic limit, the heat-affected zone (HAZ) of the 1.29 kJ/mm weldment was found to be more resistant to projectile penetration than that of the 1.55 kJ/mm weldment. The ballistic performance of the weldments was determined by analyzing the microstructure of weldment heat-affected zones, the hardness gradients across the weldments and the thermal history of the welding heat inputs considered. The result showed that the ballistic resistance of heat affected zone exist as the heat input was decreased on 1.29 kJ/mm. It was found that 1.55 kJ/mm does not have ballistic resistance.     

Application of a New Alloy and Post Processing Procedures for Laser Cladding Repairs on Hypereutectoid Rail Components

The development of a laser cladding repair strategy is critical for the continued growth of heavy-haul railway networks. Premium hypereutectoid rails have undergone laser cladding using a new martensitic stainless-steel alloy, 415SS, developed for high carbon rails after standard cladding metals were found to be incompatible. Non-destructive neutron diffraction techniques were used to measure the residual stress in different layers generated across a dissimilar metal joint during laser cladding. The internal stress distribution across the cladding, heat-affected zone (HAZ), and substrate was measured in the untempered rail, after 350 °C and 540 °C heat treatment procedures and two surface grinding operations. The martensitic 415SS depositions produce compressive stress in the cladding, regardless of tempering procedures, which may inhibit fatigue crack propagation whilst grinding operations locally relive surface stress. Balancing tensile stresses were recorded below the fusion boundary in the HAZ due to thermal gradients altering the microstructure. The combination of 540 °C tempering and 0.5 mm surface layer removal produced a desirable combination of compression in the cladding deposition with significantly reduced tensile stresses in the HAZ. A comparison with the current literature shows that this alloy achieves a unique combination of desirable hardness, low tensile stress, and compression in the cladding layer. Data obtained during strain scanning has been used to determine the location of microstructural changes at the fusion boundary and HAZ through correlation of the stress, strain, full width at half maximum (FWHM), and intensity profiles. Therefore, neutron diffraction can be used for both the accurate measurement of internal residual stress and to obtain microstructural information of a metallurgical join non-destructively.     

Effect of 580 °C (20 h) Heat Treatment on Mechanical Properties of 25Cr2NiMo1V Rotor-Welded Joints of Oscillating Arc (MAG) Narrow Gap Thick Steel

The thick plate narrow gap welding of 25Cr2NiMo1V rotor steel is achieved by metal active gas arc welding, in which the weld gap was 18.04–19.9 mm. After welding, the weldment was heat treated at 580 °C (20 h). The impact and tensile properties in the as-welded and heat-treated were studied. The results show that after heat treatment, the coarse carbides in the center of the weld were transformed into fine granular carbides distributed along the grain boundaries, and the quantity of carbide precipitates in the weld near the fusion line was reduced. The tensile fracture mode changed from a ductile fracture to a combination of brittle and ductile fractures, and the tensile strength of the weld metal changed from 605 MPa to 543 MPa. After heat-treated, the radiation zone of the weld center changed from a brittle fracture to a combination of brittle and ductile fractures, and the impact energy changed from 141 J to 183 J; the characteristics of the brittle fracture in the radial zone of the fusion line were more obvious, and the impact energy changed from 113 J to 95 J. Therefore, after heat treatment, the toughness of the welded metal was improved, without reducing the strength and hardness of the welded metal to a large extent.     

The Effect of Heat Source Path on Thermal Evolution during Electro-Gas Welding of Thick Steel Plates

In recent years, the shipbuilding industry has experienced a growing demand for tighter control and higher strength requirements in thick steel plate welding. Electro-gas welding (EGW) is a high heat input welding method, widely used to improve the welding efficiency of thick plates. Modelling the EGW process of thick steel plates has been challenging due to difficulties in accurately depicting the heat source path movement. An EGW experiment on 30 mm thickness E36 steel plates was conducted in this study. A semi-ellipsoid heat source model was implemented, and its movement was mathematically expressed using linear, sinusoidal, or oscillate-stop paths. The geometry of welding joints, process variables, and steel composition are taken from industrial scale experiments. The resulting thermal evolutions across all heat source-path approaches were verified against experimental observations. Practical industrial recommendations are provided and discussed in terms of the fusion quality for E36 steel plates with a heat input of 157 kJ/cm. It was found that the oscillate-stop heat path predicts thermal profile more accurately than the sinusoidal function and linear heat path for EGW welding of 30 mm thickness and above. The linear heat path approach is recommended for E36 steel plate thickness up to 20 mm, whereas maximum thickness up to 30 mm is appropriate for sinusoidal path, and maximum thickness up to 35 mm is appropriate for oscillate-stop path in EGW welding, assuming constant heat input.     

Effect of Mechanical Shock Treatment on Microstructure and Corrosion Properties of Manual Argon Arc Welding Joints of 2205 Duplex Stainless Steel

Pneumatic chipping hammer and ultrasonic impact peening were used to relieve the welding residual stress of 2205 duplex stainless steel by manual argon arc welding, and the influences of these mechanical shock treatment technologies on the residual stress, microstructure, and corro-sion resistance of the welding seam were studied. Results showed that after pneumatic chipping hammer or ultrasonic impact peening, a small amount of plastic deformation occurred in the welded joint of 2205 duplex stainless steel, which led to an increase in the dislocation density in the microstructure. Meanwhile, the stress state of the welded joint changed from the residual tensile stress to the residual compressive stress. The maximum residual compressive stress could reach −579 MPa. The combined action of the two effectively improved the corrosion resistance of the welded joint. Among them, the best overall effect was the ultrasonic impact peening tech-nology.