Hardness Of Heat Affected Zone Research Articles

Effect of Heat Input on M-A Constituent and Toughness of Coarse Grain Heat-Affected Zone in an X100 Pipeline Steel

The joining of 14.8 mm thick pipeline steels was achieved with developments in high-power fiber laser by laser welding or hybrid laser arc welding. However, there were few studies on the effects of single-pass welding heat input on the M-A component and impact toughness of the heat-affected zone. In this study, single-pass welding thermal cycle was performed on Gleeble 3800 thermal simulation tester; the effect of heat input on microstructure, M-A constituent, hardness, toughness and corrosion resistance of coarse-grained heat-affected zone of X100 pipeline steel was studied. The results showed: The microstructure was lath martensite with a heat input of less than 8 kJ/cm. When the heat input was 26-36 kJ/cm, the microstructure was granular bainite. The heat input had not obvious effect on hardness (only 16% hardness reduction in this heat input arrange). However, the impact toughness was strongly influenced by heat input, with an 88% hardness reduction compared to base metal, due to M-A constituent and prior austenite grain size. Few finer M-A constituent dispersing in austenite was obtained instead of necklace-like M-A constituent at the prior austenite grain boundary when the welding heat input was less than 15 kJ/cm, which was beneficial to improve the impact toughness and corrosion resistance of welded joints of X100 pipeline steels.

Effect of δ Phase on Microstructure and Hardness of Heat-Affected Zone in TIG-Welded GH4169 Superalloy

The GH4169 superalloy with different content of δ-Ni3Nb phase was welded by tungsten inert gas welding. A detailed study of microstructure and hardness of heat-affected zone (HAZ) was performed in both as-welded and aged state. The results show that the precipitation of δ phase, especially the intergranular δ phase, can lead to the enrichment of Nb and Mo elements, which promote the formation of γ/Laves eutectic constituent at grain boundaries in HAZ. In as-welded state, the hardness decreases first and then increases (exhibiting a “V” shape) with distance away from fusion line in HAZ, which is governed by grain size. After aging treatment, however, the γ″ phase plays a key role in hardness and leads to the “Λ” shape profiles of hardness in HAZ.

Modeling and Optimization of HAZ Characteristics for Submerged Arc Welded High Strength Pipeline Steel

Heat affected zone (HAZ) is the most critical part of welded pipe in oil and gas pipelines as HAZ shows more susceptibility toward embrittlement and weld cracking. It happens because microstructural changes occur due to high heat of welding. Heat input and preheating temperature together control the cooling time of weld which in turn determines the weld microstructure and its mechanical properties. Therefore, in the present study, effect of heat input as well as preheating temperature on the characteristics of the HAZ in submerged arc-welded high-strength low alloy (HSLA) pipeline steel was studied. Hardness and area of HAZ were observed and analyzed as HAZ characteristics. Heat input of the process was varied by changing the voltage, welding speed, wire feed rate and contact tube to work distance. Experiments were designed using central composite rotatable design (CCRD) approach, and using response surface methodology (RSM), process modeling was done. For the purpose of single- as well as multi-characteristic optimization, desirability approach was used. Relationship of heat input and critical cooling rate with HAZ characteristics and its microstructure was also revealed. Inclusion of preheating temperature led to significant improvement in the HAZ characteristics of the weld.

Studies and Experimental Research on Correlation Thermal Field with Mechanical Properties of Cryogenic Steels Welded Joints with MIG Procedure

The paper presents the analysis and experimental research that is performed to correlate the welding procedure with hardness in HAZ (Heat Affected Zone) and toughness of welded joints of austenitic stainless steel X6CrNiTi18-10, used to build cryogenic tanks to liquid nitrogen storage. For this were welded a sample by MIG welding process.In a first step it was estimated the hardness of HAZ with a soft computer, and then it was made a testing to its experimental verification welding procedure. The results showed that the welding procedures developed and implemented resulted in obtaining the HAZ hardness almost equal to those of basic material. This shows that the HAZ properties are unaffected and a good weldabillity of austenitic stainless steel. In a second step the toughness were measured at room temperature and work temperature, -196°C.

Thermal Cycles and Peculiar Properties of Austenite Decomposition when Laser-Hybrid Welding Steel of K60 Strength Class

Welding is an important technology of joint in engineering structures. In addition to a residual stress influence to a quality of joint, an obstacle in welding analysis are complex phenomena including phase transformation, thermal cycle and microstructure kinetics. The influence appears in microstructure development, formation of defects and in transformation of metallurgy in a welded zone. This article experimentally defines thermal cycles and shows the results in study of peculiar properties of austenite decomposition kinetics when using the technology of laser-hybrid welding in combination with multiple arc automatic sub-merged welding. There defined the rates of cooling influencing the change of properties of welded joints from tube assortment steel of K60 strength class. We found that the result of impact of laser-hybrid welding process in a heat-affected zone is that the austenite decomposition in studied steels flows in martensite area generally. The hardness of seam metal and heat-affected zone of the studied steels is of range 350-360 HV, which increases a probability of crack-like, defects formation. We revealed the normative value of hardness, which can be provided if a metal cooling rate in laser-hybrid welding is about 20 °C/s.

The effect of filler metal and butter layer on microstructural and mechanical properties of pure Cu to AISI304 stainless steel dissimilar joint

In this research, dissimilar joint properties of pure Cu to AISI304 stainless steel using three different filler metals were studied. In this regard, the welding process was done with gas tungsten arc welding process using ER308L, ER309L, and ERNiCrMo3 filler metals and ERNi1 butter layer. The microstructural evaluations were carried out using optical microscope and scanning electron microscope. The mechanical tests were conducted by microhardness, tensile, bending and impact tests, and the fracture surfaces of impact and tensile tests were studied by scanning electron microscope. The results show that there is no crack or discontinuity in the welded samples. Energy-dispersive spectroscopy analysis revealed that the diffusion of Cu from base metal to butter layer has been occurred during welding. The microhardness profiles indicated the increase of hardness in heat-affected zone and butter layer. The welded sample with ERNiCrMo3 filler metal showed higher microhardness (200 HV) as compared with two other welded samples. The welded sample with ER309L filler metal had lower microhardness of about 150 HV. The tensile test revealed that the welded sample with ER309L filler metal showed maximum (193 MPa) and the welded sample with ER308L showed minimum (147 MPa) of ultimate tensile strength. In bending test of the welded samples with ER308L and ERNiCrMo3 filler metals, the crack and discontinuity were revealed in weld metal and heat-affected zone of Cu, respectively, while in the welded sample with ER309L filler metal no crack and discontinuity were seen. Also the welded sample with ER309L filler metal had highest impact energy of about 90 J as compared to other samples (81 and 88 J for the welded samples with ER308L and ERNiCrMo3 filler metals, respectively). The welded sample with ER309L filler metal showed more ductile fracture surface as compared with other samples.

Effects of HAZ softening on the strength and elongation of resistance spot-welded joints in high-strength steel sheet in an in-plane tensile test

ABSTRACTIn this study, we investigated the effects of heat-affected zone (HAZ) softening on the strength and elongation of resistance spot-welded joints in high-strength steel sheet in an in-plane tensile test. The fracture in the softened HAZ had a little effect on the maximum stress of the resistance spot-welded specimen; however, the fracture elongation decreased. The nugget diameter and HAZ softened width had little effect on the fracture elongation of the resistance spot-welded specimen. Also, the fracture elongation decreased slightly with the decrease in the sheet thickness. The major factor affecting the fracture elongation was the HAZ hardness ratio (= Softened HAZ/Base metal × 100%). For the resistance spot-welded specimen with a thickness of 1.6 mm, when the HAZ hardness ratio decreased to less than 80%, the fracture position changed from the base metal to the softened HAZ and the fracture elongation decreased sharply. In addition, with a decrease in the hardness ratio, the fracture elongation decreased.

Microstructure Evolution and Toughness Variation of Simulation HAZ with Large Heat Input Welding for E40 Ship Plate Steel

This Charpy impact toughness and microstructure evolution of simulated heat affected zone (HAZ) for E40 ship plate steel have been investigated in this experiment. Simulation of large heat input welding was conducted by thermal simulator to research microstructure evolution of HAZ at 1400°C peak temperature. Results show that microstructure at HAZ was mainly composed of high intensity of acicular ferrite (AF) and intragranular ferrite (IGF), and grain boundaries ferrite (GBF). Hardness of HAZ decreases with heat input (HI) increasing. Impact toughness for steel specimens with HI of 500 kJ/cm was 141 J. TiN precipitates nucleation and growth at HAZ was analyzed by TEM, indicating that TiN size increases and the number of TiN decreases at HAZ with HI increasing. The reason is that the specimens with HI of 400 kJ/cm has longer cooling time from 800°C to 500°C than 120 kJ/cm, which is favorable to growth of TiN particle at HAZ.

Characterization of the Interface of an Alloy 625 Overlay on Steels Using Nanoindentation

Industry standards require postweld heat treatment (PWHT) to reduce the heat-affected zone hardness of steels such as F22 (2.25Cr-1Mo) and AISI 8630 overlaid (clad) with Alloy 625 weld metal. PWHT results in carbon diffusion and accumulation at the interface between the steel and overlay. The accumulation of carbon in a planar solidification growth zone adjacent to the fusion boundary results in high hardness and the potential for hydrogen-assisted cracking. The planar growth zone (PGZ) is so narrow that normal Vickers hardness testing cannot fully reveal the hardness distribution in this zone. This study focused on the application of nanoindentation to characterize the hardness in the narrow microstructural regions adjacent to the fusion boundary. The development of nanohardness maps revealed that the PGZ is not necessarily the region that exhibits peak hardness after PWHT. The highest hardness values were associated with clusters of M7C3 carbides in specific subregions in the PGZ and also in the partially-mixed zone adjacent to the fusion boundary or in steel “swirl” structures. It was also confirmed in this study that nanohardness has a linear correlation with Vickers hardness values. The results presented here provide new insight into the role of carbon diffusion during PWHT and its effect on interface embrittlement associated with Alloy 625 overlays on steel.

Experimental and FEM study of Ti-containing TWIP steel weldability

The mechanical and microstructural effects induced by high and low heat input of autogenous Gas Tungsten Arc Welding (GTAW) process in Fe-22Mn-1.8Al-1.2Si-0.57C TWIP steel microalloyed with titanium (TWIP-Ti) were evaluated through weld experiments. Different butt joints preparations in TWIP-Ti steel 5.8 mm thickness plates were used. A Finite Element (FE) model was applied to evaluate the deformation during welding process. The peak temperatures estimated numerically by the FE model were correlated with microhardness measurements carried out in high and low heat input welds. The lack of segregation of Mn and C at the melting zone interface contributed to avoid the hot-cracking in the welded joints at high and low heat input. The heterogeneous grain size microstructure in the welded specimens was affected by the heat input, which was correlated with the heat affected zone hardness measurements. An increase in both yield strength and ultimate tensile strength was measured in the low heat input weld as a result of the lack of hot cracking in the FZ-HAZ interface and the heterogeneous grain size distribution.

Effect of preheating on welding cold crack sensitivity of China low activation martensitic steel

The China low activation martensitic (CLAM) steel has been chosen as the primary structure material in Chinese series PbLi blankets for fusion reactors. The assembly preparation of the blanket would be seriously influenced by the weld performance of the CLAM steel. In this study, the welding cold crack sensitivity index of the CLAM steel was analyzed, then the maximum hardness in weld heat-affected zone (HAZ) and y-groove tests were performed. Based on the analysis to the maximum hardness in weld HAZ and the cracking rate of y-groove test at different preheating conditions, the results indicated that the HAZ maximum hardness of CLAM increased at firstly and then decreased with the increase of the preheating temperature (PT). The cracking rate of y-groove test reduced with the increase of the PT, and the crack rate maintained at a relative stable stage when the PT exceeded 250 °C. It revealed high welding crack tendency of the CLAM steel. Thus, the preheating before welding should be applied, and a PT at about 250 °C was proposed in order to prevent welding cracking.

The effect of postweld heat treatment on hydrogen-assisted cracking of 8630/Alloy 625 overlay

The weld interface of Alloy 625 clad onto AISI 8630 steel requires postweld heat treatment (PWHT) to reduce the heat-affected zone (HAZ) hardness of the steel to meet industry standards. This PWHT results in carbon diffusion and pile up in the transition zone at the fusion boundary which potentially embrittles the 8630/625 interface. For the 8630/625 overlay, the PWHT needs to be carefully selected to reduce the potential for hydrogen-assisted cracking (HAC) and/or sulfide stress cracking (SSC). In this work, a wide range of PWHT conditions defined by the Hollomon-Jaffe parameter (HJP) was studied using the delayed hydrogen cracking test (DHCT). The effect of PWHT on HAC behavior was quantified using this test and the optimal HJP range for resistance to HAC was determined to be in the range from 18,500 to 19,500. Fracture surface analysis was conducted on failed samples to further evaluate the effect of PWHT and confirm the optimal HJP range. The HAC behavior of the 8630/625 overlay was compared with that of the F22/625 overlay reported previously.

Influence of ultrasonic vibration on percussion drilling performance for millisecond pulsed Nd:YAG laser

The ultrasonic vibration-assisted laser drilling is a recently emerging/growing new technique, especially in laser drilling. Differently from the previous work reported, this paper proposed to use the ultrasonic vibration (25 kHz) for assisting the millisecond pulsed Nd:YAG laser percussion drilling process to improve the drilling performance. Through comparing the drilled microholes without/using ultrasonic assistance, the influence of ultrasonic vibration on the drilled blind hole morphology/geometry, the hole wall surface roughness, the recast layer microstructure, and the hardness distribution of the heat affected zone for the drilled microhole was analyzed by altering laser pulse energy and/or laser pulse number. It was shown that the ultrasonic vibration incorporated into the laser drilling process might enhance the drilling efficiency in terms of the increase of hole depth and width. However, the drilled hole taper might be decreased via using ultrasonic assistance. Moreover, the ultrasonic vibration might clean the inner hole wall surface, and the microhole morphology/geometry could be improved through using ultrasonic assistance, resulting in a relatively clean and better-profiled hole wall with less defects and smaller taper due to the contribution of ultrasonic assistance. In addition, it was indicated that ultrasonic vibration might also improve the microhole heat affected zone hardness and reduce the inner hole wall surface roughness.

Heat-affected zone property diagrams for a grade 100 microalloyed steel

The microhardness variations and microstructural alterations in the heat-affected zone (HAZ) of a grade 100 steel, microalloyed with titanium, niobium, and vanadium were examined for a range of heat inputs from 0.3 to 2.5 kJ/mm. The results of the precipitate dissolution analysis and weld thermal analysis were used to establish HAZ property diagrams and qualitatively explain grain size and microhardness profiles across the HAZ for different heat input values. The relative width of the coarse-grained HAZ (CGHAZ) increased and the grain coarsening temperature decreased with decreasing heat input, although the amount of grain growth decreased with decreasing heat input. Detailed microstructural examination using a transmission electron microscope (TEM) coupled with nanohardness measurements showed that the CGHAZ was not 100% martensite even at a low heat input of 0.5 kJ/mm, while the micro- and macrohardness values suggested a “fully martensitic” structure. Microhardness testing also revealed that the maximum HAZ hardness was in the CGHAZ at some distance from the fusion line, as opposed to being adjacent to the fusion line.

Experimentation of effect of process parameters on mechanical properties in SAW Process

Submerged Arc Welding (SAW) is most preferred metal joining process for high thickness weld material due to its productivity , ease of automation and less welding skill requirement. Weld quality and cost effectiveness of welding can be determined by analyzing mechanical properties of weld and influence of process parameters. The quality of weld bead is mainly affected by process parameters like current, voltage, weld speed, polarity, wire feed rate, thickness of material, nozzle gap etc., In this work, attempt has been made to find the effect of process parameters such as welding current, voltage and welding speed of automatic SAW on carbon steel SA 516 grade 70 material using EA-3 electrode material on the mechanical properties such as tensile strength, hardness of the weld zone and heat affected zone(HAZ) and microstructure. Experiments have been conducted as per Taguchi method using L9 array. ANOVA (Analysis of Variance) was done to find out most influencing parameter that effect mechanical properties of the weld quality. The results revealed that in weld bead, voltage is the most significant factor for tensile strength and current is the most significant factor for hardness of weld zone and HAZ.

Effect of double-pulsed gas metal arc welding (DP-GMAW) process variables on microstructural constituents and hardness of low carbon steel weld deposits

In this study, a bead on plate welding on a low carbon steel plate at different parameter combinations in double-pulsed gas metal arc welding (DP-GMAW) process has been carried out. The effect of heat input, pulse frequency and thermal pulse frequency on solidification variables and microstructure of the weld metal have been thoroughly studied. Formation of inclusion and acicular ferrite during solidification has been calculated to observe the effect of process parameters on the microstructural constituents. Furthermore, the microhardness analysis of the weld metals has been carried out to evaluate the effect of microstructural variations on the property. Several linear and non-linear equations have also been developed to predict the responses as a function of different process variables. The results indicate that decrease in heat input, pulse frequency and thermal pulse frequency increases the volume fraction of inclusion and acicular ferrite in the weld metals. The higher volume fraction of acicular ferrite ultimately results in fine grain microstructure with the higher hardness of weld metals. On the other hand, the grain size of coarse grain heat affected zone (CGHAZ) at lower heat input was finer which ultimately increases the heat affected zone hardness.

An investigation of electron beam welding of Nb-1Zr-0.1C alloy: Process parameters and microstructural analysis

Niobium based Nb-1Zr-0.1C alloy has been developed for high temperature applications. Welding of this alloy is difficult task due to its reactive nature, higher thermal conductivity and melting point. In the present work, Electron Beam (EB) welding technique, which can produce narrow deep penetration welds with nominal heat affected zone (HAZ) and minimum contamination, is used to weld the alloy. This work is aimed to produce the acceptable EB welds of Nb-1Zr-0.1C alloy. For this purpose, EB welds of Nb-alloy in bead-on-plate and square butt joint configurations were produced according to central composite design of the experiments with power (P) and weld speed (S) as input process parameters. The output of the welding process was measured in terms of depth of weld penetration (D), weld bead width (W), aspect ratio, joining efficiency and thermal efficiency. The correlations for D and W, as a function of process parameters, were obtained by non-linear statistical regression analysis. The weld joints produced were characterized by optical, Scanning Electron Microscopy (SEM) and Electron Back Scattering Diffraction (EBSD) techniques. The HAZ and base metal showed fine carbide precipitates along the grain boundaries, whereas carbides were found dissolved in the weld zone. The micro-hardness profile across the width of welds showed marginal increase in the hardness of weld zone and HAZ. Thermal and residual stress fields were estimated for the EB weld joint in square-butt configuration, using finite element technique and a good qualitative matching between the computed and experimental values was obtained. The detailed results of all these studies are described in this paper.

Microscopic structure and property of double-electrode gas metal arc welding of AZ31B magnesium alloy

This paper focuses on the research on double-electrode gas metal arc welding (DE-GMAW) of AZ31B magnesium alloy sheet with 2mm thickness. During the welding process, stable hybrid arc of metal inert gas (MIG) and tungsten inert gas (TIG) is employed as welding heat source. Optical and electron microscopes are used to observe the microstructures of the weld joint. X-ray diffraction (XRD) and energy dispersive spectroscopy (EDS) are employed to identify the components in fusion zone. Microhardness is also tested. When the MIG current is 80A, the perfect weld joint is obtained, though figures of fish scales are observed in all joints in the research. The fusion zone is formed by dendrites, where β-Mg17(Al, Zn)12 is dispersed. The hardness in fusion zone and heat affected zone (HAZ) is lower than that in base metal (BM). The average Vickers hardness of fusion zone and HAZ is about 58 and 56 respectively, while the Vickers hardness of BM is about 63.

Microstructure and local strains in GH3535 alloy heat affected zone and their influence on the mechanical properties

GH3535 alloy plates were welded by Gas Tungsten Arc Welding in order to study the evolution of microstructure and mechanical properties in the heat-affected zone (HAZ). Our results suggest that welding thermal cycles induced the morphology evolution of M6C carbides from block to eutectic near the fusion line in the HAZ. Electron backscatter diffraction (EBSD) results show that significant amounts of plastic strains occurred in the HAZ after welding. In addition, local coherent twin boundaries (Σ3) and dislocations were observed to decrease with the distance from the fusion line. Mechanical tests indicate that the hardness, yield strength and ultimate strength in HAZ are higher than those in base metal, and their values decrease with the distance from the fusion line. However, the elongation increases as the strengths decrease. The higher strength and lower elongation in the HAZ are mainly attributed to residual strains with the function of strain-hardening. Moreover, the change of Σ3 boundary which is in good agreement with that of elongation suggests a positive influence on the plastic deformation.

Dissimilar metal study on C44300 tube to AA7075 -T651 tube plate with and without thread by FWTPET process

Friction welding has vital industrial role in fabricating automobiles, aerospace, ship building, heat exchangers using similar, dissimilar and bi-metal of ferrous and non-ferrous metals at mass production level. In this study, admiralty brass C44300 tube and aluminium alloy AA7075 -T651, 6 mm thick tube plate were identified as base metals. Different joint surface area profile of with and without thread of different pitch values was chosen to study the mechanical properties and micro structures of these two base metals. 0.1 mm clearance was maintained between the AA7075-T651 tube plate and C44300 tube outer diameter to make friction welding. Taguchi’s L16 orthogonal array techniques were adopted for identifying the most significant ranking process parameters. Analysis of variance (ANOVA) has been used to analyze the input parameter contribution in terms of percentage. Genetic algorithm (GA) was used to access the suitable input parameter value to obtain effective joint strength in terms of hardness, compressive strength and microstructure formation in the interface of the joint. A Compression test (CT) was conducted to evaluate the level of compressive strength of the joint. Threaded profile pair with higher pitch value proved high compressive strength over unthreaded pair. Micro structure for base metal C44300 tube and AA7075-T651 tube plate, Heat affected zone (HAZ) and Weld zone (WZ) of the joint has been studied. Hardness of base metals, HAZ and WZ was measured by micro Vickers hardness tester and the observation shows that hardness at joint interface has been found to be higher in all pairs.