HAZ Softening Research Articles

An Investigation of the Effects of Flame Straightening Heating on the High-Strength Structural Steels Microstructure

AbstractIn this research, the effects of heating cycles that are performed correctly and excessively—well above the limitations given by the steel manufacturer—on flame straightening are assessed and analyzed. The paper focuses on the microstructural changes caused by the overheating during the flame straightening process. To create geometrical changes in a metal construction, a tiny section of the element or structure is heated to the straightening temperature during the flame straightening process. Strenx® 960 is typically produced through a combination of thermomechanical rolling and quenching and tempering, resulting in a fine-grained martensitic or bainitic microstructure. These processes are designed to achieve a balance of high strength and good toughness. The microstructural changes associated with different working conditions in the case of welding include HAZ softening and grain growth. The study aimed to highlight the influence of flame hardening on the microstructure of the material.

Strengthening the HAZ of an MIG welded joint of 6082-T6 aluminum alloy via mechanical-thermal hybrid aging treatment

In this work, mechanical vibration was applied to the weldment during welding. This technique is called simultaneous mechanical aging and combined with post-weld thermal aging to form a mechanical-thermal hybrid aging process that was used to strengthen the HAZ of the MIG welded joint of 6082-T6 aluminum alloy. The HAZ softening was significantly reduced through the mechanical-thermal hybrid aging treatment, thereby substantially enhancing the joint strength. The β″ precipitated by post-weld thermal aging and the α precipitated by simultaneous mechanical aging give rise to precipitation hardening in the HAZ and therefore strengthen the HAZ. Degassing of the weld pool and grain refinement in the weld can be achieved by means of mechanical vibration to stir the weld pool. The fracture of welded joints is ductile fracture.

Effect of heat input on HAZ softening in fiber laser welding of 22MnB5 steel

Effect of heat input on HAZ softening in fiber laser welding of 22MnB5 steel

Mitigating HAZ softening of friction stir welded ferrite-martensite DP steel followed by post weld heat treatment

This study investigates the development of microstructure and mechanical properties in welded joints of ferrite-martensite DP780 steel, with different cooling pathways applied after post-weld heat treatment (PWHT). The findings suggest that quenching in liquid nitrogen (PWHT-LNQ) effectively mitigates the softening of the heat-affected zone by suppressing the formation of tempered martensite and reducing carbide coarsening. The technique promotes a refined microstructure characterized by the discrete distribution of block martensite within the ferrite islands. This microstructural arrangement significantly enhances the strength and ductility properties of the material. Notably, PWHT-LNQ achieves the highest tensile elongation of 17%, which is approximately 2.2 times that of the as-welded joint.

Effect of Zn-coating type on intergranular Cu-penetration in steels during weld-brazing

Weld-brazing has emerged as a promising alternative to fusion welding for joining Zn-coated advanced high strength steels (AHSSs) due to its lower heat input, reduced Zn burn-off, and elimination of defects like porosity and blowholes. Additionally, the weld-brazing process minimizes HAZ softening, a phenomenon that can affect joint strength. While weld-brazing can potentially eliminate the liquid metal embrittlement (LME) caused by the penetration of molten Zn into grain boundaries (GBs), this study found that galvanized (GI) DP600 steels were more susceptible to intergranular penetration of Cu into the substrate during weld-brazing compared to galvannealed (GA) DP600. Although no Zn-related LME was observed during arc-brazing with Si-Bronze filler, the potential for Cu-related LME cracks to form in GI coated steels may affect the mechanical integrity of the joint.

Chemical composition and weld cooling time effects on heat-affected zone hardness of line pipe steels

In the past few years, the pipeline industry in North America has faced a reported increase of pipeline girth weld failures predominantly in grade X70 pipe welded with cellulosic consumables. Weld strength matching and HAZ softening were two factors believed to have contributed to the concentration of strain during, or soon after, construction which ultimately lead to an overload failure of the girth welds. The work reported in this paper aimed to establish and clarify the correlation between steel chemical composition and the HAZ hardness in typical production girth welds and a range of weld thermal simulations. The first stage was to calibrate the influence of weld cooling rate of both thermal simulations and real welds in steels over a wide range of chemical composition, typical of commercial high strength API pipe. Second, the influence of Pcm, carbon content, Mo content and cooling time in terms of minimum and maximum hardness were investigated. The comparison between simulated HAZ's and real welds showed that thermal simulation produces samples that adequately duplicate the real condition in terms of maximum and minimum hardness and can accurately assess both hardening & softening which occur in different regions of the HAZ. The simulated samples provided increased areas of different HAZ regions in order to more accurately identify the range of hardness values across the HAZ which was then correlated to real weld hardness profiles. It is concluded that ultimate hardness in the HAZ is directly related to steel chemical composition in terms of Pcm and weld cooling rate. It is however apparent that the relative percentage change in hardness from the original parent pipe hardness (also called % HAZ softening), which is important in determining the strain capacity of the weld joint, is principally dependent upon steel processing, especially the degree and severity of thermomechanical processing. This is evident by the fact that same API pipe grades have a wide range in chemical composition and most importantly Pcm, and the response to field welding conditions can be quite different depending on weld heat input, pipe wall thickness and preheat, all of which define the weld cooling rate.

Investigation of the Possibility for Compensating the HAZ Softening of AA7075-T6

New generations of high strength aluminum alloys are increasingly used in automotive industry. AA7075 is one of the strongest aluminum alloys in industrial use today. The outstanding strength properties open the possibility to use this alloy in automotive industry as a possible alternative material for car body elements instead of steels. Growing industrial demand of aluminum alloys led to the development new technologies, processes. Solution heat treatment, forming, and in-die quenching is one such technology. In our research work the different parts of the heat affected zone of AA7075-T6 high strength aluminum were examined. The thermal cycle of the heat affected zone was tested at four different temperatures (280 °C, 380 °C, 440 °C, 550 °C) with the help of physical simulation. The aim was to define the softening tendency of the heat affected zone after gas tungsten arc welding. Two heat input values 100 J/mm and 200 J/mm were selected in order to simulate a low and a high heat input welding at the given sheet thickness and welding technology by the application of Rykalin 2D model. Then the most critical subzone was selected for the further investigations. Therefore, the 380 °C temperature was examined in case of five more technical processes, which based on the solution heat treatment, forming, and in-die quenching process. The properties of the investigated subzone were examined by optical microscope and hardness test.

On the Measurability and Predictability of HAZ Softening in GMAW of Automotive DP980 Steel

Dual Phase (DP) steel, composed of a ferrite matrix with dispersed islands of martensite, has become popular in auto-body car construction due to its outstanding mechanical properties (i.e., high strength and good ductility). DP steel softens at the sub-critical heat-affected zone (SC-HAZ) when subjected to welding thermal cycles, owing to the tempering of the martensite phase. In this work, DP980 steel was subjected to varied thermal cycles: (a) furnace-tempering treatment, (b) gas metal arc welding (GMAW), and (c) resistance spot welding (RSW), in order to characterize the tempering of martensite below the Ac1 critical temperature and at the sub-critical heat-affected zone (SC-HAZ) in the case of the welded specimens. The coarsening stage of cementite phase was characterized through microstructure observations and hardness measurements. As expected, the comparative results indicated an advanced stage of the martensite tempering in the furnace heat-treated specimens, followed by the GMAW and the RSW specimens. Further, developed softening kinetic models have been suitably employed and adjusted in order to predict the extent of softening along the SC-HAZ of the GMAW specimen. Finally, as the advanced stage of cementite coarsening is due to the influence of the arc welded thermal cycle, a reasonable estimation of the hardness profile was obtained, particularly for tempering temperatures above 400 °C.

Characteristic of friction welding weld joint of AA6061 on elevated environmental temperature

Rotary Friction Welding is a solution in addressing the poblems in welding of material difficult to weld by fusion welding, such as AA6061 aluminium alloy. Fusion welding is difficult to apply to aluminium alloy because of porosity and crack which often occur during solidification. From the research on friction welding of AA6061, it can be conclude that excessive welding temperature of friction welding may result in thermal softening in weld zone and HAZ. The excessive cooling rate after friction welding run will affect to formation of hard and brittle of weld zone. Increase of environmental temperature above room temperature will accelerate workpiece to achieve solid state condition and lowering difference between weld peak temperature and inital weld temperature (ΔT) which mean decreasing of coooling rate. In this research, environmental temperature were varied of 27 °C (room temperature), 50 °C, 75 °C, 100 °C, 125 °C dan 150 °C. Some parameters are set constant such as rotation speed of 1600 rpm, friction pressure of 65 bar or 65 kg.cm−2, friction time (tf) of 6 seconds, forging pressure of 325 bar or 325 kg.cm−2, forging time of 60 seconds, contact diameter of workpiece of 15 mm and the workpiece chamfer angle of 15°. The contact area is divided into three zones, which are the plastic deformation zone (Zpl), the partial deformation zone (Zpd) and the non-deformed zone (Zud). The higher the environmental temperature will produces the wider plastic zone and plastic deformation zone (Zpl + Zpd). The higher the environmental temperature will causes the yield strength of the AA 6061 friction weld joint to increase which modelled as y = 3E-05x2 + 0.0033x + 16.582. Likewise, the tensile strength of the AA 6061 friction weld joint also increases which modelled as y = 3E-05x2 + 0.0026x + 18.119. When comparing the hardness of rotating workpiece side (spin) with workpiece side pressing (press), the previous one is higher at all variations of the temperature. From the photograph of the microstructure of base metal of Al 6061, dark particles (Mg2Si) and gray particles (Fe3SiAl12) are present in the Al matrix. The grain structure of Zud is bigger than Zpd and Zpl. Zpd microstructures at all environmental temperatures form smaller granular structures than base metal grains. Zpl microstructure in workpieces with environmental temperature of 27 °C, 50 °C, 75 °C and 100 °C were formed in small granular structure with Mg2Si (black) and Fe3SiAl12 (gray) structure which spread evenly. However Zpl microstructure with environmental temperature of 125 °C and 150 °C seems to enlarge, especially the structure of Fe3SiAl12 (gray), due to overheat and excessive softening.

The Role of HAZ Softening on Cross-Tension Mechanical Performance of Martensitic Advanced High Strength Steel Resistance Spot Welds

The Role of HAZ Softening on Cross-Tension Mechanical Performance of Martensitic Advanced High Strength Steel Resistance Spot Welds

Mechanical properties and microstructural characteristics of rotary friction welded dissimilar joints of rolled homogeneous armor steel and medium carbon steel

Abstract Distinct materials are used for the construction of battle tanks used in defense sectors. The hull and turret of the battle tanks are made up of rolled homogeneous armor steel (also known as armor steel). The inner portions like the driver cabin and control room are covered with medium carbon steel. Hence, the dissimilar joint between these materials is unavoidable in the battle tank construction. Conventional fusion welding processes like manual metal arc welding, gas metal arc welding, and gas tungsten arc welding are preferred to join the dissimilar metals. However, the high heat input nature of these processes will create hydrogen induced cracking, high residual tensile strain, and HAZ softening, etc. To minimize these issues, solid state welding processes were adopted. In the present study, mechanical properties and microstructural characteristics of rotary friction welded dissimilar joint of armor steel and medium carbon steel was analyzed. The ultimate tensile strength of the dissimilar joint is around 775 MPa and the failure occurred at the medium carbon steel side. The impact toughness value of dissimilar joints is higher than medium carbon steel and lower than armor steel. The microstructure across the dissimilar joint has distinct features and a complex pattern was observed at the weld interface.

摩擦攪拌接合したSi-Mn炭素鋼のHAZ 軟化抑制に及ぼすMoおよびV添加の影響

摩擦攪拌接合したSi-Mn炭素鋼のHAZ 軟化抑制に及ぼすMoおよびV添加の影響

Post-weld heat treatment effects on the tensile properties of cold metal arc welded AA 6061-T6 aluminum joints

Abstract Heat treatable aluminium alloys of the 6xxx series are widely used in the hood, trunk and roof sections of a car body as they offer better corrosion resistance, high strength to weight ratio and excellent weldability characteristics. Gas metal arc welding (GMAW), a high productivity process is extensively employed in the automobile sector due to its ease of automation. HAZ softening is one of the most common problems that occurs during the welding of aluminium alloys by GMAW because of its high heat input. Cold metal transfer (CMT) is the most suitable welding process for welding aluminium alloys especially for controlling HAZ softening issues that occur due to the low heat input involved in this process. However, softening continues to exist in the welded joints. In this investigation, Post -weld heat treatment (PWHT) was employed to increase joint efficiency and to minimize the HAZ softening of AA6061-T6 aluminum alloy joints welded by GMAW and CMT. The results show that the tensile strength of a post-weld heat treated CMT joint is 10 % higher i. e., 242 MPa (76 % of joint efficiency), than that of the as welded CMT joint. This is due to the nucleation of strengthening precipitates in the weld metal and heat affected zone regions.

Improving weldability of Al-Si coated press hardened steel using stepped current pulse schedule

Al-Si coated press hardened steel (PHS) were introduced into vehicle body structures for a balance of lightweighting and crashworthiness. However, the weldability of PHS is relatively poor, due to its high carbon equivalent and high strength and is characterized by severe heat affected zone, HAZ softening, and interfacial fracture. The interfacial fracture mode is defined in part by the presence of retained Al-Si coating as a sharp notch at the faying interface following the welding process, which limits the mechanical performance of the joint. To improve the weldability of PHS, a stepped current pulse schedule was proposed for the resistance spot welding (RSW) of 1.5 mm Al-Si coated PHS as a means to effectively promote nugget growth, inhibit expulsion and eliminate the residual Al-Si layer. In this manner the mechanical performance of joints were significantly improved and the desirable button pullout fracture mode was realized.

Effect of Solidification Defects and HAZ Softening on the Anisotropic Mechanical Properties of a Wire Arc Additive-Manufactured Low-Carbon Low-Alloy Steel Part

Wire arc additive manufacturing (WAAM) is a pioneer additive-based technology for fabrication of large-scale engineering components. Despite the many advances in the field of additive manufacturing, formation of solidification defects, including discontinuities and microstructural imperfections, in the fabricated components is still inevitable, regardless of the feedstock material or fabrication process applied. In this study, the effects of solidification defects on the anisotropic mechanical properties of a low-carbon low-alloy steel (ER70S-6) wall produced by WAAM have been investigated. Analysis of the microstructure and mechanical properties of the fabricated part confirmed the formation of various solidification defects, i.e., interpass lack of fusions, localized brittle zones, and grain coarsening in the heat-affected zones, leading to anisotropic behavior in the ductility along the deposition versus building directions of the component. The effect of discontinuities on the anisotropic mechanical properties was minimized through microstructural modifications of the fabricated part using postprinting normalizing heat treatment.

Physical Simulation-Based Characterization of HAZ Properties in Steels. Part 2. Dual-Phase Steels

The development of high-strength weldable steels has diversified the range of design alternatives subjected to more and more severe operation conditions. An excellent combination of high work-hardening rate and ductility improved the ultimate tensile strength of dual-phase (DP) steels and made them lucrative for application in automotive industry. The paper focuses on HAZ hardening and softening of three automotive DP steels, which affect their mechanical properties and their crack susceptibility, respectively. A Gleeble 3500 thermomechanical simulator was used to simulate the welding thermal cycles for all HAZ subzones that correspond to TIG welding of three DP steels. Steel samples were heated to different peak temperatures (650, 775, 950, and 1350°C) and cooled at two cooling times of 5 and 30 s. The Rykalin 2D model was used for the numerical simulation of this process. The hardness and microstructure of the specimens were then tested and analyzed using Vicker’s hardness test and optical microscope, respectively. In the investigated cooling time range, the HAZ of the examined cold-rolled DP steels was more susceptible to softening than to hardening. The softening occurred in almost all HAZ sub-regions but was the most pronounced in the fine-grained and intercritical HAZ, where we recorded the highest decrease in hardness for all DP steels. With an increase in heat input and longer cooling time, softening occurred in CGHAZ of all three DP steels under study, which can be attributed to the formation of upper bainite.

Effect of heat input on microstructure and mechanical properties of Ti/Cu66V34/Cu joints by electron beam welding

The variations of microstructure and mechanical properties of the joints with different welding heat input were investigated. As the heat input increased, excessive melting of TA15 alloy facilitated the formation of Ti-Cu compounds at the TA15 interface, increasing the brittleness of the TA15 interface. Moreover, high heat input also caused the HAZ softening by grain coarsening and deteriorated the performance of the joint. However, low heat input was adverse to the complete melting of Cu66V34 alloy and induced the formation of welding pores. It also weakened the strength of the joint. Under optimum welding parameters, (Ti,V) solid solution formed at the titanium interface, replacing Ti-Cu intermetallic compounds (IMCs). Therefore, the joint of sample 2 presented the highest strength (378MPa) and fractured along the HAZ of QCr0.8 alloy due to the HAZ softening resulting from grain coarsening.

Development and Application of Sour Service Pipeline Steel with Low Manganese Content

Comprehensive analysis on the requirement and evaluation result of pipeline steel for sour service is carried out in this paper. So as to provide technical support for the development of the high toughness sour service pipeline steel with low manganese content.The evaluation results shows that the high toughness sour service pipeline steel with low manganese content has excellent comprehensive properties, and the excellent comprehensive mechanical properties and corrosion resistance properties of trial products are achieved through reasonable composition and micro-structure design. The HIC and SSC test result complies with pipeline steel requirement for sour service drafted by major international manufacturers. In order to guarantee the application prospect of the trial products, the weldability of the sour service pipeline steel is analyzed finally, and the test result shows that HAZ softening can be improved when the cooling rate was higher than 20 °C /s.

Mechanical behavior of gas metal arc AA6082-T6 weldments

A series of experiments have been conducted to determine the mechanical properties of AA6082-T6 plates which have been joined by means of the Gas Metal Arc technique. Hardness Vickers tests, bending tests, tensile tests, fatigue tests and Charpy V-notch tests have been carried out to characterize the joints. In addition, an accurate microstructure analysis of selected fracture surfaces has been done. From the tests it is concluded that HAZ softening brings to a reduction in strength with respect to the parent material. It has been noticed that there is a minimum value of hardness in the heat affected zone, that corresponds to the weakest part of the component. From the Charpy V-notch impact tests it has been observed that the material in the HAZ has the highest energy absorption capacity.

Microstructure and mechanical properties of friction stir welded ferrite-martensite DP700 steel

In the present work, friction stir welding technique was applied on 2 mm thick ferrite-martensite DP700 steel sheets at rotational speeds of 600, 800 and 1000 rpm. The microstructure and mechanical properties of the welds were evaluated. It was found that Zener-Hollomon parameter decreased with increasing rotational speed that leads to grain coarsening in the stir zone. It was also found that increment of rotational speed increased softening phenomenon in sub-critical heat affected zone. The results also showed that the presence of WC particles in the stir zone, which was due to the tool wear, as well as formation of a soft ferrite band degrade the tensile properties at rotational speed of 600 rpm while HAZ softening was responsible for reduction of strength and ductility in conditions of 800 and 1000 rpm.