Mechanical Properties Of Heat Affected Zone Research Articles

Embrittlement Fracture Behavior and Mechanical Properties in Heat-Affected Zone of Welded Maraging Steel.

In welded maraging steels, mechanical properties, particularly ductility and toughness, are often compromised in the heat-affected zone (HAZ). This study focuses on 300-grade maraging steel bars, solution annealed at 1123 K for 1.5 h (5.4 ks) and welded using gas tungsten arc welding, followed by a post-weld heat treatment at 753 K for 13.33 h (48 ks). In situ observations during three-point bending tests on HAZ samples featuring coarsened prior austenite grain sizes were conducted to examine damage behavior and the crack path near the crack tip. The main crack initiated at the peak applied load during the bending test and, upon further loading, exhibited significant deflection and extension accompanied by numerous microcracks and localized crack branching. Distinctive damage features, such as transgranular cracking across block regions, intense intergranular cracking along packet boundaries with a pronounced shear component, and crowding of microcracks ahead of the crack tip, were observed in the HAZ sample during the in situ test. The interaction between the main crack tip and microcracks and its influence on the local crack propagation driving force was discussed using fracture mechanics. Experimental results, including tensile fracture surface observations and in situ images, along with analysis of the stress anti-shielding effect by microcracks, suggest that the HAZ sample exhibits embrittlement fracture behavior with lower ductility and toughness compared to the base metal sample.

Effect of intrinsic thermal cycles on the microstructure and mechanical properties of heat affect zones in laser cladding coatings on full-scale rails

Laser cladding (LC) wear-resistant alloy on the surface of pearlite rails has been proven to be able to improve their wear resistance significantly. However, the rapid cooling rate in LC will result in the formation of martensite structures with high hardness but low toughness in heat affected zone (HAZ), making the rails' service safety endangered. In this paper, a novel method was proposed to eliminate the un-tempered martensite in U71Mn rail based on the in-situ gradient tempering (IGT) effect induced by the intrinsic thermal cycles in multilayer LC. The influence mechanisms of interlayer and inter-track thermal cycles on the evolutions of microstructure and mechanical properties of HAZs were studied systematically. The results illustrate that the martensite in HAZs can be gradually tempered within the optimal IGT temperature range, and the tempering processing mechanisms are as follows: firstly, the ε-carbides precipitate from HAZs and then dissolve to form granular cementites. Then, the cementites form colonies of lathlike particles with similar orientations. Finally, a composite structure consisting of fine-tempered sorbite and granular cementites forms, in which the lamellar spacing of sorbite is <1/5 of that of the original pearlite, and the proportion of the high angle grain boundaries has increased by 2.2 times. During the tempering process, the microhardness of HAZs gradually decreases, accompanied by the increase of the bending properties therein. The ultimate bending strength and fracture strain of the specimens with fully tempered HAZs are enhanced to be about 1.6 and 5.5 times as much as those of the specimens with fully quenched HAZs, even much better than the substrate.

The effect of heat input in multi-pass GMAW of S960QL UHSS based on weaving and stringer bead procedure on microstructure and mechanical properties of HAZ

Quenched and tempered S960QL (yield strength ≥ 960 MPa) ultra-high strength steel (UHSS) thick plates were joined by multi-pass robotic gas metal arc welding (GMAW) using weaving and stringer bead techniques. The effects of microstructural changes in heat-affected zone (HAZ) of the joint on toughness and hardness were examined. Weaving and stringer bead techniques applied for the multi-pass welding procedure altered average peak temperatures and exposure time to those temperatures. Mechanical properties of HAZs were evaluated by utilizing notch impact and hardness tests, and these results were correlated with microstructural characterizations using optical (OM) and scanning electron microscopes (SEM). Prior austenite grain (PAG) coarsening occurred because of increased exposure time to peak temperature in coarse-grained HAZ (CGHAZ) of the W-5 (weaving pass) joint. CGHAZs at the face pass, which have not been subjected to a second thermal cycle, have the highest hardness in both joints. Hardness of SCHAZ and CGHAZ of S-12 joint was 7% and 1% higher compared with W-5 joint, respectively. Weld metal hardness of W-5 joint was 15% lower than that of S-12 joint. Both joints not only fulfilled the requirements of minimum 50 J per EN ISO 10025-6 at −20 °C but exceeded this limit by 50% (W-5) and 200% (S-12). Lateral expansions for impact toughness specimens were around 17.5% for S-12 joint, whereas it was 4% for W-5 joint. Since HAZ in the S-12 (stringer bead) joint is narrow compared with the one in the W-5 joint, impact toughness values were higher with the S-12 joint due to the locations of the notches of the impact specimens.

Precipitation mechanism of nanoscale Cu-rich particles in restrained welding conditions and its effect on the mechanical properties of HAZs

The effect of welding constraint on nanoscale Cu-rich precipitation in welding heat affected zones (HAZs) of Cu-bearing steel was studied in this work. Due to the constraint tensile stress of 150 MPa, α-Fe transformation start temperature (Ts) of CGHAZ and FGHAZ increased by 55 °C and 42 °C, respectively. The volume fraction and average size of 9R-structural Cu-rich particles in FGHAZ increased from 0.3 % to 0.8 % and from 5 nm to 8 nm, respectively. Three-dimensional phase field simulation shows that the increment of Ts promoted the precipitation of Cu-rich particles in α-Fe matrix. However, the Ts of restrained CGHAZ was too low to favor the precipitation of Cu-rich particles. The tensile strength of FGHAZ increased from 970 MPa to 1032 MPa due to the nanoscale Cu-rich precipitation strengthening.

Characterization of Crack Tip Mechanical Field of Inhomogeneous Materials in Welded Joints by USDFLD Subroutine

The unevenly distributed mechanical properties of welded joints are one of the important factors, which affect welded joints’ safety seriously. The user-defined field (USDFLD) subroutine in ABAQUS finite element software can introduce variable-dependent material properties. This method can define inhomogeneous materials whose mechanical parameters depend on spatial coordinates and can be used to characterize the uneven mechanical properties of heat-affected zone and fusion zone. By establishing the static crack finite element model of welded joint with continuous change in yield strength, the sudden change in mechanical field in the numerical simulation process of sandwich structure model is eliminated. Compared with the existing numerical simulation methods of local mechanical heterogeneity of welded joints, this method provides a method to realize the structural integrity evaluation of welded joints.

Effect of Repeated Weld Repairs on Microstructure and Mechanical Properties of Heat-Affected Zone in CA6NM Stainless Steel

The low-carbon martensitic stainless steel CA6NM is widely used in the impellers of hydroelectric and nuclear power units due to its advantages of high hardness, corrosion fatigue strength, and good fracture toughness. In order to analyze the number of repair welding times on the properties of heat-affected zone (HAZ, the most unstable area of welded joint property) in CA6NM, the microstructure and mechanical properties of HAZ with once-repaired welds (1R) and twice-repaired welds (2R) were tested. Through data analysis, the following conclusions are drawn for welded joints: (1) the grain size of HAZ with a different number of repair welding processes is smaller than that of the base material; (2) the density of texture concentration is reduced and the directionality is not obvious; (3) the density of twins and dislocations are increased; (4) the hardness and impact energy of HAZ of the 1R and 2R specimens are higher than that of the base material.

Microstructure and Mechanical Properties of Heat-affected Zone of Repeated Welding on 304 Stainless Steel

The effect of the repeated welding on the microstructure and mechanical properties of the heat-affected zone (HAZ) for 304 stainless steel were investigated under repeated welding up to five times by automatic gas tungsten arc welding using an optical microscope, a x-ray diffraction, a scanning electron microscope and an electron back-scattered diffraction. The repeated welding specimens were consisted with the microstructures of austenitic matrices with lath δ-ferrite. With the increasing of the repeated welding times, the average values of the austenitic grain size increased, and the δ-ferrite content decreased then increased. The preferred orientation of the HAZ changed from to . The values of location misorientation increased monotonically with the increasing number of repeated welding. The variation of the ultimate tensile strength and elongation was affected by the grain size mainly. Due to the hardening rate increasing, the yield tensile strength was increasing.

Discretization and material parameter characterization for a HAZ in direct-quenched armor steel

Studies conducted in recent years have shown that the ultimate load-bearing and deformation capacity of weldments manufactured from ultra-high-strength steel is often impacted by the heat-affected zone. Thus, to assess the strength properties of these welds, in addition to the base material properties and weld metal, the heat-affected zone's mechanical properties must be analyzed. In this study, a discretization and material parameter characterization are conducted for friction-welded joints in direct-quenched armor steel. The discretization is based on the microstructural analysis and hardness measurements conducted for the weld. After data analysis and considering the practical aspects, such as computational factors and other resources, a model with six different material parameter regions for the heat-affected zone was chosen. For all regions, the quasi-static part of the Johnson–Cook constitutive model was used. Three of the most distant zones measured from the weld interface were subcritically heated during the friction welding. The material parameters for these zones were identified using thermal simulations, tensile experiments, and numerical optimization, whereas the material parameters for the three remaining zones were identified using tensile experiments combined with numerical models and optimization routines. The generated model was successfully used in the fracture assessment of four friction-welded specimens with different degrees of metallurgical constraint. The effect of the subcritically-heated zones on the model's accuracy was studied. Neglecting the subcritical zone within the models caused an overestimation of the joint's tensile strength. Also, three alternative numerical models with different discretization's were generated and used in the fracture assessment. The validity of the generated models was tested by applying the HAZ model to models of tensile test specimens with different degrees of metallurgical constraint. The three alternative models could not correctly assess the fracture. In addition, the different models produced differing stress-strain curves.

Effect of Ce on inclusion evolution and HAZ mechanical properties of Al-killed high-strength steel

ABSTRACT The effect of Ce on inclusion evolution behaviour in 700 MPa class Al-killed high-strength steel was investigated through experimental observations and thermodynamic calculations. Simulated welding experiments and mechanical characterisation tests of the heat-affected zone (HAZ) were also carried out to investigate the effect of adding Ce on the welding performance. The results reveal that the typical inclusions of Ce-free steel are the CaS + Mg–Al–O + Ti(C,N) complex inclusion and isolated CaS inclusion. For Ce-containing steel, the typical inclusion is Ce–Ca–O–S + CaS + Ti(C,N). Furthermore, the number density of inclusions increases, and the average size of inclusions decreases after adding Ce. Lastly, the toughness and strength of the HAZ tested with heat inputs of 25 and 50 kJ cm–1 are evidently improved by adding Ce.

EVOLUTION OF STRUCTURE, PHASE AND MECHANICAL PROPERTIES DUPLEX STAINLESS STEEL (DSS) 31803 WELDING USING GMAW WITH THE ADDITION OF CO2 TO Ar - CO2 SHIELDING GAS

The purpose of this study was to analyze the effect of CO2 on the composition of the Ar- CO 2 shielding gas in DSS 31803 duplex welding using GMAW on carbon deposition, ferrite fraction, microstructure, weld and HAZ mechanical properties. This study uses A (100% Ar), M1 (95% Ar + 5% CO 2 ), M2 (90% Ar + 10% CO 2 ), M3 (85% Ar + 15% CO 2 ), M4 (80% Ar + 20 % CO 2 ), M5 (75% Ar + 25% CO 2 ) and C (100% CO 2 ). From the results of the study, the microstructure of the weld metal in each specimen contained grain boundary austenite (GBA), Widmanstätten austenite (WA), intragranular austenite (IGA), and partial transformed austenite (PTA). Scanning electron microscopy (SEM) identifies the occurrence of chrome carbide precipitation (Cr23C6) HAZ region in specimens M5 and specimen C. The equilibrium phase of ferrite and austenite in weld metal areas is fulfilled in specimens A (34.8), M1 (38.9), M2 (36.4), M3 (38.4) and M5 (45.9). The highest average hardness value of vikers in weld metal area is found in M5 specimen which is 255 HV. While the lowest value in specimen C is 238 HV.The highest Vickers average hardness value in the heat affected zone (HAZ) is in specimen A which is 271 HV and the lowest hardness is in specimen C which is 245 HV. High tensile strength values are found in specimen M5 with value 800 MPA. While the value of low tensile strength in M4 specimens which is 652 MPA.

Precipitates Dissolution, Phase Transformation, and Re-precipitation-Induced Hardness Variation in 6082-T6 Alloy During MIG Welding and Subsequent Baking

Precipitation evolution-induced hardness variation in 6082-T6 alloy during various thermal histories of welding and subsequent paint baking was characterized systematically. Precipitation evolution in various subzones of the heat-affected zone (HAZ) from the weld toe to the base materials was precisely identified by transmission electron microscopy. Under heating processes of welding and baking with different temperature and time duration, the morphology evolution of precipitates comprised dissolution, coarsening in size, and phase transformation from β″ to U2, β′ and β, etc. The mechanisms of the thermal softening and bake hardening of mechanical properties in HAZ are clarified. Quantitative calculation results showed that grain growth contributed little to the strength loss in HAZ, while precipitate evolution was responsible. Re-precipitating of Guinier–Preston zones and β″ phase from the super-saturated solid solution produced by welding was found to make main contributions to the efficient hardness recovering of joints during post-weld paint baking.

Microstructure and Mechanical Properties of Heat-Affected Zone of Repeated Welding AISI 304N Austenitic Stainless Steel by Gleeble Simulator

Heat-affected zone (HAZ) of welding joints critical to the equipment safety service are commonly repeatedly welded in industries. Thus, the effects of repeated welding up to six times on the microstructure and mechanical properties of HAZ for AISI 304N austenitic stainless steel specimens were investigated by a Gleeble simulator. The temperature field of HAZ was measured by in situ thermocouples. The as-welded and one to five times repeated welding were assigned as-welded (AW) and repeated welding 1–5 times (RW1–RW5), respectively. The austenitic matrices with the δ-ferrite were observed in all specimens by the metallography. The δ-ferrite content was also determined using magnetic and metallography methods. The δ-ferrite had a lathy structure with a content of 0.69–3.13 vol.%. The austenitic grains were equiaxial with an average size of 41.4–47.3 μm. The ultimate tensile strength (UTS) and yield strength (YS) mainly depended on the δ-ferrite content; otherwise, the impact energy mainly depended on both the austenitic grain size and the δ-ferrite content. The UTS of the RW1–RW3 specimens was above 550 MPa following the American Society of Mechanical Engineers (ASME) standard. The impact energy of all specimens was higher than that in ASME standard at about 56 J. The repeated welding up to three times could still meet the requirements for strength and toughness of welding specifications.

The Influence of the Heat-Affected Zone Mechanical Properties on the Behaviour of the Welding in Transverse Plate-to-Tube Joints.

Eurocode 3 establishes the component method to analytically characterize the structural joints between beam and columns. When one of the members involved in the joint is a hollow section (i.e., a tube) there is a lack of information for the specific components present in the joint. There are two different ways to bridge the gap: experimental testing on the actual beam column joints involving tubular sections; or numerical modelization, typically by means of finite element analysis. For this second option, it is necessary to know the actual mechanical properties of the material. As long as the joint implies a welding process, there is a concern related to how the mechanical properties in the heat-affected zone (HAZ) influence the behavior of the joint. In this work, some coupons were extracted from the HAZ of the beam-column joint. The coupons were tested and the results were implemented in the numerical model of the joint, in an attempt to bring it closer to the experimental results of the tested joints.

Experiment-based regional characterization of HAZ mechanical properties for laser welding

As for the tailor welded blanks (TWB) of dual-phase steels, heat-affected zone (HAZ) always exhibits significant changes of mechanical properties after experiencing the laser welding process. Hence, the characterization of HAZ mechanical properties is very critical for the accurate forming simulation and service performance of laser-welded blanks. However, it is still difficult to obtain the regional mechanical properties of HAZ because it has a varied transition of microstructures and mechanical properties in a very narrow range (e.g., <1 mm). In this paper, to investigate the regional mechanical properties of HAZ in the laser-welded joints of DP600 steels, an experimental approach was carried out based on the thermal simulation running on the Gleeble machine. The thermal histories of different regions in HAZ during laser welding were simultaneously measured by thermocouples, and then applied for the thermal simulation. The regional characterization of HAZ mechanical properties was realized with the thermal-simulated HAZ specimens. The results show that the thermal histories in weld and HAZ are very sensitive to the distance from the weld centerline, which results in different relevant microstructures and mechanical properties. The tensile strength of HAZ at different locations decreases with increasing distance from the weld centerline, but the elongation has the opposite tendency. The regional mechanical properties of HAZ were also applied to the finite element model of the tensile testing for welded joint by ABAQUS, an elastic-plastic finite element code. And the finite element simulation shows good agreement with the experimental.

High Strength Offshore Steel with Excellent Weldability

A new high strength low alloy (HSLA) steel in 370MPa yield strength grade with low susceptivity to weld cold cracking has been developed for offshore engineering. The microstructure feature of base steel and weld heat affected zone (HAZ) has been investigated. The systematic studies showed that the developed steel exhibited high strength(yield strength≥370MPa)、high impact toughness and excellent weldability. The complex inclusions containing fine oxides in HAZ promoted the acicular ferrite formation in weld thermal cycle and resulted in desired mechanical properties of HAZ.

Analysis of welded tensile plates with a surface notch in the weld metal and heat affected zone

Abstract The behavior of the plates with a surface notch under tensile external loading is experimentally and numerically analyzed. The specimens were made of micro-alloyed steel NIOMOL 490 K, welded by MAG (CO2) welding method. Surface notches were machined by the spark erosion method in the weld metal and heat affected zone. A finite element analysis of the specimens subjected to the tensile external loading is performed, with a simplified treatment of the heat affected zone mechanical properties. Obtained results are compared with the results of the experimental investigation, and a satisfactory agreement for the specimens containing the weld metal notch is observed. However, results for the specimen containing a notch in the heat affected zone require further investigation, including the analysis of the effects of micro structural heterogeneity.

Correlation between microstructure, hardness and strength in HAZ of dissimilar welds of rotor steels

Correlation between microstructure, hardness and strength was investigated in heat affected zone (HAZ) of dissimilar welding joints of newly developed rotor steels in terms of both the traditional micro-hardness testing and the nanoindentation technique. Relationships between micro-hardness and nano-hardness were obtained for HAZ of welds, where the mechanical properties were microstructure dependent. Lath width of the tempered martensites was selected as the characteristic microstructure size for correlating the micro-hardness. The detailed strength distribution in HAZ and the correlation with the characteristic microstructure size were discussed. A good agreement was observed for the correlated strength and the experimental results in both weld metal (WM) and base metal (BM), and therefore gave us confidence for the application of the proposed relationship between the hardness and the mechanical properties in HAZ of the dissimilar weld.

Formation and Thermal Fatigue Properties of Fine-grained Heat Affected Zone on Cast-hot-working-die Steel after Electropulsing Stimulation with High Current Density

The fatigue crack propagation behaviors of cast-hot-working die (CHWD) steel untreated and treated by electropulsing stimulation with different current densities were investigated in the present study. The elliptical heat affected zone (HAZ) was formed ahead of specimen notch tip due to the concentrating heat release induced by current bypassing and concentrating effect. The acreages of specimen HAZs were gradually enlarged because of the more heat energy input by elevating current density of electropulsing stimulation. The grain refinement and dislocation density increase in the specimen HAZs were enhanced by elevating the current density of electropulsing stimulation, which inevitably resulted in the improvement on the HAZ mechanical properties and the enhance of fatigue resistance. In addition, the induced compressive stress by electropulsing stimulation could decrease the peak value of tensile stress forming in the thermal fatigue process, which also enhanced the thermal fatigue resistance. Consequently, the resistance to thermal fatigue of CHWD steel was enhanced by grain refinement, dislocation density increase and induced compressive stress after electropulsing stimulation with high current density.

Mechanical Properties of Arc Welding Heat-Affected Zone of High Nitrogen Steel

Abstract The engineering application of high nitrogen steel (HNS) needs to obtain welded joint with good comprehensive properties. In order to acknowledge the influence of welding thermal cycle on the heat-affected zone (HAZ) of high nitrogen steel (HNS), the microstructure and mechanical properties of HAZ were investigated by using thermo-simulation technique. Experiment results indicate that the microstructure in the HAZ of HNS is composed of austenite and δ-ferrite. Carbide precipitation (Cr 23 C 6 ) occurs in the HAZ where the peak temperature of welding thermal cycle is about 800°C, and nitride (Cr 2 N) is not examined. The parameters of welding thermal cycle can affect the amount of δ-ferrite in the HAZ. Under the experimental conditions, the amount of the δ-ferrite in the coarse-grained heat-affected zone (CGHAZ) increases when the cooling rate increases, and it changes slightly while the peak temperature is lower than 1150°C. The hardness of the CGHAZ increases when the cooling rate increases, and that of the HAZ decreases while the peak temperature decreases. The results show that the hardness of the HAZ is higher than that of the base metal, indicating no softening of the HAZ under appropriate welding conditions. The impact toughness of CGHAZ is improved with the increase of cooling rate, whereas two brittle zones exist in the HAZ.

Microstructure and Mechanical Properties of Heat-affected Zone of High Nitrogen Steel Simulated for Laser Welding Conditions

In order to obtain some information on the weldability of high nitrogen steel (HNS), the microstructure and mechanical properties of the heat-affected zone (HAZ) of HNS under laser welding conditions were investigated by using thermo-simulation technique. The experimental results indicate that the microstructure in the simulated HAZ of HNS consists of austenite and d-ferrite that occurs in the grain boundary of austenite. The hardness of the simulated coarse-grained heat-affected zone (CGHAZ) increases when the cooling rate increases, and that of the simulated HAZ decreases while the peak temperature decreases. The results also show that the hardness of the simulated HAZ is higher than that of the base metal, indicating no softening of the HAZ under appropriate welding conditions. The impact toughness of simulated CGHAZ increases at first and then decreases with the increase of the cooling rate, whereas two brittle zones exist in the HAZ.