Heat-affected Zone Samples Research Articles

Corrosion Behavior of Q420qNH Plate and Welded Joint in Deicing Salt Medium by Cyclic Immersion + Infrared Drying

The corrosion behavior of Q420qNH steel plate and welded joint in deicing salt medium is investigated by cyclic immersion + infrared drying accelerated corrosion experiments. The results show that the corrosion products are mainly Fe2O3 and FeOCl under the influence of Cl− concentration differential corrosion microcells in the immersion corrosion anoxic stage, and the corrosion products are mainly β-FeOOH, γ-FeOOH, and Fe3O4 under the influence of oxygen concentration differential corrosion microcells catalyzed in the infrared drying stage. Throughout the corrosion process, the corrosion weight gain and average corrosion rate of the welded sample are always lower than that of the plate sample. The Iα-FeOOH/Iβ-FeOOH + FeOCl peak intensity ratio of the welded sample is always higher than that of the plate sample and the heat-affected zone (HAZ) sample. The corrosion types of the three samples are inhomogeneous total corrosion + pitting, and the depth of the pits in the plate is much larger than that in the weld and the HAZ. In the late stage of corrosion, the self-corrosion current density is: plate > HAZ > weld, and the resistance of the rust layer of the weld and HAZ samples is 1.66 times and 1.31 times that of the plate sample, respectively. This is because the microstructure of the weld and HAZ are composed of a large number of fine acicular ferrite and lath-shaped bainite generated inside the original austenite grains, and the small angle grain boundary is not conducive to the initiation and expansion of pitting corrosion. In addition, the higher content of Cu, Cr, Ni, and other elements in the weld can refine the rust layer products and effectively impede the intrusion of Cl−, contributing to corrosion resistance improvement. As the combined effect of Cl− and immersion anoxic environment inhibits the formation of α-FeOOH and promotes the formation of a large number of loose and unstable β-FeOOH and soluble FeOCl, the weathering steel is not well protected by the rust layer during cyclic immersion corrosion in deicing salt medium.

Stress relaxation cracking susceptibility evaluation in 347H stainless steel welds

AbstractStress relaxation cracking (SRC) has been reported as a dominant failure mechanism for 347H stainless steel welds at elevated service temperatures, occurring in either the heat-affected zone (HAZ) or fusion zone (FZ). In this study, SRC susceptibility of physically simulated HAZ and cross-welded E347-347H stainless steel welds was studied using a four-step accelerated SRC test with a thermomechanical physical simulator. The stress and temperature range studied represents weld-induced residual stress at 150–600 MPa and post-weld heat treatment temperatures between 800 and 1050 °C. For all temperature conditions, the cross-welded samples failed at a lower critical stress threshold than the simulated HAZ. A finite element model of a 50.8-mm-thick single-V groove weld was used to generate the residual stress maps induced by a 40-pass welding procedure, which in combination with the experimental threshold stress map predicted potential SRC failure locations. Postmortem microstructural evaluations were performed to identify contributing characteristics to SRC. It was found that HAZ samples exhibited a combination of creep void development, secondary cracks with intergranular fracture near grain boundary carbides, and eutectic phases. FZ samples showed brittle fracture with cracks propagating along straight, non-tortuous interdendritic grain boundaries.

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.

Analysis of microstructural evolution and mechanical properties in the simulated heat-affected zone of Fe-23Mn-0.45C-1.5Al high-Mn austenitic steel

Welding thermal simulation technology was used to process Fe-23Mn-0.45C-1.5Al high-Mn austenitic steel to reproduce the heat-affected zone (HAZ) and investigate the effect of peak temperature on microstructural evolution and cryogenic toughness. Subsequently, the simulated HAZ samples experienced isothermal aging at 500 °C for different time to clarify the embrittlement mechanism. The results revealed that phase transformation was absent in simulated HAZ sample. However, with the increase of peak temperature (Tp) in thermal cycles from 1050 °C to 1320 °C, the grain size, carbide precipitates at grain boundaries, grain boundary segregation of carbon and the proportion of low angle grain boundaries increase gradually, while the proportion of high angle grain boundaries decrease. When Tp was above 1200 °C, granular M7C3-type and rod-shaped M23C6-type carbides precipitated at grain boundaries. Impact absorbed energy of simulated sample at room and cryogenic temperatures decreased with the increase of Tp. The impact energy of experiment steel is 228 J at room temperature. When the Tp increased to 1050 °C, 1200 °C and 1320 °C, the impact absorbed energy of simulated sample decreased to 208 J, 174 J and 142 J, respectively. The variation trends of impact absorbed energy for aged samples manifested that the precipitation of M23C6-type or M7C3-type carbides at grain boundaries was the main factor causing the embrittlement of HAZ, and then the segregation of carbon at grain boundary and high proportion of low angle grain boundaries were the secondary factor causing the deterioration of impact toughness.

Improved mechanical properties of laser-repaired 15-5PH stainless steel by in-situ heat treatment and grain refinement

Mechanical properties of repaired part by laser melting deposition (LMD) mainly depend on microstructure of clad layer and heat affected zone (HAZ). For precipitation-hardened steel, the properties of as-deposited materials are usually not satisfactory. Post heat treatment is an effective way to improve mechanical properties but sometimes become infeasible or restricted due to various reasons. In this paper, by deliberately reducing the scanning speed to provide more energy than needed to melt the powder, heat accumulation in the deposited area is enhanced and an in-situ heat treatment is provoked. The strength of as-deposited clad layer is greatly enhanced (1290Mpa for ultimate tensile strength) by precipitation strengthening while maintaining good ductility. The possible influences of excessive heat on the HAZ are also evaluated. Experimental results show all the HAZ samples have a slightly lower strength compared to heat treated substrate. Excessive heat input does not deteriorate the strength of HAZ. On the contrary, the ductility of the material in HAZ is enhanced due to the effect of grain refinement and overage. In this way, the as-repaired parts can achieve a higher strength without heat treatment, which provides a new method for the repair of parts that cannot be subjected to post heat treatment.

Microstructure and Local Mechanical Properties of the Heat-Affected Zone of a Resistance Spot Welded Medium-Mn Steel.

The properties of the heat-affected zone (HAZ) are reported to have a great influence on the mechanical performance of resistance spot welded advanced high strength steels. Therefore, in the present work, the HAZ of a medium-Mn steel is characterized regarding its microstructure and its mechanical properties depending on the distance to the fusion zone (FZ). In order to obtain the local mechanical properties of the HAZ, samples were heat-treated in a joule-heating thermal simulator using different peak temperatures to physically simulate the microstructure of the HAZ. By comparing the microstructure and the hardness of these heat-treated samples and the HAZ, the local peak temperatures within the HAZ could be determined. Subsequently, tensile tests were conducted, and the austenite phase fraction was measured magnetically on the physically simulated HAZ samples in order to determine the local mechanical properties of the HAZ. As verified by energy-dispersive X-ray spectroscopy, peak temperatures above 1200 °C led to a uniform distribution of manganese, resulting in a predominantly martensitic microstructure with high strength and low total elongation after quenching. Below 1100 °C, the diffusion of manganese is restricted, and considerable fractions of austenite remain stable. The austenite fraction increases almost linearly with decreasing peak temperature, which leads to an increase of the total elongation and to a slight decrease in the strength, depending on the distance to the FZ. Temperatures below 700 °C exhibit hardly any effect on the initial microstructure and mechanical properties.

High Temperature Plasticity of TP347H Stainless Steel Welded Joint Heat Affected Zone

Simulated Heat Affected Zone (HAZ) samples of TP347H stainless steel welded joint with 800-1380°C peak temperature thermal cycles were produced using Gleeble 3180 thermal mechanical simulator. 600°C constant speed tensile tests for simulated HAZ samples were carried out, and the precipitates of the simulated samples were analyzed by EDAX. The results show that the lowest Reduction of Area (RoA) was around 53% - 56% in 900-1150°C, which was about 15% lower than the maximum RoA in 800-1380°C. The reasons for decrease of HAZ high temperature plasticity were related to the precipitation of NbC. The fine NbC precipitated in the crystal and grain boundary enhanced strength of grain at high temperature, which resulted plastic deformation or slip at high temperature were mainly concentrated in the grain boundary, and high temperature plasticity of HAZ were decreased.

Microstructure and High-Temperature Strength in the Weld Coarse-Grained Heat-Affected Zone of Fire-Resistant Steels and the Effects of Mo and Nb Additions

The microstructural evolution and fire-resistant properties in the weld heat-affected zone (HAZ) of Mo and Mo + Nb-added fire-resistant steels were investigated. For this purpose, three Fe-0.1 wt%C-1.5 wt%Mn-0.1 wt%Si steels containing various Mo and Nb contents were prepared. HAZ samples were experimentally simulated using a Gleeble simulator at a welding heat input of 30 and 300 kJ/cm. The yield strength of the HAZ samples was higher than those of base steels at both room temperature and 600 ℃, whereas a greater decrease in the yield strength at 600 ℃ compared to that at room temperature occurred in the HAZ samples than in the base steels, indicating that the fire-resistance deteriorated in the HAZs as compared to the base steels. This is due to the formation of hard phases such as bainite and martensite in the HAZs, i.e., bainite and martensite phase have very high yield strength with high dislocation density at room temperature, while their strengths decrease rapidly at high temperature due to a great annihilation and recovery of dislocations at high temperature. In addition, the fire-resistance of the HAZ improved as the heat input was increased. The alloying of Mo and Nb improved the fire-resistance of both the base steels and the HAZs. Finally, the changes in the microstructures of the base steels and the HAZs upon alloying and the heat input and corresponding effects on the fire-resistance were carefully explored and discussed through transmission electron microscopy analyses, atom probe tomography analyses, and calculations of continuous cooling transformation diagrams.

Study on Hydrogen Diffusion and Sulfide Stress Cracking Behaviors of Simulated Heat-Affected Zone of A516-65 Grade Pressure Vessel Carbon Steel

Hydrogen diffusion and sulfide stress cracking of simulated heat-affected zone (HAZ) of A516- 65 grade steel were examined using an electrochemical permeation technique, glycerin volumetric method, and constant loading method. HAZ samples were fabricated using a metal thermal cycle simulator with a welding heat input of 20, 35, and 50 kJ/cm. The fractions of bainite and martensite-austenite (M-A) constituent in coarse-grained HAZ (CGHAZ) and intercritical HAZ (ICHAZ) obtained by a simulated thermal cycle with a low heat input (20 kJ/cm) were higher than those with a higher heat input. These fractions contributed to the increase in the reversible hydrogen trap density (N<sub>[H]rev</sub>) and reversibly trapped hydrogen concentrations (C<sub>rev</sub>). Although CGHAZ had higher N<sub>[H]rev</sub> and C<sub>rev</sub> meaning that it is more likely to be vulnerable to brittle failure by hydrogen, actual fracture by sulfide stress cracking (SSC) occurred in ICHAZ composed of a mixture of soft ferrite/pearlite, and hard bainite and M-A. The hydrogen diffusion/trapping parameters, which were obtained from the electrochemical permeation or glycerin method, cannot be directly indicative of the resistance to SSC of the steel in a H<sub>2</sub>S environment. The susceptibility to SSC was more influenced by the level of M-A-localization and localized corrosion attack, acting as a stress intensifier under a tensile load.

Analysis on Fracture Toughness of the L360QS/N08825 Bimetallic Composite Pipe Welded Joint

The fracture toughness of the weld and heat-affected zone (HAZ) of the L360QS/N08825 composite pipe welded joint was evaluated by a crack tip opening displacement (CTOD) test. The fracture morphology, microstructure, and inclusion near fracture zones were observed by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy dispersive spectroscopy (EDS). The grain size and grain orientation of the crack propagation zone in the weld were investigated by electron back-scattered diffraction (EBSD). The results revealed that the average CTOD values of the weld and HAZ samples were relatively high, and a greater dispersion of CTOD values of the HAZ samples is due to the pop-in phenomenon in the P–V curve. The fracture surfaces of the weld and HAZ samples showed the characteristics of ductile fracture to a certain extent, whereas the fracture of the CTOD sample with the pop-in phenomenon exhibited a quasicleavage feature. High-density dislocation and a large number of inclusions were observed in the near fracture zone of the weld and HAZ samples. The stress concentration, caused by hindering the dislocation slip, was the main reason for microcrack formation. The existence of large-size grains and large-scale small-angle grain boundary in the weld implies that the cracks propagate toward the weld.

Hydrogen-Assisted Crack Growth in the Heat-Affected Zone of X80 Steels during in Situ Hydrogen Charging.

Herein, the hydrogen embrittlement of a heat-affected zone (HAZ) was examined using slow strain rate tension in situ hydrogen charging. The influence of hydrogen on the crack path of the HAZ sample surfaces was determined using electron back scatter diffraction analysis. The hydrogen embrittlement susceptibility of the base metal and the HAZ samples increased with increasing current density. The HAZ samples have lower resistance to hydrogen embrittlement than the base metal samples in the same current density. Brittle circumferential cracks located at the HAZ sample surfaces were perpendicular to the loading direction, and the crack propagation path indicated that five or more cracks may join together to form a longer crack. The fracture morphologies were found to be a mixture of intergranular and transgranular fractures. Hydrogen blisters were observed on the HAZ sample surfaces after conducting tensile tests at a current density of 40 mA/cm2, leading to a fracture in the elastic deformation stage.

Effects of Welding Power Input on the Microstructure and Impact Toughness of the Heat Affected Zone of 304L Austenitic Stainless Steel

The effects of welding power input on the microstructural characteristics and impact behaviour of the Heat Affected Zone (HAZ) of type 304L austenitic stainless steel were investigated. This is with a view to optimize the welding process and ensure high weldment integrity of the heat affected zone. Chemical analysis of the as-received 304L austenitic stainless steel was determined using an Optical Emission Spectrometry AR 4 30 metal analyzer. Thereafter, 30 samples of the as-received 304L austenitic stainless steel plate with dimensions of 70 mm length, 45 mm breadth and 8 mm thickness were cut and labeled into A, B and C each of 10 numbers. The grouped samples were further cut into two equal halves with hacksaw and welded using Gas Metal Arc Welding (GTAW) process and 304L electrode to produce butt joint HAZ square geometry samples. The obtained HAZ and as-received samples were machined to standard charpy impact test specimens. Also, the HAZ and as-received specimens were prepared for microscopy studies using optical microscopy. Results obtained showed that the microstructures are composed majorly of mixture of austenite and ferrite phases, also variations in volume fraction and grain size of the phases were observed under varied range of power input. In addition, chromium carbide formation and precipitation due to sensitization was seen at the grain boundaries. Optimum impact toughness (IT) of 42 J was obtained for HAZ sample at power input of 12.0 KW while the least IT of 39 J was obtained from sample welded using power input of 4.6 KW as compared with the as-received with IT of 58 J.Keywords - 304L austenitic stainless steel; gas metal arc welding; impact toughness; microstructures;

Constitutive properties and plastic instabilities in the heat-affected zones of advanced high-strength steel spot welds

Recent publications have shown that the load-bearing capability of advanced high-strength steel (AHSS) spot welds do not scale linearly with the tensile strength of the base metal. Although this unexpected degradation of welds has been linked to the tempering of the martensite phase in the heat-affected zone (HAZ), the detailed elastic–plastic stress–strain behavior in different regions of the HAZ has not been reported. In this research, the plastic flow behavior in samples subjected to simulative weld thermal cycles with peak temperatures (TPeak) ranging from 350 to 1250 °C was evaluated. Results from this study showed that the microstructural changes in the HAZ could result in large mechanical heterogeneity in AHSS spot welds. In addition, plastic instability in the form of yield point phenomena was observed. The yield point phenomena in these simulated HAZ samples, in contrast to base metal samples, were confirmed by the observation of Luders band and stress fluctuations before the onset of strain hardening using digital image correlation. The local plastic instability was correlated to the chemical composition of the steel, initial microstructure, and thermal cycle. The Luders front velocity maps revealed heterogeneous nucleation and growth of multiple Luders bands with different front speeds. Interestingly, inter-critical (Ae1 < TPeak < Ae3) HAZ samples show minimum yield strength even though the maximum softening occurs in the subcritical HAZ (TPeak < Ae1) samples.

Influence of κ-carbide precipitation on the microstructure and mechanical properties in the weld heat-affected zone in various FeMnAlC alloys

This study aims to investigate the effects of κ-carbide precipitation behavior in the heat affected zone (HAZ) in FeMnAlC lightweight steels. Three alloys with different amounts of Al were prepared by vacuum induction melting and hot rolling. After solution treatment, the HAZ samples were simulated by a Gleeble simulator with two heat inputs of 10 and 30 kJ/cm. Microstructural analysis with XRD and TEM were carried out while sub-sized tensile test, hardness test, and V-notched Charpy impact test were performed for investigating the mechanical properties of the base steels and HAZ. The results showed that the mechanical properties and precipitation of κ-carbide within the HAZ were strongly related to the Al content and heat input; the tensile strength and hardness of the HAZ increased as the Al content and heat input increased while elongation decreased. On the other hand, in the Charpy impact test, fracture mode transitions in the HAZ (ranging from ductile fracture to brittle inter-granular fracture) occurred in accordance with the Al content and heat input. The different fracture behavior was explained by TEM results, which showed precipitation behavior of κ-carbide in HAZ. Coherent intra-granular κ-carbide was found to cause a transition from ductile fracture to trans-granular cleavage, and we observed that a severe drop of the impact toughness occurred when partially coherent inter-granular κ-carbide appeared. Therefore, our results illustrate that the HAZ of lightweight steels with the proper Al content can be strengthened with minimal loss of impact toughness due to κ-carbide precipitation during the welding process.

Effect of thermomechanical parameters on mechanical properties of base metal and heat affected zone of X65 pipeline steel weld in the presence of hydrogen

In this study, the effect of different microstructures resulting from thermochemical processes of X65 pipeline steel on mechanical properties of welding in the presence of hydrogen was investigated. According to studies conducted, due to the charge of hydrogen, the hardness of base metal (BM) increased by 10%, the hardness of heat affected zone (HAZ) samples increased by about 13%, the yield strength of base metal increased by an average of 5% and the yield strength of HAZ increased by about 7%, indicating hardening. Elongation was reduced by 32–70% and the percentage of ductile fracture decreased by an average 46% which shows that the fracture of samples in the presence of hydrogen is brittle. In the study of hydrogen defect and concentration of hydrogen permeated to the material it was determined that, the ferrite-pearlite banded microstructure of base metal has a higher hydrogen defect sensitivity than HAZ with an acicular ferrite microstructure and hard phase. In base metal samples under various rolling conditions, the two-pass rolled and the final rolling temperature of 800 °C sample (2BM800), with a smaller grain microstructure and higher interface, had the most diffusive hydrogen content and therefore had the highest hydrogen defects. In the case of HAZ samples, the effect of hydrogen on the increase in hardness and strength properties is greater than that of the base metal samples due to the different microstructure (of the acicular ferrite) and the variable grain size (i.e. the presence of two coarse-grained and fine grained areas). Overall, the results of this study showed that the microstructure has a significant effect on mechanical properties, the amount of diffusive hydrogen and hydrogen defects in welds.

Effects of Electrode Types on the Microstructure, Tensile and Hardness Properties of 304 L Austenitic Stainless Steel Heat-Affected Zone (HAZ)

Submerged arc welding (SAW) has been well utilised for the production of weld joints in 304 L ASS for various industrial application. However, effective performance of the material in service has been hampered by improper choice of electrode. Therefore, in this study, effects of different types of electrode on the microstructure and tensile property of type 304 L austenitic stainless steel heat-affected zone (HAZ) were studied. Chemical composition of the as-received sample was determined. A number of samples were cut from the as-received sample. Afterwards, two half were joined together with 308 L, 312 L and 316 electrodes at a controlled welding speed, current and voltage of 4.6 mm/s, 160 A and 30 V to produce a constant heat input of 626.09 J/mm. An automatic SAW machine with Model Type: DX3-301, and Frequency: 50 Hz was used. And based on ASTM standard, tensile and hardness samples were prepared from the as-received and HAZs. Tensile and hardness measurements were made. Also, specimens for microscopy studies were prepared from the HAZ and as-received samples. From the results, microstructures of the HAZs revealed varied volume fraction of austenite and ferrite phases and grain sizes, and at austenite and ferrite grain boundaries, chromium carbide formation and precipitation were observed. The weld joint produced with 308 L electrode revealed optimum UTS value and YS value of 475 and 325 respectively. While weld joint produced with 316 L electrode has superior ductility of value 41%. Irrespective of the types of electrode used, the as-received sample revealed superior tensile properties over the weld joints. Also, optimum hardness value of 45.7 HRA was obtained with 308 L. Hardness value of the as-received sample was higher than that of HAZ samples.

An Investigation on the Microstructure Evolution and Tensile Property in the Weld Heat-Affected Zone of Austenitic FeMnAlC Lightweight Steels

IMicrostructure evolution and tensile property in the weld heat-affected zone (HAZ) of austenitic Fe-30Mn-9Al-0.9C lightweight steels were investigated. Five alloys with different V and Nb content were prepared by vacuum induction melting and hot rolling process. The HAZ samples were simulated by a Gleeble simulator with welding condition of 300kJ/cm heat input and HAZ peak temperatures of 1150°C and 1250°C. Micro-structures of base steels and HAZ samples were observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), and their mechanical properties were evaluated by tensile tests.The addition of V and Nb formed fine V and/or Nb-rich carbides, and these carbides increased tensile and yield strength of base steels by grain refinement and precipitation hardening. During thermal cycle for HAZ simulation, the grain growth occurred and the ordered carbide (κ-carbide) formed in the HAZs. The yield strength of HAZ samples (HAZ 1) simulated in 1150°C peak temperature was higher as compared to the base steel due to the formation of κ-carbide, while the yield strength of the HAZ samples (HAZ 2) simulated in 1250°C decreased as compared to HAZ 1 due to the excessive grain growth. Key words: Lightweight steel, Heat-affected zone, Grain growth, κ-carbide, Yield strength

Microstructural Evolution and Mechanical Properties of Simulated Heat-Affected Zones in Cast Precipitation-Hardened Stainless Steels 17-4 and 13-8+Mo

Cast precipitation-hardened (PH) stainless steels 17-4 and 13-8+Mo are used in applications that require a combination of high strength and moderate corrosion resistance. Many such applications require fabrication and/or casting repair by fusion welding. The purpose of this work is to develop an understanding of microstructural evolution and resultant mechanical properties of these materials when subjected to weld thermal cycles. Samples of each material were subjected to heat-affected zone (HAZ) thermal cycles in the solution-treated and aged condition (S-A-W condition) and solution-treated condition with a postweld thermal cycle age (S-W-A condition). Dilatometry was used to establish the onset of various phase transformation temperatures. Light optical microscopy (LOM), scanning electron microscopy (SEM), and energy dispersive spectrometry (EDS) were used to characterize the microstructures, and comparisons were made to gas metal arc welds that were heat treated in the same conditions. Tensile testing was also performed. MatCalc thermodynamic and kinetic modeling software was used to predict the evolution of copper (Cu)-rich body center cubic precipitates in 17-4 and β-NiAl precipitates in 13-8+Mo. The yield strength was lower in the simulated HAZ samples of both materials prepared in the S-A-W condition when compared to their respective base metals. Samples prepared in the S-W-A condition had higher and more uniform yield strengths for both materials. Significant changes were observed in the matrix microstructure of various HAZ regions depending on the peak temperature, and these microstructural changes were interpreted with the aid of dilatometry results, LOM, SEM, and EDS. Despite these significant changes to the matrix microstructure, the changes in mechanical properties appear to be governed primarily by the precipitation behavior. The decrease in strength in the HAZ samples prepared in the S-A-W condition was attributed to the dissolution of precipitates, which was supported by the MatCalc modeling results. MatCalc modeling results for samples in the S-W-A condition predicted uniform size of precipitates across all regions of the HAZ, and these predictions were supported by the observed trends in mechanical properties. Cross-weld tensile tests performed on GMA welds showed the same trends in mechanical behavior as the simulated HAZ samples. Welding in the S-W-A condition resulted in over 90 pct retention in yield strength when compared to base metal strengths. These findings indicate that welding these PH stainless steels in the solution-treated condition and using a postweld age will provide better and more uniform mechanical properties in the HAZ that are more consistent with the base metal properties.

Analysis on Fracture Toughness of the L415MS/N08825 Bimetallic Composite Pipe Welded Joint

Crack tip opening displacement (CTOD) tests were conducted on the weld and heat affected zone (HAZ) of L415MS/N08825 bimetallic composite pipe welded joint according to BS7448, ISO12135(2002) and ISO15653(2010) standards at room temperature. The fracture toughness of weld and HAZ were studied and analyzed. The fracture surface and inclusions were characterized using scanning electron microscopy (SEM) and energy-dispersive X-ray spectrometry (EDS), respectively. The results showed that the average CTOD value of the weld was less than HAZ, CTOD values of HAZ exhibited larger discrete, which was mainly caused by Pop-in effect in P-V curve of HAZ samples. CTOD value of sample with Pop-in effect dropped several times than sample without Pop-in effect. The fracture surfaces of the weld and HAZ showed tough fracture to a certain extent, and the fracture surface of HAZ sample with Pop-in effect exhibited significant quasi-cleavage feature.

Fatigue crack propagation and metallographic mechanism for steel ADB610 welded joints

High-strength steel ADB610 is a low carbon bainite steel and was newly developed in China. Fatigue crack propagation rate experiments and metallographic experiments for butt welded joints of steel ADB610 were investigated. The welding method is shielded metal arc welding. The fatigue crack propagation experiments were done under a constant load using compact tension samples and MTS810 TestStar materials testing facility at the stress ratio of 0·1. Seven data polynomial method was used to calculate fatigue crack propagation rate (da/dN) of each compact tension samples. All da/dN and △K of base metal samples, heat-affected zone samples and weld metal samples were fitted, respectively, and the formula based on Paris for base metal, heat-affected zone and weld metal were obtained. Fatigue crack propagation experimental results indicate that fatigue crack propagation rate in base metal is higher than that in heat-affected zone and weld metal, and the one in weld metal is the slowest during the early and middle stage of crack propagation, but during the end stage of crack propagation the fatigue crack propagation rates for the three regions of steel ADB610 welded joints were nearly at the same level with slight fluctuations with each other. The metallographic experiments show that the crystal grains in the weld metal were finer than those in the heat affected zone and base metal, and the heat-affected zone microstructure was meshy. So the resistance against fatigue crack propagation in the weld metal is higher than that in the heat-affected zone and base metal, and the resistance against fatigue crack propagation in the heat-affected zone is higher than that in the base metal. The fatigue crack propagation difference of steel ADB610 welded joins from metallographic experiments is consistent with the result from fatigue crack propagation experiments.