Heat Affected Zone Of Steel Research Articles

Stress corrosion property of 304 stainless steel and Q345 steel laser-MAG hybrid welded joints

The stress corrosion cracking (SCC) property of laser-MAG hybrid welded 304 stainless steel and Q345 steel was evaluated through cycle-immersion testing in 3.5 wt.% NaCl solution. The average SCC crack propagation rate of different zones under different initial stress intensity factors was calculated, and the SCC fracture and crack propagation path were observed. The microstructure and mechanical properties of the weld joint have also been examined. The result indicates that the fusion zone (FZ) is extremely prone to SCC. The average SCC crack propagation rate in FZ is [Formula: see text] mm/h, while no obvious SCC was found in the base metal (BM) and heat-affected zone (HAZ). The steel BM and HAZ may also suffer SCC, but not as fast as in FZ. Grooves caused by SCC were found on the fracture surface with a large amount of corrosion products accumulated close to the interface between the pre-crack section and SCC section. Crystallized-sugar-shaped pattern was found on the SCC zone of FZ. Crack jumping, deflection and crack closure occurred in the crack propagation path. Martensite on the FZ was considered to be the major reason that the FZ has a higher SCC propagation rate.

A Review of Austenite Memory Effect in HAZ of B Containing 9% Cr Martensitic Heat Resistant Steel

During the welding process of B containing 9% Cr martensitic heat resistant steel (9Cr-B steel), austenite memory effect (referred to that the prior austenite grains in the heat affected zone (HAZ) after welding inherit the shape and size of prior austenite grains before welding) occurs in its normalized sub-zone of HAZ and the grain refinement is suppressed, which can effectively prevent type IV crack, and improve the service life of the welded joint at high temperatures. In the present article, α/γ reverse transformation behavior in the normalized sub-zone of 9Cr-B steel HAZ is reviewed. Austenite memory effect of 9Cr-B steel is derived from B addition. The main mechanisms of austenite memory effect during α/γ reverse transformation are discussed. Various models of boron causing austenite memory effect are discussed in detail. Matrix microstructure also plays an important role in austenite memory effect. Effects of heating rate, peak temperature, and holding time at peak temperature on austenite memory effect are also discussed.

Evaluation of double-layer weld deposition technique on ASTM A182 F22 steel without post-weld heat treatment

The present work evaluates the mechanical and metallurgical behavior of ASTM A182 F22 steel heat-affected zone (HAZ) through the double-layer weld deposition technique, with different welding energies between the first and second layers. This methodology leads to the reduction of hardness levels in the HAZ and can exempt the need for post-weld heat treatment on low-alloy steel after buttering welding. The welding was performed by the automated GMAW process in flat position. As the filler metal, the AWS ER309L, ER 80S-G and ER NiCrMo-3 (Inconel 625) alloys were applied on ASTM A182 F22 steel. The analysis of the refining and/or tempering in coarse-grained HAZ (CGHAZ) of the first layer was performed by metallographic tests and microhardness measurements. The tempering of the first-layer CGHAZ is dependent on the correct overlap of the weld layers, weld bead geometry and the highest imposed heat of the second layer. The results revealed that the Higuchi technique is effective for obtaining welding parameters for the second-layer deposition that promotes thermal treating of the hard region of the first-layer HAZ. However, this technique was not able to reduce the hardness values at the 250 HV level required by NACE 0175 for the test conditions in this work.

Formation and evolution of layered structure in dissimilar welded joints between ferritic-martensitic steel and 316L stainless steel with fillers

Dissimilar high-energy beam (HEB) welding is necessary in many industrial applications. Different composition of heat-affected zone (HAZ) and weld metal (WM) lead to variation in mechanical properties within the dissimilar joint, which determines the performance of the welded structure. In the present study, appropriate filler material was used during electron beam welding (EBW) to obtain a reliable dissimilar joint between reduced-activation ferritic-martensitic (RAFM) steel and 316 L austenitic stainless steel. It was observed that the layered structure occurred in the weld metal with 310S filler (310S-WM), which had the inferior resistance to thermal disturbance, leading to severe hardening of 310S-WM after one-step tempering treatment. To further ameliorate the joint inhomogeneity, two-step heat treatment processes were imposed to the joints and optimized. δ-ferrite in the layered structure transformed into γ-phase in the first-step normalizing and remained stable during cooling. In the second-step of tempering, tempered martensite was obtained in the HAZ of the RAFM steel, while the microstructure of 310S-WM was not affected. Thus, the optimized properties for HAZ and 310S-WM in dissimilar welded joint was both obtained by a two-step heat treatment. The creep failure position of two dissimilar joints both occurred in CLAM-BM.

Physical Simulation-Based Characterization of HAZ Properties in Steels. Part 1. High-Strength Steels and Their Hardness Profiling

In the vehicle industry, there is an increasing demand for wider application of high-strength steels. New generations of high-strength steels, with higher strength and toughness properties, are continuously developed by the steel producers. They provide good strength-to-weight ratios, acceptable weldability, improved toughness, and sufficient deformation capacity. However, the weldability of high-strength steels has still challenges which are as follows: cold cracking sensitivity; reduction of strength and toughness of heat affected zone (HAZ); filler material selection. In the HAZ of high-strength steels, hardened and softened zones can be found, where the base material can significantly lose its outstanding mechanical properties. In real welded joints, HAZ properties can be limitedly analyzed by conventional material tests. Therefore, physical simulators (i.e., Gleeble) were developed for the examination of different HAZ areas. Another motivation for the application of physical simulators is the time- and material-saving, as compared to real welding experiments. In this study, the weldability, especially HAZ properties of two high-strength structural steels (S960QL and S960M) from the same strength category (Rp0.2 = 960 MPa) and thickness (t = 15 mm) were compared and discussed. Two relevant technological variants for gas metal arc welding (GMAW), t8.5/5 = 5 and 30 s were applied during HAZ simulations and the effect of cooling time on the critical HAZ areas was analyzed. The properties of the selected coarse-grained, fine-grained, intercritical, and subcritical zones were investigated by the optical microscopy and hardness tests.

Effect of Intercritical Quenching Temperature of Cu-Containing Low Alloy Steel of Long Part Forging for Offshore Applications

In our previous study, intercritical quenching from the dual-phase region of ferrite and austenite regions, which is called lamellarizing (L) treatment, brought a clear improvement of balance between the strength and toughness of Cu-containing low alloy steel based on American Society for Testing and Materials (ASTM) A707 5L grade. Moreover, the results imply that the reverse transformation behavior during L treatment is very important in order to optimize the L treatment temperature. Hence, the purpose of this paper is to clarify the mechanism by which L treatment improves the mechanical properties in terms of reverse transformation behavior. Additionally, offshore structures require good weldability, because the structures generally have a lot of weld joints. Therefore, weldability was also investigated in this study. The investigation revealed that coarse Cu precipitates are observed in the not-transformed α phase, so the strength tendency in relation to the L treatment temperature is relevant to the area ratio of the not-transformed α phase and the transformed γ phase during L treatment. From the in situ electron back scatter diffraction (EBSD) results, it is believed to be possible to enhance the mechanical properties of Cu-containing low alloy steel by controlling the area ratio of the reverse-transformed gamma phase and selecting the appropriate L treatment temperature. Furthermore, the long part forging of Cu-containing low alloy steel has a good weldability, since the maximum hardness of the heat-affected zone (HAZ) is less than 300 HV, and the HAZ of steel has a good crack tip opening displacement (CTOD) property with less than 2.3 kJ/mm of heat input of GTAW.

Study on fracture toughness evaluation method of SA738Gr.B steel heat affected zone in ductile-brittle transition region

ABSTRACT The Master Curve (MC) method is widely used to evaluate the fracture toughness of ferritic steels for reactor pressure vessels in the ductile-brittle transition zone, but this method is only applicable to macroscopically uniform ferritic steels. Based on the measured fracture toughness data of China-produced SA738Gr.B steel Heat-Affected Zone (HAZ) in the as-welded and heat-treated state, the problems of the standard MC method for characterizing the fracture toughness of the HAZ are discussed. Then the Bi-modal master curve method (BMC), SINTAP method, and Single point estimation method (SPE) were used to characterize the fracture toughness of the HAZ of SA738Gr.B steel in the ductile-to-brittle transition zone. The comparative analysis found that the BMC method is better in terms of the accuracy of the estimation and the over-dispersion envelope was caused by the heterogeneity. The estimation results of the SINTAP and SPE models are conservative but can be used for the safety evaluation of the actual structure. The study provided technical support for SA738Gr.B steel to exempt post-weld heat treatment issue.

Characterization of Static Performance and Failure of Resistance Spot Welds of High-Strength and Press-Hardened Steels

The static performances and failure characteristics of resistance spot welds (RSW) of steel sheets were studied in this work. Both similar and dissimilar joints of press-hardened steel grade 22MnB5 and as-rolled high-strength steel grade 1000 were examined. From metallographic analyses and micro-hardness measurements, it was shown that the microstructures of base metal (BM), heat affected zone (HAZ) and fusion zone of steel joints were noticeably different. In particular, the HAZ close to BM or subcritical HAZ (SCHAZ) of 22MnB5 steel exhibited greatly decreased hardness due to occurring tempered martensite, in which carbide precipitation was clearly observed. Furthermore, tensile shear test and cross-tension test of the welded steel sheets were carried out. The determined maximum loads, energy absorbability and corresponding failure mechanisms were analyzed and compared. The RSW samples of similar steel grade 1000 provided the highest load-carrying capacity and absorbed energy in both tests. Due to the large hardness difference and soft zone in weldment of dissimilar steel specimen, failure loads and static absorbed energies were deteriorated up to 17 and 68%, respectively. The observed fracture occurrences of all investigated joints were pullout failure mode, in which BM and HAZ were the crack initiation sites of grades 1000 steel and 22MnB5 steel, respectively. The SCHAZ of welded boron steel considerably caused the failure onset in tension shear test, but seemed to have negligible effect on cross-tension test.

Characterization and comparison of copper coatings developed by low pressure cold spraying and laser cladding techniques

Abstract Copper coatings of 3-mm thickness were developed by both cold spraying and laser cladding techniques on SS316 steel. The developed coatings were then characterized with various techniques to evaluate metallurgical and mechanical properties. Tensile strength (170 MPa) of the cold sprayed coating was found to be comparable with that of the laser cladded coating, whereas %age elongation of laser cladding (11%) was almost double (6%) of that for the cold sprayed coating. Porosity was found to be low in the cold sprayed coating as compared to that in the laser cladding, which indicates that the former technique could give a denser coating. This difference in porosity led to relatively higher electrical and thermal conductivity in the cold sprayed coating as compared to the laser cladding. X-ray diffraction and electron disperse spectroscopy analyses revealed the absence of oxide formation in the cold sprayed coating, however oxides were seen in the laser cladding. Also, a large heat affected zone (HAZ) was detected in the laser cladding, whereas no HAZ was observed in the cold sprayed coating. Hardening was observed along the interface and HAZ of the cladded steel, which may be attributed to the diffusion of carbon from the substrate

Simulation of residual stress using thermomechanical analysis on wire EDM cut surface

Abstract Wire EDM is widely used for machining precision components. In WEDM process, the heat of plasma spark generated between the cathode and anode is responsible for the melting of work piece material in controlled shape through series of coordinated spark in “ON” and “OFF” cycle. The part of material which melted forms cater and some melted material gets redeposited on the work piece before completely ejecting out in cooling cycle due to sudden cooling by surrounding fluid. The heat affected zone (HAZ) also contains this redeposited molten metal and forms a recast layer with complex surface texture. The recast layer exhibits residual stress at surface like other cutting process. Residual stresses limit the service life of component since it initiates cracks and which may propagate to the base metal under favorable condition. This limits performance of the engineering components. This is important to predict such stresses. In this study the FE method has been applied to simulate residual stresses generated the during WEDM cutting on the HAZ of P91 steel. The FE simulation consists of a thermal analysis, revealing the temperature profile of the machined surface during the WEDM process followed by a sequentially-coupled structural analysis, giving residual stress pattern. In FEM analysis user defined subroutine is added to simulate the volumetric strain change due to phase transformation with temperature. Metallurgical phase changes were accommodated in the form of thermal expansion in the FEM analysis. This paper also describes the size of craters and heat affected zone. Residual stresses obtained from the analysis are shown in the form of stress contours as a function of distance from the cutting edge. Trends of behavior of residual stresses shows good prediction with experimental data obtained from XRD.

Empirical Formulae to Predict Hardness, Hydrogen Diffusion Coefficient and Tensile Properties of Steel HAZ

Weld cold cracking is categorized as hydrogen cracking. To assess cold cracking susceptibility of steel HAZ (heat affected zone), it is necessary to estimate local hydrogen content and residual stress at a weld root that are ... | Find, read and cite all the research you need on Tech Science Press

Numerical Model for Predicting Charpy Impact Toughness of Weld Heat-Affected Zone of Steels

Numerical Model for Predicting Charpy Impact Toughness of Weld Heat-Affected Zone of Steels

Microstructural and mechanical evaluation of a dissimilar joining between SAE 1020 and AISI 304 steel obtained via ultra-high-frequency-pulsed GTAW

Two welding process parameters (the amplitude and frequency of the pulsed current) were varied in order to investigate their influence on the microstructure of the weld region and the mechanical properties of the joints. This investigation and the subsequent discussion were made based on the results of metallographies, tensile tests, and Vickers microhardness tests. The introduction of pulsed current at ultra-high frequencies resulted in a significant reduction in the size of the heat-affected zone (HAZ) for both materials: up to 54% for carbon steel and up to 73% for stainless steel. An increase in the grain size in the carbon steel HAZ was also noted. There are indications that the pulsed current at ultra-high frequencies has accelerated the atomic diffusion process of alloying elements from the fusion zone (FZ) to the carbon steel HAZ. Martensitic grains were observed in the FZ and the microhardness test verified this finding, once the microhardness values measured were around 400 HV0.3. The tensile strength was around 450 MPa and the rupture occurred on the carbon steel side, for all samples.

An investigation of microstructural evolution in electron beam welded RAFM steel and 316LN SS dissimilar joint under creep loading conditions

Microstructural evolution in creep tested electron beam welded Reduced Activation Ferritic Martensitic (RAFM) steel and 316LN stainless steel dissimilar weld joints has been studied at 823 K under different stress levels. The rupture life of the weld joints spanned between 17,596 and 190 h with variation in applied stress from 160 to 220 MPa. Failure of the weld joints occurred in the RAFM steel side at all stress levels. Microstructural examination showed that the failure location shifted from the unaffected base metal region of the RAFM steel to the ‘soft region’ within the heat affected zone (HAZ) in the RAFM steel side with decrease in applied stress. The strength mismatch between various regions within the HAZ of RAFM steel and the microstructural instability of ‘soft region’ in the RAFM steel are the two important factors which dictate the failure location and rupture life of the joints.

Room- and service-temperature tensile properties of repeatedly welded austenitic stainless steel by Gleeble simulation of heat-affected zone

The effects of repeated welding on the microstructure and tensile properties of the heat-affected zone (HAZ) of AISI 304N austenitic stainless steel at room and service temperatures were investigated using a Gleeble welding simulator. Thermal cycle parameters were obtained by in situ measurements of the HAZ of seven sequential weld beads. By thermal cycling in the Gleeble simulator, specimens were prepared to simulate the HAZs of steels in the as-welded condition and after one to five repeated welding processes, designated as AW and RW1–RW5, respectively. The HAZ microstructures were characterised and tensile tests were conducted at room temperature and the equipment service temperature of 260 °C. The repeatedly welded specimens showed microstructures of austenitic matrices with δ-ferrite inclusions. The average austenite grain size was 41.4–47.3 μm and the δ-ferrite content was 0.69–3.13 vol%. RW2 exhibited the maximum percentages of 31.8% and 15.9% high-angle boundary (HAB) and coincidence site lattice, respectively, while RW4 exhibited the minimum values of 22.3% and 9.0%, respectively. At room temperature, the ultimate tensile strength (UTS) and yield strength (YS) were 525–670 MPa and 190–245 MPa, respectively; at 260 °C, they were 460–475 MPa and 200–215 MPa, respectively. The room-temperature UTS and YS mainly depended on the contents of δ-ferrite and HABs. As the δ-ferrite content decreased and the frequency of HABs increased, the UTS and YS were increased. However, the boundary activation energy and dislocation resistance decreased at the service temperature, where the effects of the δ-ferrite and HAB contents on the UTS and YS were weaker.

Prediction of prior austenite grain growth in the heat-affected zone of a martensitic steel during welding

Engineering components operating at high temperature often fail due to the initiation and growth of cracks in the heat-affected zone (HAZ) adjacent to a weld. The size and morphology of the prior austenite grains (PAGs) in the HAZ of a tempered martensite steel weld can have a strong influence on the final martensitic microstructure. However, there are few available models to predict PAG size in the HAZ of martensitic steel welds. In this work two approaches are examined to predict PAG growth in the HAZ of a martensitic steel (P91) weld. Phase field (PF) methods, which explicitly represent the changing morphology of a representative volume of martensite grains, and approximate analytical solutions for grain growth at high temperature are examined. The predicted grain growth kinetics and final grain diameter using a two term analytical solution is shown to agree well with experimental data and with the validated PF simulation. The two term analytical model provides a versatile tool to analyse PAG growth at low computational costs. In addition, a simplified equation for predicting the final PAG diameter in the HAZ of P91 welds is proposed for engineering applications. The methods have been used to estimate the final grain diameter in the HAZ of a single bead-on-plate weld.

Effects of martensite-austenite constituents on mechanical properties of heat affected zone in high strength pipeline steels-review

To improve oil and gas pipelines reliability through the minimization of defects in the welded joint, many researches were conducted to control local brittle zones in weld joints, mainly Martensite-Austenite constituents (M-A). The latter may present toughness problems for the Heat Affected Zone (HAZ) in American Petroleum Institute (API) grade steels. Given the complexity of this problem due to several parameters involved in the behavior of M-A constituents and consequently the performance of the HAZ, the recent literature was reviewed. The formation, quantity and morphology of M-A in the HAZ of multi-pass welds were elucidated. The inherent potency of M-A constituents in deteriorating toughness and initiating fracture was highlighted. The purpose is to give a state of the art and extract the points not treated yet, related to the interaction between M-A constituents, metallurgical design, welding thermal cycle and toughness in HAZ of pipeline steels. In this article, a particular attention was given to the yet not clarified behavior of Niobium (Nb) and Titanium (Ti) carbonitride, in the case of two pass welding and their ability to control Austenite grain growth.

Experimental and numerical study of high-strength steel butt weld with softened HAZ

Static tensile tests were conducted on 26 butt welded joints on base steel of Q690 grade high-strength steel, which exhibits softening behaviour in the heat-affected zone (HAZ). Considering the challenges involved in simulating the butt weld with the HAZ, a new method was proposed for calibrating the true stress–strain relationship based on a trial-and-error approach using simulation through comparing the load–deformation response for three materials (base metal, weld metal and HAZ) in a butt weld. Good consistency on the load–deformation response between the simulation and the test was observed, validating the proposed method. Parametric study showed that the relative width of the softened zone and matching ratio have a significant influence on the ultimate strength of the butt weld and BS EN 1993-1-12 cannot be used directly to design a butt weld with a soft interlayer in the HAZ of high-strength steel.

Comparative study on weldability of Ti-containing TWIP and AISI 304L austenitic steels through the autogenous-GTAW process

In this study, a pair of welds was made in austenitic stainless steel AISI 304L and the novel twinning-induced plasticity (TWIP) steel microalloyed with titanium. Microstructural characterization and mechanical assessment were conducted with the aim to compare the weldability of both materials. The weld joints were performed in two passes by means of the autogenous gas tungsten arc welding (GTAW) process. The operating parameters were defined with the aid of penetration depth predictions carried out by a finite element (FE) numerical model. The results indicated that the weldability of TWIP-Ti steel compared to that of the AISI 304L steel had some advantages as the lower extension of the heat affected zone (HAZ) and a lower mechanical properties loss with respect to the base material. The ferritic solidification mode towards the outer of the FZ in the AISI 304L steel avoided hot cracking in the HAZ. Conversely, the HAZ of TWIP-Ti steel did not present hot cracking despite the austenitic solidification mode. The higher thermal diffusivity of the TWIP-Ti steel had a positive effect in the HAZ conditions improvement, which in turn was correlated with the welding cooling rates and microstructural aspects through the FEM model.

Aspekty strukturalne różnorodnych złączy spawanych ze stali Super 304H i T91

The paper presents the results of macro- and microscopic tests of heterogeneous welded joints made of Super 304H steel and T91 steel. The examined welded joints were made with the 141 (TIG) method in the PF welding position, using a Metrode EPRI P87 wire as the additional material. The tests were performed on the joint after welding and after heat treatment which consisted in the stress relief annealing at the temperature of 760 °C and soaking time of 2 hours. The investigated joints were marked respectively: S1 (the joint with- out heat treatment) and S2 (the joint after heat treatment). The process of welding, as well as the heat treatment in the area of the heat-affected zone (HAZ) in the case of Super 304H steel contributed to the precipitation processes mostly on the boundaries of grains. In the HAZ of T91 steel these processes caused the development of a degraded martensitic structure with numerous precipitates of diverse morphology.