Widmanstatten Ferrite Research Articles

Metallurgical characteristics and mechanical properties of dissimilar friction stir welded DH36 steel and UNS G10080 steel joints

The present study expanded the scientific comprehension of the friction stir welding process for dissimilar steels, namely high-strength shipbuilding grade DH36 steel and UNS G10080 steel. The effect of tool traverse speed and plunge depth on temperature history, microstructure characteristics, and mechanical properties is investigated experimentally. The metallographic characterizations were examined through an optical microscope and field emission scanning electron microscopy equipped with an energy-dispersive X-ray system. Microhardness, impact, and tensile tests were carried out on the friction-stir-welded specimens. Increasing the plunge depth and reducing the traversal speed resulted in an augmentation of the peak temperature, primarily attributable to higher heat generation. Within the range of process parameters used, the tool produced complex material movement, resulting in swirl-like and vortex-intercalated features, particularly adjacent to the stir zone/workpiece interface. These vortex-like features exhibited dynamically recrystallized fine-grained microstructures. The grain size in the stir zone and the thermo-mechanically affected zone is reduced by increasing the plunge depth and decreasing the traverse speed due to enhanced dynamic recrystallization, subsequently improving the hardness and toughness values. In the stir zone, the microstructure revealed the acicular-shaped bainite ferrite in the DH36 steel and the Widmanstatten ferrite in the UNS G10080 steel. The microhardness contours revealed the uneven hardness distribution across the weld cross-section due to the microstructural heterogeneity in the dissimilar steels. The maximum welding efficiency of 106 % and toughness of 46 J are obtained at 40 mm/min traverse speed with a plunge depth of 0.2 mm, which is attributed to sufficient heat generation and grain refinement.

Functional behaviour of novel multi-layered deposition via twin wire arc additive manufacturing: Microstructure evolution and wear tailoring characteristics

Twin wire arc additive manufacturing offers advantages such as high deposition rates and the ability to use a wide variety of materials, making it suitable for large-scale metal part production with enhanced efficiency and flexibility. Functionally graded deposition (FGD) based structure of dissimilar steels (SS316LSi and ER70S-6) fabricated via twin wire arc additive manufacturing and their detailed performance analysis are accomplished in the current research work. Microstructural, mechanical, and tribological characteristics of the deposited structure were investigated and analysed. Microstructure reveals polygonal ferrite, widmanstatten ferrite, skeletal ferrite, lathy ferrite, ferrite solidification, and ferrite to austenite (F/A) transformation. FGD structure possessed a microhardness of 371 HV. Average ultimate tensile strength, yield strength, and elongation percentage were 675.98 MPa, 414.21 MPa, and 38.37 %, respectively. In wear analysis, the average coefficient of friction value of WAAM-processed FGD samples is 0.44–0.49. 3D profilometer analysis reveals that average values of roughness, maximum height of roughness, and maximum roughness valley depth are significant with increasing applied loads. The findings of the present research focus on the quality and appropriateness of dissimilar steels for structural applications and provide a novel method for creating high-strength components.

The effect of variation of the electric current on physical and mechanical properties in A36 steel welding

The research objective was to determine the effect of current on microstructure, hardness values, and tensile strength of A36 steel before (raw material) and after welding using SMAW using electrodes E7016 diameter 3.2 mm. The research adopted an experimental method and utilized Olympus Metallurgical Microscope, Micro Vickers Hardness Tester, and Universal Testing Machine for data analysis. The results revealed that welding caused a change in the microstructure of the weld area into Grain boundary Ferrite (GF), Widmanstatten Ferrite (WF), and Acicular Ferrite (AF). The hardness test showed that higher current leads to greater hardness values. The specimens with a current of 130 Ampere had a hardness level of 181.39 VHN, which was higher than specimens with 120 Ampere (176.21 VHN) and 110 Ampere (159.56 VHN). The raw material had a hardness value of 125.4 VHN. The welding resulted in a difference in tensile stress, with specimens using 130 Ampere having the highest tensile strength level of 520.20 MPa, followed by 120 Ampere with 504.61 MPa, and 110 Ampere with 483.03 MPa. The research concludes that varying the electric current during welding affects the microstructure, tensile strength, and hardness value of Steel ASTM A36.

The impact of welding heat input on microstructure, micro-texture, and mechanical properties of stir zone in friction stir welded DP600 steel

In this research, the impact of the heat input (HI) used during friction stir welding (FSW) on the microstructure, micro-texture and mechanical properties of DP600 steel was examined. Two different sets of rotational and transverse speeds were utilized to produce robust welds, one with low HI and the other with high. The outcomes demonstrated that various products such as polygonal ferrite (PF), Widmanstatten ferrite (WF), ferrite-carbide aggregate (FCA), and bainite were created in the stir zone (SZ) during the FSW of DP600 steel. After microscopic analysis, it was found that the high HI weld exhibited a greater amount of WF and bainite, resulting in higher hardness and ultimate tensile strength values than the low HI weld. The low HI weld displayed texture components including D1, D2, and E, with a slight cube component. These components were thought to result from the transformation of a strong B texture component and a weaker R texture component of prior austenite, indicating continious dynamic recrystallization during the FSW process. On the other hand, the high HI sample had a strong cube texture component and a weaker D shear component, a result of the transformation of a strong R shear texture component of prior austenite, suggesting discountinious dynamic recrystallization during FSW. The study determined that the welding HI greatly influences the proportion of microconstituents, the development of micro-texture, and the mechanical characteristics of the SZ during the FSW of DP600 steel.

STUDY THE INFLUENCE OF WELDING PARAMETERS BY TAGUCHI’S DESIGN ON THE MECHANICAL PROPERTIES OF WELDED MILD STEEL (S235JR)

Gas metal arc welding is a leading process in fusion welding with increased productivity and good quality. The welding parameters are crucial in determining welding quality, cost, and productivity. In this study, mild steel with a 10-mm-thick sheet was welded by gas metal arc welding under predetermined parameters of welding voltage, wire feed speed, and groove shape. The analysis made by Taguchi’s design to investigate the effect of these parameters on tensile strength and Vickers micro-hardness of welding. The microstructure of the fusion zone and heat-affected zone is analyzed to monitor their change concerning the mechanical properties. The results showed that tensile strength decreased with decreased hardness. Also, the tensile strength and hardness were higher (a maximum of 305 MPa and 2170 HVN) at welding made at a lower voltage (20 volts), lower wire feed speed (5.9 m/min), and V-shaped base metal groove. The increased precipitation of perlite structure was shown during welding, which has lower tensile strength and hardness. Widmanstatten ferrite and coarser α-ferrite were presented for welding with a lower cooling time. Taguchi’s design showed that voltage at 20 volts has the highest effect on tensile strength, followed by wire feed speed at 5.9 m/min and V-shaped welding.

Investigating the effects of double-pass TIG welding on the mechanical and microstructural properties of AISI 1008 steel

ABSTRACT Most premature failures of double-pass weldments are associated with limited knowledge of the mechanical and microstructural evolution following the welding process. Thus, this study aims to investigate the effect of double-pass tungsten inert gas welding on the mechanical and microstructural properties of type AISI 1008 mild steel joints. Double-pass TIG welding in butt joint configuration was adopted to weld the plates maintaining a 2.5 mm root gap in between plates. The double-pass tungsten inert gas welded AISI 1008 joints showed improved ultimate tensile strengths in contrast to the unwelded counterpart, with the least joint efficiency of 82.67 % (weld W3). An increase in the heat input led to a corresponding increase in the weld metal hardness, whereas the hardness of the heat-affected zones increased first and then decreased. The internal geometry of the welds reveals an increase in the bead width, height of reinforcement, width of the heat-affected zone, and weld metal area as the heat input increases. Lastly, the microstructural evolutions of the weld metal zones were primarily dominated by widmanstatten ferrite, acicular ferrite, and pearlite structures, accounting for the enhanced tensile strength and hardness of the joints. Meanwhile, the heat-affected zones were characterised by coarse columnar dendrite structures resulting in lower hardness values. This study gives an insight into the mechanical and microstructural properties of the industry’s most frequently used steel grade, which has not been given much attention in past studies. The research finding enriches the welding theory of A1SI 1008 steel for industrial and academic benefits.

Microstructure and Mechanical Properties Analysis of Mild Steel with Different Groove Shape Welded Using GMAW

This paper will discuss the effect of welding variables on the transverse tensile strength and hardness of mild steel welding made by GMAW. The welding variables included are base metal thickness, welding voltage, wire feed speed (WFS), and base metal groove shape. The results show that higher welding transverse tensile strength has obtained higher FZ hardness, while they both increased with decreased welding heat input. E.g., the highest tensile strength (238 MPa) has shown 2162 HV at 768 J/mm heat input, while the lowest tensile strength (120 MPa) of welding made at 2376 J/mm has shown 2108 HV. The FZ of welding made at V groove-shaped base metal has higher hardness and transverse tensile strength, as shown 2159.5 HV and 215 MPa in order when compared to 177 MPa and 2147 HV for X groove-shaped. The hardness at V groove-shaped FZ had an average of 2159.5 HV, while the hardness at X groove-shaped had an average of 2147 HV at 10 mm base metal thickness. The increased hardness of V groove-shaped FZ could be related to the increased stresses at V groove-shaped due to interpass heat input. The intricate physical shape of FZ and HAZ for X groove configuration possibly contributes to the lower transverse tensile strength of welding. A favorably increased hardness and transverse tensile strength are associated with softer and finer ferritic and perlitic grains in FZ and less dendritic perlite structure in HAZ. The Widmanstatten ferrite has contributed to decreased tensile strength.

Laser metal deposition of low carbon 410L stainless steel and heat treatment

Additive manufacturing (AM) of 410L ferritic/martensitic stainless steel via laser metal deposition (LMD) process is investigated. The carbon content of 410L powder used is low at 0.004 wt%. Heat treatment is utilized to study the microstructure and mechanical properties evolution of the deposited material. The microstructure of as-built low carbon 410L includes equiaxed ferrite phase, widmanstatten ferrite, martensite, and (Fe,Cr)23C6 nanoprecipitates. After heat treatment at 1000 °C for 10 min, refined equiaxed grains and high fraction of martensitic phase are formed. The yield strength is 601.9 MPa for as-built condition and 930.6 MPa for heat-treated condition (1000 °C/10 min); the ultimate tensile strength (UTS) is 923.0 MPa for as-built condition and 1101.5 MPa for the heat-treated condition (1000 °C/10 min); the elongation is 17.7% for as-built condition and 15.1% for the heat-treated condition (1000 °C/10 min). The low carbon 410L fabricated using LMD shows a better combination of high strength and good ductility compared with 12Cr stainless steels with higher carbon contents fabricated using conventional processes. This study provides a benchmark of 410L stainless steel fabricated using fusion-based metal AM process.

Effect of Boron Content on Microstructure and Impact Toughness in CGHAZ of Shipbuilding Steel Plates with Ca Deoxidation

Herein, the effect of boron (B) content on the microstructure and impact toughness in the coarse‐grained heat‐affected zone (CGHAZ) after large heat input welding of 400 kJ cm−1 for the EH40 shipbuilding steel plate with Ca deoxidation is studied. As the B content is increased from 0.0002 to 0.0024 wt%, the average width of grain boundary ferrites (GBFs) is decreased from 14.6 to 11.3 μm, the formation of acicular ferrite (AF) is promoted, and the formations of GBF and Widmanstatten ferrite (WF) are hindered in CGHAZ. The heat‐affected zone (HAZ) impact toughness is increased from 39 to 97 J at −20 °C. The fraction of low‐angle grain boundaries (LAGBs) is decreased from 40 to 29%, and the high‐angle grain boundaries (HAGBs) is increased from 60 to 71%. When the B content is 0.0024 wt%, the B atom segregates on the grain boundaries, and the widths of the segregation lines range from 2.3 to 3.6 μm. GBF is found to be the weakest zone in the CGHAZ. B addition can effectively reduce the formation of GBF, enhancing the critical crack stress and improving the HAZ toughness.

Zavarivanje cijevi iz niskougljeničnog čelika TIG postupkom

In this work the results of welding the pipes from low-carbon steel St 35.8 (Č.1214, DIN17175, W.Nr. 1.0305, EN-P235GH) by TIG procedure were shown. After welding, the microstructure analysis by means of optical microscope was performed. Microstructural analysis out on the base material, heat affected zone and melting zone was carried. It was found that the base material has ferrite-pearlite microstructure with hardness 148 HV10, while in the heat affected zone is present ferrite-pearlite microstructure with Widmanstatten ferrite in some places with hardness 176 HV10. A cast microstructure consisting of ferrite and bainite was observed in the melting zone with hardness 228.7 HV10.

Investigation of expansion percentages and groove inclusions on the performance of welded, expanded, welded-expanded tube-to-tubesheet joints

Tube-to-tubesheet joints play a crucial role in providing structural integrity to the shell and tube heat exchangers. This research investigated the combined effect of roller expansion percentages and grooves on the performance of expanded and welded-expanded tube-to-tubesheet joints. The results indicated that the joint strength of welded-expanded (except for 6% tube expansion and 2 grooves) and welded joints exceeded the nominal axial strength of the tube, 404.90 MPa. The highest tube pull-out strength of 290.77 MPa in the expanded only joint (10% tube expansion and 2 grooves), lesser than the axial strength of the tube by 28.25%, suggested avoiding the expansion process alone for 23 mm thick tubesheets. High dilution and inadequate minimum leak path (<1.78 mm) result in the failure of the welded-expanded joint. The highest hardness of 216 HV is formed at the weld zone comprising of α ferrite and widmanstatten ferrite. From 4% to 10% tube expansion percentages, the grains at the inner tube edges were refined from 8.33 μm to 6.25 μm at the expanded zone and from 9.09 μm to 6.66 μm at the transition zone due to intensive plastic deformation caused by the rollers. Grain refinement by expansion process resulted in high hardness of 182.3 HV and 156.1 HV at the inner tube edges of the expanded and transition zone, respectively. The grains were coarser, and hardness was less at the outer tube edges of expanded and transition zone. This study is promising for selecting the appropriate manufacturing process and conditions for the optimum performance of tube-to-tubesheet joints.

Strengthening behaviour and failure analysis of hot-rolled Nb+V microalloyed steel processed at various coiling temperatures

The present work investigated the role of thermomechanical processing and coiling temperature on various strengthening mechanisms in a low carbon Nb + V microalloyed steel and its mechanical properties. The sample was subjected to 50 % thickness reduction by hot-rolling at 1100 °C and then air cooling directly to a coiling temperature maintained in the range of 650–500 °C. At the coiling temperature, an isothermal holding period was maintained for 1 h followed by water quenching to room temperature to preserve the sample microstructure. The microstructural characterization reveals a duplex/triplex phase mixture depending on the coiling temperature affecting its mechanical properties. For the coiling temperature range of 650–550 °C, the pro-eutectoid ferrite + pearlite phase mixture is evolved resulting an adequate ductility of ∼28 % with a tensile strength of ∼650 MPa. The strength-ductility combination was not altered much at the coiling temperature of 500 °C (i.e., near the bainitic transformation temperature domain), though a trace quantity (∼5 %) of Widmanstatten ferrite (WF) is nucleated along with the pro-eutectoid ferrite + pearlite microstructure. The isothermal holding further led to the nucleation and growth of niobium and vanadium-rich fine carbides with fcc crystal structure, which are mostly incoherent with the ferrite matrix phase. Though these precipitates were nucleated within the matrix grains due to induction of strain, the volume fraction was too low (∼1 %) to offer a substantial amount of precipitation strengthening (26–35 MPa) as compared to the grain refinement strengthening (126–156 MPa) and dislocation strengthening (115–150 MPa). The SEM analysis indicated that the segregated Mn and S atoms formed MnS inclusion at the phase interface of ferrite and pearlite, which operates as potential nucleation sites for crack initiation during tensile deformation.

Metallurgical Characteristics of Low Carbon Steel Cylindrical Components Made by Wire Arc Additive Manufacturing (WAAM) Technique

Fabrication of metal parts by wire and Arc Additive Manufacturing (WAAM) has received an increased interest in recent years, as it allows high design flexibility and reduction of material wastage compared to other traditional manufacturing routes. This article compares the effect of heat input on metallurgical characteristics of wire arc additive manufactured low carbon steel cylindrical components fabricated by Gas Metal Arc Welding (GMAW) and Cold Metal Transferred Arc Welding (CMTAW) processes. Firstly, the influence of heat input on the grain size was analyzed. Subsequently, the effect of heat input on the metallurgical characteristics of the cylindrical components was studied along the building direction. The microstructure of the built cylindrical-walled component varies from the top to the bottom regions and can be distinguished into two regions: lamellar structures (widmanstatten ferrite and grain boundary ferrite) in the top regions; and equated grains of fully ferrite in the bottom region in GMAW. In the CMT-WAAM cylindrical component samples have been noted two different regions: the bottom region characterized by a ferritic structure with thin strips of pearlite and the top region characterized by a lamellar structure typically bainite with acicular ferrite.

Study of dual pulse gas metal arc welding process characteristics on IS 2062 steel

Dual pulse gas metal arc welding (DP-GMAW) is a superior welding process where the weld quality and strength of weldment is highly dependent on weld input parameters. It is important to understand the effect of different input parameters on the effectiveness of welding, especially for commonly used mild steels such as IS 2062. This work attempts to study the effect of current, voltage, wire feed rate (WFR) and standoff distance (SOD) during DP-GMAW of IS 2062 steels. The interaction of WFR and varying welding current, voltage, weld pool geometry and %dilution was investigated through bead-on-plate weld method. A plate was welded using DP-GMAW process with a WFR of 8 m/min, SOD of 15 mm and a travel speed of 25 cm/min. The side and face bend tests of DP-GMA welded plates revealed that the weld quality was good without any crack. The hardness of the weld zone was significantly higher than the base metal. The strength, elongation and Charpy V-notch impact energy of the weldment was comparable to that of the base metal. A simultaneous increase of microhardness and toughness of the welded sample was observed. Metallographic tests revealed that this phenomenon was due to the presence of fine grain structure containing acicular ferrite and Widmanstatten ferrite in the weld metal which was generated due to the superimposition of current pulsation over thermal pulsation during DP-GMAW process.

Особливості формування неоднорідних структур у вуглецевих сталях

Obtaining a homogeneous structure and uniform-phase distribution is critical to a high set of mechanical and operational properties of rolled metal. However, in practice it is not always possible to create metal products with the specified characteristics. In order to determine the morphological features of the structure of rolled carbon steel, a comparative study of carbon steel samples with a carbon content of 0.49 % C and 0.2 % C selected from hot-rolled billets was carried out. The billets of each group were produced under the conditions of the same enterprise, with close temperature-time modes of deformation processing. The main difference was in manufacturing processes of the output continuous cast steel billets. This research shows that with identical normalized chemical composition of steel and the same thermomechanical treatment, the formation of the morphological structure features of hot-rolled steel occurs in a different way. Therefore, we can assume that the liquation, the diffusive mobility of elements is particularly influenced by the content of impurity elements and gases in steel, which leads to a different type of structures in the finished rolled metal. At the same time, these differences are observed in carbon steels with different carbon content. A sample of non-vacuumed OC grade axle steel (0.49 % C) from converter steelmaking has a more homogeneous structure without local areas of pearlite or ferrite accumulation. It was shown that the formation of ferrite rim in the microsegregation areas occurs not only in manganous sulfides, but also arises on the background of the smallest oxide inclusions. There is significant structural heterogeneity in the samples of electric steel, despite the lower sulfur content and gassiness of steel; at the same time, a dense perlite layer is formed around the sulfides. There is also a difference in steel grade 20 (0.2 % C) of different manufacturing processes. The structure is more homogeneous in qualitatively deoxidized vacuum degassed steel; no local areas with different dimensional characteristics were detected. The size of the structural elements is much larger and the structure has mostly large sections of the Widmanstatten ferrite. Since a large number of non-metallic inclusions and gassiness of steel is not a positive factor for providing a high set of properties of metal products, the modes of thermomechanical treatment used today require adjustments depending on the characteristics of steel melting. Keywords: microstructural heterogeneity, ferritic-pearlitic banding, mechanical properties, manganous sulfides.

Failure analysis of a gas transport pipe made of API 5L X60 steel

Pipelines used in the oil and gas transport usually contain some sulfur dioxide, which absorbs hydrogen from the pipe wall and accelerates hydrogen damage of steels. Also, the welding process and the type of manufacturing process can facilitate the entry of hydrogen into the steel. In this research, API 5L X60 pipes used in the refinery of Tang-e-Bijar region of Kermanshah, Iran, were studied. Microstructural studies showed that the primary microstructure of the steel consisted of 55% ferrite and 45% pearlite. The microstructure in the welding zone could include Widmanstatten ferrite, based on its morphology shown in the optical etched microstructure. The observed cracks in the microstructure were also of step-wise cracking and represent the possibility of hydrogen induced cracking. Pre-etching observations using light microscopy shows MnS impurities in the structure. Also, SEM/EDS analysis revealed that the cracks were formed from the accumulation of MnS impurities and these impurities were preferred sites for nucleation and growth of the cracks. The results of the mechanical testing including hardness, impact and tensile test showed that the steel had a ductile behavior for all the sections and no hydrogen embrittlement has been probable.

Failure analysis and the cold crack formation mechanism for the QP1180 steel welded joint

Gas metal arc welding (GMAW) is applied to fabricate the QP1180 steel welded joint. The formation of the Widmanstatten ferrite (WF) in weld metal (WM) and its effect on the cold crack generation for QP1180 welded joint was systematically discussed. It is found that the inhomogeneous distribution of the WF can result in the lowest microhardness (∼275 HV) in the WM. High cooling rate, large grain size, low content of element C and high content of element Mn in the region near the WM together trigger the formation of WF, and their epitaxial growth can lead to their extension into the heat affected zone (HAZ) along the prior austenite grain boundaries. As a result, the micro-cracks are formed at the interface between the WF and martensite. Subsequently, the harder martensite with large size further promotes the propagation of the micro-cracks along the grain boundaries in the HAZ, forming the intergranular fracture eventually.

Microstructural analysis and mechanical behavior of the HAZ in an API 5L X70 steel welded by GMAW process

This study aimed to investigate the heat-affected zone (HAZ) behavior in an API 5L X70 steel welded by the gas metal arc welding process (GMAW). In the steel welding processes, this region is very critical due to microstructural and allotropic transformations that affect the mechanical properties. Three samples were welded using a robotic arm with different welding speeds, thus obtaining three different heat inputs, which were 2.0 kJ/mm, 2.5 kJ/mm, and 3.0 kJ/mm. For all heat inputs, the microstructures of the HAZ showed the Widmanstatten ferrite, Acicular ferrite, bainite, and martensite and retained austenite, which influenced the mechanical properties of this region. The electron backscattering diffraction analysis showed that the presence of low-angle grain boundaries (2–15°) increases the fracture toughness. The kernel average misorientation map and the results of the Charpy impact test showed that the heat input of 3.0 kJ/mm lead to characteristics of the HAZ that are remarkably similar to the base metal (BM).

A three-dimensional heat transfer modelling and experimental study on friction stir welding of dissimilar steels

In this research, numerical as well as experimental analysis on friction stir welding (FSW) of dissimilar steels, i.e. DH36 steel and AISI 1008 steel, was performed. A 3D heat transfer FE model based on Abaqus/CAE using Fortran code via DFLUX subroutine was developed to investigate the effect of FSW parameters (i.e. rotational speed and traverse speed) on temperature distribution during the welding. It was observed that decreasing the traverse speed, increasing the rotational speed and shoulder diameter enhanced the peak temperature due to higher heat input. Based on the experimentally obtained sound quality welding parameters, the FE model was successfully validated with a maximum percentage error of 5.57% for peak temperature. Experimental results revealed that the higher heat generation reduced the grain size by increasing the rotational speed and decreasing the traverse speed. The inhomogeneous hardness distribution was observed across the weld cross section due to grain size variation. The higher grain refinement at a rotational speed of 600 rpm with a traverse speed of 70 mm/min produced the maximum value of the hardness and impact toughness. The tensile weld samples were fractured in the base metal zone (i.e. AISI 1008 steel) and experienced the tensile strength within the range of the AISI 1008 steel. The microstructure in the SZ exhibited the Widmanstatten ferrite in AISI 1008 steel and acicular-shaped bainite ferrite in DH36 steel. EDS analysis of the fractured surface of impact specimens confirmed the embedment of tungsten carbide particles in the weld zone due to the tool wear.

Microstructures in HAZ after Heat Treatment of Carbon Steel and Austenitic Stainless Steel Welds

The influence of post weld heat treatments (PWHT) at 400°C, 600°C, 900°C on microstructures in heat affected zone (HAZ) of dissimilar welds between carbon steel and austenitic stainless steel was studied. As-welded condition, the fully Martensitic layer along the fusion line, Widmanstatten Ferrite, Bainite, Pearlite phases in the HAZ of carbon side and the fully austenitic zone in the weld metal can be observed. After PWHT, the microstructures of these zones were dramatically modified as a result of carbon diffusion from the carbon steel toward the weld metal. Decarburization of the base metal led to the formation of a zone with large Ferrite grains. Bainite or fine Pearlite were formed by carbon diffused to both the interfacial Martensite and the purely Austenite zone. The lowest hardness value in the decarburization zone was 92HV on average after PWHT at 900°C and the peak hardness value that was documented in the carburize zone with 366HV at 600°C. Carbides precipitation (M23C6, M7C3) were found in both the HAZ of carbon steel and austenitic stainless steel.