Lathy Ferrite Research Articles

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.

A study on effect of laser overlay welding parameters of stainless steel 301 LN: tensile test, microstructure analysis and microhardness evaluation

This study investigates the effects of laser overlay welding parameters on the performance of stainless steel 301 LN. The correlation between welding conditions and material characteristics was explored through systematic experiments involving tensile testing, microstructure analysis and microhardness evaluation. The study reveals that optimizing welding parameters, such as laser power, laser speed and oscillation amplitude, significantly enhances both the mechanical strength and microstructural features of stainless steel 301 LN. The results show the maximum strength was achieved using a power of 3 kW, 2 m/min speed, oscillation amplitude of 1.5 mm and focal position of 6 mm. The microhardness results displayed a significant drop in the centre of the welded zone due to thermal dynamics. Additionally, the findings of fractography results highlighted how minimum and maximum welding parameters affect the fracture characteristics and integrity of welded joints. The study also revealed a complex range of microstructures, including skeletal, vermicular and lathy ferrite formations. The microstructural images provide valuable insights into the size and distribution of lathy ferrites, and the transformation of delta-ferrite to austenite, contributing to a comprehensive understanding of the welding process. Overall, this research contributes to the ongoing efforts to refine manufacturing processes and applications for stainless steel.

Improvement in Microstructure and Properties of 304 Steel Wire Arc Additive Manufacturing by the Micro-Control Deposition Trajectory.

In this study, the GMAW welding torch was controlled by a stepping motor to achieve a periodic swing. By controlling the swing speed, a micro-variable deposition path was obtained, which was called the micro-control deposition trajectory. The influence of the micro-control deposition trajectory on the arc characteristics, microstructure, and mechanical properties of 304 steel wire arc additive manufacturing was studied. The results showed that the micro-control deposition process was affected by the swing arc and the deposition trajectory and that the arc force was dispersed over the whole deposition layer, which effectively reduced the welding heat input. However, the arc centrifugal force increased with the increase in the swing speed, which easily caused instability of the arc and large spatter. Compared with common thin-walled deposition, the deposition width of micro-control thin-walled deposition components was increased. In addition, the swinging arc had a certain stirring effect on the molten pool, which was conducive to the escape of the molten pool gas and refinement of the microstructure. Below, the interface of the deposition layer, the microstructure of the common thin-walled deposition components, and the micro-control thin-walled deposition components were composed of lathy ferrite and austenite. Compared with the common deposition, when the swing speed increased to 800 °/s, the microstructure consisted of vermicular ferrite and austenite. The tensile strength and elongation of the micro-control thin-walled deposition components are higher than those of the common thin-walled deposition components. The tensile fracture mechanism of the common thin-walled deposition components and the micro-control thin-walled deposition components was the ductile fracture mechanism.

Effect of Weld Design of Transition Layer on Microstructure and Properties of Welded Joints of S32304/Q390C Composites

Due to the large difference in physical and chemical properties between the substrate and the cladding material, the welding of composite materials is much more difficult than that of single materials. In our work, S32304/Q390C composite material was considered as the research object. By adjusting the welding parameters, two kinds of joint geometry were obtained, namely, the transition layer weld lower (joint A) and higher the composite material interface (joint B). We studied the influence of the transition layer weld on the microstructure and properties of welded joints. The microstructure of the transition layer weld, the distribution of elements, the Schmidt factor of the interface between the transition layer and base layer weld, and the tensile strength of the joint were evaluated. The results show that with the increase of welding heat input, the microstructure of the transition layer weld changes from austenite and skeleton ferrite to austenite and lathy ferrite and austenite and acicular ferrite, while ferrite grows towards the weld center, showing a dendritic shape and a local network structure. At the side of the base layer weld of the interface between the transition and the base layer weld, the thickness of the low-carbon-content layer increased from 100 μm to 150 μm. Iron, chromium, and nickel elements on both sides of the interface were diffused, and the thickness of the diffusion layer increased from 3 μm to 10 μm. The tensile strength values of joints A and B were 648 MPa and 668 MPa, respectively, and the Schmidt factor values were 0.446 and 0.454, respectively. Combination with the analysis of the fracture morphology showed that when the transition layer weld was higher than the interface of the composite plate, the joint had better plastic deformation ability and higher tensile strength.

Effect of incident angle on weld microstructure and mechanical properties of laser beam welded nitronic −50 austenitic stainless steel joints

3 mm thick nitronic-50 stainless steel sheets were successfully butt-joined using a 2 kW fiber laser beam welding. Three weld joints were fabricated for different incident angles, namely, 70°, 80° and 90° for the other constant welding process parameters. The effect of incident angle on the weld bead geometry, microstructure evolution, and strength of the laser beam welded joints was studied in detail. The incident angle significantly affected the bead geometry and its orientation. Lowering the incident angle beyond a limit caused the beam shift near the weld root of the joint, where the bead was formed away from the joint line resulting in improper fusion and a defective weld occurred. The microstructure transformed from columnar to an equiaxed dendritic structure at the center of the weld nugget for lower incident angles. Skeletal and lathy ferrite was observed in the joints' weld zone. However, the fraction of lathy ferrite was higher at lower incident angles due to a faster cooling rate. A higher weld joint strength of 1010 MPa (97% of the base metal UTS) was achieved at an 80° incident angle, owing to the formation of more equiaxed dendritic grains and the absence of the secondary phases. All of the tensile test samples showed evidence of ductile failure, and overall, an acceptable level of elongation was achieved.

Effect of Heat Input on Hydrogen Embrittlement of TIG Welded 304 Austenitic Stainless Steel

Welds made with 304 austenitic stainless steel play an important role in high-pressure hydrogen storage systems. However, there are few investigations of the effect of heat input on the hydrogen embrittlement (HE) of tungsten inert gas (TIG) welded 304 austenitic stainless steel. In this study, the effect of heat input on the HE of TIG welded 304 austenitic stainless steel is investigated. It was found that with the increase in TIG welding heat input, the ferrite content in the weld shows a tendency to first increase and then decrease. From the perspective of morphology, it first changes from lathy ferrite and strip ferrite to dendritic ferrite, and then becomes reticular ferrite and lathy ferrite. Slow strain rate tensile (SSRT) testing shows that with the increase in heat input from TIG welding, the susceptibility of the weld to HE first increases and then decreases. Our study shows that TIG welds of 304 austenitic stainless steel exhibit the best HE resistance when the welding heat input is 0.778 kJ/mm, the relative elongation (RE) is 0.884, and the relative reduction of area (RRA) is 0.721. This work can provide a reference for the optimization of the 304 stainless steel TIG welding process.

Effect of the ferrite morphology on hydrogen embrittlement of MAG welded 304 austenitic stainless steel

Ferrite usually plays an important role in the hydrogen embrittlement (HE) of austenitic stainless steel (γ-SS) weld. However, there are few investigations on the effect of ferrite morphology on HE. In this study, the relationship between the ferrite morphology and HE of metal active gas (MAG) welded 304 austenitic stainless steel is investigated. Hydrogen distribution testing and simulation reveal that the ferrite/austenite interfaces become the hydrogen segregation regions and the degree of hydrogen segregation at the interface is affected by ferrite morphology, which shows the order of lathy ferrite > reticular ferrite > skeletal ferrite. The slow strain rate tensile (SSRT) test indicates that the susceptibility to HE of welds containing lathy ferrite, skeletal ferrite and reticular ferrite reaches 34.6%, 30.7% and 33.2%, respectively. It can be found that the HE resistance shows the order of skeletal ferrite > reticular ferrite > lathy ferrite, which corresponds to the order of increasing hydrogen segregation. Hence, the ferrite morphology influences the resistance to HE of welds by affecting hydrogen segregation at the ferrite/austenite interface. A similar ferrite morphological dependence is observed from the weld fractures.

Effect of Fillers and Autogenous Welding on Dissimilar Welded 316L Austenitic and 430 Ferritic Stainless Steels

This experimental study examines the effects of dissimilar welding of 316L austenitic and 430 ferritic stainless steels, welded with gas tungsten arc welding process with (ER316L and ER309L) and without fillers (autogenous). Microstructural examination was performed by optical and scanning electron microscopy. ER316L and ER309L fillers welds illustrated equiaxed and columnar grains; ER309L weld showed higher Creq/Nieq ratio than that of ER316L weld, produced vermicular ferrite, while autogenous weld shows lathy ferrite and martensite. Chromium carbide precipitate was also observed in autogenous weld. The mechanical properties were measured and higher hardness was obtained in autogenous weld compared to ER316L and ER309L filler weld. Higher tensile and impact strength was measured in ER316L filler weld as compared to ER309L filler and autogenous weld. The corrosion resistance of the joints was carried out by double loop electrochemical potentiokinetic reactivation and potentiodynamic polarization test to assess the sensitization and pitting resistance, respectively. Higher degree of sensitization and pitting were observed in autogenous weld as compared to ER316L and ER309L filler weld due to precipitation formation, but the pitting corrosion was found to be lower for ER309L filler weld as compared to ER316L filler and autogenous weld due to the effect of mode of solidification.

Investigation on in-situ laser cladding coating of the 304 stainless steel in water environment

Abstract The 304 stainless steel coating was prepared successfully in water environment directly through an in-situ underwater laser cladding technique utilizing an underwater gas-shielding laser cladded nozzle, and the interaction mechanism of water on cladding coating formation, grain morphology and size, microstructure and corrosion performance was investigated. For underwater laser cladding, the high-density aerosol particles decreased the laser power density and reduced the stability of cladding process, causing the conduction mode of molten pool and decreasing the wettability of molten metal. In underwater laser cladding coating, columnar dendrites nucleated near the fusion line and track band and grew up along the opposite direction of maximum temperature gradient whilst equiaxed grains formed in the center region; besides, the grain size decreased overall and the number of equiaxed grain dropped owing to the water cooling effect compared with in-air coating. For in-air and underwater cladding coatings, the solidification mode of molten metal was ferrite-austenite mode and the ferrite mainly distributed in the austenite matrix with skeleton shape. Attributed to the higher cooling rate, a small amount of lathy ferrite was observed in underwater cladding coating, and the ferrite content increased within the overlap region of tracks, causing the corrosion resistance of coating reduced.

Microstructure Evolution, Structural Integrity, and Hot Corrosion Performance of Nitrogen-Enhanced Stainless Steel Welds

This work articulated the multi-pass, gas tungsten arc welding by adopting pulsating current for joining nitrogen-enhanced, low-carbon austenitic stainless steel, AISI 316L(N). An austeno-ferrite stainless steel (ER2594) and an over-alloyed (ERNiCrMo-3) fillers were employed to join 6-mm-thick plates of AISI 316L(N). Acicular and lathy ferrite in the weld zone of ER2594 and the occurrence of secondary phases in the fusion zone of over-alloyed filler were observed. The notch tensile strength data attested that the joint strength was greater for the welds employing an over-alloyed filler. This study also affirms that the welds obtained with ER2594 filler resulted in better impact toughness (144 J) compared with ERNiCrMo-3 filler and base metal. Also the notch impact toughness of ER2594 weldment is increased to 60% in comparison with that of candidate metal. Corrosion studies were also performed by exposing the coupons in a eutectic salt mixture comprising of 40%K2SO4-60%NaCl for 50 cycles at 650 °C. It is observed that the weld zone employing over-alloyed filler experienced better high-temperature corrosion resistance compared to the base metal. The specific results of this investigation will be of greater demand to the nuclear and marine applications utilizing these joints.

Enhancing the resistance to hydrogen embrittlement of Al-containing medium-Mn steel through heavy warm rolling

This investigation attempted to enhance the resistance to hydrogen embrittlement (HE) of an Al-containing medium-Mn steel through heavy warm rolling (WR) directly after intercritical annealing. It is found that the HE index expressed by total elongation loss drops from ~78% to ~28% after heavy WR. This significantly enhanced resistance to HE is primarily associated with the well developed lamellar structure consisting of lathy ferrite and retained austenite after WR. It is thus suggested that WR is a promising and feasible approach to significantly enhance the HE resistance of medium-Mn steel while maintaining excellent strength-ductility balance.

Effect of the Surface Texture on Laser Joining of a Carbon Fiber-Reinforced Thermosetting Plastic and Stainless Steel

A carbon fiber-reinforced thermosetting plastic and stainless steel were joined by the fiber laser. The surface texture effect on the joint was investigated. The abrasive paper scratching is shown to form single directional striae on stainless steel with intermittent ridges. Laser texture processing creates uniformly distributed microdimples and ridges, which forms a rectangular cellular structure. This processing can improve the fluidity of molten polyphenylene sulfite during laser joining. Laser scanning on stainless steel results in the formation of fusion and heat-affected zones. In the heat-affected zone, lathy ferrite is located along the boundary, while in the fusion zone, ferrite forms the skeletal structure and separates austenite into a cellular structure. The surface texture modification can contribute to the adhesive strength between stainless steel and polyphenylene sulfite through on enlarged contact surface area by forming striae, microdimples, and ridges. As compared to the abrasive paper scratching, the stainless steel/plastic joint with laser texture processing exhibits a higher shear strength.

Microstructural, mechanical and corrosion properties of dissimilar joint between AISI A321 stainless steel and ASTM A537CL1 structural steel produced by GTAW process

In this research, the microstructural, mechanical and corrosion properties of the dissimilar joint of ASTM A537CL1 to AISI A321 steels produced by GTAW process were studied. The welding process was done with ER308L filler metal without pre and post weld heat treatment. The scanning electron microscope and optical microscope were used to study the microstructure and fracture surface of the welded samples. Also, the mechanical behavior of the joint was evaluated by impact, tensile, bending and microhardness tests. The results illustrated that the microstructure of the weld metal was austenite with dendritic structure contained skeletal and lathy ferrite. In tension tests, all weldments failed from A537 base metal. The results of impact test indicated that all specimens exhibit ductile fracture and indicated high impact energy of about 205 J. In fine grain HAZ of A537 steel, because of formation of fine equiaxed grains due to the allotropic transformation, high microhardness was seen. While, in coarse grain HAZ, due to the formation of bigger grains, carbon migration and decreasing in the amount of pearlite phase, the microhardness slightly decreased. The exsistence of chromium in microstructure improved the corrosion resistance and the weld metal indicated acceptable corrosion resistance as compared with both base metals.

Laser welding of dissimilar materials

Abstract This study addresses to the laser welding with active flux (SiO2 + Poly (vinyl alcohol)) for improving the geometrical profile and microstructure of the dissimilar carbon steel – stainless steel joints. The experimental tests were carried out using a TRUMPH 556 pulsed laser and a Precitec YW50 welding head manipulated by a robotic arm. AISI 321 and S235 plates with the dimensions of 50X100X0.5 mm were used as welding specimens. Several fusion lines were made in order to determine the optimal SiO2 / Poly mixing ratio and to highlight the influence of the SiO2 flux on the microstructure. Addition of the active flux results in a more stable welding process and with less plasma plume and a narrower weld bead profile. The samples have been analyzed by optical and electron microscopy showing that SiO2 addition lead to formation of mixed morphology of lathy and skeletal ferrite in the weld zone.

Effect of heat on microstructural, mechanical and electrochemical evaluation of tungsten inert gas welding of low-nickel ASS

PurposeThe purpose of the study is to evaluate Cr-Mn ASS weld using different heat inputs for its microstructure, mechanical properties and electrochemical behavior. The microstructural examination used optical and scanning electron microscopy. It was observed that ferrite content decreases with increasing heat input. The length of dendrites, inter-dendritic space and volume of lathy ferrite increase with increasing heat input. The increasing heat input caused grain coarsening near the fusion boundary and produced wider heat-affected zone (HAZ). It also decreases hardness and tensile strength. This is attributed to formation of more δ ferrite in the weld. The electrochemical evaluation suggested that the δ ferrite helps in improving the pitting potential in 3.5 per cent NaCl solution saturated with CO2. Whereas in 0.5-M H2SO4 + 0.003-M NaF solution, higher passivation current density was observed because of dissolution of dferrite. The interphase corrosion resistance decreased with increasing heat input.Design/methodology/approachThe Cr-Mn austenitic stainless steel or low-nickel ASS was procured in form of 3-mm sheets in rolled condition. The tungsten inert gas welding was performed at three different heat inputs (100 A, 120 A and 140 A), argon as shielding gas with a flow rate of 15 L/min. Different welded regions were observed using optical microscope and scanning electron microscope. Electrochemicals test were performed in solutions containing 3.5 per cent NaCl with saturated CO2 solution and 0.5 M sulfuric acid + 0.003 M NaF at a scan rate of 0.1667 mV/s at room temperature (30 °C ± 1 °C) using a potentiostat.FindingsThe test steel Cr-Mn ASS is suitable with the selected electrode (308 L) and it produces no defects. Vermicular ferrite and lathy ferrite form in welds of various heat inputs. The increase in heat input reduces the formation of lathy ferrite. The width of HAZ and un-mixed zone increases with increase in heat input. The weld zone of low heat input (LHI) has the highest hardness and tensile strength because of higher δ ferrite content and small grain size in the weld zone. The hardness at high heat input (HHI) is found to be lowest because of grain coarsening in the weld. With increase in δ ferrite, the pitting resistance increases. In 0.5-M sulfuric acid + 0.003-M NaF, the increase in ferrite content reduces the passivation current density. Interphase corrosion resistance increases with increase in δ ferrite content as higher per cent degree of sensitization was observed in LHI welds as compared to medium heat input and HHI welds.Originality/valueThis work focuses on welding of ASS by tungsten inert gas welding at different heat inputs. Welding is a critical process for joining metals in most of the fabrication industries and proper heat input is required for getting desired microstructure in the weld metal. This would highly affect the strength and corrosion behavior of the alloy. This paper would give an understanding of how the change in heat input by tungsten inert gas welding affects the microstructural and corrosion behavior in the weld metal.

Shear Strength Optimization of Laser-Joined Polyphenylene Sulfide-Based CFRTP and Stainless Steel

A thermosetting plastic and stainless steel were joined by the fiber laser with and without polyphenylene sulfide (PPS) additive. Its microstructure, interface morphology, and shear strength were investigated. The laser joining is shown to change the microstructure of the stainless steel and result in the heat-affected zone and fusion zone, which contains the lathy ferrite and skeletal ferrite, respectively. Without the PPS interlayer, the additive in the plastic can be overheated and decomposed during laser joining, which is detrimental to the interface bonding. The additive can contribute to the plastic and stainless steel interpenetration, but its amount should be controlled. Insufficient additive quantities cannot fill the gap between stainless steel and plastic, but its higher quantities can cause excessive melting, which would prevent from gaining the joint with optimum shear strength. The appropriate interlayer thickness is 300 μm, which improves the shear strength of the stainless steel and plastic joint to 15.1 MPa.

Assessment of the Microstructure and Mechanical Properties of a Laser-Joined Carbon Fiber-Reinforced Thermosetting Plastic and Stainless Steel

The thermosetting plastic and stainless steel were joined with a fiber laser. The influence of processing parameters on the joint was studied. The laser scanning on stainless steel is shown to result in the formation of the heat-affected and fusion zones. In the first zone, lathy ferrite precipitates along the boundary, which modifies austenite, while in the second zone, ferrite forms the skeleton structure and separates austenite into a small cellular structure. The laser joining improves the microstructure of both zones. With an increase in the laser scanning speed and power, the shear strength of the stainless steel/plastic joint first increases and then decreases. A low laser scanning speed or high laser power would overheat polyphenylene sulphide and lead to its decomposition. Those factors would also reduce heat transfer and lead to its insufficient melting. The stainless steel/plastic joint acquires a maximum shear strength at a laser scanning speed of 4–5 mm/s and laser power of 320-350 W.

Underwater local dry cavity laser welding of 304 stainless steel

The relationship between the gas rates and the shielding condition of the double-layer gas curtain nozzle utilized in underwater laser beam welding (ULBW) was observed. The welding morphology, weld porosity and mechanical properties of butt joints produced in different process parameters were investigated. With the increase of the heat input, the welding porosity decreased firstly and then increased. Higher welding porosity degraded the mechanical properties significantly and the formation of the welding pores could be attributed to the water vapor generating on the bottom surface of the joint and the solidification rate of the molten pool. The high-quality butt joint of ULBW without welding pores was obtained under optimal process parameters, whose tensile strength, impact toughness and microhardness profile approached to these of the in-air welded joint. Compared with in-air joint, the lathy ferrite appears in the ULBW bead and some equiaxed crystals were replaced by the columnar dendrites in the weld center region owing to the cooling effect of water.

Growth behavior and orientation relationships in AISI 304 stainless steel during directional solidification

The formation mechanism of lathy ferrite in AISI 304 stainless steel during directional solidification was discussed in terms of the orientation relationship between ferrite and austenite. Experimental results show that most of the ferrite laths are arranged parallel and a few ferrite laths with perpendicular morphology can also be observed in the solidified microstructure. Selected-area diffraction patterns by transmission electron microscopy (TEM) and pole figures by electron backscatter diffraction (EBSD) show that Nishiyama–Wassermann orientation relationship between the lathy ferrite and austenite exists in the solidified microstructure. Based on the pole figures of the ferrite, it was found that (103) and [001] of the lathy ferrite are parallel to the sample surface and heat flow direction, respectively, during directional solidification. The elongated directions of the lathy ferrite are found to be [001], [011], and [123], which means that the lathy ferrite grows without preferential direction during directional solidification.

Microstructure and mechanical properties of medium Mn steel containing 3%Al processed by warm rolling

The present study was attempted to evaluate the microstructural evolution and mechanical properties of a 3wt%Al containing medium Mn steel which was warm rolled with different thickness reductions directly after intercritical annealing at 750°C by using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction and tensile tests. The results show that the laths of ferrite and retained austenite (RA) not only gradually rotated their longitudinal axis to the rolling direction but also were refined with increasing rolling thickness reduction, and thus a well developed lamellar structure of bimodal size distributed lathy ferrite and RA was obtained after heavy rolling reduction. Though the strength increases while the ductility decreases with increasing rolling thickness reduction, an excellent combination of strength and ductility expressed by the product of ultimate tensile strength (UTS) to total elongation (TEL) of ~ 50GPa% was obtained through a wide process window of warm rolling. It is thus proposed that warm rolling is a promising way to simplify the traditional multi-stage rolling and annealing processes of Al-containing medium Mn steels, especially to overcome the cold rolling difficulty of medium Mn steels with high carbon content.