Mixture Of Austenite Research Articles

Full Density Powder Metallurgical Cold Work Tool Steel through Nitrogen Sintering and Capsule-Free Hot Isostatic Pressing

Vanadis 4E (V4E) is a powder metallurgical cold work tool steel predominantly used in application with demand for wear resistance, high hardness, and toughness. It is of interest to have a processing route that enables full density starting from clean gas-atomized powder allowing component shaping capabilities. This study presents a process involving freeze granulation of powder to facilitate compaction by means of cold isostatic pressing, followed by sintering to allow for capsule-free hot isostatic pressing (HIP) and subsequent heat treatments of fully densified specimens. The sintering stage has been studied in particular, and it is shown how sintering in pure nitrogen at 1150 °C results in predominantly closed porosity, while sintering at 1200 °C gives near full density. Microstructural investigation shows that vanadium-rich carbonitride (MX) is formed as a result of the nitrogen uptake during sintering, with coarser appearance for the higher temperature. Nearly complete densification, approximately 7.80 ± 0.01 g/cm3, was achieved after sintering at 1200 °C, and after sintering at 1150 °C, followed by capsule-free HIP, hardening, and tempering. Irrespective of processing once the MX is formed, the nitrogen is locked into this phase and the austenite is stabilised, which means any tempering tends to result in a mixture of austenite and tempered martensite, the former being predominate during the sequential tempering, whereas martensite formation during cooling from austenitization temperatures becomes limited.

Использование криогенного охлаждения при волочении нержавеющей проволоки

In the manufacture of wire with high operational and mechanical properties, the use of high total degrees of compression is irrational, since cold plastic deformation reduces the diameter of the wire, and with hot deformation the initial diameter of the wire has its limitations. Therefore, wire processing by thermomechanical method has a huge potential to reduce costs and improve product quality. The article develops a technology of thermomechanical processing of stainless wire, which consists in preliminary heat treatment to obtain an austenitic structure and traditional drawing followed by cryogenic cooling. As a result of such processing, an ultrafine-grained structure consisting of a mixture of austenite and α – martensite and high strength and plastic properties were obtained. When drawing using cryogenic cooling, a structure with an average grain size of 1 microns was obtained, and a microstructure of 2 microns was obtained at ambient temperature.

Enhancing Mechanical Properties: Exploring the Effect of Annealing Temperature on Wire Arc Additively Manufactured High-Strength Steel.

This study investigates the mechanical properties of exceptionally high-strength steel produced by wire and arc additive manufacturing (WAAM), using the 304 stainless steel wire and the low carbon wire (LCS). The study found that annealing treatment can enhance the steel's mechanical properties. The microstructure in the LCS layer changed from ferrite to bainite and then to a mixture of austenite, pearlite, and bainite with increasing annealing temperature. In contrast, the SS layer retained its martensitic structure, albeit with altered lath sizes. The annealing treatment also improved the orientation of the grains in the steel. The optimal annealing temperature observed for the steel was 900 ℃, which resulted in a maximum tensile strength of 1176 MPa along the Y direction and 1255 MPa along the Z direction. Despite the superior mechanical properties, the LCS layer still exhibited failure during tensile testing due to its lower hardness. The study suggests that annealing treatment can be a useful technique for enhancing the mechanical properties of high-strength steel in WAAM applications.

Effect of thermomechanical processing of building stainless wire to increase its durability

A traditional use of high cumulative reduction ratios is not effective for manufacturing wire with high performance and mechanical properties, since cold plastic deformation reduces the wire diameter, while hot deformation has its own limitations. Thus, thermomechanical treatment of rolled steel has a huge potential to reduce costs and improve product quality when used in the construction industry. Such processing allows metalworking industries to increase the economic effect due to a more complete satisfaction of the requirements for the mechanical properties of finished rolled products. The article developed a new technology for thermomechanical processing of stainless steel wire, consisting of preliminary heat treatment to obtain an austenitic structure and traditional drawing followed by cryogenic cooling. As a result of such treatment, an ultrafine-grained structure was obtained, consisting of a mixture of austenite and α-martensite, with high strength and plastic properties. To analyze the features of the obtained microstructures, modern methods of metallographic analysis were used, such as scanning electron microscopy, transmission electron microscopy, and analysis of backscattered electron diffraction patterns. The microstructure is obtained after deformation at both temperatures and consists of a mixture of α-martensite and austenite. A structure with an average grain size of 0.5 µm was obtained by drawing using cryogenic cooling, and a microstructure of 1 µm was obtained at room temperature. The results obtained allow us to expect an increase in the performance and durability of stainless steel wire, which can be used for various purposes.

Effect of process parameters on the clad morphology, microstructure, microtexture, and hardness of single layer 316 L stainless steel during direct energy deposition

The effect of laser power and scanning speed on the surface roughness, clad morphology, microstructure, texture, and hardness of single layers of 316 L SS during direct energy deposition (DED) was investigated in this study. A columnar to equiaxed transition was observed in the deposited clads. Cellular, dendritic, columnar, and planar substructures were observed in the equiaxed region of the clad that was near to the free surface. In the interior region of the clad, grains were columnar in nature and was observed to grow at different angles with respect to the build direction (BD) depending on the interaction angle with the substrate. At intermediate laser power and scanning speeds, 〈001〉 || BD and 〈001〉 || scan direction (SD) orientations were observed. When the laser power was at the lower level, <001> || transverse direction (TD) orientations were obtained. When the laser power was at the higher level, a uniform mixture of austenite and martensite was obtained in the clad. The compositional shift in the deposited bead was responsible for the formation of the martensite phase. When the scanning speed was at lower level, 〈111〉 || SD and 〈110〉 || BD orientations were observed. When the scanning speed was at higher level, <001> || BD orientations were observed. A hardness in the range of 187± 13 Hv was obtained for all the samples except for the sample that was built at high laser power.

Microstructure, Crystallographic Texture, and Mechanical Properties of Friction Stir Welded Mild Steel for Shipbuilding Applications.

In the current work, mild steel used in shipbuilding applications was friction-stir-welded (FSWed) with the aim of investigating the microstructure and mechanical properties of the FSWed joints. Mild steel of 5 mm thickness was friction-stir-welded at a constant tool rotation rate of 500 rpm and two different welding speeds of 20 mm/min and 50 mm/min and 3° tool tilt angle. The microstructure of the joints was investigated using optical and scanning electron microscopes. Additionally, the grain structure and crystallographic texture of the nugget (NG) zone of the FSWed joints was investigated using electron backscattering diffraction (EBSD). Furthermore, the mechanical properties were investigated using both tensile testing and hardness testing. The microstructure of the low-welding-speed joint was found to consist of fine-grain ferrite and bainite (acicular ferrite) with an average grain size of 3 µm, which indicates that the temperature experienced above A1, where a ferrite and austenite mixture is formed, and upon cooling, the austenite transformed into bainite. The joint produced using high welding speed resulted in a microstructure consisting mainly of polygonal ferrite and pearlite. This could be due to the temperature far below A1 experienced during FSW. In terms of joint efficiency expressed in terms of relative ultimate tensile, the stress of the joint to the base material was found to be around 92% for the low-speed joint and 83% for the high-welding-speed joint. A reduction in welding was attributed to the microstructure, as well as the microtunnel defect formed near the advancing side of the joint. The tensile strain was preserved at 18% for low welding speed and increased to 24% for the high welding speed. This can be attributed to the NG zone microstructural constituents. In terms of crystallographic texture, it is dominated by a simple shear texture, with increased intensity achieved by increasing the welding speed. In both joints, the hardness was found to be significantly increased in the NG zone of the joints, with a greater increase in the case of the low-welding-speed joint. This hardness increase is mainly attributed to the fine-grained structure formed after FSW.

Role of nitrogen shielding environment on microstructure and corrosion behavior of 2205 duplex stainless-steel A-GTA welds

The present study aims to understand the role of the shielding environment viz., argon (Ar) and nitrogen (N2) on microstructure, general and pitting corrosion behavior of activated gas tungsten arc (A-GTA) welds of 2205 duplex stainless steel. A-GTA welds made with activated flux SiO2 along with 100% Ar and 95% Ar + 5 % N2 are compared with conventional gas tungsten arc (C-GTA) welds made with 100% Ar. All the metallographic specimens of C-GTA and A-GTA welds are recorded to observe the microstructural changes using an optical microscope connected with image analyser. The basic GillAC electro-chemical system is used to perform potentio-dynamic polarization studies for general and pitting corrosion behavior in a 1 M NaCl solution. From the present study, it is established that activated-GTA welds with SiO2 flux resulted in reduced weld width and enhanced depth of penetrationachieved in a single pass compared to C-GTA welds. The grain morphology of the weld zone (WZ) is observed to be a mixture of austenite and delta ferrite in all the weldments. Secondary austenite is found in the interior of the ferrite whereas at the interfaces of ferrite and primary austenite, various forms of primary austenite are noticed in the weld zone of A-GTA welds. From the corrosion studies, it is found that A-GTA welds made with 95% Ar + 5 % N2 show higher general and pitting corrosion resistance compared to C-GTA and A-GTA welds made with 100% Ar.Improved corrosion behavior may be due to the favourable microstructure and presence of nitrogen as shielding environment, which favors the formation of austenite in the ferrite matrix.

Additive manufacturing of a shift block via laser powder bed fusion: the simultaneous utilisation of optimised topology and a lattice structure

ABSTRACT The precise shape of a shift block support for the turbine blade of a hovercraft was additively manufactured using 17–4 precipitation-hardened stainless steel (STS 630) powder through laser powder bed fusion (LPBF). Subsequently, heat treatment under the H900 condition increased the yield strength and fracture strain of the shift block to 1313 MPa and 11.5%, respectively, and enhanced its corrosion resistance to seawater. This improvement in mechanical and physical properties is primarily because Cu precipitates were uniformly distributed at the interfacial boundaries along with the simultaneous suppression of the formation of Cr23C6 precipitates with weak corrosion resistance. Furthermore, this was attributed to the phase transformation from the as-built STS 630 comprising a mixture of austenite, ferrite, and martensite to a dual mixture of ferrite and martensite after the heat treatment. Thereafter, we topologically optimised the shift block and adopted a lattice structure to apply the design for additive manufacturing (DfAM).

Precipitation of M23C6 Secondary Carbide Particles in Fe-Cr-Mn-C Alloy during Heat Treatment Process

The initial as-cast microstructure of high-chromium white cast iron (2.08% C, 12.1% Cr), including austenitic dendrites in a matrix of a eutectic mixture of austenite and M7C3 carbides. Heat treatment of as-cast iron leads to a transformation of the matrix from austenite to martensite phase. The secondary M23C6 carbide precipitated from matrix improving the hardness of sample from 48 HRC to 62 HRC. JMatPro simulations of volume fraction phase for Fe-C-Cr-Mn alloy shows M7C3 and austenite phases are stable at austenitization temperature (1000 °C). Eutectic carbide of M7C3 is a stable phase in the alloy which is undissolved in the matrix during the heat treatment process. The HR-TEM images of heat-treated sample revealed that both eutectic M7C3 carbide and ultrafine secondary M23C6 carbide particles distributed on the martensite matrix.

Dependence of hydrogen embrittlement mechanisms on microstructure-driven hydrogen distribution in medium Mn steels

The risk of hydrogen embrittlement (HE) is currently one important factor impeding the use of medium Mn steels. However, knowledge about HE in these materials is sparse. Their multiphase microstructure with highly variable phase conditions (e.g. fraction, percolation and dislocation density) and the feature of deformation-driven phase transformation render systematic studies of HE mechanisms challenging. Here we investigate two austenite-ferrite medium Mn steel samples with very different phase characteristics. The first one has a ferritic matrix (~74 vol.% ferrite) with embedded austenite and a high dislocation density (~1014 m−2) in ferrite. The second one has a well recrystallized microstructure consisting of an austenitic matrix (~59 vol.% austenite) and embedded ferrite. We observe that the two types of microstructures show very different response to HE, due to fundamental differences between the HE micromechanisms acting in them. The influence of H in the first type of microstructure is explained by the H-enhanced local plastic flow in ferrite and the resulting increased strain incompatibility between ferrite and the adjacent phase mixture of austenite and strain-induced α'-martensite. In the second type of microstructure, the dominant role of H lies in its decohesion effect on phase and grain boundaries, due to the initially trapped H at the interfaces and subsequent H migration driven by deformation-induced austenite-to-martensite transformation. The fundamental change in the prevalent HE mechanisms between these two microstructures is related to the spatial distribution of H within them. This observation provides significant insights for future microstructural design towards higher HE resistance of high-strength steels.

Enhancement of mechanical and functional properties of welded NiTi by controlling nickel vapourisation

ABSTRACTThis work investigates the effect of nickel vapourisation on mechanical properties and superelasticity of a NiTi wire by selecting the highest and lowest power within a laser processing window. The dominant phase at room temperature changes from austenite to a mixture of austenite and martensite under low power and high power condition, respectively due to higher nickel loss in the high power sample. Furthermore, the high power sample has more deviation from base material texture (111)B2 that causes deterioration in mechanical properties compared with the low power sample with has 81% of base material strength. Better superelasticity of the low power sample (0.38% residual strain) was explained by the existence of the martensite phase and coarser grain structure in the high power sample.

Deformation induced martensite in a Fe-Ni-Co binder phase of a hardmetal

This paper investigates deformation induced martensite in a hardmetal binder phase with target composition 50 wt% iron, 25 wt% nickel and 25 wt% cobalt. A fully austenitic ion polished cross-section surface was scratched with a diamond indenter and investigated with X-ray and electron diffraction. It was found that the top 100 nm of the scratched surface contained a mixture of austenite and a second phase identified as BCC/BCT martensite. The martensite grain size varied between a few 10 nm and a over 1 μm in dimensions.

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;

Strain-Induced Phase Transformation and Nanocrystallization of 301 Metastable Stainless Steel Upon Ultrasonic Shot Peening

The following study investigated the strain-induced phase transformation in metastable austenitic 301 stainless steels via an ultrasonic shot peening treatment (USP) for 5 to 30 minutes. Following the USP, the microhardness increased to a depth of 400 μm and from 200 to 400 HV. The deformed grains and the phase transformation were monitored via X-ray diffraction and electron backscattered diffraction analysis. The grain evolution was studied via transmission electron microscopy. Approximately 500 nm α′-martensite grains formed in the top-most region after 5 minutes of the USP treatment. The grains were then further refined to ~ 100 nm when the peening time increased to 10 and 15 minutes. The grains refined down to tens of nanometers after the specimen was treated for 30 minutes, where the phases were composed of α′-martensite (~ 50 nm). There was a mixture of austenite with α′-martensite (~ 25 nm). The grain refinement and the phase transformation of austenite to α′-martensite during ultrasonic shot peening were systematically investigated.

Investigation of local brittle zone in multipass welded joint of NiCrMoV steel with heavy section

Abstract

Structural Transformation and Hysteresis Behaviour of Ni46Cu4Mn45Sn5 Alloy Synthesized by Ball Milling Method

The present work reports synthesis and structural and magnetic studies of Ni46Cu4Mn45Sn5 shape memory alloy. The synthesis was done using solid state non‐equilibrium mechanical alloying (MA) technique. MA was performed in a Pulverisette‐6 ball milling machine using Tungsten Carbide (WC) bowl and balls. Ball to powder weight ratio of 10:1 and rotation speed of 300RPM were taken as milling parameters. After 20hr milling, the obtained powder was consolidated and quenched from high temperature to induce martensitic phase transformation. X‐ray diffraction (XRD) study indicates a phase mixture of austenite and martensite phase. Variation in lattice strain and crystallite size with milling time is calculated. Microstructural study reveals dual phase mixture after quenching. Phase transformation study carried out by Differential Scanning Calorimetric (DSC) indicates martensitic phase transformation of reversible nature. Vibrating sample magnetometer (VSM) has been utilized for magnetic characterization.

Effects of Phase Evolution on Mechanical Properties of Laser-Welded Ferritic Fe-Al-Mn-C Steel

In the present study, the evolution of microstructure in laser-welded joints of ferrite-based dual-phase Fe-Al-Mn-C steel sheets was analyzed and its effect on the mechanical properties of the joints was investigated. Laser welding was performed using different powers and welding speeds to attain different heat inputs. Electron backscatter diffraction (EBSD) examinations and hardness measurements were used to characterize the microstructure of the welds. The tensile properties were found to depend on the heat input, but joint strength exceeding that of the base metal (BM) were obtained at low heat inputs. However, the fracture location shifted from the base metal to the heat-affected zone (HAZ) as the heat input was increased. The HAZ consisted of a mixture of austenite, ferrite and martensite, and its width increased with increasing the heat input. It was supposed that the incompatibility between the ferrite, austenite and martensite phases led to early void formation and fracturing of the phase interfaces in the wide HAZ.

Research on the transformation mechanism of graphite phase and microstructure in the heated region of gray cast iron by laser cladding

A double-track lap cladding experiment involving gray cast iron was established to investigate the transformation mechanism of graphite phase and microstructure in a laser cladding heated region. The graphite phase and microstructure in different heated regions were observed under a microscope, and the distribution of elements in various heated regions was analyzed using an electron probe. Results show that no graphite existed in the cladding layer and in the middle and upper parts of the binding region. Only some of the undissolved small graphite were observed at the bottom of the binding region. Except the refined graphite size, the morphological characteristics of substrate graphite and graphite in the heat-affected zone were similar. Some eutectic clusters, which grew along the direction of heat flux, were observed in the heat-affected zone whose microstructure was transformed into a mixture of austenite, needle-like martensite, and flake graphite. Needle-like martensite around graphite was fine, but this martensite became sparse and coarse when it was away from graphite. Some martensite clusters appeared in the local area near the binding region, and the carbon atoms in the substrate did not diffuse into the cladding layer through laser cladding, which only affected the bonding area and the bottom of the cladding layer.

Microstructural Feature and Magnetocaloric Effect of Mn50Ni40.5In9.5 Melt-Spun Ribbons

The microstructure and magnetocaloric properties of the melt-spun and annealed Mn50Ni40.5In9.5 ribbons were studied. It is shown that the post-annealing results in a considerable increase of the grain size for the initial austenite, where the columnar-shaped austenite grains almost run through the whole ribbon. Both the melt-spun and annealed ribbons consist of the mixture of austenite and martensite at room temperature, where a 8-layered modulated (8M) martensite structure was identified through selected area electron diffraction (SAED). Further High-angle Annular Dark-field (HAADF) characterizations reveal that the modulation period of 8M martensite is not homogeneous in one martensite plate. Due to strong magneto-structural coupling, the inverse martensitic transformation from a weak magnetic martensite to a strong magnetic austenite can be induced by the magnetic field, resulting in the inverse magnetocaloric effect around room temperature. For a field change of 5 T, the magnetic entropy change ΔSM of 3.7 J·kg−1·K−1 and 6.1 J·kg−1·K−1, and the effective refrigerant capacity RCeff of 52.91 J·kg−1 and 99.08 J·kg−1 were obtained for melt-spun and annealed ribbons, respectively. The improvement of the magnetocaloric properties after annealing should be attributed to the enhanced atomic ordering and magnetization difference between two phases, as well as the reduced hysteresis loss. In addition, both the melt-spun and annealed ribbons can work at a relatively wide temperature range, i.e., δTFWHM = 34 K for melt-spun ribbons and δTFWHM = 28 K for annealed ribbons.

PHASE ANALYSIS OF NITI WIRE BASED ON SYNCHROTRON 2D X-RAY DIFFRACTION PATTERN IN MATLAB

This paper deals with simplified phase analysis of 2D diffraction patterns obtained using microfocused X-ray at various places of superelastic NiTi wire under combined load. For this purpose, MATLAB routines and functions were created, which carry out integration of the patterns in various sectors of Debye ring, fitting of the patterns by a mixture of austenite and martensite (having neglected the R-phase) and successive evaluation of the quantitative phase content. The most crucial simplificating assumptions were: the neglection of the R-phase and the assumption of a) fibre texture or b) no texture.