Phases In Stainless Steel Research Articles

Investigation on microstructure evolution, mechanical properties and corrosion resistance of dual phase stainless steel joints welded by GTAW and SAW methods

Duplex Stainless Steels (DSSs) have excellent mechanical properties and corrosion resistance thanks to the biphasic ferritic-austenitic microstructure. This microstructure feature is highly influenced by the welding heat cycles. In this research paper, the effect of gas tungsten arc welding (GTAW) and submerged-arc welding (SAW) on the microstructure, mechanical and corrosion properties of SAF 2507 duplex stainless steel (DSS) were investigated. The base metal had the austenite content of 45 %, while the weld metals show variation of austenite contents in different regions. The middle regions of the both welds (GTAW ∼ 60.5 %, SAW ∼ 49.3 %) showed higher austenite contents than that of the root (GTAW ∼ 25.6 %, SAW ∼ 40.9 %) and top (GTAW ∼ 44.2 %, SAW ∼ 34.2 %) regions. Subsequent heat cycles promoted the precipitation of austenite from the primary ferrite, resulting in the higher contents of austenite in the middle welds. The nanoindentation tests revealed the individual properties of the typical phases, i.e., γ-Fe ∼ 5.4 GPa and α-Fe ∼ 4.7 GPa in both weld metals. The average tensile strength of GTAW and SAW welded joints are 997 MPa and 1109 MPa, respectively. The corrosion behavior of the weld metal was also evaluated through potentiodynamic polarization curves. The as-welded joints exhibit slight decrease in corrosion resistance, as compared to the base metal. These two weld metals showed slightly difference in mechanical and corrosion resistance properties. SAW method is most recommended when large thickness or high efficiency welding is required.

Laser additive manufacturing of ductile Fe-based bulk metallic glass composite

• Fe-based BMGCs with high strength and record-breaking ductility was fabricated via LAM technique. • An appropriate amount of stainless steel can effectively ductile the Fe-based BMG without seriously sacrificing strength. • Dual-phase structure was achieved by simply transporting the second phase into laser molten pool in the form of powder during LAM process. Laser additive manufacturing (LAM) is a promising technology for processing bulk metallic glass (BMG) with freeform geometries or unlimited size. However, the inherently brittle Fe-based BMGs produced by LAM have always been plagued by the micro-cracking induced by the large thermal stresses during the LAM process. To solve this dilemma, 316L stainless steel (SS) with excellent toughness and similar elemental composition was carefully selected as the second phase to form Fe-based BMG composites (BMGCs). The obtained Fe-based BMGCs are equipped with a heterogeneous structure, i.e., the 316L SS phase is wrapped by the metallic glass and forms a unique "fishbone" structure with a micron - scale. Excitedly, the special structure nicely improves a plastic strain of the Fe-based BMGC with a strength of 2355 MPa to ∼17%, achieving a record-breaking achievement among Fe-based amorphous with critical dimensions over 1mm.

A Review on Hot Stamping of Advanced High-Strength Steels: Technological-Metallurgical Aspects and Numerical Simulation

The production of ultra-high strength automotive components requires a multi-directional approach. Hot stamping combines both forming and heat treatment processes to obtain a usually martensitic structure of complicated shaped automotive parts. The preparation for production using hot stamping must involve the latest methods of numerical analysis of both temperature changes and forming, which are applied for an increasing range of materials used. In this paper, the current state of knowledge about the basics of hot stamping, used technological lines, and the current state of material used with applied heat treatments and possible coatings have been reviewed. Moreover, the numerical modeling process has been described. The most important aspects of process automation, including the use of digital twins for simulation and optimization of operational kinetics of the robots accomplishing the production process, analysis and minimization of time of production cycles, and searching for weak operational points of the control systems and for real time visualization of operation of complete line, are considered. The digital twins and corresponding numerical models enable the symmetrical design of real production lines. The details of heat treatment profiles with so called tailored zone heat treatment are provided. Hot stamping is a dynamically developing technology as evidenced by the increasing range of materials used, also from the 3rd generation of advanced high strength (AHSS) steels. It starts to combine forming of symmetric or asymmetric elements with more complex heat treatment processes as required for dual phase (DP) stainless steels or the newest generation of high-strength and ductile medium-manganese steels.

Characterization of a Marine Wet Solar Cell with Titanium Dioxide and Copper Oxides Electrodes Coated on the Stainless Steel Substrate

Introduction Titanium dioxide (TiO2) has been widely studied and applied in solar cells, fuel cells and hydrogen production due to its photocatalytic n-type semiconductor properties. We have been studying photocatalytic properties of titanium dioxide anode which is assembled to a marine wet solar cell along with counter copper oxides cathode. We have studied photocatalytic characteristics of TiO2 electrode and copper oxides electrode, respectively. In this study, TiO2 and copper oxides were coated on the same stainless steel substrate, forming anode and cathode of a solar cell, respectively. The electrochemical and microstructural properties of those electrodes were studied.Preparation of Electrodes and Cell Type 329J4L dual phase (ferritic and austenitic) stainless steel (S.S) was used as the base substrate for coating. The surface of the substrate was polished and cleaned with acetone with ultrasonic cleaner for 10 minutes. After that, the substrate was passivated with 10% vol. nitric acid at 60 ºC for 30 minutes. Half of the surface of the substrate was then deposited with copper film using vacuum deposition method. The Cu-deposited substrate was heat treated to form copper oxides film on the surface. The other half was screen-printed with insulating layer and then heated. On top of the insulating layer, the conducting layer was printed and heated. Titanium dioxide was finally screen printed and heat treated. The finish coating with epoxy resins around the cell was conducted to get prepared for electrochemical measurements and analyses. For comparison and to better understand the photocatalytic effect of each electrode, other types of cells were prepared where only half-cell electrodes are photocatalytic and other parts are conducting layers; TiO2 vs S.S cell and conduction layer vs copper oxides electrode cell.Measurement and Analysis The electrochemical measurement of the cell was performed with a potentiostat under irradiation using a calibrated xenon light source with light intensity of 10.5 mW/cm2 and a wavelength range between 250 nm and 800 nm. The measurement was conducted using artificial seawater as the electrolyte. The microstructure of each electrode was analyzed with optical microscope, scanning electron microscope (SEM) and electron dispersion spectroscopy (EDS).Results and Discussion The power density-cell voltage measurement showed the cell where both electrodes were photocatalytic showed higher photopotential than the cell where only one electrode was photocatalytic. Moreover, cell with both electrodes coated on the same substrate showed higher photopotential than cell with electrodes being separated. This is due to the enhancement of charge flow between electrodes when the electrodes are coated on the same substrate. It is also found out that although titanium dioxide electrode can be heat treated up to 550ºC for better performance in the previous study, the heat treatment temperature for the cell becomes a limit factor since the temperature for copper oxides electrode is the best at 350 ºC to prevent photo corrosion. The different temperatures for heat treatment of the cell were set at 150 ºC, 250 ºC, and 350ºC. The preliminary analysis showed there is a relationship between the heat treatment temperatures and the photocatalytic characteristics of each electrode. The microstructural analysis by SEM of each electrode is underway and will be presented in the ECS conference meeting.

Microstructure, mechanical behavior, and crystallographic texture in a hot forged dual-phase stainless steel

In this work, the hot forging behavior of a dual phase stainless steel in the temperature range of 850–1250 °C was investigated. The study revealed the occurrence of a significant cracking phenomenon for processing temperatures below 950 °C that was attributed to the combined effect of intermetallic precipitation and severe deformation. EBSD examination highlighted the occurrence of continuous dynamic recrystallization in both ferrite and austenite microstructures for processing temperatures above 1050 °C. Increasing the hot forging temperature to 1250 °C increased the low angle grain boundaries fraction and lowered the one of the high angle grain boundaries. This was accompanied by a gradual change in the crystallographic texture of the material. The mechanical behavior investigation showed that the steel plasticity, sharply dropped after forging at 850°, was gradually recovered after hot forging at temperatures above 1050°C. This was confirmed by nanoindentation measurements that revealed a remarkable increase of the hardness and Young’s modulus of the steel after hot forging at 850°C and 950°C due to the dislocation nucleation and the σ phase precipitation at γ/δ interface. The enhancement of dislocation movement at the vicinity of the grain boundaries in the temperature range of 1050–1250 °C improved the global mechanical properties of the hot forged steel.

Controllable preparation and electrochemical properties of In-situ annealed LiCoO2 films with a specific crystalline orientation on stainless steel substrates

The crystallization characteristics of LiCoO2 (LCO) thin films are key factors that affect the electrochemical properties of films. In this paper, in-situ annealed LCO films with a specific crystalline orientation were prepared on stainless steel (SS) substrates by radio-frequency (RF) magnetron sputtering. The effects of the high-temperature pretreatment of the SS substrate, substrate temperature and sputtering power on the crystallization and electrochemical properties of the LCO films were investigated in detail. It was found that the structure of the SS substrate was transformed from the γ phase to the δ phase after the high-temperature pretreatment, and the crystallization orientation of the LCO films could be induced by the different SS phase structures. The crystallization characteristics of the LCO films were also clearly influenced by the substrate temperature. The crystallization orientation changed from the (003) orientation to the (101) orientation when the temperature increased to a high degree, but too high of a substrate temperature (such as 600 °C) ruptured the films. The discharge specific capacity of the LCO films increased with an increasing substrate temperature, showing a capacity of 53.8 μAh cm−2 μm−1 at 550 °C and exhibiting good cycling stability. At this temperature, the crystal orientation could be controlled by adjusting the sputtering power to avoid rupturing the thin films, thereby achieving high-quality LCO films with a specific orientation. The LCO films prepared at 120 and 200 W showed obvious (101) and (003) preferred orientations, respectively. The galvanostatic charge-discharge tests showed that the (101) preferred orientation film exhibited a large initial discharge capacity of 57 μAh cm−2 μm−1, but its cycling performance was poor. The (003) preferred orientation delivered a superior cycling performance with an initial discharge capacity of 55.6 μAh cm−2 μm−1 and a capacity retention of 72% after 150 cycles. Cyclic voltammetry and electrochemical impedance spectroscopy measurements showed that the (101) preferred orientation was more conducive to the full infiltration of the electrolyte and the transport of lithium ions, but the stability of the structure and surface was poor and the impedance clearly increased during cycling. The (003) preferred orientation exhibited better structural and surface stability and exhibited better lithium-ion diffusion after repeated electrochemical processes.

Transient phase fraction and dislocation density estimation from in-situ X-ray diffraction data with a low signal-to-noise ratio using a Bayesian approach to the Rietveld analysis

We describe the analysis of in-situ HT-XRD data of a dual phase stainless steel exposed to a complex thermal cycle of heating, holding and cooling. For the conditions used only low quality diffraction data could be collected. Peak positions, peak areas and peak broadening are modeled by the Rietveld method. The low signal-to noise ratio and the presence of artificial peaks due to tube tails complicate the data evaluation. In a first attempt the parameters are refined by a local optimization procedure (e.g. Levenberg-Marquardt). However, this procedure fails by being caught in one of several local minima. Next, a Bayesian approach with a Markov Chain Monte Carlo (MCMC) algorithm is used as a global optimization procedure to refine the simulated Rietveld diffractograms. Accurate estimates of the evolution of the phase fractions and dislocation densities in martensite and austenite during all stages of the thermal cycle are obtained by this MCMC algorithm. While an approach based on multivariate second order Taylor series completely underestimates the error, the uncertainties in the model parameters could be estimated appropriately from histograms obtained by the MCMC method.

Attenuation Effectiveness of Double Phase Stainless Steel Alloys for Fusion Reactor System

Aluminium, tungsten and aluminium - tungsten ferritic stainless-steel alloys were developed and produced using 30 kg pilot plant induction furnace of medium frequency at the same conditions to be applied in nuclear reactor shielding material. Higher hardness, ultimate strength, and ultimate tensile strength are appeared in the developed alloys. Aluminium stainless-steel elongation had lower values. Total slow neutrons, neutrons > 10 keV, and slow neutrons of aluminium-tungsten based ferritic stainless steel alloys which carried out using 241Am-Be neutron source as well as a wide range up to 1400 keV energies of gamma rays, which emitted from Co-60, Cs-137 and Eu-152, were used by means of sodium iodide (Tl) detector and studied using the XCOM program. Results showed that all studied stainless-steel alloys own a converge values of neutron macroscopic cross sections (Σ, cm“1). Moreover, there is no significant variation of the value of mass attenuation coefficients (σ, cm2/g) for the studied alloys. Good agreement between both experimental and calculated results of mass attenuation coefficients was achieved. A new composition for several nuclear applications such as, nuclear shielding applications were achieved.

Effects of Fe–Al intermetallic compounds on the wear and corrosion performances of AA2024/316L SS metal/metal composites

In the present study, AA2024/316L stainless steel (SS) metal/metal composites (MMCs) with different 316L SS contents (1–25 wt%) were fabricated by mechanical milling and hot pressing. The effects of 316L SS and intermetallic phase contents on the corrosion and wear performances of the as-prepared MMCs were investigated. It was found that the hardness of the AA2024/25 wt% 316L SS composite increased to 180 HBN, whereas the value was 111 HBN for the AA2024 alloy. The wear rate of the AA2024/25 wt% 316L SS composite (0.03 mm3/m) was lower than that of the AA2024 alloy (0.29 mm3/m) under 20 N load. The corrosion performance of the samples was investigated by potentiodynamic polarization scanning in 3.5 wt% NaCl solution. Corrosion test results revealed that the corrosion resistance of the AA2024/1 wt% 316L SS composite (3.58 mpy) was better than that of the base alloy (9.27 mpy). Therefore, it can be inferred that Fe–Al intermetallic compounds played an important role in the corrosion and wear properties of the composites.

Static Recrystallization Behavior and Mechanical Properties of Heterogeneous Nanostructured Duplex Phase Stainless Steel

Static Recrystallization Behavior and Mechanical Properties of Heterogeneous Nanostructured Duplex Phase Stainless Steel

Hot workability of 420 J1 martensitic stainless steel

Steel grade 420 J1 is martensitic colonies embedded with ferritic phase stainless steel. The steel under investigation contains mainly 12.42 % chromium and 0.2% carbon.Hot workability of the 420 J1 steel grade became the most critical issue to suit the different application requirements. The present article is dealing with the parameters controlling successful hot workability of the steel grade 420 J1.4-conscutive hot rolling passes were designed for a thickness reduction from 7 to 3 mm. Hot deformation passes were designed to score two parallel goals. The first goal is to avoid instability regions, while the second one is to create dynamic softening.It was found that austenite is subjected to grain refinement to reach about 17 micron.The flow stress is calculated. Dynamic recovery is clearly noticed at the last two deformation passes. Microstructural investigation as well as mechanical properties for final hot rolled steel strips was executed.

Understanding on toughening mechanism of bioinspired bulk metallic glassy composites by thermal spray additive manufacturing

Toughening mechanism of bioinspired bulk metallic glassy composites (BMGCs) reinforced with various volume fractions of ductile stainless-steel (SS) phase fabricated via newly developed thermal spray additive manufacturing was investigated. Microstructure characterizations and nanoindentation suggested a strong interface-bonding along with nanoscale compositional gradient formed between the metallic glass and SS phases. Finite element modelling and theoretical analysis revealed that the increase in toughness arose from the nacre-like soft/hard phase configuration, which exhibits the effective stress-shielding effect against crack propagation, thus mitigating stress concentration and blocking crack propagation.

Stability indicating RP-HPLC method development for docetaxel trihydrate

The purpose of present study was to develop RP-HPLC method for estimation of docetaxel trihydrate which should be a suitable, simple, precise, accurate, robust, and reproducible. The samples were assayed by the Shimadzu HPLC instrument - LC-20AD (Japan) equipped with Shimadzu SPD-M20A UV-VIS detector operated at wavelength of 230 nm. The binary gradiant pump was used for the analytical method development. The reverse phase stainless steel column (150 × 4.6 mm) packed with 5 μm particles (C-8, LiCrosphore® 100, Germany) was used to take chromatograph. A mobile phase consisting of acetonitrile/phosphate buffer 20 mM, (45:55, v/v), pH 3.5 adjusted with o-phosphoric acid at a flow rate of 1 mL/min. The method was validated by system suitability and reproducibility. The linearity was also determined using samples with five different concentrations of 20, 40, 60, 80 and 100 µg/mL. The results of the study showed that the developed RP-HPLC method is simple and robust which is useful for the estimation of docetaxel trihydrate in bulk drug and in pharmaceutical dosage form. The results of stability show that the method has stability over a period of 48 h at room temperature.
 Keyword: Docetxel trihydrate, RP-HPLC method, validation, stability

The corrosion resistance of laser surface alloyed stainless steels

Purpose: of this paper was to examine the corrosion resistance of laser surface alloyed (LSA) stainless steels using electrochemical methods in 1M NaCl solution and 1M H2SO4 solution. The LSA conditions and alloying powder placement strategies on the material's corrosion resistance were evaluated. Design/methodology/approach: In the present work the sintered stainless steels of different microstructures (austenitic, ferritic and duplex) where laser surface alloyed (LSA) with elemental alloying powders (Cr, FeCr, Ni, FeNi) and hard powders (SiC, Si3N4) to obtain a complex steel microstructure of improved properties. Findings: The corrosion resistance of LSA stainless steels is related to process parameters, powder placing strategy, that determines dilution rate of alloying powders and resulting steel microstructure. The duplex stainless steel microstructure formed on the surface layer of austenitic stainless steel during LSA with Cr and FeCr reveal high corrosion resistance in 1M NaCl solution. The beneficial effect on corrosion resistance was also revealed for LSA with Si3N4 for studied steels in both NaCl and H2SO4 solutions. Ferritic stainless steel alloyed with Ni, FeNi result in a complex microstructure, composed of austenite, ferrite, martensite depending on the powder dilution rate, also can improve the corrosion resistance of the LSA layer. Research limitations/implications: The LSA process can be applied for single phase stainless steels as an easy method to improve surface properties, elimination of porosity and densification and corrosion resistance enhancement regarding as sintered material. Practical implications: The LSA of single phase austenitic stainless steel in order to form a duplex microstructure on the surface layers result in reasonably improved corrosion performance. Originality/value: The original LSA process of stainless steels (austenitic, ferritic and duplex) was studied regarding corrosion resistance of the alloyed layer in chloride and sulphate solutions.

Comparative study of the surface oxide films on lean duplex and corresponding single phase stainless steels by XPS and ToF-SIMS

The surface oxide films formed after mechanical polishing on duplex stainless steel and corresponding single phase alloys were characterized by XPS and ToF-SIMS. The native oxide films are mixtures of oxides and hydroxides composed of Fe(III), Mo(IV) and Mo(VI) in the outer region and Cr(III) in the inner region. Nickel, molybdenum and nitrogen are enriched in the underlying metal while chromium and molybdenum are enriched in the oxide layer. The contents of alloying elements in the oxide layer and/or in the underlying metal are found to be directly related to their content in the bulk of the alloys.

Microstructure Formation of High Pressure Torsion Processed (α + γ) Two Phase Stainless Steel

(α + γ) two phase stainless steel (Fe-21%Cr-4.8%Ni-1.5%Mo) powder was processed by high pressure torsion (HPT) and consolidation at room temperature. The received powder had fully α single phase due to the rapid cooling during gas atomizing process. Specimens after HPT process were heat treated at 1173K for 3.6ks. It was revealed that the decomposition of α phase to γ took place during the heat treatment. Detailed microstructure observation showed that an equiaxed (α + γ) micro-duplex structure was developed and its average grain size was approximately 3.2 micrometers. The same heat treatment given to the material without HPT resulted in a coarse two phase microstructure.Therefore, it is considered that an ultra fine grained microstructure was caused by increasing of nucleation sites for γ phase due to severe plastic deformation (SPD) of HPT process. Electron backscatter diffraction patterns (EBSD) analysis indicated that α phase has a {110}/ND strong texture, that is, the α phase seems to have single orientated coarse grain structure. The γ precipitates indicated a {111}/ND strong texture, and the crystallographic orientation relationship of Kurdjumov-Sachs was observed.

Effect of β-SiC Particle Concentration on the Properties of the Duplex Ni-P/Ni-P-β-SiC Coating

Duplex Ni-P/Ni-P-β-SiC coatings were prepared on 2605N double phase stainless steel substrate by electroless plating process. Experiments were carried out to compare and analyze the morphologies, composition and structure of Ni-P/Ni-P-β-SiC by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), XRD and electrochemical workstation, respectively. The results show that duplex Ni-P / Ni-P-β-SiC coating has good associativity between the coating and the substrate, β-SiC particles were uniformly distributed in the coatings, without pores, crack defects and so on. When β-SiC particle concentration is 15g/L, the microhardness reached maximum 623.285HV0.20, In addition, when the β-SiC concentration is 15g/L, the corrosion reasistence is the best.

ミリングプロセスによる二相ステンレス鋼の調和組織形成過程

ミリングプロセスによる二相ステンレス鋼の調和組織形成過程

Surface Crack and Organization of Hot Rolled S31803 Duplex Stainless Steel Bars

In bar rolling of S31803 duplex stainless steel, the surface crack is easy to appear. Through the observation on the microstructure, ferrite and austenite morphology and phase ratio were analyzed. The surface cracks of S31803 duplex stainless steel bar is mainly because of the dual phase microstructure softening mechanism of different in thermal processing, and the double phase stainless steel heat plasticity decrease. When the ferrite and austenite proportion close, and the heating temperature is too high, to reduce the binding force between the grains of billet surface, easy to cause the crack surface of a bar.

Precipitation kinetics and mechanical behavior in a solution treated and aged dual phase stainless steel

The precipitation kinetics and the mechanical behavior in a solution treated and aged dual phase stainless steel (DSS) are investigated. X-ray diffraction, transmission and scanning electron microscopy techniques are used to characterize the microstructure and to identify its constituents. The precipitation kinetics analysis shows that the ferrite to σ phase transformation follows the modified Johnson Mehl Avrami (JMA) model containing an impingement parameter c that is adjusted to 0.3. Activation energies calculation leads to conclude that interface reaction is the main mechanism that controls the σ phase formation. Detailed analysis of the extent of the different tensile deformation domains reveals the significant contribution of both σ phase particles and dislocation accumulation to the strain hardening of the material.