Cr Ferritic Steel Research Articles

Effect of Hot-rolling Conditions on Texture and R-value of 16%Cr Ferritic Stainless Steel

Effect of Hot-rolling Conditions on Texture and R-value of 16%Cr Ferritic Stainless Steel

Nonlinear acoustic characterizations of simulated HAZ materials in high Cr ferritic heat resistance steel during creep

Nonlinear acoustic characterizations of simulated HAZ materials in high Cr ferritic heat resistance steel during creep

Effect of Cr Content on Softening during Aging in High Cr Ferritic Heat Resistant Steel

Effect of Cr Content on Softening during Aging in High Cr Ferritic Heat Resistant Steel

Development of a novel ZrO2 dispersion strengthened 9Cr ferritic steel: Characterization of milled powder and subsequent annealing behavior

A novel ODS ferritic steel with ZrO2 dispersoids is developed as a candidate structural material for future fast reactor applications. Encouraged by our earlier results demonstrating the retention of crystallinity by ZrO2 dispersoids during milling, the 9Cr ODS steel powder has been synthesized under optimized ball milling conditions and subsequently characterized. The analysis of milled powder showed fine dispersions of ZrO2 with a size range of 2–10nm. Upon annealing at 1223K, precipitation of non-stoichiometric FeO was observed along with fine ZrO2 dispersoids. All the constituent phases are identified using Synchrotron XRD, Conventional and HRTEM. An excellent thermal stability has been manifested by the dispersoids as it retained its fine structure during the annealing treatment with ~95% of dispersoids measuring <11nm. Additionally, ~95% of the FeO precipitates are shown to be <16nm in size, indicating itself as a strong precipitation strengthener to the material. This two-fold strengthening by ZrO2 dispersoids and FeO precipitates, along with nanostructured matrix is believed to play the major role in the high-temperature strength of the material being developed and it could lead to the development of a new generation ODS steel.

Creep Tests and Modeling Based on Continuum Damage Mechanics for T91 and T92 Steels

9-11%Cr ferritic steels play an important role in high-temperature and high-pressure boilers of advanced power plants. In this paper, a continuum damage mechanics (CDM)-based creep model was proposed to study the creep behavior of T91 and T92 steels at high temperatures. Long-time creep tests were performed for both steels under different conditions. The creep rupture data and creep curves obtained from creep tests were captured well by theoretical calculation based on the CDM model over a long creep time. It is shown that the developed model is able to predict creep data for the two ferritic steels accurately up to tens of thousands of hours.

Influence of differential speed rolling ratio on the ridging behavior of ultra purified 17%Cr ferritic stainless steel

The effect of the differential speed rolling on the ridging resistance and the crystallographic texture evolution of ultra purified 17%Cr ferritic stainless steel was investigated in order to select the optimal procedure for improving the surface quality. In the present study, the three different cold rolling processes were carried out: a conventional cold rolling and two different speed ratios asymmetric rolling. In the conventional cold rolling, the ridging of ferritic stainless steel was pronounced due to the band-like clusters of grains with similar crystallographic orientations. For differential speed rolling, ridging depth decreased and ridging was less pronounced when a higher different speed ratio was applied. The results show that severe ridging is attributed to the presence of band-like clusters of γ-fiber (〈111〉//ND) oriented grains. The shear bands introduced by differential speed rolling can enhance the nucleation for recrystallization both in grain interiors and grain boundaries, which can fragment the band-like clusters of similar orientation effectively, promoting the random grain orientation and improving surface quality.

Strain accumulation during microstructurally small fatigue crack propagation in bcc Fe-Cr ferritic stainless steel

Strain accumulation was studied by digital image correlation technique (DIC) during microstructurally small fatigue crack propagation in polycrystalline 18%Cr ferritic stainless steel. Load-controlled fatigue testing was performed with R-ratio of 0.1 and frequency 10 Hz. The maximum applied stress was well below the yield stress of the studied material. The effect of the observed strain field on crack growth rate variation is discussed. Fracture surfaces were studied by scanning electron microscopy (SEM) evidencing the connection between the mechanism of the fatigue crack growth, accumulated strain and crack growth rate. Detailed study of fracture surface morphology was carried out by atomic force microscopy (AFM). Results indicate two processes of material damage accumulation and failure during cyclic loading: 1) local shear strain zones form successively ahead of the crack tip, and 2) fatigue crack growth occurs by both single- and multiple-slip mechanisms. The place and intensity of shear strain localization zones vary during the crack growth that is related closely to the local variation of crack growth rate.

Microstructure–mechanical property correlation in oxide dispersion strengthened 18Cr ferritic steel

The tensile deformation of Oxide Dispersion Strengthened 18Cr ferritic steels (henceforth designated as ODS–18Cr steel) was studied over a temperature range of 298–1073K. At each temperature, the influence of microstructure (grain size and dispersoid size) which could be refined progressively by increasing the milling time over the range 1–6h on strength was also investigated. Oxide free 18Cr steel (NODS) provided the baseline data as compared to ODS–18Cr steel. At all the test temperatures, the flow stress of ODS–18Cr steels increased with increasing milling time or equivalently with refinement of the grains and dispersoids. The decrease in flow stress with increasing tensile test temperature was marginal up to 673K. Beyond 673K, the flow stress decreased rapidly. Enhanced strength of ODS steels when compared to NODS steel is due to the formation of ultra–fine grained structure along with fine dispersion of complex Y–Ti–O oxide particles. The concomitant roles of the grain size related strengthening and dispersion strengthening due to oxide particles in the strengthening of ODS–18Cr steels at all test temperatures were rationalized using root mean square superposition model.

Oxidation behavior and area specific resistance of La, Cu and B alloyed Fe-22Cr ferritic steels for solid oxide fuel cell interconnects

Two Fe-22 wt% Cr ferritic stainless steels containing varying concentrations of La (0.14 or 0.52 wt%), Cu (0.17 or 1.74 wt%) and B (48 or 109 ppm) are investigated with respect to oxidation behavior and high temperature area specific resistance (ASR) of the surface oxide scales. To determine the oxidation resistance of developed steels, continuous isothermal oxidation is carried out at 800 °C in air, for 2000 h, and their thermally grown oxide scale is characterized using dynamic SIMS, SEM/EDX, XRD and GI-XRD techniques. To assess their electrical performance, the ASR measurement by four-point probe method is conducted at 800 °C in air, for 400 h. In higher La content steel, the La-oxides at the scale/alloy interface promotes the oxygen transport which resulted in sub-surface oxidation of Mn, Cr, Ti and Al. Moreover, the inward growth of oxides contributes to increase of Fe-Cr alloy protrusions within the scale, which reduced the ASR. In contrast, sub-surface oxidation is reduced in high Cu-alloyed steel by segregated Cu at the scale/alloy interface. Thus, addition of Cu is effective to oxidation resistance and also to better electrical performance. However, no obvious impact of B on the scale sequence and/or ASR is observed.

Influence of Powder Outgassing Conditions on the Chemical, Microstructural, and Mechanical Properties of a 14 wt% Cr Ferritic ODS Steel

Oxide dispersion-strengthened ferritic stainless steels are foreseen as fuel cladding tube materials for the new generation of sodium fast nuclear reactors. Those materials, which exhibit remarkable creep properties at high temperature, are reinforced by a dense precipitation of nanometric oxides. This precipitation is obtained by mechanical alloying of a powder and subsequent consolidation. Before consolidation, to obtain a fully dense material, the powder is vacuumed to outgas trapped gases and species adsorbed at the surface of the powder particles. This operation is commonly done at moderate to high temperature to evacuate as much as possible volatile species. This paper focuses on the influence of outgassing conditions on some properties of the further consolidated materials. Chemical composition and microstructural characterization of different materials obtained from various outgassing cycles are compared. Finally, impact toughness of those materials is evaluated by using Charpy testing. This study shows a significant influence of the outgassing conditions on the mechanical properties of the consolidated material. However, microstructure and oxygen contents seem poorly impacted by the various outgassing conditions.

Effect of annealing temperature and time on microstructure and mechanical properties of high Cr ferritic casting steel

A new-type of high Cr ferrite cast steel was designed and investigated. Effects of annealing temperature and time on the microstructure and mechanical properties of the high Cr ferrite cast steel were studied. The results show that the microstructures of the as-cast and annealing steels are composed of ferrite and (Cr•Fe)23C6 carbide. The morphology of carbides is from long rod and the continuous network to crystal precipitation for the steels with increasing of annealing temperature and time. The impact toughness is slightly increased from 6 J/cm2 to 8 J/cm2 when the annealing temperature increases from 1180 ℃ to 1200 ℃. But the hardness is about HB 200 and no obvious differences between the as-cast and annealing steels. The most suitable annealing temperature and time are 1200 ℃ and 5 h, respectively. The wear resistance of the high Cr ferrite cast steel is increased and improved with annealing temperature and holding time at 260 ℃. The wear mechanism is changed from abrasion wear to abrasive and adhesive wear. The good wear-resistant of the high Cr ferrite cast steel is mainly attributed to the fine uniformly dispersed carbides.

Strain-induced precipitation in Nb + Ti dual stabilisation ferritic stainless steel

ABSTRACTStrain-induced precipitation was observed in Nb + Ti dual stabilisation 17%Cr ferritic stainless steels. Nb-containing precipitates were observed in the case of 0.4%Nb but not in the case of 0.2%Nb addition. The precipitation induced by strain is identified (Nb,Ti)C, which is a NbC-rich structure and different from the precipitation in undeformed specimens. The (Nb,Ti)CNbC-rich particles occupied Nb atoms and prevented Fe2Nb from precipitating. The precipitation transformation in 17Cr-0.4Nb-0.2Ti steel is shown as below:The pinning effect induced by (Nb,Ti)C makes stainless steels difficult to hot roll, which is in agreement with actual production.

Hydrogen effects on mechanical properties of 18%Cr ferritic stainless steel

Role of microstructure in susceptibility of 18Cr ferritic stainless steel to hydrogen embrittlement was studied. Specimens of the studied steel were charged with hydrogen electrochemically from 0.1N H2SO4 solution under controlled cathodic potential providing a homogeneous hydrogen distribution over the specimen cross-sections. Thermal desorption spectroscopy analyses were carried out investigating the uptake, trapping and diffusion of hydrogen in the ferritic stainless steel.Microstructural change caused by heat-treatment at 1050°C and 1200°C associated preferably with grain size growth from 18µm to 65µm and 349µm, respectively, resulting in significant degradation of the mechanical properties of the studied steel. The effect of the grain size growth on hydrogen susceptibility was studied with constant extension rate test (CERT) performed under continuous hydrogen charging. It is found that hydrogen has a remarkable effect on the elongation to fracture of the Fe-Cr ferrite: in the presence of H elongation to fracture of the steel reduces up to 75% compared to the H-free counterpart. In general, the hydrogen sensitivity of the mechanical properties increases with increase of the mean grain size of the studied ferritic stainless steel. However, the detailed analysis reveals a complicated, non-linear behavior of the hydrogen sensitivity. Scanning electron microscopy (SEM) of the fracture surfaces of the tensile specimens tested during continuous hydrogen charging reveals a quasi-cleavage fracture surface morphology. Hydrogen-induced cracking in the studied 18Cr ferritic steel was studied using electron backscatter diffraction (EBSD) analysis from the side surfaces of the tensile tested specimens.

Optimization of A-TIG process parameters using response surface methodology

ABSTRACTIn the present work, the influence of process parameters such as welding current (I), welding speed (S), and flux coating density (F) on different aspects of weld bead geometry for example depth of penetration (DOP), bead width (BW), depth to width ratio (D/W), and weld fusion zone area (WA) were investigated by using the central composite design (CCD). 9–12% Cr ferritic stainless steel (FSS) plates were welded using A-TIG welding. It was observed that all input variables have a direct influence on the DOP, BW, and D/W. However, flux coating density has no significant effect on WA. Mathematical models were generated from the obtained responses to predict the weld bead geometry. An optimized DOP, BW, D/W, and WA of 6.95 mm, 8.76 mm, 0.80, and 41.99 mm2, respectively, were predicted at the welding current of 213.78 A, the welding speed of 96.22 mm/min, and the flux coating density of 1.99 mg/cm2. Conformity test was done to check the practicability of the developed models. The conformity test results were in good agreement with the predicted values. Arc constriction and reversal in Marangoni convection were considered as major mechanisms for the deep and narrow weld bead during A-TIG welding.

Kinetics of Duplex Oxide Growth on 9Cr Steels Exposed in CO2: Application of Dimensional Metrology

Investigations into potentially extending the lives of UK advanced gas-cooled reactors have highlighted the need for improved understanding of the long-term oxidation and carburisation of 9Cr ferritic steels. These steels were used in evaporators and primary superheaters and as these are to be used beyond their original design lives, it is necessary to ensure that these degradation routes remain within acceptable levels. A dimensional metrology technique has been applied to archived autoclave samples to measure such damage. These samples had previously been exposed to a range of temperatures, pressures and gas chemistries representative of those experienced by 9Cr steels in CO2-rich AGR gases. Earlier sample assessments had focused on weight change measurements, but the dimensional technique enables measurement of duplex oxide thicknesses around samples and the extraction of related data from longer exposure times. These data also support estimation of the extent of both carbon and oxygen uptake.

The Influence of Crystallographic Texture and Niobium Stabilisation on the Corrosion Resistance of Ferritic Stainless Steel

The objective of this work is to investigate the influence of the crystallographic texture on the corrosion resistance of 16% Cr ferritic stainless steel. Samples of ASTM S43000 ferritic stainless steel, both niobium-stabilised and non-stabilised, were used. The samples were subjected to crystallographic characterisation (EBSD) and analysed using an inverse pole figure (IPF) and a crystalline orientation distribution function (CODF). The samples also underwent anodic potentiodynamic polarisation tests (deaeration by high-purity argon gas) in 3.56% NaCl and 1N H2SO4 solutions, and the surface was examined by SEM after the tests. The results showed a clear influence of the crystallographic texture on the corrosion resistance. The niobium decreases the amount of the preferred orientation and thus the influence of the texture on the corrosion resistance, although the corrosion resistance of the stainless steel is increased as niobium carbides are formed.

Composite Cu-LaFeO3 Coating on High Cr Ferritic Stainless Steels for IT-SOFC Interconnects

A molten carbonate dip-coating passivation method has been applied in this work to produce novel copper-LaFeO3 perovskite composite conversion coatings on a commercial 18Cr ferritic stainless steel. The passivation treatment promotes the formation of a multi-layer conversion coating consisting of a dense perovskite layer grown onto a spinel oxide sublayer and characterized by the presence of copper metal particles embedded in the perovskite grains. A relation between copper addition to the molten salt bath and optimal conversion conditions is observed, with higher copper concentration resulting in accelerated passivation kinetics. When exposed to short-term oxidation experiments in air at 700°C, the perovskite layer exhibits remarkable stability, while copper gets oxidized and diffuses in the spinel sublayer. The coating is found also to act as efficient barrier to the outward diffusion of chromium, being the chromium largely confined to the steel-coating interface.

Composite Cu-LaFeO3 Conversion Coatings on a 18Cr Ferritic Stainless Steel for IT-SOFC Interconnects: An Investigation on Structure and Formation Mechanism

In this work, a novel iron chemical conversion coating process has been applied to deposit a composite Cu-LaFeO3 perovskite coating layer on a commercial 18Cr ferritic stainless steel for application as Intermediate-Temperature Solid Oxide Fuel Cell (IT-SOFC) interconnect. The conversion process is carried out at 600°C under a CO2 gas atmosphere in a binary eutectic lithium-sodium molten carbonate bath containing lanthanum, magnesium and copper additions in form of their respective oxides. Multi-layer coatings are obtained, with a surface composite layer formed by a dense perovskite polycrystalline thick film with metallic copper particles encased in the perovskite grains grown on a Fe-rich spinel sublayer. Copper oxide additions significantly promote the formation of the LaFeO3 perovskite layer, and the experimental results suggest that galvanic coupling phenomena between the alloy elements and copper take place during the coating formation process. Chemical stability and Cr diffusion barrier properties of the composite coating have been evaluated in air exposure experiments at 700°C for 200 h. The perovskite phase shows high stability after the high temperature exposure, with no detectable sign of Cr diffusion in the layer. Details on functional properties of these composite conversion coatings for IT-SOFC applications will be reported in a subsequent study.

Change in Small Punch Test Property of 12%Cr Ferritic Steels Used for Turbine Due to Thermal Aging and Creep

Change in Small Punch Test Property of 12%Cr Ferritic Steels Used for Turbine Due to Thermal Aging and Creep

スモールパンチ試験法による高Crフェライト系耐熱鋼溶接継手の局所クリープ特性計測

スモールパンチ試験法による高Crフェライト系耐熱鋼溶接継手の局所クリープ特性計測