18Cr-8Ni Stainless Steel Research Articles

A Numerical Model for Cooling Rate Dependence of the Degree of Undercooling during Rapid Solidification of 18Cr-8Ni Stainless Steel.

Cooling rate dependence of the degree of undercooling at the onset of solidification for 18Cr-8Ni stainless steel was numerically analyzed using a classical nucleation theory. Transient time which can characterize the time-dependent behavior of nucleation was evaluated for iron. It is shown that temperature change in the experiment is slow enough against the transient time and no time-dependent behavior can be expected within the predictions by the classical theory. A new model for time-dependent contact angle was proposed so as to reproduce the cooling rate dependence of the degree of undercooling. This prediction model shows a good agreement with the experimental result for 18Cr-8Ni stainless steel. The effect of substrate temperature on the degree of undercooling and the primary nucleation phase of 18Cr-8Ni stainless steel was also discussed using the model.

Solidification and transformation behaviour of austenitic stainless steel weld metals solidified as primary austenite: Study of solidification and subsequent transformation of Cr-Ni stainless steel weld metals (1st Report)

Summary Weld metals solidified in the ferritic-austenitic solidification mode (FA mode) have dual phases of ferrite and austenite in their as-solidified condition, where ferrite exhibits different morphologies depending on the chemical composition and welding conditions. This paper describes an investigation of the effect of the solidification and transformation sequence on the formation of final ferrite morphologies. Austenite is formed through either a eutectic reaction or peritectic reaction at the dendrite boundaries after the primary formation of ferrite. During the eutectic formation of austenite, the δ direction of the primary ferrite and the γ direction of the eutectic austenite are parallel to each other and lie along the growth direction of the primary dendrites. However, any specific lattice plane relationship between the two phases is not identified. During cooling after solidification, the austenite extends into the primary ferrite via solid-state transformation, and the final morph...

Formation of a submicrocrystal FCC structure under irradiation with high-energy particles

The influence of a high-dose (up to 200 dpa) irradiation with 1.5 MeV Kr + ions at 500–700 °C on the formation of a submicrocrystal structure of Cr-Ni stainless steels was analyzed. In Cr16Ni15Mo3 and Cr16Ni8Mo3 unaging steels dislocations rearrange themselves to subgrains subject to the irradiation dose of 10 dpa at 600 °C, thus favoring formation of fine (30–50 nm) subgrains misoriented up to 1–3°. An increase in the irradiation dose up to 160 dpa leads to recrystallization and appearance of fine misoriented crystals 50–100 nm in size. If dislocations are pinned with dispersed Ni 3Ti particles (Cr16Ni15Mo3Ti1 aging steels), the subgrains are formed only after the irradiation dose of 160–200 dpa. Therefore the radiation method of producing nanocrystals is comparable as to its efficiency with a strong deformation.

Solidification and transformation behaviour of austenitic stainless steel weld metals solidified as primary ferrite: Study of solidification and subsequent transformation of Cr-Ni stainless steel weld metals (2nd Report)

Summary Weld metals solidified in the ferritic-austenitic solidification mode (FA mode) have dual phases of ferrite and austenite in their as-solidified condition, where ferrite exhibits different morphologies depending on the chemical composition and welding conditions. This paper describes an investigation of the effect of the solidification and transformation sequence on the formation of final ferrite morphologies. Austenite is formed through either a eutectic reaction or peritectic reaction at the dendrite boundaries after the primary formation of ferrite. During the eutectic formation of austenite, the <100>δ direction of the primary ferrite and the <100>γ direction of the eutectic austenite are parallel to each other and lie along the growth direction of the primary dendrites. However, any specific lattice plane relationship between the two phases is not identified. During cooling after solidification, the austenite extends into the primary ferrite via solid-state transformation, and the final morphology of the ferrite is vermicular without any coherent orientation relationship between the primary ferrite and eutectic austenite. During peritectic formation of austenite, the Kurdjumov-Sachs orientation relationship is established between the primary ferrite and peritectic austenite, and the <100>γ direction of the peritectic austenite is not parallel to the growth direction of the primary dendrites. During cooling after solidification, the primary ferrite transforms into austenite, and the final morphology of the ferrite is lathy, since the primary ferrite and peritectic austenite have a favourable coherent orientation.

Quantification of defect-solute coupling from inverse-Kirkendall segregation

A method has been adopted for quantifying and validating inverse-Kirkendall segregation during irradiation of an Fe Cr Ni stainless steel. Model predictions of calculated chromium depletion compared with calculated nickel enrichment were in accord with several hundred composition measurements. Compositions were measured at and near grain boundaries in a nickel-ion irradiated stainless steel. The method allows assessment of relative defect-solute coupling efficiencies independent of kinetic opportunity for segregation. The alloy had approximately 21 at% Cr and 20 at% Ni. The analysis of relative composition changes established that the Fe diffusivity is 2.0 times faster than the Ni diffusivity and the Cr diffusivity is 2.55 times faster than Ni diffusivity in the temperature range of 230 to 550°C. The relative rates are consistent with unirradiated ternary diffusion rates at higher temperatures reported in the literature.

18Cr-8Niステンレス鋼の双ロール鋳造における凝固組織の形成

18Cr-8Niステンレス鋼の双ロール鋳造における凝固組織の形成

Formation of Solidification Structure in Twin Roll Casting Process of 18Cr-8Ni Stainless Steel.

Formation of Solidification Structure in Twin Roll Casting Process of 18Cr-8Ni Stainless Steel.

Quantitative explanation of transient growth of α phase during dissolution in γ/α/γ diffusion couples of the FeCrNi system using analytical solution

In order to understand the general characteristics of the dissolution kinetics in multicomponent systems, a dissolution reaction of body-centered-cubic (b.c.c.) [alpha]-ferrite in face-centered-cubic (f.c.c.) [gamma]-austenite matrix of Cr-Ni stainless steels was chosen as a model case and was investigated in a series of studies by the present authors using [gamma]/[alpha]/[gamma] diffusion couples of the ternary Fe-Cr-Ni system. Before diffusion zones start to overlap either in the [alpha] phase or in the [gamma] phase, each half part of the [gamma]/[alpha]/[gamma]diffusion couple can be treated as a semi-infinite [alpha]/[gamma] diffusion couple. The stage, during which this treatment is valid, is hereafter called the first stage of the reaction. In this stage of the reaction, the migration of the [alpha]/[gamma] interface can be described mathematically using an analytical solution of diffusion equations for a semi-infinite two-phase diffusion couple of ternary systems. In the present article, the analytical solution was utilized to describe the migration velocity of the interface and the concentration profiles of the solutes in the [gamma]/[alpha]/[gamma] diffusion couple in the first stage of the reaction. The transient increase in the thickness of the [alpha] phase with increasing annealing time in this stage could be quantitatively reproduced by the calculation using themore » analytical solution.« less

An XPS and SEMS study of silica sol‐gel/metal substrate interaction

AbstractSome applications of ceramic materials are difficult because of the markedly differing lattice bonding characteristics of ceramic and metals. This ‘affinity barrier’ can be overcome by the modifying of structure and composition in the interphase region. In our work the silica sublayer was deposited by the sol‐gel method on metal implants prior to electrophoretical deposition of hydroxyapatite coatings to improve the oxidation resistance of the metal surface and the adhesion of apatite to metal during the annealing. The aim of this study is to determine changes in chemical state and structure of the coatings caused by thermal treatment for the better understanding of a relation between their composition and properties. Plates of titanium, WT 1‐0, FeCrNi stainless steel and of low‐carbon steel were covered with silica layer by the sol‐gel method. The coating on low‐carbon steel was produced by the deposition of silica sol‐gel directly on the metal or, the silica–titania opacified porcelain enamel was obtained by electrophoresis. In the case of direct deposition, below 400 °C, an amorphous layer was formed while at 800–900 °C for only 2‐4 min the dense, fine crystalline structure was obtained including small amount of silicates and iron scales. The silica–titania enamel was electrophoretically applied on low‐carbon steel pre‐coated with nickel. During annealing nickel is alloyed with iron and decreases oxygen transport towards iron decreasing the rate of FeO formation. The silica from the enamel reacts with FeO producing a small amount of silicates. Titania partially precipitates at the metal boundary in the form of the needle‐like crystals of FeTiO3, growing from the steel surface into the enamel. When stainless steel was annealed at 700 °C in air, the surface oxide was enriched in chromium and manganese while the silica surface was enriched in iron and manganese.

On the mean internal stresses in two-ductile-phase alloys

The mean internal stresses in each microstructural element of two-ductile-phase alloys have been theoretically calculated for FeCuMn dual-phase steels and α-γ FeCrNi stainless steels. The results show that the mean internal stress along the tensile direction in the softest element (EI, continuous α phase) is always negative, that in the hardest element (EII, continuous β phase) is positive and that in the third element (EIII, an aggregate of separated α and β phases) can be either negative or positive, depending on the volume fraction and phase contiguity of the constituent phases. The role of the mean internal stresses is to make the plastic deformation more uniform among the three microstructural elements. The effects of volume fraction, phase contiguity and the difference between mechanical properties of the constituent phases on the mean internal stresses are discussed. It is shown that the difference between the mechanical properties of the constituent phases has a significant effect not only on the magnitude of the mean internal stresses but also on their trend of variation with increasing plastic strain. It is also shown that the phase distribution described by the contiguity parameters does not affect very much the mean internal stresses in EI and EII at high strains, but it does affect those in EIII at high strains and those in EI, EII and EIII at low strains.

Phase transformations in a manganese-alloyed austenitic stainless steel

The increasing demands placed on the corrosion resistance of stainless steels has led to the successive development of more highly alloyed materials. In this context nitrogen has shown considerable value as an alloying element but its use is restricted by a solubility limit of approximately 0.2 wt% in conventional austenitic stainless steel grades. Manganese increases the nitrogen solubility appreciably and for this reason there has also been an increased interest in its use as an alloying addition but numerous questions remain to be answered about the effect of both nitrogen and manganese on structural stability. Although much work has been published on the precipitation of secondary phases in CrNi(Mo) stainless steels, there is a relative paucity of information available on manganese-alloyed steels. Brandis et al. investigated precipitation in a 25Cr 17Ni 3Mo 6Mn 0.2Nb steel and found no manganese-enriched phases to occur. Sigma phase was the predominant intermetallic precipitate at low nitrogen contents while higher nitrogen contents retarded the onset of sigma phase precipitation but caused the appearance of chi phase. Boothby et al. investigated a 12Cr 11-35Ni (3Mo) steel in which the nickel was partially replaced by 20 or 30% manganese and found the precipitation of the intermetallic sigma,more » chi and Laves phases to be promoted by manganese, although again no manganese-enriched phases were observed. Fritscher demonstrated however the existence in the Fe-Cr-Ni system of a brittle ternary Y phase containing 30--60% manganese which was destabilized by nitrogen. The present work represents part of a study designed to gain greater understanding of the precipitation and sensitization behavior of highly alloyed austenitic stainless steels and concentrates on the influence of nitrogen additions up to 0.5wt% on precipitation of secondary phases in a 20Cr 18Ni 4.5Mo 10Mn steel.« less

Initiation of recrystallized grain structure under high-temperature low-cycle fatigue in 304 stainless steel

Initiation of recrystallized grains was observed under high-temperature low-cycle fatigue conditions in austenitic 18Cr-8Ni stainless steel. The fatigue tests were carried out using unbalanced fast-tension and slow-compression triangular strain wave-shape at 973 K in air. Recrystallized grains were initiated and grew along grain boundaries with the number of fatigue cycles. Accumulated grain-boundary sliding is considered to be the driving force for the recrystallization. Effects of the recrystallized grain structure on high-temperature fatigue failure were then examined under the conditions in which intergranular fatigue failure occurred. The recrystallized grain structure had no detrimental effects on the intergranular failure. The fatigue life was somewhat increased by the initiation of recrystallized grain structure.

13Cr-4Niステンレス鋼の逆変態オーステナイトの生成と分解挙動

13Cr-4Niステンレス鋼の逆変態オーステナイトの生成と分解挙動

Diffusion welding of laminated stainless steel wafers

A laminated and diffusion welded turbine vane with fine cooling passages was designed and manufactured using 18Cr-8Ni stainless steel wafers. The turbine vane produced, was assessed using coolant flow analysis.In order to improve the joint quality, investigations were carried out using conventional diffusion welding to join the stainless steel wafers and camparisons made with diffusion welding followed by hot isostatic pressure (HIP) treatment.The tensile strength of the diffusion welds increased as the welding pressure was raised. However, the use of higher welding pressure brings about large deformation at the joint. As a result it is difficult to use conventional diffusion welding to produce good quality joints without deformation of the cooling passages at the joint region.When the welding area ratio at the joint interface is approximately 50% only isolated voids remain at the joint. Therefore, the use of HIP treatment is able to remove residual voids from the joint interface without macro deformation of the turbine vane. The use of HIP treatment allows joints to be produced with greater than 50% welded area ratio and with only 0.5% change in total length.This study has shown that by applying HIP treatment after preliminary diffusion welding it is possible to produce joints with no residual voids and with a minimum change in component shape.

ステンレス鋼ウェハーの積層拡散接合

A laminated and diffusion welded turbine vane with fine cooling passages was designed and manufactured using 18Cr-8Ni stainless steel wafers. The turbine vane produced, was assessed using coolant flow analysis.In order to improve the joint quality, investigations were carried out using conventional diffusion welding to join the stainless steel wafers and camparisons made with diffusion welding followed by hot isostatic pressure (HIP) treatment.The tensile strength of the diffusion welds increased as the welding pressure was raised. However, the use of higher welding pressure brings about large deformation at the joint. As a result it is difficult to use conventional diffusion welding to produce good quality joints without deformation of the cooling passages at the joint region.When the welding area ratio at the joint interface is approximately 50% only isolated voids remain at the joint. Therefore, the use of HIP treatment is able to remove residual voids from the joint interface without macro deformation of the turbine vane. The use of HIP treatment allows joints to be produced with greater than 50% welded area ratio and with only 0.5% change in total length.This study has shown that by applying HIP treatment after preliminary diffusion welding it is possible to produce joints with no residual voids and with a minimum change in component shape.

急速凝固18Cr-8Niステンレス鋼の初期凝固過程の解析

急速凝固18Cr-8Niステンレス鋼の初期凝固過程の解析

急速凝固18Cr-8Niステンレス鋼における初期凝固組織制御

急速凝固18Cr-8Niステンレス鋼における初期凝固組織制御

急速凝固18Cr-8Niステンレス鋼の初期凝固組織に及ぼすチル板表面粗度およびチル板表面材質の影響

急速凝固18Cr-8Niステンレス鋼の初期凝固組織に及ぼすチル板表面粗度およびチル板表面材質の影響

Corrosion under heat transfer of the CrNi stainless steels DIN W. Nr. 1.4306 n and 1.4361 ESU in aceotropic nitric acid

Corrosion under heat transfer of the CrNi stainless steels DIN W. Nr. 1.4306 n and 1.4361 ESU in aceotropic nitric acid

Nickel migration from Cr—Ni stainless steel exposed to potable water

AbstractStudies of nickel migration from Cr–Ni stainless steel exposed to potable water indicate that there is a ‘stagnant water problem’, which is also known to occur with other pipe materials. The nickel levels can reach the EC recommended upper limit within a period of one week; depending on the surface condition and volume to surfacearea ratio. The fact that hardly any chromium is found in the water indicates that the presence of nickel is not attributable to corrosion of Cr–Ni stainless steel pipes but rather to leaching of nickel from the passive layer rich in chromium oxide. The leaching stops after afew weeks, indicating that nickel migration is only a matter of concern during commissioning. Unlike copper and hot dip galvanised steel pipes, stainless steel pipes do not undergo any general corrosion in potable waters. This is also true for waters that are highly acidic (pH 4) or contain strong complex forming species, e.g. cyanides and EDTA. From the point of view of health, therefore, stainless st...