Showing papers on "Austenitic stainless steel published in 1983"

Effect of solidification conditions on the solidification mode in austenitic stainless steels

Abstract: The effect of the solidification conditions on the solidification mode in the composition range in which the primary austenitic and ferritic modes compete is studied by varying the welding parameters in gas tungsten arc (GTA) welding and by comparing the results with those obtained from other laboratory experiments. A good agreement holds if the effect of the composition is described by the ratio Creq/Nieq (Creq = pct Cr + 1.37 × pct Mo + 1.5 × pct Si + 2 × pct Nb + 3 × pct Ti and Nieq = pct Ni + 0.31 × pct Mn + 22 × pct C + 14.2 × pct N + pct Cu) and the effect of the solidification conditions by the growth rate. The critical value of the ratio Creq/Nieq corresponding to the transition from primary austenitic to ferritic solidification increases from 1.43 to 1.55 with increasing growth rate. The upper limit is valid in GTA welding at high welding speeds, while the lower limit corresponds to the practical conditions which exist in ingot and shaped casting. The validity and applicability of this solidification model are discussed.

Microstructural modification of austenitic stainless steels by rapid solidification

Abstract: The microstructural modifications in three austenitic stainless steels (types 308, 310, and 312) were evaluated after rapid solidification. These three steels are commonly used weld filler metals. Two methods of rapid solidification were investigated, autogenous laser welding and arc-hammer splat quenching. The structure of 310 stainless steel was found to be 100 pct austenite, and did not vary over the range of conditions studied. On the contrary, the structures of types 308 and 312 steels were very sensitive to the cooling rates and solidification conditions. With the highest cooling rates, the type 308 structure was fully austenitic while the type 312 structure was fully ferritic. At lower cooling rates, the structures were duplex ferrite plus austenite. The results were interpreted in terms of faster kinetics of solidification of austenite compared to ferrite under the conditions examined. A comparison of the structures produced by the two rapid solidification techniques indicated the cooling rates are comparable.

Microstructural origin of the skeletal ferrite morphology of austenitic stainless steel welds

Abstract: Scanning transmission electron microscopy (STEM) was conducted on welds exhibiting a variety of skeletal, or vermicular ferrite morphologies in addition to one lathy ferrite morphology. These ferrite morphologies result from primary ferrite solidification followed by a solid state transformation upon cooling. During cooling, a large fraction of the ferrite transforms to austenite leaving a variety of ferrite morphologies. Comparison of composition profiles and alloy partitioning showed both the skeletal and lathy ferrite structures result from a diffusion controlled solid state transformation. However, the overall measured composition profiles of the weld structure are a result of partitioning during both solidification and the subsequent solid state transformation.

Austenitic Steels at Low Temperatures

Abstract: The Properties of Austenitic Stainless Steel at Cryogenic Temperatures- Development of Cryogenic Structural Materials for Tokamak Reactor- Martensitic Transformations in Fe-Cr-Ni Stainless Steels- The Influence of Martensitic Transformation on Strength and Plasticity of Fe-Cr-Ni Alloy Single Crystals- Austenitic-Steel Elastic Constants- Temperature Dependence of Flow Strength of Selected Austenitic Stainless Steels- Cryogenic Properties of Austenitic Stainless Steels for Superconducting Magnet- Factors Influencing the Low-Temperature Dependence of Yielding in AISI 316 Stainless Steels- Toughness and Fatigue Properties of Austenitic Steels at Cryogenic Temperature and Their Application in Complex Structures- Automated Near-Threshold Fatigue Crack Growth Rate Testing of JBK-75 Stainless Steel at Cryogenic Temperatures- Effects of Magnetic Field on Tensile Behavior at 4 K of Alloys 304 and 310- Effects of Magnetic Fields on Martensite Transformations and Mechanical Properties of Steels at Low Temperatures- Effect of EB-Weld and Cold-Rolling on Low Temperature Strength and Toughness of Austenitic Stainless Steels- The Effect of c-Ferrite upon the Low Temperature Mechanical Properties of Centrifugally Cast Stainless Steels- The Mechanical Properties of Stainless Steel Castings at 4 K- Heat Treatments to Desensitize and Remove Delta Ferrite from a 21Cr-6Ni-9Mn Stainless Steel Intended for the Fabrication of Aerofoil Models for Cryogenic Wind Tunnels- Preliminary Study on Structural Material Selection for Large Superconducting Magnets- Low Temperature Mechanical and Physical Properties of Age-Hardened Fe-Ni-Cr-Mn Alloys- Automated Near-Threshold Fatigue Crack Growth Rate Testing of JBK-75 Stainless Steel at Cryogenic Temperatures- Low Temperature Properties of High-Manganese-Molybdenum Austenitic Iron Alloys- Structure and Mechanical Properties of High-Alloy Manganese-Aluminum Steels for Cryogenic Applications- Fracture Properties of a 25Mn Austenitic Steel and Its Welds at 4 K- The Weldability of 25 Mn Steel- Instrumented Charpy Impact Tests at Low Temperatures for Several Steels- Temperatures for Several Steels- GRI's Research Program on Crack Initiation and Arrest Properties of 9% Nickel Steels Used in LNG Storage Vessels- Indexes- List of Contributors- Alloy Index

Fatigue of stainless steel in hydrogen

Abstract: The fatigue crack growth rates of two austenitic stainless steel alloys, AISI 301 and 302, were compared in air, argon, and hydrogen environments at atmospheric pressure and room temperature. Under the stresses at the crack tip the austenite in type 301 steel transformed martensitically to a’ to a greater extent than in type 302 steel. The steels were also tested in the cold worked condition under hydrogen or argon. Hydrogen was found to have a deleterious effect on both steels, but the effect was stronger in the unstable than in the stable alloy. Cold work decreased fatigue crack growth rates in argon and hydrogen, but the decrease was less marked in hydrogen than in argon. Metallographic, fractographic, and microhardness surveys in the vicinity of the fatigue crack were used to try to understand the reasons for the observed fatigue behavior.

Plastic flow phenomenology of 304L stainless steel

Abstract: The isothermal plastic flow behavior of annealed 304L austenitic stainless steel in uniaxial compression and torsional modes of deformation has been established over a wide range of temperatures and strain rates. In uniaxial compression, it was found that high rates of strain hardening, which persist to large strains (≽.7) at cold-working temperatures, are found only at small values of strain (⪯0.2) at hot-working temperatures because of the influence of dynamic softening processes. The effect of deformation heating on flow behavior, which occurs primarily at high strain rates, was most significant at cold-working temperatures. Deformation heating was observed to result in flow stress maxima and flow softening. A method of estimating high-strain rate, isothermal-flow curves in such instances was derived. Shear stress-shear strain curves derived from torsion tests exhibited dependences on temperature and strain rate similar to those observed in compression data. In contrast to the compression curves, however, the shear stress-shear strain curves showed lower rates of strain-hardening at room temperature, 400 °C, 800 °C, and (for high strain rates) 1000 °C. It was shown that the choice of definition for calculating effective stress-strain from the torsion data could not be modified to bring the two types of data into coincidence. Only a structure-sensitive explanation could be invoked to explain the difference.

Fatigue of annealed and cold worked stable and unstable stainless steels

Abstract: Fatigue crack growth rates (FCGR) in AISI 301 and 302 austenitic stainless steel alloys have been measured in controlled load cycles withR = 0.05. Both annealed and cold rolled conditions were examined. The austenite phase of the AISI 301 alloy was unstable under stress and transformed martensitically to α′ to a much greater extent than the AISI 302 alloy. At low values of mean stress the unstable alloy had a lower FCGR than the more stable 302 alloy. The FCGR increased with mean stress until values of mean stress ⪞70 MPa, where the FCGR was independent of mean stress and was the same for both alloys. Various metallographic and macroscopic measurements were made to try to understand this behavior. It was concluded that residual compressive stress due to transformation at the crack tip was responsible for the lower crack growth rates of the unstable 301 alloy. Cold worked specimens had significantly lower crack growth rates than the annealed specimens, and both alloys behaved identically.

Effect of weld composition and microstructure on hydrogen assisted fracture of austenitic stainless steels

Abstract: The effect of severe hydrogen environments on the tensile fracture behavior of a variety of austenitic stainless steel welds was investigated. In all cases, second phases or particulates common only to the weld microstructure were the origin of fracture initiation in hydrogen. These second phases formed as a result of microsegregation during solidification and/or solid state transformations during cooling or aging. In addition to second phases the weld microstructure matrix phase also influences fracture behavior. The fracture behavior is discussed in terms of localized chemical variations and the presence of second phases, and th interaction of dislocations with internal boundaries.

Investigation of helium and deuteron irradiated stainless steel (and nickel) by positron annihilation

Abstract: Positron annihilation studies have been carried out in austenitic stainless steel (SS 316), irradiated with high energy helium and deuteron ions from a cyclotron. Defect states have been deduced from simultaneous measurements of positron lifetime and Doppler lineshape in post-irradiation anneal up to 1473°K. Clear differences in the annealing characteristics are observed beyond 673°K between the helium- and deuteron-irradiated specimens. Evidence is presented for helium-vacancy interaction and nucleation of helium bubbles. Results on helium in nickel are also discussed for comparison. Helium agglomeration to microbubbles, which are well below the resolution of electron microscopy, is detected around 800°K. In the growth stage of bubbles at higher temperatures, two distinct positron bound states develop both in SS 316 and nickel. Helium retention in large bubbles is found to be stable even at 1473°K in SS 316.

Influence of δ-ferrite content on transformation to intermetallic phases in heat-treated, type 316 austenitic stainless steel weld metal

Abstract: 18Cr-9Ni-2Mo and 20Cr-10Ni-3Mo type 316 weld metals containing FN6 and FN 18 δ-ferrite, heat treated at 850° and 625°C, have been investigated by microstructural and microanalytical techniques to provide a detailed study of the decomposition of the ferrite phase. As welded, the composition of the ferrite is enriched in chromium and molybdenum and depleted in nickel to such an extent that the ferrite composition is close to that of χ and σ intermetallic phases. On heat treatment at 850°C, the ferrite readily transforms to intermetallic phases with a subsequent enrichment of chromium and molybdenum in these phases. Aging at 625°C gives incomplete transformation to intermetallic and carbide phases, and the retained ferrite composition has been observed to be depleted in chromium and molybdenum compared with the as-welded ferrite composition. As a result of these observations on the 18Cr-9Ni-2Mo steel, a mechanism for the prevention of intermetallic-phase precipitation in the ferrite phase is suggest...

The microstructure and phase transformations in duplex 316L submerged arc weld metals

Abstract: The nature and kinetics of the δ-ferrite transformation in a series of duplex submerged arc 316 L weld metals has been studied under creep conditions at 600° C and an applied stress of 200 MN m−2. The δ-ferrite was found to transform first to M23C6 carbides, these occurring at either the δ/γ interface or within the δ-ferrite laths depending upon the presence of suitable nucleation sites. The remaining δ-ferrite then transforms to the intermetallic σ-phase. The kinetics of the intermetallic phase formation varied between the different welds, and STEM/EDAX analysis indicated that the kinetics were dependent on the localized segregations of chromium, nickel and molybdenum in the δ-ferrite laths. A transformation model has been developed which indicates that chromium diffusion within the γ matrix is the controlling mechanism.

Studies on Friction Welding of Carbon and Alloy Steels : 3rd Report : Adequate Welding Conditions for High Alloy Steels and Distributions of Alloy Elements near Weld Interface

Abstract: In order to obtain adequate friction-welding conditions for high alloy steels, an austenitic stainless steel (SUS304), a martensitic stainless steel (SUS440C), a high-speed steel (SKH9) and a 0.45% carbon steel (S45C) were used as test materials. The adequate welding conditions under which friction welded joints with sufficient strength in both static and cyclic loading could be obtained were established and shown in terms of the friction coefficient μ^^(SUB) at the rubbing surfaces just before upsetting. The limit of the adequate welding conditions was μ^^(SUB)≤0.08 for material combinations of (SUS304-S45C), (SUS440C-S45C), (SKH9-S45C) and (SUS304-SUS304) in the case of round bars with diameters in the range of 13 to 20mm. Two kinds of welded joints with and without sufficient strength were examined using an X-ray micro-analyzer with a scanning electron microscope, and the distributions of the alloy elements at and near the weld interface were compared. It was clearly shown that the distributions closely related to the welding conditions, and that the adequate welding conditions shown in terms of the friction coefficient are very effective in practice.

Mechanisms of Material Removal During Erosion of a Stainless Steel

Abstract: Solid particle erosion of an austenitic stainless steel was studied utilizing various metallographic techniques. Examination of single impacts on a polished surface resulted in a semiquantitative crater classification. It was, however, found that material removal generally involves the interactive effect of several cumulative impacts. Consequently, topography and internal structure of the target surface layer after multiple impacts were investigated. In particular, preeroded targets were reexamined after additional single impacts. The strength of the surface layer was estimated by a simple tape experiment, which also supplied information of the size and morphology of presumptive wear debris. Two major erosion mechanisms were distinguished: 1. Cutting erosion. Detachment of crater lips by cutting action of one or several impacts. 2. Deformation erosion. Detachment of material by surface fragmentation due to multiple cumulative impacts. Surface layer hardness and ductility are the most important material pr...

The Influence of Nitrogen from Welding on Stainless Steel Weld Metal Microstructures Soluble nitrogen is found to exert a major influence—particularly on the quantity and distribution of weld metal delta ferrite

Abstract: Small amounts of nitrogen were injected into Type 304L austenitic stainless steel weld metal. This was accomplished by using an argon-nitroge n shielding gas mixture on autogenous gas tungsten arc welds. Weld metal nitrogen as a function of nitrogen shielding gas content and applied pressure was exam­ ined. Nitrogen shielding gas contents below 5% were found to have a major effect on the weld metal microstructure. The base metal nitrogen did not influence the nitro­ gen solubility reaction and solidification behavior during welding. For Type 304L austenitic stainless steel, a nitrogen coeffi­ cient was determined for the nickel equivalent expression.

Low-cycle fatigue behavior in metastable austenitic steel accompanying deformation-induced martensitic transformation.

Abstract: The effect of deformation-induced martensitic transformation on the strain-controlled low-cycle fatigue behavior in type 304 metastable austenitic stainless steel at room temperature has been studied. The fatigue behavior in type 310 stable austenitic stainless steel has been also examined for comparison. The fatigue life (Nf) of type 304 steel was markedly affected by the α'-martensite formation. When the total strain range (Δet) was higher than 0.8%, where the α'-martensite formation started before the crack initiation, Nf of type 304 steel was about 1/5 times shorter than that of type 310 steel, when compared at the same Δep (mean plastic strain range from first cycle to final cycle). This shorter Nf of type 304 steel was attributed to the increase in σt (mean cyclic tensile stress) due to the α'-martensite formation and to the martensite acting as the preferential site of crack initiation. The degree of decrease in Nf was larger when the α'-martensite formation started in the strain hardening stage than in the saturated stress stage of fatigue process, in connection with the larger increase in σt. At low Δet such as 0.6% where the α'-martensite formation started after the crack initiation, Nf of type 304 steel was about 2 times longer than that of type 310 steel. This longer Nf, of type 304 steel was attributed to the suppression of crack propagation due to the α'-martensites fomed around the crack tip. The experimental data of Nf fell in the range of factor of 2 of the predicted Nf which were obtained on the basis of Tomkins' model by taking into consideration the increase in σt due to the α'-martensite formation.

Internal stresses in austenitic steels cathodically charged with hydrogen

Abstract: Hydrogen cathodic charging of austenitic stainless steels has been manifested by a reduction of the ductility under dynamic tensile stresses and by the appearance of nonductile fracture surfaces. The electrolytic charging process provides a huge hydrogen fugacity, and thus large amounts of hydrogen may be driven into the specimen. This process leads to the development of internal stresses, phase transition to a ' and e martensite, and intensive intergranular and transgranular cracking [1-6]. The purpose of this study is to find the reasons for the development of internal stresses as a result of cathodic charging of stainless steel and to correlate between the surface cracking and internal stresses. The studies were carried out on a type 316 austenitic stainless steel. The samples were obtained in the form of 0.1 mm thick sheets and were solution annealed. The grain size, as measured by ASTM E-112 method, was of the 10.5 number ASTM, corresponding to the mean grain size of 9.4 ~tm. The samples were cathodically charged for 24 h at room temperature in an 1 N H2SO4 solution with 0.25 g per litre of NaAsO2 added as a hydrogen recombination poison. A platinum counterelectrode and a current density of 50mAcm -: were used. A conventional Philips diffractometer equipped with step-motor, programmer, and teletype printer was used for the X-ray diffraction study. The choice of the X-ray wavelength is of special importance. In diffraction with reflection (BraggBrentano) geometry, we actually obtain information only from the thin surface layer of the flat sample. The intensity I t of rays scattered by the surface layer of thickness t is equal to [7]:

An x-ray diffraction method for quantitative determination of retained austenite in the production line of metastable austenitic stainless steel

Abstract: An X-ray diffraction method has been developed for quantitative determination of retained austenite in the production line of cold-rolled type SUS 301 metastable austenitic stainless steel sheets. A new unit of diffractometer designed for application in the mill is equipped with an X-ray source of Cr Kα and three separate scintillation detectors and is provided with mechanisms of lateral movement along the transverse direction of strip and rotation around an axis vertical to the strip surface. Intensities of {211} martensite reflection, {110} austenite reflection, and background are measured separately by the three detectors.Measurements were carried out by scanning of a coil, cold rolled in a reversing mill, during uncoiling operation in a slitting line. Diffraction intensities of austenite phase were weaker in the top and tail ends than in the middle part of the coil. Variation of the diffraction intensities throughout the whole coil length is well correlated with a conceptional distribution of retained austenite which can be deduced from the nickel equivalent and rolling temperature of the tested material. This findings suggest applicability of the present method in the production line, even though the effect of textures is not corrected.The new X-ray diffractometer unit is proved to be successfully employed in the production mill as a practical means for prediction of inhomogeneity of material properties in the stainless steel strip for use of springs by monitoring the relative amount of austenite and martensite.

Trapping and Surface Recombination of Deuterium in Fusion Reactor Metals

Abstract: Ion implantation and ion beam analysis were used to examine bulk trapping and surface recombination for deuterium in Fe, Ni, and austenitic stainless steel. Irradiation-defect traps were characterized in the three metals, and substantially stronger traps were shown to be associated with small He bubbles. The rate of deuterium release at stainlesssteel and Fe surfaces was measured as a function of temperature and solution concentration. Trapping and surface recombination parameters were extracted by applying established theory for solute diffusion within a field of traps.

Production of nonmagnetic steel plate

Abstract: PURPOSE:To maintain excellent strength and toughness at an ultra-low temp. as well in producing a nonmagnetic steel plate of high Mn austenitic stainless steel by subjecting the steel to a heat treatment under specific conditions. CONSTITUTION:A nonmagnetic steel material of a high Mn austenitic stainless steel contg. 0.01-0.20% C, 0.01-2.0% Si, 10-30% Mn, 0.01-10.0% Ni, 12-20% Cr and 0.01-0.30% N, satisfying the formula 0.20% =2 kinds among Cn, Mo, W, Nb, V, Ti, Al, Ca, Cl and Zr at 0.01- 3% in total in the case of Cu, Mo and W, 0.01-1.0% in total in the case of Nb, V, Ti and Al or 0.001-0.10 in total in the case of Ca, Cl and Zr as a structural material for supporting a superconductive magnet used in a cryogenic temp. such as liquid He or the like is held for 1-60min at 800 deg.C or is quickly cooled down to a temp. region of <=500 deg.C after air cooling upon ending of hot rolling at 950 deg.C.

Cooking vessel of stainless steel for all types of heat sources

Abstract: Cooking vessel of austenitic stainless steel (1) which in addition to being able to be heated on a conventional electric hotplate or on gas, can also be heated by induction heating … This is made possible in that the vessel, in addition to a heat distributing plate (2) of aluminium or copper, is also equipped with a plate of magnetizable material (5) This is affixed to the heat-distributing plate by means of two or three intermediate layers (6, 7) of metal with coefficients of thermal expansion which lie between the corresponding coefficients for the heat-distributing plate and the magnetizable plate