Type 304L Research Articles

Dynamic Strain Ageing in AISI 316L Type Stainless Steel as Revealed by Indentation Creep Studies

Abstract The phenomenon of dynamic strain ageing (DSA) is known to be prevalent in many of the iron and nickel based alloys which are mainly used as materials for nuclear power plant parts. This behaviour of the material is revealed as a jerky flow phenomenon in the tensile test results, when tests are performed at particular strain rate ranges. Authors probe into this aspect of the behaviour of AISI 316L stainless steel through the indentation creep test route so as to find out the implication of DSA on indentation creep test results. The occurrence of DSA is confirmed by the authors by compression tests carried out on samples of 316L with different loads at set strain rates. The authors attempt to find the evidence for DSA through creep data obtained fr m the indentation creep tests. Their findings reinforce the theory that there is a limiting stress above which the applied stress should pull the dislocations away from the solute atmosphere.

Investigation of structural, tribological and corrosion properties of electroless Ni–B coating deposited on 316L stainless steel

The AISI 316L type of stainless steel is a popular steel material, as it has excellent corrosion resistance in aqueous solutions at ambient temperatures. However, the application of the AISI 316L stainless steel is limited by its relatively low hardness and low wear resistance. In this study, the electroless Ni–B coating was deposited on the AISI 316L stainless steel, and its structural, tribological and corrosion properties were characterised. Microstructural analysis showed that the electroless Ni–B coating deposited on the AISI 316L steel substrate exhibited a typical cauliflower-like structure exhibits an amorphous growth. From this study, it may be concluded that this process cannot only improve the hardness and wear resistance of the 316L stainless steel, but can also provide cathodic protection without losing or sacrificing the original properties of the 316L stainless steel.

Assessment of Intergranular Corrosion Attack in Austenitic Stainless Steel Using Ultrasonic Measurements

The structural materials of reprocessing and waste management plants are made from AISI Type 304L (UNS S30403) grade austenitic stainless steels and are prone to localized corrosion attack like intergranular corrosion (IGC). It is very important to detect and characterize this attack non-destructively. An ultrasonic-based, non-destructive evaluation technique has been developed to detect and estimate the depth of IGC attack in Type 304 (UNS S30400) stainless steel grade plate. Samples with varying degrees of IGC attack were generated in laboratory and used for this study. Ultrasonic measurement involved determination of sound velocity in longitudinal mode, longitudinal to shear velocity ratio, sound attenuation measurement, and spectral analysis. The elastic modulus measurement using a nano-hardness tester was carried out to formulate the basis of change in sound velocity in the IGC-attacked samples as compared to the virgin sample. This paper gives the details on the sample preparation method used for generation of IGC attack in Type 304 stainless steel plate and reports the results of ultrasonic measurement on the characterization of IGC attack. The results are compared with maximum depth of IGC attack estimated by microscopic examination.

Copper nucleation and growth patterns on stainless steel cathode blanks in copper electrorefining

Surface properties of stainless steel on nucleation and growth of copper under electrorefining conditions were studied using AISI 316L type stainless steel in rotating disc electrodes (RDE), stationary electrodes and Hull cell, and also worn industrial cathode blanks. The aim was to find correlations between surface topography and nucleation and growth using deposition tests, microscopy, and image analysis. Deposition tests were done galvanostatically using synthetic copper electrorefining electrolyte and current density 330 A/m2 typical in electrorefining. On the as-received stainless steel with 2B finish, nucleation happened at grain boundaries. Wet grinding resulted in deposition on the ridges and valleys of rough surface and ridges of smooth surface. The nucleation density was in the order of 106 nuclei/cm2 in RDE and Hull cell tests, and 105 nuclei/cm2 in stationary electrode tests. Used industrial blanks did not show the same deposition patterns on grain boundaries and scratch marks, and copper deposited on edges of larger damages. The nucleation density on industrial blanks was in the order of 103 nuclei/cm2.

Residual stress variation due to piping processes of austenitic stainless steel

In nuclear power plants, stress corrosion cracking (SCC) has been observed near the heat affected zone (HAZ) of the primary loop recirculation pipes made of austenitic stainless steel type 316L. Residual stress is a major cause of SCC. In the joining process of pipes, butt-welding is conducted after machining. Machining is performed to match the inside pipe diameter. Residual stress is generated by both machining and welding. In the case of welding after machining in manufacturing processes of pipes, it appears that residual stress due to machining is varied by the welding thermal cycle. In this study, residual stress variation caused by manufacturing processes was investigated. Residual stress variation was examined by the X-ray diffraction method. The residual stress distribution generated by welding after machining has a local maximum point in the HAZ. The Vickers hardness distribution also has a local maximum point. By the EBSD method, it is clarified that recovery and recrystallization due to welding heat do not occurred in the local maximum point. Residual stress distribution results from the superposition effect of hardening due to machining and welding. The location and value of the local maximum stress are varied by welding conditions. The region of the local maximum stress corresponds to the region where SCC has been observed. Therefore, in addition to a part of the manufacturing processes such as welding or machining, evaluation of all parts of the processes is important to investigate the effect of residual stress distribution on SCC.

Apatite Formation on Rutile TiO2 Film Deposited Using Dual Cathode DC Unbalanced Magnetron Sputtering

Rutile TiO 2 films were deposited on unheated stainless steel type 316L using dual cathode DC unbalanced magnetron sputtering. The effects of deposition time ranging 30, 60, 90, and 120 mins on the films structure were investigated. Moreover, all the samples were immersed in SBF for period times of 3 and 5 days also considered. The crystal structures were characterized by thin film X-ray diffraction (TF-XRD). The film’s thickness and surface morphology were evaluated using atomic force microscopy (AFM). The crystallinity, roughness, thickness, and grain size of rutile with only (110) plane increased with increased deposition time. After immersed samples in SBF for 3 day the highest and moderate crystallinity of apatite was observed on the 30 min and 90 min, respectively. However, the films deposited with 60 and 120 min cannot be observed the peak of apatite. An increase crystallinity of apatite clearly observed when after immersed in SBF for 5 day.

Microstructural Characterization and Corrosion Behavior of Activated Flux Gas Tungsten Arc-Welded and Multipass Gas Tungsten Arc-Welded Stainless Steel Weld Joints in Nitric Acid

AISI Type 304L (UNS S30403) austenitic stainless steels are widely used in spent nuclear fuel reprocessing plants, and welding is an indispensable tool used for joining these materials. In the present study, manual gas tungsten arc-welded (M-GTAW) and activated gas tungsten arc-welded (A-GTAW) weldments of Type 304L stainless steel were prepared to examine the microstructural and corrosion behavior of the weldments. A total of 6 passes were required to complete the 6 mm thick sample welding, and 16 passes were required for 12 mm thick sample welding using the M-GTAW process, compared to single-pass A-GTAW welding. Characterization of weld joints was done by radiography, optical microscopy, microhardness tester, a feritscope, and scanning electron microscopy (SEM). The optical microstructure of the fusion zone of weld joints showed delta ferrite in various morphologies. The presence of delta ferrite stringers were observed in the weld joints, extending from the weld metal to the base metal. The corrosion rate results showed that the M-GTAW sample showed only a marginal increase in the corrosion resistance when compared to those welded by the single-pass A-GTAW process. SEM examination revealed the morphology of attack in the base metal was predominantly intergranular while in the weld metal it was interdendritic. The SEM micrograph also showed preferential attack of the delta ferrite stringers.

In vitro study of role of trace amount of Cu release from Cu-bearing stainless steel targeting for reduction of in-stent restenosis

A novel 316L type Cu-bearing stainless steel was developed in present work, aiming at reducing the occurrence of the in-stent restenosis after implantations of coronary stents, through trace amount of Cu release from surface of the steel in body fluid. It was found that there was a trace amount of Cu released from the Cu-bearing steel in a simulated body fluid, with no cytotoxicity. All the in vitro experimental results proved that this Cu-bearing steel could not only inhibit the proliferation of vascular smooth muscle cells, reducing the formation of thrombosis, which are the main reasons for happening of the in-stent restenosis, but also promote the proliferation of vascular endothelial cells needed for the revascularization, showing that this novel steel is prospective to be a new material for manufacturing coronary stents with function of reducing the in-stent restenosis.

Corrosion Behavior of Type 304L Stainless Steels in Nitric Acid Containing Free and Complexed Fluoride

Abstract The corrosion behavior of Type 304L (UNS S30403) nitric acid grade (NAG) stainless steel in boiling 9 M and 1 M nitric acid (HNO3) and with the addition of 0.03 M sodium fluoride (NaF) and with fluoride complexed with 0.06 M to 0.15 M aluminum nitrate (Al[NO3]3) and 0.015 to 0.0375 M zirconium nitrate (Zr[NO3]4) has been established. The corrosion behavior has also been studied using potentiodynamic polarization in the same environments at room temperature and at near boiling temperature and correlated to the measured corrosion rates. It was shown that the fluoride addition accelerates anodic dissolution. The surface film formed on stainless steel was analyzed using x-ray photoelectron spectroscopy to show that fluorides do not remain attached to the surface. The effect of different ratios of complexing with Al(NO3)3 and Zr(NO3)4 has been studied, showing more effectiveness of zirconium. The corrosion behavior of Types 304L, 304L (welded), 310L (UNS S31000) stainless steels and Alloy 690 (UNS N06...

Using heat sink technology to decrease residual stress in 316L stainless steel welding joint: Finite element simulation

316L type stainless steel is widely used in chemical industries due to its excellent resistance to corrosion. But the welding residual stresses have a great effect on stress corrosion cracking. This paper used finite element method to study the effect of heat sink on residual stress. The effects of contact length and the average heat transfer coefficient on residual stress have been investigated. It is found that the heat sink technology can decrease the residual stress greatly. Compared to the model without heat sink, 20% of the peak longitudinal stress has been reduced. The heat sink decreases the dwell time during cooling from 850 °C to 400 °C, which is helpful to decrease the risk of sensitization of 316L stainless steel. With the contact length increase, the transverse stress is decreased. Further increase of the contact length has no positive effect on reducing the longitudinal stress. With the average heat transfer coefficient increase, the transverse stress is decreased greatly while the longitudinal stress decreases slightly, and some tensile residual stresses have been changed to compressive in some zone.

Effects of Cold Working Ratio and Stress Intensity Factor on Intergranular Stress Corrosion Cracking Susceptibility of Non-Sensitized Austenitic Stainless Steels in Simulated BWR and PWR Primary Water

To evaluate the effects of cold working ratio, stress intensity factor and water chemistry on an IGSCC susceptibility of non-sensitized austenitic stainless steel, constant displacement DCB specimens were applied to SCC tests in simulated BWR and PWR primary water for the three types of austenitic stainless steels, Types 316L, 347 and 321. IGSCC was observed on the test specimens in simulated BWR and PWR primary water. The observed IGSCC was categorized into the following two types. The one is that the IGSCC observed on the same plane of the pre-fatigue crack plane, and the other is that the IGSCC observed on a plane perpendicular to the pre-fatigue crack plane. The later IGSCC fractured plane is parallel to the rolling plane of a cold rolled material. Two types of IGSCC fractured planes were changed according to the combination of the testing conditions (cold working ratio, stress intensity factor and simulated water). It seems to suggest that the most susceptible plane due to fabrication process of materials might play a significant role of IGSCC for non-sensitized cold worked austenitic stainless steels, especially, in simulated PWR primary water. Based upon evaluating on the reference crack growth rate (R-CGR) of the test specimens, the R-CGR seems to be mainly affected by cold working ratio. In case of simulated PWR primary water, it seems that the effect of metallurgical aspects dominates IGSCC susceptibility.

Hydrogen Embrittlement Properties of Stainless and Low Alloy Steels in High Pressure Gaseous Hydrogen Environment

Recent research on Hydrogen Environment Embrittlement (HEE) susceptibility of stainless and low alloy steels in highly pressurized gaseous hydrogen environments was reviewed from the viewpoint of tensile properties, hydrogen absorption and fatigue properties.HEE susceptibility evaluated by Slow Strain Rate Test (SSRT) in high pressure hydrogen environments strongly depended on steel chemical compositions. Austenitic stainless steels such as type 316L or iron-based superalloy as A286 showed sufficient resistance to HEE, while stainless steels with low levels of alloying elements such as type 304L showed a remarkable ductility loss in high pressure gaseous hydrogen due to martensitic transformation. Martensitic stainless or low alloy steels also showed a remarkable ductility loss in gaseous hydrogen.Relationship between HEE susceptibility and an amount of hydrogen absorption was investigated. HEE susceptibility and hydrogen embrittlement under cathodic charging in aqueous solution showed the same dependence on the amount of hydrogen absorption, which implies HEE occurs by hydrogen absorption from external gaseous hydrogen environments.Fatigue properties in high pressure gaseous hydrogen environments were evaluated by means of internal or external pressurization tests. Austenitic stainless steels such as type 316L showed little decrease in fatigue life by hydrogen, while metastable stainless steel as type 304 or precipitation hardened superalloy as A286 showed degradation in fatigue life by hydrogen gas. Low alloy steel also showed a decrease in fatigue life in hydrogen, while high strength low alloy steel with much Mo and V showed longer fatigue life than conventional steel.

Low temperature thermal aging of austenitic stainless steel welds: Kinetics and effects on mechanical properties

Abstract Austenitic stainless steel welds in components used in light water reactors are susceptible to thermal aging embrittlement at reactor operating temperature of around 300 °C after a long service life. In this study, low temperature aging embrittlement of types 304L and 316L stainless steel welds with 10% ferrite was investigated on the basis of changes in mechanical properties and microstructure after aging up to 20,000 h at 335, 365 and 400 °C. Spinodal decomposition and G-phase precipitation in the ferrite was observed after aging which lead to embrittlement in the material. In contrast to the small effect on tensile properties, the impact toughness was significantly degraded after aging. Charpy impact test of the aged samples showed decrease in upper-shelf and lower-shelf energy and increase in ductile brittle transition temperature. Large increase in the microhardness of ferrite phase was observed with no change in austenite hardness. The embrittlement in 316L weld was higher compared to 304L weld for similar aging condition. The kinetics of aging embrittlement was established based on Arrhenius relationship. A constant activation energy was determined for 304L weld in the temperature range 335–400 °C, however, 316L weld showed different activation energy values in each temperature range.

On the high cycle fatigue behavior of a type 304L stainless steel at room temperature

An extensive study of the uniaxial cyclic material behavior of an AISI 304L austenitic stainless steel is proposed in the high cycle regime and in constant amplitude loadings. More particularly, the effect on the material behavior and lifetime of a mean axial stress is evaluated imposing either a stress or a strain amplitude. Almost no effect is observed on the stress fatigue curve while a reduction of about 30% is obtained on the strain fatigue curve in the endurance regime. It appears that a stress amplitude fatigue parameter or a Smith–Watson–Topper parameter predict accurately such differences based on the material behavior at maximum cyclic softening.

High voltage retainable Ni-saving high nitrogen stainless steel bipolar plates for proton exchange membrane fuel cells: Phenomena and mechanism

In the present paper, we elucidate the possible reasons for high voltage retention during operation when a Ni-saving high nitrogen stainless steel (hereafter referred as to Ni-saving HNS) was used as bipolar plates for PEMFCs. A typical type 316L was also employed as bipolar plates to compare the cell performance. The Ni-saving HNS bipolar plate adopting cell obviously exhibited better cell performance at various current densities. After 1000 h of cell operation, the tested metallic bipolar plates were analyzed by scanning electron microscopy, inductively coupled plasma-mass spectrometry, X-ray photoelectron spectroscopy, transmission electron microscopy–energy-dispersive X-ray spectroscopy, and transmission electron microscopy–electron energy loss spectroscopy to prove the superiority of the Ni-saving HNS bipolar plates. As a result, the surface state of the bipolar plates exposed to the PEMFCs environment is the critical factor that affects cell performance. Protection of the metal surface mainly with chromium oxide-based surface layer, which was induced from a reaction of N from the Ni-saving HNS and H 2O generating proton, H +, that lowers local surface pH, was thus substantially effective to retain the voltage upon operation.

Solidification Behavior and Weldability of Dissimilar Welds Between a Cr-Free, Ni-Cu Welding Consumable and Type 304L Austenitic Stainless Steel

The solidification behavior of a Cr-free welding consumable based on the Ni-Cu system was evaluated in conjunction with Type 304L stainless steel. The weld metal microstructure evolution was evaluated with optical and secondary electron microscopy, energy dispersive spectroscopy, X-ray diffraction, button melting, and thermodynamic (CALPHAD-based) modeling. Solidification partitioning patterns showed that higher dilutions of the filler metal by Type 304L increased segregation of Ti, Cu, and Si to interdendritic regions. Button melting experiments showed a widening of the solidification temperature range with increasing dilution because of the expansion of the austenite solidification range and formation of Ti(C,N) via a eutectic reaction. The model predictions showed good correlation with button melting experiments and were used to evaluate the nature of the Ti(C,N) precipitation reaction. Solidification cracking susceptibility of the weld metal was shown to increase with dilution of 304L stainless steel based on testing conducted with the cast pin tear test. The increase in cracking susceptibility is associated with expansion of the solidification temperature range and the presence of eutectic liquid at the end of solidification that wets solidification grain boundaries.

ATI 50 ALLOY

Abstract ATI 50 Alloy is an austenitic stainless steel strengthened with nitrogen. It is superior to AISI Type 316L in both strength and corrosion resistance. This datasheet provides information on composition, physical properties, hardness, and tensile properties. It also includes information on corrosion resistance as well as forming, heat treating, machining, and joining. Filing Code: SS-1103. Producer or source: ATI Allegheny Ludlum Corporation.

Corrosion behaviour of single (Ti) and duplex (Ti–TiO 2) coating on 304L stainless steel in nitric acid medium

Sputter deposited single titanium (Ti) layer, and duplex Ti–TiO 2 coating on austenitic type 304L stainless steel (SS) was prepared, and the corrosion performance was evaluated in nitric acid medium using surface morphological and electrochemical techniques. Morphological analysis using atomic force microscope of the duplex Ti–TiO 2 coated surface showed minimization of structural heterogeneities as compared to single Ti layer coating. The electrochemical corrosion results revealed that, titanium coated 304L SS showed moderate to marginal improvement in corrosion resistance in 1 M, and 8 M nitric acid, respectively. Duplex Ti–TiO 2 coated 304L SS specimens showed improved corrosion resistance as compared to Ti coating from dilute (1 M) to concentrated medium (8 M). The percentage of protection efficiency for base material increases significantly for duplex Ti–TiO 2 coating as compared to single Ti layer coating. The oxidizing ability of nitric acid on both the coatings as well as factors responsible for improvement in protection efficiency are discussed and highlighted in this paper.

INVESTIGATION OF THERMO-PHYSICAL AND FLOW PROPERTIES OF CO2 HYDRATE SLURRY

A pilot CO2 hydrate slurry production system was built and tested. The density of CO2 hydrate slurry was experimentally investigated and the relation between the density and the solid fraction has been established. The apparent viscosity of water, CO2 solution and CO2 hydrate slurry was investigated with a XL7-100 online resonant viscometer. We find that when the solid mass fraction in slurry increases, the density and apparent viscosity of CO2 slurry also increase. CO2 hydrate solid particles contribute only slightly to the viscosity increase when the solid mass fraction increased from 1.59% to 28% from our experimental results. Higher solid mass fraction can be achieved when more CO2 gas is injected into the loop under suitable hydrate formation conditions. The pure hydrate's dissociation enthalpy was evaluated by Micro Differential Scanning Calorimetry system. The enthalpy of CO2 hydrate slurry mainly depends on solid mass fraction. Real-time coupled multielectrode array sensor probes were applied to measure the maximal localized corrosion rate of three different materials subjected to CO2 hydrate slurry and saturated CO2 solution in the temperature range of 274.15–291.15 K and pressure range of 2.5–3.0 MPa. For a long-term usage in a mixture of CO2 saturated aqueous solution and hydrate slurry environment, carbon steel materials are to be unacceptable from the corrosion resistance point of view. In contrast, stainless steel type 304L and copper 110 have presented very low corrosion rates.

Advanced Ductility Exhaustion Methods for the Calculation of Creep Damage During Creep-Fatigue Cycling

Abstract The thermal mechanical cycling of high temperature components can result in creep-fatigue cycles in which the creep dwell has a wide variety of positions within the cycle. During in-phase cycling the creep dwell is placed at the maximum strain in the cycle. Out of phase cycling gives compressive dwells and phase cycling between 0° and 180° gives a cycle in which the dwell is placed before the maximum strain is reached, i.e., at an intermediate position within the cycle. Furthermore, components often experience cycles with a variety of different strain amplitudes, which can result in cycle sequencing effects. The effects of these different types of creep dwells have been investigated as part of the development programme for the R5 High Temperature Life Assessment Procedure. The materials included in the R5 programme were two low alloy ferritic steels; a cast 1CrMoV and a cast 1/2 CrMoV and three austenitic stainless steels; a type 316H steel, a cast type 304L, and a type 347 weld metal. The analysis of these tests has resulted in the proposal of a new method to calculate creep damage. This has been shown to give better predictions for the creep damage at failure in laboratory tests compared with both the current R5 ductility exhaustion approach and the time fraction approach, which is used in typical design codes such as ASME III and RCC-MR. In particular, the new method gives significantly improved predictions of creep damage at failure for creep-fatigue cycles with intermediate dwells and for cycles with low strain ranges, which are of particular relevance to the service cycles in real plant. This paper reviews the findings of the work on the new method, the effects of multiaxial states of stress and the effects of compressive dwells.