Type 304SS Research Articles

Effect of Work‐Hardening Mechanisms in Asymmetrically Cyclic‐Loaded Austenitic Stainless Steels on Low‐Cycle and High‐Cycle Fatigue Behavior

Dislocation characteristics and deformation‐induced martensite (DIM) transformation in an asymmetrically cyclic‐loaded metastable type 304 stainless steel (SS) are investigated compared with a stable type 316SS using EBSD and X‐ray diffraction line‐profile analysis. In low‐cycle fatigue (LCF) regime, differences between dislocation densities of type 304SS and type 316SS are increased with decreasing fatigue life, and contribution of α′‐martensite to work hardening of cyclically loaded type 304SS increased with decreasing fatigue life. However, the contribution of austenite slightly changed. Higher work hardening via DIM transformation improves the fatigue life of type 304SS than that of type 316SS in LCF regime in the same fatigue stress amplitude. Thus, the contribution of α′‐martensite to work hardening is a determinant parameter, affecting the fatigue behavior of type 304SS. In HCF regime when the α′‐martensite had a small contribution to the work hardening, the fatigue life of type 304SS is slightly higher than that of type 316SS.

Evaluation on Creep Properties of Type 316SS Series

Evaluation on creep properties of type 316 stainless steel (SS) series has been done. Type of 316SS series is a candidate material for major structural components of high temperature reactor such as liquid metal reactor (LMR) because it has a good mechanical property in high temperature, compatibility with the coolant sodium, and adequate welding ability. The objective of this research is to obtain and compare creep properties between type 316SS and type 316LN SS materials. The method use by conducted creep rupture tests in ranges temperature of 600°C, 700°C and 800°C and under a constant applied stress level of 200 MPa (393 N). Research result obtained that time to rupture of type 316SS less than that of type 316LN SS. The values of extension (mm), creep strain (mm/mm), creep strain rate (mm/mm/hrs), and rupture elongation (%) of type 316SS are higher than that of type 316LN SS for the same temperatures and applied constant stress level. It is concluded that type 316LN SS has a good creep resistance than that of type 316SS.

Microstructural Evolution of Type 304 and 316 Stainless Steels Under Neutron Irradiation at LWR Relevant Conditions

Life extension of light water reactors will expose austenitic internal core components to irradiation damage levels beyond 100 displacements per atom (dpa), leading to profound microstructural evolution and consequent degradation of macroscopic properties. Microstructural evolution, including Frank loops, cavities, precipitates, and segregation at boundaries and the resultant radiation hardening in type 304 and 316 stainless steel (SS) variants were studied in this work via experimental characterization and multiple simulation methods. Experimental data for up to 40 heats of type 304SS and 316SS variants irradiated in different reactors to 0.6–120 dpa at 275–375°C were generated from this work or collected from literature reports. These experimental data were then combined with models of Frank loop and cavity evolution, computational thermodynamics and precipitation, and ab initio and rate theory integrated radiation-induced segregation models to provide insights into microstructural evolution and degradation at higher doses.

Effect of octadecylamine on the corrosion behavior of Type 316SS in acetate buffer

The inhibitory effect of octadecylamine (ODA) on the corrosion and passivity breakdown of Type 316SS in acetic acid solution was characterized using potentiodynamic polarization, cyclic voltammetry, and electrochemical impedance spectroscopy (EIS). The inhibition mechanism of ODA was defined by optimizing the Bi-layer Point Defect Model on the EIS data. The optimization results indicated that, as either the concentration of ODA or the immersion time increases, the inhibitor-modified outer layer resistance, the charge transfer resistance, and the Warburg coefficient for the transport of species through the porous outer layer of the passive film all increase, thereby accounting for the observed inhibition.

Prediction of crack growth rate in Type 304 stainless steel using artificial neural networks and the coupled environment fracture model

A crack growth rate (CGR) database has been developed to train an artificial neural network (ANN). The trained ANN and the extended coupled environment fracture model (CEFM) were used to predict the CGR in Type 304SS as a function of each of the principal variables of the system. The ANN revealed the underlying relationships that map the dependencies of the CGR on the various input independent variables. A sensitivity analysis revealed that IGSCC in sensitized Type 304SS in high temperature aqueous environments is primarily electrochemical in character. Comparison between the ANN-predicted CGR and CEFM-predicted CGR reveal good agreement.

Effects of temperature on stress corrosion cracking behavior of stainless steel and outer oxide distribution in cracks due to exposure to high-temperature water containing hydrogen peroxide

Cracking growth tests were conducted in high-temperature water containing hydrogen peroxide (H2O2) at 561–423K to evaluate the effects of H2O2 on stress corrosion cracking (SCC) of stainless steel (SS) at temperature lower than the boiling water reactor (BWR) operating temperature. Small compact tension (CT) specimens were prepared from thermally sensitized type 304SS. Despite the observation of only a small portion intergranular SCC (IGSCC) near the side groove of the CT specimen at 561K in high-temperature water containing 100ppb H2O2, the IGSCC area expanded to the central region of the CT specimens at 423 and 453K. Effects of H2O2 on SCC appeared intensely at temperature lower than the BWR operating temperature because of a reduction in the thermal decomposition of H2O2. To estimate the environment in the cracks, outer oxide distribution on the fracture surface and the fatigue pre-crack were examined by laser Raman spectroscopy and thermal equilibrium calculation was performed.

Enhancement of Corrosion Resistance of Type 304 Stainless Steel Through a Novel Thermo-mechanical Surface Treatment

The paper describes a novel thermo-mechanical surface treatment approach, involving conventional shot blasting followed by laser surface heating, to engineer microstructural modification in type 304 austenitic stainless steel for enhancing its corrosion resistance. Thermo-mechanical surface treatment resulted in the formation of fine recrystallized grains with some strain-induced martensite on the modified surface. Surface treatment of type 304 stainless steel brought about significant improvement in its resistance against uniform as well as pitting corrosion. Electrochemical impedance spectroscopic studies showed improved polarization resistance (Rp) value for thermo-mechanically treated surface indicating formation of a more protective passive film than that formed on the untreated surface. In contrast to untreated type 304 stainless steel specimens where pits preferentially initiated at the site of Al2O3 inclusions, thermo-mechanically treated specimen exhibited only general dissolution with a few repassivated and shallow pits. Grain refinement and dispersion of alumina inclusions on the modified surface are considered to be the key factors responsible for improvement in uniform and pitting corrosion resistance of type 304SS.

Development of aluminum-alloy coating on type 316SS for nuclear systems using liquid lead–bismuth

An Al-alloy coating method using Al, Ti and Fe powders and the laser beam heating has been developed for nuclear systems using liquid lead–bismuth eutectic (LBE). Main defects formed in the coating process were surface defects and cracks. It was effective to decrease a laser beam scanning rate to 20mm/min to avoid surface defects. It was necessary to adjust the Al concentration in the coating layer to be lower than 12wt.% in order to avoid significant cracking. A static corrosion test was conducted in liquid LBE at the controlled oxygen concentrations of 10−6–10−3wt.% at 550°C for 3000h. The Al-alloy coating layer on 316SS prevented severe corrosion attack such as Ni dissolution, partial loss of grains and LBE penetration which were observed in 316SS without Al-alloy coating. Liquid LBE penetrated into the surface defects formed in the Al-alloy coating layers produced using a laser beam with the scanning rate of 60mm/min. The Al-alloy coating layer, which was formed without surface defects and cracks under the optimum condition of the scanning rate of 20mm/min, exhibited good corrosion resistance in liquid LBE.

UR 2202

Abstract UR 2202 is a lean duplex stainless steel designed to match the corrosion resistance of Type 304SS. This datasheet provides information on composition, physical properties, elasticity, tensile properties, and shear strength as well as fracture toughness. It also includes information on corrosion resistance as well as forming, heat treating, and joining. Filing Code: SS-1033. Producer or source: Industeel USA, LLC.

Sodium effects on mechanical performance and consideration in high temperature structural design for advanced reactors

Sodium environmental effects are key limiting factors in the high temperature structural design of advanced sodium-cooled reactors. A guideline is needed to incorporate environmental effects in the ASME design rules to improve the performance reliability over long operating times. This paper summarizes the influence of sodium exposure on mechanical performance of selected austenitic stainless and ferritic/martensitic steels. Focus is on Type 316SS and mod.9Cr–1Mo. The sodium effects were evaluated by comparing the mechanical properties data in air and sodium. Carburization and decarburization were found to be the key factors that determine the tensile and creep properties of the steels. A beneficial effect of sodium exposure on fatigue life was observed under fully reversed cyclic loading in both austenitic stainless steels and ferritic/martensitic steels. However, when hold time was applied during cyclic loading, the fatigue life was significantly reduced. Based on the mechanical performance of the steels in sodium, consideration of sodium effects in high temperature structural design of advanced fast reactors is discussed.

NIROSTA 4640

Abstract Nirosta 4640 is a low-cost lean austenitic alloy that exhibits many of the same properties as the established alloys such as Type 304SS. This datasheet provides information on composition, physical properties, elasticity, and tensile properties. It also includes information on corrosion resistance as well as forming, heat treating, machining, and joining. Filing Code: SS-1024. Producer or source: ThyssenKrupp Nirosta GmbH.

Continuous monitoring of back wall stress corrosion cracking growth in sensitized type 304 stainless steel weldment by means of potential drop techniques

Stress corrosion cracking (SCC) tests on welded specimens of sensitized type 304SS with a thickness of 20 mm were performed in sodium thiosulphate solution at room temperature, with continuous monitoring of the SCC growth, using the techniques of modified induced current potential drop (MICPD), alternating current potential drop (ACPD) and direct current potential drop (DCPD). The MICPD and DCPD techniques permit continuous monitoring of the back wall SCC, which initiates from a fatigue pre-crack at a depth of about 4 mm, from which it propagates through more than 80% of the specimen thickness. The MICPD technique can decrease the effect of the current flowing in the direction of the crack length by focusing the induced current into the local area of measurement using induction coils, so that the sensitivity of the continuous monitoring of the back wall SCC is higher than that of the ACPD and DCPD techniques.

High Temperature Heat Capacity of Alloy D9 Using Drop Calorimetry Based Enthalpy Increment Measurements

Alloy D9 is a void-swelling resistant nuclear grade austenitic stainless steel (SS) based on AISI type 316-SS in which titanium constitutes an added predetermined alloying composition. In the present study, the high-temperature enthalpy values of alloy D9 with three different titanium-to-carbon mass percent ratios, namely Ti/C = 4, 6, and 8, have been measured using inverse drop calorimetry in the temperature range from 295 to 1323 K. It is found that within the level of experimental uncertainty, the enthalpy values are independent of the Ti–C mass ratio. The temperature dependence of the isobaric specific heat CP is obtained by a linear regression of the measured enthalpy data. The measured CP data for alloy D9 may be represented by the following best-fit expression: CP (J · kg −1 · K −1 ) = 431 + 17.7 × 10 −2 T + 8.72 × 10 −5 /T 2 . It is found that the measured enthalpy and specific heat values exhibit good agreement with reported data on 316 and other related austenitic stainless steels.

Figure of merit for the quality of ZrO 2 coatings on stainless steel and nickel-based alloy surfaces

A figure of merit (FOM) has been developed to define the quality of ceramic (e.g., ZrO 2) coatings on metal and alloy [Type 304SS and Alloy 600] surfaces. Zirconia (ZrO 2) coatings were developed as a means of protecting the metal/alloy surfaces from stress corrosion cracking (SCC) in boiling water reactor (BWR) primary heat transport circuits, by inhibiting the cathodic reaction (reduction of oxygen and hydrogen peroxide) on the surface external to the crack. The distribution of pores in the coating plays an important role in corrosion prevention, such that the lower the porosity of the coating, the better the protection afforded to the system against SCC. Since the reactors operate at high temperature (e.g., at 288 °C under full power conditions), the temperature dependence of the FOM was investigated. The figure of merit (FOM) was developed by measuring impedance data over a wide range of frequency (10 mHz–5 kHz) at temperatures of 25, 100, 200, and 288 °C in hydrogenated, buffered solutions, with the hydrogen electrode reaction (HER) being used as a “fast” redox couple. An “equivalent circuit” analog was first developed from the bare surface impedance data and this analog was then employed in a second step to model the pore bottom in defining the pore distribution on the coated surface. A lognormal distribution (LND) of the pores was assumed and the parameters of the LND were determined using a constrained optimization technique to fit the model to the experimental data for the coated surface at different temperatures. The results suggest that, as temperature increases, the coating becomes more porous, making the substrate more susceptible to corrosion cracking. At 288 °C, 87% of the SS and 85% of the Ni-alloy surfaces become porous with the pore radius varying from 0.0001 cm to 0.01 cm.

溶体化316系ステンレス鋼のIGSCCに対する統計解析

Recently, stress corrosion cracking (SCC) was observed in lots of Japanese BWR plant components made of L grade stainless steel (SS) with very low carbon content. SCC essentially has a probabilistic nature, thus the probabilistic analysis is necessary to better understand SCC behavior and establish countermeasures. However, no experimental study was made for these SCC observed on non-sensitized SS from such a probabilistic aspect. SCC test was conducted by the creviced bent beam (CBB) method in high temperature water containing 8 ppm dissolved oxygen. The test specimen was used in as-received and 10% cold rolled conditions. To examine the probabilistic aspect of SCC, 10 specimens were used for each test condition. The test duration were set to 500 h and 1000 h. After the test, the specimen surface and the fracture surface were observed by scanning electron microscopy to count the number of cracks and measure the crack length and depth. From the results, it was found that the distribution of SCC crack lengths conformed to the log-normal distribution for type 316L and type 316SS irrespective of the pre-treatment and material conditions. On the other hand, the distribution of SCC crack depths conformed to both the normal and log-normal distribution.

Application of Creep Ductility Model for Evaluation Creep Crack Growth Rate of Type 316SS Series

This paper is to evaluate the creep crack growth rate (CCGR) of the type 316SS series: 316SS, 316FR and 316LN, and to apply a creep ductility model. A number of the data are collected through wide literature surveys and experiment, and evaluated by the C* parameter. The results of the CCGR data were nearly matched with a small scattering band regardless of the different applied stresses, temperatures and test specimens configuration. In the CCGR, type 316FR and 316LN steels were slower than type 316SS. Type 316SS showed a better agreement in the application of the creep ductility model than the type 316FR and 316LN steels.

EFFECT OF TEMPERATURE AND IRRADIATION DOSE OF He+ AND N+ IONS ON SURFACE SWELLING AT GRAIN INTERIOR AND GRAIN BOUNDARY IN TYPE 316 STAINLESS STEEL

Austenitic stainless steel specimens of type 316SS were irradiated by 200 keV He + ions or 200 keV N + ions. Atomic force microscopy (AFM) and transmission electron microscopy (TEM) were employed to study the fine surface deformation of the irradiated specimens. At the high temperatures of He + ion irradiation, distinct swelling was observed at grain interior and grain boundaries by AFM and helium bubbles were found by TEM. It is suggested that helium atoms agglomerate in high doses and high temperatures. The nanometer-level step height of surface swelling induced by He + ion irradiation has obvious dependence on the irradiation dose and temperature. In the case of N + ion irradiation, the swelling was observed at grain interior but the step height was less remarkable than in the case of He + ions. The swelling is induced by void formation. The caved-in grain boundaries were recognized in N + ion irradiated area.

Corrosion Behavior of FBR Candidate Materials in Stagnant Pb-Bi at Elevated Temperature

Three materials proposed for use in fast breeder reactors—FBR grade type 316ss, high chromium type martensitic steel and oxide dispersion strengthened martensitic type steel—were subjected to corrosion tests in stagnant lead-bismuth eutectic (LBE) containing 10-6 wt% of oxygen at 500–650—C for up to 5,000 h. After each test, the specimens were analyzed metallurgically using a scanning electron microscopy with energy dispersive X-ray analyzer and an X- ray diffractometer. It proved that, at temperatures not higher than 550°C, martensitic steels containing chromium to more than 9wt% presented good resistance against corrosion by the formation of spinel layer on the base metals, though outer porous oxide formed on the steels was detached and/or dissolved into LBE. At temperatures above 600°C, the oxide layer thickness diminished. This alteration in corrosion behavior seems to be ascribable to a change taking place at 570°C in the stable form of iron oxide from magnetite to wustite. At the temperatures, dissolution attack was observed at some portions. It was estimated that the oxide became to lose its adhesion to the base metal.

Corrosion Behavior of FBR Candidate Materials in Stagnant Pb-Bi at Elevated Temperature

Three materials proposed for use in fast breeder reactors-FBR grade type 316ss, high chromium type martensitic steel and oxide dispersion strengthened martensitic type steel-were subjected to corrosion tests in stagnant lead-bismuth eutectic (LBE) containing 10 -6 wt% of oxygen at 500-650°C for up to 5,000 h. After each test, the specimens were analyzed metallurgically using a scanning electron microscopy with energy dispersive X-ray analyzer and an X-ray diffractometer. It proved that, at temperatures not higher than 550°C, martensitic steels containing chromium to more than 9 wt% presented good resistance against corrosion by the formation of spinel layer on the base metals, though outer porous oxide formed on the steels was detached and/or dissolved into LBE. At temperatures above 600°C, the oxide layer thickness diminished. This alteration in corrosion behavior seems to be ascribable to a change taking place at 570°C in the stable form of iron oxide from magnetite to wustite. At the temperatures, dissolution attack was observed at some portions. It was estimated that the oxide became to lose its adhesion to the base metal.

Stress corrosion cracking of sensitized Type 304 stainless steel in thiosulfate solution: I. Fate of the coupling current

This work explores the fate of the coupling current generated during stress corrosion cracking of sensitized Type 304 stainless steel (304SS) in thiosulfate solution at ambient temperature. The coupling current, which is generated inside the crack, may be consumed (as required by charge conservation) by cathodic reactions at two different locations: inside the crack (e.g., on the crack flanks) and on the external surfaces. Experiments were conducted using sensitized Type 304SS compact tension specimens C(T) modified to provide external surfaces isolated from the specimen itself, so that the coupling current flowing between the crack and the external cathode could be directly monitored using a zero-resistance ammeter. The results demonstrate that significant coupling current flows from the crack to the external surface, consistent with the differential aeration hypothesis for localized corrosion. Coupling current data from specimens heat treated at 650 °C for 4, 14, and 24 h show that 4 h of sensitizing heat treatment apparently does not induce significant sensitization, while 14 h of heat treatment is sufficient to produce a fully sensitized microstructure, equivalent to that obtained after 24 h of heating. Finally, the crack was determined to grow via discrete microfracture events at the crack front with a dimension of the order of the grain size. The observations are more consistent with crack growth being due to a hydrogen induced fracture mechanism rather than slip/dissolution.