Cold Worked 316L Stainless Steel Research Articles

Microstructural Engineering of Mn-Alloyed Austenitic Steel for Hydrogen Storage and Delivery

Austenitic stainless steels are commonly used for hydrogen storage and transportation. These alloys have a high nickel (Ni) content, which increases alloy cost. In this study, high manganese (Mn) austenitic alloys were evaluated as potential lower cost alternatives. Two heats of high Mn alloys with different stacking fault energies (SFE) of ~29 mJ·m-2 and 49 mJ·m-2 were acquired. Additionally, a new vanadium (V)-microalloyed high Mn alloy was designed to achieve a SFE of 47 mJ·m-2 to minimize planar slip deformation mechanisms. Post-processing via cold working in conjunction with aging was also performed on the V-microalloyed high Mn steel. Hydrogen embrittlement sensitivity was investigated using circumferential notch tensile specimens cathodically charged with hydrogen in a 0.05M NaOH electrolytic solution. The alloys were compared to a cold-worked 316L stainless steel, which exhibited no strength loss due to hydrogen. The high Mn alloys with SFE of ~29 mJ·m2 and 49 mJ·m-2 had notch strength losses of 11 and 6 pct, respectively. The V-microalloyed high Mn steel in the as-hot-rolled condition had a notch strength loss of 17 pct. The V-microalloyed high Mn steel in the cold worked and aged condition indicated no notch strength loss in hydrogen, which was comparable to the performance of the 316L stainless steel.

Improving the corrosion and stress corrosion cracking resistance of 316 L stainless steel in high temperature water by water jet cavitation peening

Water jet cavitation peening (WJP) was used to improve the corrosion and stress corrosion cracking (SCC) of cold worked 316L stainless steel (316L SS) in high temperature water. WJP induced changes in residual stress and microstructure of the surface layer on corrosion and SCC were investigated. The investigation was conducted by comparing the corrosion and SCC of the un-treated (UT) and WJP treated specimens by exposure tests and slow strain rate tensile (SSRT) tests. The results revealed that WJP obviously improved the corrosion and SCC resistance of 316L SS, which is attributed to the increase of residual compressive stress and the change of the microstructure of the surface layer.

A comparison study of void swelling in additively manufactured and cold-worked 316L stainless steels under ion irradiation

• The temperature-dependent void swelling of additively manufactured 316L SSs was investigated for the first time. • The void swelling behaviors of additively manufactured 316L and cold-worked 316L SSs were systematically compared. • The dislocations trapped at cell walls and dislocation networks induced by cold work probably functioned differently in void swelling. We studied the void swelling in stress-relieved (SR) additively manufactured (AM) 316L stainless steel (SS) in comparison with hot-isostatic pressed (HIP) AM 316L counterparts with identical chemistry. To understand the role of dislocation cell structure in SR AM 316L SS, we also included cold-worked (CW) 316L SS with various CW levels for dislocation networks. The irradiation damage of 30 displacements per atom (dpa) in AM and CW 316L SSs were compared after 5 MeV Fe 2+ ion irradiations at 500 °C, 550 °C, and 600 °C, respectively. To investigate the temperature and dose dependence, the AM 316L SSs were further irradiated to 100 dpa at 400 °C and 600 °C. Results show that the void welling in SR AM 316L SS is more severe than in HIP AM 316L SS, in terms of a higher void density and a deeper void nucleation depth through all the examined conditions. This is ascribed to a more extended incubation period in HIP AM 316L SS. Beyond the incubation, both samples proceeded at a similar swelling rate. Dislocation networks from cold-working can effectively suppress void swelling, while dislocation cell structures containing entangled dislocations on cell walls cannot. The distinct responses indicate the potential influence of dislocation configuration on void swelling. Despite some relevant data are available, our understandings of radiation damage in AM 316L SSs are still limited.

Synergistic Effect of Solid State Hydrogen and Cold Work Pretreatment on Oxide Films Grown on 316L Stainless Steel during Short Term Immersion in Deaerated High Temperature Water at 300 °C

The properties of the oxide films formed on solution-annealed and cold-worked 316L stainless steel (SS) specimens with and without charged hydrogen in deaerated pressurized water reactor primary water at 300 °C were investigated. The outer oxide layers of all specimens were composed of magnetite (Fe3O4) and NiFe2O4. Charged hydrogen resulted in larger outer iron-bearing oxide particles forming due to hydrogen-enhanced outward diffusion of iron cations. Prior cold-work accelerates the oxidation was observed. Charged hydrogen led to local cracks in the oxide film and enhanced the penetration oxidation beneath the metal/oxide interface. The Cr-rich inner oxide layer grown on the prior cold-worked specimen with charged hydrogen was thicker than that on the cold-work specimen or the hydrogen-charged specimen, revealing the combined effects of charged hydrogen and prior cold-work on the acceleration of the oxidation process. The working mechanism of the solid-state hydrogen effect on the oxide film was discussed.

Two-step annealing treatment for grain refinement of cold-worked AISI 316L stainless steel

Abstract Two-step annealing after cold rolling is proposed for the optimization of the annealing process of AISI 316L austenitic stainless steel toward more intense grain refinement. It was revealed that the first step of the annealing process at lower temperatures (i. e. 750 0C) can be used for the reversion of strain-induced martensite to austenite without uninhibited grain growth and recrystallization of the retained austenite. Afterwards, the primary recrystallization of the retained austenite takes place in the second step of the annealing process at higher temperatures (in the range of 850 to 950 0C). Carefully controlling the second annealing step resulted in a finer grain size and better mechanical response compared to those of a conventional one-step annealing approach.

Two-step annealing treatment for grain refinement of cold-worked AISI 316L stainless steel

Abstract Two-step annealing after cold rolling is proposed for the optimization of the annealing process of AISI 316L austenitic stainless steel toward more intense grain refinement. It was revealed that the first step of the annealing process at lower temperatures (i. e. 750 0C) can be used for the reversion of strain-induced martensite to austenite without uninhibited grain growth and recrystallization of the retained austenite. Afterwards, the primary recrystallization of the retained austenite takes place in the second step of the annealing process at higher temperatures (in the range of 850 to 950 0C). Carefully controlling the second annealing step resulted in a finer grain size and better mechanical response compared to those of a conventional one-step annealing approach.

Stress Corrosion Cracking Behavior of Cold Worked 316L Stainless Steel in Chloride Environment

Stress Corrosion Cracking Behavior of Cold Worked 316L Stainless Steel in Chloride Environment

XPS Analysis of the Oxide Films Formed on Non-Charged and Hydrogen-Charged 316L SS in Deaerated High Temperature Water

Austenitic stainless steel components have been used in pressurized water reactors (PWRs) coolants. These austenitic stainless steels may absorb hydrogen from either the dissociation of dissolved hydrogen in PWR primary water or the corrosion processes at the steel surfaces during the immersion in PWR primary water. It is necessary to investigate the effect of hydrogen in alloys on the oxidation and resultant environmental degradation processes in high temperature water environments. In the present study, the oxide films formed in deaerated PWR primary water at 300℃on a cold worked 316L (316LCW) stainless steel with or without prior hydrogen-charging were characterized. Hydrogen-charging of 316LCW was performed by cathodic charging in sulfuric acid solution containing thiourea at room temperature. Prior to the immersion tests, the Immersion tests were performed in a 2-L Ti-autoclave with solution deaerated by purging N2 gas before heating to test temperature. The oxide films formed on 316LCW and hydrogen-charged 316L CW (316LCW-H) specimens after exposure to deaerated PWR primary water at 300 oC for168 h were observed. The XPS depth profiles of the oxide films formed on 316LCW and 316LCW-H specimens after exposed to simulated PWR primary water are compared. The thickness of the oxide film was estimated from the half height of oxygen concentration and the sputtering rate (0.1 nm/s), for determining the thickness of the oxide film that was about 180 nm on 316LCW and about 250 nm on 316LCW-H. The oxide films formed on both 316LCW and 316LCW-H were enriched in Fe and Ni in the outer layer, and enriched in Cr in the inner part of the oxide film. The Cr content in the inner oxide layer formed on 316LCW-H specimen was lower than that on 316LCW specimen. Figure 1

Effects of zinc injection on stress corrosion cracking of cold worked austenitic stainless steel in high-temperature water environments

In the nuclear power industry, few data exist to demonstrate the effectiveness of Zn injection in reducing the crack growth rate of primary component materials. This work shows that Zn injection reduced the stress corrosion cracks growth rate of cold worked 316L stainless steel (SS) by 3 times. ZnCr2O4 oxide was detected both on the crack walls and at the crack tip, showing that Zn substitution in the spinel-type oxide occurred and mitigated stress corrosion cracking.

Stress corrosion cracking behavior of annealed and cold worked 316L stainless steel in supercritical water

The supercritical water reactor (SCWR) is one of the more promising designs considered by the Generation IV International Forum due to its high thermal efficiency and improving security. To build this reactor, standardized structural materials used in light water reactors (LWR), like austenitic stainless steels, have been proposed. These kind of materials have shown an optimum behavior to stress corrosion cracking (SCC) under LWR conditions except when they are cold worked.It is known that physicochemical properties of water change sharply with pressure and temperature inside of the supercritical region. Owing to this situation, there are several doubts about the behavior of candidate materials like austenitic stainless steel 316L to SCC in the SCWR conditions.In this work, alloy 316L was studied in deaerated SCW at two different temperatures (400°C and 500°C) and at 25MPa in order to determine how changes in this variable influence the resistance of this material to SCC. The influence of plastic deformation in the behavior of alloy 316L to SCC in SCW was also studied at both temperatures.Results obtained from these tests have shown that alloy 316L is susceptible to SCC in supercritical water reactor conditions where the susceptibility of this alloy increases with temperature. Moreover, prior plastic deformation of 316L SS increased its susceptibility to environmental cracking in SCW.

Effect of Cold Mechanical Process on the Mechanical Properties of 316L Stainless Steel for Medical Implant Application

The objective of this research was to study the mechanical properties of cold-worked 316L stainless steel (SS) after it has undergone the cold mechanical process. A 316L SS sheet was cold-rolled until a reduction in thickness was within the range of 10% to 50%. The sheet was then plastically deformed into a U-bend shape using a universal testing machine equipped with a bending jig. The mechanical properties of the cold-rolled and U-bend steel were analysed using a tensile, 3-point bending, and microhardness tests. It was found that the rolling and bending processes produced such amount of plastic strain that affect the mechanical properties of the 316L SS. The strength of the cold-rolled, U-bend 316L SS increased gradually as the cold reduction was raised above 10%, which was mainly due to the strain hardening effects. The ultimate strength of the U-bend steel increased gradually compared to the cold-rolled steel for each stage of the cold reduction process. On the other hand, the microhardness of the U-bend steel increased rapidly after a cold reduction up to 10%, and the value increased slightly after a cold reduction of 30%. This study indicated that the mechanical properties of 316L SS can be increased by using a combination of the cold rolling and bending processes.

SCC crack growth rate of cold worked 316L stainless steel in PWR environment

Many component failures in nuclear power plants were found to be caused by stress corrosion cracking (SCC) of cold worked austenitic steels. Some of the pressure boundary component materials are even cold worked up to 35% plastic deformation, leaving high residual stress and inducing high growth rate of corrosion crack. Controlling water chemistry is one of the best counter measure to mitigate this problem. In this work, the effects of temperature (200 up to 325°C) and dissolved oxygen (0 up to 2000μg/L) on SCC crack growth rates of cold worked austenitic stainless steel type 316L have been tested by using direct current potential drop (DCPD) method. The results showed that temperature affected SCC crack growth rates more significantly in oxygenated water than in deaerated water. In argon deaerated water, the crack growth rate exhibited a peak at about 250°C, which needs further verification. At 325°C, the SCC crack growth rate increased rapidly with the increase of dissolved oxygen concentration within the range from 0 up to 200μg/L, while when dissolved oxygen was above 200μg/L, the crack growth rate followed a shallower dependence on dissolved oxygen concentration.

Effect of dissolved oxygen content on stress corrosion cracking of a cold worked 316L stainless steel in simulated pressurized water reactor primary water environment

Stress corrosion crack growth tests of a cold worked nuclear grade 316L stainless steel were conducted in simulated pressurized water reactor (PWR) primary water environment containing various dissolved oxygen (DO) contents but no dissolved hydrogen. The crack growth rate (CGR) increased with increasing DO content in the simulated PWR primary water. The fracture surface exhibited typical intergranular stress corrosion cracking (IGSCC) characteristics.

Effects of prior cold working on low cycle fatigue behavior of stainless steels, titanium alloy timetal 834 and superalloy IN 718: A review

This paper gives a brief review of the efforts made to study the effects of cold rolling on low cycle fatigue (LCF) behavior of stainless steels, titanium alloy Timetal 834 and Ni-Fe based Super alloy IN 718 at different temperatures and different strain amplitudes. Low Cycle Fatigue tests on cold worked 316L stainless steel at various temperatures from room temperature to 923K have been reported. In all tests the effect of 20% prior cold work(PCW) on LCF behavior of type 316L (N) stainless steel had been studied at 873K under total axial strain controlled mode in air at strain amplitudes from ±0.25% to ±1.0%. Fatigue life in the solution annealed condition was similar to that of the PCW material at higher strain amplitudes (≥0.5%) while at lower strain amplitudes the PCW material exhibited longer life. The influence of PCW on LCF behavior of type 304 and AISI 304LN stainless steel was studied at various temperatures and it was observed that the fatigue life was strongly dependent on prior cold work, temperature, and strain amplitude employed. Cold rolling of the titanium alloy Timetal 834 and age hardenable Ni-Fe-based superalloy IN 718 has been found to cause marked enhancement in LCF life at low strain amplitude and eliminate the bilinearity from the Coffin-Manson(C-M) relationship. Work carried on this aspect, however is very limited particularly in the case of Titanium alloys and Ni-Fe based Superalloy IN 718

Transient and steady state crack growth kinetics for stress corrosion cracking of a cold worked 316L stainless steel in oxygenated pure water at different temperatures

The stress corrosion cracking (SCC) growth kinetics for a cold worked 316L stainless steel was continuously monitored in high purity water at different temperatures and dissolved oxygen (DO) levels under a K (or K max) of 30 MPa m 0.5. The total SCC test time was more than 8000 h to make sure the steady state crack growth rate under each test condition could be reached. Crack growth rate (CGR) increases with increasing temperature in the range 110–288 °C. A typical intergranular-cracking mode is identified. Depending on the previous test condition, especially the temperature, three kinds of crack growth kinetics, i.e., increasing with testing time then becoming steady, being constant during the whole period, or decreasing with test time then becoming steady, are identified and discussed. Time-dependent and testing history-dependent crack growth modes were confirmed in two series of tests in 2 ppm DO and 7.5 ppm DO pure water. The apparent activation energies are calculated and compared with other data in different environments under different applied loading levels for understanding the cracking mechanism.

Temperature effect on the low-cycle fatigue behavior of type 316L stainless steel: Cyclic non-stabilization and an invariable fatigue parameter

The temperature effect on the cyclic non-stabilization of cold-worked 316L stainless steel during low-cycle fatigue deformation was investigated. The material underwent additional cyclic hardening at room temperature and in the temperature range of 250–600 °C; the hardening at room temperature came from plasticity-induced martensite transformation and the hardening in the temperature range of 250–600 °C was attributed to dynamic strain aging. These hardening mechanisms competed with the cyclic softening induced by dynamic recovery, which is generally predominant in cold-worked materials, and this led to the cyclic non-stabilization of the material. Three fatigue parameters: the stress amplitude, plastic strain amplitude and plastic strain energy density, were evaluated to find an invariable fatigue parameter. The results revealed that the plastic strain energy density was stabilized at the early stage of fatigue life and nearly invariant through the entire life.

Dynamic strain aging under tensile and LCF loading conditions, and their comparison in cold worked 316L stainless steel

Tensile and low-cycle fatigue (LCF) tests were carried out in a wide temperature range from 20 to 750 °C at strain rates of 1 × 10 −4–1 × 10 −2/s for 17% cold worked 316L stainless steel to investigate the conditions for the occurrence of dynamic strain aging (DSA) and its effects on material properties during tensile and LCF deformations. DSA introduced anomalous changes of tensile and LCF properties, and the DSA regimes under tensile and LCF loading conditions coincided with each other. During tensile deformation, DSA can be manifested in the forms of the plateau in the variation of strength with temperature, the minima in the variation of ductility with temperature, the serrated yielding in the stress–strain curves, and the negative strain rate sensitivity (SRS). As for LCF deformation, it can be manifested in the forms of the plateau or the peak in the variation of cyclic peak stress with temperature, the negative temperature dependence of plastic strain amplitude or softening ratio, the negative SRS, and the negative strain rate dependence of plastic strain amplitude or softening ratio.

Dynamic Strain Aging during Low Cycle Fatigue Deformation in Prior Cold Worked 316L Stainless Steel

Low cycle fatigue (LCF) tests were carried out in a wide temperature range (20°C-650°C)at strain rates of 1×10-4/s-1×10-2/s for 17% cold worked (CW) 316L stainless steel to investigate the conditions for the occurrence of dynamic strain aging (DSA) and its effects on material properties during LCF deformation. DSA introduced anomalous changes of LCF properties, and the DSA regime under LCF loading condition coincided with that in tensile loading condition. During LCF deformation, dynamic stain aging can be manifested in the forms of the occurrence of the plateau or the peak in the variation of cyclic peak stress with temperature, the negative temperature dependence of plastic strain amplitude or softening ratio, the negative strain rate sensitivity, and the negative strain rate dependence of plastic strain amplitude or softening ratio.

냉간 가공된 316L 스테인리스강의 저주기 피로 거동에 미치는 온도의 영향 (I) - 인장 및 반복 거동 -

Tensile and low cycle fatigue (LCF) tests on prior cold worked 316L stainless steel were carried out at various temperatures from room temperature to 650. At all test temperatures, cold worked material showed the tendency of higher strength and lower ductility compared with those of solution treated material. The embrittlement of material occurred in the temperature region from 300 to 600 due to dynamic strain aging. Following initial cyclic hardening for a few cycles, cycling softening was observed to dominate until failure occurred during LCF deformation, and the cyclic softening behavior strongly depended on temperature and strain amplitude. Non-Masing behavior was observed at all test temperatures and hysteresis energy curve method was employed to describe the stress-strain hysteresis loops at halflife. The prediction shows a good agreement with the experimental results.

The tensile and low-cycle fatigue behavior of cold worked 316L stainless steel: influence of dynamic strain aging

Tensile and low-cycle fatigue (LCF) tests were carried out in air in a wide temperature range from 20 to 750 °C and strain rates of 1×10 −4–1×10 −2/s to investigate the influence of strain rate on tensile and LCF properties of cold worked 316L stainless steel, especially in the dynamic strain aging (DSA) regime. Dynamic strain aging caused a change in the tensile properties such as strength and ductility in the temperature range from 250 to 600 °C. This temperature range coincided well with the regime of negative strain rate sensitivity. Cyclic stress response at all test conditions was characterized by an initial hardening during the few cycles, followed by gradual softening until failure. Temperature and strain rate dependence on cyclic softening appears to come from a change of the cyclic plastic deformation mechanism and the DSA effect. The regimes of DSA between tensile and LCF loading conditions in terms of the negative strain rate sensitivity were consistent with each other. At the elevated temperature, a drastic reduction in fatigue resistance was observed, and this is attributed to the effects of oxidation, creep, and dynamic strain aging and interactions among these factors. The regime of DSA accelerated a reduction in fatigue resistance by enhancing crack initiation and propagation.