Ductility Of Austenitic Stainless Steels Research Articles

Effect of inclusion interface evolution on the thermal stability of cellular substructures in additively manufactured stainless steel

Solidification cellular substructure can improve the strength and ductility of austenitic stainless steel (SS) manufactured by laser powder-bed-fusion (L-PBF), but it is highly sensitive to elevated temperature. However, the underlying mechanisms affecting the thermal stability of cellular substructures remain unclear. Here, we demonstrate that the high annealing temperature can induce the unidirectional transformation from L-PBF 304L SS matrix to MnSiO3 inclusion to MnCrO4 inclusion, thus changing the interface properties of inclusions. The experimental results indicate that the thermal stability of cellular substructures is highly dependent on the interfacial properties between inclusions and the L-PBF 304L SS matrix. We uncover that the semi-coherent interface between MnSiO3 inclusions and L-PBF 304L SS matrix plays a crucial role in the formation of useful cellular substructures and the achievement of high strength and high ductility of L-PBF 304L SS. This new understanding of the inclusion interface properties can provide unprecedented possibilities for future development of high-performance L-PBF austenitic SS.

Prediction of creep ductility for austenitic stainless steels and copper

ABSTRACT For modern creep-resistant steels, ductility is primarily controlled by cavitation, since brittle rupture is dominating during long-term service. In recent years, the present authors have formulated fundamental models for nucleation and growth of cavities that have been verified to be able to describe experiments for austenitic stainless steels. These equations, together with models for dislocation creep, are used in this paper to present basic modelling results for the creep ductility of austenitic stainless steels for the first time. New results are also presented for ductile rupture, where the elongation values are mainly governed by plastic instability and necking. The Hart criterion is used to identify the strain where the instability forms. Modelling shows that the instability grows very slowly and that its size is not significant until close to rupture. These facts are used to demonstrate that ductility during ductile rupture can be predicted from necking behaviour.

Body-Thorough Ultrahigh Strength and Ductility of Austenitic Stainless Steel by Industry-Applicable 3-Axis Stress-Released Impact

Body-Thorough Ultrahigh Strength and Ductility of Austenitic Stainless Steel by Industry-Applicable 3-Axis Stress-Released Impact

Body-Thorough Ultrahigh Strength and Ductility of Austenitic Stainless Steel by Industry-Applicable 3-Axis Stress-Released Impact

Body-Thorough Ultrahigh Strength and Ductility of Austenitic Stainless Steel by Industry-Applicable 3-Axis Stress-Released Impact

Localization of Plastic Deformation in the Copper and Stainless Steels Samples, Irradiated with Neutrons

The reduction of ductility of austenitic stainless steels as a result of long-term operation in the nuclear reactor core is an important problem of modern radiation materials science. Understanding the mechanisms of the effect of neutron irradiation on the mechanical properties of austenitic steels is impossible without research of localization processes occurring during the deformation. In this paper, it was found that the value of the true local deformation corresponding to the onset of neck formation in face-centered cubic structured metals decreases with an increase in the radiation dose, while the true stress remains almost constant. Additional hardening of AISI 304 steel due to the intensive formation of the martensitic α’-phase increases not only the stress at which a neck is formed in this alloy, but also the true local deformation. As a result, the uniform elongation increases and remains high after neutron irradiation to 0.05 dpa. The forehanded formation of the martensitic α’-phase in sufficient quantity before the necking onset can be considered as an additional deformation mechanism that will increase the ability of the material to deform uniformly.

In-situ SEM investigation on stress-induced microstructure evolution of austenitic stainless steels subjected to cavitation erosion and cavitation erosion-corrosion

This study investigated the effect of stress on the microstructure evolution of austenitic stainless steels (316L SS and 304 SS) subjected to cavitation erosion and cavitation erosion-corrosion. Results show that continuous accumulation of stress of austenitic stainless steels at the early stage of cavitation erosion was observed from the samples tested in deionised water (DIW) but not in artificial seawater (ASW), which is due to stress release induced by ASW. In addition, a stress-induced phase transformation from austenite to martensite during the cavitation erosion tests in both DIW and ASW was observed in 304 SS, but not in 316 SS. Furthermore, primary cavitation craters formed during the cavitation erosion were not expanded directly but shrank first and then expanded due to re-accumulation of stress. More importantly, this study reports for the first time that pre-existing pores are not initiation points of cavitation erosion damage, possibly because of the ductility of austenitic stainless steels, which resulted in continuous shrinkage of the pores caused by the accumulated stress. Our findings provide new insights into understanding the failure mechanisms of austenitic stainless steels subjected to cavitation erosion, which will inform the development of high-performance cavitation erosion-resistant materials.

Effect of microstructural and environmental variables on ductility of austenitic stainless steels

Austenitic stainless steels are used extensively in harsh environments, including for high-pressure gaseous hydrogen service. However, the tensile ductility of this class of materials is very sensitive to materials and environmental variables. While tensile ductility is generally insufficient to qualify a material for hydrogen service, ductility is an effective tool to explore microstructural and environmental variables and their effects on hydrogen susceptibility, to inform understanding of the mechanisms of hydrogen effects in metals, and to provide insight to microstructural variables that may improve relative performance. In this study, hydrogen precharging was used to simulate high-pressure hydrogen environments to evaluate hydrogen effects on tensile properties. Several austenitic stainless steels were considered, including both metastable and stable alloys. Room temperature and subambient temperature tensile properties were evaluated with three different internal hydrogen contents for type 304L and 316L austenitic stainless steels and one hydrogen content for XM-11. Significant ductility loss was observed for both metastable and stable alloys, suggesting the stability of the austenitic phase is not sufficient to characterize the effects of hydrogen. Internal hydrogen does influence the character of deformation, which drives local damage accumulation and ultimately fracture for both metastable and stable alloys. While a quantitative description of hydrogen-assisted fracture in austenitic stainless steels remains elusive, these observations underscore the importance of the hydrogen-defect interactions and the accumulation of damage at deformation length scales.

Influence of hot forging and alloying with Al on the electrochemical behavior and mechanical properties of austenitic stainless steel

This paper introduces a new approach to overcome the deterioration of ductility of austenitic stainless steel (ASS) by Al alloying using vacuum induction furnace. The available data reported about the addition of Al to ASS shows that Al alloying increases the work-hardening property and deteriorates the ductility due to decreasing the austenite phase and increasing the ferrite phase. Therefore, austempering process was a vital stage to increase the austenite phase. The optimum conditions due to Al alloying have been determined. The promising samples were undergo corrosion tests using electrochemical impedance spectroscopy and cyclic voltammetry to investigate their performance and electrochemical behavior. Results showed that hot forging and alloying with Al improve the hardness and ductility but have an adverse effect on the pitting corrosion resistance.

Optimizing strength and ductility of austenitic stainless steels through equal-channel angular pressing and adding nitrogen element

Two austenitic stainless steels were processed by equal-channel angular pressing to systematically investigate the influences of alloying nitrogen and severe plastic deformation on the strength and ductility. With increasing the number of ECAP pass and adding nitrogen element, the density of deformation twins increased. It is shown that the two steels exhibit a similar general trend that the strength increases and the ductility decreases with increasing the deformation strain, but an enhanced strength–ductility synergy can be achieved by adding nitrogen element.

オーステナイト系ステンレス鋼の絞りに及ぼす水素および予き裂の影響(OS6-3 損傷評価・計測,OS6 エネルギー機器の維持管理と健全性評価)

オーステナイト系ステンレス鋼の絞りに及ぼす水素および予き裂の影響(OS6-3 損傷評価・計測,OS6 エネルギー機器の維持管理と健全性評価)

Residual and trace element effects on the high-temperature creep strength of austenitic stainless steels

The heat-to-heat variation in the creep strength and ductility of austenitic stainless steels was reviewed from the viewpoint of residual and trace element effects. Based on data reported in the literature, the creep strength of unstabilized alloys such as types 304 and 316 stainless steel increased with residual element and trace element content. Niobium appeared to be the most potent strengthener. There was no direct evidence that trace elements such as sulfur and phosphorus had a deleterious effect on either strength and ductility. It was assumed that the creep strength and ductility of the unstabilized grades of austenitic stainless steels are controlled by the precipitate characteristics. It follows from this that thermomechanical treatment or residual element additions that affect the precipitate characteristics influence subsequent time dependent mechanical properties. This view is consistant with most of the information in the literature. It was concluded that more systematic studies of trace and residual element effects would be beneficial to the improvement of steels. Incorporated into the studies should be quantitative characterization of evolving precipitate morphology and composition as they are influenced by residual elements. This information should be incorporated into modeling studies of non-equilibrium segregation. Ultimately, optimum elevated-temperature strength could be developed based on a materials science approach.

Effect of solidification mode on hot ductility of austenitic stainless steels

The effects of solidification mode and ferrite content on the hot ductility of austenitic stainless steels were investigated by means of hot bend testing. The test materials were continuously cast ...

The Tensile Ductility of Austenitic Steels in Air and Hydrogen

An empirical correlation of yield strength with reduction-in-area at fracture was demonstrated for austenitic stainless steel. The correlation is consistent with an existing fracture model that involves microvoid nucleation at isolated inclusions. Hydrogen effects on tensile ductility are also consistent with this model, if one assumes that hydrogen is transported by glide dislocations and that localized hydrogen accumulations lower the stress necessary to initiate fracture at particle-matrix interfaces. Smooth-bar tensile specimens of fourteen austenitic stainless steels were tested at room temperature in air, in 69-M Pa He, and in 69-M Pa H2. Macroscopic reductions-in-area at fracture varied between 12 and 82 percent, and yield strengths were between 179 and 1069 MN/m2. The resulting empirical correlation suggests that the ductility of austenitic stainless steels is limited by the interfacial stress required for microvoid nucleation and coalescence. For low strength steels, the required interfacial stress is reached only after extensive plastic deformation. However, as steel strength is increased, fracture occurs at lower strains.

Effect of Neutron Irradiation on the Ductility of Austenitic Stainless Steel

The effects of fast neutron irradiation on the tensile and creep-rupture ductility of austenitic stainless steels are presented. At low temperatures, below 450°C, radiation causes a reduction in th...

Reduction in Ductility of Austenitic Stainless Steel after Irradiation

RECENTLY it has been established that the reduction in ductility of austenitic stainless steel in the temperature range 650°–850° C after neutron irradiation is caused primarily by the thermal neutrons1,2. The decrease in ductility occurs in the non-uniform portion of the stress–strain curves and the fracture is intergranular2–5. The elevated temperature ductility cannot be recovered even by annealing for 0.5 h at temperatures above 1,000° C (refs. 4 and 6). Furthermore, the magnitude of the effect is associated with the boron-10 content of the steel7. It appears most probable, therefore, that one or both of the products of boron-10 (nα) lithium-7 transmutation are responsible for this effect. A mechanism, based on the presence of helium at the grain boundaries, has been suggested8 recently to explain the decrease in ductility and the tendency to intergranular fracture, and after some conditions of irradiation helium bubbles have been observed at the grain boundaries9, using transmission electron microscope techniques. However, neither the relative nor additive effects on the elevated temperature ductility is known for such small amounts of helium and lithium as those formed by the thermal neutron transformation of the boron-10 isotope present in the steel.

Increasing the ductility of austenitic stainless steels

Increasing the ductility of austenitic stainless steels

オーステナイト系ステンレス鋼の腐食疲労に関する研究 (第3報)

As repeated pre-stressing in air during the first stage, either overstressing at stress level 0.5 or 1kg/mm2 over the endurance limit with the cyclic repetition of 3.4×103 to 1.02×106, or understressing at stress level 1kg/mm2 below the endurance limit cycling from 1×106 to 7×107 was chosen, and followingly the specimen was exposed to air-saturated 5%H2SO4 at 25°C to which the repeated stress equivalent to prior endurance limit was applied during the second stage, until it was led to failure.In order to give prior corrosion, rotating specimen under stress-free condition was exposed to air-saturated 5% H2SO4 at 25°C for 1h to 100h as the first stage. After having drained out the acid after prior corrosion, the specimen was cleaned and dried, then was subjected to repeated stress in air as the second stage, and was led to failure.Secondary corrosion fatigue life in the second stage was slightly increased by primary overstressing in the first stage, but hardly any influence was given on secondary corrosion endurance by primary understressing in air. It was derived that, in view of these facts, endurance property conjoined with corrosion action was essentialy controlled by corrosion resisting property of metal within a given environment.Exposure to the aqueous acid solution as the first stage, gave no practical deterioration to the specimen in the following test in the second stage if repeated stress applied in this stage did not exceed prior endurance limit. However, if the repeated stress applied in this stage was beyond prior endurance limit, serious decrease of the fatigue strength at N cycles was exhibited by short time of prior corrosion, for some austenitic stainless steel, and the reverse was exhibited for some other austenitic stainless steel.It has been understood that this different tendency was presumably controlled by retained ductility of austenitic stainless steels, though corrosion resistance might be primary cause.