The Tensile Ductility of Austenitic Steels in Air and Hydrogen

1977 ◽  
Vol 99 (2) ◽  
pp. 153-158 ◽  
Author(s):  
T. L. Capeletti ◽  
M. R. Louthan
Keyword(s):  
Stainless Steels ◽  
Room Temperature ◽  
Tensile Ductility ◽  
Austenitic Stainless Steels ◽  
Empirical Correlation ◽  
Interfacial Stress ◽  
Austenitic Steels ◽  
Steel Strength ◽  
Reduction In Area ◽  
Extensive Plastic Deformation

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.

Derivation of Design Fatigue Curves for Austenitic Stainless Steel Grades 1.4541 and 1.4550 Within the German Nuclear Safety Standard KTA 3201.2

2013 ◽  
Author(s):  
Xaver Schuler ◽  
Karl-Heinz Herter ◽  
Jürgen Rudolph
Keyword(s):  
Austenitic Stainless Steel ◽  
Stainless Steels ◽  
Room Temperature ◽  
Elevated Temperatures ◽  
Austenitic Stainless Steels ◽  
Nuclear Safety ◽  
Safety Standard ◽  
Fatigue Design ◽  
Steel Grades ◽  
Best Fit

Titanium and niobium stabilized austenitic stainless steels X6CrNiTi18-10S (material number 1.4541, correspondent to Alloy 321) respectively X6CrNiNb18-10S (material number 1.4550, correspondent to Alloy 347) are widely applied materials in German nuclear power plant components. Related requirements are defined in Nuclear Safety Standard KTA 3201.1. Fatigue design analysis is based on Nuclear Safety Standard KTA 3201.2. The fatigue design curve for austenitic stainless steels in the current valid edition of KTA 3201.2 is essentially identical with the design curve included in ASME-BPVC III, App I (ed. 2007, add. July 2008 respectively back editions). In the current code revision activities of KTA 3201.2 the compatibility of latest in air fatigue data for austenitic stainless steels with the above mentioned grades were examined in detail. The examinations were based on statistical evaluations of 149 strain controlled test data at room temperature and 129 data at elevated temperatures to derive best-fit mean data curves. Results of two additional load controlled test series (at room temperature and 288°C) in the high cycle regime were used to determine a technical endurance limit at 107 cycles. The related strain amplitudes were determined by consideration of the cyclic stress strain curve. The available fatigue data for the two austenitic materials at room temperature and elevated temperatures showed a clear temperature dependence in the high cycle regime demanding for two different best-fit curves. The correlation of the technical endurance limit(s) at room temperature and elevated temperatures with the ultimate strength of the materials is discussed. Design fatigue curves were derived by application of the well known factors to the best-fit curves. A factor of SN = 12 was applied to load cycles correspondent to the NUREG/CR-6909 approach covering influences of data scatter, surface roughness, size and sequence. In terms of strain respectively stress amplitudes in the high cycle regime, for elevated temperatures (>80°C) a factor of Sσ = 1.79 was applied considering and combining in detail the partial influences of data scatter surface roughness, size and mean stress. For room temperature a factor of Sσ = 1.88 shall be applied. As a result, new design fatigue curves for austenitic stainless steel grades 1.4541 and 1.4550 will be available within the German Nuclear Safety Standard KTA 3201.2. The fatigue design rules for all other austenitic stainless steel grades will be based on the new ASME-BPVC III, App I (ed. 2010) design curve.

Proposal of Fatigue Life Equations for Carbon and Low-Alloy Steels and Austenitic Stainless Steels as a Function of Tensile Strength

2013 ◽  
Author(s):  
Hiroshi Kanasaki ◽  
Makoto Higuchi ◽  
Seiji Asada ◽  
Munehiro Yasuda ◽  
Takehiko Sera
Keyword(s):  
Tensile Strength ◽  
Fatigue Life ◽  
Stainless Steels ◽  
Room Temperature ◽  
Austenitic Stainless Steels ◽  
Low Alloy Steels ◽  
Strength Based ◽  
Fatigue Data ◽  
Current Design ◽  
Alloy Steels

Fatigue life equations for carbon & low-alloy steels and also austenitic stainless steels are proposed as a function of their tensile strength based on large number of fatigue data tested in air at RT to high temperature. The proposed equations give a very good estimation of fatigue life for the steels of varying tensile strength. These results indicate that the current design fatigue curves may be overly conservative at the tensile strength level of 550 MPa for carbon & low-alloy steels. As for austenitic stainless steels, the proposed fatigue life equation is applicable at room temperature to 430 °C and gives more accurate prediction compared to the previously proposed equation which is not function of temperature and tensile strength.

Application of Physical Simulation for Developing New Steel Types

2008 ◽  
Vol 575-578 ◽  
pp. 1002-1007 ◽  
Author(s):  
L. Pentti Karjalainen ◽  
Mahesh C. Somani ◽  
Atef S. Hamada
Keyword(s):  
Mechanical Properties ◽  
Stainless Steels ◽  
Physical Simulation ◽  
Austenitic Stainless Steels ◽  
High Strength ◽  
Carbon Steels ◽  
Austenitic Steels ◽  
Low Carbon ◽  
Modelling Studies ◽  
Electron Microscopes

Processing of a large number of novel steel types, such as DP, TRIP, CP and TWIP, and high-strength low-carbon bainitic and martensitic DQ-T steels, have been developed based on physical simulation and modelling studies. Among stainless steels, guidelines for processing of ultra-fine grained austenitic stainless steels have been created. Physical simulation has been used by employing a Gleeble thermo-mechanical simulator to reveal the phenomena occurring in the hot rolling stage (the flow resistance, recrystallization kinetics and microstructure evolution), and in the cooling stage (CCT diagrams) for carbon steels and in short-term annealing of cold rolled metastable austenitic steels. Connecting these data with microstructures examined in optical and electron microscopes and resultant mechanical properties have improved the understanding on complex phenomena occurring in the processing of these steels and the role of numerous process variables in the optimization of enhanced mechanical properties.

Effects of External and Internal Hydrogen on Tensile Properties of Austenitic Stainless Steels Containing Additive Elements

2015 ◽  
Author(s):  
Hisatake Itoga ◽  
Hisao Matsunaga ◽  
Junichiro Yamabe ◽  
Saburo Matsuoka
Keyword(s):  
Stainless Steels ◽  
Room Temperature ◽  
Austenitic Stainless Steels ◽  
Hydrogen Gas ◽  
Nitrogen Gas ◽  
Material Compatibility ◽  
Internal Hydrogen ◽  
The Stability ◽  
Reduction Of Area ◽  
Nickel Equivalent

Effect of hydrogen on the slow strain rate tensile (SSRT) properties of five types of austenitic stainless steels, which contain small amounts of additive elements (e.g., nitrogen, niobium, vanadium and titanium), was studied. Some specimens were charged by exposing them to 100 MPa hydrogen gas at 543 K for 200 hours. The SSRT tests were carried out under various combinations of specimens and test atmospheres as follows: (i) non-charged specimens tested in air at room temperature (RT), (ii) non-charged specimens tested in 0.1 MPa nitrogen gas at 193 K, (iii) hydrogen-charged specimens tested in air at RT, (iv) hydrogen-charged specimens tested in 0.1 MPa nitrogen gas at 193 K, and (v) non-charged specimens tested in 115 MPa hydrogen gas at RT. In the tests without hydrogen (i.e., cases (i) and (ii)), the reduction of area (RA) was nearly constant in all the materials, regardless of test temperature. In contrast, in the tests of internal hydrogen (cases (iii) and (iv)), RA was much smaller at 193 K than at RT in all the materials. It was revealed that the susceptibility of the materials to hydrogen embrittlement (HE) can successfully be estimated in terms of the nickel equivalent, which represents the stability of austenite phase. The result suggested that the nickel equivalent can be used for evaluating the material compatibility of austenitic stainless steels for hydrogen service.

scholarly journals A positron annihilation study of defect accumulation in phosphorus- and titanium-alloyed austenitic stainless steels under electron irradiation at room temperature

2020 ◽  
pp. 27-34
Author(s):  
D. A. Perminov ◽  
Keyword(s):  
Positron Annihilation ◽  
Electron Irradiation ◽  
Stainless Steels ◽  
Room Temperature ◽  
Austenitic Stainless Steels ◽  
Positron Annihilation Spectroscopy ◽  
High Concentration ◽  
Noticeable Effect ◽  
Vacancy Defects ◽  
Positron Annihilation Study

The effect of phosphorus and titanium additions on the accumulation of vacancy defects in Cr16Ni15Mo3 austenitic stainless steels under electron irradiation at room temperature is studied by positron annihilation spectroscopy. It is shown that, at this temperature, phosphorus has no noticeable effect on the accumulation of vacancy defects. This is due to the low mobility of vacancies and the low concentration of impurities. Titanium, due to its high concentration, enhances the accumulation of vacancy defects during irradiation, but this effect is weak.

A TEM/STEM and APFIM study of nitrogen distribution in inert-gas-atomized type 304 stainless steels

1994 ◽  
Vol 52 ◽  
pp. 960-961
Author(s):  
M. Zhou ◽  
T. F. Kelly ◽  
J. E. Flinn
Keyword(s):  
Stainless Steels ◽  
Austenitic Stainless Steels ◽  
Strengthening Mechanism ◽  
Austenitic Steels ◽  
Alloying Element ◽  
Atomic Size ◽  
High Toughness ◽  
Mechanical And Physical Properties ◽  
Interstitial Nitrogen ◽  
Type 304

The attraction of austenitic stainless steels lies in the combination of their mechanical and physical properties and corrosion resistance. However, a major disappointment is their relatively low strength. Over the years, continued efforts have been made to try to improve the strength of conventionally processed austenitic steels without sacrificing other properties. Using nitrogen as an alloying element can very effectively increase the strength of austenitic stainless steels while maintaining a high toughness. Improved resistance to intergranular corrosion and longer creep-to-rupture time1 werealso reported among nitrogen-containing austenitic steels. Though there is little doubt that interstitial nitrogen is responsible for the improved mechanical properties, the strengthening mechanism by nitrogen can not be explained successfully in a “conventional sense”, i.e. despite its smaller atomic size, nitrogen was found to increase the yield strength at 4K more than carbon does by a factor of about 2. One reason for the lack of understanding of nitrogen strengthening mechanism is because of thedifficulty of detecting low atomic number elements as well as possible short range order that may exist between interstitial and substitutional atoms.

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