Mn Austenitic Steel Research Articles

Grain size dependence of ductile-to-brittle transition temperature of a high-nitrogen Cr–Mn austenitic steel

With decreasing grain size, the yield and tensile strengths increased without a loss in ductility and the upper-shelf energy was also improved. However, the reduction of grain size had no beneficial influence on lowering the ductile-to-brittle transition temperature because it promoted the increase of yield stress with decreasing temperature.

Kirkendall Void Formation During Selective Oxidation

The selective oxidation of high Mn austenitic steel was investigated by transmission electron microscopy. The annealing resulted in a MnO surface layer and a Mn-depleted ferritic layer. At the MnO/steel interface, voids were formed between the a-xMnO.SiO2 and c-MnO.Al2O3 layers. This is the first time that void formation is observed during selective oxidation of steel. The Kirkendall voids grow and develop characteristic void surfaces because of the fast diffusion of MnO on the void surface.

Effect of temperature and strain rate on strain hardening and deformation mechanisms of high manganese austenitic steels

Abstract The effect of temperature and strain rate on the mechanical properties of three Fe – Mn austenitic steels with Mn contents of 20 mass.% or above has been studied by tensile tests performed at strain rates ranging from 3 × 10−3 to 200s−1 and at temperatures between −160 and +140 °C. In these steels mechanical properties and strain hardening behaviour result from the competition between different deformation mechanisms including homogeneous or inhomogeneous dislocation glide, strain induced twinning or martensite formation. Thus, the microstructure evolution during deformation was investigated. For two of the steels, a relation of the deformation mechanisms (twinning and dislocation glide) at room temperature with the grain size was found. On the other hand, for the third steel at temperatures lower than 60 °C martensite is progressively formed during deformation. For the three steels, a decreasing volume fraction of twins or martensite with increasing testing temperature was found leading consequently to a decrease in flow stress and strain hardening.

Plastic Localization Phenomena in a Mn-Alloyed Austenitic Steel

A 0.5 wt pct C, 22 wt pct Mn austenitic steel, recently proposed for fabricating automotive body structures by cold sheet forming, exhibits plastic localizations (PLs) during uniaxial tensile tests, yet showing a favorable overall strength and ductility. No localization happens during biaxial Erichsen cupping tests. Full-thickness tensile and Erichsen specimens, cut from as-produced steel sheets, were polished and tested at different strain rates. During the tensile tests, the PL phenomena consist first of macroscopic deformation bands traveling along the tensile axis, and then of a series of successive stationary deformation bands, each adjacent to the preceding ones; both types of bands involve the full specimen width and yield a macroscopically observable surface relief. No comparable surface relief was observed during the standard Erichsen tests. Because the stress state is known to influence PL phenomena, reduced-width Erichsen tests were performed on polished sheet specimens, in order to explore the transition from biaxial to uniaxial loading; surface relief lines were observed on a 20-mm-wide specimen, but not on wider ones.

Low temperature physical properties of a high Mn austenitic steel JK2LB

High manganese austenitic stainless steel JK2LB is developed by the Japan Atomic Energy Agency for applications as a conduit material for superconducting cable-in-conduit conductors for the magnets of international thermonuclear experimental reactor (ITER). The low temperature physical property data of this material are very important to ITER magnet design. Therefore in this paper, our measurements of the physical properties including room temperature Young’s modulus and thermal expansion, magnetization, thermal conductivity, specific heat and resistivity at temperatures from room temperature down to 2 K are reported. We found that JK2LB is antiferromagnetic at low temperatures with a Néel temperature of 240 K. This is consistent with a prediction based on the chemical composition of the austenite stainless steel. The antiferromagnetic phase transition is also evident in the resistivity vs. T curve. Nevertheless, no anomalies are observable in its specific heat and thermal conductivity from 2 K to 300 K. The thermal expansion of this steel between 10 K and 300 K is about 0.22%. Its Young’s modulus, specific heat and thermal conductivity are comparable to that of 316LN stainless steel.

Conversion of the hot torsion test results into flow curve with multiple regimes of hardening

The method of Fields and Backofen has been commonly used to reduce the data obtained by hot torsion test into flow curves. The method, however, is most suitable for materials with monotonic strain hardening behaviour. Other methods such as Stüwe’s method, tubular specimens, differential testing and the inverse method, each suffer from similar drawbacks.It is shown in the current work that for materials with multiple regimes of hardening any method based on an assumption of constant hardening indices introduces some errors into the flow curve obtained from the hot torsion test. Therefore such methods do not enable accurate prediction of onset of recrystallisation where slow softening occurs.A new method to convert results from the hot torsion test into flow curves by taking into account the variation of constitutive parameters during deformation is presented. The method represents the torque twist data by a parametric linear least square model in which Euler and hyperbolic coefficients are used as the parameters. A closed form relationship obtained from the mathematical representation of the data is employed next for flow stress determination. Two different solution strategies, the method of normal equations and singular value decomposition, were used for parametric modelling of the data with hyperbolic basis functions. The performance of both methods is compared.Experimental data obtained by FHTTM, a flexible hot torsion test machine developed at IROST, for a C–Mn austenitic steel was used to demonstrate the method. The results were compared with those obtained using constant strain and strain rate hardening characteristics.

Effect of applied potential on the nature of surface film and SCC of a high Mn stainless steel in 1 M HCl

The Stress Corrosion Cracking (SCC) behavior of a high Mn austenitic stainless steel (SS) with 14.67 wt % Mn was studied in 1 M hydrochloric acid at room temperature as a function of potential. At open circuit potential (OCP) thick black surface film formation and a transgranular mode of cracking were observed. At all applied anodic potentials general dissolution and ductile cracking were observed. X-ray photoelectron spectroscopy (XPS) studies were conducted to characterise the surface films formed at different potentials. The nature of the surface film was found to be different with a change in potential. The nature of the film formed was found to govern the dissolution behavior and therefore the fracture morphology of the alloy.

An investigation of the tribological behaviour of a high-nitrogen Cr [sbnd]Mn austenitic stainless steel

The tribological behaviour of a novel high-nitrogen Cr Mn austenitic stainless steel (referred to as CrMnN-steel) has been investigated using dry abrasion, abrasion-corrosion, and cavitation erosion test techniques. The performance of CrMnN-steel has been compared to AISI 304 stainless steel and Hadfield manganese steel. Hadfield steel demonstrates the highest abrasion resistance, but CrMnN-steel is far superior when a corrosive environment is introduced. The cavitation erosiion resistance of CrMnN-steel in distilled water is greater than both AISI 304 and Hadfield steel.

Change in the properties of FeCrNi and FeCrMn austenitic steels under mixed and fast neutron irradiation

Detailed investigations are performed on mechanical properties, swelling and structure of different types of FeCrNi and FeCrMn austenitic stainless steels irradiated in the SM-2 high-flux research reactor and BOR-60 fast reactor. Steel irradiation temperatures are ranging from 100 up to 800°C and the maximum achieved level of damage doses is 60 dpa for FeCrMn steel (with 4–5% of Ni) and 30 dpa for steels of the C12Cr20MnWT type. Presented are dose dependencies of swelling and mechanical properties of FeCrNi and FeCrMn steels. It is shown that at temperatures below 530°C the investigated FeCrMn steel systems are less susceptible to swelling as compared to FeCrNi ones. FeCrMn steels showed a lower value of irradiation embrittlement after irradiation in the mixed spectrum at temperatures from 100 up to 400°C and much higher embrittlement after irradiation from 350 up to 400°C in the fast spectrum in comparison with FeCrNi steels. Higher hardening rate of FeCrMn steels after their irradiation in BOR-60 is attributed to the presence of dislocation loops and defects of high density in the structure. The structural change features in FeCrMn steels under irradiation are considered taking into account austenite stabilization in the initial state.

High Nitrogen Steels. Effect of Nitrogen, Carbon and Tungsten on High-temperature Oxidation of 12%Cr-15%Mn Austenitic Steel.

Oxidation behavior of Fe-12%Cr-15%Mn alloy has been studied in air at 773 to 973 K. The oxidation rate of the alloy was very low at 773 K, and the effect of each alloying element on the oxidation did not identified. At above 873 K, the oxidation behavior was affected by the ratio of N/C and tungsten content in the alloy; the increase of N/C and tungsten content increased oxidation resistance of the alloy. Results of EPMA showed that thin Fe-Cr nitride layer was formed adjacent to the alloy surface when the ratio of N/C was proper, which was useful to prevent the oxidation of alloy. It also showed that homogeneous mono layer oxide was formed on the W-containing alloy, whereas four layer oxide was formed on the W-free alloy. Beneficial effect of tungsten may be related to this homogenization action. Small addition of vanadium and titanium was also effective to improve the oxidation resistance of the alloy. It is confirmed that the oxide formed on the alloy with good oxidation resistance was mainly composed of (Mn, Cr)2O3.

Effects of nitride distribution on internal stress during high temperature deformation of 12%Cr–15%Mn austenitic steels

Many investigations on internal stress of various materials have been performed as the internal stress is considered to be an important factor to control high temperature deformation. The present authors have researched the effect of very fine and dense vanadium nitride (VN) precipitates on internal stress and effective stress which were measured by a strain dip test during high temperature creep of 12%Cr-15%Mn austenitic steels. In the present study, the authors have investigated the difference of the response to a strain dip test among the 12%Cr-15%Mn materials which are alloyed with small amounts of V, Ti and Ta and have different distributions of nitrides formed by an aging treatment, and have discussed the effect of nitride distribution on the interaction of dislocations with the precipitates.

Improvement of high temperature strength and low temperature toughness of high manganese-chromium austenitic steels

High Mn-Cr austenitic steels are still considered to be an important high temperature structural material from the point of view of fast-induced radioactivity decay (FIRD) and non-magneticity. The objective of the present study is to investigate the mechanical properties of 12% Cr-15% Mn austenitic stainless steels and to compare these properties with those of the reference materials of JPCAs and JFMS, which are being investigated for the development of fusion reactor structural materials in Japan. The effects of the alloying elements V, Ti, Ta, etc. were investigated to determine the improvement of mechanical properties. Tiny precipitates of VN and Ti(C, N) raised the high-temperature strength considerably. Content of 0.1 to 0.2% C, however, formed very coarse precipitates of M 23C 6 type carbide on the grain boundaries, which deteriorated low temperature toughness inducing intergranular fracture. Microstructural evolution during long-term aging was also investigated.

12%Cr-15%Mn鋼の高温クリープ変形中の内部応力に及ぼす微細析出物(VN)の影響

The objective of the present study is to investigate the effects of fine precipitates of vanadium nitride on the creep deformation behaviors of 12%Cr-15%Mn austenitic steels through the measurement of internal stress and effective stress. These stresses were obtained by strain dip tests. The internal stress of VN free materials was determined as a unique function of applied stress. On the other hand, that of VN containing materials was not obtained uniquely as a function of applied stress. This indicates that fine precipitates of VN with high number density are strong barriers for the dislocation motion in spite of wide range variation of stress applied on the dislocations. At lower applied stress, the change of deformation rate during the strain dip test of the VN containing materials was very small and could not be detected with the increase of deloaded stress. Consequently this means that the forward or backward motion of almost all dislocations were inhibited by the precipitates. At higher applied stress, the VN containing materials showed the decrease of deformation rate with the slight deloading during strain dip test. This means that there exist movable dislocations which can glide without being blocked by the precipitates. The difference of stress dependence of minimum creep rate between at lower applied stress and at higher one was considered to be caused by such interaction of the fine precipitates with dislocation motion.

Effect of Fine Vanadium Nitride Precipitates on Internal Stress during High-Temperature Creep of 12%Cr-15%Mn Steels

The objective of the present study is to investigate the effects of fine precipitates of vanadium nitride (VN) on the creep deformation behavior of 12%Cr-15%Mn austenitic steels through the measurement of internal stress and effective stress. These stresses are obtained by strain dip test. The internal stress of VN free materials was unequivocally determined as a function of applied stress. On the other hand, the change of deformation rate during the strain dip test of the VN containing materials was very small and could not be detected in a range of reduced applied stress. Consequently, the internal stress and effective stress of VN containing material showed a band range of values as a function of applied stress. This range indicates that fine and dense precipitates of VN become strong barriers to the dislocation motion in a wide variation of stresses worked on the dislocations. The temperature dependence of internal and effective stresses of the VN containing material was also clarified. The difference between the stress dependence of minimum creep rate at the lower applied stress and that at the higher one was also discussed to be caused by the behavior of internal and effective stresses

高クロム‐高マンガンの窒化速度の温度依存性異常

高クロム‐高マンガンの窒化速度の温度依存性異常

High Temperature Strength and Aging Behavior of 12%Cr-15%Mn Austenitic Steels

High Mn-Cr austenitic steels are still considered to be an important high temperature structural material from the point of view of reduced radio-activation. The objective of the present study is to make a fundamental research of mechanical properties and microstructure of 12%Cr-15%Mn austenitic steels. Especially the effects of alloying elements of V and Ti on the mechanical properties and microstructure evolution of high Mn-Cr steels were studied. Precipitation behaviors of carbides, nitrides and σ phase are investigated and their remarkable effects on the high temperature strength are found. The addition of V was very effective for strengthening the materials with the precipitation of fine VN. Ti was also found to be beneficial for the improvement of high temperature strength properties

High temperature strength of simple and solute-modified 10Cr30Mn austenitic steels

In order to develop potential reduced activation manganese-stabilized austenitic steels for use in the first wall component of a fusion reactor, tensile and high temperature creep properties have been investigated for simple and solute-modified 10%Cr30%Mn austenitic steels. The yield stress increased linearly with carbon concentration over the range from room temperature to 873 K. The creep-rupture strength at 873 K increased linearly with carbon concentration at short times, below 360 ks (100 h). The contribution of carbon to the increase in creep rupture strength decreased at high carbon concentrations, above 0.2%, and at long times, above 3600 ks (1000 h). A solute-modified 10Cr30Mn2W0.2Ti0.008B0.04P0.15C (wt%) steel exhibited very high tensile and creep rupture strength that were superior to those of type 316 steel.

Microstructural and mechanical characterization of new low-activation CrMn austenitic steels

Abstract On the basis of alloy design considerations, and aiming at the disposal by shallow land burial of the waste of fusion tokamak reactors (to be achieved by limiting the long-lived radioactivity of the first wall through the optimization of the composition of the conventional CrNi austenitic steels), the authors designed a series of new low-activation austenitic steels. The paper presents the results of the last stage of the development, concerning the microstructure and the tensile properties of these steels, which have been subject of extensive experimental characterization work.

12%Cr-15%Mnオーステナイト鋼の高温強度に及ぼすVとW添加の影響

12%Cr-15%Mnオーステナイト鋼の高温強度に及ぼすVとW添加の影響

Dislocation Pinning and Channeling in a Neutron-Irradiated 10 mass%Cr-30 mass%Mn Austenitic Steel

The deformation behavior of a 10 mass%Cr-30 mass%Mn-0.1 mass%C austenitic steel was investigated over the temperature range from room temperature to 873 K after neutron irradiation in JMTR at 573 K to a fast neutron fluence of 8.5×10 22 n/m 2 (E>1 MeV). A high density of irradiation-produced dislocation loops with the size of about 5 nm and 10-30 nm was observed. Irradiation caused an increase in yield stress with a prominent yield point and a decrease in total elongation near room temperature. These behaviors became diminished with increasing test temperature