SUS304 Austenitic Stainless Steel Research Articles

Martensitic transformation behaviour in sensitized SUS304 austenitic stainless steel during isothermal holding at low temperature

We investigated martensitic transformation behaviour in sensitized SUS304 austenitic stainless steel to determine the stability of the austenitic phase at low temperatures. We found that a specimen that was sensitized at 973 K for 100 h exhibits an isothermal martensitic transformation when the specimen is held in the temperature range between 60 and 260 K. We constructed a time-temperature-transformation (TTT) diagram corresponding to the formation of 0.5 vol. % α'-martensite. A magnetization measurement was used to evaluate the volume fraction of a'-martensite. The TTT diagram shows a double-C curve with two noses located at about 100 and 200 K. In-situ optical microscope observations reveal that the double C-curve is due to two different transformation sequences. That is, the upper part of the C-curve is due to a direct γ → α' martensitic transformation and the lower part of the C-curve is due to a successive γ → ψ → α' martensitic transformation. The direct γ → α' transformation occurs in the vicinity of grain boundaries while the successive γ → ψ' → α' transformation occurs near the centre of grains. A scanning electron microscope observation reveals that carbide particles of M23C6 are formed in the grain boundaries. The concentration difference between the centre of the grains and regions near grain boundaries is the reason for the difference in the isothermal transformation sequence for the sensitized SUS304 stainless steel.

Effect of interfacial reaction layer continuity on the tensile strength of resistance spot welded joints between aluminum alloy and steels

We have joined aluminum alloy A5052 to cold-rolled steel SPCC and austenitic stainless steel SUS304 using resistance spot welding. The interfacial microstructures have been observed using scanning electron microscopy and the tensile strength of the joints have been examined by cross tension testing. We have investigated the effect of interfacial reaction layer on the tensile strength of the joints based on the analyses of the fracture surfaces and the distribution of reaction layer thickness in the welding interface for two types of dissimilar materials joints. The results reveal that the tensile strength of joint is related to the fraction of discontinuous reaction layer.

Isothermal Martensitic Transformation in Sensitized SUS304 Austenitic Stainless Steel at Cryogenic Temperature

We have investigated martensitic transformation behavior in a sensitized SUS304 austenitic stainless steel to know the stability of the austenitic phase at cryogenic temperatures. We found that the sensitized specimen exhibits an isothermal martensitic transformation when the specimen is held in the temperature range between 60 and 260K. The time-temperature-transformation (TTT) diagram corresponding to the formation of 0.5 vol% of α'-martensite shows a double-C curve with two noses located at about 100 and 200 K. An in-situ optical microscope observation has revealed that the double C-curve is due to two different transformation sequences. That is, the upper part of the C-curve is attributed to the direct γ (fcc) → α' (bcc) martensitic transformation and the lower part of the C-curve is due to the successive γ (fcc) → e' (hcp) → α' (bcc) martensitic transformation. The direct γ → α' transformation occurs in the vicinity of grain boundaries, while the successive γ → e' → α' transformation occurs near the center of each grain. The reason for appearing two types of isothermal transformation sequence in the sensitized SUS304 stainless steel will be due to the difference in concentration by sensitization heat-treatment.

Effect of Nonproportional Loading on Creep-Fatigue Life of SUS304 Steel Subjected to CC-Type Combined Push-Pull Loading and Cyclic Torsion at 973K in Air

This paper investigates the applicability of the procedure proposed by one of the authors for estimating the nonproportional loading effect on PP test lives to the estimation of the creep-fatigue lives of SUS304 austenitic stainless steel subjected to nonproportionally combined push-pull and cyclic torsion under CC type strain waveform. Fully reversed strain-controlled CC tests were conducted on thin-walled tubular specimens of SUS304 steel at 973K in air under in-phase and 90deg out-of-phase straining conditions. The partitioned inelastic strain range versus life equations, Δecc versus Ncc relationships, obtained from three different proportional loading conditions, such as push-pull, cyclic torsion, and in-phase combined push-pull and cyclic torsion, are found to be correlated with one another by the multiaxiality factor. By using the multiaxiality modified Δepp versus Npp and Δecc versus Ncc relationships, the 90deg out-of-phase straining CC test lives were estimated by the proposed procedure, where the strain range partitioning was done by superposing the hysteresis loops of PP tests on those of CC tests. As the results, the estimated lives are found to agree well with the experimental lives in adopting the superposition method rather than the rapid loading method.

Interfacial microstructure and strength of steel/aluminum alloy joints welded by resistance spot welding with cover plate

We joined aluminum alloy A5052 to cold-rolled steel SPCC (Steel Plate Cold Commercial) and austenitic stainless steel SUS304 using resistance spot welding with a cover plate. The interfacial microstructure was observed using transmission electron microscopy. A thick two-layered reaction layer contains Fe 2Al 5 and FeAl 3 and a thin serration reaction layer contains Fe 2Al 5 and FeAl 3 were observed at the A5052/SPCC and A5052/SUS304 interface, respectively. Mechanical property analysis suggested that the reaction layer has no effect on the tensile shear strength of the A5052/SUS304 joint and that the tensile shear strength of the A5052/SPCC joint is influenced by the reaction layer formed at its interface.

Influence of microstructure on fracture toughness distribution in ceramic–metal functionally graded materials

This paper deals with the influence of microstructure on fracture toughness distribution in functionally graded materials (FGMs) consisting of partially stabilized zirconia (PSZ) and austenitic stainless steel SUS 304. FGMs and non-graded composites (non-FGMs) with fine and coarse microstructures are fabricated by powder metallurgy using PSZ and two kinds of SUS 304 powders. The fracture toughness is determined by conventional tests for several non-FGMs with each material composition and by a method utilizing stable crack growth in FGMs. The obtained results on the fracture toughness are as follows: (1) The fracture toughness increases with an increase in a content of SUS 304 on both FGMs and non-FGMs. (2) On the fracture toughness of the non-FGMs, the influence of microstructure is negligible. (3) On the FGMs, the fracture toughness is higher in the FGM with fine microstructure than in the FGM with coarse microstructure. (4) The fracture toughness of the FGMs is higher than that of the non-FGMs especially in the case of fine microstructure. Finally, the residual stress in the FGMs created in a fabrication process is estimated from the difference in fracture toughness between the FGMs and non-FGMs.

1247 SUS304鋼の軸ねじりPPおよびCC試験寿命におよぼす位相角の影響(G03-8 材料力学(8)疲労・強度1,21世紀地球環境革命の機械工学:人・マイクロナノ・エネルギー・環境)

The present paper investigates the effect of phase angle on the PP and CC test lives of SUS304 steel. The PP and CC type combined push-pull and cyclic torsion tests have been conducted on thin-walled tubular specimens of SUS304 austenitic stainless steel at 1023 K in air under in-phase and 30 to 90 deg out-of-phase conditions. The experimentally obtained lives are compared with those predicted by the new parameters, that have been derived based on both the Tresca and Mises type effective inelastic strain ranges starting from the inelastic-strain-based parameter previously proposed for 90 deg out-of-phase condition.

Fatigue Properties of DLC-Coated Stainless Steel

This study was conducted to investigate the effect of DLC (diamond-like carbon) coating on fatigue properties of austenitic stainless steel SUS304. For the DLC coating, UBMS (unbalanced magnetron sputtering) equipment was used. The generated surface layer of about 2 μm thickness was composed of both the DLC layer possessing high hardness and a very thin intermediate layer to improve adhesion force between the DLC layer and the substrate. DLC coating, which was carried out at a relatively low temperature, had no influence on the microstructure so that the mechanical properties of the stainless steel were unchanged by the coating. The results of the plane-bending fatigue test showed that the DLC coating improved fatigue strength by 18%. From the results of detailed observation conducted on the fatigue fracture surface, it was suggested that the improvement in fatigue strength resulted from the suppression of fatigue crack initiation due to the surface layer, which had high adhesion force and strength.

Evaluation of Fracture Toughness Distribution and Estimation of Residual Stress in Ceramic-Metal Functionally Graded Materials

This paper deals with evaluation of fracture toughness in functionally graded materials (FGMs) consisting of partially stabilized zirconia (PSZ) and austenitic stainless steel SUS 304. FGMs and non-graded composites (non-FGMs) with fine and coarse microstructures are fabricated by powder metallurgy using PSZ and two kinds of SUS 304 powders. The fracture toughness is determined by conventional tests for several non-FGMs with each material composition and by a method utilizing stable crack growth in FGMs. The obtained results on the fracture toughness are as follows : (1) The fracture toughness increases with an increase in a content of SUS 304 on both FGMs and non-FGMs. (2) On the fracture toughness of the non-FGMs, the influence of microstructure is negligible. (3) On the FGMs, the fracture toughness is higher in the FGM with fine microstructure than in the FGM with coarse microstructure. (4) The fracture toughness of the FGMs is higher than that of the non-FGMs especially in the case of fine microstructure. Finally, the residual stress in the FGMs created in the fabrication process is estimated from the difference in fracture toughness between the FGMs and non-FGMs.

Life Estimation of SUS304 Steel Subjected to Nonproportionally Combined Push-Pull and Cyclic Torsion at 973K

The present paper summarizes the fully reversed strain-controlled creep-fatigue tests conducted on thin-walled tubular specimens of SUS304 austenitic stainless steel at 973K in air under push-pull, cyclic torsion, in-phase straining and 90deg out-of-phase straining of push-pull and cyclic torsion. It is shown that, as the results of analysis of the experimental data by the strain-range partitioning methodand the critical plane model parameter, a new inelastic-strain based parameter was proposed for life estimation of SUS304 subject to nonproportionally combined push-pull and cyclic torsion by the strain-range partitioning method.

Evaluation of Fracture Toughness Distribution in Ceramic-Metal Functionally Graded Materials

This paper deals with evaluation of fracture toughness in functionally graded materials (FGMs) consisting of partially stabilized zirconia (PSZ) and austenitic stainless steel SUS 304. FGMs and non-graded composites (non-FGMs) with fine and coarse microstructures are fabricated by powder metallurgy using PSZ and two kinds of SUS 304 powders. The fracture toughness is determined by conventional tests for several non-FGMs with each material composition and by a method utilizing stable crack growth for FGMs. Based on the experimental results, fracture mechanism, influences of microstructure on fracture toughness, and difference in fracture toughness between the FGMs and non-FGMs has been discussed.

深冷加工と焼なましを施したＳＵＳ３１６Ｌの結晶粒微細化と高温変形挙動

Strain-induced martensitic transformation followed by reverse transformation is a possible process to achieve the grain refinement necessary for the superplasticity in austenitic stainless steel SUS304. This process is expected to be applicable also to SUS316L in which working at lower temperature is required for the strain-induced transformation. In this study, the transformation behavior of SUS316L during sub-zero working and annealing was investigated. The grain size of about 1 μm was obtained by the process of 90% sub-zero rolling at liquid nitrogen temperature followed by annealing at 973K for 3600 s. Furthermore, this process condition provided the total elongation of more than 300% and the strain-rate sensitivity index (m value) of 0.3 in the strain rate range from 1.8 to 3.2×10-4/s.

Effects of Magnetic Field and Deformation on Isothermal Martensitic Transformation in SUS304 and SUS304L Steels

Effects of external fields, such as temperature, magnetic field, stress and combination of these fields have been examined on martensitic transformation of SUS304 and SUS304L austenitic stainless steels. Following results are obtained: (i) No athermal martensitic transformation occurs in all the solution-treated and sensitized stainless steels. On the contrary, isothermal transformation occurs in the sensitized SUS304 (γ→α') between about 150K and 250 K. It also occurs in the solution-treated (γ→e'→α') and sensitized SUS304L (γ→e'→α' and γ→α') between about 80 K and 160 K. The γ-phase in all the steels exhibits an antiferromagnetic transition at about 40 K. (ii) Magnetic field-induced martensitic transformation dose not occur in austenitic state of the solution-treated and sensitized SUS304 and SUS304L even when the pulsed magnetic field of up to 30 MA/m is applied in a wide temperature range between 4.2 K and 290 K. On the other hand, the solution-treated and sensitized SUS304L containing isothermally-induced e' martensite exhibit magnetic field-induced e' to α ' transformation at 4.2 K and 77 K. (iii) Deformation-induced γ→e'→α' martensite transformation easily occurs at 77 K for all the solution-treated and sensitized stainless steels. (iv) Magnetic field-induced e'→α' transformation does not occur in the e' martensite induced beforehand by deformation in all the steels.

Effect of Multiaxial Stress State on High-Temperature Low-Cycle Fatigue Properties of SUS304 Steel

Fully reversed strain-controlled low-cycle fatigue tests, so called PP tests, were conducted on thin-walled tubular specimens of SUS304 austenitic stainless steel at 973K in air under proportional and nonproportinal loading conditions. Push-pull straining, cyclic torsion straining and in-phase straining of push-pull and cyclic torsion were selected as proportional loading, and 90deg out-of-phase straining of push-pull and cyclic torsion as nonproportional loading. Experimental data were analyzed by using both the Manson-Coffin equation and the critical plane model proposed by Brown and Miller, and the effects of the multiaxial stress state on the strain range versus life relationship were discussed. As the results, a new parameter was proposed that has a hopeful potential to estimate the effect of nonproportional loading on creep-fatigue life quantitatively based on the strain range partitioning method.

2427 SUS304鋼のクリープ疲労寿命におよぼす非比例負荷の影響について(S13-3 高温材料・構造の強度と破壊(3),S13 高温材料・構造の強度と破壊)

The present paper investigates the applicability of the procedure for the life prediction proposed by one of the authors to materials subjected to the PC- and CP-type 90 deg out-of-phase straining of push-pull and cyclic torsion as well as the effect of out-of-phase angle on the PP and CC test lives. The combined push-pull and cyclic torsion tests have been conducted on thin-walled tubular specimens of SUS304 austenitic stainless steel at 1023K in air under PP-, PC-, CP- and CC-type strain waveforms.

OS3-2-4 Non-destructive characterization of laser-peened materials with synchrotron radiation of SPring-8

Laser peening without coating (LPwC) is an emerging surface technology to enhance fatigue strength and prevent stress corrosion cracking (SCC) of metallic materials. LPwC was applied to SUS304 austenitic stainless steel and AC4CH cast aluminum alloy samples with a Q-switched and frequencydoubled Nd:YAG laser. Residual stress depth profile over the top surface of the SUS304 sample was precisely measured by a constant penetration depth (CPD) method, which is in the framework of the sin^2Ψ method and can strictly control the X-ray penetration depth into the sample material. By combining the CPD method with high energy X-ray of SPring-8, the depth profile was evaluated non-destructively before, during and after heat treatment up to 673 K (400 ℃). The residual stress in the top surface of the SUS304 sample is entirely compressive despite the direct irradiation of intense laser pulses on the material and the thermal loading. High-cycle fatigue testing was performed for AC4CH samples with and without LPwC, which demonstrated that LPwC significantly prolonged the fatigue life. Replication technique was applied to evaluate the propagation behavior of fatigue cracks on surface. Three-dimensional (3D) images of fatigue cracks were reconstructed by micro tomography (μCT) with phase contrast effect using highly parallelized coherent X-ray of SPring-8. The retardation of crack growth was confirmed in the material with LPwC in the images of μCT.

238 微小試験片によるステンレス鋼高圧水素ガス曝露材の強度特性評価(OS8-2 水素環境が金属強度特性に及ぼす影響,OS8 水素環境が金属強度特性に及ぼす影響)

Tensile and fatigue properties of stainless steels exposed to highly pressurized hydrogen gaseous environment are investigated using small specimen. The hydrogen content distribution in the small specimen is nearly uniform, because the thickness of the specimen is very small (0.3mm). Metastable austenitic stainless steel SUS304 and SUS304L show the degradation of tensile ductility and the fatigue life by exposure to hydrogen gas environment. Even stable austenitic stainless steel SUS316L shows the little degradation of the tensile ductility in the high hydrogen content range, but doesn't show the degradation of the fatigue life.

Study of Internal Finishing of Austenitic Stainless Steel Capillary Tubes by Magnetic Abrasive Finishing

This paper studies the internal finishing of capillary tubes using a magnetic abrasive finishing process. Such tubes are used with nanoscale technologies and meet the demands of the present age in medical and chemical equipment. The finishing characteristics are influenced by the magnetic abrasive behavior against the inner surface of the capillary, which is controlled by the supplied amount of magnetic abrasive and the magnetic force acting on it. The development of the finishing unit identifies the characteristics of the magnetic field, which controls the magnetic force, required for the necessary magnetic abrasive behavior. Finishing experiments using SUS304 austenitic stainless steel capillary tube with 800μm inner diameter demonstrate the effects of the supplied amount of the magnetic abrasive on the finishing characteristics, and the results suggest a standard method to determine the amount to achieve sufficient finishing. The run-out of the capillary while rotating at high speed under the cantilever tube support method causes instability of the magnetic abrasive behavior. The effects on the finishing characteristics are discussed, and a method to diminish the run-out is applied. Accordingly, this paper presents the conditions required for the internal finishing of capillary tubes and proposes methods to realize them. The internal finishing of 400μm inner diameter capillary tubes conveys an understanding of the mechanisms involved and demonstrates the usefulness of the proposed methods.

Development of Solid Nitriding Method Using Thermosetting Waste Plastic

In recent years, global warming and resource exhaustion problems require the manufacturers to minimize substances of environmental concern and industrial wastes and adopt measures for expedited recycling. As a result, making effective use of wastes to try for further energy conservation and high quality products is an important assignment in the heat treatment and surface hardening treatment fields as well. This study has investigated the effectiveness of waste melamine resin in solid nitriding of JIS SUS304 austenitic stainless steel plate. After heating the stainless plate in waste melamine resin fragments and cooling in air, the surface was analyzed. It was found that a nitrided layer had formed on the surface of the plate, and the nitriding potential of waste melamine was shown to be high. It is therefore likely that this method can be effectively applied to the development of economically advantageous high-performance materials and value-added products.

Numerical Calculation of Implanted Nitrogen Diffusion in SUS304 during Plasma-Based Ion Implantation

Two-dimensional temperature rising in an austenitic stainless steel SUS304 trench object with plasma-based ion implantation (PBII) was numerically simulated, where the thermal input on the surface of the trench structure was derived from the calculation of plasma sheath evolution. The difference in temperature distribution was a few Kelvin although the convex corner of the trench had a larger thermal flux than the concave corner. Using the calculated temporal evolution of object temperature, we numerically studied the diffusion of implanted nitrogen ions in the SUS304 trench surface heated by PBII. In addition, the formation of the expanded austenitic phase γ'N-Fe, which can enhance the hardness of the material, is discussed on the basis of the calculated depth profile of the implanted nitrogen.