High Strength Austenitic Stainless Steel Research Articles

SSRT and Fatigue Crack Growth Properties of Two Types of High Strength Austenitic Stainless Steels in High Pressure Hydrogen Gas

SSRT and Fatigue Crack Growth Properties of Two Types of High Strength Austenitic Stainless Steels in High Pressure Hydrogen Gas

OS2105 高圧水素ガス中における高強度オーステナイト系ステンレス鋼のSSRT特性

OS2105 高圧水素ガス中における高強度オーステナイト系ステンレス鋼のSSRT特性

高P含有オーステナイト系ステンレス耐熱鋼の凝固割れに関する検討

New 18-8 high strength austenitic stainless steel with 0.1%P-0.2%Ti-0.2%Nb for super-heater and re-heater tubes in ultra-super critical power plants has been developed using the precipitation hardening of fine intragranular precipitates such as globular M23C6 carbides, MC type carbides and needle like FeTiP distributed inside grain. The solidification cracking susceptibility of the new 18-8 heat resistance steel was investigated by varying the Creq/Nieq and phosphorus amount. It was clarified that the solidification cracking susceptibility of new 18-8 heat resistance steel decreased by increasing Creq/Nieq to increase the amount of δ ferrite crystallization and promote the progress of welding solidification by (Nb,Ti)C crystallization in terms of microsegregation behavior using the numerical model.

OS0612 高強度ステンレス鋼の超音波腐食疲労挙動(OS6-3 材質および熱処理の影響,OS-6 金属材料の超高サイクル疲労と信頼性評価)

Ultrasonic corrosion fatigue tests were conducted for high strength stainless steels such as YUS270, SUS304N2 and SUS329 in 3%NaCl aqueous solution. The reduction of corrosion fatigue strength at 10^9 cycles for YUS270 and SUS304N2 was not observed at all, while the reduction of giga-cycle corrosion fatigue strength was 12.5% for SUS329. Corrosion pit was observed on corrosion fatigue crack initiation area. Striation was predominantly observed on crack propagation area both in air and in 3% NaCl aqueous solution. It can be concluded that the reduction of corrosion fatigue strength of 2.5%Mo containing high strength austenitic stainless steels is due to the corrosion pit formation at corrosion fatigue crack initiation area.

Microstructure and mechanical performance of resistance spot-welded cold-rolled high strength austenitic stainless steel

The microstructure, fracture and fatigue behavior of spot welds were characterized. The results showed that the improper welding parameters easily caused folding interface in HAZ between welded-sheets. Overload failure modes were interfacial fractures even if nugget diameters satisfied d > 5 t . The failure deformation introduced 29.8–32.7 (v.%) α′-martensite transformation at interfacial fractures. The hardness under the interfacial fracture surface was more than two times of that in the nugget. Fatigue specimens cracked through-thickness sheets. The stress concentration led to the actual stress exceeding the shear strength of annealed austenite in HAZ, and shear bands initiated under very low nominal stress. Fatigue cracks initiated 0.3–0.4 and 1.2–1.3 mm away from the nugget edge for spot-welded 1.5 and 4 mm sheets respectively. There was no detectable strain induced α′-martensite at fatigue fractures. The influence of the folding interface on fatigue performances depended on the folding location. When the folding coincided with the location of maximum stress concentration, it would exacerbate the stress concentration and reduce the fatigue limit remarkably. However, if the folding located outside the area of maximum stress concentration, while still the crack initiated at the interface fold, it did not reduce the fatigue limit significantly.

Corrosion fatigue crack initiation behavior of stainless steels

Corrosion fatigue crack initiation behavior of various kinds of stainless steels is reviewed mainly on the basis of the author’s experimental results. The role of corrosion pit in the corrosion fatigue crack initiation process of martensitic, ferritic, austenitic, duplex and precipitation-hardening stainless steels is briefly summarized. The recent investigation of an electrochemical noise measurement method is demonstrated for 12%Cr martensitic stainless steel and 2.5%Mo containing high strength austenitic stainless steels. Finally a couple of future problems to be solved in corrosion fatigue crack initiation are touched on briefly.

Experimental and numerical investigation of high strength stainless steel structures

The paper summarises research on high strength stainless steel tubular structures conducted at the University of Hong Kong, and the Hong Kong University of Science and Technology. Square and rectangular hollow sections were investigated. The test specimens were cold-rolled from high strength austenitic and duplex stainless steel sheets. The material properties of the test specimens were determined by tensile coupon tests at normal room and elevated temperatures. The initial geometric imperfection and residual stress of the specimens were measured. The experimental and numerical investigation focused on the design and behaviour of cold-formed high strength stainless steel structural members. The results were compared with design strengths calculated using the American, Australian/New Zealand and European specifications for cold-formed stainless steel structures.

High-strength austenitic stainless steel

Based on the studies of carbon and nitrogen effects on the electron structure, short-range atomic order, and thermodynamic stability of iron solid solutions, a physical concept for alloying steels with carbon and nitrogen is proposed. The concept is used for the design of a cost-effective austenitic corrosion-resistant steel of super-high strength and fracture toughness.

Experimental Investigation of Cold-Formed High-Strength Stainless Steel Tubular Members Subjected to Combined Bending and Web Crippling

This paper presents a test program on cold-formed stainless steel tubular sections subjected to combined bending and web crippling. A series of tests was performed on square and rectangular hollow sections fabricated by cold-rolling from high strength material of duplex and high strength austenitic stainless steel sheets. The concentrated load was applied by means of a bearing plate which acted across the full flange width of the section. The flanges of the hollow section specimens were not fastened to the bearing plates during testing. The specimens were tested using the interior-one-flange loading condition specified in the American Specification and Australian/New Zealand Standard (AS/NZS) for cold-formed stainless steel structures. Different specimen lengths were tested to obtain the interaction relationship between moment and concentrated load. The combined bending and web crippling test results were compared with the design strengths obtained using the current American Specification and AS/NZS for cold-formed stainless steel structures. Generally, it is shown that the American Specification and AS/NZS Standard conservatively predicted the strengths of cold-formed high strength stainless steel square and rectangular hollow sections subjected to combined bending and web crippling.

Structural design of high-strength austenitic stainless steel

Efficient use of material is an important factor in achieving economical and sustainable structures. Typically, annealed austenitic stainless steel has a material strength of around 220 N/mm 2, somewhat lower than that of common structural carbon steel grades. This lower strength, coupled with the higher material cost, puts stainless steel at a significant disadvantage when considering material selection, despite its other desirable properties. However, the strength of stainless steel may, at relatively low expense, be considerably enhanced through modification of the chemical composition and through the process of cold working due to the strain hardening nature of the material. This strength enhancement has not generally been utilised in practice due to a lack of knowledge on the structural behaviour of this high-strength material. Given the high material cost of stainless steel, the need to optimise the efficiency of design methods and to develop the performance, availability and diversity of the current product range is clear. To this end, this paper describes tests, numerical modelling and the development of design guidance for high-strength stainless-steel members in a range of structural configurations. Material tensile tests, member tests in compression and member tests in bending have been described. The results of the tests have been successfully replicated numerically, and subsequent sensitivity studies and parametric studies have been performed. Test and numerical results have been compared against two design methods developed for standard-strength material (Eurocode 3 Part 1.4 and the deformation capacity based design method). The comparisons have revealed that both design methods provide a similar level of reliability to that offered for standard-strength material, and thus, extension of both design methods to the high-strength grades has been recommended.

Behavior of Cold-Formed High Strength Stainless Steel Sections

This paper presents the behavior of cold-formed high strength stainless steel sections. The test specimens were cold-rolled from flat strips of duplex and high strength austenitic stainless steel. The material properties of high strength stainless steel square and rectangular hollow sections were determined. Tensile coupons at different locations in cross section were tested. Hence, the distributions of 0.2% proof stress and tensile strength measured in the cross section of cold-formed high strength stainless steel sections were plotted. The material properties of the complete cross section in the cold-worked state were also obtained from stub column tests. Detailed measurements of initial local geometric imperfections of the sections were obtained. The initial local plate imperfection profiles were plotted. Residual stress measurements of the high strength stainless steel sections were also conducted. The membrane and bending residual stress distributions in the cross section of the specimens were obtained. Furthermore, the stub column test strengths were compared with the design strengths.

Properties of weldments in high-strength ferritic heat-resistant steels

In recent years, the preservation of natural resources and the reduction of the pressure on the environment have become important tasks. In fossil-fuelled power plants, efforts have been made to improve the efficiency in electricity generation by raising the temperature and pressure of steam. The main conditions for the steam used with the ultra-super critical pressure (USC) boiler of the most recent design in Japan have reached 600°C and 31 MPa. To realise these steam conditions, it is essential to use materials with excellent high-temperature creep strength in the areas subjected to the highest temperature, such as steam and heat conduction pipes. It is not an exaggeration to say that these conditions had not been achievable until high-strength ferritic steels and austenitic stainless steels were developed.1 Incidentally, in pressure-resistant sections of a boiler like the above-mentioned pipes are welded structures of a large scale, and hence, not only base materials but also the properties of weldments affect the life and reliability of pressure-resistant sections. This article deals with the properties required for welded joints of high-strength ferritic heat-resistant steels which have been used for the most recently designed boilers for fossil power plants. It also describes the creep strength properties at the most important joints and the issues of welding consumables for high-strength materials, together with future tasks.

Filler Metal Selection for Welding a High Nitrogen Stainless Steel

Cromanite is a high-strength austenitic stainless steel that contains approximately 19% chromium, 10% manganese, and 0.5% nitrogen. It can be welded successfully, but due to the high nitrogen content of the base metal, precautions have to be taken to ensure sound welds with the desired combination of properties. Although no matching filler metals are currently available, Cromanite can be welded using a range of commercially available stainless steel welding consumables. E307 stainless steel, the filler metal currently recommended for joining Cromanite, produces welds with mechanical properties that are generally inferior to those of the base metal. In wear applications, these lower strength welds would probably be acceptable, but in applications where full use is made of the high strength of Cromanite, welds with matching strength levels would be required. In this investigation, two welding consumables, ER2209 (a duplex austenitic-ferritic stainless steel) and 15CrMn (an austenitic-manganese hardfacing wire), were evaluated as substitutes for E307. When used to join Cromanite, 15CrMn produced welds displaying severe nitrogen-induced porosity, and this consumable is therefore not recommended. ER2209, however, outperformed E307, producing sound porosity-free welds with excellent mechanical properties, including high ductility and strength levels exceeding the minimum limits specified for Cromanite.

Concept of a new high-strength austenitic stainless steel

The concept of combined addition of C and N, as persued in previous work on martensitic steels, is transferred to austenitic stainless steels in order to gain highest phase stability. Thermodynamic calculations with special respect to the influence of temperature and interstitial content (C, N or C + N) were studied in the FeCrMnNC-system. Promising compositions like Fe-13Cr-17Mn and Fe-13Cr-21Mn revealed an extended austenitic phase field. Some appropriate alloys were investigated with regard to their microscopic and electron structure. The concentration of free electrons in the austenite as the origin of phase stabilitiy increased in the order of C, N, C + N being added. Thus, the metallic character of interatomic bonding is enhanced, which entails short range atomic order. Hence, the substitutional alloy content can be minimized.

Analysis of the problems in spot welding AISI 301 high-strength austenitic stainless steels and galvanized steel plates

A study was carried out in order to evaluate the possible problems linked to spot welding of galvanized steel plates and high-strength austenitic stainless steels (AISI 301). Testpieces were made by joining two edges of galvanized plate by an AISI 301 steel plate. These testpieces were loaded at approx. 50% of σ0.2 of the stainless steel. Two steels of the same type but of different origin and supply were used: the first (steel A) was sensitised and sometimes failed, even after a few days; the second (steel B) was solution-treated and did not fail. Besides the fracture morphologies, the microstructures of the two stainless steels, the welding defects and the presence in the steels of hydrogen from the galvanized plate during fusion of the spot weld were discussed.

Overview: high-nitrogen alloying of stainless steels

High-strength austenitic stainless steels can be produced by replacing carbon with nitrogen. Nitrogen has greater solid-solubility than carbon, is a strong austenite stabilizer, potent interstitial solid-solution strengthener, and improves pitting corrosion resistance. Although the solubility of nitrogen in liquid iron is very low, 0.045 wt.% at 1600 °C and atmospheric pressure, nitrogen levels above 1 wt.% can be obtained through alloying and specialized high-pressure melting techniques. An austenitic stainless steel should be considered “high-nitrogen” if it contains more nitrogen than can be retained in the material by processing at atmospheric pressure; for most alloys, this limit is approximately 0.4 wt.%. This article describes melting and processing technologies applicable to high-nitrogen steels and the effects of interstitial nitrogen on a variety of material properties. Thermal stability, nitride precipitation kinetics, and the effects of nitride formation on mechanical properties and corrosion resistance are discussed.

Microstructure and mechanical properties of 18 mass% chromium cast stainless steel for marine propeller: Ono, S., Saito, M. and Matsuo, S. J. Jpn. Inst. Met. (July 1993) 57 (7), 761–766

High-strength austenitic stainless steels can be produced by replacing carbon with nitrogen. Nitrogen has greater solid-solubility than carbon, is a strong austenite stabilizer, potent interstitial solid-solution strengthener, and improves pitting corrosion resistance. Although the solubility of nitrogen in liquid iron is very low, 0.045 wt.% at 1600 °C and atmospheric pressure, nitrogen levels above 1 wt.% can be obtained through alloying and specialized high-pressure melting techniques. An austenitic stainless steel should be considered “high-nitrogen” if it contains more nitrogen than can be retained in the material by processing at atmospheric pressure; for most alloys, this limit is approximately 0.4 wt.%. This article describes melting and processing technologies applicable to high-nitrogen steels and the effects of interstitial nitrogen on a variety of material properties. Thermal stability, nitride precipitation kinetics, and the effects of nitride formation on mechanical properties and corrosion resistance are discussed.

Scaling of Austenitic Stainless Steels and Nickel-Base Alloys in High-Temperature Steam at 973 K

Abstract Scaling of commercial high-strength austenitic stainless steels and nickel-base alloys, possible candidates for ultra-supercritical (USC) boiler-tube materials, was studied in atmospheric ...

加工熱処理による高強度ステンレス鋼の開発

加工熱処理による高強度ステンレス鋼の開発

Thermomechanical Control Process for High Strength Austenitic Stainless Steel Plates

Thermomechanical Control Process for High Strength Austenitic Stainless Steel Plates