Stainless steels austenitics

Stainless steel, austenitic IS Cr S Ni types 0 2 0 3 < 400 Wronglit, cast, clad Good Good 90 9.6 AlSl type 304 ASTM corrosion- and heat-resisting steels stabHi2ed or LC types used for welding... 

A preliminary approach to the selection of the stainless steel for a specific application is to classify the various types according to the alloy content, microstructure, and major characteristic. Table 3 outlines the information according to the classes of stainless steels-austenitic, martensitic, and ferritic. Table 4 presents characteristics and typical applications of various types of stainless steel while Table 5 indicates resistance of stainless steels to oxidation in air. 

Stainless steel, austenitic 3 3 4 <400 Wrought, cast Cood Good 90 9.4 ACI CH-7M good resistance to sulfuric, phosphoric, and fatly... 

No Attraction Commercially pure nonferrous metals (except nickel and cobalt) Copper-nickels Hastelloys, Inconels, Incoloys Stainless steels austenitic, austenitic precipitation hardening Stellite... 

Environment Aluminum alloys Carbon steels Copper alloys Nickel alloys Stainless steels Austenitic Duplex Martensitic Titanium Zirconium alloys alloys... 

There are four main classes of stainless steel (austenitic, ferritic, ferritic-austenitic (duplex) and martensitic), and within these, a variety of different grades. The names ferritic and austenitic follow from their structures ferrite (P-Fe) and austenite (y-Fe) lattices hosting the alloying elements. The presence of Cr promotes the formation of the ferrite structure, while the austenite lattice forms when Ni is introduced. While ferritic and martensitic stainless steels are magnetic, austenitic stainless steel is non-magnetic. Further additives to some stainless steels are molybdenum (which improves corrosion resistance) and nitrogen (which adds strength and improves corrosion resistance). 

Stainless Steel. Austenitic stainless steels of the AISI 300 series are well suited for low temperature service by their strength and impact resistance properties. They are easy to weld, have a low heat conductivity and require no stress relief. Partially offsetting these factors is their higher cost. The commonly-used analyses of stainless steel are available in thin wall piping schedules 5S and lOS as well as in the normal schedules. Thinner walls are allowable for stainless steel because it is not subject to corrosion. All of its thickness is available for strength. 

FERRITIC (Fe-Cr) STAINLESS STEELS AUSTENITIC (Fe-Ni-Cr) STAINLESS STEELS... 

Superabrasive tools, primarily PCBN, have been used to successfully weld ferritic steels, ferritic stainless steels, austenitic stainless steels, nickel-base superalloys. Invar, and Narloy-Z. Attempts to weld titanium with PCBN tools have been inconclusive. Tool life of 80 m (260 ft) has been demonstrated in FSW of 1018 steel, and very low tool wear has been reported on all other alloys. The primary concern in tool life continues to be fracture, and developments in PCBN grades continue to improve the fracture toughness of the FSW tools. The PCBN tools provide an extremely smooth finish when used for FSW or FSP. 

Figure 9.10 shows the micrographs of a martensitic stainless steel, austenitic stainless steels, and duplex stainless steels [11]. 

Speidel, M. O., High Nitrogen Stainless Steels Austenitic, Duplex and Martensitic," Stainless Steels 87, The Institute of Metals, 1988. 

Use of CRA is competitive with inhibition in deep, high-pressure wells, particularly in those locations where inhibitor supply may be a space and logistic problem. CRA includes stainless steels (austenitic, ferritic, martensitic, and duplex), nickel-based alloys, cobalt-based alloys, and titanium alloys. Economics is a major factor in alloy selection. The 13 Cr tubing has often been used in gas wells for low H2S wells. Tubing materials selection for a deep well could involve price increments between alloys of 1 to 3 million. High-strength CRA is used to minimize costs. SMYS values of 150 ksi (1000 MPa) are common. The CRA is often cold-worked to achieve the required yield strength. 

Although the duplex stainless steels (austenitic-ferritic steels) have been known since 1940, they did not find wide application until 1975. This is somewhat surprising because this alloy family has a number of interesting properties. The microstracture of duplex stainless steels consists of the two phases austenite and ferrite (50% of each). This microstructure combines good corrosion behavior with interesting strength properties. 

Theoretically, the stability of austenite (which is the predominant phase at room temperature in the 300 series stainless steels) must refer to thermodynamic stability. Austenite at room temperature in most 300 series stainless steels is metastable and becomes unstable at lower temperatures in some stainless steels. Austenite can react to its unstable thermodynamic position in several ways, but in the 300 series stainless steels it evidently reacts only in one way, i,e, a brittle martensite phase is formed. Thus, specifically, instability in this paper refers to the tendency of austenite to transform to martensite. 

Conunon base metals include cast iron, low-carbon steel, medium-carbon steel, alloy steel (including tool and bearing steels), stainless steel (austenitic, martensitic, or ferritic), aluminum alloys, titanium alloys or other nonferrous metals, for example, bronzes, copper, and brasses. 

Higher veloeities than those mentioned above may, however, he required to provide a uniform and constant oxygen content in fluids, which is needed for formation of protective films on active/passive metals and those metals that are susceptable to pitting, e.g. stainless steel (austenitic — minimum 152 cm/s (5 ft/s) required). Monel, aluminum alloys, etc. 

Stainless steel, austenitic (vacuum technology) A non-magnetic, non-dispersion-hardenable stainless steel composed mainly of austenite (gamma iron with carbon in solution), stabilized by nickel. See also Stainless steel, martinsitic. 

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