JP2008545889A - Austenitic stainless steel - Google Patents

Abstract

  Specific examples of austenitic stainless steels are in weight percent based on the total weight of the steel: 0.05-0.2 carbon; 0.08-0.2 nitrogen; 20-23 chromium; 25-27 Includes nickel; 1-2 molybdenum; more than 1.5 to 4.0 manganese; 0.20 to 0.75 niobium; up to 0.1 titanium; iron; and incidental impurities. Certain other embodiments of austenitic stainless steel are in weight percent, based on the total weight of the steel: 0.05 to 0.2 carbon; 0.08 to 0.2 nitrogen; 20 to 23 chromium; 25-27 nickel; 1-2 molybdenum; up to 4.0 manganese; 0.20-0.75 niobium; at least one of 0.1 or less titanium and 0.1 or less aluminum; iron As well as incidental impurities.

Description

Federally Assisted Research or Development Statement This study is partly part of the US Department of Energy contract no. Funded under DE-FC02-00CH11062.

  The present disclosure relates to austenitic stainless steel. In particular, the present disclosure relates to austenitic stainless steels having improved creep resistance and / or improved corrosion resistance when exposed to high temperature environments.

Hot air provides a particularly corrosive environment. More aggressive corrosion conditions can occur if significant water vapor is present.
The combination of hot air and considerable water vapor is used in heat generators such as gas turbines, steam turbines, and fuel cells, and in heat exchangers that handle the gas flow used or generated by such energy generators and It is common in recovery heat exchangers as well as in equipment for processing, processing or extracting chemicals or minerals at high temperatures. Accordingly, parts of such devices that are exposed to these conditions have been manufactured from a variety of austenitic stainless steels.

  In order to improve corrosion resistance, austenitic stainless steels contain various combinations of chromium, nickel, manganese, and other alloy additives. Nevertheless, stainless steel and certain other chromium-bearing heat-resistant alloys are susceptible to attack in hot air and hot air containing water vapor. This attack takes two different forms. Low alloy content stainless steels such as AISI type 304 (nominally 18 wt.% Chromium and 8 wt.% Nickel, the rest iron) have the disadvantage of accelerated oxidation in the presence of steam. The slowly growing chromium oxide film is replaced by a thick scale composed of rapidly growing mixed iron and chromium oxide. The result is rapid metal consumption due to the conversion to oxides. High alloy content materials such as superferritic iron-chromium stainless steel and nickel-chromium superalloy do not appear to be affected by this form of attack but are exposed to water vapor. It has been observed to have the disadvantage of weight loss during. The oxide formed on the surface of some of the high alloy content materials is very pure chromium oxide and is susceptible to evaporation due to the formation of volatile chromium oxyhydroxide. The result of this evaporation loss of chromium to the atmosphere is an unusually high level of chromium depletion in the metal substrate, which can result in a loss of high temperature oxidation resistance. The transition between the aforementioned corrosion states is relatively complex, and aspects of both states are observed in some alloys.

  In addition to corrosion, articles and parts in high temperature environments may have the disadvantage of creep. Creep is an undesired plastic deformation of an alloy that is held for a long time at a stress lower than the normal yield strength. Thus, creep is, for example, in energy generating equipment and related equipment, and for high temperature processing, processing or extraction of chemicals or minerals, or for high temperature processing or processing of alloys. In equipment and components, certain structural components and other components that are subject to high stresses and high temperatures may be affected. In such applications, it is often desirable to form parts from materials that have substantial resistance to corrosion in high temperature environments and that have substantial creep resistance.

  Manganese, an alloying element, has been shown to play a role in reducing the effects of chromium oxide evaporation. Many stainless steel standards contain manganese at a level limited to 2% by weight or less, and there is no minimum level required. Manganese in these steels is not an intentional alloy additive, but rather is included in the steel as an incidental component derived from scrap starting materials. One austenitic stainless steel adapted for use in high temperature, high water vapor content environments, including considerable tolerance for accidental manganese, is NF709 alloy. NF709 alloy is available from Nippon Steel Corporation in a form that includes seamless tubing for boiler applications. The composition of NF709 alloy provided in Nippon Steel's publication "Quality and Properties of NF709 Austenitic Stainless Steel for Boiler Tubing Applications" is shown in Table 1. The published composition specifies a manganese limit of 1.5% by weight and there is no specified minimum. According to various published reports of research on this alloy, a typical industrial manganese content is about 1% by weight. Certain other austenitic stainless steels are also shown in Table 1. Element concentrations throughout this description are weight percent based on total gold weight unless otherwise noted. “NS” in Table 1 indicates that a particular UNS standard does not specify a concentration for the element.

  With reference to Table 1, basic AISI type 201 stainless steel is similar to standard 18 chrome-8 nickel stainless steel, but with a small amount of nickel replaced with manganese to reduce alloy costs. In general, Type 201 alloys do not have sufficient creep and oxidation resistance for use at high temperatures. Higher alloying materials such as the Nitronic® family of alloys, the Esshete 1250 alloy, and the 21-6-9 alloy (UNS S21900) have low nickel levels (about 11 wt% max) and significant manganese levels (5-10 wt%), typically designed for high creep strength and moderate environmental resistance. Commercial heat resistant stainless steels such as AISI types 309S and 310S generally contain manganese at levels up to about 2% by weight. Such alloys are somewhat inadequate in terms of metallurgical stability, which means that the ratio of nickel to chromium in these two grades results in the formation of significant amounts of brittle phases at typical service temperatures. As long as it brings, it may be related to the basic composition.

  It would be advantageous to provide an austenitic stainless steel having improved high temperature creep resistance and / or resistance to corrosive attack in hot air and / or in hot air containing significant levels of water vapor. Seem. For example, stainless steels that exhibit substantial corrosion resistance in hot air containing steam include, for example, gas turbines, steam turbines, and fuel cells that are exposed to highly corrosive, high temperature, high steam content environments, for example, It may be advantageously used in parts of energy generators. Such parts include heat exchangers, recovered heat exchangers, tubing, pipes, and certain structural parts. Alloys that exhibit substantial corrosion resistance in hot air may also be advantageously applied in high temperature processing, processing, or extraction of chemicals or minerals, or in specific equipment for high temperature processing or processing of alloys. Good. Stainless steels that exhibit both substantial high temperature creep resistance as well as considerable corrosion resistance can be advantageously adapted for use in the components of the aforementioned devices that are exposed to high stresses.

  According to the present disclosure, an austenitic stainless steel is provided that has improved high temperature creep resistance and / or improved resistance to corrosion when exposed to a hot air environment. As used herein, “high temperature” refers to temperatures above about 100 ° F. (about 37.8 ° C.). According to one aspect of the present disclosure, 0.05-0.2 carbon; 0.08-0.2 nitrogen; 20-23 chromium; 25-27 nickel; 1-2 molybdenum; An austenitic stainless steel is provided that contains more than ˜4.0 manganese; 0.20-0.75 niobium; up to 0.1 titanium; iron; and incidental impurities. In certain non-limiting embodiments, the manganese content of the steel is at least 1.6 up to 4.0 wt%. Also, in certain non-limiting embodiments, the austenitic stainless steel further includes one or more of the following elements: greater than 0 to 0.50 silicon; greater than 0 to 0.30 aluminum; Greater than 0 to 0.02 sulfur; greater than 0 to 0.05 phosphorus; greater than 0 to 0.1 zirconium; and greater than 0 to 0.1 vanadium. According to certain non-limiting embodiments, the titanium and / or aluminum content of the steel is not more than 0.1% by weight.

  As used herein, regardless of the lower limit, the use of “up to” includes the absence of the referenced element. Also, “below” as used herein in relation to titanium and aluminum content includes the lack of such elements.

  According to another aspect of the present disclosure, 0.05-0.2 carbon; 0.08-0.2 nitrogen; 20-23 chromium; 25-27 nickel; 1-2 molybdenum; More than 5 to 4.0 manganese; 0.20 to 0.75 niobium; up to 0.1 titanium; up to 0.50 silicon; up to 0.30 aluminum; up to 0.02 Provided are austenitic stainless steels containing sulfur; up to 0.05 phosphorus; up to 0.1 zirconium; up to 0.1 vanadium; iron; and accidental impurities. In certain non-limiting embodiments, the manganese content of the steel is at least 1.6 up to 4.0 wt%. Also, according to certain non-limiting specific examples, the titanium and / or aluminum content of the steel is 0.1% by weight or less.

  According to yet another aspect of the present disclosure, an austenitic stainless steel consisting essentially of: 0.05 to 0.2 carbon; 0.08 to 0.2 nitrogen; 20 to 23 chromium; 25-27 nickel; 1-2 molybdenum; more than 1.5-4.0 manganese; 0.20-0.75 niobium; up to 0.1 titanium; up to 0.50 Up to 0.30 aluminum; up to 0.02 sulfur; up to 0.05 phosphorus; up to 0.05 zirconium; up to 0.1 vanadium; iron; and accidental impurities. According to certain non-limiting embodiments, the manganese content of the steel is at least 1.6 up to 4.0% by weight.

  According to still further aspects of the present disclosure, 0.05-0.2 carbon; 0.08-0.2 nitrogen; 20-23 chromium; 25-27 nickel; 1-2 molybdenum; More than 5 to 4.0 manganese; 0.20 to 0.75 niobium; up to 0.1 titanium; up to 0.50 silicon; up to 0.30 aluminum; up to 0.02 An austenitic stainless steel comprising sulfur; up to 0.05 phosphorus; up to 0.1 zirconium; up to 0.1 vanadium; iron; and incidental impurities is provided. In certain non-limiting embodiments of steel, the manganese content of the steel is at least 1.6 up to 4.0 wt%.

  Another aspect of the present disclosure is in weight percent, based on the total weight of the steel: 0.05 to 0.2 carbon; 0.08 to 0.2 nitrogen; 20 to 23 chromium; 25 to 27 nickel. 1 to 2 molybdenum; up to 4.0 manganese; 0.20 to 0.75 niobium; at least one of 0.1 or less titanium and 0.1 or less aluminum; iron; and accidental The present invention relates to an austenitic stainless steel containing impurities.

  Further aspects of the present disclosure include, by weight based on the total weight of the steel: 0.05 to 0.2 carbon; 0.08 to 0.2 nitrogen; 20 to 23 chromium; 25 to 27 nickel; 1 to 2 molybdenum; up to 4.0 manganese; 0.20 to 0.75 niobium; at least one of 0.1 or less titanium and 0.1 or less aluminum; up to 0.50 Up to 0.02 sulfur; up to 0.05 phosphorus; up to 0.1 zirconium; up to 0.1 vanadium; iron; and austenitic stainless steels consisting essentially of incidental impurities About. In certain non-limiting embodiments, the steel contains at least 1.5 to up to 4.0 weight percent manganese, while in other embodiments, the steel is from 1.6 to up to 4.0 weight percent. Containing manganese.

  A still further aspect of the present disclosure includes, in weight percent, based on the total weight of the steel: 0.05 to 0.2 carbon; 0.08 to 0.2 nitrogen; 20 to 23 chromium; 25 to 27 nickel. 1 to 2 molybdenum; up to 4.0 manganese; 0.20 to 0.75 niobium; at least one of 0.1 or less titanium and 0.1 or less aluminum; up to 0.50 Up to 0.02 sulfur; up to 0.05 phosphorus; up to 0.1 zirconium; up to 0.1 vanadium; iron; and austenitic stainless steels consisting of incidental impurities. In certain non-limiting embodiments, the steel contains at least 1.5 to up to 4.0 weight percent manganese, while in other embodiments, the steel is from 1.6 to up to 4.0 weight percent. Containing manganese.

  According to yet another aspect of the invention, an article of manufacture comprising an austenitic stainless steel having a composition according to the present disclosure is provided. Non-limiting examples of articles of manufacture include, for example, energy generating devices and parts of such devices. For example, the article of manufacture may be selected from gas turbines, steam turbines, fuel cells, heat exchangers, recovered heat exchangers, tubes, pipes, structural components, and other components for any of those devices. Other examples of articles of manufacture include piping, tubing, and other parts for equipment or equipment for high temperature processing, processing, or extraction of chemicals and minerals, or for high temperature processing or processing of alloys. Including.

  The reader will appreciate the foregoing details as well as others by considering the following detailed description of specific non-limiting embodiments within the scope of this disclosure. In addition, the reader will appreciate additional advantages and details by evaluating or using alloys and articles of manufacture within the scope of this disclosure.

  The features and advantages of the alloys and articles described herein may be better understood with reference to the accompanying drawings.

  All numbers representing the amounts of ingredients, processing conditions and the like used in this description and in the claims are modified by the term “about” in all cases, except in the working examples or where indicated otherwise. It should be understood that Thus, unless stated otherwise, any numerical parameters set forth in the following description and appended claims are approximations that may vary depending on the properties desired to be obtained in the alloys and articles according to the present disclosure. . At least, and not trying to limit the application of the doctrine of equivalents to the claims, each numeric parameter should be interpreted at least by considering the number of significant figures reported and applying normal rounding techniques is there.

  Although the numerical ranges and parameters describing the broad scope of this disclosure are approximations, the numerical values set forth in any particular example are reported as accurately as possible. Any numerical value, however, inherently contains certain errors necessarily resulting from the standard deviation found in their respective testing measurements, eg, instrument and / or operator error. It should also be understood that any numerical range recited herein is intended to include the boundaries of the ranges subsumed therein and all subranges. For example, a range of “1-10” is intended to include all sub-ranges between (and including) the stated minimum value 1 and the stated maximum value 10, ie one or more minimums Value and a maximum value of 10 or less.

  Any patents, publications, or other disclosure materials mentioned to be cited herein for reference are, in whole or in part, the existing definitions, statements, or others that the cited material states in this disclosure. To the extent that they are not inconsistent with the disclosed material. Thus, and to the extent necessary, the present disclosure described herein replaces any conflicting material cited herein for reference. Any material, or part of it, that is described herein by reference for reference but contradicts the existing definitions, statements, or other disclosure materials set forth in this specification is not They are quoted only to the extent that there is no discrepancy with the material.

  As explained above, certain austenitic stainless steels have been used in articles and parts that are exposed to hot air or hot air containing significant water vapor. Parts exposed to such conditions include, for example, energy generators such as gas turbines, steam turbines, and fuel cells, and heat exchangers and recovery heat exchangers, and high temperature processing, processing, or processing of chemicals or minerals Includes affected parts in equipment and parts for extraction or high temperature processing or processing of alloys. However, these steels still have the disadvantage of a certain level of corrosive attack when exposed to these conditions for a period of time. Accordingly, the inventors have sought to determine whether certain modified austenitic stainless steel chemistries will further improve the corrosion resistance in high temperature environments. As described further below, the inventors have determined that alloys containing up to 1.5 wt.% Manganese suffer from oxide scale evaporation followed by degradation in air containing water vapor. Our work has, in part, focused on the chemistry of certain new austenitic stainless steels that contain greater than 1.5 weight percent manganese with significant levels of chromium and nickel. As a result of the study, the inventors have found that austenitic stainless steels having a broad composition, more preferably the nominal compositions listed in Table 2, are used in hot air environments and in hot air environments containing water vapor. It was concluded that it would have substantial resistance to chromium oxide scale evaporation. The manganese content of the proposed alloy was controlled at a minimum level and this was found to significantly improve resistance to hot corrosive attack.

  Table 3 provides information on some alloys evaluated during the test. All heat was melted and subsequently rolled into a foil gauge. Heats 1 and 3 were laboratory heats, heat 2 was made as a pilot coil, and heat 4 was a plant heat made as a production coil. Heats 1, 3, and 4 were made with a target of 1.0 wt% manganese, and heat 2 was made with a target of 1.6 wt% manganese.

  A comparison of the 1.6 and 1.0 wt% manganese (nominal) varieties listed in Table 3 as Heat 2 and 4 respectively shows that the lower manganese version is oxidized in humidified air, especially at higher temperatures. It was shown to be much more susceptible to object scale evaporation. This can result in significant environmental attacks over time. The test was conducted as follows.

Samples were exposed to humid air in the temperature range of 1300-1500 ° F. (704-815 ° C.). As shown in FIG. 1, both the high manganese sample (about 1.6 wt% manganese, heat 2) and the low manganese sample (about 1.0 wt% manganese, heat 3) were 1300 ° F (704 ° C). ) Showed similar oxidation kinetics in terms of weight change (mg / cm ² ) over time when exposed to air containing 10% water vapor. Low manganese samples generally showed slightly lower weight gain and had somewhat irregular behavior.

  FIG. 2 shows the time for samples of high manganese (heat 2) and low manganese (heat 4) alloys when the samples were exposed to air containing 1% steam at 1400 ° F. (760 ° C.). It shows the change in weight over time. Samples showed very different oxidation kinetics under these conditions. The high manganese sample gained weight rapidly during the first part of the test, but then the weight gain slowed down considerably. After completion of the 5,000 hour test, the two samples showed essentially the same weight gain.

  FIG. 3 shows the time for high manganese (heat 2) and low manganese (heat 4) alloy samples when the samples were exposed to air containing 1500% F (815 ° C.) and 7% water vapor. It shows the change in weight over time. The curve shows that the lower manganese sample showed significant oxide scale evaporation during the test time. The higher manganese alloy did not show the same weight change over the limited test exposure.

  Samples subjected to 5,000 hours of total exposure under the conditions of 1300 ° F. (704 °) and 1400 ° F. (760 ° C.) were mounted, polished and examined. The oxide scale formed on the surface of the high manganese sample appeared to be thin and dense with essentially no features. The low manganese variant showed void formation below the scale after exposure to humid air at 1300 ° F. (704 °). The oxide scale above these voids shown in FIG. 4a was slightly thicker than the scale elsewhere. Scattered oxide nodules were present on the surface of low manganese samples exposed to 1400 ° F. (760 ° C.) in humid air. An example of a nodule is shown in FIG. Many small “emerging” nodules appeared to be in the process of disrupting the oxide scale.

  Samples were also examined under magnification after exposure to 1500 ° F. (815 ° C.) air containing water vapor. After about 3,000 hours, small nodules of mixed oxide were observed to form in the oxide scale on the surface of the low manganese (about 1.0 wt% manganese, heat 4) sample. The low manganese sample was again examined under magnification after about 8,000 hours of exposure and the oxide nodules were found to have grown considerably in size. A high manganese (about 1.6 wt.% Manganese, heat 2) sample was examined in about 3,500 hours and no nodules were observed in the oxide scale.

Using microanalysis in a scanning electron microscope (SEM), the general compositional composition of the oxide scale was studied. The scale was relatively thin (2-3 microns), which made it difficult to obtain a detailed composition profile. Measurements were generally limited to sites near the scale / alloy interface and near the scale / gas interface. The high manganese alloy (Heat 2) was observed to exhibit much greater manganese segregation from alloy to scale. See FIG. 5, which is the MnO pair determined for several samples using X-ray energy dispersive spectroscopy (XEDS) (semi-quantitative) in SEM at the scale / alloy interface and the scale / gas interface. The oxide composition measured as the molar ratio of Cr ₂ O ₃ is plotted. Low manganese materials do not exhibit manganese saturation (ie, MnO / Cr ₂ O ₃ ratio 1.0) at 1300 ° F. (704 ° C.) at the scale / gas interface and saturate on the boundary at 1400 ° F. (760 ° C.) (Borderline saturated). Achieving manganese saturation in the spinel is considered important in providing resistance to evaporation.

  Level of chromium depletion in the underlying metal after exposure to hot air containing water vapor using the same technique (quantified using XEDS in SEM, no standard and standard based methods) And the degree was determined. FIG. 6 shows into the sample surface for high manganese and low manganese samples from heats 2 and 4, respectively, exposed to air containing 10% water vapor at 1300 ° F. (704 ° C.) for 5,000 hours. Plot chromium concentration as a function of depth. The observed depletion for the low manganese sample is much greater in terms of chromium concentration directly adjacent to the scale / metal interface. The depth of wear between samples does not appear to be significantly different. The chromium profile obtained from each sample appears to be very sharp, indicating that chromium cannot diffuse quickly from the interior of the sample to the scale / alloy interface.

  FIG. 7 shows that high and low manganese samples exposed to air containing 7% water vapor at 1400 ° F. (760 ° C.) for 5,000 hours, into the sample surface for heats 2 and 4, respectively. Figure 6 is a plot of chromium concentration as a function of depth. Similar to FIG. 6, the chromium depletion for the low manganese sample was significantly greater than for the high manganese sample at the scale / metal interface. The effect of chromium depletion at 1400 ° F. (760 ° C.) is substantially less than that shown in FIG. 6 in terms of terminal chromium content at the scale / alloy interface, but the slope shown in FIG. It was observed to go much deeper into the substrate. This may have occurred because the diffusion of chromium in the metal was fast enough at 1400 ° F. (760 ° C.) to delocalize the effects of chromium depletion due to oxidation.

FIG. 8 shows MnO vs. Cr ₂ using XEDS (semi-quantitative) in SEM for high manganese and low manganese samples obtained from heats 2 and 4, respectively, exposed to hot air containing 7% water vapor. is a graph showing an oxide composition, measured as a molar ratio of O _3. Measurements were taken at the scale / alloy interface and the scale / gas interface. Evaluations made after exposure to air at 1300 ° F. (704 ° C.) and 1400 ° F. (760 ° C.) were made after an exposure time of about 5,000 hours. What was done after exposure at 1500 ° F. (815 ° C.) was performed after an exposure time of about 3,000 hours. The low manganese material does not exhibit manganese saturation (ie, MnO / Cr ₂ O ₃ ratio 1.0) at 1300 ° F. (704 ° C.) and 1500 ° F. (815 ° C.) at the scale / gas interface. Saturated on the boundary line at (760 ° C.).

  A higher manganese alloy heat set was made to evaluate how oxidation resistance responded to further increased manganese levels. Table 4 shows the chemical composition of additional heats referred to as heats 5 and 6.

  FIG. 9 shows heat 2 (1.61 wt% manganese), heat 5 (2.04 wt% manganese), exposed to air containing 1% steam at 1400 ° F. (760 ° C.), and FIG. 4 is a plot of the change in weight of a sample over time for a sample of heat 6 (3.82 wt% manganese) alloy. The results show that higher manganese levels result in higher initial weight gain due to oxide scale formation. Although the weight gain shown in FIG. 9 did not appear to be problematic, higher manganese levels above about 4% by weight would lead to undesirable results resulting from further scale formation and weight gain, as well as material fracture. It is believed that

  Additional heats 7-11 in Table 5 were made. The heat contained less than 0.1 wt% titanium. Heats 7, 8 and 11 also contained less than 0.1% aluminum by weight.

  As discussed above, austenitic stainless steel that has been subjected to stress at high temperatures for extended periods of time can undergo creep. Most austenitic stainless steels contain relatively low levels of titanium and aluminum to promote the deoxidation of the molten metal during melting and casting. These elements also precipitate as nitrides and possibly as a solid state intermetallic phase. Such precipitated phases are very difficult or infeasible to dissolve during processing. Excessive nitridation will have the effect of reducing the level of nitrogen in the solid solution, which will reduce the creep strength of the alloy. Nitride and intermetallic phases can also make processing more difficult, especially when formed by bending or stamping steel into part shapes.

  Thus, to improve the creep strength and formability of alloys during bending, stamping, and similar mechanical processing steps, the preferred chemistry for the austenitic stainless steel of the present disclosure is 0.1 weight. % At least one of titanium and 0.1% by weight aluminum. More preferably, in order to better improve creep resistance and formability, the austenitic stainless steel of the present disclosure contains 0.1 wt% or less of titanium and 0.1 wt% or less of aluminum.

  Based on the above, austenitic stainless steels with investigated chemistry and containing manganese at a level of more than 1.5% up to about 4% by weight without the disadvantages of excessive scale formation and crushing It should show advantageous resistance to high temperature attacks in the air, which may contain significant water vapor. In particular, the broad and nominal alloy compositions shown in Table 2 are proposed as austenitic stainless steels that have substantial resistance to corrosive attack in hot air and in hot air containing water vapor. Preferred manganese levels are at least 1.6 to up to about 4 wt%, more preferred manganese levels are at least 1.6 to up to about 2.0 wt% manganese.

  Additional proposed alloy chemistries with improved creep resistance and improved formability have the general chemistry shown in Table 2, but no more than 0.1 wt% titanium and / or 0.1 wt% % Aluminum is contained. The expected improvement in creep resistance resulting from limitations on titanium and / or aluminum content is not necessarily provided by controlling the manganese content in the range from more than 1.5 wt% up to about 4 wt%. Not associated with improved high temperature corrosion resistance. Rather, the manganese content of the alloys proposed herein with improved creep resistance and formability may be at any level up to about 4.0% by weight. Thus, the alloys in Table 6 below should exhibit advantageous creep resistance and formability properties, with preferred chemistry containing no more than 0.1 wt% titanium and no more than 0.1 wt% aluminum.

  An alloy that exhibits advantageous high temperature creep resistance, improved formability, and advantageous resistance to corrosive attack in hot air containing water vapor would have the composition shown in Table 6, where manganese The content is greater than 1.5 to up to about 4.0% by weight, preferably at least 1.6 to up to about 4.0% by weight, more preferably at least 1.6 to up to about 2. The composition is further controlled to be up to 0% by weight. Such alloys produce, for example, the structural parts and other parts of the energy generators referred to above, as well as processing, processing or extraction devices that are both exposed to stress and hot air containing water vapor. May be advantageously applied.

Any limitation regarding the chemistry of the austenitic stainless steel proposed herein, established to better ensure substantial resistance to creep, is that the ratio of niobium to carbon in the alloy is: :
0.7 <0.13 (niobium / carbon) ≦ 1.0,
[Wherein the niobium and carbon contents are expressed in atomic percent. ]
Is to satisfy.

  The heat of the novel corrosion resistant austenitic stainless steel disclosed herein may be produced by conventional means, for example by conventional techniques of vacuum melting scrap and other feed materials. The resulting heat may be processed into billets, slabs, plates, coils, sheets, and other intermediate articles by conventional techniques and then further processed into final manufactured articles. The improved formability of embodiments of alloys within the scope of the present disclosure that contain no more than 0.1 wt.% Titanium and / or no more than 0.1 wt. It allows flat mill products (eg strips, sheets, plates, coils, and the like) formed from alloys to be made. This property of the alloy is an advantage over the NF709 alloy, which has more limited formability and is generally only processed by extrusion into a seamless pipe.

  The novel austenitic stainless steels according to the present disclosure may be used in any suitable application and environment, but the alloys are used in equipment and components that are exposed to high temperatures or both high temperatures and significant water vapor for extended periods of time. Especially suitable for. For example, the creep resistance and / or high temperature corrosion resistance of the alloys disclosed herein may include: high temperature processing, processing, or extraction of chemicals or minerals, or equipment adapted for high temperature processing or processing of alloys. Pipes, pipes, structural parts, and other parts; energy generators such as gas turbines, steam turbines, and fuel cell pipes, pipes, structural parts, and other parts; and used by energy generators Or make it particularly suitable for use in heat exchangers, recovery heat exchangers, and other equipment components that handle the gas stream generated. Other uses for the alloys disclosed herein will be apparent to those skilled in the art upon reviewing the present description of the alloys.

  While the foregoing description has inevitably provided a limited number of embodiments of the present invention, those skilled in the art will understand the compositions of the examples described and shown herein to illustrate the nature of the present invention. Various other changes in this and other details can be made by those skilled in the art, and all such modifications remain within the principles and scope of the invention as expressed herein and in the appended claims. I understand that. Also, those skilled in the art will appreciate that changes may be made to the above specific examples without departing from the broad inventive concept. Accordingly, it is to be understood that the invention is not intended to be limited to the particular embodiments disclosed, but is intended to encompass modifications within the principles and scope of the invention as defined by the claims. .

FIG. 5 is a plot of weight change over time for an alloy sample exposed to air containing 1% water vapor at 1300 ° F. (704 ° C.). FIG. 4 is a plot of weight change over time for an alloy sample exposed to air containing 1% steam at 1400 ° F. (760 ° C.). FIG. 5 is a plot of weight change over time for an alloy sample exposed to air containing 1500% F (815 ° C.) and 7% water vapor. FIG. 4A is a photomicrograph of an oxide scale formed on the surface of an alloy sample exposed to a high temperature environment containing water vapor.

FIG. 4B is a photomicrograph of oxide scale formed on the surface of the alloy sample exposed to a high temperature environment containing water vapor.
4 is a graph of oxide composition measured as a molar ratio of MnO to Cr ₂ O ₃ for some alloys exposed to high temperature environments including water vapor. Figure 2 is a plot of the chromium content of two alloy samples as a function of depth into the sample. Figure 2 is a plot of the chromium content of two alloy samples as a function of depth into the sample. FIG. 5 is a graph of oxide composition measured as a molar ratio of MnO to Cr ₂ O ₃ for high and low manganese samples exposed to high temperature environments containing 7% water vapor. FIG. 6 is a plot of weight change over time for an alloy sample exposed to air containing 1% water vapor at 1400 ° F. (760 ° C.).

Claims (39)

  Austenitic stainless steel, in weight percentages based on the total weight of the steel: 0.05 to 0.2 carbon; 0.08 to 0.2 nitrogen; 20 to 23 chromium; 25 to 27 Austenitic stainless steel with nickel; 1-2 molybdenum; more than 1.5 to 4.0 manganese; 0.20 to 0.75 niobium; up to 0.1 titanium; iron; and accidental impurities steel.   The austenitic stainless steel according to claim 1, wherein the steel contains 1.6 to 4.0 wt% manganese based on the total weight of the steel. The austenitic stainless steel of claim 1, further comprising at least one of the following, in weight percent, based on the total weight of the steel:
Greater than 0 to 0.50 silicon; greater than 0 to 0.30 aluminum; greater than 0 to 0.02 sulfur; greater than 0 to 0.05 phosphorus; greater than 0 to 0.1 zirconium; And more than 0 to 0.1 vanadium.   The austenitic stainless steel according to claim 1, wherein at least one of titanium and aluminum is limited to 0.1 wt% or less based on the total weight of the steel. The ratio of niobium to carbon in the steel is given by the formula:
0.7 <0.13 (niobium / carbon) ≦ 1.0,
[Wherein the niobium and carbon contents in the formula are expressed in atomic percent. ]
The austenitic stainless steel according to claim 1, satisfying   % By weight based on the total weight of the steel: 0.05-0.2 carbon; 0.08-0.2 nitrogen; 20-23 chromium; 25-27 nickel; 1-2 molybdenum; More than 1.5 to 4.0 manganese; 0.20 to 0.75 niobium; up to 0.1 titanium; up to 0.50 silicon; up to 0.30 aluminum; up to 0.02 The austenitic stainless steel of claim 1, comprising: up to sulfur; up to 0.05 phosphorus; up to 0.1 zirconium; up to 0.1 vanadium; iron; and incidental impurities.   The austenitic stainless steel according to claim 6, wherein the steel contains 1.6 to 4.0 wt% manganese based on the total weight of the steel.   The austenitic stainless steel according to claim 6, wherein at least one of titanium and aluminum is limited to 0.1% by weight or less based on the total weight of the steel.   The steel is in weight percent based on the total weight of the steel: 0.05 to 0.2 carbon; 0.08 to 0.2 nitrogen; 20 to 23 chromium; 25 to 27 nickel; 2 molybdenum; more than 1.5 to 4.0 manganese; 0.20 to 0.75 niobium; up to 0.1 titanium; up to 0.50 silicon; up to 0.30 aluminum; 2. Essentially consisting of up to 0.02 sulfur; up to 0.05 phosphorus; up to 0.1 zirconium; up to 0.1 vanadium; iron; and incidental impurities. Austenitic stainless steel.   The steel is in weight percent based on the total weight of the steel: 0.05 to 0.2 carbon; 0.08 to 0.2 nitrogen; 20 to 23 chromium; 25 to 27 nickel; 2 molybdenum; 1.6-4.0 manganese; 0.20-0.75 niobium; up to 0.1 titanium; up to 0.50 silicon; up to 0.30 aluminum; up to 0 10. Austenite according to claim 9, consisting essentially of up to 0.02 sulfur; up to 0.05 phosphorus; up to 0.1 zirconium; up to 0.1 vanadium; iron; and incidental impurities. Stainless steel.   The austenitic stainless steel according to claim 10, wherein at least one of titanium and aluminum is limited to 0.1 wt% or less based on the total weight of the steel.   The steel is in weight percent based on the total weight of the steel: 0.05 to 0.2 carbon; 0.08 to 0.2 nitrogen; 20 to 23 chromium; 25 to 27 nickel; 2 molybdenum; more than 1.5 to 4.0 manganese; 0.20 to 0.75 niobium; up to 0.1 titanium; up to 0.50 silicon; up to 0.30 aluminum; The austenitic system according to claim 1, consisting of up to 0.02 sulfur; up to 0.05 phosphorus; up to 0.1 zirconium; up to 0.1 vanadium; iron; and incidental impurities. Stainless steel.   The steel is in weight percent based on the total weight of the steel: 0.05 to 0.2 carbon; 0.08 to 0.2 nitrogen; 20 to 23 chromium; 25 to 27 nickel; 2 molybdenum; 1.6-4.0 manganese; 0.20-0.75 niobium; up to 0.1 titanium; up to 0.50 silicon; up to 0.30 aluminum; up to 0 13. Austenitic stainless steel according to claim 12, consisting of up to 0.02 sulfur; up to 0.05 phosphorus; up to 0.1 zirconium; up to 0.1 vanadium; iron; and incidental impurities. .   The austenitic stainless steel according to claim 12, wherein at least one of titanium and aluminum is limited to 0.1 wt% or less based on the total weight of the steel.   Articles of manufacture comprising austenitic stainless steel, in weight percent, based on the total weight of the steel: 0.05 to 0.2 carbon; 0.08 to 0.2 nitrogen; 20 to 23 chromium; 25-27 nickel; 1-2 molybdenum; more than 1.5-4.0 manganese; 0.20-0.75 niobium; up to 0.1 titanium; iron; and accidental impurities Articles containing austenitic stainless steel.   The manufactured article according to claim 15, wherein the austenitic stainless steel contains 1.6 to 4.0 wt% manganese based on the total weight of the steel. 16. The article of manufacture of claim 15, wherein the austenitic stainless steel further comprises at least one of the following, by weight percent, based on the total weight of the steel:
Greater than 0 to 0.50 silicon; greater than 0 to 0.30 aluminum; greater than 0 to 0.02 sulfur; greater than 0 to 0.05 phosphorus; greater than 0 to 0.1 zirconium; And more than 0 to 0.1 vanadium.   In the manufactured article, at least one of titanium and aluminum in the austenitic stainless steel is limited to 0.1% by weight or less based on the total weight of the steel.   16. The article of manufacture of claim 15, wherein the article of manufacture is one of an energy generating device and an apparatus for processing or processing at least one of a chemical, a mineral, or an alloy.   The manufactured article of claim 15, wherein the manufactured article is selected from the group consisting of a gas turbine, a steam turbine, a fuel cell, and parts for any of those articles.   16. An article of manufacture according to claim 15, wherein the article of manufacture is a device or part that receives gas used or generated by an energy generating device.   The manufactured article of claim 15, wherein the manufactured article is one of a heat exchanger, a heat exchanger component, a recovered heat exchanger, and a recovered heat exchanger component. The manufactured article is:
Processing at least one of chemicals, minerals, and alloys at high temperatures;
Apparatus adapted for at least one of treating at least one of chemicals, minerals, and alloys at high temperature; or extracting at least one of chemicals and minerals at high temperature; The manufactured article of claim 15, which is a part of   Austenitic stainless steel, in weight percentages based on the total weight of the steel: 0.05 to 0.2 carbon; 0.08 to 0.2 nitrogen; 20 to 23 chromium; 25 to 27 Nickel; 1-2 molybdenum; up to 4.0 manganese; 0.20-0.75 niobium; at least one of 0.1 or less titanium and 0.1 or less aluminum; iron; and accidental Austenitic stainless steel containing various impurities.   The austenitic stainless steel according to claim 24, wherein the steel contains 1.6 to 4.0 wt% manganese based on the total weight of the steel. 25. The austenitic stainless steel of claim 24, further comprising at least one of the following by weight percent, based on the total weight of the steel:
More than 0 to 0.50 silicon; more than 0 to 0.02 sulfur; more than 0 to 0.05 phosphorus; more than 0 to 0.1 zirconium; and more than 0 to 0.1 vanadium . The ratio of niobium to carbon in the steel is given by the formula:
0.7 <0.13 (niobium / carbon) ≦ 1.0,
[Wherein the niobium and carbon contents in the formula are expressed in atomic percent. ]
The austenitic stainless steel according to claim 24, wherein   The steel is in weight percent based on the total weight of the steel: 0.05 to 0.2 carbon; 0.08 to 0.2 nitrogen; 20 to 23 chromium; 25 to 27 nickel; 2 molybdenum; up to 4.0 manganese; 0.20-0.75 niobium; at least one of up to 0.1 titanium and up to 0.1 aluminum; up to 0.50 silicon; 25. Consisting essentially of up to 0.02 sulfur; up to 0.05 phosphorus; up to 0.1 zirconium; up to 0.1 vanadium; iron; and incidental impurities. Austenitic stainless steel.   The steel is in weight percent based on the total weight of the steel: 0.05 to 0.2 carbon; 0.08 to 0.2 nitrogen; 20 to 23 chromium; 25 to 27 nickel; 2 molybdenum; 1.6 to 4.0 manganese; 0.20 to 0.75 niobium; at least one of 0.1 or less titanium and 0.1 or less aluminum; up to 0.50 25. Consisting essentially of silicon; sulfur up to 0.02; phosphorus up to 0.05; zirconium up to 0.1; vanadium up to 0.1; iron; and accidental impurities. The austenitic stainless steel described in 1.   The steel is in weight percent based on the total weight of the steel: 0.05 to 0.2 carbon; 0.08 to 0.2 nitrogen; 20 to 23 chromium; 25 to 27 nickel; 2 molybdenum; up to 4.0 manganese; 0.20-0.75 niobium; at least one of up to 0.1 titanium and up to 0.1 aluminum; up to 0.50 silicon; 25. Austenitic system according to claim 24 consisting of up to 0.02 sulfur; up to 0.05 phosphorus; up to 0.1 zirconium; up to 0.1 vanadium; iron; and incidental impurities. Stainless steel.   The steel is in weight percent based on the total weight of the steel: 0.05 to 0.2 carbon; 0.08 to 0.2 nitrogen; 20 to 23 chromium; 25 to 27 nickel; 2 molybdenum; 1.6 to 4.0 manganese; 0.20 to 0.75 niobium; at least one of 0.1 or less titanium and 0.1 or less aluminum; up to 0.50 31. Consisting of silicon; up to 0.02 sulfur; up to 0.05 phosphorus; up to 0.1 zirconium; up to 0.1 vanadium; iron; and incidental impurities. Austenitic stainless steel.   Articles of manufacture comprising austenitic stainless steel, in weight percent, based on the total weight of the steel: 0.05 to 0.2 carbon; 0.08 to 0.2 nitrogen; 20 to 23 chromium; 25-27 nickel; 1-2 molybdenum; up to 4.0 manganese; 0.20-0.75 niobium; at least one of 0.1 or less titanium and 0.1 or less aluminum; Articles of manufacture comprising iron; and austenitic stainless steel containing incidental impurities.   33. The article of manufacture according to claim 32, wherein the austenitic stainless steel comprises 1.6-4.0% by weight manganese, based on the total weight of the steel. 33. The article of manufacture of claim 32, wherein the austenitic stainless steel further comprises at least one of the following, by weight percent, based on the total weight of the steel:
More than 0 to 0.50 silicon; more than 0 to 0.02 sulfur; more than 0 to 0.05 phosphorus; more than 0 to 0.1 zirconium; and more than 0 to 0.1 vanadium .   33. The article of manufacture of claim 32, wherein the article of manufacture is one of an energy generating device and an apparatus for processing or processing at least one of a chemical, mineral, or alloy.   33. The manufactured article of claim 32, wherein the manufactured article is selected from the group consisting of a gas turbine, a steam turbine, a fuel cell, and parts for any of those articles.   33. The article of manufacture of claim 32, wherein the article of manufacture is an apparatus or component that receives a gas flow used or generated by an energy generator.   38. The article of manufacture of claim 37, wherein the article of manufacture is one of a heat exchanger, a heat exchanger component, a recovered heat exchanger, and a recovered heat exchanger component. The manufactured article is:
Processing at least one of chemicals, minerals, and alloys at high temperatures;
Apparatus adapted for at least one of treating at least one of chemicals, minerals, and alloys at high temperature; or extracting at least one of chemicals and minerals at high temperature; 33. The article of manufacture of claim 32, wherein the article is a part of an apparatus.

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