KR20080053437A - Austentic stainless steel - Google Patents

Abstract

Embodiments of an austenitic stainless steel include, in weight percentages based on 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; greater 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 an austenitic stainless steel include, in weight percentages based on 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 4.0 manganese; 0.20 to 0.75 niobium; at least one of no greater than 0.1 titanium and no greater than 0.1 aluminum; iron; and incidental impurities.

Description

Austenitic stainless steel {AUSTENTIC STAINLESS STEEL}

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

Hot air causes certain corrosive environments. Even more aggressive corrosive environments can occur when there is a significant amount of water vapor. The combination of hot air and a significant amount of water vapor is used in heat treatment and recuperators to treat gas streams generated or used by energy generators as well as facilities for treating, processing or extracting chemicals or minerals at high temperatures; It can often be formed in energy generating devices such as, for example, gas turbines, steam turbines and fuel cells. Thus, parts of the devices exposed to this condition are made from various austenitic stainless steels.

In order to improve corrosion resistance, austenitic stainless steels include various combinations of chromium, nickel, manganese and other alloying additives. Nevertheless, stainless steel and other specific chromium-bearing heat-resistant alloys are susceptible to attack in hot air containing steam and at high temperatures. This attack has two different forms. For example, low-alloy stainless steel, such as AISI Type 304 (nominally 18 wt% chromium and 8 wt% nickel, balance iron), accelerates oxidation when water vapor is present. Slowly growing chromium oxide films are replaced by a thick scale consisting of rapidly growing mixed iron and chromium oxide. The metal is thus quickly wasted by conversion to oxide. High-alloy component materials such as, for example, superferritic iron-chromium stainless steel and nickel-chromium superalloys are shown to be resistant to the form of attack but are observed to cause weight loss during exposure to water vapor. The oxides formed in the high-alloy component material are pure chromium oxides and are likely to evaporate through the formation of volatile chromium oxyhydroxides. Due to the evaporative loss of chromium to the atmosphere, an abnormally high level of chromium may depletion in the metal substrate, thereby lowering the high temperature oxidation resistance. The conversion between the corrosion states described above is relatively complex, and the characteristics of these conditions are observed in some alloys.

In addition to corrosion, articles and components in high temperature environments may creep. Creep is where undesirable elastic deformation occurs when the alloy is held for a long time with a stress lower than its nominal yield strength. Thus, creep may be exposed to high stresses and high temperatures in equipment and components for high temperature processing or processing of alloys or for high temperature processing, processing or extraction of chemicals or minerals, for example in energy generating devices and related devices. Specific structural components and other components that may be affected. In this field, it is often preferred that the parts be made of a material having substantial creep resistance and having substantial resistance to corrosion in high temperature environments.

Alloy element manganese has been shown to play a role in mitigating the effects of chromium oxide evaporation. Various stainless steel specifications include levels of manganese limited to 2% by weight or less, with no minimum level required. Manganese in such steels is not an intentional alloying additive but instead is included in the steel as ancillary components resulting from the scrap starting material. Austenitic stainless steels suitable for use in hot and hot steam-based environments that include adequate allowance for incidental manganese are NF709 alloys. NF709 alloy is available from Nippon Steel Corporation in the form of seamless pipes for boiler installations. The composition of the NF709 alloy provided in the Nippon Steel publication "Quality and properties of NF709 austenitic stainless steel for boiler pipe fittings" is shown in Table 1. Known compositions are characterized by a 1.5% by weight manganese threshold with no specific minimum. According to various known research reports for these alloys, the typical commercial manganese content is approximately 1% by weight. Other specific austenitic stainless steels are shown in Table 1. Basic concentrations throughout the present specification are% by weight based on total alloy weight unless otherwise indicated. "NS" in Table 1 indicates that certain UNS details do not represent concentrations for components.

Table 1

NF709 Type 201L Esshete 1250 Nitronic 60 Type 309S Type 310S UNS number none S20100 S21500 S21800 S30908 S31008 carbon 0.10 max 0.03 max 0.06-0.15 0.10 max 0.08 max 0.08 max molybdenum 1.0-2.0 NS 0.8-1.2 NS NS NS chrome 19.0-23.0 16-18 14-16 16-18 22-24 24-26 nickel 22.0-28.0 3.5-5.5 9-11 8-9 12-15 19-22 Niobium 0.10-0.40 0.75-1.25 0.75-1.25 NS NS NS manganese 1.50 max 5.5-7.5 5.5-7.5 7-9 2.0 max 2.0 max silicon NS NS NS 3.5-4.5 0.75 max 0.75 max titanium 0.02-0.20 NS NS NS NS NS nitrogen 0.10-0.25 0.25 max NS 0.08-0.18 NS NS

According to Table 1, the basic AISI Type 201 stainless steel is replaced by manganese, which is similar to the standard 18 chromium-8 nickel stainless steel but with a relatively inexpensive alloy of nickel. In general, Type 201 alloys do not have sufficient creep and oxidation resistance for use at elevated temperatures. Of alloy NITRONIC ^® group, Esshete 1250 alloy and Alloy 21-6-9 alloy material of relatively high content, such as (UNS S21900) it is low levels of nickel (up to approximately 11 wt%) and significant levels of manganese (5 to 10% by weight It is generally designed for high creep strength and moderate environmental resistance. Generally, commercially available heat resistant stainless steels such as AISI Type 309S and 310S contain manganese at levels of approximately 2% by weight or less. These alloys, depending on their basic composition, are somewhat lacking in terms of metallurgical stability, since the nickel-to-chromium ratio for the two grades forms a significant amount of brittle phase at normal use temperatures.

It is desirable to provide austenitic stainless steel with improved hot creep resistance and / or resistance to corrosion attack in hot air and / or in hot air containing appropriate levels of water vapor. Stainless steels that exhibit substantial corrosion resistance, for example in hot air containing steam, are for example energy containing gas turbines, steam turbines and fuel cells, which are highly corrosive and are exposed to high temperature, high steam containing environments. It may be preferred to be used in parts of the generating device. These parts include heat exchangers, recuperators, pipes, pipes and certain structural components. Also preferably alloys exhibiting substantial corrosion resistance in hot air can be used in certain devices for high temperature processing or processing of the alloy or for high temperature processing, processing or extraction of chemicals or inorganics. Stainless steel, which exhibits substantial corrosion resistance as well as substantial high temperature creep resistance, may be suitable for use in parts of the aforementioned devices exposed to high frequency.

In accordance with the present invention, austenitic stainless steel is provided to have improved high temperature creep resistance and / or improved resistance to corrosion when exposed to hot air environments. As used herein, “high temperature” refers to temperatures in excess of approximately 100 ° F. (approximately 37.8 ° C.). According to one aspect of the present invention, austenitic stainless steel has 0.05 to 0.2 wt% carbon, 0.08 to 0.2 wt% nitrogen, 20 to 23 wt% chromium, 25 to 27 wt% nickel, 1 to 2 wt% Molybdenum, greater than 1.5% to 4.0% by weight manganese, 0.20 to 0.75% by weight niobium, up to 0.1% by weight titanium, iron and incidental impurities. In certain non-limiting examples, the manganese content of the steel is at least 1.6 to 4.0 weight percent. Also in certain non-limiting examples, austenitic stainless steels may comprise greater than 0 wt% to 0.50 wt% silicon, greater than 0 wt% to 0.30 wt% aluminum, greater than 0 wt% to 0.02 wt% sulfur, 0 And at least one of greater than 0 wt% to 0.05 wt% phosphorus, greater than 0 wt% to 0.1 wt% zirconium and greater than 0 wt% to 0.1 wt% vanadium. According to certain non-limiting embodiments, the titanium and / or aluminum content of the steel is 0.1% by weight or less.

The term "less than" as used herein, not mentioned with respect to the lower limit, includes no component mentioned. As used herein, "small" as also referred to in terms of titanium and aluminum content includes the absence of these components.

According to another feature of the invention, the austenitic stainless steel has 0.05 to 0.2 wt% carbon, 0.08 to 0.2 wt% nitrogen, 20 to 23 wt% chromium, 25 to 27 wt% nickel, 1 to 2 wt% Molybdenum, greater than 1.5% to 4.0% by weight manganese, 0.20 to 0.75% by weight niobium, up to 0.1% by weight titanium, 0.50% by weight silicon, 0.30% by weight aluminum, 0.02% by weight sulfur, It is provided to contain up to 0.05% by weight of phosphorus, up to 0.1% by weight of zirconium, up to 0.1% by weight of vanadium, iron and incidental impurities. In certain non-limiting examples, the manganese content of the steel is at least 1.6 wt% and up to 4.0 wt%. Also in certain non-limiting embodiments, the content of titanium and / or aluminum in the steel is 0.1% by weight or less.

According to another embodiment of the present invention, austenitic stainless steel consists essentially of 0.05 to 0.2 wt% carbon, 0.08 to 0.2 wt% nitrogen, 20 to 23 wt% chromium, 25 to 27 wt% nickel, 1-2 weight percent molybdenum, more than 1.5 weight percent to 4.0 weight percent manganese, 0.20 weight percent to 0.75 weight percent niobium, 0.1 weight percent or less titanium, 0.50 weight percent silicon, 0.30 weight percent aluminum, 0.02 weight Up to% sulfur, up to 0.05 weight percent phosphorus, up to 0.1 weight percent zirconium, up to 0.1 weight percent vanadium, iron and incidental impurities. According to certain non-limiting embodiments, the manganese content of the steel is at least 1.6 wt% and up to 4.0 wt%.

According to another embodiment of the present invention, austenitic stainless steel is 0.05 to 0.2 wt% carbon, 0.08 to 0.2 wt% nitrogen, 20 to 23 wt% chromium, 25 to 27 wt% nickel, 1 to 2 wt% molybdenum, greater than 1.5 wt% to 4.0 wt% manganese, 0.20 to 0.75 wt% niobium, up to 0.1 wt% titanium, up to 0.50 wt% silicon, up to 0.30 wt% aluminum, up to 0.02 wt% Of sulfur, up to 0.05% by weight of phosphorus, up to 0.1% by weight of zirconium, up to 0.1% by weight of vanadium, iron and incidental impurities. According to certain non-limiting embodiments, the manganese content of the steel is at least 1.6 wt% and up to 4.0 wt%.

According to another feature of the invention, austenitic stainless steel is based on the total weight of the steel, 0.05 to 0.2% by weight of carbon, 0.08 to 0.2% by weight of nitrogen, 20 to 23% by weight of chromium, 25 to 27% by weight Nickel, 1 to 2% molybdenum, up to 4.0% manganese, 0.20 to 0.75% niobium, at least one of 0.1% titanium and 0.1% aluminum, iron and incidental impurities .

According to a further feature of the invention, austenitic stainless steel is essentially 0.05 to 0.2 wt% carbon, 0.08 to 0.2 wt% nitrogen, 20 to 23 wt% chromium, 25 to 27 based on the total weight of the steel Wt% nickel, 1-2 wt% molybdenum, up to 4.0 wt% manganese, 0.20-0.75 wt% niobium, at least one of up to 0.1 wt% titanium and 0.1 wt% aluminum, up to 0.50 wt% silicon , Up to 0.02 wt% sulfur, up to 0.05 wt% phosphorus, up to 0.1 wt% zirconium, up to 0.1 wt% vanadium, iron and incidental impurities. According to certain non-limiting embodiments, the steel comprises a manganese content of at least 1.5 wt% to 4.0 wt% but in other embodiments includes a manganese content of 1.6 wt% to 4.0 wt%.

According to a further feature of the invention, austenitic stainless steel is based on the total weight of the steel, 0.05 to 0.2 wt% carbon, 0.08 to 0.2 wt% nitrogen, 20 to 23 wt% chromium, 25 to 27 wt% Nickel, 1-2 wt% molybdenum, 4.0 wt% or less manganese, 0.20-0.75 wt% niobium, at least one of 0.1 wt% titanium and 0.1 wt% aluminum, 0.50 wt% or less silicon, 0.02 Up to 20 wt% sulfur, up to 0.05 wt% phosphorus, up to 0.1 wt% zirconium, up to 0.1 wt% vanadium, iron and incidental impurities. According to certain non-limiting embodiments, the steel comprises a manganese content of at least 1.5 wt% to 4.0 wt% but in other embodiments includes a manganese content of 1.6 wt% to 4.0 wt%.

According to another embodiment of the present invention, an article of manufacture is provided comprising austenitic stainless steel having a composition according to the present disclosure. Non-limiting embodiments of articles of manufacture include, for example, energy generating devices and components of such devices. For example, the article of manufacture can be selected from gas turbines, steam turbines, fuel cells, heat exchangers, recuperators, tubes, pipes, structural components and other components for any of the above devices. . Other examples of articles of manufacture include facilities for high temperature processing or processing of alloys or for high temperature processing, processing or extraction of chemicals and minerals, or pipes, tubes and other components for such facilities.

The reader of the present specification may understand other details in light of the above-described details as well as the following detailed description of specific non-limiting examples within the scope of the present invention. Those who read this specification will understand additional advantages and details when using or evaluating articles of manufacture and alloys within this specification.

The features and advantages of the articles of manufacture and alloys described herein can be better understood according to the accompanying drawings.

1 shows weight change over time for alloy samples exposed to 1300 ° F. (704 ° C.) in air containing 10% water vapor.

FIG. 2 shows the weight change over time for an alloy sample exposed at 1400 ° F. (760 ° C.) in air containing 7% water vapor.

FIG. 3 shows weight change over time for alloy samples exposed to 1500 ° F. (815 ° C.) in air containing 7% water vapor.

4 (a) and 4 (b) are micrographs of oxide scales formed on alloy samples exposed to high temperature environments including water vapor;

FIG. 5 is a graph of the oxide composition, measured as the molar ratio of MnO to Cr ₂ O ₃ , relative to the alloy to some exposed to hot environments containing water vapor.

6 shows the chromium content of two alloy samples as a function of depth in the sample.

7 shows the chromium content of two alloy samples as a function of depth in the sample.

FIG. 8 is a graph of the oxide composition, measured as the molar ratio of MnO to Cr ₂ O ₃ , for high content of manganese and low content of manganese exposed to high temperature environment containing 7% water vapor.

FIG. 9 shows weight change over time for alloy samples exposed to 1400 ° F. (760 ° C.) in air containing 10% water vapor.

It is to be understood that all amounts of ingredients, process conditions, and the like as used in the specification and claims, in addition to or otherwise indicated above, may be illustratively modified by the term “approximately”. Thus, unless indicated to the contrary, any of the numerical variables set forth in the following specification and the appended claims are approximations that may vary depending on the properties desired to be implemented in articles and alloys in accordance with the present invention. Each numerical variable should at least be construed in light of the number of significant figures described and by applying ordinary approximation, which is not intended to limit the application of the doctrine of equivalents in the claims.

Notwithstanding that the numerical ranges and variables forming the broad ranges herein are approximations, the numerical values formed in certain embodiments herein are described as precisely as possible. Any numerical values essentially include certain errors such as, for example, plant and / or operator errors which are essentially a result of the standard deviation of the individual test measurements. It is also to be understood that any numeric range described herein includes the boundaries of the ranges and all subranges contained herein. For example, the range "1 to 10" includes all subranges between at least 1 and at most 10, i.e., a minimum value greater than or equal to 1 and a maximum value less than or equal to 10.

Any patent, notice or other publication made herein by reference is incorporated herein in whole or in part so as not to be contrary to the definitions, references, or other publications made herein. As such and essentially, the disclosure constituted of this specification supersedes any conflicting material constructed herein by reference. Contrary to the definitions, references, or other publications made herein, the materials incorporated herein by reference or portions thereof are so constructed that they do not cause inconsistencies between the materials of this invention and the materials constructed.

As mentioned above, certain austenitic stainless steels are used in articles and components exposed to hot air or hot air containing significant water vapor. Parts placed in this state are, for example, in parts and facilities for high temperature processing or processing of alloys or for high temperature processing, processing or extraction of inorganic or chemical products, and heat exchangers, recuperators and gas turbines, steam turbines and fuels. Includes components affected by energy generating devices such as batteries. However, such steels pose a risk of corrosion when they are too long under these conditions. The inventors of the present invention have therefore determined whether the chemistry of certain modified austenitic stainless steels further improves the corrosion resistance in high temperature environments. In addition, as described below, the inventors have determined that alloys containing 1.5 weight percent or less of manganese are subjected to oxide scale evaporation and subsequently degradation in air containing water vapor. The inventor's study focuses on the chemical properties of certain new austenitic stainless steels, including more than 1.5% by weight manganese, with appropriate levels of chromium and nickel. As a result of this study, the inventors have found that austenitic stainless steels having a wide range of compositions, more preferably the nominal compositions shown in Table 2, can be used for evaporation of chromium oxide scale in hot air environments and in hot air environments. It was concluded that they were substantially resistant. The manganese content of the proposed alloy is adjusted to the minimum level, based on significantly improving the resistance to high temperature corrosion attack.

Table 2

at least maximum Nominal carbon 0.05 0.2 0.10 nitrogen 0.08 0.2 0.15 chrome 20 23 20.5 nickel 25 27 25.5 molybdenum One 2 1.5 manganese Greater than 1.5 4.0 1.6 silicon 0 0.05 0.30 aluminum 0 0.30 0.25 sulfur 0 0.02 0.005 sign 0 0.05 0.03 Niobium 0.20 0.75 0.6 titanium 0 0.1 - zirconium 0 0.1 - vanadium 0 0.1 -

Table 3 shows information for some alloys whose values were obtained during the test. Heats 1 and 3 are melted and subsequently rolled into a foil gauge. Heats 1 and 3 are experimental heats, heat 2 is made as a pilot coil and heat 4 is plant heat made as a production coil. Heats 1, 3, and 4 are produced with a target of 1.0% by weight manganese, and heat 2 is produced with a target of 1.6% by weight manganese.

Table 3

Hit 1 Hit 2 Hit 3 Hit 4 carbon 0.10 0.087 0.076 0.078 molybdenum 1.54 1.53 1.54 1.50 chrome 20.01 21.0 20.19 20.04 nickel 25.42 26.0 25.57 26.0 Niobium 0.65 0.30 0.30 0.34 manganese 0.99 1.61 1.03 0.99 titanium 0.077 0.01 - 0.02 nitrogen 0.143 0.10 0.13 0.1

The comparison of 1.6% by weight of manganese and 1.0% by weight of manganese (nominal) variation described in Table 3 as heat (2) and heat (4) shows that the relatively low content of manganese forms are more oxidative scale, especially at relatively high temperatures. It is easy to evaporate. This can cause a significant environmental attack over time. The test follows.

The samples are exposed to a temperature range of 1300-1500 ° F. (704-815 ° C.) in wet air. As shown in FIG. 1, a high content of manganese sample (approximately 1.6% by weight manganese, heat 2) and a low content of manganese sample (approximately 1.0% by weight manganese, heat 3) contain 10% water vapor. Similar oxidation kinetics is shown in weight change over time (mg / cm 2) upon exposure to 1300 ° F. (704 ° C.). In general, low content manganese samples exhibit rather small weight grains and behave somewhat irregularly.

FIG. 2 shows time over samples of high content of manganese (heat 2) and low content of manganese (heat 4) alloys when the sample is exposed to 1400 ° F. (760 ° C.) in air containing 7% water vapor. The change in weight is shown. The samples show significantly different oxidation kinetics under these conditions. Higher manganese samples quickly gain weight in the initial part of the test but then slow down significantly. After 5000 hours of testing were completed, the two samples showed substantially the same weight gain.

FIG. 3 shows over time for samples of high content of manganese (heat 2) and low content of manganese (heat 4) alloys when the sample is exposed to 1500 ° F. (815 ° C.) in air containing 7% water vapor. The change in weight is shown. The curve shows significant oxidative scale evaporation of the low content manganese samples during the test. Higher manganese alloys do not exhibit the same weight change for a limited test exposure.

Samples that were exposed a full 5000 hours under the 1300 ° F. (704 ° C.) and 1400 ° F. (760 ° C.) were loaded, polished and inspected. The oxide scale formed on the high content of manganese samples is thin, compact and monotonous. Low content manganese variants exhibit subscale void formation after exposure to 1300 ° F. (704 ° C.) in wet air. The oxide scale above these pores is somewhat thicker than the scale at any location. Scattered oxide nodule is formed on low content manganese samples exposed in wet air at 1400 ° F (760 ° C). An example of a nod is shown in FIG. 4B. Many small "emergent" nodules are formed in a process that destroys the oxide scale.

Samples are also observed in an expanded state after exposure in 1500 ° F. (815 ° C.) air containing water vapor. After approximately 3000 hours, a small nod of mixed oxides formed within the oxide scale was observed in a low content manganese (approximately 1.0 wt.% Manganese, heat 4) sample. Low content manganese samples were observed to be enlarged after approximately 8000 hours of exposure, and oxide nodules appeared to have grown significantly in size. A high content of manganese (approximately 1.6 wt.% Manganese, heat 2) sample was observed at 3500 hours and no nodules were observed within the oxide scale.

Microanalysis in a scanning electron microscope (SEM) is used to study the makeup of the general composition of the oxide scale. The scale is relatively thin (2-3 microns), and thus it is difficult to extract a detailed compositional profile. In general, measurements were limited to locations near the scale / gas interface and near the scale / alloy interface. High content of manganese alloys (Heat 2) has been observed to show significantly greater manganese sequestration from alloy to scale. FIG. 5 is measured using X-ray energy-dispersive spectroscopy (XEDS) of SEM for several samples at scale / alloy interface and scale / gas interface, measured as molar ratio of MnO to Cr ₂ O ₃ . The oxide composition is shown graphically. The low content of manganese material saturates manganese on the scale / gas interface at 1300 ° F (704 ° C) (ie, MnO / Cr ₂ O _{3 of} 1.0). Ratio), and is saturated near 1400 ° F (760 ° C). It is important to provide resistance to evaporation in order to saturate manganese in the spinel.

The same technique (XEDS in SEM without standard and measured using standard-based methods) was used to determine the degree and level of chromium depletion in metals that were placed after exposure to hot air containing water vapor. 6 shows a high content of manganese samples and low content of manganese samples from heat (2) and heat (4), each exposed for 5000 hours to 1300 ° F. (704 ° C.) air containing 10% water vapor. The concentration of chromium as a function of depth in the sample surface for is plotted in points. The observed depletion for low content manganese samples is significant for chromium concentration at locations directly adjacent to the scale / metal interface. The depth of depletion between samples does not appear to be significantly different. The chromium profile resulting from each sample appears to be quite sharp, which means that chromium cannot diffuse quickly from the inside of the sample to the scale / alloy interface.

FIG. 7 shows a high content of manganese samples and low content of manganese samples from heat 2 and heat 4, each exposed for 5000 hours to 1400 ° F. (760 ° C.) air containing 7% water vapor. The concentration of chromium as a function of depth in the sample surface for is plotted in points. As in FIG. 6, chromium depletion for low content manganese samples is significantly greater than high content manganese samples at the scale / metal interface. The effect of chromium depletion at 1400 ° F. (760 ° C.) is not relatively large in terms of terminal chromium content at the scale / alloy interface for the scale / alloy interface shown in FIG. 6, but the slope shown in FIG. 7 is within the substrate. Fairly steep in This is because chromium in the metal diffuses quickly enough at 1400 ° F. (760 ° C.) to eliminate the effects of chromium depletion due to oxidation.

FIG. 8 shows XEDS in SEM (semi-quantitative) for high content of manganese samples and low content of manganese samples from heat 2 and heat 4, respectively, exposed to hot air containing 7% water vapor. Using Cr ₂ O ₃ for It is a graph which shows the oxide composition measured by the molar ratio of MnO. Measurements were taken at the scale / alloy interface and the scale / gas interface. Evaluations conducted after exposure to air at 1300 ° F. (704 ° C.) and 1400 ° F. (760 ° C.) were performed after approximately 5000 hours of exposure time. Evaluations conducted after exposure at 1500 ° F. (815 ° C.) were performed after approximately 3000 hours of exposure time. Low content manganese materials have manganese saturation (i.e. MnO / Cr ₂ O _{3 of} 1.0) at scale / gas interfaces of 1300 ° F (704 ° C) and 1500 ° F (815 ° C). Ratio), and was saturated near 1400 ° F (760 ° C).

A series of hits of a relatively high content of manganese alloy is prepared to assess how oxidation resistance responds to additionally increased manganese levels. Table 4 shows the chemical composition of the heat 5 and the additional heat according to the heat 6.

Table 4

Hit 5 Hit 6 carbon 0.04 0.03 manganese 2.04 3.82 sign 0.006 0.006 sulfur 0.0069 0.003 silicon 0.26 0.17 chrome 19.4 19.81 nickel 23.19 23.22 aluminum 0.07 0.17 molybdenum 1.2 1.25 Copper 0.010 0.010 titanium 0.004 0.004 nitrogen 0.051 0.058 Niobium 0.39 0.39

9 shows heat 2 (1.61 wt% manganese), heat 5 (2.04 wt% manganese) and heat 6 exposed to 1400 ° F. (760 ° C.) air containing 7% water vapor. (3.82 wt.% Manganese) of alloys is plotted as the weight change of the sample over time. This result means that relatively high manganese levels cause a relatively large initial weight gain through the formation of an oxidative scale. On the other hand, the weight gain shown in FIG. 9 appears to be indeterminate, and due to the relatively high manganese level of about 4% by weight or more, additional scales are formed, weight is increased and undesirable due to spallation of the material. The result is bad.

Table 5 shows additional hits 7-11. The hits contain less than 0.1 weight percent titanium. The heats 7, 8, 11 also contain less than 0.1% by weight of aluminum.

Hit 7 Hit 8 Hit 9 Hit 10 Hit 11 carbon 0.086 0.088 0.078 0.091 0.080 molybdenum 1.54 1.52 1.50 1.52 1.54 chrome 20.99 20.95 20.4 20.35 25.83 nickel 25.92 26.02 26.0 25.7 20.42 Niobium 0.30 0.30 0.34 0.38 0.36 manganese 1.61 1.79 0.99 1.03 1.52 titanium 0.010 <0.01 0.02 0.001 0.06 nitrogen 0.0955 0.1130 0.10 0.104 0.12 silicon 0.41 0.40 0.47 0.33 0.36 sulfur <0.01 <0.01 0.0001 0.0001 0.0005 aluminum <0.01 <0.01 0.16 0.34 0.02 boron 0.0033 0.0029 0.0047 0.0047 0.0052

Table 5

As mentioned above, hot stressed austenitic stainless steel can be creeped for extended periods of time. Most austenitic stainless steels contain relatively small levels of titanium and aluminum to assist in the deoxidation of the molten metal during melting and casting. These elements also precipitate in the nitride, possibly in the solid intermetallic phase. These precipitated phases are very difficult or substantially impossible to decompose during processing. As the excess nitride forms, the level of nitrogen in the solid solution is reduced so that the creep strength of the alloy is reduced. In addition, nitride and intermetallic phases can make machining more difficult, especially when steel is molded by being stamped or wrapped in the form of parts.

Thus, in order to improve the creep strength and formability of the alloy during folding, stamping and similar mechanical processing steps, the preferred chemical properties for the austenitic stainless steels herein do not exceed 0.1% by weight. At least one of aluminum and titanium not exceeding 0.1 weight percent. More preferably, to further increase formability and creep resistance, the austenitic stainless steels of the present invention comprise titanium not exceeding 0.1 wt% and aluminum not exceeding 0.1 wt%.

Based on the above description, austenitic stainless steels containing more than 1.5% by weight to about 4% by weight of manganese and having chemistry investigated in detail are in air which can contain significant amounts of water vapor without excessive scale formation and nucleation. It must exhibit good resistance to high temperature attack. In particular, the broad and nominal alloy compositions shown in Table 2 have been proposed for austenitic stainless steels having substantial resistance to corrosion attack in hot and hot air containing steam. Preferred manganese levels are at least 1.6 wt% to about 4 wt% or less, and more preferred manganese levels are at least 1.6 wt% to about 2.0 wt% or less.

The alloy chemistry of the further proposed alloys with improved creep resistance and improved formability does not exceed titanium and / or 0.1% by weight having the general chemical properties shown in Table 2 but not exceeding 0.1% by weight. Does not contain aluminum. The expected improvement in creep resistance caused by limiting the content of titanium and / or aluminum is not required to attempt the improved high temperature corrosion resistance provided by adjusting the manganese content in the range of more than 1.5% by weight to approximately 4% by weight or less. Do not. Instead, the manganese content of the alloys proposed herein with improved creep resistance and formability can be formed at levels up to approximately 4.0 weight percent. Thus the alloys in Table 6 below should exhibit good creep resistance and formability, with the preferred chemical properties including titanium not exceeding 0.1 wt% and aluminum not exceeding 0.1 wt%.

Table 6

at least maximum carbon 0.05 0.2 nitrogen 0.08 0.2 chrome 20 23 nickel 25 27 molybdenum One 2 manganese 0 4.0 silicon 0 0.50 aluminum* 0 0.30 sulfur 0 0.02 sign 0 0.05 Niobium 0.20 0.75 titanium* 0 0.1 zirconium 0 0.1 vanadium 0 0.1

* At least one of Ti and Al is not greater than 0.1

Alloys exhibiting good high temperature creep resistance, improved formability and good resistance to corrosion attack in hot air, including water vapor, have the compositions shown in Table 6, which compositions have a manganese content of greater than 1.5 to about 4.0 weight percent. Or further preferably at least 1.6 to about 4.0 wt% or less, more preferably at least 1.6 to about 2.0 wt% or less. Preferably, the alloy can be used to produce structural and other components of the processing, processing or extraction device and the energy generating device mentioned above which are exposed to hot air and containing stress.

An arbitrary limitation on the chemical properties of the austenitic stainless steels introduced herein to better ensure substantial resistance to creep and that the ratio of niobium to carbon in the alloy satisfies the following formula: .

0.7 <0.13 (niobium / carbon) ≤ 1.0

Niobium and carbon content in the formula are expressed in atomic percentages.

The hits of the novel corrosion resistant austenitic stainless steel disclosed herein can be made by conventional means such as the prior art of vaccum melting scrap and other feed materials. The hits thus can be processed into billets, slabs, plates, coils, sheets and other intermediate articles by conventional techniques, which are then further processed into the final articles of manufacture. Within the context of the present invention, flat mill steel products made from alloys are due to the improved formability of embodiments of alloys comprising titanium not exceeding 0.1 wt% and / or aluminum not exceeding 0.1 wt%. product) can be further processed into articles with relatively complex shapes. This property of the alloy is preferred for NF709 alloys which have relatively limited formability and are usually processed into seamless pipes by extrusion.

The novel austenitic stainless steels according to the invention can be used in any suitable installation and environment, but the alloys are used in installations and parts that are exposed to high temperatures for a long time and in installations and parts that are exposed to high temperatures and considerable steam for a long time. It is particularly suitable for becoming. For example, due to the creep resistance and / or high temperature corrosion resistance of the alloys disclosed herein, the alloys may be subjected to extraction, high temperature processing or treatment of chemical or minerals or to high temperature processing or treatment of the alloy. Other parts of pipes, pipes, structural parts and installations suitable for making, eg other parts of energy generating devices such as gas turbines, steam turbines and fuel cells, pipes, pipes and structural parts thereof and heat exchangers, recuperators And other installations for treating gas streams generated or used by energy generating devices. Other fields of application of the alloy to this specification will be apparent to those skilled in the art in view of the present specification for alloys.

Although the foregoing description describes a limited number of embodiments of the present invention, those skilled in the art will appreciate that compositions and other details of the embodiments described and illustrated herein are intended to illustrate the nature of the present invention by those skilled in the art. It will be appreciated that various modifications may be made and all modifications are within the spirit and scope of the invention in the appended claims. Those skilled in the art will also appreciate that the above embodiments may be modified without departing from the broader spirit of the invention. Thus, the present invention should not be limited to the specific embodiments disclosed, but should include modifications that fall within the spirit and scope of the invention as defined by the claims.

Claims (39)

Based on the total weight of the steel, 0.05 to 0.2 weight percent carbon, 0.08 to 0.2 weight percent nitrogen, 20 to 23 weight percent chromium, 25 to 27 weight percent nickel, 1 to 2 weight percent molybdenum, 1.5 weight Austenitic stainless steel comprising greater than% to 4.0% by weight manganese, 0.20 to 0.75% by weight niobium, up to 0.1% by weight titanium, iron and incidental impurities. The austenitic stainless steel of claim 1, wherein the steel comprises 1.6 to 4.0 weight percent manganese, based on the total weight of the steel. The method of claim 1, wherein based on the total weight of the steel, more than 0% to 0.50% by weight of silicon, more than 0% to 0.30% by weight of aluminum, more than 0% to 0.02% by weight of sulfur, 0% by weight Austenitic stainless steel further comprising at least one of greater than 0.05% by weight of phosphorus, greater than 0% by weight to 0.1% by weight of zirconium and greater than 0% by weight to 0.1% by weight of vanadium. The austenitic stainless steel of claim 1, wherein at least one of titanium and aluminum is limited to no greater than 0.1 wt% based on the total weight of the steel. The austenite of claim 1 wherein the ratio of niobium to carbon in the steel satisfies 0.7 < 0.13 (niobium / carbon) &lt; 1.0, wherein the niobium and carbon content in the formula are expressed in atomic percentages. Stainless steel. The method of claim 1, based on the total weight of the steel, 0.05 to 0.2% by weight of carbon, 0.08 to 0.2% by weight of nitrogen, 20 to 23% by weight of chromium, 25 to 27% by weight of nickel, 1 to 2% by weight % Molybdenum, greater 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% sulfur Austenitic stainless steel, characterized in that it comprises 0.05 wt% or less of phosphorus, 0.1 wt% or less of zirconium, 0.1 wt% or less of vanadium, iron and incidental impurities. 7. The austenitic stainless steel of claim 6, wherein the steel comprises 1.6 to 4.0 weight percent manganese, based on the total weight of the steel. 7. The austenitic stainless steel of claim 6, wherein at least one of titanium and aluminum is limited to no greater than 0.1 weight percent based on the total weight of the steel. The method of claim 1, wherein the steel is based on the total weight of the steel, essentially from 0.05 to 0.2 weight percent carbon, from 0.08 to 0.2 weight percent nitrogen, from 20 to 23 weight percent chromium, from 25 to 27 weight percent nickel, 1-2 weight percent molybdenum, more than 1.5 weight percent to 4.0 weight percent manganese, 0.20 weight percent to 0.75 weight percent niobium, 0.1 weight percent or less titanium, 0.50 weight percent silicon, 0.30 weight percent aluminum, 0.02 weight Austenitic stainless steel, characterized by consisting of up to% sulfur, up to 0.05 weight percent phosphorus, up to 0.1 weight percent zirconium, up to 0.1 weight percent vanadium, iron and incidental impurities. 10. The method of claim 9 wherein the steel is based on the total weight of the steel, essentially from 0.05 to 0.2 weight percent carbon, 0.08 to 0.2 weight percent nitrogen, 20 to 23 weight percent chromium, 25 to 27 weight percent nickel, 1-2% molybdenum, 1.6% -4.0% manganese, 0.20-0.75% niobium, 0.1% or less titanium, 0.50% or less silicon, 0.30% or less aluminum, 0.02% by weight Austenitic stainless steel, characterized by consisting of up to sulfur, up to 0.05% by weight phosphorus, up to 0.1% by weight zirconium, up to 0.1% by weight vanadium, iron and incidental impurities. 11. The austenitic stainless steel of claim 10, wherein at least one of titanium and aluminum is limited to no greater than 0.1 weight percent based on the total weight of the steel. The method of claim 1, wherein the steel is based on the total weight of the steel, 0.05 to 0.2% by weight of carbon, 0.08 to 0.2% by weight of nitrogen, 20 to 23% by weight of chromium, 25 to 27% by weight of nickel, 1 to 2 wt% molybdenum, greater than 1.5 wt% to 4.0 wt% manganese, 0.20 to 0.75 wt% niobium, up to 0.1 wt% titanium, up to 0.50 wt% silicon, up to 0.30 wt% aluminum, up to 0.02 wt% Austenitic stainless steel, characterized by consisting of sulfur, up to 0.05% by weight of phosphorus, up to 0.1% by weight of zirconium, up to 0.1% by weight of vanadium, iron and incidental impurities. 13. The method of claim 12 wherein the steel is based on the total weight of the steel, 0.05 to 0.2% by weight carbon, 0.08 to 0.2% by weight nitrogen, 20 to 23% by weight chromium, 25 to 27% by weight nickel, 1 to 2 wt% molybdenum, 1.6 wt% to 4.0 wt% manganese, 0.20 to 0.75 wt% niobium, 0.1 wt% or less titanium, 0.50 wt% or less silicon, 0.30 wt% or less, 0.02 wt% or less Austenitic stainless steel, characterized by consisting of sulfur, up to 0.05% by weight phosphorus, up to 0.1% by weight zirconium, up to 0.1% by weight vanadium, iron and incidental impurities. 13. The austenitic stainless steel of claim 12, wherein at least one of titanium and aluminum is limited to no greater than 0.1 weight percent based on the total weight of the steel. Based on the total weight of the steel, 0.05 to 0.2 weight percent carbon, 0.08 to 0.2 weight percent nitrogen, 20 to 23 weight percent chromium, 25 to 27 weight percent nickel, 1 to 2 weight percent molybdenum, 1.5 weight An article of manufacture comprising austenitic stainless steel consisting of greater than% to 4.0 wt% manganese, 0.20 to 0.75 wt% niobium, up to 0.1 wt% titanium, iron, and incidental impurities. 16. The article of manufacture of claim 15, wherein the austenitic stainless steel comprises 1.6 to 4.0 weight percent manganese, based on the total weight of the steel. The austenitic stainless steel according to claim 15, wherein the austenitic stainless steel is based on the total weight of the steel, based on the total weight of the steel, from 0% to 0.50% by weight of silicon, from 0% to 0.30% by weight of aluminum, from 0% to 0.02% by weight of sulfur. At least 0 wt% to 0.05 wt% phosphorus, at least 0 wt% to 0.1 wt% zirconium and at least 0 wt% to 0.1 wt% vanadium. 16. The article of manufacture of claim 15, wherein at least one of titanium and aluminum in the austenitic stainless steel is limited to no more than 0.1 wt% based on the total weight of the steel. 16. The article of manufacture of claim 15, wherein the article of manufacture is one of a device and an energy generating device for processing or processing at least one of chemicals, minerals or alloys. 16. The article of manufacture according to claim 15, wherein the article of manufacture is selected from the group consisting of gas turbines, steam turbines, fuel cells and components for any of the above articles of manufacture. 16. The article of manufacture according to claim 15, wherein the article of manufacture is a device or part containing a gas generated or used by an energy generating device. 16. The article of manufacture according to claim 15, wherein the article of manufacture is one of a heat exchanger, a part of a heat exchanger, a recuperator and a part of a recuperator. The article of manufacture of claim 15 wherein the article of manufacture is Processing at least one of chemicals, inorganics and alloys at high temperature, Treating at least one of chemicals, inorganics and alloys at high temperature or -An article of manufacture characterized in that it is part of a device suitable for one or more of the extractings of at least one of chemicals and inorganics at high temperatures. Based on the total weight of the steel, 0.05 to 0.2 weight percent carbon, 0.08 to 0.2 weight percent nitrogen, 20 to 23 weight percent chromium, 25 to 27 weight percent nickel, 1 to 2 weight percent molybdenum, 4.0 weight Austenitic stainless steel comprising up to% manganese, from 0.20 to 0.75 wt% niobium, up to 0.1 wt% titanium and up to 0.1 wt% aluminum, iron and incidental impurities. 25. The austenitic stainless steel of claim 24, wherein the steel comprises 1.6 to 4.0 weight percent manganese, based on the total weight of the steel. The method of claim 24, based on the total weight of the steel, more than 0% to 0.50% by weight of silicon, more than 0% to 0.02% by weight of sulfur, more than 0% to 0.05% by weight of phosphorus, 0% by weight Austenitic stainless steel, further comprising at least one of greater than 0.1 weight percent zirconium and greater than 0 weight percent 0.1 weight percent vanadium. 25. The austenite of claim 24 wherein the ratio of niobium to carbon in steel satisfies 0.7 < 0.13 (niobium / carbon) &lt; 1.0, wherein the niobium and carbon content in the formula are expressed in atomic percentages. Stainless steel. The method of claim 24, wherein the steel is essentially 0.05 to 0.2 wt% carbon, 0.08 to 0.2 wt% nitrogen, 20 to 23 wt% chromium, 25 to 27 wt% nickel, based on the total weight of the steel, 1-2 wt% molybdenum, up to 4.0 wt% manganese, 0.20-0.75 wt% niobium, at least one of up to 0.1 wt% titanium and up to 0.1 wt% aluminum, up to 0.50 wt% silicon, 0.02 wt% Austenitic stainless steel, characterized by consisting of up to sulfur, up to 0.05% by weight phosphorus, up to 0.1% by weight zirconium, up to 0.1% by weight vanadium, iron and incidental impurities. The method of claim 24, wherein the steel is essentially 0.05 to 0.2 wt% carbon, 0.08 to 0.2 wt% nitrogen, 20 to 23 wt% chromium, 25 to 27 wt% nickel, based on the total weight of the steel, 1-2% molybdenum, 1.6% -4.0% manganese, 0.20-0.75% niobium, at least one of 0.1% or less titanium and 0.1% or less aluminum, 0.50% or less silicon, Austenitic stainless steel, characterized by 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 method of claim 24, wherein the steel is based on the total weight of the steel, from 0.05 to 0.2 weight percent carbon, from 0.08 to 0.2 weight percent nitrogen, from 20 to 23 weight percent chromium, from 25 to 27 weight percent nickel, from 1 to 2 wt% molybdenum, up to 4.0 wt% manganese, 0.20 to 0.75 wt% niobium, at least one of up to 0.1 wt% titanium and up to 0.1 wt% aluminum, up to 0.50 wt% silicon, up to 0.02 wt% Austenitic stainless steel, characterized by consisting of sulfur, up to 0.05% by weight phosphorus, up to 0.1% by weight zirconium, up to 0.1% by weight vanadium, iron and incidental impurities. 31. The method of claim 30, wherein the steel is based on the total weight of the steel, from 0.05 to 0.2 weight percent carbon, from 0.08 to 0.2 weight percent nitrogen, from 20 to 23 weight percent chromium, from 25 to 27 weight percent nickel, from 1 to 2 weight percent molybdenum, 1.6 to 4.0 weight percent manganese, 0.20 to 0.75 weight percent niobium, at least one of 0.1 weight percent titanium and 0.1 weight percent aluminum, less than 0.50 weight percent silicon, 0.02 weight percent or less Austenitic stainless steel, characterized by consisting of sulfur, up to 0.05% by weight of phosphorus, up to 0.1% by weight of zirconium, up to 0.1% by weight of vanadium, iron and incidental impurities. Based on the total weight of the steel, 0.05 to 0.2 weight percent carbon, 0.08 to 0.2 weight percent nitrogen, 20 to 23 weight percent chromium, 25 to 27 weight percent nickel, 1 to 2 weight percent molybdenum, 4.0 weight An article of manufacture comprising austenitic stainless steel consisting of up to% manganese, from 0.20 to 0.75 wt% niobium, up to 0.1 wt% titanium and up to 0.1 wt% aluminum, iron and incidental impurities. 33. The article of manufacture of claim 32, wherein the austenitic stainless steel comprises 1.6 to 4.0 weight percent manganese, based on the total weight of the steel. 33. The method of claim 32, wherein the austenitic stainless steel is based on the total weight of the steel, based on the total weight of the steel, greater than 0% to 0.50% by weight of silicon, greater than 0% to 0.02% by weight of sulfur, greater than 0% to 0.05% by weight of phosphorus. , More than 0 wt% to 0.1 wt% zirconium and more than 0 wt% to 0.1 wt% vanadium. 33. The article of manufacture of claim 32, wherein the article of manufacture is one of a device and an energy generating device for processing or processing one or more of chemicals, minerals or alloys. 33. The article of manufacture of claim 32, wherein the article of manufacture is selected from the group consisting of a gas turbine, a steam turbine, a fuel cell and components for any of the above articles of manufacture. 33. The article of manufacture of claim 32, wherein the article of manufacture is a device or component for receiving a gas stream generated or utilized by an energy generating device. 38. The article of manufacture according to claim 37, wherein the article of manufacture is one of a heat exchanger, a part of a heat exchanger, a recuperator and a part of a recuperator. The article of manufacture of claim 32, wherein the article of manufacture is Processing at least one of chemicals, inorganics and alloys at high temperature, Treating at least one of the chemicals, inorganics and alloys at a high temperature or A device or part of a device suitable for at least one of the steps of extracting at least one of chemicals and inorganics at high temperatures.

Images