METHODS FOR PROCESSING NANOSTRUCTURED FERRITIC ALLOYS, AND ARTICLES PRODUCED THEREBY

Abstract

A method of forming an article including a nanostructured ferritic alloy is provided. The method provides steps for substantially inhibiting grain growth of a workpiece that includes nanostructured ferritic alloy, during heating and deforming at high temperatures and at high strain rates. Advantageously, the article is formed via conventional high strain rate techniques and thus, cost savings are provided. Articles are also provided which are formed by the method, and the articles so produced exhibit good mechanical properties at high operating temperatures, and thus are utilized as turbomachinery components, and in particular, component of a heavy duty gas turbine or steam turbine. A turbomachinery component comprising an NFA is provided.

Description

BACKGROUND

The present disclosure relates to nanostructured ferritic alloys (NFAs), and more particularly, methods for processing the same utilizing high temperature processing methods. The disclosure also relates to an article comprising a nanostructured ferritic alloy (NFA) that is formed by using such a method.

Gas turbines operate in extreme environments, exposing the turbine components, especially those in the turbine hot section, to high operating temperatures and stresses. In order for the turbine components to endure these conditions, they are necessarily manufactured from a material capable of withstanding these severe conditions. In other words, a material used for the turbine components limits the temperature range that can be used without inducing a significant degradation in the mechanical properties of the material.

Superalloys have been used in these demanding applications because they maintain their strength at up to 90% of their melting temperature and have excellent environmental resistance. Nickel-based superalloys, in particular, have been used extensively throughout the gas turbine engines, e.g., in turbine blade, nozzle, wheel, spacer, disk, spool, blisk, and shroud applications. In some lower temperature and stress applications, steels may be used for turbine components. However, use of conventional steels is often limited in high temperature and high stress applications because they fail to meet necessary mechanical property requirements and/or design requirements.

Nanostructured ferritic alloys (NFAs) are an emerging class of iron-based alloys that exhibit exceptional high temperature properties. These alloys are typically derived from nanometer-sized oxide particulates or clusters that precipitate during hot consolidation following a mechanical alloying step. These oxide particulates or clusters are present at high temperatures, providing a strong and stable microstructure during service.

The NFAs are a powder metallurgy alloy that is typically consolidated through hot iso static pressing (HIP), and then hot-worked to manufacture a desired article. However, processing an as-HIP NFA at a high temperature, for example higher than about 1900 degrees Fahrenheit (° F.), typically leads to a change in its final microstructure and thus results in the degradation of its mechanical properties. This change in microstructure at the high temperatures limits (1) the use of these NFA materials at desired temperatures and stresses, for example in a heavy duty gas turbine, and (2) the use of the high strain rate processing techniques that may be economically beneficial for manufacturing an article.

In order for any material to be optimally useful in the desired application, for example, components for heavy duty turbomachinery, the material should desirably be capable of being manufactured into the desired article without sacrificing its mechanical properties. It may additionally be desirable to process the material at high temperatures and high strain rates.

BRIEF DESCRIPTION

In some embodiments, a method for forming an article comprising a nanostructured ferritic alloy is provided. The method includes introducing a quantity of strain into a workpiece at a first temperature to form a strained workpiece, heating the strained workpiece to a second temperature, and deforming the strained workpiece at the second temperature. The workpiece includes a nanostructured ferritic alloy. The first temperature is below about 1900 degrees Fahrenheit and the second temperature is at least about 1900 degrees Fahrenheit. The quantity of strain introduced into the workpiece at the first temperature is effective to substantially inhibit grain growth in the strained workpiece during the subsequent heating and the deforming at the second temperature.

In some embodiments, there is provided an article comprising a nanostructured ferritic alloy, which may be formed by the method. The article may be a turbomachinery component.

In some embodiments, a method of forming a turbomachinery component comprising a nanostructured ferritic alloy is provided. The method includes introducing a quantity of strain into a workpiece at a first temperature to form a strained workpiece, heating the strained workpiece to a second temperature, and forging the strained workpiece at the second temperature at a strain rate of at least about 1 inch/inch/sec. The workpiece includes a nanostructured ferritic alloy. The first temperature is below 1900 degrees Fahrenheit and the second temperature is higher than 1900 degrees Fahrenheit. The quantity of strain introduced into the workpiece at the first temperature is effective to substantially inhibit grain growth in the strained workpiece during the subsequent heating and the forging at the second temperature.

DRAWINGS

These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawing, wherein

FIG. 1A shows scanning electron microscope (SEM) micrograph of an “as-consolidated” NFA workpiece.

FIG. 1B shows SEM micrograph of the NFA workpiece after heating the workpiece at 2000 Fahrenheit for 24 hours after the consolidation.

FIG. 2A shows SEM micrograph of a NFA workpiece that is extruded at 1700 degrees Fahrenheit, in accordance with some embodiments of the invention.

FIG. 2B shows SEM micrograph after heating the extruded NFA workpiece at 2000 degrees Fahrenheit, in accordance with some embodiments of the invention.

FIG. 3 shows stress-strain curves for NFA workpieces that are processed with high strain rates at 1900 degrees Fahrenheit and 2100 degrees Fahrenheit, in accordance with some embodiments of the invention.

DETAILED DESCRIPTION

Unless defined otherwise, technical and scientific terms used herein have the same meaning as is commonly understood by one of skill in the art to which this invention belongs. The terms “comprising,” “including,” and “having” are intended to be inclusive, and mean that there may be additional elements other than the listed elements. The terms “first”, “second”, and the like, as used herein do not denote any order, quantity, or importance, but rather are used to distinguish one element from another. Also, the terms “a” and “an” do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced item, and the terms “front”, “back”, “bottom”, and/or “top”, unless otherwise noted, are merely used for convenience of description, and are not limited to any one position or spatial orientation.

If ranges are disclosed, the endpoints of all ranges directed to the same component or property are inclusive and independently combinable (e.g., ranges of “up to about 25 wt. %, or, more specifically, about 5 wt. % to about 20 wt. %,” is inclusive of the endpoints and all intermediate values of the ranges of “about 5 wt. % to about 25 wt. %,” etc.). The modifier “about” used in connection with a quantity is inclusive of the stated value and has the meaning dictated by the context (e.g., includes the degree of error associated with measurement of the particular quantity).

As discussed in detail below, some embodiments of the invention include a method for processing a nanostructured ferritic alloy (NFA) that allows the alloy (NFA) to be processed at a high temperature, a high strain rate, or both at high temperature and high strain rate while maintaining a desired microstructure. Some embodiments provide articles (also referred to as “formed articles”) manufactured by the present method. In one embodiment, the formed article is made of a nanostructured ferritic alloy (NFA), wherein the article is formed at a high temperature, a high strain rate, or both. The formed article may be any article desirably comprising the NFA and the properties conferred thereto by the NFA.

One illustrative class of articles that may find particular benefit from application of the principles described herein includes turbomachinery components, and in particular, those that experience high operating temperatures (for example, greater than 850° F.) and/or high stresses during use. In some embodiments, the formed article may advantageously comprise a component of a gas turbine or a steam turbine. Some exemplary articles are bolts, studs, blades, wheels, and spacers.

The nanostructured ferritic alloys (NFAs) are a class of alloys that comprise a stainless steel matrix that is dispersion strengthened by a very high density, for example, at least about 10¹⁸ m⁻³ of nanometer (nm)-scale, i.e., from about 1 nanometer to about 100 nanometers, of nanofeatures comprising titanium oxide (Ti—O) and at least one other metal element from the oxide used to prepare the NFA or the alloy matrix. For example, yttrium oxide, aluminum oxide, zirconium oxide, hafnium oxide may be used to prepare the NFAs, in which case, the nanofeatures may comprise yttrium (Y), aluminum (Al), zirconium (Zr), hafnium (Hf) or combinations of these. Transition metals, such as iron (Fe), chromium (Cr), molybdenum (Mo), tungsten (W), manganese (Mn), silicon (Si), niobium (Nb), aluminum (Al), nickel (Ni), or tantalum (Ta) from the alloy matrix can also participate in the creation of the nanofeatures. In some embodiments, an average size of nanofeatures ranges from about 1 nanometer to about 50 nanometers. In certain instances, the average size ranges from about 1 nanometer to about 10 nanometers. The density of nanofeatures, in some instances, is at least about 10²⁰ m⁻³, and in some certain instances, at least about 10²² m⁻³.

In contrast, conventional oxide dispersion strengthened (ODS) alloys generally contain refined, but larger, oxide phases, and the oxide additive is stable throughout the powder metallurgy process, i.e., if yttrium oxide were added to the matrix alloy, ytrrium oxide would be present after the alloying step and there would be no significant formation of the nanofeatures (NFs) described above. In an NFA, at least the majority, and in some cases substantially all, of the added oxide is dissolved into the alloy matrix during powder attrition and participates in the formation of the aforementioned nanofeatures when the powder is raised to a temperature during the compaction process, for example hot isostatic pressing (HIP). As described above, the new oxide in the NFA may comprise one or more transition metals present in the base alloy as well as the metallic element(s) of the initial oxide addition.

In one embodiment, the nanostructured ferritic alloy (NFA) comprises a ferritic stainless steel. In certain other embodiments, a martensitic, duplex, austenitic stainless steel or precipitation hardened steel are also potential matrix alloys. The nature of the steel matrix phase may affect to some degree the environmental resistance and the material ductility of the resultant NFA.

In one embodiment, the NFA includes chromium. Chromium can be important for ensuring corrosion resistance, and may thus be included in the NFA in amounts of at least about 5 weight percent, and in some embodiments, at least about 9 weight percent. Amounts of up to about 30 weight percent, and in some instances up to about 20 weight percent can be included. Advantageously, both chromium and iron, the basis of the NFA, are readily available and relatively low in cost, in particular as compared to the nickel-based superalloys which the NFAs may replace in some applications.

In some embodiments, the NFA includes molybdenum. An amount of up to about 30 weight percent, and in some instances, up to about 20 weight percent can be included. In some instances, the amount of molybdenum ranges from about 3 weight percent to about 10 weight percent. In some other instances, the amount of molybdenum ranges from about 1 weight percent to about 5 weight percent.

The NFA may further include titanium. Titanium may participate in the formation of the precipitated oxide, and so, amounts of titanium of from about 0.1 weight percent to about 2 weight percent, and in some instances, from about 0.1 weight percent to about 1 weight percent, and in certain instances, from about 0.1 weight percent to about 0.5 weight percent, are desirably included in the NFA.

The composition of the nanofeature(s) will depend, in part, upon the oxide utilized to prepare the NFA and/or the alloy matrix. Typically, the nanofeatures comprise titanium, oxygen and one or more additional element such as Y, Zr, Hf, Fe, Cr, Mo, W, Mn, Si, Nb, Al, Ni, Ta, or any combination of aforementioned. Generally, an NFA as described herein comprises at least about 0.1% oxygen by weight. The amount of oxygen present in the alloy determines in part the resultant type and concentration of nanofeatures present in the alloy. In some embodiments, the oxygen content is in a range from about 0.1% to about 0.5%, and in particular embodiments, the range is from about 0.1% to about 0.3%, where all percentages are by total weight of the alloy.

One illustrative NFA suitable for use in the formation of the article comprises from about 5 weight percent to about 30 weight percent chromium, from about 0.1 weight percent to about 2 weight percent titanium, from about 0 weight percent to about 10 weight percent molybdenum, from about 0 weight percent to about 5 weight percent tungsten, from about 0 weight percent to about 5 weight percent manganese, from about 0 weight percent to about 5 weight percent silicon, from about 0 weight percent to about 2 weight percent niobium, from about 0 weight percent to about 2 weight percent aluminum, from about 0 weight percent to about 8 weight percent nickel, from about 0 weight percent to about 2 weight percent tantalum, from about 0 weight percent to about 0.5 weight percent carbon, and from about 0 weight percent to about 0.5 weight percent nitrogen, with the balance being iron and incidental impurities; and a number density of at least about 10¹⁸ m⁻³ nanofeatures comprising titanium, oxygen, and at least one element derived from the oxide added during the preparation of the NFA or from the alloy matrix.

In other embodiments, the NFA comprises from about 9 weight percent to about 20 weight percent chromium, from about 0.1 weight percent to about 1 weight percent titanium, from about 0 weight percent to about 10 weight percent molybdenum, from about 0 weight percent to about 4 weight percent tungsten, from about 0 weight percent to about 2.5 weight percent manganese, from about 0 weight percent to about 2.5 weight percent silicon, from about 0 weight percent to about 1 weight percent niobium, from about 0 weight percent to about 1 weight percent aluminum, from about 0 weight percent to about 4 weight percent nickel, from about 0 weight percent to about 1 weight percent tantalum, from about 0 weight percent to about 0.2 weight percent carbon, and from about 0 weight percent to about 0.2 weight percent nitrogen, with the balance being iron and incidental impurities; and a number density of at least about 10²⁰ m⁻³ nanofeatures comprising titanium, oxygen and at least one element derived from the oxide added during the preparation of the NFA or from the alloy matrix.

In yet other embodiments, the NFA comprises from about 9 weight percent to about 14 weight percent chromium, from about 0.1 weight percent to about 0.5 weight percent titanium, from about 0 weight percent to about 10 weight percent molybdenum, from about 0 weight percent to about 3 weight percent tungsten, from about 0 weight percent to about 1 weight percent manganese, from about 0 weight percent to about 1 weight percent silicon, from about 0 weight percent to about 0.5 weight percent niobium, from about 0 weight percent to about 0.5 weight percent aluminum, from about 0 weight percent to about 2 weight percent nickel, from about 0 weight percent to about 0.5 weight percent tantalum, from about 0 weight percent to about 0.1 weight percent carbon, and from about 0 weight percent to about 0.1 weight percent nitrogen, with the balance being iron and incidental impurities; wherein the NFA comprises a number density of at least about 10²² m⁻³ nanofeatures comprising titanium, oxygen and at least one element derived from the oxide added during preparation of the NFA or from the alloy matrix.

Typically, as noted previously, directly processing the as-consolidated NFAs at high temperatures (˜1900° F. or above) may degrade the mechanical properties of the alloy. This may be due, in part, to the increase in the grain size of the NFA with the increase in temperature above about 1800 degrees Fahrenheit. Usually, an “as-prepared” or “as-consolidated” NFA workpiece has a fine microstructure having an average grain size less than about 2 microns. In certain instances, the average grain size is between about 1 micron and 2 microns. In this fine microstructure, a percentage of coarse grains (grains larger than about 1 micron) may be low, for example less than about 5 percent based on the total grains in the microstructure.

FIG. 1A and FIG. 1B show the effect of a high temperature on the microstructure of a NFA workpiece. FIG. 1A is a scanning electron microscope (SEM) micrograph of an “as-consolidated” workpiece (i.e. without a heat treatment); and FIG. 1B is a SEM micrograph of the workpiece after heating it at 2000 degrees Fahrenheit for 24 hours. FIG. 1B clearly shows a grain growth (i.e., an increase in percentage of coarse that is large grains) in the NFA workpiece with the increase in temperature. It was observed that the percentage of coarse grains (that have grain size greater than about 1 micron, and in some certain instances, greater than about 5 microns) in the NFA workpiece after heating it up to 2000 degrees Fahrenheit is significantly larger (˜4 times) than the percentage of coarse grains in the alloy of the workpiece at about 1800 degrees Fahrenheit. After heating the workpiece at 2000 degrees Fahrenheit, for about 24 hours, the average grain size of the NFA workpiece is up to about 50 microns. This grain growth with the rise of temperature limits the processing of the NFA at high temperatures, i.e. at temperatures higher than about 1900 degrees Fahrenheit. Moreover, processing NFAs with coarsening grains by using a high strain rate technique (for example, forging) may lead to cracking, and thus damaging the resulting article.

It has been surprisingly discovered by the inventors that the present method enables the processing of the NFAs at high temperatures (more than about 1900° F.) and/or at high strain rates without a significant degradation in the mechanical properties of a resulting article at an operating temperature. An operating temperature, at which these articles are used, is generally lower than a processing temperature, at which the NFAs are processed. The ability to process the NFAs at high temperatures and/or high strain rates advantageously enables the use of the conventional high strain rate processing techniques for manufacturing a desired article from the NFA and thus maintaining low manufacturing costs.

According to some embodiments of the invention, the present method includes steps of introducing a quantity of strain into a workpiece that includes a nanostructured ferritic alloy (NFA) at a first temperature below about 1900 degrees Fahrenheit to form a strained workpiece, heating the strained workpiece to a second temperature and deforming the strained workpiece at the second temperature. The second temperature is at least about 1900 degrees Fahrenheit. In these embodiments, the quantity of strain is first introduced into the NFA workpiece at a temperature below about 1900 degrees Fahrenheit before heating and/or processing (i.e., hot-working) the workpiece at a higher temperature. The quantity of strain introduced into the workpiece at the first temperature is effective to substantially inhibit grain growth in the strained workpiece during the subsequent heating and the deforming at the second temperature. This introduction of strain into the workpiece at the first temperature enables the deforming and/or the heating of the workpiece at a subsequent higher temperature, and thus the workpiece can be processed or hot-worked at high temperatures while preserving the microstructure to procure the desired mechanical properties.

The workpiece may be fabricated by consolidating a powder of a nanostructured ferritic alloy (NFA) (as discussed previously) by any technique as known in the art. In one embodiment, the workpiece is fabricated by hot isostatic pressing (HIP). Other compaction techniques include hot compaction, extrusion, or roll compaction.

As noted, a quantity of strain is first introduced into the NFA workpiece at a first temperature below about 1900 degrees Fahrenheit. In other words, the workpiece is deformed at the first temperature. Without being bound by any theory, it is believed that by deforming the workpiece at the first temperature, a retained plastic strain interacts with the stable nanofeatures and effectively pins grain boundaries. This pinning of the grain boundaries does not allow the grains of the fine microstructure of the workpiece to substantially grow in size, and thus substantially inhibits grain growth of the microstructure of the strained workpiece during the heating, the processing, or both at a second temperature. Advantageously, the microstructure of the strained workpiece does not substantially change on heating or with a rise in temperature, and is maintained or stabilized for any further heating or processing, for example high strain rate processing at a high temperature.

It is desirable to have no or little (<1 percent) growth in the grain size of the strained workpiece during the subsequent heating and/or the processing at a temperature of at least about 1900 degrees Fahrenheit. However, there may be a substantial growth in the grain size of the strained workpiece. As used herein, a substantial growth may refer to an increase of up to about 10 percent in the percentage of coarse grains in the microstructure. In some embodiments, the increase in the percentage of coarse grains in the microstructure is in a range from about 1 percent to about 5 percent during the heating or the processing at the second temperature. FIG. 2A and FIG. 2B show SEM micrographs of a workpiece, respectively, after extruding the workpiece at 1700 degrees Fahrenheit and after heating the extruded workpiece at 2000 degrees Fahrenheit for about 24 hours. No significant change in the grain size of the workpiece was observed with the heat treatment at the high temperature after the extrusion at 1700 degrees Fahrenheit.

The stability of the microstructure of the strained workpiece may depend specifically on the first temperature in conjunction with the quantity of strain introduced into the workpiece. As alluded to previously, the quantity of strain introduced into the workpiece at the first temperature is effective to substantially inhibit grain growth in the strained workpiece during the heating and the deforming at the second temperature. The effectiveness of the strain introduced into the workpiece may be a result of an amount of a strain applied to the workpiece and a strain rate at which the strain is applied to the workpiece. That is, the workpiece may be deformed at the first temperature by applying a specific strain with a specific strain rate. The workpiece may be deformed by any technique including forging, compaction, extrusion, and rolling. In certain embodiments, the workpiece is deformed by extrusion at the first temperature.

In some embodiments, at least about 40 percent strain with a strain rate of less than about 1 inch/inch/sec is applied on the workpiece. In some embodiments, a strain ranging from about 40 percent to about 70 percent is desirable for effectively inhibiting the grain growth. In some embodiments, the strain is applied at a strain rate ranging from about 0.005 inch/inch/sec to about 0.9 inch/inch/sec. The first temperature is generally below 1900 degrees Fahrenheit. In some embodiments, the first temperature ranges from about 1600 degrees Fahrenheit to about 1900 degrees Fahrenheit, and in some certain embodiments, from about 1700 degrees Fahrenheit to about 1800 degrees Fahrenheit.

Advantageously, the strained workpiece having the stabilized microstructure can be processed at a high temperature (i.e., a high processing temperature) and/or at a high strain rate for forming an article. A high temperature refers to a temperature equal to or higher than 1900 degrees Fahrenheit. A high strain rate refers to a strain rate higher than about 1 inch/inch/sec. In some embodiments, the strain rate is higher than about 5 inch/inch/sec, and in particular embodiments, higher than about 10 inch/inch/sec. In some embodiments, after introducing a quantity of strain into the workpiece, the strained workpiece may be first heated to the second temperature and then deformed at the second temperature.

In some embodiments, the strained workpiece is deformed at a second temperature that is at least about 1900 degrees Fahrenheit. In some embodiments, the second temperature ranges from about 1950 degrees Fahrenheit to about 2300 degrees Fahrenheit, and in certain embodiments, from about 2000 degrees Fahrenheit to about 2200 degrees Fahrenheit.

The step of deforming at the second temperature may be performed to form an article from the strained workpiece. The deforming step may include deforming the strained workpiece with a high strain rate technique, for example high strain rate forging. In some embodiments, the strained workpiece is deformed with a strain rate in a range from about 10 inch/inch/sec to about 30 inch/inch/sec. Other suitable techniques may include extrusion, compaction, or rolling. In some embodiments, a workpiece is first extruded at the first temperature and then processed by forging at the second temperature. In some embodiments, a turbomachinery component, such as a bolt, may be manufactured by the disclosed method.

In some embodiments, it is desirable to deform, for example, by forging the strained workpiece at a temperature higher than 1900 degrees Fahrenheit. Processing a strained workpiece with a high strain rate at a low temperature, for example below 1900 degrees Fahrenheit may lead to cracking of the resulting NFA article/component. FIG. 3 shows flow stress curves for the NFA workpiece samples that were compressed at 1900 degrees Fahrenheit and 2100 degrees Fahrenheit. Each of these samples was first extruded at 1700 degrees Fahrenheit and then subsequently compressed at a strain rate of 20 inch/inch/sec. It was observed that a sample that was first extruded at 1700 degrees Fahrenheit and subsequently compressed at 1700 degrees Fahrenheit, was cracked. This demonstrated that this temperature, about 1700 degrees Fahrenheit, was too low to conduct a high strain rate processing. It was further observed that the samples that were compressed at 1900 degrees Fahrenheit and 2100 degrees Fahrenheit produced no cracks. Furthermore, as clearly seen from FIG. 3, the flow stresses for the samples are conducive to the component manufacturing.

While only certain features of the invention have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.

Claims

1. A method comprising:

introducing a quantity of strain into a workpiece at a first temperature below about 1900 degrees Fahrenheit to form a strained workpiece;

heating the strained workpiece to a second temperature, wherein the second temperature is at least about 1900 degrees Fahrenheit; and

deforming the strained workpiece at the second temperature, wherein the workpiece comprises a nanostructured ferritc alloy (NFA), and wherein the quantity of strain introduced into the workpiece at the first temperature is effective to substantially inhibit grain growth in the strained workpiece during the heating and the deforming at the second temperature.

2. The method of claim 1, wherein the workpiece comprises a grain size distribution having an average grain size less than about 2 microns.

3. The method of claim 1, wherein introducing a quantity of strain into the workpiece at the first temperature comprises applying at least about 40 percent strain.

4. The method of claim 1, wherein introducing a quantity of strain into the workpiece at the first temperature comprises deforming the workpiece at a strain rate lower than about 1 inch/inch/sec.

5. The method of claim 1, wherein the first temperature ranges from about 1600 degrees Fahrenheit to 1900 degrees Fahrenheit.

6. The method of claim 1, wherein the second temperature ranges from about 1950 degrees Fahrenheit to about 2300 degrees Fahrenheit.

7. The method of claim 1, wherein deforming the strained workpiece comprises deforming the strained workpiece at a strain rate of at least about 1 inch/inch/sec.

8. The method of claim 1, wherein deforming the strained workpiece comprises deforming the strained workpiece at a strain rate ranging from about 1 inch/inch/sec to about 30 inch/inch/sec.

9. The method of claim 1, wherein the deforming step is performed by compaction, forging, extusion, or rolling.

10. An article formed by the method according to claim 1.

11. The article of claim 10, wherein the article is a turbomachinery component.

12. A method of forming a turbomachinery component, comprising the steps of:

introducing a quantity of strain into a workpiece at a first temperature below 1900 degrees Fahrenheit to form a strained workpiece, wherein the workpiece comprises a nano structured ferritc alloy (NFA); heating the strained workpiece to a second temperature, wherein the second temperature is at least about 1900 degrees Fahrenheit; and forging the strained workpiece at the second temperature at a strain rate of at least about 1 inch/inch/sec, wherein the quantity of strain introduced into the workpiece at the first temperature is effective to substantially inhibit grain growth in the strained workpiece during the heating and the forging at the second temperature.