Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/08—Ferrous alloys, e.g. steel alloys containing nickel
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/54—Ferrous alloys, e.g. steel alloys containing chromium with nickel with boron
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese

Definitions

• the present invention relates to nickel-chromiumstainless steels and more particularly to austenitic nickel-chromium stainless steels for castings.
• austenitic nickel-chromium steels by casting methods, particularly where the desired article is of a complex shape that is difficult or expensive to forge or machine.
• stainless steels are cast in sand molds or other expendable refractory molds, e.g., investment molds or resin-bonded shell molds, inasmuch as the castability characteristics of these steels generally require pouring at temperatures at least as high as about 2,750F. and usually higher, e.g., 2,950F. or 3,100F., especially when the casting has relatively long thin sections of one'fourth inch or one-eighth inch or less in thickness.
• Good castability includes the capability of mo]- ten metal to run through thin sections of a mold and, very importantly, also to flow and merge cleanly into itself when the flow of metal in the mold divides and then merges together, in which circumstance it is especially important to obtain complete sound solidification without colds shuts, folds or oxide films. Also, cleanliness in the molten condition and a low melting point are desirable characteristics for good castability.
• a cast stainless steel have at least modest mechanical strength and ductility characteristics, e.g., 60,000 psi ultimate tensile strength, 25,000 psi yield strength with about 5% or more tensile elongation. It is also desirable that a steel casting have impact resistance to withstand rough handling such as by being dropped on a concrete floor or hammered to conform it in an assembly. Although this does not necessitate 5% elongation, the cast steel should be characterized by at least 1% elongation in order to satisfy minimal requirements, such as decorative and other nonstructural uses.
• Good general corrosion resistance includes resistance to staining in corrosive atmosphere, e.g., salt spray.
• corrosive atmosphere e.g., salt spray.
• a further object of the invention is to provide a process for producing strong corrosion-resistant stainless steel articles.
• the present invention contemplates nickelchromium stainless steel castings, and also alloys and processes for production thereof, containing by weight, about 6% to 30% nickel, about 14% to about 26% chromium, up to about 0.15% carbon, advantageously not more than 0.1% carbon, about 2% to 5% silicon, advantageously 2.8% to 3.8% silicon, up to about 20% manganese, at least 0.2% boron, e.g., about 0.25% or 0.3%, to about 1.4% boron, up to about 3% copper, up to about 8% molybdenum, up to about 1.4% phosphorus and up to about 1% columbium and wherein the amounts of nickel, manganese, chromium, molybdenum, silicon, boron and phosphorus in this subject composition are correlated according to the relationship Excellent castability characteristics that are beneficial for the melting and pouring of castings are obtainable with the subject alloy composition.
• Embodiments of the subject alloy have been successfully melted in gas fired furnaces and cast at 2,350F. in green sand molds and good filling, with sharp definition at corners, was achieved in thin-sectioned mold cavities about threesixteen inch thick by 1 /2 inches square. To achieve excellent castability the composition is advantageously correlated to provide that the: foregoing relationship R( 1) equals at least 560.
• the invention provides a restricted range composition containing about 6% to 26% or 28% nickel, about 14% to 20% or 25% chromium, up to about 0.15% carbon, advantageously not more than 0.1% carbon, about 2% to 5% silicon, advantageously 2.8% to 3.8% silicon, up to about 20% manganese, 0.3% to about 0.7% boron, up
• R(2) Phosphorus in amounts up to 1.4% can be added to the restricted composition; when the alloy contains a substantial amount of phosphorus, e.g., 0.2%, 0.5% or more, a phosphorus term +189(%P) may be included in R(2).
• the balance of the steel is hereinafter referred to as iron, or essentially iron, it is to be understood the balance usually includes small amounts of impurities and incidental elements, including residuals of melt treating agents.
• the balance may include, for instance, up to 0.04% phosphorus, up to 0.04% sulfur, and up to 0.25% selenium.
• Nitrogen may be present in amounts up to the solubility limit, e.g., up to about 0.25% nitrogen.
• Such highly oxidizable elements as titanium and aluminum are desirably avoided or carefully limited to low levels, e.g., 0.3% or less, in the steel of the present invention inasmuch as substantially greater amounts of these elements, either as metals or oxides, would be detrimental to the good castability characteristics of the steel.
• it is of advantage that the present steel provides satisfactory sound castings, free from porosity and with good strength and ductility, without need for titanium.
• Small additions of aluminum, e.g., 0.1% aluminum are effective for deoxidation.
• substantially greater amounts of aluminum would adversely affect castability and, accordingly, large additions or progressive build-up of aluminum are avoided and the amount of aluminum in the steel should not exceed about 0.3%.
• the steel of the invention is especially characterized by very good or excellent castability enabling production of complex thin-sectioned stainless steel castings with the steel poured, or cast, at temperatures of about 2,650F. or 2,350F. or lower.
• good castability characteristics it is particularly notable that the steel is clean and essentially free from films, dross,
• the steel of the invention is characterized by a freezing temperature (incipient freezing or, approximately, the liquidus) not higher than 2,350F.
• a freezing temperature incipient freezing or, approximately, the liquidus
• the freezing temperature of a steel of the invention namely alloy No. 8 which is referred to hereinafter in Tables l and 11, was determined by thermocouple measurement to be 2,322F.
• Vacuum melting may be used if desired for some purpose. Gas-fired melting was successful for steels of the invention containing more than 0.7% each of boron and phosphorus and with R( l at least about 715. Castings of the subject steel can be poured in practically all kinds of expendable foundry molds, e.g., green sand molds, dry sand molds, resin-bonded shell and investment molds.
• the steel can be cast in permanent molds or die casting molds made of cast iron or steel, or of graphite or molybdenum. Testing of embodiments containing 0.3% to 0.7% boron has shown that these steels have good resistance to hot tearing and avoid hot-shortness. Good results, including smooth surface finish and complete sound solidifiction with very good filling of thin sections and fine details in the mold, have been obtained when casting the steel of the invention in green sand molds and also in permanent iron molds.
• the R(l) factor can be as low as 180.
• the manganese content is advantageously controlled to a range of 0.1 to 5.
• a particularly good composition for economical production of sand casting contains about 8% to 14% nickel, 16% to 20% chromium, 2.5% to 3.5% silicon, 0.25% to 0.55% boron, up to 0.15% carbon, 0.2% to 2.5% manganese, up to about 4% molybdenum, up to 2% copper and balance iron and with the composition correlated in accordance with the relationship
• the cast steel of the invention has satisfactory strength and ductility, e.g., room temperature yield strength of 25,000 or 30,000 psi or more at 0.2% offset, and also corrosion resistance, for many industrial or household or other commercial uses.
• a desirable room temperature ductility characteristic of at least 5% tensile elongation is obtainable with the steel cast in thin sections and solution treated, e.g., a A inch thick cross-section cast in a dry sand mold and solution treated 1 hr. at 2,000F.
• Ductility characteristics are, in
• a recommended range for so tion treatment is 1,850F. to 2,050F. for one-half hour or longer, e.g., 1 hour, followed by air cooling, or more rapid cooling, down to 600F. or lower, e.g., room temperature.
• the microstructure of the steel is normally characterized by dendrites composed of austenite, ferrite, etc., with intermetallic precipitates, e.g., acicular borides and/lor eutectic phosphides, in the interdendritic regions.
• the solutiontreated condition of the cast steel is usually characterized by a dendritic microstructure comprising substan tially less precipitate than in the cast condition. Grain sizes of the castings and also the sizes and distributions of the microstructure particles are generally smaller and finer, e.g., interdendritic spacing of about to 50 microns, and more uniformly distributed, in the rapidly solidified castings.
• the solution-treated structure is advantageous for good ductility and corrosion-resistant characteristics of the steels with 0.3% to 0.7% boron.
• the steel contains at least 6% nickel, and more desirably at least about 8% nickel, to provide, where desired, a stable austenitic structure in practical conditions of use. Moreover, the nickel content also promotes desirable ductility characteristics, including shock resistance, and corrosion resistance of the castings. In these respects, at least about 8% nickel, more advantageously at least 1 1% nickel, in the steel is advantageous.
• silicon content does not exceed 5% in order to avoid adverse effects on ductility.
• silicon should be not greater than 3.8%.
• Compositions with silicon contents of 2.5% to 3.8% and boron contents of 0.3% to 0.7% are recommended for a particularly advantageous combination of castability and ductility characteristics.
• the stainless steels include 0.3% to about 1.4% boron and about 14% to chromium, advantageously at least 0.45% boron and at least 17.5% chromium, to contribute the combination of castability, ductility and corrosion resistance which characterize the composition as a whole.
• Embodiments containing 0.3% to 0.7% boron are desirable from the viewpoint of ductility and corrosion resistance; embodiments containing more than 0.7% boron, e.g., 0.8% boron, partic ularly 0.9% to 1.3% boron, are recommended from the fluidity viewpoint; and, where castability needs are dominant, embodiments containing a combination of 0.9% to 1.4% phosphorus along with 0.9% to 1.4% boron are advantageous for obtaining excellent castability and also for enabling melting in gas-fired foundry furnaces.
• the steel usually contains at least about 1% manganese, often about 5% or 10% or more manganese, in order to benefit castability and ductility.
• Small amounts of carbon e.g., at least about 0.02%, are advantageous for enhancing the castability of the steel.
• Presence of copper in the steel e.g., about 1.5%, 2%, or 2.7% copper, is desirable for benefiting corrosion resistance, particularly resistance to sulfuric acid solutions.
• Molybdenum e.g., about 2% to 6%, is desirably present for enhancing resistance of the steel to corrosive attack, particularly crevice corrosion and pitting 6 corrosion in chloride media.
• excessive amounts of copper and/or molybdenum e.g., 4% copper, should be avoided in order to avoid embrittling the steel.
• the steel of the invention is generally characterized in the solution treated condition by at least 30,000 psi yield strength, about 5 ft. lb. or more impact strength, a freezing temperature not greater than 2,325F. and particularly good resistance to corrosion in salt spray media.
• the invention further provides another advantageous steel which contains 23.5% to 26% nickel, 18% to 20% chromium, 3% to 3.5% silicon, 1% to 2% manganese, 0.02% to 0.08% carbon, 0.55% to 0.7% boron, 2.2% to 2.7% copper and 2.3% to 6.5% molybdenum and is especially beneficial for achieving very good corrosion resistance, particularly resistance to staining in salt spray, along with room temperature ductility of at least 5% tensile elongation and highly beneficial castability characteristics including a castable molten condition at temperatures below 2,300F., e.g., freezing temperatures of 2,290F., 2,250F. or even down to 2200F. or lower.
• Stainless steels in accordance with the invention were air-induction melted in a magnesia crucible using Armco Iron, silicomanganese, ferrosilican and metallic silicon, electrolytic manganese, ferrochromium, wash metal (iron with about 4% carbon), electrolytic nickel, copper shot, and ferroboron.
• Nickel-selenium was used when selenium was added.
• the iron, nickel, copper and manganese (about of the total manganese was charged in the electrolytic form) were charged and heated to about 2,850F. and then the wash metal, ferrochromium, silicomanganese and silicon (about 60% of the total silicon was metallic silicon), and ferroboron were added; phosphorus for alloys 21 to 27 was added as ferrophosphorus.
• the steel was cast at about 2,600F. (alloys l-20), or 2,350F.(alloys 2127), into dry sand molds for keel blocks of 1-inch or one-fourth-inch thickness at base.
• melts were cast in sand molds for demonstrating fluidity and other casting flow characteristics (spiral or flow-and-knit CP pattern molds), or for demonstrating resistance to hot tearing, or were cast in metal molds for demonstrating fluidity.
• Chemical anal- 7 yses of melts of cast steels (Alloys) produced in accordance with the invention are set forth in the following Tables 1 and IA.
• melts 28 to 31 were made with nominal compositions having a balance of iron and each with 0.08% carbon, 1% manganese, 18.5% chromium and 0.025% phosphorus and with other elements as follows: alloy 28 10.5% nickel, 2% silicon, 0.5% boron; alloy 29 10.5% nickel, 2% silicon, 0.3% boron; alloy 30 12% nickel, 3% silicon, 0.5% boron; and alloy 31 12% nickel, 3% silicon, 0.3% boron. Chemical analyses reported for the boron contents of alloys 28, 29, 30 and 31 were 0.48%, 0.25%, 0.51%, and 0.28% boron, respectively.
• Another melt, alloy 32 was made by melting stainless steel scrap and adding alloying elements to prepare alloy 32 of the invention which, when analyzed, was re- Results of room temperature tensile, impact and/or hardness testing of specimens machined from castings made of alloys in accordance with the invention (embodiments) are set forth in the following Table 11.
• A1- loys 4 to 12, 28 to 31 were cast in both l-inch and A1- inch or %-inch width keel block molds (alloys 4 to 12 and one-fourth-inch and alloys 28 to 31 in three-eighthinch), and others were cast in either the l-inch or onefourth-inch widths; then, one-half-inch diameter and/or one-eighth-inch diameter tensile test specimens (2-inch and 1-inch gage lengths respectively) machined therefrom were tested.
• the results, as set forth in Table 11, show particularly satisfactory mechanical properties of rapidly solidified steels cast in thin cross-sections.
• Table 11 illustrates that the solution treatment of compositions containing 0.3% to 0.7% boron in accordance with the invention resulted in improved ductility characteristics, particularly elongation and impact resistance, without detrimentally decreasing the ultimate tensile strength, and often somewhat increasing the tensile strength along with the improve- 1 1 ment in ductility.
• the castings of invention had highly satisfactory smooth surfaces with good filling at corners in thin sec tions of the mold cavity and without any indications of metal-mold reactions, liquid-metal penetration of the mold, burn on or other types of surface roughness or defects of kinds resulting from excessively hot metal contact with molds. Moreover, CP-pattern castings of steels of the invention showed good freedom from folds, cold shuts or other defects such as occur if metal is poured too cold or lacks good fluidity.
• This CP (Chinese Puzzle) pattern which is designed to test castability characteristics such as the ability of a molten metal to run through the passages of a complex mold with abrupt changes in flow direction that are conducive to turbulence, comprises a number of partially adjoining rectangular cavities of about three-sixteenths inch thickness.
• the CP pattern demands more of a melt than simply capability to remain fluid over the course of a long run, such as in a fluidity spiral, but requires many sharp changes in flow direction with the flow meeting and merging with itself, filling of many comers and flow through and filling of large thin flat surfaces, e.g., 1 /2 inches square by three-sixteenths inch thick.
• the steels of the invention exhibited much better castability, particularly with success in avoiding entrapped films, folds and cold shuts when cast at 2,650F. (alloys 412 and 28 through 31), or at 2,350F. (alloys 23, 25 and 27) than did the results obtained casting CF-8 steel at 2,950F.
• Both the steels of the invention and the CF-8 steel resisted hot tearing on the 6-inch and 9-inch arms but did show hot-tearing on the 12- inch arm and thus the hot-tearing resistance of the steels of the invention (alloys 2 and 13) was deemed generally about as good as that of the CF-8 steel, which is usually considered to have at least moderately good resistance to hot tearing.
• Tensile strength and ductility characteristics of the remelts were consistently satisfactory, with room temperature tensile and impact characteristics of 37.7 to 40.4 ksi YS, 73.8 to 77.2 ksi UTS, 7 to 13.5% Elong. and 4.5 to 7.5 ft.-lb. Impact, in the As-Cast condition; and 34.8 to 37.1 ksi YS, 80.2 to 80.6 ksi UTS, 15 to 19% Elong. and 9 to 13 ft.-lb. Impact in the Solution Treated Condition.
• Alloys 22, 24 and 26 were remelted in gas-fired furnaces and cast at 2,350F. into CP-pattem green sand molds. Visual examination of the resulting castings showed that these remelted alloys successfully filled mold cavities about three-sixteenths inch thick by 1 /2 inches square and pg symbolized satisfactory castings with good smooth surfaces and sharp definition without entrapped films, folds or cold shuts when poured at 2,350F., thus confirming excellent castability.
• steels of the invention e.g., embodiments of an advantageous composition containing about 8% to 10% nickel, 15% or 17.5% to 19.5% chromium, 0.02% to 0.1% carbon, 2.75% to 3.25% or 3.5% silicon, 16% to 18% or 19% manganese, 0.45% to 0.7% boron, 1.5% to 2.5% copper and balance essentially iron, were remelted and die cast (under pressure) at about 2,450F. to 2,600F.
• the resulting stainless steel 13 die castings of the invention stripped cleanly from the metal molds, were well-filled and had highly satisfactory smooth, sharply defined surfaces.
• Stainless steels of the invention e.g., alloy 8 in the ascast condition and in the solution treated condition, exhibited good machinability when drilled with high speed steel drills.
• a specimen of alloy 7 had a hardness of 51 Rockwell A in the solution annealed condition and had the same hardness of 51 Rockwell A after aging at 1,250F. for 15 hours following the solution treatment.
• Brazing is recommended if there is need to join the steel to itself.
• Specimens of a steel of the invention containing about 0.082% carbon, 8.4% nickel, 15.9% chromium, 3.18% silicon, 17.5% manganese, 2.1 1% copper and 0.48% boron were satisfactorily brazed together by torch brazing using a commercial silver-solder brazing alloy. Subsequent testing showed that the resultant brazed join had good impact resistance; moreover, metallurgical examination showed that the brazing alloy flowed satisfactorily with good wetting of the steel, and the brazed steel surfaces were free from intergranular penetration.
• Cast steels of the invention advantageously in the solution treated condition, and with boron in the range of 0.3% to 0.7%, have good corrosion resistance that is clearly superior to the corrosion resistance of martensitic stainless steels, e.g., ACI Types CA-15 and CB-30, and approaches or approximates, and in some instances equals, the corrosion resistance of austenitic stainless steels, e.g., Type CF-8, in many respects.
• Results of CASS (Copper Accelerated Salt Spray) tests corresponding to ASTM B368-61T confirmed that steels of the invention have satisfactory resistance to pitting in salt spray.
• solution treated specimens of alloys 14 through 19 which were subjected to CASS tests of seven days duration exhibited good resistance to pitting and to general corrosion in salt spray that was about as good as that of Type CF-8 steel, with the best corrosion resistance being evidenced by alloys 14, and 16.
• CASS tests of 24 hours duration specimens of alloys 4 through 12 in the solution treated condition success fully resisted pitting and showed general corrosion resistance between that of Types CB-30 and CF-8.
• Corrosion tests of steels 4 through 7 in deaerated 5% H 80 at room temperature showed corrosion resistance intermediate between that of Types CB-30 and C F-8.
• the present invention is particularly applicable to economical production of cast-to-shape stainless steel articles including home and industrial housing hardware, e.g., door handles and door stops, plumbing hardware, e.g., pipe fittings, faucets and valve bodies, marine hardware, e.g., rope cleats, and also including decorative trim, escutcheon plates, pump housings and trivets.
• the invention is applicable to providing many kinds of articles that are commonly made of cast brass and in this regard the corrosion resistant characteristics of the subject steels are deemed especially beneficial for resisting corrosive attack by ammonia, including moist ammonia and ammoniacal cleansers, such as has been found detrimental to brass. While utility referred to hereinbefore is largely at room temperature, it should be understood the present steels have useful strength at temperatures substantially below and above room temperature, such as from sub-zero temperatures up to about 1,000F. or higher.
• An austenitic nickel-chromium stainless steel consisting essentially of 6% to about 28% nickel, about 14% to about 25% chromium, 2% to about 5% silicon, 0.3% to about 0.7% boron, up to about 0.15% carbon, up to about 20% manganese, up to about 3% copper, up to about 8% molybdenum, up to about 1% columbium and balance iron and wherein the amounts of nickel, chromium, silicon, and boron and any manganese and molybdenum in the alloy are correlated in accordance with the relationship said steel being characterized by castability superior to that of austenitic steels of the AOL CF-8 type, as determined by relative freedom from cold shut defects when cast in three-sixteenths-inch thick by l /z-inch interlocking squares in green sand molds according to the Chinese Puzzle pattern, and additionally characterized by corrosion resistance superior to that of martensitic-ferritic steels of the AC].
• CA-15 and CB-30 types as determined
• An austenitic nickel-chromium stainless steel casting characterized by (a) a room temperature tensile elongation of at least about 5%, (b) a room temperature yield strength of at least 25,000 pounds per square inch, (0) a stable austenitic cast microstructure containing austenitic dendrites and (d) being formed from a steel characterized at 2,650F.
• a molten condition possessing good castability for flowing and knitting and resisting formation of cold shut defects and for merging and solidifying in the form of continuously sound cast metal in thin, relatively large area, green-sand mold cavities of three-sixteenths-inch thickness by 1 /2 inch square area interlocked in patterns conducive to turbulent flow of molten metal
• said steel consisting essentially of 8% to about 30% nickel, about 14% to about 26% chromium, 2% to 3.8% silicon, 0.2% to about 0.7% boron, up to about 0.15% carbon, up to about manganese, up to about 3% copper, up to about 6% molybdenum, up to about 1% columbium, up to about 0.2% phosphorus and balance iron and wherein the amounts of nickel, chromium, silicon, boron and any manganese, molybdenum and phosphorus in the alloy are correlated in accordance with the relationship 5.
• a process comprising establishing a molten bath of the steel set forth in claim 4, pouring the mol
• An austenitic nickel-chromium stainless steel consisting essentially of casting according to claim 4 about 8% to 14% nickel, 16% to 20% chromium, 2.5% to 3.5% silicon, 0.25% to 0.55% boron, 0.2% to 2.5% manganese, up to 4% molybdenum and up to 2% copper.
• An austenitic nickel-chromium stainless steel consisting essentially of 6% to about nickel, about 14% to about 26% chromium, 2% to about 5% silicon, 0.2% to 1.4% boron, up to about 0.15% carbon, up to about 20% manganese, up to about 3% copper, up to about 8% molybdenum, up to 1.4% phosphorus, up to about 1% columbium and balance iron and wherein the amounts of nickel, chromium, silicon, boron and any manganese, molybdenum and phosphorus in the alloy are correlated in accordance with the relationship said steel being characterized in the molten condition by castability superior to that of austenitic steels of the AC].
• CF-8 type as determined by relative freedom from cold shut defects when cast in threesixteenths-inch thick by l /z-inch interlocking squares in green sand molds according to the Chinese Puzzle pattern, and in the solid condition by a non-age hardenable austenitic microstructure having corrosion resistance superior to that of martensitic-ferritic steels of the A.C.I. CA-lS and CB-30 types, as determined by resistance to pitting and general corrosion in salt-spray CASS tests corres nding to ASTM B368-6lT.
• a stainless steel as set forth in claim 8 containing at least 8% nickel.
• a stainless steel as set forth in claim 8 containing 2.5% to 3.8% silicon.
• a stainless steel as set forth in claim 8 containing 8% to 14% nickel, 16% to 20% chromium, 0.2% to 0.55% boron, 0.2% to 2.5% manganese, up to 4% molybdenum and up to 0.2% phosphorus.
• a process comprising preparing a molten bath of steel having a composition in accordance with claim 8, casting the steel into a mold and solidifying the steel in the mold.

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