Castable nickel-chromium stainless steel

Claim 2

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 AMOUNTS OF NICKEL, CHROMIUM, SILICON, AND BORON AND ANY MANGAHESE AND MOLYBDENUM IN THE ALLOY ARE CORRELATED IN ACCORDANCE WITH THE RELATIONSHIP 8(%NI+%MN)-1.5(%CR+%MO)+22(%SI+284(%B) EQUAL AT LEAST 360 SAID STEEL BEING CHARACTERIZED BY CASTABILITY SUPERIOR TO THAT OF AUSTENITIC STEELS OF THE A.C.I. CF-8 TYPE, AS DETERMINED BY RELATIVE FREEDOM FROM COLD SHUT DEFECTS WHEN CAST IN THREE-SIXTEENTHS-INCH THICK BY 1/2-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 A.C.I. CA-15 AND CB-30 TYPES, AS DETERMINED BY RESISTANCE TO PITTING AND GENERAL CORROSION IN SALT-SPRAY CASS TESTS CORRESPONDING TO ASTM B368-6IT.

Claim 3

An austenitic nickel-chromium stainless steel consisting essentially of 8% to 10% nickel, 17.5% to 19.5% chromium, 0.02% to 0.1% carbon, 2.75% to 3.25% silicon, 0.45% to 0.7% boron, 16% to 18% manganese, 1.5% to 2.5% copper up to about 8% molybdenum, up to 1% columbium, and balance essentially iron and wherein the composition is controlled in accordance with the relationship 8(%Ni+%Mn)-1.5(%Cr+%Mo)+22(%Si)+284(%B) equal at least 385.

Claim 4

An austenitic nickel-chromium stainless steel consisting essentially of 8% to 10% nickel, 17.5% to 19.5% chromium, 0.02% to 0.1% carbon, 2.75% to 3.25% silicon, 0.45% to 0.7% boron, 16% to 18% manganese, 1.5% to 2.5% copper up to about 8% molybdenum, up to 1% columbium, and balance essentially iron and wherein the composition is controlled in accordance with the relationship 8(%Ni+%Mn)-1.5(%Cr+%Mo)+22(%Si)+284(%B) equal at least 385.

Claim 5

An austenitic nickel-chromium stainless steel consisting essentially of 23.5% to 26% nickel, 18% to 20% chromium, 0.02% to 0.08% carbon, 3% to 3.5% silicon, 0.55% to 0.7% boron, 1% to 2% manganese, 2.2% to 2.7% copper 2.3% to 6.5% molybdenum and balance essentially iron and wherein the composition is controlled in accordance with the relationship 8(%Ni+%Mn)-1.5(%Cr+%Mo)+22(%Si+284(%B) equal at least 360.

Claim 6

An austenitic nickel-chromium stainless steel consisting essentially of 23.5% to 26% nickel, 18% to 20% chromium, 0.02% to 0.08% carbon, 3% to 3.5% silicon, 0.55% to 0.7% boron, 1% to 2% manganese, 2.2% to 2.7% copper 2.3% to 6.5% molybdenum and balance essentially iron and wherein the composition is controlled in accordance with the relationship 8(%Ni+%Mn)-1.5(%Cr+%Mo)+22(%Si+284(%B) equal at least 360.

Claim 7

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, (c) a stable austenitic cast microstructure containing austenitic dendrites and (d) being formed from a steel characterized at 2,650*F. by 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 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 20% 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 8% (%Ni+Mn)-1.5(%Cr+%Mo)+22(%Si)+284(%B)+189(%P) equal at least 180.

Claim 8

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, (c) a stable austenitic cast microstructure containing austenitic dendrites and (d) being formed from a steel characterized at 2,650*F. by 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 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 20% 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 8% (%Ni+Mn)-1.5(%Cr+%Mo)+22(%Si)+284(%B)+189(%P) equal at least 180.

Claim 9

A process comprising establishing a molten bath of the steel set forth in claim 4, pouring the molten steel into a mold and then solidifying the steel to thereby produce a cast-to-shape stainless steel article.

Claim 10

A stainless steel casting as set forth in claim 4 wherein the amount of any manganese present does not exceed 5%.

Claim 11

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.

Claim 12

An austenitic nickel-chromium stainless steel consisting essentially of 6% to about 30% 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 8%(%Ni+%Mn)-1.5(%Cr+%Mo)+22(%Si)+284(%B)+189(%p) equal at least 180; said steel being characterized in the molten condition by castability superior to that of austenitic steels of the A.C.I. CF-8 type, as determined by relative freedom from cold shut defects when cast in three-sixteenths-inch thick by 1 1/2 -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-15 and CB-30 types, as determined by resistance to pitting and general corrosion in salt-spray CASS tests corresponding to ASTM B368-61T.

Claim 13

An austenitic nickel-chromium stainless steel consisting essentially of 6% to about 30% 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 8%(%Ni+%Mn)-1.5(%Cr+%Mo)+22(%Si)+284(%B)+189(%p) equal at least 180; said steel being characterized in the molten condition by castability superior to that of austenitic steels of the A.C.I. CF-8 type, as determined by relative freedom from cold shut defects when cast in three-sixteenths-inch thick by 1 1/2 -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-15 and CB-30 types, as determined by resistance to pitting and general corrosion in salt-spray CASS tests corresponding to ASTM B368-61T.

Claim 14

A stainless steel as set forth in claim 8 containing at least 8% nickel.

Claim 15

A stainless steel as set forth in claim 8 containing 2.5% to 3.8% silicon.

Claim 16

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.

Claim 17

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.

Claim 18

A process as set forth in claim 12 wherein the steel is solidified in an expendable refractory mold.

Claim 19

A process as set forth in claim 12 wherein the steel is solidified in a metal mold.

Claim 20

A process as set forth in claim 14 wherein the steel is die cast under pressure.

Claim 21

A process as set forth in claim 12 wherein the steel is rapidly solidified at a rate at least equivalent to solidification of a 1/4 -inch thick cross-section in a dry sand mold and is thereafter solution-treated for at least one-half hour at 1,850*F. to 2,050*F.