Low cost high strength martensitic stainless steel

• US 20090196784A1
• Filed: 10/25/2008
• Published: 08/06/2009
• Est. Priority Date: 02/06/2008
• Status: Active Grant

• Current Assignee: Gregory Vartanov, Vladimir A. Fedchun
• Original Assignee: Gregory Vartanov, Vladimir A. Fedchun
• Inventors: Fedchun, Vladimir A., Vartanov, Gregory
• Granted Patent: US 8,071,017 B2
• Time in Patent Office: Days
• US Class Current: 420/61
• CPC Class Codes: C22C 38/04 containing manganese
• CPC Class Codes: C22C 38/20 with copper
• CPC Class Codes: C22C 38/42 with copper
• CPC Class Codes: C22C 38/44 with molybdenum or tungsten

Abstract

A cobalt-free low cost high strength martensitic stainless steel, with concentration of Ni up to 3.0% and Mo up to 1.0% of weight, has HRC of 53, UTS of 297 ksi, YS of 220 ksi, Charpy V-notch impact energy of 17.8 ft-lb, corrosion resistance in salt spray test ASTM 117. The steel was melted in an open induction furnace and vacuum arc remelting (VAR) and/or electroslag remelting (ESR) were not used to refine the steel. Further processing included homogenized annealing, hot rolling, and recrystallization annealing. The steel was heat treated by oil quenching, refrigeration, and low tempering. The steel has a microstructure consisting essentially of small packets of fine martensite laths, retained austenite, and carbides as centers of growth of the martensite laths. The cost and energy in making the steel are substantially reduced.

Claims

1. A low cost high strength martensitic steel comprising by weight:

about 0.3% to 0.65% C;

about 7.5% to 18.0% Cr;

about 0.1% to 1.0% Mo;

about 0.1% to 3.0% Ni;

about 0.3% to 1.5% Mn;

at least one element selected from the group consisting of Si, Sn, and Ge wherein (Si+Sn+Ge) is about 0.1% to 1.5% and Ge is at most 0.1%;

about 0.3% to 1.3% Cu wherein Cu is less than (Si+Sn+Ge);

at least one element selected from the group consisting of V, Ti, and Nb, wherein (V+Ti+Nb) is about 0.15 to 1.25%;

at most 0.25% Al; and

a balance of Fe and incidental impurities.

2. The low cost high strength martensitic steel recited in claim 1 wherein said Cr is about 7.5% to 12.5% of the weight of said steel and the sum of said alloying element of said steel, except for Cr, is less than 9.0% of the weight and said steel has a Rockwell hardness of about C 51 to 55, an ultimate tensile strength of about 250 to 310 ksi, a yield strength of about 200 to 240 ksi, a Charpy V-notch impact toughness energy of about 12 to 22 ft-lb, a fracture toughness K1c of more than 40 ksi√

in, and a corrosion resistance in salt spray test ASTM B117.

3. The low cost high strength martensitic steel recited in claim 1 wherein said Cr is about 12.5% to 18.0% of the weight of said steel and the sum of said alloying elements, except for Cr, is less than 5.0% of the weight and said steel and said steel has a Rockwell of about C 52 to 57, an ultimate tensile strength of about 270 to 320 ksi, a yield strength of about 200 to 260 ksi, a Charpy V-notch impact toughness energy of about 5 to 10 ft-lb, a fracture toughness K1c of about 15 to 30 ksi√

in, and a corrosion resistance that is similar to the corrosion resistance of AISI 440A steel.

4. The low cost high strength martensitic steel recited in claim 1 wherein said steel has a microstructure consisting essentially of small packets of fine martensite laths grown on fine carbides and retained austenite and said packets are free of carbides, said steel having a ratio of the volume of said retained austenite to the volume of said martensite laths that is less than 0.20.

5. A low cost high strength martensitic steel comprising by weight:

about 0.3% to 0.65% C;

about 7.5% to 18.0% Cr;

at most about 1.0% Mo;

at most about 3.0% Ni;

about 0.3% to 1.5% Mn;

at least one element selected from the group consisting of Si, Sn, and Ge wherein (Si+Sn+Ge) is about 0.1% to 1.5% and said Ge is at most 0.1%;

about 0.3% to 1.3% Cu wherein said Cu is less than (Si+Sn+Ge);

at least one element selected from the group consisting of V, Ti, and Nb wherein (V+Ti+Nb) is about 0.15% to 1.25%;

at most about 0.25% Al; and

a balance of Fe and incidental impurities.

6. The low cost high strength martensitic steel recited in claim 5 wherein said Cr is about 7.5% to 12.5% of the weight of said steel and the sum of said alloying elements, except for said Cr, is less than 9.0% of the weight of said steel, said steel having a Rockwell hardness of about C 51 to 55, an ultimate tensile strength of about 250 to 310 ksi, a yield strength of about 200 to 240 ksi, a Charpy V-notch impact toughness energy of about 12 to 22 ft-lb, a fracture toughness K1c of more than 40 ksi√

in, and a corrosion resistance in salt spray test ASTM B117.

7. The low cost high strength martensitic steel recited in claim 5 wherein said Cr is about 12.5% to 18.0% of the weight of said steel and said Ni and Mo are not present in said steel, said steel having a Rockwell hardness of about C 52 to 57, an. ultimate tensile strength of about 270 to 320 ksi, a yield strength of about 200. to 260 ksi, a. Charpy V-notch impact toughness energy of about 5 to 10 ft-lb, a fracture toughness K1c of about 15 to 30 ksi √

in, and a corrosion resistance that is similar to the corrosion resistance of AISI 440A steel.

8. A low cost high strength martensitic stainless steel comprised of a microstructure of small packets of fine martensite laths, retained austenite, and carbides as centers of growth of said martensitic laths, wherein said packets have boundaries that are free of carbides, and a ratio of volume of said retained austenite to volume of said martensite laths that is less than about 0.20.

9. The low cost high strength martensitic stainless steel recited in claim 8 wherein said steel is comprised by weight of about 0.3% to 0.65% of C, about 7.5% to 18% of Cr and alloying elements that other than said C and said Cr that comprise about 5% to 9% of the weight of said steel and a balance of Fe and incidental impurities.

10. The low cost high strength martensitic stainless steel recited in claim 8 wherein said steel has a Rockwell Hardness of about C 53;

an ultimate tensile strength of at least 250 ksi;

a yield strength of at least 200 ksi, a Charpy V-notch impact toughness energy of at least 12 ft-lb, a fracture toughness K1c of at least 40 ksi√

in, and a corrosion resistance in salt spray test ASTM B117.

11. The low cost high strength martensitic steel recited in claim 8 wherein for reducing the cost of producing said steel, said steel is melted in an open induction furnace and high energy consumption vacuum arc remelting (VAR) and electroslag remelting (ESR) are not used to refine said steel.