Process for producing maraging steel

• US 6,309,474 B1
• Filed: 03/03/2000
• Issued: 10/30/2001
• Est. Priority Date: 03/04/1999
• Status: Expired due to Term

• Current Assignee: Honda Giken Kogyo Kabushiki Kaisha (Honda Motor Company)
• Original Assignee: Honda Giken Kogyo Kabushiki Kaisha (Honda Motor Company)
• Inventors: Yagasaki, Toru
• Primary Examiner(s): King, Roy
• Assistant Examiner(s): COY, NICOLE A
• Application Number:
  US09/518,719
• Time in Patent Office: 606 Days
• Field of Search: 148/217, 148/230
• US Class Current: 148/230
• CPC Class Codes: C21D 6/001 containing Ni C21D6/004 takes precedence
• CPC Class Codes: C23C 8/26 of ferrous surfaces
• CPC Class Codes: C23C 8/34 more than one element being applied in more than one step

Abstract

In a method for producing maraging steel, a thin plate of maraging steel is subjected to an aging treatment, is then subjected to a fluoridation processing in which the thin plate is heated and maintained in a fluoric reacting gas including fluorine so as to form a fluoride layer on a surface of the thin plate, and is then subjected to nitriding in a nitriding reaction gas including ammonia gas so as to restrict the carbon concentration of the thin plate after the nitriding to 2 weight % or less.

Claims

1. A method for producing maraging steel comprising:

performing solution treatment in a vacuum furnace to a thin plate made from maraging steel;

aging the thin plate in an inert gas;

performing fluoridation processing by heating and maintaining the thin plate in a, fluoric reacting gas including fluorine so as to form a fluoride layer on a surface of the thin plate; and

then

nitriding the thin plate in a nitriding reaction gas including ammonia gas so as to restrict the carbon concentration of the thin plate after the nitriding at 2 weight % or less;

wherein the nitriding reaction gas includes no or very low amounts of carbon.

2. A method for producing maraging steel according to claim 1, wherein the carbon concentration of the nitriding reaction gas is 10 volume % or less.

3. A method for producing maraging steel according to claim 1, wherein the maraging steel comprises in weight %, 15 to 19% of Ni;

0.05 to 0.15% of Al;

3 to 5.5% of Mo;

0.4 to 1.5% of Ti;

8 to 15% of Co;

0.01% or less of C;

0.05% or less of Si;

0.05% or less of Mn;

0.008% or less of P;

0.004% or less of S; and

the balance of Fe.

4. A method for producing maraging steel according to claim 1, wherein the maraging steel is a endless belt with a thickness in the range of 0.1 to 0.3 mm.

5. A method for producing maraging steel according to claim 1, wherein the fluoridation processing is performed in a fluoric reaction gas consisting of 1 to 10 volume % of NF₃ and the balance of nitrogen gas.

6. A method for producing maraging steel according to claim 5, wherein the fluoridation processing is performed by heating the fluoric reaction gas at a temperature in the range of 400 to 500°

C., and by maintaining the thin plate in the fluoric reaction gas for a duration in the range of 10 to 60 minutes.

7. A method for producing maraging steel according to claim 1, wherein the nitriding is performed in a nitriding reaction gas consisting of 5 to 20 volume % of ammonia gas and the balance of nitrogen gas.

8. A method for producing maraging steel comprising:

aging a thin plate made from maraging steel;

performing fluoridation processing by heating and maintaining the thin plate in a fluoric reacting gas including fluorine so as to form a fluoride layer on a surface of the thin plate; and

then,

nitriding the thin plate in a nitriding reaction gas including ammonia gas so as to restrict the carbon concentration of the thin plate after the nitriding at 2 weight % or less;

calculating the maximum size of inclusions included in the maraging steel by using a statistics extremes method;

evaluating the inclusions in the maraging steel to select the maraging steel;

wherein a sample of maraging steel is dissolved in a solution;

only the inclusions remain in the solution;

the inclusions in the solution are screened by a filter so as to remove smaller inclusions;

the inclusion remaining on the filter are sampled; and

the maximum size of the inclusions is calculated based on the statistics extremes method.

9. A method for producing maraging steel according to claim 8, wherein the filter has a mesh size at least 0.5 times the value for the standard tolerance of the size of the inclusions.