Steelmaking process

Details Steelmaking process Steelmaking process

1999-12-02

2001-08-14

Yee, Deborah (Department: 1742)

Metal treatment

Process of modifying or maintaining internal physical...

With casting or solidifying from melt

C148S547000, C164S509000, C164S515000, C164S476000, C164S477000

Reexamination Certificate

active

06273973

ABSTRACT:

CROSS-REFERENCE TO RELATED APPLICATIONS
Not Applicable
FEDERALLY SPONSORED RESEARCH
Not Applicable
TECHNICAL FIELD AND INDUSTRIAL APPLICABILITY OF THE INVENTION
The present invention is directed to martensitic stainless steels. The present invention is more particularly directed to martensitic stainless steels which may, through appropriate processing, develop a microstructure suitable for the production of razor blades. The present invention also is directed to a process for processing a martensitic stainless steel to a gage and with a microstructure suitable for the production of razor blades.
DESCRIPTION OF THE INVENTION BACKGROUND
Because the process of shaving places the blade steel in contact with moisture, stainless steel is a natural selection for razor blade applications. Razor blades typically are fabricated from a coil of stainless steel that has been rolled to a strip of very thin gage (less than ten mils) and that has been slit to an appropriate width. The coiled steel strip is uncoiled, sharpened, hardened, appropriately coated, and welded to a blade support so that it may be manipulated against the skin.
Steel used as razor blade material preferably includes secondary carbide particles that are of a uniform generally spherical shape, that have uniform size less than 15 micrometers and uniform distribution, and that are present in a concentration of about 50-200 carbide particles per 100 micrometers square as observed at high magnification. If secondary carbide particles within the steel are not of uniform size and distribution, for example, the steel may distort during the heat treatments used in razor blade fabrication. Distortion of the steel during heat treatment is referred to as “dish”, and only a minor amount of dish is cause for rejecting the steel. The steel preferably also is substantially free of primary carbides or clusters of carbides that exceed 15 micrometers in length. It is also preferred that the steel is essentially free of non-metallic microinclusions and does not include regions of segregation, carburization, or decarburization. Primary carbide particles and non-metallic microinclusions typically are large in size, brittle in nature, and have a low cohesion to the steel matrix. As such, they may cause “tear outs” during the sharpening of the steel. A tear out occurs during sharpening when the carbide particle or inclusion is pulled from the steel, leaving a jagged surface that can be felt during shaving.
In addition to meeting the foregoing microstructural criteria, stainless steels used in razor blade fabrication also must satisfy additional qualitative and quantitative criteria established by the individual razor blade manufacturers and which demonstrate a suitability for shaving. Certain of those additional criteria are evaluated after samples of the steel strip have been modified by the manufacturer to include a sharpened edge, additional martensite (i.e., enhanced hardness), and a non-metallic coating.
Razor blades are commonly fabricated from strip of certain high carbon type 420 stainless steels. (Type 420 steels have the nominal composition 0.15 min. carbon, 1.00 max. manganese, 1.00 max. silicon, and 12.0-14.0 chromium, all in weight percent.) The type 420 steels that may be used as razor blade material must have a chemistry that may be processed to meet the above microstructural requirements. The steels also must be capable of processing to a uniform thin gage strip, typically 34 mils in thickness, a uniform width, and have no appreciable surface defects or edge checking. Because the steel strip typically is produced from large ingots weighing thousands of pounds, the overall thickness reduction necessary to achieve 3-4 mils thickness during processing is extreme. The need to achieve a thin gage final material while also meeting the other requirements discussed above necessarily complicates the processing of the material and limits the array of suitable heat chemistries and processing regimens.
Accordingly, there is a need for a method of processing type 420 and other stainless steels to a uniform thin gage while satisfying the above microstructural criteria. There also is a need for improved martensitic stainless steel alloys that demonstrate a suitability for razor blade applications.
SUMMARY OF THE INVENTION
The present invention addresses the above-described needs by providing a process for producing a martensitic stainless steel to a gage and with a microstructure and other properties suitable for application as razor blade material. The process includes the step of subjecting at least a portion of a melt of a martensitic stainless steel to an electroslag remelting (ESR) treatment. In a step subsequent to the ESR treatment, the steel is heated to a temperature at least as great as the lowest temperature at which all of the carbides that may form in the steel will dissolve and no greater than the nil ductility temperature of the steel. The steel is held at that temperature for a period of time sufficient to dissolve all primary carbide particles in the steel that are greater than 15 micrometers in length. Subsequent to the heat treatment, the steel may be reduced to a strip of a desired gage (typically, less than 10 mils for razor blade applications) through a series of hot and cold reduction steps. The steel may be annealed between the cold rolling steps to appropriately recrystallize the cold worked structure within the steel and inhibit breakage or unacceptable checking during the cold reductions.
The process of the present invention may be applied to, for example, a steel having the chemical composition of a type 420 martensitic stainless steel, and is particularly well-suited for type 420 stainless steels including at least the following, all in weight percentages:
0.65 to 0.70 carbon;
0 to 0.025 phosphorus;
0 to 0.020 sulfur;
0.20 to 0.50 silicon;
0.45 to 0.75 manganese;
12.7 to 13.7 chromium;
0 to 0.50 nickel; and
incidental impurities.
The present invention also is directed to certain novel martensitic type 420 stainless which form a part of the present invention and which include at least the following, all in weight percentages:
0.65 to 0.70 carbon;
0 to 0.025 phosphorus;
0 to 0.020 sulfur;
0.20 to 0.50 silicon;
at least one of greater than 0.0004 boron and greater than 0.03 nitrogen;
0.45 to 0.75 manganese;
12.7 to 13.7 chromium;
0 to 0.50 nickel; and
incidental impurities.
Such steels may be advantageously processed by the method of the invention to include a microstructure that is substantially free of individual and clustered primary carbides exceeding 15 micrometers in length and an average of 50-200 secondary carbide particles per 100 micrometer square region when viewed at high magnification.
The reader will appreciate the foregoing details and advantages of the present invention, as well as others, upon consideration of the following detailed description of embodiments of the invention. The reader also may comprehend such additional details and advantages of the present invention upon using the invention.


REFERENCES:
patent: 3847683 (1974-11-01), Sastri
patent: 4021272 (1977-05-01), Asai et al.
patent: 4180420 (1979-12-01), Sastri et al.
patent: 5433801 (1995-07-01), Althaus et al.
patent: 1400412 (1975-07-01), None

Affiliated with

Also associated with

Rating

Steelmaking process does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Steelmaking process, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Steelmaking process will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2548209