Metal treatment – Stock – Ferrous
Reexamination Certificate
2002-11-14
2004-04-20
Yee, Deborah (Department: 1742)
Metal treatment
Stock
Ferrous
C148S328000, C148S334000, C148S335000, C148S325000, C148S321000, C148S324000
Reexamination Certificate
active
06723182
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to alloy steels, and, more specifically, to martensitic steel alloy compositions intended for use as high speed tool steels, hot work and cold work die steels, armor plate, and other applications requiring good response to hardening, resistance to softening at high work temperatures, and high yield strength, the alloy composition being characterized by the presence of intermetallic compounds and precipitates that are substituted for cobalt.
BACKGROUND OF THE INVENTION
A conventional approach to obtaining the hot hardness properties required of alloy steels useful for applications as described above has been to use cobalt as an alloying element. Cobalt is an expensive, strategic material that must be imported. In some applications, such as high speed tools, alloying amounts of cobalt are thought by some to have detrimental health effects. Cobalt additions in heat resisting steel compositions also have certain negative effects, such as reduction of material toughness. Because of these considerations, various attempts have been made to eliminate cobalt by substituting alloy systems based on carbide forming elements, such as niobium, titanium, chromium, tungsten, molybdenum and the like. A study was also made of the possibility of using silicon and aluminum additions totaling about 2.5% in order to replace or substantially reduce cobalt in high speed tool steels. One reason that none of these expedients have been commercially accepted is believed to be the inability to consistently achieve the desired hardness and strength properties and/or irregular results.,
SUMMARY OF THE INVENTION
The purpose of the present invention is to eliminate or significantly reduce cobalt in heat resisting steels, such,as high speed tool steels (HSS), die work steels, armor plate and the like, without sacrificing, and in many instances improving the properties expected of cobalt systems, particularly response to hardening and resistance to softening at elevated temperatures.
In general, the purpose of the invention is accomplished by substituting for cobalt sub-micron and nano-structural precipitates and intermetallic compounds including M
3
Si. The formation of these precipitates and compounds is promoted by the addition of each of nickel, copper, aluminum, manganese and silicon in a total amount of at least 4.0% by weight with an optimum minimum amount being 4.5%. The silicon content exceeds 1.0%. The addition of these elements improves material response to hardening, resistance to softening at elevated temperatures and yield strength in all martensitic grade steels at very low cost in comparison to cobalt alloyed steels. The resistance to softening at elevated work temperatures is so significant that it may exceed that of super cobalt alloyed HSS materials.
“As used in the following disclosure and in the appended claims, all indicated percentages are to be understood to mean percentages by weight.”
One embodiment of the invention is a martensitic alloy steel consisting essentially of about 0.15-3.5% C, 0.5-13.0% Cr, 0.05-15.0% V, 0.75-12.0% Mo, 0-15.0% W, a residual amount of Co less than 1.25%, more preferably, 0.5% or less, each of Ni, Cu, Al, Mn and Si in a total amount of at least 4.0% with the silicon content exceeding 1.0%, and the balance essentially iron.
A more specific embodiment of an HSS material within the scope of the invention having the desired properties of good hardening response, resistance to softening at elevated work temperatures and good yield strength is a martensitic alloy consisting essentially of about 0.15-1.15% C, 3.5-4.5% Cr, 1.0-1.6% V, 8.5-10.0% Mo, 1.4-2.10% W, less than 1.5% Co, each of Ni, Cu, Al, Mn and Si in a total amount of at least 4.0% with the silicon content exceeding 1.0%, and the balance essentially iron.
Still another example of the invention is an alloy system useful for armor plate including 0.15-0.35% C, 0.60-1.00% Mn, 0.40-0.90% Cu, 7.0-10.0% Ni, 0.50-1.00% Al, 1.0-1.50% Si, 0.05-0.25% V, 0.50-1.25% Cr, and 0.75-1.25% Mo.
Examples of hot work and cold work die steels contain 0.30-3.5C, 3.50-13.0% Cr, 2.75-15.0% V, 0.75-2.00% Mo, 5.75-6.75% W, less than 1.25%, and more preferably less than 1.0% Co, 0.70-1.20% Ni, 1.0-1.75% Si, 0.50-1.50% Al, 0.40-0.90% Cu, 0.60-1.00% Mn, and the balance essentially iron.
In carrying out the invention, a steel according to any of the previous paragraphs is austenitized in the range of from 1750-2250° F., rapid quenched to room temperature, and multiple tempered to a range of from 900-1050° F.
REFERENCES:
patent: 3850621 (1974-11-01), Haberling et al.
patent: 4116685 (1978-09-01), Okuno
patent: 4842818 (1989-06-01), Kato et al.
patent: 5009843 (1991-04-01), Sugimoto et al.
patent: 5106577 (1992-04-01), Fesler
patent: 5160553 (1992-11-01), Leban et al.
patent: 5169459 (1992-12-01), Fukushima et al.
patent: 5454883 (1995-10-01), Yoshie et al.
patent: 5651842 (1997-07-01), Nakamura et al.
patent: 5749140 (1998-05-01), Polito et al.
patent: 6096262 (2000-08-01), Ueta et al.
patent: 6200528 (2001-03-01), Rodney et al.
M. Murayama, Y. Katayama and K. Hono, “Microstructural Evolution in a 17-4 PH Stainless Steel after Aging at 400° C.”, Metallurgical and Materials Transactions A, vol. 30A, Feb. 1999, pp. 345-353.
A.M. Bayer, B.A. Becherer, “Aluminum Modified High Speed Steels”, Proceedings at High Speed Steel Conference, Leoben, Austria, 1990, pp. 144-151.
Crucible Tool Steel and Specialty Alloy Selector, published 1999, pp. 290-291.
George A. Roberts and Robert A. Cary, “Tool Steels”, 4thedition, 1980, p. 660.
Pearne & Gordon LLP
Yee Deborah
LandOfFree
Martensitic alloy steels having intermetallic compounds and... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Martensitic alloy steels having intermetallic compounds and..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Martensitic alloy steels having intermetallic compounds and... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3204148