Metal treatment – Process of modifying or maintaining internal physical... – Heating or cooling of solid metal
Reexamination Certificate
2000-04-18
2002-04-02
Yee, Deborah (Department: 1742)
Metal treatment
Process of modifying or maintaining internal physical...
Heating or cooling of solid metal
C148S660000, C148S637000, C148S638000, C148S320000, C266S114000, C266S259000
Reexamination Certificate
active
06364974
ABSTRACT:
BACKGROUND AND SUMMARY OF THE INVENTION
The present invention relates generally to a new and novel quenching apparatus and method for hardening steel parts. More particularly, the present invention relates to a quenching apparatus and method for hardening steel parts which achieves high strength and surface compressive stresses on all steels, including relatively low-alloy and standard carbon steels, and water and water based solutions as the quenching agent.
The quenching apparatus and method for hardening steel parts in accordance with the present invention relates generally to the heat treatment of steel parts, including carburized steel parts, steel parts heated by induction heating and other steel parts heated in electric, atmosphere, gas and vacuum furnaces. The invention has application in the metallurgic industry, including heat treating, machine construction, bearing and tool production, as well as in other branches of industry.
A steel quenching method where the depth of the quenched surface layer is controlled, which increases service life, is described in “New Induction Hardening Technology,” authored by K. Z. Shepelyakovskii and F. V. Bezmenov which appeared on pages 225 through 227 of the October 1998, publication “Advanced Materials & Processes.” Steel quenched using this method generally has low depth of hardened layer and fine grain with arrested growth of austenite grains at high temperatures. Due to limited hardenability, compressive stresses appear on the surface of such steel parts and the fine grain provides high strength. In addition to providing an increase in the service life of such heat treated steel parts, there is an opportunity to replace relatively expensive high-alloy steels with less expensive low-alloy steels and replace fire and environmentally dangerous quench oils with water and water based quenching solutions. However, the depth of hardness in steel parts hardened using this method is controlled by the chemical composition of the steel parts being hardened.
Steel quenching where the depth of the hardened surface layer is controlled in accordance with this method is made in water jets. The service life of such heat treated steel parts where the depth of the hardened surface layer is controlled generally increases when compared to oil quenching. However, it is often necessary to select or create an appropriate alloy of steel for use in steel parts having different configurations and sizes to obtain the effect of high surface compressive stresses.
In addition, with this quenching method no criteria exists to calculate the rate of water flow for steel parts having different configurations and/or sizes. Thus, a relatively high water flow rate is normally chosen for all steel parts which is not always justified and results in unnecessary energy expenses and makes the industrial process more complicated than necessary. While the high service life of steel parts where the depth of the hardened surface layer is controlled is considered an advantage for certain steel grades, other steel grades can also achieve the effect of increased strength (as compared to known prior art steel part quenching methods) and high residual compressive surface stresses if the heat treating parameters are properly controlled. In this method of heat treating steel, induction heating is primarily used and, to the applicant's knowledge, there is no data regarding oven heating, including such data for carburized parts, and the industrial regimes are not optimized. Thus, the heat treating method described above is entirely dependent on the composition of the steel alloys available. As a practical matter, it may be difficult to obtain steel alloys having a suitable composition. Accordingly, in practice, the hardening method should be adapted to those steel alloys which are available.
Another known prior art steel quenching method is described in “Intense Quenching” authored by Roy F. Kern and published on pages 19 through 23 in the No. 9 issue of “Heat Treating” in 1986. This known prior art steel quenching method involves “shell hardening,” which results in uniform quenching of all of the surface to a certain depth until reaching high hardness using intensive jet cooling. In this method, the examples of the application of medium-carbon 1045 steel are given. One advantage of this method is the opportunity to increase the service life of steel parts using standard carbon steels, rather than alloy steels where the depth of the hardened surface layer is controlled by the composition of the steel. However, this method also has many of the disadvantages present in the previous method described. Namely, as discussed in prior publications authored by the applicant, no consideration is given to the parameters necessary to optimize the depth of the hardened surface layer, and the following correlation that the depth of the hardened surface layer should be changed for steel parts having different configurations and/or sizes is ignored:
Δ
δ
D
=
constant
where:
&Dgr;&dgr; is the optimum hardened depth; and
D is the cross-sectional thickness.
This correlation was developed by the applicant and is considered to provide a foundation for the quenching apparatus and method for hardening steel parts in accordance with the present invention.
In addition, this method does not have any criteria allowing the calculation of the optimum cooling solution quench flow and the technological process is not optimized.
Another steel quenching method is described in Japanese patent application number 61-48514 to Naito Takeshi, published Aug. 16, 1984, for a “Method of Steel Quenching” now Japanese Patent No. 59-170039. In this method, alloy steel parts are quenched in such a manner that a hard surface layer of a given depth and an arbitrarily hard matrix are obtained. For given steel grades, ranges for hardening regimes are found by experimentation to increase the service life of such steel parts. One example of this method involves an alloy steel specimen containing 0.65% to 0.85% carbon, 0.23% to 0.32% silicon, 0.4% to 0.9% manganese, approximately 2% nickel, 0.5% to 1.5% chromium and 0.1% to 0.2% molybdenum which is heated to 800° C. to 850° C. and spray quenched with water fed under a 0.4 to 0.6 MPa pressure for 0.2 to 0.8 seconds. The steel specimen is then isothermally heated at 150° C. to 250° C. for ten (10) to fifty (50) minutes. One disadvantage of this method is that it considers only high-carbon alloy steels. Also, the depth of the hard surface layer is not optimal for steel parts having different configurations and/or sizes and, because of this, steel strengthening is not consistently achieved in all parts. In addition, this method does not taken into consideration the optimization of the quenchant solution circulation rate.
A steel quenching method described in Ukraine Patent No. UA 4448, Bulletin No. 6-1, to N. I. Kobasko, in 1994, describes heating, cooling until the appearance of maximum compressive surface stresses, followed by isothermal heating (tempering). This method is based on cooling in the range of 0.8≦Kn≦1, where Kn is the Kondratjev number, until reaching maximum compressive surface stresses, then isothermally heating at martensite start temperature M
s
until the complete transformation of the overcooled austenite of the matrix occurs and tempering. The Kondratjev number characterizes the intensity of cooling and is variable between zero (0) and one (1). It is the ratio between usual cooling and cooling when heat transfer is infinite. Therefore, even during very intense cooling, this ratio cannot exceed one (1).
One disadvantage of this method is that it deals only with alloy steels. To reach the maximum compressive surface stresses on the surface the cooling is stopped and due to this interruption in cooling, the effect of greater than normal steel strength is not fully achieved. In addition, there is no method to calculate the optimal rate of quenchant solution flow to ensure that increased strength (as compared to known prior art stee
Hudak James A.
IQ Technologies, Inc.
Yee Deborah
LandOfFree
Quenching apparatus and method for hardening steel parts does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Quenching apparatus and method for hardening steel parts, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Quenching apparatus and method for hardening steel parts will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2904332