Inventors: Philos Jonqho Ko and Bongsub Samuel Ko

BACKGROUND OF THE INVENTION

[ 001 ] This application claims benefit of U.S. Provisional Patent Application Serial number 61/642,759, entitled "IMPROVED PROCESS FOR DIFFUSING A SUBSTRATE INTO A BASE MATERIAL", filed May 4, 2012; U.S. Provisional Patent Application Serial number 61/642,768, entitled "IMPROVED PROCESS FOR DIFFUSING TITANIUM INTO A STAINLESS STEEL BASE MATERIAL", filed May 4, 2012; and U.S. Provisional Patent Application Serial number 61/642,781 , entitled "PROCESS FOR POLISHING A STAINLESS STEEL PRODUCT HAVING TITANIUM DIFFUSED THEREIN", filed May 4, 2012; naming Philos Jongho Ko and Bongsub Samuel Ko as the inventors, the complete disclosure being incorporated herein by reference.

BACKGROUND OF THE INVENTION

[ 002 ] The present invention generally relates to a process for diffusing a substrate into a base material and a method for polishing the resulting product. In one example, a process is provided for introducing a base material into a salt bath having a substrate with a catalyst. A select amount of catalyst and desired salt bath temperature are provided sufficient to lower the activation energy of the base material such that the substrate is able to diffuse into the surface of the base material. A select amount of catalyst and desired salt bath temperature are further provided sufficient to promote leaching of select substances from the base material that inhibit the diffusion of the substrate into such base material.

[ 003 ] U.S. Patent No. 6,645,566, describes a process for diffusing titanium and nitride into a variety of base materials including steel and steel alloys, aluminum and aluminum alloys, titanium and titanium alloys. U.S. Patent No. 6,645,566 describes various embodiments for increasing the effectiveness of the process described therein by manipulation of the process itself, but not by altering of the amount of catalyst and raising the processing temperature for a specific period of time sufficient to lower the activation energy of the base material and promote leaching of select substances from the base material. Accordingly, it is an object of the invention to improve the effectiveness of the process as described in U.S. Patent No. 6,645,566 by altering the processing steps sufficient to lower the activation energy of the base material and promote leaching of select substances from the base material while being treated.

[ 004 ] For example, as described in co-pending U.S. Patent Application No. 1 1/869,399, the content of the steel or steel alloy base material may be altered to improve the effectiveness of the process as described in U.S. Patent No. 6,645,566. For example, vanadium and cobalt may be added to the steel or steel alloy base material to enhance the diffusion of titanium and nitride into such, whereas chromium may be added to inhibit the diffusion of titanium and nitride into the base material. Accordingly, it is an object of the present invention to provide a method of diffusing a substrate (e.g., titanium) into a base material, which promotes the leaching of select substances (e.g., chromium) that inhibit the diffusion of such substrate (e.g., titanium) into such base material.

[ 005 ] However, chromium is commonly known to provide the corrosion- resistance properties of some base materials (e.g., in stainless steels) as described in U.S. Patent No. 7,896,981. Nevertheless, titanium also provides corrosion-resistance and other enhanced properties in comparison to chromium. Accordingly, it is an object of the present invention to provide a method for diffusing an enhanced corrosion- resistant substrate (e.g., titanium) into a base material by promoting leaching of a desired substance (e.g., chromium) from the base material such that such substances are replaced with an enhanced corrosion-resistant substrate (e.g., titanium) diffused from the salt bath.

[ 006 ] These and other desired benefits of the preferred embodiments, including the combinations of features thereof, of the invention will become apparent from the following description. It will be understood, however, that a process or arrangement could still appropriate the claimed invention without accomplishing each and every one of these desired benefits, including those gleaned from the following description. The appended claims, not these desired benefits, define the subject matter of the invention. Any and all benefits are derived from the multiple embodiments of the invention, not necessarily the invention in general. SUMMARY OF THE INVENTION

[007] The present invention generally relates to a process for diffusing a substrate into a base material. In one embodiment, a process is provided for introducing a base material into a salt bath having a substrate with a catalyst. A select amount of catalyst and desired salt bath temperature are provided sufficient to lower the activation energy of the base material such that the substrate is able to easily diffuse into the surface of the base material. Nevertheless, certain substances within the base material may inhibit the diffusion of the substrate into the surface of the base material. Accordingly, a select amount of catalyst and desired salt bath temperature are further provided sufficient to promote leaching of such select substances that inhibit the diffusion of such substrate into such base material. The leached substances are substantially replaced by the diffused substrate.

[ 008 ] It should be understood that the present invention includes a number of different aspects or features which may have utility alone and/or in combination with other aspects or features. Accordingly, this summary is not exhaustive identification of each such aspect or feature that is now or may hereafter be claimed, but represents an overview of certain aspects of the present invention to assist in understanding the more detailed description that follows. The scope of the invention is not limited to the specific embodiments described below, but is set forth in the claims now or hereafter filed.

DETAILED DESCRIPTION OF THE MULTIPLE EMBODIMENTS

[ 009 ] While the invention is susceptible of embodiment in many different forms and in various combinations, particular focus will be on the multiple embodiments of the invention described herein with the understanding that such embodiments are to be considered exemplifications of the principles of the invention and are not intended to limit the broad aspect of the invention.

[ 0010 ] The present invention generally relates to a process for diffusing a substrate into a base material. In one embodiment, a process is provided for introducing a base material into a salt bath having a substrate with a catalyst. A select amount of catalyst and desired salt bath temperature are provided sufficient to lower the activation energy of the base material such that the substrate is able to easily diffuse into the surface of the base material. Nevertheless, certain substances within the base material may inhibit the diffusion of the substrate into the surface of the base material. Accordingly, a select amount of catalyst and desired salt bath temperature are further provided sufficient to promote leaching of such substances. The leached substances are substantially replaced by the diffused substrate.

[ 0011 ] Specifically, a heated salt bath is used. Sodium carbonate and a salt selected from the group consisting of sodium cyanate and potassium cyan ate, in amounts of from about 80 to about 85 w/w %, is present in the salt bath with from about 15 to about 20 w/w % of NaC0 ₂ , NaC0 ₃ or sodium chloride. Added to the bath is the catalyzed substrate. Although other catalysts may be used, the catalyst may be in the form of a substrate which has been electrolyzed. The amount of catalyst is sufficient to lower the activation energy of the base material to be treated. Also, this select amount of catalyst promotes leaching of select substances from the base material. Specifically, the catalyst promotes leaching of the select substances which inhibit the diffusion of the substrate into the base material. [ 0012 ] The base material is soaked in the salt bath having the catalyzed substrate. The temperature of the salt bath is set at a value that will lower the activation energy of the base material and promote the diffusion of the substrate into the base material. A higher temperature will generally promote the lowering of the activation energy of the base material and promote diffusion of the catalyzed substrate. Furthermore, the salt bath temperature is further selected to promote leaching of such select substances that inhibit the diffusion of such substrate into such base material. In order to prevent any distortion or warping of the base material, the base material is soaked in the salt bath for a relatively short period of time. With the lowered activation energy of the base material and the catalyst, the substrate and nitride in the salt bath quickly and easily diffuses into the surface of the base material. The concentration of the substrate in the salt bath is selected such that it sufficiently replaces the substances leached from the base material during the soaking period.

Example 1

[ 0013 ] In one specific example, a 300 series stainless steel base material may be treated. 300 series stainless steel is generally referred to as ultralow carbon steel having austensitic properties. Typically, chromium provides stainless steel with its inherent corrosion resistance characteristics. It is nonetheless preferable to replace some of the chromium in the surface of the base material with titanium because titanium generally provides the enhanced characteristics of being a generally inert, light-weight material which has very high tensile strength (or toughness) and excellent corrosion resistance. At the same time, chromium generally inhibits the diffusion of titanium into the base material. Accordingly, it is preferable to diffuse titanium into the stainless steel base material using a process that promotes leaching of chromium from the surface of the base material such that it may be substantially replaced with diffused titanium.

[ 0014 ] In one example, a 300 series stainless steel housing for a consumer electronics product may be surface treated in order to enhance its hardness, tensile strength and corrosion resistance. A heated salt bath is provided. Sodium carbonate and a salt selected from the group consisting of sodium cyanate and potassium cyanate, in amounts of from about 80 to about 85 w/w %, is present in the salt bath with from about 15 to about 20 w/w % of NaC0 ₂ , NaC0 ₃ or sodium chloride.

[ 0015 ] Added to the bath is electrolyzed titanium. In order to optimally lower the activation energy of the 300 series stainless steel base material, promote leaching of chromium from the stainless steel base material and promote diffusion of titanium into the surface of the stainless steel base material, it is preferable that about 40 micrograms to about 60 micrograms of electrolyzed titanium be added to the bath such that a concentration of from about 0.005% to about 0.010% of electrolyzed titanium in the salt bath is achieved. This amount of electrolyzed titanium is preferred to replace the chromium leached from the stainless steel base material and enhance the corrosion- resistance of the treated 300 series stainless steel base material. The temperature of salt bath is heated to over 590 degrees C, and preferably from about 600 degrees C to about 620 degrees C. The electrolyzed titanium and higher temperature catalyzes the diffusion of the titanium and nitride from the salt bath into the base material.

[ 0016 ] The 300 series stainless steel base material is soaked in the salt bath for a relatively short period of time from about 10 minutes to about 90 minutes. In order to prevent any distortion or warping of the base material, it is preferable to soak the stainless steel base material in the salt bath heated at about 600 degrees C to about 620 degrees C for only about 10 to about 20 minutes. With the lowered activation energy of the stainless steel base material and leaching of chromium therefrom, the titanium in the salt bath quickly and easily diffuses into the surface of the base material. The titanium substantially replaces the chromium leached from the base material. Using this improved process, titanium is shown to diffuse into at least 20 microns of surface of the 300 series stainless steel base material.

[ 0017 ] As discussed above, titanium has enhanced properties as compared to chromium. Accordingly, the new surface of the stainless steel base material acquires these characteristics due to the newly diffused titanium. Specifically, the surface of the stainless steel base material is harder without compromising its corrosion-resistance prior to being surface treated. For example, a surface hardness of about 1300 to 1450 HV-ioog- By leaching diffusion inhibiting substances from the surface (e.g., chromium) and substantially replacing them with substrates with enhanced properties (e.g., titanium), this process may be applied to a broad range of materials. In the specific case of stainless steels, lower grade and consequently cheaper stainless steels (e.g., 304 Stainless Steel) may be surface treated using the present invention diffusion process in order to enhance their hardness, tensile strength and corrosion resistance properties.

[ 0018 ] During the titanium diffusion process of Example 1 , an oxide layer may possibly form on the surface of the stainless steel base material. Accordingly, it is preferable to polish (or otherwise lightly buff) the surface of the resulting stainless steel product in order to achieve a desired shine, it is further preferable to achieve the desired shine without scratching or otherwise remove the layer of titanium diffused into the surface of the stainless steel product. Generally, the resulting stainless steel product may be lightly buffed or otherwise polished using a chromium oxide polishing compound. In order to shine the surface without scratching or otherwise removing the diffused layer of titanium, the chromium oxide polishing compound has a particle size of less than 2 micrometers, and preferably has a particle size of from about 0.5 to about 1 micrometer. Specifically, the polishing compound may be used along with a soft polishing wheel, such as a 100% cotton domet flannel type polishing wheel or similar type of polishing wheel generally used for fine polishing. The polishing wheel is generally used at a speed of about 3000 rpm to about 5000 rpm, and preferably from about 3500 rpm to about 4500 rpm. As such, the polished stainless steel product has a shiny surface with increased hardness and corrosion resistance due to the titanium diffusion process.

Example 2

[ 0019 ] In another specific example, a 400 series stainless steel base material may be treated. 400 series stainless steel, unlike 300 series stainless steel, has martensitic properties. The 400 series stainless steel also has been tempered at a select tempering temperature between about 300 degrees C to 530 degrees C to achieve a select core hardness (e.g., about 40 to 55 HRc). Typically, chromium provides stainless steel with its inherent corrosion resistance characteristics. It is nonetheless preferable to replace some of the chromium in the surface of the base material with titanium because titanium generally provides the enhanced characteristics of being a generally inert, light-weight material which has very high tensile strength (or toughness) and excellent corrosion resistance. At the same time, chromium generally inhibits the diffusion of titanium into the base material. Accordingly, it is preferable to diffuse titanium into the stainless steel base material using a process that promotes leaching of chromium from the surface of the base material such that if may be replaced with diffused titanium.

[ 0020 ] In one example, a 400 series stainless steel housing for a consumer electronics product may be surface treated in order to enhance its hardness, tensile strength and corrosion resistance. A heated salt bath is provided. Sodium carbonate and a salt selected from the group consisting of sodium cyan ate and potassium cyanate, in amounts of from about 80 to about 85 w/w %, is present in the salt bath with from about 15 to about 20 w/w % of NaC0 ₂ , NaC0 ₃ or sodium chloride.

[ 0021 ] Added to the bath is electrolyzed titanium. In order to optimally lower the activation energy of the 400 series stainless steel base material, promote leaching of chromium from the stainless steel base material and promote diffusion of titanium into the surface of the stainless steel base material, it is preferable that about 40 micrograms to about 60 micrograms of electrolyzed titanium be added to the bath such that a concentration of from about 0.005% to about 0.010% of electrolyzed titanium in the salt bath is achieved. This amount of electrolyzed titanium is preferred to replace the chromium leached from the 400 series stainless steel base material and enhance the corrosion-resistance of the treated base material. The temperature of salt bath is heated to over 430 degrees C, and preferably from about 430 degrees C to about 530 degrees C. The temperature of the salt bath is selected so that it maintains the original tempering conditions (e.g., tempering temperature or core hardness) of the base material. The electrolyzed titanium catalyzes the diffusion of the titanium and nitride from the salt bath into the base material, but the reaction rate is slower than in Example 1. Accordingly, for 400 series stainless steel, an increased treatment time is generally required as compared to the 300 series stainless steel.

[ 0022 ] The stainless steel base material is soaked in the salt bath for a relatively short period of time from about 10 minutes to about 90 minutes. In order to prevent any distortion or warping of the base material, it is preferable to soak the stainless steel base material in the salt bath heated at about 430 degrees C to about 500 degrees C for only about 10 to about 30 minutes. With the lowered activation energy of the stainless steel base material and leaching of chromium therefrom, the titanium in the salt bath diffuses into the surface of the base material. The titanium substantially replaces the chromium leached from the base material. Using this improved process, titanium is shown to diffuse into at least 15 microns of surface of the 400 series stainless steel base material.

[ 0023 ] As discussed above, titanium has enhanced properties as compared to chromium. Accordingly, the new surface of the stainless steel base material acquires these characteristics due to the newly diffused titanium. Specifically, the surface of the stainless steel base material is harder without compromising its corrosion-resistance prior to being surface treated. For example, a surface hardness of about 900 to 1 100 HV-ioog. By leaching diffusion inhibiting substances from the surface (e.g., chromium) and replacing them with substrates with enhance properties (e.g., titanium), this process may be applied to a broad range of materials.

[0024] During the titanium diffusion process of Example 2, an oxide layer may possibly form on the surface of the stainless steel base material. Accordingly, it is preferable to polish (or otherwise lightly buff) the surface of the resulting stainless steel product in order to achieve a desired shine. It is further preferable to achieve the desired shine without scratching or otherwise remove the layer of titanium diffused into the surface of the stainless steel product. Generally, the resulting stainless steel product may be lightly buffed or otherwise polished using a chromium oxide polishing compound. In order to shine the surface without scratching or otherwise removing the diffused layer of titanium, the chromium oxide polishing compound has a particle size of less than 2 micrometers, and preferably has a particle size of from about 0.5 to about 1 micrometer. Specifically, the polishing compound may be used along with a soft polishing wheel, such as a 100% cotton domet flannel type polishing wheel or similar type of polishing wheel generally used for fine polishing. The polishing wheel is generally used at a speed of about 3000 rpm to about 5000 rpm, and preferably from about 3500 rpm to about 4500 rpm. As such, the polished stainless steel product has a shiny surface with increased hardness and corrosion resistance due to the titanium diffusion process.

Example 3

[ 0025 ] In yet another specific example, a 300 series stainless steel base material may be treated according to another process. Typically, chromium provides stainless steel with its inherent corrosion resistance characteristics. It is nonetheless preferable to replace some of the chromium in the surface of the base material with titanium because titanium generally provides the enhanced characteristics of being a generally inert, light-weight material which has very high tensile strength (or toughness) and excellent corrosion resistance. At the same time, chromium generally inhibits the diffusion of titanium into the base material. Accordingly, it is preferable to diffuse titanium into the stainless steel base material using a process that promotes leaching of chromium from the surface of the base material such that it may be replaced with diffused titanium.

[0026] In one example, a 300 series stainless steel housing for a consumer electronics product may be surface treated in order to enhance its hardness, tensile strength and corrosion resistance. A heated salt bath is provided. Sodium carbonate and a salt selected from the group consisting of sodium cyanate and potassium cyan ate, in amounts of from about 80 to about 85 w/w %, is present in the salt bath with from about 15 to about 20 w/w % of NaC0 ₂ , NaC0 ₃ or sodium chloride.

[0027] Added to the bath is electrolyzed titanium. In order to optimally lower the activation energy of the stainless steel base material, promote leaching of chromium from the stainless steel base material and promote diffusion of titanium into the surface of the stainless steel base material, it is preferable that about 40 micrograms to about 60 micrograms of electrolyzed titanium be added to the bath such that a concentration of from about 0.005% to about 0.010% of electrolyzed titanium in the salt bath is achieved. This amount of electrolyzed titanium is preferred to replace the chromium leached from the stainless steel base material and enhance the corrosion-resistance of the treated base material. The temperature of salt bath is heated to over 680 degrees C. The electroiyzed titanium catalyzes the diffusion of the titanium and nitride from the salt bath into the base material.

[ 0028 ] The stainless steel base material is soaked in the salt bath for a relatively short period of time from about 10 minutes to about 30 minutes. In order to prevent any distortion or warping of the base material, it is preferable to soak the stainless steel base material in the salt bath heated at about 680 degrees C to about 700 degrees C for only about 10 to about 17 minutes. With the lowered activation energy of the stainless steel base material, the titanium in the salt bath quickly and easily diffuses into the surface of the base material. At the same time, chromium is leached from the base material. As compared to the other examples, the higher salt bath temperature in this Example 3 increases the rate of reaction, which in turn increases the rate of diffusion of the titanium into the base material. At this higher salt bath temperature, however, leaching of chromium from the base material is slower. As a result, more chromium is retained in the base material while more titanium is diffused, resulting in a denser diffused resulting base material than in the other examples. Using this improved process, titanium is shown to diffuse into at least 30 to 35 microns of surface of the 300 series stainless steel base material.

[ 0029 ] Accordingly, the new surface of the stainless steel base material acquires characteristics of the newly diffused titanium and retained chromium. Specifically, the surface of the stainless steel base material is harder without compromising its corrosion-resistance prior to being surface treated as compared to the other examples. For example, a surface hardness of about 1400 to 1550 HV-ioog- [0030] During the titanium diffusion process of Example 3, an oxide layer may possibly form on the surface of the stainless steel base material. Accordingly, it is preferable to polish (or otherwise lightly buff) the surface of the resulting stainless steel product in order to achieve a desired shine. It is further preferable to achieve the desired shine without scratching or otherwise remove the layer of titanium diffused into the surface of the stainless steel product. Generally, the resulting stainless steel product may be lightly buffed or otherwise polished using a chromium oxide polishing compound. In order to shine the surface without scratching or otherwise removing the diffused layer of titanium, the chromium oxide polishing compound has a particle size of less than 2 micrometers, and preferably has a particle size of from about 0.5 to about 1 micrometer. Specifically, the polishing compound may be used along with a soft polishing wheel, such as a 100% cotton domet flannel type polishing wheel or similar type of polishing wheel generally used for fine polishing. The polishing wheel is generally used at a speed of about 3000 rpm to about 5000 rpm, and preferably from about 3500 rpm to about 4500 rpm. As such, the polished stainless steel product has a shiny surface with increased hardness and corrosion resistance due to the titanium diffusion process.

[0031] While this invention has been described with reference to certain illustrative aspects, it will be understood that this description shall not be construed in a limiting sense. Rather, various changes and modifications can be made to the illustrative embodiments without departing from the true spirit, central characteristics and scope of the invention, including those combinations of features that are individually disclosed or claimed herein. Furthermore, it will be appreciated that any such changes and modifications will be recognized by those skilled in the art as an equivalent to one or more elements of the following claims, and shall be covered by such claims to the fullest extent permitted by law.