US1718563A - Treatment of metals - Google Patents

Description

Patented June 25 1929.

UNITED STATES PATENT OFFICE.

FLOYD C. KELLEY, OF SCHENECTADY, NEW YORK, ASSIGNOR TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

TREATMENT OF METALS.

No Drawing.

My invention relates to the treatment of metals to prevent harmful deterloratlon when heated to high temperatures 1n the presence of oxygen.

metal andform therewith a surface alloy' which serves to protect the interior of the foundation metal. This surface alloy of chromium and the foundation metal is fundamentally a protection against corrosion, although it also resists oxidation at high temperatures to some extent.

I have discovered that if the article to be protected be suitably heated in surface con-.

tact With a mixture of powdered chromium and silicon, a surface alloy is formed with I the metal of the article which has excellent oxidation resisting properties when heated to high temperatures. Various proportions of silicon may be used. Preferably the powdered chromium-and silicon are mixed with a powdered iiiert, refractory material, such as aluminum, oxid or magnesium oxid. I have found that if 10 per cent by weight of powdered silicon be added to the regular chromium mixture of my aforesaid patentconsisting of equal-parts of powdered chr0- mium and refractory material, either aluminum oxid or magnesium oxid, an excellent heat resisting surface alloy may be formed. The articles to be treated are packed in a receptacle in the chromium silicon treating mixture and then suitably heated, for example, by placing the receptacle with its contents in' a hydrogen furnace. z 1 The duration of the heat treatment or firing to efi'ect'thefldesired penetration of the chromium and silicon with the" foundation metal Varies. with the temperature used; Temperatures offrom 1000 k to 1500 C. are satisfactory. While a te perature of approximately 12OQ C. is required to elfec t penetration of the powdered chromium alone, when thifsismall amount of powdered silicon is addedto' the treating mixture good penepreciably,

Letters Patent of the Application filed April 17, 1925. Serial No. 23,970.

tration is obtained at approximately 1000 C. Apparently the silicon alloys with the chromium and carries the chromium with it into the foundation metal at this lower temperature. When iron is bein treated, a very satisfactory surface alloy is formed by firing for six hours at a temperature of 1350 C. As with the process described in my aforesaid patent, the firing is carried out under non-oxidizing conditions, preferably in the presence of hydrogen.

The surface alloy thus formed gives excellent protection againstgoxidation at surprisingly high temperatures. A piece of iron after being given the treatment previously described, i. e. fired for six hours at a temperature of 1350 C., was heated at a temperature of 1100 C. in an open furnace for over 200 hours before any signs of breakdown in the protective coating Were perceived. Another piece of iron after being given a similar treatment was heated in the open air at a temperature of 900 C. for over 400 hpurs without showing any appreciable oxidation. This latter piece showed only an exceedingly small increase in Weight after being thus heated, which is afurther indication of the efficiency of this surface alloy as a protective coating. 1 I

f the firing temperature is reduced apfor example, to approximately 900 C. but little, if any, further penetration of the chromium silicon mixture takes place, and the surface alloy whenv subjected to temperatures of 90OC. or less remains fixed.

.In other words, there is little orno tend ency at this or lower temperatures for the chromium and silicon of the surface alloy to gradually diffuse into the interior of the foundation metal and thereby leave the surface unprotected. This is probably one explanation of the extraordinary heatresisting properties obtained by this treatment.

What I claim as new and desire to secure by United States, is, 1. The method of protecting metals against oxidation at: high emperatures which consists in heating the metal at a temperature of from 1000 C. to 150O C. in a hydrogen atmosphere in contact with a mixture of powdered chromium and silicon.

2. The method ofprotecting metals against oxidation at high temperatures which consists in heating the metal under non-oxidizing conditions at a temperature of from 1000 C. to 1500 C. in contact with a mixture of powdered chromium and silicon.

3. The methodvof providing iron with a heat protecting surface alloy of iron, chromium and silicon which consists inheating the iron in hydrogen in contact with a mixture of powdered chromium, silicon and alu- 'minum oxid at a temperature of from 1000 10 C. to 1500 0.

surface alloy which is resistant to oxidation at high temperatures, which consists in heat-' ing the iron in hydrogen in contact with powdered chromium and silicon at a temperature of approximately 1350 C.

In witness whereof, I have hereunto set my hand this 16th day of April, 1925.

FLOYD C. KELLEY.