US2219004A

US2219004A - Formation of chromium-containing layers on ferrous surfaces

Info

Publication number: US2219004A
Application number: US219920A
Authority: US
Inventors: Daeves Karl; Becker Gottfried; Steinberg Fritz
Original assignee: Individual
Current assignee: Individual
Priority date: 1937-07-21
Filing date: 1938-07-18
Publication date: 1940-10-22
Anticipated expiration: 1957-10-22

Description

Patented Oct. 22, 1940 UNITED STATES FORMATION OF CHROMIUM-CONTAININGO LAYERS ON FERROUS SURFACES Karl Daeves and Gottfried Becker, Dusseldorf, and Fritz Steinberg, Krefeld, Germany No Drawing. Application July 18, 1938, Serial No. 219,920. In Germany July 21, 1937 4Claims.

' This invention relates to the formation of chromium-containing layers on surfaces of ferrous articles.

In the art of forming such layers, a recent development is the use of gaseous chromium chloride (CrClz), which is caused to act on the ferrous surface at a high temperature.

The primary object of the present invention is to produce a more uniform and heavier layer m by means of gaseous chromium chloride.

Another object of the invention is to distribute the chromium chloride gas uniformly over the surface to be treated.

Yet another object is to render more appro- 5 priate the concentration of the chromium chloride gas during its attack on the ferrous surface.

Gaseous chromium chloride is heavy, and therefore if the gas is allowed to flow continuously through a furnace containing the article 20 the furnace must be suitably shaped or guiding surfaces be provided in order to ensure that the chromium chloride'flows uniformly over the surface or surfaces to be treated. If the article is packed with chromium chloride salt in a closed 25 container and the whole is heated, it is diflicult to obtain satisfactory results. In the first place, the salt is extremely sensitive to moisture, and in the second place, it is used up as the process continues, so that, even if it is mixed with sand or equivalent refractory material, it ceases to afford an adequate supporting bed for the heated article, which is liable to warp or become distorted when it is not properly supported.

According to the invention, the gaseous chro- 35 mium chloride is caused to act on the surface to be treated through a porous ceramic material, acting as a carrier, a transmitting medium, in-

stead of acting directly and freely on that sur face. In this way, more uniform and heavier 40 layers containing chromium are produced, and the process is substantially facilitated. The carrier may advantageously consist of porcelain or sillimanite, since these (particularly porcelain) consist primarily of constituents which are not at- 45 tacked by chromium chloride, but also contain constituents which are so attacked. The action of chromium chloride on such a carrier leads to the production of very fine pores and passages by which flowing gas is split up into a state of 50 very fine subdivision or in which chromium chloride can be condensed and subsequently volatilised. Such fine pores or passages are, of course, additional to the pores formed by the spaces between the pieces in the carrier material. Nat- 5 urally it is also possible, and in some cases advantageous, to start with a material the pieces of which are already porous. A further and important advantage obtained by using porcelain or sillimanite is that they contain no, or very few, constituents which form compounds 5 with chromium chloride, such for example as alkali or alkaline earth silicates. Ceramic materials which contain such constituents should be avoided, since they render much of the chromium inoperative and thus render the process uneconomical. Furthermore, in selecting a suitable material, one that is itself consumed during the treatment should be avoided, as otherwise the carrier will not always form a good support for the articles packed in it.

The size of the pieces forming the carrier material may vary with the dimensions of the article to be treated. The carrier material should in any case be granular and not sandy or powdered, and the pieces should be of such a size that the parts to be treated are as far as possible uniformly surrounded by the carrier material. For articles of moderate dimensions carrier material composed of pieces of from 3 to 6 mm. have been found particularly suitable.

The invention may be carried into effect in various ways. One way comprises charging the carrier material with chromium chloride and packing the article with the charged carrier material in a container, which is then closed and heated. Instead of using chromium chloride itself, substances capable of yielding chromium chloride may be mixed with the carrier or charged into the same container, and the chromium chloride may then be formed in situ, Thus chromium chloride salt may be placed in the container and hydrogen may be led through the container during the heating, so that chromium chloride gas is formed. I

Again, the article to be treated may be placed in a furnace and surrounded by the carrier materiaLand chromium chloride gas may be passed through the furnace. The gas flows through the carrier to reach the ferrous surface, and produces a particularly uniform and strong surface 5 layer. It seems that the chromium chloride concentration is rendered more satisfactory by the use of the carrier material.

The chromium chloride gas may be produced in any suitable way; for example, chromium chloride salt may be heated in the presence of hydrogen as described above, or gaseous hydrogen chloride may be passed over heated chromium or alloys or compounds of chromium.

The duration of the treatment depends on 5 the thickness ofthe layer desired and on the reaction temperature. Thus treatment for four hours at from 960 to 980 C. may hen to produce the same thickness of layer as is produced in from one to two hours at from 1000 to 1080' O.

In order to prevent any oxidation of the articles, it is desirable to carrier: the treatment said surface with heated gaseous chromium cliioride through said carrier.

3. In the formation of a chromium-containing layer on the surface of a ferrous article, the steps which comprise charging with chromium chloride a ceramic carrier material selected from the group of porcelain and sillimanite, packing said article, with said charged carrier material surrounding and in contact therewith, in a container, closing said container, and heatin: said clam container to cause the charged chromium chloride to volatilize and act on said article through said carrier material.

4. Inxthe formation of a chromium-containing 1o layer on the surface of a ferrous article, the steps which comprise introducing said article into a container, packing said article in said container with a ceramic carriermateriai selected from the group consisting of porcelain and siilimanite, and 15 at least one substance capable of yielding chromium chloride gas, sin-rounding and in contact with said article, and producing chromium chloride gas in said container from said substance,

to cause said gas to act on said article through 20 said carrier material.

xam. canvas 7 GO'I'I'FRIED BECKER. ram