US2145234A

US2145234A - Process of making surface alloyed

Info

Publication number: US2145234A
Authority: US
Publication date: 1939-01-31
Anticipated expiration: 1956-01-31

Description

Patented Jan. 31, 1939 PATENT OFFICE PROCESS OF MAKING SURFACE ALLOYED MATERIALS Hugh S. Cooper, Cleveland Heights, Ohio, as-

signor to Cooper Products, Inc., Cleveland, Ohio, a corporation of Ohio No Drawing. Application May 9, 1936,

' Serial No. 78,895

4 Claims.

The present invention relates to surface alloyed materials, and to methods of producing the same. More particularly the invention relates to a process of producing materials upon which a surface 5 alloy has been formed by cementation, especially ferrous materials having a surface alloy of ferro chrome produced thereon by cementation, which process includes subjecting the same to both hot and cold metal working operations.

An object of the invention is the provision of a. novel method of producing surface alloyed materials, especially ferrous materials provided with a surface alloy of ferro chrome, which comprises first forming a surface alloy on an object or base metal by cementation, and subsequently heat treating, and working the same by a'metal forming operation such as rolling, forging, swaging, drawing and the like.

Further objects and advantages of the invention will be apparent to those skilled in the art to which it relates from the following description thereof and the preferred method of practicing the same. 7

Surface alloys produced by cementation are not uniform in composition. In the extreme outer surface the cemented constituent is present in relatively high concentration which tapers off to lower values toward the interior. Upon being heated for several hours at a suitable temperature and preferably in a suitable reducing or ert atmosphere, the cementation metal tends to migrate toward the interior of the material, the effect of which is to increase the thickness of the surface alloy produced, but to dilute the content of the cementation metal at or adjacent the surface of the material. This is particularly true of chromized ferrous material, and to various degrees is true of surface alloys of other metals produced by cementation, such as surface alloy of silicon, boron, titanium, or tungsten produced on a foundation metal of steel or other ferrous materials. In each instance the surface alloy as produced is relatively rich in the cementation metal at the outer surface with a gradual decrease in concentration thereof toward the interior of the material, and subsequent heat treating under suitable conditions causes further migration of the cemented metal toward the interior of the article with a reduction in the concentration thereof at the outer surface.

I have found that ferrous metals which are first surface alloyed by cementation and then heat treated to reduce the concentration of the cementation metal at or adjacent the surface, as outlined above, can be readily rolled or otherwise Worked at temperatures which are not particularly critical, without cracking the surface alloy or making the same porous, and under favorable circumstances, such material may be cold rolled and otherwise cold Worked. The foregoing is particularly true of chromized steel and iron.

Briefly, the process of the present invention consists of producing on a base material a surface alloy by cementation in the usual manner, heat treating the same for a number of hours, anywhere from two hours up to fifteen or twenty hours, and even longer at temperatures anywhere from about 800 C. to those approximating the melting temperature of the base metal, preferably about ten hours at from 1200 C. to 1350 C., to dilute the concentration of the cementation metal at the surface and increase the penetration thereof, and subsequently working the metal so treated by either hot or cold metal forming operations to the desired shape.

As already stated, the present invention is particularly applicable to ferrous materials provided with a surface alloy of ferro chrome produced by cementation, and the preferred practice of the invention will be described in detail with reference to such materials. First a suitable iron or steel bar or billet is chromized, preferably by the process disclosed in my copending application, Serial No. 75,237, or by the usual method. The chromized bar or billet is then heated in a neutral atmosphere, preferably hydrogen, for about 10 hours at from 1200 C. to 1350 C., which will approximately double the thickness of the chromized shell and correspondingly reduce the concentration of the chromium adjacent the surface. Shorter heating an-d/ or lower temperatures lessen the increase in thickness of the chromized shell and the dilution of the chromium at the surface. Conversely, longer heating at the higher temperatures increases the thickness of the chromized shell and the dilution of the chromium at the surfaces.

After theaforesaid heat treatment the bar or billet is rolled, forged, or otherwise worked at about the same temperature, preferably 1000 C., or higher, and in much the same manner as ordinary steel or iron. Alternately, the bar or billet may be cold rolled or cold drawn. This is particularly true of flat sections, where the reduction and distortion per pass is not excessive. The billets or bars may be readily reduced to rods, wire, sheets, or other forms, and after being worked will have a continuous surface of ferro chrome or other cemented alloy with a core of simple steel or iron, as the case may be.

The phrase metal forming operation as used throughout the present specification and claims refers to such operations as forging, rolling, swaging, drawing, and the like.

Having thus described my invention, I claim:

1. The process of producing surface alloyed materials which comprises forming a surface alloy of ferro chrome on a ferrous base metal by cementation, heat treating the same for a reasonable time at a temperature in excess of about 1100 C. to reduce the concentration of the chromium at the surface and increase the penetration thereof into the base metal, and subsequently working the same to a desired shape by a metal forming operation.

2. The process of producing surface alloyed materials which comprises forming a surface al- 10y of ferro chrome on a ferrous base metal by cementation, heat treating the same for a reason- 20 able time in excess of six hours at a temperature of about 1200 c. to 1350 C., and subsequently working the same to a desired shape by a metal forming operation.

3. The process of producing surface alloyed materials which comprises forming the surface alloy of ferro chrome on a ferrous base metal by cementation, heat treating the same for a reasonable time in excess of six hours at a temperature of about 1200 C. to 1350 C., and subsequently working the same to a desired shape by a hot metal forming operation.

4. The process of producing surface alloyed materials which comprises forming a surface alloy of ferro chrome on a ferrous base metal by cementation, heat treating the same for a reasonable time in excess of six hours at a temperature of about 1200 C. to 1350 C., and subsequently working the same to a desired shape by a cold metal forming operation.

HUGH S. COOPER.