Process for hot working article defining hole at the center thereof

A process for hot working a tubular material having one open end and the other closed end including the steps of: injecting an inert gas into the hole of the material; then fastening a cap to the open end of the material in order to hermetically seal the hole; then heating the material and concurrently subjecting same to forging or the like. Then, the end to which cap has been fastened is separated from the remainder of the material, so that a final product results. The process has an advantage in that it easily, inexpensively prevents a layer transmuted due to heating from occurring in the surface of the hole.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a process for preventing an occurrence of 
a transmuted layer (e.g., an oxidized layer or decarburized layer) in the 
surface of a hole defined in an forged article or the like which hole is 
difficult to eliminate the transmuted layer produced when a steel of the 
forged article is heated. It relates more particularly to a process which 
prevents or reduces an occurrence of an oxidized layer or decarburized 
layer by filling the hole with an inert gas, e.g., argon gas. 
2. Description of the Prior Art 
Hitherto, a hammer or press has performed an forging. A heating temperature 
of forging is 1,000.degree.-1,200.degree. C., a higher heating temperature 
more facilitating the forging. A normalizing temperature is about 
900.degree. C. An annealing temperature is 650.degree.-850.degree. C. In 
addition, in order to prevent the occurrence of the transmuted layer in 
the surface of a hole defined in a holed forged article, copper plating or 
various coatings have been applied to the surface. However, copper plating 
can be effective only up to about 950.degree. C. and the coatings are 
difficult to eliminate after heating. 
Herein, decarburization is a phenomenon in which carbon contained in steel 
is oxidized and released as a gas to the outside of the steel when the 
steel is heated in the atmosphere, so that a carbon concentration in a 
surface layer of the steel is reduced thereby to reduce a hardness of the 
surface layer. The reduction in the hardness reduces a fatigue limit of 
the steel. Herein, an oxidized layer means a zone of the steel in which 
the steel itself has been oxidized to be transmuted and which can be 
flaked from the surface of the steel in the form of scale. 
In addition, a process of heating the holed forged article with an inert 
gas flowed has also prevalied. However, the process requires a larger 
amount of the inert gas, which is very costly. The effect of the flowed 
inert gas has been made unstable by the mixing of air. 
SUMMARY OF THE INVENTION 
In view of problems in prior art, an object of the present invention is to 
provide a novel simple process for preventing an occurrence of a 
transmuted layer produced in the surface of the hole of a holed forged 
article by heating, the prevention process being conducted at a low cost 
and enduring even a high temperature. 
In order to achieve the object, the present invention is to provide a 
process for hot working an article defining a hole at the center thereof 
from a tubular material which has a hole being open at one end of the 
material and closed at the other end of the material, the hot working 
process comprising the steps of: injecting an inert gas through said open 
end into the hole; then fastening a cap to said open end to seal the hole; 
heating the tubular material the hole of which has been filled with the 
inert gas; then hot working the tubular material; then separating said end 
to which the cap has been fastened from the reminder of the tubular 
material. If the hole is open at both ends, similar procedure can be 
applied to achieve the object. 
The other objects, arrangements, operations and advantages of the present 
invention will be apparent from the attached claims and the description of 
the preferred embodiment with reference to the attached drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
The preferred embodiment, e.g., forging of the present invention will be 
described with reference to FIGS. 1a, 1b and 1c. In FIG. 1a, a preforged 
material with a center hole 2 or tubular material is indicated at 1, the 
center hole 2 extending axially of the material 1, and a thick-walled 
portion provided around an open end of the material 1 is indicated at 3. 
The thick-walled portion 3 is to be forged. 
As shown in FIG. 1a, argon gas 4 (hereinafter referred to as Ar gas) is 
injected into the center hole 2 prior to forging. Since a specific gravity 
of Ar gas is larger than that of air (i.e., about 1.4 times that of air), 
the Ar gas completely replaces air within the center hole 2 when a hose 
for Ar gas which is extended to the bottom of the center hole 2 with the 
open end higher positioned than a closed end of the material 1 quietly 
injects Ar gas into the center hole 2. An oxygen densitometer (not shown) 
positioned near the open end of the material 1 detects a completion of the 
replacement. 
As shown in FIG. 1b, then a plug or cap 5 is fitted on the open end of the 
material 1 and a weld-all-around 6 is applied to a joint between the outer 
cylindrical portion of the cap 5 and an open end surface of the material 1 
in order to seal the Ar gas within the center hole 2. 
As shown in FIG. 1c, then forging the heated material 1 compresses same 
axially thereof and then the resulting material 1 is heat treated, i.e., 
normalized and/or annealed. Then, the upper end of the material 1 is 
separated from the remainder of the material 1 on a cutting plane line 7 
with the cap 5 remaining hermetically fastened to the upper end (see FIG. 
1c). 
Thus, an forged article of FIG. 2 results. 
The present embodiment has described the process for working the holed 
forged article. However, the present invention is applicable to hot 
workings of other holed articles other than the working of the holed 
forged article and also simply to heat treatments of holed articles. The 
use of the process of the present invention prevents an occurrence of a 
transmuted layer even in a heat treatment conducted in an atmospheric 
furnace without a need for a vacuum furnace. 
Further it will be understood that the present invention is also applicable 
to a tubular material which has an axially extending through hole and a 
lid closing the bottom end of the hole. 
In accordance with the present invention, since an inert gas, e.g., Ar gas 
is previously injected into a holed material and then the material is 
heated and forged with the inert gas completely sealed therewithin, 
1) the material can be forged regardless of the heating temperature so that 
the surface of the hole is protected from a transmutation; 
2) an amount of the employed inert gas essentially is as small as the 
volume of the hole, which is inexpensive; and 
3) no special equipment is required so as to provide a inexpensive working.