Method and apparatus for continuous compression forging of continuously cast steel

A method of continuous compression forging, with a compression forging anvil, the final solidified region of cast steel drawn out from a mold for continuously casting, comprising the step of: compressing said cast steel with said anvil at a compressing cycle which meets the following conditions: ##EQU1## where t: the compressing cycle (sec), .delta.: the overall thickness reduction, Vc: the casting speed (mm), D: the cast steel thickness before compression forging, .theta.: the inclination angle (.degree.) with respect to the flat surface of the anvil. An apparatus for continuous compression forging continuously cast steel comprising: at least a pair of anvils for vertically holding the pass line of cast steel drawn out from a mold for continuous casting and continuously compression-forging the final solidified region of the moving cast steel by moving the anvils toward and away from each other; a frame; a slider; and links, wherein either of said anvils is disposed within said frame which has a port through which said cast steel is introduced, another anvil is secured to said slider which can be reciprocated along a sliding surface formed in said frame, and said frame and said slider are hung from a crank shaft via said links, said crank shaft acting to move said anvils toward and away from each other.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a method and an apparatus for continuous 
compression forging cast steel derived from the continuous casting 
process. More specifically, the present invention relates to a method and 
an apparatus for improving the internal quality of cast steel, and, more 
particularly, for overcoming defects in casting such as central 
segregation and center porosity by performing effective compression 
forging at temperatures below the solidification point of the cast steel 
obtained by continuous casting. 
2. Description of the Prior Art 
In the conventional art, forming central segregation in continuously cast 
steel has been regarded as inevitable. This central segregation is caused 
by the condensation of carbon, sulfur, and phosphorous in the molten metal 
in the central portion of the final solidification region of the cast 
steel. The thus-condensed components in the molten metal appear in the 
form of normal segregation, causing central segregation which can 
deteriorate the mechanical properties in the direction of the thickness of 
steel plates and thus generate laminations. 
Segregation in cast steel is considered unavoidable since the condensed 
molten steel is sucked into the leading end portion of the solidified 
region of the billet obtained by continuous casting and is allowed to 
remain as normal segregation in the thicknesswise central portion of the 
cast steel. The above-described suction of the condensed molten steel can 
be realized due to: solidification shrinkage of continuously cast steel at 
the front portion of the solidified region thereof; and a vacuum suction 
force generated due to bulging of the solidified shell. 
In order to prevent central segregation, a variety of ways have been 
attempted, for example, electromagnetically stirring the second cooling 
zone. However, such attempts failed to completely eliminate semi-micro 
segregations and the effect obtained has not been satisfactory as yet. 
Furthermore, an in-line reduction method (see "Iron and steel" Vol. 7, 
1974, p. 875 to 884) has been proposed in which the cast steel is 
subjected to a heavy compression at the final stage of the solidification 
process by using a pair of rollers. However, if the portion of the cast 
steel containing a relatively large proportion of unsolidified layer is 
not sufficiently compressed, cracks can form on the interface between the 
solidified steel and the still molten portion. If excessive compression is 
applied, a strong negative segregation can be adversely generated in the 
central portion of the thickness of the cast steel. 
In order to overcome the above-described problems, a continuous casting 
method has been disclosed in Japanese Patent Laid-Open No. 49-12738 in 
which the front end portion of the solidified region of the cast steel is 
subjected to a light compression by using pairs of rollers as to 
compensate for the volume of solidification shrink at the subject portion 
by this compression. Another method has been proposed in Japanese Patent 
Laid-Open No. 52-54623 in which an anvil is used for the purpose of having 
the portion in the vicinity of the region of the cast steel subjected to a 
heavy compression near the completion of the solidification of the cast 
steel. The other method has been disclosed in Japanese Patent Laid-Open 
No. 60-148651 in which electromagnetic stirring is performed, or 
ultra-sonic waves are applied to the cast steel during the solidification, 
and compression forging is performed near the completion of the 
solidification of the cast steel. 
However, in a case of such light compression, even if a plurality of pairs 
of rollers are used to perform the light compression by several 
millimeters per meter, solidification shrinkages and bulgings generated in 
the region corresponding to the pitch between the rollers cannot be 
sufficiently prevented from being generated. Furthermore, if the 
compression is not applied to the proper position, the central segregation 
becomes worsened. According to the method in which an anvil is used for 
heavy-compressing the cast steel at its completion of the solidification, 
the interface between the solidified steel and the still molten portion 
can protect against cracking and negative segregation can be 
satisfactorily prevented from generation compared with the heavy 
compression method such as the inline-reduction method in which rollers 
are used, causing even the semi-macro segregation can be overcome. 
However, if the compression is insufficient in the region of the cast 
steel in which the unsolidified portion is in a great proportion, cracks 
can be formed on the interface between the solidified steel and the still 
molten portion. If the compression is performed excessively, intense 
negative segregation can be generated in the central portion of the cast 
steel. In addition, even if the portion of the cast steel in which 
unsolidified region is reduced is subjected to the compression, any effect 
cannot be obtained from this compression. Thus, the most suitable 
compressing conditions have not been as yet established to be performed. 
Furthermore, according to the method in which the electromagnetic stirring 
and the compression forging or application of ultrasonic waves and the 
compression forging are combined, although an equiaxed crystal ratio can 
be increased, which assist to reduce the negative segregation, generation 
of negative segregation cannot be prevented simply by the increase in the 
equiaxed crystal ratio over the wide conditions upon the thickness of the 
unsolidified region, casting speed, and temperatures. 
In order to overcome the above-described problems, a group including the 
inventor of the present invention has disclosed a method in Japanese 
Patent Laid-Open No. 60-82257 in which a compression-forging anvil is used 
for the purpose of compressing the cast steel near the completion of the 
solidification of the same. A patent application was applied for under 
U.S. Ser. No. 071,412, filed July 9, 1987, of which this application is a 
continuation-in-part. The present invention is based on the former 
application, but the claimed improvment has been added. 
Hitherto, a hydraulic press system has been usually used as a continuously 
compression-forging machine employed in each countermeasures taken against 
the above-described central segregation of the continuously cast steel. 
For example, a method is disclosed in Japanese Patent Laid-Open No. 
63-49400 in which an integrally formed frame of a "Floating Type" includes 
upper and lower anvils so that compression is equally applied from the 
upper portion by using a single hydraulic cylinder. Furthermore, a 
scissors method is disclosed in Japanese Patent Laid-Open No. 61-222663 in 
which a boosting mechanism such as lever is used. 
However, the conventional devices of the hydraulic type need a great size 
hydraulic pressure source and pipes to be provided, causing cost required 
for institution and the load for maintenance becomes too large. In 
addition, since such device involves a relative high pressure to be used, 
the life of the pump and the same of the hydraulic control valve is 
shortened to two or three years, and the involved noise can exceed B 100 
phons of loudness level. Another problem arises in that the energy loss 
during transference of the hydraulic pressure obtained by converting 
electric energy from the pump chamber to the compression forging device 
becomes 20 to 30%. Therefore, the above-described devices have not been 
satisfactory as yet in terms of the running cost. 
OBJECTS OF THE INVENTION 
An object of the present invention is to provide a method and an apparatus 
which are able to overcome the conventional problems which have arisen 
when cast steel obtained by continuous casting is subjected to compression 
forging at a point near the solidification point of the cast steel, that 
is, in the final solidification region formed by an unsolidified portion 
and the completely solidified portion, which method and apparatus are 
advantageously used for manufacturing cast steel of an excellent quality.

DETAILED DESCRIPTION OF THE INVENTION 
According to the present invention, a method is provided for continuous 
compression forging, with compression forging anvils, the final solidified 
region of cast steel drawn out from a mold for continuous casting. The 
cast steel is compressed with said anvil at a compressing cycle which 
meets the following conditions: 
##EQU2## 
where t: the compressing cycle (sec) 
.delta.: the overall thickness reduction (mm) 
Vc: the casting speed (mm/sec) 
D: the cast steel thickness (mm) before compression forging 
.theta.: the inclination angle (.degree.) with respect to the flat surface 
of the anvil. 
(2) A method of continuous compression forging cast steel in which an anvil 
having a flat surface which is in parallel to the surface of the cast 
steel and an inclined surface with .theta..ltoreq.tan.sup.-1 .mu.. where 
.mu.: the coefficient of friction between the anvil and the cast steel. 
(3) A method of continuous compression forging by using an anvil with a 
mean width which meets the requirements 
##EQU3## 
where a: the anvil mean width (mm) 
B: the cast steel width (mm) before compression forging 
.delta.: the overall thickness reduction (mm) 
D: the cast steel thickness (mm) before compression forging. 
In order to prevent generation of internal cracks at the time of 
compression-forging the continuously cast steel, it is necessary not to 
perform a compression that can cause an excessive tensile strain on the 
interface between the solidified steel and the still molten portion. 
Specifically, it is necessary to avoid using an anvil of a shape that can 
cause recessed deformation on the interface between the solidified steel 
and the still molten portion, or to arrange the compression forging cycle 
in a manner not to cause such a deformation. In a case of performing the 
compression by using compression-forging anvils 2 shown in FIG. 1, it is 
necessary for the interface between the solidified steel 1a and the still 
molten portion 1b not to be pressed by the inflection point A of the anvil 
2 (FIG. 1) when viewed in a cross-section (to be called "section L" 
hereinafter) in the longitudinal direction of the continuously cast steel. 
That is, compression needs to be performed in such a manner that the front 
end point O (FIG. 1) of the solidified region of the cast steel 1 is 
placed in the upper stream (in the unsolidified region) to a projected 
point A" on the pass line of the point A (it needs to be OA"=g.gtoreq.0). 
On the other hand, when viewed in a cross section in the direction of the 
width of the continuously cast steel (called "section C" hereinafter), it 
is necessary, as shown in FIG. 2, for the entire region of the interface 
between the solidified steel 1a and the still molten portion 1b to be 
pressed by a flat anvil, that is, the same needs to be pressed by an anvil 
2 having a mean width a that can cause the compressing pressure and 
resulting deformation on the interface between the solidified steel and 
the still molten portion to be made about equal. The present invention 
effectively prevents forming of internal cracks during a continuous 
compression forging process for the continuous cast steel by arranging a 
proper shape of the anvil employed and by setting the compression forging 
conditions. 
Then, specific conditions required to prevent generation of internal cracks 
will be described in detail hereinafter with the conditions classified 
into those required on the section L and the section C. 
The compressing conditions at the time of performing compression forging 
required on the section L are shown in FIGS. 1 and 3. Since the conditions 
required to prevent generation of cracks are, as described above: The 
distance OA"=g.gtoreq.0, the boundary case where g=0 is illustrated in 
FIG. 3. The unsolidified portion 1b of the cast steel 1 is compressed when 
the portion corresponding to the thickness of the liquid phase thereof is 
compressed. Assuming that the thickness of the unsolidified portion 
immediately below the anvil 2 is d, and that the solid phase ratio at the 
axis portion of the cast steel is f.sub.so, the thickness dl corresponding 
to the liquid phase region can be obtained as follows since the mean solid 
phase ratio is 
##EQU4## 
The solidification ratio (f.sub.so) of the axial portion of the cast steel 
is defined by an index expressing the position of the temperature of the 
center portion of the cast steel between a liquid phase line temperature 
and a solid phase line temperature, this temperature being defined in 
accordance with the type of steel, wherein a solidification ratio of 1.0 
means a fact that the temperature is within the solidification phase 
temperature region, while 0.5 means a fact that the same is within the 
intermediate region between the liquid phase line temperature and the 
solid phase line temperature. 
It is assumed that the interface between the solidified steel and the still 
molten portion is at the position at which the solidification rate is 
100%, that is at the position of the solidification phase line 
temperature, at which no liquid phase is present, but all are in the solid 
phase. In general, in the interface between the solidified steel and the 
still molten portion the phase is not gradually changed from the solid 
phase to the liquid phase, but a coexist region of the solid phase and the 
liquid phase is present, wherein the solid phase rate is 100% at the 
position in the solid phase line temperature, while the liquid phase rate 
is 100% at the position in the liquid phase line temperature. 
Then, the thickness dl corresponding to the liquid phase region can be 
expressed as follows when converted into a thickness d.sub.e corresponding 
to the liquid phase in one compression forging cycle that is compressed by 
one compression forging: 
##EQU5## 
where l.sub.a : the contact length (mm) of the slope of the anvil in the 
direction L corresponding to the overall thickness reduction .delta. 
l.sub.c : the feeding pitch (mm) in one compression forging cycle 
l.sub.b : (l.sub.a -l.sub.c) (mm) 
wherein OA".gtoreq.0 needs to be subjected to a compression forging 
corresponding to d.sub.e in l.sub.b. Therefore, the following relationship 
holds in one compression forging at a feeding pitch l.sub.c : 
##EQU6## 
and (1) into (2) gives 
##EQU7## 
where t: the compression forging cycle {time (sec) of one cycle} 
.delta.: the overall thickness reduction (mm) 
V.sub.c : the casting speed (mm/sec) 
.theta.: the inclination angle (.degree.) with respect to the flat surface 
of the anvil. 
On the other hand, a thickness reduction .delta..sub.e in one compression 
forging cycle to be obtained in the cast steel 1 can be expressed as 
follows assuming that the angle of the slope of the anvil 2 is .theta.: 
EQU .delta..sub.e =2.multidot.l.sub.c .multidot.tan .theta.=2.multidot.V.sub.c 
t.multidot.tan .theta. (4) 
where .delta..sub.e is the thickness reduction in one compression forging 
cycle (mm/cycle). 
Since the front point O when the ensuing compression forging starts needs 
to be on the portion rather adjacent to the unsolidified region compared 
to A" in order to prevent generation of internal cracks, it is necessary 
for the front end point O' at the completion point of the compression to 
be positioned forward at least by l.sub.c than A". That is, it is 
necessary for preventing generation of internal cracks to have a thickness 
d.sub.e of the liquid phase in the unsolidified portion which is 
positioned forward by l.sub.c by the thickness reduction .delta..sub.e 
caused by one forced compression, and thereby to have the interface 
between the solidified steel and the still molten portion move ahead. 
EQU .delta..sub.e .gtoreq.d.sub.e (5) 
Substitution of (3) and (4) into (5), and rearrangement terms on t gives 
(6) 
##EQU8## 
The thus-obtained equation represents the conditions required for the 
compressing cycle to prevent generation of internal cracks. 
When an improvement in the internal quality such as prevention of 
generation of central segregations is intended, the following conditions 
need to be satisfied additionally. That is, the thickness d of the 
unsolidified phase with respect to the flow of the cast steel 1 to be 
compressed needs to be within the following range: 
##EQU9## 
Furthermore, the solid phase ratio f.sub.so at the central portion of the 
cast steel needs to be within the following range: 
EQU 0.5.ltoreq.f.sub.so .ltoreq.0.9 (8) 
Substitution of (d).sub.min =1.2.sqroot.D-80 and (f.sub.so).sub.max =0.9 
into (6) for the purpose of obtaining the upper limit of t gives 
##EQU10## 
That is, a compression forging cycle performed with the anvil 2 to improve 
the internal quality and to prevent generation of internal cracks can be 
obtained from equation (9). 
Since the lower limit is defined by the response characteristics of the 
compression forging action and the institution cost of the hardware: the 
compression forging machine, and therefore is regardless of the quality of 
the products, it is not specified here. 
The above-described equation (7) is obtained as a result of an examination 
upon a carbon segregation ratio (C/Co) where C: carbon content of the 
particular portion; Co: average content of carbon with respect to the 
relationship between the cast steel thickness D and unsolidified thickness 
d of the cast steel 1 before performing compression under conditions 
.delta./d.gtoreq.0.5, and as shown in FIG. 4, the unsolidified thickness d 
is the preferred region in which the range in equation (7) displays the 
minimum normal segregation and negative segregation. The above-described 
equation (8) is obtained as a result of an examination upon the 
relationship between the solid phase ratio f.sub.so of the cast steel at 
the compressed position and the carbon segregation ratio (C/Co) at the 
thickness center when the cast steel 1 is compressed under conditions 
.delta./d.gtoreq.0.5. As shown in FIG. 5, the ideal condition for making 
C/Co=1 in compression forging is when the solid phase ratio f.sub.so =0.7. 
With the allowable rate of C/Co defined from the properties of the 
products considered, it was found that it is preferable to perform 
compression in the range where the solid phase ratio (f.sub.so)=0.5 to 0.9 
for preventing internal cracking and negative segregation. 
Furthermore, the inclination angle .theta. of the above-described anvil 2 
needs to be determined to be smaller than a frictional angle tan.sup.-1 
.mu. at the forging surface for the purpose of preventing slippage on the 
surface of the cast steel 1 when this cast steel 1 is compressed. 
On the other hand, the conditions required to be realized on the 
cross-section C need to be arranged in such a manner that the width of the 
anvil 2 is determined as to have the compression force of the anvil 2 
applied substantially equally to the unsolidified width b of the cast 
steel 1 as shown in FIG. 2, where the width of the anvil 2 is arranged to 
be the mean width a of the portion to be compressed. For example, in a 
case of a trapezoidal anvil as illustrated, the anvil width a with respect 
to the overall thickness reduction .delta./4 will represent the anvil 
width. As for the unsolidified width b, assuming that the solidifying 
speeds are the same at both longer and the shorter sides of the same, the 
thickness of the solidified portion from either side holds 
##EQU11## 
Therefore, 
EQU b=B-D+d (10) 
The compressing force obtained from the anvil 2 can be determined as 
follows: assuming that the broadening angle of a load to be substantially 
equally applied to the inside is .beta., the effective width f of the load 
to be applied to the interface between the solidified steel and the still 
molten portion can be expressed as follows: 
EQU f=a+2s tan .beta. (11) 
where 
##EQU12## 
Since the conditions required for preventing generation of internal crack 
is f.gtoreq.b, the following relationship holds from (10) and (12): 
##EQU13## 
where B: the cast steel width (mm) before compression forging 
d: the unsolidified thickness (mm) 
s: the distance between the position at which the anvil mean width a in the 
thickness direction of the cast steel at the position to be compressed and 
the interface between the solidified steel and the still molten portion: 
Furthermore, symbol c of FIG. 2 represents the width of the flat portion of 
the anvil. 
Furthermore, in order to determine the lower limit of the mean anvil width 
a in terms of the improvement in the internal quality of products, in 
needs for the condition of the above-described equation (7): (d).sub.min 
=1.2.sqroot.D-80 to be substituted into equation (13). 
The widening angle of the load .beta. of substantially 20.degree. was 
obtained from the results of experiments. Therefore, equation (13) can be 
rearranged to be: 
##EQU14## 
tan 20.degree., therefore, 
##EQU15## 
That is, by arranging the mean compression width a of the anvil to satisfy 
equation (14), internal cracks on the cross-section C can be prevented, 
and also the internal quality can be improved. 
Hereinafter the most suitable continuous compression forging apparatus for 
compressing the cast steel by using the above-described compression 
forging anvil will be described. 
A continuous compression forging machine according to the present invention 
for continuous compression forging continuously cast steel comprises: at 
least a pair of anvils for vertically holding the pass line of cast steel 
drawn out from a mold for continuous casting and continuously 
compression-forging the final solidified region of the moving cast steel; 
means causing their movement toward and away from each other; a frame; a 
slider; and links, wherein either of said anvils is disposed within said 
frame and has a port through which said cast steel is introduced, another 
anvil is secured to said slider which can be reciprocated along a sliding 
surface formed in said frame, and said frame and said slider are hung from 
a crank shaft via said links, said crank shaft acting to move said anvils 
toward and away from each other. 
It is preferable in terms of compression forging efficiency for the 
compression forging apparatus with the above-described structure to be 
arranged to provide a means for restoring the frame and the slider to the 
initial state when the anvils are positioned away from each other. 
Furthermore, the anvils are preferably provided with a position adjusting 
means capable of individually adjusting the overall thickness reduction. 
More particularly, it is preferable for the anvils to be provided with a 
position adjusting means comprising a hydraulic cylinder and a stopper for 
restricting the stroke of this cylinder. 
In the present invention, it is considerably effective to provide a 
multi-strand continuous casting machine capable of making a plurality of 
cast steel blocks arranged in such a manner that plural compression 
forging apparatuses having the above-described structure are disposed in 
accordance with the positions of each of the strands, and the 
thus-disposed compression forging apparatuses are hung from a single crank 
shaft with the compression forging cycle arranged in such a manner that 
the starts of the compression forging operations of the respective strands 
do not coincide. 
One structure of a compression forging apparatus according to the present 
invention is schematically shown in FIGS. 9(a) and 9(b). Reference numeral 
1 represents cast steel drawn out from a mold for performing the 
continuous casting, and 2a and 2b represent anvils. These anvils 2a and 2b 
vertically hold the pass line of the cast steel 1 and continuously 
compression-forge the final solidified region of the cast steel 1 by their 
movement toward and away from each other. Reference numeral 13 represents 
a frame having an inlet port 13a through which the cast steel 1 is 
introduced, and in which either of the two anvils 2a or 2b is disposed 
therein (the anvil 2b is so disposed here). Reference numeral 14 
represents a slider capable of vertically and reciprocally moving along a 
sliding surface 13c formed in the frame 13, this slider 14 being provided 
with the other anvil 2a at the front end surface thereof. Reference 
numeral 15 represents a crank shaft which acts to make the anvils 2a and 
2b move toward or away from each other. Thus, the frame 13 and the slider 
14 are hung from the crank shaft 15 with the corresponding links 13b and 
14a. 
When the crank shaft 15 supporting the frame 13 and the slider 14 in a 
pendulum manner is revolved by a motor 20 or the like via, for example, a 
decelerator 19, the anvils 2a and 2b connected to the links 13b and 14a 
via the frame 13 and the slider 14 repeat the opening and closing movement 
centering the pass line since the links 13b and 14a are made eccentric 
with respect to the rotational axis of the crank shaft 15 by distances 
e.sub.1 and e.sub.2. Thus, the cast steel 1 is continuously subjected to 
compression forging by the relative movement of the anvils 2a and 2b 
coming closer and away from each other. 
In this compression forging process caused by the movement of the anvils 2a 
and 2b, since the apparatus body can readily follow the drawing-out 
movement of the cast steel 1, the apparatus can be protected from any 
excessive force. 
FIG. 10 is a view which illustrates the relationship between the locus of 
an anvil, for example, the anvil 2, and the feed of the cast steel 1 when 
the crank shaft is rotated in a direction designated by an arrow E. This 
feed is illustrated as classified into a case where the drawing speed of 
the cast steel 1 is raised and a case where the same is lowered (it is the 
same if the rotational speed of the crank shaft 15 is varied and the 
drawing speed of the cast steel 1 is set to a constant speed) with 
rotational speed of the crank shaft 15 set to a constant speed. As 
illustrated, the anvil 2a moves from F to F' when the drawing speed is a 
relatively high speed, while the same moves from G to G' when the same is 
a relatively low speed. However, the overall thickness reduction becomes 
the same in either case. In this case, the path followed by the apparatus 
body is described as the above-described locus, but the cast steel 1 is 
moved horizontally due to the drawing. There arises a fear that an 
excessive force might be applied to the cast steel 1 or the apparatus 
during the compression forging. However, since the follow-up distance of 
the apparatus is practically limited to several tens mm in practice, such 
problem can be overcome by securing the length of the pendulum at least 3 
m. 
The anvil inclination angle .omega. becomes, as shown in FIG. 11, a reduced 
degree: 30/3,000=1/100, provided that the follow-up distance f is 30 mm. 
The influence of this inclination on the overall thickness reduction of 
the anvils is limited to a reduced value expressed regarding the height 
displacement .lambda.: 
3000 mm.times.[1-.sqroot.1-(1/100).sup.2 ]=approximately 0.15 (0.1 to 0.2 
mm), where m represents the length of the pendulum of the anvil. The 
height displacement is limited within the clearance of the apparatus, 
causing no problem. 
According to the present invention, the compression forging apparatus which 
has been moved as a result of the drawing of the cast steel 1 at the time 
of performing compression forging can be quickly restored to its original 
position by providing a hydraulic means 16 (FIGS. 9(a) and 13(b)), for 
example, a hydraulic cylinder, for the frame 13. Furthermore, the anvils 
2a and 2b can be used as a relief mechanism from abnormal loads if they 
are secured, as a position-adjusting means, to the frame 13 and the slider 
14 via, for example, the hydraulic cylinder 17. In addition, the cast 
steel 1 can be made to pass through the gap between the anvils 2a and 2b 
when the gap is widened in an emergency. Furthermore, an advantage can be 
obtained in that the work for changing the size of the cast steel 1 can be 
readly performed. 
In addition, a simple and mechanical adjusting means can be realized 
without any necessity of providing an expensive hydraulic servo system by 
arranging, as shown in FIG. 12, the structure in such a manner that the 
above-described position adjusting means comprises an electric or manual 
abutting stopper 18 and hydraulic cylinders 17a and 17b, the stopper 18 
comprising the nut 18a, a screw 18b, and an absorbing member 18c. 
In the compression forging apparatus having the structure as shown in FIG. 
15, the position adjusting means of the lower anvil 2b can be easily 
broken due to heat, water, or scale generated during operation, and its 
maintenance is difficult to be conducted. In order to overcome this, the 
hydraulic pressure cylinder 17 which serves as the position adjusting 
means needs, as shown in FIGS. 13(a) and (b), to be disposed above the 
main frame body 13 (upper than the crank shaft) and as well the main frame 
body 13 needs to be connected to the crank shaft 15 with the anvil 2b 
supported via this position adjusting means. 
When the apparatus according to the present invention is applied to, for 
example, a multi-strand continuous caster, the above-described devices 
shown in FIG. 9 are respectively provided to correspond to strands, and 
are hung from one crank shaft so as to realize a compressing cycle with 
which the start of the compression forging for each of the strands cannot 
become the same, for example, so as to make the phase difference 
180.degree. in a case of 2-strand, 120.degree. in a case of 3-strand, and 
90.degree. in a case of 4-strand. 
FIGS. 13(a) and 13(b) are views which schematically illustrate the case of 
a 4-strand continuous caster. FIG. 14 is a view which illustrates an 
operation diagram of the crank shaft 15 of FIGS. 13(a) and (b). Although 
the case is described in which the compression forging apparatus is 
disposed above the pass line of the crank shaft for hanging, and the motor 
and decelerator for rotating this crank shaft, it may disposed below the 
pass line if there is sufficient space. 
Internal cracks formed upon actual compression forging performed under 
various conditions with a press forging apparatus as shown in FIGS. 8 to 
15 were examined. 
EXAMPLE 1 
(examination of the internal cracks observed on the cross-section L) 
Casting was performed under conditions that a bloom of cast steel S53C (C: 
0.53%, Si: 0.19%, Mn: 0.81%, S: 0.015%, P: 0.025%) of thickness 270 mm, 
width 340 mm, and a bloom of cast steel S25C ((C: 0.25%, Si: 0.20%, Mn: 
0.58%, S: 0.010%, P: 0.012%) were used, and the overall thickness 
reduction .delta.=40 mm, the casting speed V.sub.c =0.72 m/min, the 
unsolidified thickness d=16 mm, the solid phase rate f.sub.so at the 
central portion f.sub.so =0.8, the inclination of the anvil 
.theta.=6.degree. with the compression forging cycle varied in a range t=5 
to 25 sec. The results are shown in FIG. 6. The axis of ordinate of this 
drawing represents the index (reference is set to 1) obtained by dividing 
the overall length of the internal cracks observed in a sulfur print test 
carried out upon the sample of the 600 mm long cross-section L after 
compression forging by the overall length of the allowable limit of the 
internal cracks of the sample. Referring to this graph, the compression 
cycles 16.3 sec and 15.2 sec for preventing internal cracks obtained from 
equations (9) and (6) are shown. As is shown in this graph, since these 
compression cycles approximate to 18 sec and are smaller than this 18 sec, 
it is apparent that they can serve as the evaluation equation. Since the 
compression forging was performed under conditions which are relatively 
approximate to the design conditions of equation (9), the values from 
equations (9) and (6) did not display a significant difference in this 
example. However, in practice, it is preferable to perform the evaluation 
with equation (6) since further elaborate conditions can be reflected 
thereto. 
EXAMPLE 2 
(examination of the internal cracks observed on the cross-section C) 
Compression forging was performed with a bloom of S53C and S25C 400 mm 
thick, 560 mm wide under conditions that the overall thickness reduction 
.delta.=100 mm and unsolidified thickness d=21 mm with the compression 
mean width a of the anvil varied at 40, 60, 80, and 100 mm. The results 
are shown in FIG. 7. In the case of the anvil width of 60 mm, the result 
approximated the limit with respect to the anvil mean width a of 64 mm 
obtained from equation (14), and no problem of internal cracks arose when 
the anvil width was 80 mm or more. Therefore, the compression width a of 
the anvil of equation (14) can be satisfactory and practically used as the 
evaluation equation for internal cracks. Consequently the advantage of the 
present invention was confirmed. 
According to the present invention and with determining the compression 
forging conditions and the shape of the anvil, the internal cracks of the 
cast steel when the same is compression forged can be prevented. In 
addition, the internal defects such as central segregations can be 
improved. As a result, a significant improvement can be obtained with 
respect to the product manufactured by the conventional continuous 
casting. 
In addition, when cast steel 250 mm thick and 300 mm in width was cast at a 
casting speed of 1.1 m/min by using 3-strand continuous caster, the 
central segregations and center porosity can be effectively reduced from 
the obtained cast steel. 
Furthermore, a comparison upon the institutional cost and the life of the 
conventional hydraulic direction drive system was made, and the following 
results were obtained: 
(1) The institutional cost was reduced by 30%. 
(2) The maintenance load was reduced to 1/10. 
(3) The running cost was reduced by 20%. 
(4) The noise level was reduced to 50 phons of loudness level with respect 
to the estimated value of 110 phons with the conventional hydraulic 
system. 
Consequently, the apparatus according to the present invention displays 
significant advantages with respect to the conventional apparatus. 
Therefore, a significantly smooth operation can be achieved according to 
the present invention. 
While the present invention has been disclosed in terms of selected 
preferred embodiments in order to facilitate better understanding of the 
invention, it should be appreciated that the invention can be embodied in 
various ways without departing from the principles of the invention. 
Therefore, the invention should be understood to include all possible 
embodiments and modifications without departing from the spirit of the 
invention set out in appended claims.