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JOURNAL OF IRON AND STEEL RESEARCH, INTEXNATIONAL. 2008, 15(3) : 47-51
Abnormal Failure Analysis of H13 Punches in
Steel Squeeze Casting Process
ZHANG Mi-lan' , XING Shu-ming' , XIN Qiao' ,XIAO Li-ming' , GOU Jun-nian' , W U Xia-ling'
(1. Semisolid Forming Research Center, Beijing Jiaotong University, Beijing 1 0 0 0 4 4 , Beijing , China1
2. Departmen t of Mathematics, Ili Normal Unive rsity, Yining 835 000 , Xinjiang. Ch ina)
Abstract: In steel squeeze casting process, the working condition of a punch was very rigorous. Th e abnormal failure
models of an H 13 punch, such as plastic rubbed dam nification, could not be avoided easily, Based on the analysis of
the flow stress and the friction-shearing stre ss of an H1 3 punch in steel squeeze casting pro cess , t he following resu lts
were obtained: if the flow stress of a n H1 3 punch was smaller than its friction-shearing str ess , these abnormal fail-
ures could not be avoided; and if there were some protection measures that enable the flow stress to have a greater
value than its friction-shearing one , t he abnormal failures would not occur. In the production of 4 5 # steel valves and
catenary system componen ts, the flow stres s of a lateral H1 3 punch without any protection measure was abou t 29
MPa and its friction-shearing stress was about 51 MP a, then, the abnormal failures occurred1 however, when the
protection measures of the punch enabled its working temperature to have a value below 682 'C , ts flow stress was
greater than its friction-shearing stress, and the abnormal failures were avoided.
Key words: steel squeeze casting; abnormal failure1 plastic rubbed damnificationi plastic chimbi H13 steel
A punch in squeeze casting process is exposed
to severe mechanical stress and thermal stress in-
duced by the thermal cycling and successive squee-
zing operations. Th e abnormal failures, such as
plastic rubbed damnification, are caused by the me-
chanical and thermal s tresses. Th e thermo-mechani-
cal cycles produce stress, which is close to or even
greater than the yield point of a punch especially on
its surface, and the problem is especially more se -vere in steel squeeze casting where exists high pres-
sure accompanied by the elevated-high tempera-
ture"*''. The service life of a punch is considerably
shortened owing to the thermemechanical stresses
caused by the high thermal stress and hydrostatic pres-
surd3', and the punches are the critical problems of the
reusable dies used in steel squeeze casting process.
For the super integrated mechanical properties
such as good hot hardness, high thermal resistance,
high thermal fatigue property, and synthetical me-
chanical properties etc. , H13 steel is widely chosen asthe material of the forming parts in steel squeeze casting
dies and is widely studied at home and Unt il
now, few studies have been found about the abnor-
mal failures of an H13 punch used in steel squeeze
casting. In this article, flow stress theo ry, devel-
oped by S. Shida and H. Kolsky and H. Suzuki et
al. [ was used to analyze the abnormal failures of
H13 punches in steel squeeze casting process and the
theory was validated in the productions of 45* steel
valves and catenary system components.
1 Failure Mechanisms
The working condition of a punch in steel
squeeze casting was very rigorous, and the abnormal
failures occur only after several working sequences,
Th e abnormal failure models of a punch, which were
caused by co-working of t he elevated-high tempera-
ture and great friction occurring when the punch was
being stripped ou t, such as plastic rubbed damnifica-
tion on the circumference and plastic chimb at the
top, shown in Fig. 1 to Fig. 3. The composition ofH13 steel is shown in Table 1.
Biogrnphy:ZHANG Mi-lan(1982-), Female, Doctor, Lectureshipi E-mail: zhangmilan - sd@sina. corn1 Revised Date: April 2 6 , 2007
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Journal of Iron and Steel Research, Intern ation al Vol. 1548
Table 1 The composition of H13 steel %
Composit ion C Mn C r Mo Si V P S
Mass percentage 0. 32-0. 42 0. 1-0. 4 4. 5-5. 5 1. 0-1. 5 0. 8-1. 2 0.8-1. 2 GO. GO. 3
A s seen in Fig. 1 and Fig. 2, there were several
pits , dots , and grooves on the circumference of the
punch, and there was plastic chimb on the top edge,
which is shown in Fig. 3. These failure models were
summarized as plastic rubbed damnification. In a se-
quence of the steel squeeze casting process, the
punch was pushed into the solidifying system of the
metal being formed and then it remained there for a
while determined by the pressure holding time,
which was the cause of the elevated-high tempera-
ture of the punch. After a while, the punch was
stripped out by a knockout force, and then seriousfriction occurred because of the packaging force
caused by the shrinkage of the formed component
and the stripping movement. If the friction-shearing
stress of the punch was greater than its flow stress
in the s tripping course, fierce flows of the material
at a certain depth on the surface of the punch oc-
curred, so as t o lead to the occurrence of the abnor-
mal failures.
The failure models shown in Fig. 1 and Fig. 2
were different from the thermal fatigue desquama-
tion in the following aspects. Firs tly , their forming
processes were different. Before the thermal fatigue
desquamation was formed on the circumference of a
punch, thermal fatigue cracks occurred, and the des-
quamation was caused by the expansion of the
cracks. However, before the failure models shown
in Fig. 1 and Fig. 2 were formed, there were no fa-
tigue cracks. Secondly, t heir forming mechanisms
were different. Thermal fatigue desquamation was
caused by thermal pulsating stress, but these abnor-
mal failure models were formed because the flow
stress of an H13 punch was smaller than its friction-
shearing stress on its circumference.
2 The Flow Stress of H13 Punch in Steel
Squeeze Casting Process
The flow stress iff of H13 steel is affected by
several factors, such as the working temperature T,
the equivalent carbon w ( C > , he average strain E ,
and the average strain velocity i . Th e relationships
between them were expressed asCg7101
a,=udcw(c> ,T,1fw<r)f,<i) (1 )
where, T,was the equivalent temperature: T,=-000'fw (d and f r ( 5 ) were functions depended upon the strain
and strain rate, respectively. The strain function f w (5)
T
was expressed as fw ( 5 ) = 1.3 --E - .3 -c ,[ 02 1 " [ 0.12 1
[O. 081w(c)- .154) T,4- - .014w (C ) + 0.20714-
the defomtion resistance function, which was expressed
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Issue 3 Abnormal Failure Analysis of H 13 Punches in Steel Squeeze Casting Process 49 9
__
1. 0 0. 01
as: ud[w(c ) T,]=O. 28exp[--T w(c ) +O . 05
could be obtained according to the formula proposed
w ( C d w(V) w ( M o )40 10 50 a
According to these formulas described above,
the value of the carbon equivalentw ( C )
was 0 .787for H13 steel and then the following results w ere ob-
tained: T , = 1.027, g [ w (0, ] = 3 . 0 9 5 , m =
0. 1 4 4 , an d n = 0. 355. Afte r several form ing se-
quences of steel squeeze casting, the temperature of
a punch remained in a cert ain interval. If the re were
no protect ion measures on the punch, the working
temperature was around 800 % . f there were some
protection m easures on the pun ch, the w orking tem-
perature was defini tely lower than that without any
protection measures. Associating with the equation
T,=- he relationship of T, < T, was ob-
tained, and th e following formula was obtained:
isl =25.8[50. 6 ( Tq - 1 . 0 0 5 ) 2 f 0 .9661 X
1 000 '
(2 . 350.355- . 55) . i)O.44 ( 2 )
3
in Steel Squeeze Casting Process
The Friction-Shearing Stress of H13 Punch
T h e friction-shearing str ess r of a punch was
gener ated by the normal force u and the str ipping
movement driven by a stripping force applied by a
hydropress, which is described in Fig. 4. T h e n o r-
mal stress contained two parts: the shrinkage stres s
caused by shrinka ge of t he formed component and the
squeezing stress g enerated by the forming method.
T h e linear shrinkage ratio of the forming material
between its solidus and its temperature when the punch
was being stripped out was E~ ; he Young's modulus of
the forming material was assumed to be E' when the
punch was being stripped out. According to the relation-
Di+Dfship of uf =E ' E / 2nD1 Im + v 1 ] , where , E is
the assumed stain and u' is the corresponding press-
ing stress, D1 nd D 2 were mean rad ius of t he punch
Fig. 4 The forcing model of a punch in squeeze casting p.rocess
and the formed component, v was Poisson ' s ra t io ,
an d E =~ D , E , . onsidering squeezing stress p syn-
chronously, the normal stress u (as shown in Fig. 4 )
was: u = u f + p .
According to the forcing equilibrium principle of
the model shown in Fig. 4 , the following equation
was obtained:
P= L d k c o w - s i n a ) ( 3 )
where, P was the strippin g force of th e punc h; s w as
the mean circumference of the pu nch ; L was the
length of th e punch packed by th e formed compo-
nen t ; k was the static friction coefficient; a was the
stripping slope degree.
Th en , the fr ict ion-shearing stress wa s calculat-
ed as:( 4 )
SLr = -
4 Validation and Discussion
4. 1 Brief introduction of the 45 ' steel valves pro-
duction condition
T h e 4 5 # steel valves w ere used for colliery sup-
por t ing , The H13 punches of th e die (s ho w n in
Fig. 5) were quenched at 1 03 0 ' C ; the f irs t tempe-
ring was for 3 h at 550 .C and the second tempering
was for 3. 5 h at 600 "C. After being heat t reated,
their hardness was within the range of HR C 48 and
HRC 52.
A special forging hydropress with the maximal
extrusion force of 1 500 kN and t he m aximal die-loc-
king force of 2 000 kN was adopted in the produc-
tion. T h e forging hydropre ss contain ed a locking
cylinder, two filling cylinders, and two lateral
squeezing cylinders, so t ha t i t was able to carry out
two individual motions: die locking and pressu re filling.
Th e product ion process was as follows: firstly,th e prepared m elt was poured into the lo wer cavity
of the die. Seco ndly, t he die was closed by th e die-
locking cylinder of the forging hydro press. Th ird ly,
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50 J o u r n a l of Iron a n d Steel R e s e a r c h , I n t e r n a t i o n a l- Val. 15
1, 3-Lateral punches; 2-Lower punchi 4-Upper punch
Fig. 5 The die used In the production
the lower punch was pushed down to a given pres-
sure by the lower filling cylinder. Fou rth ly, the up-
per punch was pushed down to a given pressure by
the upper filling cylinder. Then , these lateral pun-
ches were pushed into the solidifying system by two
lateral filling cylinders. Last ly, all cylinders were
withdrawed by sequence and the fabricated compo-
nent was pushed out by the lower punch.
4 .2 The flow stress of the lateral punch and discussion
4. 2 . 1 T h e f l o w s t re ss o f t he l a t er a l p u n c h i n t h e
exper imen t
In the squeeze casting process of 45# steel
valves production, the strain rate in back-moving of
the lateral punch was i = l l O mm/s, thus, f r < Z > =0. 522; the average strain E was 0.01 and f , ( E ) ==.
0. 433. A s discussed in the former chapters, i f there
were no protection measures on the punch, the
working tempera ture remained around 800 ‘C,
here-
fore, T ,= 0.8. Associating with Eqn. ( 2 ) and the
values obtained in the former chapters, the value of
at was 29 MPa.
4. 2. 2 The fr ic t ion-shearing s tress on the surface
o f t he l a t er a l p u n c h
The linear shrinkage ratio between the solidus and
the temperature of 45# steel when the punch was
stripped was about 1.23% ; the Young’s modulus of the
forming material was about 160 GPa while the punch
was stripped, and then the value of 0‘ was 80 MPa. The
squeezing stress was assumed to be 20 MPaC”’; then,the value of the normal stress u was 100 MPa accord-
ing to the formula u = u ’ f p . Also, in the produc-
tion, the diameter of the punch was 39 m m , th e
length of th e punch packed by the formed component
was about 40 mm, the value of a was 0.3”, and the
static friction coefficient k was assumed to be 0. 25 ;
based on these values and Eqn. ( 3 ) , the value of P
was 130 MPa.
In the production, considering the friction be-
tween the die and the punch, the value of t he lateral
stripping force was chosen to be 150 kN . When the
lateral stripping force was 150 k N , the lateral pun-
ches were stripped limpingly; however , when the
lateral stripping force was smaller than 150 k N , the
stripping motion was considerably more difficult or
even the punches could not be stripped out; thus,
150 kN was considered as the critical str ipping force.
Associating with Eqn. ( 4 1, the friction-shearingstress was about 51 MPa.
4.2. 3
Comparing the practical friction-shearing str ess
51 MPa with the theological flow stress 29 MPa ob-
tained above, the following result was concluded: i f
there were no protection measures on an H13 punch
in steel squeeze casting process, the practical critical
friction-shearing stre ss was greater th an the theolog-
ical flow stress, and therefore, the abnormal plastic
failures could not be avoided.
If there were some protection measures on an
H13 punch in steel squeeze casting process, its
working temperature T was definitely lower than
tha t withou t any protection measures, which indica-
ted that: T<800 ‘C and T,<O. 8; then, fin. ( 2 ) was
still suitable for calculating the flow stress of the H13
punch. Also, if the flow stress of the H13 punch was
greater than its friction-shearing stress, the abnormal
plastic failures would not occur, that is to say:
ot>51 MPa (5)
Based on Eqn. ( 2 ) and Eqn. ( 5 1 , the relation-
ship T,<O. 682 was gained. Considering Eqn. ( 2 ) ,
the indexes concerning the average strain E were
0.355 and 1 , and the index of the average strain ve-
locity was 0. 1 4 4 , but the index concerning the e-
quivalent temperature T, was 2 , therefore, the
effects of t he average stra in and the average stra in
velocity on flow stress af were considerably smaller
than that of the equivalent temperature. Concerning
the range of t he average strai n and the range of the
average s tra in velocity of a punch in steel squeeze
casting process, the effects of the average str ain andthe average velocity str ain were ignored provisionally
when the flow stress of the punch was discussed.
This indicated that: if the working temperature of a
Discuss ions o f the p las t i c f a i lu re
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Issue 3 A b n o r m a l F a i l u re A n a l y s i s of H 13 P u n c h e s in S t e e l S q u e e z e C a s t i n g P r o c e s s 5 1
punch was below 682 ‘C , he friction-shearing st ress
would be smaller than the flow stress, and the ab-
normal plastic failures would not occurs in other
words, if there were some protection measures that
could ensure the working temperature of a punch be-
low 682 % , the abnormal plastic failures could be
avoided.
Generally, if there were no protection measures
on a punch in steel squeeze casting, the friction-
shearing stre ss of a punch would be greater than its
flow stres s, and the abnormal failures weren’ t able
to be avoided. T o avoid or reduce the abnormal fail-
ures, some protection measures, which were able to
enable the working temperature of a punch below
682 ‘C , should be adopted. Using adiabatic coalc adop-ting the cooling systemc and adopting both simulta-
neously were proved to be effective in the production
of the 45# valves and the catenary system compo-
nents.
In the steel squeeze casting processes of the cat-
enary system components production, which were
used in railway system, it was also discovered that if
there were no protecting measures, the abnormal
plastic failures occurred on H13 punches, and when
protection measures could ensure the working tem-
perature of an H13 punch below 680 ‘ C , these ab-normal plastic failures could be avoided.
the working temperature of an H13 punch is consid-
erably lower than that in ferrous metal squeeze cast-
ing processes. A punch in nonferrous metal squeeze
casting processes mainly endures thermal fatigue,
and its friction-shearing . stress is smaller than its
flow stress, therefore, the abnormal failures of an
H13 punch in nonferrous metal squeeze casting will
not occur.
5 Conclusions
In nonferrous metal squeeze casting processes
Through the researches described above, the
following results were concluded:
(1) Th e mechanism of the abnormal failures of
an H13 punch in steel squeeze casting process, plas-
tic rubbed failures, was that the friction-shearing
stress of the punch was greater than i ts flow stress.
( 2 ) Considering Eqn. (2 ) , th e effects of t he
average strain and the average strain velocity were
considerably smaller than th at of the equivalent tem-perature. Associating the range of th e average strain
and the average strain velocity of an H13 punch in
steel squeeze casting process, the effects of the aver-
age strain and the average velocity strain on the flow
stress of an H13 punch were ignored provisionally
when the flow stress was calculated in steel squeeze
casting process. Also, Eqn. ( 2 ) can be used to calcu-
late the flow stress of an H13 punch in steel squeeze
casting process.
( 3 ) In steel squeeze casting, for the elevated
working temperature of an H13 punch, if there were
no protection measures on the punch, th e friction-
shearing stress of the punch was greater than its
flow stress, and the abnormal failures could not be
avoided. However, i f its protection measures could
ensure its working temperature below 682% ,
theabnormal failures could be avoided considerately.
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