abnormal failure analysis of h13 punches in

5/17/2018 Abnormal Failure Analysis of H13 Punches In - slidepdf.com

http://slidepdf.com/reader/full/abnormal-failure-analysis-of-h13-punches-in 1/5

Available online at www.sciencedirect.com

*.SO ScienceDirect

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



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



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,



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



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.

References :

c11

c2 1

c31

C41

c 5 i

C6 l

C71

C8 l

c9 1

c101

Clll

Chomashchi M R , V ikhrov A. Squeeze Casti ngl an Overview

[J]. Journal of Materials Processing Technology, 2000, lOl( 1-

3 ) : 1.

Lapovok R, Smirnov S, Shveykin V. Damage Mechanics for

the Fracture Prediction of Metal Forming Too ls [J]. Intern a-

tional Journal of Fracture, 2000, 103(2) l 11 .

Kim D H , Lee H C , Kim B M , et al. Estima tion of Die Service

Life Against Plastic Deformation and Wear During Hot Forging

Processes [J]. Journal of Materials Processing Technology,

LI Kemin, WEN Zhi-gao. Failure Models and Ways of Imprc-

ving Life of H13 Male Punch in Hot Extrusion [J]. Metal

Forming, 2003, ( 1 2 ) 1 50 (in Chinese).

ZHAO Chang-sheng, J U Jian-cun. Failu re Analyzing of H1 3

Steel in H ot Extrusion Die [J]. Metal Forming, 2002, (1 4) :

50 (in Chinese).

Shida S. Empirical Formula of Flow Stress of Carbon S teels-Re

sistance to Deformation of Carbon Steels at Elevated Tempera-

tu re [,I]. 2nd Report , J JSTP, 1969 , l o 1 610 (in Japanese).

Kolsky H. An Investigation of the Mechanical Properties of

Materials at Very High Rates of Loading [J]. Proc Phys Soc

Suzuki H, Hashizume S , Yabuki Y, t al. Studies on the Flow

Stress of Meta ls and Alloys [J]. Report of the Institute of In-

dustrial Science, 1 968 , 18(3 )1 40.

Rusinek A, Klepaczko J R. S hear Testin g of a Sheet Steel at

Wide Range of Strain Rates and a Constitutive Relation With

Strain-Rate and Tem pera ture Dependence of the Flow Stress

[J]. International Journal of Plasticity , 2001, 17(1)

2005 , 166 (3 ) : 372.

B, 1949 , 6 3 (4 )1 676.

87 .

Lee Y, Kim B M , Park K L , e t a l. A S tudy for the Constitu-

tive Equation of Carbon Steel Subjected to Large Strains, High

Temperature and High Strain Rates [J]. Journal of Material

Processing Technology, 2002, 130-131(1-3) 181.

LUO Shou-j ing , H E Shac-yuan , W ANG E rd e. S teel Squeeze

Casting [MI. Harb in : P ress of Harbin Institute of Technolc-gy , 1990 (in Chinese)

abnormal failure analysis of h13 punches in

Documents