M Steel Preform Behaviour During Cold Upsetting

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JOURNAL OF IRON AND STEEL RESEARCH, INTERNATIONAL. 2008, 15(5): 81-87

Sintered Fe-O. 8%C-1. O%Si-O. 4%Cu P/M Steel Preform Behaviour During Cold Upsetting A Rajeshkannan 1

,

K S Pandey" ,

S Shanmugam" ,

R Narayanasamy"

(1. Thiagarajar College of Engineering, Thiruparankundram, Madurai 625015, Tamil Nadu , India; 2. Maulana Azad National Institute of Technology, Bhopal 462007, Madhya Pradesh, India; 3. Department of Mechanical Engineering,

National Institute of Technology, Tiruchirappalli 620015, Tamil Nadu , India;

4. Department of Production

Engineering, National Institute of Technology, Tiruchirappalli 620015, Tamil Nadu , India) Abstract: Cold upsetting experiments were carried out on sintered Fe-O. 8 %C-1. 0 %Si-O. 4 %Cu steel preforms in order to evaluate their deformation characteristics. Powder preforms of 86 % of theoretieal density, with two different ratios of height to diameter, were prepared using a suitable die set assembly on a 1. 0 MN capacity hydraulic testing machine. Sintering was carried out in an electric muffle furnace for 1. 5 h at 1 150 'C. Each sintered compaet was subjected to incremental loading of O. 04 MN under dry friction condition till a crack appeared at the free surfaces. The experimental results were critically analysed, the stress as a function of strain and densification was obtained, then the work hardening behaviour was analyzed. It has been found that in the process of enhancing densification , strength and strain hardening is also induced during upsetting, but the work hardening behaviour is not homogenously enhanced against strain and densification. Key words: cold upsetting; stress; height strain; densification; work hardening behaviour

Powder metallurgy (P 1M) processes provide techno-economic benefits over ingot metallurgy processes, the advantages being cost reduction, improved performance, design flexi bili ty , and the production of unique materials'{".

The manufacturing

processes for conventional P 1M parts consist of powder production, blending (if it is an alloy), compaction, and finally sintering. Such parts are

form produced by this process will undergo large degree of plastic deformation with enhanced level of densification'P" (i. e. up to near net shape). Though the plastic deformation of P 1M parts is similar to that of the wrought materials, the additional complications are because of substantial amount of void fractions. Therefore, the mode of deformation in porous material is the function of both density and hydrostatic

used in application requiring low mechanical property levels'". Secondary processes, such as pressing or repressing, powder extrusion, powder rolling, and infiltration can be used to improve the mechanical properties of parts produced through conventional P 1M rout e l " , Attraction and interest in net shape

creases, the ly, increase faces during stresses-v".

and near net shape manufacturing find P 1M to be a

sive stress, the pores will collapse and ultimately

competitive method of manufacturing particular parts such as in the mass production of machine tool components-' ' . Powder preform upsetting involves fabrication of a preform by conventional P/M route, followed by the conventional forging[5]. In general, the pre-

close, at the same time density also enhances; whereas, with application of axial tensile stress, the pores will grow and densification will decrease'P",

Biography: A RajeshkannanC1976-), Male, Doctor, Lectureship;

stress, which is not the case in wrought materials[8]. It has been reported-f that as the density inimposed stress also increases. Similarof friction condition at die contact surdeformation substantially increases the With the application of axial compres-

Apart from the regular enhancement of densification and stress due to induced strain during forging, usually porous material would also experience work hardening char-

E-mail: [email protected].

Revised Date: March 2, 2007

Vol. 15

Journal of Iron and Steel Research, International

• 82 •

acteristics'Y", This, in fact, gives the reason for the in-

crease of compressive axial stress as the amount of axial strain increases. However, the rate of increase in the stress value with respect to strain is greater than that would be observed in a pore free material of the same composi tion under identical testing conditions, as the continued reduction in the porosity level during upsetting increases the load bearing cross sectional area. Thus, total work hardening behaviour in porous material is because of the combined effects of densification and cold workingC13.141. The primary objective of the present investigation is to unfold the effects of initial aspect ratio on the relationship between applied compressive stresses with continuous deformation and densification also the work hardening behaviour during cold upsetting of sintered Fe-0.8%C-1.0%Si-0.4%Cu PIM Table 1

preforms.

1

Experimental

Atomized iron powder of particle size less than 150 flm size was obtained from MIS Sundaram Fasteners Limited, Hyderabad , India. Silicon and copper powder of particle size less than 37 flm size of each was obtained from MIS. Metal Powder Company, Thirumangalam, Madurai , Tamil Nadu , India. Graphite powder of 2 - 3 flm particle size was supplied by MIS Ashbury Graphite Mills Inc, Ashbury Warren County, New Jersey, USA. Analysis indicated that the purity of iron, copper, and silicon powders were 99. 7 %, 99. 93 %, and 99. 90 %, respectively, and the rest were insoluble impurities. The characteristics of iron powder and Fe-O. 8 % C1. 0 % Si-O. 4 % Cu blend are shown in Table 1 and 2.

Characterization of iron powder and Fe-Il. 8%C-1. O%Si-O. 4%Cu blend

Property

Iron

Apparent density/(g· cm- 3 )

2.96

2. 89

O. 560

O. 492

6.55

6.55

Flow rate, by Hall Flow Metcr /x s

>

g-l)

Compressibility at pressure of 430 ± 10 MPa/( g • cm- 3 )

Table 2 Sieve size/ m Mass percent Ret/ %

Fe-O. 8%C-1. O%Si-O. 4%Cu blend

Sieve size analysis of iron powder

150

+ 126

+ 106

+90

+75

+63

+53

+45

+37

10. 14

21. 90

9.46

2.02

20. 10

12. 10

11. 10

5. 70

0.31

A powder mix corresponding to Fe-0.8%G-1.0%SiO. 4%Cu steel was taken in a stainless steel pot with the powder mixed to porcelain ball (10 -15 mm diameter) with a ratio of 1 : 1 by mass. The pot was very securely tightened and then fixed on the pot mill for blending operation. The mill was operated for 20 h to obtain a homogeneous powder blend. Green compacts of 27.5 mm diameter and 14 mm and 28 mm of length were prepared on a 1. 0 MN capacity hydraulic press using a suitable die, a punch, and a bottom insert. The initial preform densities were maintained in the range of 86 % ± 1 % of theoretical density by using pressure in the range of 430± 10 MPa. Indigenously formed c151 ceramic coating was applied on the entire surface of all the green compacts to protect them against oxidation during the sintering and the cooling schedules. These ceramic coated compacts were initially dried at 700 "C for 30 min in an alumina boat placed inside the electric muffle furnace. After the drying sequence was completed, the furnace temperature was raised to 1 150±10 'C. At

7.00

this temperature, the compacts were sintered for 90 min followed by furnace cooling. Sintered preforms were machined to yield the initial height to diameter ratio (aspect ratios) of 0.40 and 0.75, respectively. Initial dimensions of sintered preforms like their heights and diameters were measured and recorded. Each specimen was axially deformed on a flat die set in the increment loading step of O. 04 MN under dry friction condition. The deformation was stopped as soon as a visible crack appeared on its free surface. After each interval of loading, dimensional changes and density measurements were carried out. All dimensions were measured using digital vernier calipers and density measurements were made by evoking Archimedes principle. The procedure used is described elsewhere C1fiJ.

2

Results and Discussion

Stress-strain analysis is the fundamental for assessing the mechanical behaviour of any material,

Issue 5

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Sintered Fe-O. 8·%C-1. O%Si-O. 4%Cu P/M Steel Preform Behaviour During Cold Upsetting

when it is subjected to any mode of external loading condition. This is because stress determines the internal resistance of a material against the external loading on a particular area of cross section exposed to deformation and strain normally deals with the deformation of the body. When the applied incremental load is directly considered for original area of cross section (Do) i. e. before deformation is termed as engineering stress, whereas the same applied incremental load is considered for instantaneous deformed diameter (Dr), which is termed as true stress. Because both the stresses are the causes of the applied load, these can be technically named as applied stresses, which were drawn against true height strain to assess the resistance to deformation during cold axial upsetting (Fig. 1). The general observation of these curves show that as the strain increases, the resistance to lateral deformation also increases. The extensiveness of resistance to deformation is apparent during first and last stages of induced height strain. This shows the fact that the presence of 14% of porosity (i. e. initial theoretical density of the preform is 86 %) in the preform at initial stage cannot be deformed by initial application of incremental loading. However, these loadings would stimulate the kinetics of particle, both voids and materials. But, the fact was different in final (after approximately O. 6 value of height strain) stage because of the presence of very little amount of pores, approximately 4% (refer Fig. 2), which would behave as a second phase particle during deformation because of the influence of strain hardening[j7j. Further observation shows that the true stress values are dropped down in comparison to engineering stress values because of the enhancement of cross section of preform during deformation, and is particularly pronounced after the first stage irrespective of aspect ratios. The same reason is also applicable for vanishing out the third stage in case of true stress against true strain. Technically, the domination of lateral spread was started after O. 2 height strain value, which can be observed in Fig. 1. This means that the height strain is substantially high and the diameter strain is practically negligible up to the value of O. 2 height strain, i. e. during initial stage of deformation. The intermediate or second stage, where induced strain contributed to raise the kinetics of particles that made to reduce the slope of applied stress curves and so the resistance offered was considerably diminished in comparison to the first stage. This be-

2'100

o

6' 0040

06'0.75 • TO.40 x TO.75

E -- Engineering stress T·.. True stress

0040- Lower aspect. rat.io 0.75 Higher aspect. ratio

o Fig. 1

0.2

0.4 0.6 True height. strain

0.8

1.0

Variation of applied stress with axial strain for various initial aspect ratios

2400 r - - - - - - - - - - - - - - - - , o £0.40 o £0.75 b. TOAO x TO.75

Oltl=--~-~--~-~-~-~-----l

86

Fig.2

88

80 82 84 96 Theoret.ical densit.yfOj,)

98

100

Variation of applied stresses with densif'ication for various initial aspect ratios

haviour is true for both the aspect ratios. It is important to be noted that for any value of height strain, 0.40 aspect ratio preforms shows an enhanced amount of stress in both engineering as well as true stresses. This proves the fact that decreasing the aspect ratio increases the homogeneous distribution of deformation, which subsequently increased the height reduction and decreased the lateral spread. In general, strength of any material can be broadly described as the ability of a material to withstand externally applied load up to its fracture. It is well established that the strength of P / M preform is governed by the maximum density that is attained and the mode by which the density is being attained l l81 • By virtue of the above phenomena, it can be claimed that the degree of material resistance against deformation is a function of attained density, Therefore, a plot has been constructed between applied stresses and percentage fractional theoretical density for FeO. 8 % Cool. 0 % Si-O. 4 % Cu steel preform (Fig. 2). The influence of aspect ratio is highlighted on dry friction condition during deformation. Although, the

• 81 •

Journal of Iron and Steel Research, International

general behaviour of curves plotted in Fig. Z is similar to that of Fig. 1, the influence of aspect ratio behaves in a different manner. Observing the response of engineering stress against percent theoretical density, it was found that O. 75 aspect ratio preform predominates in the rise of stress values over O. 40 aspect ratio, which was not the fact when true stresses were considered. This is because enhancement of densification implies enhancement of mobility of particles, which ultimately reduces the stress values. This is particularly high in lower aspect ratio preforms due to fewer amounts of pore bed that made to transform load quickly and little uniformly and so the stress values are relatively lower than that of higher aspect ratio preforms against densification. Further, in engineering stresses, the instantaneous deformed contact diameter is not under consideration, therefore, it will not show true behaviour. Alternatively, in the true stress response up to 94 % theoretical density, 0.40 aspect ratio showed lower values of stresses in comparison to 0.75 aspect ratio (but it is negligibly small) and beyond that there was an enrichment in stress values, which exceeded the O. 75 aspect ratio preforms. This indicated the truth that the strain hardening rate was faster and higher in lower aspect ratio due to the less volume fraction of voids that can be deformed effectively at lower height strain value itself. In addition, any further increment of axial strain at later stages is used more to enrich the work hardening rate than for deformation, whereas relatively larger amount of void fractions in higher aspect ratio preforms will delay the densification rate and subsequently delay the resistance to deformation: Thus, it can be concluded that there is a provision to enhance densification at final stage for O. 75 aspect ratio preform, provided the specimen does not propagate the residual voids as a crack at free surfaces. It is noted from Fig. Z, that the attained densification was little extended in case of lower aspect ratio than that of higher aspect ratio, which further shows indirectly that decrease of aspect ratio increases the attainment of maximum densification before fracture appears on the free surfaces. Thus, a concrete conclusion can be made from Fig. 1 and Fig. Z that irrespective of induced strain the kinetics of densification decides the resistance to deformation, which in turn depends on the aspect ratios; however, the other process parameters like friction condition, initial preform density, and com-

Vol. 15

posrtron are kept invariable. The common observation from Fig. 1 and Fig. Z shows that three different stages are apparent for engineering stresses, but for true stresses just two stages are visible. Whereas, the third stage for all practical purpose is nil, thus, it exhibits the fact that the lateral spread of preforms is substantial for both the aspect ratios to withstand the load bearing capacity. Although Fig. 1 shows the behaviour of true stress as a function of strain, this can be better explicit only after the value of O. Z height strain, that is second and third stage can be studied, whereas in the first stage virtually all the points are merged and expose nil influence of aspect ratio in stress-strain

relationship. Therefore, to understand the real behaviour between them, a log-log scale is drawn (Fig. 3). The important point to be noted from this figure is that up to the value of 0.08 height strain, the resistance against deformation is low in O. 40 aspect ratio. Such behaviour was not observed in Fig. 1, in addition, the general behaviour of true stresses with respect to true strain was observed in two different stages. However, based on log-log scale (Fig. 3), stress-strain behaviour clearly shows only one stage. Though, at initial stage it expresses little steep rise in stress values for both aspect ratios (Fig. 3, dashed line), which can be neglected for all practical purpose because it forms for the very low values of strain. Thus, over a wide range of height strain, the stress response is of just one stage, nevertheless it can be observed that stress is continuously rising in a steady pace against induced height strain. Further, it is observed that the major mechanism lies in the span of true height strain value from O. 08 to 1. O. Because most of the data are aggregated within this span .. it shows that the decrease of aspect ratio increases the stress values overall. The slope and intercept of the respective continuous line drawn for ~ ~

~

v:

10 000 r - - - - - - - - - - - - - - - - - - - , " T0.40 x

TO.75

1000

QtJ

..s

.S

10

L-

0.001

Fig.3

~~

~

0.010 0.100 True height strain in log scale

__'

1.000

Flow stress-true height strain curve in log-log scale

• 85 •

Sintered Fe-O. 8'%C-1. O%Si-O, 4%Cu PIM Steel Preform Behaviour During Cold Upsetting

Issue 5

both aspect ratios show the strain hardening exponent and the strength coefficient respectively; however, this does not convey the real meaning. This is because at each step of incremental loading, deformation takes place in the preform, which in turn would raise the strength and/or strain coefficient. Thus, an attempt is made to use plastic flow equation a= Ken in a modified form to fit into the plastic deformation of porous material in order to determine instantaneous strength coefficient and instantaneous strain hardening exponent. In this equation a is true stress; e is true strain; K is strength coefficient, and n is strain hardening exponent. The following is the theoretical analysis of flow equation for P /M materials. Assume that the consecutive applied loads on the preform were specified as 1, 2, 3, "', (m - 1) and m, The plastic flow equation can be written as follows:

(3)

The Eqn. (3) can be further simplified into the following form.

(4) Now, dividing the Eqn. (l) by Eqn. (2), the following expression is obtained. ~-._~= n €~-l

l ] ~

n

(5)

Cm-l

Taking natural logarithm on both sides of Eqn. (5) , it follows, In[

~-] =nln[~] €m-l

(6)

(Jm-l

Eqn. (6) can further simplify into n -am -

_

n, -

~ I em ] O'm-l

r

.

OAO 00.75

o

NonImoar response-

300

.,

Linear response cO

0...

E

i i

200

o

0

(7)

n em-l

Eqn. (4) and Eqn. (7) can be used for determining the instantaneous strength coefficient (K J and instantaneous strain hardening exponent Cn,') from the experimental data corresponding to stress and strain. Fig. 4 and Fig. 5 were drawn to show the relationship for instantaneous strength coefficient (K;) against true height strain and percent theoretical density, respectively. The influence of aspect ratios was

o

::<

°i I

D

100 o

o

0.2

I

D

0.1 0.6 True height strain

0.8

1.0

Fig.4 Variation of instantaneous strength coefficient with axial strain showing the effect of initial aspect ratios

400 r - - - - - - - - - - - - - - - - . , <> OAO 00.75

..

r·_··_··.. _"···M."••...•.

Linear response

'l,

cO

~

.

Non-Iinear response

:300

10

200

0

~

c o·i ~

0

~

(1)

am=Ke~n

am-I = Ke':n-I (2) Subtracting Eqn, (1) from Eqn. (2), the following expression can be obtained.

O'm-l

400

D

o

100

D

88

90

92

94

96

98

100

Theoretical densityl"l0

Fig. 5 Variation of instantaneous strength coefficient with densification showing the effect of initial aspect ratios

highlighted during cold deformation under dry friction condition. The common observation from both the figures indicates that as the deformation enhances, densification enhances, and subsequently strength is also promoted in the deforming preforms as the gradual increase of strength coefficient is an index of proof. However, the fluctuation of points is also observed from mild to heavy. The mild fluctuation need not to be considered seriously because it maintains a linear response, whereas after the height strain value of O. 5, the extreme nonlinear behavior was observed, which is shown in respective figures as dotted box. The similar behaviour is true even with respect to percent theoretical density but after approximately 95 % of theoretical densification. This behaviour uniquely shows that certain degree of application of load on the preform enriches the pore closure kinetics. As soon as the rate of enhancement in densification reduces as the matrix gets hardened due to the induced strain, the resistance against deformation increases. In particular, the reason for high fluctuation of strength values at final stage is that

86

Journal of Iron and Steel Research, International

the application of incremental load of o. 04 MN is not sufficient to further deform the residual pores at the last stage because the material got strain hardened and the pore would act at this stage almost like a second phase particle. Any further application of external load either collapses the pores or leads to fracture of the specimen at free surfaces. Further, an interesting point can be noted that the deformation is propagated a little higher in case of 0.75 aspect ratio, whereas densification is extended a little higher in O. 40 aspect ratio in comparison to their respective counter parts. In addition, the fluctuation of points increases with increasing aspect ratio. These are the distinct proofs that the distribution of deformation was little homogeneous in lower aspect ratio preforms in comparison to higher aspect ratio. However, in reality, irrespective of aspect ratios, the deformation is inhomogeneous, in spite of all the strength that can be efficiently induced during cold deformation. Further, an attempt was made to relate the instantaneous strain hardening exponent Cn,') with respect to true height strain and percent theoretical density. Thus, plots were constructed (Fig. 6 and Fig. 7). The characteristic pattern by strain hardening exponent is similar in both the figures, except at last stage, where the span of fluctuation of points are little substantial with respect to axial strain than that of the attained density. However, initially, that is within negligible amount of true height strain or densification, there is a sudden increase in strain hardening exponent. This need not to be the index for promoting strength III the material rather strength induced can be because of linear mode of increment of strain hardening value. The further application of continuous load stimulated the material movements in the preform that made to fill and/or collapse pores and enhance densification rate. This is the reason that sudden drop down of strain hardening exponent and then gradual rise can be continuously observed. A critical examination of both the figures at last stage shows that the rise of strain hardening exponent is more in O. 40 aspect ratio than in O. 75 aspect ratio, barring exception of one or two points in both the aspect ratios fall much lower instead of rising trend, which can be neglected. An approximate trend curve was drawn accordingly. This indicates the fact that in lower aspect ratio high .strain hardening can be induced due to lower amount of void fraction because it can be deformed and den-

2.0

Vol. 15

o 0.40 00.75

o

o

0.20 0.40 0.60 True height strain

0

0.80

Fig.6 Variation of instantaneous strain hardening exponent with axial strain showing the effect of initial aspect ratios 2.0

o 0.40 00.75

c

O_----~----~---------.J

86

90

94

98

Theoretical densityfOlo

Fig.7

Variation of instantaneous strain hardening exponent with

densification showing the effect of initial aspect ratios

sified in a quite enhanced pace in comparison to larger aspect ratio.

3

Conclusions The major findings that have been drawn from

the present investigation are as follows: (1) Irrespective of the ratio of height to diameter, the induced strain enhances the values of stresses; however, kinetics of densification decides the stress response, which ultimately follows three different stages. The first stage shows high resistance to deformation followed by gradual decrease of stress rise, and finally stress rise is very less in true stress. But, high values are seen in engineering stress because the load bearing cross section area at each Illstant is not considered. ( 2) In the process of cold deformation, apart from the enhancement of densification and stress, the matrix is also induced to work hardening. The strength promotes the deformation of preforms in turn. However, at later stages of deformation and densification, the nonlinear mode of strength and strain was induced because of the incremental deformation after the material was sufficiently strain hardened. It is also difficult to maintain uniform distribution, which results in high fluctuation of data

Issue 5

~~~-

points. This behaviour is invariably true for both the aspect ratios.

[llJ

References:

[12J

[lJ

Market. Business Briefing: Global Automotive Manufacturing

[13J

[2J

Kurt H Miska. Introduction to Powder Metallurgy [M]. Samuel Bradbury, eds, Metals Park: ASM, 1979.

[3J

[14J

[4J

Gull G W. Mechanical and Metallurgical Properties of Powder Forgings [J]. Powder Metall, 1970, 13(26): 156. Lee P W. Powder Metallurgy Applications, Advantages and Limitations [M]. Klar Eo eds. Metals Park: ASM, 1983. German R M. Powder Metallurgy of Iron and Steel [M]. New

[15J

[5J

York: John Wiley and Sons Inc, 1998.

[16J

[6J

Kuhn H A, Downey C L. How Flow Fracture Affect Design of

[7J

Preforms for Powder Forging [J]. Int J of Powder Metall and Powder Techno], 1974, 100): 59. Tewari H N, Saran R. Analysis of Iron Powder Forging [J].

[9 J [10J

Lawley A. Advances in Powder Technology [A]. Chin G Y, eds, ASM Materials Science Seminar [C]. Metals Park: ASM, 1982. 75. Hansen N. Dispersion Strengthened Aluminium Products

Antes H W. Processing and Properties of Powder Forgings [A]. Burke J J, Weiss V, eds. Powder Metallurgy for High Performance Applications [CJ. Syracuse: Syracuse University Press, 1972. 171. Kahlow K J. Void Behaviour as Influenced by Pressure and Plastic Deformation [R]. Bethlehem: Institute for Metal Forming Report, Lehigh University, 1971. Pandey K S. Indigenous Ceramic Coating [D]. Tiruchirappalli , Regional Engineering College, 1983. Moyer K H. Measuring Density of PIM Materials With Improved Precision [J]. Int J of Powder Met and Powder Techno], 1979, 15: 33.

[17J

Rajeshkannan A, Pandey K S, Shanmugam S. Influence of Frictional Constraints Between the Combined Stresses and the Continued Deformation and Densification of Sintered High Carbon PIM Steel During Cold Deformation [Al Association for Iron and Steel Technology, eds, Proceedings of Green En-

Trans of P MA 1, 1985, 12: 83. Jha A K, Kumar S. Forging of Metal Powder Preforms [J]. Int J Mach Tool Des Res, 1983, 23(4): 201. Hausner H H, Mal M K. Hand Book of Powder Metallurgy [MJ. 2nd ed. New york: Chemical Press, 1982. Pandey K S. Some Investigation on the Cold Deformation Behaviour of Sintered Aluminium -4% Copper Alloy Powder Preforms [J]. Quart Int J Powder Met Sci Techno], 1991, 2 (4):35.

...

~~---~~~

Manufactured by Powder Blending [J]. Powder Metall, 1969, 12(23): 23.

Ryuichiro Goto. Powder Metallurgy Growth in the Automotive and Technology. Materials, London, 2003: 44.

[8J

• 87 •

Sintered Fe-O. 8%C-1. O%Si-O. 4%Cu P/M Steel Preform Behaviour During Cold Upsetting

[18J

gineering Materials Processing of International Conference in Materials Science and Technology 2006 [C]. Cincinnati: Association for Iron and Steel Technology. 2006. 105. Whang B B, Kobayashi S. Deformation Characterization of Powdered Compacts in Compaction [J]. 1nt J Mach Tools Manuf , 1990,30(2): 309.

(Continued From Page 65) References: [lJ

[2J

[6J

De Coo man B C. Structure-Properties Relationship in TRIP Steels Containing Carbide-Free Bainite [J]. Current Opinion in

[7J

Solid State and Materials Science, 2004, 8(3-4): 285. ZHANG Mei, FU Ren-yu , CAO Dong-dong, et al. Develop-

[8J

GB 4675. 1-89, Weldability Testing-Method of Y-Groove

[9J

Cracking Test [SJ (in Chinese). GB 4675. 2-89, Weldability Testing-Method of Controlled Thermal-Severity Cracking Test [SJ (in Chinese).

ment of the Micro-Alloyed TRIP Steels and Properties of Their [3J

Laser Welded Blanks [J]. Iron and Steel, 2005, 40(suppl): 754. ZHANG Mei, LI Lin, FU Ren-yu , et al, Application Properties of Low Carbon Transformation Induced Plasticity Steels

[5J

GB 2654-89, Method of Hardness Tests for Welded J oint and Surfacing Metal [SJ (in Chinese).

[10J

GB 4675. 3-89, Weldability Testing-Method of Cracking Test

[llJ

Tests of Welded Joint [SJ (in Chinese).

of Welded Tee Joint [SJ (in Chinese). SI Chong-yao , ZHOU Zhen-feng, QIAN Bai-nian. Welding Handbook [M]. Beijing: Mechanical Industry Press, 1992

GB 2651-89, Method of Tensile Test for Welded Joint [SJ (in

(in Chinese).

[J]. Iron and Steel, 2007, 42(3): 65 (in Chinese). [4J

Chinese). GB 2650-89, Method of Impact Test for Welded Joint [SJ (in Chinese).

GB 2649-89, Method of Sampling for Mechanical Properties