Mechanical properties and fracture behavior of high-strength steels
Typical thicknesses ofhigh-strength steels (HSS) sheets used in the car industry are inapplicablefor standardized testingprocedures. The aim ofthis study is topropose an appropriate methodologyfor testing and comparing of thin HSS sheets. Microstructures were observed by means of light and scanning...
Saved in:
| Published in: | Проблемы прочности |
|---|---|
| Date: | 2008 |
| Main Authors: | , , , , |
| Format: | Article |
| Language: | English |
| Published: |
Інститут проблем міцності ім. Г.С. Писаренко НАН України
2008
|
| Subjects: | |
| Online Access: | https://nasplib.isofts.kiev.ua/handle/123456789/48419 |
| Tags: |
Add Tag
No Tags, Be the first to tag this record!
|
| Journal Title: | Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| Cite this: | Mechanical properties and fracture behavior of high-strength steels / R. Musalek, P. Hausild, J. Siegl, J. Bensch, J. Slama // Проблемы прочности. — 2008. — № 1. — С. 155-158. — Бібліогр.: 5 назв. — англ. |
Institution
Digital Library of Periodicals of National Academy of Sciences of Ukraine| _version_ | 1859653491709968384 |
|---|---|
| author | Musalek, R. Hausild, P. Siegl, J. Bensch, J. Slama, J. |
| author_facet | Musalek, R. Hausild, P. Siegl, J. Bensch, J. Slama, J. |
| citation_txt | Mechanical properties and fracture behavior of high-strength steels / R. Musalek, P. Hausild, J. Siegl, J. Bensch, J. Slama // Проблемы прочности. — 2008. — № 1. — С. 155-158. — Бібліогр.: 5 назв. — англ. |
| collection | DSpace DC |
| container_title | Проблемы прочности |
| description | Typical thicknesses ofhigh-strength steels (HSS) sheets used in the car industry are inapplicablefor standardized testingprocedures. The aim ofthis study is topropose an appropriate methodologyfor testing and comparing of thin HSS sheets. Microstructures were observed by means of light and scanning electron microscopy. The modified Charpy impact tests andfracture toughness tests were used in order to compare thefracture properties of three different HSS sheets (Docol 1200 M, Multiphase 1200 and BTR 165). Ductile-to-brittle transition curves and tearing resistance (J —Δα) curves were measured. From thefracture toughness linked to the specimen thicknesses the value of fracture toughness KIc was estimated. Fractographic analysis of broken specimens has revealed that due to the fine microstructure of mixed ferrite-martensite fracture mechanism remains ductile even at low temperatures (down to —100° C).
Толщины листовой высокопрочной стали, применяемой в автомобильной промышленности, не соответствуют требованиям стандартных методов испытаний. Цель настоящего исследования - предложить приемлемую методологию испытаний и сравненить между собой тонколистовые высокопрочные сталей. Микроструктуру изучали с помощью оптической и сканирующей электронной микроскопии. Для сравнения особенностей разрушения трех различных сталей (Docol 1200, M. Multiphase 1200 и BTR165) использовали модифицированный метод ударных испытаний по Шарпи и метод оценки вязкости разрушения. Были получены кривые перехода из вязкого состояния в хрупкое и кривые сопротивления разрыву (J —Δα). По вязкости разрушения, зависящей от толщины образцов, оценивали величину KIc . Фрактографический анализ разрушенных образцов пока зал, что вследствие тонкой микроструктуры смешанного феррита-мартенсита сохраняется вязкий механизм разрушения даже при низких температурах (до —100° C).
|
| first_indexed | 2025-12-07T13:36:35Z |
| format | Article |
| fulltext |
UDC 539. 4
M e c h a n ic a l P r o p e r t ie s a n d F r a c tu r e B e h a v io r o f H ig h -S tr e n g t h S te e ls
R . M u sa lek ,1a P . H au sild ,1b J . S ieg l,1,c J . B en sch ,1d and J. S lam a2,e
1 Czech Technical University, Faculty o f Nuclear Sciences and Physical Engineering, Department of
Materials, Prague, Czech Republic
2 TKZ, SKODA AUTO a.s., Mlada Boleslav, Czech Republic
a radek.musalek@fjfi.cvut.cz, b hausild@fjfi.cvut.cz, c jan.siegl@fjfi.cvut.cz,
d jan.bensch@fjfi.cvut.cz, e jan.slama@skoda-auto.cz
Typical thicknesses o f high-strength steels (HSS) sheets used in the car industry are inapplicable for
standardized testing procedures. The aim o f this study is to propose an appropriate methodology fo r
testing and comparing o f thin HSS sheets. Microstructures were observed by means o f light and
scanning electron microscopy. The modified Charpy impact tests and fracture toughness tests were
used in order to compare the fracture properties o f three different HSS sheets (Docol 1200 M,
Multiphase 1200 and BTR 165). Ductile-to-brittle transition curves and tearing resistance (J — Aa)
curves were measured. From the fracture toughness linked to the specimen thicknesses the value o f
fracture toughness K Ic was estimated. Fractographic analysis o f broken specimens has revealed
that due to the fine microstructure o f mixed ferrite-martensite fracture mechanism remains ductile
even at low temperatures (down to —100°C).
K eyw ords: fracture toughness, Charpy im pact energy, fractography, high-strength steel.
In troduction . High-strength steels are w id ely used in autom obile industry for the
reinforcem ent parts, e.g., door or b-pillar reinforcem ent. Their h igh strength m akes it
possib le to use sm aller cross sections, w hich leads to the reduction o f car w eight and, thus,
o f fuel consum ption. D ues to extensive plastic deform ation, high-strength steel parts are
also able to absorb h igh im pact energy during a crash, w hich im proves car crew safety.
Therefore the m echanical properties o f these materials are o f critical importance. So far,
the standardized tests for the H SS sheets have not been designed. W e propose a
m ethodology for testing o f thin H SS sheets by m eans o f fracture m echanics and
fractographic analysis.
M ater ia ls and M ethod s. M etallographic observation using light m icroscope
(N eophot 32) and scanning electron m icroscope (JEOL JSM 5510LV) revealed fine
ferritic-martensitic microstructures show n in Fig. 1. A ccording to the observed m icro
structures and available tensile tests, it is concluded that due to therm om echanical
treatment during the manufacturing process, rolling has relatively sm all influence on the
isotropy o f the observed materials.
The m odified Charpy specim ens for the im pact toughness test [1 ] and the CT
specim ens for the fracture toughness test [2 ] were prepared from three high-strength steel
sheets using a waterjet (for steel D oco l 1200 M ) and laser (M ultiphase 1200 and BTR
165). A ll specim en dim ensions corresponded to the standard [1, 2] except for the
specim en thickness, w hich w as equal to that o f available steel sheets (Table 1).
The im pact energy required to break the m odified V -notched Charpy im pact
specim ens into tw o p ieces w as m easured using Charpy im pact equipm ent w ith the
m axim um energy 150 J. The specim ens were cooled in the liquid nitrogen or mixture o f
liquid nitrogen and ethanol. The test temperature w as m easured b y a therm ocouple. The
tim e interval betw een cooling and testing o f the specim en w as less than 5 seconds (usually
2 or 3 seconds).
Fracture toughness tests w ere conducted on CT specim ens at room temperature
using the Inova Z U Z 50 hydraulic loading m achine. The testing procedure fo llow ed the
© R. M USALEK, P. HAUSILD, J. SIEGL, J. BENSCH, J. SLAMA, 2008
ISSN 0556-171X. Проблемы прочности, 2008, N 1 155
mailto:radek.musalek@fjfi.cvut.cz
mailto:hausild@fjfi.cvut.cz
mailto:jan.siegl@fjfi.cvut.cz
mailto:jan.bensch@fjfi.cvut.cz
mailto:jan.slama@skoda-auto.cz
R. Musâlek, P. Hausild, J. Siegl, et al.
A ST M 1820-99 [2] standard: a sharp fatigue crack w as prepared, then the dependency o f
applied load vs. displacem ent w as m easured and the crack growth w as studied using the
light m icroscope.
Fractographic analysis using scanning electron m icroscope JEOL JSM -840A was
carried out on the fracture surfaces o f broken specim ens.
T a b l e 1
Chemical Composition of Tested High-Strength Steels (wt.%)
Material C Si Mn P S Cr Mo Al Ti B Nb
Docol
1200 M
0.12 0.20 1.60 0.015 0.002 - - >0.03 - - 0.015
Multiphase
1200
0.13 0.12 1.30 <0.020 <0.002 0.25 - 0.03 0.05 - -
BTR 165 0.19
0.25
0.15
0.50
1.10
1.40
<0.025 <0.015 <0.35 <0.35 0.02
0.06
0.02
0.05
0.002
0.005
-
Fig. 1. Microstructure o f tested steels: (a) Docol 1200 M, (b) Multiphase 1200, and (c) BTR 165.
E xp erim en ta l R esu lts and D iscu ssion . The m odified C harpy im pact tes t has
revealed ductile-to-brittle transition behavior o f the high-strength steel sheets show n in
Fig. 2. D uctile-to-brittle transition temperature w as determ ined to be low er than — 100oC.
D ue to the different thicknesses o f tested sheets, the im pact energy value w as norm alized
by the specim en thickness to the im pact toughness K C V The highest value o f the impact
toughness above the transition temperature w as observed for D oco l 1200 M steel.
F racture toughness K c o f the observed materials w as determ ined (Table 2). D ue to
the sm all thicknesses B o f the tested materials, the plane strain condition w as not
satisfied, and the fracture toughness value had to be linked to the specim en thickness.
H ow ever, the value o f fracture toughness under plane strain condition K Ic can be
estimated from formula [4]:
1+-
1 K ^ K Ic
R p 0.2
(1)
The load vs. displacem ent curve and know n crack lengths can be used to evaluate
the tearing resistance curves (J —Aa) (see Fig. 3) according to the formula:
J =
2A
B ( w — a ) (2)
156 ISSN 0556-171X. npoôëeubi npounocmu, 2008, N 1
Mechanical Properties and Fracture Behavior
where A is the area under the load vs. displacem ent curve, B is the specim en thickness,
w is specim en width, and a is crack length.
These curves g ive som e idea about the resistance o f the material against ductile
tearing. The steeper curve corresponds to the higher resistance. From these curves it can
be observed that D oco l 1200 M and M ultiphase 1200 have a very similar tearing
resistance. Low er resistance o f the B T R 165 steel can be due to the smaller thickness o f
this sheet and the higher influence o f shear m ode III on crack propagation.
T a b l e 2
Measured Values o f Fracture Toughness
Material B,
mm
Rp0.2,
MPa
K c ,
MPa- m1/2
K Ic,
MPa- m1/2
(estimate)
Docol 1200 M 2.0 1061 107.95 56.00
2.0 1061 115.34 57.51
Multiphase 1200 2.0 1148 136.04 64.39
2.0 1148 122.51 61.77
2.0 1148 119.05 61.06
BTR 165 1.5 1243 119.22 58.79
1.5 1243 126.31 60.14
1.5 1243 106.01 56.06
T { 'C ) A<i <"™>
Fig. 2. Ductile-to-brittle transition curves. Fig. 3. Tearing resistance curves.
F ractograph ic analysis o f broken Charpy specim ens has confirm ed that failure
m echanism s o f tested H SS sheets remain ductile even at a low temperature (dow n to
— 100°C). D ue to the sm all thickness, shear lips w ere observed on fracture surfaces o f all
specim ens tested above the transition temperature. D uctile dim ples were observed on the
w hole fracture surface o f specim ens broken above the transition temperature. B e low the
transition temperature m ostly features o f cleavage fracture were observed (Fig. 4).
Fractographic analysis o f broken CT specim ens has show n that the crack was
initiated at the tip o f the fatigue pre-crack. In the first stage crack propagated in the mode I,
and then, the crack propagated in the m ixed m ode I+III due to the sm all thickness and
shear stress present in the material.
D uctile dim ples stretched in the direction o f crack growth were observed on som e
fracture surfaces o f the specim ens broken above the transition temperature (Fig. 5).
ISSN 0556-171X. npoôëeubi npounocmu, 2008, № 1 157
R. Musalek, P. Hausild, J. Siegl, et al.
Fig. 4 Fig. 5
Fig. 4. Typical morphology o f Charpy specimen fracture surface broken below the transition
temperature. (Docol 1200 M, test temperature = — 190°C.)
Fig. 5. Typical morphology o f Charpy specimen fracture surface broken above the transition
temperature. (Docol 1200 M, test temperature = 20°C.)
C onclusions. W ith respect to the slight differences in the specim en thickness o f
different materials, it has been found that from the point o f v iew o f fracture m echanics all
the three observed high-strength steels have very similar m echanical properties.
The ductile-to-brittle transition temperature is beyond the typical high-strength steel
application range The observed H SS sheets rem ained ductile even at a rather low
temperature, w hich w as proven by the fractographic analysis.
It has been confirm ed that a new approach to the thin H SS sheets testing by the
m eans o f fracture m echanics is applicable and provides n ew inform ation on the behavior
o f high-strength steel materials under the dynam ic loading. The designed m ethod is used
for further material testing o f H SS sheets.
Acknowledgments. The authors acknowledge the support from the SKODA AUTO, a.s.
company. This project was supported by the Ministry o f Education, Youth, and Sport o f the Czech
Republic in the frame of the project MSM 6840770021.
1. CSN EN 10 045-1. Charpy Impact Test [in Czech], Cesky Normalizacni Institut (1998).
2. ASTM Standard E 1820-99. Standard Test Method fo r Measurement o f Fracture Toughness,
Annual Book o f ASTM Standards (1999), pp. 972-1005.
3. Y. J. Chao, Jr., J. D. Ward, and R. G. Sands, “Charpy impact energy, fracture toughness, and
ductile-brittle transition temperature o f dual phase 590 steel,” Mater. Design, 28, 551-557
(2007).
4. G. R. Irwin, “Fracture transition for a crack traversing a plate,” J. Basic Eng., 82, 417-425
(1960).
5. R. Musalek, Special Materials Characteristic o f High-Strength Sheet fo r Automotive Industry
[in Czech], Master’s Thesis, FNSPE, CTU Prague (2006).
Received 28. 06. 2007
158 ISSN 0556-171X. npo6neMbi npoHHocmu, 2008, № 1
|
| id | nasplib_isofts_kiev_ua-123456789-48419 |
| institution | Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| issn | 0556-171X |
| language | English |
| last_indexed | 2025-12-07T13:36:35Z |
| publishDate | 2008 |
| publisher | Інститут проблем міцності ім. Г.С. Писаренко НАН України |
| record_format | dspace |
| spelling | Musalek, R. Hausild, P. Siegl, J. Bensch, J. Slama, J. 2013-08-19T13:33:11Z 2013-08-19T13:33:11Z 2008 Mechanical properties and fracture behavior of high-strength steels / R. Musalek, P. Hausild, J. Siegl, J. Bensch, J. Slama // Проблемы прочности. — 2008. — № 1. — С. 155-158. — Бібліогр.: 5 назв. — англ. 0556-171X https://nasplib.isofts.kiev.ua/handle/123456789/48419 539.4 Typical thicknesses ofhigh-strength steels (HSS) sheets used in the car industry are inapplicablefor standardized testingprocedures. The aim ofthis study is topropose an appropriate methodologyfor testing and comparing of thin HSS sheets. Microstructures were observed by means of light and scanning electron microscopy. The modified Charpy impact tests andfracture toughness tests were used in order to compare thefracture properties of three different HSS sheets (Docol 1200 M, Multiphase 1200 and BTR 165). Ductile-to-brittle transition curves and tearing resistance (J —Δα) curves were measured. From thefracture toughness linked to the specimen thicknesses the value of fracture toughness KIc was estimated. Fractographic analysis of broken specimens has revealed that due to the fine microstructure of mixed ferrite-martensite fracture mechanism remains ductile even at low temperatures (down to —100° C). Толщины листовой высокопрочной стали, применяемой в автомобильной промышленности, не соответствуют требованиям стандартных методов испытаний. Цель настоящего исследования - предложить приемлемую методологию испытаний и сравненить между собой тонколистовые высокопрочные сталей. Микроструктуру изучали с помощью оптической и сканирующей электронной микроскопии. Для сравнения особенностей разрушения трех различных сталей (Docol 1200, M. Multiphase 1200 и BTR165) использовали модифицированный метод ударных испытаний по Шарпи и метод оценки вязкости разрушения. Были получены кривые перехода из вязкого состояния в хрупкое и кривые сопротивления разрыву (J —Δα). По вязкости разрушения, зависящей от толщины образцов, оценивали величину KIc . Фрактографический анализ разрушенных образцов пока зал, что вследствие тонкой микроструктуры смешанного феррита-мартенсита сохраняется вязкий механизм разрушения даже при низких температурах (до —100° C). The authors acknowledge the support from the SKODA AUTO, a.s. company. This project was supported by the Ministry of Education, Youth, and Sport of the Czech Republic in the frame of the project MSM 6840770021. en Інститут проблем міцності ім. Г.С. Писаренко НАН України Проблемы прочности Научно-технический раздел Mechanical properties and fracture behavior of high-strength steels Механические свойства и особенности разрушения высокопрочных сталей Article published earlier |
| spellingShingle | Mechanical properties and fracture behavior of high-strength steels Musalek, R. Hausild, P. Siegl, J. Bensch, J. Slama, J. Научно-технический раздел |
| title | Mechanical properties and fracture behavior of high-strength steels |
| title_alt | Механические свойства и особенности разрушения высокопрочных сталей |
| title_full | Mechanical properties and fracture behavior of high-strength steels |
| title_fullStr | Mechanical properties and fracture behavior of high-strength steels |
| title_full_unstemmed | Mechanical properties and fracture behavior of high-strength steels |
| title_short | Mechanical properties and fracture behavior of high-strength steels |
| title_sort | mechanical properties and fracture behavior of high-strength steels |
| topic | Научно-технический раздел |
| topic_facet | Научно-технический раздел |
| url | https://nasplib.isofts.kiev.ua/handle/123456789/48419 |
| work_keys_str_mv | AT musalekr mechanicalpropertiesandfracturebehaviorofhighstrengthsteels AT hausildp mechanicalpropertiesandfracturebehaviorofhighstrengthsteels AT sieglj mechanicalpropertiesandfracturebehaviorofhighstrengthsteels AT benschj mechanicalpropertiesandfracturebehaviorofhighstrengthsteels AT slamaj mechanicalpropertiesandfracturebehaviorofhighstrengthsteels AT musalekr mehaničeskiesvoistvaiosobennostirazrušeniâvysokopročnyhstalei AT hausildp mehaničeskiesvoistvaiosobennostirazrušeniâvysokopročnyhstalei AT sieglj mehaničeskiesvoistvaiosobennostirazrušeniâvysokopročnyhstalei AT benschj mehaničeskiesvoistvaiosobennostirazrušeniâvysokopročnyhstalei AT slamaj mehaničeskiesvoistvaiosobennostirazrušeniâvysokopročnyhstalei |