铁素体-马氏体双相组织及力学性能
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Hard phase
F-B. F-M. B-M/A.
True stress
Tw o phase stage 3 stage 2 Soft phase
internal stress
stage 1
P2
t2
P
t
P1
t1
True strain
Background
The various duplex-phase microstructure
Variation of martensite phase volume fraction with the quenching temperature.
Microstructure evolution
Summary:
XRD result shows no austenite peak, which means nearly no retained austenite existed due to the high cooling speed, the microstructure is typically dual-phase which consisted by ferrite and martensite. The martensite volume fraction increased linearly with the increase of heat treat temperature. 49% martensite was achieved when treated at 760℃, and blocky martensite phase begins to link with each other. When the temperature is as high as 840℃, almost fully martensite is obtained, and coarse prior austenite grain boundary can be clearly distinguished
Material and Experiment
The phase transformation point of base material: Ac1=690℃; Ac3=845℃.
measured by the Formastor-F Dilatometer.
The experiment process
Lower Y/T ratio.
Higher elongation, especially the uniform elongation.
Round-roof shape stress-strain curve. Higher strain hardening ability . Duplex phase microstructure has been confirmed to have better deformability. Generally, the phase composition can be:
Conclusion
Background
Subsea pipeline has better prospect
Requirement of petroleum and gas increase gradually
Before
Resourse in permafrost regions
After
Ground movement imposes large strain
The mechanical property of base material: X100 grade.
Sample As-rolled st0.5 /MPa 693 UTS /MPa 832 YS/TS 0.85 Elongation/% 18.40 Uniform Elongation/% 5.60 CVN Energy @-30℃ /J 279
Ac3 Ac1
Temperature
Water Quenching
F+M
Time
Microstructure evolution
SEM micrograph:
(a) 700℃ Q, with 15% M; (b) 720℃ Q, with 27% M; (c) 740℃ Q, with 40% M; (d) 760℃Q, with 49% M; (e) 780℃ Q, with 57% M; (f) 800℃ Q, with 67% M; (g) 820℃ Q, with 89% M; (h) 840℃ Q, with 98% M; (i) higher mag. micrograph of 740℃ Q specimen.
Mechanical properties
Tensile property and Charpy-V notch energy.
st0.5 /MPa 693 Uniform Elongation/% 5.60 CVN Energy @-30℃ /J 279
Sample As-rolled
UTS /MPa 832
YS/TS 0.85
Elongation/% 18.40
700
720 740 760
605
597 595 573
820
831 857 891
0.74
0.65 0.68 0.74
19.95
19.88 19.38 18.72
7.00
6.60 6.60 5.80
66
169 220 270
780
800 820 840
647
659 725 811
899
924 1035 1066
0.66
0.76 0.83 0.80
17.98
15.71 14.41 15.02
5.60
4.60 3.90 3.60
279
270 221 213
Mechanical properties
Stress-strain curve of all specimens.
Hale Waihona Puke Baidu
Microstructure evolution
TEM micrograph (a) dislocations in massive ferrite, in 720℃ Q specimen; and
(b) coexisted of ferrite and martensite, in 780℃ Q specimen.
Specimens with about 60% martensite fraction showed the optimum mechanical properties, with higher UTS, lower yield ratio, equivalent elongation and CVN energy.
the steel sheets were hold at 700, 720, 740, 760, 780, 800, 820, 840 ℃ (between Ac1 and Ac3 temperature) for 1 hour followed by water quenching. the higher alloy element content and water quenching make sure the re-austenized grain transformed into martensite. Austenizing
Beijing, China, 2012.09.13/14
Lian-yu Zhao, Yi-yin Shan, Ke Yang
赵连玉 单以银 杨柯
Outline
Background
Material and Experiment Results and Discussion
Microstructure Evolution Mechanical Property Strain Hardenging phenomenon
F+M/A, X80 grade
Okatsu Mitsuhiro, JFE Report
F+B, X120 grade
Ishikawa Nobuyuki, JFE Report
F+B, X70 grade
Wuyang Steel Co.
F+B, X70 grade
An steel Co.
The phase composition has great influence on the mechanical property. While how the constitute fraction affect the mechanical property?
n
(a) with 15% M
(c) with 57% M
(d) with 90% M
Strain-hardening behavior
Summary:
For the as-R specimen, the strain-hardening exponent is about 0.07 calculated by Hollomon’s equation . For the specimens with dual-phase microstructure, the n value shows nonlinear variation. The n value of the 780℃ quenched specimen, which has 57% martensite, was very high as about 0.45 when the uniform plastic deformation began, and then decreased with the accumulation of strain. When the uniform plastic deformation was over, the n value dropped to ~0.07 . Dual-phase microstructure showed better strain hardening ability than the as-rolled microstructure.
Variation of tensile and yield strength with the martensite volume fraction.
Mechanical properties
Variation of CVN impact energy with the martensite volume fraction.
Mechanical properties
The fractographies of CVN specimen.
700Q, with 15% M
720Q, with 26% M
740Q, with 49% M
760Q, with 57% M
780Q, with 67% M
Mechanical properties
Material and Experiment
The chemical composition of base material
C 0.06 Mn 1.9 Si 0.25 Mo 0.3 Ni 0.5 Cr 0.20 Cu 0.25 Nb+V+Ti 0.065 Al 0.025 B 0.006
The microstructure of as-rolled material: Banite, with little M/A.
Summary:
All curves shows round-roof shape.
The ultimate tensile strength of dual-phase specimens were increased depending on the martensite volume fraction, while the yield strength was decreased at first and then increased when the martensite volume fraction was higher than 49% The yield/tensile ratio was lower than the as-rolled specimen. The elongations of dual-phase specimens were improved at first and then decreased due to the excessive martensite fraction.
Strain-hardening behavior
Strain hardening exponent Hollomon’s equation was used to calculate the strain -hardening exponent
(a) as-rolled specimen
s K
Background
The deformability of pipeline steel was demanded in cold region, seismic region or deepwater. Generally, the following properties were demanded:
F-B. F-M. B-M/A.
True stress
Tw o phase stage 3 stage 2 Soft phase
internal stress
stage 1
P2
t2
P
t
P1
t1
True strain
Background
The various duplex-phase microstructure
Variation of martensite phase volume fraction with the quenching temperature.
Microstructure evolution
Summary:
XRD result shows no austenite peak, which means nearly no retained austenite existed due to the high cooling speed, the microstructure is typically dual-phase which consisted by ferrite and martensite. The martensite volume fraction increased linearly with the increase of heat treat temperature. 49% martensite was achieved when treated at 760℃, and blocky martensite phase begins to link with each other. When the temperature is as high as 840℃, almost fully martensite is obtained, and coarse prior austenite grain boundary can be clearly distinguished
Material and Experiment
The phase transformation point of base material: Ac1=690℃; Ac3=845℃.
measured by the Formastor-F Dilatometer.
The experiment process
Lower Y/T ratio.
Higher elongation, especially the uniform elongation.
Round-roof shape stress-strain curve. Higher strain hardening ability . Duplex phase microstructure has been confirmed to have better deformability. Generally, the phase composition can be:
Conclusion
Background
Subsea pipeline has better prospect
Requirement of petroleum and gas increase gradually
Before
Resourse in permafrost regions
After
Ground movement imposes large strain
The mechanical property of base material: X100 grade.
Sample As-rolled st0.5 /MPa 693 UTS /MPa 832 YS/TS 0.85 Elongation/% 18.40 Uniform Elongation/% 5.60 CVN Energy @-30℃ /J 279
Ac3 Ac1
Temperature
Water Quenching
F+M
Time
Microstructure evolution
SEM micrograph:
(a) 700℃ Q, with 15% M; (b) 720℃ Q, with 27% M; (c) 740℃ Q, with 40% M; (d) 760℃Q, with 49% M; (e) 780℃ Q, with 57% M; (f) 800℃ Q, with 67% M; (g) 820℃ Q, with 89% M; (h) 840℃ Q, with 98% M; (i) higher mag. micrograph of 740℃ Q specimen.
Mechanical properties
Tensile property and Charpy-V notch energy.
st0.5 /MPa 693 Uniform Elongation/% 5.60 CVN Energy @-30℃ /J 279
Sample As-rolled
UTS /MPa 832
YS/TS 0.85
Elongation/% 18.40
700
720 740 760
605
597 595 573
820
831 857 891
0.74
0.65 0.68 0.74
19.95
19.88 19.38 18.72
7.00
6.60 6.60 5.80
66
169 220 270
780
800 820 840
647
659 725 811
899
924 1035 1066
0.66
0.76 0.83 0.80
17.98
15.71 14.41 15.02
5.60
4.60 3.90 3.60
279
270 221 213
Mechanical properties
Stress-strain curve of all specimens.
Hale Waihona Puke Baidu
Microstructure evolution
TEM micrograph (a) dislocations in massive ferrite, in 720℃ Q specimen; and
(b) coexisted of ferrite and martensite, in 780℃ Q specimen.
Specimens with about 60% martensite fraction showed the optimum mechanical properties, with higher UTS, lower yield ratio, equivalent elongation and CVN energy.
the steel sheets were hold at 700, 720, 740, 760, 780, 800, 820, 840 ℃ (between Ac1 and Ac3 temperature) for 1 hour followed by water quenching. the higher alloy element content and water quenching make sure the re-austenized grain transformed into martensite. Austenizing
Beijing, China, 2012.09.13/14
Lian-yu Zhao, Yi-yin Shan, Ke Yang
赵连玉 单以银 杨柯
Outline
Background
Material and Experiment Results and Discussion
Microstructure Evolution Mechanical Property Strain Hardenging phenomenon
F+M/A, X80 grade
Okatsu Mitsuhiro, JFE Report
F+B, X120 grade
Ishikawa Nobuyuki, JFE Report
F+B, X70 grade
Wuyang Steel Co.
F+B, X70 grade
An steel Co.
The phase composition has great influence on the mechanical property. While how the constitute fraction affect the mechanical property?
n
(a) with 15% M
(c) with 57% M
(d) with 90% M
Strain-hardening behavior
Summary:
For the as-R specimen, the strain-hardening exponent is about 0.07 calculated by Hollomon’s equation . For the specimens with dual-phase microstructure, the n value shows nonlinear variation. The n value of the 780℃ quenched specimen, which has 57% martensite, was very high as about 0.45 when the uniform plastic deformation began, and then decreased with the accumulation of strain. When the uniform plastic deformation was over, the n value dropped to ~0.07 . Dual-phase microstructure showed better strain hardening ability than the as-rolled microstructure.
Variation of tensile and yield strength with the martensite volume fraction.
Mechanical properties
Variation of CVN impact energy with the martensite volume fraction.
Mechanical properties
The fractographies of CVN specimen.
700Q, with 15% M
720Q, with 26% M
740Q, with 49% M
760Q, with 57% M
780Q, with 67% M
Mechanical properties
Material and Experiment
The chemical composition of base material
C 0.06 Mn 1.9 Si 0.25 Mo 0.3 Ni 0.5 Cr 0.20 Cu 0.25 Nb+V+Ti 0.065 Al 0.025 B 0.006
The microstructure of as-rolled material: Banite, with little M/A.
Summary:
All curves shows round-roof shape.
The ultimate tensile strength of dual-phase specimens were increased depending on the martensite volume fraction, while the yield strength was decreased at first and then increased when the martensite volume fraction was higher than 49% The yield/tensile ratio was lower than the as-rolled specimen. The elongations of dual-phase specimens were improved at first and then decreased due to the excessive martensite fraction.
Strain-hardening behavior
Strain hardening exponent Hollomon’s equation was used to calculate the strain -hardening exponent
(a) as-rolled specimen
s K
Background
The deformability of pipeline steel was demanded in cold region, seismic region or deepwater. Generally, the following properties were demanded: