CN108603258A - The high-strength steel sheet of excellent in low temperature toughness - Google Patents
The high-strength steel sheet of excellent in low temperature toughness Download PDFInfo
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- CN108603258A CN108603258A CN201680080661.7A CN201680080661A CN108603258A CN 108603258 A CN108603258 A CN 108603258A CN 201680080661 A CN201680080661 A CN 201680080661A CN 108603258 A CN108603258 A CN 108603258A
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- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
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- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
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- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
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- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
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- C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
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- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
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- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/46—Ferrous alloys, e.g. steel alloys containing chromium with nickel with vanadium
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/48—Ferrous alloys, e.g. steel alloys containing chromium with nickel with niobium or tantalum
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/50—Ferrous alloys, e.g. steel alloys containing chromium with nickel with titanium or zirconium
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- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/54—Ferrous alloys, e.g. steel alloys containing chromium with nickel with boron
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- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese
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- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/002—Bainite
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- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/008—Martensite
Abstract
The high-strength steel sheet contains C based on quality %：0.08%~0.15%, Mn：0.80%~1.60%, Ni：3.00%~4.50%, Cr：0.50%~1.00%, Mo：0.50%~1.00%, Al：0.020%~0.085%, N：0.0020%~0.0070%, B：0.0005%~0.0020%, plate thickness tmm is more than 200mm and is 300mm or less, in the chemical composition, Ts is that 380~430, Ceq is 0.80~1.05, Ac1 is 580~647, x is 46~90, and based on area %, the total amount of martensite and bainite is 99%~100%, tensile strength is 780MPa~930MPa, and the absorption that plate thickness central part is obtained in 60 DEG C of Charpy-type test can be 69J or more.
Description
Technical field
The present invention relates to excellent in low temperature toughness and the big high-strength steel sheets of plate thickness.More specifically, being related to plate thickness is more than
200mm, tensile strength are 780MPa or more, and plate thickness central part can be the steel plate of 69J or more in -60 DEG C absorb.The steel plate is suitable
Share the works such as the large-scale crane of Yu Haiyang works, pressure vessel, penstocks (penstock), ship.
Background technology
It is low to the steel plate requirement used as base material generally in order to ensure the safety of works in above structure object
Warm toughness.In recent years the scale of works significantly becomes larger, and in such works, is inclined to use the steel that plate thickness is big and intensity is high
Plate.
Above structure object generally uses 780MPa grades of high-strength steel sheet.In the high-strength steel sheet, 780MPa in order to obtain
Above tensile strength uses the quenching of direct quenching method etc to be formed with the low temperature phase change of bainite and/or martensite etc
Tissue based on product.But plate thickness more thickens, cooling velocity when quenching inside steel plate more declines, and therefore, it is difficult to shapes
At low temperature phase change tissue.Therefore, into steel, addition makes the alloying element of C, Mn, Cr, Mo, V of hardenability raising etc. in right amount, to
Sufficient low temperature phase change product can be obtained cooling velocity declines.As a result, even if plate thickness is increased to about 150mm
The tensile strength of 780MPa or more can be achieved.But in the steel plate that plate thickness is more than 200mm, the reality when heat of transformation is to quenching
It is influenced significantly caused by cooling velocity, therefore phase transformation carries out at high temperature, is unable to fully obtain low temperature phase change product.
For example, Patent Document 1 discloses a kind of high-strength steel sheet, Ceq (carbon equivalent) is 0.80 hereinafter, C content, P contain
Amount, Mn contents, Ni contents and Mo contents meet pre- fixed pattern, and the center segregation portion hardness of steel plate is hard relative to a certain region of steel plate
Ratio (HVmax/HVave), C content and the plate thickness of the average value of degree meet pre- fixed pattern.In addition, in the patent document 1, disclose
The plate thickness of steel plate is 60mm~150mm.It is CeqM hereinafter, plate thickness is 75mm~200mm that a kind of Ceq is disclosed in patent document 2
High-strength steel sheet.It is 26~42 that a kind of parameter x determined by the amount of chemical element is disclosed in patent document 3, plate thickness 75
The high high-strength steel sheet of the toughness of~200mm.It, can not if steel plate plate thickness is more than 200mm but in this 3 patent documents
Expected effect is come to steel plate strip.
In addition, it is 0.005~0.02% to disclose a kind of C content in patent document 4, plate thickness is the high-strength of 50~200mm
Spend steel plate.In addition, it is 0.02~0.05% to disclose a kind of C content in patent document 5, plate thickness is the high intensity of 75~200mm
Steel plate.Moreover, in the patent document 4 and patent document 5, the cooling velocity of plate thickness central part must be made when disclosing quenching treatment
For 1.1 DEG C/sec or more of the method being quickly cooled down.But if the plate thickness of steel plate is more than 200mm, can not possibly industrially incite somebody to action
The cooling velocity of plate thickness central part increases to 1.1 DEG C/sec or more.Therefore, if the plate thickness of steel plate is more than 200mm, patent text
Offer 4 and method disclosed Patent Document 5 can not be achieved.
A kind of method is disclosed in patent document 6, the Ar in hot rolling3The temperature range of point~900 DEG C depresses accumulation
Rate is increased to 50% or more, will be limited in Ac for the heating temperature of quenching3Point~(Ac3+ 100 DEG C of point) temperature range, with
To fine austenite grain.In addition, disclosing the high-strength steel sheet that plate thickness is 40~65mm in the patent document 6.But steel plate
Plate thickness it is bigger, the influence of center on the plate thickness direction of steel plate rolling more declines.Therefore, if the plate thickness of steel plate is more than
100mm, the then effect that zerolling brings crystal grain refinement are small.Therefore, even with attempt to using zerolling by crystal grain miniaturization,
It can not carry out expected effect to steel plate strip if the plate thickness of steel plate is more than 200mm.In addition, zerolling makes deformation drag increase
Greatly, it is difficult to fill the gap inside steel plate.Therefore, zerolling is unsuitable for manufacturing the steel plate that plate thickness is more than 200mm.
A kind of high-strength steel sheet is disclosed in patent document 7, Ceq is 0.50~0.80, is determined by the amount of chemical element
Parameter beta is 8.45~15.2, and the average crystal particle diameter of the plate thickness central part of steel plate is 35 μm hereinafter, plate thickness is 25~200mm.Separately
Outside, a kind of method is disclosed in the patent document 7, the accumulation reduction ratio of 900~1150 DEG C of temperature range is increased to 50%
More than, so that average crystal particle diameter becomes 35 μm or less.But as described above, the plate thickness of steel plate is bigger, in the plate thickness side of steel plate
The influence at upward center, rolling more declines.In addition, as disclosed in Patent Document 7, if the plate thickness of steel plate is more than
200mm, then the cooling velocity of plate thickness central part be remarkably decreased, the coarsening of crystal grain occurs.Therefore, in patent document 7, if steel
Plate plate thickness then can not carry out expected effect more than 200mm to steel plate strip.
A kind of method of quenching treatment that implementing for 2 times or more is disclosed in patent document 8, it is fine to be obtained by recrystallization
And uniform austenite grain.But as shown in non-patent literature 1 and non-patent literature 2, if heating speed in low-alloy steel
Degree, which declines, then reheats the effect mitigation caused by crystal grain refinement.In addition, it is 50mm's to disclose a kind of plate thickness in patent document 8
High-strength steel sheet.But the thicker heating speed of the plate thickness of steel plate more declines.Therefore, be more than in plate thickness 200mm steel plate manufacture
In, even if implementing substantially not miniaturization if 2 times or more quenching treatment crystal grain, can only manufacturing cost be made to increase.Therefore, specially
In method disclosed in sharp document 8, expected effect can not be carried out to steel plate strip if steel plate plate thickness is more than 200mm.
Additionally, it is known that making Ni thicken in fine retained austenite crystal grain, retained austenite is stabilized, to improve steel
The method of plate toughness.For example, in patent document 9 and patent document 10, a kind of stopping brittle fracture (cracking) propagation is disclosed
The high high-strength steel sheet of characteristic, plate thickness are 150~200mm, and the amount of retained austenite is 1~10%.In addition, these patent documents
In, disclose it is a kind of steel plate is tempered in the temperature range (temperature range than Ac1 high) that can mutually become austenite, with formed
The method of fine retained austenite.It is difficult to understand in the plate thickness central part of steel plate but in the case that steel plate plate thickness is more than 200mm
Family name's body grain size becomes thick, and/or Ni becomes inadequate denseization of austenite.Therefore, the stability of retained austenite declines,
The toughness of the plate thickness central part of steel plate declines.In addition, in order to improve the stability of retained austenite, the amount for increasing Ni is needed, because
This cost is often got higher.In addition, disclosing a kind of method in patent document 9, the temperature range of finish rolling is limited to 700~850
DEG C, the accumulation reduction ratio of the temperature range is limited to 25~75%, to obtain fine austenite.In this way, in patent document 9
Zerolling is utilized, so the method for patent document 9 is unsuitable for manufacturing the steel plate that plate thickness is more than 200mm.
As described above, in previous method, if steel plate plate thickness is more than 200mm, being unable to get tensile strength is
The high-strength steel sheet of the excellent in low temperature toughness of 780MPa or more.
Existing technical literature
Patent document
Patent document 1：Japanese Laid-Open 2013-91845 bulletins
Patent document 2：Japanese Laid-Open 2011-202214 bulletins
Patent document 3：Japan's patent the 2662409th
Patent document 4：Japanese Laid-Open 2013-104065 bulletins
Patent document 5：Japan's patent the 5552967th
Patent document 6：The flat 6-240353 bulletins of Japanese Laid-Open
Patent document 7：Japan's patent the 5590271st
Patent document 8：The flat 10-265846 bulletins of Japanese Laid-Open
Patent document 9：Japan's patent the 3336877th
Patent document 10：Japan's patent the 3327065th
Non-patent literature
Non-patent literature 1：This bright Jie's " influence that the Ni of Ni-Cr-Mo-V steel brings austenite grain behavior " iron with
Steel Vol.58 (1972) No.1p.119
Non-patent literature 2：Clear first-class " reverse transformation of the low-carbon low-alloy steel " iron of matsuda and steel Vol.60 (1974)
No.2p.60
Invention content
The present invention completes in view of the above problems, is more than 200mm the purpose is to provide a kind of plate thickness, low-temperature flexibility is excellent
It is different, and the steel plate that intensity is high.
The inventors discovered that a kind of new chemical composition and tissue, even if steel plate plate thickness can be to steel if being more than 200mm
The plate thickness central portion of plate assigns high intensity and high low-temperature flexibility.In addition, the inventors discovered that, this new chemical composition with
Chemical composition difference of the high intensity with high low-temperature flexibility is assigned toward to steel plate, this steel with new chemical composition is answered
It is suitable with the new method different from previous methods.
The present invention is completed based on these opinions, and purport is as described below.
(1) there is the steel plate that a mode of the invention is related to following chemical composition to contain C based on quality %：0.08%
~0.15%, Mn：0.80%~1.60%, Ni：3.00%~4.50%, Cr：0.50%~1.00%, Mo：0.50%~
1.00%, Al：0.020%~0.085%, N：0.0020%~0.0070%, B：0.0005%~0.0020%, P：
0.000%~0.010%, S：0.000%~0.003%, Si：0.00%~0.30%, Cu：0.00%~0.50%, V：
0.000%~0.050%, Nb：0.000%~0.050%, Ti：0.000%~0.020%, Ca：0.0000%~
0.0030%, Mg：0.0000%~0.0030% and REM：0.0000%~0.0030%, surplus includes Fe and impurity, plate thickness
Tmm is more than 200mm and is 300mm hereinafter, in the chemical composition, is 380~430 by the Ts that following formula 1 defines, by following formula
The Ceq of 2 definition is 0.80~1.05, is 580~647 by the Ac1 that following formula 3 defines, and is 46~90 by the x that following formula 4 defines,
Based on area %, the total amount of martensite and bainite is 99%~100%, and tensile strength is 780MPa~930MPa, plate thickness
The absorption that central part is measured in -60 DEG C of Charpy-type test can be 69J or more.
Ts=750-4240 × (t/2)-1.4×(80×C+10×Mn+7×Ni+13×Cr+13×Mo-40×
Si) formula 1
Ceq=C+Mn/6+ (Cu+Ni)/15+ (Cr+Mo+V)/5 formula 2
Ac1=720-25 × C+22 × Si-40 × Mn-30 × Ni+20 × Cr+25 × Mo formulas 3
X=C1/2×(1+0.64×Si)×(1+4.10×Mn)×(1+0.27×Cu)×(1+0.52×Ni)×(1+
2.33 × Cr) × (1+3.14 × Mo) formula 4
(2) in the steel plate described in above-mentioned (1), the chemical composition can also meet Ti/N≤3.4.
(3) in the steel plate described in above-mentioned (1) or (2), the chemical composition can also meet C：0.09%~0.13%.
(4) in any one of them steel plate of above-mentioned (1)~(3), the chemical composition can also meet Mn：0.80%~
1.30%.
(5) in any one of them steel plate of above-mentioned (1)~(4), the chemical composition can also meet Ni：3.60%~
4.50%.
(6) in any one of them steel plate of above-mentioned (1)~(5), the chemical composition can also meet Cr：0.75%~
1.00%.
(7) in any one of them steel plate of above-mentioned (1)~(6), the chemical composition can also meet Mo：0.70%~
1.00%.
(8) in any one of them steel plate of above-mentioned (1)~(7), the chemical composition can also meet Si：0.00%~
0.10%.
(9) in any one of them steel plate of above-mentioned (1)~(8), the chemical composition can also meet V：0.020%~
0.050%.
(10) in any one of them steel plate of above-mentioned (1)~(9), the chemical composition can also meet Ti：0.000%
~0.004%.
(11) in any one of them steel plate of above-mentioned (1)~(10), the chemical composition can also meet the Ts and be
395~415 this condition.
(12) in any one of them steel plate of above-mentioned (1)~(11), the chemical composition can also meet the Ceq and be
0.85~1.05 this condition.
In accordance with the invention it is possible to which it is more than 200mm, excellent in low temperature toughness, and the steel plate that intensity is high to provide plate thickness.Therefore, energy
Enough further increase the safety of larger works.
Description of the drawings
Fig. 1 is to indicate Ts and vE-60℃Between relationship an example figure.
Fig. 2 is to indicate Ceq and vE-60℃Between relationship an example figure.
Fig. 3 is to indicate x and vE-60℃Between relationship an example figure.
Fig. 4 is the photo of the tissue for the high-strength steel sheet for indicating that one embodiment of the present invention is related to.
Fig. 5 is to show schematically the figure of effect that Ts brings quenching structure as an example.
Specific implementation mode
Hereinafter, being illustrated to the steel plate (high-strength steel sheet) that an embodiment of the present invention is related to.
First, the chemical composition of steel plate of the present embodiment is illustrated.Hereinafter, the amount (%) of each chemical element
It is indicated with quality %.
C：0.08%~0.15%
C is effective to improving intensity in order to improve the hardness of quenched steel plate tissue.Therefore, the amount of C needs to be 0.08%
More than.On the other hand, toughness is damaged if the amount surplus of C, therefore the amount of C needs to be 0.15% or less.Therefore, the amount of C is
0.08%~0.15%.In order to more improve intensity, the amount of C is preferably 0.09% or more or 0.10% or more.In addition, in order to more
Add raising toughness, the amount of C is preferably 0.14% hereinafter, more preferably 0.13% or less or 0.12% or less.
Mn：0.80%~1.60%
Mn is effective to the improvement of deoxidation and hardenability.Hardenability in order to improve steel makes intensity improve, and the amount of Mn needs
It is 0.80% or more.The amount of Mn can be set as to 0.85% or more, 0.90% or more, 0.95% or more, 1.00% or more,
1.05% or more or 1.10% or more.On the other hand, if the amount of Mn is superfluous, hardenability is superfluous, and tissue becomes hard.Separately
Outside, excess quantity Mn promote temper brittleness, so while the synergistic effect of hard tissue and temper brittleness and make under the toughness of steel
Drop.Therefore, the amount of Mn needs to be 1.60% or less.Therefore, the amount of Mn is 0.80%~1.60%.In order to more improve toughness,
The amount of Mn is preferably 1.50% hereinafter, more preferably 1.40% hereinafter, most preferably 1.35% or less or 1.30% or less.According to
It needs, the amount of Mn can be set as 1.25% or less or 1.20% or less.
Ni：3.00%~4.50%
Ni is effective to the intensity and toughness that improve steel, and the amount of Ni needs to be 3.00% or more.If the amount of Ni is excessive, by
It needs that temperature is made to reduce in the decline of Ac1, so tempering time is elongated.In addition, Ni makes stabilization of austenite, so having
The misgivings of retained austenite remaining.In addition, the price of Ni is high.Therefore, if the amount of Ni is superfluous, manufacturing cost deteriorates.Therefore,
The amount of Ni needs to be 4.50% or less.Therefore, the amount of Ni is 3.00%~4.50%.In addition, more improve steel intensity and
In the case of toughness, the amount of Ni is preferably 3.15% or more, 3.30% or more, 3.40% or more or 3.50% or more, more preferably
It is 3.60% or more.The amount of Ni can be 4.30% or less, 4.15% or less, 4.00% or less, 3.90% or less or 3.80%
Below.
Cr：0.50%~1.00%
Mo：0.50%~1.00%
Cr and Mo improves the hardenability of steel, and intensity is made to improve.The amount of Cr needs
0.50% or more.On the other hand, if the amount of Cr or the amount of Mo are superfluous, made under toughness due to the formation of alloy carbide
Drop.Therefore, the amount of Cr needs for 1.00% hereinafter, the amount of Mo needs to be 1.00% or less.Therefore, the amount of Cr be 0.50%~
The amount of 1.00%, Mo are 0.50%~1.00%.In addition, in order to steadily improve the intensity of steel, the amount of Cr is preferably 0.60%
More than, more preferably 0.65% or more, 0.70% or more, 0.75% or more or 0.80% or more.The amount of Cr can be 0.96%
Below, 0.94% or less or 0.91% or less.Similarly, the amount of Mo is preferably 0.60% or more, more preferably 0.70% or more,
0.75% or more, 0.80% or more or 0.85% or more.The amount of Mo can be 0.96% or less, 0.94% or less, 0.92% with
It is lower or 0.90% or less.
Al：0.020%~0.085%
Al is effective to deoxidation, is combined to form AlN with the solid solution N in steel.The AlN makes grain shaped beading, due in steel
The amount of solid solution N declines and makes the effect stability of the B of the hardenability of influence steel.Therefore, the amount of Al needs to be 0.020% or more.
On the other hand, if the amount of Al is superfluous, AlN's is oversized, therefore toughness declines, and slab cracks.Therefore, AlN
Amount needs to be 0.085% or less.Therefore, the amount of Al is 0.020%~0.085%.Hardenability in order to further increase B improves
The amount of Al can be set as 0.030% or more, 0.040% or more or 0.045% or more by effect.In order to more be prevented securely from life
At coarse AlN, the upper limit of the amount of Al can be set as 0.070%, 0.065% or 0.060%.
N：0.0020%~0.0070%
N is combined with alloying element to be formed compound (nitride and carbonitride) and makes grain shaped beading.Therefore, the amount of N
It needs to be 0.0020% or more.On the other hand, if the amount of N is superfluous, N is dissolved in steel becomes superfluous, and/or compound
(nitride and carbonitride) becomes thick, therefore the toughness of steel declines.Therefore, the amount of N needs to be 0.0070% or less.Cause
This, the amount of N is 0.0020%~0.0070%.The amount of N can be set as 0.0025% or more, 0.0030% or more or
0.0040% or more, 0.0065% or less or 0.0060% or less can be set as.
B：0.0005%~0.0020%
If steel contains micro B, improve the hardenability of steel, intensity improves.Therefore, the amount of B needs to be 0.0005%
More than.But in the case where the amount of B becomes surplus, the carbon boride of metal is formed, hardenability declines.Therefore, the amount of B needs
To be 0.0020% or less.Therefore, the amount of B is 0.0005%~0.0020%.It, can be by B in order to further increase hardenability
Amount be set as 0.0007% or more or 0.0008% or more.In order to make hardenability further optimize, the amount of B can be set as
0.0018% or less, 0.0016% or less or 0.0014% or less.
The steel plate of present embodiment includes that above-mentioned 8 kinds of chemical elements (C, Mn, Ni, Cr, Mo, Al, N, B) are used as requiredization
Learn element.Other than these required chemical elements, steel can include optionally chemical element below.
P：0.000%~0.010%
P is the impurity in steel, promotes embrittlement of grain boundaries, toughness is made to decline.In this way, P is harmful for the toughness of steel, therefore preferably
The amount of P is few as possible.Therefore, the amount of P needs to be 0.010% or less.The amount of P can be 0.000%.Therefore, the amount of P is
0.000%~0.010%.The amount of P can be set as 0.007% or less or 0.005% or less.Furthermore if reducing the amount of P,
Then cost for purification increases, and/or productivity declines, therefore can the amount of P be set as 0.0005% or more or 0.001% or more.
S：0.000%~0.003%
S is the impurity in steel, and the segregation of S and sulfide make toughness decline.It is therefore preferable that the amount of S is few as possible.Thus, S's
Amount needs to be 0.003% or less.The amount of S can be 0.000%.Therefore, the amount of S is 0.000%~0.003%.It can be by S's
Amount is set as 0.002% or less.Furthermore if reducing the amount of S, cost for purification increases, and/or productivity declines, therefore can be with
The amount of S is set as 0.0004% or more or 0.0006% or more.
Si：0.00%~0.30%
If the amount of Si is superfluous, promotes temper brittleness, toughness is made to decline.Therefore, the amount of Si needs to be 0.30% or less.
On the other hand, the amount of Si can be 0.00%.Therefore, the amount of Si is 0.00%~0.30%.Furthermore Si changes deoxidation and intensity
It is kind all effective, so steel can optionally contain Si.The amount of deoxidation effectiveness when purifying molten steel to improve, Si can be
0.01% or more, 0.02% or more or 0.03% or more.In addition, in order to more stably improve toughness, the amount of Si is preferably
0.25% hereinafter, more preferably 0.20% or less, 0.15% or 0.10% or less.
Cu：0.00%~0.50%
If the amount of Cu is superfluous, cracked in hot-working, and Ni metal is precipitated, toughness declines.Therefore, Cu
Amount needs to be 0.50% or less.The amount of Cu is if 0.50% hereinafter, improving hardness of steel with capable of not then damaging low-temperature flexibility.Separately
Outside, if the amount of Cu increases, Ceq becomes larger, so more stably ferrite can be inhibited to generate when quenching.Therefore, steel can be with
Optionally contain Cu.But, Cu is replaced by other alloying elements also to the effect that hardness of steel and Ceq are brought and can obtained by Cu.
Therefore, the amount of Cu can be 0.00%.Therefore, the amount of Cu is 0.00%~0.50%.Furthermore in the molten steel used as raw material
In comprising in the case of Cu, it is difficult to the amount of Cu is reduced to 0.00% by purifying, therefore the amount of Cu can be set as 0.01%
Above, 0.02% or more or 0.06% or more.The amount of Cu can be set as 0.45% or less, 0.40% or less, 0.35% or less
Or 0.030% or less.
V：0.000%~0.050%
If the amount of V is superfluous, toughness is set to decline due to forming alloy carbide.Therefore, the amount needs of V are
0.050% or less.On the other hand, V-arrangement at carbide, and/or improves hardenability, therefore the intensity of steel is made to improve.In addition, if
The amount of V increases, then Ceq becomes larger, so can more stably inhibit to generate ferrite when quenching.Therefore, steel can optionally contain
There is V.But, the effect that V brings hardness of steel and Ceq can obtain V is replaced by other alloys.Therefore, the amount of V
Can be 0.000%.Therefore, the amount of V is 0.000%~0.050%.Furthermore containing V's in the molten steel used as raw material
In the case of, it is difficult to the amount of V is reduced to 0.000% by purifying, therefore the amount of V can be set as 0.003% or more or
0.005% or more.In order to steadily improve hardness of steel, the amount that the amount of V is more preferably 0.010% or more, V is most preferably
0.020% or more.The upper limit of V can be set as 0.045%, 0.040% or 0.035%.
Nb：0.000%~0.050%
Nb forms carbonitride, makes the grain shaped beading inside steel.Therefore, steel can optionally contain Nb.Another party
The amount in face, Nb can be 0.000%.But if the amount of Nb is superfluous, carbonitride becomes large-sized, toughness declines.Cause
This, the amount of Nb needs to be 0.050% or less.Therefore, the amount of Nb is 0.000%~0.050%.Crystal grain is brought to steel imparting in Nb
In the case of the effect of refinement, the amount of Nb can be set as 0.001%.In this case, the upper limit of Nb can be set as
0.040%, 0.035%, 0.030% or 0.025%.It, can also the case where not needing the grain refining effect that Nb is brought etc.
Without intentionally adding for Nb.
Ti：0.000%~0.020%
Ti forms stable nitride, makes grain shaped beading.Therefore, steel can optionally contain Ti.On the other hand, Ti
Amount can be 0.000%.But if the amount of Ti is superfluous, nitride becomes large-sized, toughness declines.Therefore, the amount of Ti
It needs to be 0.020% or less.Therefore, the amount of Ti is 0.000%~0.020%.The effect for bringing crystal grain refinement is assigned to steel in Ti
In the case of fruit, the amount of Ti can be set as 0.001% or more.In addition, can also realize crystal grain refinement, therefore Ti by AlN
Amount can be 0.010% or less, or 0.004% or less or 0.002% or less.Not needing, the crystal grain that Ti is brought is thin
The case where changing effect etc., can intentionally adding without Ti.
Ca：0.0000%~0.0030%
Mg：0.0000%~0.0030%
REM：0.0000%~0.0030%
Ca, Mg, REM are all combined with objectionable impurities such as S, form harmless field trash, therefore improve the engineering properties of steel.
Therefore, steel can optionally contain at least one kind of in Ca, Mg, REM.On the other hand, the amount of Ca, the amount of Mg, the amount of REM
Can be all 0.0000%.If the amount of these chemical elements is superfluous, the refractory material melting loss of ozzle etc. is cast.Therefore, Ca
Amount, the amount of Mg, the amount of REM all need to be 0.0030% or less.Therefore, the amount of Ca, the amount of Mg, the amount of REM are all
0.0000%~0.0030%.In the case where Ca, Mg, REM bring the effect of engineering properties of steel to steel imparting, the amount of Ca,
The amount of Mg, the amount of REM are preferably all 0.0001% or more.It should if the amount of these chemical elements respectively reaches 0.0030%
Effect is saturated.It can intentionally adding without Ca, Mg, REM.
As long as the effect that other parts chemical element does not bring essence unfavorable the steel plate characteristic of present embodiment, so that it may with
Included in the steel plate of present embodiment.For example, as its tolerance, the amount that the amount of W is 0.00%~0.10%, Co is
The amount that the amount that the amount of 0.00%~0.10%, Sb are 0.000%~0.010%, As is 0.000%~0.010%, Sn is
The amount of 0.000%~0.010%, Pb are 0.000%~0.050%.These chemical elements such as sometimes from iron filings be mixed into steel
Liquid.The amount of W or the amount of Co can be respectively 0.05% or less, 0.02% or less, 0.01% or less or 0.005% or less.
The steel plate of present embodiment has following chemical composition：Containing chemical element necessary to above-mentioned 8 kinds, surplus includes Fe
And impurity, or contain at least one kind of, the surplus in chemical element and above-mentioned optional chemical element necessary to above-mentioned 8 kinds
Including Fe and impurity.In steel plate of the present embodiment, need that the chemical composition is made further to meet the following conditions.
Ts：380~430
Ts is defined by following formula 5, compared with the steel plate tissue after being more than the steel plate water hardening of 200mm with plate thickness has
Strong correlation.In the case where Ts is too low, tissue becomes geneva phosphor bodies, and steel plate toughness declines.Therefore, as shown in Figure 1, Ts
It needs to be 380 or more.On the other hand, in the case where Ts is excessively high, tissue becomes upper bainite main body, the intensity and toughness of steel plate
Decline.Therefore, as shown in Figure 1, Ts needs to be 430 or less.Therefore, ranging from the 380~430 of Ts.The range of Ts is determined in this way
Justice is 380~430, therefore Ts itself is characteristic.It therefore, there is no need to limit the unit of Ts.Assuming that assigning unit to Ts, then
The unit of Ts is mm-1.4%.In addition, in order to more stably improve steel plate toughness, Ts is preferably 385 or more, 390 or more, 395
Above or 400 or more.For the same reason, Ts is preferably 425 or less, 420 or less, 415 or less or 412 or less.
Ts=750-4240 × (t/2)-1.4
× (80 × C+10 × Mn+7 × Ni+13 × Cr+13 × Mo-40 × Si) ‥ ‥ formulas 5
Here, t is steel plate plate thickness mm, each element symbol is the amount % of corresponding chemical element.
Ceq：0.80~1.05
Ceq is defined by following formula 6, indicates the hardenability of steel.If Ceq is too low, ferrite crystallization, the intensity of steel plate and
Low-temperature flexibility is insufficient.Therefore, as shown in Fig. 2, Ceq needs to be 0.80 or more.On the other hand, if Ceq is excessively high, steel plate is strong
Degree becomes excessively high, while steel plate toughness is remarkably decreased.Therefore, as shown in Fig. 2, Ceq needs to be 1.05 or less.Therefore, the model of Ceq
Enclose is 0.80~1.05.The range of Ceq is defined as 0.80~1.05 in this way, therefore Ceq itself is characteristic.Therefore, no
Need the unit of restriction Ceq.Assuming that assigning unit to Ceq, then the unit of Ceq is %.In addition, in order to further increase steel plate
Intensity and low-temperature flexibility, Ceq be preferably greater than 0.80, Ceq be more preferably 0.85 or more, 0.86 or more, 0.87 or more or 0.89 with
On.The upper limit of Ceq can be 1.02,0.99,0.96 or 0.94.
Ceq=C+Mn/6+ (Cu+Ni)/15+ (Cr+Mo+V)/5 ‥ ‥ formulas 6
Here, each element symbol is the amount % of corresponding chemical element.
x：46~90
X is defined by following formula 7, indicates the hardenability of steel.If x is too low, the amount of upper bainite increases, the low temperature of steel plate
Toughness is insufficient.Therefore, as shown in figure 3, x needs to be 46 or more.On the other hand, if x is excessively high, the amount of martensite became
It is more, therefore the low-temperature flexibility of steel plate is insufficient.Therefore, as shown in figure 3, x needs to be 90 or less.Therefore, ranging from the 46 of x~
90.The range of x is defined as 46~90 in this way, therefore x itself is characteristic.It therefore, there is no need to limit the unit of x.Assuming that
Unit is assigned to x, then the unit of x is %6.5.The lower limit of x can be set as 50,53,56,59,61 or 63, it can be by the upper limit of x
It is set as 85,82,79,76 or 73.
X=C1/2×(1+0.64×Si)×(1+4.10×Mn)×(1+0.27×Cu)×(1+0.52×Ni)×(1+
2.33 × Cr) × (1+3.14 × Mo) formula 7
Here, each element symbol is the amount % of corresponding chemical element.
β
β is defined by following formula 8, indicates the hardenability of steel.If β is too low, quenching structure becomes upper bainite main body, steel
The intensity and low-temperature flexibility of plate are insufficient.Therefore, β needs to be 22 or more.On the other hand, if β is excessively high, quenching structure becomes
The low-temperature flexibility of geneva phosphor bodies, steel plate is insufficient.Therefore, β needs to be 60 or less.Therefore, ranging from the 22~60 of β.But,
In present embodiment, it is 46~90 that the amount of Si, which is 0.00%~0.30%, x, therefore the range of β necessarily becomes 22~60.Therefore,
The range of β need not be limited.Furthermore the range of β is defined as 22~60, therefore β itself is characteristic.It therefore, there is no need to
Limit the unit of β.Assuming that assigning unit to β, then the unit of β is %6.5.The lower limit of β can be set as 25,28,31 or 34, it can
The upper limit of β is set as 56,53,50 or 48.
β=0.65 × C1/2×(1+0.27×Si)×(1+4.10×Mn)×(1+0.27×Cu)×(1+0.52×Ni)
× (1+2.33 × Cr) × (1+3.14 × Mo) formula 8
Here, each element symbol is the amount % of corresponding chemical element.
Ac1：580~647
Ac1 indicates the temperature that austenite phase transformation starts when heating steel, is defined by following formula 9.With including tempered martensite
In the steel of the tissue of tempering bainite, if Ac1 is lower than 580, for impurity to cyrystal boundary segregation, the low-temperature flexibility of steel is insufficient.
Therefore, Ac1 needs to be 580 or more.Furthermore in present embodiment, the amount of C, the amount of Si, the amount of Mn, the amount of Ni, the amount of Cr and Mo
Amount need in above range, so Ac1 is 647 or less.Therefore, ranging from the 580~647 of Ac1.In this way by the model of Ac1
It encloses and is defined as 580~647, therefore Ac1 itself is characteristic.It therefore, there is no need to limit the unit of Ac1.It is single being assigned to Ac1
In the case of position, the unit of Ac1 is DEG C.The upper limit of Ac1 can be set as 640,635,630 or 625, its lower limit can be set as
585,590 or 595.
Ac1=720-25 × C+22 × Si-40 × Mn-30 × Ni+20 × Cr+25 × Mo ‥ ‥ formulas 9
Here, each element symbol is the amount % of corresponding chemical element.
Ti/N
In the case where adding Ti to steel, Ti is combined with N generates TiN.If ratio ratios of the Ti relative to N in the reaction
Stoichiometric ratio (3.4) is small, then the chemical element (such as C) other than Ti and N can be inhibited to combine.Therefore, it is possible to steadily obtain
The effect of crystal grain refinement is brought to TiN, can more improve low-temperature flexibility.Therefore, the chemical composition of steel preferably satisfy Ti/N≤
3.4。
Then, steel plate tissue of the present embodiment is illustrated.
The total amount of martensite and bainite：99%~100%
Martensite and bainite improve armor plate strength.Therefore, the total amount of martensite and bainite need for 99%~
100%.The surplus of tissue includes ferrite, pearlite, retained austenite sometimes.Amount (ferrite, the pearlite and residual of the surplus
Stay the total amount of austenite) it is 0%~1%.The amount of the surplus can be set as 0.5% or less, 0.2% or less or 0.1% with
Under.I.e., it is possible to which the total amount of martensite and bainite is set as 99.5% or more, 99.8% or more or 99.9% or more.It is optimal
It is 100% to select the total amount that the amount of the surplus is 0% namely martensite and bainite.
May include martensite, bainite, pearlite, ferrite and retained austenite in metal structure.Present embodiment
In, the total amount of martensite and bainite is 99% or more, therefore directly determines that the total amount of this 2 kinds tissues is extremely difficult.Cause
This, the amount of surplus, the i.e. total amount of ferrite, pearlite and retained austenite are predefined using following methods.Thereafter, pass through
The total amount of this 3 kinds tissues is subtracted from 100% to calculate the total amount of martensite and bainite.
Ferritic amount and the amount of pearlite are showed by Line Integral rate (area %), pass through light according to the multiplying power with 500 times
The photo for learning microscope photographing determines.Sample is produced by leaving the plate thickness central part more than the positions 100mm away from steel plate edge.The examination
The longitudinal section of material (includes the face in plate thickness direction and rolling direction；The face vertical with width direction) corroded using nitric acid ethyl alcohol, by
The surface being corroded shoots 3 visual fields.Furthermore this 3 visual fields not determine in a manner of repeat region each other.For example, iron
After the amount of ferritic is by adding up the white area (ferritic region) in optical microscope photograph, by accumulative area
Divided by area is measured, and obtained Line Integral rate is averagely thereby determined that.
The amount of retained austenite is embodied by volume fraction (volume %), is measured using X-ray diffraction method.Sample is from away from steel
Edges of boards edge leaves the plate thickness central part more than the positions 100mm and produces.(plate thickness direction and rolling side are included to the longitudinal section of the sample
To face；The face vertical with width direction) X-ray is injected, the volume fraction of retained austenite is determined by obtained data.It should
The volume fraction (volume %) of austenite is considered as on an equal basis with the Line Integral rate (area %) of retained austenite, determines retained austenite
Line Integral rate.Furthermore the amount of retained austenite is trace degree, and 0% is seen as in the case of no standard measure.Therefore, geneva
The total amount of body and bainite is also embodied by Line Integral rate (area %).Furthermore in steel plate of the present embodiment, can
The possibility of most of retained austenite for generating the amount that can be quantified of the chemical composition range of use there's almost no.At this
In the case of sample, it is convenient to omit the measurement carried out using X-ray diffraction method.
Furthermore plate thickness central part (portions t/2) means to leave the steel plate of plate thickness half along plate thickness direction from surface of steel plate
Interior position.In the plate thickness central part, it is most difficult to generate martensite and bainite.Therefore, in plate thickness central part, martensite and bayesian
The total amount of body is if 99%~100%, then the depth from surface of steel plate (thickness) is 1mm or so below throughout except decarburization
The martensite of steel plate entirety and the total amount of bainite other than layer are considered as 99%~100%.Therefore, as long as only to plate thickness
The tissue of central part is evaluated i.e. enough.
The example of steel plate tissue of the present embodiment is shown in Fig. 4.In the figure, ferrite and pearly-lustre are not observed
Body.Using X-ray diffraction method without standard measure retained austenite, the conjunction of ferrite, pearlite and retained austenite
Metering is 0%, therefore the total amount of martensite and bainite is 100%.
Tensile strength：780MPa~930MPa
The absorption energy that plate thickness central part is obtained in -60 DEG C of Charpy-type test：69J or more
In present embodiment, the tensile strength of steel plate is 780MPa~930MPa, and plate thickness central part is rushed in -60 DEG C of Charpy
It can be that 69J or more is necessary to hit the absorption that experiment obtains.Illustrate its reason below.
Tempering lower bainite most effectively improves the intensity and low-temperature flexibility of steel plate.Tempered martensite also improves the strong of steel plate
Degree and low-temperature flexibility.But, the intensity of steel plate can be more improved although tempered martensite is compared with being tempered lower bainite, be not so good as
Tempering lower bainite improves the low-temperature flexibility of steel plate like that.Therefore, steel plate it is optimal have the tissue being made of tempering lower bainite,
Or the tissue being made of tempering lower bainite and tempered martensite.If being tempered the total amount of lower bainite and tempered martensite
Fully, then steel plate can also include tempering upper bainite.But, tempering upper bainite is not as good as tempering lower bainite, tempered martensite
Body improves the intensity and low-temperature flexibility of steel plate like that.Therefore, the amount for being tempered upper bainite is preferably few as possible.On the other hand, do not have
Tempering martensite (virgin (untempered) martensite), the upper bainite (virgin that is not tempered
(untempered) upper bainite) and lower bainite (virgin (untempered) lower for not being tempered
Bainite) low-temperature flexibility is made to be greatly reduced.The upper bayesian that therefore, it is necessary to reduce the martensite not being tempered to the greatest extent, be not tempered
Body and the lower bainite not being tempered.Furthermore in steel plate of the present embodiment, in the case of temper, as long as aftermentioned
Temperature be no more than Ac1, just there is no the martensite not being tempered, the upper bainite that is not tempered and be not tempered down
Bainite.That is, in order not to generate the martensite not being tempered, the upper bainite not being tempered and the lower shellfish not being tempered
Family name's body is heat-treated (tempering) in such a way that aftermentioned temperature is no more than Ac1.The martensite that is not tempered does not have
The total of lower bainite for having the upper bainite of tempering and not being tempered is preferably 0%.
Therefore, it is necessary in the above-mentioned martensite of suitable control and bainite tempered martensite, tempering upper bainite, under tempering
The amount of bainite, the martensite not being tempered, the upper bainite not being tempered, the lower bainite not being tempered.But it is adopted as
The usually used light microscope of tissue point rate is measured to differentiate tempered martensite, tempering upper bainite, tempering lower bainite, do not have
The martensite for having tempering, the upper bainite not being tempered and the lower bainite not being tempered are extremely difficult.Therefore, substantially can not
Tempered martensite can suitably be measured, tempering upper bainite, tempering lower bainite, the martensite not being tempered, be not tempered
The amount of upper bainite, the lower bainite not being tempered.But, if the chemical composition of steel plate meets above-mentioned condition, steel plate resists
Tensile strength is 780MPa~930MPa, and the absorption that plate thickness central part is obtained in -60 DEG C of Charpy-type test can be 69J or more,
The amount for being then considered as this 6 tissues is suitable.
For example, Ts has stronger correlation with quenching structure, as shown in figure 5, can realize quenching structure by adjusting Ts
Quite a few of the amount of lower bainite, upper bainite (martensite).But quenching can't completely only be embodied by Ts
Tissue can not also determine the tissue after tempering.In turn, chemical composition is only leaned on, the tissue after tempering (final tissue) can not be embodied
In precipitate (such as carbide and nitride) form, but in present embodiment, sometimes precipitate it is very fine, and/or
Particle diameter distribution is very wide, therefore the measurement of precipitate is extremely difficult.Therefore, pass through chemical composition, tensile strength and Charpy impact
The form for combining amount and precipitate to embody above-mentioned 6 tissues of experiment.Therefore, as described above, the tensile strength of steel plate is
780MPa~930MPa, the absorption that plate thickness central part is obtained in -60 DEG C of Charpy-type test can be that 69J or more is necessary.
Furthermore plate thickness central part -60 DEG C of Charpy-type test obtain absorb can the upper limit need not limit, can be 400J with
Under.Furthermore tempered martensite and the martensite not being tempered are the subordinate concepts of martensite, tempering upper bainite, the lower shellfish of tempering
Family name's body, the upper bainite not being tempered and the lower bainite not being tempered are the subordinate concepts of bainite.
In order to keep the form of above-mentioned 6 amounts organized and precipitate in steel plate more suitable, the tensile strength of steel plate is excellent
Choosing is less than 930MPa.The preferred upper limit of such tensile strength, by until be most preferably sequentially arranged in order for 900MPa,
880MPa、870MPa.Similarly, the yield strength of steel plate is preferably 880MPa or less.The preferred upper limit of such yield strength,
By until being most preferably sequentially arranged in order as 850MPa, 830MPa, 810MPa.In addition, the yield strength of steel plate is preferably
665MPa or more or 685MPa or more.
Tensile strength uses the stretching test measurement of 2241 defineds of JIS Z.In the experiment, JIS Z2201 defineds
No. 14 tension test sheets are produced by the portions t/4.The length direction (draw direction) of No. 14 tension test sheets is the directions T
(Transverse Direction, laterally), i.e., direction vertical with rolling direction (directions C).Furthermore the portions t/4 mean from
Surface of steel plate plays the position in the steel plate that plate thickness 1/4 is left in plate thickness direction.
Plate thickness central part can be using the Charpy of 2242 defineds of JIS Z in absorbing of obtaining of -60 DEG C of Charpy-type test
Impact test measures.In the experiment, the Charpy-type test piece of 2242 defineds of JIS Z is produced by plate thickness central part.The Charpy
The length direction of impact test piece is the directions T (Transverse Direction), i.e., the direction (side C vertical with rolling direction
To).In addition, the depth direction of V notch is rolling direction.Furthermore what plate thickness central part was obtained in -60 DEG C of Charpy-type test
Absorption can also save slightly vE sometimes-60℃。
Plate thickness：More than 200mm and it is 300mm or less
In order to more improve future large-scale structure object safety, it is excellent in the limit that can manufacture and handle steel plate
Select plate thickness thick as possible.Therefore, plate thickness is needed more than 200mm, and the preferred lower limit of plate thickness is by until being most preferably sequentially arranged in order
For 210mm, 215mm, 220mm, 225mm or 230mm.On the other hand, if plate thickness becomes blocked up, manufacture have high intensity and
The steel plate of excellent low-temperature flexibility is more difficult from, and above-mentioned chemical composition brings high intensity and excellent low-temperature flexibility in addition
Effect declines.Therefore, plate thickness need for 300mm hereinafter, the preferred upper limit of plate thickness by until be most preferably sequentially arranged in order for
290mm、280mm、270mm、260mm.For the above reasons, plate thickness needs more than 200mm and is 300mm or less.
Steel plate of the present embodiment is suitble to be related to using following embodiments from the viewpoint of reducing manufacturing cost
Steel plate manufacturing method manufacture.
Then, the manufacturing method for the steel plate (high-strength steel sheet) being related to for an embodiment describes.
First, molten steel of the casting with above-mentioned chemical composition obtains strand.The strand can be by continuous casting or by ingot casting
It is obtained with piecemeal roll mill piecemeal.
In the case of not carrying out soaking to strand with 1200 DEG C or more of temperature before hot rolling, remaining is coarse in steel
AlN (1.5 μm or more of AlN), the coarse AlN make the toughness of steel plate decline.Therefore, right with 1200 DEG C~1380 DEG C before hot rolling
Strand soaking.In order to more reduce the maximum value of AlN grain sizes in plate thickness central part, which is preferably 1250 DEG C or more.
In addition, in order to more improve productivity, soaking temperature is preferably 1300 DEG C or less.Furthermore judge that 1.5 μm or more of AlN is basic
It is upper that there is no extremely difficult.It is, for example, possible to use the AlN of 1.5 μm of transmission electron microscope observation or more, but use transmitted electron
The region of micro- sem observation is very small.Therefore, 1.5 μm or more of AlN can not possibly be judged substantially not with actual measurement number
In the presence of.On the other hand, 1.5 μm or more of AlN is substantially absent from Charpy impact that can be by plate thickness central part at -60 DEG C and tries
The absorption tested can (69J or more) confirm.
After soaking, strand hot rolling obtains having more than in the conduct of the hot rolled steel plate of 200mm and 300mm plate thickness below
Between product.In addition to target plate thickness, the condition of hot rolling does not limit.In order to ensure surface of steel plate quality well and to plate thickness center
Portion fully applies the effect that pressure brings crystal particle diameter etc., the preferably hot rolling since 950 DEG C~1250 DEG C of temperature.
The tissue that the total amount of martensite and bainite is 99% or more in order to obtain, in quenching treatment, again by steel plate
Water cooling is heated to after Ac3 DEG C or more of temperature to the temperature less than 300 DEG C.If steel plate is heated in the quenching treatment
Ac3 DEG C or more of temperature, then steel plate tissue become austenite one phase.If the austenite one phase tissue is quenched, austenite
Mutually become martensite or bainite, steel plate tissue becomes uniform.In quenching treatment, the martensite of sufficient amount and lower shellfish in order to obtain
Family name's body needs the average water speed of cooling that the temperature of plate thickness central part is dropped to the plate thickness central part during 500 DEG C from 800 DEG C to set
It is 0.4 DEG C/sec~0.8 DEG C/sec.Furthermore the temperature and water cooling speed of the plate thickness central part can be determined by Calculation of Heat Transfer.
Ac3 is defined by following formula 10.
Ac3=937.2-476.2 × C+56 × Si-19.7 × Mn-16.3 × Cu-26.6 × Ni-4.9 × Cr+38.1 ×
Mo+124.8 × V+198.4 × Al+3315 × B-19.1 × Nb+136.3 × Ti ‥ ‥ formulas 10
Here, each element symbol is the amount % of corresponding chemical element.
In order to improve the toughness of hot rolled steel plate, in temper, quenched steel plate is heated to 580 DEG C~Ac1 DEG C
Temperature, the temperature less than 300 DEG C is as cold as from 580 DEG C~Ac1 DEG C of temperature water thereafter.If steel plate is heated to above Ac1
DEG C temperature, then generate austenite in steel plate, the bainite that remaining is not tempered after temper, therefore steel plate toughness declines.Separately
On the one hand, if temperature is less than 580 DEG C, it cannot get the tempered structure of sufficient amount, and/or temper embrittlement occur.Therefore,
Steel plate toughness is insufficient.Therefore, temperature needs to be 580 DEG C~Ac1 DEG C.Furthermore Ac1 is defined by previously described formula 9.
In present embodiment, the plate thickness of hot rolled steel plate is more than 200mm, therefore is also carried out partially in the cooling of temper
Embrittlement occurs for analysis.The temperature range that the embrittlement occurs is mainly at 300 DEG C~500 DEG C.Therefore, steel plate needs as quickly as possible after hot rolling
Fast ground passes through the temperature range.Therefore, it in temper, needs the temperature of plate thickness central part dropping to 300 DEG C from 500 DEG C
The average water speed of cooling of the plate thickness central part of period is set as 0.3 DEG C/sec~0.7 DEG C/sec.Furthermore the temperature of the plate thickness central part
It can be determined according to Calculation of Heat Transfer with water cooling speed.In addition, the embrittlement of surface of steel plate in order to prevent, start to need when water cooling by
The temperature of surface of steel plate is set as 580 DEG C or more.The temperature of surface of steel plate radiation thermometer practical measurement.
Embodiment
By the steel melting with chemical composition shown in table 1~3, the steel disc that melting is obtained is with soaking temperature shown in table 5
Hot rolling is carried out after degree soaking, room temperature is cooled to, has obtained the hot rolled steel plate as intermediate.Moreover, the condition shown in table 5
Under, which is heated again, is quenched into room temperature.Thereafter, under the conditions shown in Table 6, quenched steel plate is tempered, it is cooling
To room temperature, the hot rolled steel plate (No.1~50) as end article has been obtained.Table 5~6 indicate by the temperature of steel disc soaking, in order to
Quench the temperature that steel plate heat, the average water speed of cooling in quenching from 800 DEG C to 500 DEG C, temperature, tempering it is rigid after
Start the average water from 500 DEG C to 300 DEG C in the temperature (temperature of surface of steel plate) of water cooling and the water cooling after tempering just
Speed of cooling.The plate thickness of hot rolled steel plate is 210mm~270mm.
Thereafter, JIS Z2201 defineds are produced in such a way that length direction is consistent with the directions T from the portions t/4 of whole steel plates
No. 14 tension test sheets, implement the tension test of 2241 defineds of JIS Z.In addition, from the plate thickness central part of whole steel plates
The Charpy-type test piece that JIS Z2242 defineds are produced in such a way that length direction is consistent with the directions T, implements experiment.It will
The results are shown in tables 7.
In addition, producing test film from plate thickness central part, the test film is corroded using nitric acid ethyl alcohol.It is aobvious using optics
The test film that micro mirror has corroded from the width direction orthogonal with rolling direction.The multiplying power of light microscope is 500 times, is surveyed
It is 3 to determine visual field.Furthermore so that sample is only moved along rolling direction in such a way that visual field is unduplicated, have taken the optics of 3 visual fields
Microscope photo.The Line Integral rate of ferrite and pearlite is determined from these optical microscope photographs.As a result, in No.1~50
In, all without pearlite is detected, the amount of pearlite is 0%.In addition, in No.12,29,35 and 41, ferritic amount is
0.5% less than 1.0%, and in No.37 and 38, ferritic amount is 4.5% less than 5.0%.Table 4 indicates will
The ferritic amount that decimal point the 1st or less has rounded up.
Test film separately is produced from plate thickness central part, the volume fraction of austenite is measured using X-ray diffraction method, makes the body
Integration rate is identical as Line Integral rate.In X-ray diffraction method, X-ray is injected from the width direction of test film.It is complete in No.1~50
Retained austenite is all not detected, the amount of retained austenite is trace degree, therefore without standard measure.Therefore, retained austenite
Amount in No.1~50 all be 0%.
The necessary condition of the column of the subsidiary underscore foot present invention with thumb down in table below.
Table 1
Table 2
Table 3
Table 4
Table 5
Table 6
Table 7
In No.1~11, end article has the chemical composition and tissue of the present invention, has excellent low-temperature flexibility and height
Intensity.By these No.1~11 it is found that if Ti/N is reduced to 3.4 hereinafter, if can further increase low-temperature flexibility.
In No.12, the amount of C is low, therefore tensile strength and impact absorbing can be low.On the other hand, in No.13, the amount of C is high,
Therefore impact absorbing can be very low.In No.14, the amount of Si is high, therefore impact absorbing can be low.
In No.15, the amount of Mn is low, therefore tensile strength and impact absorbing can be low.On the other hand, in No.16, the amount of Mn
Height, therefore impact absorbing can be very low.
In No.17, the amount of P is high, therefore impact absorbing can be low.In No.18, the amount of S is high, therefore impact absorbing can be low.
In No.19, the amount of Cu is high, therefore impact absorbing can be low.In No.20, the amount of Ni is low, therefore impact absorbing can be low.
In No.21, the amount of Cr is low, therefore tensile strength and impact absorbing can be low.On the other hand, in No.22, the amount of Cr
Height, therefore impact absorbing can be low.In No.23, the amount of Mo is low, therefore tensile strength and impact absorbing can be low.On the other hand,
In No.24, the amount of Mo is high, therefore impact absorbing can be low.In No.25, the amount of V is high, therefore impact absorbing can be low.
In No.26, the amount of Al is low, therefore tensile strength and impact absorbing can be low.On the other hand, in No.27, the amount of Al
Height, therefore impact absorbing can be low.In No.28, the amount of N is low, therefore impact absorbing can be low.On the other hand, in No.29, the amount of N
Height, therefore tensile strength and impact absorbing can be low.In No.30, the amount of B is low, therefore tensile strength and impact absorbing can be low.It is another
Aspect, in No.31, the amount of B is superfluous, therefore tensile strength and impact absorbing can be low.
In No.32, Ac1 is low, therefore impact absorbing can be low.In No.34 and 36, Ts is low, therefore impact absorbing can be low.
In No.33 and 35, Ts high, therefore tensile strength and impact absorbing can be low.In No.37 and 38, Ceq is low, thus tensile strength and
Impact absorbing can be low.In No.39, Ceq high, therefore tensile strength is excessively high, impact absorbing can be low.In No.40, Ac1 is low, therefore rushes
Hitting absorption can be low.In the No.40, steel uses low temperature in a manner of not being tempered in two phase region.
In No.41, x is low, therefore impact absorbing can be low.In No.42, x high, therefore impact absorbing can be low.In No.43, remove
Other than x, β is also low, therefore tensile strength and impact absorbing can be low.In No.44, other than x, β is also high, therefore impact absorbing
It can be low.
In No.45, temperature is less than 580 DEG C, therefore impact absorbing can be low.
It in No.46, is tempered at a temperature of more than Ac1 DEG C, therefore impact absorbing can be low.In No.47, start water
The temperature of surface of steel plate when cold is less than 580 DEG C, therefore impact absorbing can be low.
In No.48, the soaking temperature of strand is less than 1200 DEG C, therefore impact absorbing can be low.In No.49, plate thickness when quenching
The water cooling speed that the temperature of central part drops to the plate thickness central part during 500 DEG C from 800 DEG C is less than 0.4 DEG C/sec.Therefore, resist
Tensile strength and impact absorbing can be low.In No.50, the temperature of plate thickness central part drops to the plate during 300 DEG C from 500 DEG C after tempering
The water cooling speed of thick central part is less than 0.3 DEG C/sec.Therefore, impact absorbing can be low.
Industrial availability
According to the present invention, excellent in low temperature toughness is provided, plate thickness is more than the high-strength steel sheet of 200mm, so can more carry
The safety of high larger works.Therefore, the utilizability of the present invention industrially is big.
Claims (12)
1. a kind of steel plate, which is characterized in that have following chemical composition to contain based on quality %：
C：0.08%~0.15%,
Mn：0.80%~1.60%,
Ni：3.00%~4.50%,
Cr：0.50%~1.00%,
Mo：0.50%~1.00%,
Al：0.020%~0.085%,
N：0.0020%~0.0070%,
B：0.0005%~0.0020%,
P：0.000%~0.010%,
S：0.000%~0.003%,
Si：0.00%~0.30%,
Cu：0.00%~0.50%,
V：0.000%~0.050%,
Nb：0.000%~0.050%,
Ti：0.000%~0.020%,
Ca：0.0000%~0.0030%,
Mg：0.0000%~0.0030%,
REM：0.0000%~0.0030%,
Surplus includes Fe and impurity,
Plate thickness tmm be more than 200mm and for 300mm hereinafter,
In the chemical composition, the Ts defined by following formula 1 is 380~430, by the Ceq that following formula 2 defines be 0.80~
1.05, it is 580~647 by the Ac1 that following formula 3 defines, is 46~90 by the x that following formula 4 defines,
Based on area %, the total amount of martensite and bainite is 99%~100%,
Tensile strength is 780MPa~930MPa, and the absorption that plate thickness central part is obtained in -60 DEG C of Charpy-type test can be 69J
More than,
Ts=750-4240 × (t/2)-1.4× (80 × C+10 × Mn+7 × Ni+13 × Cr+13 × Mo-40 × Si) ... formulas 1
Ceq=C+Mn/6+ (Cu+Ni)/15+ (Cr+Mo+V)/5 ... formula 2
Ac1=720-25 × C+22 × Si-40 × Mn-30 × Ni+20 × Cr+25 × Mo ... formulas 3
X=C1/2×(1+0.64×Si)×(1+4.10×Mn)×(1+0.27×Cu)×(1+0.52×Ni)×(1+2.33×
Cr) × (1+3.14 × Mo) ... formula 4.
2. steel plate according to claim 1, which is characterized in that the chemical composition also meets：
Ti/N≤3.4。
3. steel plate according to claim 1 or 2, which is characterized in that the chemical composition also meets：
C：0.09%~0.13%.
4. according to any one of them steel plate of claims 1 to 3, which is characterized in that the chemical composition also meets：
Mn：0.80%~1.30%.
5. according to any one of them steel plate of Claims 1 to 4, which is characterized in that the chemical composition also meets：
Ni：3.60%~4.50%.
6. according to any one of them steel plate of Claims 1 to 5, which is characterized in that the chemical composition also meets：
Cr：0.75%~1.00%.
7. according to any one of them steel plate of claim 1~6, which is characterized in that the chemical composition also meets：
Mo：0.70%~1.00%.
8. according to any one of them steel plate of claim 1~7, which is characterized in that the chemical composition also meets：
Si：0.00%~0.10%.
9. according to any one of them steel plate of claim 1~8, which is characterized in that the chemical composition also meets：
V：0.020%~0.050%.
10. according to any one of them steel plate of claim 1~9, which is characterized in that the chemical composition also meets：
Ti：0.000%~0.004%.
11. according to any one of them steel plate of claim 1~10, which is characterized in that the chemical composition also meets following
Condition：
The Ts is 395~415.
12. according to any one of them steel plate of claim 1~11, which is characterized in that the chemical composition also meets following
Condition：
The Ceq is 0.85~1.05.
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| CN108603258B (en) | 2021-06-29 |
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