CN110100026A

CN110100026A - Thick steel plate and its manufacturing method with excellent low-temperature impact toughness and CTOD characteristic

Info

Publication number: CN110100026A
Application number: CN201780078777.1A
Authority: CN
Inventors: 金佑谦; 严庆根; 房基铉
Original assignee: Posco Co Ltd
Current assignee: Posco Holdings Inc
Priority date: 2016-12-23
Filing date: 2017-12-22
Publication date: 2019-08-06
Anticipated expiration: 2037-12-22
Also published as: KR20180074470A; EP3561115B1; CN110100026B; WO2018117727A1; EP3561115A1; JP6824415B2; EP3561115A4; KR101899694B1; JP2020509206A

Abstract

An aspect of of the present present invention is related to a kind of thick steel plate with excellent low-temperature impact toughness and CTOD characteristic, the thick steel plate includes in terms of weight %: 0.02% to 0.06% C, 0.005% to 0.08% Si, 1.0% to 2.0% Mn, 0.01% or less P, 0.003% or less S, 0.001% to 0.01% Al, 0.5% to 2.0% Ni, 0.001% to 0.02% Ti, 0.005% to 0.03% Nb, 0.05% to 0.4% Cu, 0.002% to 0.006% N, and the Fe and inevitable impurity of surplus, and meet following formula, wherein, thick steel plate has the ferrite of the amount comprising 95 area % or more, and summation is The microscopic structure of the MA and cementite of 2 area % or less amount: formula 1:3.0≤Mn+2Ni≤4.3 and formula 2:0.05≤C+Si+10Al≤0.25 (wherein, the symbol of element respectively indicates its content in terms of weight %).

Description

Thick steel plate and its manufacturing method with excellent low-temperature impact toughness and CTOD characteristic

Technical field

This disclosure relates to thick steel plate and its manufacturing method with excellent low-temperature impact toughness and CTOD characteristic, the thickness steel Plate can be preferably applied to offshore structure steel.

Background technique

The arctic have been considered to be store the area of future source of energy, and centered on the country of the neighbouring Arctic Circle into The exploitation gone to oil and natural gas resource.Due to the lack of energy of land, greater coasting area and blue water, will add Exploitation of the speed to the energy in Arctic.

Steel applied to the offshore structure equipment for digging up mine, drilling, being stored in the energy developed in the region of polar region can It can need that there is toughness at -60 DEG C or under lower low temperature, and may need special with the fatigue fracture indicated at -60 DEG C The CTOD value of property.In addition, the intensity and thickness of steel increase due to the increase of equipment size and the integration of equipment.

For resistance to brittle fracture, in general, there may be the resistance formed to brittle crack and to brittle crack extension Resistance.The formation of brittle crack can refer to: the fatigue crack growth started in defect part in the tissue to certain size it Afterwards, when applying higher external stress, brittle crack is generated by the fatigue crack grown.It can prevent brittle crack from being formed The resistance trait of material can be referred to as the resistance formed to brittle crack, and the resistance be using 7448 standard of BS or The CTOD (crack tip opening displacement, Crack Tip Opening Displacement) of defined in 1290 standard of ASTM Test method is tested.Therefore, it is excellent to may indicate that the resistance formed to brittle crack can be for excellent CTOD characteristic.

Numerous studies and exploitation have been carried out to ensure low-temperature impact toughness and CTOD characteristic.For example, bibliography 1 is public A kind of method for manufacturing steel plate is opened, this method is by including that the low operation of rolling (such as width widens rolling) of reduction ratio is rolled The reduction ratio of the certain level of final three passage is kept during steel plate processed to keep excellent CTOD characteristic.

However, bibliography 1 there are problems that being likely difficult to obtain enough low-temperature flexibilities and CTOD characteristic.

In addition, needing to develop can also be true even if under about -80 DEG C of extremely low temperature since use environment becomes harsh The technology of excellent impact flexibility is protected, and needs to develop thick steel plate and its manufacturer with excellent CTOD characteristic and intensity Method.

(prior art)

(bibliography 1) South Korea speciallys permit patent disclosure No.10-2010-0066757

Summary of the invention

Technical problem

The one side of the disclosure be to provide a kind of thick steel plate with excellent low-temperature impact toughness and CTOD characteristic and its Manufacturing method, the thick steel plate can be preferably applied to offshore structure steel.

However, the aspect of the disclosure is without being limited thereto.In terms of other will be set forth in part in the description which follows, and for For those of ordinary skill in the related art, other aspects be will be apparent from the description.

Technical solution

An aspect of of the present present invention is related to a kind of thick steel plate with excellent low-temperature impact toughness and CTOD characteristic, the thickness steel Plate includes in terms of weight %: 0.02% to 0.06% C, 0.005% to 0.08% Si, 1.0% to 2.0% Mn, 0.01% or less P, 0.003% or less S, 0.001% to 0.01% Al, 0.5% to 2.0% Ni, 0.001% To 0.02% Ti, 0.005% to 0.03% Nb, 0.05% to 0.4% Cu, 0.002% to 0.006% N, Yi Jiyu The Fe of amount and inevitable impurity, the thick steel plate meet the following Expression 1 and formula 2,

And microscopic structure include the ferrite of 95 area % or more and summation be 2 area % or less MA and Cementite.

A kind of thick steel plate for relating in one aspect to manufacture and there is excellent low-temperature impact toughness and CTOD characteristic of the disclosure Method, this method comprises: heating at 1020 DEG C to 1150 DEG C to slab, which includes in terms of weight %: 0.02% to 0.06% C, 0.005% to 0.08% Si, 1.0% to 2.0% Mn, 0.01% or less P, 0.003% or less S, 0.001% to 0.01% Al, 0.5% to 2.0% Ni, 0.001% to 0.02% Ti, 0.005% to 0.03% Nb, 0.05% to 0.4% Cu, 0.002% to 0.006% N and surplus Fe and inevitable impurity, and Meet the following Expression 1 and formula 2；

It is at 900 DEG C or higher to heated slab progress recrystallization zone rolling；

After recrystallization zone rolling by the final rolling temperature at Ar3 to 850 DEG C carry out the non-recrystallization zone operation of rolling come Obtain thick steel plate；

Thick steel plate is cooled to 250 DEG C or lower with 2 DEG C/sec to 15 DEG C/sec of cooling rate；

And it is tempered at 500 DEG C to 650 DEG C to through cooling thick steel plate.

Formula 1:3.0≤Mn+2Ni≤4.3

Formula 2:0.05≤C+Si+10Al≤0.25

(in formula 1 and formula 2, each element symbol indicates the content of each element in terms of weight %.)

Above-mentioned technical proposal does not list all features of the disclosure.It, will referring to specific embodiment described below Further understand the various feature and advantage and its effect of the disclosure.

Beneficial effect

According to the exemplary implementation scheme in the disclosure, the effect of the disclosure are as follows: for 50mm or bigger thickness Thick steel plate, it can be ensured that excellent yield strength；Even if being also ensured that excellent impact is tough under about -80 DEG C of extremely low temperature Property；And thick steel plate and its manufacturing method with impact flexibility and CTOD characteristic at -60 DEG C can be provided.

Detailed description of the invention

Fig. 1 is the image of the microscopic structure of example 1；And

Fig. 2 is to show the figure of the yield strength according to the CTOD value at Mn+2Ni value and -60 DEG C.

Specific embodiment

In the following description, the preferred embodiments of the invention will be described.However, it is possible to modify the disclosure in various ways Embodiment, and the embodiment that the scope of the present disclosure unlimited can be described further below.Furthermore it is possible to provide embodiment party Case is to be described in more detail below the disclosure to those of ordinary skill in the art.

Thick steel plate with excellent low-temperature flexibility and CTOD characteristic

Hereinafter, it will be described in the thick steel plate of the low-temperature impact toughness and CTOD characteristic that have excellent.

Thick steel plate with excellent low-temperature impact toughness and CTOD characteristic can include in terms of weight %: 0.02% to 0.06% C, 0.005% to 0.08% Si, 1.0% to 2.0% Mn, 0.01% or less P, 0.003% or less S, 0.001% to 0.01% Al, 0.5% to 2.0% Ni, 0.001% to 0.02% Ti, 0.005% to 0.03% Nb, 0.05% to 0.4% Cu, 0.002% to 0.006% N and surplus Fe and inevitable impurity, and It can satisfy the following Expression 1 and formula 2, and microscopic structure may include the ferrite of 95 area % or more and summation is 2 faces Product % or less MA and cementite.

Formula 1:3.0≤Mn+2Ni≤4.3

Formula 2:0.05≤C+Si+10Al≤0.25

It will be described in the composition of alloy of the disclosure.Unless otherwise stated, the content unit of each element can be with Weight % meter.

C:0.02% to 0.06%

C be can effectively solution strengthening element, and intensity can be improved by forming carbide with Nb etc..

When the content of C is lower than 0.02%, said effect may be insufficient.When the content of C is more than 0.06%, may promote The formation of MA, and it is likely to form pearlite, so that the impact and fatigue properties under low temperature may deteriorate.Therefore, C preferably contains Amount can be 0.02% to 0.06%.

The preferred lower limit content of C can be 0.025%, and the even more preferably lower limit content of C can be 0.03%.The preferred upper limit content of C can be 0.055%, and the even more preferably upper limit content of C can be 0.05%.

Si:0.005% to 0.08%

Si is can to assist Al's to make the element of deoxidation of molten steel, and can help improve yield strength and tension is strong Degree, but impact and fatigue properties under low temperature may be negatively affected.

When the content of Si is more than 0.08%, Si may interfere with the dispersion of C, allow to promote the formation of MA, this may Negatively affect the impact and fatigue properties under low temperature.In addition, in order to be 0.005% or less by the control of the content of Si, steel-making The processing time of process may greatly increase, and allow to reduce productivity.Therefore, the preferred content of Si can be 0.005% To 0.08%.

The preferred lower limit content of Si can be that the preferred upper limit content of 0.01%, Si can be 0.07%, and And the even more preferably upper limit content of Si can be 0.055%.

Mn:1.0% to 2.0%

Mn can have the effect of very big by solution strengthening in terms of improving intensity, therefore can add 1.0% or more More Mn.However, due to the formation of MnS field trash and the segregation of central part, toughness may be decreased when Mn content is excessive. Therefore, the preferred upper limit content of Mn can be 2.0%.

P:0.01% or less

P is the element that can cause cyrystal boundary segregation, it is thus possible to be the reason of weakening steel.Accordingly, it may be desirable to containing P Amount control is as low as possible, because P is one of impurity, and can be preferably 0.01% or less by the content control of P.It is real Can not control the content of P in matter is 0%, can not include 0% therefore.

S:0.003% or less

S can be can be by forming the factor of MnS field trash in conjunction with Mn, and MnS field trash can reduce low temperature Toughness.Accordingly, it may be desirable to by the control of the content of S be it is as low as possible because S is one of impurity.It can be preferably by the content of S Control is 0.003% or less, to ensure low-temperature flexibility and fatigue at low temperatures characteristic.The content of S can not substantially be controlled and be 0%, it can not include 0% therefore.

Al:0.001% to 0.01%

Al is the main deoxidier in the disclosure, and may need to add 0.001% or more Al.When the content of Al When more than 0.01%, Al may be due to Al₂O₃The score of field trash and the original for increasing but leading to low-temperature flexibility gradual change of size Cause.In addition, similar with Si, Al can promote to form MA phase in basis material and welding heat affected part, so that low-temperature flexibility It may be decreased with fatigue at low temperatures characteristic.Therefore, the preferred content of Al can be 0.001% to 0.01%.

Ni:0.5% to 2.0%

The increase of Ni content may not greatly improve intensity, but Ni can improve intensity and toughness simultaneously.

When the content of Ni is lower than 0.5%, said effect may be insufficient.When the content of Ni is more than 2.0%, Ni may be by In harden ability increase and promote the formation of MA so that impact and CTOD toughness may deteriorate.

Ti:0.001% to 0.02%

Ti be can form the element of precipitate and in conjunction with oxygen or nitrogen, therefore microstructure coarsening can be prevented, and It can contribute to refine and improve toughness.

When the content of Ti is lower than 0.001%, said effect may be insufficient.When the content of Ti is more than 0.02%, Ti can It can be due to thick precipitate becomes fracture.

Nb:0.005% to 0.03%

Nb is the element that can be prevented by the way that solute or carbonitride is precipitated in rolling or cooling period recrystallization, and Therefore with thinning microstructure and intensity can be improved.

When the content of Nb is lower than 0.005%, said effect may be insufficient.When the content of Nb is more than 0.03%, due to C Compatibility, it may occur however that C aggregation, this may promote the formation of MA phase and therefore may be decreased the toughness under low temperature and fracture spy Property.

Cu:0.05% to 0.4%

Cu is the element that may not greatly reduce impact characteristics, and can be improved by force by being dissolved and separating out Degree.

When the content of Cu is lower than 0.05%, said effect may be insufficient.When the content of Cu is more than 0.4%, Ke Nengcun There is the risk of surface of steel plate crackle because of Cu thermal shock.

N:0.002% to 0.006%

N is the member that can refine austenite structure during reheating and being formed together precipitate with Ti, Nb, Al etc. Element, therefore can help improve intensity and toughness.0.002% or more N can preferably be added.

When the content of N is more than 0.006%, face crack may be generated at high temperature, and after forming precipitate The remaining N of reservation may exist with state of atom and may be decreased toughness.Therefore, the preferred content of N can for 0.002% to 0.006%.

Remainder in addition to above-mentioned composition is Fe.However, may inevitably add in general manufacturing process Calais is from raw material or the inevitable impurity of ambient enviroment, it is thus possible to be not excluded for impurity.Those skilled in the art can be with Know impurity, therefore, does not provide the description to impurity in the disclosure.

The composition of alloy of the disclosure may need to meet above-mentioned constituent content, and can also meet the following Expression 1 and formula 2.

Formula 1:3.0≤Mn+2Ni≤4.3

Formula 2:0.05≤C+Si+10Al≤0.25

Formula 1 and formula 2 can ensure excellent low-temperature impact toughness and CTOD characteristic in the case where not reducing intensity, and It is contemplated that influencing MA prevents the correlation of effect and intensity to design.

In order to prevent MA according to formula 2, the content of C, Si and Al can control, and in order to compensate for containing by control each element The reduction of intensity caused by measuring, it may be necessary to which Mn and Ni are added according to formula 1.

When the value of formula 1 is lower than 3.0, the effect for improving intensity may be insufficient.When the value is more than 4.3, low-temperature impact is tough Property and CTOD characteristic may be decreased.

For the steelmaking process of deoxidation etc., the preferred value of formula 2 can be 0.05 or higher.When the value of formula 2 is low When 0.05, it may be difficult to ensure intensity.When the value is more than 0.25, it is possible to create a large amount of MA phase, so that low-temperature impact is tough Property and CTOD characteristic may be decreased.

The composition of alloy of the disclosure can also comprising in terms of weight % 0.001% to 0.05% Mo and 0.0002% to One of 0.005% Ca or more person.

Mo:0.001% to 0.05%

Mo is the element that intensity can be effectively improved by improving harden ability.For this purpose, the preferred content of Mo can be 0.001% or higher.When the content of Mo is more than 0.05%, toughness may due to harden ability increase and reduce, and toughness It may be reduced because forming the precipitate of molybdenum carbide.

Ca:0.0002% to 0.005%

When Ca during steelmaking process by Al deoxidation and when being added in molten steel, by the Ca of Al deoxidation can (S be main with S The presence in the form of MnS) it combines, allow to prevent that the formation of MnS, and spherical CaS can be formed, allowing to have prevents The cracked effect of the central part of steel.For this purpose, 0.0002% or more Ca can be added preferably.When the content of Ca When more than 0.005%, remaining Ca can be in conjunction with O, and can form thick oxide inclusion, this is due in the operation of rolling The elongation and fracture of period field trash and may be used as the crack initiation point under low temperature.

It will be described in the microscopic structure of the thick steel plate of the disclosure.

The microscopic structure of thick steel plate may include the ferrite of 95 area % or more and summation is 2 area % or more Few MA and cementite.

When ferrite is 95 area % or less, the CTOD characteristic at impact flexibility and -60 DEG C at -80 DEG C may drop It is low.

In order to ensure low-temperature impact toughness and CTOD characteristic, the tissue of basis material and the score of MA may be important. When C is when rolling and cooling period combine and assemble, harden ability can be can increase, and C can be transformed into high-hardenability Martensite can remain austenite, this can be referred to as martensite-austenite (MA).MA may be due to the spy of high rigidity Property and be easy to be broken, and may cause stress concentration when soft ferrite transformation around MA, and therefore can play disconnected Split the effect of germinating.

In addition, cementite can have the characteristic similar with the characteristic of MA, and can be with more needle-shaped than basis material The hard phase of the high harden ability of ferritic harden ability, and cementite may make low-temperature impact toughness and CTOD deterioration in characteristics.

It therefore, is 2 faces by the control of the summation of MA and cementite in order to ensure excellent low-temperature impact toughness and CTOD characteristic Product % may be less important.

Ferrite has 20 μm or smaller crystallite dimension by equivalent diameter measurement.When crystallite dimension is more than 20 μm When, the dislocation in ferrite can increase, and allow to be easy to happen propagation path, so that low-temperature impact toughness and CTOD characteristic It may deteriorate.Crystallite dimension is smaller, can be more it is advantageously ensured that low-temperature impact toughness and CTOD characteristic, therefore, ferritic lower limit Content can be not particularly limited.

Ferrite can also include polygonal ferrite and acicular ferrite, and polygonal ferrite and acicular ferrite Specific score can be unrestricted.

Thick steel plate can have 420MPa or higher yield strength, at -80 DEG C 200J or higher impact flexibility and The 0.5mm or higher CTOD at -60 DEG C.By ensuring these characteristics, thick steel plate can be suitably applied in extremely low temperature Spend offshore structure steel used in environment.It is highly preferred that the CTOD at -60 DEG C can be 1.0mm or higher.

Thick steel plate can have 500MPa or higher tensile strength, 25% or higher elongation percentage and at -60 DEG C 400J or higher impact flexibility.

Thickness steel plate can have the thickness of 50mm to 100mm.

Manufacture the method with the thick steel plate of excellent low-temperature impact toughness and CTOD characteristic

In the following description, the manufacture that will be described in another aspect of the present disclosure has excellent low-temperature impact toughness With the method for the thick steel plate of CTOD characteristic.

Manufacture have the thick steel plate of excellent low-temperature impact toughness and CTOD characteristic method may include: at 1020 DEG C extremely The slab comprising above-mentioned composition of alloy is heated at 1150 DEG C；Higher heated slab is tied at 900 DEG C or again Crystalline region rolling；After recrystallization zone rolling by the final rolling temperature at Ar3 to 850 DEG C carry out the non-recrystallization zone operation of rolling come Obtain thick steel plate；Thick steel plate is cooled to 250 DEG C or lower with 2 DEG C/sec to 15 DEG C/sec of cooling rate；And extremely at 500 DEG C It is tempered at 650 DEG C to through cooling thick steel plate.

Each process will be described in detail in the following description.

Heat slab

The slab for meeting above-mentioned composition of alloy can be heated at 1020 DEG C to 1150 DEG C.

When slab heating temperature is more than 1150 DEG C, austenite grain may be thicker, so that toughness may be decreased.Work as slab When heating temperature is lower than 1020 DEG C, possibly the solid solution such as enough Ti, Nb can not be obtained, so that intensity may be decreased.

Recrystallization zone rolling

It can be at 900 DEG C or higher to heated slab progress recrystallization zone rolling.It, can when temperature is lower than 900 DEG C It can be difficult to realize the abundant recrystallization of austenite.

Recrystallization zone rolling is the situation in each of reduction ratio of last two passage in 15% to 20% range Lower progress, this may insure uniform and fine final microscopic structure.

Non- recrystallization zone rolling

Recrystallization zone rolling after, can recrystallization zone rolling after by Ar3 to 850 DEG C final rolling temperature into The non-recrystallization zone rolling of row is to obtain thick steel plate.

When final rolling temperature is lower than Ar3, the temperature on the surface of thick steel plate can be the temperature of two phase region, and can be Two-phase structure is formed at thickness away from surface 1/4t, so that impact flexibility may deteriorate.It is brilliant when final rolling temperature is more than 850 DEG C Grain refinement is possible insufficient and intensity and toughness may deteriorate.

Can carry out non-recrystallization zone rolling to make thick steel plate with a thickness of 50mm to 100mm.

It is cooling

Thick steel plate can be cooled to 250 DEG C or lower with 2 DEG C/sec to 15 DEG C/sec of cooling rate.

When cooling rate is more than 15 DEG C/sec, due to the difference of the cooling rate between the surface and central part of thick steel plate It is different, it is thus possible to which that there are the differences of characteristic.When cooling rate is lower than 2 DEG C/sec, the distribution of acicular ferrite is likely to reduced, and And the distribution of polygonal ferrite can increase.

When cooling termination temperature is more than 250 DEG C, target strength may be not being met.

Tempering

It can be tempered at 500 DEG C to 650 DEG C to through cooling thick steel plate.Dislocation in MA phase and ferrite may It is the factor that possible greatly affect low-temperature impact toughness and CTOD characteristic.Therefore, it can be tempered to dissolve MA phase and subtract Dislocation in few ferrite.

When tempering temperature is lower than 500 DEG C, said effect may be insufficient.When temperature is more than 650 DEG C, it is possible to create carbonization Object, this may be decreased toughness.

Invention embodiment

In the following description, the exemplary implementation scheme of the disclosure will be described in further detail.Show it should be pointed out that providing Example property embodiment does not limit the interest field of the disclosure so that the disclosure is more fully described.It can be based on claim The theme of middle record and the item rationally inferred from subject matter determine the interest field of the disclosure.

(embodiment)

The molten steel with composition shown in the following table 1 is prepared, and manufactures slab using continuous metal cast process.In such as the following table 2 Slab is heated under manufacturing condition, recrystallization zone rolling, the rolling of non-recrystallization zone, cooling and tempering, and manufactures and provide There is the thick steel plate of the thickness of 80mm.In the case that recrystallization zone rolling is that each is 18% in the reduction ratio of final two passage It carries out.

Microstructure mechanical property, low-temperature impact toughness and the CTOD characteristic for measuring thick steel plate, are listed in the following table 3.

Microscopic structure is observed using scanning electron microscope (SEM) and transmission electron microscope (TEM), and analyzes MA and infiltration The summation (secondary phase) of carbon body is listed in table 3.Part other than secondary phase is ferrite, which includes polygon Ferrite and acicular ferrite.

For ferritic crystallite dimension, it is listed in Table 3 below by the average value that equivalent diameter measures.

Yield strength, tensile strength and elongation percentage are measured by tension test.

Low-temperature impact toughness is measured by Charpy (charpy) impact test at -80 DEG C and -60 DEG C.

For CTOD characteristic, sample and rolling direction are vertically processed into 60mm according to 7448 standard of BS × The size of 120mm × 300mm, insertion fatigue crack make fatigue crack length become the 50% of Sample Width, and at -60 DEG C Lower progress CTOD test.It carries out CTOD three times for each steel plate to test, and will be from testing three times in the test value obtained most Small value is listed in Table 3 below.

[table 1]

In upper table 1, the unit of each element content is weight %.The unit of P*, S* and N* are ppm.

Formula 1 is the value of Mn+2Ni, and formula 2 is the value of C+Si+10Al, and each element symbol indicates each member in terms of weight % The content of element.

[table 2]

[table 3]

Meet proposed in the disclosure overall alloy composition and manufacturing condition the embodiment of the present invention ensure 420MPa or Higher yield strength, 200J or higher impact flexibility and the 0.5mm or higher CTOD at -60 DEG C at -80 DEG C Value, is excellent this demonstrate low-temperature impact toughness and CTOD characteristic.

Fig. 1 is the image of the microscopic structure of example 1.A small amount of MA and cementite are formd, and crystallite dimension is also Tiny.

Comparative example 1 to 3 meets composition of alloy proposed in the disclosure, but is unsatisfactory for manufacturing condition.

For comparative example 1 and 2, in the impact flexibility at -80 DEG C and the CTOD deterioration in characteristics at -60 DEG C.For comparing Example 3, the impact flexibility at -80 DEG C reduces, and is difficult to ensure intensity.

Comparative example 4 to 7 meets the manufacturing condition proposed in the disclosure, but is unsatisfactory for composition of alloy.

For comparative example 4, the content range of C exceeds proposed range, and for comparative example 5, Mn+2Ni range exceeds institute The range of proposition so that although intensity be it is excellent, in the impact flexibility at -80 DEG C and the CTOD characteristic at -60 DEG C It greatly reduces.

For comparative example 6, Mn+2Ni range is less than proposed range, intensity and deteriorated impact toughness at -80 DEG C.

For comparative example 7, the range of C+Si+10Al is more than proposed range, impact flexibility at -80 DEG C and - CTOD characteristic at 60 DEG C greatly deteriorates.

Fig. 2 is to show the figure of the yield strength according to Mn+2Ni value and the CTOD value at -60 DEG C.As shown in Figure 2, In order to ensure 420MPa or higher yield strength and 0.5mm or higher CTOD value, it may be necessary to meet 3.0≤Mn+2Ni≤ 4.3.When Mn+2Ni value is lower than 3.0, strength reduction.When the value is more than 4.3, the CTOD value at -60 DEG C is greatly reduced.

Exemplary implementation scheme has shown and described although having been described above, the scope of the present disclosure is without being limited thereto, and And it will be obvious to a person skilled in the art that in the feelings for not departing from the scope of the present invention being defined by the following claims Remodeling and modification can be made under condition.

Claims

1. a kind of thick steel plate with excellent low-temperature impact toughness and CTOD characteristic, includes in terms of weight %:

0.02% to 0.06% C, 0.005% to 0.08% Si, 1.0% to 2.0% Mn, 0.01% or less P, 0.003% or less S, 0.001% to 0.01% Al, 0.5% to 2.0% Ni, 0.001% to 0.02% Ti, 0.005% to 0.03% Nb, 0.05% to 0.4% Cu, 0.002% to 0.006% N and surplus Fe and can not The impurity avoided,

Wherein the thick steel plate meets the following Expression 1 and formula 2,

Formula 1:3.0≤Mn+2Ni≤4.3

Formula 2:0.05≤C+Si+10Al≤0.25

Wherein each element symbol indicates the content of each element in terms of weight %；And

Wherein microscopic structure includes the ferrite of 95 area % or more and summation is 2 area % or less MA and carburizing Body.

2. thick steel plate according to claim 1,

Wherein the thick steel plate also includes 0.001% to 0.05% Mo and 0.0002% to 0.005% in terms of weight % One of Ca or more person.

3. thick steel plate according to claim 1,

Wherein ferrite has 20 μm or smaller crystallite dimension by equivalent diameter measurement.

4. thick steel plate according to claim 1,

Wherein ferrite includes polygonal ferrite and acicular ferrite.

5. thick steel plate according to claim 1,

Wherein the thick steel plate have 420MPa or higher yield strength, at -80 DEG C 200J or higher impact flexibility and The 0.5mm or higher CTOD at -60 DEG C.

6. thick steel plate according to claim 1,

Wherein the thick steel plate has 500MPa or higher tensile strength, 25% or higher elongation percentage and at -60 DEG C 400J or higher impact flexibility.

7. thick steel plate according to claim 1,

Wherein the thick steel plate has the thickness of 50mm to 100mm.

8. a kind of method that manufacture has the thick steel plate of excellent low-temperature impact toughness and CTOD characteristic, which comprises

Slab is heated at 1020 DEG C to 1150 DEG C, the slab includes in terms of weight %: 0.02% to 0.06% C, 0.005% to 0.08% Si, 1.0% to 2.0% Mn, 0.01% or less P, 0.003% or less S, 0.001% to 0.01% Al, 0.5% to 2.0% Ni, 0.001% to 0.02% Ti, 0.005% to 0.03% Nb, The Fe and inevitable impurity of 0.05% to 0.4% Cu, 0.002% to 0.006% N and surplus, and meet with Following formula 1 and formula 2,

Formula 1:3.0≤Mn+2Ni≤4.3

Formula 2:0.05≤C+Si+10Al≤0.25

Wherein, each element symbol indicates the content of each element in terms of weight %；

The thick steel plate is cooled to 250 DEG C or lower with 2 DEG C/sec to 15 DEG C/sec of cooling velocity；And

It is tempered at 500 DEG C to 650 DEG C to through cooling thick steel plate.

9. according to the method described in claim 8,

Wherein the slab includes in the Ca of 0.001% to 0.05% Mo and 0.0002% to 0.005% in terms of weight % One of or more person.

10. according to the method described in claim 8,

Wherein recrystallization zone rolling be in each of reduction ratio of last two passage in 15% to 20% range In the case of carry out.

11. according to the method described in claim 8, wherein carrying out the non-recrystallization zone rolls thickness to make the thick steel plate Degree is 50mm to 100mm.