CN109642285A - Thick steel plate and its manufacturing method - Google Patents

Abstract

A kind of thick steel plate, wherein, containing C:0.04~0.06 mass %, the mass of Si:0.35~0.45 %, the mass of Mn:1.49~1.59 %, P: it is higher than 0 mass % and below 0.01 mass %, S: it is higher than 0 mass % and below 0.002 mass %, the mass of Cu:0.23~0.33 %, the mass of Al:0.02~0.06 %, the mass of Ni:0.24~0.34 %, the mass of Nb:0.015~0.021 %, the mass of Ti:0.012~0.018 %, the mass of B:0.0007~0.0013 %, the mass of Ca:0.0010~0.0030 %, with the mass of N:0.0040~0.0060 %, surplus is made of iron and inevitable impurity , the first phase is contained in metal structure, with second phase as hard phase mutually harder than first, which is the phase being made of pearlite, and the hardness of second phase is 260HV or less.

Description

Thick steel plate and its manufacturing method

Technical field

The present invention relates to thick steel plate and its manufacturing methods.

Background technique

In the large structure of ship, building, bridge and building machinery etc., the enlargement of works is promoted, another party Face requires higher reliability for its structural elements from the magnitude of damage when occurring damaged.It follows that Steel plate for constituting works requires high-intensitive.On the other hand, as steel plate tends to be high-intensitive, as representated by uniform elongation Processability be in reduced tendency, it is desirable that a kind of steel plate for having both both sides.

Such as in patent document 1, a kind of technology was studied, by obtaining the fine metal group based on α phase It knits, then by seeking precipitation strength, to manufacture uniform elongation and the good steel of intensity.

As the method for obtaining above-mentioned metal structure, disclose, after steel disc is heated to transformation temperature~1050 DEG C Ac3, Carried out start temperature be 850 DEG C hereinafter, terminate temperature be 750 DEG C or more, accumulation reduction ratio be 50~95% hot rolling after, from 750 DEG C or less begin to cool the acceleration cooling that speed is 5~100 DEG C/s, stop at 600 DEG C or more.

A kind of technology is had studied in patent document 2, passes through the hard phase and retained austenite for obtaining having fine Metal structure is not accompanied by the deterioration of toughness and improves uniform elongation.

It as the method for obtaining above-mentioned metal structure, discloses, is heated to Ac3 transformation temperature or more and 1300 DEG C or less Temperature, at least carry out range more than 950 DEG C~Ar3 transformation temperature, accumulation reduction ratio is 30% or more containing austenite After hot rolling including the rolling of non-recrystallization domain, from temperature more than Ar3 transformation temperature, the acceleration for carrying out 3~100 DEG C/s is cooling, Until austenite divides rate to be 20~70% temperature, after accelerating cooling stop, being heated up, kept, cooling velocity is 0.5 DEG C/s The a combination of one or more of cooling below maintains the temperature of steel away between 10s~100s after accelerating cooling to stop Accelerating to be cooled down later within cooling stopping temperature ± 100 DEG C.

In patent document 3, a kind of technology is had studied, by meeting ferritic duty system shared in all tissues Number: be higher than 90%, average-ferrite partial size: 3~12 μm, maximum ferrite partial size: 40 μm hereinafter, and the second phase average equivalent Circular diameter: 0.8 μm hereinafter, and make tensile strength 490MPa or more, thus manufacture hit absorbability (i.e. uniform elongation) and The excellent steel of base metal tenacity.

It as the method for obtaining above-mentioned metal structure, discloses, makes 700~850 DEG C of finishing temperature, for 700 ~500 DEG C of temperature field is cooled down with 3 DEG C/s or more, is reheated with defined temperature, after reheating, for 600~500 DEG C Temperature field cooled down again with 2 DEG C/s.

[existing technical literature]

[patent document]

[patent document 1] Japanese Unexamined Patent Publication 2002-105534 bulletin

[patent document 2] Japanese Unexamined Patent Publication 2003-253331 bulletin

[patent document 3] Japanese Unexamined Patent Publication 2007-162101 bulletin

Patent document 1 and 2 accurately controls cooling velocity and utilizing acceleration cooling after rolling, to realize fine Tissue, but in actual manufacturing process, it is difficult to from first to last closely be managed long and big thick steel plate, according to steel The position of plate is different, and characteristic is likely to occur deviation, reduces productivity.

In addition, in the manufacturing method of patent document 3, in order to make the retained austenite for facilitating uniform elongation in room temperature Lower remaining needs to carry out above-mentioned reheating operation, this just has manufacturing process's number more, and productivity reduces such problems.

In patent document 1 to 3, such as it is above-mentioned, the viewpoint based on uniform elongation, intensity, toughness etc. and carried out various Research, but when concentrating particularly on uniform elongation, status is, from the viewpoint of productivity, it has to say also leave it is problematic.

Summary of the invention

Embodiments of the present invention are done in view of above-mentioned such situation, its main purpose is, providing a kind of uniform The excellent thick steel plate of elongation and its manufacturing method.

The thick steel plate of embodiments of the present invention, containing C:0.04~0.06 mass %, Si:0.35~0.45 mass %, Mass %, P of Mn:1.49~1.59: it is higher than 0 mass % and below 0.01 mass %, S: is higher than 0 mass % and in 0.002 matter Measure % or less, mass %, Al:0.02 of Cu:0.23~0.33~0.06 mass %, Ni:0.24~0.34 mass %, Nb:0.015 ~0.021 mass %, Ti:0.012~0.018 mass %, B:0.0007~0.0013 mass %, Ca:0.0010~0.0030 The quality mass % of % and N:0.0040~0.0060, surplus are made of iron and inevitable impurity, and metal structure contains first Mutually with second phase as hard phase mutually harder than first, which is the phase being made of pearlite, second phase it is hard It spends for 260HV (Vickers hardness) below.

The manufacturing method of the thick steel plate of embodiments of the present invention, comprises the following steps: will (a) have the chemical component The steel disc of composition is heated to 900~1250 DEG C of heating process；(b) after the process (a), with 680~800 DEG C of finish to gauge The process of temperature progress finish to gauge；(c) after the process (b), room temperature is cooled to meet the cooling velocity A of following (1) formulas Until process.

736.02×[C]+8.5×A+208.53≤260(1)

Here, [C] is the content (quality %) of C, A is the cooling velocity (DEG C/s) after finish to gauge.

Embodiment according to the present invention, it is possible to provide the excellent thick steel plate of uniform elongation and its manufacturing method.

Detailed description of the invention

Fig. 1 is the figure for indicating the relationship of the value on the left side of hardness and (1) formula of the second phase.

Fig. 2 is the figure for indicating uniform elongation with the relationship of the hardness of the second phase.

Specific embodiment

Present inventor has carried out sharp study in order to solve the above problems, as a result, it has been found that, by appropriately controlling thick steel The chemical component of plate forms, and containing the first phase and second phase as hard phase mutually harder than first in metal structure, makes this Hard phase is controlled for the phase that pearlite is constituted, in addition, again controlling the hardness of the second phase in 260HV hereinafter, then can Obtain the excellent thick steel plate of uniform elongation.

Still further, it was discovered that the cooling velocity after the content (quality %) of C and finish to gauge, and the second phase is formed by after rolling The correlation of hardness, and find to control the cooling velocity after the content and finish to gauge of C in a manner of meeting following (1) formulas and be cooled to Until room temperature, the hardness of the second phase just can be made to reach 260HV hereinafter, excellent uniform elongation can be obtained.

736.02×[C]+8.5×A+208.53≤260 (1)

Here, [C] is the content (quality %) of C, A is the cooling velocity (DEG C/s) after finish to gauge.

Hereinafter, the thick steel plate and its manufacturing method for embodiments of the present invention are illustrated in detail.

1. thick steel plate > of <

[1-1. metal structure]

The thick steel plate (hereinafter referred to as " steel ") of embodiments of the present invention, as metal structure, containing the first phase and than the Hard the second phase (hereinafter referred to as " the second phase ", " hard second phase ") as hard phase of one phase.By by hard second phase Hardness control is in 260HV hereinafter, desired uniform elongation can be obtained.

In the thick steel plate that plate thickness is t, for example, second of the position away from surface of steel plate t/4 can be controlled in a manner described The hardness of phase.

Hereinafter, each composition is described in detail.

(hard second phase)

In the thick steel plate of embodiments of the present invention, the hard phase as hard second phase is made of pearlite.In addition, In the thick steel plate of embodiments of the present invention, there is the case where containing martensite as the third phase other than the first phase and the second phase, but Without bainite.From the viewpoint of obtaining high uniform elongation, the area ratio of hard second phase is preferably 10% hereinafter, more excellent It is selected as 5% or less.

(hardness of the second phase: 260HV or less)

If second is mutually really up to the mark, become highly brittle phase, toughness reduces, in addition, uniform elongation is insufficient, it is therefore desirable to Make the hardness 260HV of the second phase hereinafter, preferably 255HV is hereinafter, more preferably 250HV or less.

First phase of the thick steel plate of embodiments of the present invention is not particularly limited, such as can enumerate and be made of ferrite Soft phase.When first phase is made of ferrite, if ferritic average grain diameter is excessive, toughness deterioration, and uniform elongation It is insufficient, therefore preferably make 30 μm of ferritic average grain diameter or less.On the other hand, if ferritic average grain diameter is too small, Then the restriction of manufacturing condition becomes larger, therefore preferably make 5 μm of ferritic average grain diameter or more.Ferritic average grain diameter, example Such as, scanning electron microscope (Scanning Electron Microscope:SEM) shooting metal structure can be used, pass through Segment method measurement.

The plate thickness of the thick steel plate of embodiments of the present invention is not particularly limited, but preferably 10mm or more and 50mm with Under.

[1-2. chemical component composition]

In the thick steel plate of embodiments of the present invention, containing C:0.04~0.06 mass %, Si:0.35~0.45 matter Measure mass %, P of %, Mn:1.49~1.59: being higher than 0 mass % and below 0.01 mass %, S: be higher than 0 mass % and 0.002 mass % or less, mass %, Al:0.02 of Cu:0.23~0.33~0.06 mass %, Ni:0.24~0.34 mass %, Mass %, Ti:0.012 of Nb:0.015~0.021~0.018 mass %, B:0.0007~0.0013 mass %, Ca:0.0010 ~0.0030 mass mass % of % and N:0.0040~0.0060, surplus are made of iron and inevitable impurity.

By controlling chemical component composition in the above described manner, the excellent thick steel plate of uniform elongation can be obtained.

Hereinafter, each element is described in detail.

(the mass % of C:0.04~0.06)

C has the effect of improving the intensity of steel plate, but is also to increase hard phase, makes the element of ductility deterioration.If C contains Amount is lower than 0.04 mass %, then will be difficult to ensure the intensity of needs.

Therefore C content is 0.04 mass % or more.C content is preferably 0.042 mass % or more, more preferably 0.045 matter Measure % or more.On the other hand, if C content is higher than 0.06 mass %, intensity it is easy to ensure that, but increase hard phase, bring and prolong The deterioration of malleability.Therefore C content is 0.06 mass % or less.C content is preferably 0.058 mass % hereinafter, more preferably 0.055 Quality % or less.

(the mass % of Si:0.35~0.45)

Si so as to efficiently use solution strengthening obtains that elongation will not be caused obstruction by the inhibition being precipitated First phase is for ensuring that element required for high intensity.In order to effectively play this effect, Si amount needs for 0.35 matter Measure % or more.Si amount is preferably 0.36 mass % or more, more preferably 0.37 mass % or more.But if Si amount becomes superfluous, Then martensite-austenite mixed phase is easy to generate, and it is therefore possible to reduce other characteristics such as toughness.Therefore, Si amount needs For 0.45 mass % or less.Si amount is preferably 0.44 mass % hereinafter, more preferably 0.43 mass % or less.

(the mass % of Cu:0.23~0.33)

Cu, in order to effectively play this effect, is needed for ensuring element required for intensity by solution strengthening Cu amount is 0.23 mass % or more.Cu amount is preferably 0.24 mass % or more, more preferably 0.25 mass % or more.But if Cu amount is superfluous, then being not only due to be precipitated causes ductility reduction, and hardenability becomes superfluous, and when hot-working is easy to happen crackle Deng, therefore Cu amount needs for 0.33 mass % or less.Cu amount be preferably 0.32 mass % hereinafter, more preferably 0.31 mass % with Under.

(the mass % of Mn:1.49~1.59)

Mn improves hardenability, is effective element on ensuring intensity and toughness.In order to play such effect, need Mn is set to contain 1.49 mass % or more.Mn content is preferably 1.50 mass % or more, more preferably 1.51 mass % or more.But It is that if containing Mn excessively, weldability etc. is deteriorated, therefore makes 1.59 mass % of the upper limit.Mn content is preferably 1.58 mass % are hereinafter, more preferably 1.57 mass % or less.

(mass of Al:0.02~0.06 % or less)

Al is element required for deoxidation, and the N in fixed steel, and also having prevents solid solution N from base metal tenacity being caused to deteriorate Effect.In order to play such effect, need that Al is made to contain 0.02 mass % or more.Al content be preferably 0.025 mass % with On, more preferably 0.030 mass % or more.On the other hand, if Al is excessively included the coarse folder for forming alumina series Sundries, base metal tenacity reduce, therefore Al content needs below 0.06 mass %.Al content be preferably 0.055 mass % hereinafter, More preferably 0.050 mass % or less.

(the mass % of Ni:0.24~0.34)

Ni improves hardenability, has the effect of keeping tissue fine, while there is inhibition to be easy to produce because adding Cu The effect of crackle when hot-working.In order to play such effect, need that Ni amount is made to contain 0.24 mass % or more.Ni content is excellent It is selected as 0.25 mass % or more, more preferably 0.26 mass % or more.But if containing Ni excessively, hardenability becomes Surplus cannot get desired uniform elongation.Therefore, Ni amount needs for 0.34 mass % or less.Ni content is preferably 0.33 matter % is measured hereinafter, more preferably 0.32 mass % or less.

(the mass % of Nb:0.015~0.021)

Nb forms carbide, carbonitride, is effective element for making intensity raising.Such effect in order to obtain, It needs that Nb is made to contain 0.015 mass % or more.Nb content is preferably 0.016 mass % or more, more preferably 0.017 mass % with On.On the other hand, if Nb includes by surplus, the carbide and carbonitride being precipitated become excessively, and precipitation strength ability is superfluous, Yield tensile ratio is brought to increase.Therefore Nb content needs for 0.021 mass % or less.Nb content is preferably 0.020 mass % hereinafter, more Preferably 0.019 mass % or less.

(the mass % of Ti:0.012~0.018)

Ti forms TiN in conjunction with N, and austenite grain when heating before preventing hot rolling, the i.e. coarsening of γ crystal grain are Facilitate the element of base metal tenacity raising.In addition, also have the N in fixed steel, the effect for preventing solid solution N from base metal tenacity being caused to deteriorate Fruit.In order to play these effects, need that Ti is made to contain 0.012 mass % or more.Ti content is preferably 0.013 mass % or more, More preferably 0.014 mass % or more.On the other hand, if Ti content becomes superfluous, TiN coarsening, base metal tenacity deterioration, because This is needed for 0.018 mass % or less.Ti content is preferably 0.017 mass % hereinafter, more preferably 0.016 mass % or less.

(the mass % of B:0.0007~0.0013)

B is easy to inhibit the generation of coarse ferritic structure.In order to play such effect, need that B is made to contain 0.0007 Quality % or more.B content is preferably 0.0008 mass % or more, more preferably 0.0009 mass % or more.But if B quantitative change Must be superfluous, then hardenability becomes superfluous, cannot get desired uniform elongation, it is therefore desirable to be 0.0013 mass % or less.B contains Amount is preferably 0.0012 mass % hereinafter, more preferably 0.0011 mass % or less.

(the mass % of Ca:0.0010%~0.0030)

Ca facilitates the nodularization of MnS, and the ductility for improving base metal tenacity and plate thickness direction is effective element.In order to Such effect is played, 0.0010 mass % of Ca content or more is preferably made.Ca content is preferably 0.0012 mass % or more, more Preferably 0.0015 mass % or more.But if Ca content is higher than 0.0030 mass % and becomes superfluous, field trash is coarse Change, base metal tenacity deterioration.Therefore Ca content is 0.0030 mass % or less.Ca content is preferably 0.0028 mass % hereinafter, more Preferably 0.0025 mass % or less.

(the mass % of N:0.0040~0.0060)

N generates TiN, AlN, tough for making base material when heating before preventing hot rolling and the coarsening of γ crystal grain when welding Toughness (the hereinafter referred to as HAZ toughness of property and welding heat affected zone (Heat Affected Zone:HAZ).) improve be effective Element.If the content of N is lower than the deficiencies of 0.0040 mass %, above-mentioned TiN, above-mentioned γ crystal grain is become thick, and base metal tenacity is bad Change.Therefore N content needs for 0.0040 mass % or more.N content is preferably 0.0042 mass % or more, and more preferably 0.0044 Quality % or more.On the other hand, if N content is higher than 0.0060 mass % and becomes superfluous, due to being dissolved the increase of N, to mother Material toughness HAZ toughness adversely affects.Therefore, N content is 0.0060 mass % or less.N content is preferably 0.0058 matter % is measured hereinafter, more preferably 0.0056 mass % or less.

(P: being higher than 0 mass % and below 0.010 mass %)

P is the inevitable impurity adversely affected to the toughness of base material and weld part.It needs this not incur The mode of problem inhibits its content below 0.010 mass %.P content is preferably 0.009 mass % hereinafter, more preferably 0.008 mass % or less.It has any problem in addition, industrially reaching 0%, lower limit is 0.002 mass % or so.

(S: being higher than 0 mass % and below 0.002 mass %)

S is the inevitable impurity adversely affected to the ductility in the plate thickness direction of toughness and steel plate, preferably few Aspect.From this viewpoint, S content needs to inhibit below 0.002 mass %.S content is more preferably 0.001 mass % Hereinafter, further preferably 0.0005 mass % or less.

The basis of the thick steel plate of embodiments of the present invention is for example above-mentioned, and surplus is substantially iron.

But allow to be mixed into because of the situation of raw material, material or manufacturing equipment etc. certainly inevitable other than P and S Impurity is included in steel.

In addition, inevitably in impurity, as due to waste material etc. use or it is other will thus it is mixed other Impurity can also contain Cr, Mo and/or V.

If containing Cr excessively, hardenability becomes superfluous, cannot get desired uniform elongation.Therefore, as miscellaneous Matter and contain Cr when, Cr content is preferably 0.1 mass % or less.Cr content is more preferably 0.09 mass hereinafter, further preferably For 0.08 mass % or less.

It is anti-weld crack deterioration as a result if Mo is excessively become superfluous comprising, hardenability, therefore conduct Impurity and contain Mo when, Mo content is preferably 0.05 mass % or less.Mo content is more preferably 0.04 mass hereinafter, further excellent It is selected as 0.03 mass % or less.

If V is excessively included that the carbide being precipitated or carbonitride are excessive, precipitation strength ability is superfluous, brings in the wrong Strong ratio increases.Therefore, as impurity when containing V, V content is preferably 0.005 mass % or less.V content is more preferably 0.003 Quality % is hereinafter, further preferably 0.001 mass % or less.

Thick steel plate with the embodiments of the present invention constituted in this way, uniform elongation is excellent, can be used as ship, The structure material of building, bridge, building machinery etc. it is preferable to use.

The manufacturing method > of 2. thick steel plate of <

In order to manufacture the thick steel plate of embodiments of the present invention, the steel disc formed containing above-mentioned chemical component, example are used Such as use slab, the appropriate heating temperature for adjusting steel disc, finishing temperature and cooling velocity thereafter.

Specifically, comprise the following steps: (a) steel disc that will be formed with the chemical component is heated to 900~1250 DEG C heating process；(b) after the process (a), with the process of 680~800 DEG C of finishing temperature progress finish to gauge；(c) exist After the process (b), the cooling velocity A to meet following (1) formulas be cooled to room temperature until process.

736.02×[C]+8.5×A+208.53≤260(1)

Here, [C] is the content (quality %) of C, A is the cooling velocity (DEG C/s) after finish to gauge.

Hereinafter, being described in detail for each process.In addition, " temperature " specified in this specification, is the temperature of material.

[steel disc formed with the chemical component is heated to 900~1250 DEG C of heating process by (a)]

By the steel disc with above-mentioned chemical component composition, such as slab, being heated to can be with 900~1250 DEG C of hot rolling. Heating temperature is preferably 1000 DEG C or more, more preferably 1050 DEG C or more, preferably 1200 DEG C hereinafter, more preferably 1150 DEG C with Under.

[(b) after the process (a), process that finish to gauge is carried out with 680~800 DEG C of finishing temperature]

It is in order to ensure intensity and elongation, finishing temperature control is whole in 680~800 DEG C of progress after the process (a) It rolls.Finishing temperature is preferably 690 DEG C or more, more preferably 700 DEG C or more, preferably 790 DEG C hereinafter, more preferably 780 DEG C with Under.

[(c) after the process (b), process] until the cooling velocity A of satisfaction (1) formula is cooled to room temperature

After the process (b), until the cooling velocity A to meet following (1) formulas is cooled to room temperature.

736.02×[C]+8.5×A+208.53≤260(1)

Here, [C] is the content (quality %) of C, A is the cooling velocity (DEG C/s) after finish to gauge.

Hereinafter, the meaning of the technology of above-mentioned (1) formula of explanation.

Fig. 1 is the figure for indicating the relationship of the value on the left side of hardness and above-mentioned (1) formula of the second phase.In addition, Fig. 2 is to indicate The figure of the relationship of the hardness and uniform elongation of two-phase.

In Fig. 1 and 2, plotting represented by " " indicates the sheet manufactured to meet the cooling of the cooling velocity of above-mentioned (1) formula The thick steel plate of the embodiment example of invention.On the other hand, the plotting indicated by "○" is indicated to meet the cooling speed of above-mentioned (1) formula Spend the thick steel plate of the comparative example of manufacture.

As shown in Figure 1, the hardness of the second phase becomes larger if the value on the left side of above-mentioned (1) formula becomes larger.In addition, such as Fig. 2 institute Show, if the hardness of the second phase becomes larger, uniform elongation becomes smaller.By the result of Fig. 1 and 2 it is found that by controlling above-mentioned (1) formula The value on the left side, that is, by control thick steel plate in C content and finish to gauge after cooling velocity, can control uniform elongation and Both hardness of hard second phase.

The inventors have found that implementing the process (a) for the steel disc with defined chemical component composition in the application (b), according to the content [C] of the C in steel disc, cooling velocity A after controlling finish to gauge in a manner of meeting above-mentioned (1) formula, thus The hardness of the second phase can be made to be in 260HV hereinafter, 17.5% or more excellent uniform elongation can be reached, thus at this Above-mentioned (1) formula is provided in application.

From the viewpoint of obtaining the excellent thick steel plate of uniform elongation, the value on the left side of above-mentioned (1) formula be preferably 200 with On, more preferably 210 or more, preferably 255 hereinafter, more preferably 250 or less.

Accumulation reduction ratio in whole hot-rolled process is preferably 60% or more.More preferably 65% or more.In order to make meticulously Make α crystal grain, needs to apply adequately pressure in non-recrystallization temperature domain.The drafts in non-recrystallization temperature domain be preferably 20% with On, more preferably 25% or more, further preferably 30% or more.

The manufacturing method of the thick steel plate of embodiments of the present invention as described above, but understand embodiments of the present invention Those skilled in the art of desired characteristic of thick steel plate carry out trial and error method, there is the uncommon of embodiments of the present invention in manufacture In the method for the thick steel plate of the characteristic of prestige, it is also possible to find the method other than above-mentioned manufacturing method.

[embodiment]

Hereinafter, enumerating embodiment further illustrates embodiments of the present invention, but the present invention is not certainly by following implementations Example limitation, in the range that can meet aforementioned or aftermentioned objective, naturally it is also possible to suitably be changed implementation, these include Within the technical scope of the present invention.

Common smelting process is followed, after the steel disc of the chemical component composition of steel grade A~X shown in melting and casting table 1, with table Manufacturing condition shown in 2 carries out heating, finish to gauge and the cooling of steel disc, manufactures the thickness of test No.1~24 with a thickness of 12~50mm Steel plate.

In table 1 and 2, means and be detached from except the regulation of embodiments of the present invention with underscore.

[table 2]

The observation of metal structure is carried out in accordance with main points below for each thick steel plate, carry out ferritic average grain diameter, The survey of the hardness and tensile property (uniform elongation (Uniform elongation): U.E1, tensile strength: TS) of second phase Amount.

[observations of 1. metal structures]

The observation of metal structure is carried out by following step.

(1) be able to observe that it is parallel with rolling direction and relative to surface of steel plate it is vertical, containing surface of steel plate and the back side The mode in plate thickness section inside, extracts sample from above-mentioned steel plate.

(2) as the grinding with wet type diamond dust pouncing paper (#150~#1000), or there is the grinding of same function therewith, Such as the grinding etc. of the grinding agent by using diamond paste etc., carry out the mirror finish of viewing surface.

(3) for the sample by grinding, corroded with 3% nitric acid ethyl alcohol etchant solution, show crystal grain boundary.

(4) at the position plate thickness t/4, the tissue shown is observed with 400 times of multiplying power using optical microscopy, tissue has When ferrite, it will be used as hard second phase other than ferrite, ferrite is as the first phase.That is, hard second phase is mutually harder than first. When organizing no ferrite, but having bainite and martensite, using bainite as the first phase, the martensite harder than bainite is made For the second phase.

[2. ferritic average grain diameter]

It is aobvious with optics at the position plate thickness t/4 for the said sample corroded with 3% nitric acid ethyl alcohol etchant solution Micro mirror observes the first phase with 100 times of multiplying power, shoots the photo in 10 visuals field.According to the microscope photo, with comparison method (JIS G0551 ferritic partial size) is acquired, using its average value as ferritic average grain diameter.

[measurement method of the hardness of 3. second phases]

For the said sample corroded with 3% nitric acid ethyl alcohol etchant solution, at the position of plate thickness t/4, using aobvious Micro- Vickers is with the measurement load measurement of the 0.05N hardness of the second phase.Hardness is measured more than at the second phase is with 10, it will Hardness of its average value as the second phase.In addition, the hardness of the phase is made when tissue only has martensite, as martensite single phase Hardness for the second phase measures.

[4. tension test]

The longitudinally of test film and rolling direction is set to extract overall thickness plate test film (No. 5) at right angle, by JIS The main points of Z2241:2015 carry out tension test, measure tensile strength (TS) and uniform elongation (U.E1).

The thick steel plate that U.E1 is 17.5% or more is determined as level that can be practical.

Metal structure, ferritic average grain diameter, the hardness of the second phase and tensile property (uniform elongation: U.E1, tension Intensity: TS) it is shown in table 3.In table 3, means and be detached from except the regulation of embodiments of the present invention with underscore.

[table 3]

By table 3 as a result, it is possible to be investigated as follows.Testing No.1~4 and 19~24 is to meet implementation of the invention The example of whole important documents of mode defined, uniform elongation are excellent.

On the other hand, test No.5~18 are the examples for being unsatisfactory for any important document of embodiments of the present invention defined.

Test No.5 be had not been met using the steel grade E of Si, Cu and Ni surplus (1) formula fast cooling velocity progress it is cold But the example of the thick steel plate manufactured, due to Cu surplus, ductility reduction, in addition, the hardness of the second phase is higher than 260HV, it can not Reach desired uniform elongation.

Test No.6 and 7 is the steel grade F and G using C surplus respectively, with the temperature higher than finishing temperature specified in the application Degree carries out finish to gauge, the example of the thick steel plate also manufactured to be unsatisfactory for the fast cooling velocity cooling of (1) formula, the hardness of the second phase Higher than 260HV, desired uniform elongation can not be reached.

Test No.8~11 are the example to be unsatisfactory for the thick steel plate of the fast cooling velocity cooling of (1) formula and manufacture respectively Son can not reach desired uniform elongation.

No.12 and 13 is tested, is that finish to gauge is carried out with the temperature higher than finishing temperature specified in the application, also to be unsatisfactory for (1) the fast cooling velocity of formula is cooling and the example of thick steel plate that manufactures, the hardness of the second phase are higher than as defined in the application 260HV can not reach desired uniform elongation.

Test No.14 is cooled down using the steel grade N of Si, Cu and Ni surplus, and to be unsatisfactory for the fast cooling velocity of (1) formula And the example of the thick steel plate manufactured, the hardness of the second phase are higher than 260HV as defined in the application, can not reach desired even elongation Rate.

Testing No.15~18 is using steel grade O~R of C surplus, with the temperature higher than finishing temperature as defined in the application respectively Degree carries out finish to gauge, the example of the thick steel plate also manufactured to be unsatisfactory for the fast cooling velocity cooling of (1) formula, the hardness of the second phase Higher than 260HV, desired uniform elongation can not be reached.

The application with the applying date be the Japanese Patent Application on the 29th of August in 2016, Patent 2016-166817 Number, it is 2017 that the applying date, which is the Japanese Patent Application on May 30th, 2017, Patent the 2017-106674th and the applying date, The claim of priority applied based on Japanese Patent Application, the Patent No. 2017-122479th number on June 22, in.Patent No. 2016-166817, Patent the 2017-106674th and Patent the 2017-122479th are incorporated into this explanation as reference Book.

Claims (2)

1. a kind of thick steel plate, contains

The mass of C:0.04~0.06 %,

The mass of Si:0.35~0.45 %,

The mass of Mn:1.49~1.59 %,

P: be higher than 0 mass % and below 0.01 mass %,

S: be higher than 0 mass % and below 0.002 mass %,

The mass of Cu:0.23~0.33 %,

The mass of Al:0.02~0.06 %,

The mass of Ni:0.24~0.34 %,

The mass of Nb:0.015~0.021 %,

The mass of Ti:0.012~0.018 %,

The mass of B:0.0007~0.0013 %,

The mass of Ca:0.0010~0.0030 % and

The mass % of N:0.0040~0.0060,

Surplus is made of iron and inevitable impurity,

Metal structure contains the first phase and second phase as hard phase mutually harder than first, which be made of pearlite Phase,

The hardness of second phase is 260HV or less.

2. a kind of manufacturing method of thick steel plate, is the manufacturing method of thick steel plate described in claim 1, comprises the following steps:

(a) steel disc that will be formed with the chemical component is heated to 900~1250 DEG C of heating process；

(b) after the process (a), with the process of 680~800 DEG C of finishing temperature progress finish to gauge；With

(c) after the process (b), the cooling velocity A to meet following (1) formulas be cooled to room temperature until process,

736.02×[C]+8.5×A+208.53≤260 (1)

Here, [C] is content of the C in terms of quality %；A is the cooling velocity after finish to gauge, and unit is DEG C/s.