CN102666884B

CN102666884B - Production method for thick steel plate

Info

Publication number: CN102666884B
Application number: CN201180004575.5A
Authority: CN
Inventors: 中岛清孝; 星野学
Original assignee: Nippon Steel Corp
Current assignee: Nippon Steel Corp
Priority date: 2010-02-08
Filing date: 2011-01-27
Publication date: 2013-07-31
Anticipated expiration: 2031-01-27
Also published as: CN102666884A; WO2011096456A1; JPWO2011096456A1; JP4874435B2; BR112012019769B1; BR112012019769A2

Abstract

Disclosed is a thick steel plate production method wherein: a steel piece having a specified component composition is heated to 1000-1200 DEG C; then, with the plate-thickness centre temperature at 950-1200 DEG C, initial rolling is carried out for 4-16 passes at a cumulative rolling reduction rate of 50-95%; next, with the plate-thickness centre temperature at 850-950 DEG C, latter rolling is carried out for 2-8 passes with each pass being at a rolling reduction rate of 10-25% and pass time being 3-25 seconds; then, accelerated cooling is carried out wherein the plate-thickness centre temperature is cooled from 750 DEG C or above to 650 DEG C or lower at a cooling speed of 1-50 DEG C/s. The thick steel plate produced is characterised by having a plate thickness of 10-40mm and yield stress of 315-550 MPa, having a microstructure which is a mixed structure of ferrite and bainite, or, ferrite, perlite and bainite, and having an average crystal particle diameter of 5-20 [mu]m.

Description

The manufacture method of Plate Steel

Technical field

The present invention relates to the manufacture method of Plate Steel, relate in particular to the manufacture method of the welded construction of Rolling Production rate high and low temperature tenacity excellent with Plate Steel.

Background technology

The Plate Steel that uses in welded structures such as shipbuilding, building, oil tank, marine structure, line pipe is in order to suppress the brittle rupture of works, require low-temperature flexibility, particularly use yielding stress to increase gradually as the situation of the Plate Steel of 10mm～40mm as 315MPa～550MPa, thickness of slab.

Generally speaking, in rolling process,, crystal grain is attenuated, improve low-temperature flexibility thus by implementing rollingly being called as under about 750～850 ℃ the low temperature of γ non-recrystallization temperature province.

In the past, the method about the low-temperature flexibility that makes Plate Steel improves had proposed various schemes, and patent documentation 1～5 disclosed technology is for example arranged.

Having put down in writing thickness of slab in patent documentation 1 is the steel plate of the crack arrest excellence of the brittlement crevasse crack more than the 40mm.

The steel plate and the manufacture method thereof of the excellent in workability of having stipulated the Vickers' hardness in the steel plate in patent documentation 2, have been put down in writing.

In patent documentation 3, put down in writing the manufacture method of the uneven few steel of following material, its with final the 5th passage in the finish rolling finish time between passage till the beginning to final the 4th passage be made as more than 30 seconds, will be before final the 4th passage between each passage till the final passage time be made as below 15 seconds.

Put down in writing following method in patent documentation 4: the mode with the relation of the rolling temperature that satisfies regulation and draft in each rolling pass is set rolling condition, enjoy the miniaturization and the rolling effect of non-recrystallization of recrystallize γ crystal grain to greatest extent, make and finally organize miniaturization, have excellent intensity/flexible steel plate thereby make.

In patent documentation 5, put down in writing following method: use 2 roller mills, by between passage be 5 seconds with the interior tandem rolling that carries out, promote the accumulation draft in the non-recrystallization zone to be made as more than 70% recrystallize, make the steel plate of intensity, tenacity excellent thus.

The prior art document

Patent documentation

Patent documentation 1 TOHKEMY 2007-302993 communique

Patent documentation 2 TOHKEMY 2006-193816 communiques

Patent documentation 3 TOHKEMY 2002-249822 communiques

Patent documentation 4 TOHKEMY 2004-269924 communiques

Patent documentation 5 Japanese kokai publication hei 11-181519 communiques

Summary of the invention

Invent problem to be solved

But, have the following problems point in the above-mentioned patent documentation 1～5.

The manufacture method of record must be the low temperature rolling (CR) at the thick position of thickness of slab in the patent documentation 1.If implement low temperature rolling, crystal grain is attenuated, low-temperature flexibility improves.But, if carry out low temperature rolling, then after high temperature rolling finishes, produce the time that waiting temperature reduces, therefore, the Rolling Production rate reduces.

The manufacture method of record must be low temperature rolling in the patent documentation 2, and therefore, productivity is low.And then, be that yielding stress is the high-strength steel more than the 600MPa as the steel plate of object, be that 315MPa～550MPa, thickness of slab are the Plate Steel of 10mm～40mm for the yielding stress as object of the present invention, because therefore the microstructure difference can't be used.

As the manufacture method of record in the patent documentation 3, if the time between passage was made as more than 30 seconds, then according to the present invention people's result of study as can be known, thickization of recrystallize γ.

The manufacture method of record is owing to manage rolling temperature by surface temperature in the patent documentation 4, and therefore not only material is uneven big, and owing to do not stipulate time till the recrystallize, therefore, is difficult to obtain the miniaturization of recrystallize γ crystal grain.

In patent documentation 5, use the restriction of tandem rolling on equipment of 2 roller mills big, impracticable the manufacture method of record.

Therefore, problem of the present invention provide can improve prior art because of need the low of productivity that low temperature rolling causes so that can be applied to yielding stress be 315MPa～550MPa, thickness of slab be 10mm～40mm Plate Steel, do not need special equipment, the material inequality is little, low-temperature flexibility is excellent welded construction manufacture method with Plate Steel.Particularly, even not carry out low temperature rolling, only also can will organize the manufacture method of Plate Steel of miniaturization as problem by high temperature rolling.

Be used to solve the means of problem

People of the present invention further investigate the manufacture method of Plate Steel.Consequently, even found by under about 850～950 ℃ the high temperature that is called as γ recrystallization temperature zone rolling, also can utilize miniaturization that the recrystallize by γ brings, can make and organize creating conditions of miniaturization, thereby realized taking into account the manufacture method of the Plate Steel of Rolling Production rate and low-temperature flexibility.

Particularly, the hot rolled back segment (below be also referred to as " back segment is rolling ".In addition, also the hot rolled leading portion is called " leading portion is rolling " below.) in, make the draft ratio manufacturing in the past of per 1 passage big, with time optimization between passage.If the draft of per 1 passage is increased, then the road number of times reduces, and therefore, productivity improves.In the low temperature rolling under γ non-recrystallization temperature province in the past, because rolling reactive force increases, therefore, draft is suppressed in and is lower than 10%.

But, according to the present invention people's research as can be known, in the high temperature rolling in γ recrystallization temperature zone, draft is made as 10～25%, and then by the time between passage was made as 3～25 seconds, thereby the miniaturization that can utilize the recrystallize by γ to cause can make and organize miniaturization.

The present invention is based on above-mentioned opinion, further considered that the one-tenth of the steel of productivity and low-temperature flexibility excellence is grouped into and makes, its main points are as described below.

(1) a kind of manufacture method of Plate Steel is characterized in that, steel billet is heated to 1000～1200 ℃,

Then, it is rolling to implement the leading portion that the accumulation drafts are 50～95%, the road number of times is 4～16 passages down 950～1200 ℃ of thickness of slab core temperatures,

Then, be at 850～950 ℃ of following enforcement of thickness of slab core temperature road number of times that draft in 2～8 passages, each passage is 10～25%, the time is that 3～25 seconds back segment is rolling between passage,

Then, more than 750 ℃, implement to quicken cooling till the temperature below 650 ℃ with 1～50 ℃/second speed of cooling from the thickness of slab core temperature,

Thereby the formation thickness of slab is 10～40mm, yielding stress is that 315～550MPa, microstructure are that the mixed structure of ferrite and bainite or the mixed structure of ferrite, perlite and bainite and the average crystalline particle diameter of thickness of slab central part are the Plate Steel of 5～20 μ m

Described steel billet contains in quality %:

C：0.04～0.16％、

Si：0.01～0.5％、

Mn：0.2～2.5％、

Below the P:0.03%,

Below the S:0.02%,

Al：0.001～0.10％、

Nb：0.003～0.02％、

Ti：0.003～0.05％、

N：0.001～0.008％，

As selecting element, contain in the following element more than a kind or 2 kinds:

Cu：0.03～1.5％、

Ni：0.03～2.0％、

Cr：0.03～1.5％、

Mo：0.01～1.0％、

V：0.003～0.2％、

B：0.0002～0.005％、

Ca：0.0005～0.01％、

Mg：0.0005～0.01％、

REM：0.0005～0.01％，

The carbon equivalent Ceq. of following (A) formula is 0.2～0.5%, and remainder comprises Fe and unavoidable impurities,

Ceq.＝C＋Mn／6＋（Cu＋Ni）／15＋（Cr＋Mo＋V）／5（A）。

(2) according to the manufacture method of the Plate Steel of above-mentioned (1), it is characterized in that, after described acceleration cooling finishes, 300～650 ℃ of following tempering.

The invention effect

Owing to do not carry out low temperature rolling, so the temperature waiting time is short with the manufacture method of Plate Steel for welded construction of the present invention, and because draft is big, so the road number of times is few, Rolling Production rate height.And then, manufacturing method according to the invention, the miniaturization that causes by the recrystallize that utilizes by γ, the high temperature rolling by γ recrystallization temperature zone makes organizes miniaturization, can make the welded construction Plate Steel of low-temperature flexibility excellence.

Embodiment

At first, the preferred manufacture method of welded construction of the present invention with Plate Steel described.

At first, carry out melting by the known melting method that has used converter etc., make steel billet by known castmethods such as continuous castings with being adjusted to molten steel that desirable one-tenth is grouped into.

In the cooling way in when casting or after the cooling, steel billet is heated to 1000～1200 ℃ temperature.Be lower than in the Heating temperature of steel billet under 1000 ℃ the situation, solutionizing is insufficient.When Heating temperature surpassed 1200 ℃, thickization of heating γ crystal grain was difficult to carry out miniaturization in the operation of rolling after this, and then, between till the beginning of high temperature rolling, produce the time that waiting temperature reduces, therefore, productivity reduces.The scope of preferred Heating temperature is 1050～1150 ℃.

Then, implement the hot rolling (leading portion is rolling) of leading portion according to the condition of 950～1200 ℃ of thickness of slab core temperatures, accumulation draft 50～95%, road number of times 4～16.

If the thickness of slab core temperature surpasses 1200 ℃, then can't make recrystallize γ crystal grain become fine.If the thickness of slab core temperature is lower than 950 ℃, then productivity reduces.Preferred thickness of slab core temperature is 1000～1150 ℃.

If the accumulation draft is lower than 50%, then recrystallize can't fully carry out, and can't make recrystallize γ crystal grain become fine.If the accumulation draft surpasses 95%, then rolling load increases, and productivity reduces.Preferred accumulation draft is 60%～90%.

If the road number of times is lower than 4, then can't make recrystallize γ crystal grain become fine.If the road number of times surpasses 16, then productivity reduces.Preferred road number of times is 5～14.

Then, under 850～950 ℃ of thickness of slab core temperatures, the draft of implementing per 1 passage is 10～25%, the time is that 3～25 seconds, road number of times are the hot rolling (back segment is rolling) of the back segment of 2～8 passages between passage.

If the thickness of slab core temperature surpasses 950 ℃, then can't make recrystallize γ crystal grain become fine.If the thickness of slab core temperature is lower than 850 ℃, then productivity reduces.Preferred thickness of slab core temperature is 870～930 ℃.

If the draft of per 1 passage is lower than 10%, then the road number of times increases, and therefore, productivity reduces.If the draft of per 1 passage surpasses 25%, then the burden of roller mill becomes very big, therefore is difficult to realize.The preferred draft of per 1 passage is 13～22%.

In order to make the draft in each passage be more than 10%, productivity is improved, the time becomes important factor between passage.

In the scope of draft 10～25% of per 1 passage, if between passage the time be lower than 3 seconds, then between the karyogenesis of recrystallize needed latent period or enter time a time in the recrystallize initial stage, therefore, recrystallize does not carry out fully.If the time surpasses 25 seconds between passage, then before entering following a time, primary recrystallization finishes, begin with the secondary recrystallization of crystal boundary energy as motivating force, therefore, thickization of recrystallize γ crystal grain.That is, if then the miniaturization as the tissue under high temperature rolling of problem of the present invention can't realize not 3～25 seconds scope the time between passage.The time is 5～23 seconds between preferred passage.

If the road number of times is lower than 2, then can't make recrystallize γ crystal grain become fine.If the road number of times surpasses 8, then productivity reduces.Preferred road number of times is 3～7.

Follow above-mentioned hot rolling, more than 750 ℃, implement to quicken cooling till the temperature below 650 ℃ with 1～50 ℃/second speed of cooling from the thickness of slab core temperature.

If the thickness of slab core temperature during the cooling beginning is lower than 750 ℃, then ferrite transformation carries out, and therefore is difficult to obtain ferrite fine grained structure.

If speed of cooling is lower than 1 ℃/second, then be difficult to obtain micro organization.If speed of cooling surpasses 50 ℃/second, then be difficult to obtain the ferrite branch rate more than 20%.

Surpass 650 ℃ if cooling stops temperature, then be difficult to obtain micro organization.

Preferred thickness of slab core temperature when quickening the refrigerative condition for the cooling beginning more than 770 ℃, 5～40 ℃/second of speed of cooling, cooling stop temperature below 600 ℃.

In addition, use the thickness of slab core temperature of steel plate to control the feature that manufacturing also is the manufacture method of steel plate of the present invention.By using the thickness of slab core temperature, compare with the situation of the surface temperature of using steel plate, in situation that thickness of slab changes etc., also can suitably control and create conditions, can make little, the colory steel plate of material inequality efficiently.

In rolling process, usually, from be heated to rolling till between, the equilateral calculating steel plate of the surface temperature temperature inside that steel plate is measured on the limit distributes, the result predicts rolling reactive force etc. according to this calculation of Temperature distribution, the control that is rolled simultaneously.Like this, can easily in rolling, obtain the steel plate core temperature.Quickening under the refrigerative situation, rand prediction thickness of slab temperature inside divides selvedge to quicken Cooling Control too.

After implementing to quicken cooling, in 300～650 ℃, carry out tempering as required.

In being lower than 300 ℃ tempering, be difficult to obtain the tempered effect.If tempering temperature surpasses 650 ℃, then softening amount increases, and is difficult to guarantee intensity.

Preferred tempering temperature is 400～600 ℃.

Manufacture method of the present invention can be applicable to that thickness of slab is that 10～40mm, yielding stress are the manufacturing of the steel plate of 315～550MPa.The yielding stress that especially can be applicable to ship hull structure use is the manufacturing of 315MPa level, 355MPa level or 390MPa grade steel plate.

Therefore be lower than the steel plate of 10mm for thickness of slab, owing to plate shape deterioration can't be used and quicken cooling.For the steel plate of thickness of slab,,, therefore be difficult to take into account productivity owing to must carry out low temperature rolling in order to ensure toughness above 40mm.

Be lower than in the manufacturing of steel plate of 315MPa in yielding stress, do not need to quicken cooling, therefore do not need to use the present invention.In the manufacturing of yielding stress, in order to ensure toughness, must carry out low temperature rolling, thereby be difficult to take into account productivity above the steel plate of 550MPa.

Create conditions according to above-mentioned, the miniaturization that utilizes the recrystallize by γ to cause is organized miniaturization even also can make by high temperature rolling.And then manufacture method of the present invention does not need to carry out low temperature rolling, therefore, be the temperature waiting time short, that draft is big is rolling, is that number of times is few, the manufacture method of Rolling Production rate excellence therefore.

The one-tenth of using the Plate Steel of manufacture method of the present invention is grouped into considers intensity, toughness, welding heat affected zone (HAZ) toughness and weldability etc., as described below.

C is in order to ensure the intensity of mother metal and toughness and add more than 0.04%.If the content of C surpasses 0.16%, then be difficult to guarantee good HAZ toughness, so the content of C is made as below 0.16%.In order to ensure the intensity of mother metal, also the lower limit of the content of C can be made as 0.06% or 0.08%.In addition, in order to improve HAZ toughness, also the upper content limit of C can be restricted to 0.15% or 0.14%.

Si is effectively as deoxidant element and strengthening element, therefore adds more than 0.01%.If the content of Si surpasses 0.5%, HAZ toughness variation significantly then, so the addition of Si is made as below 0.5%.In order to carry out deoxidation reliably, can be 0.05% or 0.10% also with the lower limit of the content of Si.In addition, in order to improve HAZ toughness, be 0.40% or 0.34% with the ceiling restriction of the content of Si.

Mn is in order to ensure the intensity of mother metal and toughness and add more than 0.2%.If the content of Mn surpasses 2.5%, then center segregation becomes significantly, the mother metal of the part of generation center segregation and the toughness variation of HAZ, and therefore, the content of Mn is made as below 2.5%.For intensity and the toughness that improves mother metal, can be 0.6% or 0.8% also with the lower limit of the content of Mn.For the deterioration of the material that prevents to cause, can be 2.0%, 1.8% or 1.6% also with the ceiling restriction of the content of Mn by center segregation.

P is an impurity element.In order stably to guarantee HAZ toughness, the content of P need be reduced to below 0.03%.In order to improve HAZ toughness, also the content of P can be made as below 0.02% or below 0.015%.

S is an impurity element.Characteristic and HAZ toughness in order stably to guarantee mother metal need be reduced to the content of S below 0.02%.For characteristic and the HAZ toughness that improves mother metal, also the content of S can be made as below 0.01% or below 0.008%.

In order to undertake deoxidation, to reduce the O as impurity element, Al is an essential element.Except that Al, Mn and Si also have contribution to deoxidation.But, even under the situation of adding Mn and Si, be lower than at 0.001% o'clock at the content of Al, can't stably reduce O.But, if the content of Al surpasses 0.10%, then generating thick oxide compound or its nanocluster of alumina series, mother metal and HAZ toughness are impaired, so the addition of Al is made as below 0.10%.In order to carry out deoxidation reliably, also the lower limit of the content of Al can be made as 0.01% or 0.015%.For generation of suppressing thick oxide compound etc., also the upper limit of the content of Al can be made as 0.08% or 0.06%.

Nb is by adding more than 0.003%, and the intensity of mother metal and flexible are improved contribution.But if the content of Nb surpasses 0.02%, then HAZ toughness or weldability reduce, and therefore, the content of Nb is made as below 0.02%.The grain refined effect of being brought by Nb for further performance also can be made as 0.005% with the lower limit of the content of Nb.For HAZ toughness and weldability are improved, also the upper limit of the content of Nb can be made as 0.015% or 0.012%.

Ti forms TiN by adding, and suppresses the austenite particle diameter and increase when steel billet heats.If the austenite particle diameter increases, then the crystal particle diameter after the phase transformation also increases, and toughness reduces.For toughness being reduced and, needing to add the Ti more than 0.003% for the crystal particle diameter of the size that needing to obtain.But if the content of Ti surpasses 0.05%, then owing to form TiC, HAZ toughness reduces, so the content of Ti is made as below 0.05%.For HAZ toughness is improved, also the upper limit of the content of Ti can be made as 0.03% or 0.02%.

N forms TiN, suppresses the austenite particle diameter and increase when steel billet heats, and therefore adds more than 0.001%.If the content of N surpasses 0.008%, then steel embrittlement, so the content of N is made as below 0.008%.

As the selection element that except above-mentioned interpolation element, can add as required, in quality % can contain in Cu:0.03～1.5%, Ni:0.03～2.0%, Cr:0.03～1.5%, Mo:0.01～1.0%, V:0.03～0.2%, B:0.0002～0.005% more than a kind or 2 kinds.By adding these elements, can improve the intensity and the toughness of mother metal.As required, with the ceiling restriction of the content of Cu is 1.0%, 0.5% or 0.3%, with the ceiling restriction of the content of Ni is 1.0%, 0.5% or 0.3%, with the ceiling restriction of the content of Cr is 1.0%, 0.5% or 0.3%, with the ceiling restriction of the content of Mo is 0.3%, 0.2% or 0.1%, with the ceiling restriction of the content of V is 0.1%, 0.07% or 0.05%, is 0.003%, 0.002 or 0.001% with the ceiling restriction of the content of B.

If the content of these elements is too much, then HAZ toughness and weldability worsen, and therefore, stipulate the upper limit of content as mentioned above.

And then, select element as other, in quality % contain in Ca:0.0005～0.01%, Mg:0.0005～0.01%, REM:0.0005～0.01% more than a kind or 2 kinds.By adding these elements, HAZ toughness improves.

For the intensity that improves mother metal and toughness etc., can add these wittingly and select element.But,, can not add these fully yet and select element in order to reduce cost of alloy etc.Even do not add wittingly under the situation of these elements, as unavoidable impurities, in steel, can contain below the Cu:0.05%, below the Ni:0.05%, below the Cr:0.05%, below the Mo:0.03%, below the V:0.01%, below the B:0.0004%, below the Ca:0.0008%, below the Mg:0.0008%: below the REM:0.0008%.Even under the situation that these elements contain as unavoidable impurities in steel, for the manufacture method of Plate Steel of the present invention without any influence.

The steel plate made from the manufacture method of Plate Steel by welded construction of the present invention will be made as 0.2～0.5% by the carbon equivalent that above-mentioned (A) formula is obtained.Under the situation of selecting element to contain, carbon equivalent is obtained in its content substitution as unavoidable impurities.

If carbon equivalent is lower than 0.2%, then can't satisfy the desired intensity of making by manufacture method of the present invention of steel plate.If carbon equivalent surpasses 0.5%, then can't satisfy the desired ductility of steel plate, toughness and the weldability made by manufacture method of the present invention.In order to ensure intensity, can be 0.25%, 0.28% or 0.30% with the lower limit of carbon equivalent also.In order to improve HAZ toughness and weldability, can be 0.43%, 0.4% or 0.38% with the lower limit of carbon equivalent also.

Is the mixed structure of ferrite and bainite or the mixed structure of ferrite/perlite and bainite by welded construction of the present invention with the microstructure of the steel plate of the manufacture method manufacturing of Plate Steel.By forming such tissue, can guarantee desired intensity of steel plate and the toughness made by manufacture method of the present invention.

Is 5～20 μ m by welded construction of the present invention with the average crystalline particle diameter in the thickness of slab central part of the steel plate of the manufacture method manufacturing of Plate Steel.Consequently, become the satisfied desired flexible steel plate made from the manufacture method of Plate Steel by welded construction of the present invention of steel plate.

Is about 20～80% by welded construction of the present invention with the ferrite area occupation ratio in the thickness of slab central part of the steel plate of the manufacture method manufacturing of Plate Steel.Consequently, be the steel plate of ductility, toughness and excellent strength by welded construction of the present invention with the steel plate of the manufacture method manufacturing of Plate Steel.

Embodiment

The one-tenth of adjusting molten steel in steel making working procedure is grouped into, and then, makes steel billet by continuous casting.

Then, with this steel billet reheat, and then, implement heavy plate rolling, forming thickness is the Plate Steel of 10～40mm, then, with the Plate Steel water-cooled.In the steel plate of test No.18, replace water-cooled, carry out air cooling (comparative example).

Then, heat-treat as required, having made yield strength is the Plate Steel of 315MPa～550MPa.The one-tenth that each Plate Steel has been shown in table 1～2 is grouped into.The underscore of table 1 represents that content is outside scope of the present invention.The bracket literary style of table 2 is represented the quantitative analysis value that contains as unavoidable impurities.

For each Plate Steel of making, microstructure phase fraction, average crystalline particle diameter and mechanical properties have been measured.

The microstructure phase fraction is taken microstructure to the thickness of slab central position with 500 times multiplying power by opticmicroscope, the mean value of obtaining by image analysis with respect to the area occupation ratio of each phase of full area of visual field.

The average crystalline particle diameter is by EBSP(Electron Back Scattering Pattern, electron backscattered pattern) method is measured with 1 μ m spacing the zone of 500 μ m * 500 μ m, to be that boundary definition more than 15 ° is the crystal crystal boundary with the crystalline orientation difference of adjacency crystal grain, be made as the mean value of the crystal particle diameter of this moment.

In mechanical properties, yielding stress uses the test film of taking from total thickness to test, and the test film that Xia Shi section transition temperature (vTrs) use is taked from the thickness of slab central part is tested, with the typical value of its result as each steel plate.

Tension test is according to JIS Z 2241(1998) " metal material stretching test method ", each 2 carry out test determination, obtain its mean value.The tension test sheet is made as JIS Z 2201(1998) the 1B test film.

Xia Shi section transition temperature (vTrs) uses 2mmV type breach charpy impact test sheet, according to JIS Z 2242(2005) " the charpy impact test method of metallic substance ", respectively test 3 for 1 temperature, under 5 temperature, test the temperature when measuring 50% percentage of brittle fracture surface.

These measurement results of each Plate Steel are shown in table 3～8 with manufacture method.In addition, temperature in the manufacture method and speed of cooling are the values of thickness of slab central position, resolve by the heat conduction that utilizes known method of finite difference from the surface temperature of actual measurement and obtain.

In the present embodiment, with below the section transition temperature-60 ℃, 200 seconds following provisions of rolling time are good.The underscore of table 3～8 represent condition outside scope of the present invention or the characteristic of steel plate, productivity to depart from afore mentioned rules be good value.

Test NO.1～NO.13 is the example of the present invention that satisfies all conditions of the present invention, and intensity, toughness, productivity are all good.

Test NO.14～NO.33 is the comparative example that the condition of underscore departs from scope of the present invention.

The rolling pass number of the test leading portion of NO.14 and back segment is many, and the rolling end temp of back segment is low, and therefore, rolling time is long, and productivity is low.

Test NO.15 is because speed of cooling is too fast, so the intensity height, and toughness is low.

Test NO.16 is because slab heating temperature is too high, so the average crystalline particle diameter is big, and toughness is low, and rolling time is long, and productivity is low.

Test NO.17 is because cooling beginning temperature is low excessively, and therefore, the average crystalline particle diameter is big, and intensity and toughness are low.

Test NO.18 is owing to the rolling road number of times of back segment is few, so the average crystalline particle diameter is big, and toughness is low.

Test NO.19 since between the rolling passage of back segment the time short, so the average crystalline particle diameter is big, toughness is low.

Test NO.20 is owing to the rolling accumulation draft of leading portion is little, so the average crystalline particle diameter is big, and toughness is low, and rolling time is long, and productivity is low.

Test NO.21 is because the cooling end temp is too high, so the average crystalline particle diameter is big, and intensity and toughness are low.

Test NO.22,29,30 since between the rolling passage of back segment the time long, therefore, the average crystalline particle diameter is big, toughness is low, and rolling time is long, productivity is low.

Test NO.23 owing to utilize air cooling to cool off, so the average crystalline particle diameter is big, toughness.

Test NO.24～28 are because composition range departs from scope of the present invention, so toughness is low.

Test NO.31～33 are because the draft in rolling each passage of back segment is little, so the average crystalline particle diameter is big, and toughness is low.About No.32,33, the time still have a few length a little, and the draft in each passage is too small, so rolling time is also long within the limits prescribed between passage, and productivity is low.

Can confirm from above embodiment, manufacturing method according to the invention, the miniaturization that utilizes the recrystallize by γ to cause makes by the high temperature rolling in the γ recrystallization temperature zone and to organize miniaturization, can obtain the Plate Steel of low-temperature flexibility excellence thus.

In addition, the present invention is not limited to above-mentioned embodiment.Can carry out various changes in the scope that does not break away from purport of the present invention implements.

Utilizability on the industry

The manufacture method of Plate Steel of the present invention is not owing to there is the low temperature rolling operation, so the temperature waiting time is short, and because draft is big, so the road number of times is few, Rolling Production rate height.According to the present invention, the miniaturization that utilization is caused by the recrystallize of γ, organize miniaturization even also can make by the high temperature rolling in the γ recrystallization temperature zone, the manufacture method of the welded construction of low-temperature flexibility excellence with Plate Steel can be provided, therefore, use in the manufacturing of the Plate Steel that can use in welded structures such as shipbuilding, building, oil tank, marine structure, line pipe, the utilizability on the industry is big.

Claims

1. the manufacture method of a Plate Steel is characterized in that, steel billet is heated to 1000～1200 ℃,