Summary of the invention
Invent problem to be solved
But, have the following problems point in the above-mentioned patent documentation 1~5.
The method of manufacture 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 method of manufacture 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 plow-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 microstructure is different, therefore can't use.
As the method for manufacture of record in the patent documentation 3, if the time between passage was made as more than 30 seconds, then people's result of study can be known according to the present invention, thickization of recrystallize γ.
The method of manufacture of record is owing to manage rolling temperature through surface temperature in the patent documentation 4, and therefore not only material is uneven big, and owing to do not stipulate the 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 rollss big, impracticable the method for manufacture 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 devices, the material inequality is little, low-temperature flexibility is excellent welded construction method of manufacture with Plate Steel.Particularly, though with do not carry out low temperature rolling, only also can be with the method for manufacture of the Plate Steel of organizing miniaturization as problem through high temperature rolling.
Be used to solve the means of problem
People of the present invention further investigate the method for manufacture of Plate Steel.Consequently; Even found through 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 method for manufacture 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 people's research can be known according to the present invention, in the high temperature rolling in γ recrystallization temperature zone; Draft is made as 10~25%; And then through 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 that productivity and low-temperature flexibility are excellent is grouped into and makes, its main points are described below.
(1) a kind of method of manufacture 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, begin 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 ferritic and bainite or the mixed structure of ferritic, perlite and bainite and the average crystalline particle diameter of thickness of slab central part are the Plate Steel of 5~20 μ m
Said 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 method for manufacture of the Plate Steel of above-mentioned (1), it is characterized in that, after said 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 method for manufacture of Plate Steel for welded construction of the present invention, and because draft is big, so the road number of times is few, the Rolling Production rate is high.And then, manufacturing method according to the invention, the miniaturization that causes through the recrystallize that utilizes by γ, the high temperature rolling through γ recrystallization temperature zone makes organizes miniaturization, can make the excellent welded construction of low-temperature flexibility and use Plate Steel.
Embodiment
At first, the preferred method of manufacture of welded construction of the present invention with Plate Steel described.
At first, carry out melting through the known melting method that has used converter etc., process steel billet through 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 rolls 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 nucleus formation of recrystallize needed latent period, or in the recrystallize initial stage a time under the entering, therefore, recrystallize does not carry out fully.If the time surpasses 25 seconds between passage, then before getting into down a time, the primary recrystallization end begins with the secondary recrystallization of crystal boundary energy as motivating force, therefore, and 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, begin 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 ferritic 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 ferritic 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 characteristic that manufacturing also is the method for manufacture of steel plate of the present invention.Through 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 ℃.
Method of manufacture 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, need do not quicken cooling, therefore need not 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 through high temperature rolling.And then method of manufacture of the present invention need not carried out low temperature rolling, therefore, be the temperature waiting time short, that draft is big is rolling, therefore is the method for manufacture that number of times is few, the Rolling Production rate is excellent.
The one-tenth of using the Plate Steel of method of manufacture of the present invention is grouped into considers intensity, toughness, welding heat affected zone (HAZ) toughness and weldableness etc., is 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 can the lower limit of the content of C be made as 0.06% or 0.08%.In addition, in order to improve HAZ toughness, also can the upper content limit of C 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, need the content of P be reduced to below 0.03%.In order to improve HAZ toughness, also can the content of P 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 can the content of S 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 can the lower limit of the content of Al be made as 0.01% or 0.015%.For generation of suppressing thick oxide compound etc., also can the upper limit of the content of Al be made as 0.08% or 0.06%.
Nb is through adding more than 0.003%, and the intensity of mother metal and flexible are improved has contribution.But if the content of Nb surpasses 0.02%, then HAZ toughness or weldableness 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 weldableness are improved, also can the upper limit of the content of Nb be made as 0.015% or 0.012%.
Ti forms TiN through adding, and when steel billet heats, suppresses the austenite particle diameter and increases.If the austenite particle diameter increases, then the crystal particle diameter after the phase transformation also increases, and toughness reduces.In order toughness to be reduced and, to need 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 can the upper limit of the content of Ti be made as 0.03% or 0.02%.
N forms TiN, when steel billet heats, suppresses the austenite particle diameter and increases, 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.Through 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%, is 1.0%, 0.5% or 0.3% with the ceiling restriction of the content of Cr, is 0.3%, 0.2% or 0.1% with the ceiling restriction of the content of Mo; 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 weldableness worsen, and therefore, stipulate the upper limit of content as stated.
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.Through 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 under the situation of these elements wittingly; 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, has no influence for the method for manufacture of Plate Steel of the present invention in steel.
The steel plate made from the method for manufacture of Plate Steel through 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 method of manufacture 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 weldableness made by method of manufacture 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 weldableness, can be 0.43%, 0.4% or 0.38% with the lower limit of carbon equivalent also.
Use the microstructure of the steel plate that the method for manufacture of Plate Steel makes to be the mixed structure of ferritic and bainite or the mixed structure of ferritic/perlite and bainite through welded construction of the present invention.Through forming such tissue, can guarantee desired intensity of steel plate and the toughness made by method of manufacture of the present invention.
Being used the average crystalline particle diameter in the thickness of slab central part of steel plate of method of manufacture manufacturing of Plate Steel by welded construction of the present invention is 5~20 μ m.Consequently, become the satisfied desired flexible steel plate made from the method for manufacture of Plate Steel through welded construction of the present invention of steel plate.
Using the ferritic area occupation ratio in the thickness of slab central part of steel plate of method of manufacture manufacturing of Plate Steel through welded construction of the present invention is about 20~80%.Consequently, use steel plate that the method for manufacture of Plate Steel makes steel plate through welded construction of the present invention as ductility, toughness and excellent strength.
Embodiment
The one-tenth of adjustment molten steel is grouped in steel making working procedure, then, makes steel billet through 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 ys 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 representes 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 through opticmicroscope, the MV of obtaining through image analysis with respect to the area occupation ratio of each phase of full area of visual field.
The average crystalline particle diameter is through 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 crystalline orientation difference, be made as the MV of the crystal particle diameter of this moment in abutting connection with crystal grain.
In mechanical properties, yielding stress uses the test film of from total thickness, taking to make an experiment, and Xia Shi section transition temperature (vTrs) uses the test film of taking from the thickness of slab central part to make an experiment, 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 ", and each 2 mensuration that make an experiment is obtained its MV.The tension test sheet is made as the 1B test film of JIS Z 2201 (1998).
Xia Shi section transition temperature (vTrs) uses 2mmV type breach charpy impact test sheet; " the charpy impact test method of metallic substance " according to JIS Z 2242 (2005); Respectively test 3 for 1 temperature, under 5 temperature, make an experiment the temperature when measuring 50% percentage of brittle fracture surface.
These mensuration result of each Plate Steel is shown in table 3~8 with method of manufacture.In addition, temperature in the method for manufacture and speed of cooling are the values of thickness of slab central position, resolve through 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 present invention's example 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 leading portion and the back segment of test NO.14 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 intensity is high, 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 between passage in the scope of regulation, 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 through the high temperature rolling in the γ recrystallization temperature zone and to organize miniaturization, can obtain the excellent Plate Steel of low-temperature flexibility thus.
In addition, the present invention is not limited to above-mentioned embodiment.In the scope that does not break away from purport of the present invention, can carry out various changes implements.
Utilizability on the industry
The method of manufacture 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, the Rolling Production rate is high.According to the present invention; The miniaturization that utilization is caused by the recrystallize of γ; Even also can make through the high temperature rolling in the γ recrystallization temperature zone and to organize miniaturization, the method for manufacture of the excellent welded construction of low-temperature flexibility with Plate Steel can be provided, therefore; Use in the manufacturing of the Plate Steel that can in welded structures such as shipbuilding, building, oil tank, marine structure, line pipe, use, the utilizability on the industry is big.