CN101535518B - Steel plate for linepipe having ultra-high strength and excellent low temperature toughness and manufacturing method of the same - Google Patents
Steel plate for linepipe having ultra-high strength and excellent low temperature toughness and manufacturing method of the same Download PDFInfo
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- CN101535518B CN101535518B CN2007800410343A CN200780041034A CN101535518B CN 101535518 B CN101535518 B CN 101535518B CN 2007800410343 A CN2007800410343 A CN 2007800410343A CN 200780041034 A CN200780041034 A CN 200780041034A CN 101535518 B CN101535518 B CN 101535518B
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
- C21D8/0263—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment following hot rolling
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/46—Ferrous alloys, e.g. steel alloys containing chromium with nickel with vanadium
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/48—Ferrous alloys, e.g. steel alloys containing chromium with nickel with niobium or tantalum
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/50—Ferrous alloys, e.g. steel alloys containing chromium with nickel with titanium or zirconium
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese
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Abstract
A steel plate for linepipes having ultra-high strength and excellent low temperature toughness, and a method for manufacturing the same are disclosed. The steel plate has strength of 930 MPa or more and excellent toughness even with much smaller amounts of alloying elements than that of conventional steel plates, and a method for manufacturing the same. The steel comprises by weight %: 0.03-0.10% C; 0-0.6% Si; 1.6-2.1% Mn; 0-1.0% Cu; 0-1.0% Ni; 0.02-0.06% Nb; 0-0.1% V; 0.1-0.5% Mo; 0-1.0% Cr; 0.005-0.03% Ti; 0.01-0.06%Al; 0.0005-0.0025% B; 0.001-0.006% N; 0-0.006% Ca; 0.02% or less P; 0.005% or less S; and the balance of Fe and unavoidable impurities. The microstructure comprises at least about 75 area percent of a mixture of bainitic ferrite and acicular ferrite.
Description
Technical field
The present invention relates to a kind of steel plate for linepipe and manufacture method thereof that superstrength and excellent low-temperature flexibility are arranged.More specifically, lack in than conventional steel plates and also have 930MPa or the higher intensity and the steel plate for linepipe and the manufacture method thereof of excellent toughness under a lot of situations even the present invention relates to a kind of content at alloying element.
Background technology
Pipeline refers to be embedded in the underground steel pipe that is used for long-distance transportation crude oil and Sweet natural gas, and will bear the high pressure that the high pressure gas of flowing through or crude oil fluid cause usually.
For improving the transmission efficiency of pipeline, per hour must improve the transmission quantity of crude oil or gas (being designated hereinafter simply as " former wet goods ").For this purpose, the outside diameter of pipeline must be increased to very big size.
When the pipeline outside diameter increased, the amount of the former wet goods of wherein flowing through also can increase, and this has increased the pressure that former wet goods puts on pipeline then.In this, although pipeline needs the very high steel of intensity, the X70 grade steel plate is only used according to the strength criterion of pipeline usually in this area.The X70 grade steel plate has the intensity of 70ksi, promptly about 480MPa.Therefore, when with the pipeline of the big external diameter of steel plate manufacturing of this intensity rank, must increase the thickness of steel plate, this has increased economical load.
Therefore, although more and more need intensity to compare the steel plate for linepipe of remarkable improvement with conventional steel plates, this area is also untapped to go out this steel plate that can fully satisfy high-intensity requirement.
This not only is attributed to the technology barriers that improve armor plate strength, but also owing to other technical problem of following armor plate strength to improve.
Particularly, for improving armor plate strength, although in steel, add usually, yet add described alloying element intensity is fully increased, and the increase of alloying element add-on also can cause the low-temperature flexibility deterioration of welding zone and matrix to improving the effective alloying element of intensity.Therefore, when increasing the intensity of steel plate, also must improve low-temperature flexibility.
And, when improving the intensity of steel plate with conventional art, usually with steel plate quenching in steel plate, generating low temperature microstructure such as lower bainite or martensite, thereby improve the hardness and the intensity of steel plate simultaneously.Yet when forming described microstructure such as martensite etc. in the steel plate, the residual stress in the steel plate can cause the not enough or tangible toughness deterioration of armor plate strength.
As mentioned above, intensity and toughness are considered to inconsistent mechanical properties usually, i.e. the raising of intensity can cause flexible to reduce.
Therefore, people attempt to guarantee the intensity and the toughness of steel plate always, thereby the steel plate of high-intensity high-tenacity is provided.One of this trial is a hot mechanical CONTROL PROCESS (TMCP).TMCP is a technical term, refers to by heat and machinery control steel plate character be changed in rolling and process for cooling the process of required character.Although TMCP is widely used by various modification, it generally includes the rolling technology of a control, wherein rollingly carries out in specified temp under the condition of strictness control; With an accelerated cooling process, its light plate is cooled with suitable rate of cooling.
The advantage of TMCP is by can forming particulate and the microstructure wanted in this technology steel plate, becomes possibility thereby make mechanical property with steel plate effectively control to required degree in theory.
Yet,, must form as the rigid structure with conventional art in order to have the steel plate of desirable strength by the accelerated cooling process manufacturing among the TMCP.Therefore, even for the steel plate of making by TMCP, the increase of intensity also causes flexible to reduce inevitably.
Therefore, in the high-strength steel product scope, constantly study, to develop a kind of method that improves intensity and low-temperature flexibility simultaneously always.
Particularly, tempering is adopted the most widely to address this problem.
For example, U.S. Patent No. 5545269,5755895,5798004,5900075,6045630,6183573,6245290 and 6532995 discloses a kind of method of making steel plate, it comprises and carries out TMCP with rolling and cooling metal sheets, as shown in Figure 1, is being lower than A then
C1Under the temperature of transition temperature (is austenite at ferritic transformation under this temperature) steel plate is carried out tempering.Yet owing to must carry out second-heating to carry out tempering to steel plate behind cooling metal sheets, this method needs the height consumption of energy.In addition, increase the increase that drawing process causes production cost.
In addition, multiple alloying element is added in the steel to increase the intensity of steel, and Mo is added into as a kind of in the effective elements especially usually.For example, U.S. Patent No. 6224689,6228183,6248191 and 6264760 discloses and has contained a large amount of Mo---being in particular 0.2wt% or more Mo---to have lower bainite and the lath martensite steel as the steel microstructure.Similarly, according to Korean Patent No.2000-00533890, the steel that contains 0.35wt% or more Mo is disclosed as a kind of example of this invention, and the case of comparative examples that contains 0.14wt%Mo has the low tensile strength less than 930MPa.
Yet because Mo is a kind of element of costliness, the Mo content that surpasses 0.15wt% or 0.2wt% can become the reason that manufacturing cost increases.In addition, because lower bainite shown in Figure 3 has very narrow transformation temperature scope, as shown in Figure 2, therefore described steel needs the cooling conditions and the very high rate of cooling of non-strictness, and this causes that the performance of equipment is had very specific requirement.In addition, because this high rate of cooling can cause the problem such as steel plate deformed, therefore must carry out a kind of additional process that is used for the control of plate shape after making steel plate, this makes processing conditions more complicated and loaded down with trivial details.
Summary of the invention
Technical problem
The present invention has made solving aforementioned prior art problem, so one aspect of the present invention provides a kind of steel plate and manufacture method thereof that has high-tensile and excellent low-temperature flexibility and do not contain a large amount of Mo.
Technical scheme
According to an aspect of the present invention, the invention provides a kind of steel plate, it contains (in weight %): 0.03-0.10%C, 0-0.6%Si, 1.6-2.1%Mn, 0-1.0%Cu, 0-1.0%Ni, 0.02-0.06%Nb, 0-0.1%V, 0.1-0.5%Mo, 0-1.0%Cr, 0.005-0.03%Ti, 0.01-0.06%Al, 0.0005-0.0025%B, 0.001-0.006%N, 0-0.006%Ca, 0.02% or P still less, 0.005% or S still less, and the Fe of surplus and unavoidable impurities, wherein microstructure contains at least about the Bei Shi ferrite of 75 area percentages and the mixture of acicular ferrite.
According to a further aspect in the invention, the invention provides a kind of steel plate, it contains (in weight %): 0.03-0.10%C, 0-0.6%Si, 1.6-2.1%Mn, 0-1.0%Cu, 0-1.0%Ni, 0.02-0.06%Nb, 0.1% or V still less, 0.1-0.5%Mo, 1.0% or Cr still less, 0.005-0.03%Ti, 0.01-0.06%Al, 0.0005-0.0025%B, 0.001-0.006%N, 0-0.006%Ca, 0.02% or P still less, 0.005% or S still less, and the Fe of surplus and unavoidable impurities, wherein microstructure contains at least about the Bei Shi ferrite of 75 area percentages and the mixture of acicular ferrite, yield strength is 930MPa or higher, and-40 ℃ of charpy impacts absorption energy are 230J or more.
Preferably, described steel plate contains 0.15wt% or Mo still less.
Preferably, the granular bainite that contains of the microstructure of described steel plate should not surpass 5 area percentages.
More preferably, the full thickness size of austenite crystal (through thickness dimension) should be less than 15 μ m.
According to another aspect of the invention, a kind ofly be used to produce superstrength with the microstructure that mainly contains Bei Shi ferrite, acicular ferrite or its mixture and the preferred method of high-ductility steel comprises: slab is heated to one is enough to melt substantially the carbide of whole vanadium and niobium and the temperature of carbonitride; In first temperature range of austenite recrystallization, on one or more hot rolling passes, described slab rolling is become steel plate; Be lower than T
NrTemperature (be lower than this temperature austenite recrystallization does not take place) and be higher than Ar
3Further rolling described steel plate on the inherent one or more hot rolling passes of second temperature range of point of inversion (being that austenite begins to change into ferritic temperature in the process of cooling); Steel plate with the rate of cooling cold rolling of 20-50 ℃/s; Under 200-400 ℃ temperature, stop cooling metal sheets; And will be through the air cooling of refrigerative steel plate to room temperature.
Preferably, described slab contains 0.15wt% or Mo still less.
Preferably, described method also is included in and stops with will be through the air cooling of refrigerative steel plate to room temperature behind the rate of cooling cooling metal sheets of 20-50 ℃/s.
Description of drawings
The present invention is above-mentioned can more to be expressly understood by the following detailed description in conjunction with the accompanying drawings with others, feature and other advantage, in the described accompanying drawing:
Fig. 1 is that comparison is not carried out synoptic diagram that tempering just can guarantee the manufacture method of mechanical property with the manufacture method of guaranteeing mechanical property with another kind based on carrying out tempering by steel plate rolling and that cooling is made;
Fig. 2 shows that to contain lower bainite and lath martensite be the steel of main microstructure and contains the Bei Shi ferrite and acicular ferrite is the TTT figure of cooling conditions of the steel of main microstructure;
Fig. 3 is the transmission electron micrograph of lower bainite;
Fig. 4 is the ferritic transmission electron micrograph of Bei Shi;
Fig. 5 is the transmission electron micrograph of acicular ferrite; With
Fig. 6 is the transmission electron micrograph of granular bainite;
Embodiment
Now will describe exemplary of the present invention in conjunction with the accompanying drawings in detail.
By extensive and deep research to the problem of conventional art, the present inventor has found the following fact: by adding the Mo than existing invention less amount---it adds in the steel to increase armor plate strength, even do not form as formed lower bainite or lath martensite in the ultrahigh-strength steel of existing invention, steel plate also can show enough intensity; Simultaneously, steel plate also can and make stone microstructure replace forming the austenite particulate by other type microstructure (as lower bainite or lath martensite) by the controlled rolling condition to have good toughness.The present invention is based on that these discoveries make.
Particularly, the content of Mo is lowered in the steel plate of the present invention, and the add-on of other alloying element also has adjustment; And its microstructure is adjusted to and comprises Bei Shi ferrite and acicular ferrite, and the two all has close grain, has identical or higher intensity to guarantee to compare with the steel plate with hard microstructure, lower bainite or lath martensite of existing invention.In addition, in the steel plate of the present invention, these microstructures form having fine granularity, thereby compare with the conventional steel plates that comprises lower bainite or lath martensite, and excellent low-temperature flexibility can be provided.The present invention also provides a kind of method of making this steel plate.
Hereinafter will describe steel plate of the present invention in detail according to component, microstructure and manufacture method.
(steel plate composition)
For obtaining sufficient intensity and toughness (comprising welding zone toughness), provide the composition of following steel plate of the present invention.
C：0.03-0.10wt％
Carbon (C) is the effective element that is used to strengthen welding zone and matrix thereof by the solution strengthening effect.In addition, the carbonitride of carbon by in steel, forming thin iron carbide, V and Nb [Nb (C, N)] and molybdenum carbide [Mo
2C] deposit harden strengthening effect be provided.In addition, the carbonitride of Nb also is used for delaying austenite recrystallization and suppressing grain growing at course of hot rolling, thereby improves intensity and low-temperature flexibility simultaneously by grain refining.Carbon also increases hardenability, and this is a kind of ability that forms strong microtexture in process of cooling in steel plate.Usually, if C content less than 0.03wt%, just can not obtain these strengthening effects.If C content surpasses 0.1wt%, steel plate welds the back cold cracking usually easily at the scene so, and the toughness of steel plate and welded heat affecting zone (weld HAZ) thereof reduces easily.
Si：0-0.6wt％
The auxiliary Al of silicon (Si) carries out deoxidation to molten steel and works as a kind of solution strengthening element.Yet the upper limit is made as 0.6wt% with the on-the-spot weldability avoiding too much being caused by silicone content and and the obvious deterioration of welding heat influence area toughness.Because Al or Ti can exercise identical function, thus optional in joining Si just for deoxidation.
Mn：1.6-2.1wt％
Manganese (Mn) is a kind of effective element in the steel solution strengthening.
Be to improve hardenability and intensity, need to add the 1.6wt% or the manganese of volume more.Yet Mn content surpasses 2.1wt% and tend to cause center segregation in continuous casting steel machine, also can cause steel flexible deterioration.In addition, the Mn too high levels can cause on-the-spot weldability and and the deterioration of welding heat influence area toughness by the excessive increase of hardenability.
Cu：0-1.0wt％
Copper (Cu) is a kind of element of strengthening matrix metal and welded heat affecting zone.Yet the Cu too high levels can cause the deterioration of on-the-spot weldability and welding heat influence area toughness.
Ni：0-1.0wt％
Nickel (Ni) is a kind of element that mechanical property does not make the on-the-spot weldability and the low-temperature flexibility deterioration of soft steel again that improves.Compare with Mo with Mn, Ni forms the martensite-austenite composition of the made low-temperature flexibility deterioration of less amount, and has improved the toughness of welded heat affecting zone.In addition, Ni can effectively prevent the surface cracking that copper causes in continuous casting and course of hot rolling.Yet Ni is a kind of element of costliness, and excessive interpolation Ni can cause the toughness deterioration of welded heat affecting zone.
Nb：0.02-0.06wt％
Niobium (Nb) adds to promote the grain refining of steel rolling microstructure, and this can improve intensity and toughness simultaneously.The carbonitride of the Nb that in course of hot rolling, forms [Nb (C, N)] by delaying austenite recrystallization and suppress grain growing to generate tiny austenite crystal.When Nb was added in the steel with Mo, Nb can improve the effect of grain refining by suppressing austenite recrystallization, and makes the steel reinforcement that positive effect be arranged by precipitation strength and hardenability raising.In the presence of boron, niobium can be worked in coordination with the raising hardenability.Obtain this effect, the niobium of adding preferably is at least 0.02wt%.Yet the Nb content that surpasses 0.06wt% makes the further raising of unlikely desired result, and is unfavorable to the toughness of weldability and welded heat affecting zone on the contrary.
V：0-0.1wt％
Although vanadium (V) has the similar effects with Nb, the effect of adding V is more not outstanding.Yet when V was added into Nb, described effect can obviously strengthen.Yet, take the toughness of weldability and welded heat affecting zone into account, be limited to 0.1wt% on the V content.
Mo：0.1-0.5wt％
Molybdenum (Mo) can improve hardenability, and very obvious when adding fashionable this effect with B.In addition, fashionable when adding with Nb, Mo helps grain refining by suppressing austenite recrystallization.Yet because the excessive of Mo adds the deterioration that affiliation causes welding heat influence area toughness in the site welding process, so the content of Mo is 0.5wt% or lower.More preferably, the Mo of adding is 0.15wt% or still less.
Cr：0-1.0wt％
Chromium (Cr) is used to improve hardenability.Yet, welds the back at the scene and produce the toughness deterioration that cold cracking causes welded heat affecting zone and matrix owing to Cr excessive adds affiliation, so the upper content limit of Cr is 1.0wt%.
Ti：0.005-0.03wt％
Titanium (Ti) combines with nitrogen and forms tiny titanium nitride (TiN), suppresses austenite crystal alligatoring when the heating slab, thereby helps grain refining.In addition, TiN not only prevents the grain coarsening of welded heat affecting zone, but also nomadic nitrogen is fixed in the molten steel, thereby improves toughness.For abundant fixedly nomadic nitrogen, the titanium amount of adding is preferably at least 3.4 times (by weight) of nitrogen amount.Therefore, Ti is a kind of high strength and grain refining effective elements to matrix metal and welded heat affecting zone, and its form with TiN exists to suppress the grain growing in the rolling heat-processed.In addition, react remaining Ti with N and be dissolved in the steel with the form of sosoloid and combine with C and form very tiny TiC precipitation, it can significantly improve the intensity of steel.When aluminium content is very low (less than 0.005wt%), titanium forms the nucleation site of oxide compound as intergranular acicular ferrite in the heat affected zone.Therefore, suppress the effect of austenite crystal growth and, must add 0.005wt% or more Ti with the TiN precipitation for obtaining with forming the effect that TiC gains in strength.On the other hand, if Ti content surpasses 0.03wt%, too much Ti content can cause the grain coarsening of titanium nitride and cause titanium carbide inductive deposit sclerosis, thereby significantly reduces low-temperature flexibility.And when coming welding steel with the production steel pipe by heating steel plate to fusing point, TiN is dissolved in the steel plate once more, thereby makes the toughness deterioration of welded heat affecting zone.Therefore, Ti content on be limited to 0.03wt%.
Al：0.01-0.06wt％
Aluminium (Al) is a kind of element that adds in order to make the steel deoxidation usually.In addition, Al not only helps the refinement microstructure, but also improves the toughness of heat affected zone by the nomadic nitrogen of removing in the coarse grain of heat affected zone, thereby welding heat can make TiN be partly dissolved liberating nitrogen in described heat affected zone.Yet,, will form aluminum oxide (Al if Al content surpasses 0.06wt%
2O
3) type impurity, described inclusion can damage the toughness of matrix metal and heat affected zone.Because deoxidation can realize that Al is not an element essential among the present invention by adding Ti and Si.
B：0.0005-0.0025wt％
Boron (B) can significantly improve hardenability and increase the weldability and the cold cracking resistance of soft steel.Particularly, thereby B is used to improve the effect that hardenability improves Mo and Nb, and is used to suppress the intergranular cracking that hydrogen causes by increasing grain-boundary strength.Yet, add too much B and can promote embrittlement crystal grain Fe
23(C, B)
6Formation.Therefore, the content of B must determine that its preferable range is 0.0005-0.0025wt% according to the content of other element that adds for the raising hardenability.
N：0.001-0.006wt％
Nitrogen (N) is a kind of element that suppresses the austenite crystal growth, thereby it forms the austenite crystal growth that the TiN precipitation suppresses welded heat affecting zone in slab heat-processed.Yet the N of too much content can cause the surface imperfection of slab and reduce effective hardenability of boron.In addition, solute N can damage the toughness of matrix and welded heat affecting zone.
Ca：0-0.006wt％
Ca is a kind of element that is used to control MnS inclusion shape and improves low-temperature flexibility.Yet when adding the Ca of volume in steel, a large amount of CaO-CaS can form and be converted into big bunch and big inclusion, and it can damage the cleanliness factor and the on-the-spot weldability of steel.
P:0.02wt% or still less
Phosphorus (P) is a kind ofly can combine the element that forms non-metallic inclusion and cause steel brittleness with Mn etc.Therefore, the necessary P content that reduces in the steel.Yet the content of too controlling P makes it have low-down content can cause serious burden in the steel production process, and the problems referred to above P content in steel is 0.02wt% or when lower and not serious.Therefore, P content on be limited to 0.02wt%.
S:0.005wt% or still less
Sulphur (S) is a kind ofly to combine with Mn etc. and cause for example hot short element of steel brittleness.According to the present invention, for causing the same consideration of burden of steel production process with control P, the upper content limit of S is 0.005wt%.
(microstructure of steel plate)
For obtaining high strength and excellent toughness, want steel plate and except that containing above-mentioned composition, also have following microstructure.
Particularly, according to the present invention, the microstructure of steel plate comprise as shown in Figure 4 the Bei Shi ferrite and acicular ferrite as shown in Figure 5, and the area fraction of the mixture of Bei Shi ferrite and acicular ferrite is 75% or higher.
Except that above-mentioned microstructure phase, described steel plate also can contain little fractional granular bainite.Yet,, be limited to 5% on its area fraction because granular bainite can cause the deterioration of low-temperature flexibility.
In addition, steel plate of the present invention has very thin microstructure.Because described steel plate has thinner microstructure, so it can more effectively stop crack propagation, thereby prevents brittle rupture.In view of the size of austenite crystal, the present inventor advises that the most preferred size of described crystal grain is 15 μ m or littler.
Steel plate of the present invention with above-mentioned composition and microstructure has 930MPa or higher yield strength, and 230J or more-40 ℃ of impelling strength, thereby satisfies character required for the present invention.
(manufacture method)
Below describe the method for making steel plate of the present invention in detail.Described method is that inventor of the present invention conceives for the steel plate that reaches target of the present invention is provided.
Method of the present invention generally includes: the second-heating slab; In the austenite recrystallization temperature scope on one or more hot rolling passes rolling slab through second-heating; Be lower than T
NrTemperature and be higher than Ar
3Further rolling described steel plate on the inherent one or more hot rolling passes of the temperature range of point of inversion; Steel plate with the rate of cooling cold rolling of 20-50 ℃/s; Under 200-400 ℃ temperature, stop cooling metal sheets subsequently.Preferably, institute's refrigerative steel plate carries out air cooling or cooling at room temperature.
Below will describe each condition of described method in detail:
Slab second-heating: 1050-1150 ℃
Owing to carry out slab heating and be in order effectively to carry out subsequently rolling and to make described steel have the mechanical property of wanting, so the slab heating must be carried out in a suitable temperature range.In the process of the described slab of heating, the even heating slab prevents that as much as possible excessive grain growth from being very important simultaneously so that sedimentary element fully is dissolved in the slab.If described heating is carried out being lower than under 1050 ℃, Nb or V can not be dissolved in the slab once more, and this makes and is difficult to obtain high tensile steel plate.And because the part recrystallization, austenite crystal forms unevenly, therefore is difficult to obtain high tenacity.On the contrary, if described heating is carried out being higher than under 1150 ℃, it is excessively thick that austenite crystal becomes, and causes the crystal grain of steel plate to increase, thus the toughness of the described steel plate of grievous injury.Therefore, the temperature range of described second-heating is preferably l050-l150 ℃.
Rolling condition
In order to obtain low-temperature flexibility, must contain thin austenite crystal in the steel plate, described crystal grain can obtain by controlled rolling temperature and draft.According to the present invention, rollingly preferably in two different temperature ranges, carry out.Because these two temperature ranges provide different recrystallization behaviors, so rolling condition need carry out different settings according to described different rolling temperature.At first, in the austenite recrystallization temperature scope, described slab is rolled with the total draft with respect to original slab thickness 20-80% by one or more hot rolling system passages.The rolling effect that can reach the reduction grain size in the austenite recrystallization temperature scope by austenite recrystallization.At this moment, when carrying out multi-pass when rolling, must suitably control the draft of each passage and time to prevent the grain growing after the austenite recrystallization.The low-temperature flexibility that is used to improve final steel plate by the thin austenite crystal of said process formation.Then, at T
Nr(temperature of recrystallization does not take place austenite) and Ar
3In the temperature range of austenite not re-crystallization, rolling slab further is rolled into steel plate by one or more rolling passes between (austenite-ferrite invert point).At this moment, rollingly carry out with total draft with respect to slab thickness 40-80% rolling in the austenite recrystallization temperature scope.At T
Nr(temperature of recrystallization does not take place austenite) and Ar
3The described crystal grain of rolling crushing in the temperature range between (austenite-ferrite invert point) also causes the strain-induced dislocations of crystal grain, thereby provides the nucleation site mutually for the low temperature conversion in the rolling postcooling process.
Rate of cooling: 20-50 ℃/s
Rate of cooling is to improve one of the toughness of described steel plate and important factor of intensity.Above cooling conditions is provided with in order to form above-mentioned Bei Shi ferrite or acicular ferrite.If steel plate cools off with low rate of cooling, will form crystal grain thick such as shown in Figure 6 the polygonal ferrite or the bad microstructure of granular bainite, thereby obviously reduce the intensity and the toughness of steel plate.On the contrary, if steel plate cools off with 50 ℃/s or high faster rate of cooling, steel plate can be because too much water coolant forms hard mutually as martensite or have shape defect as being out of shape.
Cooling is finished temperature: 200-400 ℃
Be the microstructure of control steel plate, steel plate must be cooled to the temperature that the effect of rate of cooling can fully realize.If to finish temperature be 400 ℃ or higher in cooling, what just be difficult to form q.s in steel plate has compact grained Bei Shi ferrite and an acicular ferrite, and this can cause the raising deficiency of yield strength.Cooling of the present invention finish temperature on be limited to 400 ℃.On the contrary, be 200 ℃ or lower if temperature is finished in cooling, not only cooling performance is saturated, and steel plate can be owing to undercooling is out of shape.
Embodiment
Have shown in the table 1 slab of forming to every kind and carry out second-heating, rolling and cooling steel plate with preparation 16mm thickness.That is, every kind of steel plate is all made under the same conditions.No matter the kind of steel how, slab all carries out second-heating under 1120 ℃, rolling 1050-1100 ℃ (austenite recrystallization temperature) then with the multi-pass that the total draft with respect to second-heating slab 73% carries out the 9-11 passage, under 750-950 ℃ (temperature of austenite not re-crystallization), carry out the rolling steel plate of making of secondary multi-pass of 9-11 passage then with total draft with respect to rolled slab 76%.Described steel plate cools off with the rate of cooling of 25-35 ℃/s after rolling immediately, and finishes in 250-350 ℃.Then, place air to carry out air cooling described steel plate.
Table 1
[table 1]
[table]
| Numbering | C | Si | Mn | Mo | Cr | Ni | Ti | Nb | V | Al | Cu | Ca ＊ | ?B ＊ | ?N ＊ | ?P ＊ | ?S ＊ |
| IS1 | 0.049 | 0.15 | 1.89 | 0.14 | 0.47 | 0.47 | 0.01 4 | 0.03 7 | 0.03 7 | 0.02 5 | 0.2 | 14 | 16 | 43 | 54 | 12 |
| IS2 | 0.051 | 0.15 | 1.89 | 0.13 | 0.50 | 0.50 | 0.01 5 | 0.04 0 | 0.04 0 | 0.02 3 | 0.2 | 10 | 10 | 39 | 70 | 10 |
| IS3 | 0.052 | 0.15 | 1.89 | 0.15 | 0.49 | 0.50 | 0.01 5 | 0.03 8 | 0.03 9 | 0.02 2 | 0.2 | 11 | 20 | 36 | 70 | 8 |
| IS4 | 0.050 | 0.15 | 1.90 | 0.30 | 0.30 | 0.49 | 0.01 5 | 0.04 0 | 0.04 3 | 0.02 2 | 0.2 | 14 | 11 | 45 | 58 | 9 |
| CS1 | 0.024 | 0.16 | 1.91 | 0.25 | 0.38 | 0.51 | 0.01 6 | 0.04 1 | 0.04 2 | 0.02 0 | 0.2 | 13 | 18 | 39 | 65 | 11 |
| CS2 | 0.122 | 0.15 | 1.88 | 0.16 | 0.45 | 0.51 | 0.01 6 | 0.04 3 | 0.03 8 | 0.02 1 | 0.2 | 10 | 15 | 38 | 56 | 9 |
| CS3 | 0.052 | 0.16 | 2.32 | 0.18 | 0.46 | 0.48 | 0.01 5 | 0.04 1 | 0.04 2 | 0.02 0 | 0.2 | 10 | 14 | 37 | 52 | 11 |
| CS4 | 0.051 | 0.15 | 1.88 | 0.20 | 0.46 | 0.49 | 0.03 8 | 0.04 2 | 0.04 0 | 0.02 0 | 0.2 | 12 | 14 | 42 | 62 | 10 |
| CS5 | 0.051 | 0.15 | 1.89 | 0.15 | 0.50 | 0.50 | 0.01 5 | 0.04 1 | 0.03 9 | 0.02 0 | 0.2 | 12 | 31 | 35 | 70 | 7 |
| CS6 | 0.052 | 0.16 | 1.91 | 0.25 | 0.53 | 0.51 | 0.01 7 | 0.04 3 | 0.03 7 | 0.02 1 | 0.2 | 12 | 43 | 37 | 60 | 8 |
IS: steel of the present invention, CS: contrast steel
In table 1, the content unit that is marked with the element of " * " is ppm, and the content unit of other element is in weight % (wt%).
As seen from Table 1, steel 1-4 of the present invention satisfies condition of the present invention.Yet the C content of contrast steel 1 is low excessively, and the C too high levels of contrast steel 2.In addition, the Mn too high levels of contrast steel 3, and the Ti too high levels of contrast steel 4.The B content that contrasts steel 5 and 6 is all too high.
To carry out tension test, shock test and measure ductile-brittle transition temperature with steel plate sample, the results are shown in the table 2 with slab manufacturing of forming shown in the table 1.
Table 2
[table 2]
[table]
| Numbering | The mark of BF+AF (%) | Initial austenite grain size (μ m) | Tensile strength (MPa) | vE-40 (J) | vTrs (℃) |
| IS1 | 83 | 12 | 984 | 276 | -113 |
| IS2 | 88 | 13 | 993 | 254 | -94 |
| IS3 | 78 | 11 | 976 | 258 | -93 |
| IS4 | 92 | 13 | 965 | 245 | -79 |
| CS1 | 65 | 12 | 467 | 285 | -98 |
| CS2 | 86 | 13 | 1053 | 102 | -48 |
| CS3 | 88 | 12 | 1012 | 175 | -64 |
| CS4 | 84 | 11 | 983 | 187 | -58 |
| CS5 | 62 | 13 | 1034 | 192 | -52 |
| CS6 | 57 | 13 | 1038 | 136 | -43 |
IS: steel of the present invention, CS: contrast steel
In table 2, vE-40 represents-40 ℃ of impelling strength, and vTrs represents ductile-brittle transition temperature, and BF represents the Bei Shi ferrite, and AF represents acicular ferrite.
As seen from Table 2, all have the steel capital of the present invention that the present invention forms and have 930MPa or higher tensile strength, 230J or higher-40 ℃ of impelling strength and-70 ℃ ductile-brittle transition temperature, thereby show the favorable mechanical performance.For the low excessively contrast steel 1 of C content, although its impelling strength is good, its tensile strength is very low, has only about half of steel of the present invention.For the contrast steel 2 of C too high levels, although it has 1000MPa or higher ultra-high tensile strength, its-40 ℃ of impelling strength are 102J, and its ductile-brittle transition temperature is-48 ℃.So, contrast steel 2 shows as the intensity and the flexible of conventional steel incompatible.In addition, the contrast steel 3 of Mn too high levels shows the character similar to contrasting steel 2.For the contrast steel 4 of Ti too high levels, its-40 ℃ of impelling strength and ductile-brittle transition temperature are undesirable.For the contrast steel 5 and 6 of B too high levels, although its intensity is good, its impelling strength and ductile-brittle transition temperature are not fully up to expectations.
So, can find the influence of depending on that steel plate of the present invention is formed.
For the slab of composition, under condition shown in the table 3, be rolled with steel 1 of the present invention.
Table 3
[table 3]
[table]
| Numbering | Slab second-heating temperature (℃) | Draft in the annealed zone (%) | Draft in the not re-crystallization district (%) | Rate of cooling (℃/s) | The cooling finish temperature (℃) |
| IE1 | 1110 | 73 | 76 | 22 | 225 |
| IE2 | 1122 | 74 | 75 | 25 | 350 |
| IE3 | 1134 | 70 | 78 | 29 | 372 |
| IE4 | 1145 | 77 | 72 | 33 | 296 |
| CE1 | 1112 | 75 | 74 | 24 | 425 |
| CE2 | 1165 | 75 | 74 | 32 | 250 |
| CE3 | 1185 | 74 | 75 | 27 | 472 |
| CE4 | 1114 | 73 | 76 | 15 | 289 |
| CE5 | 1120 | 70 | 78 | 17 | 466 |
| CE6 | 1130 | 90 | 35 | 25 | 244 |
IE: example of the present invention, CS: case of comparative examples
As in the table 3 as seen, example 1-4 of the present invention satisfies all conditions of the present invention.Yet case of comparative examples 1 is cooled with too high rate of cooling.Case of comparative examples 2 and 3 under too high second-heating temperature by second-heating.Especially, for case of comparative examples 3, not only the second-heating temperature is too high, and cooling to finish temperature also too high.For case of comparative examples 4 and 5, rate of cooling is low excessively.Especially, for case of comparative examples 5, not only rate of cooling is low excessively, and cooling to finish temperature too high.For case of comparative examples 6, low excessively at the draft in not re-crystallization district.
To carry out tension test, shock test by the steel plate sample of table 3 condition manufacturing and measure ductile-brittle transition temperature, the results are shown in table 4.
Table 4
[table 4]
[table]
| Numbering | The mark of BF+AF (%) | Initial austenite grain size (μ m) | Tensile strength (MPa) | vE-40 (J) | vTrs (℃) |
| IE1 | 88 | 8 | 984 | 276 | -113 |
| IE2 | 84 | 12 | 993 | 254 | -94 |
| IE3 | 88 | 14 | 976 | 258 | -93 |
| IE4 | 94 | 13 | 965 | 245 | -79 |
| CE1 | 65 | 14 | 865 | 268 | -98 |
| CE2 | 86 | 25 | 934 | 197 | -64 |
| CE3 | 88 | 30 | 823 | 189 | -50 |
| CE4 | 64 | 15 | 834 | 187 | -48 |
| CE5 | 61 | 12 | 852 | 218 | -52 |
| CE6 | 57 | 15 | 879 | 143 | -42 |
IE: example of the present invention, CE: case of comparative examples
In table 4, vE-40 represents-40 ℃ of impelling strength, and vTrs represents ductile-brittle transition temperature, and BF represents the Bei Shi ferrite, and AF represents acicular ferrite.
As seen from Table 4, have 930MPa or higher tensile strength and 230J or higher-40 ℃ of impelling strength all by the example 1-4 of the present invention of condition manufacturing of the present invention, thereby show the favorable mechanical performance.Yet,, therefore can not form thin low temperature phase suitably, and tensile strength is low because contrast steel 1 is cooled with too high rate of cooling.For contrast steel 2, because too high slab second-heating temperature has formed the austenite crystal of alligatoring, thereby reduced low-temperature flexibility.The too high contrast steel 3 of temperature is finished in too high and cooling for slab second-heating temperature, and its low-temperature flexibility is because identical with case of comparative examples 2 former thereby lower, and its tensile strength is owing to the reason identical with case of comparative examples 1 is also lower.For the low excessively contrast steel 4 of rate of cooling, the microstructure that has formed polygonal ferrite and granular ferritic mixture rather than wanted, thus reduced tensile strength and low-temperature flexibility.For contrast steel 5, low excessively rate of cooling is finished temperature owing to having caused low tensile strength and low-temperature flexibility with top identical reason with too high cooling.For in the not re-crystallization district with the rolling contrast steel 6 of low excessively draft, not only austenite crystal extends fully, and dislocation do not pile up in crystal grain, this causes the formation of low temperature phase insufficient.As a result of, case of comparative examples 6 has extremely fully low low-temperature flexibility.
By The above results, can find out the effect of manufacture method of the present invention.
As can obviously being found out by above description, the present invention can provide the steel plate that does not contain a large amount of Mo with high strength and excellent low-temperature flexibility.
Claims (8)
1. steel plate with superstrength and excellent low-temperature flexibility, % comprises in weight: 0.03-0.10%C, 0-0.6%Si, 1.6-2.1%Mn, 0-1.0%Cu, 0-1.0%Ni, 0.02-0.06%Nb, 0-0.1%V, 0.1-0.5%Mo, 0-1.0%Cr, 0.005-0.03%Ti, 0.01-0.06%Al, 0.0005-0.0025%B, 0.001-0.006%N, 0-0.006%Ca, 0.02% or P still less, 0.005% or S still less, and the Fe of surplus and unavoidable impurities, wherein microstructure contains the Bei Shi ferrite of at least 75 area percentages and the mixture of acicular ferrite.
2. steel plate with superstrength and excellent low-temperature flexibility, % comprises in weight: 0.03-0.10%C, 0-0.6%Si, 1.6-2.1%Mn, 0-1.0%Cu, 0-1.0%Ni, 0.02-0.06%Nb, 0-0.1%V, 0.1-0.5%Mo, 0-1.0%Cr, 0.005-0.03%Ti, 0.01-0.06%Al, 0.0005-0.0025%B, 0.001-0.006%N, 0-0.006%Ca, 0.02% or P still less, 0.005% or S still less, and the Fe of surplus and unavoidable impurities, wherein microstructure contains the Bei Shi ferrite of at least 75 area percentages and the mixture of acicular ferrite, and tensile strength is that to absorb energy be 230J or more for 930MPa or higher and-40 ℃ of charpy impacts.
3. claim 1 or 2 steel plate, wherein said steel plate contains 0.15wt% or Mo still less.
4. claim 1 or 2 steel plate, the microstructure of wherein said steel plate comprise with area fraction counts 5% or still less granular bainite.
5. claim 1 or 2 steel plate, wherein the full thickness size of austenite crystal should be less than 15 μ m.
6. a manufacturing has the method for the steel plate of superstrength and excellent low-temperature flexibility, and described method comprises:
With the plate slab second-heating to 1050-1150 ℃, described slab comprises in weight %: 0.03-0.10%C, 0-0.6%Si, 1.6-2.1%Mn, 0-1.0%Cu, 0-1.0%Ni, 0.02-0.06%Nb, 0-0.1%V, 0.1-0.5%Mo, 0-1.0%Cr, 0.005-0.03%Ti, 0.01-0.06%Al, 0.0005-0.0025%B, 0.001-0.006%N, 0-0.006%Ca, 0.02% or P still less, 0.005% or S still less, and the Fe of surplus and unavoidable impurities;
In the austenite recrystallization temperature district on one or more hot rolling passes with the rolling plate slab of the draft of 20-80% through second-heating;
In austenite recrystallization temperature or more be low to moderate Ar
3Draft with 40-80% on the inherent one or more hot rolling passes of temperature or higher temperature range will be rolled into steel plate through rolling plate slab;
Cool off through rolling steel plate with the rate of cooling of 20-50 ℃/s; With
Under 200-400 ℃ temperature, stop to cool off described steel plate.
7. the method for claim 6, wherein said plate slab contains 0.15wt% or Mo still less.
8. claim 6 or 7 method also comprise: behind the cooling completing steps with air cooling or at room temperature cool off described steel plate.
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| KR1020060107917A KR100851189B1 (en) | 2006-11-02 | 2006-11-02 | Steel plate for linepipe having ultra-high strength and excellent low temperature toughness and manufacturing method of the same |
| PCT/KR2007/005510 WO2008054166A1 (en) | 2006-11-02 | 2007-11-02 | Steel plate for linepipe having ultra-high strength and excellent low temperature toughness and manufacturing method of the same |
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- 2006-11-02 KR KR1020060107917A patent/KR100851189B1/en active IP Right Grant
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2007
- 2007-11-02 CA CA2668069A patent/CA2668069C/en not_active Expired - Fee Related
- 2007-11-02 CN CN2007800410343A patent/CN101535518B/en not_active Expired - Fee Related
- 2007-11-02 WO PCT/KR2007/005510 patent/WO2008054166A1/en active Application Filing
- 2007-11-02 JP JP2009535212A patent/JP5439184B2/en not_active Expired - Fee Related
- 2007-11-02 US US12/447,666 patent/US20100074794A1/en not_active Abandoned
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2013
- 2013-08-12 US US13/964,432 patent/US20140158259A1/en not_active Abandoned
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| CN1265711A (en) * | 1997-07-28 | 2000-09-06 | 埃克森美孚上游研究公司 | Ultra-high strength, weldable, essentially boron-free steels with superior toughness |
| CN1806062A (en) * | 2003-06-12 | 2006-07-19 | 杰富意钢铁株式会社 | Steel plate and welded steel tube exhibiting low yield ratio, high strength and high toughness and method for producing thereof |
Also Published As
| Publication number | Publication date |
|---|---|
| CN101535518A (en) | 2009-09-16 |
| CA2668069C (en) | 2012-06-12 |
| US20100074794A1 (en) | 2010-03-25 |
| KR20080040233A (en) | 2008-05-08 |
| JP2010509494A (en) | 2010-03-25 |
| US20140158259A1 (en) | 2014-06-12 |
| KR100851189B1 (en) | 2008-08-08 |
| JP5439184B2 (en) | 2014-03-12 |
| CA2668069A1 (en) | 2008-05-08 |
| WO2008054166A1 (en) | 2008-05-08 |
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