CN102753719B - There is high tensile steel plate and the manufacture method thereof of excellent resistance to brittle fracture - Google Patents

There is high tensile steel plate and the manufacture method thereof of excellent resistance to brittle fracture Download PDF

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Publication number
CN102753719B
CN102753719B CN201080063862.9A CN201080063862A CN102753719B CN 102753719 B CN102753719 B CN 102753719B CN 201080063862 A CN201080063862 A CN 201080063862A CN 102753719 B CN102753719 B CN 102753719B
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steel plate
fragility
high tensile
plate
excellent resistance
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CN102753719A (en
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金相镐
房基铉
徐仁植
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Posco Holdings Co ltd
Posco Holdings Inc
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Posco Co Ltd
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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
    • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
    • 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
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21B—ROLLING OF METAL
    • B21B3/00—Rolling materials of special alloys so far as the composition of the alloy requires or permits special rolling methods or sequences ; Rolling of aluminium, copper, zinc or other non-ferrous metals
    • B21B3/02—Rolling special iron alloys, e.g. stainless steel
    • 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
    • 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
    • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • 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
    • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0226—Hot rolling
    • 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
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • 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
    • C22C38/08—Ferrous alloys, e.g. steel alloys containing nickel
    • 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
    • C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
    • 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
    • C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
    • 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
    • C21D2201/00—Treatment for obtaining particular effects
    • C21D2201/05—Grain orientation
    • 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
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/002—Bainite
    • 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
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/005—Ferrite
    • 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
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/50—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for welded joints

Abstract

The present invention relates to a kind of steel plate in mother metal district and welded heat affecting zone with excellent resistance to embrittlement.More specifically, the present invention relates to a kind of high tensile steel plate with excellent resistance to embrittlement, and the manufacture method of this high tensile steel plate, wherein said steel plate comprises, in % by weight, C:0.02-0.06%, below Si:0.1%, Mn:1.5-2.0%, below P:0.012%, below S:0.003%, Ni:0.5-1.5%, Al:0.003-0.015%, Ti:0.005-0.02%, Nb:0.005-0.015%, N:0.002-0.006%, with Fe and the inevitable impurity of surplus, wherein the value of C+0.5Si-0.1Ni+6Al+3Nb is less than 0.1%.

Description

There is high tensile steel plate and the manufacture method thereof of excellent resistance to brittle fracture
Technical field
The present invention relates to the high tensile steel plate for offshore structures and building structure, more specifically, relate to at mother metal and welded heat affecting zone (Heat Affected Zone, HAZ) fragility opens splits the high tensile steel plate that (brittle crack initiation) has superior resistance, and its manufacture method.
Background technology
According to emerging economy center if the nations of China and India is to the quick growth of energy requirement, setting about the exploitation of the petroleum resources to extremely cold region, particularly Karafuto and the Arctic Ocean, these regions are not being developed before due to low income.
In order to ensure the safety of buildings, the steel used in the buildings in extremely cold region need to have high low temperature resistant fragility and open and split characteristic.Main use opens as the low temperature resistant fragility of assessment the method splitting characteristic based on crack tip opening displacement (Crack Tip Opening Displacement, the CTOD) test of fracture mechanics.
Up to the present, CTOD test is mainly used to assessment and opens to the fragility of welded heat affecting zone the resistivity split.Unlike this, for mother metal district be with shock test replace CTOD test.But, because consider that iceberg is collided, the high-strength steel plate with more than 50mm is widely used on the offshore structures being built in region as extremely cold in Karafuto and the Arctic Ocean etc., in addition, embrittlement may be produced after propagating into mother metal district along the direction applying cyclic stress in the fatigue crack originating from welding region by fatigue crack (fatigue crack) under special conditions, for mother metal district and welded heat affecting zone, there is high-caliber resistance to fragility and open that to split characteristic be required.
Open about having excellent low temperature resistant fragility the steel plate splitting characteristic, its correlation technique is as described below.
Open No. 2002-0028203rd, the text of korean patent application discloses the method that one prevents brittle rupture in welded heat affecting zone (brittle fracture) from producing, the grain coarsening produced near welded bonds (Fusion Line) when it suppresses to weld by adding magnesium (Mg).But this patent only guarantees preventing for the brittle rupture at temperature more than-10 DEG C, the resistivity for the brittle rupture such as under-40 DEG C of low temperature therefore can not be guaranteed.
Equally, open No. 2008-0067957th, the text of korean patent application discloses a kind of technology, specific as follows: by preventing the toughness occurred in welded heat affecting zone from sharply reducing aluminium (Al) or niobium (Nb) lower than the restriction of preset limit value, and by using the less manganese (Mn) of the Toughness of welded heat affecting zone even if guarantee that opening ripper to the fragility of welded heat affecting zone under the low temperature of-40 DEG C has resistivity.But, this patent not to the fragility in the mother metal district differing from welded heat affecting zone open split how to guarantee resistivity method be described.
Simultaneously, the fragility that open No. 2006-0090287th, the text of korean patent application discloses mother metal district under a kind of p-40 DEG C of low temperature and welded heat affecting zone opens the manufacture method that ripper has the steel of superior resistance, as the technology guaranteeing steel plate physical properties, it suppresses the formation on martensite island by reducing carbon (C) content, and make use of copper (Cu) precipitation that the Cu owing to adding more than 0.8% is formed and the deposit sclerosis produced.But, because this patent is in order to obtain Cu precipitation, after carrying out controlled rolling and accelerating cooling under the state of adding Cu wherein in a large number, needing extra ageing treatment, the loaded down with trivial details and manufacturing cost of manufacturing processed therefore may be caused to improve.
Summary of the invention
the problem that invention will solve
One aspect of the present invention provides one to have excellent resistance to fragility and opens and split characteristic, the fragility of mother metal district and welded heat affecting zone (HAZ) at low temperatures can be suppressed to open split and have 420MPa with the high tensile steel plate of upper yield strength, and manufactures the method for this high tensile steel plate.
the scheme of dealing with problems
One aspect of the present invention provides to be had excellent resistance to fragility and opens the high tensile steel plate splitting characteristic, and it comprises: the C(carbon of 0.02wt%-0.06wt%); The Si(silicon of below 0.1wt%); The Mn(manganese of 1.5wt%-2.0wt%); The P(phosphorus of below 0.012wt%); The S(sulphur of below 0.003wt%); The Ni(nickel of 0.5wt%-1.5wt%); The Al(aluminium of 0.003wt%-0.015wt%); The Ti(titanium of 0.005wt%-0.02wt%); The Nb(niobium of 0.005wt%-0.015wt%); The N(nitrogen of 0.002wt%-0.006wt%); With the Fe(iron of surplus) and inevitable impurity, wherein, the value of C+0.5Si-0.1Ni+6Al+3Nb is at below 0.1wt%.
Another aspect of the present invention provides to manufacture has the method that excellent resistance to fragility opens the high tensile steel plate splitting characteristic, and it comprises: within the scope of 1000 DEG C-1100 DEG C, heating meets the plate slab of above-mentioned compositing range; Accumulative draft (cumulativereduction rate) slab to described heating with more than 40% at temperature more than 950 DEG C carries out roughing; Within the scope of 700-800 DEG C, finish rolling is carried out after roughing; And the steel plate after cold rolling.
invention effect
One aspect of the present invention, the fragility of the mother metal under the low temperature of yield strength, simultaneously p-60 DEG C and-40 DEG C with more than 420MPa and welded heat affecting zone can be provided to open the high tensile steel plate that ripper has superior resistance, and manufacture the method for described high tensile steel plate.Above-mentioned Plate Steel may be used for offshore structures, building structure, boats and ships and the oil tanker etc. that run in extreme environment.
Accompanying drawing explanation
Fig. 1 represents the chart of crack tip opening displacement (CTOD) test-results of the welded heat affecting zone according to C+0.5Si-0.1Ni+6Al+3Nb numerical value.
Fig. 2 represents the chart of the CTOD test-results in the mother metal district according to effective size of grain (effective grain size).
Embodiment
Below, the present invention is specifically described.
The present inventor recognizes that the martensite island structure resulting from welded heat affecting zone is the reason producing embrittlement in welded heat affecting zone at low temperatures.Specifically, even if because very small amount of martensite island is present in welded heat affecting zone also may cause brittle rupture in crack tip opening displacement (CTOD) test under the such as low temperature of-40 DEG C, therefore the present inventor recognizes that the suppression on martensite island is very important, and conducts in-depth research the generation of the martensite island structure suppressing welded heat affecting zone.
In addition, as the result studied the reason producing embrittlement in the Plate Steel mother metal of more than 50mm thickness, the present inventor has also found that brittle rupture mainly occurs in the plate center on steel plate thickness direction, and embrittlement originates from the crystal grain place of relative coarseness in the crystal grain of thickness direction Shang Ban center in microtexture, simultaneously as the result furtherd investigate the method for suppression embrittlement, the present inventor completes the present invention.
Below, the compositional range counted with part by weight (hereinafter, wt%) of the present invention is specifically described.
Carbon (C): 0.02%-0.06%
Because C forms to betide welded heat affecting zone thus the important alloying element causing the martensite island of brittle rupture, be therefore necessary that the content first limiting C is to suppress the formation on martensite island.If the content of C is higher than 0.06%, then can not realize object of the present invention owing to fully not suppressing martensite island.Therefore, the upper limit of C preferably defines 0.06%.But, if the content of C is too low, be difficult to ensure the intensity of steel plate, therefore preferably by its lower limit 0.02%.
Silicon (Si): less than 0.1% (not comprising 0%)
Si improves necessary element in the tensile strength in mother metal district and the deoxidation of steel, but, by formed through Thermal Cycle do not change austenite cool and form final structure time, Si prevents not changing austenite decomposition and becomes ferrite and cementite, thus promote the formation on martensite island, therefore significantly reduce CTOD toughness in welding heat affected region.Therefore, the addition of Si preferably defines below 0.1%.
Manganese (Mn): 1.5%-2.0%
Because Mn is the useful element guaranteeing intensity, the Mn of more than 1.5% must be added to guarantee the intensity of steel plate.But, if the addition of Mn is too much, then promote the formation of the center segregation in a thickness direction at plate center, and facilitate the formation on the martensite island in the part being formed with center segregation partly, therefore it is significantly degrading the CTOD characteristic in welding heat affected region.Therefore the upper limit of Mn preferably defines 2.0%.
Phosphorus (P): less than 0.012%, sulphur (S): less than 0.003%
Because P and S is the element producing embrittlement of grain boundaries (grain boundaryembrittlement) in welded heat affecting zone, be necessary minimized for the content of P and S.But it is inconvenient for P and S being reduced to very low level in steelmaking process, therefore the content of P is limited to less than 0.012%, and the content of S is limited to less than 0.003%.
Nickel (Ni): 0.5%-1.5%
Ni can improve hardening capacity and promote the formation on martensite island.But effect is compared therewith, the toughness strengthening effect of the matrix brought is more outstanding, therefore with other alloying element differently, Ni can to the toughness effect that be improved in welding heat-affected zone.In addition, the toughness of the matrix caused by Ni is improved effect and also can be presented in mother metal district, and the toughness therefore for reinforcement mother metal district is also effective.In addition, in order to ensure armor plate strength required in the present invention under the state that the content at C and Si is extremely limited, Ni needs the content of interpolation more than 0.5%.But if add excessive Ni, the effect that substrate tissue toughness strengthens will reach capacity, and therefore preferably its upper limit will be limited to 1.5%.
Aluminium (Al): 0.003%-0.015%
Similar to Si, Al is by preventing from impelling by unconverted austenitic formation ferrite and cementite the element that martensite island is formed in Thermal Cycle process.If Al adds the content more than 0.015%, then significantly reduce the toughness of welded heat affecting zone, therefore preferably its upper limit is limited to 0.015%.But Al is very effective elements for the deoxidation of steel.If the content of Al is low too under the state that Si content is limited to less than 0.1% in the present invention, the deoxidation of steel can not fully realize, and therefore the spatter property of steel may significantly worsen.Therefore, Al preferably adds the content of more than 0.003%.
Titanium (Ti): 0.005%-0.02%
Ti, by forming tiny nitride to prevent the grain coarsening produced near weld-fusion line place in conjunction with nitrogen (N), therefore improves the toughness of welded heat affecting zone.If the content of Ti is too low, then due to the formation that Ti nitride is insufficient, the grain coarsening near weld-fusion line place possibly cannot be prevented.Therefore, Ti preferably adds the amount of more than 0.005%.But, if Ti adds with the content more than 0.02%, while formation Ti nitride, also form Ti carbide, and the hardness of mother metal district and welded heat affecting zone may improve due to the precipitation hardening effect of Ti carbide, therefore, fragility opens the possibility split can increase.Therefore, its upper limit preferably defines 0.02%.
Niobium (Nb): 0.005%-0.015%
Nb be reduce when adding to the resistivity of the brittle rupture of welded heat affecting zone alloying element.But Nb very contributes to refined structure in controlled rolling-accelerating cooling process, therefore Nb be improve to the resistivity of the brittle rupture in mother metal district important element.Specifically, in the Plate Steel of more than 50mm thickness, the effective size of grain of required for the present invention less than 30 μm is difficult to obtain, even if carried out controlled rolling-accelerating cooling process, carries out structure refinement except non-concurrent adds Nb.Therefore, Nb preferably adds more than 0.005% content to guarantee the resistivity of the brittle rupture to mother metal district wanted required for the present invention.But when Nb adds excessive, may promote the generation on martensite island to such an extent as to the toughness of deterioration welded heat affecting zone, therefore, its upper limit preferably defines 0.015%.
Nitrogen (N): 0.002%-0.006%
N forms TiN particle in conjunction with Ti, therefore prevents the grain coarsening near weld-fusion line.Therefore, the content of more than 0.002% may be needed to comprise to obtain above-mentioned effect.But when N is by excessive interpolation, the toughness of mother metal district and welded heat affecting zone may worsen due to the free atom N be not combined with Ti.Therefore, the upper limit of N preferably defines 0.006%.
In the present invention, enough physical propertiess can be ensured by above-mentioned basal component.But, the characteristic that copper (Cu) improves steel plate further can be added.The content of Cu can be less than 0.35%.Cu can guarantee armor plate strength and the alloying element relatively less to the toughness infringement of welded heat affecting zone.But armor plate strength excessively improves when Cu excessive interpolation, therefore, stable CTOD toughness can not be obtained in mother metal district, and Cu crackle may start the surface occurring in slab and steel plate.Therefore, the upper limit of Cu preferably defines 0.35%.
Fe and inevitable impurity involved as surplus.
In the present invention, the value of the C+0.5Si-0.1Ni+6Al+3Nb in component preferably less than 0.1%.
On affecting after alloying element that martensite island, welded heat affecting zone produces done to further investigate, the present inventor obtain a kind of hot input range be 0.8kJ/mm-4.5kJ/mm low-in heat input welding condition under by the minimized method of generation on the martensite island of welded heat affecting zone.
In order to infer the mutual relationship between alloying element and welded heat affecting zone based on above-mentioned result of study, present inventor has performed welded heat affecting zone simulated experiment, it is used for simulating critical reheating coarse-grain (intercritically reheated coarse grained) district, and this district is known to a region forming a large amount of martensite islands in welded heat affecting zone.
Carry out in such manner to the simulation of critical reheating coarse grain zone: the small samples with 10mm thickness, 10mm width and 60mm length is heated to the temperature of 1400 DEG C, then cool in the temperature range of 800 DEG C-500 DEG C with the rate of cooling of 20 DEG C/s, and critical reheating, afterwards with the cooling of the rate of cooling of 20 DEG C/s in the temperature range of maximum heating temperature to 500 DEG C.Introduce fatigue crack be up to heat affected zone analog sample width 50%, then at-40 DEG C, carry out CTOD test.Relation between the CTOD toughness that the result of test infers alloying element and welded heat affecting zone, and its result presents in FIG.
Fig. 1 illustrates the relation between the critical CTOD trial value at the value of C+0.5Si-0.1Ni+6Al+3Nb and obtain from the analog sample of heat affected zone-40 DEG C.Can know, the value of C+0.5Si-0.1Ni+6Al+3Nb is lower, and the CTOD threshold value of the welded heat affecting zone at-40 DEG C is higher.If the value of C+0.5Si-0.1Ni+6Al+3Nb is higher than 0.2%, then all there is brittle rupture in all samples.According to Fig. 1, can know, the value of C+0.5Si-0.1Ni+6Al+3Nb must be less than 0.1% reach more than 0.25mm to make the CTOD threshold value measured at-40 DEG C.
In formula C+0.5Si-0.1Ni+6Al+3Nb, during interpolation C, Si, Al and Nb alloying element, the fragility facilitated in welded heat affecting zone opens and splits, but only has Ni to have adverse effect.The substrate tissue toughness's stiffening effect to the explanation of its reason being Ni is more obvious than the effect reducing toughness by increase martensite island as hardening element in welded heat affecting zone.
In steel plate of the present invention, the average circular equivalent diameter of the crystal grain of the size in minimum more than 5000 crystal grain with---the described crystal grain plate center be defined as in steel plate thickness direction is the border of more than 15 degree by the grain orientation difference that Electron Back-Scattered Diffraction figure (ElectroBack-Scattered Pattern, EBSP) method is measured---front 5% is preferably below 30 μm.In the present invention, thickness direction Shang Ban center be defined as being positioned at distance steel plate thickness 1/2 place in a thickness direction ± 1mm.
Usually, the image analysis method based on optical microscope image is used for the measurement of granularity.But, in described image analysis method, only have when microtexture is made up of polygonal ferrite and perlite, can analyze relatively accurately it; Because grain boundary have pin type ferrite or its to be mixed with in the microtexture of bainite be unsharp, may be therefore very difficult to the accurate measurement of granularity.
Therefore, the present inventor adopts the EBSP method based on Kikuchi pattern, its objective is the granularity at detect thickness direction upper plate center more accurately.EBSP method has the advantage can not carrying out quantitative analysis by Effects on Microstructure ground to intergranular misorientation.When by this method definition crystal grain, there are more than the 15 degree borders measuring intergranular misorientation and be defined as wide-angle grain boundary.
By the size-grade distribution of the plate center on the thickness direction utilizing EBSP method to obtain and CTOD characteristic are compared, can find, resistance to fragility open split characteristic be by have belong to whole size-grade distribution before 5% the crystal grain of size determine, instead of by be defined as wide-angle grain boundary whole crystal grain size crystal grain and determine.That is, open to mother metal district fragility the resistivity split in order to improve, some coarse grains suppressing the microtexture at thickness direction Shang Ban center are very important.
In the present invention, be defined as in minimum more than 5000 particles on border (wide-angle grain boundary) what in the plate center measurement in steel plate thickness direction there are more than 15 degree grain orientation differences by EBSP method, there is the average circular equivalent diameter of the crystal grain (Effective grain size) of the size of front 5%, be defined as effective size of grain.
In order to infer the effective size of grain that defines in the present invention and to the correlationship between the resistivity of the brittle rupture in mother metal district, by changing heating and rolling condition, being prepared the sample with multiple granularity by the slab consisting of 0.05C-0.04Si-1.62Mn-0.95Ni, and by utilize sample carry out CTOD test at various temperatures after obtain the critical CTOD transition temperature of 0.25mm.Here, transition temperature when 0.25mm critical CTOD transition temperature represents that the critical CTOD value of mensuration is 0.25mm.Show in fig. 2 from the mutual relationship between the effective size of grain of each sample and the critical CTOD transition temperature of 0.25mm.
As shown in Figure 2, when the effective size of grain defined in the present invention is below 30 μm, can obtain-60 DEG C of lower critical CTOD minimum value is the steel plate of more than 0.25mm.When effective size of grain is greater than 30 μm, the critical CTOD value in the steel plate mother metal district of-60 DEG C becomes below 0.25mm, therefore, possibly cannot reach target of the present invention.
In addition, here the basic microtexture at thickness direction upper plate center preferably comprise ferrite, bainite or by them not containing martensitic composite structure.Reason is, though due to martensitic hardness too high to such an extent as under the such as extremely low temperature of-60 DEG C, also easily cause phenomenon of advancing by leaps and bounds (pop-in phenomenon) having in fine-grained situation, thus cannot guarantee target CTOD threshold value.
That is, in steel plate of the present invention, because be more than 0.25mm the mother metal district CTOD threshold value of-60 DEG C, and welded heat affecting zone (HAZ) the CTOD threshold value in the welding process of-40 DEG C is more than 0.25mm, the therefore mother metal district also characteristic that obtain excellent anti-low-temperature embrittleness the same as welded heat affecting zone.
Below manufacture method of the present invention is specifically described.
The plate slab meeting described composition heats in the temperature range of 1000 DEG C-1100 DEG C.
Described slab preferably uses the slab of continuous casting.Because casting process has than ingot iron process molten steel solidification speed and the rate of cooling after solidifying faster, meticulousr TiN particle can be obtained in material, therefore can improve and the resistivity split is opened to mother metal district and welded heat affecting zone fragility.
The Heating temperature of slab is the important factor affecting final structure granularity.When the Heating temperature of slab is higher than 1100 DEG C, can not fully refinement final structure, and make the TIN particle in structure become coarse and reduce the toughness in welding heat affected region.Therefore, its upper limit preferably defines at 1100 DEG C.On the contrary, when the Heating temperature of slab is lower than 1000 DEG C, alloying element may dissolve insufficient, and the abundant rolling on recrystallization temperature may be difficult.Therefore, the heating of slab can be carried out under the temperature more than 1000 DEG C.
After heating slab, at the temperature of the accumulation draft with more than 40% more than 950 DEG C, carry out roughing.The recrystallization of austenite grains occurs in the temperature of more than 950 DEG C actively, and therefore granularity can reduce.In addition, the reason with more than 40% accumulation draft be accumulation draft lower than 40% time may produce mixing crystal grain (mixed grain) because the recrystallization of austenite crystal occurs insufficient in final structure.
Finish rolling can be carried out in the temperature range of 700 DEG C-800 DEG C.When final rolling temperature is higher than 800 DEG C, opening to fragility the resistivity split may can not be guaranteed because the structure refinement at thickness direction upper plate center completes insufficient.Final rolling temperature is lower, and the structure at thickness direction upper plate center may be meticulousr.But, when final rolling temperature is too low, cause too low therefore may being difficult to of the yield of rolling industrially to be applied.Therefore, its lower limit preferably defines at 700 DEG C.
In addition, finish rolling is preferably carried out when accumulation draft is at least more than 40%, with further refinement final structure.
Cooling is carried out after described controlled rolling, and here, rate of cooling and cooling termination temperature are preferably respectively in the scope of 3 DEG C/s-20 DEG C/s and 350 DEG C-550 DEG C.Because when intensity is excessively split higher than promoting during target value that fragility opens, it is very important for therefore not having too high intensity.Viewpoint like this, rate of cooling and cooling termination temperature can be more than 20 DEG C/below s and 350 DEG C respectively.But because target strength of the present invention can not obtain when cooling insufficient, rate of cooling and cooling termination temperature can be below 3 DEG C/more than s and 550 DEG C respectively for this reason.
Embodiment
Below embodiment of the present invention are specifically described.But the present invention is not limited to following embodiment.
(embodiment)
In 300 tons of electric furnaces, prepare molten steel according to the component shown in table 1, and prepare the slab of 300mm by continuous cast method.As shown in table 2, the slab prepared thus carries out heating and carrying out roughing and finish rolling, and prepares steel by final accelerating cooling.
Electron Back-Scattered Diffraction figure (EBSP) equipment being installed on scanning electronic microscope (SEM) can be used to measure the effective size of grain of prepared steel plate.Enlargement ratio used is in the scope of 300 times-500 times, and step-length is 0.75 μm, observes at the thickness direction of rolling cross section and thickness direction Shang Ban center.In order to obtain significant data value, contain minimum more than 5000 crystal grain on the border being defined as the grain orientation difference with more than 15 degree.By using the software can analyzing the misorientation measured by EBSP method, calculate the effective size of grain defined in the present invention.Tension test is undertaken by the sample collecting the steel plate prepared through the condition shown in table 1 and 2, and carries out CTOD test with the resistivity of assessment to the brittle rupture in mother metal district.After carrying out collection sample with 1/4 place of the steel plate thickness on distance surface, the mode that becomes the length direction of sample perpendicular to the direction of rolling direction, sample machine is machined for the clavate sample of tension test.Thick sample is helped in the processing of CTOD sample evidence BS7448 standard, and the length direction of sample is perpendicular to rolling direction.After making groove by electrodischarge machining(E.D.M.) in CTOD sample, produce until the fatigue crack of 50% specimen width, CTOD test afterwards carries out three times to each sample at the temperature of-60 DEG C and its minimum value of each sample is assessed.
Split characteristic in order to the resistance to fragility assessing the welded heat affecting zone of made Plate Steel opens, assess according to APIRP2Z standard.Make according to API RP2Z standard and singly burst at the seams, and weld under medicine core welding arc weldering (Flux Cored Arc Welding) and the thermal weld stress of submerged arc welding (Submerged Arc Welding) are respectively 0.8kJ/mm and 4.5kJ/mm.According to BS7448 standard, in mother metal district, thick sample is helped in welded sample processing, and fatigue crack is incorporated in the coarse grain region of weld-fusion line.CTOD test afterwards carries out three times to each sample at-40 DEG C and its minimum value of each sample is assessed.
Table 3 represents the steel plate yield strength and tensile strength that are obtained by tension test, and the CTOD threshold value of the mother metal district assessed at-60 DEG C and-40 DEG C respectively and welding region.Wherein, each CTOD threshold value shown in table 3 is minimum in three trial values, and CTOD-60 represents the CTOD trial value assessed in the mother metal district of-60 DEG C, and CTOD-40 represents the CTOD trial value assessed the welded heat affecting zone of-40 DEG C.
[table 1]
[table 2]
[table 3]
In the example 1-16 institute of correspondence composition of the present invention and manufacture method, the effective size of grain that the present invention determines is less than 30 μm, at-60 DEG C, the CTOD threshold value in the mother metal district of assessment is more than 0.25mm, and the CTOD minimum value of the welded heat affecting zone under low middle heating initial conditions at-40 DEG C is also more than 0.25mm, therefore, extraordinary anti-fragility can be obtained and open fragility.
On the contrary, in comparative example 1, the CTOD value of welded heat affecting zone, not higher than 0.25mm, is because the value of C+0.5Si-0.1Ni+6Al+3Nb is beyond 0.1%.Si and Al in comparative example 2 do not meet scope of the present invention and the value of C+0.5Si-0.1Ni+6Al+3Nb also up to 0.199%, therefore, the CTOD characteristic of the welded heat affecting zone of-40 DEG C is non-constant.
In comparative example 3, Nb has departed from the scope of the invention and the value of C+0.5Si-0.1Ni+6Al+3Nb is also more than 0.1%.In comparative example 4, the value of C+0.5Si-0.1Ni+6Al+3Nb is less than 0.1%, and it reaches target of the present invention.But the toughness of the scope that the content due to C defines higher than the present invention thus welded heat affecting zone is inadequate.In comparative example 5, due to the deficiency of Ni content, armor plate strength is inadequate, and the toughness of mother metal district and welded heat affecting zone is all inadequate.
About comparative example 6-8, alloy compositions belongs to the scope of the invention, and the value of C+0.5Si-0.1Ni+6Al+3Nb is less than 0.1%, and therefore, the toughness of welded heat affecting zone is not very poor.But because manufacturing condition required for the present invention does not meet, effective size of grain is more than 30 μm.In addition, in comparative example 7, intensity does not reach level of the present invention yet.In comparative example 9, the toughness of welded heat affecting zone worsens beyond 0.1% due to the value of C+0.5Si-0.1Ni+6Al+3Nb, and due to the rate of cooling in manufacturing condition insufficient and cause the yield strength of steel plate not reach 420MPa.

Claims (5)

1. there is excellent resistance to fragility and open the high tensile steel plate splitting characteristic, comprise:
The C of 0.02wt%-0.06wt%,
The Si of below 0.1wt%,
The Mn of 1.5wt%-2.0wt%,
The P of below 0.012wt%,
The S of below 0.003wt%,
The Ni of 0.5wt%-1.5wt%,
The Al of 0.003wt%-0.015wt%,
The Ti of 0.005wt%-0.02wt%,
The Nb of 0.005wt%-0.015wt%,
The N of 0.002wt%-0.006wt% and
As Fe and the inevitable impurity of surplus,
Wherein, the value of C+0.5Si-0.1Ni+6Al+3Nb is below 0.1wt%, and wherein, the average circular equivalent diameter of the crystal grain of the size in minimum more than 5000 crystal grain with---the grain orientation difference that described crystal grain is defined as being measured at the plate center in steel plate thickness direction by Electron Back-Scattered Diffraction drawing method is the border of more than 15 degree---front 5% is less than 30 μm, and wherein said steel plate is thickness is the Plate Steel of more than 50mm, CTOD threshold value in steel plate mother metal district at-60 DEG C is more than 0.25mm, and the CTOD threshold value in the welded heat affecting zone (HAZ) at-40 DEG C is more than 0.25mm,
And described steel plate is prepared by a method comprising the following steps:
A kind of plate slab is heated in 1000 DEG C of-1100 DEG C of temperature ranges, described plate slab comprise the C of 0.02wt%-0.06wt%, Mn, the P of below 0.012wt% of Si, 1.5wt%-2.0wt% of below 0.1wt%, Ni, 0.003wt%-0.015wt% of S, 0.5wt%-1.5wt% of below 0.003wt% Al, 0.005wt%-0.02wt% Ti, 0.005wt%-0.015wt% Nb, 0.002wt%-0.006wt% N and as the Fe of surplus and inevitable impurity, and there is the value of the C+0.5Si-0.1Ni+6Al+3Nb of less than 0.1%;
The temperature roughing of accumulation draft with more than 40% more than 950 DEG C is heated plate slab,
After roughing, in the temperature range of 700 DEG C-800 DEG C, carry out finish rolling; And
The steel plate that cooling is rolled.
2. the excellent resistance to fragility that has of claim 1 opens the high tensile steel plate splitting characteristic, and its light plate also comprises the Cu of below 0.35wt%.
3. the excellent resistance to fragility that has of claim 1 opens the high tensile steel plate splitting characteristic, and wherein, the structure being arranged in the plate center in steel plate thickness direction comprises any one of ferrite, bainite and its composite structure.
4. the excellent resistance to fragility that has of claim 1 opens the high tensile steel plate splitting characteristic, and wherein, finish rolling is carried out with the accumulation draft of more than 40%.
5. the excellent resistance to fragility that has of claim 1 opens the high tensile steel plate splitting characteristic, and wherein, the rate of cooling in process of cooling and cooling termination temperature are respectively within the scope of 3 DEG C/s-20 DEG C/s and 350 DEG C-550 DEG C.
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