CN101545080B - 590 mpa high yield ratio round steel pipe for building structure with excellent shock resistance and production process - Google Patents

590 mpa high yield ratio round steel pipe for building structure with excellent shock resistance and production process Download PDF

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Publication number
CN101545080B
CN101545080B CN2009101296897A CN200910129689A CN101545080B CN 101545080 B CN101545080 B CN 101545080B CN 2009101296897 A CN2009101296897 A CN 2009101296897A CN 200910129689 A CN200910129689 A CN 200910129689A CN 101545080 B CN101545080 B CN 101545080B
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steel pipe
round steel
hardness
thickness
steel plate
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CN101545080A (en
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小林克壮
盐饱丰明
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Kobe Steel Ltd
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Kobe Steel 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
    • C22C38/18—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
    • 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
    • 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
    • C21D8/10—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of tubular bodies
    • C21D8/105—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of tubular bodies of ferrous alloys
    • 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
    • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
    • 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
    • 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
    • C22C38/18—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
    • 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
    • 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
    • C22C38/54—Ferrous alloys, e.g. steel alloys containing chromium with nickel with boron

Abstract

The round steel pipe not only satisfies the determined relational expression, but also regulates chemical composition, satisfies following conditions (A)-(C): (A) a microscopic constitution has bainitic steel with length-width ratio over 3 times, area percentage over 50% and dislocation density from 1.0*10[5](m[-2]) to 6.0*10[5](m[-2]); (B) the central portion for removing the surface portion 2mmfrom the front and the back face of the steel pipe has an average Vickers hardness of 180-280; (C) the surface portion 2mm from the front and the back face of the steel pipe has an average Vickers hardness below 1.4 times of the average Vickers hardness of the central portion. According to the construction, in utility of building steel reinforcement, hardness on external surface of steel pipe constituting a tensile stress field as an intrinsic subject of high hardness round steel pipe can be reduced, for a steel pipe of high hardness with tensile strength at 590MPa, which is helpful for shockresistance enhancement.

Description

The building structure of excellent shake proof property 590MPa level high-yield-ratio round steel pipe and manufacture method thereof
Technical field
The present invention relates generally to round steel pipe and the manufacture method thereof towards the building iron purposes that requires vibration strength, particularly relate to tensile strength (590MPa level) more than 590MPa, yield tensile ratio is 85～95% high strength high-yield-ratio round steel pipe and the useful method that is used to make this round steel pipe.
Background technology
Steel for building are in order to ensure the vibration strength of building structure, utilize the viscous deformation after the recoverable deformation to absorb seismic energy, under this thought, regulation is a lot of by the situation of the upper limit of the represented yield tensile ratio YR of the ratio (YS/TS) of yielding stress YS and tensile strength TS.With respect to this, in recent years, though the plastification of the post portion during huge earthquake can not cause the avalanche of building structure integral body and can rescue the people, but the assets value of building structure has not existed, need to rebuild, therefore make the characteristic of steel for building terminate in that such method of design also obtains research in the elastic limit.
Above-mentioned such round steel pipe that building structure was suitable for because be to be shaped by steel plate being pushed bending machining etc., changes so can produce the material that causes because of work hardening, and yield tensile ratio YR rises.Particularly the exterior side of round steel pipe is big with the rising of thickness of slab central part comparison hardness, so ductility reduces.
That is, the load when bearing violent earthquake and when being out of shape, the inherent problem that has are to chap easily from the outside that side takes place, and round steel pipe can not take place at the four sides box column.When particularly being welded to attached metal die etc. on the round steel pipe, because the sclerosis of heat affected zone (HAZ) causes the reduction of the ductility on round steel pipe surface (outside surface) to become problem.
So as the method for making steel pipe by cold shaping, the UOE moulding method (Uing press-Oing press-expander method) that the effective steel tube place of exception pipeline is suitable for adopts pressing-bend cool-forming method (following only be called " press-bending method ") in addition substantially.Among the above-mentioned moulding method, steel plate thickness thick (for example thickness of slab: surpass 30mm) need be forced man-hour and can adopt the press-bending method.
Above-mentioned press-bending method is that the part (line part) to steel plate is carried out the mold pressing bending machining, makes the mold pressing position move and be configured as the method for circle successively, is the high method of working ability.During with such press-bending method shaping round steel pipe, it is remarkable especially that the sclerosis of the outside surface of round steel pipe becomes, but as the method that reduces this hardness is known stress relief annealing (Stress Relieving: hereinafter referred to as " SR thermal treatment ") arranged.Yet if implement such SR thermal treatment, the hardness of thickness of slab central part still can reduce, and is difficult to guarantee more than 590MPa as the tensile strength TS of the desired strength of round steel pipe.
In addition, so that heat treated should to be used for reducing surface hardness be prerequisite by SR, be applicable to when tensile strength is the above steel plate of 590MPa, need make the metal structure hardization by the interpolation of alloying element, and under the effect of this hard tissue, cause the flexible of the mother metal (steel pipe) after the SR thermal treatment to guarantee very difficulty.
Make ship steel, pressurized vessel and general line-pipes steel etc.,, then have the Hardness Distribution of metal structure and thickness of slab direction, exist the material deviation to be encouraged such problem by cold bend(ing) processing if directly apply to round steel pipe purposes for building.On the other hand, for the requirement of material of construction, the character of machinery such as high strength and high tenacity is from needless to say, and large-line energy welding characteristic and the good weldability of guaranteeing to be used to reduce building cost are also very important.
As the technology that relates to above-mentioned such multitube, propose to have various technology up to now.For example open proposition in flat 7-166293 number the spy, as the steel plate of the crackle of anti-sulfide property excellence, the regulation micro-vickers hardness distributes.This technology is that the former material of the line pipe about 20mm is effective for thickness of slab, and such steel plate dwindles micro-vickers hardness and distributes easily, but that thickness of slab is the building structure of 25～100mm is just very difficult with the Hardness Distribution that round steel pipe dwindles the thickness of slab direction.In addition, steel that this technology relates to is focusing on the crackle of anti-sulfide property, and do not consider for the vibration strength of construction applications, not the toughness deterioration after bending machining when being applied to round steel pipe.
In addition, open in 2007-138210 number, disclose about reducing the little effective steel plate of high-strength line-pipe at Bauschinger (Bauschinger) effect lower yield stress the spy.This technology is to be object with the line-pipes thin plate that is shaped by the UOE moulding method, and the disclosed method of this technology can not be dwindled the Hardness Distribution that thickness of slab reaches the heavy wall material thickness of slab direction of 100mm.In addition, therefore the disposal that need heat rapidly immediately after quickening cooling also has to add the such problem of thermal control difficulty.And the method for work hardening amount that becomes problem when being applicable to the press-bending method for control is also without any consideration, and the sclerosis of the exterior side of the round steel pipe after the cold working can be envisioned and can not guarantee good vibration strength.
The spy opens in 2006-257499 number, proposes about being object with the line-pipes steel plate about thickness of slab 20mm, by the Welded Steel Pipe of UOE moulding method shaping.This technology becomes the mixed structure that iron is body and bainite by making the tissue in the steel plate, thereby reduces the surface hardness of steel plate, dwindles Hardness Distribution.Yet if the heavy wall material, the ferrite branch rate of thickness of slab central part uprises and softens, and therefore directly method is applied to the Hardness Distribution that the heavy wall material can not dwindle the thickness of slab direction.In addition, this method is to implement to quench behind steel tube forming, but big footpath, the back heavy wall round steel pipe that bends is implemented the quench treatment difficulty.And the method for work hardening amount that becomes problem when being applicable to the press-bending method for control is also without any consideration, and the sclerosis of the exterior side of the round steel pipe after the cold working can be envisioned and can not guarantee good vibration strength.
On the other hand, open in 2004-143500 number, propose about " circular steel plate of the high strength of the excellent of anti-buckling the and manufacture method thereof " the spy.This technology is that the high-strength thin-walled steel pipe based on the tissue of ferrite (more than 70%) is an object, and can not dwindle the Hardness Distribution of thickness of slab direction.This technology is the same with above-mentioned each technology in addition, for the method for control work hardening amount without any open.And in manufacture method, the rolling end temp that also just will become the main points of organizational controls is defined as more than the Ar3 transformation temperature, and can not realize uniform tissue, hardness on the thickness of slab direction of round steel pipe.
Open in 2006-63351 number open high-intensity high-tenacity steel plate of inducing the crackle excellence about anti-hydrogen the spy.The steel plate of the line-pipes of this technology about with thickness of slab 25mm is an object, though considered the hardness of the long-pending partially portion in center, does not but do any consideration for surface hardness.In addition, the Hardness Distribution of thickness of slab direction though the value of being tried to achieve by the relational expression of regulation is defined in below 330, is not but done any open about the method for control work hardening amount.And in manufacture method, the rolling end temp that just will become the main points of organizational controls is defined as (Ar 3More than transformation temperature+20 ℃), and can not on the thickness of slab direction of round steel pipe, realize uniform tissue, hardness.
Open in 2003-293075 number the spy in addition, propose about " High Tensile Steel Tube that surface hardness behind the tubing and yield tensile ratio are low ".In this technology, form, do not form the regulation of the B and the N of nitride, can not control BN and TiN as chemical ingredients, because the hardenability instability, so be difficult to the stable desired intensity that obtains.In addition, organize and become ferrite owing to not containing B, the Hardness Distribution of thickness of slab direction is inhomogeneous.
Summary of the invention
The present invention is under such situation and do, its purpose is, a kind of useful method that can help the round steel pipe of vibration strength raising and be used to make this round steel pipe is provided, its mode is, in the building iron purposes, be arranged in the steel pipe of the tensile strength 590MPa level of high strength level, reduce hardness round steel pipe inherent problem, that constitute the steel pipe exterior side of trending extensional tectonic stress field as the high strength state.
Can reach the round steel pipe of the present invention of above-mentioned purpose, contain the C:0.01～0.05% (meaning of quality % respectively, down together), Si:0.05～0.35%, Mn:1.00～1.70%, Al:0.015～0.045%, Ni:0.05～0.45%, Cr:0.20～1.50%, Ti:0.008～0.020%, B:0.0010～0.0025%, Nb:0.010～0.030%, Ca:0.0005～0.0035%, N:0.0035～0.0060%, surplus is made of Fe and unavoidable impurities, among the described unavoidable impurities, P is suppressed at below 0.020%, S is suppressed at below 0.005%, PCM value by following formula (1) expression is below 0.20%, satisfy the important document of following (A)～(C), tensile strength is more than the 590MPa, and yield tensile ratio is 85～95%
PCM value=[C]+[Si]/30+[Mn]/20+[Cu]/20+[Ni]/60+[Cr]/20+[Mo]/15+[V]/10+ ([B] * 5) ... (1)
Wherein, [C], [Si], [Mn], [Cu], [Ni], [Cr], [Mo], [V] and [B] represent the content (quality %) of C, Si, Mn, Cu, Ni, Cr, Mo, V and B respectively.
(A) microstructure, long-width ratio is that the face integration rate of the bainite more than 3 is more than 50% at least, dislocation desity ρ is 1.0 * 10 5(m -2) more than, 6.0 * 10 5(m -2) below,
(B) degree of depth of removing respectively table apart from described steel pipe, the back side is that the average Vickers' hardness Hv of central part of the skin section of 2mm is 180～280,
(C) the average Vickers' hardness Hv from the table of described steel pipe, the back side to the dark skin section of 2mm respectively is 1.1 times～1.4 times of the average Vickers' hardness Hv of described central part.
Also have, in above-mentioned (A), so-called " long-width ratio is that the face integration rate of the bainite more than 3 is more than 50% at least ", the meaning is to allow to contain long-width ratio to be lower than 3 bainite (for example adding up to more than the 80 area %) in tissue, and wherein long-width ratio is that the face integration rate (with respect to the ratio of integral body) of the bainite more than 3 is to get final product more than 50%.In addition, as beyond the bainite phase (surplus), ferrite, martensite, bainite ferrite etc. can have been enumerated.
In round steel pipe of the present invention, also preferably contain at least a kind among Cu:0.05～0.45%, V:0.005～0.050% and Mo:0.05～0.35% as required, in view of the above, the characteristic of steel pipe will be further improved.
When making above-mentioned such round steel pipe, after will being heated to 950～1200 ℃ by the ingot casting that described chemical ingredients constitutes, making finishing temperature is that 700～850 ℃ scope is carried out the thickness of slab that hot rolling becomes regulation, then (t: the speed of cooling of position thickness of slab) is 2～25 ℃/second and carries out water-cooled with t/4, reach below 500 ℃ to surface temperature and obtain steel plate, the steel plate that uses is configured as round steel pipe by the press-bending method and gets final product.
According to the present invention, chemical ingredients by suitable adjustment steel plate (constituting the steel plate of steel pipe) is formed, and suitably control microstructure, and make the Hardness Distribution of thickness direction suitable, the hardness of the steel pipe exterior side that the bending machining in the time of just can reducing the steel tube forming of the above high strength state of 590MPa is brought and guarantee ductility realizes the round steel pipe that can help vibration strength to improve thus.
Embodiment
Present inventors are in order both to guarantee the high strength more than the 590Ma, reduce the sclerosis that adds the round steel pipe exterior side that the work hardening in man-hour causes because of press-bending again, and study from various angles.Its result distinguishes, at first importantly, as the basic microstructure of steel pipe (being steel plate) based on bainite, and wherein at least long-width ratio be that the area occupation ratio of (ratio of major diameter and minor axis is more than 3) so flat low C bainite is [important document of described (A)] more than 50% more than 3.
In order to become above-mentioned such microstructure, though need suitably to create conditions, as its prerequisite, the chemical ingredients that also needs suitably to control steel plate is formed.As its basic direction, be by chemical ingredients based on low C, compound interpolation by Nb-B promotes austenitic flattening and bainitic transformation then, and the compound interpolation by Ni-Cr realizes the stable of hardenability, can access the uniform bainite structure of thickness of slab direction thus, the homogenizing of the hardness of thickness of slab direction can be reached.
Promptly distinguish, based on above-mentioned such design guidelines, form by adjusting chemical ingredients, even speed of cooling is changed, bainitic transformation temperature after rolling is also almost constant, and the increase of the long-width ratio of the austenite crystal that the control of the draught during by hot rolling brings can make the toughness of steel pipe improve.Thing is also distinguished in addition, in suitable chemical ingredients is formed, suitably changes by making hot-rolled temperature, can stablize to generate flat low C bainite structure.
Being used to improve the intensity effective means of steel plate, is that the alloying element amount is increased.Particularly in order to reach the such high strength of 590MPa level, and need make the interpolation of alloying element more, to utilize the various mechanism for intensifying that bring thus.Yet the increase of this alloying element can cause the deterioration of characteristic of the machinery of the weldability of anti-crackle etc. and welding joint.Present inventors find, the interpolation by suitable alloying element and make it contain suitableization, the work hardening that can reduce high strength and be caused by bending machining.
By satisfying above-mentioned each important document (microstructure and chemical ingredients are formed), can make the Hardness Distribution homogenizing of thickness of slab direction, and make work hardening amount stabilization, the ratio that can suppress to round steel pipe outside the Vickers' hardness Hv in the zone (apart from the table of steel plate, the skin section that the back side reaches 2mm deeply) of 2mm and thickness of slab direction central part down [t/2 portion (t: thickness of slab)] improves as the vibration strength of round steel pipe.
From above-mentioned viewpoint, the chemical ingredients of round steel pipe of the present invention is formed and to be determined, for containing above-mentioned alloying constituent (C, Ni, Cr, B, Nb), limits reason with regard to the scope of each element and describes.In the present invention, as above-mentioned, need contain the C:0.01～0.05% (meaning of quality % respectively, Si:0.05～0.35%, Mn:1.00～1.70%, Al:0.015～0.045%, Ni:0.05～0.45%, Cr:0.20～1.50%, Ti:0.008～0.020%, B:0.0010～0.0025%, Nb:0.010～0.030%, Ca:0.0005～0.0035%, N:0.0035～0.0060% down together),, and the PCM value that needs described (1) formula is represented is controlled at suitable scope, and the scope of these elements limits and the reasons are as follows.
(C：0.01～0.05％)
C has the effect of the intensity that improves steel plate, is to be used to control the important element of hardness, and also is can be because of add the element that makes weldability deteriorations such as anti-crackle superfluously.C content is lower than at 0.01% o'clock can not guarantee necessary mother metal (steel plate) intensity.Yet if C content surpasses 0.05%, island martensite body [containing martensite, austenitic mixed phase (M-A phase)] generates anti-welding crack deterioration superfluously.Also have, the preferred lower limit of C content is 0.02%, and preferred upper limit is 0.04%.
(Si：0.05～0.35％)
Si is effective elements by suitably adding making in the raising of base metal tenacity and intensity.In order to bring into play such mechanism for intensifying, Si is contained more than 0.05%.Yet if Si content surplus, therefore anti-welding crack deterioration is below 0.35%.Also have, the preferred lower limit of Si content is 0.07%, and preferred upper limit is 0.25%.
(Mn：1.00～1.70％)
Mn improves hardenability, and the common element that improves of intensity and toughness is effective as making.In order to bring into play such effect, Mn is contained more than 1.00%.Yet, if contain Mn superfluously, the intensity surplus, therefore the base metal tenacity deterioration makes and is limited to 1.70% on it.Also have, the preferred lower limit of Mn content is 1.10%, and preferred upper limit is 1.60%.
(Al：0.015～0.045％)
Al is a deoxidant element, is in addition to guarantee the necessary element of base metal tenacity by the microstructure miniaturization.In order to bring into play such effect, need make it to contain more than 0.015%, but, then form the thick inclusion of alumina series if surplus contains, base metal tenacity reduces, therefore need be below 0.045%.Also have, the preferred lower limit of Al content is 0.020%, and preferred upper limit is 0.040%.
(Ni：0.05～0.45％)
Ni is in the raising of base metal tenacity and improve hardenability so that intensity is effective elements on improving.In order to bring into play such effect, Ni is contained more than 0.05%.Yet if Ni content surplus, the oxide skin flaw takes place easily, therefore need be for below 0.45%.Also have, the preferred lower limit of Ni content is 0.10%, and preferred upper limit is 0.35%.
(Cr：0.20～1.50％)
The multi-faceted bainite of cutting apart thick austenite crystal when Cr makes the large-line energy welding generates, and is improving hardenability so that intensity is effective elements on improving in addition.In order to bring into play such effect, Cr need contain more than 0.20%.Yet if Cr content surplus, anti-welding crack deterioration therefore need be below 1.50%.Also have, the preferred lower limit of Cr content is 0.55%, and preferred upper limit is 1.35%.
(Ti：0.008～0.020％)
Ti and N form nitride (TiN), and thickization of the austenite crystal (γ grain) when preventing the heating before the hot rolling is the element that generates carbide easily in addition.In order to bring into play γ grain micronized effect, Ti is contained more than 0.008% from Ti.Yet, if Ti content surplus, the generation surplus of carbide, the base metal tenacity deterioration therefore need be below 0.020%.Also have, the preferred lower limit of Ti content is 0.010%, and preferred upper limit is 0.018%.
(B：0.0010～0.0025％)
Free B is present in crystal boundary, is effective elements in that hardenability is improved in the raising of realization strength of parent.If the content of B is lower than 0.0010%, then the raising effect of strength of parent is little, can not guarantee the intensity that tensile strength 590MPa is above.Yet, if B content surplus, the hardenability surplus, anti-welding crack and base metal tenacity deterioration therefore need be below 0.0025%.Also have, the preferred lower limit of B content is 0.0012%, and preferred upper limit is 0.0015%.
(Nb：0.010～0.030％)
Nb is important element in steel pipe of the present invention, by the compound interpolation of Nb and B, can access the low uniformly C bainite structure of thickness of slab direction.It also makes the non-recrystallization temperature range in austenite territory enlarge in addition, and utilize the rolling strain in this zone and phase transformation nuclear is increased, be to promote the needed element of phase transformation.If the content of Nb is lower than 0.010%, then this effect is little, and base metal tenacity reduces.Surpass 0.030% if Nb content is superfluous in addition, then the carbide generation is excessive, and this becomes the destructive starting point and makes the base metal tenacity deterioration.Also have, the preferred lower limit of Nb content is 0.013%, and preferred upper limit is 0.025%.
(Ca：0.0005～0.0035％)
It is effective elements for anti-welding crack making the MnS balling on innoxious that Ca makes it.In order to bring into play such effect, Ca is contained more than 0.0005%.Yet, superfluous if Ca content becomes above 0.0035%, make thickization of inclusion, it becomes the destructive starting point and makes the base metal tenacity deterioration.Also have, the preferred lower limit of Ca content is 0.0015%, and preferred upper limit is 0.0030%.
(N：0.0035～0.0060％)
N and Ti reaction generates TiN, is the thickization effective elements of the γ grain when preventing the heating before the hot rolling.If N content is lower than 0.0035%, then the TiN deficiency heats the γ grain and becomes thick, and therefore the base metal tenacity deterioration need make it to contain more than 0.0035%.In addition, surpass 0.0060% if N content is superfluous, then the embrittlement that causes owing to bending machining makes the toughness deterioration of steel pipe.Also have, the preferred lower limit of N content is 0.0040%, and preferred upper limit is 0.0055%.
(PCM value: below 0.20%)
By the PCM value that aforementioned (1) formula is represented, be the most general important document of index as the low temperature crackle that prevents to cause because of welding procedure.In order to prevent welding crack, need the PCM value below 0.20%.PCM is preferably below 0.18%.Also have, in following formula (1), also stipulated composition (C, Si, Mn, Ni, Cr, the B) element (element that contains as required) (Cu, V, Mo etc.) in addition of steel plate regulation of the present invention, because these elements are influential to the low temperature crackle, so contain as required sometimes, its content also needs to add in the calculating of PCM value.Therefore, when not containing these elements, these elements are got final product as 0 calculating according to following formula (1).
In round steel pipe of the present invention, constitute (for example P, S etc.) by Fe and unavoidable impurities beyond the mentioned component, but also can contain the trace ingredients (permission composition) (for example Zr, H, O etc.) of unavoidably sneaking in the melting, such round steel pipe is also contained in the scope of the present invention.But P, S etc. for as unavoidable impurities from following viewpoint, need be suppressed at it respectively in the following scope.
(P:0.020% is following)
As the P of unavoidable impurities, the toughness of mother metal, weld part is brought disadvantageous effect, in order not cause such problem, its content is suppressed at below 0.020%, preferably below 0.015%.
(S:0.005% is following)
S forms MnS and makes anti-welding crack deterioration, therefore preferred the least possible aspect.From this viewpoint, the S amount need be suppressed at below 0.005%, preferably below 0.003%.
In the round steel pipe of the present invention, at least a kind of also containing as required among Cu:0.05～0.45%, V:0.005～0.050% and Mo:0.05～0.35% is also useful, and these compositions all improve effectively the intensity of steel pipe.The action effect of this each composition is as follows.
(Cu：0.05～0.45％)
Cu is useful element make in the strong raising of mother metal by solution strengthening.In order to bring into play such effect, Cu is contained more than 0.05%.Yet,, therefore be preferably below 0.45% if Cu content surplus produces the Cu crackle during gas cutting.Also have, Cu content more preferably be limited to 0.07% down, be limited to 0.40% on more preferably.
(V：0.005～0.050％)
V-arrangement becomes carbide, is effective elements making in the intensity raising.In order to bring into play such effect, V is contained more than 0.005%.If yet V content surplus, carbide generates thick, and it becomes starting point and makes the base metal tenacity deterioration, therefore is preferably below 0.050%.Also have, be limited to 0.010% under V content is preferred, be limited to 0.040% on preferred.
(Mo：0.05～0.35％)
Mo improves hardenability, and is useful to improving intensity, is the element that generates carbide easily in addition.In order to bring into play such effect, Mo is contained more than 0.05%.Yet if Mo content surplus, hardenability is excessive, and therefore anti-welding crack deterioration is preferably below 0.35%.Also have, Mo content more preferably be limited to 0.08% down, be limited to 0.25% on more preferably.
In round steel pipe of the present invention, long-width ratio is that the face integration rate of the bainite more than 3 is more than 50%, and dislocation desity ρ is 1.0 * 10 5(m -2) more than, 6.0 * 10 5(m -2) below also be important important document [important document of described (A)].The face integration rate of the long-width ratio of old austenite crystal and bainite is one of factor of arranging the material variation that causes because of work hardening.If the long-width ratio of old austenite crystal is lower than 3, the face integration rate of bainite is lower than 50%, and then the material deviation of round steel pipe becomes big, anti-welding crack deterioration.
On the other hand, one of factor of changing of the dislocation desity ρ material that also to be Zhi Peijia cause because of worker's sclerosis.If dislocation desity ρ is lower than 1.0 * 10 5(m -2), then, consequently make anti-welding crack deterioration because work hardening causes material to change greatly.In addition if dislocation desity ρ surpasses 6.0 * 10 5(m -2), then being in so-called dislocation state of saturation, hardness becomes superfluous and makes anti-welding crack deterioration.
In round steel pipe of the present invention, the average Vickers' hardness Hv that removes respectively the central part of table apart from the steel plate that constitutes steel pipe, skin section that the back side reaches 2mm deeply is 180～280 also very important [important documents of described (B)].This Vickers' hardness Hv is relevant with tensile strength TS, and for the tensile strength TS and the yield tensile ratio YR that obtain expecting, the average Vickers' hardness Hv that needs central part is 180～280.That is, the average Vickers' hardness Hv of central part is lower than at 180 o'clock, becomes low YR characteristic, and tensile strength TS also reduces.In addition, if the average Vickers' hardness Hv of central part surpasses 280, then will make anti-welding crack deterioration.
In round steel pipe of the present invention, also need respectively the table apart from described steel pipe, the average Vickers' hardness Hv of skin section that the back side reaches 2mm deeply, be below 1.4 times of average Vickers' hardness Hv [important document of described (C)] of described central part.If the hardness ratio of exterior side (skin section) and thickness of slab central part is above 1.4 times, then the plastic deformation ability of surface of steel plate portion reduces, the tensile stress on surface uprises, therefore chap from the surface, surface hardening during with attached metal solder interacts and becomes the starting point of crackle, and the destructive possibility is arranged when violent earthquake.This ratio is preferably below 1.3 times.
In order to make round steel pipe of the present invention, as long as after will being heated to 950～1200 ℃ by the ingot casting that described chemical ingredients constitutes, making finishing temperature is that 700～850 ℃ scope is carried out the thickness of slab that hot rolling becomes regulation, then (t: the speed of cooling of position thickness of slab) is 2～25 ℃/second and carries out water-cooled with t/4, reach below 500 ℃ to surface temperature and obtain steel plate, the steel plate that uses is configured as round steel pipe by the press-bending method and gets final product, and stipulates the reasons are as follows of condition of each operation.
(ingot casting is heated to 950～1200 ℃)
This Heating temperature is given the organizational controls before the hot rolling and could rollingly be brought very big influence.If Heating temperature is lower than 950 ℃, then can not guarantee rolling final mill train (finish to gauge) surface temperature before more than 700 ℃, therefore ferrite is just separated out before water-cooled, and strength of parent reduces, and hot rolled depresses the load height, and productivity is deterioration significantly.On the other hand, if Heating temperature surpasses 1200 ℃, then thickization of γ particle diameter causes strength of parent to reduce and the base metal tenacity deterioration.
(making finishing temperature is that 700～850 ℃ scope is carried out the thickness of slab that hot rolling becomes regulation)
Controlled chilling is to be prerequisite with before this organizational controls, therefore need and cool off the rolling end temp (finishing temperature) controlled rolling under to begin temperature and manage.If finishing temperature is lower than 700 ℃, then ferrite is just separated out before the cooling beginning, can not obtain desired intensity.In addition, thick if finishing temperature above 850 ℃, is then organized before the cooling, the base metal tenacity deterioration.
(t/4 (t: the speed of cooling of position thickness of slab) is 2～25 ℃/second)
Refrigerating work procedure after rolling is the important operation that is used to carry out organizational controls.When speed of cooling at this moment was lower than 2 ℃/second, the face integration rate that can not guarantee bainite was more than 50%, undercapacity, and the work hardening amount is excessive, anti-welding crack deterioration.In addition, if speed of cooling surpasses 25 ℃/second, then intensity is excessive, the base metal tenacity deterioration.Why also have, be t/4 (t: thickness of slab), be because be the position of the average performance of performance steel plate here as the position of measuring speed of cooling.
(cooling stops temperature: the surface temperature of steel plate is below 500 ℃)
It is the important controlling factor that makes Strength Changes that cooling stops temperature.If stopping temperature, cooling surpasses 500 ℃, undercapacity then, and can not get dislocation desity, the work hardening quantitative change that bending machining causes is big, makes anti-welding crack deterioration.
(being configured as round steel pipe) by the press-bending method
Finally steel pipe is carried out cold bend(ing) and become steel pipe by the press-bending method.As described above, if the following steel plate of this thickness of slab 30mm that line pipe was suitable for is then made round steel pipe by the UOE moulding method, but building structure is thick at thickness of slab with round steel pipe, when intensity is high, need to be configured as round steel pipe by press-bending method (promptly pushing bending machining).If this method of application, then the bending machining strain is big, and therefore the work hardening on surface is big.Therefore,, push bending forming, can make the low round steel pipe of surface hardness by the steel pipe that uses as above-mentioned mode is made.
Also have, round steel pipe of the present invention is not implemented above-mentioned such SR and is handled and can use yet, even if but implement SR thermal treatment, can guarantee that also tensile strength TS as the desired strength of round steel pipe is more than 590MPa.
Below, be described more specifically the present invention by embodiment, but the present invention is not limited by following embodiment certainly, certainly changed enforcement can meeting the forward and backward scope of stating aim, these all are included in the technical scope of the present invention.
[embodiment]
(embodiment 1)
By the steel that the chemical ingredients shown in the common following table 1 of smelting process melting, 2 is formed, become steel billet after, implement hot rolling, quicken cooling (cooling after rolling), tempering, make steel plate.The steel plate that use obtains is configured as round steel pipe by the press-bending method.Also have, in table 1,2, also shown about PCM value by aforementioned (1) formula defined.Creating conditions at this moment as following.
(creating conditions)
After ingot casting is heated to 1150 ± 10 ℃, make finishing temperature (surface temperature) carry out hot rolling 850 ± 30 ℃ scope, form thickness of slab 70mm, then (t: the speed of cooling of position thickness of slab) is controlled at 5～15 ℃/second to t/4, and the surface temperature when cooling is stopped is below 420 ± 50 ℃.In addition, become steel plate, use the steel plate that obtains, be configured as round steel pipe by the press-bending method 450～650 ℃ scope tempering.At this moment bending machining degree is, the diameter of establishing round steel pipe is D (mm), and establishing steel plate thickness is t (during mm), and D/t is 10 (t/D=0.1).
Figure G2009101296897D00131
Figure G2009101296897D00141
Figure G2009101296897D00151
For each round steel pipe that obtains, with the microstructure (bainite face integration rate) and the hardness of following method evaluation steel pipe, and according to following method evaluation material (yielding stress YS, tensile strength TS, yield tensile ratio YR and toughness vE -20).
(measuring method of microstructure and hardness)
Microstructure is carried out image analysis, and measuring long-width ratio thus is the face integration rate of the bainite phase more than 3, and measures the Vickers' hardness (Hv of steel plate skin section 0) and the Vickers' hardness (Hv of central part 1) (load: 98N), try to achieve its hardness ratio (Hv 0/ Hv 1).At this moment hardness Hv 0, hardness Hv 1Mensuration, on thickness direction,, try to achieve its mean value (for example, Vickers' hardness Hv of skin section with the measuring space of 2mm 0, for respectively apart from the mean value of the hardness that reaches 2mm deeply at table, the back side).
(evaluation method of yielding stress YS, tensile strength TS)
Exterior side from round steel pipe, at the tubular axis of the t/4 of steel plate portion (t is a thickness of slab) on (the main rolling direction that is equivalent to steel plate), extract No. 22014 test films of JIS Z, carry out tension test, measure yielding stress YS (the upper yield point YP or the yielding stress σ of steel pipe by the main points of JIS Z 2241 0.2), tensile strength TS, yield tensile ratio YR (yielding stress YS/ tensile strength TS).Criterion of acceptability is, in 2 times mean value, and more than the yielding stress YS:500MPa, tensile strength TS:590～740MPa, yield tensile ratio YR: surpass below 85%～90%.
(toughness evaluation method)
Exterior side from round steel pipe, at the tubular axis of the t/4 of steel plate portion (t is a thickness of slab) on (the main rolling direction that is equivalent to steel plate), extract JIS Z 2204V notch impact test sheet, carry out pendulum impact test (mean values of 3 tests) according to the main points of JIS Z 2242, measure temperature: the average absorption under-20 ℃ can vE -20This average absorption can vE -20For being evaluated as more than the 47J qualified.
[weldability (anti-welding crack)]
Maximum hardness test according to the welding heat affected zone (HAZ) of JIS Z 3101 defineds, exterior side at round steel pipe is provided with welding bead, investigate with regard to having or not of surface crack by chalk test, investigate for having or not of internal fissure by ultrasonic test.
The micro-composition of steel plate and Hardness Distribution (hardness of steel plate central part, hardness ratio) are presented in the following table 3,4, material (yielding stress YS, tensile strength TS, yield tensile ratio YR and toughness vE -20) and the evaluation result of weldability be presented in the table 5,6.Also have in following table 5,6, show the maximum hardness (Hv) of HAZ as " weldability ".
(measuring method of dislocation desity)
Separate K α 1 from the diffracted intensity curve of the characteristic X-ray that obtains by X-ray diffraction, measure the scope of the half breadth of K α 1 line.Revise this half breadth, only extract the scope of the half breadth that causes by strain and calculate strain.Calculate dislocation desity according to this strained value.
[table 3]
Steel № The Vickers' hardness of steel plate central part (Hv) The face integration rate (%) of bainite Hardness ratio (Hv 0/Hv 1) Dislocation desity (m -2)?
1? 187? 55? 1.3? 3.0?
2? 237? 55? 1.3? 3.8?
3? 207? 64? 1.2? 2.8?
4? 279? 72? 1.1? 2.9?
5? 205? 62? 1.2? 3.8?
6? 240? 88? 1.1? 2.9?
7? 233? 66? 1.1? 2.8?
8? 229? 71? 1.1? 4.2?
9? 256? 58? 1.1? 2.5?
10? 223? 63? 1.2? 2.9?
11? 260? 53? 1.2? 1.2?
12? 279? 62? 1.2? 5.8?
13? 231? 79? 1.4? 2.5?
14? 272? 52? 1.3? 4.0?
15? 183? 71? 1.1? 3.4?
16? 276? 64? 1.1? 2.5?
17? 254? 68? 1.1? 4.1?
18? 229? 65? 1.2? 2.6?
19? 206? 66? 1.3? 3.0?
20? 269? 65? 1.1? 3.8?
21? 206? 92? 1.3? 2.8?
22? 269? 60? 1.1? 2.8?
23? 239? 87? 1.4? 4.1?
24? 240? 95? 1.4? 2.9?
25? 180? 69? 1.2? 2.7?
26? 213? 64? 1.1? 3.8?
27? 256? 91? 1.2? 2.8?
28? 238? 82? 1.3? 3.0?
29? 255? 69? 1.4? 3.9?
30? 210? 61? 1.2? 2.4?
31? 209? 59? 1.2? 2.6?
[table 4]
Figure G2009101296897D00171
[table 5]
Figure G2009101296897D00182
Figure G2009101296897D00191
[table 6]
Figure G2009101296897D00201
Can carry out following investigation by these results.At first, steel No.1～31 (table 1,3,5) satisfies the important document of the present invention's regulation, satisfies target value (comprehensive evaluation: zero) in whole characteristics.With respect to this, a certain important document of steel No.32～62 (table 2,4,6) discontented unabridged version invention regulation, a certain at least deterioration in characteristics (comprehensive evaluation *) that requires.
(embodiment 2)
Use steel No.1～8 shown in the described table 1 (chemical ingredients is formed the scope that satisfies the present invention's regulation), make steel plate (experiment No.1～15) according to various the creating conditions shown in the following table 7.The steel plate that use obtains is configured as round steel pipe by the press-bending method.The same for the round steel pipe that obtains with embodiment, to material (yielding stress YS, tensile strength TS, yield tensile ratio YR and toughness vE -20) and weldability estimate.In addition, the same micro-composition and the Hardness Distribution (hardness of steel plate central part, hardness ratio) of measuring steel plate with embodiment, its result is presented in the table 8.
Also have, the experiment No.9 of table 7,10 expression billet heating temperature break away from the scope of the present invention's regulation, experiment No.11,12 expression finishing temperatures break away from the scope of the present invention's regulation, test the scope of No.13,14 expression speed of cooling disengaging the present invention regulations, experiment No.15 represents to cool off the scope that stops temperature disengaging the present invention regulation.
[table 8]
Figure G2009101296897D00221
Thus the result as can be known, the round steel pipe for the important document that is met the present invention regulation also needs suitably to control and creates conditions.

Claims (3)

1. round steel pipe, it is characterized in that, the chemical ingredients of described round steel pipe contains C:0.01～0.05% in quality %, Si:0.05～0.35%, Mn:1.00～1.70%, Al:0.015～0.045%, Ni:0.05～0.45%, Cr:0.20～1.50%, Ti:0.008～0.020%, B:0.0010～0.0025%, Nb:0.010～0.030%, Ca:0.0005～0.0035%, N:0.0035～0.0060%, surplus is Fe and unavoidable impurities
In the described unavoidable impurities, P is suppressed at below 0.020%, and S is suppressed at below 0.005%,
The PCM value by following formula (1) expression of described round steel pipe is below 0.20%,
Satisfy the important document of following (A)～(C),
Tensile strength is more than the 590MPa,
And yield tensile ratio is 85～95%,
PCM value=[C]+[Si]/30+[Mn]/20+[Cu]/20+[Ni]/60+[Cr]/20+[Mo]/15+[V]/10+ ([B] * 5) ... (1)
Wherein, [C], [Si], [Mn], [Cu], [Ni], [Cr], [Mo], [V] and [B] represent the mass percentage content of C, Si, Mn, Cu, Ni, Cr, Mo, V and B respectively,
(A) in microstructure, long-width ratio is that the face integration rate of the bainite more than 3 is more than 50% at least, and dislocation desity ρ is 1.0 * 10 5m -2More than, 6.0 * 10 5m -2Below,
(B) removing respectively from table, the back side of described steel pipe is 180～280 to the average Vickers' hardness Hv of the central part of the described steel pipe of the dark skin section of 2mm,
(C) the average Vickers' hardness Hv from the table of described steel pipe, the back side to the skin section of the dark part of 2mm is 1.1 times～1.4 times of average Vickers' hardness Hv of described central part respectively.
2. the described round steel pipe of claim 1 is characterized in that, also contains in Cu:0.05～0.45%, V:0.005～0.050% and Mo:0.05～0.35% at least a kind in quality %.
3. method of making claim 1 or 2 described round steel pipes, it is characterized in that, after will being heated to 950～1200 ℃ by the ingot casting that described chemical ingredients constitutes, making finishing temperature is that 700～850 ℃ scope is carried out the thickness of slab that hot rolling forms regulation, then, is that 2～25 ℃/second condition is carried out water-cooled with the speed of cooling of t/4 position, being cooled to surface temperature is to become steel plate below 500 ℃, use resulting steel plate to be configured as round steel pipe by the press-bending method, wherein, t is a thickness of slab.
CN2009101296897A 2008-03-27 2009-03-26 590 mpa high yield ratio round steel pipe for building structure with excellent shock resistance and production process Expired - Fee Related CN101545080B (en)

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