CN105143487B - The thick section and high strength spool steel plate of acid resistance, resistance to crushing characteristic and excellent in low temperature toughness and spool - Google Patents

The thick section and high strength spool steel plate of acid resistance, resistance to crushing characteristic and excellent in low temperature toughness and spool Download PDF

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Publication number
CN105143487B
CN105143487B CN201480021680.3A CN201480021680A CN105143487B CN 105143487 B CN105143487 B CN 105143487B CN 201480021680 A CN201480021680 A CN 201480021680A CN 105143487 B CN105143487 B CN 105143487B
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steel plate
thickness
resistance
spool
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CN105143487A (en
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原卓也
藤城泰志
篠原康浩
津留英司
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Nippon Steel Corp
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Nippon Steel Corp
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    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/08—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for tubular bodies or pipes
    • C21D9/14—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for tubular bodies or pipes wear-resistant or pressure-resistant pipes
    • 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
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/78—Combined heat-treatments not provided for above
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • C21D8/0263—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment following hot rolling
    • 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
    • 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
    • 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
    • C21D2221/00—Treating localised areas of an article
    • C21D2221/10—Differential treatment of inner with respect to outer regions, e.g. core and periphery, respectively
    • 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

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Heat Treatment Of Steel (AREA)
  • Manufacturing & Machinery (AREA)

Abstract

The present invention provides thick section and high strength spool steel plate and its manufacture method of acid resistance, resistance to crushing characteristic and excellent in low temperature toughness.It is thickness of slab is more than 25mm and the thick section and high strength spool steel plate of below 45mm, and the metal structure of skin section contains processing ferrite：More than 5% and the S that obtained by following formula 1afe1Below %, martensitic-austenitic composite (MA) is less than 8%, and remainder is made up of polygonal ferrite and/or bainite, and the metal structure of thickness of slab central part is processing ferrite：Less than 5%, MA：Less than 5%, remainder by one of acicular ferrite and/or bainite or both constitute, the meansigma methodss of the effective crystal particle diameter in skin section and thickness of slab central part are less than 20 μm.Sfe1=0.6552 × TH4.7826 formulas 1a wherein, TH：The thickness of slab of steel plate.

Description

The thick section and high strength line tube steel of acid resistance, resistance to crushing characteristic and excellent in low temperature toughness Plate and spool
Technical field
The present invention relates to the thick section and high strength spool steel plate of acid resistance, resistance to crushing characteristic and excellent in low temperature toughness, especially Be be related to be best suited for the raw material of the spool of natural gas or Crude Oil Transportation acid resistance, resistance to crushing characteristic and low-temperature flexibility excellent Different thick section and high strength spool steel plate and spool.
Background technology
In recent years, as the long-distance delivery method of crude oil, natural gas, the importance more and more higher of pipeline.Distance is defeated The idea of the design of main line spool sent is based primarily upon American Petroleum Institute (API) standard, in the past, in order to prevent load intrinsic pressure When rupture, develop the spool of tensile strength, excellent in low temperature toughness.
In order to improve crude oil, the transfer efficiency of natural gas and when improving intrinsic pressure, need high intensity and the heavy wall of spool Change, and then specially require low-temperature flexibility in the case that spool is layed in cold district.But, normally due to high intensity, Wall thickening, the guaranteeing of the toughness of steel becomes difficult.
In order to reduce the firmness change in the thickness of slab direction of thick-wall materials, improve low-temperature flexibility, in patent documentation 1 it is proposed that The method being rolled in the temperature field (2 phase region) that metal structure becomes austenite and ferritic 2 phases.By above-mentioned side The metal structure of thick-wall materials can be formed in the tissue being mixed into island-like martensite in fine acicular ferrite structure by method.
Additionally, recently, for the requirement characteristic variation of spool, in addition to intensity and low-temperature flexibility, sometimes also require The resistance to crushing characteristic that will not crush because of external pressure, the acid resistance that will not crack in the acid environment containing hydrogen sulfide etc..Special It is not when by pipe installation in deep-sea it is desirable to take into account resistance to crushing characteristic and the such contrary characteristic of low-temperature flexibility.But, Due to the wall thickening of spool, this resistance to crushing characteristic and taking into account of low-temperature flexibility become extremely difficult.
Prior art literature
Patent documentation
Patent documentation 1：Japanese Unexamined Patent Publication 8-041536 publication
Patent documentation 2：Japanese Unexamined Patent Publication 2010-084170 publication
Patent documentation 3：Japanese Unexamined Patent Publication 2010-084171 publication
Patent documentation 4：Japanese Unexamined Patent Publication 2011-132599 publication
Patent documentation 5：Japanese Unexamined Patent Publication 2011-163455 publication
Content of the invention
Invent problem to be solved
As described above, in recent years, for the requirement characteristic of the natural gas being layed in deep-sea, the spool of Crude Oil Transportation There is the tendency complicating, become also to require wall thickening, high intensity, low-temperature flexibility, acid resistance and then crush characteristic.
In the case of above-mentioned patent documentation 1, do not account for the reply to acid resistance, resistance to crashing.It is especially in the presence of Because island-like martensite becomes the starting point of destruction, so that destroying the problem that toughness reduces.
For this problem it is proposed that suppressing the generation of martensite of hard and suppressing the difference of hardness of ferrite and bainite Method, to suppress the method (for example, referring to patent documentation 2～4) of Bao Xinge effect by using fine bainite.
In recent years, there is diversified tendency for the requirement characteristic of spool, wherein the requirement of particularly deep-sea spool Characteristic complicates.Specifically, except wall thickening, yield stress (YS), tensile strength (TS), low-temperature flexibility are (at -10 DEG C DWTT ductile fracture rate) beyond, also require acid resistance so that crush the characteristic (pressure of the circumferencial direction after timeliness at 200 DEG C 0.2% flow stress of contracting).
However, for existing technology (such as patent documentation 2～5 etc.), can all take into account these characteristics is to be stranded very much Difficult.
Invention disclosed in patent documentation 2 considers the reply to brittle-cracking propagation Stopping Ability and low-temperature flexibility, but Do not account for the reply to acid resistance, resistance to crashing.Additionally, the invention disclosed in patent documentation 3 considers low-temperature flexibility, crushing Characteristic, but do not account for acid proof reply.Additionally, compressive strength and low temperature have been sought in the invention disclosed in patent documentation 4 The taking into account of the balance of toughness, high compressive strength and acid resistance, but do not account for above-mentioned crushing characteristic (at 200 DEG C when 0.2% flow stress of the compression of the circumferencial direction after effect).
Find in patent documentation 5：In American Petroleum Institute (API) standard x 80 for more than 25mm for the thickness of slab, (tensile strength is More than 620MPa) in the case of following spool steel pipe, it is extremely that the central part of thickness of slab is made fine bainite structure Difficult.In order to solve such technical task, it is proposed that so that the content of C reduces, by metal structure system in patent documentation 5 Based on becoming the tissue of the low temperature phase change based on bainite to make the steel that toughness improves, add Mo and improve hardenability, suppression The interpolation of Al processed and the manufacture method of the transgranular bainite of effectively utilizes.
The hardenability by raising mother metal for the invention disclosed in patent documentation 5, and by with steel plate generally bayesian phosphor bodies Uniform metal structure constitute, thus the Effective grain size miniaturization by HAZ.Being intended that of invention disclosed in patent documentation 5 The low-temperature flexibility of weld part, but do not account for the reply to acid resistance, resistance to crashing.
Additionally, in the central part of thickness of slab, pressure based on controlled rolling and being become based on the rate of cooling controlling cooling Insufficient.Therefore, even in the case of hardenability raising, along with the increase of thickness of slab, steel plate is made integrally to become uniformly gold It is also difficult for belonging to tissue.
Additionally, in the past, the thickness of slab of spool steel plate was often the thin-walled of below 20mm, if being that X65 level is left in API standard Right intensity, then can readily insure that acid resistance, low-temperature flexibility, the such diverse nature of resistance to crushing characteristic.This is because, Reduction ratio is substantially ensured that and effective crystal particle diameter becomes fine in hot rolling, and then using the top layer accelerating cooling and thickness of slab central part Rate of cooling difference little, metal structure homogenizes.If however, becoming thickness of slab is more than 25mm, particularly more than 30mm Heavy wall, then meet acid resistance, low-temperature flexibility, the whole of resistance to crushing characteristic become difficult.
Particularly resistance to crushing characteristic guarantee with low-temperature flexibility guarantee contrary, for prior art, also do not design Go out to take into account resistance to crushing characteristic and material as low-temperature flexibility.
In view of such practical situation, problem is to provide the spool being best suited for natural gas, Crude Oil Transportation to the present invention Thick section and high strength spool raw material, that there is acid resistance, resistance to crushing characteristic and low-temperature flexibility with good balance and above-mentioned thickness The effective steel plate of wall high intensity line.
Means for solving the problem
The present inventor is high-strength for the heavy wall obtaining acid resistance in spool steel plate, resistance to crushing characteristic and excellent in low temperature toughness Degree spool steel plate, is conceived to metal structure and crystal particle diameter has made intensive studies.Itself it was found that heavy wall spool ( In referred to as " thick walled steel tube "), with regard to be used for reaching (1) intensity with acid proof take into account, the intensity of (2) thick walled steel tube and resistance to crushing The composition taken into account of the taking into account of characteristic, the intensity of (3) thick walled steel tube and low-temperature flexibility, metal structure, manufacture method etc., respectively can With according to proceeding as described below arrangement.
(1) intensity is taken into account with acid proof
In order to do not damage acid proof in the case of improve spool intensity, using the steel plate of the mother metal as above-mentioned spool It is effective that metal structure makes acicular ferrite or the uniform tissue of bainite.Additionally, in order to improve acid resistance it is necessary to press down The hardening in center segregation portion processed.
Here, the mechanism of the crackle producing in acid environment is illustrated.Crackle in acid environment, particularly hydrogen induction Crackle (HIC) is especially due to lacking in the steel such as MnS system field trash of the elongation in the center segregation portion being present in steel plate The hydrogen that sunken surrounding assembles.That is, in acid environment, the hydrogen invading in steel is gathered in the surrounding of these defects and becomes gas, In the case that its pressure exceedes the destruction toughness value (KIC) of steel, crack.And then, if the center segregation portion of steel, field trash Periphery etc. hardens, then crackle becomes easily to propagate.Therefore, for spool used in acid environment, suppression elongation The generation of MnS, the formation of the hardening phase of center segregation are effective, specifically, make acceleration be cooled in stopping, example under slightly higher temperature It is effective that temperature as the center segregation portion according to steel reach more than 400 DEG C of mode to stop the cooling of the acceleration after hot rolling.Separately Outward, so-called center segregation portion refers to result from solidifying segregation during casting, and in the thickness of slab central part of steel plate, the composition such as Mn occurs The position of denseization.
(2) intensity of thick walled steel tube crushes taking into account of characteristic with resistance to
In the case of thick walled steel tube, in order to ensure both intensity and resistance to crushing characteristic, add Mo etc. and improve quenching Property, the acceleration after hot rolling cools down the high martensite of product dislocation density, bainite, promotes strain-aging to be effective.Tool For body, if control the stopping temperature accelerating cooling according to the mode that slightly lower temperature, such as surface of steel plate temperature reach less than 400 DEG C Degree, then generate martensite, and the application sintering processes of thick walled steel tube can be promoted (to be heated to 200 DEG C during application in front and back and keep Process) when strain-aging.
(3) the taking into account of the intensity of thick walled steel tube and low-temperature flexibility
In the case of thick walled steel tube, compared with the situation of the steel pipe of thin-walled, original austenite (is occurred by accelerating cooling Austenite before phase transformation) become thick, low-temperature flexibility reduces.If additionally, compared with the independent tissue of bainite, needle-like ferrum is plain However nor say that low-temperature flexibility is sufficient effective crystal particle diameter of the independent tissue of body is little,.Therefore, in order to ensure Low-temperature flexibility, the generation of polygonal ferrite is effective.But, because polygonal ferrite makes intensity decreases, so in order to Guarantee intensity, it is effective for making with the complex tissue of bainite, acicular ferrite.
As described above, know and meet above-mentioned (1)～(3) it is ensured that acid resistance, low-temperature flexibility, resistance to crushing simultaneously Characteristic is entirely difficult.For example, for the resistance to crushing characteristic of (2), martensite is effective, but acidproof for (1) For the low-temperature flexibility of property and (3), martensite is harmful.Additionally, polygonal ferrite is for the low-temperature flexibility of (3) Effectively, but the acid resistance of (1) is organized due to the generation because of polygonal ferrite and is become uneven, so reduce.Additionally, position The low polygonal ferrite of dislocation density makes resistance to crushing characteristic reduce.
Therefore, present inventors studied the such feature of effectively utilizes heavy wall, i.e. pass through hot rolling and subsequent accelerate cooling Using resulting from the method that the surface of thickness of slab and the temperature difference of central part control tissue.And notice in thickness of slab central part Acid proof guarantee so that in top layer resistance to crushing characteristic guarantee respectively this point extremely important.Additionally, in order to ensure low temperature is tough Property, have studied the miniaturization of effective crystal particle diameter.
Know first, in thickness of slab central part, in order to ensure acid resistance, intensity and low-temperature flexibility, suppression processing ferrite And martensite-austenite composite is (hereinafter referred to as " MA ".) generation and suppress harden, make by acicular ferrite, bainite One of or both tissues of homogenizing of constituting be effective.
Wherein, in thickness of slab central part, by segregation there is denseization in Mn, and hardenability is high, and ferritic generation is pressed down System.But, in order to ensure low-temperature flexibility, ferritic generation is effective, and making the ferrite content towards top layer increases like that Metal structure become necessary.
On the other hand, if generate soft polygonal ferrite in order to ensure low-temperature flexibility, the circumferencial direction on top layer Compressive yield stress reduce, resistance to crushing characteristic reduce.For this problem, as long as adding inventors believe that making to generate in top layer Work ferrite, improves ferritic dislocation density and promotes strain-aging, so that resistance to crushing characteristic is improved.Consequently found that, close In the tissue on top layer, in order to meet resistance to crushing characteristic, more than 5% processing ferrite is become preferably with area occupation ratio family planning, in order to ensure Low-temperature flexibility, suppresses MA, and remainder is made by one of polygonal ferrite, bainite or tissue that both are constituted relatively Good.
If processing ferrite is many, crushing strength increases, but therefore leads to low-temperature flexibility to deteriorate.In order to ensure low temperature is tough Property it is necessary to a certain extent limit processing ferrite content.I.e. it is necessary to by the part undertaking crushing strength and undertake low temperature The part of toughness is suitably distributed according to thickness of slab.That is, thickness of slab gets thinner, then the ferritic allowance of the processing of skin section becomes Fewer, thickness of slab becomes thicker, then the ferritic allowance of the processing of skin section becomes more.Therefore, inventor has investigated processing The relation of ferritic allowance and thickness of slab is it was found that optimal relation.
The present invention is recognized based on these and completes, and its purport is as follows.
[1] the thick section and high strength spool steel plate of a kind of acid resistance, resistance to crushing characteristic and excellent in low temperature toughness, its feature exists In, it is thickness of slab is more than 25mm and the steel plate of below 45mm,
Its composition is contained in terms of quality %：
C：0.04～0.08%,
Mn：1.2～2.0%,
Nb：0.005～0.05%,
Ti：0.005～0.03%,
Ca：0.0005～0.0050%,
N：0.001～0.008%,
It is limited to Si：Less than 0.5%,
Al：Less than 0.05%,
P：Less than 0.03%,
S：Less than 0.005%,
O：Less than 0.005%,
Remainder is made up of Fe and inevitable impurity,
Start from surface of steel plate to be the tissue of skin section for the part within more than 0.9mm and 1.1mm towards thickness direction It is limited in terms of area occupation ratio：
Processing ferrite：For more than 5% and the S that obtained by following formula 1afe1Below %,
Martensite-austenite composite：Less than 8%,
Remainder by one of polygonal ferrite, bainite or both constitute,
Part within two directions that thickness of slab center starts the table back side towards steel plate are 1mm is the gold of thickness of slab central part Belong to tissue to be limited in terms of area occupation ratio：
Processing ferrite：Less than 5%,
Martensite-austenite composite：Less than 5%,
Remainder by one of acicular ferrite, bainite or both constitute,
The meansigma methodss of the effective crystal particle diameter being measured by EBSD method in skin section and thickness of slab central part For less than 20 μm.
Sfe1=0.6552 × TH- 4.7826 formulas 1a
Wherein, TH：The thickness of slab of thick section and high strength spool steel plate
[2] the thick section and high strength spool of the acid resistance according to above-mentioned [1], resistance to crushing characteristic and excellent in low temperature toughness is used Steel plate is it is characterised in that contained further in terms of quality %：
Cu：Less than 0.50%,
Ni：Less than 0.50%,
Cr：Less than 0.50%,
Mo：Less than 0.50%,
W：Less than 0.50%,
V：Less than 0.10%,
Zr：Less than 0.050%,
Ta：Less than 0.050%,
B：Less than 0.0020%,
Mg：Less than 0.010%,
REM：Less than 0.0050%,
Y：Less than 0.0050%,
Hf：Less than 0.0050%,
Re：Less than 0.0050%
In one kind or two or more.
[3] thick section and high strength of the acid resistance, resistance to crushing characteristic and excellent in low temperature toughness according to above-mentioned [1] or [2] Spool steel plate is it is characterised in that the content of Al is less than 0.005%.
[4] thickness of the acid resistance according to any one of above-mentioned [1]～[3], resistance to crushing characteristic and excellent in low temperature toughness The effective steel plate of wall high intensity line is it is characterised in that tensile strength is 500～700MPa.
[5] thickness of the acid resistance according to any one of above-mentioned [1]～[3], resistance to crushing characteristic and excellent in low temperature toughness It is characterised in that the yield stress after tubing reaches more than 440MPa, tensile strength reaches 500 to the effective steel plate of wall high intensity line ～700MPa, 0.2% flow stress of the compression of the circumferencial direction after timeliness at 200 DEG C reaches more than 450MPa.
[6] a kind of thick section and high strength spool is it is characterised in that it is will be acidproof any one of above-mentioned [1]～[4] After the thick section and high strength spool steel formability of property, resistance to crushing characteristic and excellent in low temperature toughness is tubulose, docking section is carried out electricity Arc welding and manufacture,
Yield stress is more than 440MPa, and tensile strength is 500～700MPa, the circumferencial direction after timeliness at 200 DEG C Compression 0.2% flow stress be more than 450MPa.
Invention effect
In accordance with the invention it is possible to provide raw material the, acid resistance of the spool being best suited for natural gas, Crude Oil Transportation, Resistance to crushing characteristic and the thick section and high strength spool steel plate of excellent in low temperature toughness.Particularly can provide wall thickness reach 25～ YS after 45mm, tubing reaches more than 440MPa, TS reaches 500～700MPa, the DWTT ductile fracture rate at -10 DEG C reaches More than 85% and 200 DEG C at timeliness after the compressive strength (0.2% flow stress) of circumferencial direction reach more than 450MPa Acid resistance, resistance to crushing characteristic and excellent in low temperature toughness thick section and high strength spool steel plate, the contribution in industry is extremely notable.
Brief description
Fig. 1 is the optical microscope photograph in the section of skin section of thick section and high strength spool steel plate of the present invention.
Fig. 2 is the ferritic area occupation ratio of processing in the skin section of thick section and high strength spool steel plate of the regulation present invention The upper limit and the chart of lower limit.
Specific embodiment
Hereinafter, the thick section and high strength spool steel plate to the acid resistance of the present invention, resistance to crushing characteristic and excellent in low temperature toughness (below, also referred to as " spool steel plate " or " steel plate ") and its manufacture method illustrate.
Hereinafter, to the spool of the present embodiment restriction reason of the composition in thick high-strength steel plate (mother metal of spool) Illustrate.
In addition, referring to quality % when the record of % is not particularly illustrated.
C：C is the element making the intensity of steel plate improve, and must add more than 0.04% in present embodiment.Preferably add More than 0.05%, more preferably add more than 0.055% C.On the other hand, if due to adding the C more than 0.08%, low temperature is tough Property reduce, so the upper limit that C is measured is set to 0.08%.Preferably the upper limit that C measures is set to 0.07%, more preferably the upper limit is set to 0.065%.
Mn：Mn is the element of the raising contributing to the intensity of steel plate and toughness.In present embodiment, in order to ensure steel plate Intensity, adds more than 1.2% Mn.Preferably add more than the 1.4%, Mn of more preferably interpolation more than 1.5%.On the other hand, by If add Mn in excessively, the hardness of thickness of slab central part rises, and damages acid resistance, so the upper limit that Mn is measured is set to 2.0% Below.Preferably the upper limit that Mn measures is set to less than 1.8%, is more preferably set to less than 1.7%.
Nb：Nb is to form carbide, nitride, contributes to the element of the raising of intensity.Additionally, tying again in suppression hot rolling Crystalline substance, promotes grain refined.Therefore, the lower limit of Nb amount is set to more than 0.005%.Preferably the lower limit that Nb measures is set to more than 0.010%, More preferably it is set to more than 0.015%.On the other hand, if due to excessively adding Nb, intensity exceedingly rises and to damage low temperature tough Property, so the upper limit that Nb is measured is set to less than 0.05%.Preferably the upper limit that Nb measures is set to less than 0.04%, is more preferably set to Less than 0.03%.
Ti：Ti is to form nitride, for the element of the grain refined performance effect of metal structure.Ti amount lower limit in order that Effectively crystal particle diameter becomes fine, is set to more than 0.005%.Preferably the lower limit that Ti measures is set to more than 0.008%, more preferably sets For more than 0.01%.On the other hand, if due to excessively adding Ti, generating thick TiN, damage low-temperature flexibility, so by Ti The upper limit of amount is set to less than 0.03%.Preferably the upper limit that Ti measures is set to less than 0.02%, is more preferably set to 0.015%.
Ca：Ca is the form controlling sulfide, makes the element that acid resistance improves.In present embodiment, in order to promote CaS's Generate and suppress the generation of the MnS along rolling direction elongation it is ensured that acid resistance, the lower limit that Ca is measured is set to more than 0.0005%. Preferably the lower limit that Ca measures is set to 0.0010%, is more preferably set to 0.0015%.On the other hand, if excessively adding Ca, Generate thick oxide, low-temperature flexibility reduces, so the upper limit that Ca is measured is set to 0.0050%.Preferably the upper limit that Ca measures is set For less than 0.0040%, more preferably it is set to less than 0.0030%.
N：In present embodiment, by the metal structure miniaturization of steel the content of N is set in order to using nitride More than 0.001%.Preferably N amount is set to more than 0.002%, is more preferably set to more than 0.003%.On the other hand, if due to mistake Amount ground contains N, then generate thick nitride, damages low-temperature flexibility, so the upper limit that N is measured is set to 0.008%.Preferably by N The upper limit of amount is set to less than 0.007%, is more preferably set to less than 0.006%.
Si and Al is deoxidant element, if using deoxidation add as purpose when using any one can but it is also possible to When use.If further, since excessively adding Si and Al, the characteristic of infringement steel plate, so in present embodiment, by Si and Al The upper limit of content limit as follows.
Si：If because Si excessively adds, particularly in welding heat affected zone (Heat Affected Zone, referred to as HAZ.) the middle MA generating hard, so that the toughness in the seam welding portion of steel pipe is reduced, so the ceiling restriction that Si is measured is less than 0.5%. Preferably Si amount is set to less than 0.3%, is more preferably limited to less than 0.25%.Further, since as described above, Si is for taking off The element of oxygen, and be also the element of the rising contributing to intensity, it is advantageous to the lower limit that Si is measured is set to more than 0.05%, more It is preferably set to more than 0.10%.
Al：Al is useful deoxidant element as described above, preferably the lower limit that Al measures is set to more than 0.001%, more excellent Choosing is set to more than 0.003%.But, if because Al excessively adds, generate thick oxide, so that low-temperature flexibility is reduced, So the ceiling restriction measuring Al is less than 0.05%.Preferably the upper limit that Al measures is set to less than 0.04%, is more preferably limited to Less than 0.03%.Additionally, by Al amount is limited to less than 0.005%, it is possible to increase the toughness in HAZ portion.
P, S and O (oxygen) contain as inevitable impurity, if due to excessively containing, the characteristic of infringement steel plate, So in the present embodiment, the upper limit of the content of P, S and O is limited as follows.
P：P is the element making steel brittle, if due to containing more than 0.03%, the low-temperature flexibility of infringement steel, so will Ceiling restriction is less than 0.03%.The ceiling restriction preferably measured P is less than 0.02%, is more preferably limited to less than 0.01%.
S：S is the element generating MnS sulfides, if due to containing having more than 0.005%, making low-temperature flexibility, acid resistance Reduce, so ceiling restriction is less than 0.005%.Preferably S amount is set to less than 0.003%, is more preferably limited to 0.002%.
O：If because O contains more than 0.005%, generate thick oxide, so that the low-temperature flexibility of steel is reduced, so The ceiling restriction of content is less than 0.005%.Preferably the upper limit that O measures is set to less than 0.003%, is more preferably limited to Less than 0.002%.
And then, in the present invention, as the element improving intensity, low-temperature flexibility, can add Cu, Ni, Cr, Mo, W, V, Zr, One kind or two or more in Ta, B.
Cu：Cu is the effective element that low-temperature flexibility will not be made to reduce and make intensity rising.Preferably add more than 0.01% Cu, more preferably add more than 0.1%.On the other hand, Cu is due to being when heating to steel billet or to carry out the seam welding of steel pipe The element that Shi Rongyi cracks, it is advantageous to Cu amount is set to less than 0.50%.More preferably Cu amount is set to less than 0.35%, Further preferably it is set to less than 0.2%.
Ni：Ni is to improving low-temperature flexibility and the effective element of intensity.Preferably add more than 0.01% Ni, more preferably add More than plus 0.1%.On the other hand, Ni is the element of high price, from the viewpoint of economy, preferably by Ni amount be set to 0.50% with Under.More preferably Ni amount is set to less than 0.35%, is further preferably set to less than 0.2%.
Cr：Cr is the element being improved by the intensity that precipitation strength makes steel.Preferably add more than 0.01% Cr, more preferably Add more than 0.1%.On the other hand, if due to excessively adding Cr, because of the rising of intensity, low-temperature flexibility reduces sometimes, institute Preferably the upper limit that Cr measures to be set to less than 0.50%.More preferably Cr amount is set to less than 0.35%, is further preferably set to Less than 0.2%.
Mo：Mo is so that hardenability is improved, and forms carbonitride and improves the element of intensity.Preferably add more than 0.01% Mo, more preferably adds more than 0.05%.On the other hand, if due to excessively adding Mo, the low temperature because of the rising of intensity sometimes Toughness reduces, it is advantageous to the upper limit that Mo is measured is set to less than 0.50%.More preferably Mo amount is set to less than 0.2%, further It is preferably set to less than 0.15%.
W：W and Mo is equally so that hardenability is improved, and forms carbonitride and improves the element of intensity, preferably adds More than 0.0001%.More preferably W amount is set to more than 0.01%, further preferably adds more than 0.05%.On the other hand, due to If excessively adding W, because of the rising of intensity, low-temperature flexibility reduces sometimes, it is advantageous to the upper limit that W is measured is set to 0.50% Below.More preferably W amount is set to less than 0.2%, is further preferably set to less than 0.15%.
V：V be formed carbide, nitride and contribute to the element of the raising of intensity.Preferably add more than 0.001% V, more preferably adds more than 0.005%.On the other hand, if due to adding V more than 0.10% ground, sometimes making low-temperature flexibility drop Low, it is advantageous to V amount is set to less than 0.10%.More preferably by V amount be set to less than 0.05%, be more preferably set to 0.03% with Under.
Zr、Ta：Zr and Ta and V be equally formed carbide, nitride and contribute to the element of the raising of intensity.Zr、Ta Preferably add more than 0.0001% respectively, more preferably add more than 0.0005%, further preferably add more than 0.001%.Separately On the one hand, if due to adding Zr, Ta more than 0.050% ground, low-temperature flexibility reduces sometimes, it is advantageous to Zr is measured, Ta measures respectively From the upper limit be set to less than 0.050%.More preferably it is set to less than 0.030%.
B：B can be by micro interpolation and makes the element of hardenability raising.In order to improve intensity, preferably add More than 0.0001% B.Preferably add more than 0.0003% B.On the other hand, if due to excessively adding B, sometimes generating The precipitate of B, makes low-temperature flexibility deteriorate, it is advantageous to B amount is set to less than 0.0020%.More preferably B amount is set to Less than 0.0010%.
And then, in the present invention, in order to control the form of the field trashes such as sulfide, oxide, improve low-temperature flexibility, acidproof Property, can add one kind or two or more in Mg, REM, Y, Hf, Re.
Mg：Mg is to contribute to acid resistance, low-temperature flexibility by the morphology Control of sulfide, the formation of fine oxide Raising element.Preferably add more than 0.0001% Mg, more preferably add more than 0.0005%, further preferably add More than 0.001%.On the other hand, if adding Mg more than 0.010% ground, sometimes becoming easily to generate thick oxide, damaging The toughness of evil HAZ, it is advantageous to Mg amount is set to less than 0.010%.More preferably Mg amount is set to less than 0.005%, further It is preferably set to less than 0.003%.
REM、Y、Hf、Re：REM, Y, Hf, Re generate sulfide, the generation of the MnS along rolling direction elongation for the suppression, especially Contribute to acid proof improvement.REM, Y, Hf, Re preferably all add more than 0.0001%, be more preferably set to 0.0005% with On, further preferably it is set to more than 0.0010%.On the other hand, if because REM, Y, Hf, Re all add more than 0.0050% ground, Then oxide increases sometimes, damages toughness, it is advantageous to the upper limit is set to less than 0.0050%.More preferably be set to 0.0030% with Under.
Additionally, in present embodiment, the remainder in addition to above-mentioned element is substantially made up of Fe, can be micro Add the element of the action effect without compromising on the present invention headed by inevitable impurity.Inevitable impurity refers to former Composition that is comprising in material or being mixed into during manufacturing, makes the composition containing in steel with being not intended that.
Specifically, Si, Al, P, S, O, N, Sb, Sn, Co, As, Pb, Bi and H can be included.Wherein, P, S, O and N have Necessary respectively as described above according to reaching Si：Less than 0.5%, Al：Less than 0.05%, P：Less than 0.03%, S：0.005% with Under, O：Less than 0.005%, N：Less than 0.008% mode controls.
With regard to other elements, usual Sb, Sn, Co and As can have less than 0.1% as inevitable impurity It is mixed into, Pb and Bi can have less than 0.005% being mixed into as inevitable impurity, H can have less than 0.0005% As being mixed into of inevitable impurity, if common scope, then there is no need especially to be controlled.
Additionally, the arbitrary addition element in thick section and high strength spool steel plate of the present invention be Cu, Ni, Cr, Mo, Even if W, V, Zr, Ta, B, Mg, REM, Y, Hf and Re do not have a mind to containing sometimes can also being mixed into as inevitable impurity.But It is, if below the above-mentioned upper limit of content intentionally containing sometimes of these elements, then also will not be to the present invention even below lower limit Have undesirable effect, so having no problem.
And then, in the present invention, in order to ensure hardenability, improve intensity and low-temperature flexibility, preferably will by C, Mn, Ni, Cu, Carbon equivalent Ceq of following (formulas 2) that the content [quality %] of Cr, Mo, V calculates is set to 0.30～0.50.In order to improve intensity, The lower limit of Ceq is more preferably set to more than 0.32, is further preferably set to more than 0.35.Additionally, the upper limit of Ceq is in order to improve low temperature Toughness, is more preferably set to less than 0.45, is further preferably set to less than 0.43.
Ceq=C+Mn/6+ (Ni+Cu)/15+ (Cr+Mo+V)/5 (formula 2)
Additionally, in order to ensure the low-temperature flexibility of steel plate and HAZ, preferably by the content by C, Si, Mn, Cu, Cr, Ni, Mo, V Crack sensitivity indices P cm of following (formulas 3) that [quality %] calculates is set to 0.10～0.20.In order to improve intensity, under Pcm Limit is more preferably set to more than 0.12, is further preferably set to more than 0.14.Additionally, in order to improve low-temperature flexibility, the upper limit of Pcm is more It is preferably set to less than 0.19, be further preferably set to less than 0.18.
Pcm=C+Si/30+ (Mn+Cu+Cr)/20+Ni/60+Mo/15+V/10 (formula 3)
In addition, intentionally not adding in the case that the element optionally containing is Ni, Cu, Cr, Mo, V, above-mentioned (formula 2), and in (formula 3), calculated as 0.
Then, the metal structure of the steel plate of the present invention is illustrated.
The steel plate thickness of slab of the present invention is more than 25mm and then the thickness for more than 30mm, as heavy wall (25mm～45mm) The steel plate of spool be suitable.In addition the steel plate of the present invention is between top layer and thickness of slab central part, using the temperature of hot rolling Differ from, accelerate the differing from of rate of cooling of cooling to carry out organizational controls, metal structure is different in top layer with thickness of slab central part.Separately Outward, in the present invention, the skin section of steel plate is to start to thickness direction to be more than 0.9mm and below 1.1mm from the surface of steel plate Partly (that is, start from surface of steel plate to carry on the back two surface direction and be towards the table of steel plate to centered on the position as 1mm for the thickness direction Region within 0.1mm), the central part of steel plate is within the table back of the body two surface direction of the centrally directed steel plate of thickness of slab are 1mm Region.
More than 5% processing ferrite in skin section, in order to improve resistance to crushing characteristic, is become with area occupation ratio family planning.Processing Ferrite is the ferrite being extended along rolling direction by hot rolling, with the cooling after rolling and the polygonal ferrite that generates Compare, dislocation density is high, be effective for improving resistance to crushing characteristic.Optics by the section of the skin section of the steel plate of the present invention Microphotograph is shown in Figure 1.In addition, the part of dense Lycoperdon polymorphum Vitt is processing ferrite, one part is depicted with arrows.Institute in Fig. 1 The skin section shown contains 9.3% processing ferrite.
Additionally, if processing ferrite is many, crushing strength increases, but therefore low-temperature flexibility deterioration.Consequently found that, pass through The processing ferrite of suppression central part can improve low-temperature flexibility.Wall thickness with steel plate becomes big, the top layer temperature central with wall thickness Degree difference becomes big.Therefore, the wall thickness with steel plate is thickening, and the processing ferrite content that can manufacture in the central part of thickness of slab tails off, On the other hand, the processing ferrite quantitative change that can manufacture in skin section is big.Therefore, inventor has investigated wall thickness and the table of steel plate The relation of the processing ferrite content in layer portion is it was found that optimum range.
Fig. 2 represent thickness of slab be 25mm～45mm and the thickness of slab of steel plate and skin section in the ferritic area occupation ratio of processing Upper limit Sfe1Relation.
Known by Fig. 2, in order to obtain the resistance to crushing characteristic of the raw material of the spool being best suited for natural gas, Crude Oil Transportation And low-temperature flexibility, in the skin section of steel plate process ferritic area occupation ratio be necessary to be set to more than following lower limit and the upper limit Value is following.
The lower limit of the ferritic area occupation ratio of processing in the skin section of steel plate：5%
The higher limit of the ferritic area occupation ratio of processing in the skin section of steel plate：
Sfe1=0.6552 × TH- 4.7826 formulas 1a
(wherein, TH：The thickness of slab of thick section and high strength spool steel plate)
If further, since processing ferritic area occupation ratio to exceed above-mentioned Sfe1%, then top layer harden, infringement low temperature tough Property, so being set to above-mentioned S by processing ferritic area occupation ratiofe1Below %.Furthermore it is preferred that the processing ferrum in the skin section of steel plate The upper limit of the area occupation ratio of ferritic meets Formula 1 below b.
Preferred higher limit：Sfe2=0.8 × TH- 15 formulas 1b
As shown in above-mentioned formula 1a and formula 1b, for obtaining being best suited for the spool of natural gas, Crude Oil Transportation The ferritic area occupation ratio of processing of the acid resistance of raw material, resistance to crushing characteristic and low-temperature flexibility there is thickness of slab dependency.Think Due to the hot rolling between top layer and thickness of slab central part temperature difference, accelerate cooling rate of cooling difference easily be subject to thickness of slab shadow Ring, so processing ferritic above-mentioned area occupation ratio there is thickness of slab dependency.
In skin section, in order to improve resistance to crushing characteristic, preferably become more than 0.1% dislocation density height with area occupation ratio family planning MA, if but MA becomes the starting point of destruction, excessively generate then infringement low-temperature flexibility.Therefore, by the MA of skin section with area occupation ratio Meter is limited to less than 8%.Preferably the area occupation ratio of the MA of skin section is set to less than 5%, is more preferably set to less than 3%.
In skin section, with regard to the remainder of above-mentioned processing ferrite and MA, make by polygonal ferrite, bayesian One of body or the metal structure that both are constituted.Polygonal ferrite is effective for improving low-temperature flexibility, in skin section Easily generate, gradually decrease towards thickness of slab central part.Bainite is effective for improving intensity, with polygonal ferrite not With, few in skin section, it is gradually increased towards thickness of slab central part.This is because, in thickness of slab central part, compared with top layer, heat The rolling temperature rolled, the started temperature accelerating cooling uprise.
In thickness of slab central part, in order to ensure low-temperature flexibility and acid resistance are it is necessary to ferritic generation is processed in suppression, will add The ferritic area occupation ratio of work is limited to less than 5%.Process ferritic area occupation ratio and be preferably less than 3%, more preferably 0%.
In thickness of slab central part, preferably suppression becomes the generation of the MA of starting point of destruction and suppresses the hard of thickness of slab central part Change, in order to ensure low-temperature flexibility, the area occupation ratio of MA is limited to less than 5%.Preferably the area occupation ratio of the MA of thickness of slab central part is set For less than 4%, more preferably it is set to less than 2%.
In thickness of slab central part, the remainder of above-mentioned processing ferrite and MA is made by acicular ferrite, bainite One of or both constitute metal structure.Although because polygonal ferrite is effective for improving low-temperature flexibility, damaging Evil acid resistance, so in thickness of slab central part, is preferably made by one of acicular ferrite, bainite or homogenizing that both are constituted Metal structure.
Wherein, each metal structure of above-mentioned skin section and thickness of slab central part can be observed by optical microscope.
Specifically, by graphical analyses are carried out to optical microscope macrograph, processing ferrite and MA can be obtained Area occupation ratio.In addition, with regard to MA, carrying out Lepera etching, by graphical analyses are carried out to the area occupation ratio not having the tissue colouring And obtain.Additionally, being granular in the form accelerating the polygonal ferrite generating during cooling, processing ferrite enters along rolling direction Row elongation.Additionally, processing ferrite is high due to dislocation density, so hardening compared with polygonal ferrite.
Therefore, processing ferrite and polygonal ferrite can be carried out by the ratio (length-width ratio) of major diameter and minor axis, hardness Difference.Acicular ferrite, bainite are the tissue of lath-shaped, can be distinguished with processing ferrite and polygonal ferrite.
In order to ensure the low-temperature flexibility of steel plate, the crystal crystal boundary becoming the resistance of the progress of cracking increases, reduces crystalline substance Body particle diameter is effective.In the present invention, the size reducing the region that the high inclination-angle crystal boundary being more than 15 ° by gun parallax surrounds has Effect crystal particle diameter, makes low-temperature flexibility improve.By EBSD method will be passed through in skin section and thickness of slab central part (Electron Backscatter Diffraction, also referred to as EBSD.) meansigma methodss of effective crystal particle diameter that measure are set to Less than 20 μm it can be ensured that low-temperature flexibility.Effectively crystal particle diameter is more little, more can obtain stable high toughness, and preferably 10 Below μm.
In addition, the low-temperature flexibility of steel plate is passed through to measure effective crystal particle diameter at thickness of slab central part, obtain meansigma methodss and enter Row is evaluated.Additionally, as the means of the effective crystal particle diameter measuring different metal structures, using EBSD method. Effectively crystal particle diameter is set to the round equivalent that the tissue of the length direction using EBSD to the steel plate after rolling is analyzed and obtains Diameter.In addition, in skin section, by using processing ferrite, polygonal ferrite can grain refined, but due in thickness of slab In the portion of centre, processing ferrite, the generation of polygonal ferrite are inhibited, so hot rolling must be passed through, original austenite is fine Change.
Then, the characteristic of the steel plate of the present invention is illustrated.
In the case of the pressure improving conveyed crude oil, natural gas in order to improve the transfer efficiency of pipeline, in order to Prevent from rupturing because intrinsic pressure it is necessary to improve the intensity of spool, increase wall thickness.From such a viewpoint, in order to avoid because of spool Intrinsic pressure and produce fracture (rupture), preferably the thickness of slab of steel plate used in spool is set to more than 25mm.Additionally, steel plate is excellent Choosing has the tensile strength of more than 500MPa.Additionally, steel plate after tubing, i.e. steel tubing portions in addition to weld part and HAZ, example As similarly preferred for the steel tubing portions of 90 °～180 ° positions (position for 3 points～6 points from welding seam part) from welding seam part There is the yield stress of more than 440MPa and the tensile strength of 500～more than 700MPa.In addition, the thickness of slab of steel plate is in order to avoid broken Split, more preferably more than 30mm, be further preferably set to more than 35mm.
In the case that pipeline is layed in cold district, need the low-temperature flexibility of spool.Low-temperature flexibility can be passed through to fall Hammer tear test (" Drop Weight Tear test "：Referred to as " DWT test ") evaluated, in the present invention, preferably by tubing DWTT ductile fracture rate at front steel plate have -10 DEG C is set to more than 85%.Further, since the heavy wall along with spool Change and high intensity, the guaranteeing of low-temperature flexibility becomes difficult, it is advantageous to the thickness of slab of steel plate is set to below 45mm, by steel plate Tensile strength is set to below 700MPa.In the case of by cold working to manufacture steel pipe, the intensity of the steel plate after tubing exists The tendency uprising than the intensity of the steel plate before tubing, but the tensile strength of the steel pipe after tubing is it is also preferred that be set to below 700MPa.
In the case of seabed, need the resistance (resistance to crushing characteristic) of the external pressure for spool by pipe installation.Due to Resistance to crushing characteristic by being affected in the strain forming steel plate by cold working and importing when making steel pipe, so from steel Pipe gathers test film, is evaluated by compression test.In order to prevent spool from crushing because of external pressure, preferably by 200 DEG C when The compressive strength (0.2% flow stress) of the circumferencial direction after effect is set to more than 450MPa.
Then, the manufacture method of the steel plate of the present invention is illustrated.
Steel plate of the present invention in order to obtain in the top layer tissue different with thickness of slab central part, by hot rolling on top layer Metal structure becomes the rolling carrying out more than 1 passage in ferrite and the temperature field (two-phase temperature field) of this two-phase of austenite, enters And under the conditions of the temperature that the acceleration after hot rolling is cooled in the surface of steel plate is carried out as backheat after reaching less than 400 DEG C, stopping Carried out by means such as water-cooleds.
In the case that steel plate is for heavy wall, the reduction compared with the temperature of thickness of slab central part of the temperature on top layer during hot rolling, In thickness of slab central part, ferritic generation compared with top layer is inhibited.If additionally, being set to compared with surface in thickness of slab central part The middle stopping temperature accelerating cooling uprises, the temperature on surface carries out condition as backheat after accelerating cooling, then can will accelerate The temperature of the central part of steel plate after the stopping of cooling is set to more than 400 DEG C, can suppress the hardening of thickness of slab central part, can be true Protect acid resistance.
Additionally, in order to ensure low-temperature flexibility, average effective crystal particle diameter of top layer and thickness of slab central part is set to 20 μm Below.In top layer, by processing the generation of ferrite, polygonal ferrite, effective crystal particle diameter diminishes.On the other hand, exist In thickness of slab central part, the generation due to processing ferrite, polygonal ferrite is suppressed, it is therefore necessary to by original austenite Particle diameter miniaturization.By will in top layer measure effective crystal particle diameter and in thickness of slab central part measure effective crystal particle diameter Meansigma methodss miniaturization, the overall effective crystal particle diameter of thickness of slab become fine it can be ensured that low-temperature flexibility.
Therefore, it is necessary to the pressure ratio in recrystallization domain is set to more than 2.0, by the pressure in non-recrystallization domain in hot rolling Lower ratio is set to more than 3.0.
As described above, by the condition of suitable control hot rolling and subsequent acceleration cooling, except the intensity of thick steel sheet And additionally it is possible to meet the composite attribute with the acid resistance after tubing and resistance to crushing characteristic beyond low-temperature flexibility.
Successively the manufacturing process of steel plate of the present invention is illustrated.
First, by steel operation processed, the steel containing mentioned component is carried out, after melting, being cast and being made steel billet.Casting As long as being carried out by conventional method, but preferred continuously casting from the viewpoint of productivity ratio.Then to obtained steel billet Heated, carried out hot rolling, accelerate cooling to manufacture steel plate.In addition, in present embodiment, the steel billet that will carry out for hot rolling Heating also referred to as heat again, the heating-up temperature of steel billet now is also referred to as relation reheating temperature.
The relation reheating temperature of hot rolling, in order that the solid solution in steel such as the carbide of generation, nitride in steel billet, is set to 1000 More than DEG C.Additionally, by relation reheating temperature is set to more than 1000 DEG C, the heat in 900 DEG C of recrystallization domain can be performed for more than Roll (rolling of recrystallization domain), can be by the tissue miniaturization of steel.In addition, the upper limit of relation reheating temperature is not specified by, in order to suppress Relation reheating temperature is preferably set to less than 1250 DEG C by the coarsening of effective crystal particle diameter.In addition relation reheating temperature is in order to ensure low Warm toughness, is more preferably set to less than 1200 DEG C, is further preferably set to less than 1150 DEG C.
Hot rolling described in present embodiment possess successively more than 900 DEG C recrystallization domain in rolling process, less than 900 DEG C Non-recrystallization domain in rolling and the temperature of surface of steel plate be to become the temperature field (two-phase of austenite and this two-phase of ferrite Domain) in rolling.
Further, since hot rolling can also immediately begin to after the heating furnace being heated again is extracted out, so the beginning of hot rolling Temperature does not have special provision.
In order to by effective crystal particle diameter miniaturization of the thickness of slab central part of steel plate it is necessary to by the recrystallization domain more than 900 DEG C In pressure ratio be set to more than 2.0, promote recrystallization.Wherein, the pressure ratio in recrystallization domain is at the thickness of slab and 900 DEG C of steel billet Thickness of slab ratio.
Then, carry out the hot rolling (rolling of non-recrystallization domain) in less than 900 DEG C of non-recrystallization domain.In order to by after hot rolling Accelerate effective crystal particle diameter miniaturization of the skin section of steel plate after cooling it is necessary to be set to the pressure ratio of non-recrystallization domain rolling More than 3.0, promote using the phase transformation accelerating cooling.More preferably the pressure ratio of non-recrystallization domain rolling is set to more than 4.0.Separately Outward, in the present invention, the pressure of so-called non-recrystallization domain rolling is than being after thickness of slab at 900 DEG C terminates divided by non-recrystallization rolling The ratio of thickness of slab.
In hot rolling, the temperature carrying out surface of steel plate is to become the temperature field (two phase regions) of austenite and this two-phase of ferrite In rolling (two phase regions rolling).Two phase regions roll as the rolling in following temperature fields, and described temperature field is：The surface of steel plate Temperature reaches ferrite transformation started temperature Ar3Hereinafter, but in the period starting to terminating from two phase region rollings, steel plate Thickness of slab central part temperature according to higher than the temperature of surface of steel plate and more than Ar3Mode be maintained.Such Temperature Distribution Cooling can also be accelerated by for example carrying out the short time, make the temperature on only top layer reduce to realize.In the rolling of this two phase region, road Number of times is set to more than 1, and reduction ratio is set to 0.1～40%.Due to carry out two phase region rollings as a result, acceleration followed by is cold But started temperature also becomes two phase regions, so the hardening of thickness of slab central part is inhibited, it is possible to increase low-temperature flexibility.In addition, Above-mentioned " reduction ratio " be using rolling the slip of the thickness of steel plate, i.e. roll before the thickness of steel plate with rolling after steel plate Thickness difference divided by rolling before steel plate value obtained from thickness it is also possible to be indicated with percentage ratio (%) etc..Additionally, In position between top layer and thickness of slab central part, promote the generation of polygonal ferrite, contribute to the raising of low-temperature flexibility.
Additionally, Ar3Can be calculated by the content (quality %) of C, Si, Mn, Ni, Cr, Cu, Mo.
Ar3=905-305C+33Si-92 (Mn+Ni/2+Cr/2+Cu/2+Mo/2)
Wherein, C, Si, Mn, Ni, Cr, Cu, the Mo in above-mentioned formula is the content [quality %] of each element.Additionally, Ni, Cu, Cr, Mo are the element that in the present invention, selectivity adds, and in the case of not intentionally adding, in formula are counted content as " 0 " Calculate.
The lower limit of the reduction ratio in two phase region rollings, in order to generate the processing ferrite along rolling direction elongation, is set to More than 0.1%.Preferably the reduction ratio of two phase region rollings is set to more than 1%, is more preferably set to more than 2%.On the other hand, two-phase Domain rolling in reduction ratio the upper limit due to be difficult to ensure that deformation drag uprise in a low temperature of reduction ratio, so be set to 40% with Under.Preferably the reduction ratio of two phase region rollings is set to less than 30%, is more preferably set to less than 20%, is further preferably set below 10%.
With regard to the end temp of two phase region rollings, i.e. hot rolling end temp, in order to excessively generate processing ferrite, It is set to more than 700 DEG C with the thermometer of surface of steel plate.If hot rolling end temp gets lower than 700 DEG C, sometimes in thickness of slab central authorities Produce ferrite transformation in portion, result from processing ferrite, low-temperature flexibility and acid resistance reduce.If additionally, hot rolling end temp Reduce, then C denseization in austenite sometimes through ferritic generation, promotes the generation of MA.On the other hand, if hot rolling terminates Temperature is too high, then, in the case that the stopping temperature making acceleration cool down reduces, thickness of slab central part hardens sometimes, low-temperature flexibility Reduce.
Then, after the end of hot rolling, immediately begin to accelerate cooling.But, after hot rolling, allow to go out side from roll mill The air cooling of the period being transported to accelerated cooling device.
Within the temperature range of accelerating the stopping temperature of cooling to be set to 200～400 DEG C with surface of steel plate thermometer.If in steel plate Surface temperature more than 400 DEG C at a temperature of stop accelerate cooling, then in thickness of slab central part generate polygonal ferrite, resistance to Acid reduction.On the other hand, in the case of carrying out accelerating the temperature on the surface being cooled to steel plate to get lower than 200 DEG C, thickness of slab Central part hardens, and low-temperature flexibility reduces.
After stopping accelerating cooling, directly carry out air cooling.If reach 200～400 DEG C of temperature in the surface temperature of steel plate During scope stop accelerate cooling, then after, in air cooling steel plate top layer temperature occur backheat.Therefore, the temperature of thickness of slab central part Degree reaches more than 400 DEG C, and hardness reduces, it is possible to increase low-temperature flexibility and acid resistance.
By above manufacture method, the effective steel plate of high intensity line of the present invention can be manufactured.
Additionally, in the case of using the effective steel plate of high intensity line of the present invention as raw material, can manufacture acidproof The steel pipe of the thick section and high strength spool of property, resistance to crushing characteristic and excellent in low temperature toughness.In addition, in the case of manufacturing steel pipe, Preferably employ the UOE operation that effective for high intensity line of the present invention steel plate is carried out C compacting, U compacting, O compacting.Or, JCOE operation can be passed through, manufacture steel pipe using the effective steel plate of high intensity line of the present invention.Heavy wall of the present invention High intensity line Gutron is crossed and effective for high intensity line of the present invention steel plate is configured to after tubulose, and docking section is carried out electric arc welding To manufacture.Electric arc welds from the viewpoint of the toughness and productivity ratio of welding metal, it is preferred to use submerged arc welding.
In addition, the resistance to crushing characteristic of thick section and high strength spool of the present invention can be from being obtained by above-mentioned method Steel pipe gathers the compression test piece of circumferencial direction being evaluated.
Embodiment
Then, embodiments of the invention are illustrated, but the present invention is not limited to employing in below example Condition.
The steel being made up of the chemical composition of table 1-1, table 1-2, table 2-1 and table 2-2 is carried out melting, casts and make steel Base." slab is thick " of table 3-1 and table 3-2 represents the thickness (mm) of obtained steel billet.Above-mentioned steel billet is heated respectively again, Carry out hot rolling in the recrystallization domain more than 900 DEG C.In addition, " heating-up temperature " of table 3-1 and table 3-2 represents above-mentioned heats temperature again Degree, after the hot rolling that " transfer thick " of table 3-1 and table 3-2 represents in above-mentioned recrystallization domain and less than 900 DEG C described later do not tie again The thickness of slab at 900 DEG C before hot rolling in domain.Additionally, " the pressure ratio in recrystallization domain " of table 3-1 and table 3-2 is above-mentioned plate The thick ratio thick divided by transfer of base.
Then, carry out hot rolling to having in non-recrystallization domain below 900 DEG C for the thick steel plate of transfer.Table 3-1 and table 3-2 " thickness of slab " represent in above-mentioned non-recrystallization domain hot rolling after and two phase regions rollings described later before thickness of slab, table 3-1's and table 3-2 " non-recrystallization pressure ratio " is the value obtained from thickness of slab after the thick value of above-mentioned transfer terminates divided by the rolling of above-mentioned non-recrystallization.
After the hot rolling in above-mentioned non-recrystallization domain, and carry out final hot-rolled process before accelerating cooling.By above-mentioned The surface temperature of the steel plate at the end of whole hot-rolled process is shown in " finish rolling end temp (DEG C) " of table 3-1 and table 3-2.This Outward, by the rolling number of times carrying out in above-mentioned final hot-rolled process, road number of times be shown in table 3-1 and table 3-2 " α+γ depresses In passage number of times ", the reduction ratio of the steel plate using above-mentioned final hot-rolled process is shown in the " α+γ pressure of table 3-1 and table 3-2 In rate (%) ".
After above-mentioned final hot-rolled process, water-cooled after being transferred in cooled region, is utilized to implement to accelerate cooling immediately.Will The started temperature of above-mentioned acceleration cooling carrying out in the manufacture process of the steel plate of steel No.1～46 and stopping temperature being shown in In " water-cooled started temperature (DEG C) " of table 3-1 and table 3-2 and " water-cooled stops temperature (DEG C) ".
By above manufacturing process, obtain the steel plate of steel No.1～46.
Gather test film from the skin section of the steel plate of obtained No.1～46 and thickness of slab central part, using optical microscope Carry out structure observation, obtain the area occupation ratio processing ferritic area occupation ratio and MA, confirm remainder tissue.
Remainder be organized in the steel plate of No.1～46 whole in, be by polygonal ferrite, bayesian in skin section One of body or both constitute metal structure, in thickness of slab central part be by one of acicular ferrite, bainite or both The metal structure constituting.In addition, the mensure of the area occupation ratio of MA is carried out using the test film implementing Lepera etching.
Additionally, obtain the meansigma methodss of effective crystal particle diameter of top layer and thickness of slab central part by EBSD.
(mensure of the intensity of steel plate)
Additionally, the plate alleviating distention in middle-JIAO center portion of the steel plate from obtained No.1～46, width is made to be length direction, each collection 2 entirely thick test films according to american petroleum institute standard API 5L (hreinafter referred to as " API 5L "), according to API standard 2000, carry out tension test at room temperature and obtain yield stress and tensile strength.Based on the maximum load in this tension test, ask Go out tensile strength.
(mensure of the DWTT ductile fracture rate of steel plate)
Additionally, the plate alleviating distention in middle-JIAO center portion of the steel plate from obtained No.1～46, gathering makes width be length direction Thick DWT test film entirely.DWT test is also carried out at -10 DEG C according to API standard 2000, measures DWTT ductile fracture rate.
(strength detection of steel pipe and compression test)
Using the steel plate of obtained No.1～46, tubing is carried out by UOE operation, table 5-1, table are utilized for interior outside Heat input shown in 5-2 carries out submerged arc welding, thus manufacturing steel pipe (the steel plate No. and steel pipe No. that external diameter is 30～36 inches Correspond to respectively).Then, gather test film from steel pipe, carry out strength detection and compression test.
With regard to the mensure of the intensity of steel pipe, by the seam welding portion of steel pipe be set to 0 point from 3 points of positions according to tension test sheet length The degree direction mode consistent with length of steel pipe direction is processed to test film, to carry out according to ASTM E9-09, measures spool The yield strength of length direction and tensile strength.Wherein, 0.5% underload endurance is defined as yield strength.
For steel pipe compression test compression test piece by the seam welding portion of steel pipe is set at 0 point 6 points of positions from steel Gather the part of 22mm diameter 66mm length on the medial surface 3mm of pipe and obtain.Compression test to be carried out according to ASTM E9-09, Obtain the compressive strength (0.2% flow stress) after carrying out 10 minutes timeliness at 200 DEG C.
(the HIC test of steel pipe)
Additionally, the seam welding portion of steel pipe is set at 0 point, from the HIC of 3 points, 6 points each station acquisition 20mm width 100mm length Test film.HIC test film gathers according to the mode that the central part of the wall thickness of steel pipe becomes testing position.HIC test basis NACE The TM0284 of (National Association of Corrosionand Engineer), testing liquid uses SolutionB To carry out, to be evaluated with crack length rate (Crack Length Ratio, referred to as CLR).
The characteristic of steel plate is shown in table 4-1 and table 4-2, the characteristic of steel pipe is shown in table 5-1,5-2.
The steel plate of No.1～28 represents the example of the present invention.As shown by table 4-1,4-2 and table 5-1,5-2, make The yield stress of the steel pipe being manufactured with these steel plates is more than 440MPa, and tensile strength is in the range of 500～700MPa.This Outward, as shown in table 4-1,4-2, the tensile strength of steel plate is more than 500MPa, the DWTT ductile fracture rate at -10 DEG C For more than 85%.Additionally, as shown in table 5-1,5-2, these steel plates are carried out tubing, welding and the steel pipe that manufactures The CLR of HIC test is less than 10%, and the compression test after strain-aging at 200 DEG C is more than 450MPa, well.
On the other hand, steel No.29～46 are comparative example, and the content of the chemical composition of steel No.29～40 is the model of the present invention Enclose outer, the metal structure of steel No.41～46 becomes outside the scope of the present invention, intensity, low-temperature flexibility, resistance to crushing characteristic, acid resistance At least one of poor.
The C amount of steel No.29 is few, and intensity and resistance to crushing characteristic reduce.On the other hand, the C amount of steel No.30 is many, steel No.31's Si amount is many, and the Mn of steel No.32 amount is many, and the equal tensile strength of all comparative examples exceedingly rises, low-temperature flexibility reduction.
In addition, the Ar of steel No.303Less than 700 DEG C, the steel plate of steel No.30 is not carried out in two phase regions in the present invention Rolling.But, due to contained C measure many, so in the thickness of slab central part of steel No.30 in austenite C denseization, promotion MA Generation, acid resistance reduce.Additionally, steel No.32 is due to Mn up to 3%, so acid resistance reduces.
The content of the impurity (P, S, O) of steel No.33,34 and 40 is many, and low-temperature flexibility reduces.Steel No.35～39 contribute to Carbide, nitride, oxide, the element of the generation of sulfide content many, result from precipitate, field trash and low-temperature flexibility The example reducing.
Steel No.41 and 42 be respectively recrystallize the reduction ratio in domain and non-recrystallization domain reduction ratio is not enough, effective crystal grain Footpath becomes big, low-temperature flexibility reduction example.
Although the end temp of steel No.43 hot rolling is more than 700 DEG C, due to Ar3Low, do not carry out in the present invention Rolling in two phase regions, so not generating processing ferrite in top layer, thickness of slab central part hardens, and low-temperature flexibility reduces.
Steel No.44 be accelerate cooling stopping temperature high, excessively generate in thickness of slab central part processing ferrite and MA, The example of intensity decreases.Further, since the temperature on the surface of steel plate more than 400 DEG C at a temperature of stop accelerate cooling, so Generate polygonal ferrite in thickness of slab central part, acid resistance reduces.
Steel No.45 and 46 is that rolling end temp is low, excessively generates processing ferrum element in skin section and thickness of slab central part Body and the example of MA, low-temperature flexibility and acid resistance reduction.
Table 1-1
Table 1-2
Table 4-1
Table 4-2
Table 5-1
Table 5-2

Claims (7)

1. a kind of acid resistance, resistance to crushing characteristic and excellent in low temperature toughness thick section and high strength spool steel plate it is characterised in that its For the steel plate for more than 25mm and below 45mm for the thickness of slab,
Its composition is contained in terms of quality %：
C：0.04～0.08%,
Mn：1.2～2.0%,
Nb：0.005～0.05%,
Ti：0.005～0.03%,
Ca：0.0005～0.0050%,
N：0.001～0.008%,
It is limited to Si：Less than 0.5%,
Al：Less than 0.05%,
P：Less than 0.03%,
S：Less than 0.005%,
O：Less than 0.005%,
Remainder is made up of Fe and inevitable impurity,
Start from surface of steel plate to be the metal structure of skin section for the part within more than 0.9mm and 1.1mm towards thickness direction It is limited in terms of area occupation ratio：
Processing ferrite：For more than 5% and the S that obtained by following formula 1afe1Below %,
Martensite-austenite composite：Less than 8%,
Remainder by one of polygonal ferrite, bainite or both constitute,
Part within two directions that thickness of slab center starts the table back side towards steel plate are 1mm is the metal group of thickness of slab central part Knit and be limited in terms of area occupation ratio：
Processing ferrite：Less than 5%,
Martensite-austenite composite：Less than 5%,
Remainder by one of acicular ferrite, bainite or both constitute,
The meansigma methodss of the effective crystal particle diameter being measured by EBSD method in skin section and thickness of slab central part are 20 μ Below m,
Sfe1=0.6552 × TH- 4.7826 formulas 1a
Wherein, TH：The thickness of slab of thick section and high strength spool steel plate.
2. the thick section and high strength line tube steel of acid resistance according to claim 1, resistance to crushing characteristic and excellent in low temperature toughness Plate is it is characterised in that contained further in terms of quality %：
Cu：Less than 0.50%,
Ni：Less than 0.50%,
Cr：Less than 0.50%,
Mo：Less than 0.50%,
W：Less than 0.50%,
V：Less than 0.10%,
Zr：Less than 0.050%,
Ta：Less than 0.050%,
B：Less than 0.0020%,
Mg：Less than 0.010%,
REM：Less than 0.0050%,
Y：Less than 0.0050%,
Hf：Less than 0.0050%,
Re：Less than 0.0050%
In one kind or two or more.
3. the thick section and high strength line tube steel of acid resistance according to claim 1, resistance to crushing characteristic and excellent in low temperature toughness Plate is it is characterised in that the content of Al is less than 0.005%.
4. the thick section and high strength line tube steel of acid resistance according to claim 2, resistance to crushing characteristic and excellent in low temperature toughness Plate is it is characterised in that the content of Al is less than 0.005%.
5. the heavy wall of the acid resistance according to any one of Claims 1 to 4, resistance to crushing characteristic and excellent in low temperature toughness is high-strength Degree spool steel plate is it is characterised in that tensile strength is 500～700MPa.
6. the heavy wall of the acid resistance according to any one of Claims 1 to 4, resistance to crushing characteristic and excellent in low temperature toughness is high-strength Degree spool steel plate it is characterised in that the yield stress after tubing reaches more than 440MPa, tensile strength reaches 500～ 700MPa, 0.2% flow stress of the compression of the circumferencial direction after timeliness at 200 DEG C reaches more than 450MPa.
7. a kind of thick section and high strength spool is it is characterised in that it is by the acid resistance any one of Claims 1 to 5, resistance to After the thick section and high strength spool steel formability of crushing characteristic and excellent in low temperature toughness is tubulose, docking section is carried out electric arc welding And manufacture,
Yield stress is more than 440MPa, and tensile strength is 500～700MPa, the pressure of the circumferencial direction after timeliness at 200 DEG C 0.2% flow stress of contracting is more than 450MPa.
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