CN105143487A - Steel sheet for thick-walled high-strength line pipe having exceptional souring resistance, crush resistance properties, and low-temperature ductility, and line pipe - Google Patents

Steel sheet for thick-walled high-strength line pipe having exceptional souring resistance, crush resistance properties, and low-temperature ductility, and line pipe Download PDF

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CN105143487A
CN105143487A CN201480021680.3A CN201480021680A CN105143487A CN 105143487 A CN105143487 A CN 105143487A CN 201480021680 A CN201480021680 A CN 201480021680A CN 105143487 A CN105143487 A CN 105143487A
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steel plate
thickness
less
low
resistance
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CN105143487B (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)
  • Mechanical Engineering (AREA)
  • Materials 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

Provided are a steel sheet for thick-walled high-strength line pipe having exceptional souring resistance, crush resistance properties, and low-temperature ductility, and a production method for the same. The steel sheet for thick-walled high-strength line pipe has sheet thickness of 25 mm to 45 mm, inclusive, the metal texture of the surface layer including worked ferrite at a level of 5% or more and Sfe1% or less as calculated using the following equation 1a, and a martensite-austenite hybrid (MA) at a level of 8% or less, with the remainder comprising polygonal ferrite and/or bainite, and the metal texture of a center section of the sheet thickness including worked ferrite at a level of 5% or less, and MA at a level of 5% or less, with the remainder comprising either acicular ferrite and/or bainite, or both. The average value of effective crystal grain diameter in the surface layer and the center section is 20 mum. Sfe1 = 0.6552*TH - 4.7826...Equation 1a. TH is the sheet thickness of the steel sheet.

Description

The thick section and high strength spool steel plate of acid resistance, resistance to crushing characteristic and excellent in low temperature toughness 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, particularly relate to thick section and high strength spool steel plate and the spool of the raw-material acid resistance of the spool being best suited for Sweet natural gas or Crude Oil Transportation, resistance to crushing characteristic and excellent in low temperature toughness.
Background technology
In recent years, as the long-distance delivery method of crude oil, Sweet natural gas, the importance of pipeline is more and more higher.The idea of the design of the main line spool of long distance delivery, mainly based on API (API) standard, in the past, in order to prevent breaking when pressing in load, developed the spool of tensile strength, excellent in low temperature toughness.
In order to improve crude oil, Sweet natural gas transport efficiency and improve interior pressure time, need high strength and the wall thickening of spool, and then specially require low-temperature flexibility when spool being layed in cold district.But generally due to high strength, wall thickening, the guaranteeing of the toughness of steel becomes difficulty.
In order to reduce the changes in hardness in the thickness of slab direction of thick-wall materials, improving low-temperature flexibility, in patent documentation 1, proposing and becoming at metal structure the method be rolled in the temperature field (2 phase region) of austenite and ferritic 2 phases.By aforesaid method, the metal structure of thick-wall materials can be formed in fine acicular ferrite structure and be mixed into the tissue of island-like martensite.
In addition, recently, for the requirement characteristic variation of spool, except intensity and low-temperature flexibility, also requirement resistance to crushing characteristic, the acid resistance that can not crack in containing the acid environment of hydrogen sulfide etc. that can not crush because of external pressure sometimes.Particularly by pipe laying in deep-sea time, require 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 very difficult.
Prior art document
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
Summary of the invention
Invent problem to be solved
As described above, in recent years, there is complicated tendency in the requirement characteristic for the spool of the Sweet natural gas be layed in deep-sea, Crude Oil Transportation, becomes and also require wall thickening, high strength, low-temperature flexibility, acid resistance and then crush characteristic.
When above-mentioned patent documentation 1, do not have to consider the reply to acid resistance, resistance to crashing.Particularly exist because island-like martensite becomes the starting point of destruction, thus make the problem that destruction toughness reduces.
For this problem, propose and suppress the martensitic generation of hard and suppress the method for the difference of hardness of ferrite and bainite, method (for example, referring to patent documentation 2 ~ 4) by utilizing fine bainite to suppress Bao Xinge effect.
In recent years, there is diversified tendency in the requirement characteristic for spool, and wherein particularly the requirement characteristic of deep-sea spool occurs complicated.Specifically, except wall thickening, yielding stress (YS), tensile strength (TS), low-temperature flexibility (the DWTT ductile fracture rates at-10 DEG C), also require acid resistance and then crush characteristic (0.2% stress of fluidity of the compression of the circumferential direction after the timeliness at 200 DEG C).
But with regard to existing technology (such as patent documentation 2 ~ 5 etc.), it is very difficult for all taking into account these characteristics.
Invent the reply considered brittle-cracking propagation Stopping Ability and low-temperature flexibility disclosed in patent documentation 2, but do not have to consider the reply to acid resistance, resistance to crashing.In addition, invention disclosed in patent documentation 3 considers low-temperature flexibility, crushes characteristic, but does not consider acid proof reply.In addition, taking into account of the balance of compressive strength and low-temperature flexibility, high compressive strength and acid resistance has been sought in invention disclosed in patent documentation 4, but does not consider above-mentioned crushing characteristic (0.2% stress of fluidity of the compression of the circumferential direction after the timeliness at 200 DEG C).
Find in patent documentation 5: when thickness of slab is the following spool steel pipe of API (API) standard x 80 (tensile strength is more than 620MPa) of more than 25mm, it is extremely difficult that the central part of thickness of slab is made fine bainite structure.In order to solve such technical task, in patent documentation 5, propose making the content of C reduce, metal structure made the low temperature phase change tissue based on bainite and based on the steel that toughness is improved, add Mo and improve hardenability, suppress the interpolation of Al and effectively utilize the manufacture method of intracrystalline bainite.
Invent disclosed in patent documentation 5 by improving the hardenability of mother metal, and formed for the uniform metal structure of bainite main body by so that steel plate is overall, thus by the Effective grain size miniaturization of HAZ.The low-temperature flexibility being intended that weld part of invention disclosed in patent documentation 5, but do not have to consider the reply to acid resistance, resistance to crashing.
In addition, in the central part of thickness of slab, the pressure based on controlled rolling and the speed of cooling based on controlled cooling model become insufficient.Therefore, even when hardenability improves, along with the increase of thickness of slab, it is also difficult for making steel plate entirety become uniform metal structure.
In addition, in the past, the thickness of slab of spool steel plate was often the thin-walled of below 20mm, if be the intensity about X65 level in API standard, then easily can guarantee the diverse nature that acid resistance, low-temperature flexibility, resistance to crushing characteristic are such.This is because, in hot rolling, fully guarantee draft and effectively crystal particle diameter become fine, and then utilize the difference of the speed of cooling of the top layer of accelerating cooling and thickness of slab central part little, metal structure homogenizes.But, the heavy wall that thickness of slab is more than 25mm, particularly more than 30mm if become, then meet acid resistance, low-temperature flexibility, resistance to crushing characteristic whole become difficulty.
Particularly resistance to crushing characteristic guarantee with low-temperature flexibility guarantee contrary, with regard to prior art, also do not design and can take into account resistance to crushing characteristic and the such material of low-temperature flexibility.
The present invention is in view of such practical situation, and problem is to provide and is best suited for Sweet natural gas, raw-material, the thick section and high strength spool with good balance with acid resistance, resistance to crushing characteristic and low-temperature flexibility of spool of Crude Oil Transportation and above-mentioned thick section and high strength spool steel plate.
For the means of dealing with problems
The present inventor, in order to obtain the thick section and high strength spool steel plate of acid resistance in spool steel plate, resistance to crushing characteristic and excellent in low temperature toughness, is conceived to metal structure and crystal particle diameter conducts in-depth research.It found that, in heavy wall spool (also referred to as " thick walled steel tube "), about for reach (1) intensity and acid proofly to take into account, the taking into account of the intensity of (2) thick walled steel tube and resistance to crushing characteristic, the intensity of (3) thick walled steel tube and the composition taken into account, metal structure, manufacture method etc. of low-temperature flexibility, can arrange according to as described below respectively.
(1) intensity and acid proofly to take into account
In order to not damage the intensity improving spool in acid proof situation, the uniform tissue metal structure of the steel plate of the mother metal as above-mentioned spool being made acicular ferrite or bainite is being effective.In addition, in order to improve acid resistance, the sclerosis in center segregation portion must be suppressed.
Here, the mechanism of the crackle produced in acid environment is described.The hydrogen assembled around defect in the steel such as the MnS system inclusion of the elongation that the crackle in acid environment, particularly hydrogen-induced crack (HIC) particularly result from the center segregation portion being present in steel plate.That is, in acid environment, the hydrogen invaded in steel is gathered in the surrounding of these defects and becomes gas, when its pressure exceedes destruction toughness value (KIC) of steel, cracks.And then if the periphery etc. of the center segregation portion of steel, inclusion hardens, then crackle becomes easy propagation.Therefore, with regard to the spool used in acid environment, the generation of MnS that suppression is extended, the formation of the sclerosis phase of center segregation are effective, specifically, make accelerating cooling stop under slightly high temperature, such as reach according to the temperature in the center segregation portion of steel the mode of more than 400 DEG C stop hot rolling after accelerating cooling be effective.In addition, so-called center segregation portion refers to solidifying segregation when resulting from casting, and in the thickness of slab central part of steel plate, the position of denseization occurs the composition such as Mn.
(2) intensity of thick walled steel tube and taking into account of resistance to crushing characteristic
When thick walled steel tube, in order to ensure intensity and resistance to both crushing characteristics, add Mo etc. and improve hardenability, by martensite, bainite that the accelerating cooling product dislocation density after hot rolling is high, promoting that strain aging is effective.Specifically, if the mode reaching less than 400 DEG C according to slightly low temperature, such as surface of steel plate temperature controls the stopping temperature of accelerating cooling, then generate martensite, the strain aging time application sintering processes of thick walled steel tube (being heated to 200 DEG C of front and back during application and the process kept) can be promoted.
(3) intensity of thick walled steel tube and taking into account of low-temperature flexibility
When thick walled steel tube, compared with the situation of the steel pipe of thin-walled, original austenite (austenite before being undergone phase transition by accelerating cooling) becomes thick, and low-temperature flexibility reduces.In addition, if compared with the independent tissue of bainite, effective crystal particle diameter of the independent tissue of acicular ferrite is little, however can not say that low-temperature flexibility is sufficient.Therefore, in order to ensure low-temperature flexibility, the generation of polygonal ferrite is effective.But because polygonal ferrite makes intensity reduce, so in order to ensure intensity, it is effective for making with the complex tissue of bainite, acicular ferrite.
As described above, know and meet above-mentioned (1) ~ (3) simultaneously, guarantee acid resistance, low-temperature flexibility, the whole of resistance to crushing characteristic are difficult.Such as, for the resistance to crushing characteristic of (2), martensite is effective, but martensite is harmful for the acid resistance of (1) and the low-temperature flexibility of (3).In addition, for the low-temperature flexibility of (3), polygonal ferrite is effective, but the acid resistance of (1) is organized due to the generation because of polygonal ferrite and become uneven, so reduce.In addition, the polygonal ferrite that dislocation desity is low makes resistance to crushing characteristic reduce.
Therefore, present inventors studied and effectively utilize the such feature of heavy wall, namely utilized by hot rolling and subsequent accelerating cooling and result from the surface of thickness of slab and the temperature head of central part and control the method for 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.In addition, in order to ensure low-temperature flexibility, have studied the miniaturization of effective crystal particle diameter.
First know, in thickness of slab central part, in order to ensure acid resistance, intensity and low-temperature flexibility, suppress processing ferrite and martensite-austenite composite (hereinafter referred to as " MA ".) generation and suppress sclerosis, the tissue making the homogeneous be made up of the one or both of acicular ferrite, bainite is effective.
Wherein, in thickness of slab central part, by segregation there is denseization in Mn, and hardenability is high, and ferritic generation is inhibited.But in order to ensure low-temperature flexibility, ferritic generation is effective, making the ferrite content towards top layer increases such metal structure and becomes necessary.
On the other hand, if generate soft polygonal ferrite in order to ensure low-temperature flexibility, then the compressive yield stress of the circumferential direction on top layer reduces, and resistance to crushing characteristic reduces.For this problem, make in top layer, to generate processing ferrite as long as the present inventor thinks, improve ferritic dislocation desity and promote strain aging, resistance to crushing characteristic is improved.Therefore find, about the tissue on top layer, become the processing ferrite of more than 5% better, in order to ensure low-temperature flexibility in order to meet resistance to crushing characteristic with area occupation ratio family planning, suppress MA, remainder is made by organizing of forming of the one or both of polygonal ferrite, bainite better.
If processing ferrite is many, then crushing strength increases, but therefore causes low-temperature flexibility to worsen.In order to ensure low-temperature flexibility, be necessary to limit processing ferrite content to a certain extent.That is, be necessary the part bearing crushing strength suitably to distribute according to thickness of slab with the part bearing low-temperature flexibility.That is, thickness of slab becomes thinner, then the ferritic tolerance of the processing of skin section becomes fewer, and thickness of slab becomes thicker, then the ferritic tolerance of the processing of skin section becomes more.Therefore, contriver has investigated the relation of the ferritic tolerance of processing and thickness of slab, has found best relation.
The present invention completes based on these understanding, and its purport is as follows.
[1] a thick section and high strength spool steel plate for acid resistance, resistance to crushing characteristic and excellent in low temperature toughness, is characterized in that, the steel plate of its to be thickness of slab be more than 25mm and below 45mm,
Its composition contains in mass %:
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％，
Be restricted to below Si:0.5%,
Below Al:0.05%,
Below P:0.03%,
Below S:0.005%,
Below O:0.005%,
Remainder is made up of Fe and inevitable impurity,
From surface of steel plate, be more than 0.9mm and the tissue of part within 1.1mm and skin section is restricted in area occupation ratio towards thickness direction:
Processing ferrite: be more than 5% and the S obtained by following formula 1a fe1below %,
Martensite-austenite composite: less than 8%,
Remainder is made up of the one or both in polygonal ferrite, bainite,
Part be 1mm towards two directions at the table back side of steel plate from thickness of slab center within and the metal structure of thickness of slab central part are restricted in area occupation ratio:
Processing ferrite: less than 5%,
Martensite-austenite composite: less than 5%,
Remainder is made up of the one or both in acicular ferrite, bainite,
The mean value of the effective crystal particle diameter measured by Electron Back-Scattered Diffraction method in skin section and thickness of slab central part is less than 20 μm.
S fe1=0.6552 × T h-4.7826 formula 1a
Wherein, T h: the thickness of slab of thick section and high strength spool steel plate
The thick section and high strength spool steel plate of the acid resistance [2] according to above-mentioned [1], resistance to crushing characteristic and excellent in low temperature toughness, is characterized in that, contain further in mass %:
Below Cu:0.50%,
Below Ni:0.50%,
Below Cr:0.50%,
Below Mo:0.50%,
Below W:0.50%,
Below V:0.10%,
Below Zr:0.050%,
Below Ta:0.050%,
Below B:0.0020%,
Below Mg:0.010%,
Below REM:0.0050%,
Below Y:0.0050%,
Below Hf:0.0050%,
Below Re:0.0050%
In one kind or two or more.
The thick section and high strength spool steel plate of the acid resistance [3] according to above-mentioned [1] or [2], resistance to crushing characteristic and excellent in low temperature toughness, is characterized in that, the content of Al is less than 0.005%.
The thick section and high strength spool steel plate of the acid resistance [4] according to any one of above-mentioned [1] ~ [3], resistance to crushing characteristic and excellent in low temperature toughness, is characterized in that, tensile strength is 500 ~ 700MPa.
The thick section and high strength spool steel plate of the acid resistance [5] according to any one of above-mentioned [1] ~ [3], resistance to crushing characteristic and excellent in low temperature toughness, it is characterized in that, yielding stress after tubing reaches more than 440MPa, tensile strength reaches 500 ~ 700MPa, and 0.2% stress of fluidity of the compression of the circumferential direction after the timeliness at 200 DEG C reaches more than 450MPa.
[6] a kind of thick section and high strength spool, it is characterized in that, it is, after tubulose, arc welding is carried out the thick section and high strength spool steel formability of the acid resistance according to any one of above-mentioned [1] ~ [4], resistance to crushing characteristic and excellent in low temperature toughness in docking section and manufactures
Yielding stress is more than 440MPa, and tensile strength is 500 ~ 700MPa, and 0.2% stress of fluidity of the compression of the circumferential direction after the timeliness at 200 DEG C is more than 450MPa.
Invention effect
According to the present invention, the thick section and high strength spool steel plate of raw-material, acid resistance, resistance to crushing characteristic and excellent in low temperature toughness of spool being best suited for Sweet natural gas, Crude Oil Transportation can be provided.Wall thickness particularly can be provided to reach 25 ~ 45mm, tubing after YS reaches more than 440MPa, TS reaches 500 ~ 700MPa, DWTT ductile fracture rate at-10 DEG C reaches more than 85% and the compressive strength (0.2% stress of fluidity) of circumferential direction after timeliness at 200 DEG C reaches the thick section and high strength spool steel plate of the acid resistance of more than 450MPa, resistance to crushing characteristic and excellent in low temperature toughness, the contribution in industry is extremely remarkable.
Accompanying drawing explanation
Fig. 1 is the optical microscope photograph in the cross section of the skin section of thick section and high strength spool steel plate of the present invention.
Fig. 2 specifies the upper limit of the ferritic area occupation ratio of processing in the skin section of thick section and high strength spool steel plate of the present invention and the chart of lower limit.
Embodiment
Below, the thick section and high strength spool steel plate of acid resistance of the present invention, resistance to crushing characteristic and excellent in low temperature toughness (following, also referred to as " spool steel plate " or " steel plate ") and its manufacture method are described.
Below, the restriction reason of the composition in the spool thick high-strength steel plate (mother metal of spool) of present embodiment is described.
In addition, quality % is referred to when the record of % is not particularly illustrated.
C:C is the element that the intensity of steel plate is improved, and must add more than 0.04% in present embodiment.Preferred interpolation more than 0.05%, more preferably adds the C of more than 0.055%.On the other hand, if owing to adding the C more than 0.08%, then low-temperature flexibility reduces, so the upper limit that C measures 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 contributing to the intensity of steel plate and the raising of toughness.In present embodiment, in order to ensure the intensity of steel plate, add the Mn of more than 1.2%.The Mn of preferred interpolation more than 1.4%, more preferably interpolation more than 1.5%.On the other hand, if owing to excessively adding Mn, then the hardness of thickness of slab central part rises, and damages acid resistance, so the upper limit that Mn measures is set to less than 2.0%.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 forms carbide, nitride, contributes to the element of the raising of intensity.In addition, suppress the recrystallize in hot rolling, promote 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%, is more preferably set to more than 0.015%.On the other hand, if owing to excessively adding Nb, intensity exceedingly rises and damages low-temperature flexibility, so the upper limit that Nb measures 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 forms nitride, and the grain refined for metal structure plays the element of effect.The lower limit of Ti amount becomes fine to make effective crystal particle diameter, is set to more than 0.005%.Preferably the lower limit that Ti measures is set to more than 0.008%, is more preferably set to more than 0.01%.On the other hand, if owing to excessively adding Ti, generate thick TiN, infringement low-temperature flexibility, so be set to less than 0.03% by the upper limit that Ti measures.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 the generation promoting the generation of CaS to suppress the MnS extended along rolling direction, guarantee acid resistance, the lower limit that Ca measures is set to more than 0.0005%.Preferably the lower value that Ca measures is set to 0.0010%, is more preferably set to 0.0015%.On the other hand, if excessively add Ca, then generate thick oxide compound, low-temperature flexibility reduces, so the upper limit that Ca measures is set to 0.0050%.Preferably the upper limit that Ca measures is set to less than 0.0040%, is more preferably set to less than 0.0030%.
N: in present embodiment, by the metal structure miniaturization of steel, is set to more than 0.001% by the content of N in order to utilize nitride.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 excessively containing N, then generate thick nitride, infringement low-temperature flexibility, so be set to 0.008% by the upper limit that N measures.Preferably the upper limit that N measures is set to less than 0.007%, is more preferably set to less than 0.006%.
Si and Al is deoxidant element, as long as use any one when deoxidation is added as object, but also can use simultaneously.In addition, if owing to excessively adding Si and Al, then damage the characteristic of steel plate, so in present embodiment, the upper limit of the content of Si and Al is limited as follows.
Si: if excessively add due to Si, then particularly (HeatAffectedZone, be called HAZ at welding heat affected zone.) the middle MA generating hard, the toughness in the seam weldering portion of steel pipe is reduced, so the ceiling restriction of being measured by Si is less than 0.5%.Preferably Si amount is set to less than 0.3%, is more preferably restricted to less than 0.25%.In addition, due to as described above, Si is the element for deoxidation, and also for contributing to the element of the rising of intensity, so preferably the lower limit that Si measures is set to more than 0.05%, is more preferably set to more than 0.10%.
Al: Al is useful deoxidant element as described above, is preferably set to more than 0.001% by the lower limit that Al measures, is more preferably set to more than 0.003%.But, if excessively add due to Al, then generate thick oxide compound, low-temperature flexibility reduced, so the ceiling restriction of being measured by Al is less than 0.05%.Preferably the upper limit that Al measures is set to less than 0.04%, is more preferably restricted to less than 0.03%.In addition, by Al amount is restricted to less than 0.005%, the toughness in HAZ portion can be improved.
P, S and O (oxygen) contain as inevitable impurity, if owing to excessively containing, then damage the characteristic of steel plate, so in the present embodiment, the upper limit of the content of P, S and O are limited as follows.
P:P is the element making steel embrittlement, if owing to containing more than 0.03%, then damages the low-temperature flexibility of steel, so be less than 0.03% by ceiling restriction.The ceiling restriction of preferably being measured by P is less than 0.02%, is more preferably restricted to less than 0.01%.
S:S is the element generating MnS sulfides, if due to containing more than 0.005%, then make low-temperature flexibility, acid resistance reduce, so be less than 0.005% by ceiling restriction.Preferably S amount is set to less than 0.003%, is more preferably restricted to 0.002%.
O: if contain more than 0.005% due to O, then generate thick oxide compound, the low-temperature flexibility of steel is reduced, so be less than 0.005% by the ceiling restriction of content.Preferably the upper limit that O measures is set to less than 0.003%, is more preferably restricted to less than 0.002%.
And then in the present invention, as the element improving intensity, low-temperature flexibility, that can add in Cu, Ni, Cr, Mo, W, V, Zr, Ta, B is one kind or two or more.
Cu:Cu is the effective element that low-temperature flexibility can not be made to reduce and make intensity increase.The Cu of preferred interpolation more than 0.01%, more preferably adds more than 0.1%.On the other hand, Cu owing to being when heating steel billet or the element that easily cracks when carrying out the seam weldering of steel pipe, so preferably Cu amount is set to less than 0.50%.More preferably Cu amount is set to less than 0.35%, is preferably set to less than 0.2% further.
Ni:Ni is to improving low-temperature flexibility and the effective element of intensity.The Ni of preferred interpolation more than 0.01%, more preferably adds more than 0.1%.On the other hand, Ni is the element of high price, from the view point of economy, preferably Ni amount is set to less than 0.50%.More preferably Ni amount is set to less than 0.35%, is preferably set to less than 0.2% further.
Cr:Cr is the element intensity of steel being improved by precipitation strength.The Cr of preferred interpolation more than 0.01%, more preferably adds more than 0.1%.On the other hand, if owing to excessively adding Cr, then because of the rising of intensity, low-temperature flexibility reduces sometimes, so preferably the upper limit that Cr measures is set to less than 0.50%.More preferably Cr amount is set to less than 0.35%, is preferably set to less than 0.2% further.
Mo:Mo makes hardenability improve, and forms carbonitride and improves the element of intensity.The Mo of preferred interpolation more than 0.01%, more preferably adds more than 0.05%.On the other hand, if owing to excessively adding Mo, then because of the rising of intensity, low-temperature flexibility reduces sometimes, so preferably the upper limit that Mo measures is set to less than 0.50%.More preferably Mo amount is set to less than 0.2%, is preferably set to less than 0.15% further.
W:W and Mo makes hardenability improve, and forms carbonitride and improves the element of intensity, preferably adding more than 0.0001%.More preferably W amount is set to more than 0.01%, preferably adds more than 0.05% further.On the other hand, if owing to excessively adding W, then because of the rising of intensity, low-temperature flexibility reduces sometimes, so preferably the upper limit that W measures is set to less than 0.50%.More preferably W amount is set to less than 0.2%, is preferably set to less than 0.15% further.
V:V forms carbide, nitride and contribute to the element of the raising of intensity.The V of preferred interpolation more than 0.001%, more preferably adds more than 0.005%.On the other hand, if owing to adding V more than 0.10% ground, then sometimes make low-temperature flexibility reduce, so preferably V amount is set to less than 0.10%.More preferably V amount is set to less than 0.05%, is more preferably set to less than 0.03%.
Zr, Ta:Zr and Ta and V form 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%, preferably add more than 0.001% further.On the other hand, if owing to adding Zr, Ta more than 0.050% ground, then low-temperature flexibility reduces sometimes, so preferably Zr amount, Ta are measured the respective upper limit and be set to less than 0.050%.More preferably less than 0.030% is set to.
B:B is the element that hardenability can be improved by the interpolation of trace.In order to improve intensity, preferably add the B of more than 0.0001%.The B of preferred interpolation more than 0.0003%.On the other hand, if owing to excessively adding B, then sometimes generate the precipitate of B, make low-temperature flexibility deterioration, so preferably 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 inclusion such as sulfide, oxide compound, improve low-temperature flexibility, acid resistance, that can add in Mg, REM, Y, Hf, Re is one kind or two or more.
Mg:Mg is by the morphology Control of sulfide, the formation of fine oxide compound and contribute to the element of raising of acid resistance, low-temperature flexibility.The Mg of preferred interpolation more than 0.0001%, more preferably adds more than 0.0005%, preferably adds more than 0.001% further.On the other hand, if add Mg more than 0.010% ground, then sometimes become and easily generate thick oxide compound, the toughness of infringement HAZ, so preferably Mg amount is set to less than 0.010%.More preferably Mg amount is set to less than 0.005%, is preferably set to less than 0.003% further.
REM, Y, Hf, Re:REM, Y, Hf, Re generate sulfide, suppress the generation of the MnS extended along rolling direction, particularly contribute to acid proof improvement.REM, Y, Hf, Re preferably all add more than 0.0001%, are more preferably set to more than 0.0005%, are preferably set to more than 0.0010% further.On the other hand, if because REM, Y, Hf, Re are all more than 0.0050% ground interpolation, then oxide compound increases sometimes, and infringement toughness, so be preferably set to less than 0.0050% by the upper limit.More preferably less than 0.0030% is set to.
In addition, in present embodiment, the remainder except above-mentioned element is made up of Fe in fact, can be micro-add the element that can not damage action effect of the present invention headed by inevitable impurity.Inevitable impurity refer to comprise in starting material or in the process manufactured the composition that is mixed into, and inadvertently make the composition that contains in steel.
Specifically, Si, Al, P, S, O, N, Sb, Sn, Co, As, Pb, Bi and H can be listed.Wherein, P, S, O and N be necessary as mentioned above respectively according to reach below Si:0.5%, below Al:0.05%, below P:0.03%, below S:0.005%, below O:0.005%, below N:0.008% mode control.
About other element, usual Sb, Sn, Co and As can have being mixed into as inevitable impurity of less than 0.1%, Pb and Bi can have being mixed into as inevitable impurity of less than 0.005%, H can have being mixed into as inevitable impurity of less than 0.0005%, if common scope, then there is no need to control especially.
In addition, even if the arbitrary Addition ofelements in thick section and high strength spool steel plate of the present invention and Cu, Ni, Cr, Mo, W, V, Zr, Ta, B, Mg, REM, Y, Hf and Re do not have a mind to contain, sometimes also can be mixed into as inevitable impurity.But, if below the above-mentioned upper limit wittingly containing content sometimes of these elements, even if then also detrimentally affect can not be caused to the present invention lower than lower limit, so no problem.
And then in the present invention, in order to ensure hardenability, improve intensity and low-temperature flexibility, the carbon equivalent Ceq of following (formula 2) that preferably calculated by the content [quality %] by C, Mn, Ni, Cu, Cr, Mo, V 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 preferably set to more than 0.35 further.In addition, the upper limit of Ceq, in order to improve low-temperature flexibility, is more preferably set to less than 0.45, is preferably set to less than 0.43 further.
Ceq=C+Mn/6+ (Ni+Cu)/15+ (Cr+Mo+V)/5 (formula 2)
In addition, in order to ensure the low-temperature flexibility of steel plate and HAZ, the crack sensitivity indices P cm of following (formula 3) that preferably calculated by the content [quality %] by C, Si, Mn, Cu, Cr, Ni, Mo, V is set to 0.10 ~ 0.20.In order to improve intensity, the lower limit of Pcm is more preferably set to more than 0.12, is preferably set to more than 0.14 further.In addition, in order to improve low-temperature flexibility, the upper limit of Pcm is more preferably set to less than 0.19, is preferably set to less than 0.18 further.
Pcm=C+Si/30+ (Mn+Cu+Cr)/20+Ni/60+Mo/15+V/10 (formula 3)
In addition, when not adding the element and Ni, Cu, Cr, Mo, V that optionally contain wittingly, in above-mentioned (formula 2) and (formula 3), calculate as 0.
Then, the metal structure of steel plate of the present invention is described.
Steel plate thickness of slab of the present invention is more than 25mm and then the thickness for more than 30mm, and the steel plate as the spool of heavy wall (25mm ~ 45mm) is applicable.In addition steel plate of the present invention is between top layer and thickness of slab central part, and utilize the temperature head of hot rolling, the differing from of speed of cooling of accelerating cooling and carry out organizational controls, in top layer with thickness of slab central part, metal structure is different.In addition, in the present invention, the skin section of steel plate be from the surface of steel plate to thickness direction be more than 0.9mm and the part of below 1.1mm (namely, centered by the position being 1mm to thickness direction, two surface direction are carried on the back for the region within 0.1mm towards the table of steel plate from surface of steel plate), the central part of steel plate is that to carry on the back two surface direction be region within 1mm for table from thickness of slab center towards steel plate.
In skin section, in order to improve resistance to crushing characteristic, become the processing ferrite of more than 5% with area occupation ratio family planning.Processing ferrite is the ferrite extended along rolling direction by hot rolling, and compared with the polygonal ferrite generated by the cooling after rolling, dislocation desity is high, is effective for the resistance to crushing characteristic of raising.By shown in Figure 1 for the optical microscope photograph in the cross section of the skin section of steel plate of the present invention.In addition, the part of dense grey is processing ferrite, and its part represents with arrow.Skin section shown in Fig. 1 contains the processing ferrite of 9.3%.
In addition, if processing ferrite is many, then crushing strength increases, but therefore low-temperature flexibility deterioration.Therefore finding, can low-temperature flexibility be improved by suppressing the processing ferrite of central part.Wall thickness along with steel plate becomes large, and the temperature head of top layer and wall thickness central authorities becomes large.Therefore, along with the wall thickness of steel plate is thickening, the processing ferrite content that can manufacture in the central part of thickness of slab tails off, and on the other hand, the processing ferrite quantitative change that can manufacture in skin section is large.Therefore, contriver has investigated the relation of the wall thickness of steel plate and the processing ferrite content of skin section, has found optimum range.
Fig. 2 represents that thickness of slab is 25mm ~ 45mm and the upper limit S of the ferritic area occupation ratio of processing in the thickness of slab of steel plate and skin section fe1relation.
Known by Fig. 2, in order to obtain being best suited for Sweet natural gas, the raw-material resistance to crushing characteristic of spool of Crude Oil Transportation and low-temperature flexibility, the ferritic area occupation ratio of the processing in the skin section of steel plate is necessary to be set to more than lower value below and below higher limit.
The lower value of the ferritic area occupation ratio of the processing in the skin section of steel plate: 5%
The higher limit of the ferritic area occupation ratio of the processing in the skin section of steel plate:
S fe1=0.6552 × T h-4.7826 formula 1a
(wherein, T h: the thickness of slab of thick section and high strength spool steel plate)
In addition, if exceed above-mentioned S owing to processing ferritic area occupation ratio fe1%, then harden in top layer, and infringement low-temperature flexibility, so be set to above-mentioned S by ferritic for processing area occupation ratio fe1below %.In addition, the upper limit of the ferritic area occupation ratio of processing in the skin section of preferred steel plate meets following formula 1b.
Preferred higher limit: S fe2=0.8 × T h-15 formula 1b
As shown in above-mentioned formula 1a and formula 1b, there is thickness of slab dependency for the ferritic area occupation ratio of processing obtaining being best suited for Sweet natural gas, the raw-material acid resistance of spool of Crude Oil Transportation, resistance to crushing characteristic and low-temperature flexibility.Think that the difference due to the temperature head of the hot rolling between top layer and thickness of slab central part, the speed of cooling of accelerating cooling is easily subject to the impact of thickness of slab, so process 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 with area occupation ratio family planning the MA that the dislocation desity of more than 0.1% is high, if but MA becomes the starting point of destruction, and excessively generate, damage low-temperature flexibility.Therefore, the MA of skin section is restricted to less than 8% in area occupation ratio.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, about the remainder of above-mentioned processing ferrite and MA, make the metal structure be made up of the one or both of polygonal ferrite, bainite.Polygonal ferrite is effective for raising low-temperature flexibility, easily generates, reduce gradually towards thickness of slab central part in skin section.Bainite is effective for raising intensity, different from polygonal ferrite, few in skin section, increases gradually towards thickness of slab central part.This is because, in thickness of slab central part, compared with top layer, the rolling temperature of hot rolling, the beginning temperature of accelerating cooling uprise.
In thickness of slab central part, in order to ensure low-temperature flexibility and acid resistance, must suppress to process ferritic generation, ferritic for processing area occupation ratio is restricted to less than 5%.Process ferritic area occupation ratio and be preferably less than 3%, be more preferably 0%.
In thickness of slab central part, preferably suppress to become the generation of the MA of the starting point of destruction and suppress the sclerosis of thickness of slab central part, in order to ensure low-temperature flexibility, the area occupation ratio of MA being restricted to less than 5%.Preferably the area occupation ratio of the MA of thickness of slab central part is set to less than 4%, is more preferably set to less than 2%.
In thickness of slab central part, above-mentioned processing ferrite and the remainder of MA make the metal structure be made up of the one or both of acicular ferrite, bainite.Although due to polygonal ferrite for raising low-temperature flexibility be effective, infringement acid resistance, so in thickness of slab central part, preferably make the metal structure of the homogeneous be made up of the one or both of acicular ferrite, bainite.
Wherein, each metal structure of above-mentioned skin section and thickness of slab central part can be observed by opticmicroscope.
Specifically, by carrying out image analysis to opticmicroscope macrograph, the area occupation ratio of processing ferrite and MA can be obtained.In addition, about MA, carry out Lepera etching, by obtaining not having the area occupation ratio of painted tissue to carry out image analysis.In addition, the form of the polygonal ferrite generated when accelerating cooling is granular, and processing ferrite extends along rolling direction.In addition, processing ferrite due to dislocation desity high, so harden compared with polygonal ferrite.
Therefore, processing ferrite and polygonal ferrite can be distinguished by the ratio (long-width ratio) of long and short diameter, hardness.Acicular ferrite, bainite are the tissue of lath-shaped, can distinguish with processing ferrite and polygonal ferrite.
In order to ensure the low-temperature flexibility of steel plate, it is effective for the crystal crystal boundary of the resistance of the progress becoming be full of cracks being increased, namely reduces crystal particle diameter.In the present invention, reducing by azimuth difference is the size in the region of the high spud angle crystal boundary encirclement of more than 15 ° and effective crystal particle diameter, and low-temperature flexibility is improved.By by skin section and thickness of slab central part, by Electron Back-Scattered Diffraction method, (ElectronBackscatterDiffraction, also referred to as EBSD.) mean value of effective crystal particle diameter that measures is set to less than 20 μm, can guarantee low-temperature flexibility.Effective crystal particle diameter is less, more can obtain stable high toughness, is preferably less than 10 μm.
In addition, the low-temperature flexibility of steel plate, by measuring effective crystal particle diameter at thickness of slab central part place, is obtained mean value and evaluates.In addition, as the means of effective crystal particle diameter measuring different metal structure, Electron Back-Scattered Diffraction method is adopted.The tissue that effective crystal particle diameter is set to the length direction utilizing EBSD to the steel plate after rolling is analyzed and the equivalent circle diameter obtained.In addition, in skin section, by utilizing processing ferrite, polygonal ferrite can grain refined, but owing to processing ferrite in thickness of slab central part, the generation of polygonal ferrite is inhibited, so must pass through hot rolling, by original austenite miniaturization.
Then, the characteristic of steel plate of the present invention is described.
Improve at the transport efficiency in order to improve pipeline carried crude oil, Sweet natural gas pressure, in order to prevent rupturing because of interior pressure, the intensity of spool must be improved, increase wall thickness.From such a viewpoint, in order to avoid the fracture (breaking) produced because of pressure in spool, preferably the thickness of slab of the steel plate used in spool is set to more than 25mm.In addition, steel plate preferably has the tensile strength of more than 500MPa.In addition, the steel plate after tubing, steel tubing portions namely except weld part and HAZ, be such as that the steel tubing portions of 90 ° ~ 180 ° positions (be 3 point ~ 6 position) preferably has the yielding stress of more than 440MPa and the tensile strength of 500 ~ more than 700MPa similarly from welding seam part from welding seam part.In addition, the thickness of slab of steel plate, in order to avoid breaking, is more preferably more than 30mm, is preferably set to more than 35mm further.
When pipeline is layed in cold district, need the low-temperature flexibility of spool.Low-temperature flexibility can be passed through Drop-Weight Tear Test (DWTT) (" DropWeightTeartest ": be called " DWT test ") and evaluate, and in the present invention, the DWTT ductile fracture rate at-10 DEG C that are preferably had by the steel plate before tubing is set to more than 85%.In addition, due to along with the wall thickening of spool and high strength, the guaranteeing of low-temperature flexibility becomes difficulty, so preferably the thickness of slab of steel plate is set to below 45mm, the tensile strength of steel plate is set to below 700MPa.When manufacturing steel pipe by cold working, there is the tendency uprised than the intensity of the steel plate before tubing in the intensity of the steel plate after tubing, but the tensile strength of steel pipe after tubing is also preferably set to below 700MPa.
When by pipe laying in seabed, need the resistance of the external pressure for spool (resistance to crushing characteristic).Because resistance to crushing characteristic is subject to the impact of the strain imported when making steel pipe being formed by cold working by steel plate, so from steel pipe acquisition test sheet, evaluated by compression testing.In order to prevent spool from crushing because of external pressure, preferably the compressive strength (0.2% stress of fluidity) of the circumferential direction after the timeliness at 200 DEG C is set to more than 450MPa.
Then, the manufacture method of steel plate of the present invention is described.
Steel plate of the present invention is in order to obtain at the top layer tissue different with thickness of slab central part, to be become the rolling carrying out more than 1 passage in the temperature field (two-phase temperature field) of ferrite and this two-phase of austenite at the metal structure on top layer by hot rolling, so the accelerating cooling after hot rolling reach less than 400 DEG C in the temperature on the surface of steel plate, stop after carrying out the such condition of backheat under undertaken by means such as water-cooleds.
When steel plate is heavy wall, temperature reduction compared with the temperature of thickness of slab central part on top layer during hot rolling, in thickness of slab central part, ferritic generation is inhibited compared with top layer.In addition, if the stopping temperature being set to accelerating cooling in thickness of slab central part compared with surface uprises, the temperature on surface carries out the such condition of backheat after accelerating cooling, the temperature that then can will speed up the central part of the steel plate after the stopping of cooling is set to more than 400 DEG C, the sclerosis of thickness of slab central part can be suppressed, can acid resistance be guaranteed.
In addition, in order to ensure low-temperature flexibility, average effective crystal particle diameter of top layer and thickness of slab central part is set to less than 20 μm.In top layer, by the generation of processing ferrite, polygonal ferrite, effective crystal particle diameter diminishes.On the other hand, in thickness of slab central part, because the generation of processing ferrite, polygonal ferrite is suppressed, so be necessary the particle diameter miniaturization of original austenite.By by the effective crystal particle diameter measured in top layer and the mean value miniaturization of effective crystal particle diameter measured in thickness of slab central part, effective crystal particle diameter of thickness of slab entirety becomes fine, can guarantee low-temperature flexibility.
Therefore, in hot rolling, the pressure ratio in recrystallize territory must be set to more than 2.0, the pressure ratio in non-recrystallization territory is set to more than 3.0.
As described above, by suitably controlling the condition of hot rolling and subsequent accelerating cooling, except the intensity of thick steel sheet and low-temperature flexibility, can also meet with tubing after acid resistance and the composite attribute of resistance to crushing characteristic.
Successively the manufacturing process of steel plate of the present invention is described.
First, after the steel containing mentioned component being carried out melting by steel operation processed, carry out casting and making steel billet.As long as casting is undertaken by ordinary method, but preferably cast continuously from the viewpoint of productivity.Then obtained steel billet is heated, carry out hot rolling, accelerating cooling and manufacture steel plate.In addition, in present embodiment, by the heating of the steel billet carried out in order to hot rolling also referred to as reheating, by the Heating temperature of steel billet now also referred to as reheating temperature.
Hot rolling reheat temperature to make the solid solution in steel such as carbide, nitride generated in steel billet, be set to more than 1000 DEG C.In addition, be set to more than 1000 DEG C by temperature will be reheated, the hot rolling (rolling of recrystallize territory) in the recrystallize territory of 900 DEG C can be performed for more than, steel can be organized miniaturization.In addition, the upper limit reheating temperature does not specify, in order to suppress the coarsening of effective crystal particle diameter, preferably will reheat temperature and being set to less than 1250 DEG C.In addition reheat temperature in order to ensure low-temperature flexibility, be more preferably set to less than 1200 DEG C, be preferably set to less than 1150 DEG C further.
The temperature that hot rolling described in present embodiment possesses rolling in rolling process in the recrystallize territory more than 900 DEG C, the non-recrystallization territory of less than 900 DEG C and surface of steel plate is successively become the rolling in the temperature field (two phase regions) of austenite and this two-phase of ferrite.
In addition, due to hot rolling also can from after the process furnace that carries out reheating is extracted out immediately, so the beginning temperature of hot rolling does not have special stipulation.
In order to effective crystal particle diameter miniaturization of the thickness of slab central part by steel plate, the pressure ratio in the recrystallize territory more than 900 DEG C must be set to more than 2.0, promote recrystallize.Wherein, the pressure in recrystallize territory is than being the thickness of slab of steel billet and the ratio of the thickness of slab at 900 DEG C.
Then, the hot rolling (rolling of non-recrystallization territory) in the non-recrystallization territory of less than 900 DEG C is carried out.In order to effective crystal particle diameter miniaturization of the skin section by the steel plate after the accelerating cooling after hot rolling, the pressure of non-recrystallization territory rolling ratio must be set to more than 3.0, promote the phase transformation utilizing accelerating cooling.More preferably the pressure of non-recrystallization territory rolling ratio is set to more than 4.0.In addition, in the present invention, the ratio of the thickness of slab after the pressure of so-called non-recrystallization territory rolling terminates divided by non-recrystallization rolling than the thickness of slab at being 900 DEG C.
In hot rolling, the temperature of carrying out surface of steel plate is the rolling (two phase region rollings) become in the temperature field (two phase regions) of austenite and this two-phase of ferrite.Two phase region rollings are the rolling in following temperature field, and described temperature field is: the surface temperature of steel plate reaches ferrite transformation and starts temperature Ar 3below, but from two phase region rollings to end during, the temperature of the thickness of slab central part of steel plate is according to higher than the temperature of surface of steel plate and more than Ar 3mode be maintained.Such temperature distribution also by such as carrying out short period of time accelerating cooling, can make the temperature on only top layer reduce and realizing.In this two phase regions rolling, road number of times is set to more than 1, and draft is set to 0.1 ~ 40%.Due to carry out two phase region rollings as a result, the beginning temperature of the accelerating cooling carried out thereafter also becomes two phase regions, so the sclerosis of thickness of slab central part is inhibited, can low-temperature flexibility be improved.In addition, above-mentioned " draft " is the value that the difference of the thickness of steel plate after the thickness of steel plate before utilizing the decrement of the thickness of the steel plate of rolling, i.e. rolling and rolling obtains divided by the thickness of the steel plate before rolling, also can represent with per-cent (%) etc.In addition, in the position between top layer and thickness of slab central part, promote the generation of polygonal ferrite, contribute to the raising of low-temperature flexibility.
In addition, Ar 3can be calculated by the content (quality %) of C, Si, Mn, Ni, Cr, Cu, Mo.
Ar 3＝905-305C+33Si-92(Mn+Ni/2+Cr/2+Cu/2+Mo/2)
Wherein, C, Si, Mn, Ni, Cr, Cu, Mo in above-mentioned formula are the content [quality %] of each element.In addition, Ni, Cu, Cr, Mo are the element that in the present invention, selectivity is added, and when not having a mind to add, are calculated by content in formula as " 0 ".
The lower limit of the draft in two phase region rollings, in order to generate the processing ferrite extended along rolling direction, is set to more than 0.1%.Preferably the draft of two phase region rollings is set to more than 1%, is more preferably set to more than 2%.On the other hand, the upper limit of the draft in two phase region rollings due to the draft under the low temperature that is difficult to guarantee that resistance to deformation uprises, so be set to less than 40%.Preferably the draft of two phase region rollings is set to less than 30%, is more preferably set to less than 20%, be preferably set to lower than 10% further.
About the end temp of two phase region rollings, i.e. hot rolling end temp, in order to excessively generate processing ferrite, be set to more than 700 DEG C with the thermometer of surface of steel plate.If hot rolling end temp becomes lower than 700 DEG C, then sometimes in thickness of slab central part, produce ferrite transformation, result from processing ferrite, low-temperature flexibility and acid resistance reduce.In addition, if hot rolling end temp reduces, then C denseization in austenite by ferritic generation sometimes, the generation of promotion MA.On the other hand, if hot rolling end temp is too high, then when making the stopping temperature of accelerating cooling reduce, thickness of slab central part hardens sometimes, and low-temperature flexibility reduces.
Then, after the end of hot rolling, accelerating cooling is started immediately.But, after hot rolling, allow the air cooling gone out during side carries out transporting to accelerated cooling device from roller mill.
The stopping temperature of accelerating cooling is set in the temperature range of 200 ~ 400 DEG C with surface of steel plate thermometer.If stop accelerating cooling at the temperature of the temperature on the surface of steel plate more than 400 DEG C, then in thickness of slab central part, generate polygonal ferrite, acid resistance reduces.On the other hand, when carrying out the temperature of accelerating cooling to the surface of steel plate and becoming 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 stop accelerating cooling when the surface temperature of steel plate reaches the temperature range of 200 ~ 400 DEG C, then after, the temperature generation backheat on steel plate top layer when air cooling.Therefore, the temperature of thickness of slab central part reaches more than 400 DEG C, and hardness reduces, and can improve 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.
In addition, using the effective steel plate of high intensity line of the present invention as in raw-material situation, the steel pipe of the thick section and high strength spool of acid resistance, resistance to crushing characteristic and excellent in low temperature toughness can be manufactured.In addition, when manufacturing steel pipe, preferably adopt the UOE operation of effective for high intensity line of the present invention steel plate being carried out C compacting, U compacting, O compacting.Or, also can pass through JCOE operation, use the effective steel plate of high intensity line of the present invention to manufacture steel pipe.Docking section, by after effective for high intensity line of the present invention steel plate is configured as tubulose, is carried out electric-arc welding and is fetched manufacture by thick section and high strength spool of the present invention.Arc welding, from the view point of the toughness of welding metal and productivity, preferably adopts submerged arc welding.
In addition, the resistance to crushing characteristic of thick section and high strength spool of the present invention can be evaluated from the compression testing sheet of the steel pipe collection circumferential direction obtained by above-mentioned method.
Embodiment
Then, embodiments of the invention are described, but the present invention is not limited to the condition that adopts in following embodiment.
Melting is carried out, casting and make steel billet by by the steel that forms of chemical composition of table 1-1, table 1-2, table 2-1 and table 2-2." slab is thick " of table 3-1 and table 3-2 represents the thickness (mm) of the steel billet obtained.Above-mentioned steel billet is reheated respectively, in the recrystallize territory more than 900 DEG C, carries out hot rolling.In addition, " Heating temperature " of table 3-1 and table 3-2 represents above-mentioned and reheats temperature, the thickness of slab at 900 DEG C before the hot rolling after table 3-1 and table 3-2 " transferring thick " represents the hot rolling in above-mentioned recrystallize territory and in the non-recrystallization territory of less than 900 DEG C described later.In addition, " the pressure ratio in recrystallize territory " of showing 3-1 and table 3-2 is the thick ratio thick divided by transfer of above-mentioned slab.
Then, hot rolling is carried out to having in the non-recrystallization territory of the thick steel plate of transfer below 900 DEG C.Thickness of slab after the hot rolling that " thickness of slab " of table 3-1 and table 3-2 represents in above-mentioned non-recrystallization territory and before two phase region rollings described later, " the non-recrystallization pressure than " of table 3-1 and table 3-2 for value that above-mentioned transfer is thick terminate divided by above-mentioned non-recrystallization rolling after thickness of slab and the value that obtains.
After hot rolling in above-mentioned non-recrystallization territory, and carry out final hot-rolled process before accelerating cooling.The surface temperature of the steel plate at the end of above-mentioned final hot-rolled process is shown in " the finish rolling end temp (DEG C) " of table 3-1 and table 3-2.In addition, the rolling number of times carried out when above-mentioned final hot-rolled process, road number of times are shown in " α+γ depresses passage number of times " of table 3-1 and table 3-2, the draft of the steel plate utilizing above-mentioned final hot-rolled process are shown in " α+γ draft (%) " of table 3-1 and table 3-2.
After above-mentioned final hot-rolled process, be transferred to after in cooled region and utilize water-cooled to implement accelerating cooling immediately.The beginning temperature of the above-mentioned accelerating cooling carried out in the manufacturing processed of the steel plate of steel No.1 ~ 46 and stopping temperature being shown in " water-cooled starts temperature (DEG C) " and " water-cooled stops temperature (DEG C) " of table 3-1 and table 3-2.
By above manufacturing process, obtain the steel plate of steel No.1 ~ 46.
From skin section and the thickness of slab central part acquisition test sheet of the steel plate of obtained No.1 ~ 46, utilize opticmicroscope to carry out structure observation, obtain the area occupation ratio of the ferritic area occupation ratio of processing and MA, confirm remainder tissue.
Remainder be organized in the steel plate of No.1 ~ 46 whole in, metal structure for being made up of the one or both of polygonal ferrite, bainite in skin section, the metal structure for being made up of the one or both of acicular ferrite, bainite in thickness of slab central part.In addition, the mensuration of the area occupation ratio of MA uses the test film implementing Lepera etching to carry out.
In addition, the mean value of effective crystal particle diameter of top layer and thickness of slab central part is obtained by EBSD.
(mensuration of the intensity of steel plate)
In addition, from the wide central part of the plate of the steel plate of obtained No.1 ~ 46, width is made to be length direction, each collection 2 is (following according to american petroleum institute standard API5L, referred to as " API5L ") complete thick test film, according to 2000 of API standard, at room temperature carry out tension test and obtain yielding stress and tensile strength.Based on the ultimate load in this tension test, obtain tensile strength.
(mensuration of the DWTT ductile fracture rate of steel plate)
In addition, from the wide central part of the plate of the steel plate of obtained No.1 ~ 46, gather and make width be the entirely thick DWT test film of length direction.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 testing)
Use the steel plate of No.1 ~ 46 obtained, tubing is carried out by UOE operation, submerged arc welding is carried out for the heat input shown in interior outside utilization table 5-1, table 5-2, thus manufactures the steel pipe (steel plate No. is corresponding respectively with steel pipe No.) that external diameter is 30 ~ 36 inches.Then, from steel pipe acquisition test sheet, strength detection and compression testing is carried out.
About the mensuration of the intensity of steel pipe, the seam weldering portion of steel pipe being set at 0 o'clock from 3 o'clock positions processes test film according to the mode that the length direction of tension test sheet is consistent with steel pipe length direction, carry out according to ASTME9-09, measure yield strength and the tensile strength of the length direction of spool.Wherein, 0.5% underload endurance is defined as yield strength.
Compression testing sheet for the compression testing of steel pipe gathers the part of 22mm diameter 66mm length from the medial surface 3mm of steel pipe by the seam weldering portion of steel pipe being set at 0 o'clock 6 o'clock positions and obtaining.Compression testing is carried out according to ASTME9-09, obtains the compressive strength (0.2% stress of fluidity) to carry out 10 minutes timeliness at 200 DEG C after.
(the HIC test of steel pipe)
In addition, the seam weldering portion of steel pipe is set to 0 point, from the HIC test film of 3 points, 6 wide 100mm length of each station acquisition 20mm.The mode that HIC test film becomes test position according to the central part of the wall thickness of steel pipe gathers.The TM0284 of HIC test basis NACE (NationalAssociationofCorrosionandEngineer), testing liquid uses SolutionB to carry out, evaluate with crack length rate (CrackLengthRatio is called 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 example of the present invention.As by table 4-1,4-2 and table, 5-1,5-2 show, use these steel plates and the yielding stress of steel pipe that manufactures is more than 440MPa, tensile strength is in the scope of 500 ~ 700MPa.In addition, as shown in table 4-1,4-2, the tensile strength of steel plate is more than 500MPa, and the DWTT ductile fracture rate at-10 DEG C is more than 85%.In addition, as shown in table 5-1,5-2, these steel plates are carried out tubing, the CLR of HIC test of welding and the steel pipe that manufactures is less than 10%, the compression testing at 200 DEG C after strain aging is more than 450MPa, well.
On the other hand, steel No.29 ~ 46 are comparative example, the content of the chemical composition of steel No.29 ~ 40 is outside scope of the present invention, and the metal structure of steel No.41 ~ 46 becomes outside scope of the present invention, and at least one in intensity, low-temperature flexibility, resistance to crushing characteristic, acid resistance is 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, and the Si amount of steel No.31 is many, and the Mn amount of steel No.32 is many, and the equal tensile strength of all comparative examples exceedingly rises, and low-temperature flexibility reduces.
In addition, the Ar of steel No.30 3lower than 700 DEG C, the steel plate of steel No.30 does not carry out the rolling in two phase regions in the present invention.But, because contained C measures many, thus in the thickness of slab central part of steel No.30 in austenite C denseization, promote the generation of MA, acid resistance reduces.In addition, steel No.32 reaches 3% due to Mn, so acid resistance reduces.
Steel No.33,34 and 40 the content of impurity (P, S, O) many, low-temperature flexibility reduces.Steel No.35 ~ 39 be contribute to carbide, nitride, oxide compound, sulfide the content of element of generation many, result from precipitate, inclusion and example that low-temperature flexibility reduces.
Steel No.41 and 42 is respectively the draft in recrystallize territory and the example that draft is not enough, effectively crystal particle diameter becomes large, low-temperature flexibility reduces in non-recrystallization territory.
Although the end temp of steel No.43 hot rolling is more than 700 DEG C, due to Ar 3low, do not carry out the rolling in two phase regions in the present invention, so do not generate processing ferrite in top layer, thickness of slab central part hardens, and low-temperature flexibility reduces.
Steel No.44 be the stopping temperature of accelerating cooling high, in thickness of slab central part excessively generate processing ferrite and MA, intensity reduce example.In addition, owing to stopping accelerating cooling at temperature more than 400 DEG C of the temperature on the surface at steel plate, so generate polygonal ferrite in thickness of slab central part, acid resistance reduces.
Steel No.45 and 46 is the example that rolling end temp is low, excessively generate processing ferrite and the reduction of MA, low-temperature flexibility and acid resistance in skin section and thickness of slab central part.
Table 1-1
Table 1-2
Table 4-1
Table 4-2
Table 5-1
Table 5-2

Claims (6)

1. a thick section and high strength spool steel plate for acid resistance, resistance to crushing characteristic and excellent in low temperature toughness, is characterized in that, its for thickness of slab be the steel plate of more than 25mm and below 45mm,
Its composition contains in mass %:
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％，
Be restricted to below Si:0.5%,
Below Al:0.05%,
Below P:0.03%,
Below S:0.005%,
Below O:0.005%,
Remainder is made up of Fe and inevitable impurity,
From surface of steel plate, be more than 0.9mm and the metal structure of part within 1.1mm and skin section is restricted in area occupation ratio towards thickness direction:
Processing ferrite: be more than 5% and the S obtained by following formula 1a fe1below %,
Martensite-austenite composite: less than 8%,
Remainder is made up of the one or both in polygonal ferrite, bainite,
Part be 1mm towards two directions at the table back side of steel plate from thickness of slab center within and the metal structure of thickness of slab central part are restricted in area occupation ratio:
Processing ferrite: less than 5%,
Martensite-austenite composite: less than 5%,
Remainder is made up of the one or both in acicular ferrite, bainite,
The mean value of the effective crystal particle diameter measured by Electron Back-Scattered Diffraction method in skin section and thickness of slab central part is less than 20 μm,
S fe1=0.6552 × T h-4.7826 formula 1a
Wherein, T h: the thickness of slab of thick section and high strength spool steel plate.
2. the thick section and high strength spool steel plate of acid resistance according to claim 1, resistance to crushing characteristic and excellent in low temperature toughness, is characterized in that, contain further in mass %:
Below Cu:0.50%,
Below Ni:0.50%,
Below Cr:0.50%,
Below Mo:0.50%,
Below W:0.50%,
Below V:0.10%,
Below Zr:0.050%,
Below Ta:0.050%,
Below B:0.0020%,
Below Mg:0.010%,
Below REM:0.0050%,
Below Y:0.0050%,
Below Hf:0.0050%,
Below Re:0.0050%
In one kind or two or more.
3. the thick section and high strength spool steel plate of acid resistance according to claim 1 and 2, resistance to crushing characteristic and excellent in low temperature toughness, is characterized in that, the content of Al is less than 0.005%.
4. the thick section and high strength spool steel plate of the acid resistance according to any one of claims 1 to 3, resistance to crushing characteristic and excellent in low temperature toughness, is characterized in that, tensile strength is 500 ~ 700MPa.
5. the thick section and high strength spool steel plate of the acid resistance according to any one of claims 1 to 3, resistance to crushing characteristic and excellent in low temperature toughness, it is characterized in that, yielding stress after tubing reaches more than 440MPa, tensile strength reaches 500 ~ 700MPa, and 0.2% stress of fluidity of the compression of the circumferential direction after the timeliness at 200 DEG C reaches more than 450MPa.
6. a thick section and high strength spool, it is characterized in that, it is, after tubulose, arc welding is carried out the thick section and high strength spool steel formability of the acid resistance according to any one of claim 1 ~ claim 4, resistance to crushing characteristic and excellent in low temperature toughness in docking section and manufactures
Yielding stress is more than 440MPa, and tensile strength is 500 ~ 700MPa, and 0.2% stress of fluidity of the compression of the circumferential direction after the timeliness at 200 DEG C is more than 450MPa.
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CN113564485B (en) * 2021-09-24 2021-12-31 江苏省沙钢钢铁研究院有限公司 Steel plate for wind power and production method thereof

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CN105143487B (en) 2017-03-08
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EP3042976A4 (en) 2017-05-10
KR101730756B1 (en) 2017-04-26

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