CN108431274A - The low yield strength ratio high strength steel of resisting stress corrosion cracking and excellent in low temperature toughness - Google Patents

The low yield strength ratio high strength steel of resisting stress corrosion cracking and excellent in low temperature toughness Download PDF

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CN108431274A
CN108431274A CN201680075892.9A CN201680075892A CN108431274A CN 108431274 A CN108431274 A CN 108431274A CN 201680075892 A CN201680075892 A CN 201680075892A CN 108431274 A CN108431274 A CN 108431274A
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steel
stress corrosion
corrosion cracking
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CN108431274B (en
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张成豪
李学哲
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Posco Holdings Inc
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Posco Co Ltd
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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/001—Heat treatment of ferrous alloys containing Ni
    • 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
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/005—Heat treatment of ferrous alloys containing Mn
    • 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
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/008—Heat treatment of ferrous alloys containing Si
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0205—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips of ferrous alloys
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/08—Ferrous alloys, e.g. steel alloys containing nickel
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
    • C—CHEMISTRY; METALLURGY
    • 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
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/008—Martensite

Abstract

One aspect of the present invention is related to the low yield strength ratio high strength steel of resisting stress corrosion cracking and excellent in low temperature toughness, includes following component in terms of weight %：Carbon (C)：0.02%~0.10%, manganese (Mn)：0.5%~2.0%, silicon (Si)：0.05%~0.5%, nickel (Ni)：0.05%~1.0%, titanium (Ti)：0.005%~0.1%, aluminium (Al)：0.005%~0.5%, niobium (Nb)：Less than or equal to 0.005%, phosphorus (P)：Less than or equal to 0.015%, sulphur (S)：Less than or equal to the Fe of 0.015%, surplus and other inevitable impurity, microstructure includes at least one of the acicular ferrite more than or equal to 60%, the bainite of surplus, polygonal ferrite, martensitic-austenitic constituent element in terms of area %.

Description

The low yield strength ratio high strength steel of resisting stress corrosion cracking and excellent in low temperature toughness
Technical field
The present invention relates to a kind of resisting stress corrosion cracking and the low yield strength ratio high strength steels of excellent in low temperature toughness.
Background technology
Steel for liquefied gas storage are different according to the type of liquefied gas, but the condensing temperature of gas is generally normal Pressure is low temperature (LPG is -52 DEG C), therefore does not require nothing more than base material with excellent low-temperature flexibility, and requires welding portion With excellent low-temperature flexibility.
Furthermore it is known that liquefied ammonia (LAG) can cause stress corrosion cracking (SCC, the Stress Corrosion of steel Cracking it), therefore in IGC CODE (International Code for the Construction and Equipment of Ships Carrying Liquefied Gases in Bulk) provides, to oxygen The operating condition when manufactures such as pressure, temperature is limited, while the Ni contents of steel are limited in 5% hereinafter, and being bent practical It takes intensity and is limited in 440MPa or less.
In addition, when carrying out welding manufacture at gas tank (Gas Tank) with steel to gas tank (Gas Tank), weld part is eliminated The stress divided accounts for consequence.Therefore, as the method for eliminating welding portion stress, such as there is the PWHT based on heat treatment (post weld heat treatment) method and the mechanical stress elimination (MSR for adding the elimination stress such as hydrostatic pressing by being given to weld part： Mechanical Stress Relief) method.When eliminating (MSR) method elimination welding portion stress using mechanical stress, Deformation caused by hydraulic pressure can also act on base material portion, therefore the yield tensile ratio of base material is limited in 0.8 or less.This is because in profit During eliminating stress with MSR, spraying water with high pressure leads to the metamorphosis of yield strength or more when base material, if yield strength It is high with the ratio between tensile strength, it will surrender, that is, reach tensile strength, there is a possibility that destroy, therefore be constrained to Yield strength relative tensile strength has very big difference.
In particular, for gas tank (Gas Tank), substantially need to realize enlargement, it is difficult to answer by the elimination of PWHT methods Power, then most of shipyard selection mechanical stress elimination (MSR) method, is accordingly used in the steel of manufacture gas tank (Gas Tank) Require low yield strength ratio characteristic.
As described above, in the gas tank field for loading in mixture the LPG and LAG, great project is to realize low-temperature flexibility simultaneously And based on originating from low yield strength ratio as defined in the yield strength upper limit of liquefied ammonia.
In addition, proposing the Ni of addition 6.5%~12.0% in patent document 1 to realize the skill of excellent low-temperature flexibility Art.Q-tempering processing is implemented with mixed tempering (Tempered) horse to the steel of specific components in addition, being proposed in patent document 2 The technology of family name's body and bainite.
However, in general, if a large amount of Ni is added, since atomic distance is narrow, it will generation, which much has, to be easily deformed FCC lattice structures austenite phase, when repeated stress and corrosive environment act on this FCC lattice structures being easily deformed When, it is easy to happen corrosion, so as to cause cracking is generated.Therefore, there are the following problems for foregoing invention：Due to the content of high price Ni Height, economy decline, and stress corrosion dehiscence resistant (SCC) property is caused to decline.
Sofening treatment only is carried out to realize the technology of low yield strength ratio to steel plate surface layer in addition, being proposed in patent document 3. However, although the technology can realize low-temperature flexibility and low yield strength ratio respectively, it can be difficult to realizing low-temperature flexibility simultaneously and low bending Strong ratio.
In addition, as the method for improving another characteristic steel strength required by steel, such as have precipitation strength, solid solution strong Change, martensite (Martensite) reinforcing etc. can but cause toughness and elongation percentage to become although these methods improve intensity Difference.
In addition, when making crystal grain refinement improve intensity using various manufacturing conditions, high intensity can not only be obtained, and due to Impact flexibility transition temperature reduces, and can prevent degraded toughness, but crystal grain refinement causes yield strength to rise, to be more than ammonia Cause the yield strength upper limit 440MPa of stress corrosion cracking (SCC), it is difficult to ensure low yield strength ratio.
Therefore, it is necessary to develop the low yield strength ratio high strength steel of a kind of resisting stress corrosion cracking and excellent in low temperature toughness And its manufacturing method.
Citation
Patent document 1：Clear No. 63-290246 of Japanese Laid-Open Patent Publication
Patent document 2：Clear No. 58-153730 of Japanese Laid-Open Patent Publication
Patent document 3：Flat No. 4-17613 of Japanese Laid-Open Patent Publication
Invention content
Technical problem
One aspect of the present invention is intended to provide the low yield strength ratio of a kind of resisting stress corrosion cracking and excellent in low temperature toughness High strength steel and its manufacturing method.
In addition, the technical problems to be solved by the invention are not limited to above-mentioned content.Pass through the entire content of this specification It will be seen that the technical problems to be solved by the invention, this hair understood for those skilled in the art Bright other technologies problem to be solved does not have hell and high water.
Technical solution
One aspect of the present invention is related to a kind of resisting stress corrosion cracking and the low yield strength ratio of excellent in low temperature toughness is high-strength Steel are spent, include following component in terms of weight %：Carbon (C)：0.02%~0.10%, manganese (Mn)：0.5%~2.0%, silicon (Si)：0.05%~0.5%, nickel (Ni)：0.05%~1.0%, titanium (Ti)：0.005%~0.1%, aluminium (Al)：0.005% ~0.5%, niobium (Nb)：Less than or equal to 0.005%, phosphorus (P)：Less than or equal to 0.015%, sulphur (S)：Less than or equal to 0.015%, it is remaining The Fe of amount and other inevitable impurity, microstructure include the acicular ferrite more than or equal to 60% in terms of area % (Acicular Ferrite), bainite (Bainite), polygonal ferrite (Polygonal Ferrite), the MA of surplus At least one of (Martensite-Austenite constituent, martensite-austenite constituent).
In addition, another aspect of the present invention be related to a kind of resisting stress corrosion cracking and excellent in low temperature toughness it is low bend it is strong Than the manufacturing method of high strength steel, it includes following steps：
By heating steel billet to 1000 DEG C~1200 DEG C, the steel billet includes following component in terms of weight %：Carbon (C)： 0.02%~0.10%, manganese (Mn)：0.5%~2.0%, silicon (Si)：0.05%~0.5%, nickel (Ni)：0.05%~1.0%, Titanium (Ti)：0.005%~0.1%, aluminium (Al)：0.005%~0.5%, niobium (Nb)：Less than or equal to 0.005%, phosphorus (P)：It is less than Equal to 0.015%, sulphur (S)：Less than or equal to the Fe of 0.015%, surplus and other inevitable impurity；
Roughing is carried out at a temperature of 1100 DEG C~900 DEG C to the steel billet after the heating；
Central part temperature is subject to after the roughing in Ar3+ 100 DEG C~Ar3Finish to gauge is carried out at a temperature of+30 DEG C；And
The finish to gauge postcooling to less than the temperature equal to 300 DEG C.
Additionally, above-mentioned technical problem solution does not enumerate all features of the present invention.To all of the present invention It multiple features and is described in further detail with reference to following specific implementation modes with effect the advantages of based on these features.
Invention effect
According to the present invention resisting stress corrosion cracking and low temperature can be provided by controlling alloy compositions and microstructure The low yield strength ratio high strength steel and its manufacturing method of excellent tenacity.
Description of the drawings
Fig. 1 is the phase transformation figure of the invention steel A based on cooling velocity.
Fig. 2 is the photo (1- of Fig. 1 of microstructure at the steel plate 1/4t with the i.e. A-5 of light microscope observation comparative example (1))。
Fig. 3 is the photo (1- of Fig. 1 of microstructure at the steel plate 1/4t with the i.e. A-1 of light microscope observation example (2))。
Fig. 4 is the photo (1- of Fig. 1 of microstructure at the steel plate 1/4t with the i.e. A-6 of light microscope observation comparative example (3))。
Specific implementation mode
The preferred embodiment of the present invention is described below.However, the present invention can deformation implementation in a variety of different ways, this The range of invention is not limited to following embodiments.In addition, embodiments of the present invention are in order to the ordinary skill of fields Personnel more completely illustrate of the invention and offer.
Present inventors understand that making anti-ammonia cause some all excellent difficulties of stress corrosion cracking and low-temperature flexibility, in order to solve This problem has made intensive studies.
Itself as a result, it has been found that, by controlling alloy compositions and microstructure, resisting stress corrosion cracking and low temperature can be provided The all excellent low yield strength ratio high strength steel of toughness and its manufacturing method, so as to complete the present invention.
The low of resisting stress corrosion cracking according to an aspect of the present invention and excellent in low temperature toughness is described below in detail Yield tensile ratio high strength steel.
The low yield strength ratio high intensity of resisting stress corrosion cracking and excellent in low temperature toughness according to an aspect of the present invention Steel include following component in terms of weight %：Carbon (C)：0.02%~0.10%, manganese (Mn)：0.5%~2.0%, silicon (Si)：0.05%~0.5%, nickel (Ni)：0.05%~1.0%, titanium (Ti)：0.005%~0.1%, aluminium (Al)：0.005% ~0.5%, niobium (Nb)：Less than or equal to 0.005%, phosphorus (P)：Less than or equal to 0.015%, sulphur (S)：Less than or equal to 0.015%, it is remaining The Fe of amount and other inevitable impurity,
Microstructure includes the acicular ferrite (Acicular Ferrite) more than or equal to 60%, surplus in terms of area % Bainite (Bainite), polygonal ferrite (Polygonal Ferrite), MA (Martensite-Austenite At least one of constituent).
First, the low of resisting stress corrosion cracking according to an aspect of the present invention and excellent in low temperature toughness is described in detail The alloy compositions of yield tensile ratio high strength steel.The content unit of each ingredient is weight % below.
C (carbon)：0.02%~0.10%
C is to ensure that the important element of basic intensity, it is therefore desirable to is included in steel with range appropriate, in order to obtain this Kind additive effect, is preferably added to the C more than or equal to 0.02%.
If C content is less than 0.02%, it is possible to cause intensity to decline and decline with yield tensile ratio, therefore is undesirable.If C Content is more than 0.10%, will the low-temperature transformations phase such as a large amount of bainites, exist and cause stress corrosion to open more than ammonia may be caused The problem of splitting the yield strength upper limit of (SCC).
Therefore, the content of the C is preferably limited to 0.02%~0.10%, is more preferably limited in 0.05%~0.08%.
Si (silicon)：0.05%~0.5%
Si has the effect of useful as deoxidier by solid solution strengthening effect raising intensity, and in process for making Element.
If Si contents are less than 0.05%, deoxidation effect and strength-enhancing effect may be insufficient.If Si contents More than 0.5%, then weldability is also deteriorated while there are problems that low-temperature flexibility is caused to decline.
Therefore, the content of the silicon is preferably limited to 0.05%~0.5%.More preferably it is limited in 0.05%~0.3%.
Mn (manganese)：0.5%~2.0%
Manganese is contributed to fetrite grain refinement and to improving the useful element of intensity by solution strengthening.
In order to obtain the effect of this manganese, need to be added more than or equal to 0.5%.But if the content of manganese is more than 2.0%, then hardenability can excessively increase, promote the generation of upper bainite (Upper bainite) and martensite, so as to cause Impact flexibility and anti-ammonia cause stress corrosion cracking (SCC) property to decline to a great extent, and the toughness of welding heat affected part is also caused to decline.
Therefore, the Mn contents are preferably limited to 0.5%~2.0%, are more preferably limited in 1.0%~1.5%.
Ni (nickel)：0.05%~1.0%
Ni is that dislocation cross-slip (Cross slip) can at low temperature become easy, to improve impact flexibility, and And be improve hardenability to improve the important element of intensity, in order to obtain this effect, be preferably added to be more than or equal to 0.05% Ni.But if Ni contents are more than 1.0%, it is possible to cause ammonia to cause stress corrosion cracking (SCC), and can with other Hardenability element is compared, and the price of Ni is high, thus manufacturing cost can also rise.
Therefore, the Ni contents are preferably limited to 0.05%~1.0%, are more preferably limited in 0.2%~0.5%.
Nb (niobium)：Less than or equal to 0.005%
When there is Nb high temperature to reheat the Nb that is dissolved in the form of NbC micro precipitation and inhibit the recrystallization of austenite to make group Knit the effect of refinement.
It due to this structure refinement, is likely to result in yield strength and excessively increases, and then stress is caused more than ammonia may be caused The yield strength upper limit of corrosion cracking (SCC), therefore Nb is controlled preferably to be less than or equal to 0.005%, more preferably less than or equal to 0.003%.
Ti (titanium)：0.005%~0.1%
The growth of crystal grain, it is tough can to greatly improve low temperature when titanium forms oxide and nitride in steel and inhibits to reheat Property, and welding portion microstructure is refined effective.
In order to obtain this effect, need that the titanium more than or equal to 0.005 weight % is added.But if Ti content is more than 0.1 weight % will have that continuous casting sprue (nozzle) blocks or central part crystallization causes low-temperature flexibility to decline.
Therefore, Ti content is preferably 0.005%~0.1%, and more preferably 0.01%~0.03%.
Al (aluminium)：0.005%~0.5%
Aluminium is the element to keeping deoxidation of molten steel useful, needs to be added more than or equal to 0.005 weight % thus.But if The content of aluminium is more than 0.5 weight %, and the mouth of a river (nozzle) blocks when may result in continuous casting, so undesirable.Therefore, aluminium content is preferred It is 0.005%~0.5%, more preferably 0.005%~0.05%.
P (phosphorus)：Less than or equal to 0.015%
Phosphorus is the element for causing cyrystal boundary segregation in base material and welding portion, there is a problem of leading to generate steel embrittlement, therefore Need the content of actively reduction phosphorus.But when minimizing the content of this phosphorus, the load of process for making can aggravate, if The content of phosphorus is less than or equal to 0.015%, is not in above-mentioned problem mostly, therefore the upper limit of phosphorus content is preferably limited to 0.015%, more preferably it is limited in 0.010 weight %.
S (sulphur)：Less than or equal to 0.015%
Sulphur (S) is to cause hot short element, it will forms MnS etc. and impact flexibility is caused to decline to a great extent, preferably control It is as low as possible at content, therefore sulfur content is preferably limited to be less than or equal to 0.015 weight %, is more preferably limited to 0.005 weight Measure %.
The surplus ingredient of the present invention is iron (Fe).But it can be inevitably mixed into from raw material in conventional manufacturing process Or the unexpected impurity of ambient enviroment, therefore cannot exclude and be mixed into impurity.These impurity are the technologies of conventional manufacturing process Anyone impurity for both knowing about of personnel, therefore repeated no more in relevant all the elements this specification.
Next, resisting stress corrosion cracking according to an aspect of the present invention and excellent in low temperature toughness is described in detail The microstructure of low yield strength ratio high strength steel.
The microstructure of the steel of the present invention includes the acicular ferrite (Acicular more than or equal to 60% in terms of area % Ferrite), the bainite (Bainite) of surplus, polygonal ferrite (Polygonal Ferrite), MA (Martensite- At least one of Austenite constituent).
When bainite (bainite) score increase causes acicular ferrite score to be less than 60%, it may occur that hard phase Increase cause impact flexibility to be deteriorated.When polygonal ferrite (Polygonal Ferrite) score increase leads to needle-shaped iron element When body score is less than 60%, it may occur that intensity is deteriorated.Therefore, the Line Integral of acicular ferrite (Acicular Ferrite) Number preferably greater than or equal to 60%.
In addition, if comprising pearlite, then tensile strength and low-temperature impact toughness may be deteriorated, therefore the steel of the present invention The microstructure of material can not include pearlite.
At this point, the acicular ferrite is smaller than with the size that equivalent diameter measures equal to 30 μm.If the size More than 30 μm, then impact flexibility may be deteriorated.
In addition, the bainite is preferably granular bainite (granular bainite) and upper bainite (upper bainite)。
In addition, the bainite area fraction is preferably smaller than equal to 30%.If bainite area fraction is more than 30%, just Can be more than the yield strength upper limit (440MPa) that may cause ammonia and cause stress corrosion cracking (SCC), it is therefore desirable to limit bainite Score.
In addition, the MA phases are preferably smaller than equal to 10 area % and are less than or equal to 5 μm with the size that equivalent diameter measures. MA (martensite-austenite constituent) is also referred to as island-like martensite.
When the score of the MA phases is more than 10% or equivalent diameter is more than 5 μm, the toughness of base material and welding portion Have the tendency that declining to a great extent, it is therefore desirable to limit the score and size of MA phases.
In addition, its yield tensile ratio (YS/TS) of the steel of the present invention for meeting above-mentioned condition is preferably smaller than less than or equal to 0.85 Equal to 0.8.Moreover, the steel have excellent tensile strength, tensile strength be more than or equal to 490MPa, for example, 510MPa~ 610MPa or so.
In addition, the yield strength upper limit of the steel is less than or equal to 440MPa, does not exceed initiation ammonia and stress corrosion is caused to open The yield strength upper limit of (SCC) is split, therefore anti-ammonia causes stress corrosion cracking (SCC) property excellent.
In addition, the impact transition temperature along the 1/4t of the thickness direction of the steel is less than or equal to -60 DEG C, can have excellent Different low-temperature flexibility, wherein the t indicates the thickness of steel.
At this point, the steel have the thickness more than or equal to 6mm, it preferably can be with the thickness of 6mm~50mm.
As described above, the steel of the present invention can ensure high intensity, low yield strength ratio, excellent low-temperature flexibility and anti-ammonia simultaneously Cause stress corrosion cracking (SCC) property.
The following detailed description of according to another aspect of the present invention resisting stress corrosion cracking and excellent in low temperature toughness The manufacturing method of low yield strength ratio high strength steel.
The low yield strength ratio of resisting stress corrosion cracking and excellent in low temperature toughness according to another aspect of the present invention is high-strength The manufacturing method of steel is spent, it includes following steps：
By the heating steel billet with the alloy compositions to 1000 DEG C~1200 DEG C；
Roughing is carried out at a temperature of 1100 DEG C~900 DEG C to the steel billet after the heating；
Central part temperature is subject to after the roughing in Ar3+ 100 DEG C~Ar3Finish to gauge is carried out at a temperature of+30 DEG C；And
The finish to gauge postcooling to less than the temperature equal to 300 DEG C.
Heating stepses
By the heating steel billet with the alloy compositions to 1000 DEG C~1200 DEG C.
Billet heating temperature is preferably greater than or equal to 1000 DEG C, this is the Ti carbonitrides solid solution in order to make to be formed in casting. Moreover, if billet heating temperature is too low, deformation drag is excessively high when rolling, and cannot be significantly increased in subsequent rolling process every Percentage pass reduction, therefore its lower limit is preferably limited to 1000 DEG C.But if being heated to excessively high temperature, austenite becomes Coarsening may result in toughness decline, therefore the upper limit of the heating temperature is preferably 1200 DEG C.
Roughing step
Roughing is carried out at a temperature of 1100 DEG C~900 DEG C to the steel billet after the heating.
Roughing temperature is preferably greater than or equal to the temperature (Tnr) of austenite recrystallization stopping.Due to rolling, formed in casting The cast sturctures such as dendrite are destroyed, and can also obtain the effect for making the size of austenite become smaller.In order to obtain this effect, roughing Temperature is preferably limited to 1100 DEG C~900 DEG C.
At this point, the roughing can be implemented in such a way that last three every time reduction ratios are more than or equal to 10%.
In roughing, for the fully deformed until central part, last three every time preferred reduction ratio are more than or equal to 10%, total reduction ratio of accumulating is more than or equal to 30%.
In roughing, initial rolling causes the tissue of recrystallization that grain growth occurs because of high temperature, but implements last three Road roll when, with etc. it is to be rolled during steel bar by air cooling, grain growth speed is slack-off, therefore last three when roughing The reduction ratio in road can generate biggest impact to the granularity of final microstructure.
In addition, when every time reduction ratio of roughing reduces, adequately deformation is not transferred to central part, it may occur that Toughness caused by central part coarsening declines.It is therefore preferable that every time reduction ratio by last three is limited to be more than or equal to 10%.
In addition, for the refinement of central part tissue, when roughing, always accumulates reduction ratio and is preferably provided to be more than or equal to 30%.
Finishing step
Central part temperature is subject to after the roughing in Ar3+ 100 DEG C~Ar3Finish to gauge is carried out at a temperature of+30 DEG C.
This is in order to obtain the microstructure more refined, if in Ar3(ferritic transformation initial temperature)+100 DEG C~Ar3+ Implement finish to gauge at a temperature of 30 DEG C, then can largely generate Zona transformans inside austenite, and then ensures a large amount of ferrite life core position It sets, the effect for ensuring microstructure up to the central part of steel can be obtained.
If finishing temperature is dropped below Ar3+ 30 DEG C, then ferrite grain size become excessively to refine, it will cause More than the yield strength upper limit (440MPa) for causing ammonia cause stress corrosion cracking (SCC), if more than Ar3+ 100 DEG C of temperature Lower carry out finish to gauge, then do not have effect to granularity refinement.It is therefore preferable that finishing temperature is limited in Ar3+ 100 DEG C~Ar3+ 30 DEG C, Only implement finish to gauge under these conditions, the microstructure of manufactured steel plate can just become with feature as described above Complex tissue.
At this point, the Ar3Ar can be passed through3=910- (310*C)-(80*Mn)-(55*Ni) is calculated and is obtained, each element symbol Indicate the content of each element measured with weight % units, Ar3Unit be DEG C.
In addition, in order to make effectively largely to generate Zona transformans inside austenite, in finish to gauge, accumulation reduction ratio is maintained at More than or equal to 60%, every time reduction ratio, which is remained above, further preferably other than so that final shape is uniformly rolled is equal to 10%.
Cooling step
The finish to gauge postcooling to less than the temperature equal to 300 DEG C.
The cooling Ar preferably after finish to gauge3+ 30 DEG C~Ar3At a temperature of begin to cool until be cooled to be less than or equal to 300 DEG C, Such as 100 DEG C~300 DEG C or so of cooling end temp (FCT, Finish Cooling Temperature).
If cooling end temp (FCT, Finish Cooling Temperature) is more than 300 DEG C, then due to tempering (Tempering) effect, fine MA meet decomposition, it is possible to be difficult to realize low yield strength ratio, therefore cooling end temp is preferred Less than or equal to 300 DEG C.
At this point, the step for implementing the cooling, it can be in a manner of being more than or equal to 15 DEG C/s by central part cooling velocity After implementing until the first step is cooled to Bs-10 DEG C~Bs+10 DEG C, in such a way that central part cooling velocity is 10 DEG C/s~50 DEG C/s Until implementation second step is cooled to less than or equal to 300 DEG C.
In addition, the beginning of cooling temperature can be Ar3+ 30 DEG C~Ar3。
First step cooling Ar preferably after finish to gauge3+ 30 DEG C~Ar3At a temperature of begin to cool and with the steel plate Central part cooling velocity is greater than the cooling velocity equal to 30 DEG C/s more than or equal to 15 DEG C/s and is cooled to Bs-10 DEG C~Bs+10 ℃。
In first step cooling, if until the central part cooling velocity of Bs-10 DEG C~Bs+10 DEG C steel plate is small In 15 DEG C/s, coarse polygonal ferrite (Polygonal Ferrite) will be formed, tensile strength and punching are may result in Hit toughness decline.
At this point, the Bs can be calculated by Bs=830- (270*C)-(90*Mn)-(37*Ni) and be obtained, each element symbol Indicate the content of each element measured with weight % units, the unit of Bs is DEG C.
Second step cooling preferably after first step cooling with the central part cooling velocity of the steel plate be 10 DEG C/ The cooling velocity of s~50 DEG C/s is cooled to cooling end temp of such as 100 DEG C~300 DEG C less than or equal to 300 DEG C.
In second step cooling, if the cooling velocity of the steel plate is more than 50 DEG C/s, such as the 1- (1) of Fig. 1 Microstructure, bainite score can be more than or equal to 30 area %, will cause to be more than to cause ammonia to cause bending for stress corrosion cracking (SCC) Upper intensity limit (440MPa) is taken, since intensity excessively rises, may result in elongation percentage and impact toughness decreased.
On the contrary, in second step cooling, if the cooling velocity of the steel plate is less than 10 DEG C/s, such as 1- (3) of Fig. 1 Microstructure, will not form fine acicular ferrite, but form coarse polygonal ferrite and pearlite, may Tensile strength is caused to be less than or equal to 490MPa and Charpy impact transition temperature more than or equal to -60 DEG C.
According to above-mentioned manufacturing method, it is possible to produce the low yield strength ratio of resisting stress corrosion cracking and excellent in low temperature toughness High strength steel.
The present invention is more specifically described below by embodiment.But it is noted that following embodiments are only for illustration Purpose of the present invention to be described more fully, and it is not intended to the interest field of the limitation present invention.The interest field of the present invention takes The reasonable derived content certainly in the content of claims and thus.
After the steel billet that the thickness of component with the following table 1 is 300mm is again heated to 1100 DEG C of temperature, at 1050 DEG C At a temperature of implement roughing, to manufacture steel bar.It is 30% identical that reduction ratio is accumulated when roughing.In addition, calculating based on each steel constituent Ar3And it Bs temperature and is recorded in the following table 1.
After the roughing, to meet finishing temperature and Ar shown in the following table 23The mode of temperature difference carries out finish to gauge, to The steel plate of the thickness with the following table 2 is obtained, is then cooled down by multi-step and implements to cool down with various cooling velocities.At this point, first The cooling cooling end temp of step is the Bs temperature of each steel.
Microstructure, yield strength, tensile strength, yield tensile ratio, Charpy impact transformation temperature are carried out to the steel plate so manufactured Degree, ammonia cause stress corrosion cracking (SCC) to test, and the results are shown in table 3.
For microstructure, mirror ultrafinish is carried out after acquiring sample from the 1/4t of steel plate, then utilizes Nital corrosive liquids Corroded, after recycling optical microphotograph sem observation, phase fraction is found out by image analysis.
For the score of MA phases, mirror ultrafinish is carried out after acquiring sample from 1/4t, then utilize LePera corrosive liquids into Row corrosion finds out phase fraction after recycling optical microphotograph sem observation by image analysis.
For tension test, JIS4 samples are acquired along perpendicular to the direction of rolling direction from the 1/4t of steel plate, and Implement tension test under room temperature, thus determines yield strength, tensile strength, yield tensile ratio.
For low-temperature impact toughness, sample is acquired along perpendicular to the direction of rolling direction from the 1/4t of steel plate, and V is made After type notched specimen, Charpy-type tests are carried out with 20 DEG C of intervals at -20 DEG C~-100 DEG C, each humid test 3 times, then The regression equation for exporting each temperature averages finds out the temperature for reaching 100J as transition temperature.
In addition, causing stress corrosion cracking (SCC) to test ammonia, NOL ring (proof ring) sample is made, and with table 4 Shown in testing liquid and experimental condition tested, for the stress applied at this time, be actually applied with 80% surrender Stress, if being evaluated as qualification without being broken in 720 hours, if be broken before 720 hours, being evaluated as It is unqualified.
【Table 1】
【Table 2】
【Table 3】
In upper table 3, AF, B, PF and MA indicate acicular ferrite (AF：Acicular Ferrite), bainite (B： Bainite), polygonal ferrite (PF：Polygonal ferrite) and martensite-austenite (MA：Martensite/ Austenite)。
【Table 4】
As shown in upper table 1 to 3, for meeting the example of the component and manufacturing condition that are proposed in the present invention, not only have The characteristic of high intensity and high tenacity, and anti-ammonia causes stress corrosion cracking (SCC:Stress Corrosion Cracking) property Excellent, yield tensile ratio, which is less than or equal to 0.8, has low yield strength ratio characteristic.In addition, to the micro- sem observation microstructures of example A-1 As a result, it includes the acicular ferrite for being more than or equal to 60% that the microstructure as shown in the 1- (2) of Fig. 1, which is in terms of area %, (Acicular Ferrite), bainite (Bainite), polygonal ferrite (Polygonal Ferrite), the MA of surplus The line and staff control of at least one of (martensite-austenite constituent).
In contrast, although component meets the present invention, manufacturing condition does not meet the comparative example A -2 of the present invention, A- 4, A-6, B-2, B-4 and B-6 cannot since the score of polygonal ferrite is excessively high or ferrite grain size is excessively coarse Ensure tensile strength and low-temperature flexibility.
In addition, comparative example A -3, A-5, A-7 or B-3, B-5, B-7, since acicular ferrite crystallite dimension is too small or shellfish The score of family name's body is excessively high or basic without generating MA phases, causes to be more than that may cause ammonia to cause bending for stress corrosion cracking (SCC) Upper intensity limit (440MPa) is taken, causes stress corrosion cracking to which ammonia occur, and cannot ensure low yield strength ratio and low-temperature flexibility.
In addition, although manufacturing condition meets the present invention, component does not meet the comparative example C-1 to F-1 of the present invention, by In the excessively high either acicular ferrite crystallite dimension of the score of bainite is too small or the score of MA phases is excessively high, cause to be more than that may draw The yield strength upper limit (440MPa) that ammonia causes stress corrosion cracking (SCC) is sent out, causes stress corrosion cracking to which ammonia occur, and not It can ensure that low yield strength ratio and low-temperature flexibility.
The present invention is described above with reference to embodiment, but in the technology without departing from the present invention described in claim In the range of design and field, those of ordinary skill in the art can be with various modification can be adapted and change.

Claims (12)

1. the low yield strength ratio high strength steel of a kind of resisting stress corrosion cracking and excellent in low temperature toughness, includes in terms of weight % Following component：
Carbon (C)：0.02%~0.10%, manganese (Mn)：0.5%~2.0%, silicon (Si)：0.05%~0.5%, nickel (Ni)： 0.05%~1.0%, titanium (Ti)：0.005%~0.1%, aluminium (Al)：0.005%~0.5%, niobium (Nb)：It is less than or equal to 0.005%, phosphorus (P)：Less than or equal to 0.015%, sulphur (S)：Less than or equal to the Fe of 0.015%, surplus and other inevitably Impurity,
Microstructure is in terms of area % comprising more than or equal to 60% acicular ferrite, the bainite of surplus, polygonal ferrite, horse At least one of family name's body-austenite constituent element.
2. the low yield strength ratio high strength steel of resisting stress corrosion cracking according to claim 1 and excellent in low temperature toughness, It is characterized in that：
The acicular ferrite is less than or equal to 30 μm with the size that equivalent diameter measures.
3. the low yield strength ratio high strength steel of resisting stress corrosion cracking according to claim 1 and excellent in low temperature toughness, It is characterized in that：
The bainite is less than or equal to 30 area %.
4. the low yield strength ratio high strength steel of resisting stress corrosion cracking according to claim 1 and excellent in low temperature toughness, It is characterized in that：
The martensite-austenite is mutually less than or equal to 10 area % and is less than or equal to 5 μm with the size that equivalent diameter measures.
5. the low yield strength ratio high strength steel of resisting stress corrosion cracking according to claim 1 and excellent in low temperature toughness, It is characterized in that：
The yield tensile ratio of the steel is less than or equal to 0.85, and tensile strength is more than or equal to 490MPa.
6. the low yield strength ratio high strength steel of resisting stress corrosion cracking according to claim 1 and excellent in low temperature toughness, It is characterized in that：
The yield strength of the steel is less than or equal to 440MPa.
7. the low yield strength ratio high strength steel of resisting stress corrosion cracking according to claim 1 and excellent in low temperature toughness, It is characterized in that：
The impact transition temperature of the steel is less than or equal to -60 DEG C.
8. a kind of manufacturing method of the low yield strength ratio high strength steel of resisting stress corrosion cracking and excellent in low temperature toughness, it includes Following steps：
By heating steel billet to 1000 DEG C~1200 DEG C, the steel billet includes following component in terms of weight %：Carbon (C)：0.02%~ 0.10%, manganese (Mn)：0.5%~2.0%, silicon (Si)：0.05%~0.5%, nickel (Ni)：0.05%~1.0%, titanium (Ti)： 0.005%~0.1%, aluminium (Al)：0.005%~0.5%, niobium (Nb)：Less than or equal to 0.005%, phosphorus (P)：It is less than or equal to 0.015%, sulphur (S)：Less than or equal to the Fe of 0.015%, surplus and other inevitable impurity；
Roughing is carried out at a temperature of 1100 DEG C~900 DEG C to the steel billet after heating；
Central part temperature is subject to after the roughing in Ar3+ 100 DEG C~Ar3Finish to gauge is carried out at a temperature of+30 DEG C；And
The finish to gauge postcooling to less than the temperature equal to 300 DEG C.
9. the low yield strength ratio high strength steel of resisting stress corrosion cracking according to claim 8 and excellent in low temperature toughness Manufacturing method, it is characterised in that：
For implementing the step of the cooling, cold more than or equal to the first step is implemented in a manner of 15 DEG C/s by central part cooling velocity But until Bs-10 DEG C~Bs+10 DEG C after,
Implement in such a way that central part cooling velocity is 10 DEG C/s~50 DEG C/s until second step is cooled to less than or equal to 300 DEG C.
10. the low yield strength ratio high strength steel of resisting stress corrosion cracking according to claim 8 and excellent in low temperature toughness Manufacturing method, it is characterised in that：
The beginning of cooling temperature is Ar3+ 30 DEG C~Ar3。
11. the low yield strength ratio high strength steel of resisting stress corrosion cracking according to claim 8 and excellent in low temperature toughness Manufacturing method, it is characterised in that：
The roughing is implemented in such a way that last three every time reduction ratios are more than or equal to 10%.
12. the low yield strength ratio high strength steel of resisting stress corrosion cracking according to claim 8 and excellent in low temperature toughness Manufacturing method, it is characterised in that：
The finish to gauge is implemented in such a way that every time reduction ratio is more than or equal to 10% and accumulation reduction ratio is more than or equal to 60%.
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