CN102690997A - Ferritic stainless steel and method of manufacturing the same - Google Patents

Ferritic stainless steel and method of manufacturing the same Download PDF

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Publication number
CN102690997A
CN102690997A CN2011104220308A CN201110422030A CN102690997A CN 102690997 A CN102690997 A CN 102690997A CN 2011104220308 A CN2011104220308 A CN 2011104220308A CN 201110422030 A CN201110422030 A CN 201110422030A CN 102690997 A CN102690997 A CN 102690997A
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equal
stainless steel
smaller
ferritic stainless
temperature
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金相锡
柳度烈
徐辅晟
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Posco Holdings Inc
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Posco Co Ltd
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Priority claimed from KR1020110027104A external-priority patent/KR20120108785A/en
Priority claimed from KR1020110027105A external-priority patent/KR20120108786A/en
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Publication of CN102690997A publication Critical patent/CN102690997A/en
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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/22—Ferrous alloys, e.g. steel alloys containing chromium with molybdenum or tungsten
    • 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
    • C21D6/002—Heat treatment of ferrous alloys containing Cr
    • 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
    • C21D8/0273—Final recrystallisation annealing
    • 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
    • C21D8/04—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing
    • C21D8/0447—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing characterised by the heat treatment
    • C21D8/0473—Final recrystallisation annealing
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—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
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/26—Ferrous alloys, e.g. steel alloys containing chromium with niobium or tantalum
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/28—Ferrous alloys, e.g. steel alloys containing chromium with 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
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/005—Ferrite

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

Abstract

The present disclosure relates to a ferritic stainless steel and fabrication method of a ferritic stainless steel comprising, by weight %, C: above 0 wt % to 0.01 wt % or less, Si: above 0 wt % to 0.5 wt % or less, Mn: above 0 wt % to 2.0 wt % or less, P: 0 wt % or more to 0.04 wt % or less, S: 0 wt % or more to 0.02 wt % or less, Cr: 12 wt % or more to 19 wt % or less, Mo: 0 wt % or more to 1.0 wt % or less, W: 2 wt % of more to 7 wt % or less, Ti: 0 wt % or more to 0.3 wt % or less, Nb: above 0 wt % to 0.6 wt % or less, N: above 0 wt % to 0.01 wt % or less, Al: 0 wt % or more to 0.1 wt % or less; and the balance of Fe and other inevitable impurities.

Description

Ferritic stainless steel and method of manufacture thereof with excellent high-temperature intensity
Technical field
The present invention relates to be used for the ferritic stainless steel with excellent high-temperature character and formability of the exhaust manifold of vehicle; Specifically, the content through the control alloying element has the ferritic stainless steel of good high-temperature oxidation, high temperature resistant salt damage corrodibility, hot strength, thermal fatigue character and formability and the method for making this ferritic stainless steel.
Background technology
Recently, implemented law, resisted because the serious environmental problem that the waste gas of vehicle causes about discharging toxic substance in waste gas in many countries.Consider this trend, the technology of utilizing catalyzer to improve the effect of waste-gas cleaning has become focus.Temperature is high more, NO x, HC and CO the purification reaction increase manyly more.Therefore, in order to reduce the discharging of pollutent, the temperature that improves constantly waste gas has become a kind of trend, therefore, needs to improve the hot properties of the parts that constitute the exhaust system of controlling waste gas strongly.
Exhaust manifold is to collect waste gas and discharge the exhaust to the parts of vapor pipe from the cylinder of mover.Usually, because the temperature of waste gas is up to 900 ℃, so exhaust manifold is the parts that need good scale resistance, hot strength and thermal fatigue character.In the prior art, although use the material of spheroidal graphite cast iron as exhaust manifold usually, the demand according to the decline of the raising of spent air temp and component weight replaces spheroidal graphite cast iron with ferritic stainless steel.In addition, recently, compare,, increase by 30 ℃ to 50 ℃ so estimate the temperature of waste gas because the size of turbo-supercharger being installed and having reduced mover improves the fuel efficiency of vehicle with existing vehicle.
Therefore, the trade mark that is used for exhaust manifold of the prior art is the quality product requirement that 429EM, 441 and 444 ferritic stainless steel can not satisfy the human consumer, has therefore carried out the various researchs about the ferritic stainless steel with improved high-temperature behavior.
Summary of the invention
It is a kind of through preventing to produce the ferritic stainless steel that σ improves high temperature durability mutually that the present invention is devoted to provide.
In addition, the present invention is devoted to provide a kind of ferritic stainless steel with predetermined high-tensile and good formability.
In addition, the present invention is devoted to provide a kind of method of manufacture of having improved the ferritic stainless steel of high temperature durability.
In addition, the present invention be devoted to provide a kind of through reducing expensive element addition and replace expensive unit usually to reduce the ferritic stainless steel of manufacturing cost with cheap element.
The present invention is devoted to provide the ferritic stainless steel with excellent high-temperature intensity, and said ferritic stainless steel comprises by weight percentage: C, greater than 0wt% and smaller or equal to 0.01wt%; Si is greater than 0wt% and smaller or equal to 0.5wt%; Mn is greater than 0wt% and smaller or equal to 2.0wt%; S is more than or equal to 0wt% and smaller or equal to 0.02wt%; Cr is more than or equal to 12wt% and smaller or equal to 19wt%; Mo is more than or equal to 0wt% and smaller or equal to 1.0wt%; W is more than or equal to 2wt% and smaller or equal to 7wt%; Ti is more than or equal to 0wt% and smaller or equal to 0.3wt%; Nb is greater than 0wt% and smaller or equal to 0.6wt%; N is greater than 0wt% and smaller or equal to 0.01wt%; Al is more than or equal to 0wt% and smaller or equal to 0.01wt%; The Fe of surplus and other unavoidable impurities.
In addition, the thermal annealing tissue of ferritic stainless steel comprises that ratio is 5% or is lower than 5% σ phase.
By weight percentage, W can be more than or equal to 3wt% and smaller or equal to 6wt%.
By weight percentage, Mo+0.83W can be more than or equal to 3.5wt% and smaller or equal to 5.0wt%.
In addition, [(Ti+1/2Nb)/(C+N)] can be more than or equal to 19.5 and smaller or equal to 32.
According to aforesaid the present invention, through preventing to produce the σ phase, can provide to have the ferritic stainless steel of improved opposing pyritous structure.
In addition, according to the present invention, formability that keeps high and the ferritic stainless steel with good formability can be provided.
Another embodiment of the present invention is devoted to provide a kind of method of manufacture with ferritic stainless steel of excellent high-temperature intensity; Said method of manufacture is with the ductile-brittle transition temperature that satisfies equation of ferritic stainless steel (DBTT (℃)) be controlled to be 90 ℃ or be lower than 90 ℃; Ferritic stainless steel comprises by weight percentage: C, greater than 0wt% and smaller or equal to 0.01wt%; Si is greater than 0wt% and smaller or equal to 0.5wt%; Mn is greater than 0wt% and smaller or equal to 2.0wt%; S is more than or equal to 0wt% and smaller or equal to 0.02wt%; Cr is more than or equal to 12wt% and smaller or equal to 19wt%; Mo is more than or equal to 0wt% and smaller or equal to 0.8wt%; Ti is more than or equal to 0wt% and smaller or equal to 0.3wt%; Nb is greater than 0wt% and smaller or equal to 0.6wt%; N is greater than 0wt% and smaller or equal to 0.01wt%; Al, more than or equal to 0wt% and smaller or equal to 0.01wt%, the Fe of surplus and other unavoidable impurities; Wherein, The value of Mo+0.83W is more than or equal to 3.5wt% and smaller or equal to 5wt%, and [(Ti+1/2Nb)/(C+N)] is more than or equal to 19.5 and smaller or equal to 32
DBTT(℃)＝-184.6+3.2(Crwt％)+27.5(Mowt％)+4243.4(Cwt％+Nwt％)-295.6(Al?wt％)+0.9[Nb?wt％/(C?wt％+N?wt％)]。
The method of manufacture of ferritic stainless steel can may further comprise the steps: the step of heating base; Thermal anneal step; Cold annealing steps; Cold rolling step under the room temperature, wherein, the step of heating base has more than or equal to 1180 ℃ and smaller or equal to 1240 ℃ base Heating temperature.
To the plate temperature, thermal anneal step can have more than or equal to 1020 ℃ and smaller or equal to 1070 ℃ thermal annealing temperature.
In addition, the grain-size of ferritic stainless steel can be that ASTM No.3.0 is perhaps greater than ASTMNo.3.0.
To the plate temperature, cold annealing steps can have more than or equal to 1030 ℃ and smaller or equal to 1080 ℃ cold annealing temperature.
About the thermal annealing temperature of thermal anneal step and the cold annealing temperature of cold annealing steps, (cold annealing temperature)/(thermal annealing temperature) can be more than or equal to 1.0 and smaller or equal to 1.1.
According to aforesaid the present invention, through preventing to produce the σ phase, can provide to have the ferritic stainless steel of improved opposing pyritous structure.
In addition, according to the present invention, formability that keeps high and the ferritic stainless steel with good formability can be provided.
In addition, according to aforesaid the present invention, a kind of method of manufacture with ferritic stainless steel of improved weather resistance can be provided.
In addition, according to the present invention, a kind of method of manufacture that has reduced the ferritic stainless steel of manufacturing cost can be provided.
Description of drawings
Fig. 1 illustrates Mo and the W figure to the test result of the influence of hot strength.
Fig. 2 A is the optical microscope photograph of thermal annealing tissue that has added the steel of Mo.
Fig. 2 B is the optical microscope photograph of thermal annealing tissue that has added the steel of Mo+W.
Fig. 3 is the figure of test according to the thermal fatigue character of the ferritic stainless steel of the addition of Mo and W.
Fig. 4 is the figure of test according to the high-temperature oxidation of the ferritic stainless steel of the addition of Mo and W.
Fig. 5 is the high temperature resistant salt damage corrosive figure of test according to the ferritic stainless steel of the addition of Mo and W.
Fig. 6 is the schema of the method for manufacture of schematically illustrated ferritic stainless steel according to the preferred embodiment of the invention.
Fig. 7 is the figure that illustrates according to the grain-size of the ferritic stainless steel of base Heating temperature.
Fig. 8 is the average r-bar value according to the ferritic stainless steel of base Heating temperature.
Fig. 9 is the figure that illustrates according to the average r-bar value of the thermal annealing temperature in the thermal annealing process.
Figure 10 is the figure that illustrates according to the high temperature tensile strength of the cold annealing temperature in the cold annealing process.
Figure 11 is the figure that illustrates according to the average r-bar value of cold annealing temperature/thermal annealing temperature.
Figure 12 is the figure that illustrates according to the high temperature tensile strength of cold annealing temperature/thermal annealing temperature.
Embodiment
The details of other embodiment is included in the detailed specification sheets and accompanying drawing.
From the exemplary embodiment of describing in detail with reference to the accompanying drawings, advantage of the present invention and characteristic and realize that the method for these advantages and characteristic will be clearly.Yet, the embodiment that the invention is not restricted to describe below, and embodiment of the present invention in every way.In addition, parts and the direct connection that comprises parts being connected of another parts and have the electrical connection of the parts under the situation of other devices between the parts.In addition, clear in order to make description of the invention, removed the parts that have nothing to do with the present invention, and in whole specification sheets, the designated identical label of identical assembly.
Hereinafter, illustrate and describe the present invention.
Ferritic stainless steel has excellent high-temperature intensity according to the preferred embodiment of the invention, and comprises by weight percentage: C, greater than 0wt% and smaller or equal to 0.01wt%; Si is greater than 0wt% and smaller or equal to 0.5wt%; Mn is greater than 0wt% and smaller or equal to 2.0wt%; S is more than or equal to 0wt% and smaller or equal to 0.02wt%; Cr is more than or equal to 12wt% and smaller or equal to 19wt%; Mo is more than or equal to 0wt% and smaller or equal to 1.0wt%; W is more than or equal to 2wt% and smaller or equal to 7wt%; Ti is more than or equal to 0wt% and smaller or equal to 0.3wt%; Nb is greater than 0wt% and smaller or equal to 0.6wt%; N is greater than 0wt% and smaller or equal to 0.01wt%; Al is more than or equal to 0wt% and smaller or equal to 0.01wt%; The Fe of surplus and other unavoidable impurities.
Have the method for manufacture of the ferritic stainless steel of excellent high-temperature intensity according to the preferred embodiment of the invention, in ferritic stainless steel, comprise by weight percentage: C, greater than 0wt% and smaller or equal to 0.01wt%; Si is greater than 0wt% and smaller or equal to 0.5wt%; Mn is greater than 0wt% and smaller or equal to 2.0wt%; S is more than or equal to 0wt% and smaller or equal to 0.02wt%; Cr is more than or equal to 12wt% and smaller or equal to 19wt%; Mo is more than or equal to 0wt% and smaller or equal to 1.0wt%; Ti is more than or equal to 0wt% and smaller or equal to 0.3wt%; Nb is greater than 0wt% and smaller or equal to 0.6wt%; N is greater than 0wt% and smaller or equal to 0.01wt%; Al; More than or equal to 0wt% and smaller or equal to 0.01wt%; The Fe of surplus and other unavoidable impurities, wherein, the value of Mo+0.83W is more than or equal to 3.5wt% and smaller or equal to 5wt%; [(Ti+1/2Nb)/(C+N)] more than or equal to 19.5 and smaller or equal to 32, ductile-brittle transition temperature (DBTT (℃)) can be controlled at 90 ℃ or be lower than 90 ℃.
DBTT(℃)＝-184.6+3.2(Crwt％)+27.5(Mowt％)+4243.4(Cwt％+Nwt％)-295.6(Alwt％)+0.9[Nbwt％/(Cwt％+Nwt％)]。
In addition, the method for manufacture of ferritic stainless steel can comprise heating base (S1), thermal annealing (S2), cold annealing (S3) and at room temperature cold rolling (S4), and the step that heats base has more than or equal to 1180 ℃ and smaller or equal to 1240 ℃ base Heating temperature.
Ferritic stainless steel constructed in accordance has good high-temperature oxidation, high temperature resistant salt damage corrodibility, hot strength, thermal fatigue character and formability.These character can receive the influence of the addition of the element that comprises in the ferritic stainless steel and element.Hereinafter, the components system that constitutes ferritic stainless steel of the present invention is described in more detail.Following components system is represented with weight percent (wt%).
In ferritic stainless steel, C can be greater than 0wt% and smaller or equal to 0.01wt%.Because C can increase the room temperature strength of ferritic stainless steel, so can add the C greater than 0wt%.On the contrary, when the addition of C during greater than 0.01wt%, the room temperature strength of ferritic stainless steel increases, and the decline relatively of hot strength and ductility, mechanical workability and room temperature toughness.Therefore, preferably, add greater than 0wt% and smaller or equal to the C of 0.01wt%.More preferably, can add 0.005wt% or less than the C of 0.005wt%.
Can comprise greater than 0wt% and smaller or equal to the Si of 0.5wt%.Si is the element as the reductor of the ferritic stainless steel of molten metal attitude, and Si is essential in process for making.In addition, Si can be favourable aspect the scale resistance that improves ferritic stainless steel.On the contrary, when the Si that adds greater than 0.5wt%, because the solid solution hardening of Si and can increase the hardness of ferritic stainless steel, so the ductility of ferritic stainless steel and mechanical workability descend.
Can comprise greater than 0wt% and smaller or equal to the Mn of 2.0wt%.When ferritic stainless steel during, at high temperature can produce scale as the material of the exhaust manifold of vehicle.In this case, the scale of generation can easily separate, and isolating scale can flow into catalyst and stop the passage of catalyst.Therefore, ferritic stainless steel must have the anti-separation property to scale, thereby ferritic stainless steel can comprise and is used for anti-Mn separatory.On the other hand, when the addition of Mn during, can produce MnS owing to the reaction of Mn and S greater than 2.0wt%.MnS can have a negative impact to the erosion resistance of ferritic stainless steel, therefore, preferably, comprises greater than 0wt% and smaller or equal to the Mn of 2.0wt%.
Although P can increase the intensity of ferritic stainless steel, P can reduce mechanical workability.In addition, it has been generally acknowledged that P is the impurity in the process for making of ferritic stainless steel, preferably reduces P as far as possible.On the other hand, aspect refining cost or productivity, in technology, exceedingly reducing P is poor efficiency, therefore preferably, comprises the P that is no more than 0.02wt%.
Can comprise more than or equal to 0wt% and smaller or equal to the S of 0.02wt%.S can be used as the inclusion in the ferritic stainless steel and exists, and perhaps can be used as the impurity that reduces erosion resistance.Therefore, although preferably reduce the addition of S as much as possible, to improve the erosion resistance of ferritic stainless steel, aspect cost and time, in technology, exceedingly reducing S can be poor efficiency.Therefore, the addition of preferably controlling S is 0.02wt% or is lower than 0.02wt%, and the addition of S is controlled at 0.003wt% or is lower than 0.003wt% possibly be preferred especially.
Can comprise more than or equal to 12wt% and smaller or equal to the Cr of 19wt%.Cr is for the erosion resistance that improves ferritic stainless steel and scale resistance and the alloying element that must add.That is,, so can comprise 12wt% or greater than the Cr of 12wt% because ferritic stainless steel is difficult to have enough erosion resistances when the addition of Cr is low.On the other hand, when the addition of Cr during greater than 19wt%, the erosion resistance of ferritic stainless steel is improved, and intensity excessively increases, and ductility and shock feature can significantly descend like this.Therefore, preferably, in ferritic stainless steel, comprise more than or equal to 12wt% and smaller or equal to the Cr of 19wt%.
Can comprise more than or equal to 0wt% and smaller or equal to the Ti of 0.3wt%.Ti is for the hot strength that improves ferritic stainless steel and intergranular corrosion resistance property and the alloying element that adds.When the addition of the Ti in the ferritic stainless steel during greater than 0.3wt%, the steel-making inclusion increases, and can produce the surface imperfection that for example scabs continually, and the mouth of a river can be blocked in casting process, therefore can reduce process efficiency.In addition, along with the increase of sosoloid Ti, the ductility of ferritic stainless steel and low temperature impact properties can descend.In addition, when interpolation Nb and Ti and this ferritic stainless steel at high temperature used for a long time in ferritic stainless steel, the Fe3Nb3C carbide can be separated out, and roughening can occur, therefore can cause the high temperature deterioration.Therefore, in the present invention, the addition of Ti can or be lower than 0.3wt% for 0.3wt%.
The addition of N can be greater than 0wt% and smaller or equal to 0.01wt%.Although similar with C, N increases the intensity of ferritic stainless steel, and N can reduce ductility and mechanical workability.Specifically, preferably, comprise greater than 0wt% and smaller or equal to the N of 0.01wt%, to ensure the sufficient ductility and the mechanical workability of welding portion.Can particularly preferably be the N that comprises 0.007wt% or be lower than 0.007wt%.
In ferritic stainless steel, the addition of Mo can be more than or equal to 0wt% and smaller or equal to 1.0wt%.In addition, can particularly preferably be, Mo is 0.8wt% or is lower than 0.8wt%, and wherein, the thermal annealing tissue of ferritic stainless steel can comprise 5% or be lower than 5% σ phase ratio.Preferably, W can be for more than or equal to 2wt% and smaller or equal to 7wt%, more preferably, can comprise more than or equal to 3wt% and smaller or equal to the W of 6wt%.
For the hot strength of ferritic stainless steel, various researchs and the effort of Mo have been carried out for example adding.In adding the method for Mo,, produce the ferritic stainless steel of σ phase when the Mo that adds in the ferritic stainless steel is 3wt% or during greater than 3wt%.σ not only can cause mutually making the defective in the process of ferritic stainless steel, and can cause the endurance issues when this ferritic stainless steel being used for the exhaust manifold of vehicle.Through reducing, can prevent to produce the σ phase according to the Mo in the ferritic stainless steel of the present invention.In addition, in ferritic stainless steel according to the present invention, the addition of Mo can be for 1wt% or less than 1wt%, to guarantee hot strength.
Can be particularly preferably, the addition of Mo is 0.8wt% or is lower than 0.8wt%.In the process for making of ferritic stainless steel, because with extensive execution process for making, so be not easy amount of substance is controlled in the very little rank, the effort of therefore carrying out for the amount of controlling Mo possibly be a poor efficiency.On the other hand, aspect the reduction manufacturing cost, because for example the element of Mo is expensive starting material, the addition of therefore accurately controlling Mo possibly be favourable.Therefore, can be controlled at 0.8wt% through addition or be lower than character and the raising process efficiency that 0.8wt% keeps ferritic stainless steel Mo.
When the addition of W during less than 2wt%, for example the amount of the sosoloid of the growing amount of the meticulous precipitate of the nano-scale of Fe2W and the W in the matrix reduces, and therefore is difficult to provide the ferritic stainless steel with enough hot strengths and thermal fatigue character.In addition, when the addition of W during greater than 7wt%, the material cost of ferritic stainless steel can increase, and in ferritic stainless steel, produces a large amount of Fe2W, and this is unfavorable and reduce production efficiency to logistics, and can reduce weldability and formability.Through further comprising W, this ferritic stainless steel demonstrates 40MPa or greater than the tensile strength of 40MPa in 900 ℃ high temperature tensile test, so this ferritic stainless steel need can be used to the exhaust manifold of the high strength vehicle under the high temperature.
When the addition of Mo is 0.8wt% or when being lower than 0.8wt%, in order to ensure high-temperature oxidation, high temperature resistant salt damage corrodibility, hot strength and thermal fatigue character, this ferritic stainless steel can also comprise W.Consider the influence to the hot strength of ferritic stainless steel, the elements Mo and the relation between the W of two kinds of interpolations can be expressed as: Mo+0.83W is more than or equal to 3.5wt% and smaller or equal to 5.0wt%.As Mo+0.83W during less than 3.5wt%; The character of ferritic stainless steel (hot strength, high temperature fatigue life-span, high-temperature oxidation and high temperature resistant salt damage corrodibility) can descend; And as Mo+0.83W during greater than 5.0wt%; High temperature properties is good, but descends as the ductility of the factor of room temperature mechanical workability, and the toughness of welding portion and fertile material also can descend.
Ferritic stainless steel can comprise more than or equal to 3.5wt% and smaller or equal to the Mo+0.83W of 5.0wt%.For Mo that comprises in the ferritic stainless steel and W,, be difficult to be provided for the ferritic stainless steel with enough hot strengths and thermal fatigue character of the exhaust manifold of vehicle when the value of Mo+0.83W during less than 3.5wt%.That is, comprise Mo+0.83W in the ferritic stainless steel, be 900 ℃ or be lower than 900 ℃ by the maximum usable temp of the exhaust manifold of the vehicle of this ferritic stainless steel manufacturing, so this ferritic stainless steel is unavailable under higher temperature less than 3.5wt%.In addition,, in the logistics progress of ferritic stainless steel, have problems, so productivity descends, and formability and weldability also can descend when the value of Mo+0.83W during greater than 5.0wt%.
In ferritic stainless steel, Ti can be more than or equal to 0wt% and smaller or equal to 0.3wt%, and Nb can be greater than 0wt% and smaller or equal to 0.6wt%, and N can be greater than 0wt% and smaller or equal to 0.01wt%, and Al can be for 0.01wt% or less than 0.01wt%.In this structure, the relation between the element [(Ti+1/2Nb)/(C+N)] can be more than or equal to 19.5 and smaller or equal to 32.
The Ti and the Nb that should add predetermined amount are with hot strength and the thermal fatigue character of guaranteeing ferritic stainless steel.When the addition of Ti and Nb is predeterminated level when following, receiving welding heat affected part grain attack can occur, perhaps hot strength and thermal fatigue character can descend.Therefore, can control the addition of Ti and Nb, thereby add 19.5 or greater than 19.5 (Ti+1/2Nb)/(C+N).On the other hand, when (Ti+1/2Nb)/(C+N) greater than 32 the time, can be favourable aspect the high temperature properties of ferritic stainless steel, the addition of sosoloid Nb excessively increases, and causes room temperature ductility, toughness and mechanical workability to descend.Therefore, can comprise more than or equal to 19.5 and smaller or equal to 32 [(Ti+1/2Nb)/(C+N)].
Hereinafter, describe the present invention, with for easily the present invention will be described, and the invention is not restricted to following embodiment and comparative example with reference to embodiment and comparative example.
1. the preparation of sample
Table 1 shows the chemical composition of the sample that uses among embodiment and the comparative example.With reference to table 1, embodiment and comparative example comprise the Fe-15wt%Cr as essentially consist, the addition through changing Mo, W and Nb and (Ti+1/2Nb)/(C+N) make ferritic stainless steel.Adopt the local thermal annealing of carrying out of 20mmt and 5mmt, and make the coiled material and sample that thickness is 2.0mm with 20mmt bar through thermal anneal process and cooling and annealing process.The sample of making as stated is that embodiment 1 to embodiment 7 and comparative example 1 in the table 1 is to comparative example 4.
(table 1)
Figure DEST_PATH_GSB00000799345300091
2. the performance test of ferritic stainless steel under room temperature and the high temperature
As shown in table 1; Carry out room temperature tensile test and high temperature tensile test; And for the embodiment 1 to embodiment 7 that checks manufacturing as shown in table 1 and comparative example 1 to the high temperature properties of comparative example 4 component, at high temperature carry out the corrosive test of thermal fatigue life, scale resistance and salt tolerant.
At first, make the thermal fatigue sample through processing according to the sample of table 1.Through utilizing the thermal fatigue sample of making as stated, in 200 ℃～900 ℃ TR and 0.3 constraint factor test thermal fatigue life.In addition, 1000 ℃ with embodiment 1 to embodiment 7 and comparative example 1 to comparative example's 4 heating 200 hours, with the test scale resistance.Clean and remove with acid after, measure weight change and inspection high-temperature oxidation through the oxidation scale that adds thermogenesis.The NaCl solution of employing 26% is tested salt tolerant evil corrodibility.Will according to embodiment 1 to embodiment 7 and comparative example 1 to comparative example 4 sample after 500 ℃ keep 2 hours; NaCl solution impregnation sample with 26% 5 minutes; So carry out 10 times, measure alleviating of weight then, and test high temperature resistant salt damage corrodibility.
Following table 2 shows the test result according to the embodiment and the comparative example of table 1, and room temperature tensile strength, r-bar value, thermal fatigue life, high-temperature oxidation and the corrosive value of high temperature resistant salt damage have been shown in the table 2.
(table 2)
Figure DEST_PATH_GSB00000799345300101
With reference to table 1 and table 2, can find out, to comparative example 4, be prone to the room temperature tensile strength and all satisfied expected value of being scheduled to of r-bar value of the factor of plasticity embodiment 1 to embodiment 7 and comparative example 1 as assessment.On the other hand; Can find out; Although the needed predetermined expected value of exhaust manifold that in embodiment 1 to embodiment 7, satisfies vehicle as high temperature tensile strength, thermal fatigue life, high-temperature oxidation and the high temperature resistant salt damage corrodibility of factor of test high-temperature behavior; But to comparative example 4, above-mentioned test event does not satisfy the needed predetermined expected value of exhaust manifold of vehicle comparative example 1.
It is 0.8wt% or the Mo that is lower than 0.8wt% that all embodiment 1 to embodiment 7 according to the present invention comprise addition.In addition, all embodiment 1 to embodiment 7 comprise more than or equal to 3wt% and smaller or equal to the W of 6wt%.In this case, can find out,, show 41MPa or higher intensity, the needed high temperature tensile strength of the material that this high temperature tensile strength satisfies exhaust manifold in the high temperature tensile strength of 900 ℃ of tests although steel has added the Mo that is lower than common addition.In addition, can find out, good as the room temperature tensile strength and the r-bar value of the project of the formability that can test ferritic stainless steel in an embodiment of the present invention, respectively more than or equal to 31% with more than or equal to 0.9.In addition, can find out that be respectively 2250,2260,1860,2520 according to the thermal fatigue life of embodiments of the invention 1～3 and embodiment 5, all these satisfies 188 circulations or more circulation.
In the high temperature oxidation resisting property testing of embodiment 1 to embodiment 7, can find out that weight change is 10.56mg/cm to the maximum 2(embodiment 6), minimum is 7.8mg/cm 2(embodiment 5).On the other hand, can find out, in the comparative example 2 of comparative example 1 to the comparative example 4 and comparative example 3, scale occur and separated.
For high temperature resistant salt damage corrodibility, can find out, in embodiment 1 to embodiment 7, be 2.996g/mm to the maximum 2, weight drops to 3g/mm 2, and comparative example 1 to comparative example 4, be 20.2g/mm to the maximum 2, minimum is 14.378g/mm 2(comparative example 4) promptly, are compared with embodiment, and weight descends obviously to be increased.
Promptly; According to test result; Can find out; Room temperature ductility and r-bar value as the character of room temperature formability have illustrated the basic value that equates in embodiment and comparative example, and compare with embodiment, descend as thermal fatigue character, high-temperature oxidation, the high temperature resistant salt damage corrodibility of high temperature properties.Say that at length for the high-temperature oxidation among the embodiment 1 to embodiment 7, weight change is 11mg/cm 2Perhaps less than 11mg/cm 2, all samples all satisfies high-temperature oxidation.On the other hand, for the comparative example, in comparative example 1 and comparative example 4, the condition that high-temperature oxidation does not meet the expectation in addition, is isolated scale in comparative example 2 and comparative example 3.In addition, about the high-temperature corrosion resistance property of testing repeatedly, can find out that in embodiment 1 to embodiment 7, weight drops to 3g/mm 2Or be lower than 3g/mm 2, and in the comparative example, weight descends and is 20.2g/mm to the maximum 2, so all four samples all do not satisfy high-temperature corrosion resistance property.
Can find out, except the room temperature formability, the character that all embodiment 1 to embodiment 7 according to the present invention all satisfy under the high temperature.Therefore, at high temperature be available according to ferritic stainless steel of the present invention, and formability also can satisfy predetermined condition.Therefore, can find out that embodiment can be used for the exhaust manifold of the vehicle of the accurate formability of needs.
Ferritic stainless steel according to the present invention comprises the starting material Mo of more a spot of costliness, and has the character that is applicable to exhaust manifold, therefore, can reduce manufacturing cost.On the other hand, in the comparative example of the said content that does not satisfy Mo and W, can find out, all character under the high temperature, promptly thermal fatigue life, high-temperature oxidation and high temperature resistant salt damage corrodibility all do not satisfy.
In addition; With reference to table 1 and table 2; Show through value and be controlled at more than or equal to 3.5% and smaller or equal to 5% with Mo+0.83W; And with the value of [(Ti+1/2Nb)/(C+N)] be controlled at more than or equal to 19.5 and the sample made smaller or equal to 32 satisfy the character that is necessary, this all is good because of high temperature properties and high temperature formability.
Fig. 1 illustrates Mo and the W figure to the test result of the influence of hot strength.
With reference to Fig. 1, by weight percentage, comprise C:0.005wt% in all cases; N:0.0006wt%; Cr:15wt%; Nb:0.4wt% and Ti:0.1wt%, and in the addition that changes Mo and W, test Mo and W influence to the hot strength of ferritic stainless steel.
At first, in order to test Mo and the W influence to hot strength, the steel of Mo and the addition of the steel that adds Mo+W are added in change, and test high temperature tensile strength down at 900 ℃.The addition of the addition that the X axle shows (add Mo steel) Mo perhaps (adds the steel of Mo+W) Mo+W, the Y axle shows high temperature tensile strength corresponding among the figure, and has obtained relational expression.Utilize regression equation to show the relation of the addition of Mo or Mo+W to the influence of hot strength.As a result, can obtain relational expression: 900 ℃ of following high temperature tensile strength (MPa)=22.4+4.67Mo+3.91W, therefore, can find out that W is 84% (W/Mo=3.91/4.67=0.84) to the percentage contribution of the influence of hot strength.
Fig. 2 A is the optical microscope photograph of thermal annealing tissue that adds the steel of Mo, and Fig. 2 B is the optical microscope photograph of thermal annealing tissue of the steel of interpolation Mo+W.
Fig. 2 A is the optical microscope photograph that the σ in the thermal annealing tissue of steel that adds Mo and the steel (corresponding respectively to Fig. 2 A and Fig. 2 B) that adds Mo+W is compared mutually with Fig. 2 B.Fig. 2 A shows the thermal annealing tissue of the ferritic stainless steel of the Mo that comprises 3wt%, in Fig. 2 A, can find out, in the thermal annealing tissue of ferritic stainless steel, the ratio of σ phase reaches 20%.In addition, Fig. 2 B shows the ferritic stainless steel of the W of the Mo that comprises 0.5wt% and 4.5wt%, can find out that in Fig. 2 B the ratio of the σ phase in the thermal annealing tissue of ferritic stainless steel is 5% or is lower than 5%.With reference to Fig. 2 A and Fig. 2 B, can find out, compare with the steel that adds Mo, in the steel that adds Mo+W, can the σ of thermal annealing tissue be controlled at lower ratio mutually.
Fig. 3 is the figure of test according to the thermal fatigue character of the ferritic stainless steel of the addition of Mo and W.
With reference to Fig. 3, can find out that compare with the comparative example, in an embodiment, the thermal fatigue life under 900 ℃ is good.That is, suppose that the X axle is the high temperature tensile strength under 900 ℃, the Y axle is the process circulation of thermal fatigue life, can find out that the value of embodiment all is arranged in the upper right side of figure, and comparative example's value is arranged in the left downside of figure.That is, can find out that good in 900 ℃ of following high temperature tensile strength and thermal fatigue life in an embodiment, and in the comparative example, 900 ℃ of following high temperature tensile strength and thermal fatigue life are low relatively.
Fig. 4 is the figure of test according to the high-temperature oxidation of the ferritic stainless steel of the addition of Mo and W.
With reference to Fig. 4, in the comparative example, have two of relatively little weight change and demonstrate and produced scale from the teeth outwards; And can find out, except above comparative example, in other comparative examples; Compare with embodiment, it is big that the result of high-temperature oxidation demonstrates weight change.That is, can find out that compare with the comparative example, embodiment demonstrates good high-temperature oxidation.
Fig. 5 is the high temperature resistant salt damage corrosive figure of test according to the ferritic stainless steel of the addition of Mo and W.
Fig. 5 is the figure that illustrates according to the corrosive test result of high temperature resistant salt damage with the corresponding weight change of the addition of Mo or Mo+W.Can find out that along with the addition increase of Mo or Mo+W, at about 3wt% place, weight change is 7.5g/cm 2Or be lower than 7.5g/cm 2, and when the addition of Mo or Mo+W be 2wt% or when being lower than 2wt%, weight change is 12.5g/cm 2Or greater than 12.5g/cm 2That is, can find out that the addition of Mo+W can influence the high temperature resistant salt damage corrodibility of ferritic stainless steel, when the addition of Mo+W is 3wt% rather than 2wt%, better simultaneously for the corrosive weight change of high temperature resistant salt damage.
(method of manufacture)
Fig. 6 is the schema of the method for manufacture of schematically illustrated ferritic stainless steel according to the preferred embodiment of the invention.
With reference to Fig. 6; Ferritic stainless steel of the present invention can comprise aforesaid material; And the present invention can comprise the method for manufacture of the ferritic stainless steel with excellent high-temperature intensity, and said method of manufacture comprises for the steel with above composition, cold rolling step (S4) under step (S1), thermal anneal step (S2), cold annealing steps (S3) and the room temperature of heating base; Wherein, the step of heating base has more than or equal to 1180 ℃ and smaller or equal to 1240 ℃ base Heating temperature.
As stated, can more than or equal to 1180 ℃ and smaller or equal to 1240 ℃ base Heating temperature under carry out the step (S1) of heating base.
When in the step (S1) of heating base, when Heating temperature is lower than 1180 ℃, in follow-up course of hot rolling, bond, that is, ferritic stainless steel is bonded on the roller, and the surface of ferritic stainless steel comes off.In addition, when the Heating temperature of base during greater than 1240 ℃, the grain-size of ferritic stainless steel increases, and therefore, toughness is understood decline with r-bar value.Therefore, can through with the heating and temperature control of base more than or equal to 1180 ℃ and to make the crystal grain of ferritic stainless steel smaller or equal to 1240 ℃ be fine size, can guarantee formability and mechanical workability through improving toughness and r-bar value like this.
In thermal anneal step (S2), to the plate temperature, the thermal annealing temperature can be more than or equal to 1020 ℃ and smaller or equal to 1070 ℃.
In thermal anneal step (S2), the thermal annealing temperature should be arranged in the scope of ferritic stainless steel at the annealing process recrystallize, preferably in the TR that recrystallize takes place, under alap temperature, carries out annealing simultaneously.The thermal annealing temperature is low more, and after thermal annealing, the recrystal grain of ferritic stainless steel possibly be embodied as fine size more, and therefore, the r-bar value that finally experiences cold annealed ferritic stainless steel can demonstrate excellent characteristic.That is, when in thermal anneal step (S2), when the thermal annealing temperature was lower than 1020 ℃, the recrystallize of ferritic stainless steel was insufficient, so formability and ductility can descend.In addition, when thermal annealing temperature during greater than 1070 ℃, after thermal annealing; The toughness of ferritic stainless steel descends; Thereby sheet material can rupture in ME, and the grain-size of the ferritic stainless steel after the perhaps cold annealing increases, and in forming process, the orange peel defective can occur.Therefore, can use more than or equal to 1020 ℃ and carry out toughness and the r-bar value that thermal anneal step (S2) improves ferritic stainless steel to the plate temperature smaller or equal to 1070 ℃ thermal annealing temperature.
The grain-size of ferritic stainless steel can be for ASTM No.3.0 or greater than ASTM No.3.0.Along with the increase of ASTM No. value, ferritic stainless steel has meticulousr grain-size.Therefore, because the ASTM No. value of grain-size is big more, the crystal grain of the fine size that provides is many more, so this can be preferred.When the grain-size of ferritic stainless steel during less than ASTM No.3.0, the grain-size of ferritic stainless steel increases, and therefore, it is frangible that ferritic stainless steel becomes in thermal annealing process, and can produce the for example defective of sheet material fracture.
In cold annealing steps (S3),, can make cold annealing temperature more than or equal to 1030 ℃ and smaller or equal to 1080 ℃ to the plate temperature.
In cold annealing steps (S3), when cold annealing temperature was lower than 1030 ℃, recrystallize can be insufficient in cold annealing process, so the ductility of ferritic stainless steel and formability can descend.In addition, when cold annealing temperature during greater than 1080 ℃, the grain-size of ferritic stainless steel increases, and in forming process, can produce the orange peel defective.Therefore, for the meticulous hot strength that improves that becomes through the precipitate that makes ferritic stainless steel, preferably, to the plate temperature, cold annealing temperature is controlled at more than or equal to 1030 ℃ and smaller or equal to 1080 ℃ in carry out cold annealing.
For the thermal annealing temperature of thermal anneal step (S2) and the cold annealing temperature of cold annealing steps (S3), (cold annealing temperature)/(thermal annealing temperature) can be more than or equal to 1.0 and smaller or equal to 1.1.
Can make according to ferritic stainless steel of the present invention through thermal anneal step (S2) and cold annealing steps (S3), the temperature of the temperature of thermal anneal step (S2) and cold annealing steps (S3) can interact.Specifically; Although when the cold annealing temperature of cold annealing ferritic stainless steel increases; Formability and r-bar value increase and can improve hot strength, but in the relation of cold annealing temperature and thermal annealing temperature, when (cold annealing temperature)/(thermal annealing temperature) less than 1.0 the time; The r-bar value of cold annealing ferritic stainless steel descends, and formability can descend.In addition, when cold annealing temperature excessively increase and (cold annealing temperature)/(thermal annealing temperature) greater than 1.1 the time, grain-size increases, and in the process that ferritic stainless steel is shaped, can produce the orange peel defective.Therefore, preferably,, (cold annealing temperature)/(thermal annealing temperature) is controlled at more than or equal to 1.0 and smaller or equal to 1.1 in order to increase r-bar value and high temperature tensile strength simultaneously.
Manufacturing method according to the invention, in ferritic stainless steel, satisfy equation DBTT (℃) can or be lower than 90 ℃ for 90 ℃.
DBTT(℃)＝-184.6+3.2(Crwt％)+27.5(Mowt％)+4243.4(Cwt％+Nwt％)-295.6(Al?wt％)+0.9[Nb?wt％/(C?wt％+N?wt％)]。
DBTT (℃) be low more favourable more factor, when DBTT (℃) during greater than 90 ℃, ferritic stainless steel is fracture easily, therefore, can produce the for example defective of sheet material fracture.
In ferritic stainless steel; When DBTT (℃) during greater than 90 ℃, in process for making, because the toughness deterioration; So in thermal anneal step (S2) and cold annealing steps (S3), the sheet material fracture can occur in the weld part office that can form through laser welding and electric-resistance seam-welding.In addition, because in ferritic stainless steel, in cold rolling step (S4), rupture with sheet material because of the pressure part can appear not in room temperature toughness deterioration, thus preferably, make DBTT (℃) at 90 ℃ or be lower than 90 ℃, to prevent above problem and to guarantee stainless toughness.
The present invention relates to a kind of method of making ferritic stainless steel, said ferritic stainless steel has 900 ℃ of tolerances or greater than thermotolerance, the hot strength of 40MPa and the formability that is equal to or greater than 444 steel of 900 ℃ temperature.
Usually, the element that has a big relatively atomic radius through interpolation for example Nb, Mo, W, Ta and Hf causes solid solution hardening, so can improve the hot strength of ferritic stainless steel.Being used for the ferritic stainless steel that heat-stable ferritic stainless steel has the hot strength of most excellent is 444 steel, and 444 ladles contain 2wt% or are lower than the Mo of 2wt%.In the ferritic stainless steel that only adds Mo, even the addition of Mo is increased to 3wt% or greater than 3wt%, the increase effect of hot strength neither be very big.In addition, when the addition of Mo increases, in the ME of ferritic stainless steel, separate out the σ phase easily,, thereby reduced manufacturing efficient therefore because the toughness deterioration of fertile material and welding portion causes the defective of for example sheet material fracture or orange peel to increase.
Therefore; The present invention concentrates and has studied the alloy designs that can farthest use meticulous Laves phases; And this alloy designs is based on the addition that has reduced Mo and increased the ferritic stainless steel of the addition of W, and this considers with Mo and compare that Laves phases is separated out fast.In addition; The present invention relates to a kind of method of manufacture of ferritic stainless steel; This method prevents the defective in ME that possibly caused by the deterioration of a plurality of welding portions of coiled material or a welding portion, and this method comprises the thermal anneal step of optimization, cold annealing steps and cold rolling step.
Through will according to the embodiment 1 to embodiment 7 of table 1 and comparative example 1 to comparative example 4 sample (2.0t) be processed into v-notch impact sample and carry out shock test obtain DBTT (℃).Can find out, according to the DBTT of the embodiment 1 to embodiment 7 of table 1 (℃) be 90 ℃ or less than 90 ℃.
3. according to the performance test of the ferritic stainless steel of temperature
Change 1230 ℃ and 1280 ℃ into and come the perparation of specimen through utilizing according to the ferritic stainless steel of the embodiment in the table 12 and will heating Heating temperature in the step of base.
Fig. 7 is the figure that illustrates according to the grain-size of the ferritic stainless steel of base Heating temperature, and Fig. 8 is the average r-bar value according to the ferritic stainless steel of base Heating temperature.
Fig. 7 shows in the base heating steps with the different heating temperature manufacturing and subsequently at the figure of the grain-size of the ferritic stainless steel of 1050 ℃ of thermal annealings.Can find out, can receive the influence of base Heating temperature according to the grain-size of the thermal annealing ferritic stainless steel of base Heating temperature.Specifically, can find out that in the thermal annealing ferritic stainless steel, when base Heating temperature during 1280 ℃ more than 1240 ℃, grain-size is big, when the base Heating temperature was low relatively 1230 ℃, grain-size was little.
Fig. 8 is illustrated in the base heating steps with the different heating temperature manufacturing, at the figure of the average r-bar value of 1050 ℃ of cold then annealed ferritic stainless steels of thermal annealing.Can find out that along with the base Heating temperature descends, the average r-bar of cold annealing ferritic stainless steel increases.
Based on top description, can find out that when in the base heating steps, reducing Heating temperature, the grain-size of ferritic stainless steel reduces, and average r-bar increases.
Fig. 9 is the figure that illustrates according to the average r-bar value of the thermal annealing temperature in the thermal annealing process, and Figure 10 is the figure that illustrates according to the high temperature tensile strength of the cold annealing temperature in the cold annealing process.
With reference to Fig. 9, measure the average r-bar value of ferritic stainless steel when in thermal anneal step, the thermal annealing temperature change being 1040 ℃ and 1080 ℃.Result as measuring can find out that along with temperature in the thermal anneal step is low more, the r-bar value is high more.
Figure 10 shows the result of measurement according to the hot strength of the ferritic stainless steel of the cold annealing temperature in the cold annealing steps.Measure said hot strength at 900 ℃, and cold annealing temperature is changed into 1030 ℃ and 1060 ℃.With reference to this result, can find out that when cold annealing temperature was high, the hot strength of ferritic stainless steel increased.
Figure 11 is the figure that illustrates according to the average r-bar value of cold annealing temperature/thermal annealing temperature, and Figure 12 is the figure that illustrates according to the high temperature tensile strength of cold annealing temperature/thermal annealing temperature.
With reference to Figure 11, can find out, along with cold annealing temperature/thermal annealing temperature increases,, after cold annealing, measure the average r-bar value of ferritic stainless steel through changing cold annealing temperature/thermal annealing temperature.That is, along with increasing cold annealing temperature with respect to the thermal annealing temperature, average r-bar value increases.On the other hand, can find out, when cold annealing temperature/thermal annealing temperature greater than 1.1 the time, in ferritic stainless steel, produce the orange peel defective.
Figure 12 shows through changing the value of the thermometric high temperature tensile strength of cold annealing temperature/thermal annealing.Measure hot strength at 900 ℃.Can find out that along with the cold annealing temperature/thermal annealing temperature as the annealing temperature ratio in thermal anneal step and the cold annealing steps in the ferritic stainless steel uprises, hot strength increases.
It will be appreciated by those skilled in the art that under the situation of the spirit that does not change essential feature of the present invention, in every way embodiment of the present invention.Therefore, equipment described herein should not be limited to the described embodiments.In the claim that scope of the present invention limits, should be understood that within the scope of the present invention by implication and all modification of scope deutero-of claim and equivalent concepts thereof.

Claims (12)

1. the ferritic stainless steel that has excellent high-temperature intensity, said ferritic stainless steel comprises by weight percentage: C, greater than 0wt% and smaller or equal to 0.01wt%; Si is greater than 0wt% and smaller or equal to 0.5wt%; Mn is greater than 0wt% and smaller or equal to 2.0wt%; S is more than or equal to 0wt% and smaller or equal to 0.02wt%; Cr is more than or equal to 12wt% and smaller or equal to 19wt%; Mo is more than or equal to 0wt% and smaller or equal to 1.0wt%; W is more than or equal to 2wt% and smaller or equal to 7wt%; Ti is more than or equal to 0wt% and smaller or equal to 0.3wt%; Nb is greater than 0wt% and smaller or equal to 0.6wt%; N is greater than 0wt% and smaller or equal to 0.01wt%; Al is more than or equal to 0wt% and smaller or equal to 0.01wt%; The Fe of surplus and other unavoidable impurities.
2. ferritic stainless steel according to claim 1, wherein, by weight percentage, Mo is 0.8wt% or is lower than 0.8wt%.
3. ferritic stainless steel according to claim 2, wherein, the thermal annealing tissue of ferritic stainless steel comprises that ratio is 5% or is lower than 5% σ phase.
4. ferritic stainless steel according to claim 1, wherein, by weight percentage, W is more than or equal to 3wt% and smaller or equal to 6wt%.
5. ferritic stainless steel according to claim 1, wherein, by weight percentage, Mo+0.83W is more than or equal to 3.5wt% and smaller or equal to 5.0wt%.
6. according to any described ferritic stainless steel of claim in claim 1 to the claim 5, wherein, [(Ti+1/2Nb)/(C+N)] is more than or equal to 19.5 and smaller or equal to 32.
7. method of manufacture with ferritic stainless steel of excellent high-temperature intensity; Said method of manufacture is controlled to be 90 ℃ or be lower than 90 ℃ with the ductile-brittle transition temperature DBTT that satisfies equation of ferritic stainless steel; Ferritic stainless steel comprises by weight percentage: C, greater than 0wt% and smaller or equal to 0.01wt%; Si is greater than 0wt% and smaller or equal to 0.5wt%; Mn is greater than 0wt% and smaller or equal to 2.0wt%; S is more than or equal to 0wt% and smaller or equal to 0.02wt%; Cr is more than or equal to 12wt% and smaller or equal to 19wt%; Mo is more than or equal to 0wt% and smaller or equal to 0.8wt%; Ti is more than or equal to 0wt% and smaller or equal to 0.3wt%; Nb is greater than 0wt% and smaller or equal to 0.6wt%; N is greater than 0wt% and smaller or equal to 0.01wt%; Al is more than or equal to 0wt% and smaller or equal to 0.01wt%; The Fe of surplus and other unavoidable impurities,
Wherein, the value of Mo+0.83W is more than or equal to 3.5wt% and smaller or equal to 5wt%, and [(Ti+1/2Nb)/(C+N)] more than or equal to 19.5 and smaller or equal to 32,
DBTT(℃)＝-184.6+3.2(Crwt％)+27.5(Mowt％)+4243.4(Cwt％+Nwt％)-295.6(Al?wt％)+0.9[Nb?wt％/(C?wt％+N?wt％)]。
8. the method for manufacture of ferritic stainless steel according to claim 7, said method of manufacture may further comprise the steps:
The step of heating base;
Thermal anneal step;
Cold annealing steps;
Cold rolling step under the room temperature,
Wherein, the step of heating base has more than or equal to 1180 ℃ and smaller or equal to 1240 ℃ base Heating temperature.
9. the method for manufacture of ferritic stainless steel according to claim 8, wherein, to the plate temperature, thermal anneal step has more than or equal to 1020 ℃ and smaller or equal to 1070 ℃ thermal annealing temperature.
10. the method for manufacture of ferritic stainless steel according to claim 8, wherein, the grain-size of ferritic stainless steel is ASTM No.3.0 or greater than ASTM No.3.0.
11. the method for manufacture of ferritic stainless steel according to claim 8, wherein, to the plate temperature, cold annealing steps has more than or equal to 1030 ℃ and smaller or equal to 1080 ℃ cold annealing temperature.
12. the method for manufacture of ferritic stainless steel according to claim 8, wherein, about the thermal annealing temperature of thermal anneal step and the cold annealing temperature of cold annealing steps, (cold annealing temperature)/(thermal annealing temperature) is more than or equal to 1.0 and smaller or equal to 1.1.
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