CN101812647A - Diphase stainless steel and manufacturing method thereof - Google Patents
Diphase stainless steel and manufacturing method thereof Download PDFInfo
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Abstract
The invention discloses a diphase stainless steel, which comprises the following components in percentage by weight: less than or equal to 0.05 percent of C, 0.2 to 1.0 percent of Si, 0 to 2.0 percent of Mn, 22 to 27 percent of Cr, 0 to 2.0 percent of W, less than or equal to 0.1 percent of S, less than or equal to 0.03 percent of P, 0 to 0.003 percent of B, more than 0 and less than or equal to 0.2 percent rare earth of which the Ce content is more than 50 percent, and the balance of Fe and inevitable impurities, wherein a casting blank of the diphase stainless steel comprises over 60 percent of isometric crystal. A method for manufacturing the diphase stainless steel comprises the following steps of: performing smelting, die casting or continuous casting to form the casting blank, wherein the thickness of a steel die is more than 30 mm during the die casting to ensure that the cooling velocity of the steel is more than 10 DEG C per minute, and in the process of the continuous casting, the degree of superheating of the casting is between 30 and 100 DEG C, and the casting speed is over 1.2 meters per minute; putting the casting blank into a heating furnace, heating the casting blank to the temperature of between 1,100 and 1,250 DEG C, performing heat preservation on the casting blank, and then forging or hot-rolling the casting blank to a required thickness; and annealing and pickling a steel plate or a plate coil after forging or hot-rolling, and controlling the annealing temperature to be between 1,000 and 1,100 DEG C. The diphase stainless steel has high corrosion resistance and high hot-working performance, and can be widely applied in the fields of petroleum, chemical industry, papermaking, marine engineering and the like in rigorous corrosion environments.
Description
Technical field
The present invention relates to a kind of duplex stainless steel and manufacture method thereof that contains ferrite and austenite two-phase matrix, particularly relate to have high anti-corrosion, mechanicalness and good thermal processability energy, strand has the duplex stainless steel and the manufacture method thereof of the equiax crystal content more than 60%.
Background technology
Duplex stainless steel by austenite and ferrite two phase composites has superior anti-chlorine ion corrosion and anticorrosion stress-resistant ability, and its yield strength is the twice of 300 serial austenitic stainless steels.Duplex stainless steel is widely used in fields such as oil, chemical industry, papermaking, oceanographic engineering, building.
Duplex stainless steel with respect to 300 traditional serial austenitic stainless steels in performance with have remarkable advantages economically, but the production difficulty of this series products is bigger, its production difficulty is mainly reflected in duplex stainless steel and is easy to generate various crackles in hot procedure, thereby has influenced the lumber recovery and the quality of product.
At improving hot workability, Pohang Iron ﹠ Steel Co., Ltd. discloses the duplex stainless steel of a kind of W2.0% of containing～5.0% and Mo1.0%～2.0% and Ce≤1.0% at Chinese patents CN1155908A, this patent reduces the tendency of separating out of intermetallic precipitated phase by the content that reduces Mo, thereby improves hot workability.But the anti-spot corrosion value PREN=Cr%+3.3Mo%+30N% of this patent duplex stainless steel will significantly descend, so the corrosion-resistant ability of this duplex stainless steel significantly reduces.
Improving aspect the hot workability of duplex stainless steel, the investigator of various countries has adopted modes such as adding some B, Ca, rare earth, microalloy element to improve the intensity of duplex stainless steel phase boundary or has improved the modes such as purity of molten steel.Relate at Chinese patents CN1125965A as Sandvik company and to contain Cr 28%～35%, the duplex stainless steel of Ce≤0.2%.This steel grade has very excellent corrosion resistance nature owing to have very high Cr, thereby can be applied in the quite harsh urea industry of corrosive environment.But, the hot workability of steel has been produced negative influence because high Cr content has seriously strengthened the tendency of separating out of intermetallic intermediate phase.
In addition, also the research of some duplex stainless steel is in order to bring into play the advantage that it saves the Ni resource more fully, as the Chinese patent CN1970815A of Shanghai university.The steel that this patent relates to contains 1.0%～2.0% Ni, 8%～12% Mn and 0.05%～0.2% Ce or Y.This steel for the ultralow Ni of balance after the deficiency of austenite element, strengthen the content of austenite element N, in order to improve the solubleness of N in steel, improved the content of Mn.But the raising of N content has strengthened the condition of high temperature in the intensity of austenite phase and the difference of ferritic phase intensity, thereby has strengthened the proneness that crackle produces in the hot-work, has worsened the hot workability of steel.A large amount of addings of Mn have also produced negative influence to corrosive nature in addition.
Summary of the invention
The purpose of this invention is to provide a kind of have excellent corrosion resistance nature and good thermal processability can the equiax crystal content of duplex stainless steel, particularly its strand at the super-duplex stainless steel more than 60%.This steel grade is widely used in the fields such as oil, chemical industry, papermaking and oceanographic engineering of corrosive environment harshness.
Another object of the present invention provides a kind of manufacture method with duplex stainless steel of excellent corrosion resistance nature and good thermal processability energy.
The invention provides a kind of duplex stainless steel, its weight percent consists of: C≤0.05%, Si0.2%～1.0%, Mn≤2.0%, Cr 22%～27%, and Ni 5.0%～7.0%, 2.0%＜Mo≤4.2%, N 0.18%～0.4%, and Cu 0～2.0%, W 0～2.0%, S≤0.01%, P≤0.03%, B 0～0.003%, and 0＜rare earth≤0.2%, Ce content is greater than 50% in the described rare earth, and all the other are Fe and unavoidable impurities.
Preferably, C≤0.03%, more preferably, C≤0.02%.
Preferably, Mo＞2.0%～4.0%, N 0.2%～0.4%
Preferably, duplex stainless steel composition middle-weight rare earths content is 0.02%～0.2%.
Preferably, described duplex stainless steel, its strand has the equiax crystal more than 60%.
The invention provides a kind of manufacture method of duplex stainless steel, comprise the steps:
According to following composition: C≤0.05%, Si 0.2%～1.0%, and Mn 0～2.0%, Cr 22%～27%, and Ni 5.0%～7.0%, 2.0%＜Mo≤4.2%, N 0.18%～0.4%, and Cu 0～2.0%, and W 0～2.0%, S≤0.01%, P≤0.03%, B 0～0.003%, and 0＜rare earth≤0.2%, Ce content is greater than 50% in the described rare earth, and all the other are Fe and unavoidable impurities, smelt, die casting or continuous casting form strand then; Wherein, when carrying out die casting, the thickness of punching block is greater than 30mm, with the speed of cooling that guarantees steel greater than 10 ℃/min; When carrying out continuous casting, the superheating temperature of cast is 30～100 ℃, and the pulling rate of continuous casting is more than or equal to 1.2m/min;
With described strand put into process furnace be heated to 1100～1250 ℃ and the insulation after, forge or be hot-rolled down to desired thickness;
Steel plate or coiled sheet after forging or the hot rolling are carried out annealing and pickling, and its annealing temperature is controlled at 1000～1100 ℃.
Preferably, during die casting, the thickness of punching block is 35～45mm.
Preferably, during die casting, guarantee that the speed of cooling of steel is 15～20 ℃/min.
Preferably, during continuous casting, the superheating temperature of cast is 40～60 ℃.
Preferably, the pulling rate of continuous casting is 1.2～1.6m/min.
Preferably, described smelting adopts vacuum induction smelting, electric furnace-argon oxygen decarburization (AOD) to smelt or outer ladle refining furnace (LF stove) smelting of electric furnace-argon oxygen decarburization-stove.
Preferably, the soaking time after the strand heating is more than 30 minutes; Strand is when forging or hot rolling, and finish-forging or finishing temperature are more than 900 ℃; The time of the steel plate annealing after rolling is controlled according to 2min/mm; Steel plate after the annealing is cooled to below 400 ℃ with the speed of cooling greater than 10 ℃/s.
Preferably, the soaking time after the strand heating is 30～45 minutes.
Preferably, the temperature of finish-forging or finish to gauge is 950～1000 ℃.
Preferably, the steel plate after the annealing is cooled to below 400 ℃ with the speed of cooling of 10～20 ℃/s.
The present invention is for providing a kind of duplex stainless steel with excellent corrosion resistance nature and good thermal processability energy, particularly the equiax crystal content of its strand is at the super-duplex stainless steel more than 60%, the employing weight percent consists of: C≤0.05%, Si 0.2%～1.0%, Mn≤2.0%, Cr 22%～27%, and Ni 5.0%～7.0%, 2.0%＜Mo≤4.2%, N 0.18%～0.4%, Cu≤2.0%, W≤2.0%, S≤0.01%, P≤0.03%, B 0～0.003%, and 0＜rare earth≤0.2%, all the other are the steel grade of Fe and unavoidable impurities, and Ce content is greater than 50% in the used rare earth.Preferably, content of rare earth is 0.02%～0.2%.
Steel grade of the present invention is main alloying element with Cr, Ni, Mo, N, adds rare earth (Ce is greater than 50%) and reaches trace elements such as optionally adding B.The adding of rare earth by with the cooperating of when casting processing condition such as speed of cooling, continuous casting pulling rate, when solidifying, form more forming core point, thereby hinder the orientation development of solidifying dendrite, obtain to contain in the strand equiax crystal more than 60%, the improved duplex stainless steel of hot workability and erosion resistance.
B is easy in phase boundary and crystal boundary poly-partially, adds the intensity that B can improve duplex stainless steel austenite and ferrite phase boundary in the duplex stainless steel; The adding of an amount of B can provide more nucleation site in the process of setting of steel, thereby the solidified structure of refinement steel improves the proportion of equiaxed grain of strand, thereby improves the hot workability of duplex stainless steel.
For this reason, as follows to the content control of each element among the present invention:
Carbon: exactly, carbon is a kind of impurity element in steel grade of the present invention, all has limited solubleness in austenite and ferrite.When carbon content surpassed certain per-cent, carbide formed and separates out the corrosion resistance nature that has reduced steel at crystal boundary, and carbide separates out the impelling strength that also reduces steel in addition.Therefore, carbon be≤0.05% to greatest extent, preferable limited field is≤0.03%.Best limited field is≤0.02%.
Silicon: silicon is the element that contains usually in the Manufacture Of Iron And Steel By Melting.In duplex stainless steel, silicon is that ferrite forms and stable element.Silicon is used for deoxidation in fusion process, silicon can improve the hot strength of ferritic phase simultaneously, contains the silicon more than 0.2% in the therefore general dual phase steel.Will reduce the solubleness of nitrogen when but silicone content is too high, and quicken separating out of intermetallic phase.Therefore, the design silicone content is 0.2%～1.0% in the steel of the present invention.
Manganese: manganese is that a kind of austenite forms and stable element.Can utilize manganese to replace nickel to a certain extent, obtain austenite structure.Unfavorable during the manganese too high levels to corrosion resistance nature, and easily promote the generation of intermetallic phase to influence impelling strength and corrosion resistance nature.Therefore, in the steel of the present invention manganese content be controlled at≤2.0%.
Chromium: chromium is ferrite former, and it is stable that chromatize can make the ferritic structure with body centered structure in the steel.Stainless solidity to corrosion increases with the increase of chrome content, and chromium can also increase steel resistance of oxidation at high temperature.But higher chromium amount also can promote to form the intermetallic phase of duplex stainless steel, thereby worsens the hot workability and the welding property of steel.Thereby design chromium content is 22%～27% in the steel of the present invention.
Molybdenum: the synergy of molybdenum and chromium can improve stainless resisting chlorides corrosive ability.When containing 18%Cr at least in the stainless steel, molybdenum ability of anti-pitting and crevice corrosion in the environment of chloride is three times (referring to PRE formula) of chromium.Molybdenum is a ferrite former, can promote to form intermetallic phase equally.Therefore design molybdenum content is 2.0%＜Mo≤4.2% in the steel of the present invention, preferred Mo2.0%＜Mo≤4.0%.
Nickel: nickel is the element of stable austenite.Adding nickel in the ferrous alloy can impel stainless steel to be converted into face-centered cubic crystal structure (austenite) from body-centered cubic crystal structure (ferrite).The interpolation of nickel can balance each other with ferrite elements such as chromium, molybdenums and make it obtain ideal two-phase ratio in the duplex stainless steel steel, adds the formation that nickel also can delay phase between poisonous metal, and increases the toughness of steel.Therefore design nickel content is 5.0%～7.0% in the steel of the present invention.
Nitrogen: nitrogen is the intensive austenite former, can be partly for nickel in austenitic stainless steel.Generally add in the duplex stainless steel, reach the nickel amount that balances each other in order to adjustment almost near the nitrogen amount of solubility limit.Ferrite former chromium and molybdenum and austenite former nickel and nitrogen need reach balance, could obtain the duplex structure of expectation.Nitrogen increases austenite and the anti-pitting of duplex stainless steel and the ability of crevice corrosion.It can improve the intensity of steel significantly, and it is the most effective element of solution strengthening.Nitrogen delays the formation of intermetallic phase, makes duplex stainless steel have time enough to process and make.Another useful effect of nitrogen is to have improved ferrite to begin to change into austenitic temperature, makes duplex stainless steel welding back under condition of fast cooling, the level when the Ovshinsky scale of construction also almost can reach equilibrium state.Therefore design N content is 0.18%～0.4% in the steel of the present invention, preferred 0.2%～0.4%.
Boron: boron is the very little interstitial atom of atomic radius, and boron phase boundary poly-partially in duplex stainless steel can be improved the intensity of phase boundary, improves the hot workability of steel.In addition, the adding of B can provide more nucleation site in the process of setting of steel, thus the solidified structure of refinement steel, the proportion of equiaxed grain of raising strand.But the adding of too much boron easily forms low-melting BN at crystal boundary, thus the phase boundary intensity of reduction steel, the hot workability of deterioration steel.Therefore optionally add boron in the steel of the present invention, preferably its add-on is≤0.003%.
Rare earth: the interpolation of rare earth element in duplex stainless steel, match with the continuous casting process of steel, more nucleation site can be provided in the process of setting of steel, thereby the refinement steel solidify dendritic structure, the proportion of equiaxed grain of strand is obviously improved.Rare earth can also form dystectic rare earth oxysulfide (REO with the harmful elements such as S in the steel in addition
xS
y) (wherein RE is a rare earth, and x, y are the coefficient of O, S) etc., avoid low-melting sulfide to be segregated in the phase boundary place, thereby improved the hot workability and the corrosion resistance nature of steel.But the adding of too high rare earth produces a large amount of oxide compound drosses in the time of can making the steel cast, worsens production performance.Therefore, steel middle-weight rare earths content of the present invention is controlled at≤and 0.2%, be preferably 0.02%～0.2%.Better be to select for use Ce content greater than 50% rare earth.
Copper: be austenite phase forming element, the adding of Cu can improve the cold shaping performance of steel, but too much the adding of Cu causes the copper brittleness phenomenon easily when rolling, thereby brings the surface imperfection of steel, so Cu≤2.0%.
Tungsten: be the ferritic phase forming element, can partly substitute the effect of Mo in duplex stainless steel, and reduce separating out of σ phase, but too much replace Mo will damage the corrosion resistance nature of steel so W≤2.0% with W.
Sulphur: be to be difficult to the harmful element removed in the smelting iron and steel, S is with the corrosion resistance nature and the hot workability of grievous injury duplex stainless steel, so S≤0.01%.Preferred S≤0.002%
Phosphorus: be to be difficult to the harmful element removed in the smelting iron and steel, P will damage the corrosion resistance nature of duplex stainless steel, so P≤0.03%.
Because duplex stainless steel of the present invention, the weight percent of its chemical ingredients is: C≤0.05%, Si0.2%～1.0%, Mn≤2.0%, Cr 22%～27%, and Ni 5.0%～7.0%, Mo＞2.0%～4.2%, N 0.18%～0.4%, Cu≤2.0%, W≤2.0%, S≤0.01%, P≤0.03%, B 0～0.003%, and rare earth 0.02%～0.2% (as Ce content greater than 50%), all the other are Fe and unavoidable impurities.Therefore the composition of duplex stainless steel of the present invention combination makes it satisfy the requirement of the duplex stainless steel of anti-spot corrosion equivalent PRE 〉=50.Wherein anti-spot corrosion equivalent PRE=Cr wt%+3.3Mo wt%+30Nwt%.
The present invention adds 0.02%～0.2% rare earth elements such as (Ce content are greater than 50%) in steel, and optionally add B 0～0.003%, the adding of rare earth has increased the forming core that the solidify point of steel in casting process, thereby make ratio 〉=60% of equiax crystal in the continuous casting billet structure of steel, thereby improved the plasticity of steel in hot procedure, improved the lumber recovery and the quality product of steel.B phase boundary poly-partially in duplex stainless steel can be improved the intensity of phase boundary, and the adding of an amount of B can improve the hot workability of steel.
The manufacture method of duplex stainless steel of the present invention, the employing vacuum induction is smelted, or electric furnace-argon oxygen decarburization (AOD) smelts or electric furnace-argon oxygen decarburization (AOD)-external refining LF stove smelting process smelting weight percent consists of: C≤0.05%, Si0.2%～1.0%, Mn 0～2.0%, Cr22%～27%, Ni 5.0%～7.0%, 2.0%＜Mo≤4.2%, N 0.18%～0.4%, Cu≤2.0%, W≤2.0%, S≤0.01%, P≤0.03%, B 0～0.003%, and rare earth (as Ce content greater than 50%) is 0.02%～0.2%, and all the other are the steel of Fe and unavoidable impurities.
Steel grade of the present invention must be controlled the speed of cooling of molten steel in carrying out casting process, and its control method is:
The speed of cooling of molten steel: when carrying out die casting, the thickness of punching block must be greater than 30mm, and the thickness of preferred punching block is 35～45mm, with the speed of cooling that guarantees steel greater than 10 ℃/min.
When carrying out continuous casting, the superheating temperature of cast is 30～100 ℃, is preferably 40～60 ℃, and the pulling rate of continuous casting is greater than 1.2m/min, and the pulling rate of preferred continuous casting is 1.2～1.6m/min.
After die casting base or continuous casting steel billet put into process furnace and be heated to 1100～1250 ℃ and insulation, preferred soaking time was 30～45 minutes, is machined to desired thickness on forging line or hot rolling unit, and the temperature of preferred finish-forging or finish to gauge is 950～1000 ℃.
Steel plate or coiled sheet after forging or the hot rolling are carried out annealing and pickling, and its annealing temperature is controlled at 1000～1100 ℃, and the steel plate after the preferred annealing is cooled to below 400 ℃ with the speed of cooling of 10～20 ℃/s.
By above implementation of processes, steel grade of the present invention has following positively effect:
(1) improved the hot workability of duplex stainless steel: add＞0～0.2% rare earth (Ce content is greater than 50%) and optionally add element such as 0～0.003%B.The adding of rare earth has increased the forming core that the solidify point of steel in casting process, makes that proportion of equiaxed grain increases in the continuous casting billet structure of steel, thereby has improved the plasticity of steel in hot procedure; B phase boundary poly-partially in duplex stainless steel can be improved the intensity of phase boundary, further improves the hot workability of steel.
Control die casting speed of cooling, the superheating temperature and the strand pulling rate of control continuous casting, the control setting rate of strand in process of setting and the thickness of continuously cast bloom shell, thereby proportion of equiaxed grain in the control strand 〉=60%, make steel in the relative reduction in area in 1000～1200 ℃ of intervals greater than 65%, the hot workability of steel improves greatly.
(2) provide good mechanical property and corrosive nature: steel grade of the present invention through forge hot or hot rolling after, 1000～1100 ℃ carry out solution treatment after, be quenched to room temperature, the two-phase proportion of its steel is controlled at 45%～55%.The steel grade yield strength that obtains is 590MPa～700MPa, and tensile strength is 850MPa～920MPa, and unit elongation is 35%～43%.Its room temperature ballistic work is 240J～300J.Its PRE of anti-spot corrosion value is: 50≤PRE≤119.
The room temperature ballistic work records according to GB/T229-1994 " the metal summer is than test with notched test piece method " among the present invention.
(3) this duplex stainless steel can utilize existing stainless steel production line, concrete as die casting or casting after smelting through vacuum induction furnace, electric furnace-AOD stove smelting or electric furnace-AOD-LF stove, strand forging or hot rolling be after specific annealing process is handled back pickling etc. produces in batches, and be convenient for production, cost is low.
Description of drawings
Fig. 1 represents the drawing by high temperature relative reduction in area of measured duplex stainless steel of the present invention under differing temps.Wherein, X-coordinate is represented temperature, and ordinate zou Ψ represents the relative reduction in area that stretches.
Embodiment
Below by specific embodiment the present invention is described in more detail.
Embodiment is an example with the Production Flow Chart that electric furnace-AOD smelts, raw materials such as ferrochrome, ferronickel, molybdenum-iron and steel scrap are added electric furnace to be melted, pour molten steel into the AOD stove after melting clearly, in the AOD stove, take off C, take off S and increase N, control the blowing of N, when the smelting composition reaches requirement, pour molten steel into ladle, in ladle or crystallizer, add 0～0.003%B, and 0.02%～0.2% Ce content is greater than 50% rare earth in the mode of feeding silk.The alloy silk of its middle-weight rare earths is a bilayer structure, and inner core is the rare earth alloy that contains 50% above Ce, and outer main component is Fe, can be not oxidized and the intensity that strengthens alloy wire with the protection rare earth.The adding of element such as B, rare earth, the forming core point when having increased solidification of molten steel hinders the orientation development of solidifying dendrite.Though the Production Flow Chart of smelting with electric furnace-AOD is an example, is not limited thereto, and also can adopt the Production Flow Chart of vacuum metling, perhaps the Production Flow Chart of electric furnace-AOD-external refining LF stove smelting also can obtain similar result.
The molten steel that composition is qualified is cast on vertical-bending caster.The superheating temperature of casting is 40～60 ℃, and the slab pulling rate is 1.2～1.6m/min.Pulling rate needs the continuous casting two cold section to be equipped with higher speed of cooling faster, and the specific water of its secondary cooling zone is 0.3～0.9l/kg.Elements such as performance and B, Ce hinder the effect of the directed development of dendrite when solidifying so better.
By the cooperation of composition and technology, can obtain the continuous casting steel billet of proportion of equiaxed grain greater than 60% duplex stainless steel, the proportion of equiaxed grain of the composition of each embodiment and the continuously cast bloom that obtains is as shown in table 1.
Alloying constituent of table 1 embodiment of the invention and Comparative Examples (weight %) and proportion of equiaxed grain
| Embodiment | ??C | ??Si | ??Mn | ??Cr | ??Mo | ??Ni | ??N | ??B | Rare earth | Slab pulling rate (m/min) | Proportion of |
| Embodiment | |||||||||||
| 1 | ??0.019 | ??0.5 | ??1.4 | ??22.7 | ??2.3 | ??5.0 | ??0.18 | ??0.0020 | ??0.05 | ??1.4 | ??80 |
| Embodiment | |||||||||||
| 2 | ??0.021 | ??0.4 | ??0.8 | ??26.5 | ??4.0 | ??6.5 | ??0.35 | ??0.0030 | ??0.19 | ??1.2 | ??70 |
| Embodiment | |||||||||||
| 3 | ??0.014 | ??0.5 | ??1.0 | ??24.5 | ??4.2 | ??6.9 | ??0.27 | ??0.10 | ??1.2 | ??77 | |
| Embodiment | |||||||||||
| 4 | ??0.023 | ??0.5 | ??0.8 | ??24.8 | ??3.8 | ??6.0 | ??0.25 | ??0.0030 | ??0.03 | ??1.2 | ??62％ |
| Comparative Examples 1 | ??0.024 | ??0.5 | ??0.8 | ??24.8 | ??3.69 | ??6.9 | ??0.28 | ??1.0 | ??50％ |
The raising of strand proportion of equiaxed grain has improved the elevated temperature heat processing characteristics of duplex stainless steel.
Fig. 1 represents the relative reduction in area of the drawing by high temperature of duplex stainless steel under differing temps of four embodiment of the present invention.
From table 1 and Fig. 1 as can be seen, the present invention is by the design of alloying constituent and the control of casting process, the ratio that makes the strand equiax crystal is greater than 60%, and greater than 65%, hot workability obviously is better than contrasting steel grade in the relative reduction in area of 1000 ℃～1300 ℃ of temperature ranges.
Above-mentioned strand is heated to 1100 ℃～1250 ℃, and insulation is more than 30 minutes, preferred 30～45 minutes, forge or hot rolling to required thickness, the temperature of its finish-forging or finish to gauge is more than 900 ℃, preferred 950～1000 ℃.Again steel plate is cooled to room temperature.
Steel plate after rolling is annealed in 1000 ℃～1100 ℃ intervals with the ratio that guarantees the austenite phase 45%～55%, the annealed time is pressed 2min/mm control, steel plate after the annealing is with greater than 10 ℃/s, and the speed of cooling of preferred 10～20 ℃/s is cooled to below 400 ℃.The iron scale of surface of steel plate is removed in pickling then.
Mechanics and corrosive nature through the duplex stainless steel after solution annealing and the pickling are as shown in table 2.Wherein, impact property was measured than v-notch normal of impact according to the GB/T229 summer, specimen size 10 * 10 * 55mm, and the sampling direction is along rolling direction, 20 ℃ of probe temperatures.Anti-pitting attack equivalent calculates according to general formula PRE=Cr (wt%)+3.3Mo (wt%)+30N (wt%).
The mechanical property of steel and calculating PRE value after table 2 solution treatment
| Thermal treatment temp (℃) | Austenite phase ratio (%) | Yield strength (MPa) | Tensile strength (MPa) | Unit elongation (%) | ??Akv??(J) | ??PRE | | |
| Embodiment | ||||||||
| 1 | ??1020 | ??49 | ??570 | ??855 | ??43 | ??270 | ??50 | ??23.5 |
| Thermal treatment temp (℃) | Austenite phase ratio (%) | Yield strength (MPa) | Tensile strength (MPa) | Unit elongation (%) | ??Akv??(J) | ??PRE | | |
| Embodiment | ||||||||
| 2 | ??1100 | ??53 | ??700 | ??915 | ??38 | ??250 | ??119 | ??28.5 |
| |
??1050 | ??54 | ??630 | ??875 | ??40.5 | ??260 | ??99 | ??27.7 |
| |
??1060 | ??52 | ??650 | ??883 | ??41 | ??245 | ??87 | ??26.6 |
| Comparative Examples 1 | ??1080 | ??51 | ??580 | ??857 | ??40 | ??253 | ??93 | ??25.9 |
The present invention is by the rational proportion of ferrite element Cr, Mo, Si and austenite element Ni, N, Mn, after 1000～1100 ℃ temperature solution treatment, can obtain to have the duplex stainless steel of 45%～55% austenite ratio.Technical superiority of the present invention is by adding rare earth (Ce), optionally adding the B element and cooperating makes the equiaxed zone ratio of strand greater than 60% with appropriate casting process for cooling, thereby make the relative reduction in area of duplex stainless steel when stretching for 1000 ℃～1250 ℃ more than 65%, improve the hot workability of steel effectively, improved the lumber recovery of the hot rolling (or forge hot) of steel.
Duplex stainless steel of the present invention not only has excellent mechanical property, and its yield strength is at 570～700MPa, and tensile strength is at 850～920MPa, unit elongation is 38～43%, the room temperature impact property is 245～270J, and HRC hardness is 23.5～28.7, and its equivalent of anti-pitting attack PRE 〉=50.
Therefore, duplex stainless steel of the present invention has excellent corrosion resistance nature and good thermal processability energy, can be widely used in the fields such as oil, chemical industry, papermaking and oceanographic engineering of corrosive environment harshness.
It is worthy of note; the embodiment that more than provides can not be interpreted as limiting the scope of the invention; the person skilled in art can make some nonessential improvement and adjustment to the present invention according to above-mentioned design of the present invention, and these improvement and adjustment must belong to protection scope of the present invention.
Claims (13)
1. duplex stainless steel, its weight percent consists of: C≤0.05%, Si 0.2%～1.0%, Mn≤2.0%, Cr 22%～27%, and Ni 5.0%～7.0%, 2.0%＜Mo≤4.2%, N0.18%～0.4%, Cu 0～2.0%, W 0～2.0%, S≤0.01%, P≤0.03%, B 0～0.003%, and 0＜rare earth≤0.2%, all the other are Fe and unavoidable impurities, Ce content is greater than 50% in the described rare earth.
2. duplex stainless steel as claimed in claim 1 is characterized in that, rare earth is 0.02%～0.2%.
3. duplex stainless steel as claimed in claim 1 is characterized in that, described duplex stainless steel, and its strand has the equiax crystal more than 60%.
4. as the manufacture method of arbitrary described duplex stainless steel in the claim 1～3, comprise the steps:
Smelt according to described composition, die casting or continuous casting form strand then; Wherein, when carrying out die casting, the thickness of punching block is greater than 30mm, with the speed of cooling that guarantees steel greater than 10 ℃/min; When carrying out continuous casting, the superheating temperature of cast is 30～100 ℃, and the pulling rate of continuous casting is more than or equal to 1.2m/min;
With described strand put into process furnace be heated to 1100～1250 ℃ and the insulation after, forge or be hot-rolled down to desired thickness;
Steel plate or coiled sheet after forging or the hot rolling are carried out annealing and pickling, and its annealing temperature is controlled at 1000～1100 ℃.
5. the manufacture method of duplex stainless steel as claimed in claim 4 is characterized in that, during die casting, the thickness of punching block is 35～45mm.
6. as the manufacture method of the described duplex stainless steel of claim 4～5, it is characterized in that, during die casting, guarantee that the speed of cooling of steel is 15～20 ℃/min.
7. as the manufacture method of the described duplex stainless steel of claim 4～6, it is characterized in that the superheating temperature of cast is 40～60 ℃.
8. as the manufacture method of the described duplex stainless steel of claim 4～7, it is characterized in that the pulling rate of continuous casting is 1.2～1.6m/min.
9. as the manufacture method of the described duplex stainless steel of claim 4～8, it is characterized in that described smelting adopts vacuum induction smelting, electric furnace-argon oxygen decarburization to smelt or the outer ladle refining furnace of electric furnace-argon oxygen decarburization-stove is smelted.
10. as the manufacture method of the described duplex stainless steel of claim 4～9, it is characterized in that the soaking time after the strand heating is more than 30 minutes; Strand is when forging or hot rolling, and finish-forging or finishing temperature are more than 900 ℃; The time of the steel plate annealing after rolling is controlled according to 1.5～2.5min/mm; Steel plate after the annealing is cooled to below 400 ℃ with the speed of cooling greater than 10 ℃/s.
11. the manufacture method of duplex stainless steel as claimed in claim 10 is characterized in that, the soaking time after the strand heating is 30～45 minutes.
12. the manufacture method as the described duplex stainless steel of claim 10～11 is characterized in that, the temperature of finish-forging or finish to gauge is 950～1000 ℃.
13. the manufacture method as the described duplex stainless steel of claim 10～12 is characterized in that, the steel plate after the annealing is cooled to below 400 ℃ with the speed of cooling of 10～20 ℃/s.
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