CN101580917A

CN101580917A - High-grade duplex stainless steel

Info

Publication number: CN101580917A
Application number: CNA2007101044878A
Authority: CN
Inventors: 朴庸秀; 金淳太; 李仁诚
Original assignee: Individual
Current assignee: Individual
Priority date: 2002-03-25
Filing date: 2003-03-24
Publication date: 2009-11-18
Also published as: EP1495150A4; KR20030077239A; AU2003221202A1; KR100460346B1; DE60313763D1; DE60313763T8; JP2005520934A; WO2003080886A1; JP4834292B2; JP2011174183A; US20050158201A1; CN100343410C; EP1495150B1; EP1495150A1; DE60313763T2; CN1643176A; EP1803832A1

Abstract

The invention provides a high-grade duplex stainless steel, of which the chemical composition consists essentially, on a weight basis, of : Cr : 21.0% - 38.0%, Ni : 3.0% - 12.0%, Mo : 1.5% -.6.5%, W : 6.5% or less, Si : 3.0% or less, Mn : 8.0% or less, N : 0.2% - 0.7%, C :0.1% or less, at least one element selected from the group consisting of Ba : 0.0001 - 0.6% and one or more elements of Mischmetal (MM) and Y : 0.0001 - 1.0% in total, and a balance of Fe and incidental impurities. The pitting resistance equivalent has a value of 40 <= PREW<= 67 defined by the following formula (1): PREW = wt.%Cr + 3.3(wt.%Mo + 0.5wt.%W) + 30wt.%N. The present high-grade duplex stainless steel exhibits an excellent corrosion resistance, embrittlement resistance, castability and hot workability.

Description

High-grade duplex stainless steel

The application is the dividing an application that be March 24, application number in 2003 be 03806936.9 (PCT number be PCT/KR03/00568), denomination of invention the applying date for the application for a patent for invention of " be formed with intermetallic phase still less and have the high-grade duplex stainless steel of excellent erosion resistance, anti-embrittlement, castability and hot workability ".

Technical field

The present invention relates to have the duplex stainless steel of excellent anticorrosive, relate more specifically in production process (casting, hot rolling or welding) in by suppress intermetallic phase (for example, σ mutually and χ mutually) formation and the high-grade duplex stainless steel of erosion resistance, anti-embrittlement, castability and the hot workability that form with excellence.

Background technology

Wherein combination fine has austenite (γ) phase of the workability that provides high and the duplex stainless steel that ferrite (α) phase of high corrosion resistance is provided, at least 1.7 times of its strength ratio austenitic stainless steel height, and demonstrate high pitting resistance and high anticorrosion stress-resistant line (SCC) property.Have and be about 46 pitting resistance equivalent (the commodity high-grade duplex stainless steel of PREW=wt%Cr+3.3 (wt%Mo+0.5wt%W)+30wt%N), for example SAF2507 (UNS S32750), UR52N+ (UNS 32550) and ZERON 100 (UNS 32760) have been used for various purposes since nineteen nineties.Because the progress of melting technology makes the quality of duplex stainless steel improve, therefore it is used in the various fields day by day in recent years.

But, compare with commodity PREW38 level duplex stainless steel (for example SAF 2205), PREW46 level high-grade duplex stainless steel contains a large amount of Cr, Mo and W, they are σ phase and χ principal element mutually, thereby therefore the mechanical property of making and erosion resistance variation form its precipitated phase easily during producing or using.In fact, observed the embrittlement that causes by these precipitated phases in after the duplex stainless steel continuous casting, cooling off, after hot rolling, slowly cool off, after welding, heat affected zone slowly cooled off and after casting, the ingot casting centre portions slowly being cooled off.In addition, the Mo that is used to improve anti-local corrosion and anticorrosion stress-resistant line in the alloying element that is added helps forming σ mutually and 475 ℃ of brittle high valence elements, so its use is restricted.σ is the intermetallic compound that is highly brittle that forms under 650 ℃ to 1000 ℃ temperature mutually.The σ that is higher than 1vol.% meets and obviously reduces the impelling strength and the erosion resistance of duplex stainless steel.

Therefore, in the production of duplex stainless steel or the formation that suppresses the σ phase during using made a large amount of research and development.But there is following problem in traditional research and development.

1) when adding 1 to 3% Al or Al and Nb in the ferritic stainless steel that is containing 39%Cr, the formation speed of σ phase descends, the formation temperature scope of σ phase reduces, therefore the speed of separating out of σ phase reduces (K.Permachandra etc., Materials science and technology (Materials Scienceand Technology), the 8th volume, the 2477th page (1997)).But it is with to contain austenite and ferritic duplex stainless steel irrelevant.

2) when joining Zr in the stainless steel, the formation speed of σ phase reduces.But, alloying element (for example, Al or Zr) be ferrite former, they have reduced austenite phase ratio and have formed the intermetallic compound of the multiple N of containing, thereby the erosion resistance of making and mechanical property variation (people such as M.B Cotrie, metallurgy and material processing (Metallurgical andMaterials Transaction) 28A (1997) 2477).

3) when Sn being joined when containing in 43 to 46%Cr the ferritic stainless steel, Sn separates out in the nucleation zone of σ phase (for example, crystal boundary or crystal boundary triple point), thereby has reduced the formation speed of σ phase.When alloy was subjected to being higher than 232 ℃ high temperature, ferritic stainless steel can ftracture owing to the low melting point (232 ℃) of Sn.It also with duplex stainless steel irrelevant (A 139 (1993) 83 for people such as Costa, Physica Status Solidi).

4) people such as Okamoto discloses by carry out adding W in the timeliness thermal treatment in 10 minutes under 850 ℃, thereby the high-grade duplex stainless steel DP3W (UNS S39274) that includes 3%Mo+2%W and the commodity high-grade duplex stainless steel that includes 3.8%Mo are (for example, SAF 2507, UR 52N+ and ZERON 100) compare, more can postpone the speed of separating out of σ phase.But, when hot rolling large-scale steel ingot and slab, perhaps during fusion casting large-scale workpiece since χ mutually with σ separating out mutually, and make erosion resistance and mechanical property variation, thereby demonstrate high fragility (people such as H.Okamoto, the 4th international duplex stainless steel symposial (4 ^ThInternational Conferences onDuplex Stainless Steels), (1994) Paper91 and United States Patent (USP) 5,298,093).

Especially, according to United States Patent (USP) 5,298,093, though added a large amount of W (1.5 to 5.0%) to improve erosion resistance, the formation of intermetallic phase is not accelerated.Therefore, W adds certainly, S and O use constant, and by making S and O constant, add at least a element be selected from following group improving hot workability, this group comprises altogether and is less than or equal to 0.02% Ca, is less than or equal to 0.02% Mg, at least a REM (rare earth metal) that is less than or equal to 0.02% B and is less than or equal to 0.2%.Surpass under the situation of its upper limit at Ca, B, Mg and REM, formed many oxide compounds and sulfide.As the spot corrosion point, this has reduced erosion resistance to non-metallic inclusion (for example, oxide compound and sulfide).

In addition, United States Patent (USP) 5,733,387 have proposed a kind of like this duplex stainless steel, it contains and is less than or equal to 0.03% C, is less than or equal to 1.0% Si, be less than or equal to 2.0% Mn, be less than or equal to 0.04% P, be less than or equal to 0.004% S, be less than or equal to Ni, 22 to 27% Cr, 1.0 to 2.0% Mo, the 2.0-5.0% of 2.0% Cu, 5.0-8.0% W, 0.13 to 0.30% N, be selected from least a element in the group that comprises a certain amount of Ca, Ce, B and Ti and the Fe of measurement.Above-mentioned patent has reduced the content that is beneficial to the Mo that intermetallic phase forms, and the content that has increased W is to improve erosion resistance.But as confirming in after a while with the PREW formula of describing, the effect that Mo is used for improving pitting resistance is the twice of W.Therefore the content that reduces Mo is invalid.

On the other hand, in order to suppress to have the formation of high brittle intermetallic phase, it is necessary cooling off fast in the two-phase stainless Heat Treatment Of Steel.When thermal treatment temp begins to cool down duplex stainless steel, its is through the temperature of separating out of intermetallic phase.If speed of cooling is not high enough in this humidity province, then intermetallic phase is separated out rapidly.When intermetallic phase is separated out at a high speed in cooling off at a slow speed, the duplex stainless steel embrittlement, and demonstrate low erosion resistance.Therefore, be used to suppress the another kind of traditional method that intermetallic phase separates out and be intended to controlled chilling process during heating treatment.

According to the open No.5-271776 of Japanese Patent Laid, separate out in order to suppress intermetallic phase, during heating treatment, duplex stainless steel is cooled to just in time be lower than the minimum temperature of separating out the district of intermetallic phase with the much higher speed of speed of cooling of separating out, and kept 5 minutes minimum separating out under the low temperature more than 200 ℃ in humidity province than intermetallic phase than intermetallic phase.

In addition, the open No.62-6615 of Japanese Patent has proposed a kind of method that intermetallic phase forms that suppresses when using duplex stainless steel to come the manufacturing machine member by casting.Usually, when using duplex stainless steel to make hardware, pouring molten steel is advanced in the sand mold, make it to solidify and keep somewhere at room temperature.But when the high-grade duplex stainless steel that uses intermetallic phase wherein to separate out was easily made foundry goods, some ferritic phases were cooled to after casting and are transformed into σ phase and austenite in the process of room temperature mutually, so σ comprises fragility mutually.In order to suppress separating out of σ phase, above-mentioned Japanese Patent has openly instructed a kind of being used for to remove mould and make the rapid refrigerative method of workpiece when temperature is higher than 1000 ℃.If speed of cooling is not high enough through separating out in the humidity province, then σ separates out rapidly mutually.That is, when in process of cooling, separating out the σ phase time, this stainless steel embrittlement and demonstrate low erosion resistance.

But the above-mentioned method that is used for during heating treatment adding the third alloying element or controlled chilling process can not be suppressed at the σ phase in the high-grade duplex stainless steel fully.

Summary of the invention

Main purpose of the present invention is, postpone the intermetallic phase diffusion and separate out by the Ba with thick atom diameter, Y, Ce, La, Nd, Pr, Ta, Zr and the Ti atom that adds appropriate amount, and in addition by using trace rare-earth element compound or barium oxide to stop the diffusion of Cr, Mo, Si and W, thereby reduce the speed of separating out and the embrittlement amount of intermetallic phase, eliminate fragility thus and improve erosion resistance.

Another object of the present invention is, by (mixed rare earth alloy: by the mischmetall of its nucleidic mass as the atomic building of 57-71, it includes at least more than or equal to 50% Ce, a certain amount of La, Nd and Pr, trace P m, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and Sc and the Fe that is less than or equal to 1% according to using Ti, Mg, Ca, Al and Ca+Al and adding MM.Afterwards, detailed description of the present invention and embodiment use such MM, the Fe that its principal element comprises 51%Ce-26%La-15%Nd-5.5%Pr, trace P m, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and Sc and is less than or equal to 1%) and/or the usual way of Y carry out suitable preliminary deoxygenation, thereby prevent to form separately the Al that can have disadvantageous effect to rigidity ₂O ₃With the MnS inclusion.

Another purpose of the present invention is, thulium (REM with MM in the molten steel and/or Y, in chemical formula, abbreviate ' RE ' below as) solubility product control within the specific limits, thereby provide different nucleation sites during forming, to form fine structure, and by in molten steel, forming the rare earth compound mixture (RE that its diameter is lower than 5 μ m at the dentrite that solidifies _xO _yOr (RE, Al) _xO _y+ RE _xO _yS+RE _xS _y) control the segregation of solute element (for example Cr, Mo, W, Ni, Mn and Si), thus cause improving mechanical property, physicals and erosion resistance.

A further object of the present invention is, is suppressed at intermetallic phase in the duplex stainless steel (for example, the σ phase) formation, and the output capacity of improvement during scale operation significantly by adding new alloying element.

A further object of the present invention is that (for example, the σ phase) speed of separating out improves anti-embrittlement and prevents cracking, thereby improves the output capacity in casting and hot-work greatly by reducing intermetallic phase.

A further object of the present invention is, the σ that can weaken erosion resistance and mechanical property by inhibition in as-cast condition mutually with χ separating out mutually, and when in various Application Areass, must after welding, controlling these separating out in the heat affected zone during welding set member, thereby improve erosion resistance and mechanical property, and improve the weather resistance of equipment.

To achieve these goals, will explain content of the present invention below:

(1), has high corrosion resistance, anti-embrittlement, but the high-grade duplex stainless steel of castibility and hot workability, it has suppressed the formation of intermetallic phase, it consists predominantly of by weight: 21.0 to 38.0% Cr, 3.0 Ni to 12.0%, 1.5 Mo to 6.5%, 0 to 6.5% W, be less than or equal to 3.0% Si, be less than or equal to 8.0% Mn, 0.2 N to 0.7%, be less than or equal to 0.1% C, 0.0001 the Ba to 0.6% and the Fe of measurement and unavoidable impurities, pitting resistance equivalent (PREW) is 1. limited by the following formula that satisfies 40≤PREW≤67:

PREW＝wt％Cr+3.3(wt％Mo+0.5wt％W)+30wt％N---①。

(2), the high-grade duplex stainless steel of (1), also include 0.0001 to 1.0% MM and/or Y altogether.

(3), the high-grade duplex stainless steel of (2), wherein the addition scope of Ba is 0.001 to 0.2%.

(4), has high corrosion resistance, anti-embrittlement, but the high-grade duplex stainless steel of castibility and hot workability, it has suppressed the formation of intermetallic phase, it consists predominantly of by weight: 21.0 to 38.0% Cr, 3.0 Ni to 12.0%, 1.5 Mo to 6.5%, 0 to 6.5% W, be less than or equal to 3.0% Si, be less than or equal to 8.0% Mn, 0.2 N to 0.7%, be less than or equal to 0.1% C, the Fe of 0.0001 to 1.0% MM and/or Y and measurement and unavoidable impurities altogether, described MM is for being the mischmetall of the atomic building of 57-71 by nucleidic mass, it includes at least the Ce more than or equal to 50%, a certain amount of La, Nd and Pr, trace P m, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and Sc and the Fe that is less than or equal to 1%, pitting resistance equivalent (PREW) is 1. limited by the following formula that satisfies 40≤PREW≤67:

PREW＝wt％Cr+3.3(wt％Mo+0.5wt％W)+30wt％N---①。

(5) high-grade duplex stainless steel of any in (2) to (4), wherein the numerical range as [MM and/or Y+Al] [O+S] of the solubility product formula of the MM of steel and/or Y and Al, O and S is from 0.001 * 10 ^-5To 30000 * 10 ^-5[%] ²

(6), the high-grade duplex stainless steel of (5), wherein under the situation of foundry goods, the numerical range of solubility product formula is from 1 * 10 ^-5To 5000 * 10 ^-5[%] ²

(7), the high-grade duplex stainless steel of (5), wherein under the situation of hot-work part, the numerical range of solubility product formula is from 0.1 * 10 ^-5To 2000 * 10 ^-5[%] ²

(8), any high-grade duplex stainless steel in (2) to (4), wherein total weight range of MM and/or Y is from 0.01 to 0.6%.

(9), the high-grade duplex stainless steel of (8), wherein total weight range of MM and/or Y is from 0.2 to 0.5%.

(10), the high-grade duplex stainless steel of any in (1) to (4), also comprise at least a element that is selected from following group, this group comprises and is less than or equal to 0.5% Ca, is less than or equal to 0.5% Mg, be less than or equal to 1.0% Al, be less than or equal to 0.5% Ta, be less than or equal to 0.5% Nb, be less than or equal to 1.5% Ti, be less than or equal to 1.0% Zr, the In that is less than or equal to 1.0% Sn and is less than or equal to 1.0%.

(11), any high-grade duplex stainless steel in (1) to (4), also comprise and be less than or equal to 0.1% B.

(12), any high-grade duplex stainless steel in (1) to (4), also be included in and be less than or equal to 3.0% Cu and be less than or equal among 3.0% the Co one or more.

(13), any high-grade duplex stainless steel in (1) to (4), wherein as austenite mutually and [PREW (γ)-PREW[α] of the measurement of the erosion resistance of ferritic phase] numerical range be-5 to 10.

(14), any high-grade duplex stainless steel in (1) to (4), wherein the volume percent scope of ferritic phase is 20-70%, and the volume percent scope of austenite phase is 30-80%.

Description of drawings

Figure 1A to 1F is a photo, shows under 850 ℃ the microtexture through 30 minutes aging heat treatment steel 4 of the present invention (Figure 1A), steel of the present invention 10 (Figure 1B) and steel of the present invention 36 (Fig. 1 C), comparative steel 47 (Fig. 1 D) and merchant steel UR 52N+ (Fig. 1 E) and SAF 2507 (Fig. 1 F);

Fig. 2 A to 2D is a graphic representation, shows under 850 ℃ the X-ray diffraction test-results through 30 minutes aging heat treatment steel 4 of the present invention (Fig. 2 A), comparative steel 47 (Fig. 2 B) and merchant steel UR 52N+ (Fig. 2 C) and SAF 2507 (Fig. 2 D);

Fig. 3 A to 3D is a photo, shows in steel ingot (steel 10 of the present invention (Fig. 3 A) and the macrostructure of comparative steel 47 (Fig. 3 B) and the microtexture of steel of the present invention 10 (Fig. 3 C) and comparative steel 47 (Fig. 3 D) in the middle portion of φ 110mm * L550mm);

Fig. 4 is a graphic representation, shows steel of the present invention and the anti-anodic polarization test-results of merchant steel in 50 ℃ of degassing 0.5N HCl+1.0N NaCl solution in as-cast condition;

Fig. 5 is a chart, shows steel of the present invention and merchant steel at 6%FeCl ₃Critical pitting temperature test-results in the solution;

Fig. 6 A, 6B and 6C are graphic representation, show through steel of the present invention (Fig. 6 A), commodity high-grade duplex stainless steel (Fig. 6 B) and commodity high-quality austenitic stainless steel (Fig. 6 C) the anti-anodic polarization test-results in 70 ℃ of degassing 0.5N HCl+1.0N NaCl solution 1130 ℃ of following solution heat treatment;

Fig. 7 A and 7B are graphic representation, show under 850 ℃ through 10 minutes aging heat treatment steel of the present invention (Fig. 7 A) and commodity high-grade duplex stainless steel (Fig. 7 B) the anti-anodic polarization test-results in 50 ℃ of degassing 0.5NHCl+1.0N NaCl solution; And

Fig. 8 A and 8B are graphic representation, show under 850 ℃ through 30 minutes aging heat treatment steel of the present invention (Fig. 8 A) and commodity high-grade duplex stainless steel (Fig. 8 B) the anti-anodic polarization test-results in 50 ℃ of degassing 0.5NHCl+1.0N NaCl solution.

Embodiment

Now, but describe in detail with reference to these accompanying drawings and to have suppressed the high-grade duplex stainless steel that intermetallic phase forms according to the present invention with excellent anticorrosive, anti-embrittlement castibility and hot workability.

Even erosion resistance and mechanical property in the mother alloy that produced by optimum alloy designs, thin laboratory is used be improved significantly, also should satisfy specified conditions to improve the thick foundry goods in scale operation and the output capacity of hot-work part, and improve its erosion resistance and mechanical property, based on the above fact, but the inventor to the intermetallic phase that has disadvantageous effect at erosion resistance, anti-embrittlement castibility and hot workability (for example, σ mutually with χ mutually) mechanism carried out thorough research, and obtain following result.

Promptly, the inventor finds, help the Cr that intermetallic phase forms when adding its atomic diameter than constituting to contain, Mo, the basic alloy element of the duplex stainless steel of Si and W (for example, Fe, Cr, Mo, Ni, Mn and Si) much bigger alloying element is (for example, Ba, MM (Ce, La, Nd, Pr) and/or Y) time, having more these alloying element atoms of thick atom diameter has filled as constituting σ mutually and χ Cr mutually, Mo, the atom vacancy of the diffusion admittance of Si, especially be filled in austenite mutually and the atom vacancy in the crystal grain of ferritic phase crystal boundary and ferritic phase, thereby reduced the formation speed of the intermetallic phase under 1000 to 650 ℃ temperature.

In addition, the inventor finds, because have alloying element than the thick atom diameter have than Fe, Cr, Mo, W, Ni, Mn and Si much lower, be used for the free energy that heat forms oxide compound or oxysulfide movingly, and so can form its diameter and be lower than the tiny of 5 μ m and uniform oxide and oxysulfide.Mischmetall that these are small or barium oxide can further stop Cr, Mo, Si and the W diffusion under 1000 to 650 ℃ temperature, thereby reduce the speed of separating out of intermetallic phase.

The inventor finds that also the MnS non-metallic inclusion is because its erosion resistance is lower than matrix, and therefore usually as the corrosive starting point, but the rare earth non-metallic inclusion is because its erosion resistance is higher than matrix, therefore can be as the corrosive starting point.

That is, the present invention is by adding its atomic diameter greater than the Fe as the main alloy element of commodity duplex stainless steel

Cr

Mo W Ni

Mn

And Si

, 0.0001 to 0.6% Ba

(bracket in numeral atomic diameter) and suppressed the formation of intermetallic phase.

In addition, the present invention by add MM (its principal element comprises for example Ce: La:

Nd:

And Pr:

Trace P m, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and Sc, and the Fe that is less than or equal to 1%) and/or its atomic diameter greater than Fe as the main alloy element of commodity duplex stainless steel

Cr

Mo W

Ni

Mn

And Si

Y

Perhaps add the formation that Ba suppresses intermetallic phase to it.Here, in order to promote these effects, the numerical range of the formula of the solubility product of MM in the steel and/or Y and Al, O and S [MM and/or Y+Al] [O+S] is 0.001 * 10 ^-5To 30000 * 10 ^-5

In addition, when add its an amount of atomic diameter greater than alloying element, Ca

Mg

Al

Ta Nb

Ti

Zr

Sn

And In

In at least a alloying element the time, can more effectively suppress σ mutually and χ formation mutually.

When with its atomic diameter than Fe, Cr, Mo, W, Ni, Mn and Si much smaller, be used for filling the spatial B that has than these alloying elements of thick atom diameter, add with these alloying elements fashionable, B be used for these alloying elements reduce together σ mutually with the speed of separating out of χ phase.

In addition, can use at least a alloying element among Cu and the Co to improve acid resistance and intensity.

To describe joining below according to the effect of the alloying element in the duplex stainless steel of the present invention and the reason that limits its chemical ingredients scope.

Cr:21.0 to 38.0%

Cr is the basic important element that is used to keep stainless erosion resistance.Need at least 12% Cr to keep erosion resistance.Therefore in the present invention, this alloy need have the austenite-ferrite double structure, considers the Cr defined in the formula below _EquivalentAnd Ni _EquivalentAnd, must use at least 21% Cr by they determined austenite/ratio of ferrite.In order to make duplex stainless steel by balance C, N, Ni, Mo, W, Si, Mn and Cu, the upper limit of Cr is set at 38%, and more preferably 24 to 28%.

Cr _Equivalent=%Cr+2%Si+1.5%Mo+0.75%W+5%V+5.5%Al+1.75%Nb+1.5%Ti---2.

Ni _Equivalent=%Ni+0.5%Mn+30%C+0.3%Cu+25%N+%Co---3.

Austenite phase ratio (volume percent)=100-[55 * (Cr _Equivalent/ Ni _Equivalent)-66.1]---4.

Ferritic phase ratio (volume percent)=55 * (Cr _Equivalent/ Ni _Equivalent)-66.1---5.

In addition, in order to make the erosion resistance maximum of duplex stainless steel, the scope that obtains to compare by following example of the present invention.The ratio of ferrite scope is 20 to 70vol.% (austenite phase proportional range be 30 to 80vol.%).

Ni:3 to 12%

At least need 3% Ni, this is because it is the austenite stable element that is used to improve even corrosion resistant.Consider Cr _Equivalent, Ni _Equivalent, compare and its expensive use 3.0 to 12.0%, more preferably 6 to 9% Ni.

Mo:1.5 to 6.5%

The same important element of Mo for the erosion resistance that is used to keep alloy with Cr.Mo is used for stablizing ferritic phase.Because alloy of the present invention need have the austenite-ferrite double structure, therefore consider Cr _Equivalent, Ni _EquivalentWith compare, should add at least 1.5% Mo.Especially, when Mo adds fashionablely with Cu, it can improve significantly at high-density SO ₄ ^2-And Cl ^-Erosion resistance in the environment.Mo is very useful for mechanical property and the erosion resistance improved in as-annealed condition, but forms the intermetallic phase (for example, σ phase) with disadvantageous effect in timeliness thermal treatment, hot rolling or welding.Therefore, consider Cr _Equivalent, Ni _Equivalent, erosion resistance and phase stability use and be less than or equal to 6.5% Mo.As confirming in the PREW formula, the effect that Mo improves pitting resistance is the twice of W.Therefore, the content of Mo more preferably surpasses 2%, to obtain good pitting resistance.

W:0 to 6.5%

W is a ferritic stabilizer, and is the homology alloying element that has with the similar chemical property of Mo.W has improved at high-density SO ₄ ^2-And Cl ^-Erosion resistance in the environment, and, improved erosion resistance and mechanical property by postponing fragility σ phase and χ speed of separating out mutually after sensitization thermal treatment or welding.But W is the high price alloying element, and if use a large amount of W, then it helps forming intermetallic compound.Therefore, consider that phase stability, mechanical property and erosion resistance use are less than or equal to 6.5%, more preferably are less than or equal to 4.0% W.

Si: be less than or equal to 3%

Si is a ferritic stabilizer, and it has desoxydatoin in melting, and has improved molten steel flow and reduced surface imperfection in castings production.When use surpassed 3% Si, it had increased the speed of separating out of phase between friable metal, and has reduced the ductility of steel.Consider erosion resistance, use to be less than or equal to 3.0%, more preferably for being less than or equal to 1.0% Si.

Mn: be less than or equal to 8%

Mn is the austenite stable element, the Ni of its alternative high price.Mn is used to increase the solid solubility of N and reduces high temperature resistant deformability.In order to improve erosion resistance, mainly use an amount of Mn by the content that increases N.It has desoxydatoin to dissolving and melting.But a large amount of Mn have reduced erosion resistance, and are beneficial to the formation of phase between friable metal.Therefore, the content of Mn is set at and is less than or equal to 8%, and more preferably 1.0 to 3.0%.

N:0.2 to 0.7%

N is very useful for improving pitting resistance, and its effect is than high about 30 times of Cr.N is strong austenite stable element, and also is to be used to one of most important element that improves erosion resistance.When N existed with Mo, it can improve erosion resistance significantly.When the content that reduces C when improving the crystal boundary erosion resistance, N can compensate mechanical property.In addition, N has suppressed the formation of Cr carbide, and has improved tensile strength and yield strength, and can not reduce unit elongation.The content of N must consideration with the balance of C, Cr, Ni, Mo and W and austenite mutually ratio control.From the erosion resistance aspect, preferred at least 0.2% the N that uses.But when N content surpasses 0.7%, but it can reduce castibility (pore, contraction) and rollability.More preferably, the content range of N is 0.32 to 0.45%.

C: be less than or equal to 0.1%

C is the important element that is used to make the mutually stable typical element of austenite and is used to keep physical strength.But, if used a large amount of C, its carbide precipitate and therefore reduce erosion resistance then.Therefore, use to be less than or equal to 0.1%, preferably be less than or equal to 0.05% C, more preferably, use is less than or equal to 0.03% C to improve the erosion resistance in timeliness.

PREW value: 40 to 67

Except by the content of above-mentioned restriction Cr, Mo, W and N, the numerical value of the PREW that is 1. limited by following formula satisfies 40≤PREW≤67:

PREW=wt％Cr+3.3(wt％Mo+0.5wt％W)+30wt％N---①

When the numerical value of PREW is lower than lower value, can not fully obtain erosion resistance, and prescribe a time limit when the numerical value of PREW is higher than, be beneficial to the formation of intermetallic phase.Preferably, the numerical value of PREW is greater than 45.

And in order to make the erosion resistance maximum of duplex stainless steel, [PREW (γ)-PREW (α)] as the erosion resistance of these phases is weighed is preferably-5 to 10 according to the example of the present invention that will describe after a while.

Ba:0.0001 to 0.6%

As mentioned above, Ba is one of most important element of the present invention.The atomic diameter of Ba is

Its atomic diameter is much larger than the Ba of other alloying element (Fe, Cr, Mo, W, Ni, Mn, Si etc.) of duplex stainless steel, therefore the element that stops as being used to stop as the diffusion of Cr, the Mo of the main moiety of phase between friable metal and W can reduce velocity of diffusion, speed of separating out and the amount of separating out effectively.In addition, Ba combines with solute element and oxygen to form oxide compound, has reduced σ phase and χ speed of separating out mutually thus.In order to obtain above-mentioned effect, need be less than or equal to 0.6% Ba.When the content of Ba surpassed 0.6%, it was disadvantageous economically.In addition, a large amount of Ba separate out in crystal boundary, thereby have reduced grain-boundary strength at high temperature and offset improvement to the high temperature cracking sensitivity.Therefore, the upper limit of Ba is set at 0.6%.On the other hand, if the content of Ba is lower than 0.0001%, then its adding effect is difficult to expect.

MM and/or Y:0.0001 to 1.0%

(mixed rare earth alloy: by its nucleidic mass is the mischmetall of the atomic building of 57-71 to MM, and it includes at least more than or equal to 50% Ce, a certain amount of La, Nd and Pr, trace P m, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and Sc and the Fe that is less than or equal to 1%.As mentioned above, detailed description of the present invention and embodiment use such MM, the Fe that its principal element includes 51%Ce-26%La-15.5%Nd-5.5%Pr, trace P m, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and Sc and is less than or equal to 1%) and/or Y be can be with Ba or one of most important alloying element of adding not together.When adding MM and/or Y, it can prevent to form separately the Al that the overall performance of steel is had disadvantageous effect ₂O ₃With the MnS non-metallic inclusion, in molten steel, form the rare earth compound mixture (RE of diameter less than 5 μ m _xO _yOr (RE, Al) _xO _y+ RE _xO _yS+RES _y), be used as and in solidifying, make the tiny heterogeneous nucleation position of consolidated structure, and the segregation of control solute element, thereby mechanical property, physicals and erosion resistance improved.

In addition, it is very effective for the speed of separating out that postpones between friable metal mutually to remain on Y, MM in the steel, that have the thick atom diameter (Ce, La, Nd, Pr etc.), Ba, Zr and Ti with atomic condition.MM and/or Y are the very important elements that is used to improve weldability, high-temperature oxidation, machinable and high temperature process.The content range of MM and/or Y is 0.0001 to 1.0%.If the content of MM and/or Y surpasses 1.0%, then this to be added on be disadvantageous economically, and too much amount has disadvantageous effect on the overall performance of steel.When the content of MM and/or Y is lower than 0.0001%, then can not obtain above-mentioned additive effect.

And, in order to obtain because at rare earth compound mixture (RE _xO _yOr (RE, Al) _xO _y+ RE _xO _yS+RE _xS _y) the dentrite that solidifies during forming heterogeneous nucleation and the macro-uniformity in the segregation zone of the fine structure that produces and the solute element that causes by the speed of separating out that makes Y, MM (Ce, La, Nd, Pr etc.), Ba, Zr and Ti to stop to be beneficial to the diffusion of Cr, Mo, Si and W that intermetallic phase forms to reduce intermetallic phase, the numerical range of the formula of the solubility product of MM in the steel and/or Y and Al, O and S [MM and/or Y+Al] [O+S] is set at 0.001 * 10 ^-5To 30000 * 10 ^-5[%] ²When the numerical value of the formula of this solubility product is lower than 0.001 * 10 ^-5, then be difficult to control this consolidated structure, thereby reduced the segregation of solute element and the formation of inhibition intermetallic phase.If the numerical value of the formula of this solubility product is higher than 30000 * 10 ^-5[%] ², then the rare earth compound mixture forms too much, thereby has reduced mechanical property, physicals and the corrosion resistance nature of steel.More preferably, in the situation of foundry goods, the numerical range of the formula of this solubility product is 1 * 10 ^-5To 5000 * 10 ^-5[%] ², and in the situation of hot-work part, the numerical range of the formula of this solubility product is 0.1 * 10 ^-5To 2000 * 10 ^-5[%] ²

The content of MM is preferably 0.01 to 0.6%, and more preferably 0.2 to 0.5%.

Ca: be less than or equal to 0.5%

Ca is the deoxidant element that is used to improve anti-embrittlement and reduces high temperature resistant deformability and anti-machinable.When adding a large amount of Ca, it has reduced the purity and the erosion resistance of steel.Preferably, adding is less than or equal to 0.5% Ca.

Al, O and S

Al is the ferritic stabilizer that is used to improve oxidation-resistance and anti-embrittlement.When joining Al in the steel, it has improved the purity of steel by desoxydatoin, and has reduced high temperature deformation resistance.Preferably, adding is less than or equal to 1.0% Al.

Steel includes O and S basically in addition, and they have reduced ductility after solidificating period produces crackle and producing.Therefore, should limit the adding that can produce brittle O and S.In the situation of foundry goods, should add O that is less than or equal to 200ppm and the S that is less than or equal to 50ppm, and in the situation of forging, should add O that is less than or equal to 100ppm and the S that is less than or equal to 20ppm.

Ti: be less than or equal to 1.5%

Ti demonstrates desoxydatoin in fusion process, and forms titanium sulfide to improve machinable.In order to improve the intercrystalline erosion resistance, determine the content of Ti according to the amount of C.Add and to be less than or equal to 1.5% Ti and to improve erosion resistance in the environment that after sensitization thermal treatment, is comprising chlorion.

Mg: be less than or equal to 0.5%, Ta: be less than or equal to 0.5%, Nb: be less than or equal to 0.5%, Zr: be less than or equal to 1.0%, Sn: be less than or equal to 1.0%, In: be less than or equal to 1.0%

As disclosed, except the Ca of its atomic diameter greater than Fe, Cr, Mo and W by the inventor

Al

And Ti Outside, Mg

Ta

Nb

Zr

Sn And In

Can be used for suppressing effectively σ mutually with χ mutually.Therefore, add and to be less than or equal to 0.5% Mg, to be less than or equal to 0.5% Ta, to be less than or equal to 0.5% Nb, to be less than or equal to 1.0% Zr, the In that is less than or equal to 1.0% Sn and is less than or equal to 1.0%.

Prescribe a time limit when above-mentioned alloying element surpasses on it, they are disadvantageous economically, and produce the crystal boundary embrittlement, thereby but weaken castibility and hot workability.

B: be less than or equal to 0.1%

B helps improving anti-embrittlement and reduces high temperature deformation resistance, and prevents to occur in welding heat cracking.When B adds fashionablely with N, form and to have low-melting boron nitride, thereby change Bodhisattva's machinable.Especially, therefore the atomic diameter of B has filled minim gap much smaller than Fe, Cr, Mo, W, Ni, Mn and Si.Therefore, when B when having than the coexistence of the alloying element of thick atom diameter, it can improve blocking effect, thereby reduces σ mutually and χ speed of separating out mutually.Preferably, adding is less than or equal to 0.1% B.

Cu: be less than or equal to 3%

Cu is the austenite stable element that is used to improve erosion resistance.Especially, when Cu adds fashionablely with Mo, it has improved the erosion resistance in the sour environment of enrichment sulfuric acid and spirit of salt significantly.Cu also causes the solid solution hardening effect of replacement, thereby improves tensile strength and yield strength.

If do not consider not compare, Cr and Mo and add proper C u, then Cu can reduce pitting resistance.In addition, Cu can improve the important element of machinable by reducing work hardening speed.When Cu content surpassed 3%, it produced red brittleness.Therefore, adding is less than or equal to 3% Cu.

Co: be less than or equal to 3.0%

Co is a kind of austenite stable element, and it can replace Ni.Co is very effective for improving erosion resistance and intensity, but its expense is higher.Consider the equilibrium of comparing with erosion resistance, add and be less than or equal to 3.0% Co.

Example 1: the method that is used for Computer-Assisted Design, Manufacture And Test steel of the present invention

Now, will describe design and the method for making according to optimum alloy of the present invention.By with the alloy designs factor (for example, 1. PREW of equation, be used for [PREW (γ)-PREW[α] that the erosion resistance of each phase is weighed], equation Cr 2. _EquivalentWith equation Ni 3. _Equivalent) optimally combine the method that obtains to design this alloy, and be displayed in Table 2 out resulting numerical value.

2. and 3. calculate Cr by equation _EquivalentAnd Ni _EquivalentTo determine this component, use as at technical purity grade Fe, Cr, Mo, Ni, W, Cu, Si, Mn and the Fe-Cr-N described in the claim of the present invention and with the fusion in high frequency furnace of these alloying elements, and (for example according to general method, Ti, Mg, Al, Ca or the deoxidation of Al+Ca component) be able to deoxidation, fused foundry goods in air is taken a sample, and fused forging in vacuum and nitrogen atmosphere is taken a sample.As shown in table 4, by analyze to constitute austenite mutually and Cr, Mo, W and the N unit of ferritic phase usually obtain table 2, as [PREW (γ)-PREW[α] of erosion resistance measurement] numerical value, and with resulting these numerical value import into the PREW equation 1. in.

According to another aspect of the present invention, according to conventional methods (for example, Al, Ca or the deoxidation of Al+Ca component) make the preliminary deoxidation of molten steel that contains just like at the element described in the claim of the present invention, and Ba and/or MM and/or Y are joined in the molten steel, to form barium oxide or rare earth compound mixture (RE _xO _yOr (RE, Al) _xO _y+ RE _xO _yS+RE _xS _y), thereby solubility product can satisfy ' [Ba and/or MM and/or Y+Al] [O+S] '=0.001 * 10 ^-5To 30000 * 10 ^-5[%] ²

Afterwards, by poured with molten metal being produced the heavy tabular foundry goods (9mm is thick) of 25Kg in the board-like ceramic mold, and by poured with molten metal being advanced produce in the pre-warmed rectangle steel mold the heavy steel ingot of 30Kg.Be used for the ingot casting situation of forging, using grinding or process for machining that it is processed into appropriate size,, and be hot-rolled down to 6mm thickness 1250 ℃ of following soaking.In 1050 to 1150 ℃ temperature range, foundry goods and the thick hot rolling part of 6mm are carried out solution heat treatment.Table 1 shows the chemical ingredients of the steel through solution heat treatment of the present invention of comparing with comparative steel and merchant steel.

In order to estimate through the product of solution heat treatment and under 850 ℃, to have carried out the overall performance of 10 minutes aging heat treatment products, measure microtexture, X-ray diffraction test result, anodic polarization test result, critical pitting temperature, critical crevice corrosion temperature and its mechanical property.

Use the SiC polishing paper that these samples are polished to 2000grit, use the aluminum oxide polishing at last, under 80 ℃ at Murakami solution (30gK ₃Fe (CN) ₆+ 30gKOH+100ml distilled water) handle etching and in acetone and distilled water, carry out ultrasonic cleaning in.Then, use the microtexture of these samples of observation by light microscope.

Carry out X-ray diffraction test with confirm according under 850 ℃, carry out σ that timeliness thermal treatment in 30 minutes separates out mutually with χ mutually.Use Rikagu D/MAX-B as test set, under the electric current of the alternating voltage of 35kV and 35mA, these samples are analyzed, and the Ni strainer is used with the Cu target.Result according to the observation, analyze wherein having separated out perhaps these samples of heterogenetic in 30 to 120 ° angular range with 12 °/minute speed, and 40 ° to 50 ° the angle place that observes the peak concentration of precipitated phase therein with 1 °/minute speed again carries out Accurate Analysis.

Use the 1mV/ sweep velocity of second, in 50 and 70 ℃ degassing 0.5N HCl+1.0N NaCl solution, each ASTM G5 is carried out the anodic polarization test.

Measure the critical pitting resistance of each ASTM G48A-92, and measure the critical crack corrosion temperature of each ASTM G48D.

These samples are polished to 600grit, and by using Rockwell hardness test meter to measure the hardness of these samples as unit with C.

Example 2: the comparison of the microtexture of ageing prod

Figure 1A to 1F is the photo of microtexture, show under 850 ℃ through friable metal 30 minutes aging heat treatment steel 4 of the present invention (Figure 1A), steel of the present invention 10 (Figure 1B) and steel 36 of the present invention (Fig. 1 C), comparative steel 47 (Fig. 1 D) and commodity high-grade duplex stainless steel UR 52N+ (Fig. 1 E) and SAF 2507 (Fig. 1 F), that can weaken erosion resistance and mechanical property between mutually (for example, σ mutually with χ mutually) separate out.Light demonstrates the austenite phase, and dark part demonstrates the ferritic phase that resolves into σ phase+austenite phase in timeliness thermal treatment.The degree of separating out of intermetallic phase is " steel 4=of the present invention steel 10=of the present invention steel 36 of the present invention " merchant steel UR52+ " merchant steel SAF2507≤comparative steel 47 ".Therefore,

steel

4,10 of the present invention and 36 is compared with merchant steel UR52+ and SAF2507 and comparative steel 47, has suppressed separating out of intermetallic phase more, thereby has improved anti-embrittlement significantly.

The test of example 3:X x ray diffraction analysis x

Fig. 2 A to 2D is the graphic representation of X-ray diffraction analysis test-results, show under 850 ℃ through friable metal 30 minutes aging heat treatment steel 4 of the present invention (Fig. 2 A), comparative steel 47 (Fig. 2 B) and commodity high-grade duplex stainless steel UR 52N+ (Fig. 2 C) and SAF 2507 (Fig. 2 D), that can weaken erosion resistance and mechanical property between mutually (for example, σ mutually with χ mutually) separate out.Compare with comparative steel 47 and merchant steel UR 52N+ and SAF 2507, steel 4 of the present invention is not separated out the σ phase, and separates out χ phase seldom, thereby has improved anti-embrittlement significantly.

Example 4: the macrostructure in as-cast condition and the comparison of microtexture

Fig. 3 A to 3D is a photo, and (φ 110mm * middle portion neutralization L550mm) is in the macrostructure (Fig. 3 A and 3B) and the microtexture (Fig. 3 C and 3D) of the comparative steel 47 of as-cast condition to show method steel ingot that produce, steel 10 of the present invention according to the formation of segregation that is used for controlling consolidated structure, solute element and intermetallic phase.

With wherein to cause the numerical value of solubility product be zero comparative steel 47 (0.015%O owing to not adding MM and Al, macrostructure 0.007%S) (Fig. 3 B) is compared, and wherein solubility product [MM+Al] [O+S] numerical value of the MM of molten steel (Ce, La, Nd, Pr) and/or Y and Al, O and S is 352.0 * 10 ^-5[%] ²Steel of the present invention 10 (0.09%MM, 0.02%Al, 0.025%O and 0.007%S) macrostructure (Fig. 3 A) be trickle equiaxed crystal structure, wherein limited the growth of styloid, have fine and close consolidated structure, and can not produce V segregation and oppositely V segregation.

In addition, compare with the microtexture (Fig. 3 D) of comparative steel 47, the microtexture of steel 10 of the present invention (Fig. 3 C) suppressed significantly to weaken erosion resistance and mechanical property intermetallic phase (for example, σ mutually with χ mutually) separate out, and reduced the size of austenite and ferritic phase.

Example 5: the anodic polarization test-results in as-cast condition

Fig. 4 is a graphic representation, shows the steel of the

present invention

4,10,26 that is not subjected to solution heat treatment and 36 and be in the anti-anodic polarization test-results of the comparative steel 47 in the as-cast condition.The degree of pitting resistance is " steel 10 of the present invention＞steel 4 of the present invention＞steel 36 of the present invention 〉=steel 26＞comparative steel 47 of the present invention ".

Example 6: the result of critical spot corrosion and the test of critical crack corrosion temperature

Fig. 5 is a chart, shows the critical pitting temperature through steel of the

present invention

4,10,26 and 36, commodity high-grade duplex stainless steel UR 52N+, SAF 2507 and ZERON100, commodity duplex stainless steel SAF2205, commodity high-quality austenitic stainless steel SR-50A and the commodity austenitic stainless steel AISI316L of solution heat treatment.When critical pitting temperature raise, pitting resistance improved.The degree of the pitting resistance of steel of the present invention and merchant steel is " steel 10=of the present invention steel 26=of the present invention steel 36＞merchant steel of the present invention SR-50A＞steel 4＞merchant steel UR 52N+=merchant steel ZERON100 of the present invention＞merchant steel SAF 2507＞merchant steel SAF 2205＞merchant steel AISI 316L ".

Steel

10,26 and 36 of the present invention demonstrates its pitting resistance and is higher than commodity high-grade duplex stainless steel UR 52N+, SAF 2507 and ZERON100, and its erosion resistance is higher than commodity high price austenitic stainless steel SR-50A.The critical pitting temperature of steel of the present invention is far above comparative steel and merchant steel, and therefore as shown in table 2 have a higher critical crack corrosion temperature, improved cracking resistance seam corrodibility thus significantly.Table 2 shows the critical pitting temperature and the critical crack corrosion temperature of these steel.

Example 7: through the anodic polarization test-results of solution heat treatment product

Fig. 6 A to 6C is a graphic representation, shows through steel of the

present invention

4,10,26 and 36 (Fig. 6 A), commodity high-grade duplex stainless steel UR 52N+, SAF 2507 and the ZERON100 (Fig. 6 B) of solution heat treatment and the anti-anodic polarization test-results of commodity high-quality austenitic stainless steel AL-6XN, SR-50A and 254SMO (Fig. 6 C).The degree of pitting resistance is " steel 26=of the present invention steel 36=of the present invention merchant steel SR-50A＞steel 10 of the present invention＞steel 4 〉=merchant steel AL-6XN of the present invention＞merchant steel 254SMO 〉=merchant steel UR 52N+=SAF 2507=ZERON 100 ".

In example 6, therefore the critical pitting temperature of steel of the present invention and critical crack corrosion temperature have high spot corrosion possibility (with reference to table 2) far above comparative steel and merchant steel in the anodic polarization test.That is, these three tests demonstrate similar result.

Example 8: the anodic polarization test-results of ageing prod (850 ℃ * 10 minutes)

Fig. 7 A and 7B are graphic representation, show under 850 ℃ the anti-anodic polarization test-results through 10 minutes aging

heat treatment steel

4,10,26 of the present invention and 36 (Fig. 7 A) and commodity high-grade duplex stainless steel UR 52N+, SAF 2507 and ZERON 100 (Fig. 7 B).The degree of pitting resistance is " a steel 4=of the present invention steel 10=of the present invention steel 26 of the present invention＞steel 36＞merchant steel ZERON 100＞merchant steel SAF 2507＞merchant steel UR 52N+ of the present invention ".

Therefore, with merchant steel UR52N+, SAF 2507 and ZERON 100 compare,

steel

4,10 and 26 of the present invention reduced intermetallic phase during timeliness thermal treatment (for example, σ mutually with χ mutually) speed of separating out, thereby improved pitting resistance.

Example 9: the anodic polarization test and the hardness measurement result of ageing prod (850 ℃ * 30 minutes)

Fig. 8 A and 8B are graphic representation, show under 850 ℃ the anti-anodic polarization test-results through 30 minutes aging

heat treatment steel

4,10,26 of the present invention and 36 (Fig. 8 A) and commodity high-grade duplex stainless steel UR 52N+, SAF 2507 and ZERON 100 (Fig. 8 B).The degree of pitting resistance is " steel 10 of the present invention＞steel 4 of the present invention＞steel 36=of the present invention steel 26=of the present invention merchant steel SAF 2507＞merchant steel ZERON 100＞merchant steel UR 52N+ ".

Therefore, compare with merchant steel UR52+, SAF 2507 and ZERON 100, intermetallic phase (for example during steel 4 of the present invention and 10 had reduced timeliness thermal treatment, σ mutually with χ mutually) speed of separating out, thereby improved pitting resistance significantly, and steel of the

present invention

36 and 26 demonstrates the pitting resistance similar or higher with merchant steel.

Table 2 shows by the hardness numerical value H from passing through at 850 ℃ of following 30 minutes aging heat treatment steel of the present invention _AIn deduct hardness numerical value H through the steel of the present invention of solution heat treatment _S.AHardness number value difference value (the Δ H=H that is obtained _A-H _S.A).In general, when having high brittle σ when increasing mutually with χ mutually, Δ H also increases, thereby has seriously reduced erosion resistance, intensity, unit elongation and shock strength.As shown in table 2, owing to the speed of separating out of intermetallic phase postpones to make that the scope of Δ H of steel of the present invention is 0.1 to 3.7, the Δ H scope of comparative steel is 10.3 to 16.2, and the Δ H scope of merchant steel is 5.6 to 6.2.That is, steel of the present invention demonstrates the anti-embrittlement more excellent than comparative steel.

Example 10: mechanical property

Table 3 shows yield strength, tensile strength and the unit elongation after foundry goods being carried out 1130 ℃ solution heat treatment and carrying out tension test thereon.Steel of the present invention obtains calking solution hardening effect and has high strength by the fixedly grain boundary of Ba and rare-earth oxide or sulfide (＜5 μ m) owing to having added high N, thereby improves intensity and unit elongation simultaneously.Therefore, mechanical property ratio comparative steel of the present invention is much better.

Example 11: the performance of hot rolling sample

Critical pitting temperature, mechanical property and the hot workability of the hot rolling sample after Fig. 5 shows and casts in vacuum and nitrogen atmosphere.The hot rolling sample demonstrates mechanical property and the microtexture than the steel of casting of the present invention high 10% in air, and demonstrates and they similar erosion resistances.

The hot rolling sample is producing on the edge than the crackle still less of the comparative product during hot rolling, thereby keeps high hot workability.

Industrial applicibility

As mentioned above, by add an amount of Ba with thick atom diameter, Y, Ce, La, Nd, Pr, Ta, Zr and Ti atom postpone the diffusion of intermetallic phase and separate out, and by adding trace RE metallic compound mixture or barium monoxide additionally stop the diffusion of Cr, Mo, Si and W, thereby fall The speed of separating out of low high embrittlement intermetallic phase and the amount of separating out, the present invention has removed fragility also thus And improved corrosion resistance.

In addition, carry out suitable preliminary deoxidation by the conventional method according to use Ti, Mg, Ca, Al and Ca+Al and interpolation MM and/or Y, thereby the present invention has prevented that independent formation is to the Al that totally is formed with adverse effect of steel₂O ₃With the MnS non-metallic inclusion. For this reason, by forming diameter less than 5 μ m Rare earth compound mixture (RE_xO _yOr (RE, Al)_xO _y+RE _xO _yS+RE _xS _y), during solidifying dendrite formation, provide the heterogeneous nucleation position so that consolidated structures is trickle, and use solubility product formula " [MM and/or Y+Al] [O+S]=0.001 * 10^-5To 30000 * 10^-5[％] ²" control solute The segregation of element (for example, Cr, Mo, W, Ni, Mn and Si), thus the present invention has improved mechanicalness Energy, physical property and corrosion resistance.

Therefore, the invention provides for being suppressed at significantly two by adding new alloying element The formation of the intermetallic phase in the phase stainless steel (for example, θ phase) and improvement are during large-scale production The method of output capacity.

And, by improving anti-embrittlement and analysing by reduction intermetallic phase (for example, θ phase) Go out speed and prevent crackle, thereby the present invention has improved the output capacity in casting and hot-working. In addition, by be suppressed in the as-cast condition can weaken corrosion resistance and mechanical performance θ mutually with χ mutually Form, and also controlled when the equipment building block welded when in various applications, needing Separating out of these phases in the heat affected zone, thus the present invention has improved corrosion resistance and machine significantly Tool performance and improved the durability of equipment.

Claims

1. has high corrosion resistance, anti-embrittlement, but the high-grade duplex stainless steel of castibility and hot workability, it has suppressed the formation of intermetallic phase, it consists predominantly of by weight: 21.0 to 38.0% Cr, 3.0 Ni to 12.0%, 1.5 Mo to 6.5%, 0 to 6.5% W, be less than or equal to 3.0% Si, be less than or equal to 8.0% Mn, 0.2 N to 0.7%, be less than or equal to 0.1% C, the Fe of 0.0001 to 1.0% MM and/or Y and measurement and unavoidable impurities altogether, described MM is for being the mischmetall of the atomic building of 57-71 by nucleidic mass, it includes at least the Ce more than or equal to 50%, a certain amount of La, Nd and Pr, trace P m, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and Sc and the Fe that is less than or equal to 1%, pitting resistance equivalent (PREW) is 1. limited by the following formula that satisfies 40≤PREW＜67:

PREW＝wt％Cr+3.3(wt％Mo+0.5wt％W)+30wt％N---①。

2. high-grade duplex stainless steel as claimed in claim 1 is characterized in that, is 0.001 * 10 as the numerical range of [MM and/or Y+Al] [O+S] of the solubility product formula of the MM of steel and/or Y and Al, O and S ^-5To 30000 * 10 ^-5[%] ²

3. high-grade duplex stainless steel as claimed in claim 2 is characterized in that, in the foundry goods situation, the numerical range of described solubility product formula is 1 * 10 ^-5To 5000 * 10 ^-5[%] ²

4. high-grade duplex stainless steel as claimed in claim 2 is characterized in that, in the hot-work part, the numerical range of described solubility product formula is 0.1 * 10 ^-5To 2000 * 10 ^-5[%] ²

5. described according to claim 1 high-grade duplex stainless steel is characterized in that total weight range of MM and/or Y is 0.01 to 0.6%.

6. high-grade duplex stainless steel as claimed in claim 5 is characterized in that, total weight range of MM and/or Y is 0.2 to 0.5%.

7. high-grade duplex stainless steel as claimed in claim 1, it is characterized in that, also comprise at least a element that is selected from following group, this group comprises: be less than or equal to 0.5% Ca, be less than or equal to 0.5% Mg, be less than or equal to 1.0% Al, be less than or equal to 0.5% Ta, be less than or equal to 0.5% Nb, be less than or equal to 1.5% Ti, be less than or equal to 1.0% Zr, the In that is less than or equal to 1.0% Sn and is less than or equal to 1.0%.

8. as claim 1 or 7 described high-grade duplex stainless steels, it is characterized in that, also comprise and be less than or equal to 0.1% B.

9. as each described high-grade duplex stainless steel in the claim 1,7 and 8, it is characterized in that, also be included in and be less than or equal to 3.0% Cu and be less than or equal among 3.0% the Co one or more.

10. high-grade duplex stainless steel as claimed in claim 1 is characterized in that, as austenite mutually and [PREW (γ)-PREW[α] of the measurement of the erosion resistance of ferritic phase] numerical value be-5 to 10.

11. high-grade duplex stainless steel as claimed in claim 1 is characterized in that, the volume percent scope of ferritic phase is 20-70%, and the volume percent scope of austenite phase is 30-80%.