CN116334506A - Economical duplex stainless steel for pump valve castings - Google Patents
Economical duplex stainless steel for pump valve castings Download PDFInfo
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- ATJFFYVFTNAWJD-UHFFFAOYSA-N Tin Chemical compound [Sn] ATJFFYVFTNAWJD-UHFFFAOYSA-N 0.000 description 1
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Classifications
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
- C21C5/00—Manufacture of carbon-steel, e.g. plain mild steel, medium carbon steel or cast steel or stainless steel
- C21C5/005—Manufacture of stainless steel
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C33/00—Making ferrous alloys
- C22C33/04—Making ferrous alloys by melting
- C22C33/06—Making ferrous alloys by melting using master alloys
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/001—Ferrous alloys, e.g. steel alloys containing N
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/005—Ferrous alloys, e.g. steel alloys containing rare earths, i.e. Sc, Y, Lanthanides
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
- F04B—POSITIVE-DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS
- F04B53/00—Component parts, details or accessories not provided for in, or of interest apart from, groups F04B1/00 - F04B23/00 or F04B39/00 - F04B47/00
- F04B53/10—Valves; Arrangement of valves
- F04B53/108—Valves characterised by the material
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/001—Austenite
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/005—Ferrite
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P10/00—Technologies related to metal processing
- Y02P10/20—Recycling
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Abstract
The invention provides economic duplex stainless steel for pump valve castings. The duplex stainless steel comprises the following components in percentage by mass: c is less than or equal to 0.03wt percent, si is less than or equal to 1.00wt percent, mn:4.00 to 6.50 weight percent, P is less than or equal to 0.04 weight percent, S is less than or equal to 0.03 weight percent, cr:20.0 to 22.5 weight percent of Ni:1.00 to 1.70 weight percent, mo:0.10 to 0.80 weight percent, cu:0.10 to 0.80 weight percent, N:0.20 to 0.35 weight percent of Re less than or equal to 0.05 weight percent, and the balance of Fe and unavoidable impurities. The ferrite content in the economical duplex stainless steel structure is 50% +/-10%. Scrap steel, pure iron and alloy are added into a furnace for smelting, a molten steel sample obtained after smelting is subjected to component detection, the molten steel component in the furnace is adjusted according to the component detection result, and a small amount of CaSi alloy and trace Re alloy are added into a steel ladle before tapping. The economical duplex stainless steel can be used for castings, reduces the alloy cost of the cast duplex stainless steel by reducing the content of noble metals such as Cr, ni, mo and the like, saves non-renewable resources, and has excellent mechanical property and corrosion resistance.
Description
Technical Field
The invention relates to the technical field of cast stainless steel materials, in particular to economic duplex stainless steel for pump valve castings.
Background
The duplex stainless steel is a stainless steel with ferrite phase (namely alpha phase) and austenite phase (namely gamma phase) in a tissue accounting for about half of each other, and combines the excellent toughness of the austenite stainless steel with the higher strength and the chloride stress corrosion resistance of the ferrite stainless steel, so that the duplex stainless steel has the advantages of two types of stainless steel materials, and the development is very rapid. The research and development and industrial application of the duplex stainless steel have been in the past hundred years, and the duplex stainless steel is widely applied to the fields of petroleum and natural gas, chemical industry, papermaking, construction, ocean platforms, ships, food, light industry and the like with high corrosion resistance requirements, and the excellent comprehensive performance, particularly the corrosion resistance, is widely accepted.
At present, duplex stainless steel has various types, and can be divided into four types according to alloy components and corrosion resistance: the first type does not contain Mo, has low alloying degree, is typically composed of 23 percent Cr, 4 percent Ni and 0.1 percent N, has certain corrosion resistance, has excellent stress corrosion resistance, has better corrosion resistance than 304, is equivalent to 316 in certain aspects, and is typically represented by steel grade SAF2304. The second type is standard duplex stainless steel, the typical components are 22% Cr, 5% Ni, 3% Mo and 0.17% N, the corrosion resistance is excellent, the corrosion resistance is between 316 and 6% Mo super austenitic stainless steel, and the typical representative steel grade SAF2205. The third type is high-grade duplex stainless steel, the typical components are 25% Cr, mo, N, cu, W and other alloy elements, and the typical steel type UNSS32550 (25 Cr-6Ni-3Mo-2 Cu-0.2N) is the duplex stainless steel with corrosion resistance higher than that of 22% Cr. The fourth type is super duplex stainless steel, the typical components are 25% Cr, 6-8% Ni, 3-5% Mo and 0.2-0.3% N, and the super duplex stainless steel has extremely high corrosion resistance, is commonly used in environments with severe corrosion environments, can replace super austenitic stainless steel and titanium materials, and typically represents steel grade SAF2507. The alloy components of the four types of duplex stainless steel are characterized by high chromium, high nickel and molybdenum (without molybdenum), and the alloy cost is high.
In recent years, the price of noble metal alloys such as chromium, nickel, molybdenum and the like has increased, so that the enterprise cost has increased, and the development of economic duplex stainless steel is urgent. The stainless steel industry company is fully researched aiming at the component system design, corrosion resistance, phase change, mechanical properties and the like of the economic duplex stainless steel. At present, the economic nickel-saving duplex stainless steel mainly has two development directions, one is to add manganese into the alloy components of the duplex stainless steel to replace all or part of nickel, namely, the manganese is used for replacing the nickel-type duplex stainless steel; one is to increase the nitrogen content or add nitrogen and manganese in a compound way, reduce the nickel content and achieve the aim of saving nickel in the duplex stainless steel. LDX 2101 (EN 1.4162,UNS S32101) developed by Outokumpu Stainless has typical compositions of 21.5% Cr, 5% Mn, 1.5% Ni, 0.22% N, 0.3% Mo, 0.3% Cu. LDX 2101 is representative of economic duplex stainless steel, has the strength twice that of A1SI304 austenitic stainless steel, has better pitting corrosion resistance, has the material cost remarkably lower than 304, is widely applied to the industries of nuclear power, storage tanks and the like at present, and is already appointed to be used for parts such as nuclear power AP1000 heap type pool cladding plates and the like.
The economic duplex stainless steel developed at home and abroad at present is based on structural materials, has less research and development on the economic duplex stainless steel for casting, does not establish corresponding standards or specifications, and is basically blank in China.
Disclosure of Invention
In view of the above, the invention aims to provide the economic duplex stainless steel for the pump valve castings, which reduces the content of noble metals such as chromium, nickel, molybdenum and the like through optimizing chemical components, can reduce the alloy cost of the duplex stainless steel for the castings, can save non-renewable resources, and can meet the requirements of corrosive environments on the duplex stainless steel castings.
In order to achieve the above purpose, the technical scheme of the invention is realized as follows:
an economical duplex stainless steel for pump valve castings, characterized in that the economical duplex stainless steel comprises the following components in percentage by mass:
the balance of Fe and unavoidable impurities.
The economical duplex stainless steel for pump valve castings has the following alloying mechanism:
the alloying elements have significant effects on the structure and performance of duplex stainless steel. The influence on the structure mainly means influence on the metallographic structure type, grain size, grain boundary state, shape distribution and dispersion degree of the strengthening phase, microscopic defects (lattice distortion, vacancies, dislocations) and the like. The alloy element mainly affects the structure of the steel, thereby playing a role in the mechanical property and corrosion resistance of the steel. The alloying elements in duplex stainless steel are mainly classified into two types, one type is austenite forming elements such as C, mn, ni, N and the like, and the other type is ferrite forming elements such as Si, cr, mo and the like, and these alloying elements directly affect the structure and performance of duplex stainless steel.
C: the gamma phase is strongly formed, and its ability to form the gamma phase is 30 times that of Ni, but its corrosion resistance decreases with an increase in C content.
Si: the alpha phase is strongly formed, the formation of the sigma phase is promoted, and the effect of Si is stronger along with the increase of Cr and Mo contents in steel. The Si content of the dual-phase steel is properly increased, so that the oxidation resistance of the dual-phase steel can be remarkably improved, but the excessive Si content can promote the precipitation of sigma phase, and the plasticity, toughness and processing performance of the steel are reduced.
Mn: and a gamma phase is formed, and can replace Ni element and be used as an alloy element of the economic duplex stainless steel together with N. Mn is unfavorable for pitting corrosion resistance of the duplex stainless steel, and most of MnS inclusions formed by combination of Mn and S are distributed along grain boundaries to form pitting corrosion sensitive points, but the adverse effect of Mn can be eliminated to a certain extent after Mo is added into the steel, so that the effect of Mn in improving the solubility of N in the duplex stainless steel is exerted. The Mn content is properly increased, the hot workability of the steel can be improved, and the strength of the steel is also improved to a certain extent.
Cr: elements that strongly form and stabilize the alpha phase and narrow the gamma phase region are also basic alloying elements for stainless steel to attain corrosion resistance. The Cr content in the duplex stainless steel is properly increased, so that the alpha phase can be stabilized, the gamma phase area can be reduced, the martensitic transformation temperature can be reduced, and the yield strength, general corrosion resistance, pitting corrosion resistance and dilute sulfuric acid corrosion resistance of the duplex steel can be improved. Meanwhile, with the increase of Cr amount, the precipitation of intermetallic phases such as alpha', sigma and the like can be accelerated, so that the brittleness tendency of steel is increased, and the brittleness transition temperature is obviously increased. In order to control the proper two-phase ratio, the chromium content in the steel is increased, and then the nickel content in the steel is increased.
Ni: the elements of the gamma phase region are strongly formed and enlarged, the Ni content in the dual-phase steel is properly increased, the gamma phase is stabilized, the gamma phase region is enlarged, the martensitic transformation temperature is reduced, and the cold processing performance, the pitting corrosion resistance, the crevice corrosion resistance and the pitting corrosion resistance of the dual-phase steel are remarkably improved, and the sulfuric acid and phosphoric acid corrosion resistance is improved. However, when the nickel content is too high, elements such as chromium and molybdenum which promote sigma brittle phase transformation are enriched in ferrite phase, the toughness of the steel is reduced, the embrittlement sensitivity of the steel is increased, and the embrittlement sensitivity temperature of the steel is promoted to move to a high temperature direction. Too low a nickel content will result in a high iron content in the steel and likewise in a reduced ductility and toughness of the steel.
Mo: the alloy is an alpha phase forming element, and the Mo content of the duplex stainless steel is properly increased, so that the pitting corrosion resistance, crevice corrosion resistance, chloride stress corrosion resistance and reducing medium corrosion resistance of the duplex stainless steel can be improved. However, when the Mo content is too high, precipitation of intermetallic phases such as alpha', sigma, χ and the like is promoted, the precipitation range of a TTT curve is widened, the precipitation temperature is shifted upward, and the embrittlement tendency and notch sensitivity of the duplex stainless steel are increased. For the duplex stainless steel with the Mo content of more than 3.5%, the influence of the increase of the Mo content on brittleness is more serious, which is a main obstacle to the development and application of the high-Mo duplex stainless steel with the Mo content of more than 3.5% at present.
Cu: the corrosion resistance of the steel in the reducing acid can be improved. On the premise of existence of enough Cr, cu and Mo are added in a compounding way, which is more beneficial to improving the H2SO4 corrosion resistance of the duplex stainless steel. The solubility of Cu in the gamma phase (4%) is higher than in the alpha phase (0.2%), which results in precipitation of the epsilon phase at 500-600 c.
N: the element which strongly forms and expands the gamma-phase region has the capacity of forming the gamma-phase which is 30 times that of Ni element, can replace part or even all of Ni in the duplex stainless steel, and is the main element of the economic duplex stainless steel. The content of N element is properly increased, the appearance of a single-phase ferrite structure and the precipitation of a harmful intermetallic phase at high temperature (such as after welding) of the duplex stainless steel can be obviously delayed, the pitting corrosion resistance, crevice corrosion resistance and stress corrosion resistance of the steel are improved, the distribution difference of elements such as Cr, ni and the like in two phases can be reduced, and the selective corrosion tendency is reduced; however, the high content of N can reduce the stress corrosion resistance of the duplex stainless steel, and N can be combined with Al and Ti in the steel to form harmful inclusions AlN and TiN, so that the fatigue life of the duplex stainless steel is reduced, and for casting the duplex stainless steel, the high content of N can easily cause the air hole defect of the casting.
Re: the rare earth alloy is added into the steel, so that the effects of purifying molten steel, modifying and microalloying can be achieved, and the mechanical property and corrosion resistance of the steel are beneficially affected. Rare earth elements are extremely effective non-spontaneous nucleating agents, and can refine grains, reduce the content of harmful gases and impurities in steel, change the property, shape and distribution of inclusions in steel, increase gamma phase and reduce alpha phase by microalloying action of rare earth, and improve high-temperature plasticity and hot working performance of steel.
Residual elements: p, S and the like are easy to gather and separate out near a grain boundary in the cooling and crystallization processes of molten steel, and form low-melting eutectoid with iron, so that the grain boundary is weakened, and a liquid phase appears in hot working, thereby generating a hot embrittlement phenomenon, reducing the workability and creep plasticity of the steel, and often causing weakening of the strength of a welding joint and creep failure; p in steel also enhances the sensitivity of intergranular corrosion in an acidic medium, and S also causes anisotropy of mechanical properties, resulting in reduced pitting corrosion resistance and crevice corrosion resistance.
Further, the ferrite content in the economical duplex stainless steel structure is 50% ± 10%.
Furthermore, the economical duplex stainless steel is prepared by smelting any one of an intermediate frequency induction furnace, an intermediate frequency induction furnace and an AOD furnace, and an intermediate frequency induction furnace and a VOD furnace.
Further, the economical duplex stainless steel is smelted by adding scrap steel, furnace returns, pure iron and alloy into a furnace, after the furnace returns are smelted, sampling is carried out for spectral component analysis, the addition amount of the alloy is calculated according to the component range requirement, and the molten steel component is adjusted until the designed component range is reached.
Furthermore, before tapping, adding a silicon-calcium alloy for final deoxidation before tapping, and adding 0.5-1.5kg/t silicon-calcium alloy and 0.3-1.5kg/tRe alloy into a ladle.
Further, the alloy furnace burden comprises scrap steel, ferrosilicon, pure iron, metallic chromium, ferrochromium nitride, electrolytic nickel, metallic molybdenum, ferromolybdenum, ferrosilicon, re alloy, electrolytic manganese, electrolytic copper, furnace returns and crystalline silicon, and the alloy furnace burden requires surface cleaning, drying, no rust, no oil stain and water removal through high-temperature baking.
Further, the economical duplex stainless steel is used for pump valve corrosion resistant castings.
Compared with the prior art, the economic duplex stainless steel for pump valve castings has the following advantages:
(1) The contents of N and Mn are increased, the contents of noble metals such as Cr, ni, mo and the like are reduced, the alloy cost of casting the duplex stainless steel is reduced, and non-renewable resources can be saved;
(2) The ferrite content in the prepared duplex stainless steel casting structure is controlled within the range of 50% +/-10% through the selection of each element and the selection of the dosage, and the duplex stainless steel casting has excellent mechanical property and corrosion resistance, and can meet the requirements on the mechanical property and corrosion resistance of the duplex stainless steel casting in a corrosion environment;
(3) The economic duplex stainless steel is prepared by adopting a smelting casting method, and the blank that the existing economic duplex stainless steel is used for structural materials and lacks pump valve castings is overcome.
Drawings
The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the invention. In the drawings:
FIG. 1 shows a microstructure of a duplex stainless steel according to example 1 of the present invention.
Detailed Description
The invention is further described below in conjunction with the detailed description. It should be noted that the data in the following examples are obtained by the inventors through a lot of experiments, and are only shown in some of the descriptions, and those skilled in the art can understand and practice the present invention under the data. These examples are only for illustrating the present invention and are not intended to limit the scope of the present invention. Further, it should be understood that after reading the present disclosure, those skilled in the art may make various changes or modifications to the present disclosure, which also fall within the scope of the present disclosure.
It should be noted that, without conflict, the embodiments of the present invention and features of the embodiments may be combined with each other.
The invention will be described in detail below with reference to the drawings in connection with embodiments.
The composition of the economical duplex stainless steel for pump valve castings is shown in table 1.
TABLE 1 economical two-phase stainless steel chemical composition (wt%)
Remarks: h is less than or equal to 4ppm, O is less than or equal to 150ppm, and the balance is Fe and unavoidable impurities.
According to the economic duplex stainless steel for the pump valve casting, the contents of N and Mn are increased in a nitrogen-manganese composite mode, the contents of noble metals such as Cr, ni and Mo, particularly the content of Ni, are reduced, and the contents of elements such as C, si, S, P are reasonably controlled. The two-phase structure is affected by the types and the contents of the elements, the alloy cost of the dual-phase stainless steel for casting can be reduced by selecting and using the elements, the profit level of enterprises is improved, and the ferrite content in the prepared dual-phase stainless steel casting structure is controlled within the range of 50% +/-10%. The mechanical property and the corrosion resistance of the duplex stainless steel casting are excellent, and the requirements of the mechanical property and the corrosion resistance of the duplex stainless steel casting in a corrosion environment can be met.
Furthermore, the economical duplex stainless steel for the pump valve casting is prepared by smelting any one of an intermediate frequency induction furnace, an intermediate frequency induction furnace and an AOD furnace, and an intermediate frequency induction furnace and an VOD furnace. Adding scrap steel, furnace returns, pure iron and alloy into the furnace for smelting, sampling for spectral component analysis after the furnace returns, calculating the addition amount of the alloy according to the component range requirement, and adjusting the molten steel component until reaching the design component range. The following conditions are satisfied for the content of each element: c is less than or equal to 0.03wt percent, si is less than or equal to 1.00wt percent, mn:4.00 to 6.50 weight percent, P is less than or equal to 0.04 weight percent, S is less than or equal to 0.03 weight percent, cr:20.0 to 22.5 weight percent of Ni:1.00 to 1.70 weight percent, mo:0.10 to 0.80 weight percent, cu:0.10 to 0.80 weight percent, N:0.20 to 0.35 weight percent.
Still further, the alloys include scrap steel, ferrosilicon, pure iron, metallic chromium, ferrochromium nitride, electrolytic nickel, metallic molybdenum, ferromolybdenum, ferrosilicon, alloys of calcium and silicon, re alloys, electrolytic manganese, electrolytic copper, recycled materials and crystalline silicon, and the alloy materials require surface cleaning, drying, no rust, no oil stain, and water removal by high temperature baking.
Further, 0.5-1.5kg/t of silicon-calcium alloy and 0.3-1.5kg/tRe alloy are added into the ladle before tapping, so that the content of rare earth elements is less than or equal to 0.05wt% of Re. The molten steel is deoxidized by adding the calcium-silicon alloy, so that molten steel oxidation and air hole defects of castings are avoided, and the adding amount of the calcium-silicon alloy is determined according to the total amount of the molten steel and the oxygen content in the molten steel.
In the prior art, economic duplex stainless steel is mostly prepared by adopting methods such as rolling, forging and the like, firstly, steel ingots with serious component and tissue segregation and coarse grain size are obtained, and then, a forging stock with excellent quality is obtained by adopting an electroslag remelting mode. Because the casting method is adopted, the content of N element and the content of impurity element S, P are difficult to control in the process of smelting into molten steel, and the casting method adopted for casting to obtain the duplex stainless steel has certain difficulty. For example, the N content is higher in the casting process, nitrogen can be overflowed, and air holes can be formed after molten steel is solidified, so that the quality of the duplex stainless steel casting is affected. Therefore, in the invention, when the duplex stainless steel casting is cast by adopting a smelting method, the content of N, S, P is reasonably controlled. By adding Re, impurity elements can be separated out or the property, shape and distribution of impurities can be changed to form other things, so that the impurity content in the stainless steel is reduced. Re also has the effect of refining grains. The invention controls the ferrite content in the dual-phase stainless steel casting structure within the range of 50% +/-10% by reasonably controlling the types and the dosage of each element. The casting has excellent mechanical property and corrosion resistance.
Example 1
Adding scrap steel, pure iron, return furnace material and alloy into the medium frequency induction furnace for smelting; detecting components of molten steel samples obtained after smelting, and adjusting the molten steel in the furnace according to the component detection results; after the temperature of the molten steel reaches the tapping temperature, carrying out final deoxidation, tilting the furnace and tapping, and adding a small amount of CaSi alloy and Re alloy into a steel ladle before tapping; and then casting to obtain the duplex stainless steel casting. The as-cast samples were subjected to spectroscopic analysis. The duplex stainless steel comprises the following components in percentage by mass: c:0.028%, si:0.65%, mn:5.35%, P:0.027%, S:0.012%, cr:22.2%, ni:1.65%, mo:0.55%, cu:0.32%, N:0.26%, re:0.026%, H:2.3ppm, O:88ppm, the balance being Fe. As shown in FIG. 1, the ferrite content in the metallographic structure of the duplex stainless steel casting after solution treatment is 54%.
Example 2
Adding scrap steel, pure iron, return furnace material and alloy into the medium frequency induction furnace for smelting; detecting components of molten steel samples obtained after smelting, and adjusting the molten steel in the furnace according to the component detection results; after the temperature of the molten steel reaches the tapping temperature, carrying out final deoxidation, tilting the furnace and tapping, and adding a small amount of CaSi alloy and Re alloy into a steel ladle before tapping; and then casting to obtain the duplex stainless steel casting. The as-cast samples were subjected to spectroscopic analysis. The duplex stainless steel comprises the following components in percentage by mass: c:0.022%, si:0.54%, mn:6.12%, P:0.029%, S:0.017%, cr:21.2%, ni:1.52%, mo:0.65%, cu:0.42%, N:0.27%, re:0.023%, H:2.1ppm, O:63ppm and the balance of Fe, and the ferrite content in the metallographic structure of the duplex stainless steel casting is 48 percent after solution treatment.
Example 3
Adding scrap steel, pure iron, return furnace material and alloy into the medium frequency induction furnace for smelting; detecting components of molten steel samples obtained after smelting, and adjusting the molten steel in the furnace according to the component detection results; after the temperature of the molten steel reaches the tapping temperature, carrying out final deoxidation, tilting the furnace and tapping, and adding a small amount of CaSi alloy and Re alloy into a steel ladle before tapping; and then casting to obtain the duplex stainless steel casting. The as-cast samples were subjected to spectroscopic analysis. The duplex stainless steel comprises the following components in percentage by mass: c:0.027%, si:0.75%, mn:5.66%, P:0.030%, S:0.015%, cr:22.1%, ni:1.56%, mo:0.68%, cu:0.38%, N:0.31%, re:0.036%, H:2.5ppm, O:86ppm and the balance of Fe, and the ferrite content in the metallographic structure of the duplex stainless steel casting is 51 percent after solution treatment.
The foregoing description of the preferred embodiments of the invention is not intended to be limiting, but rather is intended to cover all modifications, equivalents, alternatives, and improvements that fall within the spirit and scope of the invention.
Claims (7)
1. An economical duplex stainless steel for pump valve castings, characterized in that the economical duplex stainless steel comprises the following components in percentage by mass:
the balance of Fe and unavoidable impurities.
2. The economical duplex stainless steel for pump valve castings according to claim 1, wherein the ferrite content in the economical duplex stainless steel structure is 50% ± 10%.
3. The economical duplex stainless steel for pump valve castings according to claim 1, wherein the economical duplex stainless steel is prepared by smelting in any one of an intermediate frequency induction furnace, an intermediate frequency induction furnace with an AOD furnace, and an intermediate frequency induction furnace with a VOD furnace.
4. The economical duplex stainless steel for pump valve castings according to claim 1, wherein the economical duplex stainless steel is smelted by adding scrap steel, pure iron, returned burden and alloy burden into a furnace, and after the burden is smelted, a sample is taken for spectral component analysis, the addition amount of alloy is calculated according to the component range requirement, and the molten steel component is adjusted until the designed component range is reached.
5. The economical duplex stainless steel for pump valve castings according to claim 1, wherein the economical duplex stainless steel is added with a silicon-calcium alloy for final deoxidization before tapping, and 0.5-1.5kg/t of the silicon-calcium alloy and 0.3-1.5kg/tRe alloy are added into a ladle.
6. The economical duplex stainless steel for pump valve castings according to claim 4, wherein said alloy charge includes scrap steel, ferrosilicon, pure iron, metallic chromium, ferrochromium nitride, electrolytic nickel, metallic molybdenum, ferromolybdenum, silico-calcium alloy, re alloy, electrolytic manganese, electrolytic copper, reflow stock and crystalline silicon, and the alloy charge requires surface cleaning, drying, rust-free, oil-free, and water removal by high temperature baking.
7. The economical duplex stainless steel for pump valve castings according to claim 1, wherein said economical duplex stainless steel is used on pump valve corrosion resistant castings.
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