CN109504916B - Copper-titanium-containing high-strength high-corrosion-resistance austenitic stainless steel and preparation method thereof - Google Patents
Copper-titanium-containing high-strength high-corrosion-resistance austenitic stainless steel and preparation method thereof Download PDFInfo
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Abstract
A copper-titanium-containing high-strength high-corrosion-resistance austenitic stainless steel and a preparation method thereof are disclosed, and the content of alloy elements is as follows: c is less than or equal to 0.08, Ni is 10.0-14.0, Cr is 16.0-18.5, Mo is 2.0-3.0, Ti is less than or equal to 0.32, Cu is 0.2-0.8, Mn is less than or equal to 2.0, Si is less than or equal to 1.0, P is less than or equal to 0.035, S is less than or equal to 0.030, wherein 3.98 x (C-0.01) is less than or equal to Ti is less than or equal to 3.98 xC, and the balance is Fe. After alloy smelting, the TiC is fully crushed and dispersed and distributed through thermal deformation cogging and cold deformation, and coarse austenite grains are obtained through high-temperature solution treatment. Hydrogen is introduced at 80 deg.C and 5 × 10‑6F‑0.5mol/L of H2SO4The alloy corrosion current in the electrolyte is 6.9-9.8 muA/cm2Compared with 316 stainless steel, the corrosion rate is greatly reduced, and the mechanical property is slightly superior to that of the 316 stainless steel.
Description
Technical Field
The invention belongs to the field of austenitic stainless steel, relates to a method for designing, processing and heat treating components of high-corrosion-resistance austenitic stainless steel, and can be widely applied to the fields of energy, electric power, chemical industry and daily life.
Technical Field
The stainless steel has excellent mechanical and corrosion resistance, and is widely applied to the fields of energy, electric power, chemical industry and the like. The austenitic stainless steel has good mechanical property, processability, corrosion resistance and neutron irradiation resistance, and is widely applied to nuclear power industry. The main materials of key equipment such as a main pipeline of a primary circuit of a pressurized water reactor, in-reactor components, a driving mechanism, a main pump, a pump shaft and the like all adopt 304L and 316LN type austenitic stainless steel as structural materials. The materials are used in harsh water chemical environments such as high temperature, high pressure, irradiation and the like for a long time, the structural integrity is ensured, and the materials also need to resist the scouring and corrosion of various special working media so as to reduce the abrasion and the activation of corrosion products in a reactor core and a radiation field outside the reactor core.
A primary circuit main pipeline of a pressurized water reactor nuclear power station is an important barrier for preventing fission products of nuclear reaction from leaking to a containment vessel under normal, abnormal, accident and test working conditions of the nuclear power station. Therefore, the main nuclear power pipeline is required to be resistant to high temperature, high pressure and corrosion. Part of main pipelines of the early nuclear power station adopt low-alloy steel pipes, and stainless steel is built up in the pipes; later nuclear power main pipelines generally adopt 18-8 type austenitic stainless steel, and continuously optimize components and production processes to form the following conditions: (1) stabilized austenitic stainless steel: titanium (Ti) or niobium (Nb) is added into the 18-8 type stainless steel to improve the intergranular corrosion resistance, but the welding performance is poor and the inclusion is too much to influence the processing of the bent pipe; (2) standard 304 and 316 austenitic stainless steels: the carbon content of the 304 stainless steel is reduced on the basis of 18-8 type austenitic stainless steel, 2 percent of molybdenum (Mo) is added into 316 steel, but the 304 stainless steel still has a sensitization tendency after long-term retention at 480-820 ℃; (3) low carbon 304L and 316L austenitic stainless steels: the carbon content is continuously reduced on the original steel grade, and excellent intergranular corrosion resistance, welding performance and processing performance are obtained, but the greatest problem is insufficient strength. The main pipeline of the primary loop of the 2 nd generation pressurized water reactor nuclear power station adopts cast duplex stainless steel, a small amount of ferrite (12-20 percent) is added in an austenite matrix, the strength and the heat crack resistance of the material are improved, and the stress corrosion can be inhibited. But the ferrite content cannot exceed 20%, otherwise a more severe heat aging phenomenon occurs. A main pipeline of a primary circuit of a 3 rd generation pressurized water reactor A P1000 nuclear power plant is made of integrally forged 316LN austenitic stainless steel, belongs to ultra-low carbon nitrogen-controlled austenitic stainless steel, and is added with nitrogen elements on the basis of 316L, so that the strength of the material can be improved, and a higher plastic toughness level is kept.
The in-reactor component refers to all structural components except the fuel assembly and related components in the pressure vessel, and has the defects of multiple components, complex structure, high precision requirement, high temperature and high pressure, neutron irradiation, corrosion of a coolant and the like. Therefore, the principle of selecting the materials of the reactor internals is generally as follows: the strength is properly high, the plasticity and toughness are good, and the shock resistance and the fatigue resistance can be realized; the neutron absorption interface, the neutron capture cross section and the induced radioactivity are small; the coating is radiation-resistant, corrosion-resistant and good in compatibility with a coolant; the thermal expansion coefficient is small; good welding and machining process performance. The main body structure material in the 2 nd generation pressurized water reactor nuclear power station is generally austenitic stainless steel such as 304L, 304LN, 321, 347 and 310, the bolt material is 316L N and 321H stainless steel, and some special parts adopt martensitic stainless steel such as 1Cr13 of a compression spring. The 3 rd generation pressurized water reactor AP1000 nuclear power station has the advantages of higher power, longer service life and tighter requirements on the components and performance of reactor internals. The main structural material of the pressure spring is forged austenitic stainless steel F304 and F304H, and the pressure spring is improved austenitic stainless steel 403.
The ventilation purification equipment of the nuclear power station is mainly used in air supply and exhaust systems, and different types of air filtering units can be installed according to different use working conditions. The air purifier is used for realizing air purification, is particularly suitable for air supply and exhaust systems of polluted or harmful gases, and can effectively protect the safety of system workers and the sanitation of the surrounding environment. Most of the ventilation purification devices of nuclear power plants are made of austenitic stainless steel. The austenitic stainless steel has excellent corrosion resistance and better radiation resistance. However, most nuclear power plants are built in coastal areas, seawater has high air humidity and high salt content, and chloride ions are one of the main causes of corrosion of stainless steel. In order to ensure the safety of a ventilation and purification system of a nuclear power plant, the improvement of the corrosion resistance of austenitic stainless steel is particularly important.
The sodium-cooled fast reactor is one of six fourth-generation nuclear power alternative reactor types, is the second step of three-step development and planning of nuclear energy in China, and is also an important loop of closed cycle of nuclear energy in China. Compared with a pressurized water reactor, the sodium-cooled fast reactor has the characteristics of higher temperature (above 500 ℃), higher irradiation dose and the like. Higher requirements are put on the structural materials of the reactor core assembly, such as the stainless steel cladding tube. Pipelines of sodium-cooled fast reactor steam generators, heat exchangers and the like also need a large number of high-performance austenitic stainless steel pipes, such as 316Ti, 316H and the like.
As can be seen, the austenitic stainless steels commonly used in nuclear power plants are 304(0Cr18Ni9), 304L (00Cr19Ni10), and 316L (00Cr17Ni14Mo 2). 304 stainless steel is a versatile stainless steel that is widely used for manufacturing equipment and parts that require good balance of properties (corrosion resistance and formability). The 304 stainless steel has excellent corrosion resistance and better intercrystalline corrosion resistance. 304L stainless steel is a variant of 304 stainless steel having a relatively low carbon content and is used in applications requiring welding. The lower carbon content minimizes carbide precipitation in the heat affected zone near the weld, which may lead to intergranular corrosion of the stainless steel in certain environments. Therefore, 304L stainless steel is superior to 304 stainless steel in its ability to resist intergranular corrosion. The 316L stainless steel is also called titanium steel, Mo (2-3%) is added, and the stability of the passive film can be improved. The 316L stainless steel has excellent pitting corrosion resistance and intergranular corrosion resistance, also has good chloride corrosion resistance, and has corrosion resistance greatly superior to that of 304 stainless steel and 304L stainless steel in marine environment or aggressive industrial atmosphere. 316L stainless steel >304 stainless steel in terms of corrosion resistance, and ultra-low carbon stainless steel is superior to common stainless steel with the same steel grade. Addition of Ti, Mo or solution treatment is the main method for preventing stainless steel pitting corrosion.
Generally, stainless steel has good corrosion resistance, and has wide application in factory buildings of nuclear power plants and numerous system equipment, and the stainless steel has satisfactory corrosion resistance from large containers, pipelines inside nuclear islands to various valves, instrument pipelines, parts of various equipment and the like. The corrosion resistance mechanism of the stainless steel is that a layer of ultrathin, compact and good-adhesion passive film is generated on elements such as Cr and the like on the surface of the stainless steel and oxygen in the air and is used as a protective barrier to isolate a corrosion medium from a substrate; although the metal under the protection of the passivation film still has certain reaction capability, the passivation film has good self-repairing function. However, stainless steel materials such as pipelines and equipment of nuclear power plants are in complex environments, and it is difficult to ensure the integrity of the passive film under some conditions, and corrosion can be caused if the passive film is corroded by high-concentration chloride ions. The nuclear power station equipment has complex operation conditions and environment, and under certain special conditions, the stainless steel material not only can not effectively resist corrosion, but also can generate phenomena such as pitting corrosion, intergranular corrosion, crevice corrosion, stress corrosion and the like, the local corrosion is not easy to find, and the influence on the equipment is fatal along with the development of the corrosion. Foreign nuclear power plants have had many cases of corrosion of stainless steel and are costly.
The corrosion characteristics of stainless steel common to nuclear power plants are as follows:
(1) pitting corrosion: is localized corrosion of metal surfaces relatively concentrated in a small area. Micro-pits with a diameter of a few micrometers are formed in the protective oxide layer on the surface of the stainless steel before the actual pitting, and the rapid increase of the micro-pits is a cause of the large-scale corrosion of the stainless steel. The stainless steel forms CrO after the acid cleaning and passivation of the surface3Or Cr2O3The oxide film enables the stainless steel to exert the maximum corrosion resistance, and effectively prevents the corrosion and the damage of corrosive media. The corrosion of stainless steel equipment in a nuclear power plant is generally pitting corrosion, and the pitting corrosion part generally appears on the surface with damaged passive film, such as a gap, a scratched surface and the like. If the surface of the stainless steel is moist and contains chloride ions, a strong acid dissolution passivation film can be formed locally, and a stable passivation state is destroyed, resulting in large-area corrosion. Stainless steel corrodes in general air or fresh water environment, and a layer of compact oxide film is formed on the surface of the stainless steel, so that the steel corrosion process is inhibited. However, in the marine environment, the content of chloride ions in the air is high, and the chloride ions can easily replace oxygen in the oxide film to damage the oxide film, so that a stable passive state is difficult to establish in the environment with a certain concentration of chloride ions. As the chloride ions accumulate on the equipment, the concentration of the chloride ions is higher and higherThe corrosion to stainless steel will be greater and greater.
(2) Intergranular corrosion: the corrosion is a common local corrosion of metal corrosion, and the corrosion starts from the surface of the metal and extends towards the interior of the crystal grains along the boundary surface between the metal crystal grains, so that the bonding force between the crystal grains is greatly weakened. It is a selective corrosion that penetrates inside the metal along grain boundaries, which, without any indication of the metal on the external surface, can cause the material to lose its mechanical properties, even its strength completely, and is one of the most harmful forms of localized corrosion. In the long-time running process of the ventilation and purification equipment of the nuclear power station, chloride ions are accumulated to a certain degree to cause intercrystalline corrosion of a stainless steel shell. Stainless steel subjected to such corrosion is not subjected to any corrosion or damage on the surface, but the grain boundary region inside the stainless steel is destroyed. Corrosion to a certain extent can cause damage to components or equipment, and in severe cases can affect the safe operation of the entire nuclear power plant. The austenitic stainless steel has good toughness, plasticity, weldability and corrosion resistance at normal temperature and low temperature, and has the capability of resisting chemical corrosion and electrochemical corrosion.
(3) Corrosion fatigue: in the operation process of a nuclear power station, stress loading effect can be caused to a main loop pipeline by the temperature and pressure change of a coolant or the process of starting and stopping a reactor, and meanwhile, oxidation or corrosion effect can be caused to the inner wall by high-temperature and high-pressure water in the main pipeline, so that corrosion fatigue is also one of main failure modes of the main pipeline material.
(4) Stress corrosion: stress Corrosion Cracking (SCC) is an important failure mode of a dissimilar metal welded joint at a safety end of a nuclear power primary circuit in a service process. In the process of stress corrosion, the nuclear power structural material works at high temperature and high pressure for a long time, and meanwhile, due to the existence of a high stress area of a crack tip area, a creep phenomenon can be generated near the crack tip. As the water environment temperature of the nuclear power primary circuit is 288-340 ℃, the creep deformation generated in the actual working condition belongs to the low temperature (the creep deformation temperature is 0.3T)mBelow, TmThe melting point of the material) and the crack tip has a high stress area, so that the creep phenomenon under high stress at low temperature is more prone to occur. Stainless steel materialStress Corrosion Cracking (SCC) still occurs in a high-concentration alkaline solution or a high-temperature low-concentration alkaline solution, and thus its SCC behavior in a high-temperature alkaline solution has been a major research point.
Disclosure of Invention
The invention aims to provide copper-titanium-containing high-strength high-corrosion-resistance austenitic stainless steel and a preparation method thereof. The technical scheme adopted by the invention for solving the technical problem is that on the basis of 316 austenitic stainless steel alloy components, strong carbide forming element titanium (Ti) and austenite forming element copper (Cu) are added, which are called 316-CT stainless steel for short. The concrete components (mass percent) are as follows: c is less than or equal to 0.08, Ni is 10.0-14.0, Cr is 16.0-18.5, Mo is 2.0-3.0, Ti is less than or equal to 0.32, Cu is 0.2-0.8, Mn is less than or equal to 2.0, Si is less than or equal to 1.0, P is less than or equal to 0.035, S is less than or equal to 0.030, wherein more than or equal to 3.98 x (C-0.01), Ti is less than or equal to 3.98 x C, and the balance of Fe. After alloy smelting, the formed TiC is fully crushed and dispersed and distributed through thermal deformation cogging and cold deformation treatment, and then a coarse grain austenite structure is obtained through high-temperature solution treatment, so that the TiC has high strength and corrosion resistance.
316 is American grade, corresponding to Chinese stainless steel grade 0Cr17Ni12Mo 2; the corrosion resistance is superior to that of 304 stainless steel, and the corrosion resistance is good in the production process of pulp and paper making. Also 316 stainless steel is resistant to corrosion by the ocean and aggressive industrial atmospheres. The performance indexes of the plate are as follows: the yield strength is more than or equal to 205MPa, the tensile strength is more than or equal to 520MPa, the elongation is more than or equal to 40 percent, and the hardness is less than or equal to HV 200.
316 stainless steel contains no more than 0.08% C. C in austenitic stainless steel has a strong solid solution strengthening effect, but C is easily combined with Fe to form cementite Fe3C, is precipitated as a sheet layer, which makes it difficult to improve the corrosion resistance of the stainless steel. Therefore, the strong carbide forming element Ti is added into the alloy to form a high-stability spherical particle TiC compound, so that the actual solid solution content of C in austenite grains is greatly reduced, and the corrosion resistance of the stainless steel is improved. Since the atomic weight of Ti is 50.94 and the atomic weight of C is 12.01, the atomic weight ratio of Ti to C is 3.98, when Ti is 3.98X (C-0.01) or more and 3.98X C or less, for example, C is 0.08%, the Ti content is 0.28% to 0.32%, the austenite grains are substantially of CThe solid solution content is less than 0.01%, and the Ti element is not excessive.
Cu is a non-carbide forming element and forms a substitutional solid solution when added to steel. The solid solution strengthening effect of 38-70 MPa can be generated by adding 1.0% of Cu in the steel, the yield strength increment caused by adding the Cu is higher than the increment of the tensile strength, and the yield ratio of the steel can be obviously improved. The Cu ions dissolved out of the surface of the steel cannot be induced to destroy the protein structure in the bacteria, inhibit the replication of bacterial DNA and the synthesis of related protein/enzyme, destroy the metabolic activity in the bacteria, inactivate the bacteria and cause the death of the bacteria. Therefore, 1-3% of Cu is often added into some weather-resistant steel, so that the corrosion resistance of the alloy in marine environment is improved.
In the invention, a small amount of Cu is added, and the important significance is to make up the deficiency of the C element during high-temperature heat treatment. In austenitic stainless steel, a large amount of Cr and Ni elements are present, and segregation of Cr and Ni elements is also a factor that makes it difficult to further improve the corrosion resistance of stainless steel. Therefore, the heat preservation at high temperature is needed, the diffusion and homogenization of Cr and Ni are promoted, and the existence of C is beneficial to improving the diffusion capability of alloy elements. Because the strong carbide forming element is added, the solid solution content of C in austenite grains is low, which is not beneficial to homogenization, so a small amount of Cu needs to be supplemented, the diffusion capacity is improved, the segregation of Cr and Ni elements is overcome, and the corrosion resistance is further improved.
The preparation method of the 316-CT stainless steel comprises the following main steps:
(1) smelting and casting of 316-CT stainless steel
The method comprises the steps of selecting electrician pure iron, metal chromium sheets, metal nickel plates, metal molybdenum, stainless steel waste, pure copper plates, ferrotitanium or metal titanium and graphite blocks as raw materials, carrying out electric arc melting or induction melting, and then casting into alloy cast ingots.
Because the alloy is added with elements such as Cu, Ti and the like, the stainless steel industrial production methods such as a converter vacuum oxygen blowing decarburization method and the like are not suitable, and the alloy can be prepared only by adopting an electric arc melting or induction melting method. During smelting, vacuum or argon protection is adopted to avoid oxidation.
The stainless steel waste is mainly austenitic stainless steel waste with high nickel, high chromium and high molybdenum contents such as 316, 316L and the like, then raw materials such as electrician pure iron, metal chromium sheets, metal nickel plates, metal molybdenum, pure copper plates, ferrotitanium or metal titanium, graphite blocks and the like are used for preparing alloy in the composition range of the 316-CT stainless steel, main elements such as C, Cr, Ni, Cu, Ti and the like in the alloy are controlled, and impurity elements such as Mn, Si, P, S and the like are ensured through the purity of the raw materials.
The temperature of a molten pool is maintained to be 1700 +/-20 ℃ during smelting; and (3) before casting, keeping the molten steel stationary for 5-10 minutes, and casting the molten steel at 1550 +/-50 ℃ under vacuum or argon protection. And casting the ingot into a square ingot or a round ingot according to the specification requirement of a subsequent product.
(2) Thermal deformation cogging of cast ingot
Pipes, bars, wires, sections and cold punching parts, and the ingot casting can be performed by hot forging, hole-pattern rolling or universal rolling for cogging; the plate can be hot rolled and cogging by adopting a flat roller mill.
The forging scheme is that a casting blank is heated to 1250 +/-10 ℃, is subjected to heat preservation for 3-5 hours and then is taken out of a furnace for forging, the initial forging temperature is 1150 +/-20 ℃, the final forging temperature is more than or equal to 1000 ℃, the forging ratio is more than or equal to 2.0, the extension ratio is more than or equal to 2.0, and the total ratio is more than or equal to 4.0;
performing cross piercing on the hot forged blank to obtain a pipe blank;
the hot rolling scheme is that a casting blank is heated to 1280 +/-10 ℃, the temperature is kept for 3-5 hours, then the casting blank is taken out of a furnace for rolling, the initial forging temperature of hot rolling is 1180 +/-20 ℃, and the final rolling temperature is more than or equal to 950 ℃. The reduction of area of the hole rolling or universal rolling cogging should be more than or equal to 60 percent; the total lower amount of the hot rolled plate is more than or equal to 60 percent.
(3) Cold deformation
The pipe, rod, wire and section bar can be cold deformed by adopting a reciprocating pipe rolling, hole pattern rolling, universal rolling or drawing method to obtain the required size and specification of the product, and the total deformation of the cold deformation is not less than 80 percent according to the calculation of the reduction of area;
the stainless steel parts required by the mechanical industry can also be obtained by adopting a thermal deformation cogging raw material and then cold stamping, wherein the forging ratio of the cold stamping is more than or equal to 5.0. If the forging ratio is insufficient, the stamping blank should be subjected to cold forging treatment in advance to ensure the total cold deformation.
The plate is deformed by cold rolling, and the total rolling reduction of the cold rolling is more than or equal to 80 percent.
The main purpose of hot and cold deformation is to break down the carbides in the alloy sufficiently; the large cold deformation is beneficial to ensuring that a coarse and large crystal structure is formed during subsequent heating treatment.
(4) High temperature heat treatment
After cold deformation, annealing treatment is carried out at 1085 +/-30 ℃, the heat preservation time is 30-120 minutes, and vacuum or inert gases such as argon, nitrogen, helium and the like are adopted for protection during heating; after annealing, the steel is rapidly cooled by using gas media such as water, oil or argon, nitrogen, helium and the like.
The purpose of the high temperature hold is to form coarse recrystallized grains, so that the broken spherical carbide particles are transferred from the grain boundary to the inside of the coarse recrystallized grains, thereby reducing the tendency of grain boundary corrosion. The rapid cooling can avoid grain boundary precipitation of a small amount of residual carbide, and the main purpose is to control segregation of the Cu element, improve the solid solubility of the Cu element and obtain high strength and hardness.
According to the size of the product and the requirement for surface quality, a cooling medium is selected, when the size of the product is larger, liquid media such as water, oil and the like can be adopted to realize rapid cooling, and gas media such as argon, nitrogen, helium and the like can be adopted to rapidly cool the thin plate or the small part.
The high-temperature heat treatment method can be implemented by vacuum heating-gas quenching, continuous heating-water cooling quenching, continuous heating-high-pressure gas quenching, gas shielded heating-water (oil) quenching and the like. And straightening or shaping after annealing, wherein the deformation of the straightening or shaping treatment is less than 2%.
The 316-CT stainless steel subjected to high-temperature heat treatment adopts a Tafel (Tafel) line extrapolation method to obtain corrosion current as a basis for comparing the corrosion resistance of the alloy, and the hardness and the tensile mechanical property of the alloy are measured.
Tafel (Tafel) line extrapolation is a method to determine corrosion rate. The method is to make metal sample into electrode and immerse it in corrosive medium, measure steady-state volt-ampere (E-I) data, make log I-E picture, and extend the straight line part of the negative and positive polarization curveIs long. The obtained intersection points are corresponding to logIcorFrom corrosion current IcorDivided by the area S of the sample measured accurately in advance0Thus obtaining the corrosion rate. The method is fast and time-saving, and is suitable for measuring the uniform corrosion of metal.
The water environment temperature of the nuclear power loop is 288-340 ℃, and 80 ℃ is selected as a test temperature for comparing corrosion performance because a high-pressure water environment is difficult to obtain during measurement. The specific measurement conditions of the corrosion rate are: at 1cm2Stainless steel is used as a working electrode, a saturated calomel electrode is used as a reference electrode, and a platinum sheet is used as an auxiliary electrode; containing 5X 10-6F-0.5mol/L of H2SO4Heating the electrolyte to 80 ℃ by using a water bath box, and introducing hydrogen into the electrolyte at a flow rate of 20 ml/min; the samples were subjected to a linear potential scan at a scan rate of 2 mV/s. The measurement is completed by using the function of a constant potential electrochemical tester or a constant potential instrument of an electrochemical workstation, and the measured polarization curve is subjected to Tafel (Tafel) fitting by using the test software of the instrument to obtain the corrosion current. The corrosion current of 316 stainless steel measured by the method is 74 mu A/cm at room temperature2355 muA/cm at 80 DEG C2。
The invention is mainly characterized in that on the basis of 316 stainless steel alloy, a strong carbide forming element Ti is added to reduce the solid solubility of actual C in austenite grains; the Cu element is added to improve the high-temperature diffusion capacity, so that the segregation of Cr and Ni elements is avoided, and the solid solution strengthening effect is achieved; and then, carbide is crushed through thermal deformation and cold deformation, and coarse grains and supersaturated solid solution strengthening of a Cu element are formed through high-temperature quenching treatment, so that the alloy has high hardness and strength and excellent corrosion resistance. The corrosion current of the 316-CT alloy after high-temperature quenching treatment is 5 multiplied by 10 under the condition of hydrogen introduction at 80 DEG C-6F-0.5mol/L of H2SO46.9-9.8 muA/cm in the electrolyte2The corrosion rate is greatly reduced compared to the 316 alloy. The hardness is 183-192 HV1, the yield strength is 269-298 MPa, the tensile strength is 580-631 MPa, and the elongation is 40-44%, which is superior to that of 316 alloy.
Drawings
FIG. 1 polarization graph of inventive example 2;
FIG. 2 graph of tensile mechanical properties for inventive example 3;
FIG. 3 scanning electron microscope image of corroded surface of example 4 of this invention.
Detailed Description
The various melting and casting methods of the present invention are not limited by the following examples, and any modifications and variations within the scope of the claims of the present invention are within the scope of the present invention.
The alloy is prepared from electrician pure iron, chromium metal sheets, nickel metal plates, molybdenum metal, stainless steel waste, pure copper plates, ferrotitanium or titanium metal and graphite blocks as raw materials within the component range required by the invention.
The stainless steel and its parts prepared by the method can be processed by mechanical processing, polishing and corresponding chemical cleaning and polishing treatment for shape, dimension and surface quality, and the invention is not limited in detail.
Example 1
Selecting electrician pure iron, a metal chromium sheet, a metal nickel plate, metal molybdenum, 316 stainless steel waste, a pure copper plate and metal titanium as raw materials, wherein the prepared stainless steel comprises the following components: c is 0.03, Ni is 12.5, Cr is 17.0, Mo is 2.2, Ti is 0.12, Cu is 0.2, Mn is 1.2, Si is 0.8, P is less than or equal to 0.035, S is less than or equal to 0.030, and Fe is the rest. After weighing corresponding raw materials according to the component requirement, performing argon protection arc melting, and keeping the temperature of a molten pool at 1720 ℃ during melting; before casting, the molten steel is kept still for 10 minutes, and the molten steel is cast at 1650 ℃ under the protection of argon. And casting into a round ingot.
Hot forging and cogging can be adopted for the cast ingot, and oblique rolling and perforation are carried out on the hot-forged blank to obtain a pipe blank; and heating the hot forging and cross rolling perforation to 1260 ℃, keeping the temperature for 5 hours, discharging from the furnace and forging, wherein the initial forging temperature is 1170 ℃, the final forging temperature is 1020 ℃, and the total elongation is 3.
The tube blank adopts reciprocating tube rolling, and then adopts air drawing and fixed short core rod drawing, and the total deformation amount of cold deformation is 80% according to the reduction of area.
Annealing the pipe at 1115 ℃, keeping the temperature for 30 minutes, and heating under the protection of argon; and after annealing, cooling by water quenching.
The corrosion current of the 316-CT alloy after high-temperature quenching treatment is 5 multiplied by 10 at 80 ℃ under the condition of hydrogen introduction-6F-0.5mol/L of H2SO49.8 muA/cm in the electrolyte2. The hardness was 187HV1, the yield strength was 276MPa, the tensile strength was 580MPa, and the elongation was 40%.
Example 2
Selecting 316 stainless steel waste, a pure copper plate and ferrotitanium as raw materials, wherein the prepared stainless steel comprises the following components: 0.04% of C, 12.0% of Ni, 17.8% of Cr, 2.7% of Mo, 0.16% of Ti, 0.3% of Cu, 1.2% of Mn, 0.7% of Si, less than or equal to 0.035% of P, less than or equal to 0.030% of S, and the balance of Fe.
Weighing corresponding raw materials according to the component requirement, and then carrying out vacuum induction smelting, wherein the temperature of a molten pool is kept at 1680 ℃ during smelting; before casting, the molten steel is kept still for 5 minutes, and the molten steel is cast in vacuum at 1550 ℃. And casting to form a square ingot.
Heating the casting blank to 1270 ℃, preserving heat for 3 hours, discharging the casting blank out of the furnace, and then adopting pass rolling for cogging, wherein the initial rolling temperature is 1160 ℃, the final rolling temperature is 980 ℃, and the total reduction of area of rolling is 62%; the bar material is obtained by pass rolling, and the total rolling deformation is 82% according to the reduction of area. The bar is insulated for 120 minutes at 1055 ℃, and helium gas quenching is adopted after vacuum annealing.
The corrosion current of the 316-CT alloy after high-temperature quenching treatment is 5 multiplied by 10 at 80 ℃ under the condition of hydrogen introduction-6F-0.5mol/L of H2SO4The electrolyte content is 8.9 muA/cm2The polarization curve is shown in FIG. 1. The hardness is 185HV1, the yield strength is 289MPa, the tensile strength is 612MPa, and the elongation is 42%.
Example 3
Selecting 316 stainless steel waste, a pure copper plate, ferrotitanium and a graphite block as raw materials, wherein the prepared stainless steel comprises the following components: c is 0.08, Ni is 12.2, Cr is 17.5, Mo is 2.4, Ti is 0.32, Cu is 0.8, Mn is 1.2, Si is 0.6, P is less than or equal to 0.035, S is less than or equal to 0.030, and Fe is the rest.
Weighing corresponding raw materials according to the component requirement, and then carrying out vacuum induction smelting, wherein the temperature of a molten pool is kept at 1710 ℃; before casting, the molten steel is kept still for 8 minutes, and the molten steel is cast in vacuum at 1580 ℃. And casting to form a square ingot.
The ingot casting can be cogging by hot forging. The forging scheme is that a casting blank is heated to 1250 ℃, heat preservation is carried out for 3 hours, then the casting blank is taken out of a furnace for forging, the initial forging temperature is 1150 ℃, the final forging temperature is 1000 ℃, and the total forging ratio is 4.0;
the blank is subjected to cold forging treatment and then is subjected to cold stamping forming to obtain a stamping part, and the total forging ratio of cold deformation is 5.0.
After cold deformation, annealing treatment is carried out at 1065 ℃, the heat preservation time is 85 minutes, and nitrogen gas protection and oil cooling are adopted.
The corrosion current of the 316-CT alloy after high-temperature quenching treatment is 5 multiplied by 10 at 80 ℃ under the condition of hydrogen introduction-6F-0.5mol/L of H2SO4The electrolyte content is 7.6 muA/cm2. The hardness was 184HV1, the yield strength was 298MPa, the tensile strength was 600MPa, and the elongation was 41%, and the tensile properties are shown in FIG. 2.
Example 4
The stainless steel is prepared from the following raw materials of electrician pure iron, a metal chromium sheet, a metal nickel plate, metal molybdenum, a pure copper plate, ferrotitanium and a graphite block: c is 0.05, Ni is 11.0, Cr is 16.0, Mo is 2.2, Ti is 0.20, Cu is 0.4, Mn is 0.8, Si is 0.5, P is less than or equal to 0.035, S is less than or equal to 0.030, and Fe is the rest.
Weighing corresponding raw materials according to the component requirement, and then carrying out induction smelting under the protection of argon, wherein the temperature of a molten pool is maintained at 1700 ℃ during smelting; before casting, the molten steel is kept still for 7 minutes, and the molten steel is cast at 1600 ℃ under the protection of argon. And casting into a round ingot.
The ingot can be rolled and cogging by adopting a universal mill with two pairs of parallel rollers, the ingot blank is heated to 1280 ℃, the ingot blank is taken out of the furnace and rolled after heat preservation for 4 hours, the initial rolling temperature is 1180 ℃, the final rolling temperature is 1020 ℃, and the total reduction of area of rolling is calculated to be 65%;
preparing a T-shaped section by adopting universal rolling, wherein the total rolling deformation is 85% according to the reduction of area;
annealing treatment is carried out at 1100 ℃ after cold rolling, the heat preservation time is 60 minutes, and nitrogen protection is adopted; annealing in a continuous annealing furnace, and rapidly cooling with high-pressure nitrogen after annealing.
The corrosion current of the 316-CT alloy after high-temperature quenching treatment is 5 multiplied by 10 under the condition of hydrogen introduction at 80 DEG C-6F-0.5mol/L of H2SO46.9 muA/cm in the electrolyte2. The hardness was 192HV1, the yield strength was 297MPa, the tensile strength was 631MPa, and the elongation was 43%.
FIG. 3 is an electron microscope scanning image of the corrosion surface, and it can be seen from FIG. 3 that the corrosion surface is very smooth, no corrosion product is generated, but there are many smooth pores, fine carbides on the surface are corroded and shed preferentially, and the remaining smooth surface has uniform texture and strong corrosion resistance.
Example 5
Selecting 316L stainless steel waste, molybdenum metal, a pure copper plate, titanium metal and a graphite block as raw materials, wherein the prepared stainless steel comprises the following components: c is 0.06, Ni is 14.0, Cr is 18.5, Mo is 2.2, Ti is 0.24, Cu is 0.5, Mn is 1.3, Si is 0.3, P is less than or equal to 0.035, S is less than or equal to 0.030, and Fe is the rest.
Weighing corresponding raw materials according to the component requirement, and then carrying out vacuum induction smelting, wherein the temperature of a molten pool is kept at 1690 ℃ during smelting; before casting, the molten steel is kept still for 8 minutes, and the molten steel is cast in vacuum at 1620 ℃. And casting to form a square ingot.
The ingot casting adopts hot rolling cogging, and the hot rolling scheme is that a casting blank is heated to 1290 ℃, the temperature is kept for 3 hours, then the casting blank is discharged from a furnace for rolling, the hot rolling initial forging temperature is 1200 ℃, the final rolling temperature is 950 ℃, and the total hot rolling reduction is 60%.
The plate is deformed by cold rolling, and the total rolling reduction of the cold rolling is 80 percent.
Annealing treatment is carried out at 1105 ℃ after cold rolling, the heat preservation time is 45 minutes, and vacuum annealing and oil quenching are adopted during heating.
The corrosion current of the 316-CT alloy after high-temperature quenching treatment is 5 multiplied by 10 under the condition of hydrogen introduction at 80 DEG C-6F-0.5mol/L of H2SO4The electrolyte content is 8.4 muA/cm2. The hardness was 190HV1, the yield strength was 273MPa, the tensile strength was 609MPa, and the elongation was 44%.
Example 6
Selecting electrician pure iron, a metal chromium sheet, a metal nickel plate, metal molybdenum, a pure copper plate, ferrotitanium and a graphite block as raw materials, wherein the prepared stainless steel comprises the following components: c is 0.07, Ni is 11.0, Cr is 17.0, Mo is 2.5, Ti is 0.21, Cu is 0.7, Mn is 0.6, Si is 0.3, P is less than or equal to 0.035, S is less than or equal to 0.030, and Fe is the rest.
After weighing corresponding raw materials according to the component requirement, carrying out arc melting in an argon atmosphere, and keeping the temperature of a molten pool at 1700 ℃ during melting; before casting, the molten steel is kept still for 6 minutes, and the molten steel is cast at 1620 ℃ under the protection of argon. And casting to form a square ingot.
Hot forging and cogging can be adopted for the cast ingot, the cast ingot is heated to 1255 ℃, the temperature is kept for 3 hours, then the cast ingot is taken out of a furnace and forged, the initial forging temperature is 1150 ℃, the final forging temperature is 1050 ℃, and the total forging ratio is 4.0;
carrying out hole-pattern rolling after hot forging to obtain a wire rod, and carrying out drawing deformation on the wire rod, wherein the total deformation is 86% calculated according to the reduction of area;
annealing the cold-drawn wire at 1100 ℃ for 90 minutes, heating under vacuum protection, and quenching with high-pressure argon after the heat preservation is finished.
The corrosion current of the 316-CT alloy after high-temperature quenching treatment is 5 multiplied by 10 at 80 ℃ under the condition of hydrogen introduction-6F-0.5mol/L of H2SO47.7 mu A/cm in the electrolyte2. The hardness is 183HV1, the yield strength is 269MPa, the tensile strength is 591MPa, and the elongation is 42%.
The performance test of the 316-CT alloy obtained in the preparation process of the above embodiment is as follows:
1. the hardness of the alloy material of the example was measured by using an HVS-50 Vickers hardness tester under a load of 1Kg, and the average value was taken after beating 5 points and is shown in Table 1.
2. An electronic universal tester is adopted to carry out a tensile test on the example alloy material, a rectangular sample with the nominal section size of 1-2 multiplied by 5 multiplied by 30mm is taken, and the average values of the tensile strength, the yield strength and the elongation of 3 samples treated in the same way are listed in Table 1
3. The corrosion current measurements were carried out on the example alloys using the electrochemical workstation CHI660D under the following test conditions: the area of the corroded surface is 1cm2Example alloy as working electrode, saturated calomel electrodeAs a reference electrode, a platinum sheet is used as an auxiliary electrode; containing 5X 10-6F-0.5mol/L of H2SO4Heating the electrolyte to 80 ℃ by using a water bath box, and introducing hydrogen into the electrolyte at a flow rate of 20 ml/min; the sample was subjected to a linear potential sweep at a sweep rate of 2 mV/s. The average values obtained after 3 samples were measured are shown in Table 1.
Table 1 compositions and corrosion currents, hardness and tensile properties of the examples
The compositions of Mn, Si, P, S and the like of the examples in Table 1 meet the alloy invention requirements, and Fe is the balance and is not listed in Table 1.
Claims (4)
1. A high-strength high-corrosion-resistance austenitic stainless steel containing copper and titanium is characterized in that: the stainless steel comprises the following elements in percentage by mass: c is less than or equal to 0.08, Ni = 10.0-14.0, Cr = 16.0-18.5, Mo = 2.0-3.0, Ti is less than or equal to 0.32, Cu = 0.2-0.8, Mn is less than or equal to 2.0, Si is less than or equal to 1.0, P is less than or equal to 0.035, S is less than or equal to 0.030, wherein Ti is less than or equal to 3.98 xC and less than or equal to 3.98 xC (C-0.01), and the balance is Fe; the high-strength high-corrosion-resistance austenitic stainless steel containing copper and titanium comprises the following steps:
(1) smelting and casting of stainless steel
Selecting electrician pure iron, a metal chromium sheet, a metal nickel plate, metal molybdenum, stainless steel waste, a pure copper plate, ferrotitanium or metal titanium and a graphite block as raw materials according to the mass percentage of each element of the stainless steel, and casting the raw materials into an alloy ingot after electric arc melting or induction melting;
the temperature of a molten pool is maintained to be 1700 +/-20 ℃ during smelting; before casting, the molten steel is kept still for 5-10 minutes, and the molten steel is cast at 1550 +/-50 ℃ under the protection of vacuum or argon to be cast into square ingots or round ingots;
(2) thermal deformation cogging of cast ingot
Tubes, rods, wires, sections and cold punching parts, and hot forging, hole-pattern rolling or universal rolling cogging is adopted for ingot casting; the plate is hot rolled and cogging by adopting a flat roller mill;
the forging scheme is that a casting blank is heated to 1250 +/-10 ℃, is subjected to heat preservation for 3-5 hours and then is taken out of a furnace for forging, the initial forging temperature is 1150 +/-20 ℃, the final forging temperature is more than or equal to 1000 ℃, the forging ratio is more than or equal to 2.0, the extension ratio is more than or equal to 2.0, and the total ratio is more than or equal to 4.0;
performing cross piercing on the hot forged blank to obtain a pipe blank;
the hot rolling scheme is that a casting blank is heated to 1280 +/-10 ℃, the temperature is kept for 3-5 hours, and then the casting blank is discharged from a furnace for rolling, the hot rolling starting temperature is 1180 +/-20 ℃, and the final rolling temperature is more than or equal to 950 ℃; the reduction of area of the hole rolling or universal rolling cogging should be more than or equal to 60 percent; the total reduction of the hot rolling of the plate is more than or equal to 60 percent;
(3) cold deformation
Cold deformation is carried out on the pipe, the rod, the wire and the section by adopting a reciprocating pipe rolling, hole pattern rolling, universal rolling or drawing method to obtain the required size and specification of the product, and the total deformation amount of the cold deformation is not less than 80 percent according to the calculation of the reduction of area;
stainless steel parts required by the mechanical industry are obtained by adopting a thermal deformation cogging raw material and then cold stamping, wherein the forging ratio of the cold stamping is more than or equal to 5.0; if the forging ratio is insufficient, cold forging treatment is adopted for the stamping blank in advance to ensure the total cold deformation;
the plate is deformed by cold rolling, and the total cold rolling reduction is more than or equal to 80 percent;
(4) high temperature heat treatment
After cold deformation, annealing treatment is carried out at 1085 +/-30 ℃, the heat preservation time is 30-120 minutes, and vacuum or gas protection is adopted during heating; after annealing, adopting water, oil or gas medium of argon, nitrogen and helium to rapidly cool;
the high-temperature heat treatment of the copper-titanium-containing high-strength high-corrosion-resistance austenitic stainless steel is vacuum heating-gas quenching, continuous heating-water cooling quenching, continuous heating-high-pressure gas quenching, gas protection heating-water quenching or gas protection heating-oil quenching;
the high-strength and high-corrosion-resistance austenitic stainless steel containing copper and titanium is prepared by adding a strong carbide forming element Ti on the basis of 316 stainless steel alloy, and reducing the solid solubility of actual C in austenite grains; the Cu element is added to improve the high-temperature diffusion capacity, so that the segregation of Cr and Ni elements is avoided, and the solid solution strengthening effect is realized; subsequent hot and cold deformationThe carbide is crushed, and the supersaturated solid solution strengthening of coarse grains and Cu elements is formed through high-temperature quenching treatment, so that the alloy has high hardness and strength and excellent corrosion resistance; the corrosion current of the high-strength high-corrosion resistant austenitic stainless steel containing copper and titanium after high-temperature quenching treatment is 5 multiplied by 10 at 80 ℃ under the condition of hydrogen introduction-6F-0.5mol/L of H2SO46.9-9.8 muA/cm in the electrolyte2Compared with 316 alloy, the corrosion rate is greatly reduced; the hardness is 183-192 HV1, the yield strength is 269-298 MPa, the tensile strength is 580-631 MPa, and the elongation is 40-44%, which is superior to that of 316 alloy.
2. The method for preparing a high-strength high-corrosion-resistance austenitic stainless steel containing copper and titanium according to claim 1, comprising the steps of:
(1) smelting and casting of stainless steel
Selecting electrician pure iron, a metal chromium sheet, a metal nickel plate, metal molybdenum, stainless steel waste, a pure copper plate, ferrotitanium or metal titanium and a graphite block as raw materials according to the mass percentage of each element of the stainless steel, and casting the raw materials into an alloy ingot after electric arc melting or induction melting;
the temperature of a molten pool is maintained to be 1700 +/-20 ℃ during smelting; before casting, the molten steel is kept still for 5-10 minutes, and the molten steel is cast at 1550 +/-50 ℃ under the protection of vacuum or argon to be cast into square ingots or round ingots;
(2) thermal deformation cogging of cast ingot
Pipes, rods, wires, sections and cold punching parts, and hot forging, pass rolling or universal rolling is adopted for ingot casting to perform cogging; the plate is hot rolled and cogging by adopting a flat roller mill;
the forging scheme is that a casting blank is heated to 1250 +/-10 ℃, is subjected to heat preservation for 3-5 hours and then is taken out of a furnace for forging, the initial forging temperature is 1150 +/-20 ℃, the final forging temperature is more than or equal to 1000 ℃, the forging ratio is more than or equal to 2.0, the extension ratio is more than or equal to 2.0, and the total ratio is more than or equal to 4.0;
performing cross piercing on the hot-forged blank to obtain a pipe blank;
the hot rolling scheme is that a casting blank is heated to 1280 +/-10 ℃, is subjected to heat preservation for 3-5 hours and then is discharged for rolling, the starting temperature of hot rolling is 1180 +/-20 ℃, and the finishing temperature is more than or equal to 950 ℃; the reduction of area of the hole rolling or universal rolling cogging should be more than or equal to 60 percent; the total rolling reduction of hot rolling of the plate is more than or equal to 60 percent;
(3) cold deformation
Cold deformation is carried out on the pipe, the rod, the wire and the section by adopting a reciprocating pipe rolling, hole pattern rolling, universal rolling or drawing method to obtain the required size and specification of the product, and the total deformation amount of the cold deformation is not less than 80 percent according to the calculation of the reduction of area;
stainless steel parts required by the mechanical industry are obtained by adopting a thermal deformation cogging raw material and then cold stamping, wherein the forging ratio of the cold stamping is more than or equal to 5.0; if the forging ratio is insufficient, cold forging treatment is adopted in advance for stamping the blank, and the total cold deformation is ensured;
the plate is deformed by cold rolling, and the total cold rolling reduction is more than or equal to 80 percent;
(4) high temperature heat treatment
After cold deformation, annealing treatment is carried out at 1085 +/-30 ℃, the heat preservation time is 30-120 minutes, and vacuum or gas protection is adopted during heating; after annealing, adopting water, oil or gas medium of argon, nitrogen and helium to rapidly cool;
the high-temperature heat treatment of the copper-titanium-containing high-strength high-corrosion-resistance austenitic stainless steel is vacuum heating-gas quenching, continuous heating-water cooling quenching, continuous heating-high-pressure gas quenching, gas protection heating-water quenching or gas protection heating-oil quenching.
3. The method of preparing a high-strength high-corrosion-resistance austenitic stainless steel containing copper and titanium according to claim 2, wherein: the protective gas is: argon, nitrogen or helium.
4. The method of preparing a high-strength high-corrosion-resistance austenitic stainless steel containing copper and titanium according to claim 2, wherein: and straightening or shaping after annealing, wherein the deformation of the straightening or shaping treatment is less than 2%.
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