CN114045384B - Method for improving low-temperature impact toughness of low-nickel ferrite-austenitic stainless steel - Google Patents
Method for improving low-temperature impact toughness of low-nickel ferrite-austenitic stainless steel Download PDFInfo
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- C21D1/18—Hardening; Quenching with or without subsequent tempering
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Abstract
The invention relates to a method for improving low-temperature impact toughness of low-nickel ferrite-austenitic stainless steel, which comprises the following steps: 1) And (3) hot rolling: hot rolling the low-nickel stainless steel obtained after smelting after forging to obtain a hot rolled material; 2) Solution annealing: carrying out solution annealing treatment on the hot rolled material, wherein the solution temperature is 1000-1100 ℃, the heat preservation time is 20-40 min, and then water cooling is carried out; 3) Low temperature tempering: tempering the plate obtained in the step 2), wherein the tempering temperature is 300-400 ℃, the heat preservation time is 10-60 min, and then air cooling is carried out. The method ensures the strength of the low-nickel ferrite-austenite stainless steel and simultaneously effectively improves the low-temperature impact toughness, thereby improving the service safety and prolonging the service life.
Description
Technical Field
The invention belongs to the technical field of steel alloy materials, and particularly relates to a method for improving low-temperature impact toughness of low-nickel ferrite-austenitic stainless steel.
Background
The microstructure of the existing ferrite-austenite stainless steel consists of ferrite and austenite in a certain proportion, and chemical component design, forging rolling technology, heat treatment state and the like have important influences on the two-phase proportion and element distribution in the ferrite-austenite stainless steel, so that the performance of the stainless steel is influenced. The main alloy element in the stainless steel is Fe, cr, mn, ni, mo, C, N and a small amount of Si element. In recent years, in order to save Ni resources, the method of replacing Ni with Mn and N is adopted to cope with the influence of Ni metal price fluctuation on stainless steel market, on one hand, the cost of raw materials can be reduced, and on the other hand, the interstitial N can be utilized to improve the strength of ferrite-austenite stainless steel.
However, the low-temperature toughness of the ferrite-austenite stainless steel is affected due to the reduction of the Ni element content, and the low-nickel stainless steel has low impact toughness at the low temperature of-40 ℃ and cannot meet the low-temperature requirement, wherein Ni is more than 0 and less than or equal to 2 percent.
The Chinese patent No. ZL201810305967.9 issued to the public No. CN 108526750B) discloses a high-strength high-toughness high-nitrogen austenitic stainless steel welding wire comprising the following alloy components in percentage by weight: c <0.1%, S <0.02%, P <0.03%, si:0.1-0.9%, mn:5-21%, cr:15-23%, ni:0-8%, mo:0-5%, N:0.2-0.95%, fe is the rest, and other impurities are less than 0.1%; the preparation process comprises the following steps: induction furnace smelting, electroslag remelting, hot forging, hot rolling, heat treatment and welding wire drawing. The prepared austenitic stainless steel has the impact toughness of not less than 90J at room temperature and not less than 75J at a low temperature of minus 40 ℃ and the tensile strength of more than 900 MPa. Although the prepared austenitic stainless steel has good impact toughness at low temperature, electroslag remelting is required before hot forging, wire drawing is required after heat treatment, and the preparation method is complex. In addition, although the composition ranges given in this patent are Mn:5-21%, ni:0-8%, N:0.2-0.95%, but in order to ensure that a complete austenitic structure is formed, the content of at least one element of the three elements is necessarily high, and if the content of Mn element is high, the corrosion resistance of the material is reduced, and the requirement on the corrosion resistance cannot be met; if the content of Ni element is very high, the material cost is greatly increased; if the content of N element is very high, defects such as air holes and the like are easy to generate, and the preparation difficulty is increased. On the other hand, although the austenitic stainless steel proposed in this patent has good impact toughness and a tensile strength of 900MPa or more, the austenitic stainless steel is generally lower in yield strength than the ferritic-austenitic stainless steel due to a single-phase structure. Austenitic stainless steel is a complete austenitic structure, and the microstructure of ferritic-austenitic stainless steel is such that ferrite and austenite are distributed in nearly equal proportion, and therefore, the low-temperature impact toughness improvement method for austenitic stainless steel is not applicable to ferritic-austenitic stainless steel.
For another example, the Chinese patent of invention, "a low-nickel type medium chromium ferrite stainless steel and its manufacturing method", the patent number is ZL201510359843.5 issued to the public number is CN 106319382B), the chemical composition weight percentage of the low-nickel type medium chromium ferrite stainless steel is: ni:0.7 to 1.2 percent, C: 0.002-0.012%, N: 0.002-0.020%, si:0.10 to 0.50 percent, mn:0.1 to 0.50 percent, cr: 17.00-22.50%, mo:1.70 to 2.50 percent, nb:0.15 to 0.45 percent, ti:0.05 to 0.25 percent, O: 0.005-0.010%, and the balance of Fe and unavoidable impurities, and satisfies the relation: (C+N) is less than or equal to 0.030 percent, and Nb/Ti=1.5 to 4; (nb+ti)/(c+n) =12 to 22. The low-nickel type medium-chromium ferrite stainless steel obtained by the invention has excellent low-temperature toughness and high strength, the tensile strength is more than 445MPa, the impact energy at the temperature of minus 40 ℃ is more than 106J, and the impact energy at the temperature of 20 ℃ is more than 143J; although the low-nickel type medium-chromium ferrite stainless steel has better impact energy at low temperature, the content of corrosion resistant elements such as Cr, N and the like in the ferrite stainless steel is relatively low, the corrosion resistance is poor, and the strength and the elongation are low. The ferrite-austenite type stainless steel is a mixed structure of ferrite and austenite phases, alloy components, a preparation process, two-phase proportion regulation and control and the like have important influences on strength, plasticity, toughness and corrosion resistance of the ferrite-austenite type stainless steel, and the low-temperature impact toughness regulation and control process aiming at the ferrite-austenite type stainless steel (a ferrite structure) is not suitable for the ferrite-austenite type stainless steel.
Therefore, there is a need for further improvement in the low temperature impact toughness of low nickel ferritic-austenitic stainless steels.
Disclosure of Invention
The technical problem to be solved by the invention is to provide a method for improving the low-temperature impact toughness of low-nickel ferrite-austenite stainless steel aiming at the current state of the art, so that the low-nickel ferrite-austenite stainless steel has high strength and good low-temperature impact toughness.
The technical scheme adopted for solving the technical problems is as follows: a method for improving the low temperature impact toughness of a low nickel ferrite-austenitic stainless steel comprising the steps of:
1) And (3) hot rolling: hot rolling the low-nickel stainless steel obtained after smelting after forging to obtain a hot rolled material;
2) Solution annealing: carrying out solution annealing treatment on the hot rolled material, wherein the solution temperature is 1000-1100 ℃, the heat preservation time is 20-40 min, and then water cooling is carried out;
3) Low temperature tempering: tempering the plate obtained in the step 2), wherein the tempering temperature is 300-400 ℃, the heat preservation time is 10-60 min, and then air cooling is carried out.
Preferably, the low-nickel ferrite-austenite stainless steel comprises the following components in percentage by mass: 0.01% or less C or less than 0.04%,19% or less Cr or less 23%,0.1% or less Mo or less 0.3%,0.8% or less Ni or less 2.0%,4% or less Mn or less 7%,0.1% or less Si or less 0.3%,0.2% or less N or less 0.30%, and the balance of iron and other unavoidable impurities.
In the step 1), the initial rolling temperature is 1150-1230 ℃, the final rolling temperature is 900-1000 ℃, and the total rolling reduction is 75-95%. The rolling cracking is prevented by adopting the initial rolling temperature and the final rolling temperature; and the ferrite/austenite deformation structure is thinned so as to ensure that fine grains are obtained in the subsequent heat treatment process, so that the impact toughness of the ferrite-austenite stainless steel can be greatly improved on the basis of obtaining higher strong plasticity.
Preferably, the initial temperature in the forging process in step 1) is 1100 to 1200 ℃ and the final forging temperature is 980 to 1050 ℃.
Further preferably, the initial temperature of the forging is 1150 ℃ and the final forging temperature is 1000 ℃.
Specifically, the impact energy of the low-nickel ferrite-austenite stainless steel at the temperature of minus 40 ℃ is 61J-90J. Thus, the low-nickel ferrite-austenitic stainless steel has good impact toughness at low temperature.
Preferably, the low-nickel ferrite-austenite stainless steel has only ferrite phase and austenite phase, wherein the austenite phase is 45% -60% and the ferrite phase is 40% -55%. Because the ferrite and the austenite are in close proportion, the austenite is in close connection to form a net-shaped or approximate net-shaped structure, and the nucleation and the expansion of impact cracks can be effectively blocked, so that the low-temperature impact toughness is improved.
Compared with the prior art, the invention has the advantages that: the solid solution temperature is 1000-1100 ℃, the precipitation temperature range of the brittle phase is avoided, ferrite and austenite phases are obtained at the same time, the austenite proportion is 45% -60%, and because the ferrite and austenite phases are close in proportion, the austenite phase is close to form a net-shaped or approximate net-shaped structure, nucleation and expansion of impact cracks can be effectively prevented, and therefore the low-temperature impact toughness is improved. By low-temperature tempering, elements such as C, N in ferrite and austenite are redistributed, the solid solution amount of interstitial atoms such as C, N in ferrite is reduced, the adverse effect of the interstitial atoms on the impact toughness of ferrite phase is weakened, more interstitial atoms such as C, N are embedded in austenite phase, the austenite phase is strengthened, cracks generated in ferrite phase are difficult to expand into austenite, and therefore the expansion of the cracks is blocked, and the overall low-temperature toughness of the low-nickel ferrite-austenitic stainless steel is improved. Tempering is carried out at 300-400 ℃ for 10-60 min, so that elements such as C, N in ferrite and austenite are redistributed, the solid solution quantity of interstitial atoms such as C, N in ferrite is reduced, the adverse effect of the interstitial atoms on impact toughness of ferrite phase is weakened, more interstitial atoms such as C, N are embedded in austenite phase, the austenite phase is strengthened, cracks generated in the ferrite phase are difficult to expand into the austenite, and the expansion of the cracks is blocked, so that the whole low-temperature toughness, strength and corrosion resistance of the low-nickel ferrite-austenitic stainless steel are improved. The method ensures the strong plasticity of the low-nickel ferrite-austenite stainless steel and simultaneously effectively improves the low-temperature impact toughness, thereby improving the service safety and prolonging the service life.
Drawings
FIG. 1 shows the low temperature impact toughness of example 1 under different heat treatment processes
Detailed Description
The invention is described in further detail below with reference to the embodiments of the drawings.
Example 1:
as shown in fig. 1, there is a 1 st preferred embodiment of the present invention.
The low-nickel ferrite-austenite stainless steel related to the embodiment comprises the following components in percentage by mass: c:0.03%, cr:21.5%, mo:0.25%, ni:1.5%, mn:4.9%, si:0.2%, N:0.24%, the balance being iron and other unavoidable impurities.
And placing the stainless steel into a vacuum induction melting furnace, melting under a nitrogen atmosphere to obtain an ingot, forging the ingot, wherein the initial temperature of forging is 1150 ℃, the final forging temperature is 1000 ℃, and then air cooling to obtain a forging blank.
The method for improving the low-temperature impact toughness of the low-nickel ferrite-austenite stainless steel sequentially comprises the following steps of:
1) And (3) hot rolling: carrying out multi-pass hot rolling on the forging blank, controlling the initial rolling temperature to 1150 ℃, the final rolling temperature to 900 ℃ and the total rolling reduction to 90%, thus obtaining a hot rolled plate;
2) Solution annealing: carrying out solution annealing treatment on the hot rolled plate, controlling the solution temperature to 1030 ℃ and the heat preservation time to 25min, and then carrying out water cooling to inhibit Cr 2 Precipitating brittle phases such as N and the like to obtain stainless steel with a ferrite proportion of 47% and an austenite proportion of 53%;
3) Low temperature tempering: and (3) carrying out low-temperature tempering treatment and air cooling on the plate subjected to solution annealing treatment.
As shown in fig. 1, P1 to P6 are changes of impact energy of the stainless steel of this embodiment under different low temperature tempering process conditions after the above hot rolling and solution treatment, specifically, P1 is low temperature tempering with a tempering temperature of 300 ℃ and a tempering time of 30min, and the impact energy of the stainless steel under the condition of-40 ℃ is 65J. P2 is tempered at a low temperature of 300 ℃ for 60min, and the impact energy of the stainless steel under the condition is 61J at the temperature of minus 40 ℃. P3 is stainless steel, the tempering temperature is 350 ℃, the tempering time is 30min, the impact power of the stainless steel under the condition is 70J at the temperature of minus 40 ℃, the tensile strength of the ferrite-austenite stainless steel prepared under the condition is 920MPa, the yield strength is 530MPa, the elongation is 50%, and the pitting potential in a 3.5% NaCl aqueous solution is 470mV. P4 is low temperature tempering at the tempering temperature of 350 ℃ and the tempering time of 60min, and the impact energy of the stainless steel at the temperature of minus 40 ℃ is 67J. P5 is low temperature tempering with tempering temperature of 400 ℃ and tempering time of 10min, and the impact power of the stainless steel under the condition of minus 40 ℃ is 65J. P6 is low temperature tempering with tempering temperature of 400 ℃ and tempering time of 30min, and the impact power of the stainless steel under the condition of minus 40 ℃ is 67J.
Comparative example 1: the only difference from the above-described embodiment 1 is that: without hot rolling and low temperature tempering, the comparative example had an impact energy of 57J at-40 ℃. Further performance indexes of this comparative example were tested, with a tensile strength of 910MPa, a yield strength of 530MPa, an elongation of 46%, and a pitting potential of 460mV in a 3.5% aqueous NaCl solution.
From the above, it is understood that the low-temperature impact toughness, tensile strength, elongation and corrosion resistance of example 1 were significantly improved as compared with comparative example 1, which had been subjected to only the solution annealing treatment.
Example 2:
the main difference between this embodiment and embodiment 1 is that: the process parameters are different, specifically, in the step 1), the initial rolling temperature is 1200 ℃, the final rolling temperature is 950 ℃, and the total rolling reduction is 95%; in the step 2), the solid solution temperature is 1000 ℃, the heat preservation time is 40min, and the ferrite proportion is 45% and the austenite proportion is 55%; in the step 3), the low-temperature tempering temperature is 350 ℃, and the tempering time is 30min.
The ferritic-austenitic stainless steel of the present example has a low temperature impact energy of 80J at-40 ℃ after tempering at 350 ℃ for 30min. The tensile strength was 950MPa, the yield strength was 600MPa, the elongation was 45%, and the pitting potential in a 3.5% aqueous NaCl solution was 460mV.
Comparative example 2: compared with this example 2, the difference is that: without hot rolling and low temperature tempering, the comparative example had an impact energy of 60J at-40 ℃. Further performance indexes of this comparative example were tested, with a tensile strength of 945MPa, a yield strength of 580MPa, an elongation of 41% and a pitting potential of 450mV in a 3.5% aqueous NaCl solution.
From the above, it is understood that the low-temperature impact toughness, yield strength, elongation and corrosion resistance of example 2 were significantly improved as compared with comparative example 2, which was subjected to only solution annealing.
Example 3:
the main difference between this embodiment and embodiment 1 is that: 1. the low-nickel ferrite-austenite type stainless steel is different, and specifically, the low-nickel ferrite-austenite type stainless steel according to the embodiment comprises the following components in percentage by mass: c:0.02%, cr:22.8%, mo:0.30%, ni:0.9%, mn:6.7%, si:0.3%, N:0.28%, the balance being iron and other unavoidable impurities.
2. The process parameters are different, specifically, in the step 1), the initial rolling temperature is 1230 ℃, the final rolling temperature is 1000 ℃, and the total rolling reduction is 95%; in the step 2), the solid solution temperature is 1100 ℃, the heat preservation time is 20min, and the ferrite proportion is 46% and the austenite proportion is 54%; in the step 3), the low-temperature tempering temperature is 350 ℃, and the tempering time is 30min.
The ferritic-austenitic stainless steel of the present example has a low temperature impact energy of 77J at-40 ℃ after tempering at 350 ℃ for 30min. The ferritic-austenitic stainless steel of this example had a tensile strength of 900MPa, a yield strength of 550MPa, an elongation of 53% and a pitting potential of 490mV in a 3.5% aqueous NaCl solution.
Comparative example 3: compared with this example 3, the difference is that: without hot rolling and low temperature tempering, the comparative example had an impact energy of 53J at-40 ℃. Further, other performance indexes of the comparative example were tested, with a tensile strength of 870MPa, a yield strength of 510MPa, an elongation of 46%, and a pitting potential of 475mV in a 3.5% aqueous NaCl solution.
From the above, it is understood that the low-temperature impact toughness, tensile strength, yield strength, elongation and corrosion resistance of example 3 were significantly improved as compared with comparative example 3, which was subjected to only solution annealing.
Example 4:
the main difference between this embodiment and embodiment 1 is that: 1. the low-nickel ferrite-austenite type stainless steel is different, and specifically, the low-nickel ferrite-austenite type stainless steel according to the embodiment comprises the following components in percentage by mass: c:0.02%, cr:19.5%, mo:0.30%, ni:1.8%, mn:4.5%, si:0.1%, N:0.20%, the balance being iron and other unavoidable impurities.
2. The process parameters are different, specifically, in the step 1), the initial rolling temperature is 1200 ℃, the final rolling temperature is 960 ℃, and the total rolling reduction is 95%; in the step 2), the solid solution temperature is 1050 ℃, the heat preservation time is 30min, and the ferrite proportion is 51% and the austenite proportion is 49%; in the step 3), the low-temperature tempering temperature is 350 ℃, and the tempering time is 30min.
The stainless steel of the embodiment has a low-temperature impact energy of 85J at-40 ℃ after tempering at 350 ℃ for 30min. The tensile strength of this example 4 was 915MPa, the yield strength was 580MPa, the elongation was 44%, and the pitting potential in a 3.5% aqueous NaCl solution was 436mV.
Comparative example 4: compared with this example 4, the difference is that: without hot rolling and low temperature tempering, the comparative example had an impact energy of 64J at-40 ℃. Further, other performance indexes of the comparative example were tested, and the tensile strength was 890MPa, the yield strength was 570MPa, the elongation was 40%, and the pitting potential in a 3.5% aqueous NaCl solution was 420mV.
From the above, it is understood that the low-temperature impact toughness, tensile strength, yield strength, elongation and corrosion resistance were significantly improved in this example 4 as compared with the comparative example 4 which was subjected to only the solution annealing treatment.
Example 5:
the main difference between this embodiment and embodiment 1 is that: 1. the low-nickel ferrite-austenite type stainless steel is different, and specifically, the low-nickel ferrite-austenite type stainless steel according to the embodiment comprises the following components in percentage by mass: c:0.02%, cr:21.8%, mo:0.15%, ni:1.5%, mn:6.3%, si:0.15%, N:0.27% of iron and other unavoidable impurities in balance;
2. the process parameters are different, specifically, in the step 1), the initial rolling temperature is 1200 ℃, the final rolling temperature is 950 ℃, and the total rolling reduction is 95%; in the step 2), the solid solution temperature is 1050 ℃, the heat preservation time is 30min, and the obtained ferrite proportion is 40% and the austenite proportion is 60%; in the step 3), the low-temperature tempering temperature is 350 ℃, and the tempering time is 30min.
The stainless steel of the embodiment has a low-temperature impact energy of 90J at-40 ℃ after tempering at 350 ℃ for 30min. The tensile strength of this example 5 was 955MPa, the yield strength was 600MPa, the elongation was 42%, and the pitting potential in a 3.5% aqueous NaCl solution was 475mV.
Comparative example 5: compared with this example 5, the difference is that: without hot rolling and low temperature tempering, the comparative example had an impact energy of 68J at-40 ℃. Further performance indexes of this comparative example were tested, with a tensile strength of 930MPa, a yield strength of 630MPa, an elongation of 40% and a pitting potential of 460mV in a 3.5% aqueous NaCl solution.
From the above, it is understood that the low-temperature impact toughness, tensile strength, yield strength, elongation and corrosion resistance of example 5 were significantly improved as compared with comparative example 5, which was subjected to only solution annealing.
Example 6:
the main difference between this embodiment and embodiment 1 is that: 1. the low-nickel ferrite-austenite type stainless steel is different, and specifically, the low-nickel ferrite-austenite type stainless steel according to the embodiment comprises the following components in percentage by mass: c:0.01%, cr:23%, mo:0.1%, ni:2.0%, mn:4%, si:0.20%, N:0.28%, the balance being iron and other unavoidable impurities. The initial temperature of forging was 1100 ℃, and the final forging temperature was 1050 ℃. The total reduction in step 1) was 75%.
The impact toughness of this example was improved.
Example 7:
the main difference between this embodiment and embodiment 1 is that: 1. the low-nickel ferrite-austenite type stainless steel is different, and specifically, the low-nickel ferrite-austenite type stainless steel according to the embodiment comprises the following components in percentage by mass: c:0.04%, cr:19%, mo:0.15%, ni:0.8%, mn:7%, si:0.15%, N:0.30% of iron and other unavoidable impurities in balance; the initial temperature of forging was 1200 ℃ and the final forging temperature was 980 ℃.
The impact toughness of this example was improved.
Claims (4)
1. The method for improving the low-temperature impact toughness of the low-nickel ferrite-austenitic stainless steel is characterized by comprising the following components in percentage by mass: 0.01% or less C or less than 0.04%,19% or less Cr or less 23%,0.1% or less Mo or less than 0.3%,0.8% or less Ni or less than 2.0%,4% or less Mn or less than 7%,0.1% or less Si or less than 0.3%,0.2% or less N or less than 0.30%, and the balance being iron and other unavoidable impurities, and the low-nickel ferrite-austenitic stainless steel has only ferrite phase and austenite phase, wherein the austenite phase is 45% -60%, and the ferrite phase is 40% -55%, the method comprises the following steps:
1) And (3) hot rolling: hot rolling the low-nickel stainless steel obtained after smelting after forging to obtain a hot rolled material, wherein the initial rolling temperature is 1150-1230 ℃, the final rolling temperature is 900-1000 ℃, and the total reduction is 75-95%;
2) Solution annealing: carrying out solution annealing treatment on the hot rolled material, wherein the solution temperature is 1000-1100 ℃, the heat preservation time is 20-40 min, and then water cooling is carried out;
3) Low temperature tempering: tempering the plate obtained in the step 2), wherein the tempering temperature is 300-400 ℃, the heat preservation time is 10-60 min, and then air cooling is carried out.
2. The method according to claim 1, characterized in that: the initial temperature in the forging treatment in the step 1) is 1100-1200 ℃, and the final forging temperature is 980-1050 ℃.
3. The method according to claim 2, characterized in that: the initial temperature of the forging is 1150 ℃, and the final forging temperature is 1000 ℃.
4. The method according to claim 1, characterized in that: the impact energy of the low-nickel ferrite-austenite stainless steel at the temperature of minus 40 ℃ is 61J-90J.
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