CN116162848A - High-temperature anti-fatigue low-alloy steel plate and manufacturing method thereof - Google Patents
High-temperature anti-fatigue low-alloy steel plate and manufacturing method thereof Download PDFInfo
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- C21D2211/00—Microstructure comprising significant phases
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Abstract
The invention discloses a high-temperature anti-fatigue low-alloy steel plate which contains Fe and unavoidable impurities and also contains the following chemical elements in percentage by mass: c:0.08 to 0.2 percent, si:0.10 to 0.30 percent, mn:0.30 to 0.60 percent, cr:2.20 to 2.50 percent, mo:0.90 to 1.10 percent, V is less than or equal to 0.03 percent, ca:0.0015 to 0.0045 percent. In addition, the invention also discloses a manufacturing method of the high-temperature anti-fatigue low-alloy steel plate, which comprises the following steps: (1) smelting and casting to obtain a continuous casting blank; (2) Electroslag remelting is carried out by taking a continuous casting blank as an electrode raw material so as to obtain an electroslag ingot; (3) heating; (4) rolling; (5) heat treatment: firstly, normalizing, wherein the normalizing temperature is 870-970 ℃, and fully preserving heat to form a single uniform austenite structure; then immediately spraying water to cool the steel plate to below 200 ℃; and tempering, wherein the tempering temperature is 700-800 ℃.
Description
Technical Field
The present invention relates to a steel material and a method for manufacturing the same, and more particularly, to a low alloy steel sheet and a method for manufacturing the same.
Background
The pressure vessel is a common pressure-bearing device, and most of the pressure vessels work at high temperature and high pressure; statistics show that about 40-50% of the failures of pressure vessels are caused by metal fatigue, i.e. failures of steel materials due to metal fatigue.
Fatigue is the process that a material is damaged under the action of alternating stress or alternating strain, the damage gradually accumulates, the material performance gradually decreases until the material is finally failed and destroyed, and is one of main destruction forms of the material.
In recent years, with the rapid development of industry, pressure vessel equipment is gradually developed to high temperature, high speed and large size, and with the increase of stress level, more and more severe service conditions and the massive application of low alloy high strength steel, the welding process is more prone to generate defects such as cracks, and the risk of high temperature fatigue damage of the pressure vessel equipment is increased.
Therefore, in order to ensure the normal use of the pressure vessel and to extend the service life of the pressure vessel, there is a need for a high temperature fatigue resistant low alloy steel sheet that can be used to make the pressure vessel.
In the prior art, the steel with fatigue performance at high temperature mainly relates to die steel, stainless steel, steel rails and the like, but cannot be applied to pressure vessels with severe service environments.
For example, chinese patent document with publication number CN106756509a, publication date 2017, 5 and 31, entitled "high temperature alloy structural steel and heat treatment process thereof". The patent technical literature adopts an electric furnace, external refining and electroslag remelting method to obtain the high-temperature resistant alloy structural steel, which contains Cr, mo, ni, nb and other alloy elements, but the C content of the alloy structural steel is obviously higher than 0.23-0.27%, is not suitable for occasions needing welding processing, and cannot be used for manufacturing pressure vessels.
Also, for example, chinese patent document publication No. CN1978690a, publication No. 2007, 6 and 13, entitled "rail of bainitic structure having excellent fatigue resistance and method for producing the same". The patent technical literature discloses a steel with fatigue resistance and bainite structure, the content of C element is 0.35% at the highest, the steel is not suitable for welding and processing of a pressure vessel, the product is in the form of a steel rail non-steel plate, the size of a single non-metal inclusion is below 40 mu m, and the inclusion control level is poor.
For another example, chinese patent document, publication No. CN101092678A, publication No. 2007, 12-26, entitled "an austenitic thermal fatigue steel". The patent technical literature discloses an austenitic heat-fatigue-resistant steel, which has high Cr, ni and Mn contents, and further contains alloying elements such as Nb, V and Si, and the alloying elements greatly increase the alloying components of the steel; in addition, the technical scheme does not relate to the yield strength of steel, but the yield strength of austenitic steel is generally lower, so that the range of allowable design stress is severely limited, and the austenitic steel cannot be suitable for manufacturing pressure vessels.
Based on the above, the invention is expected to obtain a novel high-temperature anti-fatigue low-alloy steel plate which has excellent mechanical properties and excellent high-temperature anti-fatigue performance, can be used for manufacturing a pressure vessel serving at high temperature after being molded and welded, and can effectively resist metal fatigue and prolong the service life of the pressure vessel.
Disclosure of Invention
One of the objects of the present invention is to provide a high temperature fatigue resistant low alloy steel sheet having excellent mechanical properties as well as excellent high temperature fatigue resistance, a yield strength of more than 295MPa, a tensile strength of 450-585MPa, an elongation of more than 22%, an impact energy of more than 200J at-20 ℃, and more importantly, excellent fatigue resistance at high temperature of 530 ℃ and cycle at a cycle load of 200MPa maximum stress of 100 ten thousand cycles without breaking.
The high-temperature anti-fatigue low-alloy steel plate has wide application prospect, can be used for manufacturing a pressure vessel serving at high temperature after being molded and welded, can effectively resist metal fatigue, and prolongs the service life of the pressure vessel.
In order to achieve the above object, the present invention provides a high temperature fatigue-resistant low alloy steel sheet, which contains Fe and unavoidable impurities, and further contains the following chemical elements in mass percent:
C：0.08～0.2％，Si：0.10～0.30％，Mn：0.30～0.60％，Cr：2.20～2.50％，Mo：0.90～1.10％，V≤0.03％，Ca：0.0015～0.0045％。
further, in the high-temperature anti-fatigue low-alloy steel plate, the mass percentages of the chemical elements are as follows:
c:0.08 to 0.2 percent, si:0.10 to 0.30 percent, mn:0.30 to 0.60 percent, cr:2.20 to 2.50 percent, mo:0.90 to 1.10 percent, V is less than or equal to 0.03 percent, ca:0.0015 to 0.0045 percent; the balance being Fe and unavoidable impurities.
In the high-temperature anti-fatigue low-alloy steel plate, the design principle of each chemical element is as follows:
c: in the high-temperature anti-fatigue low-alloy steel plate, C is the most basic strengthening element in the steel, and is also an essential element for converting austenite into bainite strengthening phase. When the content of C element in steel is too low, the hardenability of the steel plate is poor, partial ferrite and other structures are easy to form when the thick steel plate is cooled, and a uniform bainite structure is damaged; conversely, the content of C element in the steel is not too high, and when the content of C element in the steel is too high, the plasticity, toughness and weldability of the steel are adversely affected. Based on the above, in the high-temperature fatigue-resistant low-alloy steel sheet, the mass percentage of the C element is controlled to be between 0.08 and 0.2 percent in consideration of the influence of the C element on the steel performance.
Si: in the high-temperature anti-fatigue low-alloy steel plate, si element not only can play a role in deoxidization, but also can play a role in solid solution strengthening; however, it should be noted that too high a content of Si element in the steel may cause brittleness of the steel, which may adversely affect the steel. Therefore, in order to exert the beneficial effect of Si element, the mass percent of Si element is controlled to be between 0.10 and 0.30 percent in the high-temperature anti-fatigue low-alloy steel plate.
Mn: in the high-temperature anti-fatigue low-alloy steel plate, proper amount of Mn element is added to play a solid solution strengthening role, so that the strength and hardness of the steel plate can be effectively improved. In addition, mn delays the formation of ferrite and pearlite, thereby expanding the range of cooling rates for cooling to form a bainitic structure, and thus it improves hardenability at the same time. Based on the above, in the high-temperature anti-fatigue low-alloy steel plate, the mass percentage of Mn element is controlled to be between 0.30 and 0.60 percent.
Cr: in the high-temperature anti-fatigue low-alloy steel plate, cr element can form compact and stable oxide at high temperature, and the compact and stable oxide can be distributed on the surface of a component to play a key role in resisting high-temperature oxidation; in addition, cr is also a carbide forming element which can exist in various carbides, so that the thermodynamic stability of the carbides is improved, and the decomposition of the carbides is prevented, and the stability of the material in high-temperature service is improved; in addition, the addition of a proper amount of Cr to the steel can also remarkably improve the hardenability of the steel and is beneficial to the formation of a bainite structure during high-temperature austenite cooling. Based on the above, in consideration of the beneficial effects of Cr element, the high-temperature anti-fatigue low-alloy steel plate disclosed by the invention has the advantage that the mass percentage of Cr element is controlled to be 2.20-2.50%.
Mo: in the high-temperature anti-fatigue low-alloy steel plate, mo element can enlarge an austenite phase region, strongly inhibit pearlite formation and promote bainite formation, and plays an important role in controlling a phase change structure. In the invention, the hardenability of the steel plate can be increased by increasing the content of Mo element in the steel; meanwhile, the binding capacity of Mo element and C element is strong, and carbide formed during heat treatment contributes to the room temperature strength and the high temperature strength of the steel. In addition, mo element in steel is also advantageous in reducing temper brittleness. Therefore, in order to exert the beneficial effect of Mo element, the mass percent of the Mo element is controlled to be between 0.90 and 1.10 percent in the high-temperature anti-fatigue low-alloy steel plate.
V: in the high-temperature anti-fatigue low-alloy steel plate, V element can play a role in strengthening steel through precipitation and grain refinement, but V has a large influence on the welding performance of the steel, and a small amount of V element can be added according to the requirement so as to improve the high-temperature tempering resistance of the steel. Based on the above, in the high-temperature anti-fatigue low-alloy steel plate, the mass percentage of the V element is controlled to be as follows: v is less than or equal to 0.03 percent.
Ca: in the high-temperature fatigue-resistant low-alloy steel sheet according to the present invention, ca treatment is generally required to convert strip-shaped sulfide inclusions in the steel into spherical sulfides. Therefore, in order to ensure the effect of the Ca treatment, the mass percentage of Ca element in the high-temperature fatigue-resistant low-alloy steel sheet according to the present invention is controlled to be 0.0015 to 0.0045%.
Further, in the high-temperature fatigue-resistant low-alloy steel sheet of the present invention, among the unavoidable impurities, P is 0.012% or less and/or S is 0.0015% or less.
In the present invention, P and S are both unavoidable impurity elements, and in order to ensure the quality of the wear-resistant steel, the lower the content of the impurity elements in the steel is, the better the condition is allowed.
P, S are all harmful elements whose content is to be strictly controlled, wherein P element is deviated at grain boundary to cause temper brittleness, and thus in the present invention, the impurity element P is controlled to satisfy: p is less than or equal to 0.012 percent.
Accordingly, S element can be combined with Mn and the like in steel to form plastic inclusion manganese sulfide, which is unfavorable for the fatigue performance of the steel, so that S element can be controlled to satisfy S less than or equal to 0.0015% (namely less than 15 ppm) in the invention. The inclusion morphology of the sulfide can be controlled by the design of the ultra-low sulfur and the Ca treatment, so that the harmful influence on the fatigue performance can be greatly reduced.
Further, in the high-temperature fatigue-resistant low-alloy steel plate, the microstructure is tempered bainite.
Further, in the high-temperature fatigue-resistant low-alloy steel sheet according to the present invention, the level of each of the class a, the class B, the class C and the class D inclusions is lower than 1.0, and the level of the total sum of all the inclusions is lower than 1.5. The inclusion content at such a low level greatly reduces the position of fatigue crack initiation, delays the formation time of the fatigue crack, and effectively prolongs the fatigue life.
In the above-described embodiments, the group a represents sulfide inclusions, the group B represents alumina inclusions, the group C represents silicate inclusions, and the group D represents spherical oxide inclusions.
Further, in the high-temperature fatigue-resistant low-alloy steel plate, the equivalent diameter of more than 97% of inclusions is less than 5 mu m.
Furthermore, in the high-temperature anti-fatigue low-alloy steel plate, the thickness is more than or equal to 5mm.
Further, in the high-temperature fatigue-resistant low-alloy steel plate, the thickness is 5-70mm.
Further, in the high-temperature fatigue-resistant low-alloy steel sheet according to the present invention, the performance thereof satisfies at least one of the following:
the yield strength is more than 295MPa, the tensile strength is 450-585MPa, the elongation is more than 22%, and the impact energy at the temperature of minus 20 ℃ is more than 200J;
the fatigue performance meets the following conditions: no fracture occurred at a high temperature of at least 530 ℃ for 100 ten thousand cycles under a cycle load with a maximum stress of 200 MPa.
Accordingly, another object of the present invention is to provide a method for manufacturing a high-temperature anti-fatigue low alloy steel plate, which is simple, convenient and feasible in process, and has excellent mechanical properties and fatigue properties, and good popularization prospects and application values.
In order to achieve the above object, the present invention provides a method for manufacturing the high-temperature fatigue-resistant low alloy steel sheet, comprising the steps of:
(1) Smelting and casting to obtain a continuous casting blank;
(2) Electroslag remelting is carried out by taking a continuous casting blank as an electrode raw material so as to obtain an electroslag ingot;
(3) Heating;
(4) Rolling;
(5) And (3) heat treatment: firstly, normalizing, wherein the normalizing temperature is 870-970 ℃, and fully preserving heat to form a single uniform austenite structure; then immediately spraying water to cool the steel plate to below 200 ℃; and tempering, wherein the tempering temperature is 700-800 ℃.
In the invention, the inventor realizes effective manufacturing process path and simple component proportion design, and simultaneously adopts a heat treatment process of accelerating cold speed tempering after normalizing, so that the content of inclusions in steel can be obviously reduced, and a tempered bainitic structure is obtained, thereby ensuring the mechanical property and high-temperature fatigue resistance of the steel plate.
In the manufacturing method of the high-temperature anti-fatigue low-alloy steel plate, the smelting raw materials are added according to the chemical composition ratio designed by the inventor, and the high-temperature anti-fatigue low-alloy steel plate can be obtained through the heat treatment steps of smelting, casting, electroslag remelting, heating, rolling and normalizing and tempering in sequence.
In the step (1) of the invention, the high purity molten iron is obtained by the blast furnace ironmaking, the ratio of the added scrap steel is controlled to be less than 5%, and then the molten iron is smelted by a converter and refined outside the converter, harmful elements are further removed, alloying is completed, and then the molten iron is cast into a continuous casting blank. In order to continuously remove impurities, more importantly, the content of nonmetallic inclusion is continuously reduced, so that in the step (2) of the invention, the continuous casting billet is controlled to be used as an electrode raw material for electroslag remelting smelting so as to obtain high-quality electroslag ingots.
Correspondingly, in the step (5) of the invention, the rolled steel plate needs to be subjected to heat treatment to obtain the required mechanical properties, and the invention adopts a typical heat treatment process of normalizing and tempering, which comprises the following specific procedures: normalizing, accelerating the cooling speed and tempering. In the invention, the normalizing temperature is controlled to 870-970 ℃ and the heat is fully preserved, so that the internal and external temperatures of the steel plate are consistent, and a single uniform austenite structure is formed; when the heat preservation of the steel plate is finished, water is sprayed immediately, and water cooling is carried out until the temperature of the steel plate is at least reduced to below 200 ℃; after water cooling, the steel sheet is then tempered to adjust the final properties. In tempering treatment, the tempering temperature is controlled to be 700-800 ℃, and the temperature is kept for a long time enough to fully recover metastable structural units such as bainite formed by the steel plate after normalizing and accelerated cooling, and fully precipitate carbide so as to form a stable structure.
Further, in the manufacturing method according to the present invention, in the step (3), the electroslag ingot is heated to 1100 to 1250 ℃ to homogenize the austenite structure.
In the technical scheme of the invention, the electroslag ingot is preferably heated to 1100-1250 ℃ to homogenize the austenite structure, so that chromium and molybdenum carbide in the steel can be fully dissolved; meanwhile, the lower limit of the heating temperature is controlled to consider the temperature drop of the slab during rolling and ensure that rolling is completed at a specified temperature.
Further, in the manufacturing method according to the present invention, in the step (4), the compression ratio is controlled to be larger than 4 at the time of rolling: 1.
compared with the prior art, the high-temperature anti-fatigue low-alloy steel plate and the manufacturing method thereof have the following advantages and beneficial effects:
the invention designs low alloy steel with excellent fatigue performance at high temperature, and through a realistic and effective manufacturing process path and simple component proportion, simultaneously adopts a heat treatment process of accelerating cold speed tempering after normalizing, remarkably reduces the content of inclusions in the steel, obtains tempered bainite structure, and ensures the mechanical property and high temperature fatigue resistance of the steel plate.
All the process steps of the manufacturing method are typical technical means of the current metallurgical industry, but the aim of effective combination is achieved by unified design and reasonable arrangement order, and the steel plates with various thicknesses can obtain the required performance through reasonable matching of various alloy elements. After the chemical element components and the production process are adopted, the heat-treated state yield strength of the prepared high-temperature anti-fatigue low-alloy steel plate is more than 295MPa, the tensile strength is 450-585MPa, the 50mm gauge length elongation exceeds 22%, the impact energy at the temperature of minus 20 ℃ is more than 200J, and most importantly, the steel plate has excellent anti-fatigue performance at the high temperature of 530 ℃, and can reach 100 ten thousand cycles without breaking under the cyclic load with the maximum stress of 200 MPa.
The high-temperature fatigue resistance of the steel plate is closely related to nonmetallic inclusion, and the inclusion is often the origin position of the initiation of fatigue cracks, so that the length of the fatigue life of the steel plate is determined. The invention can strictly control the content of S, P and other harmful elements in steel through a series of technological measures such as high-purity molten iron, secondary refining, electroslag remelting and the like, so that the content of inclusion forming elements is reduced to a very low level. In addition, the high-quality continuous casting billet is further electroslag remelted, so that the inclusion level in the steel is further reduced. Finally, it can be ensured that the grade of each of the class A, B, C and D inclusions in the steel is lower than 1.0, and the grade of the sum of all inclusions is lower than 1.5; the inclusion content at such a low level greatly reduces the position of fatigue crack initiation, delays the formation time of the fatigue crack, and effectively prolongs the fatigue life of the steel.
In addition, another measure adopted by the invention is to control the microstructure of the steel to be the design of tempered bainite in a large thickness range of the steel. According to the invention, through the design of effective components, a heat treatment process of accelerating cooling after normalizing and then tempering is adopted, a tempered bainitic structure can be formed completely within a large steel plate thickness range, the appearance of a softened ferrite structure is avoided, the fatigue stress resistance level of steel is further improved, and the fatigue resistance performance of the steel is improved.
Drawings
FIG. 1 is a photograph showing the microstructure of a high temperature fatigue resistant low alloy steel sheet of example 5 under a microscope.
FIG. 2 is a graph showing the relationship between the fatigue performance of the high temperature fatigue resistant low alloy steel sheet of example 5 at 530 ℃ and ASME specification design curve.
FIG. 3 schematically shows a distribution diagram of class D inclusions in example 5 of the present invention.
Detailed Description
The high temperature fatigue resistant low alloy steel sheet and the method of manufacturing the same according to the present invention will be further explained and illustrated with reference to specific examples, which, however, do not constitute an undue limitation on the technical solution of the present invention.
Examples 1 to 6
The high temperature fatigue resistant low alloy steel sheets of examples 1-6 were all made by the following steps:
(1) Smelting and casting according to the chemical composition ratio shown in Table 1, during smelting, firstly, smelting iron by a blast furnace to obtain high-purity molten iron, controlling the ratio of added scrap steel to be less than 5%, then conveying the blast furnace molten iron into a converter for smelting, and then carrying out external refining (LF desulfurization, RH vacuum degassing and wire feeding Ca treatment), and casting after finishing refining to obtain a continuous casting blank.
(2) And (3) performing electroslag remelting by taking the continuous casting blank as an electrode raw material to obtain an electroslag ingot.
(3) Heating: the electroslag ingot is heated to 1100-1250 ℃ to homogenize the austenitic structure.
(4) Rolling: the control compression ratio is larger than 4 during rolling: 1.
(5) And (3) heat treatment: firstly, normalizing, controlling the normalizing temperature to 870-970 ℃, and fully preserving heat to form a single uniform austenite structure; then immediately spraying water to cool the steel plate to below 200 ℃; and tempering, wherein the tempering temperature is controlled to be 700-800 ℃.
It should be noted that, in the present invention, the high temperature fatigue-resistant low alloy steel plates of examples 1 to 6 are all prepared by the process flows of step (1) to step (5), and the chemical components and the relevant process parameters thereof meet the control requirements of the design specification of the present invention.
Table 1 lists the mass percentages of the chemical elements in the high temperature fatigue resistant low alloy steel sheets of examples 1 to 6.
Table 1 (wt.%), the balance Fe and unavoidable impurities other than P, S
Table 2 shows specific process parameters of the high temperature fatigue resistant low alloy steel sheet of examples 1 to 6 in each step of the above manufacturing method.
Table 2.
The finally prepared high-temperature anti-fatigue low-alloy steel plates of examples 1-6 are respectively sampled, and the high-temperature anti-fatigue low-alloy steel plate samples of examples 1-6 are observed and analyzed, and the microstructure of the high-temperature anti-fatigue low-alloy steel plates of examples 1-6 is observed to be tempered bainite.
Accordingly, in the present invention, further analysis was performed on the grades of various inclusions in the obtained high-temperature fatigue-resistant low alloy steel sheets of examples 1 to 6 to obtain each grade of inclusions in the A, B, C and D groups of the respective example steels, the specific analysis results of which are shown in Table 3 below.
Table 3.
Note that: class a indicates sulfide inclusions, class B indicates alumina inclusions, class C indicates silicate inclusions, class D indicates spherical oxide inclusions, and class Ds indicates single-particle spherical inclusions. Each type of inclusion is divided into a coarse system and a fine system according to different thickness or diameter, and the specific size is the same as the specification of a microscopic examination method of a standard rating chart for measuring the content of nonmetallic inclusion in national standard GB/T10561-2005 steel.
Referring to the above Table 3, it can be seen that the high temperature fatigue resistant low alloy steel sheets of examples 1 to 6 of the present invention have very low inclusion levels of class A, class B, class C and class D, and the class A, class B, class C and class D each have a inclusion level of less than 1.0. In the present invention, all the A+B+C+D type inclusions in the steels of each example were added, the A+B+C+D type (coarse system) was not more than 1.0 level, the A+B+C+D type (fine system) was not more than 1.0 level, and the A+B+C+D type (coarse system+fine system) was not more than 1.5 level.
After the microstructure observation and inclusion analysis of the high temperature fatigue resistant low alloy steel sheets according to examples 1 to 6 of the present invention were completed, the mechanical properties of the high temperature fatigue resistant low alloy steel sheet samples of examples 1 to 6 were further tested to obtain the mechanical properties parameters of the high temperature fatigue resistant low alloy steel sheets of examples 1 to 6, and the obtained test results were listed in table 4 below.
The relevant mechanical property testing means are as follows:
tensile test: the yield strength, tensile strength and elongation at room temperature were measured for the high temperature fatigue resistant low alloy steel sheet samples of examples 1-6, as specified by the GB/T228.1 standard at room temperature.
Impact test: the impact energy at-20℃was measured for the high temperature fatigue resistant low alloy steel sheet samples of examples 3-6, as specified by GB/T229 standard.
Table 4 shows the mechanical properties of the high temperature fatigue resistant low alloy steel sheets of examples 1-6.
Table 4.
Note that: the steel sheets of example 1 and example 2 had thicknesses of 5mm and 8mm, respectively, and could not be processed into 10X 55mm Charpy impact specimens.
Referring to the above table 4, it can be seen that the high temperature fatigue-resistant low alloy steel plates of examples 1 to 6 according to the present invention have very excellent mechanical properties, the yield strength at room temperature is 363 to 448MPa, the tensile strength is 520 to 577MPa, and the elongation is 29 to 34%. Meanwhile, the Charpy impact test samples of 10 multiplied by 55mm processed by the method in the embodiment 3-6 have the impact energy of more than 200J at the temperature of minus 20 ℃ and have excellent low-temperature impact performance.
Accordingly, after the mechanical properties of the high temperature fatigue resistant low alloy steel sheets of examples 1 to 6 described above were obtained, the high temperature fatigue resistant low alloy steel sheet of example 5 was resampled and the fatigue properties of each example steel sheet was tested to obtain the fatigue properties of the high temperature fatigue resistant low alloy steel sheets of examples 1 to 6, and the obtained fatigue property test results were listed in table 5 below.
The relevant fatigue performance test means are as follows:
fatigue test: the fatigue life (cycle times) of the high temperature fatigue resistant low alloy steel sheets of examples 3 to 6 was obtained according to the test method prescribed in GB15248 at a high temperature of 530℃in the range of 0.20 to 0.80% of the maximum control strain.
Table 5 shows the fatigue performance test results of the high temperature fatigue resistant low alloy steel sheet of example 3.
Table 5.
Table 6 lists the fatigue performance test results of the high temperature fatigue resistant low alloy steel sheet of example 4.
Table 6.
| Sequence number | Maximum control strain | Fatigue life N f (cycle) |
| 1 | 0.80％ | 690 |
| 2 | 0.60％ | 1615 |
| 3 | 0.40％ | 11820 |
| 4 | 0.30％ | 35737 |
| 5 | 0.25％ | 73938 |
| 6 | 0.20％ | ＞1000000 |
Table 7 lists the fatigue performance test results of the high temperature fatigue resistant low alloy steel sheet of example 5.
Table 7.
Table 8 lists the fatigue performance test results of the high temperature fatigue resistant low alloy steel sheet of example 6.
Table 8.
| Sequence number | Maximum control strain | Fatigue life Nf (cycle) |
| 1 | 0.80％ | 1015 |
| 2 | 0.60％ | 2145 |
| 3 | 0.40％ | 15847 |
| 4 | 0.30％ | 34800 |
| 5 | 0.25％ | 84932 |
| 6 | 0.20％ | ＞1000000 |
As shown in the above tables 5 to 8, in the present invention, the high temperature fatigue resistant low alloy steel sheets of examples 3 to 6 were able to be subjected to a cyclic loading of 100 ten thousand cycles without breaking at a maximum control strain of 0.20% (corresponding to a maximum control stress of 200 MPa) at a high temperature of at least 530 ℃, i.e., the fatigue life was 100 ten thousand cycles or more.
Since the round bar fatigue test pieces with a diameter of 10mm were not processed in examples 1 and 2 because the plate thickness was small, no fatigue performance test was performed.
FIG. 1 is a photograph showing the microstructure of a high temperature fatigue resistant low alloy steel sheet of example 5 under a microscope.
As shown in fig. 1, in example 5, the microstructure of the high-temperature fatigue-resistant low-alloy steel sheet according to the present invention is tempered bainite.
FIG. 2 is a graph showing the relationship between the fatigue performance of the high temperature fatigue resistant low alloy steel sheet of example 5 at 530 ℃ and ASME specification design curve.
As shown in fig. 2, in example 5, compared with the ASME specification design curve, the fatigue performance result (Experiment) of the high-temperature fatigue-resistant low-alloy steel sheet according to the present invention is significantly higher than that of the ASME specification design curve at 530 ℃, and has quite excellent fatigue performance.
Fig. 3 schematically shows the distribution diagram of class D inclusions in example 5.
In the present invention, more detailed information on the size and distribution of inclusions in example 5 was obtained by scanning image analysis, wherein the size distribution of the most serious class D inclusion is shown in fig. 3. As shown in FIG. 3, the high-temperature fatigue-resistant low-alloy steel plate of the invention has fewer inclusions, the inclusions are small in size, and the equivalent diameter of 97% of the inclusions is less than 5 mu m.
From the above, the invention adopts reasonable chemical element design and matches with optimized manufacturing process to effectively prepare the high-temperature anti-fatigue low-alloy steel plate with moderate strength, good toughness and good high-temperature anti-fatigue performance.
In the invention, the production process is practical and feasible, only a small amount of alloy elements are needed to be added into the steel, and the continuous casting blank can be prepared by smelting according to the designed chemical element composition range, pure molten iron, steelmaking and secondary refining and then casting; the prepared continuous casting billet is remelted by electroslag to prepare an electroslag ingot, and the electroslag ingot is rolled by a thick plate rolling mill, and is subjected to heat treatment in a way of normalizing, accelerated cooling and tempering, so that the high-temperature anti-fatigue low-alloy steel plate can be effectively prepared.
The high-temperature anti-fatigue low-alloy steel plate has very wide application prospect, and can be used for manufacturing chemical, nuclear and boiler containers with anti-fatigue design requirements, which operate at high temperature and high pressure.
It should be noted that the combination of the technical features in the present invention is not limited to the combination described in the claims or the combination described in the specific embodiments, and all the technical features described in the present invention may be freely combined or combined in any manner unless contradiction occurs between them.
It should also be noted that the above-mentioned embodiments are merely examples of the present invention, and it is obvious that the present invention is not limited to the above-mentioned embodiments, and many similar variations are followed. All modifications attainable or obvious from the present disclosure set forth herein should be deemed to be within the scope of the present disclosure.
Claims (12)
1. The high-temperature anti-fatigue low-alloy steel plate contains Fe and unavoidable impurities, and is characterized by also containing the following chemical elements in percentage by mass:
C：0.08～0.2％，Si：0.10～0.30％，Mn：0.30～0.60％，Cr：2.20～2.50％，Mo：0.90～1.10％，V≤0.03％，Ca：0.0015～0.0045％。
2. the high-temperature fatigue-resistant low-alloy steel plate according to claim 1, wherein the mass percentages of the chemical elements are:
c:0.08 to 0.2 percent, si:0.10 to 0.30 percent, mn:0.30 to 0.60 percent, cr:2.20 to 2.50 percent, mo:0.90 to 1.10 percent, V is less than or equal to 0.03 percent, ca:0.0015 to 0.0045 percent; the balance being Fe and unavoidable impurities.
3. The high-temperature fatigue-resistant low-alloy steel sheet according to claim 1 or 2, wherein among unavoidable impurities, P is 0.012% or less and/or S is 0.0015% or less.
4. The high temperature fatigue resistant low alloy steel sheet according to claim 1 or 2, wherein the microstructure thereof is tempered bainite.
5. The high temperature fatigue resistant low alloy steel sheet according to claim 1 or 2, wherein each of class a, class B, class C and class D has a class of inclusion of 1.0 or less and the total of all inclusions has a class of less than 1.5.
6. The high temperature fatigue resistant low alloy steel sheet according to claim 1 or 2, wherein 97% or more of the inclusions have an equivalent diameter of < 5 μm.
7. The high-temperature fatigue-resistant low-alloy steel sheet according to claim 1 or 2, wherein the thickness is not less than 5mm.
8. The high temperature fatigue resistant low alloy steel sheet according to claim 1 or 2, wherein the thickness thereof is 5 to 70mm.
9. The high temperature fatigue resistant low alloy steel sheet according to claim 1 or 2, wherein the performance satisfies at least one of the following:
the yield strength is more than 295MPa, the tensile strength is 450-585MPa, the elongation is more than 22%, and the impact energy at the temperature of minus 20 ℃ is more than 200J;
the fatigue performance meets the following conditions: no fracture occurred at a high temperature of at least 530 ℃ for 100 ten thousand cycles under a cycle load with a maximum stress of 200 MPa.
10. A method for manufacturing a high-temperature fatigue-resistant low-alloy steel sheet according to any one of claims 1 to 9, comprising the steps of:
(1) Smelting and casting to obtain a continuous casting blank;
(2) Electroslag remelting is carried out by taking a continuous casting blank as an electrode raw material so as to obtain an electroslag ingot;
(3) Heating;
(4) Rolling;
(5) And (3) heat treatment: firstly, normalizing, wherein the normalizing temperature is 870-970 ℃, and fully preserving heat to form a single uniform austenite structure; then immediately spraying water to cool the steel plate to below 200 ℃; and tempering, wherein the tempering temperature is 700-800 ℃.
11. The method of claim 10, wherein in step (3), the electroslag ingot is heated to 1100-1250 ℃ to homogenize the austenitic structure.
12. The manufacturing method according to claim 10, wherein in the step (4), the compression ratio is controlled to be larger than 4 at the time of rolling: 1.
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