A method for improving the impact toughness of 1cr12ni3mo2vnbn blade steel

Abstract

This invention discloses a method for improving the impact toughness of 1Cr12Ni3Mo2VNbN blade steel, belonging to the field of steel smelting technology. This invention controls the Cr content in the elemental composition of 1Cr12Ni3Mo2VNbN steel. eq The value is: 5.5≤[Cr eq =6Si+1Cr+4Mo+1.5W+11V+5Nb-(40C+2Mn+4Ni+30N)]≤6.0, and further prepared 1Cr12Ni3Mo2VNbN blade steel according to alloy smelting method. This invention improves the Cr eq The value is limited, thus achieving the effect of Rp 0.02 ≥866MPa, R m Under the premise of ≥1260MPa, the V-notch impact value is ≥34J, and it effectively improves the impact toughness and impact stability of 1Cr12Ni3Mo2VNbN blade steel, showing good application prospects.

Description

Technical Field

[0001] This invention relates to a method for improving the impact toughness of turbine blade steel, specifically a method for improving the impact toughness of 1Cr12Ni3Mo2VNbN blade steel, belonging to the technical field of gas turbine blade material methods and applications. Background Technology

[0002] Guided by the goals of carbon peaking and carbon neutrality, and with the increase in domestic electricity consumption, my country's gas turbine manufacturing technology has been continuously developing, with clean energy and high-efficiency supercritical and ultra-supercritical units as the main development direction. 1Cr12Ni3Mo2VNbN is a martensitic stainless heat-resistant steel with high Cr, Ni, Mo, V, Nb, and N content, possessing good strength and toughness properties, and is commonly used for turbine blades.

[0003] Turbine blades are relatively large, placing more stringent requirements on operating temperature, pressure, working environment, and operational safety. Currently, the mechanical property requirements for 1Cr12Ni3Mo2VNbN blade steel are Rp0.02≥866MPa, Rm≥1260MPa, and a V-notch impact value≥34J. However, for currently produced 1Cr12Ni3Mo2VNbN material, while meeting the strength requirements, the impact energy fluctuates greatly, the data is unstable, and some batches do not meet the ≥34J requirement. Therefore, research on improving the performance stability of supercritical blade steel and advancing the development of blade materials for supercritical and ultra-supercritical gas turbines is of great significance.

[0004] Reports indicate that by optimizing the chemical composition and heat treatment process, it is possible to achieve the combined performance requirements of high yield strength ratio and high ductility and toughness in blades. However, this method cannot achieve a comprehensive improvement in impact toughness.

[0005] For example, patent CN 102794538A mentions that optimizing the chemical composition and heat treatment process cannot achieve the desired improvement in the low-temperature impact toughness of martensitic stainless steel. The final method used was to achieve the effect of improving low-temperature impact toughness through pre-weld treatment, preheating, welding, and post-weld heat treatment.

[0006] Patent CN 105378135 A discloses a duplex ferritic austenitic stainless steel with a microstructure consisting of 40-60 vol% ferrite and 40-60 vol% austenite, which can control the creq between 20 and 24.5. However, it requires the addition of copper to achieve improved cold working and impact toughness, and the method is not suitable for 1Cr12Ni3Mo2VNbN steel.

[0007] Therefore, how to provide a simple method to improve the impact toughness of 1Cr12Ni3Mo2VNbN steel blades has become an urgent technical problem to be solved. Summary of the Invention

[0008] The purpose of this invention is to solve the aforementioned technical problems and provide a method for improving the impact toughness of 1Cr12Ni3Mo2VNbN blade steel to meet the requirements for use in the field of supercritical turbine blade steel materials. The technical objective of this invention is to provide a simple processing method that can significantly improve the impact toughness of 1Cr12Ni3Mo2VNbN blade steel from both elemental composition and preparation process perspectives.

[0009] To achieve the above objectives, the present invention employs the following technical solution:

[0010] A method for improving the impact toughness of 1Cr12Ni3Mo2VNbN blade steel involves controlling the Cr content in the elemental composition of the 1Cr12Ni3Mo2VNbN blade steel. eq The value is: 5.5≤[Cr eq =6Si+1Cr+4Mo+1.5W+11V+5Nb-(40C+2Mn+4Ni+30N)]≤6.0, and to achieve this by processing 1Cr12Ni3Mo2VNbN blade steel through the following preparation process steps:

[0011] Step A: The primary smelting method is IM+LF+VD, Al deoxidation is used, the pre-tapping calming time is ≥8min, and the steel is cast into electrode rods.

[0012] Step B: Electroslag remelting is carried out under a protective atmosphere, with the melting rate controlled at 6.0-7.0 kg / min, and the product is remelted into electroslag ingots.

[0013] Step C: Heat and hold the steel ingot for a certain period of time. The heating and holding period is as follows: heat up to 1230-1270℃ and hold for ≥6h. The heating and holding period for the forged product and the final heat treatment is as follows: cool down to 1140-1180℃ and hold for 30-120min. Then, it is taken out of the furnace for forging and is forged and drawn into shape using a press.

[0014] Furthermore, step A controls the white slag retention time during the LF furnace refining period to be ≥30 min.

[0015] Furthermore, in step A, the total vacuuming time of VD is controlled to be ≥20 min, the high vacuum is ≤133 Pa, and the holding time is ≥10 min.

[0016] Furthermore, the diameter of the remelted steel ingot in step B is...

[0017] Furthermore, in step C, a 2000T or 6000T press is used for forging and drawing.

[0018] Furthermore, in step C, the steel ingot is forged for 2-3 heats before being finished, and the total forging ratio is controlled to be ≥6.

[0019] Furthermore, the elemental composition of the 1Cr12Ni3Mo2VNbN blade steel, by weight percentage, includes:

[0020] C: 0.12–0.14%, Mn: 0.35–0.55%, Si: ≤0.20%, Ni: 2.45–2.75%, Cr: 11.20–11.80%, Mo: 2.0–2.4%, V: 0.20–0.30%, Nb: 0.08–0.15%, N: 0.04–0.07%, balance being Fe and unavoidable impurities.

[0021] Furthermore, the residual elements of the 1Cr12Ni3Mo2VNbN blade steel include: P≤0.020%; Ti≤0.01%; Sn≤0.001%; ​​Sb≤0.002%; As≤0.005%; Pb≤0.002%.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0023] (1) This invention achieves its goal by designing and controlling the composition of various chemical elements, and innovatively controls Cr. eq The equivalent value (chromium equivalent) is limited by controlling 5.5 ≤ Cr eq ≤6.0, Cr eq The effect of equivalent values ​​on the microstructure transformation during the quenching process of 1Cr12Ni3Mo2VNbN blade steel, Cr eq Different equivalent values ​​result in different contents of retained austenite in the microstructure after quenching. By controlling Cr... eq The equivalent value is used to control the content of martensite and austenite phases after quenching, thereby controlling the mechanical properties of the material. This invention discovers that by controlling 5.5≤Cr... eq With an impact toughness of ≤6.0, a material with stable impact toughness was obtained.

[0024] (2) This invention obtains a steel ingot structure with good purity and crystallization by controlling the melting rate and protective atmosphere electroslag. Subsequently, by heating the steel ingot at a high temperature of 1230 to 1270°C and combining it with a large deformation forging process, the segregation of the steel ingot is further improved, and a material with uniform structure is obtained. This is of great help to improve the impact toughness and stability of the material.

[0025] (3) The 1Cr12Ni3Mo2VNbN blade steel material produced by the method of the present invention has good impact toughness and stability, and has good economic and social benefits in the field of steam turbines, and is suitable for promotion and use. Detailed Implementation

[0026] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0027] Prepare 1Cr12Ni3Mo2VNbN alloy raw materials according to the weight percentage of each element in Table 1 below.

[0028] Table 1 Chemical composition of 1Cr12Ni3Mo2VNbN alloy raw materials

[0029] Elemental composition percentage (%) C Mn Si P S Ni Cr Cu V Mo Sample 1 0.14 0.49 0.17 0.012 0.0012 2.6 11.38 0.01 0.28 2.09 Sample 2 0.12 0.58 0.15 0.018 0.0025 2.57 11.43 0.03 0.225 2.05 Sample 3 0.13 0.55 0.185 0.0125 0.0014 2.65 11.3 0.02 0.27 2.05 Sample 4 0.13 0.5 0.16 0.014 0.0013 2.61 11.32 0.026 0.28 2.08 Sample 5 0.12 0.48 0.17 0.014 0.001 2.59 11.33 0.035 0.28 2.15 Elemental composition percentage (%) W Al Ti N Nb Sn As Sb <![CDATA[Cr eq ]]> Sample 1 0.001 0.012 0.001 0.052 0.11 0.0001 0.0006 0.0001 5.852 Sample 2 0.001 0.015 0.005 0.047 0.1 0.001 0.0027 0.0001 5.857 Sample 3 0.01 0.015 0.002 0.05 0.115 0.0001 0.0004 0.0001 5.770 Sample 4 0.001 0.015 0.001 0.051 0.14 0.046 0.0001 0.0008 6.212 Sample 5 0.005 0.012 0.001 0.045 0.115 0.0001 0.0008 0.0001 7.143

[0030] Example 1

[0031] The alloy was prepared according to the elemental composition of Sample 1 above, and then the following preparation method steps were used:

[0032] Step A: The primary smelting method is IM+LF+VD. The white slag holding time during the LF furnace refining period is 30 min. The total vacuum time of VD is 20 min, the high vacuum is 133 Pa, and the holding time is 10 min. Al deoxidation is used. The pre-tapping calming time is 8 min, and the steel is cast into electrode rods.

[0033] Step B: Electroslag remelting is performed under a protective atmosphere. The melting rate of the protective atmosphere electroslag is 6.0 kg / min, and the diameter of the steel ingot is [missing information]. Remelted into electroslag ingots;

[0034] Step C: Heat and hold the steel ingot at that temperature for a certain period of time, with a diameter of... The heating regime for the steel ingot is as follows: heat up to 1270℃ and hold for 6 hours. The heating regime for the forging / final heating is as follows: cool down to 1180℃ and hold for 30 minutes. Then, the ingot is taken out of the furnace for forging. The forging process from steel ingot to finished product is completed in 2 heats with a total forging ratio of 6. A 2000T press is used for forging and drawing.

[0035] Example 2

[0036] An alloy was prepared according to the elemental composition of Sample 2 above, and then the following preparation method steps were used:

[0037] Step A: The primary smelting method is IM+LF+VD. The white slag holding time during the LF furnace refining period is 32 min. The total vacuum time of VD is 23 min, the high vacuum is 131 Pa, and the holding time is 12 min. Al deoxidation is used. The pre-tapping calming time is 9 min, and the steel is cast into electrode rods.

[0038] Step B: Electroslag remelting is performed under a protective atmosphere. The melting rate of the protective atmosphere electroslag is 6.5 kg / min, and the diameter of the steel ingot is [missing information]. Remelted into electroslag ingots;

[0039] Step C: Heat and hold the steel ingot at that temperature for a certain period of time, with a diameter of... The steel ingot heating process is as follows: heating to 1250℃ and holding for 8 hours. The forging / final heating process is as follows: cooling to 1160℃ and holding for 90 minutes. Then, the steel ingot is taken out of the furnace for forging. The forging process from steel ingot to finished product is completed in 3 heats with a total forging ratio of 7. A 6000T press is used for forging and drawing.

[0040] Example 3

[0041] An alloy was prepared according to the elemental composition of sample three above, and then the following preparation method steps were used:

[0042] Step A: The primary smelting method is IM+LF+VD. The white slag holding time during the LF furnace refining period is 33 min. The total vacuum time of VD is 22 min, the high vacuum is 130 Pa, and the holding time is 14 min. Al deoxidation is used. The pre-tapping calming time is 10 min, and the steel is cast into electrode rods.

[0043] Step B: Electroslag remelting is performed under a protective atmosphere. The melting rate of the protective atmosphere electroslag is 7.0 kg / min, and the diameter of the steel ingot is [missing information]. Remelted into electroslag ingots;

[0044] Step C: Heat and hold the steel ingot at that temperature for a certain period of time, with a diameter of... The steel ingot heating process is as follows: heating to 1230℃ and holding for 7 hours. The forging / final heating process is as follows: cooling to 1140℃ and holding for 60 minutes. Then, the steel ingot is taken out of the furnace for forging. The forging process from steel ingot to finished product is completed in 3 heats with a total forging ratio of 8. A 2000T press is used for forging and drawing.

[0045] Comparative Example 1

[0046] Except that the chemical composition was prepared according to the elemental composition of Sample 4, the preparation method and steps were basically the same as in Example 1, with the only difference being:

[0047] In step B, the melting rate of the protective atmosphere electroslag is controlled at 7.5 kg / min. In step C, the melting rate is controlled at 7.5 kg / min. The heating regime for steel ingots is 1220℃*6h, and the heating regime for forged products / finishing is 1130℃*30min.

[0048] Comparative Example 2

[0049] Except that the chemical composition was prepared according to the elemental composition of Sample 5, the preparation method and steps were basically the same as in Example 2, with the only difference being:

[0050] In step A, the pre-tapping calming time is 6 minutes, and the steel is cast into an electrode rod.

[0051] In step C The heating regime for steel ingots is 1280℃ for 10 hours, and the heating regime for forged products / finishing is 1190℃ for 150 minutes.

[0052] Comparative Example 3

[0053] Except for the elemental composition of the chemical composition, the preparation method is the same as that in Example 1.

[0054] Comparative Example 4

[0055] Except for the elemental composition of the chemical composition, the preparation method is the same as that in Example 1.

[0056] Test case

[0057] The samples prepared in Examples 1-3 and Comparative Examples 1-4 were subjected to performance tests, and the results are shown in Table 2. The results from Examples 1-3 show that the gas turbine blade material prepared using the above process method meets the technical requirements in terms of mechanical properties after room temperature testing, exhibiting stable impact performance with a large margin.

[0058] However, while the test results of Comparative Example 1 met the technical requirements, the impact margin of Sample 4 was not large. In Comparative Example 2, although the strength of Sample 5 met the technical requirements, the impact toughness did not. In Comparative Examples 3 and 4, due to changes in elemental composition, even using the same preparation method as Example 1, resulted in a significant deterioration in the performance of the samples.

[0059] Therefore, the experimental results of this invention show that the gas turbine blade material manufactured using the methods of Examples 1-3 can significantly improve the impact toughness and stability of the material, creating more substantial production and technical benefits. While the methods of Comparative Examples 1 and 3 can also meet the material performance requirements, their effect on improving the overall performance of the steel ingot samples is poor. The samples obtained by the methods of Comparative Examples 2 and 4 have poorer performance.

[0060] Table 2. Test data (A corresponds to the feeding end of the steel ingot; B corresponds to the arc-starting end of the steel ingot)

[0061] project Rp0.02 / MPa Rm / MPa A / ％ Z / ％ KV2 / J quality Technical Requirements ≥866 ≥1260 ≥13 ≥30 ≥34 standard Example 1#-A 913 1304 17.0 74 150 / 145 / 178 qualified Example 1#-B 915 1297 17.0 75 152 / 141 / 158 qualified Example 2#-A 889 1281 17.0 72 108 / 124 / 171 qualified Example 2#-B 896 1289 17.5 72 138 / 176 / 168 qualified Example 3#-A 893 1278 18.0 73 134 / 186 / 162 qualified Example 3#-B 897 1275 18.5 73 128 / 147 / 158 qualified Comparative Example 1#-A 901 1283 17.0 70 34 / 40 / 36 qualified Comparative Example 1#-B 908 1284 17.5 72 35 / 42 / 39 qualified Comparative Example 2#-A 911 1267 18.0 71 28 / 34 / 40 Unqualified Comparative Example 2#-B 929 1285 18.0 71 28 / 34 / 35 Unqualified Comparative Example 3#-A 911 1279 17.0 72 56 / 63 / 60 qualified Comparative Example 3#-B 912 1286 17.0 73 51 / 37 / 39 qualified Comparative Example 4#-A 900 1276 17.0 70 32 / 41 / 28 Unqualified Comparative Example 4#-B 903 1271 17.5 71 26 / 40 / 33 Unqualified

[0062] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No markings in the claims should be construed as limiting the scope of the claims.

[0063] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for improving the impact toughness of 1Cr12Ni3Mo2VNbN blade steel, characterized in that, The elemental composition of the 1Cr12Ni3Mo2VNbN blade steel, by weight percentage, includes: C: 0.12–0.14%, Mn: 0.35–0.55%, Si: ≤0.20%, Ni: 2.45–2.75%, Cr: 11.20–11.80%, Mo: 2.0–2.4%, V: 0.20–0.30%, Nb: 0.08–0.15%, N: 0.04–0.07%, with the balance being Fe and unavoidable impurities; the 1Cr12Ni3Mo2VNbN blade steel... The residual elements include: P≤0.020%; Ti≤0.01%; Sn≤0.001%; ​​Sb≤0.002%; As≤0.005%; Pb≤0.002%; the Creq value in the elemental composition of 1Cr12Ni3Mo2VNbN blade steel is controlled to be: 5.5≤[Creq=6Si+1Cr+4Mo+1.5W+11V+5Nb-(40C+2Mn+4Ni+30N)]≤6.0, and the following preparation process steps are performed on the 1Cr12Ni3Mo2VNbN blade steel: Step A: The primary smelting method is IM+LF+VD, Al deoxidation is used, the pre-tapping calming time is ≥8min, and the steel is cast into electrode rods. Step B: Electroslag remelting is carried out under a protective atmosphere, with the melting rate controlled at 6.0-7.0 kg / min, and the product is remelted into electroslag ingots. Step C: Heat and hold the steel ingot for a certain period of time. The heating and holding period is as follows: heat up to 1230-1270°C and hold for ≥6 hours. The heating and holding period for the forged product and the final heat treatment is as follows: cool down to 1140-1180°C and hold for 30-120 minutes. Then, it is taken out of the furnace for forging and is forged and drawn into shape using a press.

2. The method for improving the impact toughness of 1Cr12Ni3Mo2VNbN blade steel according to claim 1, characterized in that, Step A controls the white slag retention time during the refining period of the LF furnace to be ≥30 min.

3. The method for improving the impact toughness of 1Cr12Ni3Mo2VNbN blade steel according to claim 1, characterized in that, Step A controls the total vacuuming time of VD to be ≥20min, the high vacuum to be ≤133Pa, and the holding time to be ≥10min.

4. The method for improving the impact toughness of 1Cr12Ni3Mo2VNbN blade steel according to claim 1, characterized in that, The diameter of the steel ingot after remelting in step B is φ720mm.

5. A method for improving the impact toughness of 1Cr12Ni3Mo2VNbN blade steel according to claim 4, characterized in that, In step C, a 2000T or 6000T press is used for forging and drawing.

6. A method for improving the impact toughness of 1Cr12Ni3Mo2VNbN blade steel according to claim 1, characterized in that, In step C, the steel ingot is forged for 2-3 times to complete the process, and the total forging ratio is controlled to be ≥6.