Method for preparing P91 steel welding seam sample with abnormal hardness based on CMT method

Abstract

The invention belongs to the technical field of metal material welding, and provides a method for preparing a P91 steel abnormal hardness welding seam sample based on a CMT method, and the method comprises the following steps: selecting and cleaning a CMT welding substrate; an ER90S-B9 welding wire matched with the P91 steel in composition is selected as a stacking metal material; cMT is adopted for surfacing on a substrate, the motion path of a welding gun is reciprocating motion, and the height of each layer of weld bead is 1-2 mm; the accumulated surface oxides in the step S3 are polished and cleaned, and the interlayer temperature is kept at 180-220 DEG C; repeating the steps S3-S4 until the welding seam sample is stacked; carrying out wire cutting on the stacked sample to obtain a sample, and carrying out normalizing treatment; and the sample obtained in the step S6 is subjected to tempering treatment at different temperatures, and the high-hardness welding seam sample is prepared. The P91 steel high-hardness welding seam sample structure prepared through the method meets the actual welding seam center structure, the hardness is larger than the site welding seam hardness recommended in the standard, the interval range of high-hardness welding seams appearing on site is met, and then a sample is provided for the high-hardness P91 steel welding seam sample.

Description

Technical Field

[0001] The present invention belongs to the technical field of metal material welding, and in particular relates to a method for preparing a P91 steel abnormal hardness weld sample based on a CMT method. Background Art

[0002] 9Cr martensitic heat-resistant steel boasts advantages such as low cost, high high-temperature creep strength, excellent oxidation resistance, high thermal conductivity, and superior processability. It is widely used in high-temperature structural components such as pressure vessels, steam piping, and turbine blades in thermal power plants, becoming a key material for their development. However, welded joints, as weak points in piping systems, have always been a high-risk area for accidents. Research has shown that long-term service in high-temperature and high-pressure environments can gradually degrade the microstructure of P91 steel, reducing its high-temperature endurance strength and creep strength. Since hardness can, to a certain extent, reflect material strength, this degradation in material properties is often reflected in low hardness during field testing. However, conventional hardness testing of welds often reveals elevated hardness. Therefore, while hardness testing can effectively determine the safe service life of welded joints and their local components to a certain extent, empirical equations cannot accurately determine material properties and service life under conditions of elevated hardness. Establishing an effective relationship between high hardness, microstructure, properties, and service life is crucial for determining the service performance of structures. To obtain high-hardness weld samples for subsequent analysis, destructive cutting of pipeline welds is typically required on-site. However, this method causes the associated equipment to cease operation, making it impractical in practice. Therefore, if weld materials with similar high-hardness characteristics could be prepared in the laboratory based on weld hardness data obtained from on-site measurements, the drawbacks of directly collecting samples from the field could be effectively avoided without affecting the normal operation of the on-site pipeline system. Therefore, it is necessary to provide a method for preparing high-hardness weld specimens for subsequent microstructure analysis and life assessment.

[0003] For the welding of P91 steel, weld cracking is the main consideration, followed by the δ-Fe phase in the weld. According to research, when the heat input increases, the longer the residence time in the 1438℃~1506℃ range means that the liquid phase transforms to the δ-Fe phase more fully. In the 1286℃~1438℃ range, due to the limited increase in its residence time, it is difficult for the δ-Fe phase to fully transform into the γ-Fe phase, so some δ-Fe phase will remain. In other words, when the heat input is smaller, the time the solidified metal stays in the 1438℃~1506℃ range is shorter, and it is difficult for the liquid phase to fully transform into the δ-Fe phase. When entering the 1286℃~1438℃ range, the shorter residence time can make a small amount of δ-Fe phase transform into γ-Fe phase.

[0004] Therefore, cold metal transfer (CMT) welding, based on its low heat input and high deposition efficiency characteristics, can inhibit the formation of δ-ferrite (δ-Fe) and optimize the deposition rate, providing key technical support for the preparation of high-hardness weld specimens of P91 steel. Summary of the Invention

[0005] In order to solve the above technical problems, the present invention provides a method for preparing P91 steel abnormal hardness weld specimens based on the CMT method to solve the problems in the prior art. The technical solution adopted by the present invention is:

[0006] The method for preparing a P91 steel abnormal hardness weld specimen based on the CMT method comprises the following steps:

[0007] S1: Select the CMT welding substrate and clean it;

[0008] S2: ER90S-B9 welding wire that matches the composition of P91 steel is selected as the filler metal material;

[0009] S3: CMT is used for cladding on the substrate. The welding gun movement path is reciprocating, and the height of each weld bead is 1-2mm.

[0010] S4: Grind and clean the accumulated surface oxides in step S3, and maintain the interlayer temperature at 180-220°C;

[0011] S5: Repeat steps S3-S4 until the accumulation of weld samples is completed;

[0012] S6: Perform wire cutting on the deposited sample to obtain the sample and then perform normalizing treatment;

[0013] S7: The sample obtained in step S6 is subjected to tempering treatment at different temperatures to prepare a high-hardness weld sample.

[0014] Furthermore, the CMT welding wire is ER90S-B9 welding wire.

[0015] Furthermore, the composition of the ER90S-B9 welding wire includes: C: 0.10wt%; Si: 0.30wt%; Mn: 0.50wt%; Cr: 9.0wt%; Mo: 1.0wt%; Ni: 0.5wt%; P≤0.008wt%; S≤0.005wt%; Nb: 0.06wt%; V: 0.2wt%.

[0016] Furthermore, during the CMT cladding process, pure argon gas with a purity of more than 99.95% is simultaneously input as a shielding gas, and the shielding gas flow rate is 15-20 L / min.

[0017] Furthermore, during the CMT welding, the welding current is 190-200A, the voltage is 14-16V, the welding speed is 20-30cm / min, the wire feeding speed is 6-8m / min, the interlayer temperature is 200°C, and the wire extension length is 4-6mm.

[0018] Furthermore, the normalizing heat treatment temperature is 1060° C. and the holding time is 1 hour.

[0019] Furthermore, the holding temperature during the tempering treatment is lower than 760°C.

[0020] Furthermore, the holding time during the tempering treatment is 2.5 hours, and the cooling method is air cooling.

[0021] The present invention has the following beneficial effects:

[0022] (1) By using CMT welding technology to perform single-layer multi-pass welding on the P91 steel base plate, P91 high-hardness weld specimens were prepared to replace the high-hardness P91 steel welds that actually appear. By normalizing at 1060℃ for 1h and then tempering at different temperatures, the prepared P91 steel high-hardness weld specimens not only meet the actual weld center structure, but also have a hardness greater than the field weld hardness recommended in the standard, meeting the range of high-hardness welds that appear on site, thereby providing specimens for high-hardness P91 steel welds.

[0023] (2) A new method is provided that is simple, fast, and targeted at specific situations to approximately replace the high-hardness P91 steel welds that occur in practice.

[0024] (3) The P91 steel weld samples obtained after CMT welding were normalized at 1060℃ and tempered at different temperatures. The hardness of the prepared P91 steel high-hardness weld samples was greater than the field weld hardness recommended in the standard, meeting the range of high-hardness welds that appeared on site.

[0025] (4) The P91 steel weld samples obtained after CMT welding were subjected to normalizing at 1060℃ and tempering at different temperatures to prepare P91 steel high hardness weld samples. They do not need to be welded and post-weld heat treated according to the actual complex pipeline welding process, and also overcome the unevenness of the P91 weld joint and eliminate the hardness gradient. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 is a flow chart of the present invention;

[0027] Figure 2 The principle diagram of the abnormal hardness weld of P91 steel prepared by the CMT surfacing method supplemented by different normalizing and tempering heat treatment processes is used to approximately replace the abnormal high hardness weld of P91 steel that occurs in practice;

[0028] Figure 3 Figure 1 shows the microstructure of the P91 steel weld sample prepared by the CMT cladding method after normalizing at 1060℃ for 1h. (a) and (b) show the metallographic images of the P91 steel weld sample prepared by the CMT cladding method after normalizing at 1060℃ for 1h at different magnifications. (c) and (d) show their scanning electron images.

[0029] Figure 4 This is a diagram showing the Brinell hardness test results of the high-hardness P91 steel weld samples prepared in Examples 1-3 of the present invention. DETAILED DESCRIPTION

[0030] The following is a combination of the embodiments of the present invention Figure 1-Figure 4 , the technical solutions in the embodiments of the present invention are described clearly and completely. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Unless otherwise specified, the technical means used in the embodiments are conventional means well known to those skilled in the art.

[0031] like Figure 1 The method for preparing a P91 steel abnormal hardness weld specimen based on the CMT method comprises the following steps:

[0032] S1: Select the CMT welding substrate and clean it;

[0033] S2: ER90S-B9 welding wire that matches the composition of P91 steel is selected as the filler metal material;

[0034] S3: CMT is used for cladding on the substrate. The welding gun movement path is reciprocating, and the height of each weld bead is 1-2mm.

[0035] S4: Grind and clean the accumulated surface oxides in step S3, and maintain the interlayer temperature at 180-220°C;

[0036] S5: Repeat steps S3-S4 until the accumulation of weld samples is completed;

[0037] S6: Perform wire cutting on the deposited sample to obtain the sample and then perform normalizing treatment;

[0038] S7: The sample obtained in step S6 is subjected to tempering treatment at different temperatures to prepare a high-hardness weld sample.

[0039] Furthermore, the CMT welding wire is ER90S-B9 welding wire.

[0040] Furthermore, the composition of the ER90S-B9 welding wire includes: C: 0.10wt%; Si: 0.30wt%; Mn: 0.50wt%; Cr: 9.0wt%; Mo: 1.0wt%; Ni: 0.5wt%; P≤0.008wt%; S≤0.005wt%; Nb: 0.06wt%; V: 0.2wt%.

[0041] Furthermore, during the CMT cladding process, pure argon gas with a purity of more than 99.95% is simultaneously input as a shielding gas, and the shielding gas flow rate is 15-20 L / min.

[0042] Furthermore, during the CMT welding, the welding current is 190-200A, the voltage is 14-16V, the welding speed is 20-30cm / min, the wire feeding speed is 6-8m / min, the interlayer temperature is 200°C, and the wire extension length is 4-6mm.

[0043] Furthermore, the normalizing heat treatment temperature is 1060° C. and the holding time is 1 hour.

[0044] Furthermore, the holding temperature during the tempering treatment is lower than 760°C.

[0045] Furthermore, the holding time during the tempering treatment is 2.5 hours, and the cooling method is air cooling.

[0046] P91 steel welds consist of distinct zones that experience varying temperatures during the welding thermal cycle. During the welding thermal cycle, the temperatures experienced by the weld range from the melting temperature (Tm) to slightly above Ac1 (the temperature at which pearlite transforms to austenite). The heat-affected zone (HAZ) of a P91 steel welded joint varies continuously across the lateral direction, making it difficult to distinguish. Furthermore, in actual testing, the highest hardness zone is primarily located in the center of the weld, so the microstructure and properties of this center were considered.

[0047] Because the actual weld joint is not only composed of the welding wire, but also includes the melted base material around the molten pool, the weld fusion zone is a complex area; however, because the pipe wall is very thick and the groove is deep, multi-layer and multi-pass welding is often used, so the actual weld area is very large, and the composition of the weld center can be approximately only the welding wire composition, and the actual high hardness area only appears in the weld center. Therefore, it is reasonable to prepare P91 steel weld specimens using CMT cladding technology.

[0048] CMT weld specimens of P91 steel welds clearly show that the specific characteristics of CMT welds lead to variations in microstructure and properties between layers. Extensive prior art research has demonstrated these differences in properties, both transversely and longitudinally. Although PWHT (post-weld heat treatment) overcomes the heterogeneity of P91 welds, it does not completely eliminate hardness gradients. Normalizing and tempering (N&T) treatments were performed immediately after welding to overcome these microstructural and hardness heterogeneities in P91 welds, and it was observed that N&T treatment was more effective than PWHT. Furthermore, when the welds were normalized and tempered (N&T) treated, the hardness remained nearly identical across various heat input conditions. This is due to the high degree of microstructural homogeneity (similar to that of tempered martensite) achieved under all heat input conditions following normalizing and tempering, due to the recrystallization effect of the normalizing treatment. Based on this, a CMT-based surfacing method supplemented by normalizing and tempering heat treatment at different temperatures was used to prepare P91 steel abnormal hardness weld samples to approximately replace the abnormally high hardness welds of P91 steel that appeared in practice, as shown in the attached figure. Figure 1 The figure shows the principle behind the CMT method for preparing P91 steel weld specimens with exceptional hardness. The microstructure during normal groove welding is similar to that during normalizing after CMT welding. After cooling, the resulting structure is martensitic, which can then be further tempered. According to relevant data, the weld area is designed to achieve optimal mechanical properties by normalizing at 1060°C for 1 hour, followed by immediate air cooling, and then tempering at 760°C for 2.5 hours. After normalizing, the entire microstructure becomes uniform, with a consistent hardness.

[0049] Compared with existing technologies, the present invention's technical contribution lies in providing a simple and rapid method for preparing high-hardness P91 steel weld specimens, specifically for high-hardness welds encountered in the field. This method changes the traditional practice of preparing P91 steel weld specimens based on actual welding procedures, significantly simplifying the preparation process.

[0050] Specific embodiments are given below to illustrate the progress of the present invention:

[0051] Example 1: A method for preparing a P91 steel abnormal hardness weld specimen based on the CMT method, comprising the following steps:

[0052] S1: Select a CMT welding substrate and perform mechanical grinding and cleaning before CMT welding to remove surface oil and oxides.

[0053] S2: ER90S-B9 welding wire, which matches the composition of P91 steel, is selected as the filler metal material. The wire diameter is 1.2 mm to prevent impurities from affecting the arc and thus affecting the welding quality of the first pass. The composition of ER90S-B9 welding wire is shown in Table 2.

[0054] S3: Single-pass multi-layer welding on a P91 steel substrate using CMT welding technology. The shielding gas used during welding was 99.95% pure argon (≥ 15 L / min), with a gas flow rate of 15 L / min, a welding current of 191 A, a voltage of 14 V, a welding speed of 24 cm / min, a wire feed speed of 8 m / min, a wire stickout of 6 mm, and a single weld layer thickness of 1.8 mm. The P91 steel substrate's base plate dimensions were 300 × 50 × 6 mm.

[0055] S4: Grind and clean the oxide on the surface of each layer of the weld in step S3 until the weld reveals metallic luster, and the interlayer temperature is maintained at 200°C.

[0056] The specific grinding and cleaning process in this step includes: using sandpaper to grind the surface of the workpiece, using an angle grinder to grind away defects, removing impurities and oxides on the surface of the workpiece, and then wiping the surface of the workpiece with alcohol or acetone to remove oil stains.

[0057] S5: Repeat steps S3 and S4 to complete the accumulation of weld specimens.

[0058] S6: Normalizing heat treatment: The P91 steel weld sample obtained in step S5 is treated by normalizing process. The normalizing holding temperature is 1060°C, the holding time is 1 hour, and the cooling method is air cooling.

[0059] S7: performing a tempering and holding test on the P91 steel weld sample after normalizing treatment in step S6, with the holding temperature being 650° C. and the holding time being 2.5 h, to prepare a high hardness P91 steel weld sample.

[0060] S8: Grind the sample tempered in step S7 to obtain a P91 steel high hardness weld sample.

[0061] S9: Apply GB / T231.1-2018 "Brinell hardness test part 1: test method" to measure the Brinell hardness of the sample after tempering heat treatment test prepared in step S8. The results are as follows: Figure 4 As shown in Table 1, after testing, the Brinell hardness of the P91 steel high hardness weld sample prepared in this embodiment is 277.4HB.

[0062] Example 2: A method for preparing a P91 steel abnormal hardness weld specimen based on the CMT method, comprising the following steps:

[0063] S1: Select a CMT welding substrate and perform mechanical grinding and cleaning before CMT welding to remove surface oil and oxides.

[0064] S2: ER90S-B9 welding wire that matches the composition of P91 steel is selected as the filler metal material. The wire diameter is 1.2 mm to prevent impurities from affecting the arc and thus affecting the welding quality of the first pass.

[0065] S3: Single-pass multi-layer welding on a P91 steel substrate using CMT welding technology. The shielding gas used during welding was 99.95% pure argon (≥ 99.95%), with a gas flow rate of 20 L / min, a welding current of 200 A, a voltage of 16 V, a welding speed of 20 cm / min, a wire feed speed of 6.1 m / min, a wire stickout of 6 mm, and a single weld layer thickness of 2 mm. The P91 steel substrate's base plate dimensions were 300 × 50 × 6 mm.

[0066] S4: Grind and clean the oxide on the surface of each layer of the weld in step S3 until the weld reveals metallic luster, and the interlayer temperature is maintained at 200°C.

[0067] The specific grinding and cleaning process in this step includes: using sandpaper to grind the surface of the workpiece, using an angle grinder to grind away defects, removing impurities and oxides on the surface of the workpiece, and then wiping the surface of the workpiece with alcohol or acetone to remove oil stains.

[0068] S5: Repeat steps S3 and S4 to complete the accumulation of weld specimens.

[0069] S6: Normalizing heat treatment: The P91 steel weld sample obtained in step S5 is treated by normalizing process. The normalizing holding temperature is 1060°C, the holding time is 1 hour, and the cooling method is air cooling.

[0070] S7: performing a tempering and holding test on the P91 steel weld sample after normalizing treatment in step S6, with the holding temperature being 580° C. and the holding time being 2.5 h, to prepare a high hardness P91 steel weld sample.

[0071] S8: Grind the sample tempered in step S7 to obtain a P91 steel high hardness weld sample.

[0072] S9: Apply GB / T231.1-2018 "Brinell hardness test part 1: test method" to measure the Brinell hardness of the sample after tempering heat treatment test prepared in step S8. The results are as follows: Figure 4 As shown in Table 1, after testing, the Brinell hardness of the P91 steel high hardness weld sample prepared in this embodiment is 322HB.

[0073] Example 3: A method for preparing a P91 steel abnormal hardness weld specimen based on the CMT method, comprising the following steps:

[0074] S1: Select a CMT welding substrate and perform mechanical grinding and cleaning before CMT welding to remove surface oil and oxides.

[0075] S2: ER90S-B9 welding wire that matches the composition of P91 steel is selected as the filler metal material. The wire diameter is 1.2 mm to prevent impurities from affecting the arc and thus affecting the welding quality of the first pass.

[0076] S3: Single-pass multi-layer welding on a P91 steel substrate using CMT welding technology. The shielding gas used was 99.95% or higher pure argon at a flow rate of 17 L / min, a welding current of 195 A, a voltage of 14 V, a welding speed of 30 cm / min, a wire feed speed of 7.6 m / min, a wire stickout of 4 mm, and a single weld layer thickness of 1.5 mm. The P91 steel substrate's base plate dimensions were 300 × 50 × 6 mm.

[0077] S4: Grind and clean the oxide on the surface of each layer of the weld in step S3 until the weld reveals metallic luster, and the interlayer temperature is maintained at 200°C.

[0078] The specific grinding and cleaning process in this step includes: using sandpaper to grind the surface of the workpiece, using an angle grinder to grind away defects, removing impurities and oxides on the surface of the workpiece, and then wiping the surface of the workpiece with alcohol or acetone to remove oil stains.

[0079] S5: Repeat steps S3 and S4 to complete the accumulation of weld specimens.

[0080] S6: Normalizing heat treatment: The P91 steel weld sample obtained in step S5 is treated by normalizing process. The normalizing holding temperature is 1060°C, the holding time is 1 hour, and the cooling method is air cooling.

[0081] S7: performing a tempering and holding test on the P91 steel weld sample after normalizing treatment in step S6, with the holding temperature being 560° C. and the holding time being 2.5 h, to prepare a high hardness P91 steel weld sample.

[0082] S8: Grind the sample tempered in step S7 to obtain a P91 steel high hardness weld sample.

[0083] S9: Apply GB / T231.1-2018 "Brinell hardness test part 1: test method" to measure the Brinell hardness of the sample after tempering heat treatment test prepared in step S8. The results are as follows: Figure 4 As shown in Table 1, after testing, the Brinell hardness of the P91 steel high hardness weld sample prepared in this embodiment is 348.2HB.

[0084] The present invention ensures appropriate welding speed, interlayer temperature, wire feeding speed and heat treatment temperature by rationally optimizing various parameters during the welding process, and adopts a reasonable welding process to achieve optimally matched weld sample preparation, thereby providing a guarantee for the preparation of high-hardness P91 steel weld samples.

[0085] like Figure 3 Figures 2 and 3 show the microstructure of a P91 steel weld specimen prepared using the CMT cladding method described in the above example after normalizing at 1060°C for 1 hour. Figures (a) and (b) are metallographic microstructure images, while Figures (c) and (d) are scanning electron microscope images at higher magnifications. Under normalizing conditions, precipitates are negligible, resulting in a homogenized structure. As shown in the SEM images, the structure is typical of untempered lath martensite, with distinct prior austenite grain boundaries and martensite laths oriented in unidirectional bundles or groups within the prior austenite grains. This is consistent with the weld microstructure obtained in actual welding.

[0086] Figure 4 The Brinell hardness values ​​obtained at different tempering temperatures after normalizing are shown. For a given normalizing temperature, the hardness of the specimen increases with decreasing tempering temperature. Furthermore, the Brinell results obtained with the N&T treatment demonstrate the formation of a completely homogeneous microstructure and the elimination of the heat-affected zone. After N&T, the hardness variation remains stable at a certain tempering temperature. Furthermore, from a mechanistic perspective, as the tempering temperature decreases, the amount of precipitated phase decreases, allowing a larger number of solute atoms to dissolve in the martensite, increasing solid solution strengthening and leading to an increase in hardness.

[0087] Table 1 shows the Brinell hardness results of high hardness P91 steel weld samples in Examples 1-3

[0088]

[0089] In summary, according to the results of Examples 1-3, it can be seen that the present invention adopts CMT welding technology to perform single-layer multi-pass welding on a P91 steel base plate to prepare a P91 high-hardness weld sample to replace the high-hardness P91 steel weld that actually occurs. By normalizing at 1060°C for 1h and tempering at different temperatures, the prepared P91 steel high-hardness weld sample structure not only meets the actual weld center structure, but also has a hardness greater than the on-site weld hardness recommended in the standard, meeting the range of high-hardness welds that occur on site, thereby providing a sample for high-hardness P91 steel welds.

[0090] Table 2 ER90S-B9 welding wire composition (wt%)

[0091]

[0092] The embodiments described above are merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the spirit of the present invention, various deformations, modifications, and substitutions made to the technical solutions of the present invention by ordinary technicians in this field should fall within the scope of protection determined by the claims of the present invention.

Claims

1. A method for preparing abnormal hardness weld specimens of P91 steel based on the CMT method, characterized in that: The following steps are involved: S1: Select the substrate and clean it; S2: ER90S-B9 welding wire that matches the composition of P91 steel is selected as the filler metal material; S3: CMT is used for cladding on the substrate. The welding gun movement path is reciprocating, and the height of each weld bead is 1-2mm. S4: Grind and clean the accumulated surface oxides in step S3, with the interlayer temperature maintained at 180-220°C; S5: Repeat steps S3-S4 until the accumulation of weld samples is completed; S6: Perform wire cutting on the deposited sample to obtain the sample and then perform normalizing treatment; S7: The sample obtained in step S6 is subjected to tempering treatment at different temperatures to prepare a high-hardness weld sample.

2. The method for preparing P91 steel abnormal hardness weld specimens based on the CMT method according to claim 1, characterized in that: The CMT welding wire is ER90S-B9 welding wire.

3. The method for preparing P91 steel abnormal hardness weld specimens based on the CMT method according to claim 2, characterized in that: The composition of ER90S-B9 welding wire includes: C: 0.10wt%; Si: 0.30wt%; Mn: 0.50wt%; Cr: 9.0wt%; Mo: 1.0wt%; Ni: 0.5wt%; P≤0.008wt%; S≤0.005wt%; Nb: 0.06wt%; V: 0.2wt%.

4. The method for preparing a P91 steel abnormal hardness weld specimen based on the CMT method according to claim 1 or 2, characterized in that: During the CMT cladding process, pure argon gas with a purity of more than 99.95% is simultaneously input as a shielding gas, and the shielding gas flow rate is 15-20 L / min.

5. The method for preparing a P91 steel abnormal hardness weld specimen based on the CMT method according to claim 1 or 2, characterized in that: During the CMT welding, the welding current is 190-200A, the voltage is 14-16V, the welding speed is 20-30cm / min, the wire feeding speed is 6-8m / min, the interlayer temperature is 200°C, and the wire dry extension is 4-6mm.

6. The method for preparing P91 steel abnormal hardness weld specimens based on the CMT method according to claim 1 or 2, characterized in that: The normalizing heat treatment temperature is 1060° C. and the holding time is 1 hour.

7. The method for preparing P91 steel abnormal hardness weld specimens based on the CMT method according to claim 1 or 2, characterized in that: The holding temperature during the tempering treatment is lower than 760°C.

8. The method for preparing P91 steel abnormal hardness weld specimens based on the CMT method according to claim 1 or 2, characterized in that: The holding time during the tempering treatment is 2.5 hours, and the cooling method is air cooling.

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