A method for determining characteristic thermal cycle curve of F / M heat-resistant steel welding heat-affected zone resistant to liquid lead (lead bismuth) corrosion

Abstract

The application discloses a kind of F / M heat-resistant steel welding heat-affected zone characteristic thermal cycle curve determination methods of liquid lead (lead bismuth) corrosion resistance, belong to the technical field of metal material weldability research.In order to obtain characteristic thermal cycle curve, main steps include: (1) carry out steel plate autogenous welding, test temperature field;(2) corrosion weld section organization, obtain weld section morphology;(3) simulate autogenous welding heat process, compare measured weld section morphology and thermal cycle curve, if it is good, then determine welding temperature field;(4) according to weld section organization features and temperature field, determine coarse grain zone, fine grain zone and incomplete crystallization zone characteristic thermal cycle curve;(5) utilize thermal force simulation machine to prepare heat-affected zone each micro area sample, observe organization, verify characteristic thermal cycle curve accuracy.The application will be combined with weld section organization features and computer numerical simulation technology, can be easily, accurately determine heat-resistant steel welding heat-affected zone characteristic thermal cycle curve.

Description

Technical Field

[0001] This invention relates to the field of weldability research technology for metallic materials, and specifically to a method for obtaining characteristic thermal cycle curves of the heat-affected zone of F / M heat-resistant steel resistant to liquid lead (lead bismuth) corrosion. Background Technology

[0002] With increasingly strained global energy supplies and growing concern about global warming and sustainable development, nuclear energy will undoubtedly play a crucial role in the future development of the world. Due to the excellent neutronic properties, thermal conductivity, and radiation damage resistance of lead (lead-bismuth) alloys, lead (lead-bismuth) fast reactors are considered one of the fourth-generation reactor types for future development and represent a major direction for the future development of my country's nuclear power industry. F / M heat-resistant steel is an important candidate key structural material, but its resistance to lead (lead-bismuth) corrosion is poor. Adding an appropriate amount of Si can improve its resistance to lead (lead-bismuth) corrosion (Invention title: A ferritic / martensitic heat-resistant steel resistant to liquid lead (lead-bismuth) corrosion and its preparation method; Patent No.: ZL202110724436.5). However, excessive Si content can cause embrittlement of the weld heat-affected zone, thereby deteriorating its impact resistance. To further determine the appropriate Si content, it is necessary to first determine the characteristic thermal cycling curves of each micro-region within the heat-affected zone (HAZ). This allows for the preparation of samples for each micro-region, and subsequently, the evaluation of the impact performance of each micro-region under different Si contents. The HAZ is very narrow (1.5–3 mm), making it difficult to divide it into different micro-regions and experimentally measure the thermal cycling curves. Therefore, finding a simple method to accurately determine the characteristic thermal cycling curves of each micro-region is a pressing issue that needs to be addressed to further determine the chemical composition of the developed F / M heat-resistant steel. Summary of the Invention

[0003] To facilitate and accurately obtain characteristic thermal cycle curves of the heat-affected zone in welding, this invention provides a method for obtaining characteristic thermal cycle curves of the heat-affected zone in F / M heat-resistant steel resistant to liquid lead (lead bismuth) corrosion.

[0004] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0005] (1) The surface of the heat-resistant steel plate was treated with acetone and alcohol to remove oil stains. The calibrated K-type thermocouples were spot welded onto the steel plate using a spot welding machine. Self-fusion welding was performed using a certain welding process, and the welding thermal cycle curves at the spot welding positions were recorded.

[0006] (2) After welding, the weld section was etched with Wöhler's reagent to obtain the weld section morphology.

[0007] (3) Establish a finite element model for self-fusion welding of steel plates. Combine the weld width and depth measured in step (2) to initially set the relevant parameters in the welding heat source model. Simulate the self-fusion welding process and compare it with the weld cross-sectional morphology and thermal cycle curve measured in step (2). If the match is not good, correct the parameters in the heat source model until the match is good. Then complete the simulation of the self-fusion welding thermal process and determine the temperature field.

[0008] (4) Observe the microstructure of the weld section in step (2) to determine the microstructure characteristics; combine the temperature field obtained in step (3) to extract the characteristic thermal cycle curves of each micro-region of the weld heat-affected zone;

[0009] (5) Samples of each micro-area of ​​the weld heat-affected zone were prepared using a thermal simulator, and the microstructure was observed to verify the accuracy of the characteristic thermal cycle curves; thus, the determination of the characteristic thermal cycle curves of the weld heat-affected zone was completed.

[0010] In step (1), the welding process is TIG welding, the welding current is 100-250A, the voltage is 10-20V, and the welding speed is 60-180mm / min.

[0011] In step (1), the thermocouple spot welding position is on the outside of the weld and within 1 to 10 mm from the edge of the weld.

[0012] In step (4), the peak temperature of the characteristic thermal cycle curve of the coarse-grained region is between 1200℃ and 1350℃, the peak temperature of the characteristic thermal cycle curve of the fine-grained region is between 1000℃ and 1200℃, and the peak temperature of the characteristic thermal cycle curve of the incomplete recrystallization region is between 900℃ and 1000℃.

[0013] The beneficial effects of this invention are as follows: This invention provides a method for determining the characteristic thermal cycle curve of the weld heat-affected zone (HAZ) of F / M heat-resistant steel resistant to liquid lead (lead-bismuth) corrosion. Because the HAZ of this material is small (1.5–3 mm), it is difficult to measure the HAZ using thermocouples or other tools. Furthermore, empirical models are significantly affected by the welding process. The method described in this invention, combining microstructure characteristics and temperature field, can conveniently and accurately obtain the characteristic HAZ curve, providing direct technical support for further determining the chemical composition of the developed F / M heat-resistant steel. Attached Figure Description

[0014] Figure 1 The cross-sectional morphology of the TIG self-fusion weld of high Si-9Cr heat-resistant steel in this embodiment of the invention is shown.

[0015] Figure 2 This is a 3D finite element mesh model of steel plate self-fusion welding established in an embodiment of the present invention.

[0016] Figure 3This invention presents a comparison of simulated and measured cross-sectional morphology of the TIG self-fusion weld seam in high-Si-9Cr heat-resistant steel in an embodiment of the present invention; wherein: (a) measured; (b) simulated.

[0017] Figure 4 This is a comparison between the simulated and measured thermal cycle curves of high Si-9Cr heat-resistant steel TIG self-fusion welding in the embodiments of the present invention.

[0018] Figure 5 The microstructure of the TIG self-fusion weld section of high Si-9Cr heat-resistant steel in this embodiment of the invention is shown.

[0019] Figure 6 This invention relates to the determination of the characteristic thermal cycle curves of the heat-affected zone of high Si-9Cr heat-resistant steel welded in this embodiment of the invention; wherein: (a) coarse-grained zone; (b) fine-grained zone; (c) incomplete recrystallization zone.

[0020] Figure 7 The microstructure of each micro-region sample was prepared using a Gleeble thermal simulator for high Si-9Cr heat-resistant steel in this embodiment of the invention; wherein: (a) coarse-grained region; (b) fine-grained region; (c) incomplete recrystallization region. Detailed Implementation

[0021] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0022] Example 1:

[0023] This invention provides a method for determining the characteristic thermal cycle curve of the heat-affected zone (HAZ) of F / M heat-resistant steel resistant to liquid lead (lead-bismuth) corrosion. This embodiment uses the acquisition of the characteristic HAZ of high-Si-9Cr heat-resistant steel as an example to illustrate and verify the beneficial effects of this invention. The chemical composition (wt.%) of the high-Si-9Cr heat-resistant steel is: C 0.08–0.13%, Si 0.70–1.50%, Ni 0.70–1.40%, Cr 7.0–10.0%, Mo 0.50–1.0%, Mn 0.45–0.95%, V 0.10–0.35%, Nb 0.10–0.35%, Fe balance.

[0024] The specific process of obtaining the characteristic thermal cycle curve of the heat-affected zone in this embodiment is as follows:

[0025] Step 1: Process high-Si-9Cr heat-resistant steel plates, with test plate dimensions of 120mm × 90mm × 5mm. Before welding, clean the steel plate surface with acetone and alcohol. The thermocouple spot welding positions are located on the outer side of the weld seam, within 1–10mm of the weld edge. Use a spot welding machine to spot weld the calibrated K-type thermocouples to the determined spot welding positions. Perform autogenous fusion welding (TIG welding) on ​​the steel plate using a Panasonic TA1600TIG welding robot. The welding process parameters are: current 140A, voltage 14V, and welding speed 140mm / min. Test the welding thermal cycle curve at the spot welding position.

[0026] Step 2: After welding, a cross-section of the weld seam was cut using wire cutting. After grinding and polishing, it was etched using Wöhler's reagent (50ml HCl + 1g picric acid + 100ml alcohol). The weld cross-sectional morphology was obtained using a stereomicroscope. Figure 1 ).

[0027] Step 3: Establish a 3D finite element mesh model for flat plate self-fusion welding, prioritizing the meshing of the weld seam and its surrounding area. See the finite element mesh model below. Figure 2 The number of cells is 48,588 and the number of nodes is 40,565.

[0028] The welding heat source model is fitted using a double ellipsoidal heat source model, as shown in formulas (1)-(3):

[0029]

[0030]

[0031] q V1 =q f +q r (3);

[0032] In formulas (1) to (3): Q V For the energy possessed by the double ellipsoidal heat source, a f a r b and c are the shape parameters of the double ellipsoidal heat source; q f and q r These represent the heat flux density distributions within the front and rear hemispheres, respectively; q V The heat flux density distribution of a double ellipsoidal heat source;

[0033] The parameters of the simulated double ellipsoidal heat source model are shown in Table 1 below:

[0034] Table 1

[0035]

[0036] The workpiece surface was designed to transfer heat via conduction between the workpiece and the workbench, with thermal convection and radiation as the thermal boundary conditions for other surfaces. The SYSWELD software was used to solve for the welding thermal process, obtaining the transient welding temperature field distribution. The simulated welding thermal cycle curves and weld cross-sectional morphology were compared with the measured results, as shown below. Figure 3 and Figure 4 The comparison shows that the weld cross-sectional morphology and welding temperature field simulated using the established heat source model are in good agreement with the test results.

[0037] Step 5: Observe the microstructure of the weld cross-section using an optical microscope. The coarse-grained zone is characterized by the presence of large δ-ferrite, the fine-grained zone by fine quenched martensite, and the incomplete recrystallization zone by tempered martensite. Figure 5 Based on the above-mentioned organizational characteristics, thermal cycle curves are extracted from corresponding locations in the temperature field to obtain the characteristic thermal cycle curves of the micro-region, such as... Figure 6 As a verification, the peak temperature of the characteristic thermal cycle curve of the coarse-grained region should be between 1200℃ and 1350℃, the peak temperature of the characteristic thermal cycle curve of the fine-grained region should be between 1000℃ and 1200℃, and the peak temperature of the characteristic thermal cycle curve of the incomplete recrystallization region should be between 900℃ and 1000℃.

[0038] Step 6: Prepare thermal cycling samples of the above three microregions using a Gleeble thermal simulator, and then observe the microstructure. Figure 7 The characteristic thermal cycle curves extracted are compared with the weld cross-sectional microstructure characteristics in step 5 to verify their accuracy.

Claims

1. A method for determining the characteristic thermal cycle curve of the weld heat-affected zone of F / M heat-resistant steel resistant to liquid lead or lead bismuth corrosion, the chemical composition of the F / M heat-resistant steel being, in mass percentage: C 0.08-0.13%, Si 0.70-1.50%, Ni 0.70-1.40%, Cr 7.0-10.0%, Mo 0.50-1.0%, Mn 0.45-0.95%, V 0.10-0.35%, Nb 0.10-0.35%, Fe balance; characterized in that: The method comprises the following steps: (1) The surface of the processed heat-resistant steel plate is treated with acetone and alcohol to remove oil stains; the calibrated K-type thermocouple is spot-welded on the steel plate by using a spot-welding machine, self-melting welding is carried out by using a certain welding process, and the welding thermal cycle curve of the spot-welding position is recorded; the welding process is a TIG welding method, the welding current is 100-200 A, the voltage is 10-20 V, and the welding speed is 60-180 mm / min; (2) After the welding is completed, the weld cross section is etched with a Vile reagent to obtain the weld cross section morphology; (3) A finite element model of the self-melting welding of the steel plate is established, the related parameters in the welding heat source model are preliminarily set in combination with the measured weld width and depth in step (2); the self-melting welding process is simulated, and the measured weld cross section morphology and thermal cycle curve in step (2) are compared; if the comparison is not good, the parameters in the heat source model are corrected until the comparison is good, then the self-melting welding thermal process simulation is completed, and the temperature field is determined; (4) The microstructure of the weld cross section in step (2) is observed to determine the microstructure characteristics; in combination with the temperature field obtained in step (3), the characteristic thermal cycle curves of each microzone in the welding heat-affected zone are extracted; the microstructure characteristics of the coarse-grained zone are large blocky δ-ferrite, the peak temperature of the characteristic thermal cycle curve is between 1200 DEG C and 1350 DEG C, the microstructure characteristics of the fine-grained zone are fine quenched martensite, the peak temperature of the characteristic thermal cycle curve is between 1000 DEG C and 1200 DEG C, and the microstructure characteristics of the incomplete recrystallization zone are tempered martensite, and the peak temperature of the characteristic thermal cycle curve is between 900 DEG C and 1000 DEG C; (5) The welding heat-affected zone microzone samples are prepared by using a thermal power simulator, the microstructure is observed, and the accuracy of the characteristic thermal cycle curve is verified; thus, the determination of the characteristic thermal cycle curve of the welding heat-affected zone is completed.

2. The method of claim 1, wherein the F / M heat-resistant steel weld heat-affected zone characteristic thermal cycle curve determination method against liquid lead or lead bismuth corrosion is characterized by: In step (1), the thermocouple spot-welding position is outside the weld and within 1-10 mm from the edge of the weld.

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