A method for determining the homogenization heat treatment process of GH2909 alloy

Abstract

The present invention relates to a method for determining a homogenization heat treatment process of a GH2909 alloy, comprising the steps of: characterizing the Laves phase transition point temperature in the alloy, and setting the temperature as Tc. Calculating the critical time t0 for the alloy to completely dissolve the Laves phase at a temperature T0; selecting a small range of dendrite structures, testing and counting the Nb element content, calculating the Nb element segregation coefficient and counting the Laves phase content; placing the cast alloy in a heat treatment furnace, heating it to a temperature T0, holding it for a time of t1, cooling it to room temperature and counting the Laves phase content in a non-overburned sample; fitting the Laves phase content changes under different processes, and determining the homogenization time for the Laves phase to completely melt back; placing the alloy with the Laves phase completely melted back in a heat treatment furnace, heating it and holding it for a time of t2, cooling it to room temperature and measuring the Nb element content, calculating the residual segregation coefficient δ, and if δ>0.2, extending the time t2 until δ<0.2. The present invention can effectively promote the melting back of the precipitated phase, eliminate component segregation, and obtain a more uniform structure.

Description

Technical Field

[0001] The present invention relates to the technical field of high temperature alloys, and more particularly to a method for determining a homogenization heat treatment process for a GH2909 alloy. Background Art

[0002] GH2909 is a Fe-Ni-Co based low expansion deformation high temperature alloy with good strength, plasticity, low expansion coefficient, stable elastic modulus, high stability and wide application. Due to the serious component segregation of Nb element during the solidification process of GH2909, a Nb-rich blocky Laves phase is produced. Laves phase is a low melting point phase that is easy to melt at a higher temperature, which is not conducive to further processing of the alloy. Therefore, it is necessary to use homogenization annealing to make the Laves phase melt back and the segregated elements diffuse to a uniform state, ultimately improving the alloy performance.

[0003] Therefore, it is desirable to find a method to determine the homogenization heat treatment process of GH2909 alloy. Summary of the invention

[0004] In view of the deficiencies in the prior art, the present invention provides a method for determining a homogenization heat treatment process for a GH2909 alloy.

[0005] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0006] According to aspects of the present invention, there is provided a method for determining a homogenization heat treatment process for a GH2909 alloy, comprising the following steps:

[0007] 1) The Laves phase transition point temperature in GH2909 alloy was characterized by DSC, and the lowest precipitation temperature of Laves phase was determined as Tc;

[0008] 2) Use JMatPro software to calculate the critical time t0 for the complete dissolution of the Laves phase of GH2909 alloy at temperature T0, where temperature T0 = Tc-ΔT;

[0009] 3) Use SEM and EDS to characterize the microstructure of the central position of GH2909, select a small range of dendrite structure somewhere in the center of the ingot, randomly select multiple test points, count the Nb element content, calculate the Nb element segregation coefficient of the as-cast structure of the GH2909 alloy, and use Image-Pro Plus software to count the Laves phase content of the as-cast structure;

[0010] 4) placing the as-cast GH2909 alloy in a heat treatment furnace, heating it to a temperature T0, and keeping it at that temperature for a duration of t1, and then rapidly cooling it to room temperature, observing the microstructure of the obtained sample, and counting the Laves phase content in the non-overburned sample;

[0011] 5) fitting the changes in the Laves phase content under different homogenization processes through mathematical calculation to determine the homogenization time required for the Laves phase to be completely melted back, wherein the residual Laves phase content less than 20% is defined as the complete melting back of the Laves phase;

[0012] 6) The GH2909 alloy with all the Laves phase melted back is placed in a heat treatment furnace, heated and kept warm for a duration of t2, then quickly cooled to room temperature, the microstructure of the sample is observed, the Nb element content in the GH2909 alloy is measured by EDS, and the residual segregation coefficient of GH2909 is calculated. If the residual segregation coefficient is >0.2, the duration t2 is extended until the residual segregation coefficient is <0.2.

[0013] In one embodiment of the present invention, in step 2), the value range of ΔT is 20-100°C.

[0014] In one embodiment of the present invention, in step 3), the plurality of test points are at least ten test points.

[0015] In one embodiment of the present invention, in step 3), the Nb element segregation coefficient of the as-cast structure of the GH2909 alloy is calculated according to the formula: element segregation coefficient K=average concentration of solute elements between dendrites / average concentration of solute elements in the dendrites.

[0016] In one embodiment of the present invention, in step 3), the Laves phase content of the microstructure of the central part of ten GH2909 images is counted by Image-Pro Plus, and the average value is taken to obtain the Laves phase content value of GH2909.

[0017] In one embodiment of the present invention, in step 4), t1 is 10h higher than t0.

[0018] In one embodiment of the present invention, in step 5), the variation of the Laves phase content under different homogenization processes is fitted by mathematical calculation to t=Aexp(-B*T), where A and B are constants, T is the homogenization temperature, and t is the homogenization time required for all the Laves phases to melt back.

[0019] In one embodiment of the present invention, in step 6), the temperature is increased by 30-60°C, and 0h≤t2≤6h.

[0020] In one embodiment of the present invention, in step 6), the residual segregation coefficient δ=the solute element concentration difference after homogenization Cmax-Cmin / the solute element concentration difference in the cast structure Comax-Comin.

[0021] In one embodiment of the present invention, in step 4) and step 6), rapid cooling to room temperature is performed by water cooling.

[0022] By adopting the above technical solution, the present invention has the following advantages compared with the prior art:

[0023] The present invention can effectively promote the melting back of the precipitated phase, eliminate component segregation, and obtain a more uniform structure. Moreover, the present invention can shorten the research and development cycle and reduce the research and development cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 A schematic flow chart of a method for determining a homogenization heat treatment process for a GH2909 alloy provided by the present invention is shown. DETAILED DESCRIPTION

[0025] It should be understood that the embodiments of the present invention shown in the exemplary embodiments are only illustrative. Although only a few embodiments are described in detail in the present invention, it is easy for those skilled in the art to appreciate that multiple modifications are feasible without actually departing from the teaching of the subject matter of the present invention. Accordingly, all such modifications should be included within the scope of the present invention. Without departing from the gist of the present invention, other replacements, modifications, changes and deletions may be made to the design, operating conditions and parameters of the following exemplary embodiments.

[0026] like Figure 1 As shown, the present invention provides a method for determining the homogenization heat treatment process of GH2909 alloy, comprising the following steps:

[0027] S101: Characterize the Laves phase transition point temperature in GH2909 alloy by DSC, and define the lowest precipitation temperature of Laves phase as Tc;

[0028] S102: using JMatPro software to calculate the critical time t0 for the complete dissolution of the Laves phase of the GH2909 alloy at temperature T0, where temperature T0 = Tc-ΔT;

[0029] S103: Use SEM and EDS to characterize the microstructure at the center of GH2909, select a small range of dendrite structure at the center of the ingot, randomly select multiple test points, count the Nb element content, calculate the Nb element segregation coefficient of the as-cast structure of the GH2909 alloy, and use Image-Pro Plus software to count the Laves phase content of the as-cast structure;

[0030] S104: placing the as-cast GH2909 alloy in a heat treatment furnace, heating it to a temperature T0, and keeping it at that temperature for a duration of t1, and then rapidly cooling it to room temperature, observing the microstructure of the obtained sample, and counting the Laves phase content in the non-overburned sample;

[0031] S105: fitting the changes in the Laves phase content under different homogenization processes through mathematical calculation to determine the homogenization time required for the Laves phase to be completely melted back, wherein the residual Laves phase content less than 20% is defined as the complete melting back of the Laves phase;

[0032] S106: The GH2909 alloy in which the Laves phase is completely melted back is placed in a heat treatment furnace, the temperature is raised and kept at the temperature for a duration of t2, and then rapidly cooled to room temperature, the microstructure of the sample is observed, the Nb element content in the GH2909 alloy is measured by EDS, and the residual segregation coefficient of GH2909 is calculated. If the residual segregation coefficient is >0.2, the duration t2 is extended until the residual segregation coefficient is <0.2.

[0033] Through the present invention, the present invention can effectively promote the melting back of the precipitated phase, eliminate component segregation, and obtain a more uniform structure.

[0034] In the above method, in step S102, the value range of ΔT is 20-100°C.

[0035] In the above method, in step S103, the plurality of test points are at least ten test points.

[0036] In the above method, in step S103, the Nb element segregation coefficient of the as-cast structure of the GH2909 alloy is calculated according to the formula: element segregation coefficient K=average concentration of solute elements between dendrites / average concentration of solute elements in the dendrites.

[0037] In the above method, in step S103, the Laves phase content of the microstructure of the central part of ten GH2909 images is counted by Image-Pro Plus, and the average value is taken to obtain the Laves phase content value of GH2909.

[0038] In the above method, in step S104, t1 is higher than t0 by 10h.

[0039] In the above method, in step S105, the change in Laves phase content under different homogenization processes is fitted by mathematical calculation to t=Aexp(-B*T), where A and B are constants, T is the homogenization temperature, and t is the homogenization time required to melt all the Laves phases back.

[0040] In the above method, in step S106, the temperature is raised by 30-60°C, and 0h≤t2≤6h.

[0041] In the above method, in step S106, the residual segregation coefficient δ=the solute element concentration difference after homogenization Cmax-Cmin / the solute element concentration difference in the cast structure Comax-Comin.

[0042] In the above method, in step S104 and step S106, the solution is rapidly cooled to room temperature by water cooling.

[0043] The above technical solution of the present invention is described in detail below through specific embodiments.

[0044] The invention provides a method for determining a homogenization heat treatment process of a GH2909 alloy, which can more effectively promote the melting back of precipitated phases, eliminate component segregation, and obtain a more uniform structure.

[0045] The present invention provides a method for determining a homogenization heat treatment process of a GH2909 alloy, comprising the following steps:

[0046] (1) The Laves phase transition temperature in GH2909 alloy was characterized by DSC, and the lowest precipitation temperature of the Laves phase was determined as Tc.

[0047] (2) JMatPro software was used to calculate the critical time t0 for the complete dissolution of the Laves phase of GH2909 alloy at temperature T0. The temperature T0 was ΔT lower than Tc, and the ΔT value range was 20-100℃.

[0048] (3) Use SEM to photograph the microstructure of the center of the cast GH2909, and use Image-Pro Plus software to count the Laves phase content of the cast structure. Use EDS to select a small range of dendrite structure at the center of the ingot, randomly select ten test points, and count the Nb element content. According to the formula, element segregation coefficient K = average concentration of solute elements between dendrites / average concentration of solute elements in the dendrite dry, calculate the Nb element segregation of the cast structure of the GH2909 alloy.

[0049] (4) The as-cast GH2909 alloy was placed in a heat treatment furnace, heated to temperature T0, and kept at temperature 0-t1, where t1 was 10 hours higher than t0, and then rapidly cooled to room temperature. The microstructure of the obtained sample was observed, and the Laves phase content in the non-overheated sample was counted.

[0050] (5) Fitting the mathematical formula of the change of Laves phase content under different homogenization processes. The residual Laves phase content is less than 20%, which is defined as the complete dissolution of the Laves phase.

[0051] (6) Based on the process of completely melting back the Laves phase, the temperature is raised by 30-60°C and kept for t2 h (0h≤t2≤6h), then quickly cooled to room temperature, and the sample microstructure is observed for overburning, and the Nb content in the GH2909 alloy is measured by EDS. According to the formula, the residual segregation coefficient δ = the solute element concentration difference after homogenization Cmax-Cmin / the solute element concentration difference in the cast structure Comax-Comin, the residual segregation coefficient of GH2909 is calculated. If δ>0.2, the previous step t2 is extended by 6h and defined as the new t2, until δ<0.2.

[0052] Example

[0053] A method for determining the homogenization heat treatment process of GH2909 alloy, the specific steps are as follows:

[0054] (1) The Laves phase transition temperature of GH2909 was measured by DSC to be 1180°C, and 1180°C was defined as Tc.

[0055] (2) Taking ΔT = 60, 80°C, T0 = Tc-ΔT = 1120, 1100°C, and using JmatPro software to calculate the critical time t0 for the complete melting of the Laves phase of GH2909 alloy at 1120 and 1100°C, it is 10h and 20h respectively.

[0056] (3) Use SEM and EDS to characterize the microstructure of the center of GH2909, select a small range of dendrite structure at the center of the ingot, randomly select ten test points, and count the Nb element content of each test point. According to the formula, element segregation coefficient K = average concentration of solute elements between dendrites / average concentration of solute elements in the dendrite, the Nb element segregation coefficient of the cast structure of GH2909 alloy is calculated to be 2.18. Use Image-Pro Plus to count the Laves phase content of the microstructure of the central part of ten GH2909, and take the average value of 2.196% as the Laves phase content value of GH2909.

[0057] (4) A batch of as-cast GH2909 alloy was placed in a heat treatment furnace, heated to 1100°C, kept warm for 30 hours, and a sample was taken every 2 hours. A batch of as-cast GH2909 alloy was placed in a heat treatment furnace, heated to 1120°C, kept warm for 20 hours, and a sample was taken every 2 hours. The microstructure of the obtained samples was observed, and no overburning was found. The Laves phase content after homogenization at different temperatures and times was counted.

[0058] (5) Through mathematical calculation, it is fitted as t = Aexp(-B*T), where A and B are constants, T is the homogenization temperature, and t is the homogenization time required to completely melt the Laves phase. It is calculated that the GH2909 alloy needs to be homogenized at 1120°C for 20.56 hours to completely melt the Laves phase; homogenization at 1130°C only requires 14.61 hours. Therefore, the first stage homogenization time at different homogenization temperatures can be predicted for the GH2909 alloy.

[0059] (6) After the first stage homogenization at 1120°C, the GH2909 alloy with all the Laves phase melted back is placed in a heat treatment furnace, the temperature is increased by 40°C to 1160°C, and kept at this temperature for 6 hours, and then quickly cooled to room temperature by water cooling. The microstructure of the obtained sample is observed, and the residual segregation coefficient δ is tested and calculated. If the residual segregation coefficient δ>0.2, t2 in the previous step is extended by 6 hours. When t2 is extended to 36 hours, the microstructure of the obtained sample is observed, the residual segregation coefficient δ<0.2, and there are no holes left by overburning. t2=36 hours is determined as the second stage homogenization time of the GH2909 alloy.

[0060] The above description is only a preferred embodiment of the present invention and is not intended to limit the scope of implementation of the present invention. If the present invention is modified or replaced by equivalents without departing from the spirit and scope of the present invention, it should be included in the protection scope of the claims of the present invention.

Claims

1. A method for determining the homogenization heat treatment process of GH2909 alloy, characterized in that: The following steps are involved: 1) The Laves phase transition point temperature in GH2909 alloy was characterized by DSC, and the lowest precipitation temperature of Laves phase was determined as Tc; 2) Use JMatPro software to calculate the critical time t0 for the complete dissolution of the Laves phase of GH2909 alloy at temperature T0, where temperature T0 = Tc-ΔT; 3) Use SEM and EDS to characterize the microstructure of the central position of GH2909, select a small range of dendrite structure at the center of the ingot, randomly select multiple test points, count the Nb element content, calculate the Nb element segregation coefficient of the as-cast structure of GH2909 alloy, and use Image-Pro Plus software to count the Laves phase content of the as-cast structure; 4) The as-cast GH2909 alloy was placed in a heat treatment furnace, heated to temperature T0, and kept at temperature for t1, where t1 was 10 hours higher than t0, and then rapidly cooled to room temperature. The microstructure of the obtained sample was observed, and the Laves phase content in the non-overburned sample was counted. 5) The change of Laves phase content under different homogenization processes in step 4) is fitted by mathematical calculation as t=Aexp(-B*T), where A and B are constants, T is the homogenization temperature, and t is the homogenization time required for all Laves phases to melt back. The residual Laves phase content less than 20% is defined as the complete melting back of the Laves phase. The first stage homogenization time at different homogenization temperatures is predicted for the GH2909 alloy according to the above fitting formula; 6) The GH2909 alloy in which the Laves phase is completely melted back is placed in a heat treatment furnace, and the temperature is raised by 30-60°C on the basis of the homogenization temperature in step 5) and kept at this temperature for a duration of t2, and then quickly cooled to room temperature, the microstructure of the sample is observed, the Nb element content in the GH2909 alloy is measured by EDS, and the residual segregation coefficient of GH2909 is calculated. If the residual segregation coefficient is >0.2, the duration t2 is extended until the residual segregation coefficient is <0.2, and the homogenization time of the second stage of the GH2909 alloy is determined.

2. The method for determining the homogenization heat treatment process of GH2909 alloy according to claim 1, characterized in that: In the step 2), the value range of ΔT is 20-100°C.

3. The method for determining the homogenization heat treatment process of GH2909 alloy according to claim 1, characterized in that: In the step 3), the plurality of test points are at least ten test points.

4. The method for determining the homogenization heat treatment process of GH2909 alloy according to claim 3, characterized in that: In the step 3), the Nb element segregation coefficient of the as-cast structure of the GH2909 alloy is calculated according to the formula: element segregation coefficient K=average concentration of solute elements between dendrites / average concentration of solute elements on the dendrite.

5. The method for determining the homogenization heat treatment process of GH2909 alloy according to claim 4, characterized in that: In step 3), the Laves phase content of the microstructure of the central part of ten GH2909 images is counted by Image-Pro Plus, and the average value is taken to obtain the Laves phase content value of GH2909.

6. The method for determining the homogenization heat treatment process of GH2909 alloy according to claim 1, characterized in that: In the step 6), 0h≤t2≤6h.

7. The method for determining the homogenization heat treatment process of GH2909 alloy according to claim 1, characterized in that: In the step 6), the residual segregation coefficient δ=the solute element concentration difference after homogenization Cmax-Cmin / the solute element concentration difference in the cast structure Comax-Comin.

8. The method for determining the homogenization heat treatment process of GH2909 alloy according to claim 1, characterized in that: In the step 4) and the step 6), the mixture is rapidly cooled to room temperature by water cooling.

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