A method for optimizing the heat treatment process of CMT arc cladding of 9Cr1Mo heat-resistant coating on Q235 steel surface
By optimizing the heat treatment process of CMT arc cladding of 9Cr1Mo coating on low-carbon steel surface using the controlled variable method and multiple linear regression fitting, the problem of poor material bonding strength and toughness was solved, achieving high interfacial bonding strength and toughness under high-temperature service conditions and reducing production costs.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- ANHUI UNIVERSITY OF TECHNOLOGY
- Filing Date
- 2023-04-14
- Publication Date
- 2026-06-30
AI Technical Summary
In the existing technology, the heat treatment process of cladding 9Cr1Mo material on the surface of low carbon steel has failed to effectively solve the problems of poor material bonding strength and toughness, easy deformation, cracking and high cost, especially under high temperature service conditions, which leads to component failure.
Experiments were conducted using the controlled variable method. Through multiple linear regression fitting, the heat treatment temperature and time were optimized. Combined with shear strength and impact absorption energy data, a mathematical model was developed to optimize the heat treatment process, ensuring interfacial bonding strength and toughness, avoiding deformation and cracking, and reducing production costs.
It achieves high interfacial bonding strength and toughness of 9Cr1Mo coating on low carbon steel surface under high temperature service conditions, avoiding deformation, cracking and premature failure, and reducing production costs.
Smart Images
Figure CN117947365B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of heat treatment technology, and provides a method for optimizing the heat treatment process of CMT arc cladding of 9Cr1Mo heat-resistant coating on the surface of Q235 steel. Background Technology
[0002] In thermal power generating units, low-carbon steel is widely used in components operating below 350℃-450℃, such as heated surface pipes and valves, due to its good toughness and plasticity, excellent weldability, good machinability, and relatively low cost. However, this type of steel is prone to failure when operating at higher temperatures. 9Cr1Mo steel is a fine-grained, strong, and tough martensitic heat-resistant steel. The addition of Cr and Nb elements not only ensures the formation of a Cr-rich passivation film but also improves the high-temperature stability of the passivation film, allowing it to withstand temperatures up to 600℃. This makes it an ideal material for high-temperature components in thermal power boilers. Furthermore, compared to other heat-resistant materials such as nickel-based alloys, MCrAlY, and high-entropy alloys, 9Cr1Mo is easier to obtain and less expensive. Coating the surface of low-carbon steel with 9Cr1Mo as a protective layer not only preserves the original performance of the low-carbon steel but also greatly enhances the heat resistance properties of the heat-resistant material, significantly expanding the application range of low-carbon steel.
[0003] To achieve high bonding strength and toughness in clad components, heat treatment is necessary to balance the various problems arising from differences in composition, physical properties, and performance between materials. The study "Influence of High-Temperature Tempering on the Microstructure and Properties of Q235 / P91 Dissimilar Steel Welded Joints" (Electric Welding Machine, June 2017) investigated the effects of different holding times on the microstructure and hardness of the joint. The hardness of the joint decreased with increasing holding time; however, this study limited the variable to heat treatment time, failing to explore the influence of heat treatment temperature on microstructure and properties, and the performance characterization method only mentioned hardness, without considering the influence of the variable on other properties. Since the heat treatment processes for low-carbon steel and 9Cr1Mo differ significantly, finding suitable heat treatment temperatures (T) and times (t) is particularly important. If T and t are too small, problems such as internal stress generated after cladding and Widmanstätten structure caused by overheating in the heat-affected zone (HAZ) of the substrate cannot be resolved, which may lead to deformation and cracking of the component. If T and t are too large, the migration of carbon elements will cause the width of the carbon-depleted and carbon-rich layers at the interface to increase, resulting in a decrease in interfacial bonding strength. The sample may fail prematurely during use. Although a reduction in the width of the carbon-depleted and carbon-rich layers can be observed under heat treatment conditions exceeding the Ac1 temperature of the substrate, the cost of heat treatment will be higher at this time. Therefore, how to reduce costs while taking into account the performance of both materials is an urgent problem to be solved. Summary of the Invention
[0004] The problem to be solved by the present invention is to provide a method for optimizing the heat treatment process of CMT arc cladding of 9Cr1Mo heat-resistant coating on Q235 steel surface. It ensures that the cladding sample has sufficient interfacial bonding strength and toughness, avoids deformation, cracking and premature failure, and also reduces production costs and waste of manpower and material resources.
[0005] This invention discloses a method for optimizing the heat treatment process of CMT arc cladding of 9Cr1Mo heat-resistant coating on Q235 steel surface, the specific steps of which are as follows:
[0006] Step 1: Conduct experiments using the controlled variable method: First, divide the heat treatment temperature into m gradients and the heat treatment time into n gradients. Then, while keeping the heat treatment temperature constant, change the heat treatment time and repeat n times to obtain n sets of large samples. Repeat this process m times to obtain m×n sets of cladding large samples. Process the m×n sets of cladding large samples to obtain shear samples and impact samples under corresponding conditions. Then, test the samples to obtain data on the shear strength and impact absorption energy of the samples under different heat treatment conditions.
[0007] Step 2: Preprocess the obtained (m×n) shear strength and impact absorption energy data, use plotting software to draw scatter plots, and use multiple linear regression fitting method to obtain mathematical models of shear strength and impact absorption energy with respect to heat treatment temperature and heat treatment time.
[0008] Step 3: Integrate the two mathematical models described in Step 2 to obtain a mathematical model for evaluating the comprehensive mechanical properties of the sample. Based on the added constraints, solve the model and obtain the best comprehensive mechanical properties by optimizing the combination of heat treatment temperature and heat treatment time, thereby optimizing the heat treatment process.
[0009] Further, step 1 specifically includes: Step 1.1, dividing the heat treatment temperature range T into m gradients and the heat treatment time t into n gradients, obtaining m×n groups of large cladding samples through the controlled variable method; where each group of large cladding samples has a Q235 substrate size of 100mm×100mm×8mm, and 9Cr1Mo is clad onto the Q235 substrate using ER90S-B9 heat-resistant steel wire via the CMT method; Step 1.2, each group of heat-treated large cladding samples is cut into two smaller samples: a shear sample and an impact sample. The shear sample is a non-standard sample with a size of 3mm×3mm×10mm, and the impact sample is a standard sample with a size of 55mm×10mm×2.5mm; Step 1.3, performing a shear test on the shear sample to obtain the shear strength, and performing an impact test on the impact sample to obtain the impact absorption energy. The impact test is performed according to the Charpy impact test specifications.
[0010] Furthermore, in step 1.1: the heat treatment temperature T ranges from 700℃ to 780℃, and the heat treatment time t ranges from 1 to 6 hours.
[0011] Further, step 2 specifically involves: Step 2.1, preprocessing the shear strength and impact absorption energy performance data of the m×n samples obtained in step 1, and organizing them to obtain data points on shear strength and impact absorption energy with respect to heat treatment temperature and heat treatment time; Step 2.2, importing the data points on shear strength with respect to heat treatment temperature and heat treatment time obtained in step 2.1 into the calculation software and plotting a scatter plot, and using multiple linear regression fitting to obtain the model τ(T, t) of shear strength with respect to heat treatment temperature and heat treatment time, and similarly obtaining the model of impact absorption energy with respect to heat treatment temperature and heat treatment time.
[0012] Further, in step 2.2: use Origin software to draw a scatter plot and use Matlab software to fit the curve.
[0013] Furthermore, in step 2.2: the model used to fit the data points is p. 01 +p 02 x+p 03 y+p 04 x 2 +p 05 xy+p 06 y 2 +p 07 x 3 +p 08 x 2 y+p 09 xy 2 +p 10 y 3 p 01 p 02 …p 10 is the coefficient of each term in the above formula.
[0014] Furthermore, step 3 specifically includes: Step 3.1, setting τ(T, t), Integrated into a comprehensive mechanical property model for the specimen Step 3.2: Considering performance and production costs, add constraints to ω(T, t): T a ≤T≤T b , t a ≤t≤t b At the same time, τ a ≤τ(T, t), Among them, T a T b Let t be the upper and lower limits of temperature T.a t b τ is the upper and lower bounds of time t; a It is the lower constraint point of the shear strength τ(T, t); It is impact absorption energy The lower limit point; Step 3.3: Based on the comprehensive mechanical performance model ω(T, t) and the constraint conditions, the model can be solved to obtain the combination of heat treatment temperature and heat treatment time that meets the requirements, thereby optimizing the heat treatment process.
[0015] Furthermore, in step 3.2: the tempering temperature of 9Cr1Mo steel is generally 740℃-760℃ for 1-4 hours, while the heat treatment temperature for stress-relief annealing of Q235 steel can reach up to 650℃; to ensure that the cladding sample has sufficient interfacial bonding strength and toughness, and to avoid performance degradation due to improper heat treatment, and also to reduce production costs, the constraints can be defined as: 700℃≤T≤760℃, 1≤t≤4, τ(T,t)≥370MPa.
[0016] Further, step 3.3 specifically involves: firstly, taking the first-order partial derivatives of ω(T, t) with respect to T and t respectively to obtain... and make We can obtain the stationary point of ω(T, t) (T i , t i ), i = 1, 2; next, determine whether the obtained stationary point is an extreme point of ω(T, t): I obtain the second-order partial derivative of ω(T, t) with respect to T. Similarly, taking the second-order partial derivative with respect to t, we get... Taking the mixed partial derivatives with respect to T and t, we get Order II Substituting the obtained stationary points into A, B, and C respectively, we can obtain A. i B i C i Let i = 1, 2; let R = A * CB 2 ① If R < 0, then the point is not an extreme point; ② If R > 0 and A > 0, then the point is a minimum point of ω(T,t); ③ If R > 0 and A < 0, then the point is a maximum point of ω(T,t); finally, the point corresponding to the maximum point (T) i ,t i ) Make a judgment and exclude the points that are not subject to the constraints given in step 3.2. Then the remaining (T) i ,t i This refers to the optimal combination of heat treatment temperature and heat treatment time.
[0017] This invention optimizes the heat treatment temperature (T) and heat treatment time (t) by performing multiple linear regression fitting on experimental data obtained under different heat treatment conditions, with the shear strength τ(T,t) and impact absorption energy of the sample as the target. With cost as a constraint, the optimal combination of T and t for the comprehensive mechanical properties ω(T,t) of the sample is obtained by finding the extreme value of the bivariate function. This ensures that the cladding sample has high comprehensive performance of interfacial bonding strength and impact toughness, avoids deformation, cracking and premature failure, and at the same time reduces production costs and waste of manpower and resources as much as possible. Attached Figure Description
[0018] Figure 1 This is a flowchart of the method of the present invention;
[0019] Figure 2 This is a scatter plot of the experimental data on shear strength and impact absorption energy.
[0020] Figure 3 This is a graph showing the fitting effect of shear strength and impact absorption energy on heat treatment temperature and time.
[0021] Figure 4 This is a comparison diagram of the microstructure of the deposited sample and the sample treated with the optimized heat treatment process. Detailed Implementation
[0022] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described below in conjunction with the accompanying drawings and embodiments, but the present invention is not limited to the following embodiments.
[0023] This invention discloses a method for optimizing the heat treatment process of CMT arc cladding of 9Cr1Mo heat-resistant coating on Q235 steel surface, the specific steps of which are as follows:
[0024] Step 1: Conduct experiments using the controlled variable method: First, divide the heat treatment temperature into m average gradients and the heat treatment time into n average gradients. Then, while keeping the heat treatment temperature constant, change the heat treatment time, repeating this process n times to obtain n sets of large samples. Repeat this process m times to obtain m×n sets of cladding large samples. Process the m×n sets of cladding large samples to obtain shear and impact samples under corresponding conditions. Then, test the samples to obtain data on the shear strength and impact absorption energy of the samples under different heat treatment conditions. The specific process is as follows:
[0025] Step 1.1: The heat treatment temperature T: 700℃-780℃ was divided into 5 average gradients, and the heat treatment time t: 1-6h was divided into 6 average gradients. The experiment was conducted using the controlled variable method, and a total of 5×6=30 groups of cladding large samples were obtained. The dimensions of each group of cladding large samples were: Q235 substrate with Q235 substrate size of 100mm×100mm×8mm. 9Cr1Mo was clad onto the Q235 substrate by ER90S-B9 heat-resistant steel wire using the CMT method.
[0026] Step 1.2: Each heat-treated cladding specimen is cut into two smaller specimens: a shear specimen and an impact specimen. The shear specimen is a non-standard specimen with a size of 3mm×3mm×10mm, while the impact specimen is a standard small specimen with a size of 55mm×10mm×2.5mm.
[0027] Step 1.3: Perform a shear test on the shear specimen to obtain the shear strength, and perform an impact test on the impact specimen to obtain the impact absorption energy. The impact test shall be performed in accordance with the Charpy impact test specifications.
[0028] Step 2: Preprocess the 30 shear strength and 30 impact absorption energy data points obtained, plot scatter plots using graphing software, and use multiple linear regression fitting to obtain mathematical models of shear strength and impact absorption energy with respect to heat treatment temperature and time. The specific process is as follows:
[0029] Step 2.1: Preprocess the 30 shear strength and 30 impact absorption energy data obtained in Step 1, and sort them out to obtain the data points of shear strength and impact toughness with respect to heat treatment temperature and heat treatment time.
[0030] Step 2.2: Import the shear strength data points obtained in Step 2.1 regarding heat treatment temperature and time into the calculation software Origin and plot a scatter plot (e.g., Figure 2 As shown), the model of shear strength with respect to heat treatment temperature and heat treatment time was obtained in Matlab software through multiple linear regression fitting (e.g., Figure 3 As shown):
[0031] τ(T,t)=-118900+490.52T+160.48t-0.66736T 2 -0.33475Tt-1.92t 2 +0.0003038T 3 +0.000199T 2 t+0.002679Tt 2 +0.1593t 3
[0032] Similarly, the model for impact absorption work with respect to heat treatment temperature and heat treatment time is obtained:
[0033]
[0034] The model used to fit the data points is p. 01 +p 02 x+p 03 y+p 04 x 2 +p 05 xy+p 06 y 2 +p 07 x 3 +p 08 x 2 y+p 09 xy 2 +p 10 y 3 p 01 p 02 …p 10 represents the coefficients of each term in the above equation;
[0035] Step 3: Integrate the two mathematical models described in Step 2 to obtain a mathematical model for evaluating the comprehensive mechanical properties of the sample. Based on the added constraints, solve the model and obtain the best comprehensive mechanical properties by optimizing the combination of heat treatment temperature and heat treatment time, thereby optimizing the heat treatment process. The specific process is as follows:
[0036] Step 3.1, set τ(T,t), Integrated into a comprehensive mechanical property model for the specimen:
[0037]
[0038] Step 3.2: Because the industrial requirements for the heat treatment process of 9Cr1Mo steel are stringent, its tempering temperature is generally 740℃-760℃ and held for 1-4 hours; the heat treatment temperature of Q235 steel during stress-relief annealing can reach up to 650℃. Therefore, to ensure that the cladding sample has sufficient interfacial bonding strength and toughness, and to avoid performance degradation caused by improper heat treatment, and to reduce production costs, the constraints can be defined as: 700℃≤T≤760℃, 1≤t≤4, τ(T,t)≥370MPa.
[0039] Step 3.3, solving for ω(T,t) includes the following steps:
[0040] First, take the first-order partial derivatives of ω(T,t) with respect to T and t respectively.
[0041]
[0042]
[0043] make The stationary points of ω(T,t) are (736.68℃, 2.39h) and (731.28℃, 2.17h).
[0044] Next, determine whether the obtained stationary point is an extreme point of ω(T,t):
[0045] I. By taking the second-order partial derivative of ω(T,t) with respect to T, we obtain
[0046]
[0047] Similarly, taking the second-order partial derivative with respect to t, we get...
[0048]
[0049] Taking the mixed partial derivatives with respect to T and t, we get
[0050]
[0051] Order II Let R = A * CB 2 .
[0052] When T = 736.68℃ and t = 2.39h, A = 0.00484, B = -0.03882, and C = 0.15596. At this time, R < 0, so this point is not an extreme point of ω(T,t).
[0053] When T = 731.28℃ and t = 2.17h, A = -0.00558, B = -0.0305, and C = -0.1675. At this time, R > 0 and A < 0, so this point is the maximum point of ω(T,t).
[0054] Finally, for the maximum point corresponding to (T) i ,t i ) Make a judgment, and exclude the points other than those under the constraints given in step 3.2, 700℃≤T≤760℃, 1≤t≤4, then the remaining (T i ,t i This refers to the optimal combination of heat treatment temperature and heat treatment time. Obviously, according to the method proposed by the present invention for optimizing the heat treatment process of CMT arc cladding of 9Cr1Mo heat-resistant coating on Q235 steel surface, the optimal combination of heat treatment temperature and heat treatment time for a plate with dimensions of 200mm×100mm×8mm is (731.28℃, 2.17h).
[0055] A 9Cr1Mo coating was clad onto a 100mm×100mm×8mm thick Q235 steel plate using CMT technology, and then the plate was heat-treated at 731.28℃ for 2.17h. The resulting sample was compared with a sample with an unoptimized heat treatment process. The results are shown in Table 1.
[0056]
[0057] Table 1 and Figure 4 The results show that, under the combined heat treatment temperature and time obtained by the method of this invention, the microstructure of the cladding layer transforms from hard and brittle untempered martensite to tempered martensite with better performance. The deteriorated microstructure in the heat-affected zone of the matrix disappears. While meeting the requirements of GB / T 8165-2008, the shear strength of the sample increases by approximately 208.6% in impact toughness. Therefore, the method of this invention can ensure that the cladding sample has sufficient interfacial bonding strength and toughness, avoiding performance degradation caused by improper heat treatment, and preventing deformation, cracking, and premature failure. Simultaneously, it reduces production costs while ensuring the overall performance of the sample.
[0058] This invention optimizes the heat treatment process of CMT arc cladding of 9Cr1Mo coating on Q235 steel surface using numerical fitting method based on experimental results. This solves the Widmanstätten structure problem caused by overheating in the heat-affected zone (HAZ) of the substrate. At the same time, it improves the deterioration of shear performance caused by carbon-depleted and carbon-rich layers at the interface and the problem of excessively high production costs. By using the optimized heat treatment process, the cladding sample is guaranteed to have high interfacial bonding strength and impact toughness, and the production cost is further reduced.
[0059] The present invention has been described above with reference to the accompanying drawings, but the invention is not limited to the specific embodiments described above. Furthermore, the method described in this invention can be used to optimize the process when applying a 9Cr1Mo heat-resistant coating to the surface of low-carbon steels such as Q235, Q345, and Q245R(20G). Any modifications or variations to this technical solution without departing from the principle of the method are within the scope of protection of this invention.
Claims
1. A method for optimizing the heat treatment process of CMT arc cladding of 9Cr1Mo heat-resistant coating on Q235 steel surface, characterized in that, The specific steps are as follows: Step 1: Conduct experiments using the controlled variable method: First, divide the heat treatment temperature into m gradients and the heat treatment time into n gradients. Then, while keeping the heat treatment temperature constant, change the heat treatment time and repeat n times to obtain n groups of large samples. Repeat this process m times to obtain m×n groups of cladding large samples. Process the m×n groups of cladding large samples to obtain shear samples and impact samples under corresponding conditions. Then test the samples to obtain data on shear strength and impact absorption energy under different heat treatment conditions. Step 2: Preprocess the obtained (m×n) shear strength and impact absorption energy data, use graphing software to draw scatter plots, and use multiple linear regression fitting to obtain mathematical models of shear strength and impact absorption energy with respect to heat treatment temperature and heat treatment time. Step 3: Integrate the two mathematical models from Step 2 to obtain a mathematical model for evaluating the comprehensive mechanical properties of the samples. Based on the addition of constraints, calculate the model. Solution: By optimizing the combination of heat treatment temperature and heat treatment time, the best comprehensive mechanical properties are obtained, thereby optimizing the heat treatment process. Specifically, step 2 involves: Step 2.1: Preprocessing the shear strength and impact absorption energy data of the m×n samples obtained in step 1, and organizing the data points of shear strength and impact absorption energy with respect to heat treatment temperature and heat treatment time; Step 2.2: Importing the data points of shear strength with respect to heat treatment temperature and heat treatment time obtained in step 2.1 into the calculation software and plotting a scatter plot, then using multiple linear regression fitting to obtain a model of shear strength with respect to heat treatment temperature and heat treatment time. Similarly, a model for the impact absorption work with respect to heat treatment temperature and heat treatment time can be obtained. Step 3 specifically includes: Step 3.1, ... , Integrated into a comprehensive mechanical property model for the specimen Step 3.2: Taking into account performance and production costs, Add constraints: ≤ ≤ , ≤ ≤ ,at the same time ≤ , ≤ ;in, , These are the upper and lower limits of temperature T. , These are the upper and lower limits of time t; Shear strength The lower limit point; It is impact absorption energy The lower limit point; Step 3.3, based on the comprehensive mechanical performance model By defining the constraints and solving the model, the desired combination of heat treatment temperature and time can be obtained, thus optimizing the heat treatment process. In step 3.2: the tempering temperature of 9Cr1Mo steel is 740℃-760℃, held for 1-4 hours; the heat treatment temperature for stress-relief annealing of Q235 steel can reach up to 650℃. To ensure that the cladding samples have sufficient interfacial bonding strength and toughness, and to avoid performance degradation due to improper heat treatment, and also to reduce production costs, the constraint conditions are defined as follows: ℃≤ 760℃ ≤ ≤ , 370MPa 27J.
2. The method according to claim 1, characterized in that: Step 1 is as follows: Step 1.1: Divide the heat treatment temperature range T into m gradients and the heat treatment time t into n gradients. Using the controlled variable method, m×n groups of large cladding specimens can be obtained. Each group of large cladding specimens has a Q235 substrate size of 100mm×100mm×8mm. ER90S-B9 heat-resistant steel wire is used to clad 9Cr1Mo onto the Q235 substrate using the CMT method. Step 1.2: Each group of heat-treated large cladding specimens is cut into two smaller specimens: a shear specimen and an impact specimen. The shear specimen is a non-standard specimen with a size of 3mm×3mm×10mm, and the impact specimen is a standard small specimen with a size of 55mm×10mm×2.5mm. Step 1.3: Perform a shear test on the shear specimen to obtain the shear strength, and perform an impact test on the impact specimen to obtain the impact absorption energy. The impact test is performed according to the Charpy impact test specifications.
3. The method according to claim 2, characterized in that: In step 1.1: the heat treatment temperature T ranges from 700℃ to 780℃, and the heat treatment time t ranges from 1 to 6 hours.
4. The method according to claim 1, characterized in that: In step 2.2: Use Origin software to draw a scatter plot and use Matlab software to fit the curve.
5. The method according to claim 1, characterized in that: In step 2.2: the model used to fit the data points is... , is the coefficient of each term in the above formula.
6. The method according to claim 1, characterized in that: Step 3.3 specifically involves: firstly, through... To each Finding the first-order partial derivative yields and ,make , achievable outposts ( ), ; Next, determine whether the obtained stationary point is... Extreme points: Ⅰ Through right Finding the second-order partial derivative yields Similarly, for Finding the second-order partial derivative yields ,right Finding the mixed partial derivatives yields Order II The obtained station points are respectively brought into , and From the middle ; make ,like If, then that point is not an extreme point, and Then the point is The minimum point, ③ if and Then the point is The maximum point; finally, the point corresponding to the maximum point ( ) Make a judgment, exclude the points that are not subject to the constraints given in step 3.2, then the remaining ( This refers to the optimal combination of heat treatment temperature and heat treatment time.