A method for pre-controlling hardness of a welding and tempering zone of a rapid-cooling steel

Abstract

The application relates to the field of welding technology and discloses a pre-control method for the hardness of a welding tempering zone of a fast-cooled steel. The method comprises the following steps: obtaining the strength increment caused by micro-alloying in the fast-cooled steel; calculating the non-dimensional parameter of the fast-cooled steel; obtaining a K value according to the non-dimensional parameter; and calculating the maximum hardness of the welding tempering zone of the fast-cooled steel according to the K value and the strength increment. According to the composition performance of the fast-cooled steel and welding conditions, the hardness of the welding tempering zone is calculated in advance, so that the pre-control purpose is achieved.

Description

Technical Field

[0001] This application relates to the field of welding technology, and in particular, to a method for pre-controlling the hardness of the tempering zone in rapid-cooling steel welding. Background Technology

[0002] To adapt to the trend of green manufacturing and reduce alloy costs, ultra-fast cold rolling technology for high-strength steel has become an important technology. By reducing the content of alloying elements, using Nb, Ti, and V microalloying, and rolling in the non-recrystallization zone followed by rapid cooling, the steel's dislocation strengthening, precipitation strengthening, grain refinement strengthening, and microstructure strengthening are enhanced, resulting in steel grades with strength comparable to traditional steels and higher toughness. Steel grades produced using ultra-fast cold rolling are mainly in the 600–850 MPa range. Welding tests on these steel grades have revealed a large number of nanoscale precipitates in the weld heat-affected zone, which can alleviate coarsening in the overheated weld zone to some extent. Extensive welding tests have shown that, unlike traditional steel grades, the highest hardness of the weld heat-affected zone in ultra-fast cold-rolled steel often occurs in the tempering zone, exceeding that of the base metal, and is influenced by various factors such as welding thermal cycling.

[0003] Weld hardness is an important indicator of welded joints. The highest hardness in traditional steel weld zones is generally in the overheated coarse-grained zone. Therefore, most previous literature on weld hardness prediction has focused on the hardness of the overheated coarse-grained zone, with a few focusing on the incompletely normalized zone. Summary of the Invention

[0004] The purpose of this application is to provide a method for pre-controlling the hardness of the welding tempering zone of rapidly cooled steel. Based on the composition and properties of the rapidly cooled steel and the welding conditions, a series of formulas are used to calculate and predict the hardness of the welding tempering zone, thereby achieving the pre-control objective.

[0005] Other features and advantages of this application will become apparent from the following detailed description, or may be learned in part from practice of this application.

[0006] According to one aspect of the present application, a method for pre-controlling the hardness of the weld tempering zone of rapidly cooled steel is provided. The method includes: obtaining the strength increment in the rapidly cooled steel caused by microalloying; calculating the dimensionless parameter in the rapidly cooled steel; obtaining a K value based on the dimensionless parameter; and calculating the maximum hardness of the weld tempering zone of the rapidly cooled steel based on the K value and the strength increment.

[0007] In some embodiments, the microalloying includes Nb, Ti, and V.

[0008] In some embodiments, the strength increment ΔRm is calculated using the following formula in obtaining the strength increment caused by microalloying in the rapidly cooled steel:

[0009] ΔRm=1420Nb+68000V×(N-14 / 48Ti-14 / 93Nb);

[0010] Wherein, Nb represents the niobium content in the rapidly cooled steel, V represents the vanadium content in the rapidly cooled steel, Ti represents the titanium content in the rapidly cooled steel, and N represents the nitrogen content in the rapidly cooled steel.

[0011] In some embodiments, the method for calculating the dimensionless parameters of the rapidly cooled steel further includes: obtaining the welding power, volumetric specific heat capacity, welding speed, thickness, preheating temperature, and characteristic temperature of the rapidly cooled steel; and calculating the dimensionless parameters based on the welding power, volumetric specific heat capacity, welding speed, thickness, preheating temperature, and characteristic temperature of the rapidly cooled steel.

[0012] In some embodiments, in calculating the dimensionless parameter based on the welding power, volumetric specific heat capacity, welding speed, thickness, preheating temperature, and characteristic temperature of the rapidly cooling steel, the dimensionless parameter ε is calculated using the following formula:

[0013]

[0014] Where q represents welding power, cρ represents volumetric specific heat capacity, v represents welding speed, h represents the thickness of the rapidly cooled steel, T0 represents preheating temperature, and T represents characteristic temperature.

[0015] In some embodiments, the method for obtaining the K value based on the dimensionless parameter includes:

[0016] If 0 ≤ dimensionless parameter ε ≤ 3, then K = 1 - 0.29ε;

[0017] If there is no dimensionless parameter ε>3, then the value of k = 0.13.

[0018] In some embodiments, when calculating the maximum hardness Hv of the weld tempering zone of the rapidly cooled steel based on the K value and the strength increment, the maximum hardness Hv of the weld tempering zone of the rapidly cooled steel is calculated using the following formula:

[0019]

[0020] In some embodiments, the carbon equivalent in the rapidly cooled steel is 0.30% to 0.40%.

[0021] In some embodiments, the carbon weight ratio in the rapidly cooled steel is 0.05wt% to 0.08wt%.

[0022] In some embodiments, the tensile strength Rm of the rapidly cooled steel is 600MPa to 850MPa.

[0023] Compared with the prior art, the significant advantages of the technical solution of this application are as follows: the method for predicting the maximum hardness of the tempering zone in the heat-affected zone of rapidly cooled steel welding described in this technology has been verified by a large number of experiments and has good conformity. It can be used for the deduction and design of welding performance and welding process for pipeline steel, vehicle structural steel, etc., to achieve the purpose of pre-controlling the welding hardness of ultra-rapidly cooled steel.

[0024] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and do not limit this application. Attached Figure Description

[0025] The above and other features and advantages of this application will become more apparent from a detailed description of exemplary embodiments thereof with reference to the accompanying drawings.

[0026] Figure 1 A flowchart according to one embodiment of this application is shown. Detailed Implementation

[0027] Exemplary embodiments will now be described more fully with reference to the accompanying drawings. However, these exemplary embodiments can be implemented in many forms and should not be construed as limited to the examples set forth herein; rather, these embodiments are provided to make this application more comprehensive and complete, and to fully convey the concept of the exemplary embodiments to those skilled in the art.

[0028] Furthermore, the described features, structures, or characteristics can be combined in any suitable manner in one or more embodiments. Numerous specific details are provided in the following description to give a thorough understanding of embodiments of this application. However, those skilled in the art will recognize that the technical solutions of this application can be practiced without one or more of the specific details, or other methods, components, apparatuses, steps, etc., can be employed. In other instances, well-known methods, apparatuses, implementations, or operations are not shown or described in detail to avoid obscuring various aspects of this application.

[0029] The block diagrams shown in the accompanying drawings are merely functional entities and do not necessarily correspond to physically independent entities. That is, these functional entities can be implemented in software, in one or more hardware modules or integrated circuits, or in different network and / or processor devices and / or microcontroller devices.

[0030] The flowcharts shown in the accompanying drawings are merely illustrative and do not necessarily include all content and operations / steps, nor do they necessarily have to be performed in the described order. For example, some operations / steps can be broken down, while others can be combined or partially combined; therefore, the actual execution order may change depending on the specific circumstances.

[0031] The implementation details of the technical solutions in the embodiments of this application are described in detail below:

[0032] During welding, different areas of the weld joint will experience different welding thermal cycles. For rapidly cooling steel, the hardness evolution of different welding zones is as follows:

[0033] Overheated zone: The base material is heated to above 1100℃, undergoing austenitization and significant grain growth. Due to the controlled alloy content in rapidly cooled steel, it generally forms bainite, pearlite, and ferrite structures after cooling. Typically, its hardness is lower than that of the base material.

[0034] Normalized zone: Heated to Ac3–1000℃, it austenitizes but the grains do not grow. After cooling, it generally forms a finer structure of bainite, pearlite, and ferrite. Under normal circumstances, its hardness is generally lower than that of the base metal.

[0035] Incompletely normalized zone: When heated to Ac1–Ac3, some austenitic grains fail to grow, while untransformed ferrite grows. The microstructure and size in this zone are highly uneven. Its hardness is generally lower than that of the base material.

[0036] Tempered zone: The region heated below Ac1. In this region, supersaturated carbon diffusion in the bainitic ferrite reduces the solid solution strengthening effect. Factors such as the merging and recovery of lath bundles and dislocations, as well as the decomposition of M / A islands, lead to a decrease in hardness. On the other hand, tempering promotes the formation of a large number of finely dispersed precipitates, which pin dislocations. Combined with precipitation strengthening, this increases the hardness. For rapidly cooled steels containing Nb, Ti, and V, the latter often dominates. Therefore, the hardness of the weld tempered zone of such steel is generally increased, and it may even become the region with the highest hardness in the weld heat-affected zone.

[0037] To enable those skilled in the art to better understand this application, the following will be combined with Figure 1 A brief description of this application is provided.

[0038] According to some embodiments, this application provides a method for pre-controlling the hardness of the tempering zone in the weld of rapidly cooled steel, the method comprising:

[0039] Step 101: Obtain the strength increment caused by microalloying in the rapidly cooled steel;

[0040] Step 102: Calculate the dimensionless parameters in the rapidly cooled steel;

[0041] Step 103: Obtain the K value based on the dimensionless parameter;

[0042] Step 104: Calculate the maximum hardness of the weld tempering zone of the rapidly cooled steel based on the K value and the strength increment.

[0043] Based on the above embodiments, in step 101, the strength increment caused by microalloying in the rapidly cooled steel is obtained. The rapidly cooled steel is characterized by: a carbon equivalent of 0.30–0.40% and a carbon weight ratio of 0.05–0.08 wt%. It is produced using a rapid cooling process after rolling in the non-recrystallization zone with Nb, Ti, and V microalloying. The tensile strength Rm of the rapidly cooled steel is 600–850 MPa.

[0044] The intensity increment ΔRm is calculated using the following formula:

[0045] ΔRm=1420Nb+68000V×(N-14 / 48Ti-14 / 93Nb);

[0046] Wherein, Nb represents the niobium content in the rapidly cooled steel, V represents the vanadium content in the rapidly cooled steel, Ti represents the titanium content in the rapidly cooled steel, and N represents the nitrogen content in the rapidly cooled steel.

[0047] In step 102, the dimensionless parameters of the rapidly cooled steel are calculated. The hardness and strength of the tempered zone in the weld heat-affected zone increase.

[0048] The welding power, volumetric specific heat capacity, welding speed, thickness, preheating temperature, and characteristic temperature of the rapidly cooled steel are obtained.

[0049] The dimensionless parameters are calculated based on the welding power, volumetric specific heat capacity, welding speed, thickness, preheating temperature, and characteristic temperature of the rapidly cooled steel.

[0050] Furthermore, the dimensionless parameter ε is calculated using the following formula:

[0051]

[0052] Where q represents welding power, cρ represents volumetric specific heat capacity, v represents welding speed, h represents the thickness of the rapidly cooled steel, T0 represents preheating temperature, and T represents characteristic temperature.

[0053] In step 103, when obtaining the value of K based on the dimensionless parameter:

[0054] If 0 ≤ dimensionless parameter ε ≤ 3, then K = 1 - 0.29ε;

[0055] If there is no dimensionless parameter ε>3, then the value of k = 0.13.

[0056] In step 104, the maximum hardness of the weld tempering zone of the rapidly cooled steel is calculated based on the K value and the strength increment. The maximum hardness Hv of the weld tempering zone of the rapidly cooled steel is calculated using the following formula:

[0057]

[0058] Furthermore, this application includes multiple sets of experimental embodiments to compare the calculated values ​​with the actual measured values, and then compare the differences between the calculated values ​​and the actual measured values.

[0059] Please refer to Tables 1 and 2:

[0060] Table 1

[0061]

[0062] Table 1 shows the Nb, Ti, V, N content, hardness value HV, strength Rm, and thickness of the steel plates in the examples and comparative examples.

[0063] Table 2 shows the data for each welding process condition, including HV. 算 Calculate the maximum hardness and HV of the weld tempering zone. 测 This represents the highest hardness measured in the welding tempering zone.

[0064] Table 2

[0065]

[0066] Example 1 is used as an example: The steel grade is a fast-cooling steel rolled in the non-austenitic recrystallization region, with a thickness of 14 mm. Its microstructure is flat bainite + ferrite, with a tensile strength Rm of 680 MPa and a hardness of 222 HV10; the calculated ΔRm is 61.8 MPa. During welding, the preheating temperature is 100℃, the power is 7840 W, the welding speed is 0.53 cm / s, the calculated ε is 1.53, and then the calculated k is 0.56. Finally, the calculated hardness of the weld tempering zone is 246 HV. A welded sample is taken, its cross-section is polished, and the Vickers hardness of the weld tempering zone is measured under a load of 10 kg. The highest hardness measured is 244 HV, and the difference between the calculated hardness and the measured hardness is only 0.8%. It also shows that the hardness of the tempering zone is higher than that of the base material.

[0067] Example 2: When the welding power is 19100W, the welding speed is 0.58cm / s, the preheating temperature is 30℃, the ε value is 3.04, and the K value is 0.13, the calculated maximum hardness Hv is 234; the actual measured value is 230; the difference is 1.7%.

[0068] Example 3: When the welding power is 8500W, the welding speed is 0.9cm / s, the preheating temperature is 120℃, the ε value is 1, and the K value is 0.71, the calculated maximum hardness Hv is 243; the actual measured value is 242; the difference is 0.4%.

[0069] Example 4: When the welding power is 51500W, the welding speed is 1.38cm / s, the preheating temperature is 100℃, the ε value is 2.61, and the K value is 0.24, the calculated maximum hardness Hv is 212; the actual measured value is 213; the difference is 0.5%.

[0070] Example 5: When the welding power is 62500W, the welding speed is 1.5cm / s, the preheating temperature is 100℃, the ε value is 2.59, and the K value is 0.25, the calculated maximum hardness Hv is 228; the actual measured value is 230; the difference is 0.9%.

[0071] Example 6: When the welding power is 7200W, the welding speed is 0.5cm / s, the preheating temperature is 30℃, the ε value is 1.13, and the K value is 0.67, the calculated maximum hardness Hv is 265; the actual measured value is 267; the difference is 0.8%.

[0072] Examples 2, 3, 4, 5, and 6 were completed. These steels were all fast-cooling steels, and the differences between their calculated and measured hardness were 1.7%, 0.4%, 0.5%, 0.9%, and 0.8%, respectively, which were less than 2%. It was also shown that the hardness of the tempered zone increased to varying degrees compared to the base material.

[0073] Compared with traditional methods, Comparative Example 1 is QT steel, i.e., quenched and tempered steel, with a microstructure of tempered martensite. Its calculated hardness in the weld tempered zone is 365 HV, while the measured maximum hardness in the weld tempered zone is 280 HV, a difference of 28.5%. It also shows that the measured hardness in the tempered zone is significantly lower than that of the base material. Comparative Example 2 is normalized steel, with a microstructure of blocky ferrite and pearlite. Its calculated hardness in the weld tempered zone is 182 HV, while the measured maximum hardness in the weld tempered zone is 176 HV, a difference of 3.4%. Therefore, this technology is not suitable if the steel is not the rapidly cooled steel described above.

[0074] Other embodiments of this application will readily occur to those skilled in the art upon consideration of the specification and practice of the embodiments disclosed herein. This application is intended to cover any variations, uses, or adaptations of this application that follow the general principles of this application and include common knowledge or customary techniques in the art not disclosed herein.

[0075] It should be understood that this application is not limited to the precise structure described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of this application is limited only by the appended claims.

Claims

1. A method for pre-controlling the hardness of the tempering zone in the weld of rapidly cooled steel, characterized in that, The method includes: Obtain the strength increment caused by microalloying in the rapidly cooled steel; Calculate the dimensionless parameters in the rapidly cooled steel; The value of K is obtained based on the dimensionless parameter; The maximum hardness of the weld tempering zone of the rapidly cooled steel was calculated based on the K-value and the strength increment; among which, In calculating the dimensionless parameter based on the welding power, volumetric specific heat capacity, welding speed, thickness, preheating temperature, and characteristic temperature of the rapidly cooling steel, the dimensionless parameter ε is calculated using the following formula: ； in, Indicates welding power. Indicates specific heat capacity by volume. The value represents the welding speed, h represents the thickness of the rapidly cooled steel, T0 represents the preheating temperature, and T represents the characteristic temperature. In obtaining the K value based on the dimensionless parameter, the method includes: If 0 ≤ dimensionless parameter ε ≤ 3, then ; If there is no dimensionless parameter ε>3, then the value of K is 0.13; In calculating the maximum hardness of the weld tempering zone of the rapidly cooled steel based on the K value and the strength increment, the maximum hardness Hv of the weld tempering zone of the rapidly cooled steel is calculated using the following formula: 。 2. The method according to claim 1, characterized in that, The microalloying includes Nb, Ti, and V.

3. The method according to claim 1, characterized in that, In obtaining the strength increment caused by microalloying in the rapidly cooled steel, the strength increment ΔRm is calculated using the following formula: ； Wherein, Nb represents the niobium content in the rapidly cooled steel, V represents the vanadium content in the rapidly cooled steel, Ti represents the titanium content in the rapidly cooled steel, and N represents the nitrogen content in the rapidly cooled steel.

4. The method according to claim 1, characterized in that, In calculating the dimensionless parameters of rapidly cooled steel, the method further includes: The welding power, volumetric specific heat capacity, welding speed, thickness, preheating temperature, and characteristic temperature of the rapidly cooled steel are obtained. The dimensionless parameters are calculated based on the welding power, volumetric specific heat capacity, welding speed, thickness, preheating temperature, and characteristic temperature of the rapidly cooled steel.

5. The method according to claim 1, characterized in that, The carbon equivalent in the rapidly cooled steel is 0.30%~0.40%.

6. The method according to claim 1, characterized in that, The carbon weight ratio in the rapidly cooled steel is 0.05wt%~0.08wt%.

7. The method according to claim 1, characterized in that, The tensile strength Rm of the rapidly cooled steel is 600MPa~850MPa.

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