A method for predicting the hardness of a nugget of a low-alloy steel resistance spot weld

Abstract

The present application relates to the field of metal material processing, and particularly relates to a low alloy steel resistance spot welding nugget hardness prediction method, which comprises obtaining a Vickers hardness detection value of a steel plate; obtaining a hardness calculation value of the steel plate through chemical composition, a hardness related value of spot welding parameters; and calculating a welding spot nugget hardness prediction value.The present application has the following advantages: the hardness value is calculated and predicted, the welding piece is not damaged, the detection time and workload are greatly reduced; the hardness of the welding spot nugget can be quickly predicted before or during welding, potential quality problems can be found in time, and production efficiency is improved; the present application comprehensively considers the Vickers hardness detection value of the original steel plate, the hardness calculation value of the steel plate obtained through chemical composition, and the hardness related value of the spot welding parameters, and the welding spot nugget hardness prediction value is calculated and predicted, so that the actual hardness of the welding spot nugget can be comprehensively and accurately reflected.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of metal material processing, in particular to a low alloy steel resistance spot welding nugget hardness prediction method. BACKGROUND

[0002] Low alloy steel is widely used in industrial production, especially in the field of automobile manufacturing, low alloy steel is widely used in the manufacture of body-in-white. Resistance spot welding is a common welding method for body-in-white manufacturing, and the hardness of the welding spot is one of the key indicators for evaluating the quality of the welding spot. The conventional detection method is to weld the steel plate and then detect the hardness of the welding spot. The steel plate needs to be welded, the welding spot needs to be processed and the hardness needs to be detected, which requires the destruction of the overall structure of the welded part, the process is complicated and the cycle is long. At present, there are few studies on the prediction of the hardness of the steel plate resistance spot welding nugget, and there is no effective scheme for predicting the hardness of the welding spot.

[0003] In the prior art, patent publication number CN 116337924 A discloses a "Vickers hardness evaluation method and system for ship steel welded joint", which is based on the joint thermal cycle curve, product chemical composition and microstructure to evaluate and calculate the Vickers hardness value of the steel plate welded joint.

[0004] Patent publication number CN 118559243 A discloses a "method for predicting the hardness of laser welded steel plate", which predicts the hardness of the laser welded joint of the steel plate by the chemical composition of the steel plate, the welding process and the material characteristics of the welded steel plate, and obtains the hardness value of the laser welded joint of the steel plate.

[0005] The above-mentioned patents predict the hardness of the ship steel plate and the laser welded joint. Due to the different welding methods, they cannot be applied to the hardness of the resistance spot welded joint of the steel plate. SUMMARY

[0006] The purpose of the present application is to provide a low alloy steel resistance spot welding nugget hardness prediction method, which effectively avoids a series of welding experiments, detection and other processes of the steel plate, and conveniently and quickly predicts the Vickers hardness of the resistance spot welded joint of the steel plate to obtain the hardness prediction value of the resistance spot welding of the steel plate.

[0007] To achieve the above-mentioned purpose, the present application realizes the following technical scheme:

[0008] A low alloy steel resistance spot welding nugget hardness prediction method, which obtains the welding spot nugget hardness prediction value by the Vickers hardness detection value of the steel plate, the hardness calculation value obtained by the chemical composition of the steel plate and the hardness related value of the spot welding parameter, specifically comprising:

[0009] obtaining the Vickers hardness detection value of the steel plate;

[0010] The hardness calculation value obtained by the chemical composition of the steel plate, the hardness related value of the spot welding parameter;

[0011] The spot welding nugget hardness prediction value is calculated, and the calculation formula is as follows:

[0012] H=H1+H2-H3①;

[0013] In formula ①, H1 represents the Vickers hardness detection value of the steel plate, H2 represents the hardness calculation value obtained by the chemical composition of the steel plate, H3 represents the hardness related value of the spot welding parameter, and H represents the spot welding nugget hardness prediction value.

[0014] The chemical composition of the steel plate is C, Si, Mn, Cr, Mo, and the sum of the contents of the remaining elements is less than 0.05, wherein, in terms of mass fraction:

[0015] The content of C is 0.05% to 0.18%, the content of Si is 0.5% to 1.5%, the content of Mn is 1.50% to 2.50%, the content of Cr is 0% to 0.8%, and the content of Mo is 0% to 0.6%;

[0016] The hardness calculation value obtained by the chemical composition of the steel plate is calculated, and the calculation formula is as follows:

[0017] H2=98*C+10*Si+35*Mn+3*Cr+5*Mo+45②.

[0018] The hardness related value of the spot welding parameter is calculated, and the calculation formula is as follows:

[0019] H3=t*log(Q,P)③;

[0020] Q=I 2 *T④;

[0021] In formulas ③ and ④, I represents the welding current, the unit is kA, the value range is 5 to 10 kA; T represents the welding time, the unit is ms, the value range is 200 to 600 ms; P represents the electrode pressure, the unit is kN, the value range is 2.5 to 5 kN; and t represents the thickness of the steel plate, the unit is mm.

[0022] The steel plate is a low alloy steel plate, the tensile strength is ≦1200 MPa, and the thickness of the steel plate is ≦3 mm.

[0023] The microstructure of the low alloy steel plate is composed of ferrite, pearlite, martensite and bainite, two or more.

[0024] The Vickers hardness detection value of the steel plate is the Vickers hardness value at the position of 1 / 4 in the thickness direction of the steel plate.

[0025] Compared with the prior art, the beneficial effects of the present application are:

[0026] 1. Traditional methods require welding experiments and damage to the welded parts for hardness testing, which is cumbersome and time-consuming. This invention calculates and predicts hardness values ​​without damaging the welded parts, greatly reducing testing time and workload. It can quickly predict the hardness of the weld nugget before or during welding, promptly identify potential quality problems, and improve production efficiency.

[0027] 2. This invention comprehensively considers the original Vickers hardness test value (H1) of the steel plate, the hardness calculation value obtained from the chemical composition of the steel plate (H2), and the hardness correlation value of the spot welding parameters (H3). By calculating the predicted value of the weld nugget hardness (H), it can more comprehensively and accurately reflect the actual hardness of the weld nugget.

[0028] 3. It eliminates the need for extensive welding experiments and destructive testing, reducing material waste and equipment wear, and lowering production costs; through rapid and accurate hardness prediction, welding process parameters can be adjusted in a timely manner, reducing the defect rate and improving product quality and production efficiency; during the production process, welding parameters can be adjusted in real time based on the prediction results to ensure the stability of welding quality. Attached Figure Description

[0029] Figure 1 This is a flowchart of a method for predicting the hardness of resistance spot weld nuggets in low alloy steel. Detailed Implementation

[0030] The present invention will now be described in detail with reference to the accompanying drawings, but it should be noted that the implementation of the present invention is not limited to the following embodiments.

[0031] The following embodiments are implemented based on the technical solution of the present invention, providing detailed implementation methods and specific operation processes. However, the scope of protection of the present invention is not limited to the following embodiments. Unless otherwise specified, the methods used in the following embodiments are conventional methods.

[0032] Example 1

[0033] See Figure 1 A method for predicting the hardness of resistance spot weld nuggets in low-alloy steel is disclosed. This method utilizes the Vickers hardness test value (H1) of the steel plate, the chemical composition of the steel plate to obtain a calculated hardness value (H2), and the hardness correlation value of the spot welding parameters (H3) to obtain a predicted hardness value (H) for the weld nugget. The steel plate is a low-alloy steel plate with a tensile strength ≤1200MPa and a thickness ≤3mm. Specifically, the method includes:

[0034] S1. Obtain the Vickers hardness test value (H1) of the steel plate;

[0035] The Vickers hardness test value (H1) of a steel plate is the Vickers hardness value at a position 1 / 4 of the thickness of the steel plate.

[0036] S2, obtain the hardness calculation value (H2) of the steel plate and the spot welding parameter hardness correlation value (H3) through the chemical composition of the steel plate;

[0037] The chemical composition of the steel plate is C, Si, Mn, Cr, Mo, S, P, and the sum of the contents of the remaining elements is less than 0.05, wherein the mass fraction is:

[0038] The content of C is 0.05% to 0.18%, the content of Si is 0.5% to 1.5%, the content of Mn is 1.50% to 2.50%, the content of Cr is 0% to 0.8%, and the content of Mo is 0% to 0.6%; the microstructure of the low alloy steel plate is composed of two or three of ferrite, pearlite and martensite, and the microstructure may contain less than 5% of bainite or austenite.

[0039] The chemical composition of the steel plate has a significant effect on predicting the nugget hardness:

[0040] C is a strengthening element in steel and significantly improves the hardenability of the steel plate. With the increase of C content, the carbon content in the nugget martensite phase increases, and the hardness increases. This element has the most significant effect on the nugget hardness.

[0041] Si is a steel element that can dissolve in ferrite and austenite to improve the hardness and strength of the steel, and its effect on the nugget hardness is relatively weak. With the increase of Si content, the nugget hardness also shows an increasing trend.

[0042] Mn is a major element in the nugget metal that promotes the formation of martensite. With the increase of Mn content, the strength and hardness of the nugget metal increase.

[0043] Cr and Mo are strengthening elements for steel and welds. With the increase of Cr and Mo content, the hardenability of the nugget metal increases, and the hardness of the obtained martensite is higher. With the gradual increase of Cr and Mo content in the nugget metal, the nugget structure gradually changes from lath martensite to sheet martensite, and the hardness also gradually increases.

[0044] Calculate the nugget hardness prediction value (H) of the welding spot, and the calculation formula is as follows:

[0045] H = H1 + H2 - H3 ①;

[0046] Obtain the hardness calculation value (H2) of the steel plate through the chemical composition of the steel plate, and the calculation formula is as follows:

[0047] H2 = 98 * C + 10 * Si + 35 * Mn + 3 * Cr + 5 * Mo + 45 ②;

[0048] The calculation value of the spot welding parameter is as follows:

[0049] H3 = t * log (Q, P) ③;

[0050] Q=I 2 *T④;

[0051] In the formula 3 and 4, I represents the welding current, the unit is kA, the value range is 5-10 kA; T represents the welding time, the unit is ms, the value range is 200-600 ms; P represents the electrode pressure, the unit is kN, the value range is 2.5-5 kN; t represents the thickness of the steel plate, the unit is mm.

[0052] The original hardness value of the steel plate (i.e. the Vickers hardness detection value of the steel plate) is an indirect embodiment of the production process of the steel plate, and different rolling processes will produce different hardness values, therefore, the Vickers hardness detection value (H1) of the steel plate is added, which is equivalent to indirectly introducing the production process of the steel plate into the calculation of the hardness of the nugget.

[0053] The spot welding process has an influence on the hardness of the nugget, the welding parameters (welding current, welding time and electrode pressure are all single pulse welding parameters), and the welding tempering process has a certain reducing effect on the hardness of the nugget, and therefore, the present application does not consider the influence of the tempering process on the strength of the welding nugget.

[0054] After the welding spot forms the nugget, the cooling speed under the conventional conditions all exceeds the cooling speed of the formation of the martensite, and therefore, the nugget structure of the present application is all martensite structure.

[0055] The thickness of the steel plate has a certain influence on the hardness of the nugget, mainly the tempering effect of the welding heat affected zone heat on the nugget, and the tempering effect slightly increases with the increase of the thickness of the steel plate.

[0056] Table 1 is the chemical composition of the example, table 2 is the welding parameter, and table 3 is the hardness value of the nugget, the measured value and the prediction deviation.

[0057] Table 1 Product chemical composition

[0058]

[0059] Table 2 Welding process system

[0060]

[0061] Table 3 Vickers hardness table

[0062]

[0063] The implementation effect of the present application is verified by the examples, the example components of Table 1 cover the components of steel plates under different strengths, the component range is large and the coverage is wide. Table 2 shows the relevant data of the influence of the welding process parameters of the steel plate on the nugget hardness, and the hardness correlation value related to the welding parameters is obtained. Table 3 integrates the hardness test value H1, the hardness calculation value H2 and the hardness correlation value H3, and obtains the hardness prediction test H of the present application. By comparing the predicted value H and the measured value of the nugget hardness, the deviation between the predicted value and the measured value of the present application is within ±4%, which is completely within the fluctuation value range of the nugget hardness detection, and completely meets the detection deviation requirement of the nugget hardness in the professional field. In Example 1 and Example 2, the predicted value and the detected value only differ by 3-4HV, which shows that the prediction result of the present application is very accurate, and with the increase of the nugget hardness value, the predicted value is slightly higher than the measured value, and the fluctuation range is completely within the fluctuation range of the spot welding nugget hardness value (±10%). In summary, the nugget hardness prediction model of the present application is accurate and has high precision, and can be used as a means for predicting the nugget hardness of low alloy steel, which has a positive effect on the development of low alloy steel welding work and reduces the work intensity.

[0064] In the present application, the traditional method needs to perform welding experiments and destroy the structure of the welded part for hardness detection, which is complicated and time-consuming. The present application predicts the hardness value by calculation, without damaging the welded part, greatly reducing the detection time and workload; the hardness of the spot welding nugget can be quickly predicted before or during welding, potential quality problems can be found in time, and production efficiency can be improved; the present application comprehensively considers the original vickers hardness test value (H1) of the steel plate, the hardness calculation value (H2) obtained from the chemical composition of the steel plate and the hardness correlation value (H3) of the spot welding parameters, and predicts the welding nugget hardness prediction value (H) by calculation, which can more comprehensively and accurately reflect the actual hardness of the welding nugget; without a large number of welding experiments and destructive detection, material waste and equipment loss are reduced, and production cost is reduced; through fast and accurate hardness prediction, welding process parameters can be adjusted in time, the scrap rate can be reduced, and product quality and production benefit can be improved; in the production process, the welding parameters can be adjusted in real time according to the prediction result, and the stability of the welding quality is ensured.

Claims

1. A method of predicting nugget hardness of low alloy steel resistance spot welds, characterized by, The Vickers hardness detection value of the steel plate, the hardness calculation value obtained from the chemical composition of the steel plate, and the hardness related value of the spot welding parameter are used to obtain a weld nugget hardness prediction value, and specifically include: obtaining the Vickers hardness detection value of the steel plate; obtaining the hardness calculation value from the chemical composition of the steel plate and the hardness related value of the spot welding parameter; calculating the weld nugget hardness prediction value, and the calculation formula is as follows: H=H1+H2-H3 ①; In formula ①, H1 represents the Vickers hardness detection value of the steel plate, H2 represents the hardness calculation value obtained from the chemical composition of the steel plate, H3 represents the hardness related value of the spot welding parameter, and H represents the weld nugget hardness prediction value.

2. The method for predicting the hardness of resistance spot weld nuggets in low alloy steel according to claim 1, characterized in that, The chemical composition of the steel plate is C, Si, Mn, Cr, Mo, and the sum of the contents of the remaining elements is less than 0.05, wherein the mass fraction is: The content of C is 0.05% to 0.18%, the content of Si is 0.5% to 1.5%, the content of Mn is 1.50% to 2.50%, the content of Cr is 0% to 0.8%, and the content of Mo is 0% to 0.6%; The hardness calculation value obtained from the chemical composition of the steel plate is calculated according to the following formula: H2=98*C+10*Si+35*Mn+3*Cr+5*Mo+45 ②.

3. The method of claim 1, wherein the low alloy steel is a high strength steel. The hardness related value of the spot welding parameter is calculated according to the following formula: H3=t*log(Q,P) ③; Q = I 2 *T④; In formulas ③ and ④, I represents the welding current, with a unit of kA, and a value range of 5 to 10 kA; T represents the welding time, with a unit of ms, and a value range of 200 to 600 ms; P represents the electrode pressure, with a unit of kN, and a value range of 2.5 to 5 kN; and t represents the thickness of the steel plate, with a unit of mm.

4. The method of claim 1, wherein the low alloy steel is a high strength steel. The steel plate is a low-alloy steel plate with a tensile strength of ≦1200 MPa and a thickness of ≦3 mm.

5. The method of claim 4, wherein the low alloy steel is a high strength steel. The microstructure of the low-alloy steel plate is composed of ferrite, pearlite, martensite, and bainite.

6. The method of claim 1, wherein the low alloy steel is a high strength steel. The Vickers hardness detection value of the steel plate is the Vickers hardness value at the 1 / 4 position in the thickness direction of the steel plate.

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