阅读说明：本技术 一种先进高强钢点焊焊接性的预判评价方法 (Advanced high-strength steel spot welding weldability pre-judgment evaluation method ) 是由 罗海文 李硕硕 于 2021-07-07 设计创作，主要内容包括：一种先进高强钢点焊焊接性的预判评价方法,涉及合金钢焊接性的评价领域,包括以下步骤:S1：建立描述单个合金元素对钢凝固收缩率的定量影响的数据库；S2：基于所述数据库进一步建立描述钢中所有合金元素含量与钢凝固收缩率定量关系的多元线性模型；S3：确定所述多元线性模型中的各项系数获得完整多元线性模型并检验误差；S4：利用所述完整多元线性模型,确定用于预判点焊焊接性的钢凝固收缩率判断阈值,判断点焊焊接性。本发明模型基于清晰的凝固收缩物理背景,比由经验总结的碳当量公式评价法能更加准确可靠地评估预测更高合金含量钢种的焊接性。(A prejudgment and evaluation method for the spot weldability of advanced high-strength steel relates to the field of alloy steel weldability evaluation, and comprises the following steps of S1: establishing a database describing the quantitative influence of a single alloy element on the solidification shrinkage of the steel; s2: further establishing a multivariate linear model for describing the quantitative relation between the content of all alloy elements in the steel and the solidification shrinkage rate of the steel based on the database; s3: determining each coefficient in the multivariate linear model to obtain a complete multivariate linear model and checking errors; s4: and determining a steel solidification shrinkage rate judgment threshold value for pre-judging the spot welding weldability by using the complete multivariate linear model, and judging the spot welding weldability. The model of the invention is based on the clear solidification shrinkage physical background, and can more accurately and reliably evaluate and predict the weldability of the steel grade with higher alloy content than a carbon equivalent formula evaluation method summarized by experience.)

1. The advanced pre-judging and evaluating method for the spot welding weldability of the high-strength steel is characterized by comprising the following steps of:

s1: establishing a database describing the quantitative influence of a single alloy element on the solidification shrinkage of the steel;

s2: further establishing a multivariate linear model for describing the quantitative relation between the content of all alloy elements in the steel and the solidification shrinkage rate of the steel based on the database;

s3: determining each coefficient in the multivariate linear model to obtain a complete multivariate linear model and checking errors;

s4: and determining a steel solidification shrinkage rate judgment threshold value for pre-judging the spot welding weldability by using the complete multivariate linear model, and judging the spot welding weldability.

2. The advanced prejudgment and evaluation method for spot weldability of high-strength steel as claimed in claim 1, wherein said determining a steel solidification shrinkage rate judgment threshold value for prejudging spot weldability specifically comprises:

and if a part of interface fracture form between the interface fracture and the nugget pulling fracture occurs in the spot welding of a certain steel grade, taking the steel solidification shrinkage rate calculated by the complete multivariate linear model of the steel grade as a judgment threshold value.

3. The advanced prejudgment evaluation method of spot weldability of high-strength steel as claimed in claim 2, wherein,

when the solidification shrinkage rate of the steel to be detected, which is calculated through the complete multivariate linear model, is larger than or equal to a judgment threshold value, the spot welding weldability of the steel to be detected is poor;

and when the solidification shrinkage rate of the steel grade to be detected, which is calculated by the complete multivariate linear model, is smaller than a judgment threshold value, the spot welding weldability of the steel grade to be detected is considered to be excellent.

4. The advanced high-strength steel spot weldability prejudgment evaluation method according to claim 1, wherein the S2 specifically includes:

establishing a multivariate linear model to determine the relation between the content of all alloy elements and the solidification shrinkage of steel, wherein the basic expression of the multivariate linear model is as follows:

wherein, Delta l is the solidification shrinkage rate of steel and the unit is%; alpha is alpha₀Is a constant term; n is the number of the types of the alloy elements; alpha is alpha_iCoefficient of the content of the ith alloying element; x is the number of_iIs the mass percentage of the ith alloy element; i is a positive integer.

5. The advanced high-strength steel spot weldability prejudgment evaluation method according to claim 4, wherein said S3 specifically includes:

solving by utilizing multivariate linear regression, fitting to obtain each coefficient in the multivariate linear model, and checking errors to obtain a complete multivariate linear model, wherein the complete multivariate linear model can be expressed as:

Δl＝1.259+0.301W_C+0.0183W_Mn-0.0359W_Cr-0.0153W_Ni-0.00556W_Mo+0.0354W_Si+0.0168W_Cu-0.118W_V

wherein the coefficients of the formula can be varied within an error range, W_C、W_Mn、W_Cr、W_Ni、W_Mo、W_Si、W_Cu、W_VAre the mass percentages of alloy elements C, Mn, Cr, Ni, Mo, Si, Cu and V respectively.

6. The advanced high-strength steel spot weldability prejudgment evaluation method according to claim 5, wherein the inspection error specifically comprises:

and calculating the steel solidification shrinkage rate of the steel grade by using the complete multivariate linear model, and when the error between the calculated steel solidification shrinkage rate and the actual steel solidification shrinkage rate of the steel grade is less than 3%, determining that the complete multivariate linear model is accurate.

7. The advanced high-strength steel spot weldability prejudged evaluation method as claimed in claim 1, wherein said alloy elements include at least one or more of C, Mn, Cr, Ni, Mo, Si, Cu, V.

8. The advanced prejudgment evaluation method of spot weldability of high-strength steel as claimed in claim 2, wherein said judgment threshold value can fluctuate within a range of plus or minus 3%.

9. The advanced prejudgment evaluation method of spot weldability of high-strength steel according to claim 2, characterized in that said judgment threshold value is 1.39%.

10. The advanced high-strength steel spot weldability prejudgment evaluation method according to claim 1, wherein the S1 specifically includes:

s11: obtaining the quantitative influence of a single alloy element on the solidification shrinkage of the steel by adopting an experimental method, a literature data extraction method or a software calculation method;

s12: a database was established describing the quantitative effect of individual alloying elements on steel solidification shrinkage.

Technical Field

The invention relates to the field of evaluation of weldability of alloy steel, in particular to an advanced prejudgment evaluation method of spot weldability of high-strength steel.

Background

Automobiles represent a great advance in human play and social development, but also cause severe consumption of non-renewable energy. In order to reduce fuel consumption, the weight of a vehicle is reduced, and the weight of an automobile is required to be reduced. In the materials for forming automobile body parts, metal materials still account for the main part, particularly, steel materials are widely applied, and when the thickness of a steel plate is reduced by 0.05mm, the weight of an automobile body can be reduced by 6%. Compared with common steel, the high-strength steel with high strength is adopted, the thickness of the automobile body plate can be reduced on the premise of not losing the strength of the automobile body component, the automobile weight is further reduced, and the high-strength steel is one of main materials for reducing the automobile weight. In order to improve the strength of the advanced high-strength steel, a plurality of alloy elements are introduced, and the weldability of the steel for automobiles is seriously influenced. The method for evaluating the weldability of the steel material widely applied at present is mainly a carbon equivalent method, namely, the method for evaluating the weldability of the steel grade by using the sum of the carbon content in the steel and the carbon content equivalent to other alloy elements. The international society for welding (IIW) uses the formula for carbon equivalent as follows:

CE_IIW＝C+(Mn/6)+(Cr+Mo+V)/5+(Ni+Cu)/15(wt.％) (1)

when the above carbon equivalent CE_IIWA value of less than 0.4%, the weldability of the steel grade is considered to be good, when the CE of the steel grade is considered to be good_IIWThe value is between 0.4% and 0.6%, and the general steel does not have good weldability.

In the connection welding of automobile parts, resistance spot welding is one of the most widely used techniques. Three failure modes of Interface Fracture (IF), Partial Interface Fracture (PIF) and nugget pull-out fracture (PF) usually occur in a weld nugget formed by spot welding in a mechanical test, wherein the interface fracture usually corresponds to a lower load peak value, IF only the interface fracture occurs in the spot welding of a steel type, the spot welding performance of the steel type is poor, and IF the nugget pull-out fracture corresponds to a high load peak value, the spot welding performance of the steel type represented by the nugget pull-out fracture in the spot welding is excellent. When the alloy content in the automobile steel is small, the Carbon Equivalent (CE) is_IIW) The value is generally less than 0.4%, the fracture of the spot welding nugget shows that the nugget is pulled out and fractured, and the welding performance is good; however, when the content of alloy in the advanced high-strength steel is increased, the Carbon Equivalent (CE) is increased_IIW) The value is between 0.4 and 0.6 percent, the fracture of the spot welding nugget of the steel grade presents a mixed mode of interface fracture and nugget pull-out fracture, and carbon equivalent is used at the moment(CE_IIW) The value cannot clearly distinguish the welding performance of the advanced high-strength steel spot welding, so a new calculation model is needed to prejudge and evaluate the weldability of the advanced high-strength steel spot welding containing more alloy elements.

Disclosure of Invention

The present invention aims to overcome the above Carbon Equivalent (CE)_IIW) The method can accurately predict and evaluate the weldability of the advanced high-strength steel spot welding containing more alloy elements.

In order to achieve the purpose, the advanced prejudgment and evaluation method for the spot weldability of the high-strength steel is based on the solidification shrinkage principle of a spot welding nugget and comprises the following steps:

s1: establishing a database describing the quantitative influence of a single alloy element on the solidification shrinkage of the steel;

s2: further establishing a multivariate linear model for describing the quantitative relation between the content of all alloy elements in the steel and the solidification shrinkage rate of the steel based on the database;

s3: determining each coefficient in the multivariate linear model to obtain a complete multivariate linear model and checking errors;

s4: and determining a steel solidification shrinkage rate judgment threshold value for pre-judging the spot welding weldability by using the complete multivariate linear model, and judging the spot welding weldability.

Further, if a partial interface fracture form between the interface fracture and the nugget pull-out fracture occurs in the spot welding of a certain steel grade, the steel solidification shrinkage rate calculated by the complete multivariate linear model of the steel grade is used as a judgment threshold.

Further, when the solidification shrinkage rate of the steel grade to be detected, which is calculated through the complete multivariate linear model, is larger than or equal to a judgment threshold value, the spot welding weldability of the steel grade to be detected is poor;

and when the solidification shrinkage rate of the steel grade to be detected, which is calculated by the complete multivariate linear model, is smaller than a judgment threshold value, the spot welding weldability of the steel grade to be detected is considered to be excellent.

Further, the S2 specifically includes: establishing a multivariate linear model to determine the relation between the content of all alloy elements and the solidification shrinkage of steel, wherein the basic expression of the multivariate linear model is as follows:

wherein, Delta l is the solidification shrinkage rate of steel and the unit is%; alpha is alpha₀Is a constant term; n is the number of the types of the alloy elements; alpha is alpha_iCoefficient of the content of the ith alloying element; x is the number of_iIs the mass percentage of the ith alloy element; i is a positive integer.

Further, the S3 specifically includes: solving by utilizing multivariate linear regression, fitting to obtain each coefficient in the multivariate linear model, and checking errors to obtain a complete multivariate linear model, wherein the complete multivariate linear model can be expressed as:

Δl＝1.259+0.301W_C+0.0183W_Mn-0.0359W_Cr-0.0153W_Ni-0.00556W_Mo+0.0354W_Si+0.0168W_Cu-0.118W_V

wherein the coefficients of the formula can be varied within an error range, W_C、W_Mn、W_Cr、W_Ni、W_Mo、W_Si、W_Cu、W_VAre the mass percentages of alloy elements C, Mn, Cr, Ni, Mo, Si, Cu and V respectively.

Further, the checking the error specifically includes: and calculating the steel solidification shrinkage rate of the steel grade by using the complete multivariate linear model, and determining that the complete multivariate linear model is accurate when the error between the calculated steel solidification shrinkage rate and the actual steel solidification shrinkage rate of the steel grade is less than 3%.

Further, the alloy elements at least comprise one or more of C, Mn, Cr, Ni, Mo, Si, Cu and V.

Further, the judgment threshold value takes any one value of 1.35% to 1.43%.

Further, the determination threshold value can fluctuate within a range of plus or minus 3%.

Further, the judgment threshold is 1.39%.

Further, the S1 specifically includes:

s11: obtaining the quantitative influence of a single alloy element on the solidification shrinkage of the steel by adopting an experimental method, a literature data extraction method or a software calculation method;

s12: a database was established describing the quantitative effect of individual alloying elements on steel solidification shrinkage.

Compared with the prior art, the advanced prejudgment and evaluation method for the spot weldability of the high-strength steel has the following advantages:

the advanced prejudgment and evaluation method for the spot weldability of the high-strength steel is established on the basis of a new model for calculating the solidification shrinkage rate delta l (solidification linear shrinkage) in the spot welding process based on steel components, and for steel with the alloy content range which is much larger than the content commonly used in a carbon equivalent model, the delta l value of the steel can be calculated by using a formula (3) through components, when the delta l is higher than or equal to a threshold value, the interface fracture mode of a spot welding nugget can be prejudged, and the spot welding performance is poor; when Δ l is lower than the threshold value, the nugget pull-out fracture mode of the spot welding nugget can be predicted, and the spot welding performance is excellent. Based on a clear solidification shrinkage physical background, in the spot welding nugget solidification shrinkage process, when Δ l is larger than or equal to a threshold value, namely, steel solidification shrinkage is too large and cannot be completely compensated by electrode pressure during welding, a plurality of shrinkage gaps are left at the junction of upper and lower dendrites of the nugget, the bonding force of the nugget is weakened, and crack grains crack along the shrinkage gaps in a tensile test, so that an interface fracture mode appears, as shown in fig. 3. Compared with an empirically summarized carbon equivalent formula evaluation method, the Delta l calculation model can more accurately and reliably evaluate and predict the weldability of steel grades, particularly high-alloy steel.

Drawings

The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the invention and not to limit the invention.

FIG. 1 is a flow chart of the present invention;

FIG. 2 is a data diagram and a verification diagram for establishing a Δ l calculation model according to the present invention;

FIG. 3 is a graph of shrinkage gaps (a-b) resulting from solidification shrinkage of a nugget when Δ l is too large according to the present invention and a graph of interfacial fracture (c-d) resulting from a tensile test;

FIG. 4 is a comparison of the model of the present invention and carbon equivalent in predicting the manner of spot weld failure and weldability, wherein (a) is a conventional carbon equivalent discriminant map and (b) is a discriminant map using the Δ l calculation model of the present invention.

Detailed Description

Reference will now be made in detail to the exemplary embodiments, examples of which are illustrated in the accompanying drawings. When the following description refers to the accompanying drawings, like numbers in different drawings represent the same or similar elements unless otherwise indicated. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present invention. Rather, they are merely examples of apparatus and methods consistent with certain aspects of the invention, as detailed in the appended claims.

The terms first, second and the like in the description and in the claims of the present invention are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It is to be understood that the data so used is interchangeable under appropriate circumstances such that the embodiments of the invention described herein are, for example, capable of operation in sequences other than those illustrated or otherwise described herein. Furthermore, the terms "comprises," "comprising," and "having," and any variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, system, article, or apparatus that comprises a list of steps or elements is not necessarily limited to those steps or elements expressly listed, but may include other steps or elements not expressly listed or inherent to such process, method, article, or apparatus.

A plurality, including two or more; and/or, it should be understood that, as used herein, the term "and/or" is merely one type of association that describes an associated object, meaning that three types of relationships may exist. For example, a and/or B, may represent: a exists alone, A and B exist simultaneously, and B exists alone.

Firstly, the spot welding mechanical test fracture form of steel grades with different components is obtained through resistance spot welding, the weldability evaluation is carried out according to the fracture form, the weldability evaluation of the steel grades with the forms of Interface Fracture (IF) and Partial Interface Fracture (PIF) is poor, the weldability evaluation of the steel grades with the forms of nugget extraction fracture (PF) is good, the results and the steel grade components corresponding to the steel grades are listed in a table 2, and then the CE of the steel grades is calculated according to the steel grade components through a carbon equivalent formula adopted by the international society for welding (IIW) as shown in the formula (1)_IIWAlso shown in Table 2.

Then, the carbon equivalent CE calculated and evaluated in the point welding mechanical test fracture form and weldability of Table 2_IIWBy comparison, it can be found that when the carbon equivalent CE is small_IIWThe value is less than 0.4%, PF fracture occurs, and the welding performance of steel grades is good, such as steel grades DQSK, HSLA, MS1200, MS1400 and the like; when carbon equivalent of CE_IIWThe values lie in the range from 0.4% to 0.6%, the spot weld failure corresponding to a mixed failure mode of PF and IF, e.g. CE of steel grades DP600-1/2/3, DP980, 590R, 22MnB5_IIWThe value is 0.4% -0.6%, the fracture is PF fracture, and the welding performance is good, while the TRIP800 and QP980-1 of the steel grades are also 0.4% -0.6%, the fracture is IF fracture, and the welding performance is poor, namely the IF/PF fracture of certain steel grades with higher carbon equivalent values cannot be distinguished by using the value of the carbon equivalent, and the good and poor welding performance of the steel grades cannot be distinguished. When the carbon equivalent of steel grade CE_IIWWhen the value is higher than 0.6%, PF fracture occurs in the steel CP1100, and the welding performance of the steel is good; IF fracture occurs in QP980-2 and 7Mn steels, etc., and the weldability of steel grades is poor, so that it is not possible to effectively evaluate the quality of spot weldability of steel grades predicted by using the carbon equivalent even for steel grades having a high alloy content (i.e., high carbon equivalent).

At this time, the weldability of the steel grades is evaluated by adopting the newly invented advanced prejudgment evaluation method of the spot weldability of the high-strength steel, and compared with the conventional carbon equivalent method. The new method is based on a new model for calculating the total solidification shrinkage rate delta l in the welding process based on steel type components, and the calculation flow is as follows, as shown in figure 1:

1) establishing a database describing the quantitative influence of the single alloying element on the solidification shrinkage (Δ l) of the steel, and obtaining the influence of the single alloying element on the solidification shrinkage (Δ l) of the steel by using an experimental method or a literature data extraction method or a software calculation method, wherein the result calculated by using a jmatpro12.4 software plots data points as shown in a-c in fig. 2, wherein about 80 groups of data points are included, and the eight most common alloying elements in the steel and all the alloying elements in the CE formula (1) are related.

2) Establishing a description of the contents (x) of all alloying elements in the steel_i) A multivariate linear model of the quantitative relationship to solidification shrinkage (Δ l) is shown by the following formula:

in the formula of alpha₀Is a constant term; n is the number of the ith element species; alpha is alpha_iIs a coefficient of the content of the ith alloying element, and the unit of delta l is percent.

3) The values of the coefficients in the multivariate linear model were determined using a multiple linear regression optimization fit, see Table 1, for the correlation coefficient R²Above 0.9, significance factors F and P values were much less than 0.05, indicating that the multiple linear regression analysis was efficient and sufficiently accurate. Equation (2) can be expressed as follows from the values of the parameters in table 1:

Δl＝1.259+0.301W_C+0.0183W_Mn-0.0359W_Cr-0.0153W_Ni-0.00556W_Mo+0.0354W_Si+0.0168W_Cu-0.118W_V (3)

in the formula, W_C、W_Mn、W_Cr、W_Ni、W_Mo、W_Si、W_Cu、W_VAre the mass percentages of alloy elements C, Mn, Cr, Ni, Mo, Si, Cu and V respectively.

TABLE 1 multiple Linear regression analysis results

4) Error checking, calculating the Δ l values for all composition points as shown in a-c in FIG. 2 from the chemical composition using equation (3). The calculated result is then compared to the Δ l original value, as shown in fig. 2 d. It can be clearly seen that the error between them is less than 3%, indicating that simple equation (3) can predict the solidification shrinkage with high efficiency and convenience and with sufficient accuracy.

TABLE 2 carbon equivalent values CE of different steel compositions_IIWDelta l value, spot weld failure mode and weldability evaluation

5) The threshold value for evaluating the spot weldability was determined, and the 5Mn steel spot welding having the composition of 0.1C to 5Mn exhibited a Partial Interfacial Fracture (PIF) form between the interfacial fracture and nugget extraction fracture, as shown in table 2, which was used as a critical condition for evaluating the quality of the spot weldability, i.e., when the Δ l value calculated by the formula (3) using the composition of the 5Mn steel was 1.39% or more as the threshold value for evaluating the spot weldability, it was found from the results of table 2 that when the Δ l value calculated by the formula (3) for the other steel species was 1.39% or more, it was judged that the spot weldability of this steel species was poor, interfacial fracture occurred in the mechanical test of the nugget, and when the Δ l value calculated by the formula (3) for the other steel species was less than 1.39%, it was judged that the spot weldability of this steel species was excellent, and ideal nugget extraction fracture occurred in the mechanical test of the nugget. The delta l calculation model is based on a clear solidification shrinkage physical background, when delta l is larger than or equal to a threshold value in the spot welding nugget solidification shrinkage process, namely, the steel solidification shrinkage is too large and cannot be completely compensated by electrode pressure during welding, so that a plurality of shrinkage gaps are left on a nugget central line (an upper dendrite and a lower dendrite boundary), as shown in fig. 3a-b, the bonding force of the nugget is weakened, crack grains crack along the shrinkage gaps in a tensile test, and an interface fracture mode appears, as shown in fig. 3 c-d.

Then, the Δ l values of the steel grades were calculated using the same steel grade composition used in the carbon equivalent evaluation method in Table 2, and the results are also shown in Table 2, from which it can be seen that when the Δ l value of the steel grade is less than 1.39%, ideal nugget Pullout Fracture (PF) occurs in the spot welding mechanical test, and the spot weldability of this steel grade is excellent, such as DP600/780/980, MS1200/1400, 22MnB5, etc.; when the Δ l value of the steel grade is 1.39% or more, Interfacial Fracture (IF) occurs in spot welding, and spot weldability is poor, such as TRIP800, QP980, 7Mn steel, and the like. The comparison result of the model and the carbon equivalent in the invention in table 2 in the aspect of prejudging and evaluating the spot welding fracture mode and weldability is shown in fig. 4, and it can be seen more clearly that in the carbon equivalent judging graph shown in fig. 4a, IF and PF appear corresponding to the same carbon equivalent value interval (0.4-0.6); in the model discrimination chart of the present invention as shown in fig. 4b, IF and PF can be clearly distinguished from each other by using a value of Δ l of 1.39% as a threshold for evaluating the spot weldability, i.e., the Δ l model can more accurately and reliably distinguish and evaluate the weldability of steel grades, particularly high alloy steels, than the carbon equivalent formula evaluation method summarized empirically. Since the Δ l error obtained during the error check is within 3%, the threshold value may fluctuate within 3%, and the coefficient of equation (3) varying within 3% is considered to be an acceptable equation model.

Although the present invention has been described in detail with reference to specific embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the spirit and scope of the invention as defined in the appended claims.