阅读说明：本技术 一种焊接热循环冷却过程中相变温度的测定方法 (Method for measuring phase transition temperature in welding thermal cycle cooling process ) 是由 赵宝纯 王佳骥 黄磊 王英海 马惠霞 甄文杰 于 2021-08-19 设计创作，主要内容包括：本发明涉及一种焊接热循环冷却过程中相变温度的测定方法,包括：1)根据实际焊接工艺过程及实际焊接过程的温度曲线,结合材料的各项参数确定焊接热循环模型；2)进行焊接热循环工艺模拟,采集试验材料的温度和膨胀量,并绘制膨胀量与时间的关系曲线；3)得到假定材料在冷却过程中未发生相变时,随着温度的降低体积逐渐减小的变化曲线；4)对比相变前膨胀曲线与膨胀量与时间关系曲线曲线,偏折点即为相变开始点；5)对比相变后膨胀曲线与膨胀量与时间关系曲线,偏折点即为相变结束点。本发明能够准确测定钢铁材料在焊接冷却过程中的相变温度,为掌握钢铁材料在焊接过程中的相变特征参数,优化焊接工艺以及研发新钢种提供基础。(The invention relates to a method for measuring phase change temperature in a welding heat circulation cooling process, which comprises the following steps: 1) determining a welding thermal cycle model by combining various parameters of materials according to an actual welding technological process and a temperature curve of the actual welding process; 2) carrying out welding thermal cycle process simulation, collecting the temperature and the expansion amount of a test material, and drawing a relation curve of the expansion amount and time; 3) obtaining a change curve that the volume is gradually reduced along with the reduction of the temperature when the material is not subjected to phase change in the cooling process; 4) comparing an expansion curve before phase change with a curve of the relation between the expansion amount and time, wherein a deflection point is a phase change starting point; 5) and comparing the expansion curve after the phase change with the expansion amount-time relation curve, wherein the deflection point is the phase change end point. The invention can accurately measure the phase transition temperature of the steel material in the welding and cooling process, and provides a basis for mastering the phase transition characteristic parameters of the steel material in the welding process, optimizing the welding process and researching and developing new steel types.)

1. A method for measuring phase transition temperature in a welding heat circulation cooling process is characterized by comprising the following steps:

1) according to the temperature curve of the actual welding process and the actual welding process, determining a welding thermal cycle model by combining various parameters of the material, including density, specific heat capacity, thermal conductivity, welding energy input and preheating temperature, and expressing by a formula (1):

T_(y,t)＝f(A,B,C,…,t) (1)

wherein T is time, T_(y,t)A, B, C … are constants associated with the process parameters and materials for the temperature after time t;

2) adopting the welding heat cycle model in the step 1) to carry out welding heat cycle process simulation, collecting the temperature and the expansion amount of the test material, and drawing a relation curve of the expansion amount and the time according to the collected data, wherein the relation of the two is expressed by a formula (2):

E_(D,t)＝g(t) (2)

in the formula, E_(D,t)Is the amount of swelling;

3) selecting N points (t) in the curve of the expansion amount and the time in the step 2)₁,g(t₁))，(t₂,g(t₂) …, these points are taken in the section of the curve before the phase change occurs; n is determined according to the number of constant parameters in the formula (1); substituting the coordinates of the N points into formula (3) and formula (4), respectively, obtains the following equation system:

g(t₁)＝f(A',B',C',…,t₁) (3)

g(t₂)＝f(A',B',C',…,t₂) (4)

……

solving the equation set to determine parameters A ', B ', C ' …; to obtain the formula (5)

E'_(D,t)＝f(A',B',C',…,t) (5)

The curve corresponding to equation (5) represents: a change curve that the volume is gradually reduced along with the reduction of the temperature when the material is not subjected to phase change in the cooling process; namely the calculated value of the expansion curve before phase change;

4) drawing a curve by the formula (5), and simultaneously drawing a curve of the relation between the expansion amount and the time corresponding to the formula (2); because N points on the 2 curves are the same, the parts of the 2 curves before phase change are overlapped; when phase change occurs, the expansion amount determined by the formula (2) does not change along with time according to the rule before phase change, and the expansion curve changes suddenly and deviates from the other curve; comparing 2 curves, determining the point where deflection begins to occur as the phase change starting point; then determining the temperature when the phase change occurs according to the temperature and the corresponding relation between the time and the expansion amount acquired in the step 2);

5) after the phase change is finished, the expansion amount shows the same change trend with the temperature along with the change of time; on the curve determined by the formula (2), selecting N points after the phase change is finished, repeating the step 3) and processing the coordinate values of the N points to obtain the formula (6):

E”_(D,t)＝f(A”,B”,C”,…,t) (6)

wherein, A ", B", C "… are constants;

the curve corresponding to the formula (6) is a calculated value of an expansion curve after phase change; and (3) finding the deflection point of the curve determined by the formula (2) and the curve determined by the formula (6), wherein the deflection point is the end point of the phase change.

Technical Field

The invention relates to the technical field of heat treatment, in particular to a method for measuring phase change temperature in a welding heat circulating cooling process.

Background

The phase change research is the basis of researching and developing steel materials and is also the key of optimizing a material hot working process, and the tissue with excellent performance can be obtained through process improvement only by comprehensively mastering and researching characteristic parameters of phase change of steel grades in the continuous cooling process and the isothermal process. One of the most common methods for measuring solid-state phase change in steel is a thermal expansion method, which determines a phase change point by measuring a volume change signal when phase change occurs, and is mainly used for measuring solid-state phase change in continuous cooling, heating and isothermal processes.

At present, the phase transition characteristics of steel materials are researched, the steel materials are generally heated to a certain temperature at a constant heating speed, the temperature is kept for a period of time at the temperature, then the steel materials are cooled at a constant cooling speed, the expansion amount at different cooling speeds is obtained to obtain an expansion curve, and the phase transition point temperatures at different cooling speeds are determined by utilizing a tangent method.

The Chinese patent application with the application number of CN201710464662.8 discloses a method for measuring the SH-CCT curve of the pipeline steel with large deformation resistance, which adopts the method. However, not all heating or cooling rates for heating and continuous cooling processes are constant; for example, in the cooling section of the welding thermal cycle process curve, the temperature has an exponential decay trend with time, that is, the cooling speed changes with the change of time in the cooling process, and researchers build a corresponding welding thermal cycle model based on the characteristics of the actual welding process. Because the cooling curve during welding shows the variation trend of exponential decay, the expansion curve is promoted to show a similar variation trend; in this case, it is difficult to measure the phase transition temperature by analyzing the obtained expansion curve by a tangent method.

In summary, it is necessary to develop a method suitable for determining the transformation temperature during the welding thermal cycle cooling process.

Disclosure of Invention

The invention provides a method for measuring the phase transition temperature in the welding heat cycle cooling process, which can accurately measure the phase transition temperature of a steel material in the welding cooling process and provides a basis for mastering the phase transition characteristic parameters of the steel material in the welding process, optimizing the welding process and researching and developing new steel grades.

In order to achieve the purpose, the invention adopts the following technical scheme:

a method for measuring phase transition temperature in a welding heat circulation cooling process comprises the following steps:

1) according to the temperature curve of the actual welding process and the actual welding process, determining a welding thermal cycle model by combining various parameters of the material, including density, specific heat capacity, thermal conductivity, welding energy input and preheating temperature, and expressing by a formula (1):

T_(y,t)＝f(A,B,C,…,t) (1)

wherein T is time, T_(y,t)A, B, C … are constants associated with the process parameters and materials for the temperature after time t;

2) adopting the welding heat cycle model in the step 1) to carry out welding heat cycle process simulation, collecting the temperature and the expansion amount of the test material, drawing a relation curve of the expansion amount and the time according to the collected data, wherein the relation of the expansion amount and the time is expressed by a formula (2):

E_(D,t)＝g(t) (2)

in the formula, E_(D,t)Is the amount of swelling;

3) selecting N points (t) in the curve of the expansion amount and the time in the step 2)₁,g(t₁))，(t₂,g(t₂) …, these points are taken in the section of the curve before the phase change occurs; n is determined according to the number of constant parameters in the formula (1); substituting the coordinates of the N points into formula (3) and formula (4), respectively, obtains the following equation system:

g(t₁)＝f(A',B',C',…,t₁) (3)

g(t₂)＝f(A',B',C',…,t₂) (4)

……

solving the equation set to determine parameters A ', B ', C ' …; to obtain the formula (5)

E'_(D,t)＝f(A',B',C',…,t) (5)

The curve corresponding to equation (5) represents: a change curve that the volume is gradually reduced along with the reduction of the temperature when the material is not subjected to phase change in the cooling process; namely the calculated value of the expansion curve before phase change;

4) drawing a curve by the formula (5), and simultaneously drawing a curve of the relation between the expansion amount and the time corresponding to the formula (2); because N points on the 2 curves are the same, the parts of the 2 curves before phase change are overlapped; when phase change occurs, the expansion amount determined by the formula (2) does not change along with time according to the rule before phase change, and the expansion curve changes suddenly and deviates from the other curve; comparing 2 curves, determining the point where deflection begins to occur as the phase change starting point; then determining the temperature when the phase change occurs according to the temperature and the corresponding relation between the time and the expansion amount acquired in the step 2);

5) after the phase change is finished, the expansion amount shows the same change trend with the temperature along with the change of time; on the curve determined by the formula (2), selecting N points after the phase change is finished, repeating the step 3) and processing the coordinate values of the N points to obtain the formula (6):

E”_(D,t)＝f(A”,B”,C”,…,t) (6)

wherein, A ", B", C "… are constants;

the curve corresponding to the formula (6) is a calculated value of an expansion curve after phase change; and (3) finding the deflection point of the curve determined by the formula (2) and the curve determined by the formula (6), wherein the deflection point is the end point of the phase change.

Compared with the prior art, the invention has the beneficial effects that:

according to the cooling characteristics of the welding heat cycle process, a model of the change of the expansion amount of the non-phase-change situation along with the time is constructed based on the welding heat cycle model, a corresponding curve is drawn, the curve is compared with the actually obtained change curve of the expansion amount along with the time, the moment of the phase change can be accurately determined, the moment corresponds to the temperature, the phase change temperature is accurately found, and the control of the phase change characteristic parameters of the steel material in the welding process is facilitated.

Drawings

FIG. 1 is a plot of the amount of expansion versus time during cooling of the material of example 1 of the present invention.

Fig. 2 is a schematic diagram illustrating the determination of the phase change point of the material in embodiment 1 of the present invention.

In fig. 2, 1 is a calculated expansion curve before phase transition; 2, calculating to obtain a post-phase-change expansion curve; 3 is a phase change end point; 4 is phase transition starting point; and 5 is the actual expansion curve.

FIG. 3 is a temperature profile of the material during cooling in example 1 of the present invention.

In fig. 3, 6 is a temperature point corresponding to the start of phase transition; and 7 is a temperature point corresponding to the end of the phase change.

Detailed Description

The invention relates to a method for measuring phase transition temperature in a welding heat circulation cooling process, which comprises the following steps:

1) according to the temperature curve of the actual welding process and the actual welding process, determining a welding thermal cycle model by combining various parameters of the material, including density, specific heat capacity, thermal conductivity, welding energy input and preheating temperature, and expressing by a formula (1):

T_(y,t)＝f(A,B,C,…,t) (1)

wherein T is time, T_(y,t)A, B, C … are constants associated with the process parameters and materials for the temperature after time t;

2) adopting the welding heat cycle model in the step 1) to carry out welding heat cycle process simulation, collecting the temperature and the expansion amount of the test material, drawing a relation curve of the expansion amount and the time according to the collected data, wherein the relation of the expansion amount and the time is expressed by a formula (2):

E_(D,t)＝g(t) (2)

in the formula, E_(D,t)Is the amount of swelling;

3) selecting N points (t) in the curve of the expansion amount and the time in the step 2)₁,g(t₁))，(t₂,g(t₂) …, these points are taken in the section of the curve before the phase change occurs; n is determined according to the number of constant parameters in the formula (1); substituting the coordinates of the N points into formula (3) and formula (4), respectively, obtains the following equation system:

g(t₁)＝f(A',B',C',…,t₁) (3)

g(t₂)＝f(A',B',C',…,t₂) (4)

……

solving the equation set to determine parameters A ', B ', C ' …; to obtain the formula (5)

E'_(D,t)＝f(A',B',C',…,t) (5)

The curve corresponding to equation (5) represents: a change curve that the volume is gradually reduced along with the reduction of the temperature when the material is not subjected to phase change in the cooling process; namely the calculated value of the expansion curve before phase change;

4) drawing a curve by the formula (5), and simultaneously drawing a curve of the relation between the expansion amount and the time corresponding to the formula (2); because N points on the 2 curves are the same, the parts of the 2 curves before phase change are overlapped; when phase change occurs, the expansion amount determined by the formula (2) does not change along with time according to the rule before phase change, and the expansion curve changes suddenly and deviates from the other curve; comparing 2 curves, determining the point where deflection begins to occur as the phase change starting point; then determining the temperature when the phase change occurs according to the temperature and the corresponding relation between the time and the expansion amount acquired in the step 2);

5) after the phase change is finished, the expansion amount shows the same change trend with the temperature along with the change of time; on the curve determined by the formula (2), selecting N points after the phase change is finished, repeating the step 3) and processing the coordinate values of the N points to obtain the formula (6):

E”_(D,t)＝f(A”,B”,C”,…,t) (6)

wherein, A ", B", C "… are constants;

the curve corresponding to the formula (6) is a calculated value of an expansion curve after phase change; and (3) finding the deflection point of the curve determined by the formula (2) and the curve determined by the formula (6), wherein the deflection point is the end point of the phase change.

In the step 1), the welding thermal cycle model adopts the existing corresponding model according to the actual welding process.

The following further describes embodiments of the present invention with reference to the accompanying drawings:

the following examples are carried out on the premise of the technical scheme of the invention, and detailed embodiments and specific operation processes are given, but the scope of the invention is not limited to the following examples.

[ example 1 ]

In this embodiment, the phase transition temperature in the welding thermal cycle cooling process is measured as follows:

1. the actual welding process is a two-dimensional heat conduction process, a two-dimensional Leekarlin model is selected, and the model is represented by the following formula:

wherein t is time in units of s; e is input linear energy, and the unit is J/cm; delta is the thickness of the plate in cm; rho is density in g/cm³(ii) a λ is thermal conductivity, in W/(cm ℃.); c is heat capacity, unit J/(g ℃.); r is the distance of a point from the arc centerline in cm.

Equation (7) can be simplified as:

in the formula (8), the first and second groups,

materials selected in this embodimentMaterial constant: the thickness delta of the sheet was 2cm, and the density rho was 6.7g/cm³The thermal conductivity λ was 0.29W/(cm ℃), and the heat capacity c was 1J/(g ℃).

When the input linear energy E is 150KJ/cm, A is 15980 and B is 53 through calculation.

2. And (3) carrying out a welding thermal cycle process simulation process by adopting the model represented by the formula (7), collecting the temperature and the expansion amount in the process, and drawing a relation curve of the expansion amount and the time according to the collected data, as shown in figure 1.

3. In the time-expansion curve plotted in step 2, two points were selected: (15, 0.432), (16, 0.437), the coordinates of these two points are respectively substituted into equation (8) to obtain:

A'＝0.841，B'＝-10.336；

a new equation is thus obtained, such as equation (9), which corresponds to a curve that is an expansion curve assuming that no phase change has taken place.

4. Drawing formula (9) in step 3 into a curve, such as curve 1 shown in fig. 2; i.e. a curve of change in volume that gradually decreases with decreasing temperature, assuming that the material does not undergo a phase change during cooling. And simultaneously, a curve of the expansion amount in the step 2 in relation to the time is also drawn, namely a curve 5 shown in figure 2. By comparing the curve 1 and the curve 5, the deflection point at which the deflection of the 2 curves starts can be determined as the phase transition starting point 4. Then, according to the corresponding relationship between the temperature, the time and the expansion amount collected in step 2, the temperature at which the phase change occurs, i.e., the temperature point at 6 in the curve of fig. 3, can be found out.

5. Finding out coordinates of the two points in the same way as the step 3 to obtain an expansion curve equation of which the corresponding curve is assumed to have no phase change, such as a curve 2 in fig. 2; it can be seen from fig. 2 that curves 2 and 5 have a deflection point, i.e. the end point 3 of the phase change, which corresponds to the temperature point at curve 7 in fig. 3, i.e. the end temperature of the phase change.

The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art should be considered to be within the technical scope of the present invention, and the technical solutions and the inventive concepts thereof according to the present invention should be equivalent or changed within the scope of the present invention.