JP2004082150A - Continuous casting method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method by which a cast block with good quality such as aluminum, copper and steel is efficiently, stably and continuously cast. <P>SOLUTION: A solidification stress model is constituted of a loading effect caused by solidification shrinkage strain and a temperature dependency of a flow stress, and a principal stress distribution of the cast block is calculated based on the above model and a cracking sensitivity index is calculated from the above principal stress distribution. When the above index lies in the range of value which is difficult to develop the solidification crack, the casting is continued as it is, and when the above index lies in the range of value which easily develops the solidification crack, the casting is performed while adjusting the casting condition so that the above index falls within in the range of value which is difficult to develop the solidification crack. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for efficiently and stably continuously casting an ingot of aluminum, copper, steel or the like with high quality.
[0002]
[Prior art]
Conventionally, when continuously casting aluminum, copper, steel, etc. by the DC method or the like, the casting conditions are varied by changing the ingot descent speed (drawing speed), pouring temperature, etc. based on past experience, and performing trials. It was decided by repeating mistakes.
[0003]
[Problems to be solved by the invention]
However, with such a method, it has been difficult to cast a high-quality ingot with good yield and stability.
For this reason, the present inventors have investigated and analyzed solidification cracks for the purpose of efficiently casting high quality ingots. (1) Solidification cracks (cracks during casting) are located in the solid-liquid coexistence region. (2) In the solid-liquid coexistence area, it was found that the crack susceptibility distribution could properly indicate the region where solidification cracking was more likely to occur than the main stress distribution, and was further examined. To complete the present invention.
An object of the present invention is to provide a method for continuously casting a high-quality ingot efficiently and stably without trial and error.
[0004]
[Means for Solving the Problems]
The present invention constructs a solidification stress model from the load effect due to solidification shrinkage strain and the temperature dependence of flow stress, calculates the main stress distribution of the ingot based on the model, and calculates the crack susceptibility index from the main stress distribution. Calculate, if the index falls into a numerical range in which solidification cracking is unlikely to occur, continue casting as it is, and if the index falls in a numerical range in which solidification cracking is likely to occur, the index is a numerical range in which solidification cracking is unlikely to occur. This is a continuous casting method characterized in that casting is performed while adjusting casting conditions so as to be as follows.
[0005]
BEST MODE FOR CARRYING OUT THE INVENTION
The present invention uses a mechanical property value and a thermal physical property value of a cast alloy to numerically simulate whether or not solidification cracks occur, and adjusts a preset casting condition based on a result of the simulation. This is a method of continuous casting.
According to the present invention, the location (region) of solidification cracking and crack propagation behavior can be predicted, and casting conditions are adjusted based on the prediction, so that a high-quality ingot can be obtained efficiently without trial and error. Can be In particular, the effect is great when applied to the casting of a new alloy.
[0006]
The procedure for implementing the present invention will be described below with reference to FIG.
(1) Enter the mechanical and thermal properties of the cast alloy and prepare a calculation system.
(2) The temperature distribution in the ingot is calculated by substituting the characteristic values and physical property values into the basic formula of the solidification temperature model.
(3) Calculate the stress distribution in the ingot by the basic equation of the solidification thermal stress model.
(4) Calculate the main stress distribution and the crack susceptibility distribution.
(5) The possibility of crack generation is evaluated from the calculation result of the magnitude of solidification crack sensitivity (crack sensitivity index).
(6) If there is a possibility of cracking, return to (1) and review the casting conditions. If there is no possibility of cracking, the casting is continued while performing the calculations from (2) to (4) and the evaluation of (5). During this time, a high quality ingot is cast.
[0007]
As for the solidification temperature model basic expression of the above (2), as shown in FIG. 2 (a), a general heat conduction equation taking latent heat release into consideration by the temperature recovery method is converted into a finite element by the Galerkin method, and the time is also reduced. Discrete by the Crank-Nicholson method to obtain a final finite element method equation. The boundary condition of aluminum DC casting simulates casting by increasing the descent speed for the system. FIG. 2B is an explanatory diagram of the ingot.
[0008]
As for the solidification thermal stress model of (3), as shown in FIG. 3, an elasto-plastic stress model based on the strain increment theory was adopted. By expressing it as a change, the former is calculated only for the solid phase region and the latter is calculated only for the solid-liquid coexisting region.
[0009]
In the present invention, in the formula based on the strain increment theory, the strain increment of heat shrinkage and solidification shrinkage, elasticity equation of hook, subsequent yield function, adaptation condition of plugger, definition of equivalent plastic strain, normal rule of plastic strain increment Are combined to obtain a constitutive equation that is the basis of the solidification stress model. Finally, using the principle of virtual work, a finite element formula of a rigidity equation for the contact displacement increment is finally obtained.
The load vector on the right side expresses the surface force, body force, elastic and plastic thermal strain load, elastic and plastic solidification shrinkage strain load, and apparent load due to temperature dependence of flow stress. I have.
[0010]
Surface cracks of ingots during solidification are hot cracks that progress from the starting point of the surface of the ingot to the inside of the ingot.To fundamentally prevent this surface cracking, first find the starting point of the crack, and then You need to find out the cause. In that case, the present invention can be used effectively.
[0011]
【Example】
Hereinafter, the present invention will be described specifically with reference to Examples.
(Example 1)
In order to prevent surface cracks running vertically on the rolling surface of the JIS-3004 aluminum alloy (Al-Mn alloy) ingot, the temperature distribution of the ingot was measured, and the stress distribution (equivalent to the vertical stress in the x direction) was measured. Stress) was calculated. FIG. 4 shows the results.
As is clear from FIG. 4, along the sump surface, which is a solid-liquid coexistence region, a high stress distribution region that can be a solidification crack initiation point is recognized, and in addition, a high stress distribution region is present in the already solidified ingot butt. Admitted.
[0012]
Next, a crack susceptibility distribution was calculated based on the stress distribution of Example 1. FIG. 5 shows the results. As is clear from FIG. 5, a high stress distribution region which can be a starting point of solidification cracking is clearly shown from the stress distribution diagram shown in FIG.
[0013]
When calculating the crack susceptibility index of the high stress distribution region, since it entered a numerical range in which solidification cracking is likely to occur, which was obtained in preliminary experiments, the casting conditions were set so that the index was in a numerical range in which solidification cracking was unlikely to occur. It was adjusted. That is, the pouring temperature was lowered and the secondary cooling capacity was increased. As a result, a high quality ingot without cracks could be cast stably.
[0014]
(Example 2)
It has been empirically found that surface cracking generally worsens as the pouring temperature increases. Here, this tendency was confirmed by the method of the present invention in the case of pouring temperatures of 720 ° C. and 680 ° C. using a JIS-3004 aluminum alloy ingot.
FIG. 6 shows the results. 6A is a temperature distribution diagram of the ingot, FIG. 6B is a vertical stress distribution diagram (width direction), and FIG. 6C is a crack susceptibility distribution diagram (width direction).
[0015]
The effect of the pouring temperature on the surface cracks was observed inside the ingot from the vertical stress distribution diagram shown in FIG. 6B, but was hardly observed in the surface layer of the ingot.
On the other hand, the crack susceptibility distribution diagram shown in FIG. 6 (c) clearly shows the difference even in the surface layer of the ingot, and clearly shows that the higher the pouring temperature, the easier the crack.
As described above, according to the method of the present invention, the location (region) where a crack occurs can be accurately predicted, so that the casting conditions can be properly adjusted.
[0016]
As shown in Fig. 7 (c) (right side), the crack susceptibility without considering the solidification strain is the crack susceptibility on the sump surface that controls the crack propagation when the crack initiation point is out of the solid-liquid coexistence region. Is not in a state of tensile stress, so that surface cracks cannot be expressed.
[0017]
Since commercially available analysis software expresses the crack susceptibility by the vertical stress distribution, the behavior of the surface crack cannot often be predicted correctly as in the present invention.
Also, regarding the model formula, since there are many heat treatment methods that incorporate solidification strain into thermal strain, it is impossible to predict hot crack propagation. That is, in the heat treatment method, tensile stress due to solidification strain cannot be concentratedly distributed in the solid-liquid coexistence region.
[0018]
Although the JIS-3004 aluminum alloy has been described in the above embodiments, the present invention can be applied to other aluminum alloys, pure aluminum, pure copper, copper alloys, steels, and the like, and similar effects can be obtained.
[0019]
【The invention's effect】
As described above, the present invention constructs a solidification stress model from the load effect due to solidification shrinkage strain and the temperature dependence of flow stress, calculates the main stress distribution of the ingot based on the model, Calculate the crack susceptibility index from the stress distribution, and when the index falls within a numerical range in which solidification cracking is likely to occur, the index is adjusted to a numerical range in which solidification cracking is unlikely to occur. In addition, appropriate casting conditions that do not cause solidification cracking can be efficiently and stably obtained, and have a remarkable industrial effect.
[Brief description of the drawings]
FIG. 1 is a flowchart showing an embodiment of the present invention.
2A is a basic equation of a solidification temperature model, and FIG. 2B is an explanatory diagram of an ingot.
FIG. 3 is a basic equation of a solidification thermal stress model.
FIG. 4 (a) is a temperature distribution diagram, (b) is a vertical stress distribution diagram, and (c) is an equivalent stress distribution diagram obtained by calculation. .
FIG. 5 (a) is a principal stress direction diagram, (b) is a main stress distribution diagram, (c) is a crack susceptibility distribution diagram obtained by calculation, and (b) and (c) are the left side of the ingot. The right side is the outside of the ingot.
FIG. 6 is a (a) temperature distribution diagram, (b) a vertical stress distribution diagram, and (c) a crack susceptibility distribution diagram in consideration of the solidification strain of the JIS-3004 aluminum alloy ingot. In the case of, the right side is a case where the pouring temperature is 680 ° C.
FIG. 7 is a diagram showing (a) a temperature distribution diagram, (b) a main stress distribution diagram, and (c) a crack susceptibility distribution diagram when the pouring temperature of the JIS-3004 aluminum alloy ingot is 720 ° C. When considering, the right side is a case where solidification strain is not considered.

Claims (1)

Construct a solidification stress model from the load effect due to solidification shrinkage strain and the temperature dependence of the flow stress, calculate the main stress distribution of the ingot based on the model, calculate the crack susceptibility index from the main stress distribution, When the index falls within the numerical range in which solidification cracking is unlikely to occur, the casting is continued as it is. A continuous casting method characterized by casting under adjusted conditions.

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