CN105945248B - A kind of creep bending creep straightening method of straight mold type caster - Google Patents

Abstract

The invention discloses a straight arc type continuous casting machine creep bending creep straightening method, the content of which is: determine the yield stress σ _s of the continuous casting slab material in the temperature range from the bending section to the straightening section, select the continuous casting slab The constant stress σ of the high-temperature creep tensile test of the material, so that σ<σ _s , determines the minimum creep strain rate of the continuous casting slab material at a certain temperature and lower than the yield stress σ _s ; according to the thickness of the continuous casting slab D and the allowable strain ε ₀ , according to the casting machine height, metallurgical length and casting speed process parameters of the straight arc type continuous casting machine, the curvature change rate of the bending section is higher than that of the straightening section, and the basic arc section is shortened The arc length increases the creep time of the continuous casting slab, so that the continuous casting slab has sufficient time for creep deformation during the bending and straightening process; select the appropriate model curve to make the continuous casting slab When the strain rate is lower than the minimum creep strain rate determined by the test, creep deformation occurs in a state lower than the yield stress, and finally the creep bending and creep straightening of the continuous casting slab are realized.

Description

A Creep Bending Creep Straightening Method for Straight Arc Continuous Casting Machine

technical field

The invention belongs to the field of continuous steel casting, in particular to a creep bending creep straightening method of a straight arc continuous casting machine.

Background technique

Bending and straightening technology of continuous casting slab is a key technology in continuous casting of iron and steel. The bending and straightening process of the straight arc continuous casting machine refers to the process that the continuous casting slab bends from vertical under the action of external torque, and then the continuous casting slab with a certain radius of curvature becomes horizontal through the straightening torque. With the development of today's high-efficiency continuous casting technology, the bending and straightening methods of continuous casting slabs have gradually developed from single-point bending and single-point straightening to multi-point bending, multi-point straightening, progressive bending, progressive straightening, continuous bending and Continuous straightening etc. Bending and straightening technology of continuous casting slab is very important to avoid cracks, improve slab quality and production efficiency.

At present, straight arc continuous casting machines are widely used in China, and most of them adopt multi-point bending and multi-point straightening technology. In recent years, some newly built continuous casting machines generally adopt continuous bending and continuous straightening technology. It is considered that the bending and straightening deformation of the continuous casting slab must meet the plastic yield condition, that is, the bending and straightening moment is greater than the plastic bending moment, and the bending and straightening stress is greater than the yield stress, but the plastic deformation during the bending and straightening process may cause cracks and other quality problems in the slab. defect. When designing the bending section of the straight arc type continuous casting machine, the straightening section is mostly used as the basis, and the bending is considered as the reverse situation of straightening. The deformation principle used in the bending section and the straightening section is the same, but because the continuous casting billet The temperature in the straightening section is obviously higher than that in the straightening section, and the existing design method does not give full play to the creep performance of the material. In addition, most straight-arc continuous casting machines have a very long arc section, which will not deform the continuous casting slab, and the arc length of the bending section and straightening section is relatively short, resulting in the continuous casting slab The strain rate in the deformation zone is high, which increases the probability of crack occurrence.

Therefore, a creep bending creep straightening method for straight arc continuous casting machines is proposed, which relies on the high temperature creep deformation of the continuous casting slab material, reasonably distributes and prolongs the arc length of the bending section and the arc length of the straightening section, so that The continuous casting slab increases the creep deformation time in the roller table of the whole model, and the creep deformation occurs fully in the bending section and the straightening section without plastic deformation, which can reduce the bending straightening moment and bending straightening stress, thereby reducing the occurrence of cracks risk and improve the quality of the slab.

Contents of the invention

The invention provides a creep bending creep straightening method for a straight arc continuous casting machine. The technical problem to be solved is: according to the high-temperature creep characteristics of the continuous casting billet material, the continuous casting billet deforms quickly in the bending section, and the continuous casting billet deforms quickly in the bending section. The straightening section deforms slowly, reasonably distributes and prolongs the arc length of the bending section and the straightening section, and shortens the arc length of the basic arc section, so that the stress of the billet during bending and straightening deformation is less than the yield stress, and no plastic deformation occurs. Relying on creep deformation for creep bending and creep straightening can avoid the generation of cracks and improve the quality of cast slab.

In order to solve the above problems, the technical solution of the present invention is achieved in the following way: a creep bending creep straightening method for a straight arc type continuous casting machine, the content of the method includes the following steps:

1. Determine the yield stress σ _s of the continuous casting slab material in the temperature range from the bending section to the straightening section, select the constant stress σ of the continuous casting slab material for high temperature creep tensile test, make σ<σ _s , and then determine the continuous casting slab material The minimum creep strain rate of a material at a certain temperature and below the yield stress σ _s

2. According to the thickness D of the continuous casting slab and the allowable strain ε ₀ , the formula Determine the basic arc radius R ₀ of the continuous casting machine, and design a reasonable bending section curve and straightening section with low curvature change rate according to the caster height, metallurgical length and casting speed process parameters of the straight arc continuous casting machine Curve, give full play to the high temperature creep performance of continuous casting slab materials, reasonably distribute the curvature and arc length of the bending section and straightening section, make the curvature change rate of the bending section higher than the straightening section curvature change rate, shorten the arc length of the basic arc section, Increase the creep time of the continuous casting slab, so that the continuous casting slab has sufficient time for creep deformation during the bending and straightening process;

3. Select the appropriate model curve so that the strain rate of the continuous casting slab in the bending section and straightening section is lower than the minimum creep strain rate determined by the test At this time, the stress on the continuous casting slab during the bending and straightening deformation process is lower than the yield stress, and creep deformation occurs in a state lower than the yield stress, and no plastic deformation occurs during the entire bending and straightening process, and finally the creep of the continuous casting slab is realized. Bending and creep straightening.

Compared with the prior art, the present invention has the following advantages:

(1) During the bending and straightening deformation process, the continuous casting slab relies on creep deformation and does not undergo plastic deformation. The bending and straightening stress is always lower than the yield stress, which reduces the possibility of cracks;

(2) The arc length of the bending section and the straightening section are extended, and the arc length of the basic arc section is greatly shortened, so that the creep deformation time of the continuous casting slab is increased in the entire roll row, and the rolls of the bending section and the straightening section are The rows are arranged with different curvature change rates, making full use of the high-temperature creep properties of the material;

(3) The arc length of the bending section and the arc length of the straightening section of the straight arc continuous casting machine creep bending creep straightening method make the strain rate of the continuous casting slab lower, which is beneficial to improve the quality of the continuous casting slab, and is well adapted to continuous casting High billet drawing speed.

Description of drawings

Figure 1 is a graph of creep strain and creep strain rate at 1200°C;

Figure 2 is a curve diagram of the traditional five-point bending and five-point straightening technology model;

Fig. 3 is a curve diagram of creep bending creep straightening technology models;

Figure 4 is a comparison chart of strain rate and creep strain rate.

detailed description

The technical solution of the present invention will be further specifically described below in conjunction with the accompanying drawings. The described embodiments are only some of the embodiments of the invention.

First of all, Q345C is selected as the material of the continuous casting slab. Since the cracks of the continuous casting slab due to bending and straightening are all inside, the surface temperature of the continuous casting slab during the bending and straightening process in actual production is above 1000 ° C, so 1200 ° C is selected as the refer to. The tensile test was carried out at 1200°C with a constant strain rate of 0.01S ^-1 , and the yield stress at this temperature was measured to be 16.20MPa, and then the tensile test was carried out at 1200°C with a constant stress of 14MPa, and the creep of the material at 1200°C was measured. The deformation curve and creep rate curve, Fig. 1 shows the creep strain and creep strain rate diagram at 1200°C. From Fig. 1, it can be seen that the minimum creep rate of the material at 1200°C is 7.45×10 ^-5 S ^{- 1} .

Figure 2 shows the curve diagram of the traditional five-point bending and five-point straightening technology model. Refer to the R9300mm five-point bending and five-point straightening model curve in Figure 2. The casting speed is 1.5m/min, the height of the continuous casting machine is 12305.55mm, the metallurgical length is 35.8m, the arc length of the vertical section is 1465mm, the arc length of the CD section of the bending section is 1030mm, the arc length of the BC section of the basic arc section is 13300mm, and the arc length of the AB section of the straightening section is 1520mm. For the continuous casting slab with a thickness of 230mm, the allowable strain ε0 is 1.5% to ₂ %. If 1.5% is taken, the basic arc radius R0 should be greater than _7666mm , and the basic arc radius R0 should be _8000mm . Figure 3 shows the curve diagram of creep bending and creep straightening technology models. The curve of the new model whose curvature changes sinusoidally in Figure 3 is selected. The arc length of the straight section AB is 10000mm, and the relational equation of the curve relative to the arc length is:

In the formula, L is the total arc length of the bending section or the straightening section. According to the relationship between the rotation angle and the curvature, the relationship equation between the curve rotation angle and the arc length is obtained as:

The expression of the curve parameter equation of the straightening section AB in the XOY coordinate system is:

The expression of the curve parameter equation of the curved section CD in the X'O'Y' coordinate system is:

Where s is the arc length of the curve, mm.

From the slope tanα(s), it can be calculated that the slope of the end point of the bending section is 0.7393 and the slope of the starting point of the straightening section is 1.0210. Since the initial coordinate systems of the two curves are different in design, the coordinates are unified by translation and rotation of the coordinate axes The slope of the end point of the lower bending section is 1.3526, and the bending section and the straightening section cannot be smoothly connected. The transition arc section is selected in the middle, the radius R ₀ is 8000mm, the starting central angle is -0.7393rad, and the ending central angle is -0.9794rad. The transition arc section can connect the curve of the straightening section and the curve of the bending section smoothly without abrupt changes. According to the model curve in Figure 3, the bending straightening strain of the continuous casting slab is calculated. Since the continuous casting slab is prone to cracks under tension on the outer arc side during the bending process, the position of the neutral layer at 1200 °C inside the outer arc side of the continuous casting slab is taken. Calculate the strain; the continuous casting slab is prone to cracks when the inner arc side is pulled during the straightening process, and the strain rate is calculated at the position where the neutral layer is biased toward the inner arc side of the continuous casting slab at 1200 °C. The comparison between the strain rate at this position and the minimum creep strain rate is shown in Fig. 4. It can be seen from Fig. 4 that the roller row arranged according to the model curve shown in Fig. 3 makes the strain rate of the continuous casting slab lower, and The changing trend conforms to the sinusoidal law. As shown in Figure 4, the maximum strain rate in the bending section of the new model curve is 7.3×10 ^-5 S ^-1 , and the maximum strain rate in the straightening section is 3.7×10 ^-5 S ^-1 . It can be seen that the new model curve The continuous casting slab deforms faster in the bending section than in the straightening section, which is also in line with the law of high temperature and fast creep of the material, which can give full play to the high temperature creep performance of the continuous casting slab material, and the maximum value of the strain rate is smaller than the minimum creep rate. With variable strain rate, the continuous casting slab has achieved creep bending and creep straightening during the whole operation process, which proves the feasibility of this method.

Claims (1)

1. a kind of creep bending creep straightening method of straight mold type caster, it is characterised in that：This method content includes following step Suddenly：

(1) yield stress σ of the continuous casting billet material in bending section to straightening section temperature range is determined_s, choose continuous casting billet material and carry out height The constant stress σ of warm creep tension test, makes σ<σ_s, it is then determined that continuous casting billet material is in a certain temperature and less than yield stress σ_sFeelings Minimized creep strain rate under condition

(2) according to thickness of strand D and permissible ε₀, by formulaDetermine the basic arc radius R of conticaster₀, Low curvature is reasonably had according to the casting machine of straight mold type caster type height, metallurgical length and casting speed process parameters design The bending section curve and straightening section curve of rate of change, give full play to continuous casting billet material at high temperature croop property, reasonable distribution bending section With the curvature and arc length of straightening section, bending section curvature variation is higher than straightening section curvature variation, shorten basic arc section arc It is long, increase continuous casting billet creep time, continuous casting billet is being bent and is being had the sufficient time to carry out the deformation of creep in straightening process；

(3) suitable type curve is chosen, continuous casting billet is determined most less than experiment in the strain rate of bending section and straightening section Small creep strain speedNow continuous casting billet suffered stress in bending straightening deformation process is less than yield stress, with less than in the wrong The deformation of creep occurs for the state for taking stress, and whole bending straightening process is not plastically deformed, and finally realizes the creep of continuous casting billet Bending and creep straightening.