KR100222067B1 - Controlled rolling method of metal materials - Google Patents

Abstract

The present invention is a rolling process that can be applied to a rollable metal material capable of generating dynamic recrystallization (DRX) during high temperature processing, and in the hot rolling process by controlling the amount of deformation of the rolling pass to generate dynamic recrystallization in a specific pass. The present invention relates to a method for controlled rolling of an economical metal material which can reduce the rolling force of the and reduce the grain size, thereby making the process simple and excellent mechanical properties.

The controlled rolling method of the present invention is a rolling method of a metal material in which a rolling step is performed in a rolling pass consisting of a multi-stage rolling pass of a metal material in which dynamic recrystallization occurs during high-temperature processing, wherein the multistage rolling forming the rolling step is performed. It is a technical subject matter to perform rolling while giving the deformation amount exceeding the critical deformation amount required to generate dynamic recrystallization in any one or more rolling passes of a pass.

The metal material to which the present invention is applied may be any one of carbon steel, 304 stainless steel, and copper. In the present invention, rolling by applying a strain amount exceeding a critical strain amount in order to generate dynamic recrystallization may be performed at any of the initial and end stages of rolling. It can be done in one step, and the critical deformation amount for generating dynamic recrystallization can be determined in relation to the work hardening speed and the deformation amount.

Description

Controlled rolling method of metal materials for grain refinement and reduction of rolling force

The present invention relates to a rolling process that can be applied to a rollable metal material that can generate dynamic recrystallization (DRX) during high temperature processing. More particularly, the present invention relates to dynamic recrystallization in a specific pass by adjusting the deformation amount of the rolling pass. The present invention relates to an economically controlled rolling method in which the reduction in the rolling force in the hot rolling process and the fineness of the grain size can be reduced to generate a simple and excellent mechanical property.

In particular, the present invention provides a process by controlling only the amount of deformation in one or two passes compared to rolling techniques such as recrystallization controlled rolling (RCR) or dynamic recrystallization controlled rolling (DRCR), which have recently been studied. It can be applied to all rollable metal materials, which can produce dynamic recrystallization during high temperature processing, covering not only steel materials but also special steels and nonferrous materials.

In general, controlled rolling technologies include Conventional Controlled Rolling (CCR), Recystallization Controlled Rolling (RCR), and Dynamic Recrystallization Controlled Rolling (DRCR). In addition to controlling the hot working parameters such as the pass strain amount, strain temperature, and strain rate suitable for the process before or after the rolling process, as well as to obtain fine ferrite particles and pearlite particles in a relatively low temperature region (area where recrystallization hardly occurs). In the pancaking process, in which austenite particles which are not recrystallized by stretching are stretched for a long time, the transformation of ferrite and pearlite is promoted by increasing the ratio of the grain boundary area to the particle area, thereby obtaining fine ferrite particles and pearlite particles. It is a rolling process.

In addition, the recrystallization controlled rolling technique is one of the processing processes mainly performed to obtain fine grains in the rolling of general steel, and the static recrystallization phenomenon occurring after rolling by performing the final rolling in the austenite region, which is a high temperature region where recrystallization is easily generated. This is a controlled rolling step of obtaining fine grains by recrystallization by appropriately controlling the path strain amount, strain rate, and interruption time.

In addition, the dynamic recrystallization control rolling is a control rolling process using the dynamic recrystallization of the material, and the dynamic recrystallization phenomenon in the dynamic recrystallization control rolling is obtained from the hot rolling process variables such as the path deformation amount, the deformation rate, the interpass holding time, and the deformation temperature. As it is controlled, particle refinement by dynamic recrystallization can be obtained by adjusting these process variables.

If the interruption time between passes is very short, the degree of work hardening increases as the second half of the rolling process causes dynamic recrystallization with little deformation.

Dynamic recrystallization control rolling utilizes this effect to generate dynamic recrystallization to refine grains.

However, in such a general controlled rolling process, the temperature must be lowered to a low temperature region, so that the interruption time between the pass and the pass is long, and thus the overall rolling time is long, thereby reducing productivity.

In addition, since rolling must be performed in a region where recrystallization does not occur (relatively low temperature region), the reduction force is increased accordingly, and thus roll force is increased.

In the recrystallization controlled rolling process, since the grains are refined by static recrystallization, the grain refinement degree is not so excellent and the mechanical properties at room temperature are not excellent.

In addition, in the case of dynamic recrystallized control rolling, as the degree of work hardening increases toward the second half of rolling, the rolling force increases as in general control rolling, and the rolling speed must be reduced because the overall rolling time must be reduced. There is a disadvantage that must be large.

However, hot rolling is made of multi-stage deformation of about 8-20 passes at a temperature of 1000 ° C. or higher in the case of steel materials, where not only the deformation temperature (T), the deformation rate (ε), but also the path deformation amount (ε _i ), And the mechanical properties of the final steel material is changed according to the change in the interruption time (t _i ) between the passes.

In particular, the deformation at high temperature is carried out by the combination of hardening and softening, and the softening occurring at the same time occurs at the same time as the deformation unlike the static recrystallization (SRX) generated during heat treatment after cold working. do.

Unlike static recrystallization, such dynamic recrystallization has many advantages, such as no time required for recrystallization to occur and it occurs at the same time as deformation, thus eliminating the heat treatment process. However, such dynamic recrystallization does not occur only by deformation. It only occurs when strain is applied that exceeds the critical strain required.

In order to solve the problems of the conventional control rolling process as described above, the present invention focuses on the dynamic recrystallization when a deformation exceeding the critical deformation amount as described above in the hot rolling process, In this regard, the critical strain is calculated and the strain exceeding the threshold value is used in any of the steps of the rolling pass, for example, the initial stage or the final stage, so that not only the grain size can be further refined but also the reduction in the reduction force can be achieved. It is designed with the focus on the deformation of the rolling pass that proceeds in multiple stages to generate dynamic recrystallization in a specific pass to reduce the rolling force in the hot rolling process and to refine the grain size, so that the process is simple and excellent mechanical properties can be obtained. Controlled rolling method of economical metal materials The purpose is to provide.

1 shows carbon steel at 1000 ° C. Graph showing flow curves obtained by deformation under strain conditions of 0.5 / second.

2 is a graph showing the relationship between the work hardening rate and the deformation amount.

3 (a) to 3 (c) are views showing flow stress curves and microstructures when the controlled rolling process of the present invention is applied to carbon steel.

4 (a) to 4 (c) show flow stress curves and microstructures when the controlled rolling process of the present invention is applied to 304 stainless steel.

5 (a) to 5 (c) are views showing flow stress curves and microstructures when the controlled rolling process of the present invention is applied to copper (Cu), which is a nonferrous metal.

* Explanation of symbols for main parts of the drawings

δ: stress ε: strain

θ (= dδ / dε): Strain Hardening Rate

ε _c : Critical Strain for Dynamic Recrystallization

ε _p : Peak Strain ε (= dε / dt): Strain (rate) velocity

In order to achieve the above object, in the present invention, in the rolling method of a metal material for performing a rolling step of the metal material in which dynamic recrystallization occurs during the high temperature processing in a rolling pass made of a multi-stage zinc pass, the multi-stage constituting the rolling process The method of rolling a metal material for refining grain size and reducing a reduction force, characterized in that rolling is performed while giving a deformation amount exceeding a critical deformation type necessary for generating dynamic recrystallization in any one of the rolling passes. to provide.

The metal material to which the present invention is applied may be any one of carbon steel, 304 stainless steel, and copper.

Further, in the present invention, rolling by applying a strain amount exceeding a critical strain amount to generate dynamic recrystallization may be performed at either stage of the initial stage and the final stage of rolling.

Moreover, in the present invention, the critical deformation amount for generating dynamic recrystallization can be determined in relation to the work hardening speed and the deformation amount.

Hereinafter, with reference to the accompanying drawings will be described in detail a method of rolling control of a metal material for reducing the grain size and reduction of the reduction of the present invention.

In the controlled rolling method of the metal material for refining grain size and reducing the rolling force of the present invention, in the rolling method of the metal material which performs the rolling process with a rolling pass consisting of a multi-stage rolling pass, the metal material in which dynamic recrystallization occurs during high temperature processing, Rolling is performed while giving a deformation amount exceeding a critical deformation amount necessary for generating dynamic recrystallization in any one of the rolling passes of the multi-stage rolling pass constituting the rolling step.

The controlled rolling process of the present invention can be applied to non-ferrous metal materials such as carbon steel, special steel such as 304 stainless steel, copper alloy, etc., and can be applied to all metal materials such as 316 stainless steel, aluminum alloy, brass (Brass), It is apparent that the examples of some metals in the present specification are only examples.

In addition, in the present invention, rolling by applying a deformation amount exceeding a critical deformation amount to generate dynamic recrystallization may be performed at any one of the initial stage and the final stage of rolling, and may be easily understood in the middle stage. The critical strain amount for generating dynamic recrystallization can be determined in relation to the work hardening rate and the strain amount.

To perform the dark rolling by applying the deformation amount exceeding the critical deformation amount in any one of the multi-step rolling passes, the rolling pass performed by applying the deformation amount exceeding the critical deformation amount regardless of whether the initial stage, the intermediate stage, or the late stage is performed. After that, it is possible to refine the grain and lower the deformation resistance, thereby reducing the reduction force.

However, it is advantageous to perform rolling while adding a deformation amount exceeding the critical deformation amount in the early rolling pass during the rolling process.

FIG. 1 is a graph showing a flow curve obtained by deforming carbon steel under strain conditions of 1000 ° C. and 0.5 / sec. It is used as the most basic data during hot rolling. From this, it is possible to know the rolling force and the maximum elongation.

In addition, Figure 2 shows the relationship between the rate of work hardening and the amount of deformation, and shows a curve that can determine the amount of deformation that causes dynamic recrystallization, which is the most important part of the present invention. The velocity is indicated by the maximum value and gradually decreases during subgrain formation and dynamic recrystallization, and becomes zero at the peak strain.

At this time, when the relationship with the deformation amount of the work hardening rate is shown, an inflection point is shown at each point, where the critical deformation amount can be determined.

On the other hand, as a result of studying the relationship between strain temperature, strain rate and critical strain, for V-added carbon steel (= Fe-0.23C-1.0Mn-0.2Si-0.054V), the critical strain (ε _c ) = 0.013 Z ^0.1043 ( Where Z = strain rate xExp [Q / RT]), and for 304 stainless steel, the critical strain (ε _c ) = 0.73x10 ^-1.26 Z ^0.07 (where Z = strain rate xExp [Q / RT)). As a result, when the critical strain is obtained, the V-added carbon steel becomes 0.2-0.7 when deformed at a strain rate of 0.05-5 / sec in the strain temperature range of 800-1000 ° C, and 900 for 304 stainless steel. In the deformation temperature range of −1100 ° C., the deformation was 0.33-0.68 at a strain rate of 0.05-5 / sec.

As an example, the critical strain values of carbon steel, 304 stainless steel (304STS), and Cu obtained at specific strain temperatures and strain rates are shown in Table 1 below.

Hereinafter, the present invention will be described in more detail with reference to Examples.

Example 1

3 (a) to 3 (c) show flow stress and microstructure in the case where the controlled rolling process of the present invention is applied to carbon steel, which is C: 0.23% by weight, Mn: 1.03% by weight, and P: Consisting of 0.029% by weight, S: 0.039% by weight, and the remaining amount of Fe and unavoidable impurities, the strain temperature, strain rate, and intermittent intermittent time are equalized, and then only the pass strain is adjusted to exclude the influence of the remaining process variables and recrystallize. The case where it has not occurred is shown in FIG. 3 (a), the case where recrystallization is generated in the previous step is shown in FIG. 3 (b), and the case where recrystallization is generated in the second step is shown in FIG. Shown.

In each case, the recrystallization occurred and the Young's amount on the microstructure and the reduction force were investigated. In FIG. 3 (a), the pass strain was fixed at 20% and the 15 pass was deformed, similar to the general rolling process. , It was confirmed that the peak stress level of the continuous flow curve was continuously reached in the entire deformation region.

FIG. 3 (b) shows a case where dynamic recrystallization is generated at the beginning of the process by adding 80% of deformation amount exceeding the critical deformation amount (32%) for operation recrystallization in the second pass. Comparing the continuous strain flow curves, it was found that they match the steady state stress levels of the flow curves as shown in FIG. 3 (a).

Therefore, by using such a process, it can be said that rolling can be carried out even if it reduces flow stress. The ability to lower the flow stress has the advantage of reducing the production cost because the rolling can be performed even with a smaller reduction force during rolling.

Figure 3 (c) shows a process opposite to that shown in Figure 3 (b), where dynamic recrystallization occurs later in the deformation by applying 80% of deformation in the eleventh pass. As was the maximum stress level of continuous deformation.

Microstructure photographs obtained from this process are shown next to each flow curve. In the case of the general rolling process, the crystal grain size of about 130 μm is obtained as in the case of the third (a), whereas the control rolling in which the deformation amount is controlled is the same as the third (b) and the third (c). By showing the grain size of 80㎛, 70㎛ which is about half the level by the microcrystalline grain size is improved by the mechanical properties at room temperature by 10% or more, according to the rolling process of the present invention is smaller than the conventional rolling process It can be seen that the ability to produce much better steels.

Example 2

4 (a) to 4 (c) show flow stress and microstructure when the controlled rolling process of the present invention is applied to 304 stainless steel. The composition of the stainless steel is Cr: 18.21 wt% and Ni: 8.06% by weight, C: 0.045% by weight, Si: 0.57% by weight, Mn: 1.03% by weight, P: 0.025% by weight and the remaining amount of Fe and unavoidable impurities, in which case the reduction force as shown in FIG. Not only can it be lowered, but the grain size can be made fine.

The rolling process of the present invention is particularly effective in materials such as stainless steel, because most of the special steels have a very large deformation resistance during hot rolling (usually more than two times), so that the rolling reduction in hot rolling can be reduced. The effect is much larger than when applied to ordinary steel, and if it is possible to roll with a smaller pressing force, it is possible to reduce the defects generated during hot rolling and to control the shape of the surface beautifully. In steel grades such as stainless steel, which determine quality, the controlled rolling process of the present invention is of particular high application.

Example 3

5 (a) to 5 (c) show flow stress curves and microstructures when the controlled rolling process of the present invention is applied to copper (Cu), which is a non-ferrous metal. FIG. And as shown in Figure 4, it can be seen that not only lowers the reduction force, but also can make fine grains.

In total, the flow stress and the grain size as a result of applying the control rolling process of the present invention are summarized in Table 2, and as can be seen, the rolling reduction is reduced by about 10% and the average grain size is about. Could be further refined by 50%

Therefore, according to the control rolling method for miniaturizing the crystal grains of the present invention and reducing the reduction force as described above, the grains are reduced to about twice as much as the conventional ones, thereby improving mechanical properties and producing excellent products while reducing the reduction force. As such, a useful effect can be obtained such that economic efficiency is improved.

Claims (4)

In the rolling method of a metal material which performs a rolling process by the rolling pass which consists of a multistage rolling pass, the metal material which dynamic recrystallization generate | occur | produces at the time of high temperature processing WHEREIN: The rolling process of any one of the multistage rolling passes which comprises the said rolling process A method of controlled rolling of a metal material for grain refinement and reduction of rolling force, characterized in that rolling is performed while giving a deformation amount exceeding a critical deformation amount necessary for generating dynamic recrystallization. The method of claim 1, wherein the metal material is one of carbon steel, 304 stainless steel, and copper. The method of claim 1, wherein rolling by applying a strain amount exceeding a critical strain amount to generate a dynamic recrystallization is performed at any one of an initial stage and a final stage of rolling. The method of claim 1, wherein the critical deformation amount for generating the dynamic recrystallization is determined in relation to the work hardening rate and the deformation amount.

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