KR100484091B1 - Method for distributing the forging amount of square bar in hot free forging - Google Patents

Abstract

The present invention relates to a hot free forging reduction amount distribution method for distributing a rolling reduction from the middle bar in the middle of the ingot to the target square bar process immediately before the finishing round bar in the hot free forging process, the square bar dimensions of the middle of the steel ingot And a first step of calculating the allowable forging load of the forging press from the target rectangular bar dimensions, and calculating the deviation between the forging load and the forging allowance and calculating the difference between the minimum and maximum rolling reductions to determine the first rolling reduction in the allowable condition. A second step of comparing the first reduction amount with a pore compression ratio by determining a reduction amount of a condition that maximizes pore compression, and a reduction in the allowable crack generation condition when forging the reduction amount. A fourth step of determining a reduction amount of the current path compared to the amount; and a fifth calculation of a next pass exit thickness, a spread amount, an exit width, and a temperature from the reduction amount; Thereby providing a hot free forging rolling reduction distribution characterized in that the configuration step. As described above, the present invention has an effect of improving productivity by deriving a reduction amount to minimize the pores inside the ingot, as well as improving the quality of the forged product and reducing the number of forgings according to proper pass schedule management.

Description

METHOD FOR DISTRIBUTING THE FORGING AMOUNT OF SQUARE BAR IN HOT FREE FORGING}

The present invention relates to a hot free forging reduction distribution method, and more particularly to a method for distributing the reduction amount from the rectangular bar process in the middle of the ingot to the target square bar process immediately before the finishing round bar in the hot free forging process. The present invention relates to a hot free forging reduction distribution method having a reduction in the amount of pores remaining in an ingot cast in a casting process under a press allowable limit and an optimal number of reduction passes.

In general, as shown in Figure 1, the forging method of the steel ingot, after heating to a constant temperature in the heating furnace is extracted in the middle through a number of passes from the head side to the center side or from the tail side to the center portion Square bars of stages are manufactured and reheated to produce round bars and wide bars, which are used as crank shafts or knife materials for shears. When casting the molten steel in the mold, the difference in the solidification speed between the outside and the inside occurs, and microporous pores or segregation exist in the center of the ingot, thereby providing a fundamental cause of internal defects. The distribution of these pores exists between the hot water part at the center of the ingot.

The internal defects generated as described above are present in the state of being partially squeezed and the other part is not squeezed according to the forging method during the forging process, which causes the internal quality defect of the forged product.

Hot free forging processes are usually classified into two to three processes. 2, a first step of making a square bar as a primary standard using a square mold, a second step of making a target bar immediately before a final round bar from the first bar, and an octagonal bar at a target rectangular bar as shown in FIG. In addition, there is a third process of manufacturing a round bar using a round mold after trimming 16 bars, and a second process of manufacturing a square bar in the form of a wide bar directly from a primary standard bar.

From steel ingot to primary square bar process, the mold width ratio (material diameter or material thickness divided by mold width) before forging is large, depending on the steel ingot specification, but the pore compression ranges within about 20%. The process from the ingot to the first square bar does not mean rolling down because the material specification is not constant, but it can be said to be a selection step to make the square bar. Therefore, the design of the rolling reduction schedule is important because the rolling reduction stage is the most from the small square bar stage to the second square bar stage immediately before the circular bar, and most of the total reduction ratio is performed in this process.

The prior art related to the pore compression in the steel ingot is disclosed in Japanese Patent No. 58-10391, which reduces the amount of fishtail generated on the hot water side and eliminates defects such as pores and segregation remaining near the hot water portion. A forging method is proposed in which the pressure is reduced from the center side to the hot water part or the pouring part so as to move outwardly.

However, in the forging method described above, since the pores exist only between the pressure centers at the extraneous part, the compression of the remaining pores cannot be expected only by changing the forging order. If the rolling is carried out in one direction from the hot water → center side or the hot water side → center side, the forging time increases because the manipulator holding the steel ingot must be moved back to the hot water side after pressing down to the center side. To lower productivity.

In addition, Japanese Patent No. 53-102223 discloses a casting method that can improve internal segregation occurring in a conventional casting method. Such a casting method does not completely remove pores in the steel ingot generated by the difference in solidification speed. Therefore, there is a need for an improved method for improving the casting method to have a minimum size of pores in the casting process and to effectively compress it in the forging process.

In addition, there is no known patent on the method of calculating the rolling reduction schedule during the forging process. The rolling reduction is mainly performed based on experience, and the rolling reduction schedule varies according to the operator. Therefore, there is a need for a steel sheet forging process pressing distribution method that compresses the pores remaining in the steel ingot and has a minimum number of reduction passes.

In order to solve the above problems, the present invention increases the compression efficiency of the pores generated during the casting process during the forging process, and minimize the number of passes by the appropriate pressure reduction distribution method hot free forging pressing distribution method that can increase the yield The purpose is to provide.

In order to achieve the above object, the present invention is the first step of calculating the allowable forging load of the forging press from the square bar size and the target square bar size of the steel ingot stage, and the forging load and tolerance calculated in the first step The second step of determining the first reduction amount within the allowable condition by calculating the deviation from the forging load and calculating the difference between the minimum and maximum reduction amount, and the pore compression is determined from the pore compression ratio equation. A third step of determining and comparing a reduction amount of the condition to be maximized; and a fourth step of determining the reduction amount of the current path by comparing the reduction amount determined in the third step with the reduction amount of the crack generation tolerance condition for forging. And a fifth step of calculating a next pass exit exit thickness, a width spreading amount, an exit width, and a temperature from the reduction amount determined in the fourth step; To thereby provide the hot free forging rolling reduction allocation method which comprises repeating the step 5 in the first stage acid.

Hereinafter, the hot free forging reduction amount distribution method according to the present invention will be described in detail for each step.

Step 1

The allowable forging load is calculated from the capacity of the forging press from the initial square bar, the target square bar dimension, and the furnace extraction material temperature from Equation 1 below. (See Figure 4)

Second stage

The first reduction from the allowable forging load of the first step is calculated by inverse from the forging load model equation, the forging load (P _f ) at this time is calculated from the following equation (2).

In Equation 2, the forging load factor Qf and the deformation resistance Km are calculated by Equations 3 to 4 below.

In the forging load model, since the rolling amount is included as a function in the formula for calculating the strain, strain rate, and load coefficient, the solution is solved using the equal method shown in FIG.

The forging loads P (Δ1), P (Δ2), and P (Δ) of the minimum, maximum, and average rolling reduction conditions are calculated from the equations (2) to (4), respectively.

In Fig. 4, Δ1: minimum rolling amount, Δ2: maximum rolling amount, Δ: average rolling amount, α1: difference between allowable load Pw and minimum rolling condition, α2: difference between allowable load and maximum rolling condition, α: The difference between the allowable load and the average rolling condition is shown.

The procedure for obtaining the solution is shown in the flowchart of FIG. 5. A brief introduction of the procedure for obtaining the first rolling reduction is as follows.

Step.1: Assume the minimum and maximum rolling reductions and assume the initial number of repetitions as 1.

Step.2: Calculate the average rolling reduction, and calculate the load difference (ΔP) and the rolling reduction difference (Δ *) under the conditions Δ1, Δ2, and Δ.

Step.3: If the forging load difference between the allowable forging load and the average rolling reduction condition is zero or the rolling reduction difference (Δ ^* ) is within the limit value, it is the first calculated rolling reduction (ΔH ₁ = Δ) to be obtained. If P (Δ) × P (Δ1) is less than 0, replace it with Δ2 = Δ, and if P (Δ) × P (Δ1) is greater than 0, replace with Δ1 = Δ until it converges. Step. Step 2 Repeat calculation 3

Step 3

The reduction amount calculated in the second step is a first calculated value without considering the conditions for minimizing the degree of compression of the pores as the reduction amount of the allowable forging load condition. Therefore, the reduction amount is calculated from the pore compression model that can evaluate the degree of compressive effect during the forging process of the pores present in the center of the steel ingot, and compared with the primary calculated reduction amount (ΔH _c) ) Is calculated. The formula representing the void crushing ratio (ψ i) is as shown in Equation 8 below, wherein the formula (ΔH ₁ = Δ) is a formula for 61 kinds of tool steel, the thickness, width, rolling reduction, This is a model equation for the calculation result of the compression ratio of pores in steel ingots according to the change of conditions such as mold width.

The Rigid-Plastic Finite Element Method was used to calculate the volume of the pore after pressing down the rectangular pore inside the square bar (diameter: 10 mm).

From the above Equation 5, the reduction amount ΔH _c , which minimizes the pore compression ratio ψ _i , is obtained by inversion. If the primary calculated pressure drop (ΔH ₂ = ΔH ₁ ) of the allowable forging load condition is within the rolling range obtained under the condition that the pore compression ratio is minimum (ψ _i = 0), determine this value as the appropriate rolling reduction and if it exceeds, Replace the reduced amount with the reduced amount (ΔH ₂ = ΔH _c ) under the condition that the pore compression ratio is minimum (see FIG. 5).

4th step

The reduction amount determined in the third step is compared with the forging limit pressure _drop amount ΔH _lim of the hot free forging condition in which no crack is generated during forging. The forging limit pressure drop at this time is calculated from the following limit reduction rate γ _i determined by steel grade, material temperature and experience.

When the threshold pressure drop amount of Equation 7 is exceeded, the optimum pressure drop amount is replaced with the threshold pressure drop amount ΔH ^* = ΔH _lim , and within the range, the pressure reduction amount ΔH ^* = ΔH ₂ determined in the third step is determined.

Step 5

The thickness, width, length, etc. after the reduction are calculated using the optimum reduction amount ΔH ^* determined in the fourth step, and the first to fifth steps are repeatedly calculated for the next pass (see FIG. 6).

1) Thickness after pressing (H _i )

2) Width after pressing (W _i )

3) Length after pressing (L _i )

In the method of setting the square bar reduction schedule of the middle stage of the ingot of the hot forging process by the above-described procedure, the condition for deriving the first reduction of the allowable load of the forging press and maximizing the pore compression ratio in the ingot After selecting the secondary reduction by comparing the reduction amount of, and using the method of deriving the optimum reduction amount by comparing the limit reduction amount that does not cause cracks in forging processing with the secondary reduction amount, the internal quality of the forged product is improved and forged. Productivity improvement by reducing the number of passes is great.

EXAMPLE

According to the present invention, the results of comparing the off-line results with the conventional reduction schedule method when using the reduction distribution method. Table 1 shows the material specifications and forging conditions. Table 2 shows the off-line simulation results at this time, and FIG. 7 shows the pore compression ratios for each pressing down pass.

Materials and forging conditions used for off-line simulation Steel grade SKD61 (oral) Target width 200 mm Thickness margin 5 mm Square Bar Thickness 530 mm Material length 1370 mm Mold width 320 mm Square bar width 530 mm Material temperature 1160 ℃ Press capacity 1500 Ton Target thickness 200 mm Margin Margin 5 mm Forged pitch 200 mm

Offline simulation result division Average pressure drop Total Loss Final pass pore compression ratio (volume after pressure reduction / initial volume) Before Invention 60 14 8% (pore non-compression) After Invention 80 10 0 (pore closed)

As shown in the results of the above embodiment, using the pressure reduction distribution method proposed in the present invention increases the compression rate in the pores in the steel ingot, thereby improving the quality and number of passes in the forging, thereby reducing the forging time.

As described above, the present invention relates to a rolling method for optimally rolling down steel ingots during hot forging, and to derive a rolling reduction amount that can minimize the pores inside the steel ingot, thereby improving the quality of the forged product as well as proper pass schedule management. The productivity is improved by reducing the number of forgings.

1 is a schematic diagram showing pore defects in a steel ingot;

2 is a schematic diagram showing a free forging step of steel ingot;

Figure 3 is a method diagram showing a method of rolling ingot during hot free forging;

4 is a graph of the reduction amount for the load difference for determining the reduction amount;

5 is a first process flow diagram for deriving a hot free forging reduction distribution method according to the present invention;

Figure 6 is a second process flow diagram for deriving a hot free forging reduction distribution method according to the present invention;

Figure 7 is a graph of the results of the embodiment of the pore compression ratio for each pressing pass when performing the hot free forging according to the hot free forging reduction method according to the present invention.

 ♣ Explanation of symbols for main part of drawing ♣

1: Ingot 2: Pressure part 3: Pouring part 4: Pore 5: Mold 6: Square bar

7: round bar

Claims (6)

In the rolling reduction distribution method of the hot free forging step of forging a steel ingot, A first step of calculating an allowable forging load (P _W ) of the forging press from the rectangular bar size and the target rectangular bar size of the steel ingot stage by the following equation; A second step of determining a deviation between the forging load calculated in the first step and the allowable forging load, and calculating a difference between the minimum and maximum rolling reductions and determining a primary rolling reduction (forging load; P _f ) within an allowable condition; A third step of comparing the first reduction amount determined in the second step by determining a reduction ratio of a condition that maximizes pore compression from a pore compression ratio (ψ _i ); A fourth step of determining a reduction ratio of the current path by comparing the reduction ratio determined in the third step with a reduction ratio of the crack generation tolerance condition for forging; A fifth step of calculating a next pass exit exit thickness, a width spreading amount, an exit width, and a temperature from the reduction ratio determined in the fourth step; The method of claim 1, wherein the first step to the fifth step is repeated for calculating the reduction amount of the remaining next pass. P _W = βP _max Where β: allowable load factor (typically 0.8 to 0.9) P _max : Forging press capacity delete The method of claim 1, The first free reduction amount (forging load; P _f ) determined in the second step is calculated by the following equation. The method of claim 1, Reduction rate (r _i) is to the amount of the hot free forging rolling, characterized in that determined by the equation of the condition that the pore pressure bonded to the first rolling reduction in the third step from the pores compression ratio (ψ _i) modified with up to Distribution method. The method of claim 1, The reduction ratio (H) of the current path, which is determined by comparing with the reduction ratio of the crack generation tolerance condition in the fourth step, is calculated from the equation of the limit reduction ratio (γ _i ) described below. Volume allocation method. The method of claim 1, The next free-pass forging thickness, the width spreading amount, the exit width, the temperature calculated in the fifth step is calculated by the following equation.