JPH04178201A - Method for hot roll rolling of forging preform - Google Patents

Abstract

PURPOSE:To prevent the generation of fish tail by cooling all surface of the bottom part to be applied with drawing so as to satisfy a prescribed expression in regard to the ratio of the deforming resistance of the surface of stock against the deforming resistance of the central part of stock. CONSTITUTION:The cooling of the surface of bottom part of the stock is executed so as to satisfy 1.4<K<3.0 in regard to the ratio K of deforming resistance of the surface of stock against the deforming resistance of the central part of stock. Therefore, the generation of fish tail at the drawing time of the bottom part can be prevented, and the quality of forging products and the moss yield can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention relates to a method for hot roll forming of a forged blank when manufacturing, for example, an automobile crankshaft or the like by a forging method.

(Prior art) In general, hot rough forming using forging rolls is performed for the purpose of improving forging yield, reducing the number of forgings, etc. (see, for example, Japanese Patent Application Laid-Open No. 137135/1983). As shown in Fig. 1, fish tails are likely to occur in the bottom part of the material (FI rough ground) (Fig. The part becomes forging group 2 (Figure (C))
.

Conventionally, assuming the occurrence of forging flaws due to this fishtail, in order to prevent flaws from remaining on the forged product 3, the length of the rough area (roll rough area) after rolling was set in advance by a length l less than the optimum rough area length Ll. (FIG. 2(a)), after forging, the problem was dealt with by cutting and removing a portion (burr 4) corresponding to the portion 1. L2 is the required length of the forged product 3 (Fig. 2 et al.)).

For this reason, the yield of forged products is poor, and energy, etc. is required to heat and form excess material that does not become the final product, and production costs, including material costs and heating costs, are low. An increase in costs is unavoidable.

(What the invention is trying to solve! In> The present invention aims to prevent the occurrence of fishtails during hot roll forming of such forged raw material, and to improve the yield and quality of forged products.

(Means for solving the problem) Fishtail is a phenomenon in which during material forming, the material in the surface layer of the material that comes into contact with the roll moves in the rolling direction, and at the bottom of the material, the material in the surface layer becomes an unrestricted material. It is thought that this occurs due to the flow in the direction of the end face of the Therefore, in order to prevent this, the surface of the bottom part of the material is cooled immediately before hot roll forming of the forged raw material to make the deformation resistance of the material surface higher than that of the center part of the material. It is thought that if the metal flow is suppressed, the reduction blade during roll forming will be transmitted to the center of the material, and fishtail can be prevented.

The present invention was made based on this idea, and its gist lies in the following hot roll forming methods for forged raw material.

■ When drawing the bottom part of the material using a grooved roll, draw the material before processing so that the ratio K of the deformation resistance of the material surface to the deformation resistance of the material center satisfies the following formula (1). A method for hot roll forming of forged raw material, which is characterized by cooling the entire surface of the bottom portion to be processed.

1.4<K<3.0...(1) ■ Above ■
In the invention, only the surface portion of the material that comes into contact with the periphery of the groove bottom including the groove bottom of the grooved roll is cooled, out of the entire surface of the bottom portion of the material to be subjected to the drawing process before processing. Hot roll forming method for forged raw material.

■ In the invention of (■) above, only the entire surface in the circumferential direction of the radius X determined by the following formula (2) centering on the part of the bottom surface of the material before processing that corresponds to the base end on the material side of the bottom after drawing processing. A hot roll forming method for forged raw material characterized by cooling.

X=(0,1~0.2)De...(2) However, D
e is the diameter or virtual diameter of the material before processing.The above-mentioned material is not limited to a square material, but may be a round or polygonal material, and the cross section after drawing is also limited to a square. It may be circular or polygonal.

In the inventions (1) and (2), in order to cool only a part of the material, for example, the part that is not to be cooled may be covered and cooled by spraying or jetting water.

The invention (2) is a method of cooling the entire surface of the bottom portion to be subjected to the drawing process as described above.

Figure 3 is a diagram showing the cooling part when the material is a square timber.
) figure is a side view of the material, (b) figure is its A-A arrow view, (
C) The figure is a side view after applying a drawing process to the material (90° inversion and applying a two-pass drawing process. The same applies to Figures 4 and 6, which will be described later). Figure (d) is a side view of the material. B-B
It is an arrow view. In Figures (a) and (b), the shaded area is the area to be cooled, and the bottom portion to which the drawing process is to be applied, that is, the entire surface of the area to which the drawing process is applied, is cooled before processing.

In the case of a round material, that is, a material with a circular cross-sectional shape, and in the case of a polygonal material, the entire surface of the bottom portion is cooled in the same way as in the case of a square material.

The invention (2) does not cool the entire surface of the bottom portion to which the drawing process is applied as described above, but cools the bottom of the groove formed between the rolls when drawing the material with the grooved roll. That is, this is a method in which only the surface portion of the material that comes into contact with the periphery of the groove bottom, including the portion corresponding to the groove bottom of the grooved roll, is cooled before processing.

Figure 3 shows the case of a square timber, and Figures (a) to (d) correspond to Figures (a) to (d) in Figure 3, respectively. As shown in the figure, the material surface portion 6 (hatched portion) that comes into contact with the peripheral portion of the groove bottom of the grooved roll 5 is the portion that is cooled.

The cooling range lc is the total circumference length Lc of the material centered on the corner point of the material.
It is effective to set it to about 0.1 to 0.16 times.

That is, if the cooling range 1c is wider than 0.16 times the total circumferential length Lc, the occurrence of fishtail is prevented but the convergence spread becomes large, and if it is narrower than 0°1 times Lc, the effect of preventing the occurrence of fishtail is almost lost. It is from.

Figure 5 is a front view showing the cooling part in the case of a round material, but in this case as well, the drawing process is applied while turning the material 90 degrees, so the shaded part is cooled as in the case of a square material. It becomes a part. In the figure, arrow El1wl indicates the load direction in odd-numbered passes, arrow W indicates the load direction in even-numbered passes, and pc indicates the cooling range (cooling arc length).
, Lc is the total circumference length, and in this case as well, it is effective to set lc to 0.1 to 0.16 times Lc as in the case of square timber.

In the invention (2), on the surface of the bottom part of the raw material before processing, after the drawing process, the material side 15fa of the bottom part (the bottom part that undergoes the predetermined drawing process), that is, the taper part formed by the drawing process is This is a method of cooling a certain area around the entire circumference before processing, centering on the part corresponding to the root part (the tapered part is the root part).

FIG. 6 shows the case of a square timber, and FIGS. (a) to Td) correspond to FIG. 3, respectively. As shown in the figure, the entire circumferential surface (shaded area) of the radius X determined by the above formula (2), centered on the area corresponding to the base end 7 on the material side of the bottom part after drawing, is cooled. It is. (2)
In the formula, the virtual diameter De is the diameter when the square or polygonal material before processing is assumed to be a round material having the same cross-sectional area as the cross-sectional area of the square or polygonal material. In the case of a round material, its diameter is De, and as in the case of a square material, using this De, the entire circumferential surface of the width X determined from equation (2) becomes a portion to be cooled.

(Function) The present invention is a method of roll forming after cooling the bottom surface of the material, thereby suppressing metal flow on the surface,
The occurrence of fishtail can be prevented.

It is clear from the experimental results described below that the bottom surface of the material is cooled so that the ratio (K) of the deformation resistance of the material surface to the deformation resistance of the center of the material satisfies the above equation (1). Particularly, when K is more than 1.4 and less than 3.0, that is, when there is deformation resistance at the center of the material, the occurrence of fishtail can be effectively prevented.

Medium carbon f! A (American Society of Automotive Engineers Standard SAE 10
35), the temperature at the center of the material was set to 1200°C, and the surface of the material was cooled by spraying water to bring the surface temperature to 80°C.
The temperature was varied in the range of 0 to 1150°C, and the depth d of the fishtail (see Fig. 1(b)) was measured.

The deformation resistance at each temperature of the materials used in Table 1 is
The table shows the deformation resistance ratio K calculated from Table 1 when the temperature at the center of the material is 1200°C, and Fig. 7 shows the measurement results of the fishtail depth d. , ◎ indicates the case where the material was not cooled,
The O mark indicates that there was no flaw 80 due to overcooling of the material in the part shown in Figure 8, and the X mark indicates that flaw 8 has occurred.Flaw 8 due to material overcooling refers to the area where the surface of the material is not cooled. In the case of excess material, the material near the center of the material is extruded outward from the end face of the material as shown by the arrow (Figure 8), and the boundary between this extruded part and the cooled part becomes TH8. It is.

As is clear from Table 1, Table 2, and Figure 7, when the deformation resistance ratio K is less than 1.4, that is, when the cooling of the material is insufficient, the improvement of fishtail is insufficient. When the deformation resistance ratio K is 3.0 or more, that is, when the material is cooled excessively, flaws 8 occur.

In this way, the conditions in which neither forging flaws caused by finst tails nor flaws caused by overcooling of the material shown in FIG. 8 occur are expressed by the above equation (1). It was confirmed that this relationship was the same not only for steel but also for Ti-based alloys and Ni-based alloys, as shown in the later examples.

In actual operation, if the surface of the material is left for a long time after being cooled, the heat will recover from within the material and the temperature difference between the surface and the center of the material will become small, so roll forming is usually completed within 30 seconds after cooling. However, since this time varies depending on the material, dimensions, temperature, etc., it should be determined appropriately.

By the way, when the entire surface of the bottom part of the material is cooled as in the invention (2) above, the occurrence of fish till can be prevented, but the convergence of the bottom part becomes large and the length of the rough ground is insufficient after rolling.

Figure 9 is a schematic diagram for explaining the cause of this widening and the lack of rough ground length after rolling ((a) is a front view of the end after drawing, (b) is a front view of the end after drawing, and (b) is In the side cross-sectional view), the solid line is the case when the material surface is not cooled, and the broken line is the case when the entire surface of the material is cooled.As shown in this figure,
The material in the surface layer, whose deformation resistance has increased due to cooling, becomes difficult to extend in the rolling direction (the axial direction of the material) and spreads in the radial direction.

In other words, by cooling the surface, the cooling material layer with high surface deformation resistance is connected in a ring shape in the circumferential direction, and the material in the part corresponding to the fishtail (hatched area S in the figure (b)) moves in the width direction. , it does not elongate in the rolling direction and deforms into a diamond shape.

As a result, radial expansion occurs (dashed line in figure (a)), and the length of the rough ground becomes insufficient after rolling (figure (b)). Therefore, the material should be made with a longer length to account for this shortfall. It is necessary to prepare the material, which reduces the yield.

The above-mentioned inventions (1) and (2) are hot roll forming methods for forged raw material that can prevent the occurrence of fin tails and also prevent an increase in radial expansion.

Invention (2), by cooling only the surface portion of the material that contacts the periphery of the groove bottom of the grooved roll as described above, the cooling material layer with high deformation resistance is connected to the ring as in invention (2). As a result, the elongation in the axial direction in the non-cooled material layer formed at the center of each piece increases, and the width expansion is suppressed by an amount corresponding to this elongation. , it is possible to simultaneously prevent the occurrence of fishtails and increase in width, regardless of whether the material is square timber or not.

Cooling range of the material surface that comes into contact with the periphery of the groove bottom j! If 1 exceeds the upper limit, there will be almost no axial extension at the center of the side, and although the occurrence of fishtail will be prevented, the convergence will increase; if it is smaller than the lower limit, the axial extension at the center of the side will increase. The extension in the direction becomes large, and the occurrence of fish till becomes large.

As mentioned above, the invention (2) cools the entire periphery in a width X range centered on the base end of the bottom part on the material side (root part for tapered parts). Since only the axial movement of the material is suppressed at the portion where the axial movement of the member material is the largest, prevention of fish till and width expansion can be achieved at the same time. If the cooling range is wider than Radius The occurrence becomes large.

(Example 1) A square material and a round material having the chemical composition and dimensions shown in Table 3 are hot roll-formed, and the bottom part is subjected to a drawing process to eliminate flaws caused by fish till and overcooling of the material. The occurrence of defects (flaws numbered 8 in Figure 8) was investigated. In addition, cooling of the material surface is performed at a distance of 30 m from the bottom end surface.
This was done by spraying water on the entire surface of the area up to m.

For each material, temperature and deformation resistance have the relationship shown in Figure 1O (a) and (b).The temperature at the center and bottom surface of each material after water cooling was measured, and the deformation resistance ratio K I asked for Table 4 shows the surface temperature and center temperature of each material after water cooling, the deformation resistance ratio, and the time from the end of water cooling to the start of roll forming.

O
The mark indicates good condition (no flaws), and the X mark indicates defective condition (with flaws).For the square timbers, 2, 5 and N[16 are examples of the present invention (invention of ■), and others. is a comparative example. Further, the round material 3 is an example of the present invention (invention (■)).

As is clear from the results in Table 4, when the deformation resistance ratio K was 1.2 (Nal), flaws caused by fishtails occurred on the square timber, but under other conditions, flaws caused by fishtails occurred. No occurrence was observed. In addition, when cooling is strengthened and the deformation resistance ratio K is set to 3.2 (
In case 4), defects occurred due to overcooling of the material.

Similar results were obtained for Ti-based alloys and Ni-based alloys, and as long as the value of the deformation resistance ratio was within the above range, no flaws caused by fishtail or flaws due to overcooling of the material were observed ( Na5 and disease 6).

Regarding the round shaped material, no flaws caused by Finsteel were observed within the scope of the present invention (Satoshi 3).

(Example 2) The square materials used in Example 1 (carbon steel, Ti-based alloy, and Ni
After taking out the base alloy from the heating furnace at 1200°C, the cooling conditions (cooling area) were changed and water-cooled to 1000°C, and two-pass roll forming resulted in an area reduction of 58% in the bottom part.
, 52% and 54% drawing processing is performed,
Fishtail depth and divergence ratio were measured.

The cooling parts are as shown in (a) to (=) below (see FIGS. 11(a) to (C), the shaded areas in the figure indicate the cooling parts).

(B) Entire bottom part (Invention example (■)...see figure (a)) (Nail) Only the opposite side of the bottom part (comparative example...see figure (b), s+=40锎-) (C) Diagonal corner of the bottom part Only (invention example (■)...see (C) diagram, sz-24mm) (d) Comparative example without cooling) The fishtail depth is d shown in Figure 1 0)). In addition, the width expansion ratio is the ratio of the width expansion length (b-b,) obtained by subtracting the width when not cooled from the width when cooled to the width (b b
e)/be.

The measurement results are shown in FIG. 12 using carbon steel as an example.

As is clear from Fig. 12, the Finst tail depth is significantly reduced when cooled ((a) to (c)) compared to the case without cooling (=), especially (a) (■ Example of invention)
It was noticeable in On the other hand, the improvement effect on the radial spread was the greatest in (1%) (invention example (■)), in which both the occurrence of fishtail and the radial spread could be suppressed.

Although not shown, similar results were obtained for Ti-based alloys and Ni-based alloys.

(Example 3) The square materials used in Example 1 (carbon steel, Ti-based alloy, and Ni
The base alloy and De are 101.6+u+ and 110.6, respectively.
am and 101.6 mm) was taken out of the heating furnace at 1200°C, then water-cooled to 1000°C by changing the cooling width around the base end of the bottom part on the material side (the tapered part for drawing is the root), and then 2-pass roll forming. The bottom portion was formed by drawing with a liquid level ratio of 58%, 52%, and 54%, respectively, and the fish till depth ratio and the convergence spread ratio were measured.

For the cooling part, X in the above formula (2) is Omm (not cooled),
9ms+, 20mm- and 30mm.

The fishtail depth ratio is the ratio of the fishtail depth d to De (d 2 /De), and the divergence ratio is the same as in Example 2, which is (b be)/be.

The measurement results are shown in FIG. 13 using carbon steel as an example, similar to the case of Example 2.

As is clear from Fig. 13, when the entire circumferential surface of the width Any increase in convergence spread is suppressed.

On the other hand, when X/De (%) is smaller than 10, the fishtail is large and many flaws occur at the boundary between the cooled and uncooled parts of the reduced diameter section, and when it exceeds 20, the cracks expand. This resulted in many cases where the length of the rough ground was insufficient after rolling.

Although not shown as in Example 2, similar results were obtained for Ti-based alloys and Xi-based alloys.

(Hereinafter, blank space) (Effects of the invention) By applying the method of the present invention in hot roll forming of forged raw material, the occurrence of fin tails during drawing of the bottom part can be prevented, and the quality of the forged product and the material used can be improved. Yield can be improved. Furthermore, out of the entire surface of the bottom of the material, only the surface that comes into contact with the periphery of the groove bottom of the grooved roll is cooled, or a predetermined width is cooled around the area corresponding to the tapered base of the bottom of the material. By adopting this method, it is possible to suppress not only the occurrence of fishtails but also the increase in convergence at the bottom, and it is possible to prevent the occurrence of insufficient length of rough ground after rolling, making it possible to further improve material yield. It is.

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram showing the occurrence of forging flaws caused by fishtails and fintails in the bottom part of forged wasteland, where (a) is a schematic diagram of the bottom part, and (a) is a diagram showing the occurrence of fishtails. Cross section of roll wasteland, (C)
The figure is a cross-sectional view of a forged product with forging flaws. Figure 2 is an explanatory diagram of the conventional method for removing forging flaws, (a)
“The figure is a cross-sectional view of the roll roughness, and the (b) figure is a cross-sectional view of the forged product. These are diagrams showing the cooling parts of the material. Fig. 3 shows cooling of the entire surface of the bottom part, and Fig. 4 shows cooling of only the surface of the entire bottom part that comes into contact with the periphery of the groove bottom of the grooved roll. In this case, Fig. 6 shows the case where the taper drawing process cools a predetermined width around the root. FIG. 7 is a diagram showing the cooling portion of the surface when only the surface that contacts the periphery of the groove bottom of the grooved roll is cooled. FIG. 7 shows the relationship between the deformation resistance ratio and the fishtail depth, and the material supercooling Fig. 8 is an explanatory diagram showing the location of occurrence of flaws due to overcooling of the material. Fig. 9 is a diagram showing an increase in radius spread due to cooling of the bottom part. , (a) is a front view, and (b) is a side sectional view. Figure 1θ is a diagram showing the relationship between material temperature and deformation resistance,
Figure (a) shows the case of medium carbon steel and Ti-based alloy, and figure (b) shows the case of Ni-based alloy. Fig. 1t is a diagram showing the cooling part of the material before processing in the example, and Fig. 1(a) shows the case where the entire surface of the bottom part is cooled;
(B) The figure shows a case where only the center of the opposite side is cooled out of the entire surface of the bottom part, and the figure (C) shows a case where only the surface that comes into contact with the periphery of the groove bottom of the grooved roll is cooled out of the whole bottom part surface. It is. FIG. 12 and FIG. 13 are results of an example for carbon steel, and both are diagrams showing the relationship between cooling conditions, width expansion ratio, and fishtail depth.

Claims (1)

[Claims] (1) When drawing the bottom part of the material using a grooved roll, the ratio K of the deformation resistance of the material surface to the deformation resistance of the center of the material satisfies the following formula (1). A method for hot roll forming of forged raw material characterized by cooling the entire surface of the bottom portion of the material to be subjected to drawing processing before processing. 1.4<K<3.0...(1) (2) When drawing the bottom part of the material using a grooved roll, the ratio K of the deformation resistance of the material surface to the deformation resistance of the material center is In order to satisfy the following formula (1), out of the entire surface of the bottom portion of the material before processing to which drawing is to be applied, only the surface portion of the material that comes into contact with the periphery of the groove bottom including the groove bottom of the grooved roll is A hot roll forming method for forged raw material characterized by cooling. 1.4<K<3.0...(1) (3) When drawing the bottom part of the material using a grooved roll, the ratio K of the deformation resistance of the material surface to the deformation resistance of the material center is In order to satisfy the following formula (1), the circumference of the width A hot roll forming method for forged raw material characterized by cooling only the entire surface in the direction. 1.4<K<3.0...(1) X=(0.1~0.2)De...(2) However, De is the diameter or virtual diameter of the material before processing