JP2009006379A - Center defect prevention method for large-sized hard-to-work product - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a center defect prevention method for preventing a center defect attributed to an anvil used when a large-sized product is manufactured by cogging. <P>SOLUTION: A center defect prevention method for a large-sized hard-to-work product is characterized in that when an upper anvil is reduced toward a lower anvil in a direction perpendicular to an axial direction of material to be forged comprising a large-sized hard-to-work steel ingot, and the material is subjected to cogging while being intermittently fed in the longitudinal direction, a reduction of area per one pass to the material to be forged is set to be in the range of 10-20% and also, W/H of the anvil used for the cogging is set to be 0.3-0.7 until the cross sectional area of the material to be forged becomes 100-50% of a blank material cross sectional area, and W/H of the anvil is set to be 0.8-1.2 until the cross sectional area becomes <50%-15% of the blank material cross sectional area. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a central defect prevention method using an anvil used when manufacturing a large product by forging.

  Conventionally, forging is used as a method for producing a large diameter round steel bar. This forging is a kind of free forging method. In forging, the steel ingot is pressed by the upper and lower anvils while being intermittently fed in the longitudinal direction. In pressing, the upper anvil is rolled down toward the lower anvil. The cross-sectional dimension of the steel ingot is reduced by the reduction, and the steel ingot is elongated. On the other hand, the cross-sectional shape of the steel ingot is adjusted by the reduction. By this multi-stage forging, a round bar steel which is a forged product is obtained. In this case, there are two major factors that cause the occurrence of two types of defects, that is, residual voids and overheating in difficult-to-process large products.

  As a method for solving these defects, as disclosed in, for example, Japanese Patent Application Laid-Open No. Sho 58-167045 (Patent Document 1), a hot steel material that forges an axially symmetrical steel material between an upper anvil and a lower anvil. In the forging method, the ratio of the length of the long side to the length of the short side is at least 1.4 in the cross-sectional shape perpendicular to the forging direction of the steel material between the start of forging and the end of forging. There has been proposed a hot forging method of a steel material provided with a process of making a certain rectangular shape or a substantially rectangular shape.

  In addition, as disclosed in JP-A-1-309745 (Patent Document 2), a large steel material having a circular cross section or a rectangular cross section perpendicular to the axial direction is heated to a predetermined temperature, and a flat metal mat facing the press A hot forging method for large steel materials is proposed in which at least one flat anvil is hot-forged using a flat anvil with a pressing surface having a square with sides shorter than the diameter or width of the cross section of the steel material. .

Further, as disclosed in Japanese Patent Laid-Open No. 1-284447 (Patent Document 3), a forged material made of cold tool steel is simultaneously pressed down by a metal lay from a plurality of directions perpendicular to the axial direction. When forging a forging material by swaging, the area reduction rate per pass for the forging material made of cold tool steel is set in the range of 20 to 30% and the feed speed of the forging material is 7 to 10 m / min. There has been proposed a forging method for tool steels in the range described above.
JP 58-167045 A JP-A-1-309745 JP-A-1-284447

  However, none of the above-mentioned patent documents solves the two problems of remaining voids and overheating in difficult-to-process large products. For example, Patent Document 1 or 2 only describes that the gap is pressure-bonded, and does not describe any concept regarding overheating. Moreover, although patent document 3 has description of a feed rate, the view regarding anvil width and the height of a to-be-forged material is not described at all.

  In order to solve the above-mentioned two problems at the same time, the inventors have made extensive developments. As a result, the steel ingots were formed in a difficult-to-work large product that is prone to defects due to voids and defects due to overheating. Heat to a predetermined temperature, and the appropriate anvil ratio from the direction perpendicular to the axial direction from the upper anvil to the lower anvil (= W / H, W is the width of the anvil used for forging, H is the material to be forged The center defect prevention method for large-size difficult-to-work products, which can prevent the occurrence of center defects by forging and extending the forged material intermittently in the longitudinal direction. Is to provide.

The gist of the invention is that
(1) When forging a to-be-formed material consisting of large steel ingots that are difficult to process, from the direction perpendicular to the axial direction from the upper metallization toward the lower metallurgy and forging the material to be forged while being intermittently fed in the longitudinal direction. The area reduction ratio per pass for the forged material is in the range of 10 to 20%, and the W / H of the anvil used for forging is 100 to 50% of the cross-sectional area of the forged material. Until, W / H is 0.3 to 0.7, and the cross-sectional area is less than 50% to 15% of the material cross-sectional area, the anvil ratio is 0.8 to 1.2. Central defect prevention method for workable large products.
(2) The W / H described in (1) is set to 0.4 to 0.6 when the cross-sectional area of the material to be forged is 100 to 50% of the cross-sectional area of the material, and the cross-sectional area is 50% of the cross-sectional area of the material. If the ratio is less than 15%, the center defect prevention method of the difficult-to-process large product is characterized in that the anvil ratio is 1.0 to 1.2.

  As described above, according to the present invention, a large difficult-to-process large product having no central defect is obtained. That is, voids due to solidification shrinkage at the time of casting of the steel ingot center disappear, generation of overheating due to microsegregation can be prevented, defect rate can be greatly reduced, and quality can be improved. It has an excellent effect.

Hereinafter, the present invention will be described in detail.
First, as an object according to the present invention, a large steel ingot having a chrysanthemum-shaped cross section or a square cross section perpendicular to the axial direction and having a diameter and a diagonal dimension of 900 mm or more, the composition of which is mass%, C : 0.8-1.7%, Si: 0.2-1.5%, Cr: 6.0-12.0%, Mo: 0.9-2.0%, V: 0.25-1 The steel contains 0.0% and the balance is Fe and inevitable impurities. Such a steel ingot of the above conditions is heated to a predetermined temperature, the upper metal is rolled down from the direction perpendicular to the axial direction toward the lower metal, and the forging is carried out while intermittently feeding the material to be forged in the longitudinal direction. In doing so, it is to provide processing conditions that can prevent the occurrence of central defects.

  That is, there may be a void (so-called nest) due to solidification shrinkage during casting at the center of the steel ingot. This void is crushed by forging. By crushing, the metal around the gap is pressed. However, if the pressure bonding is insufficient, voids remain in the round bar steel that is the product. This void is a so-called defect. On the other hand, when the temperature of the steel ingot is set sufficiently high, or the processing amount is set sufficiently high, the remaining voids are suppressed.

  Further, the temperature of the steel ingot greatly affects the workability, and there is a problem that when the temperature is low, the processing amount cannot be set large. Further, in order to obtain a product with a small amount of processing, the number of passes increases, and as a result, the temperature of the steel ingot needs to be set sufficiently high from the viewpoint of workability.

  On the other hand, when the steel ingot is cast, microsegregation occurs. Specifically, a region rich in carbon atoms or the like is generated along the crystal grain boundary. In the phase diagram, the higher the carbon atom concentration, the lower the solidus temperature. In addition, a region rich in carbon atoms is easily melted. On the other hand, in forging, processing heat is generated by reduction. This processing heat raises the temperature of the center of the steel ingot. For this reason, the processing heat is further generated in the steel ingot heated to a high temperature, so that the center of the steel ingot reaches a very high temperature. Therefore, melting may occur in a region rich in carbon atoms near the center. This phenomenon is called overheating. Overheating causes defects inside the round bar steel that is the product.

  As described above, it is necessary to set the temperature of the steel ingot to be high from the viewpoint of suppressing voids and workability. On the other hand, from the viewpoint of suppressing overheating, an excessively high temperature of the steel ingot is not preferable. Further, in forging, temperature control of the steel ingot is extremely important. However, since the temperature range in which voids and overheating do not occur and excellent workability is obtained is extremely narrow, there is a very difficult problem in controlling the temperature of the steel ingot. That said, it is important to suppress defects due to voids and defects due to overheating. To suppress this defect rate, the heating temperature, heating time, rolling reduction, shape of anvil, anvil It has been found that it depends on various processing conditions such as the ratio (= W / H), and it has been found that these conditions need to be optimally controlled.

Hereinafter, the present invention will be described in detail with reference to the drawings.
FIG. 1 is a perspective view for explaining a manufacturing method according to the present invention. FIG. 1 shows a state of forging, which is a kind of hot free forging. In forging, the steel ingot 1 is obtained through processes such as melting and casting. The steel ingot 1 has a gap near the center due to solidification shrinkage during casting. In the vicinity of the center of the steel ingot 1, microsegregation also occurs. This steel ingot 1 is put into a heating furnace and heated. When the heating time is short, the temperature of the center of the steel ingot 1 is lower than that of the surface. In other words, the steel ingot 1 has a temperature distribution. When the heating time is sufficiently long, the temperature of the steel ingot 2 is uniform.

  As shown in FIG. 1, when the steel ingot 1 is set at a predetermined position, the upper anvil 2 is lowered to the lower anvil 3. In other words, the steel ingot 1 is reduced. By the reduction, the cross-sectional dimension of the steel ingot 1 is reduced or the cross-sectional shape is deformed. The steel ingot 1 is intermittently conveyed in the direction of arrow A by conveying means (not shown). The reduction is repeated in synchronization with this conveyance.

  When the first forging is completed, the base material is turned 90 °. The base material is subjected to the second forging. This forging also reduces the cross-sectional area of the base material and deforms the cross-sectional shape. The base material is further subjected to forging a predetermined number of times. After that, when the base metal is forged and rotated evenly at a certain angle, it gradually approaches a circle. Finally, a round bar steel which is a forged product is obtained by forging with a tool called a tap.

  In order to obtain a round steel bar having no defects, it is necessary to completely press the gap by forging and to prevent overheating of the steel ingot 1. The presence or absence of defects greatly depends on the processing conditions. In the case of forging in that case, it is necessary to always perform the area reduction rate per pass for the material to be forged in the range of 10 to 20%. If the area reduction per pass is less than 10%, the gap is not sufficiently crimped by forging, and if it exceeds 20%, overheating occurs. Therefore, the optimal range was made 10 to 20%.

  Moreover, since the temperature which the center of the steel ingot 1 reaches is so large that the temperature of a heating furnace is high, it is easy to produce overheating. From the viewpoint of suppressing this overheating, the temperature of the heating furnace is preferably set low. However, if the temperature is too low, the forging efficiency is poor. Moreover, since the temperature which the center of the steel ingot 1 reaches is so large that heating time is long, it is easy to produce overheating. From the viewpoint of suppressing overheating, a short heating time is preferable. However, if the heating time is too short, the surface temperature of the steel ingot 1 is too low and the forging efficiency is poor.

  On the other hand, the larger the rolling reduction, the easier the gap is crimped. However, a large processing heat is generated by a large rolling reduction. There is a possibility that overheating may occur due to large processing heat. In addition to the temperature of the heating furnace, the heating time, and the reduction rate, there are various processing conditions that affect the defect rate. Other processing conditions include W / H, the shape of the anvil, the initial shape of the steel ingot 1 and the like. In order to suppress defects, it is necessary to determine appropriate processing conditions.

  Further, in order to pressure-bond the gap, it is necessary to increase W / H. However, in terms of the ability of the press, in the large steel ingot shown above, the maximum value is 1.2, and if it is less than 0.3 from experience, almost no gap can be crimped. Therefore, the appropriate value of W / H is set to 0.3 to 1.2. Moreover, W / H is set to 0.3 to 0.7 when the cross-sectional area of the material to be forged is 100 to 50%. If it is less than 0.3, the pressure-bonding of the gap is insufficient, and if it exceeds 0.7%, it is an anvil ratio in a state where the cross-sectional area of the material to be forged is large, and overheating occurs. Preferably it is set to 0.4-0.6. Further, W / H is set to 0.8 to 1.2 when the cross-sectional area is less than 50% to 15%. When W / H is less than 0.8, the effect of pressure bonding of the gap is insufficient, and when it exceeds 1.2, the range is determined from the above equipment. Preferably, it is set to 1.0 to 1.2.

  As described above, from the viewpoint of overheating, since it is necessary to suppress the processing heat as much as possible, W / H needs to be reduced. When the center temperature is estimated during forging by FEM simulation, the temperature is likely to increase as the cross-sectional area of the material to be forged increases. In other words, it was found that overheating tends to occur when the cross section is large. Therefore, when the cross section is large, W / H is reduced to prevent overheating, and when a small cross section is obtained where overheating is difficult to occur, if W / H is increased and the gap is crimped, there is no internal defect. Round bar steel is obtained.

The above-mentioned FEM simulation means simulation by the finite element method, and the specific method is to estimate the center temperature of the material to be forged by performing a deformation-temperature coupled analysis in the forging process. The presence or absence of the occurrence of overheating is evaluated based on the center temperature. The presence or absence of voids is specifically evaluated by the void pressure bonding parameter Gm + represented by the equation (1) obtained from hydrostatic pressure stress, equivalent stress, and strain.
Gm + = ∫ (σm / σeq) dε (1) where σm: hydrostatic stress, σeq: equivalent stress, ε: strain

  As a material to be forged, C: 1.50%, Si: 0.20%, Cr: 11.3%, Mo: 0.9%, V: 0.25%, the balance consisting of the balance Fe and inevitable impurities The tool steel was also used as a steel ingot shape with a diameter of 925 mm as the material. The forged material 2 is heated to about 1125 ° C. in a heating furnace, and is held in a cantilever state by a manipulator, and the forging material is axially moved at a reduction rate of 10 to 20% per pass by a press. The product was reduced while being fed, and further rotated 90 degrees, and then forging was repeated to make a product. At this time, the anvil used for forging was forged as shown in Table 1, and the internal quality of each shaft-shaped round product obtained by forging was investigated. The results are also shown in Table 1.

  The cross-sectional area of the material to be forged shown in Table 1 is the material to be forged at the time when the initial cross-sectional area before forging of the ingot 1 in FIG. The cross-sectional area is 100 to 50%, the subsequent forging is repeated, and the result is less than 50% to 15%, and the ratio W / H between the anvil width W and the height H of the forged material is changed. I let you. As a result, the internal defect occurrence rate as an evaluation of internal quality is evaluated and calculated by FEM simulation.

表１に示したように、Ｎｏ．１〜８は本発明例であり、Ｎｏ．９〜１６は比較例である。比較例Ｎｏ．９は、１パス当たりの減面率が低いために鍛伸による空隙の圧着が不十分で、内部欠陥の発生が見られる。比較例Ｎｏ．１０は、１パス当たりの減面率が低く、かつ断面積が素材断面積の１００〜５０％までのＷ／Ｈの値が低いために空隙を圧着できないために内部欠陥の発生が生じた。

As shown in Table 1, no. 1-8 are examples of the present invention. 9 to 16 are comparative examples. Comparative Example No. In No. 9, since the area reduction rate per pass is low, the press-bonding of the voids by forging is insufficient, and internal defects are observed. Comparative Example No. No. 10 has a low surface area reduction per pass, and the cross-sectional area is low in the value of W / H up to 100 to 50% of the cross-sectional area of the material.

  Comparative Example No. No. 11 has a low W / H value of 100 to 50% of the cross-sectional area of the material as low as 0.2, so that the press-bonding of the voids is insufficient by forging, and internal defects are generated. Comparative Example No. No. 12 was overheated because the cross-sectional area was as high as 0.8 with a W / H value of 100 to 50% of the cross-sectional area of the material. Comparative Example No. In No. 13, since the cross-sectional area had a low W / H value of less than 50% to 15% of the cross-sectional area of the material, the effect of crimping the gap was insufficient and internal defects were generated.

  Comparative Example No. No. 14, the cross-sectional area is overheated because the value of W / H up to 100 to 50% of the material cross-sectional area is as high as 0.8, and the cross-sectional area is W less than 50% to 15% of the material cross-sectional area. Since the value of / H is low, the effect of press-bonding the gap is insufficient, resulting in large occurrence of internal defects. Comparative Example No. No. 15 causes overheating due to a high area reduction rate per pass, and further causes overheating because the cross-sectional area has a high W / H value of 0.8 to 100% of the material cross-sectional area of 0.8. As a result, internal defects occurred frequently.

  Comparative Example No. No. 16 has a high area reduction rate per pass, causes overheating, and has a high W / H value of 100 to 50% of the cross-sectional area of the material. In addition, since the cross-sectional area has a low W / H value of less than 50% to 15% of the cross-sectional area of the material, the pressure-bonding effect of the air gap is insufficient, so that the incidence of internal defects is extremely high. Thus, all of the comparative examples had poor internal quality due to internal defects. On the other hand, the present invention example No. Since 1-8 satisfy | fills all conditions, it turns out that a good thing with a low internal defect rate is obtained.

FIG. 1 is a perspective view for explaining a manufacturing method according to the present invention.

Explanation of symbols

1 Steel ingot 2 Upper anvil 3 Lower anvil


Patent Applicant Sanyo Special Steel Co., Ltd.
Attorney: Attorney Shiina

Claims (2)

  When forging a to-be-formed material consisting of a difficult-to-work large steel ingot from the direction perpendicular to its axial direction, the upper metallization is squeezed toward the lower metallurgy, and the forging material is forged while being intermittently fed in the longitudinal direction. The area reduction per pass for the material is in the range of 10-20%, the anvil width W of the anvil used for forging, and the height H of the forged material, the cross-sectional area of the forged material is the material cross-sectional area 100 to 50%, W / H is set to 0.3 to 0.7, and W / H is set to 0.8 to 1.2 when the sectional area is less than 50% to 15% of the material sectional area. A central defect prevention method for difficult-to-process large-sized products.   The W / H according to claim 1 is 0.4 to 0.6 when the cross-sectional area of the material to be forged is 100 to 50% of the cross-sectional area of the material, and the cross-sectional area is less than 50% to 15% of the cross-sectional area of the material. Up to, the center defect prevention method for difficult-to-process large-sized products, wherein W / H is 1.0 to 1.2.

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