JP4877293B2 - Manufacturing method of anvil for forging - Google Patents

Description

  The present invention relates to a method for manufacturing a forging anvil used during hot forging, and is particularly suitable as a free forging anvil that is rolled down by a flat anvil from two directions, and is suitable for forging of difficult-to-work materials with high deformation resistance. The present invention relates to a method for manufacturing a forging anvil.

  An anvil used for forging and forging a difficult-to-work material such as a high Cr-high Ni alloy at a high frequency of 100 times or more per minute is severely worn by an impact load at the time of reduction, a high-temperature thermal cycle, and the like. For this reason, when the anvil reaches the end of its life, it is used by repeatedly performing maintenance and overlay repair on the rolling surface. In order to reduce the forging cost, it is essential to improve the life of this anvil and reduce the number of repair steps.

  Conventionally, as an anvil for forging, for example, γ ′ precipitation strengthening is applied to the surface layer portion directly on a base metal made of hot die steel such as SKT4 or through an intermediate layer made of a matrix-reinforced Ni-base alloy or the like. A type Ni-based alloy was used as a work surface portion. The anvil with the γ 'precipitation strengthened Ni-base alloy is intended to improve the life by the precipitation layer of the work surface portion being subjected to aging by the temperature rise during use and being strengthened by precipitation.

  However, since it is very early in use and before precipitation strengthening is achieved, it undergoes crushing, and surface cracks (hereinafter also referred to as “heat check”) due to thermal fatigue due to repeated heating and cooling occur. Can not achieve a sufficient life. In addition, when the aging treatment is performed by heating the whole after the build-up, at the treatment temperature, the hardness should be reduced by an undertemper of a base metal composed of a lower mold that should firmly support the work surface, that is, a hot die steel. Since it falls, processing temperature is restrict | limited to about 650 degreeC or less. As a result, sufficient precipitation strengthening of the work surface portion is not performed at the above processing temperature, and cracking due to heat check occurs, so that a sufficiently long life cannot be obtained.

  Regarding an anvil with improved resistance to the above heat check, Patent Document 1 discloses a high-speed four-side forging anvil formed of an integral γ ′ precipitation-strengthened Ni-base alloy and a base metal made of Ni-base. An anvil for high-speed four-sided forging is disclosed in which a work surface (pressed surface) is built up with a γ ′ precipitation strengthened Ni-based alloy. However, when steel for hot forging die is used for the base metal, if the aging treatment is performed at 700 to 900 ° C. for the purpose of strengthening the deposition of the build-up layer, the strength of the base metal is lowered. It was.

  With respect to this problem, if the entire anvil is made of a Ni-based alloy, it is possible to extend the life. However, Ni-based alloys are very expensive, and in a forging machine having a heavy anvil, using an Ni-based alloy for the entire anvil increases equipment costs and causes an increase in forging costs. It is not realistic to take appropriate measures.

  The anvil targeted by the present invention is an anvil used in a horizontally opposed high-speed forging machine equipped with a flat anvil, and this horizontally opposed high-speed forging is per shot compared to forging by a high-speed four-sided forging device. This is a forging method in which the amount of rolling and the amount of material elongation are large, and the contact time between the anvil and the material is long. In this way, the anvil used for the horizontally opposed high-speed forging machine is used under extremely severe conditions with large wear, so the manufacture of an anvil for forging that can improve the life while satisfying the economy. A method was desired.

JP 2001-62541 A (claims, paragraphs [0002] to [0009], [0013], etc.)

  As described above, for example, in the conventional anvil in which the work surface of the base metal is overlaid with a γ ′ precipitation strengthened Ni-based alloy, when the aging heat treatment is performed to precipitate and strengthen the overlaid portion, the strength of the base metal There was a problem of causing a drop.

  The present invention has been made in view of the above problems, and the problem is that the life of an anvil is improved more than before while using cheap steel for hot forging die as compared with a Ni-based alloy as a base metal. An object of the present invention is to provide a method for manufacturing an anvil for hot forging that can be made.

The present invention has been completed based on the knowledge obtained by the studies made to solve the problems described above, the gist lies in the manufacturing method of forging for anvil below.

An intermediate layer made of a solid solution strengthened Ni alloy was interposed between a base metal made of hot die steel and a surface layer made of a γ 'precipitation strengthened Ni alloy and serving as a pressing surface of the forged material. a method of manufacturing a forging anvil, the gold sock, cooled after soaking for more than 10 hours at from 620 to 670 ° C., further 670 to 750 forging anvil subjected to a two-stage heat treatment of cooling after soaking for more than 10 hours at ° C. Is a manufacturing method of
The surface layer γ ′ precipitation-strengthened Ni alloy is, by mass, C: 0.03 to 0.10%, Cr: 18.0 to 21.5%: Mo: 5.0 to 6.5%, Co: 11.0 to 15.0%, Al: 1.8 to 2.3%, Ti: 2.90 to 3.15%, Fe: 5.0% or less, and W: 0.5 to 1.25 %, With the balance being composed of Ni and impurities,
The solid solution strengthened Ni alloy of the intermediate layer is, by mass, C: 0.10% or less, Cr: 20.0-23.0%, Mo: 8.0-10.0%, Nb and Ta. A method for producing an anvil for forging comprising : 3.15 to 4.15% in total and Fe: 5.0% or less, with the balance being composed of Ni and impurities .

In the present invention, “γ ′ precipitation-strengthened Ni alloy” means a precipitation-strengthened Ni alloy that increases the strength by using precipitation of γ ′ phase (Ni ₃ (Al, Ti)).

  Moreover, in the following description of this specification, the description of "%" regarding alloy component content shall represent "mass%".

  The present inventors have studied a method for manufacturing a forging anvil that can improve the life of an anvil more than before while using cheap steel for hot forging die as compared with a Ni-based alloy as a base metal. Repeatedly, the following knowledge (a) to (d) was obtained and the present invention was completed.

  (A) It is necessary to raise the strength (hardness) of the γ ′ precipitation strengthened Ni alloy of the surface layer by performing an aging heat treatment. However, when a normal aging heat treatment is carried out in an anvil in which a steel layer for hot metal forming the base metal, an intermediate layer, and a surface layer made of γ ′ precipitation strengthened Ni alloy are integrated by overlay welding, The hardness of the layer is increased, the hardness difference between the intermediate layer and the surface layer is increased, and cracks are likely to occur.

  (B) On the other hand, when heat treatment at a relatively low temperature of about 650 ° C. is performed, sufficient precipitation strengthening in the surface layer is not achieved, cracking due to heat check occurs, and a sufficient life of the anvil cannot be obtained. .

  (C) In order to solve the problems (a) and (b) above, it is possible to reduce the difference in hardness between the intermediate layer and the surface layer by increasing the hardness of the surface layer by aging treatment. It is possible to suppress the occurrence of cracks during hot forging.

  That is, if the hardness of only the surface layer of the anvil is high, the impact load during forging is borne only by the hard and thin surface layer, so that the surface layer is likely to crack due to insufficient hot ductility. On the other hand, by reducing the hardness difference between the surface layer and the intermediate layer, the impact load is borne by the total thickness of both the surface layer and the intermediate layer, and the layer thickness that bears the impact load is increased. Only the impact load is relaxed. Furthermore, since the hardness of the surface layer does not become excessively high, cracks due to insufficient hot ductility hardly occur in the surface layer.

  (D) Based on the knowledge of (c) above, as a result of conducting a preliminary test to investigate the effect of suppressing cracking by variously changing the heat treatment conditions, as described in detail below, at 620 to 670 ° C. for 10 hours or more It was confirmed that the generation of cracks during forging could be suppressed by performing a two-stage heat treatment after cooling after soaking, followed by further soaking at 670-750 ° C. for 10 hours or more.

1) Alloy material used for preliminary investigation test on cracking suppression effect On the upper surface of a test piece of SKD61 equivalent steel of hot mold steel of length 100mm, width 100mm and thickness 40mm, an intermediate layer equivalent to Inconel 625 Overlay welding of the first layer with a thickness of 4 mm using an alloy, and overlay welding of the second layer with a thickness of 6 mm using an alloy equivalent to Udimet 520 as the surface layer on the upper surface, Was used as a test material.

  Table 1 shows the representative chemical composition of each alloy material used for the test material.

2) Heat treatment conditions and test results Using the above test materials, heat treatment was performed under the four types of heat treatment conditions shown in Table 2 below, and the hardnesses of the surface layer and the intermediate layer were measured. Asked. Here, as for each hardness of the surface layer and the intermediate layer, the value of HV10 was measured at a test force of 98.07 N according to the method defined in JIS Z2244.

  From the results in the table, by appropriately selecting the temperature and processing time of the two-stage heat treatment, the heat treatment can be performed at a temperature lower than about 800 ° C., which is an aging treatment temperature usually performed for precipitation strengthening of the Ni-base alloy. However, it was confirmed that a long-life anvil with a high hardness of the surface layer and a small difference in hardness between the intermediate layer and the surface layer was obtained.

  The method for manufacturing an anvil for forging according to the present invention has been completed in support of the findings shown in the above (a) to (d).

  According to the method of the present invention, a solid solution strengthened Ni alloy is formed between a base metal made of hot mold steel and a surface layer made of a γ 'precipitation strengthened Ni alloy. An anvil including an intermediate layer made of an alloy is cooled by soaking for 10 hours or more at 620 to 670 ° C., and then subjected to a two-stage heat treatment after cooling for 10 hours or more at 670 to 750 ° C. An anvil for hot forging with low cost and improved life can be manufactured.

  FIG. 1 is a diagram showing an example of the shape of a flat anvil targeted by the method of the present invention. As described above, the method of the present invention comprises a solid metal 4 between a base metal 4 made of hot die steel and a surface layer 2 made of a γ ′ precipitation-strengthened Ni alloy and serving as the pressure face 1 of the forged material. A method for producing a forging anvil including an intermediate layer 3 made of a melt strengthened Ni alloy, wherein the anvil is soaked at 620 to 670 ° C. for 10 hours or more and then cooled, and further at 670 to 750 ° C. for 10 hours. This is a method for manufacturing an anvil for forging which is subjected to two-stage heat treatment to cool after soaking. The reason why the method of the present invention is defined as described above and preferred embodiments will be described in detail below.

1. Hot mold steel is used as the base metal As the base metal for the forging anvil, cheap steel for hot mold is used as compared with the Ni-based alloy. In the method of the present invention, the life of an anvil can be improved more than before even when such inexpensive steel for hot mold is used. Specifically, SKD6, SKD61, SKD62, SKD7, SKD8, SKT3, SKT4, SKT6, and the like, which are steels for hot dies among alloy tool steels defined in JIS G4404. Among these, SKD61 has a relatively high quenching and tempering hardness and is preferable as a material for the base metal.

2. Γ 'precipitation-strengthened Ni alloy is used as the surface layer. For the surface layer of the forging anvil used as the pressed surface of the forged material, it is necessary to use a material having high hardness. A γ ′ precipitation-strengthened Ni alloy that can easily obtain high hardness is used. Here, the γ ′ precipitation-strengthened Ni alloy means a precipitation-strengthened Ni alloy that increases the strength by utilizing precipitation of the γ ′ phase (Ni ₃ (Al, Ti)) as described above.

  As the γ ′ precipitation strengthened Ni-based alloy used for the surface layer of the forging anvil, an alloy containing one or more of Al, Ti, Nb and Ta is preferable. Alloy names include Inconel 713C, Inconel 718, M252, Waspaloy, Rene 41, Udimet 500, Udimet 520, and the like.

  Among the above alloys, in particular, alloys corresponding to Udimet 520, C: 0.03 to 0.10%, Cr: 18.0 to 21.5%, Mo: 5.0 to 6.5%, Co : 11.0 to 15.0%, Al: 1.8 to 2.3%, Ti: 2.90 to 3.15%, Fe: 5.0% or less and W: 0.5 to 1.25% It is preferable to use an alloy containing Ni and the balance of Ni and impurities.

3. Use of solid solution strengthened Ni-base alloy as intermediate layer When γ 'precipitation strengthened Ni alloy constituting surface layer is directly overlay welded to hot die steel constituting base metal for forging anvil Since cracks due to dissimilar material welding are likely to occur, overlay welding of a solid solution strengthened Ni-based alloy is performed on the upper surface of the base metal as a buffer material for dissimilar material welding, and this is used as an intermediate layer on its upper surface, and γ ′ Overlay welding of precipitation-strengthened Ni alloy.

  The solid solution strengthened Ni-based alloy used as the intermediate layer of the forging anvil preferably includes one or more of Al, Ti, Nb, and Ta. The alloy trade names include Inconel 610, Inconel 625, Inconel 82, and the like.

  In particular, an alloy equivalent to Inconel 625, which is often used for dissimilar material welding, C: 0.10% or less, Cr: 20.0 to 23.0%, Mo: 8.0 to 10.0%, the total of Nb and Ta : 3.15-4.15% and Fe: It is preferable to use an alloy having a composition composed of Ni and impurities with the balance of Ni and 5.0% or less.

4). In the method for producing an anvil for forging according to the present invention, as shown in the following (1) and (2), the first-stage heat treatment is performed. Then, by performing a two-stage heat treatment for performing a second-stage heat treatment, the hardness difference between the surface layer and the intermediate layer is reduced, cracking is prevented, and the strength of the base metal is also prevented from being lowered.

(1) First-stage heat treatment The first-stage heat treatment is a process of cooling after soaking at 620 to 670 ° C. for 10 hours or more. When the soaking temperature is less than 620 ° C., the hardness is insufficient due to insufficient aging of the surface layer and intermediate layer of the forging anvil, and cracking occurs. On the other hand, when the soaking temperature is higher than 670 ° C., the hardness of the surface layer is excessively increased, and cracks are generated due to an increase in the hardness difference between the intermediate layer and the surface layer. If the soaking time is less than 10 hours, cracks occur due to insufficient hardness of the intermediate layer and the surface layer.

  Therefore, in the first stage heat treatment, cooling was performed after soaking at 620 to 670 ° C. for 10 hours or more.

(2) Second-stage heat treatment The second-stage heat treatment is a treatment of cooling after soaking at 670 to 750 ° C. for 10 hours or more. If the soaking temperature is less than 670 ° C., the hardness is insufficient due to insufficient aging of the surface layer of the forging anvil, and cracking occurs. On the other hand, when the soaking temperature is higher than 750 ° C., the hardness of the surface layer is excessively increased, and cracks are generated due to an increase in the difference in hardness between the intermediate layer and the surface layer. If the soaking time is less than 10 hours, cracks occur due to insufficient hardness of the intermediate layer and the surface layer.

  Therefore, in the second heat treatment, cooling was performed after soaking at 670 to 750 ° C. for 10 hours or more.

5. Forged material targeted by the present invention The forged material targeted by hot forging using the forging anvil manufactured by the method of the present invention is not particularly limited, but the anvil manufactured by this method is an anvil life It is suitable for forging of the following difficult-to-process materials having a high deformation resistance that significantly reduces For example, it is suitable for hot forging of stainless steel such as SUS316 or SUS310 having a high Cr or Ni content, high alloy steel such as NCF800 or NCF825, or Ni-based alloy.

  In order to confirm the effect of the method for manufacturing a forging anvil according to the present invention, an anvil manufacturing test shown below was conducted and the results were evaluated.

  Overlaying the first layer with a thickness of 3-5 mm using an Inconel 625 equivalent alloy as the intermediate layer on the upper surface (pressure side) of 140 mm thick hot mold steel SKD61 equivalent steel, The second layer is overlay welded with a thickness of 5 to 7 mm using an alloy equivalent to Udimet 520 as the surface layer, and has the shape shown in FIG. 1, with a thickness (H) of 150 mm and a width (W) of 360 mm. A flat anvil with a length (L) of 900 mm was obtained. Here, as the SKD61 equivalent steel, the Inconel 625 equivalent alloy and the Udimet 520 equivalent alloy, those having the component compositions shown in Table 1 were used.

  The anvil manufactured as described above was subjected to heat treatment under three conditions. Table 3 shows an anvil material and heat treatment conditions.

  Test No. 1 which is a test of the comparative example was soaked at 650 ° C. for 24 hours, and test No. 2 was soaked at 700 ° C. for 24 hours and Test No. 3 which was a test of the present invention example. Then, after soaking at 650 ° C. for 24 hours, cooling was performed, and further, soaking at 700 ° C. for 24 hours was performed.

  The forging test is performed by attaching a flat anvil subjected to the above heat treatment to a horizontally opposed high-speed forging machine and using a steel ingot of high alloy steel (25% Cr-35% Ni-3% Mo steel) which is a difficult-to-work material as a material. This was done by a forging method. A square with a length of 500 mm on one side, a corner having a rounded shape with a radius of curvature of 120 mm, and a steel ingot with a length of 2000 mm as a forging material, after heating this forging material to 1290 ° C, Using a flat metal laying having the materials and layer configurations shown in Table 3 and further heat-treated, hot forging was performed with a reduction amount of 80 mm per shot. Here, forging for reducing the material to be forged over the entire length in the longitudinal direction was defined as one pass.

  In the forging using the above horizontal opposed high-speed forging machine, the amount of reduction per shot is larger than forging by a high-speed four-sided forging device, the contact time between the material to be forged and the anvil is longer, and the material to be forged and the anvil are The friction of is also great. Therefore, the forging conditions in the above embodiment are extremely severe forging conditions.

  The life of the anvil found as a result of the forging test is also shown in Table 3 above. In the anvil life column in the table, a circle indicates that no cracks were observed on the pressed surface of the anvil even if forging was performed for 20,000 passes or more, and an X indicates a pressed surface of the anvil by forging less than 20000 passes. Indicates that cracking was observed.

  From the results in the table, in Test Nos. 1 and 2, which are tests of comparative examples that do not satisfy the heat treatment conditions defined in the present invention, cracks were observed on the pressure surface of the anvil despite forging of less than 20,000 passes. On the other hand, in test number 3, which is a test of the present invention example that satisfies the conditions specified in the present invention, even if forging over 20000 passes, no cracks are observed in the anvil and it has a long life. confirmed.

  As described above, according to the method of the present invention, the life of an anvil can be improved more than before while using inexpensive tool steel as a base metal for an anvil.

  According to the method of the present invention, a solid solution strengthened Ni alloy is formed between a base metal made of hot mold steel and a surface layer made of a γ 'precipitation strengthened Ni alloy. An anvil with an intermediate layer made of an alloy is cooled after soaking for 10 hours or more at 620 to 670 ° C., and then subjected to two-stage heat treatment for cooling after soaking for 10 hours or more at 670 to 750 ° C. It is possible to manufacture an anvil for hot forging which has excellent properties and has an improved life. Therefore, the method for manufacturing an anvil for forging according to the present invention is particularly effective in reducing the manufacturing cost of a flat anvil used in a hot forging process using a horizontally opposed high-speed forging machine having a high deformation resistance and improving its life. It is an excellent technology that can make a significant contribution.

It is a figure which shows an example of the shape of the flat anvil which the method of this invention makes object.

Explanation of symbols

  1: pressed surface, 2: surface layer, 3: intermediate layer, 4: base metal

Claims (1)

An intermediate layer made of a solid solution strengthened Ni alloy was interposed between a base metal made of hot die steel and a surface layer made of a γ 'precipitation strengthened Ni alloy and serving as a pressing surface of the forged material. a method of manufacturing a forging anvil, the gold sock, cooled after soaking for more than 10 hours at from 620 to 670 ° C., further 670 to 750 forging anvil subjected to a two-stage heat treatment of cooling after soaking for more than 10 hours at ° C. Is a manufacturing method of
The surface layer γ ′ precipitation-strengthened Ni alloy is, by mass, C: 0.03 to 0.10%, Cr: 18.0 to 21.5%: Mo: 5.0 to 6.5%, Co: 11.0 to 15.0%, Al: 1.8 to 2.3%, Ti: 2.90 to 3.15%, Fe: 5.0% or less, and W: 0.5 to 1.25 %, With the balance being composed of Ni and impurities,
The solid solution strengthened Ni alloy of the intermediate layer is, by mass, C: 0.10% or less, Cr: 20.0-23.0%, Mo: 8.0-10.0%, Nb and Ta. A method for producing an anvil for forging comprising : 3.15 to 4.15% in total and Fe: 5.0% or less, with the balance being composed of Ni and impurities .

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