JP4645303B2 - Overlay welding material for hot forging die and hot forging die using the welding material - Google Patents

Description

The present invention relates to a welding material capable of significantly improving the life of a hot forging die used under severe conditions, and a hot forging die using the same, specifically a tool. By overlay welding on the surface of a mold made of steel, a mold wall that can improve the life by providing an overlay weld layer with excellent toughness, heat check resistance and high temperature wear resistance on the surface. The present invention relates to a prime welding material and a hot forging die using the welding material.

Hot forging is a technology in which a workpiece heated to 1000 to 1300 ° C is placed in a forging die and molded by mechanical force or hydraulic pressure pressurization means, and is processed cold by heating to a high temperature. Compared to the case, deformation resistance is reduced, and even relatively large parts can be manufactured with high productivity. Therefore, they are used in many functional parts such as engine parts such as crankshafts and connecting rods.

However, hot forging is characterized by the fact that a workpiece heated to a high temperature is repeatedly processed and a large number of parts are continuously manufactured using a single mold, and the workpiece is heated to a high temperature. Therefore, although the deformation resistance is lower than that of cold, since a considerably high load is applied at a high temperature, the forging die is subjected to severe mechanical stress and thermal stress, There is a problem that the lifetime is relatively short. Therefore, in order to improve the life of the forging die, the following characteristics are required to be particularly excellent.

(1) Heat check resistance that can withstand the heat load caused by repeated contact with high-temperature workpieces
(2) Impact resistance (toughness) that can withstand repeated impact loads
(3) High temperature wear resistance under repeated high temperature and high surface pressure

SKD61, SKT4, etc. are standardized by JIS as tool steels used for such hot working molds and are still used. However, when used under severe conditions such as hot forging, the expected life is often not obtained, high temperature wear resistance compared to the matrix material on the surface of the mold, A method of improving the mold life is generally performed by overlay welding a material having excellent heat resistance such as heat check resistance particularly on a portion where wear is likely to increase. As this overlay welding material, a Ni-based alloy or a Co-based alloy is often used. Recently, iron alloys whose performance has been improved by adding appropriate amounts of elements such as Cr, Mo, W, and V have also been used (see Patent Document 1 and Non-Patent Document 1).

Japanese Patent Laid-Open No. 11-77375 Forging Technical Report No. 71, pages 10-17

The invention described in Patent Document 1 describes a Co-based alloy that has been developed for the purpose of improving the build-up property that has been a problem with Co-based alloys that have been conventionally used as welding materials for building-up. . It also describes Co-based alloys that were already used at the time of filing this patent.

  Non-Patent Document 1 describes the overlay welding material used in hot mold materials in Germany, and Ni-based alloys and iron alloys to which appropriate amounts of Cr, Mo, W, V, etc. are added. The example which applied is described.

However, the build-up welding material used up to now has the following problems.
In general, when overlay welding is performed, machining for correcting the surface shape is performed after overlay welding. However, although stellite-based Co-based alloys and Ni-based alloys are superior in various properties at high temperatures, such as wear resistance and heat check resistance at high temperatures, the machinability is greatly inferior. However, there is a problem that the alloy itself is very expensive. Therefore, although various characteristics at high temperature are excellent, there is a problem that there is a case where it is unavoidable to adopt the adoption in consideration of the problem in terms of cost.

In addition, Fe alloys that have improved properties such as wear resistance at high temperatures by adding appropriate amounts of Cr, Mo, W, V, etc. have higher temperatures than hot tool steels such as SKD61 used as a base material. Although the characteristics of the above are improved, there is a problem in that the degree of improvement is not sufficient because it is inferior to the aforementioned Co-base alloy and Ni-base alloy. Furthermore, when an alloy element is added to improve the high temperature wear resistance, the toughness is greatly reduced, and there is a problem that the expected life improvement effect cannot be obtained.

The present invention has been found as a result of studies to solve these problems, and is equivalent to or substantially equivalent to stellite-based Co-based alloys and Ni-based alloys in terms of various properties such as wear resistance at high temperatures. The aim is to propose a new Fe-based alloy as a build-up welding material that has close characteristics but is significantly superior in machinability and is cheaper than Co-based alloys and Ni-based alloys. .

Invention of Claim 1 of this invention is mass%, C: 0.30-0.55%, Si: 0.2-1.5%, Mn: 0.4-2.0%, Cr: 4.0-9.0%, V: 0.1-1.0% Mo: 2.0 to 5.0%, W: 2.0 to 11.0%, Ni: 0.3 to 2.0%, a balance welding material for hot forging dies characterized by comprising the balance Fe and inevitable impurities.

The point of the present invention is to add carbide-forming elements such as Cr, V, Mo, W, etc., to precipitate fine carbides, increase temper softening resistance when heated to high temperature, high temperature strength, high temperature wear resistance Of course, by adjusting the addition amount appropriately, the high temperature characteristics will be improved to a level close to that of Co-based alloys and Ni-based alloys without significantly degrading the machinability and weldability. The success is that the addition of an appropriate amount of Ni has achieved a significant improvement in high temperature wear resistance while minimizing the reduction in toughness.

In addition, since the welding material according to claim 1 is designed with an emphasis on improving wear resistance particularly at high temperatures, it cannot be said that the toughness is excellent, and the tool steel, which is the base material, is directly subjected to the meat. In the case of live welding, there is a possibility that cracking may occur with a short life in a portion where a violent material flow occurs or a portion where the surface pressure is high. Therefore, in such a portion, as shown in claim 2, in mass%, C: 0.05 to 0.25%, Si: 0.1 to 1.0%, Mn: 0.2 to 2.0%, Cr: 0.6 to 3.5%, V: 0.1 to 0.5%, Mo: 0.2 to 2.0%, W: 0.2 to 4.0%, Ni: One or more of 0.3 to 3.0%, and V + Mo + W ≧ 0.3%, and the balance Fe and First, overlay welding of a welding material made of inevitable impurities is performed, and overlay welding consisting of a plurality of layers for overlay welding the above-described alloy according to claim 1 as an overlay material is performed on the upper layer portion. It has been found that the occurrence of cracks in a short life can be suppressed. The alloy of claim 2 is characterized in that, by suppressing the C content, high temperature wear resistance is inferior to that of claim 1 but toughness is improved on the contrary. It exhibits a role as a so-called cushion when pressure is applied, and is characterized by being capable of preventing the occurrence of cracks in a short lifetime.

Next, the reasons for limiting each component range of the overlay welding material according to claims 1 and 2 will be described.
First, the alloy according to claim 1 used as the overlay material will be described first.

C: 0.30 to 0.55%
The present invention secures the required high-temperature characteristics, particularly high-temperature wear resistance, by producing an appropriate amount of fine carbides. Moreover, when C is low, there is also a problem that the adhesion between the molten metal flow during welding and the base material is lowered. Therefore, in order to produce the required amount of carbide, it is necessary to add a certain amount or more of C, so the lower limit was made 0.30%. However, if the content is too large, the toughness decreases, so the upper limit was made 0.55%.

Si: 0.2-1.5%
Si is an element necessary as a deoxidizer during the production of steel, increases high-temperature oxidation resistance, and improves hot water flow and adhesion during welding. Therefore, in order to sufficiently obtain the effect for that purpose, the lower limit was made 0.2%. However, if the content is too large, the toughness decreases and the heat check resistance decreases, so the upper limit was made 1.5%.

Mn: 0.4-2.0%
Mn is an element that has the effect of improving the hot water flow and adhesion during welding, so the lower limit was made 0.4%. However, if it is contained in a large amount, the toughness is lowered and the hardness after welding is increased and the machinability is also lowered, so the upper limit was made 2.0%.

Cr: 4.0-9.0%
Cr has the effect of improving heat resistance and corrosion resistance at high temperatures, and also forms carbides by combining with C, and has the effect of increasing high temperature hardness and softening resistance associated with high temperature heating. Therefore, in order to ensure sufficient characteristics as a welding material for the overlay material that places importance on high-temperature wear resistance, it is necessary to contain 4% or more. However, if the content is too large, the toughness and machinability are lowered, and cracking is likely to occur with a low life, so the upper limit was made 9.0%.

V: 0.1-1.0%
V is an element necessary for producing a stable high-hardness carbide, suppressing a decrease in hardness due to precipitation hardening during high-temperature heating, and ensuring high wear resistance. V is effective in reducing the crystal grain size, thereby improving toughness. Therefore, in order to obtain these effects, a content of at least 0.1% is necessary. However, if it is contained in a large amount, the generated carbide becomes coarse and conversely the toughness is lowered and the machinability is also lowered. Therefore, the upper limit was made 1.0%.

Mo: 2.0-5.0%
Mo is an element that forms fine carbides and improves high-temperature strength by improving wear resistance, toughness and resistance to softening. Prone to cracking. Therefore, the addition range is set to 2.0 to 5.0%.

W: 2.0-11.0%
W has the effect of making carbide finer, strengthening the substrate in solid solution, and improving high temperature hardness. Therefore, in the overlay material that requires excellent high temperature wear resistance, it is necessary to obtain the effect sufficiently, so the lower limit was made 2.0%. However, if too much is added, the hot water flow deteriorates during welding and the machinability also decreases, so the upper limit was made 11%.

Ni: 0.3-2.0%
Ni is an element that has an effect of improving toughness, and is an indispensable element for preventing cracking even when a high load is repeatedly applied at a high temperature. Therefore, in order to sufficiently obtain the effect for that purpose, the lower limit was made 0.3%. In addition, if too much is added, the machinability deteriorates, so the upper limit was made 2.0%.

Next, the reasons for limiting each component range of the welding material used as the underlaying material (Claim 2) will be described.
C: 0.05-0.25%
For the underlaying material, it does not need to be in direct contact with the workpiece during forging, so it is not necessary to increase the high temperature wear resistance as the overlaying material. Therefore, it is necessary to set the C content lower than that of the overlay, and the lower limit is set to 0.05% and the upper limit is set to 0.25%.

Si: 0.1-1.0%
Si is an element necessary as a deoxidizer during the production of steel, increases high-temperature oxidation resistance, and improves hot water flow and adhesion during welding. Therefore, in order to sufficiently obtain the effect for that purpose, the lower limit was made 0.1%. The underlay material is used for the purpose of preventing a crack from occurring even if used under severe conditions by repeatedly and continuously being used as a mold by acting as a cushion. Therefore, since the toughness is required to be superior to the overlay material, the upper limit of the amount of Si added, which causes these properties to deteriorate, is suppressed to a lower level than the overlay material, and is set to 1.0%. did.

Mn: 0.2-2.0%
Mn is an element that has the effect of improving the hot water flow and adhesion during welding, so the lower limit was made 0.2%. However, since the toughness decreases when a large amount is contained, the upper limit was made 2.0%.

Cr: 0.6-3.5%
Cr has the effect of improving heat resistance and corrosion resistance at high temperatures, and also forms carbides by combining with C, and has the effect of improving high temperature hardness and softening resistance associated with high temperature heating. However, high temperature wear resistance is not required in the underlaying material as in the overlaying material. Therefore, since the addition amount may be a small amount as compared with the overlay material, the range is set to 0.6 to 3.5%.

  In addition, by including one or more of V, Mo, W, and Ni in the underlaying material, the minimum necessary strength as an underlaying material is ensured and the toughness is also improved. . Hereinafter, the reasons for limiting the component ranges of V, Mo, W, and Ni will be described.

V: 0.1-0.5%, Mo: 0.2-2.0%, W: 0.2-4.0%
V, Mo, and W are elements that improve the high temperature wear resistance by forming carbides with all three elements. Therefore, it is necessary to add a certain amount in a large amount that requires excellent high temperature wear resistance to ensure excellent wear resistance. On the contrary, a higher level of toughness (impact resistance) is required. In addition, since the underlay is also subjected to a high load during use, it is necessary to secure a hardness of HRC30 or more (preferably HRC33 or more) at room temperature. Therefore, in order to obtain the necessary hardness and toughness (impact resistance), V is 0.1% and Mo and W are 0.2% or more.

For the above reasons, the upper limit is set lower than the upper material, considering that the hardness and wear resistance of the upper material are not required and considering the cost, V is 0.5%, Mo is 2 0% and W were 4.0%.

Ni: 0.3-2.0%
Unlike V, Mo, and W, Ni is not a carbide-forming element, but is an element that has a large effect of increasing the toughness of the substrate. Therefore, in order to prevent cracking with a short life, it is an element that is necessary in the same manner as the overlay material for the overlay material that needs to improve toughness. Therefore, it was decided to add in the range of 0.3 to 2.0% as in the case of the overlay.

Of the four elements V, Mo, W and Ni described above, V, Mo and W are not only elements added for improving the toughness of the underlaying material, but also necessary for the underlaying material. It is also an indispensable element for ensuring hardness. Therefore, the lower limit of the total content (V + Mo + W) of the three elements is defined as 0.3%.

When the present invention is actually applied, a welding material made of a wire or a rod (welding rod) is manufactured using the material composed of the above components, and a tool steel such as SKD61 or SKT4 serving as a mother die. Needless to say, it is possible to perform overlay welding by performing TIG welding, arc welding, gas welding, etc. at an appropriate position on the manufactured mold surface, but in addition, the welding material comprising the components of the present invention is dissolved. Even when the molten metal is powdered using the gas atomizing method and overlay welding is performed by the powder plasma welding method, the same excellent effect can be obtained.

  In addition, overlay welding may be performed only in a part where the burden on the die is particularly large in actual forging and wear increases, and the mother die is made of a relatively inexpensive material. The entire surface of the part that contacts the workpiece during forging may be subjected to overlay welding to improve the wear resistance of the entire surface.

In addition, during overlay welding, the base metal to be welded is preheated to about 300-500 ° C and then welded under conditions that do not drop below 200 ° C until post-heating, and 400-500 ° C after welding. It is important to gradually cool after post-heating to the extent of preventing defect formation after welding.

  Next, the invention of claim 3 is mass%, C: 0.30 to 0.55%, Si: 0.2 to 1.5%, Mn: 0.4 to 2.0%, Cr: 4.0 to 9.0%, V: 0.1 to 1.0%, Mo: Gold for hot forging containing 2.0 to 5.0%, W: 2.0 to 11.0%, Ni: 0.3 to 2.0%, and overlay welding a welding material consisting of the remainder Fe and inevitable impurities on the surface of the master die It is a type.

As described above, since the welding material according to claim 1 has excellent high-temperature characteristics, gold that is preliminarily welded to a portion of the master die that requires particularly wear resistance during forging. By using the mold, the life of the mold can be greatly extended as compared with the case where overlay welding is not performed. In addition, when the build-up welding is not performed, an excellent wear resistance is required for the mother die itself, and therefore it is necessary to use an expensive mold material. When using a mold that is welded and welded at a possible position, it is sufficient that the matrix material has a high temperature strength that does not cause plastic deformation or cracking when used as a hot forging die. In addition, since a high level of heat resistance is not required because the welded part does not directly contact the workpiece, the material cost of the mother die can be significantly reduced.

The material of the mother die used may of course be alloy tool steel such as SKD61, which is prescribed for hot molds by JIS, but sufficient performance such as surface wear resistance can be secured by overlay welding. In this case, it is possible to select a cheaper material.

Next, the invention of claim 4 is the mass%, C: 0.05-0.25%, Si: 0.1-1.0%, Mn: 0.2-2.0%, Cr: 0.6-3.5%, V: 0.1-0.5%, Mo : 0.2-2.0%, W: 0.2-4.0%, Ni: One or more of 0.3-3.0%, V + Mo + W ≧ 0.3%, the balance is Fe and inevitable impurities. A hot forging die characterized in that build-up welding is performed on the surface as a build-up material, and the welding material according to claim 1 is build-up welded on the upper layer of the build-up material as a build-up material.

As described above, when the welding material according to claim 1 is not directly welded to the surface of the master mold, but when the welding material shown in claim 2 is used as a building material, the building material is a cushion. By acting as a role, it is possible to prevent the occurrence of cracks in the mold when continuously forging under severe conditions such as high temperature and high surface pressure, and it has excellent wear resistance and is resistant to cracking and has a long life It is possible to provide a hot forging die.

Next, the effect when the present invention is applied will be clarified by examples. Table 1, Table 2
These show the chemical composition of the welding material used as an Example.

  Table 1 shows alloys prepared as overlay materials, among which Nos. 1 to 4 are alloys corresponding to the present invention, and Nos. 5 to 9 have some components outside the scope of the invention. Comparative alloy. In addition, Nos. 10 to 14 are alloys that have already been used as overlay materials, and Nos. 10 and 11 increase the wear resistance by adding Cr, Mo, W, The welding alloy for overlaying, 12 is a welding alloy for overlaying Ni-based, and 13 and 14 are welding alloys of Co-based called stellite. In addition, 15 and 16 are not overlay welding alloys but SKD61 and SKT4 that have been widely used for mother molds.

  Table 2 shows alloys prepared as welding alloys for underlaying, Nos. 17 to 20 are welding alloys satisfying the conditions of the component range of the present invention, and Nos. 21 to 22 It is a comparative alloy whose components are out of range.

  These match golds were prepared by adjusting the components and melting, casting the molten metal in a mold, and forming it into a rod shape to produce a welding rod. Moreover, about No. 1 alloy, the powder was prepared simultaneously by the gas atomization method. Then, a No. 15 alloy (SKD61) steel plate with a thickness of 16 mm and a groove processed to a depth of 10 mm and a width of 15 mm was prepared, and the alloys shown in Tables 1 and 2 were applied to the groove portion by TIG welding (No. About the powder of the .1 alloy, by overlay welding (by powder plasma welding), if necessary, the overlay portion was cut out to produce a test piece, and the test described later was performed. Table 3 shows the conditions for TIG welding. Also, 15 and 16 alloys, which are conventional molds, are heat-treated iron plates (15 alloys are tempered at 1030 ° C for 30 minutes, 580 ° C for 90 minutes, 16 alloys are quenched at 950 ° C for 30 minutes, 550 ° C X90 minutes tempering) and cut out to prepare a test piece.

  The test was conducted for each of wear resistance, impact resistance (toughness), heat check resistance, and machinability. However, for the underlay material, the heat check resistance and the machinability are not essential required characteristics, and thus the evaluation was omitted.

The wear resistance was evaluated by measuring the hardness as welded and the high temperature hardness. In particular, the overlay material must have excellent wear resistance at high temperatures, so accurate evaluation cannot be performed only by hardness at room temperature. Therefore, the temperature is maintained after heating to 600 ° C, and the hardness after 2 hours has passed. Was evaluated by measuring. This is because in the case of an Fe alloy, the hardness tends to drop rapidly around 600 ° C., and the hardness is different between room temperature and 600 ° C. Note that the temperature of 600 ° C corresponds to a temperature slightly higher than the die surface temperature reached when processing is continued continuously in normal hot forging (excluding locations that are locally hot). Therefore, it was judged that the hardness measurement at this temperature was appropriate for the evaluation. In addition, since the underlaying material does not require the wear resistance as high as the overlaying material, it is necessary to omit the measurement of the high temperature hardness and ensure the strength to withstand the compressive force applied. For the purpose of confirming that it has the strength to be welded, the hardness as welded was measured (room temperature).

  Impact resistance (toughness) was evaluated based on the load at the time of breaking by performing a four-point bending test. The bending test was performed by machining the welded portion of the above-mentioned No. 14 alloy (SKD61) steel plate that was welded to the center of each steel plate so that the height of the welded portion was the same as the other portions. Prepare a notched plate with dimensions of 200mm x 100mm x 16mm, with the welding point located in the center and facing down, the distance between the lower fulcrum is 150mm and the distance between the upper fulcrum is 40mm Evaluation was performed by performing a four-point bending test under the conditions. The reason why the 5R notch processing was performed was that when the evaluation was performed in a smooth state, the result was more likely to simply depend on the strength of the material, making it difficult to evaluate toughness correctly. The results are shown as a ratio with the breaking load of No. 15 alloy (SKD61), which is a conventional mold, being 100.

The heat check resistance was cut out from the welded portion described above to produce a cylindrical test piece of φ10, 20 mm in length, and this test piece was heated to 700 ° C. at high frequency, maintained for 2 seconds and then water-cooled 500 times. This is an investigation of the occurrence of cracks after testing. In actual use, the test conditions are considerably more severe than actual conditions because they are not cooled by water and the temperature does not rise to 700 ° C. And as a result of investigating the crack occurrence situation, even when cracks are not recognized or cracks are recognized, if they are small cracks of D / 8 or less from the side, ○, cracks from the side D / 8 to D / 4 The case where the crack was moderate was judged as Δ, and the case where the crack had progressed more than that was judged as x.

The machinability was evaluated by the end milling of the welded portion welded on the No. 15 alloy described above under the conditions shown in Table 4 and the cutting distance until the flank corner average wear width reached 0.08 mm. For the conventional mold materials No. 15 and 16, the machinability of the mold material itself was evaluated by the same method. In addition, the result showed the value as a ratio when the cutting distance of No. 15 alloy was 100. The results including the above-described evaluation are shown in Table 5 (superior material) and Table 6 (underscore material).

  As is apparent from Table 5, the No. 5 and 7 alloys, which are comparative alloys, have a low C content in the No. 5 alloy, and the No. 7 alloy has a low content of Cr and Mo as carbide forming elements. Strength improvement effect due to precipitation of carbides becomes insufficient, hardness as welded, low-temperature hardness is low, high-temperature wear resistance is lowered, heat checkability is inferior, No. 6 alloy contains C Since the ratio is high, the toughness is reduced, the bending test breaking load is lowered, and the machinability is slightly lowered. The No. 8 alloy has a low W content which has a large effect on improving high-temperature strength. Although the hardness at room temperature is sufficiently high, the high temperature hardness and heat checkability are greatly inferior, and the No. 9 alloy has low Ni content, so toughness (bending test breaking load), heat resistance check It is inferior in nature.

  In addition, among No.10-14 alloys that have been used in the past, No.10 and 11 alloys that are built-up materials of Fe alloy are V, Mo, W that improve high temperature wear resistance. Is not sufficient, wear resistance, heat check property is greatly inferior, and 11 alloy is not added Ni, toughness is also inferior, Ni-based alloy, Co-based alloy No. 12 The ~ 14 alloy does not decrease in hardness even when heated to a high temperature and has excellent heat check properties, but is extremely inferior in machinability.

  In addition, the conventional mold materials (SKD61, SKT4) No.15 and 16 alloys have a high temperature hardness at 600 ° C of 20.4 (SKD61) and 15.4 (SKT4) at HRC, which is significantly lower than the hardness at room temperature. At the same time, the heat check property is inferior.

  On the other hand, the No. 1-4 alloys that are the build-up materials of the present invention have a hardness at room temperature of HRC55 or higher, and a high temperature hardness at 600 ° C. of HRC34 or higher that is equal to or higher than that of Ni-based alloys and Co-based alloys The heat check property is excellent, the high temperature wear resistance, the toughness due to the addition of components for improving the heat check property, and the machinability are reduced to a smaller extent than the conventional materials.

  Next, it is the evaluation result of the underlaying material, the No.17-20 alloy which is the underlaying material satisfying the conditions of the component range of the present invention, the hardness as welded is HRC33 or more, and The bending test breaking load was 1.3 times or more that of the conventional mold material, and it was confirmed that the bending test fracture load was excellent for the role of a cushion. On the other hand, No. 21 and 22 which are comparative alloys have low Cr content in Alloy 22, and 22 alloy has a low total content of carbide forming elements V, Mo and W. Although it was excellent with respect to a certain bending test breaking load, the hardness as welded is inferior to the No. 17-20 alloy.

  From the above results, we were able to grasp the range of chemical composition of the overlay material with excellent high temperature wear resistance and heat check resistance and the overlay material with excellent toughness, so it was actually manufactured using the conventional type SKD61. The welded material tested and evaluated in the above example was welded to a portion of the flange yoke where the surface of the die was heavily worn, and heated and hot forged at a temperature of 1200 ° C. Was investigated. Overlay welding was evaluated by selecting a portion of the mold surface that was known to have a large amount of wear in past manufacturing and overlay welding at that location. In addition, during overlay welding, in order to prevent welding defects from occurring, perform preheating of 400 ° C x 2 hr before welding, and weld so that it does not fall below 250 ° C until after heating. After welding, after-heating was performed at 450 ° C. for 5 hours, and then gradually cooled to room temperature. Then, finishing processing of the necessary surface was performed after overlay welding, and hot forging of 10,000 shots and 15000 shots was actually performed, and the presence or absence of cracking and the amount of wear of the overlay welds were measured after forging.

In addition, since the amount of wear for each part of the die surface caused by the forging of the flange yoke has been clarified from past forging results, the wear becomes particularly large from the parts subjected to the above-described overlay welding. The part was selected, and the measurement part of the wear amount was determined. And since it is difficult to directly measure the mold itself during forging, the forged product after 100 shots and the forged product after 10,000 shots are sampled and the forged products are determined as described above. The surface shape of the measured part was measured with a three-dimensional shape measuring instrument, and the wear amount was calculated by converting the difference between the two surface shapes as an area value. Although the overlay welding was not performed about the conventional type | mold material, it evaluated by measuring the amount of wear of the same site | part by the same method. The amount of wear shown in Table 7 (after 10,000 shots) is a ratio value obtained by setting the amount of wear when the conventional mold material is hot forged without overlay welding as 100.

  As is apparent from Table 7, the molds (test Nos. 9 to 11) using the overlay material composed of No. 5 and 7 alloys as comparative examples and the No. 10 alloy as conventional alloys are compared with the conventional mold materials. Since the degree of improvement in wear resistance at high temperatures is not sufficient, the amount of wear can be reduced slightly compared to when used as it is without overlay welding to the conventional mold (SKD61), but the effect is small, The occurrence of cracks could not be prevented.

  On the other hand, when the overlay material of the present invention was used, not only was the amount of wear reduced to 1/2 or less compared to the conventional mold material, but it was also possible to completely prevent cracking up to 10,000 shots. Is. In addition, this wear amount is almost the same as the wear amount of the Ni-base alloy and Co-base alloy shown in the comparative example, and in addition to the cost difference of the alloy itself, it is large in terms of machinability. Considering that there is a difference, the cost can be greatly reduced as compared with the case of using a Ni-based alloy or a Co-based alloy.

  Even when the overlay material of the present invention was used, some cracks were observed after 15,000 shots. However, even after 15000 shots, if the overlay material is welded in advance after welding the overlay material (Test Nos. 5 to 8), there is no cracking and the wear amount is only the overlay material Compared with, it was good with almost no difference. From this result, it was confirmed that the presence of the overlay material is effective in preventing cracking and improving the life.

As described above, the present invention is an Fe-based alloy, and by adding an appropriate amount of Cr, V, Mo, W, Ni, excellent high temperature wear resistance and heat check resistance can be achieved without greatly degrading the machinability. While it was possible to obtain, there was a problem that the Ni-based and Co-based overlaying materials, which had the best high-temperature characteristics of the conventional overlaying materials, were expensive and the machinability was significantly inferior, It has a feature that it can greatly contribute to solving the problem.

Claims (4)

In mass%, C: 0.30 to 0.55%, Si: 0.2 to 1.5%, Mn: 0.4 to 2.0%, Cr: 4.0 to 9.0%, V: 0.1 to 1.0%, Mo: 2.0 to 5.0%, W: 2.0 to A build-up welding material for hot forging dies, comprising 11.0%, Ni: 0.3 to 2.0%, and remaining Fe and inevitable impurities. As an underlay material, in mass%, C: 0.05 to 0.25%, Si: 0.1 to 1.0%, Mn: 0.2 to 2.0%, Cr: 0.6 to 3.5%, V: 0.1 to 0.5%, Mo: 0.2 to 2.0 %, W: 0.2 to 4.0%, Ni: 0.3 to 3.0%, one or more of them, V + Mo + W ≧ 0.3%, and the balance Fe and inevitable impurities are used. Overlay welding material for hot forging dies characterized by using the described welding material as an overlay material. In mass%, C: 0.30 to 0.55%, Si: 0.2 to 1.5%, Mn: 0.4 to 2.0%, Cr: 4.0 to 9.0%, V: 0.1 to 1.0%, Mo: 2.0 to 5.0%, W: 2.0 to A die for hot forging, characterized in that a welding material containing 11.0%, Ni: 0.3 to 2.0%, and the balance Fe and unavoidable impurities is welded on the surface of the mother die. In mass%, C: 0.05-0.25%, Si: 0.1-1.0%, Mn: 0.2-2.0%, Cr: 0.6-3.5%, V: 0.1-0.5%, Mo: 0.2-2.0%, W: 0.2 -4.0%, Ni: One or more of 0.3-3.0%, V + Mo + W ≧ 0.3%, and material consisting of the balance Fe and unavoidable impurities as overlay material on the matrix surface Further, a hot forging die characterized in that the welding material according to claim 1 is overlay welded as an overlay material on an upper layer portion of the overlay material.