阅读说明：本技术 工具材料的再生方法及工具材料 (Regeneration method of tool material and tool material ) 是由 石川毅 萨田寿隆 高桥和仁 横田知宏 吉田健太郎 中村纪夫 本泉佑 于 2019-02-07 设计创作，主要内容包括：本发明提供一种在高速工具钢基材的任意区域形成适当的堆焊层来进行修补的工具材料的再生方法及通过该再生方法制造出的工具材料,尤其提供一种即使是具有急冷凝固组织的高速工具钢基材也能够形成适当的堆焊层而不会产生剥离或裂纹等的工具材料的再生方法。为了解决上述课题,本发明提供一种工具材料的再生方法,其特征在于,具有：热处理工序,以超过700℃且低于825℃的温度对高速工具钢基材进行热处理；及修补堆焊工序,在实施了热处理后的高速工具钢基材的表面上形成修补堆焊层。热处理温度优选设为超过775℃且低于825℃,高速工具钢基材优选为高速工具钢激光堆焊层。(The present invention provides a method for regenerating a tool material for repairing a high-speed tool steel base material by forming an appropriate weld overlay in an arbitrary region of the base material, and a tool material manufactured by the regeneration method, and particularly provides a method for regenerating a tool material capable of forming an appropriate weld overlay without peeling, cracking, or the like even in a high-speed tool steel base material having a rapid solidification structure. In order to solve the above problem, the present invention provides a method for recycling a tool material, comprising: a heat treatment step of heat-treating the high-speed tool steel substrate at a temperature exceeding 700 ℃ and lower than 825 ℃; and a repair weld overlay step of forming a repair weld overlay on the surface of the high speed tool steel base material subjected to the heat treatment. The heat treatment temperature is preferably set to more than 775 ℃ and less than 825 ℃, and the high speed tool steel substrate is preferably a high speed tool steel laser weld overlay.)

1. A method for recycling a tool material, comprising:

a heat treatment step of heat-treating the high-speed tool steel substrate at a temperature exceeding 700 ℃ and lower than 825 ℃; and

and a repair weld overlay step of forming a repair weld overlay on the surface of the high speed tool steel base material subjected to the heat treatment.

2. The method for recycling a tool material according to claim 1,

the temperature of the heat treatment is set to exceed 775 ℃ and be lower than 825 ℃.

3. The method for recycling a tool material according to claim 1 or 2,

the high-speed tool steel base material is a high-speed tool steel laser surfacing layer.

4. The method for recycling a tool material according to any one of claims 1 to 3,

the retention time of the heat treatment is set to 30 minutes or more.

5. The method for recycling a tool material according to any one of claims 1 to 4,

the hardness of the high-speed tool steel base material is reduced to 500HV or less by the heat treatment.

6. The method for recycling a tool material according to any one of claims 1 to 5,

the heat treatment is performed by laser irradiation.

7. The method for recycling a tool material according to any one of claims 1 to 6,

the composition of the high speed tool steel substrate is substantially the same as the composition of the repair weld overlay.

8. A tool material characterized in that,

a repair weld overlay is formed on at least a portion of the high speed tool steel substrate,

in the vicinity of a bonding interface between the repair overlay layer and the high speed tool steel base material, precipitated carbides of the high speed tool steel base material are substantially spherical and do not segregate at a base material grain boundary.

9. The tool material of claim 8,

the high-speed tool steel base material is a high-speed tool steel laser surfacing layer.

10. The tool material according to claim 8 or 9,

the hardness of the high-speed tool steel base material in the vicinity of the joint interface is 500HV or less.

11. The tool material according to claim 9 or 10,

the high-speed tool steel laser surfacing layer is a multilayer surfacing layer.

12. The tool material according to any one of claims 8 to 11,

the high-speed tool steel base material is cylindrical.

Technical Field

The present invention relates to a method for regenerating a tool material for forming a repair weld overlay on an arbitrary region of a high-speed tool steel substrate, and a tool material produced by the regeneration method.

Background

Conventionally, as one of surface treatment techniques, a technique has been known in which a high-hardness material different from a metal base material is deposited on a surface of the metal base material to improve wear resistance and the like of the outermost surface. In this technique, even if the build-up layer formed on the surface using the high-hardness material is worn, the base material can be kept in the original shape, and therefore, the base material can be repeatedly used by performing the same build-up welding again on the base material. For example, patent document 1 (japanese patent application laid-open No. 2013-176778) discloses a laser cladding (laser cladding) method for forming a high-hardness build-up layer on the surface of a metal base material by a laser as a method for building up a build-up weld.

Here, as a typical high-hardness material used for overlay welding, high-speed tool steel used for high-speed cutting of metal parts and the like can be given. For example, patent document 2 (japanese patent application laid-open No. 2016 and 155155) discloses a technique of depositing a multilayer high-speed tool steel on the surface of a metal base material by a laser cladding method, wherein the deposited layer has hardness and wear resistance equal to or higher than those of a HIP (hot isostatic pressing) material.

Prior art documents

Patent document

Patent document 1: japanese patent laid-open publication No. 2013-176778

Patent document 2: japanese patent laid-open publication No. 2016-155155

Disclosure of Invention

Technical problem to be solved by the invention

If an appropriate build-up layer can be formed only in a region of a metal base material where, for example, cracks or chipping has occurred by the laser cladding method, it is possible to provide an extremely efficient and inexpensive repair method. Further, if a method for repairing a laser build-up layer formed by laser cladding can be established, a new business model from the production of a tool material to recycling can be constructed. For example, if an appropriate laser weld overlay can be formed on the surface of an inexpensive steel material and used as a tool material to reduce material costs and repair only a damaged area of the laser weld overlay, the laser weld overlay can be continuously used at only the cost required for the repair.

However, high-speed tool steel, which is commonly used as a tool material, has high hardness, excellent wear resistance, and the like, but the toughness thereof is essentially reduced as a trade-off for these characteristics. As a result, when the metal base material is high-speed tool steel, the phenomenon that the build-up layer after the repair is peeled off from the heat affected zone of the metal base material becomes a big problem. In particular, when the high speed tool steel base material has a rapidly solidified structure, precipitated carbides segregate at the base material grain boundaries, which significantly reduces toughness, and it is extremely difficult to form a weld overlay for repair.

In view of the problems of the prior art described above, an object of the present invention is to provide a method for regenerating a tool material for repairing a high-speed tool steel substrate by forming an appropriate build-up layer in an arbitrary region thereof, and a tool material produced by the method. In particular, a method for regenerating a tool material capable of forming a suitable repair weld overlay without causing separation, cracking, or the like even in a high-speed tool steel weld overlay having a rapidly solidified structure is provided.

Means for solving the technical problem

The present inventors have made diligent studies on a method for forming a build-up layer on a high speed tool steel base material in order to achieve the above object, and as a result, have found that it is extremely effective to perform heat treatment or the like in an appropriate temperature range on the high speed tool steel base material, and have completed the present invention.

That is, the present invention provides a method for recycling a tool material, comprising:

a heat treatment step of heat-treating the high-speed tool steel substrate at a temperature exceeding 700 ℃ and lower than 825 ℃; and

and a repair weld overlay step of forming a repair weld overlay on the surface of the high speed tool steel base material subjected to the heat treatment.

The high speed tool steel base material on which the repair weld overlay is to be formed has various structures and mechanical properties, but by performing heat treatment at a temperature exceeding 700 ℃ and lower than 825 ℃, toughness and the like that can withstand the repair weld overlay process can be imparted. More specifically, if the region of the high speed tool steel base material where the repair weld overlay layer is to be formed can be appropriately softened, the occurrence of peeling, cracks, or the like in the repair weld overlay process can be suppressed.

In contrast, the present inventors have conducted diligent studies and, as a result, have found that there is an appropriate heat treatment temperature range, which is more than 700 ℃ and less than 825 ℃, in order to effectively soften a high-speed tool steel base material. The reason why softening is promoted in this temperature range is not clear, but it is considered that when the heat treatment temperature is set to more than 700 ℃ and less than 825 ℃, ferrite transformation does not occur in the base material, carbon and alloying elements dissolved in the base material precipitate as carbides and aggregate to have a certain size, and the amount of carbon and alloying elements originally contributing to solid solution strengthening is reduced, so that the movement of dislocations easily causes a reduction in hardness. And, a more effective temperature range for softening the high speed tool steel substrate is more than 775 ℃ and less than 825 ℃.

The overlay welding method in the repair overlay welding step is not particularly limited as long as the effect of the present invention is not impaired, and various conventionally known overlay welding methods can be used. For example, laser cladding, plasma arc welding, or the like can be used, but laser cladding is preferably used. By using laser cladding, the build-up layer can be accurately formed only in a desired region. Further, by using laser cladding, it is possible to suppress heat input to the high speed tool steel base material and also suppress dilution between the build-up layer and the high speed tool steel base material.

In the method for regenerating a tool material of the present invention, the high speed tool steel base material is preferably a high speed tool steel laser weld overlay. Since the high-speed tool steel laser weld overlay is rapidly cooled in the forming process, it becomes a typical rapidly-cooled solidification structure in which precipitated carbides are segregated at the grain boundaries of the base metal, but a good repair weld overlay can be formed on the surface of the high-speed tool steel laser weld overlay by using the method for regenerating the tool material of the present invention. Further, by repairing the laser weld overlay of the high speed tool steel, it is possible to reuse the tool material which minimizes the use of expensive and rare raw materials.

The metal structure of the laser overlay welding layer of the high-speed tool steel formed by the laser cladding method becomes a rapid solidification structure, and precipitated carbides such as tungsten carbide, chromium carbide, vanadium carbide, molybdenum carbide and the like are segregated in a net shape at the grain boundary of the base metal. The segregation of the precipitated carbides lowers the bending stress, toughness, impact resistance, and the like of the weld overlay layer, but particularly by performing the heat treatment in a temperature range of more than 775 ℃ and less than 825 ℃, the precipitated carbides can be spheroidized and the network distribution can be split.

When a build-up layer formed by a laser cladding method is subjected to regenerative repair, if the build-up layer is subjected to laser cladding, peeling occurs from a heat-affected zone. In contrast, in the tool material regeneration method of the present invention, since segregation of precipitated carbides in the weld overlay layer is improved and the hardness is appropriately lowered in the heat treatment step, separation can be effectively suppressed even when the weld overlay layer is formed for the purpose of regeneration repair.

In the method for recycling a tool material according to the present invention, the retention time of the heat treatment is preferably 30 minutes or longer. By setting the retention time of the heat treatment to 30 minutes or more, the precipitated carbides segregated in the form of a network can be sufficiently split, and the hardness of the high speed tool steel base material can be reduced to 500HV or less. As a result, the toughness, impact resistance, and the like of the high-speed tool steel base material can be improved, and the occurrence of separation during the regenerative repair can be suppressed. Further, the hardness of the high speed tool steel base material is more preferably 400HV or less, the holding time is more preferably one hour or more, and the holding time is most preferably three hours or more.

In the method for regenerating a tool material of the present invention, the heat treatment is preferably performed by laser irradiation. By using laser irradiation in the heat treatment, a laser irradiation apparatus for laser cladding can be used without separately preparing equipment such as a heat treatment furnace. Further, the heat treatment can be performed only on a desired region, and the energy consumption amount required for the heat treatment can be reduced. Further, since the laser irradiation position can be easily controlled, heat treatment can be easily performed also on a large-sized member such as a roll.

In the method for regenerating a tool material according to the present invention, it is preferable that the composition of the high speed tool steel base material is substantially the same as the composition of the repair weld overlay. By making the composition of the high speed tool steel base material substantially the same as the composition of the repair weld overlay formed on the surface of the high speed tool steel base material, it is possible to suppress a decrease in material characteristics due to dilution. Further, when the high speed tool steel base material is a high speed tool steel laser build-up layer, the conditions used in the build-up welding can be basically followed directly by the conditions used for repair build-up welding, and the work accompanying the replacement of the raw material powder is not required.

Furthermore, the invention also provides a tool material, which is characterized in that,

a repair weld overlay is formed on at least a portion of the high speed tool steel substrate,

in the vicinity of a bonding interface between the repair overlay layer and the high speed tool steel base material, precipitated carbides of the high speed tool steel base material are substantially spherical and do not segregate at a base material grain boundary.

The material of the high-speed tool steel base material is not particularly limited as long as the effects of the present invention are not impaired, and various conventionally known high-speed tool steel materials can be used. Examples of the high-speed tool steel material include various SKH materials and SKH40 defined in JIS G4403: 2006.

In the tool material of the present invention, the high speed tool steel substrate is preferably a high speed tool steel laser weld overlay. Since a weld overlay of high-speed tool steel having excellent high-temperature softening resistance is formed on the surface of an inexpensive metal base material and precipitated carbides of the weld overlay are substantially spherical and do not segregate at grain boundaries, the weld overlay can be suitably used for applications requiring toughness, impact resistance, and the like. Here, "the precipitated carbide is substantially spherical" means that the spheroidization progresses more than the precipitated carbide segregated at the grain boundary. Further, "the precipitated carbides are not segregated at the matrix grain boundaries" means that the precipitated carbides segregated at the matrix grain boundaries in the normal rapid solidification structure exist not only at the matrix grain boundaries but also within the matrix grains, and the arrangement of the precipitated carbides is split. As a result, the crack can be suppressed from spreading along the precipitated carbide.

The repair weld overlay is not particularly limited as long as the effects of the present invention are not impaired, and various conventionally known metal materials can be used, but it is preferably selected from the viewpoints of adhesion to the high speed tool steel base material, suppression of dilution, mechanical properties, and the like.

The region where the repair build-up layer is formed and the thickness of the repair build-up layer are not particularly limited, and the repair build-up layer having an appropriate thickness may be formed only in a necessary region on the surface of the high speed tool steel base material.

In the tool material of the present invention, the hardness of the high speed tool steel base material is preferably 500HV or less. By setting the hardness of the high-speed tool steel base material to 500HV or less, excellent toughness, impact resistance, and the like can be imparted to the high-speed tool steel base material, and peeling at the time of forming a repair weld overlay for the purpose of regenerative repair can be suppressed. Further, by setting the hardness of the high speed tool steel base material to 400HV or less, the toughness, impact resistance, and the like can be further improved, and the separation at the time of the regenerative repair can be more effectively suppressed. Here, the hardness of the region where the repair weld overlay is to be formed may be adjusted without making the entire region of the high speed tool steel base material the above hardness.

In the tool material of the present invention, the high speed tool steel base material is preferably a high speed tool steel laser weld overlay, and the high speed tool steel laser weld overlay is more preferably a multilayer weld overlay. The multilayer build-up layer may be formed by a laser cladding method, and for example, may be obtained by continuously forming the build-up layer in a horizontal direction and/or a vertical direction. By providing the build-up layer as a multilayer build-up layer, the formation area and thickness of the build-up layer can be easily controlled.

Further, in the tool material of the present invention, the high speed tool steel base material is preferably cylindrical. Further, it is more preferable that a high-speed tool steel laser build-up layer is formed on the surface of a cylindrical inexpensive metal base material. By forming a build-up layer of high-speed tool steel on the surface of a cylindrical high-speed tool steel base material, it can be preferably used as a relatively inexpensive roll, for example. In addition, when the build-up layer is damaged, etc., the repair can be easily performed.

In addition, the tool material of the present invention can be suitably produced by the method for recycling a tool material of the present invention.

Effects of the invention

According to the present invention, it is possible to provide a method for regenerating a tool material for repairing a high-speed tool steel base material by forming an appropriate weld overlay layer in an arbitrary region of the base material, and a tool material manufactured by the regeneration method, and in particular, to provide a method for regenerating a tool material capable of forming an appropriate weld overlay layer without causing separation, cracking, or the like even in a high-speed tool steel base material having a rapidly solidified structure.

Drawings

Fig. 1 is a process diagram of a method for regenerating a tool material according to the present invention.

Fig. 2 is a schematic view of the metallic structure of the build-up layer before the heat treatment process.

Fig. 3 is a schematic view of the metallic structure of the build-up layer after the heat treatment process.

Fig. 4 is a schematic cross-sectional view showing an example of the tool material of the present invention.

FIG. 5 is a schematic sectional view of a tool material (hot rolling roll) of the present invention.

Fig. 6 is a schematic cross-sectional view of a tool material (roll for a steel rod or a wire rod) according to the present invention.

FIG. 7 is a schematic sectional view of a tool material (billet or steel sheet roll) according to the present invention.

Fig. 8 is a cross-sectional photomicrograph of the high speed tool steel substrate obtained in example 1.

Fig. 9 is a graph showing vickers hardness of the weld overlay obtained in the example.

Fig. 10 is a structural photograph of the weld overlay before the heat treatment in example 1.

Fig. 11 is a structural photograph of the weld overlay after the heat treatment of example 1.

Fig. 12 is an appearance photograph of the repair weld overlay formed in example 1.

Fig. 13 is a graph showing vickers hardness of the build-up layer obtained in the comparative example.

Fig. 14 is an optical micrograph of a cross section of the build-up layer obtained in comparative example 1.

Fig. 15 is an optical micrograph of a cross section of the build-up layer obtained in comparative example 3.

Fig. 16 is an optical micrograph of a cross section of the build-up layer obtained in comparative example 4.

Fig. 17 is a photograph of the external appearance of the repair build-up layer formed in comparative example 5.

Detailed Description

Hereinafter, a tool material regeneration method and a representative embodiment of a tool material according to the present invention will be described in detail with reference to fig. 1 to 4. However, the present invention is not limited to the drawings, and the drawings are only for conceptually illustrating the present invention, and thus, in order to facilitate understanding, the scale and the number may be exaggerated or simplified as necessary. In the following description, the same or corresponding portions are denoted by the same reference numerals, and redundant description thereof is omitted.

1. Regeneration method of tool material

Fig. 1 shows a process diagram of a method for recycling a tool material according to the present invention. The method for regenerating a tool material of the present invention includes, as essential steps, a heat treatment step (S01) and a repair weld overlay step (S02) for forming a repair weld overlay (welding layers) on a high-speed tool steel base material after the heat treatment step (S01).

(1) Heat treatment Process (S01)

The heat treatment step (S01) is a step of heat treating the high-speed tool steel base material on which the repair weld overlay is to be formed.

The high speed tool steel base material on which the repair weld overlay is to be formed has various structures and mechanical properties, but by performing heat treatment at a temperature exceeding 700 ℃ and lower than 825 ℃, toughness and the like that can withstand the repair weld overlay process can be imparted. More specifically, if the region of the high speed tool steel base material where the repair weld overlay is to be formed can be appropriately softened, the occurrence of peeling, cracks, or the like in the repair weld overlay process (S02) can be suppressed.

In particular, when the heat treatment temperature is set to more than 775 ℃ and less than 825 ℃, in the microstructure of the high speed tool steel base material which becomes the rapidly solidified microstructure, precipitated carbides segregated in a network form at the grain boundaries of the base material can be spheroidized, and the network distribution can be split. The change in the precipitated carbide can improve toughness, impact resistance, and the like.

Fig. 2 and 3 are schematic diagrams showing the metal structure of the high speed tool steel base material before and after the heat treatment step (S01). For example, when the high speed tool steel base material is a high speed tool steel laser weld overlay, the weld overlay is in a state in which precipitated carbides 4 are segregated in a network form at the grain boundaries of the base material grains 2 before the heat treatment step (S01). Most of the carbides 4 are flat or plate-like. On the other hand, by performing the heat treatment step (S01), the precipitated carbide 4 is also dispersed in the crystal grains of the base material crystal grains 2, and the apparent net-like network structure disappears. Further, the shape of the precipitated carbide 4 is changed to a globular shape by the heat treatment.

The distribution and shape change of the precipitated carbides 4 are effectively progressed by the heat treatment in the temperature range exceeding 775 ℃ and lower than 825 ℃, and are particularly remarkable in the heat treatment at approximately 800 ℃. The present inventors have found that this temperature range is a range in which the heat treatment conditions of the high-speed tool steel weld overlay having a rapidly solidified microstructure are examined in detail, and found that this effect cannot be sufficiently obtained by performing the heat treatment at other temperatures.

The heat treatment time in the heat treatment step (S01) is preferably 30 minutes or longer. By setting the retention time of the heat treatment to 30 minutes or more, the precipitated carbides 4 segregated in the form of a network can be sufficiently split, and the hardness of the high speed tool steel weld overlay can be reduced to 500HV or less. As a result, the bending stress, toughness, impact resistance, and the like of the high-speed tool steel build-up layer can be improved, and the occurrence of separation during the repair can be suppressed. Further, the hardness of the high speed tool steel weld overlay is more preferably 400HV or less, the holding time is more preferably one hour or more, and the holding time is most preferably three hours or more.

As a heating means for the heat treatment, a heat treatment furnace, a heat treatment bath, or the like can be used, but from the viewpoint of preventing oxidation, it is preferable to perform the heat treatment in an inert gas atmosphere or a reduced pressure/vacuum atmosphere. Further, the heat treatment is preferably performed by laser irradiation. By using laser irradiation in the heat treatment, a laser irradiation apparatus for laser cladding can be used without separately preparing equipment such as a heat treatment furnace. Further, the heat treatment can be performed only on a desired region, and the energy consumption amount required for the heat treatment can be reduced. Further, since the laser irradiation position can be easily controlled, heat treatment can be easily performed also on a large-sized member such as a roll.

As a specific method of heat treatment by laser irradiation, parameters such as power and focus of laser light are adjusted to be optimum so that a region to be heat treated of a high speed tool steel base material can be maintained at the predetermined temperature, and then the target region is irradiated with laser light for a predetermined time to heat the target region.

In addition, when the entire region of the surface cannot be irradiated with the laser light even if the irradiation range is adjusted to the widest focus setting due to the wide area of the target region, the entire region of the target is scanned by moving the laser irradiation range after adjusting the scanning speed of the laser light to the optimum speed or repeating the movement. In this case, although there is a difference in the amount of input heat between the laser irradiation region and the non-laser irradiation region, the heat treatment conditions can be satisfied by using the scanning speed and the focus setting that can maintain the predetermined temperature over the entire target region.

(2) Repairing build-up welding process (S02)

In the method for regenerating a tool material according to the present invention, even when the high-speed tool steel base material has a rapidly solidified structure, the precipitated carbides 4 segregated in a network form at the grain boundaries of the base material can be spheroidized and the network distribution can be split by the heat treatment step (S01). In addition, since the high-speed tool steel base material is moderately softened, the regenerative repair can be easily performed by laser cladding.

When a laser build-up layer of high-speed tool steel formed by a laser cladding method is subjected to regenerative repair, delamination from a heat-affected zone occurs when the build-up layer is subjected to laser cladding. In contrast, since the segregation of the precipitated carbide 4 in the weld overlay is improved and the hardness is appropriately lowered in the heat treatment step (S01), the separation can be effectively suppressed even when the repair weld overlay is formed.

Laser cladding can be performed, for example, as follows: laser cladding is performed by supplying high-speed tool steel powder to the surface of a metal base material and irradiating the high-speed tool steel powder with a laser beam. In addition, although there are a plurality of types of powder having different compositions in part, the powder may be appropriately selected according to the required properties such as wear resistance and toughness.

The method of laser cladding is not particularly limited as long as the effect of the present invention is not impaired, and various conventionally known laser cladding methods can be used. The laser cladding method is a surface treatment method in which a build-up layer is integrally formed on a metal base material by supplying fine metal powder having a uniform particle diameter to a laser irradiation region on the surface of the metal base material, and is also used for manufacturing an intermediate (that is, a tool material) in a manufacturing stage of a cutting tool, a rolling tool, or the like.

In this laser cladding method, the build-up layer is formed by rapid melting and rapid solidification because the metal powder is melted by condensing a laser beam emitted from a laser light source and performing local heat input. In addition, thermal strain and a heat affected zone to the base material can be reduced, and the dilution ratio between the base material and the formed build-up layer can be reduced. Further, since the blowpipe portion (torch) from which the laser beam and the metal powder are emitted can be controlled by a robot by a program, the formation position and the shape of the build-up layer can be controlled relatively accurately, and therefore, the method can be suitably used for repairing cracks or the like appearing on a part of the metal member.

In laser cladding, high-speed tool steel powder having an appropriate composition, particle size distribution, and the like may be used as a raw material, and process conditions may be appropriately adjusted to be optimal according to the size, characteristics, and the like of a build-up layer to be formed, but high-speed tool steel powder having a diameter of 50 to 150 μm is preferably used. Further, the metal base material is not particularly limited as long as the effects of the present invention are not impaired, and various conventionally known metal base materials can be used, but a steel material is preferably used from the viewpoint of adhesion to a high-speed tool steel build-up layer formed on the surface, suppression of dilution, mechanical properties, and the like, and tool steel, bearing steel, and the like can be suitably used. More specifically, for example, a medium carbon steel material (S45C, etc.), a chromium molybdenum steel material, an alloy tool steel material, a high carbon chromium bearing steel material, or the like can be used.

In the laser cladding, basically, the multilayer build-up layer having a substantially planar shape is formed by reciprocating the entire body a plurality of times by linear movement of the laser beam and parallel movement with a predetermined interval therebetween, but the laser cladding is not limited to this, and for example, the build-up portion may be formed by repeating only linear movement a predetermined number of times, or the linear movement and the curved movement may be combined according to the shape of the repair portion, and the combination may be repeated a predetermined number of times.

Preferably, the composition of the high speed tool steel base material is substantially the same as the composition of the repair weld overlay formed by the repair. By making the composition of the high speed tool steel base material substantially the same as the composition of the repair weld overlay, the deterioration of the material characteristics due to dilution can be suppressed. Further, when the high speed tool steel base material is a high speed tool steel laser weld overlay, the composition of the high speed tool steel laser weld overlay is made substantially the same as the composition of the repair weld overlay, thereby making it possible to omit the work involved in the replacement of the raw material powder.

2. Tool material

A schematic cross-sectional view of the tool material of the present invention is shown in fig. 4. Here, an embodiment in which a high speed tool steel laser build-up layer is formed on the surface of a metal base material and a repair build-up layer is formed on a part of the high speed tool steel laser build-up layer will be described. In the tool material 10 of the present invention, the high-speed tool steel laser weld overlay 14 is formed on the surface of the metal base material 12, and the precipitated carbide 4 of the high-speed tool steel laser weld overlay 14 is substantially spherical and does not segregate at the grain boundaries of the base material crystal 2. Further, a repair weld overlay 16 is formed on a portion of the high speed tool steel laser weld overlay 14.

As shown in fig. 3, the metallic structure in the vicinity of the bonding interface between the high-speed tool steel laser build-up layer 14 and the repair build-up layer 16 is such that the precipitated carbides 4 are dispersed in the crystal grains of the base material crystal grains 2, and the apparent net-like network structure of the precipitated carbides 4 disappears. The precipitated carbide 4 is further spheroidized, and the precipitated carbide 4 having a substantially spherical shape is included. Here, the "vicinity of the bonding interface" differs depending on the material, thickness, and cladding condition of the high-speed tool steel laser build-up layer 14 and the repair build-up layer 16, but corresponds to a range of about 2mm from the bonded interface, for example.

When the precipitated carbide 4 segregates at the grain boundary of the base material grain 2, the bending stress decreases and the cohesion between adjacent base material grains decreases, so that when a crack occurs, the crack progresses along the base material grain boundary, but the dispersion of the precipitated carbide 4 improves the cohesion between adjacent base material grains 2, and therefore the progress of the crack, the separation, and the like can be suppressed.

The hardness in the vicinity of the bonding interface between the high speed tool steel laser weld overlay 14 and the repair weld overlay 16 is preferably 500HV or less, and more preferably 400HV or less. By adjusting the hardness of the high speed tool steel laser weld overlay 14 to this range, the bending stress and toughness are sufficiently improved, so that the impact resistance is improved, and the occurrence of cracks and separation can be suppressed even when the shrinkage at solidification, which occurs when regenerative repair is performed using laser cladding, is applied to the high speed tool steel laser weld overlay 14.

Also, the high speed tool steel laser weld overlay 14 is preferably a multilayer weld overlay. The multilayer build-up layer can be formed by, for example, a laser cladding method, and can be obtained by, for example, continuously forming a build-up layer formed by 1-time laser cladding in the horizontal direction and/or the vertical direction. By providing the high speed tool steel laser build-up layer 14 as a multilayer build-up layer, the formation area and thickness can be easily controlled.

Further, the metal base material 12 is preferably cylindrical. By forming the high speed tool steel laser weld overlay 14 of the high speed tool steel on the surface of the cylindrical metal base material 12, the tool material 10 can be suitably used as a roll. In addition, when the high speed tool steel laser build-up layer 14 is damaged, etc., the repair can be easily performed.

As a raw material of the high speed tool steel laser build-up layer 14, high speed tool steel powder is used. In the high-speed tool steel powder, there are a plurality of kinds of powders having different compositions in part, but they may be selected appropriately according to the required properties such as wear resistance and toughness. The composition of the high-speed tool steel powder is preferably such that C is 1.3 mass% or more, Cr is 3 mass% or more, Mo is 4 mass% or more, W is 4 mass% or more, and V is 2 mass% or more.

The metal base material 12 is not particularly limited as long as the effects of the present invention are not impaired, and various conventionally known metal base materials can be used, but a steel material is preferably used from the viewpoint of adhesion to the high-speed tool steel laser build-up layer 14 formed on the surface, suppression of dilution, mechanical properties, and the like, and tool steel, bearing steel, and the like can be suitably used. More specifically, as the metal base material 12, for example, a medium carbon steel material (S45C or the like), a chromium molybdenum steel material, an alloy tool steel material, a high carbon chromium bearing steel material, or the like can be used.

The material of the repair build-up layer 16 is not particularly limited as long as the effects of the present invention are not impaired, and various conventionally known metal materials can be used, but a high-speed tool steel material having a composition substantially equal to that of the high-speed tool steel laser build-up layer 14 is preferably used. By making the repair build-up layer 16 of a high-speed tool steel material having a composition substantially equal to the composition of the high-speed tool steel laser build-up layer 14, the tool material 10 having the most uniform surface can be obtained.

The tool material of the present invention can be applied to the case where the tool material is oversized or economically uneconomical in the conventional HIP (hot isostatic pressing). Further, for example, by applying a cylindrical tool material having the high-speed tool steel laser build-up layer 14 to a large-sized roll or the like, an extremely economical commercial model can be constructed.

Fig. 5 to 7 show cross-sectional views of representative rolls using the tool material 10. FIG. 5 shows a hot rolling roll, FIG. 6 shows a steel bar or wire rod roll, and FIG. 7 shows a steel slab or steel sheet roll. In each roll, a high-speed tool steel laser build-up layer 14 is formed on the surface of the metal base material 12 in contact with the workpiece, thereby ensuring sufficient bending stress, toughness, impact resistance, and wear resistance.

Further, since the high speed tool steel laser weld overlays 14 are formed only in the desired areas of the surface of these rolls, they are relatively inexpensive, and since the portions where damage, wear, or the like occurs with use are the high speed tool steel laser weld overlays 14, reuse can be achieved by repairing the high speed tool steel laser weld overlays 14 in the areas where damage, wear, or the like occurs. As a result, it is possible to achieve significant energy saving, resource saving, and low environmental load compared to the case of using rolls manufactured by casting.

Here, in the tool material of the present invention, since the high speed tool steel laser weld overlay 14 can be formed in an arbitrary region, the hardness and hardness distribution of the high speed tool steel laser weld overlay 14 can be appropriately adjusted by selecting raw material powder of the high speed tool steel laser weld overlay, or the like. For example, in the high-speed tool steel laser weld overlay 14 of a roll for a bar steel or wire rod shown in fig. 6, the hardness can be adjusted for each region according to the degree of wear caused by the interaction with the workpiece. In general, since the boundary region between the bottom surface and the side surface is significantly worn, it is preferable to set the region to have a higher hardness.

Further, for example, in the roll for billet or slab shown in fig. 7, it is also possible to provide appropriate mechanical properties to each high speed tool steel laser weld overlay by using different raw material powders for each high speed tool steel laser weld overlay 14. Specifically, for example, the hardness of the high speed tool steel laser weld overlay 14 may be sequentially increased or decreased in the direction of extension of the roll axis.

The method for recycling a tool material and the tool material of the present invention will be further described below with reference to examples, but the present invention is not limited to these examples.