JP2018176282A - Surface treatment method for mold cooling hole, and mold - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface treatment method that can impart corrosion resistance and stress corrosion crack resistance at a surface of a cooling hole of a mold.SOLUTION: A surface treatment method for a mold cooling hole includes jetting a jetting particulate matter constituted of particle of tin or tin alloy to a surface of a cooling hole formed in a mold and causing it to collide with the surface of the cooling hole, thereby dispersing Sn element contained in the jetting particulate matter at the surface of the cooling hole. Thus, corrosion resistance that is not lost even when being subject to friction or wear is imparted at the surface of the cooling hole.SELECTED DRAWING: Figure 10

Description

  The present invention relates to a method for surface treatment of mold cooling holes, and a mold provided with cooling holes surface-treated by the above method, and more specifically, a hot mold for introducing a coolant such as cooling water. The present invention relates to a surface treatment method capable of providing stress corrosion cracking resistance to the surface of a cooling hole provided in the above, and a mold provided with a cooling hole surface-treated by the above method.

  In the case of a hot die where high temperature material is introduced into the cavity like a die-casting die where molten material is poured into the cavity, cooling holes are provided in the die to facilitate cooling of the die. Cooling is performed by introducing a coolant such as cooling water into the cooling holes.

  In a mold provided with such cooling holes, in recent years, cooling holes tend to be formed close to the cavity surface side for the purpose of improving the cooling performance, and as a result, the influence of repeated thermal stress on the cooling holes Stress corrosion cracking is likely to occur on the surface of the cooling hole which is large and in a corrosive environment, and there is an increased risk of large cracks of the mold starting from this and leakage of the refrigerant.

  Therefore, various methods for preventing such stress corrosion cracking on the surface of the mold cooling hole are being studied.

  Here, stress corrosion cracking is caused by three factors: the presence of tensile stress, the presence of a corrosive environment, and material properties, which can be avoided by removing one or more of these factors.

  Therefore, in response to these factors, the following proposals have been made as methods for preventing stress corrosion cracking.

[Addition of compressive residual stress]
Among the factors that cause stress corrosion cracking, applying compressive residual stress to the surface of the cooling hole is performed to relieve tensile stress, and to impart such compressive residual stress, the cooling hole It has been proposed to process the surface layer of the above by shot peening (claim 1 of Patent Document 1).

[Coating with protective film]
In addition, covering the surface of the cooling hole with a protective film isolates it from the corrosive environment (water, dissolved oxygen, chlorine ion, etc.), thereby preventing the occurrence of corrosion on the surface of the cooling hole, and hence the occurrence of stress corrosion cracking. It has also been proposed that, as an example of such protection by a protective film, the surface of the cooling hole be covered with an electroless plating (Ni-P plating) layer (claim 1 of Patent Document 2). .

[Combined use of compressive stress and formation of protective film]
Furthermore, it is also proposed to use both the application of the compressive residual stress described above and the formation of the protective film, and after applying low concentration nitriding to the surface of the cooling hole, the surface is covered with an electroless Ni-P plating layer. After that, it is also proposed to perform shot peening (claims 1 and 2 of Patent Document 3).

  In the configuration described in Patent Document 3 described above, the electroless Ni-P plating layer covering the surface of the cooling hole is made of a metal which is more resistant to corrosion (smaller ionization tendency) than Fe, so-called "barrier type". In such a barrier type anticorrosion film, when a scratch or a hole reaching the substrate is generated in such a barrier type corrosion film, a local cell is formed with the plating layer as the cathode and the substrate as the anode to become the anode. Corrosion (elution) accelerates.

  In order to solve the problems with such barrier type anticorrosion films, vacuum pulse nitriding is performed on the surface of the cooling holes, then peening treatment is performed, and further, Zn or Zn alloy having a higher ionization tendency than Fe by electrolytic plating. It has also been proposed to form a sacrificial film of the above to coat the surface of the cooling hole (claim 1, claim 3 and 4 of Patent Document 4).

  Thus, in the configuration in which the surface of the cooling hole is covered with a sacrificial film of Zn or Zn alloy having a larger ionization tendency than Fe, there is a case where a scratch or a hole reaching the substrate is generated in the sacrificial film to form a local cell. However, since this local cell uses the plating layer as the anode and the base as the cathode, the corrosion on the base side can be delayed by the corrosion of Zn on the anode side first. .

[Improvement of material properties]
In addition, as prevention of stress corrosion cracking by improvement of material properties, selection of steel type with high nickel content, addition of silicon, cracking along grain boundary, for intragranular cracking in which cracking progresses through crystal grains It is generally performed by reviewing the steel grade of the whole mold to a material with low stress corrosion cracking sensitivity, such as using an intergranular corrosion resistant steel for intergranular cracking in which Stress corrosion cracking resistance is achieved by modifying the material itself of the surface portion to a property that is less likely to cause stress corrosion cracking by changing the crystal structure, components, etc. in the vicinity of the surface of the cooling hole by local surface treatment on the surface. It has also been proposed to grant

As an example of such surface treatment, Patent Document 5 mentioned later is formed by changing the surface of the cooling hole to magnetite (Fe ₃ O ₄ ) by exposing it to steam at 480 to 600 ° C. for 1 to 3 hours. It is proposed to provide a surface modified layer (magnetite layer) as described above (sample 2 of Patent Document 5 [0027] column [Table 2]).

[Others]
Although the invention does not relate to the surface treatment of mold cooling holes, and it also discloses the treatment for preventing stress corrosion cracking, it is not described to predict that it has the effect of preventing stress corrosion cracking. Patent Document 6 describes a normal temperature diffusion, penetration plating method in which elements in the composition in the metal particles are diffused to the surface of the metal product by injecting the metal particles onto the surface of the metal product. Patent Document 6 also suggests the use of tin as the metal particles to be jetted (Patent Document 6 [0084]).

  Although Patent Document 6 refers to the method described herein as "plating method", the surface layer formed by the method described in Patent Document 6 is formed on the surface of a steel product by carburizing, nitriding, etc. Similar to the layers to be formed, it is a "surface modified layer" formed by diffusing and infiltrating other elements into the substrate, and formed by electroless plating or electrolytic plating as in Patent Documents 2 to 4, It differs from the "plating layer" that covers the substrate by components other than the substrate.

Japanese Patent Application Laid-Open No. 7-290222 Japanese Patent Application Laid-Open No. 9-217923 JP, 2009-72798, A JP, 2013-159831, A JP, 2016-204754, A JP-A-8-333671

  The method of applying compressive residual stress by shot peening in the conventional surface treatment method for mold cooling holes described above (see Patent Document 1) relates to tensile residual stress generated by forming processing of cooling holes and the like and external force applied during use Although stress can be relieved, tensile stress is not completely eliminated, and it is used in combination with other methods.

  As described in Patent Document 3 as a combination of application of compressive residual stress by such shot peening, a barrier type protective film is formed by electroless Ni-P plating to corrode the surface of the cooling hole. Isolation from (water, dissolved oxygen, chloride ions, etc.) is also considered, but in this configuration, if scratches or holes that lead to the substrate occur in the protective film, the corrosion of the substrate is further advanced by the action of the local cell. Is as described above.

  On the other hand, in the configuration described in Patent Document 4 in which the protective film is a sacrificial film made of Zn or Zn alloy, the occurrence of corrosion of the substrate can be delayed even if a scratch or a hole reaching the substrate is generated in the sacrificial film. Although it is advantageous in that it can be done, this configuration can only "delay" the corrosion of the substrate, and the corrosion of the substrate will eventually occur as the corrosion of the protective film progresses.

  Moreover, in the structure which forms the sacrificial film which consists of Zn and Zn alloy as a protective film, when the flaw and the hole to the base are produced, although it is advantageous in being able to delay corrosion of the base, ionization tendency is large. The sacrificial film formed of a material (which is therefore easy to corrode) becomes thin as it corrodes with time and its protective effect is reduced, and this corrosion causes rust (white rust) on the surface of the plated layer The reduction of the flow passage area may lead to a decrease in the cooling efficiency.

  In order to prevent such corrosion of the sacrificial film itself, after forming the sacrificial film on the surface of the cooling hole, it is necessary to perform further treatment such as chemical conversion treatment on the surface of the sacrificial film. However, the increase in the number of processing steps leads to an increase in the time and cost of surface treatment of the cooling holes.

  Thus, since the formation of the protective film imparts resistance to stress corrosion cracking by isolating the substrate from the corrosive environment, the substrate can not be protected from corrosion when the protective film is damaged or the like. .

  On the other hand, if it is possible to modify at least the surface of the cooling hole to material properties that are less likely to cause stress corrosion cracking, cooling is possible even if the plating layer is not formed as a protective film by electrolytic plating or electroless plating. Stress corrosion cracking of the hole surface can be prevented, and if such surface modification is carried out as the surface treatment for forming the protective film described above, stress corrosion will occur even if the protective film is damaged or the like. It is possible to prevent the occurrence of cracking.

As a method of preventing stress corrosion cracking by such surface modification, Patent Document 5 changes the surface structure of the cooling hole of the mold into magnetite (Fe ₃ O ₄ ), thereby causing corrosion and hence stress corrosion cracking. Report that it can prevent the mold life significantly.

However, in Patent Document 5, in order to change the surface structure of the cooling hole into magnetite (Fe ₃ O ₄ ), the surface of the cooling hole is exposed to water vapor at 480 to 600 ° C. for 1 to 3 hours ( It is convenient if the surface modified layer having stress corrosion cracking resistance can be formed on the surface of the cooling hole by a simple and short-time process, as disclosed in Patent Document 5 [0014].

  In addition, the surface modification layer of magnetite formed by the above method has a relatively low hardness and has low wear resistance, so if the magnetite layer is lost due to friction, stress corrosion cracking resistance is lost.

  Therefore, the present invention is relatively simple and for a short time, the surface modified layer which has been modified to the property that corrosion is unlikely to occur near the surface of the cooling hole of the mold, and thus the stress corrosion cracking is unlikely to occur. Cooling holes by providing a method for surface treatment of mold cooling holes, which can form a surface modified layer which is resistant to stress corrosion cracking resistance even by friction with other members. It is an object of the invention to prevent the occurrence of stress corrosion cracking on the surface of the metal mold and to prolong the life of the mold.

In order to achieve the above object, the surface treatment method for mold cooling holes of the present invention is
A diffusion process is performed to diffuse Sn element on at least the surface of the cooling hole formed in the mold (claim 1).

  In the diffusion process, jet particles consisting of tin and / or tin alloy particles having an average particle diameter of 10 to 100 μm are jetted together with compressed gas having a jet pressure of 0.4 to 0.8 MPa to collide with the surface of the cooling hole This can be performed by diffusing the Sn element in the blast particles to the surface of the cooling hole (claim 2).

  In the present invention, the average particle size refers to the median diameter (d50).

When the surface of the cooling hole whose end is a closed end is to be treated,
The injection nozzle of the injection particles in the diffusion process has an injection nozzle with a diameter smaller than the cooling hole, and the tip of the injection nozzle has a distance of several mm from the inner end of the cooling hole, for example, the inner surface of the closed end. It is preferable to perform the diffusion process by continuing the injection of the injection particles until, for example, the injection nozzle is removed from the cooling hole while gradually extracting the injection nozzle while starting in the state of being inserted up to (Claim 3).

  Further, it is preferable to perform shot peening on the surface of the cooling hole (claim 4). Since this shot peening has an effect of removing the scale of the surface, the above-mentioned diffusion to diffuse the Sn element It is preferable to perform shot peening before performing processing.

  The shot peening in this case can be performed by injecting a shot having an average particle diameter of 20 to 149 μm together with a compressed gas having an injection pressure of 0.3 to 0.8 MPa (claim 5).

When the surface of the cooling hole whose end is a closed end is to be treated,
Also for the injection of the shot in the shot peening, the injection nozzle having a diameter smaller than the cooling hole is a tip of the injection nozzle close to the closed end of the cooling hole, for example, a few mm from the inner surface of the closed end. It is preferable to start in the inserted state and continue the injection of the shot until, for example, the injection nozzle is removed from the cooling hole while gradually extracting the injection nozzle (Claim 6).

  In this case, it is preferable to swing the tip of the nozzle in the cooling hole.

  The above-described surface treatment method of the present invention can be performed on the surface of the cooling hole which has been subjected to the nitriding or soft nitriding treatment (claim 8).

Also, the mold of the present invention is
In a mold in which a cooling hole for introducing a refrigerant for cooling is formed,
A surface modified layer in which Sn is diffused is formed on the surface of the cooling hole.

  It is preferable that the surface modification layer is further provided with compressive residual stress (claim 10).

  Furthermore, the cooling hole may be provided with a nitrided layer or a soft nitrided layer on the surface, and the surface modified layer may be formed in the nitrided layer or the soft nitrided layer (claim 11).

  According to the configuration of the present invention described above, in the mold provided with the cooling hole surface-treated by the method of the present invention, the corrosion resistance is exhibited by diffusing the Sn element on the surface of the cooling hole. The occurrence of stress corrosion cracking was able to be suitably prevented by preventing the occurrence of corrosion on the surface of the cooling hole.

  Moreover, the surface treated by the method of the present invention exhibited excellent corrosion resistance even after frictional wear, and was excellent in abrasion resistance.

  Such diffusion of Sn element is carried out in a short time by a relatively simple method of injecting jetted particles, which are particles of tin and / or tin alloy of a predetermined particle diameter, at a predetermined injection pressure It is possible.

  In the configuration in which shot peening is performed on the surface of the cooling hole, the stress corrosion cracking resistance is further imparted by the synergetic effect of imparting the corrosion resistance accompanied by the diffusion of the Sn element described above and the application of compressive residual stress by shot peening. I was able to.

  Furthermore, injection of injection particles in diffusion processing and injection of shots in shot peening are started with the injection nozzle having a diameter smaller than that of the cooling hole inserted to the vicinity of the closed end of the cooling hole, In the configuration in which the injection is continued while gradually drawing out, the gap between the outer circumference of the injection nozzle and the inner circumference of the cooling hole is narrow, so the shot and the jetted particles are hard to come out of the hole and easily clogged. Even when the surface was to be treated, shot peening and diffusion treatment of Sn element could be suitably performed.

  In particular, by performing the above-described injection while swinging the tip end side of the injection nozzle in the cooling hole, it is possible to preferably prevent the occurrence of processing unevenness and the like.

  The surface treatment of the present invention can be performed on the surface of the cooling hole where nitriding or soft nitriding is performed to obtain a synergetic effect with the nitriding or soft nitriding treatment.

Explanatory drawing which described typically a metal mold | die and its cooling hole. It is explanatory drawing of the injection method of injection | pouring particle | grain / shot with respect to the cooling hole surface which has a closed end, (A) is whole structure, (B) is the enlarged view of the front-end | tip part of injection nozzle, (C) is the front-end of injection nozzle (B) the figure seen from the C arrow direction shown to the figure. (A) is sample 1 (comparative example), (B) is sample 2 (comparative example), (C) is sample 3 (example), (D) is a contour curve of sample 4 (example). It is a SEM image of the surface of sample 1 (comparative example), (A) is 1000 times and (B) is 3000 times. It is a SEM image of the surface of sample 2 (comparative example), (A) is 1000 times, (B) is 3000 times. It is a SEM image of sample 3 (example) surface, and (A) is 1000 times and (B) is 3000 times. It is a SEM image of sample 4 (example) surface, and (A) is 1000 times and (B) is 3000 times. Sample 1 (comparative example) EDX qualitative analysis result of the surface. Sample 2 (comparative example) EDX qualitative analysis result of the surface. Sample 3 (Example) EDX qualitative analysis result of the surface. Sample 4 (example) EDX qualitative analysis result of the surface. Explanatory drawing of a friction wear test (ball on disk test). The photograph which image | photographed the surface of each sample before and behind the test which shows a corrosion-resistant test result. Explanatory drawing of the test piece and test method which were used by the evaluation test with respect to the injection method of a projectile.

  Below, the surface treatment method of the mold cooling hole of this invention is demonstrated, referring an accompanying drawing.

[Object to be processed: Mold cooling hole]
The surface treatment method of the present invention treats the surface (inner wall) of a cooling hole provided for introducing a coolant such as cooling water into a hot die such as a die casting die.

  The steel type of the mold to be treated is not particularly limited, and as an example, SKD hot die steel (SKD4, SKD5, SKD6, SKD61, SKD62, SKD7, SKD8) represented by SKD61 (JIS G4404 2006) or Any of the steel types used for hot molds, such as SKT type hot forging type steel (SKT3, SKT4, SKT6), etc. can be the object of the surface treatment of the present invention.

  As the cooling holes formed in such a mold, as schematically shown in FIG. 1, for example, the thickness of the mold from the back side of the mold (opposite to the cavity surface) toward the cavity surface Cooling holes with one end closed like a cooling hole formed in the direction and cooling formed as a through hole like a cooling hole represented in the direction perpendicular to the thickness direction of the mold in FIG. 1 There are various cooling holes such as holes. And, for example, these various cooling holes are connected to each other, and the refrigerant circulates in the connected cooling holes. The surface treatment method of the present invention is applicable to any of these cooling holes.

  The size of the target cooling hole is not particularly limited, but as for the cooling hole having a closed end, as the hole diameter becomes smaller, shots and jetted particles are easily clogged in the cooling hole and processing becomes difficult. When applying the injection method described later adopted in the present invention, it has been confirmed that the surface can be treated up to the cooling hole having a diameter of 2 mm which is the size of the cooling hole of the minimum level formed in the mold.

  Although the surface treatment method of the present invention can be applied to the surface of the cooling hole as it has been subjected to cutting, etc., in the case where irregularities such as tool marks are formed on the surface of the cooling hole. (2) If cracks are likely to be generated starting from the recess, and if the formation of the cooling holes is carried out by electrical discharge machining, remove in advance the oxide scale attached to the surface and the discharge hardened layer that causes micro cracks. Since it is preferable that the surface of the cooling hole is subjected to polishing treatment such as sand blasting, in which abrasive grains are jetted and polished, may be performed on the surface of the cooling hole.

  In addition, the surface of the cooling hole may be treated by nitriding, soft nitriding, etc. by a known method as necessary. In this way, the cooling hole after the nitriding or soft nitriding treatment is performed The process of the present invention may be performed on the surface.

〔surface treatment〕
The surface treatment of the present invention is applied to the cooling hole surface of the mold described above.

  This surface treatment method includes at least a diffusion treatment for diffusing Sn in at least the surface of the cooling hole formed in the mold, and preferably, shot peening is applied to the surface of the cooling hole besides the diffusion treatment, It is preferable to apply compressive residual stress.

  In the present embodiment, first, shot peening is performed on the surface of the cooling hole to apply compressive residual stress, and then the above-described diffusion process of diffusing the Sn element is described as an example.

  Shot peening is a type of cold working in which a shot consisting of substantially spherical particles of metal, ceramic, glass, etc. is injected and collided with the compressed gas onto the surface of a cooling hole, and this shot peening is performed by performing this shot peening. An increase in surface hardness (work hardening) of the cooling holes due to the refinement of the surface structure can be obtained, and compressive residual stress can be imparted.

  As the shot to be used, as described above, shots of various materials known as shot materials used for shot peening, such as metal, ceramic, glass, etc., can be used, but preferably they are to be treated Use one with a hardness higher than the surface hardness of the cooling holes.

  As the particle size of the shot, one having an average particle size of 20 to 149 μm can be used, and this shot is jetted together with a compressed gas such as compressed air having a jet pressure of 0.3 to 0.8 MPa.

  Shot peening may be performed only once, or may be performed multiple times, for example, by changing the injection pressure and the particle size of the shot stepwise, etc., and cooling after processing It may be done to improve the surface roughness of the holes.

  In the present embodiment, the above-described diffusion processing for diffusing the Sn element is performed on the surface of the cooling hole after the above-described shot peening is performed.

  Such diffusion of the Sn element can be performed by injecting and colliding the jetted particles made of tin or tin alloy onto the surface of the cooling hole, and the energy at the time of collision makes it possible to A part can be diffused to the surface of the cooling hole.

  The injection particles used for this diffusion treatment need to contain Sn elements to be diffused to the surface of the cooling hole, and of course the particles of pure tin as well as the particles of a tin alloy containing tin as the main component Some or all of tin particles, such as tin particles having an oxide film formed on the surface by natural oxidation, may take the form of tin oxide.

  Unlike the shot used for the shot peening described above, the shape of the injection particles used for the diffusion process is not limited to the substantially spherical one, but can be used for the one having a corner, and the shape is not limited. .

  The average particle diameter of the injection particles used is in the range of 10 to 100 μm, and the injection particles are injected together with compressed gas such as compressed air at an injection pressure of 0.4 to 0.8 MPa to the surface of the cooling hole. Sn element can be diffused.

  In the present embodiment, after performing the above-described shot peening, the case of performing the diffusion process of diffusing tin elements by injecting the spray particles of tin or tin alloy is described as an example, but two processes are performed. The order is not particularly limited as long as both the application of compressive residual stress and the diffusion of the Sn element can be performed on the surface of the cooling hole, and shot peening is performed on the surface of the cooling hole after the Sn element is diffused. Alternatively, the diffusion of the Sn element and the application of the compressive residual stress may be simultaneously performed by simultaneously performing the injection (diffusion process) of the injection particles and the injection (shot peening) of the shot.

  However, since shot peening has the effect of removing the scale on the surface, it is preferable to perform shot peening before performing the above-described diffusion process of diffusing the Sn element.

  The injection of shot in shot peening and the injection of injection particles in the diffusion process can be performed by the following method.

  In addition, prior to performing the process of the present invention, the method of jetting shots or jetted particles described below can be applied to the jetting of abrasive grains, etc., when the surface of the cooling hole is polished by the jetting of abrasive grains, etc. It is.

  In the case where the cooling hole to be treated is formed as a through hole having an inlet and an outlet among the cooling holes shown in FIG. 1, the shot with the compressed gas such as compressed air is made from one of the inlet and the outlet. Alternatively, the shot particles may be made to collide with the surface of the cooling hole by introducing the spray particles and injecting them from the other.

  When the cooling hole to be treated is a hole whose end is a closed end among the cooling holes shown in FIG. 1, as shown in FIG. 2 (A), it is smaller than the hole diameter of the cooling hole, And an injection nozzle having an outer diameter capable of forming an allowable passage of a mixed fluid of at least compressed gas and shot or injection particles between the surface of the cooling hole and the outer peripheral surface of the injection nozzle, the injection nozzle Is inserted into the cooling hole and injected. In addition, this method is applicable also to the cooling hole formed as a through-hole.

  The shot and injection particle spray using such an injection nozzle cools the injection nozzle until the tip of the injection nozzle has an interval of about several mm, for example, an interval of about 3 to 5 mm, to the inner surface of the closed end of the cooling hole. Insert into the hole, start injection of shot and spray particles at this position, and continue the injection until the injection nozzle comes out of the cooling hole while gradually pulling out the injection nozzle from the cooling hole, the inner surface of the closed end The shot and blast particles can collide with the entire surface of the cooling hole including the

  If the ejection nozzle is pulled out too early, the surface of the cooling hole can not be sufficiently treated, and if it is too late, the shot or jetted particles clogged in the cooling hole and can not be jetted, so 0.1 to 50 mm It is preferable to withdraw at a withdrawal rate of 1 / s, for example, 0.5 to 50 mm / s for injection to a cooling hole with a diameter of 4 mm.

  During injection of the shot or injection particles, the tip side of the injection nozzle is swung in the cooling hole as shown by the arrows in FIGS. 2 (B) and 2 (C) to uniformly process the surface of the cooling hole It may be possible to

  When a cooling hole with a relatively large hole diameter is to be treated, it is easy to secure a gap between the outer periphery of the injection nozzle and the inner periphery of the cooling hole. It becomes difficult to secure the distance between the outer periphery of the nozzle and the inner periphery of the cooling hole, and it becomes difficult for the shot and the jetted particles to be discharged out of the cooling hole, so that the shot and the jetted particles are easily clogged in the cooling hole. Therefore, it is necessary to select a jet nozzle of an appropriate size for the hole diameter of the cooling hole.

  Table 1 below shows an example of the combination of injection nozzles used for the cooling holes having a hole diameter of 8 mm or less where the injection particles are difficult to be jetted among the cooling holes having the closed end.

  In addition, the process example of the surface treatment of the cooling hole in this invention containing the diffusion process which diffuses Sn element, and shot peening, and an example of the process conditions in each process are shown in following Table 2.

  The example shown in Table 2 shows an example of the surface treatment to the mold in which the cooling holes are formed by electric discharge machining, and the SiC abrasive is jetted in step 1 and the oxidation generated on the surface of the cooling holes by electric discharge machining Shot peening is performed in step 2 after sandblasting to remove the scale and the discharge-hardened layer.

  After shot peening is performed in step 2, iron content on the surface of the cooling hole is removed by shot peening in step 3, and shots are sprayed to improve surface roughness. The body is injected and diffusion processing is performed to diffuse the Sn element on the surface of the cooling hole.

1. Evaluation by Test Pieces The results of evaluation of surface condition and corrosion resistance evaluation test are shown below for the test pieces treated by the surface treatment method of the present invention, and evaluation test for the shot material injection method adopted in the present application The results of the above are shown below.

[Evaluation test of surface condition]
(1) Purpose of test The condition of the surface of the test piece after surface treatment by the method of the present invention is confirmed based on compressive residual stress, surface shape, and components.

(2) Test method Four SKD 61 test pieces (quenched and tempered products: width 25 mm x length 25 mm x thickness 5 mm, hardness 45 HRC) were obtained by performing the treatments shown in Table 3 below. For the surface of samples 1 to 4, X-ray residual stress measurement using cos α method, surface shape observation based on laser microscope and scanning electron microscope (SEM), and elemental analysis by energy dispersive X-ray analysis (EDX) Did.

(3) Test results
(3-1) Result of measurement of residual stress The results of measurement of residual stress in the width direction (X direction) and the length direction (Y direction) of the above four types of test pieces are shown in Table 4 below.

  In addition, as a result of measuring the residual stress of Sample 2 (soft nitrided product), it was confirmed that high compressive residual stress was applied, but the variation of measured values is large (standard deviation is large). In view of the low reliability of the accuracy of the numerical values, Table 4 is left blank.

  From the above results, in the samples treated by the method of the present invention (Samples 3 and 4), a larger compressive residual stress is imparted as compared with the test piece of Sample 1 (untreated (quenched / tempered)). It was confirmed that it was possible.

  Moreover, in the test piece of sample 1, the stress value is largely different in the X direction and the Y direction, but in the test piece treated by the method of the present invention, the stress value almost differs in the X direction and the Y direction. It was confirmed that in the method of the present invention, compressive residual stress could be applied uniformly in any direction on the surface of the test piece.

(3-2) Surface Shape The contour curves of the samples 1 to 4 are shown in FIG. 3 and the SEM images of the surface are shown in FIGS.
According to the method of the present invention, a large number of deep and sharp recesses (valleys) which can be the origin of cracking are formed on the surfaces of sample 1 and sample 2 which are comparative examples, from the contour curve shown in FIG. It can be seen that the surfaces of the treated sample 3 and the sample 4 have a generally smooth contour as compared with the samples 1 and 2.

  In addition, as a result of measuring the arithmetic mean curvature (Spc: ISO 25178) of the peak point in the surface of the sample 1 (untreated product) and the sample 4 processed by the method of this application, it is 1/12477 in the sample 1 (untreated product). In the test piece treated according to the method of the present invention, the peaks of the asperities are crushed and the surface becomes a smooth shape. Has been confirmed.

  Also, according to the SEM image of the surface of each sample, tool marks remain on the surface of sample 1 as a comparative example (see FIG. 4), and similarly, on the surface of sample 2 as a comparative example, Although the presence of fine asperities was confirmed (see FIG. 5), the presence of such granular fine asperities could not be confirmed on the surfaces of sample 3 and sample 4 treated by the method of the present invention (FIG. 6, As shown in FIG. 7), it can be seen that the shape is less likely to be cracked than samples 1 and 2.

(3-3) EDX quantitative analysis result The result of having performed elemental analysis by energy dispersive X ray analysis (EDX) to the surface of samples 1-4 is shown in Drawings 8-11.
Moreover, the semi-quantitative value of EDX of each sample surface is shown in the following Table 5.

  The chemical components of SKD 61 in JIS G 4404 2006 are shown in Table 6 below for reference.

  As shown in FIG. 8, C, Fe, Si, Mo, V, Cr, and Mn are detected from the surface of sample 1, but these components are all components of SKD 61 as shown in Table 6. At the same time, the semi-quantitative values (see Table 5) of the respective components also substantially match the composition of SKD 61, so that it can be seen that in Sample 1, the component of SKD 61 which is the substrate is detected as it is as the component of the surface.

  As shown in FIG. 9, N and O other than C, Fe, Si, Mo, V, Cr, and Mn, which are components of green body (SKD 61), are detected from the surface of sample 2 and nitrogen on the surface by soft nitriding. It can be confirmed that N is diffused.

  From FIG. 10, C, Fe, Si, Mo, V, Cr, and Mn, which are components of green body (SKD 61), and N diffused to the surface by soft nitriding are detected from the surface of sample 3 and Sn is detected. Also, the detected amount of O is increased compared to the sample 2.

  In addition, as a result of quantification by semi-quantitative analysis, it was confirmed that Sn is contained in a large amount of 55.1%.

  From this, it can be seen that a large amount of Sn element was diffused to the surface of the substrate (SKD 61) of sample 3 by the surface treatment method of the present invention.

  Moreover, it is thought that the surface was oxidized by performing the process of this application from the increase of O.

  From FIG. 11, from the surface of sample 4, C, Fe, Si, Mo, V, Cr, and Mn, which are components of base (SKD 61), and N diffused to the surface by soft nitriding, as well as Sn are detected. Also, the detected amount of O is increased compared to the sample 2.

  In addition, as a result of quantification by semi-quantitative analysis, it was confirmed that Sn is contained as much as 28.5%.

  From this, it can be understood that a large amount of Sn element was diffused to the surface of the sample 4 by the surface treatment method of the present invention.

  Moreover, it is thought that the surface was oxidized by performing the process of this application from the increase of O.

(3-4) Measurement of element distribution by FE-EPMA The surface analysis of sample 2 and sample 4 mentioned above was carried out by field emission electron probe micro analyzer (FE-EPMA), and the element was analyzed. The distribution was measured.

  Samples 2 and 4 were cut with a wire in the thickness direction and the cut surface was embedded in a conductive resin and mirror-polished. Then, the element distribution near the surface layer of the cross-section after mirror-polishing was mapped by FE-EPMA.

  As a result of measurement, in the test piece of sample 2 (comparative example), Fe is partially thin in the internal Fe portion, and a place where Cr is thick is present in a point shape, and Cr carbide which is an alloy component is present in this point It is thought that it exists.

  In addition, in the surface layer portion of sample 2, it was confirmed that the concentration of N which is considered to be the influence of the compound layer accompanying the soft nitriding treatment was confirmed, and that the O was partially concentrated.

  In addition, in the test piece of the sample 2 which is not injecting Sn particle | grains, Sn element is not detected.

  On the other hand, even in the internal Fe portion of the test piece of sample 4 (example), the point is that Fe is partially thin and the place where Cr is thick is present in the form of dots, similar to sample 2; Also shows that the internal structure is maintained without change.

  Also, unlike the sample 2, in the surface layer part of the sample 4, while the concentration of N can not be observed, the existence of the place where Sn is concentrated is confirmed, and the nitrogen compound layer is treated by the method of the present invention. It was confirmed that the Sn element was diffused to the surface of the sample by the injection of Sn particles while

[Evaluation test of corrosion resistance]
(1) Purpose of test The test piece surface-treated by the method of the present invention has corrosion resistance (in particular, the corrosion resistance is imparted by diffusion of Sn element), and the corrosion resistance is not lost even by the frictional wear test. Make sure.

(2) Test method Surface treatment of each of six test pieces (hardened and tempered product; width 25 mm × length 25 mm × thickness 5 mm, hardness 45 HRC) made of SKD 61 under the conditions shown in Table 7 below. The surface was friction-abraded by a ball-on-disk type abrasion machine.

  After washing each test piece after frictional wear, the occurrence of corrosion (red rust) after immersion in industrial water (about 25 ° C.) for 240 hours was visually observed.

Friction abrasion test specimen surface, A5052 manufactured balls (diameter 10 mm), the pressing under a load 9.8N on the surface of the test piece as shown in FIG. 12, the friction radius 6 mm, at a rotational speed 100 min ^-1, 500 sec I made it slide.

  In the immersion of each sample in industrial water, the water was replaced about every 50 hours to replenish the dissolved oxygen in order to make the environment prone to rusting.

(3) Test Results The surface condition of each sample before and after immersion in industrial water is shown in FIG. 13, and the evaluation results of corrosion resistance based on this surface condition are shown in Table 8 below.

  From the above results, it was confirmed that high surface corrosion resistance can be obtained by performing surface treatment with the surface treatment method of the present invention.

  In addition, since generation | occurrence | production of remarkable rust is confirmed in the sample 6 to which high compressive residual stress is provided by the soft nitriding process, it turns out that corrosion resistance is not obtained only by giving compressive residual stress.

  Therefore, the corrosion resistance in samples 9 and 10 treated by the surface method of the present invention is not obtained by application of compressive residual stress by soft nitriding (sample 10) or shot peening (samples 9, 10), and the Sn element It is reasonably speculated that this is obtained by changing the material properties of the cooling hole surface by the diffusion of

In addition, even in the test piece of the sample 8 in which the surface modification layer of magnetite (Fe ₃ O ₄ ) is formed on the surface of the test piece after the soft nitriding treatment, the sample 9 which has been surface treated by the method of the present application Similar to the specimen of sample 10, the corrosion resistance of the friction surface was not lost after the friction and wear test.

However, even also obtained by forming a surface modification layer of magnetite (Fe ₃ O _4), directly to the surface of the untreated (left-hardened), surface modification of magnetite (Fe ₃ O ₄₎ In sample 7 where a layer is formed, the magnetite layer wears and loses corrosion resistance in the portion in contact with the ball in the friction test, and a large amount of red rust is generated, and the surface modification layer of magnetite (Fe ₃ O ₄ ) is Although it has high corrosion resistance, it has been confirmed that it is vulnerable to friction and wear when it is not subjected to surface strengthening treatment such as soft nitriding.

  On the other hand, in the surface treatment method of the present invention, in addition to the case where the surface treatment of the present invention is applied to the surface after soft nitriding treatment (Sample 10), directly on the surface of untreated (as-quenched and tempered) In any of the surface treatments of the present invention (Sample 9), the corrosion resistance including the portion in contact with the ball was not lost in the friction test, and nitriding (soft nitriding) was performed as the surface treatment. It was confirmed that the surface treatment resistant to friction was performed even when there was no case.

  The reason why such high wear resistance is obtained is unclear, but as shown in the EDX qualitative analysis results of FIG. 10 and FIG. 11, oxygen is observed on the surface of the sample subjected to the surface treatment by the method of the present invention. As the detected amount of (O) increases, one of the causes is that it exhibits high wear resistance by becoming tin oxide with high hardness (maximum hardness 1650 HV) by oxidizing Sn (hardness 5 HV) It is guessed that it is not.

[Evaluation test for injection method of projectiles]
(1) Purpose of test It is confirmed that the processing can be performed even for a relatively small diameter cooling hole having a closed end by the shot and / or spray particle injection method adopted in the present invention.

(2) Test method As shown in FIG. 14, a hole in which two test pieces (SKD 61) in which grooves having a semicircular cross-section are formed are overlapped so that the grooves overlap each other, and one end is a closed end. These holes were subjected to the surface treatment of the present invention.

As each test piece, one in which a magnetite (Fe ₃ O ₄ ) layer is formed by exposing the groove formation surface to high temperature water vapor (corresponding to the treatment of Patent Document 5) is used, and the groove formation surface of this test piece is overlapped. By combining, a hole 4 mm in diameter and 290 mm in length was formed.

  Insert an injection nozzle with an outer diameter of 2.0 mm, an inner diameter of 1.4 mm, and a length of 350 mm into this hole, and after injecting a shot of SiC (53-45 μm) at an injection pressure of 0.7 MPa The body (50-20 μm) was injected at an injection pressure of 0.7 MPa.

  Shots and injections of injection particles are inserted until the tip of the injection nozzle is several mm apart from the closed end, and injection is started at this position, and while the injection nozzle is gradually drawn out of the hole, The injection was continued until the tip came out of the hole.

  After performing the above surface treatment, the overlapped test pieces are separated, and the residual stress on the surface of the hole (groove) near the closed end and the surface of the other portion (portion of the hole cylinder) ( The residual stress in the longitudinal direction of the hole was measured by X-ray residual stress measurement using the cos α method.

(3) Test results The residual stress value of the hole surface measured by the above method was -25MPa near the closed end before the surface treatment of the present invention, and + 450MPa at the other parts. After surface treatment, it was -585MPa near the closed end and -831MPa at other parts.

  When shot or jetted particles are jetted from a jet nozzle inserted in a cooling hole having a small diameter and a closed end, the gap between the outer periphery of the jet nozzle and the inner wall of the cooling hole is narrow, and the jetted shot or jetted granules As described above, it is difficult to treat the surface of the cooling hole because the cooling hole is clogged.

  However, as proposed in the surface treatment method of the present application, in the process of injecting shots and injection particles while withdrawing the injection nozzle, the injection can be performed without causing such clogging, and It was confirmed that the shot and the jet particles collided with the energy that could give high compressive residual stress to the surface.

  Moreover, as a result of confirming the diffusion of Sn element to the surface after the treatment, it is found that the Sn element is diffused to the surface of the cooling hole as in the test results for samples 3 and 4 (see FIGS. 10 and 11) confirmed.

  Therefore, the injection method employed in the surface treatment method of the present application is an effective injection method for performing the diffusion treatment of Sn element performed by shot peening or injection particles being jetted to the surface of the cooling hole having the closed end. It can be said.

2. Evaluation by mold (1) Purpose of test It is confirmed that stress corrosion cracking resistance is imparted by applying the processing method of the present invention to the cooling hole of the mold.

(2) Test method Heating and cooling of the mold were repeated while cooling water was introduced into the cooling holes of the mold (SKD 61) surface-treated by the method of the present invention and the untreated cooling holes. After that, the surface condition inside the cooling hole was visually observed.

(3) Test results As a result of observation, it is confirmed that, on the surface of the untreated cooling hole, rusting is generated on the entire surface of the cooling hole and the crack is generated due to repeated heating and cooling of 20,000 cycles. The

  On the other hand, on the surface of the cooling hole subjected to the surface treatment according to the method of the present invention, the generation of a very slight rust was confirmed even after repeated 30,000 cycles of heating and cooling. Most of them were kept clean without rust.

  Further, it was not possible to confirm the occurrence of cracks on the surface of the cooling hole treated by the method of the present invention.

From the above results, it was confirmed that the surface treatment method of the present invention has the effect of imparting stress corrosion cracking resistance to the surface of the cooling hole of the mold.

Claims (11)

  1. A method of surface treatment of a mold cooling hole, comprising performing a diffusion treatment for diffusing Sn element on at least the surface of a cooling hole formed in the mold.   In the diffusion process, jetted particles consisting of tin and / or tin alloy particles having an average particle diameter of 10 to 100 μm are jetted together with compressed gas having a jet pressure of 0.4 to 0.8 MPa to collide with the surface of the cooling hole The surface treatment method for mold cooling holes according to claim 1, wherein the method is performed by diffusing Sn elements in the blast particles to the surface of the cooling holes. Processing the surface of the cooling hole whose end is a closed end,
The injection of the injection particles in the diffusion process is started with the injection nozzle having a diameter smaller than that of the cooling hole inserted in the tip of the injection nozzle close to the closed end of the cooling hole, and the injection nozzle is gradually drawn out 3. The method according to claim 2, wherein the injection of the injection particles is continued.   The method for surface treatment of a mold cooling hole according to any one of claims 1 to 3, wherein shot peening is performed on the surface of the cooling hole.   5. The method according to claim 4, wherein the shot peening is performed by injecting a shot having an average particle diameter of 20 to 149 [mu] m with a compressed gas having an injection pressure of 0.3 to 0.8 MPa. Processing the surface of the cooling hole whose end is a closed end,
The injection of the shot in the shot peening starts with the injection nozzle having a diameter smaller than that of the cooling hole inserted into the vicinity of the closed end of the cooling hole with the tip of the injection nozzle being inserted. 6. The method according to claim 5, wherein the injection of the shot is continued.   The surface treatment method of a mold cooling hole according to claim 3 or 6, wherein the tip of the nozzle is swung within the cooling hole.   The surface treatment method of a mold cooling hole according to any one of claims 1 to 7, wherein a surface of the cooling hole which has been nitrided or soft nitrided is treated. In a mold in which a cooling hole for introducing a refrigerant for cooling is formed,
A surface-modified layer in which Sn is diffused is formed on the surface of the cooling hole.   The mold according to claim 9, wherein compressive residual stress is applied to the surface modified layer. 11. The mold according to claim 9, wherein the cooling hole has a nitrided layer or a soft nitrided layer on the surface, and the surface modified layer is formed in the nitrided layer or the soft nitrided layer.