JP4799291B2 - Alloy steel and manufacturing method thereof - Google Patents

Description

  The present invention relates to an alloy steel and a manufacturing method thereof.

  Hard steel used for tools is called tool steel, and is roughly classified into carbon tool steel, alloy tool steel, and high-speed tool steel in JIS. Among alloy tool steels, hot tool steels used at high temperatures, such as forging dies and die casting dies, and high-speed tool steels used for cutting tools, etc. have high toughness and high hardness. , It is required not to soften by heat. In order to impart these performances, the alloy steel is subjected to heat treatment in the manufacturing stage. The heat treatment is performed by procedures such as annealing, quenching, and tempering. As the tempering, high temperature tempering generally performed at 500 to 600 ° C. is performed using a curing phenomenon called secondary curing. Secondary hardening means that alloy elements such as Cr, W, Ni, Mo, V, Mn, Si, Nb, Ta, and Ti contained in the alloy form carbides during tempering, and fine grain boundaries of iron and This is a phenomenon in which the hardness increases due to precipitation in the grains.

The alloy tool steel is also required to further increase the surface hardness in order to improve its durability. Therefore, at present, surface treatment such as carburizing and nitriding is performed on alloy steel after tempering, or coating is performed by PVD method or CVD method. For example, Patent Document 1 discloses a tool having a specific composition. It is disclosed that the surface of steel is modified by PVD or CVD.
JP 07-009350 A

  However, as a method for increasing the hardness of the alloy steel surface, if a surface treatment such as carburizing or nitriding is performed, or a method of coating by PVD or CVD as in Patent Document 1, work is not easy. And there were problems such as film peeling.

  Then, an object of this invention is to provide the alloy steel which has high surface hardness simply.

  As a result of intensive studies to solve the above problems, the present inventors have found that the surface hardness of the alloy steel can be increased by surface treatment with fullerene before the tempering step.

  Thus, according to a first aspect of the present invention, there is provided an alloy steel which is subjected to high temperature tempering by applying fullerenes to the surface of the alloy steel before the high temperature tempering. The problem is solved.

  According to this invention, it can be set as the alloy steel which has high surface hardness.

  In this embodiment, the alloy steel is preferably tool steel.

  According to this invention, it can be set as the tool steel which has high surface hardness.

  According to a second aspect of the present invention, there is provided an alloy steel manufacturing method characterized in that, in alloy steel to be subjected to high temperature tempering, the high temperature tempering is performed by applying fullerenes to the surface of the alloy steel before the high temperature tempering. Thus, the above-mentioned problem is solved.

  According to this invention, it can be set as the simple manufacturing method of the alloy steel which has high surface hardness.

  According to the present invention, fullerene forms an alloy element and carbide in the alloy steel and finely precipitates in the iron grain boundaries and grains, so that the surface hardness can be increased. The surface hardness of the alloy steel can be increased only by performing normal high-temperature tempering without performing a special heat treatment only by a simple operation of applying fullerene. There is no need to perform a surface treatment such as carburizing, nitriding, or coating. Further, by performing tempering in an inert atmosphere, fullerenes that have not reacted with the alloy steel do not burn and react with each other to form an amorphous carbon film. This film can be easily coated without using an expensive apparatus such as a PVD method or a CVD method, and also has good adhesion to the alloy steel surface, and thus acts as a surface protective film.

  Such an operation and a gain of the present invention will be clarified from the best mode for carrying out the invention described below.

  In the present invention, the alloy steel as a base material is not particularly limited as long as it causes a secondary hardening phenomenon by high temperature tempering. Specific examples thereof include hot tool steel and high-speed tool steel among alloy tool steels. Specific examples of additive elements that can be added to the alloy steel include Mo, V, W, Nb, Ta, Ti, etc., which easily form carbides required for secondary hardening, and alloys to general steels. Examples of the element include C, N, P, S, Si, Ni, Cr, Cu, Mn, Zn, Al, Nb, Co, Zr, and Hf.

  The alloy steel of the present invention is obtained by annealing the alloy steel as a base material, quenching, applying fullerene to the surface, and tempering at a high temperature. For annealing and quenching, a method similar to that for general alloy tool steel is used. Specifically, annealing is performed at 700 ° C to 1000 ° C, and quenching is performed at 700 ° C to 1300 ° C.

The fullerenes applied to the alloy steel after quenching are carbon clusters in which carbon atoms form a hollow closed shell structure, and the number of carbons forming the closed shell structure is usually an even number of 60 to 130. Specific examples of fullerene include C ₆₀ , C ₇₀ , C ₇₆ , C ₇₈ , C ₈₂ , C ₈₄ , C ₉₀ , C ₉₄ , C ₉₆ , and higher-order carbon clusters having more carbon than these. Can be mentioned. In the present invention, each of these fullerenes and a mixture of the above fullerenes can be used as appropriate, and the number of carbons is not particularly limited. However, from the viewpoint of cost, ease of production, etc., mixed product, or it is preferable to use _{C 60.} It is also possible to use a fullerene derivative in which a substituent is added to fullerene or a metal or molecule is included inside. In the following description, fullerenes are described as representative examples of fullerenes for convenience.

  In the present invention, the method of applying fullerene to the surface of the base alloy steel is not particularly limited, and any method may be used as long as the fullerene and the base material can be contacted. Specific examples include a method of sprinkling fullerene powder on the surface of the base material, a method of airtightly filling the base material in the fullerene powder, a method of rubbing the compacted fullerene compact on the surface of the base material, dispersed in water or an organic solvent, or A method of spraying the dissolved fullerene on the surface of the base material, a method of applying the dispersed or dissolved fullerene to the surface of the base material using a brush, a method of forming a fullerene film on the surface of the base material by vacuum deposition, etc. Can be mentioned.

  For tempering performed after fullerene coating, high-temperature tempering that causes secondary curing is used, which is performed at a temperature of 400 ° C. to 800 ° C., preferably 500 ° C. to 700 ° C. In low temperature tempering of 200 ° C. or less used for general carbon steel and cold alloy tool steel, fullerene reaction does not occur and secondary hardening phenomenon does not occur. Also, the vicinity of 200 to 300 ° C. is not used because of low temperature temper embrittlement. The tempering time varies depending on the hardness and toughness required for the alloy steel, but is generally about 60 minutes per 25 mm thickness.

  The alloy steel obtained in this way has a very high surface hardness compared to the alloy steel not subjected to fullerene coating. This is because fullerene is applied to the outermost surface of the alloy steel after quenching and then tempered, so that the highly reactive fullerene is a part of the martensite structure and residual austenite present in the alloy steel after quenching. This is due to solid solution in residual austenite or by reacting with alloy elements such as Mo, V, W, Nb, Ta, Ti and forming carbides. As a result of this fullerene reaction, only the outermost surface of the alloy steel can be made to have high hardness. Therefore, the alloy steel of the present invention is particularly useful as an alloy tool steel that requires surface hardness.

  Moreover, when performing a tempering process in inert atmosphere, the fullerene which did not react with the alloy steel surface reacts with fullerene without burning, and forms an amorphous carbon film. This film has good adhesion to the surface of the metal material and acts as an excellent surface protective film for alloy steel.

  Hereinafter, the present invention will be specifically described by way of examples. In addition, this invention is not limited to the form of the Example shown below, unless the summary is exceeded.

1. Sample preparation
Fullerene mixture product (nano arm mix (registered trademark), manufactured by Frontier Carbon _{Corporation, C 60} 61 _{wt%, C 70} 25% by weight, the molecular weight of the otherwise high fullerenes 14 wt%) and of 5 mm × 5 mm × 30 mm A fullerene molded body was obtained by compression molding to a size. On the other hand, as the alloy steel, hot alloy tool steel SKD61 was cut into a size of 10 mm × 10 mm × 2 mm, annealed at 850 ° C., and quenched at 1020 ° C.

2. Sample preparation (Example 1)
The fullerene compact was rubbed against the alloy steel surface to form a brown fullerene film, thereby attaching the fullerene to the iron piece surface. The alloy steel was heated to 550 ° C. in an argon atmosphere for 18 minutes and held for 10 minutes, and then cooled in a furnace where heating was stopped for 1 hour. Thereafter, the alloy steel was taken out of the furnace and the surface was washed with alcohol to prepare a sample.

(Comparative Example 1)
A sample was manufactured through the same process as in Example 1 except that the fullerene was not rubbed.

(Comparative Example 2)
Instead of rubbing the fullerene compact, graphite was deposited on the alloy steel by rubbing the alloy steel to the graphite powder, and thereafter, the same process as in Example 1 was performed to prepare a sample.

(Example 2)
Fullerene mixed powder is put in an iron container, and alloy steel is hermetically filled in the fullerene. The entire container is heated to 550 ° C. in an argon atmosphere in a furnace for 180 minutes and held for 30 minutes. Then, it was cooled for 1 hour in a furnace where heating was stopped. Then, this alloy steel was taken out of the furnace and the surface was washed with alcohol to prepare a sample.

(Example 3)
A sample was prepared in the same manner as in Example 2 except that the holding time at 550 ° C. was 60 minutes.

(Comparative Example 3)
A sample was prepared in the same manner as in Example 2 except that an iron container containing no fullerene mixed powder was used.

(Comparative Example 4)
A sample was prepared in the same manner as in Example 3 except that an iron container containing no fullerene mixed powder was used.

3. Evaluation of Sample The hardness HV at a load of 1.96133N (200 gf) was determined for the samples of Example 1 and Comparative Examples 1 and 2 obtained above using a Vickers hardness tester. The results are shown in Table 1.

  When Table 1 is seen, it turns out that the sample of the Example to which fullerene was rubbed has higher hardness compared with Comparative Examples 1 and 2 which are samples to which fullerene was not rubbed. That is, it was confirmed that the surface hardness can be increased by applying fullerene to the surface of the alloy steel during high temperature tempering.

  For the materials of Examples 2 and 3 and Comparative Examples 3 and 4 obtained above, the hardness HV at a load of 1.96133N (200 gf) was determined using a Vickers hardness meter. The results are shown in Table 2.

  Referring to Table 2, the samples of Examples 2 and 3 were prepared by filling the fullerene mixed powder, and alloy steel was hermetically embedded in the fullerene, and were prepared without the fullerene mixed powder. It can be seen that the hardness is higher than that of Comparative Example 3 or 4 which is a sample. That is, it was confirmed that the surface hardness can be increased by applying fullerene to the surface of the alloy steel during high temperature tempering.

  Although the present invention has been described with reference to the most practical and preferred embodiments at the present time, the present invention is not limited to the embodiments disclosed herein. However, the present invention can be modified as appropriate without departing from the spirit or concept of the invention which can be read from the claims and the entire specification, and alloy steels accompanying such changes and the manufacturing method thereof are also included in the technical scope of the present invention. Must be understood.

Claims (3)

An alloy steel which is subjected to high temperature tempering, wherein the high temperature tempering is performed by applying fullerenes to the surface of the alloy steel before the high temperature tempering. The alloy steel according to claim 1, wherein the alloy steel is tool steel. An alloy steel to be tempered at high temperature, wherein the alloy steel is subjected to the high temperature tempering by applying fullerenes to the surface of the alloy steel before the high temperature tempering.