JP6164552B2 - Manufacturing method of iron-based sintered parts - Google Patents

Description

This invention relates to the production how iron-based sintered component makes it possible to produce excellent iron base sintered parts wear resistance at low cost.

  For example, sprocket wheels and gears are known as typical sintered parts that require wear resistance. These sintered parts are required to have high hardness, and the demand is usually met by increasing the density, using a high alloy material, adding a heat treatment step, and the like.

  In Patent Document 1 below, sintering is performed in two steps, primary and secondary, and an intermediate process of surface modification by shot peening is performed between the primary sintering process and the secondary sintering process. It has been proposed to increase the hardness of the surface by performing carburizing quenching and tempering or induction quenching after insertion and further secondary sintering.

JP 2001-294904 A

  The advantage is that sintered parts made of iron-based materials are inexpensive. However, the advantage of increasing the density by satisfying the demand for higher hardness is impaired.

  As measures to increase the density of sintered parts, for example, there are techniques such as using special molding methods such as warm molding and mold lubrication molding, or using high-purity raw iron powder. Then, cost increase is inevitable.

  The method using a high alloy material is also expensive because the raw material cost is high.

  Further, the method disclosed in Patent Document 1 is expected to increase the mass productivity because it takes a long time to perform shot peening when it is intended to increase the hardness of a complex surface having a large area. This is not possible, and this also increases costs.

  The present invention has been made in view of the above-described present technology, and an object thereof is to make it possible to manufacture an iron-based sintered part excellent in wear resistance at a low cost.

  In order to solve the above-mentioned problems, in the present invention, in the manufacture of iron-based sintered parts, a steam treatment is performed on the parts that have undergone the sintering process to form an iron oxide film on the surface of the parts. A method is adopted in which a high-temperature heat treatment is performed on a desired part of the component to form a martensite layer in the surface layer portion of the heat-treated part.

In the sintered part manufactured by the method of the present invention, a martensite layer is formed on a surface layer portion at a desired location, and an iron oxide film is further formed on the martensite layer .

  According to the manufacturing method of the present invention, an iron-based sintered part having excellent wear resistance can be manufactured at low cost.

It is a figure which shows the procedure of the manufacturing method of this invention. It is a perspective view which shows an example of the sintered component manufactured by the method of this invention. It is a schematic diagram of the cross section of the surface layer part of the components by which the oxide film was formed on the martensite layer. It is an image figure of the structure of the section of the surface layer part of the sintered compact manufactured by the method of this invention. It is a structure | tissue photograph of the cross section of the surface layer part of the sintered compact manufactured by the method of this invention.

  Hereinafter, an embodiment of a method for producing an iron-based sintered part of the present invention will be described.

  In the production of iron-based sintered parts, the parts subjected to the sintering process are subjected to steam treatment to form an iron oxide film on the surface of the parts, and then subjected to induction heat treatment at desired parts of the parts. Then, a method is adopted in which a martensite layer is formed in the surface layer portion of the part subjected to heat treatment.

  According to this method, a martensite layer is generated in the surface layer portion of the component by quenching by induction heat treatment. In addition, the steam treatment that is performed prior to the high-frequency heat treatment produces a hard iron oxide film on the surface of the component and the pores of the pores in the structure of the surface layer portion, and the surface layer portion has high hardness and excellent wear resistance. You can make parts.

  Note that both steam treatment for forming an oxide film and induction heat treatment for quenching are both commonly used methods and can be performed at low cost. In addition, a large number of steam treatments can be performed simultaneously, and a high-frequency heat treatment has a very short treatment time per piece. Therefore, good mass productivity can be ensured, which enables manufacturing at low cost.

  The production of iron-based sintered parts by the method of the present invention will be described in more detail. In this method, first, a raw material powder is formed using a powder forming apparatus (not shown) having a die including a die, an upper punch, and a lower punch, and further including a core rod as required (FIG. 1). The green compacting step I in the production procedure of the above is carried out).

  Next, the compact obtained through the compacting process I is sintered at a predetermined temperature (the sintering process II in the manufacturing procedure of FIG. 1 is performed).

  An example of a sintered part obtained through the sintering step II is shown in FIG. The illustrated sintered part 1 is a gear. This gear is required to have excellent tooth surface wear resistance. Therefore, the sintered gear is sent to the steam processing step III of the manufacturing procedure of FIG. 1, where an oxide film is generated by the steam processing.

In the steam treatment step III, a sintered component to be treated is placed in a treatment kettle (not shown), and high-temperature steam at 450 ° C. to 600 ° C. is fed into the kettle. When the steam treatment here is carried out for 30 minutes or more, preferably about 1 hour, an oxide film (Fe) having a thickness of about 5 μm is formed on the surface of the sintered part and the pores of the pores in the surface layer located in the surface layer. ₃ O ₄ ) can be generated.

  Thereafter, the sintered part 1 on which the oxide film is formed is sent to the heat treatment step IV of FIG. In the high frequency heat treatment, an induction heating coil (also not shown) heats the tooth portion 2 of the sintered component 1 set inside the coil so as to have a temperature of about 900 ° C. to 1000 ° C. This temperature is the temperature at which the metal structure austenites. The heating time at this time can heat a tooth | gear part to the target temperature in about 2 second, for example.

  If the heating time in the high-frequency heat treatment becomes too long, the iron oxide film produced by the steam treatment is decomposed, and the prior steam treatment becomes meaningless. Therefore, the heating time by the induction heating coil is preferably 30 seconds or less. By limiting the heating time to 30 seconds or less, decomposition of the oxide film can be avoided.

  The general idea is that heating the part to a temperature higher than the temperature of the steam treatment after the steam treatment is impossible because the oxide film formed by the steam treatment is decomposed by the temperature of the heat treatment. In fact, the oxide film is decomposed when the entire part is subjected to heat treatment (quenching, tempering, or carburizing heat treatment by so-called sub-firing).

  On the other hand, if the heat treatment is performed in a short time using a high frequency, the oxide film remains without being decomposed. The inventor confirmed that through experiments.

  In consideration of productivity, the heating time in the high-frequency heat treatment is 7 seconds or less, more preferably 3 seconds or less. As long as this heating time can be heated to the target temperature, the shorter it is, the better.

  In heat treatment step IV, the heated sintered part is rapidly cooled to change the structure of the surface layer portion to martensite. The rapid cooling may be performed either by gas cooling, which is normally performed, or by immersion in a refrigerant liquid.

  After the above steps, as shown in FIG. 3, a martensite layer 4 is formed on a surface layer portion of a desired portion of the base material 3, and an iron oxide film 5 is further formed on the martensite layer 4. A bonded part 1 is obtained.

  Note that the upper limit of the hardening depth of the surface of the sintered part by the high-frequency heat treatment (region where the martensite layer 4 is formed) is limited to about 5 mm because the heating time by the high-frequency heat treatment is regulated.

  As shown in FIG. 4, the sintered part obtained by the method of the present invention is not only on the surface of the martensite layer 4 but also on the inner surface of the fine pores 6 existing in the base material 3 and the martensite layer 4. The iron oxide film 5 is formed, and the surface layer has a structure in which the martensite layer and the oxide film are combined.

  Therefore, the hardness of the hardened surface layer portion is higher than that of a sintered part subjected only to heat treatment, and the wear resistance is further improved.

  In addition, the void 6 in the surface layer portion is blocked by the generation of the oxide film by the steam treatment, so that the penetration of corrosion factors such as moisture into the structure is suppressed, and the rust prevention performance of the parts is improved.

  Furthermore, since the base iron and the oxide film on the surface are a combination of different materials, it is also possible to expect effects related to sound attenuation and resonance prevention.

Example 1
A steam temperature of 550 ° C. with respect to a sintered body (ordinary material) having a density of 6.9 g / cm ³ and a density of 7.2 g / cm ^{3 made} of a raw material powder having a composition of 2 wt% Cu-0.8 wt% C-balance Fe Steam treatment was performed under the condition of a treatment time of 1 hour, and then the sintered body was subjected to high-frequency heat treatment.

Induction heat treatment was performed using an induction heating coil with an output of 35 W and an output of 15 W. The heating of the sintered body by the induction heating coil with an output of 35 W was 3 seconds, and the heating of the sintered body by the induction heating coil with an output of 15 W was 30 seconds. And it cooled by quenching oil as a refrigerant | coolant liquid after that.
A photograph of the cross-sectional structure of the surface layer portion of the sintered body thus obtained is shown in FIG. FIG. 5 is a structural photograph of a sintered part obtained by heating a sintered body having a density of 7.2 g / cm ³ for 3 seconds after steam treatment.

  A sample was also prepared by subjecting a sintered body (ordinary material) having the same composition and density to high-frequency heat treatment under the same conditions as above without subjecting to steam treatment.

  Next, the hardness of the surface layer part of each obtained sample was evaluated. The hardness was evaluated using a Rockwell hardness tester. Moreover, the remaining state of the oxide film was also investigated about the sample which performed the steam process. The results are shown in Table 1.

  In the wear resistance test of Table 1, a gear meshing test was performed and the state of the tooth surface after 100 hours was observed. Test results A, B, and C are evaluated in three stages of damage. A is the best evaluation result, followed by B and C.

  As can be seen from the test results, the hardness of the sintered part subjected to high-frequency heat treatment after the steam treatment is the same as that of the normal material and the high-density high-alloy material (Fe—Ni—Cu—Mo, Fe—Mo, Fe—Ni—). Mo-based materials) were higher than those subjected to heat treatment only (the hardness of some alloy materials is described in Table 2 below).

-Example 2-
A sintered body (high alloy material) with a density of 7.2 g / cm ^{3 and} a raw material powder having a composition of 2 wt% Ni-0.5 wt% Mo-0.6 wt% C-balance Fe and 4 wt% Ni-1.5 wt% A steam temperature of 550 ° C. is applied to a sintered body (also a high alloy material) having a density of 7.2 g / cm ^{3 made} of a raw material powder having a composition of Cu—0.5 wt% Mo—0.6 wt% C—balance Fe. Steam treatment was performed for 1 hour, and then the sintered body was subjected to induction heat treatment.

  The time of the high-frequency heat treatment and the cooling after the heating were performed under the same conditions as in Example 1.

  A sample was also prepared by subjecting a sintered body (high alloy material) having the same composition and the same density to high frequency heat treatment under the same conditions as described above without subjecting to steam treatment.

  Next, the hardness of the surface layer portion of each obtained sample and the remaining state of the oxide film of the sample subjected to the steam treatment were examined. The results are shown in Table 2. The abrasion resistance test in Table 2 is the same test as in Example 1.

Thus, a sintered material obtained by subjecting a high alloy material to steam treatment and induction heat treatment under the above conditions is a sintered material obtained by subjecting a normal material to steam treatment and induction heat treatment by the method of the present invention. Higher hardness is obtained.

DESCRIPTION OF SYMBOLS 1 Sintered part 2 Tooth part 3 Base material 4 Martensite layer 5 Iron oxide film 6 Vacancy

Claims (1)

Steam treatment is applied to the parts that have undergone the sintering process, and an iron oxide film is formed on the surface of the parts.
Thereafter, a method for producing an iron-based sintered part in which a martensite layer is generated in a surface layer portion of a part subjected to high-frequency heat treatment on the surface of a desired part of the part and subjected to the heat treatment ,
The steam treatment is performed under the conditions of steam temperature: 450 ° C. to 600 ° C., treatment time: 30 minutes or more.
In addition, the high-frequency heat treatment is performed at a temperature at which the metal structure becomes austenite.
Temperature: 900 ° C. to 1200 ° C., heating time by induction heating coil: 30 seconds or less, cooling after heating
Rejection: A method for producing an iron-based sintered part that is carried out under conditions of a cooling rate at which martensite appears in a continuous cooling transformation curve .