JP2006118033A - Method for producing compositionally gradient cemented carbide - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a compositionally gradient sintered compact combining wear resistance, weldability and machine workability using several kinds of cemented carbides with different compositions and different optimum sintering temperatures, to provide a method for producing a composite body obtained by joining them and steel, and to provide a compact obtained thereby. <P>SOLUTION: In this invention, green compacts with prescribed shape are beforehand molded, and they are piled or arranged inside a die, and are subjected to pulse electric sintering while being pressurized with punches, thus a dense sintered compact of compositionally gradient cemented carbides free from variation in shape and dimensions can be obtained. Further, since the sintering is performed in such a manner that the optimum temperature gradient is provided for the body to be sintered in the die using spacers, or punches and a die subjected to groove working, the sintered compact having desired uniform layers and gradient layers can be obtained. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  In the present invention, a composition gradient sintered body having wear resistance, weldability, and machinability, or steel and these are joined using several kinds of cemented carbides having different compositions and different optimum sintering temperatures. The present invention relates to a method for producing a composite and a molded body obtained thereby.

  As a method for producing a composition graded cemented carbide with wear resistance, weldability and machinability in one step, the conventional method is to provide a step or taper on the outer diameter side of the die and powder of each composition inside the die. Are sequentially filled and laminated, and pulsed energized while being pressed with upper and lower punches, and sintered. As a result, the workpiece in the die has a temperature gradient in the thickness direction corresponding to the step or taper, and is sintered at the optimum temperature corresponding to each composition. When adding a step or taper to the outer diameter of this die, the larger the die thickness difference, the larger the sintering temperature difference. However, if the thickness is made too thin, it will not withstand the sintering pressure and will be damaged. However, if it is too thick, temperature control is difficult and there is a limit such as no temperature difference.

  In addition, when pulsed current sintering of cemented carbide, which is a liquid phase sintered body, is naturally performed by short-time heating (rapid temperature rise), which is a feature of this sintering method. In the plane perpendicular to the pulse current direction, a uniform sintering temperature cannot be obtained, and the temperature on the outer peripheral side is lower than the central part and the outer peripheral side is undersintered, or the central part is oversintered. It is a common experience for the binder phase components to elute. The inventors used a graphite die and punch to heat the pulse until the temperature reached by the sample in the die reached 1000 ° C., and examined the temperature difference of the sample in the die (φ30 × 5 mm). As a result, even when the gap (diameter difference) between the punch and the die is about 0.2 mm, a temperature difference of 100 ° C. is observed in the central portion and the outer peripheral portion. (Reference: Hokkaido Prefectural Industrial Technology Center, Hokkaido Prefectural Industrial Experiment Station 2001 Joint Research Report “Development of Functional Materials Applying Gradient Composition and Reaction Sintering Technology”).

  For this reason, a semiconductive layer made of a heat-resistant conductive material and a heat-resistant insulating material is interposed on the surface where the powder material is in contact with the forming die and / or the punch, and the electric conductivity (energization amount from the punch side and die side) ) Has been devised and a patent application has already been filed (Japanese Patent Laid-Open No. 2000-239071).

  In the conventional method, a powder of each composition is filled and laminated in a die in sequence, and the powder is energized and sintered by applying pressure with upper and lower punches. However, if the layers are thin, there is no problem, but if the layer is thin, there will be a shortage of the layer after powder filling, and the shape of each layer will be complicated or asymmetric In order to manufacture the product, a jig for preventing mixing is required every time the powder is filled, and in some cases, it is necessary to fill the die by turning it upside down. In addition, naturally, the thickness and width of each layer after filling vary greatly, making it difficult to produce the same sintered body.

  In addition, in the conventional method, a step or taper is provided on the outer diameter side of a die made of graphite or the like, and a temperature gradient is provided in the internal sintered body. In some cases, no union can be obtained. Moreover, this method is difficult to apply to a sintered body having an asymmetric shape or composition (layer), and the degree of freedom in designing the material and shape is small.

  Furthermore, the method of interposing a semiconductive layer composed of a heat-resistant conductive material and a heat-resistant insulating material on the surface where the powder material is in contact with the molding die and / or the punch, the processes such as coating, baking, and drying are complicated. It takes a lot of processing time. Moreover, since this coating-film surface becomes a contact surface with powder and the surface roughness is transcribe | transferred, the demerit that the contact surface with the coating film of a to-be-sintered body becomes smooth also arises.

  The present invention has a predetermined shape in the process of producing a composition gradient sintered body using several types of cemented carbide powders having different compositions and different optimum sintering temperatures, and has a predetermined shape in advance, and is divided, cut out and lightly cut. The present invention relates to a manufacturing method in which green compacts having strength to withstand, etc. are molded, and these are stacked or arranged in a die mold and subjected to pulse current sintering while being pressed with a punch, and a molded article thereby Is.

  Also, in this case, by using a grooved spacer, punch, or die, the energization path of the grooved part is cut off or the energization amount is controlled so that the optimum temperature gradient is applied to the sintered body in the die. The present invention relates to a method of providing and sintering and a molded body obtained thereby.

  According to the present invention, a sintered body of a dense composition gradient cemented carbide with no variation in shape and dimensions can be obtained. In addition, since a good temperature gradient can be given even in the sintering of an asymmetric composition gradient alloy, which was difficult with the conventional method, the range of material design is expanded. Furthermore, when producing a large number of sintered bodies, a high-quality sintered body is produced in a short time, and as a result, a highly durable composite structure that is welded or directly joined can be obtained.

  In the present invention, a spacer intended to be used up is used on the contact surface side with the object to be sintered together with a die and a punch used for repeated sintering many times. In this case, with respect to the contact side of the spacer with the punch and the die, or with respect to the punch and the die that comes in contact with the spacer, in order to adjust the sintering temperature of the sintered body, a recess or sawtooth-shaped groove is formed in a predetermined place. Give it.

  In addition, a green compact (block) having a predetermined shape is previously prepared for each composition for the object to be sintered. For this production, a normal press, a cold isostatic pressure (CIP) method, or a pre-sintering method by pressing and heating at a temperature lower than the sintering temperature is applied. Next, blocks formed into a predetermined shape or blocks cut out from a large green compact are stacked or arranged in a die. Thereafter, pulse current sintering is performed while pressing with upper and lower punches. The sintering conditions are not particularly limited, but the pressure may be lower than the punch and die strength, and the temperature elevation rate may be about 100 to 300 ° C./min.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
In order to make a composition gradient cemented carbide that is easy to weld or machine while maintaining wear resistance, an alloy having a composition that becomes super hard and an alloy that does not cause cracks, cracks, etc. even when welded, Furthermore, it is necessary to combine a total of three or more kinds of alloys having intermediate compositions to alleviate these differences in thermal expansion coefficients. The inventors TIG welded each cemented carbide and steel in which the amount of Co in the WC-Co-based alloy or the amount of Ni in the WC-Ni-based alloy was changed to 10 to 40 wt%, and the penetration, welding strength, etc. Was examined in detail. As a result, it has been clarified that good bonding properties are exhibited when the Co content and Ni content are 30 wt% or more. These research results are reported in Hokkaido Industrial Research Institute Report: No. 299, “Effect of Co content in cemented carbide on TIG welding with steel”, FGM2003 in Sapporo, 15th Functionally Graded Materials Symposium, “Development and application of compositionally graded Ni-based cemented carbide” Even reporting. In this case, an alloy having an ultra-hard composition (for example, WC-10 wt% Ni) and a weldable alloy (an alloy having Co content or Ni content of 30 wt% or more) are directly laminated and sintered. It has also been clarified that when steel is welded to it, cracks or cracks are formed on the super-hard composition alloy side, and that improvement requires one or more alloys with an intermediate composition to relieve stress. .
Based on these findings, a composition gradient cemented carbide with a three-layer structure of WC-10 wt% Co as the super hard layer, WC-15 Ni wt% as the intermediate layer, and WC-30 wt% Ni as the weld layer was produced. The WC particle size was 4.5 μm in all cases. First, the molded body (block) of each layer was produced. As described above, various methods such as CIP can be applied as a method for producing the block, but here, using a graphite die having a predetermined shape and a punch, low-temperature heating at 800 to 840 ° C. by a pulse current sintering method, It was produced with a pressure of 10 kN. FIG. 3 is a combination of the blocks obtained by this method. Thereafter, each block is loaded into a predetermined graphite die, and a sintered body is produced under the conditions of 1235 ° C. (die outer peripheral temperature) and 20 kN by the pulse current sintering method while pressing with the upper and lower punches. did. FIG. 4 shows the cross-sectional hardness of the composition gradient cemented carbide sintered body obtained by these methods. The hardness of the outermost surface is 1500 HV, the intermediate layer is about 1000 HV, and the weld layer is 600 HV. Each layer has a substantially constant hardness and exhibits a stepwise hardness distribution as a whole. This hardness distribution was measured on four samples sintered under the same conditions, and all were the same. FIG. 5 is a cross-sectional macrostructure after TIG welding of a composition gradient cemented carbide and a stainless steel plate. It can be seen that the composition gradient cemented carbide has a desired layer structure, and no cracks, cracks, or the like are observed in the vicinity of the welded portion, and a good welded body is obtained.

Next, an example will be shown in which it is demonstrated that a uniform sintered body can be obtained by cutting the energization path by performing groove processing on a spacer or the like and adjusting the temperature.
A WC-10 wt% Ni cemented carbide (diameter: 20 mm, thickness: about 4.5 mm) was sintered using a graphite die, punch and spacer having the shape shown in FIG. In this case, a flat recessed groove with a depth of about 0.1 mm in the range from the center to a radius of 4 mm on one side (contact surface with the punch) of the spacer having a diameter of 20 mm and a thickness of 5 mm, and from here to a radius of 6 mm. A serrated groove having a depth of about 0.1 mm and a pitch of about 0.5 mm was dug. Cemented carbide is filled in the die, and this spacer is placed between the upper punch and the cemented carbide (the groove processing surface is on the punch side), the final pressure is 6.5 kN, the temperature reached at the die outer periphery is 1235 ° C, the average rise Pulse current sintering was performed at a temperature rate of 140 ° C./min.
FIG. 7 shows the hardness distribution in the plane of the sintered body obtained by this method. In addition, as a comparison, the hardness distribution of a sintered body produced under the same condition using a spacer made of the same material having a smooth surface on both sides without performing groove processing is shown. In both cases, the measurement surface of the sintered body was ground by about 0.1 mm, and then buffed with diamond (15 μm). The hardness of the sintered body in the case of using a spacer that has not been grooved exhibits a so-called mountain-shaped hardness distribution that is extremely high in the central portion and decreases as it goes to the outer peripheral portion. On the other hand, the hardness when using the spacer by the groove processing according to this method is slightly lower at the outer peripheral portion as shown in FIG. It is clear that the temperature adjustment during the ligation is good.
Note that the maximum hardness is higher when spacers that are not grooved are used, but this is because the central part has become higher than the optimum sintering temperature, and Ni is the binder phase component from there. This is because of elution. This also confirms that a uniform sintered temperature and a uniform sintered body were obtained by using the groove processing spacer.

  FIG. 1 is a perspective view (half-split state) of a molded body (block) laminated state and sintering dies, punches, and spacers showing an example of an embodiment of the present invention.   FIG. 2 is an example of an embodiment of the present invention, and is a perspective view showing a method of welding a composition gradient cemented carbide to a steel base material or the like.   FIG. 3 is an appearance of a molded body (block) of each composition in a compacted state at a low temperature.   FIG. 4 shows the hardness distribution of the composition gradient cemented carbide obtained by charging the compact of FIG.   FIG. 5 is a cross-sectional macrostructure of a composite in which the molded body of FIG. 3 is loaded into a mold and a composition gradient cemented carbide alloy and a stainless steel plate, which are pulse-electrically sintered, are TIG welded.   FIG. 6 is a perspective view (half-split state) of the groove processing state of the spacer and the dies and punches showing an example of the embodiment of the present invention.   FIG. 7 is a comparison of the hardness distribution of a cemented carbide that has been pulse-electrically sintered using the spacer, die, and punch of FIG. 6 with a smooth spacer (without groove processing).

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Cemented carbide used as wear-resistant layer 2 Cemented carbide used as intermediate layer 3 Cemented carbide used as weld layer 4 Die 5 Upper punch 6 Lower punch 7 Upper spacer (grooving spacer)
7-1 Recessed groove 7-2 Sawtooth groove 8 Lower spacer 9 Side spacer (Groove processing spacer)
DESCRIPTION OF SYMBOLS 10 Composition gradient cemented carbide 11 Welded part 12 Steel base material 13 Cemented carbide (single layer)

Claims (5)

In the process of making a composition gradient sintered body using several types of cemented carbide powders with different compositions and different optimum sintering temperatures, green compacts of a predetermined shape are formed in advance and stacked in a die. Or a method of manufacturing by performing pulsed current sintering while pressing with a punch. In the process of producing a composition gradient sintered body by pulse electric current sintering method using several kinds of cemented carbide powders with different compositions and different optimum sintering temperatures, a grooved spacer, punch, or die is used. This is a method in which the energization path of the groove processed portion is cut or the energization amount is controlled, and an optimum temperature gradient is provided to the sintered body in the die for sintering. 3. The manufacturing method according to claim 1, wherein the die mold is filled in a combination of a cemented carbide sintered body and a green compact prepared in advance, and pulsed current sintering while pressing with a punch. Manufacturing method. 3. The manufacturing method according to claim 1 or 2, wherein each of the dies is a combination of a melted material such as steel that has been processed in advance and a sintered body of cemented carbide or a green compact that has been prepared in advance. A manufacturing method that fills in a mold and performs pulsed current sintering while pressing with a punch. A composition-graded cemented carbide and composite produced by the production method according to claim 1, 2, 3, 4.