JPS6320433A - Production of high strength sintered material - Google Patents

Abstract

PURPOSE:To obtain a high strength sintered material without carrying out sintering at a high temp. or using graphite powder by mixing Fe or Fe alloy powder with sintering activating powder, compacting the mixture, sintering it and carburizing or carbonitriding the resulting sintered material. CONSTITUTION:Fe or Fe alloy powder is mixed with 0.5-10wt% sintering activating powder prepd. by adding 0.5-7% C to powder having the same composition as the Fe or Fe alloy powder or similar in composition to the Fe or Fe alloy powder. The powdery mixture is compacted and sintered and the resulting sintered material is carburized or carbonitrided, hardened and tempered. The activating action of the sintering activating powder is completely demonstrated and the matrix of the sintered material is strengthened by the carburization or carbonitriding, so a high strength sintered material can be obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention relates to a method for manufacturing a ferrous sintered material having high strength.

(Conventional technology) Iron-based sintered materials have recently been adopted for parts that require strength, and adding carbon to improve the strength of iron-based sintered materials is efficient and easy, and is cost-effective. However, it is commonly used because it is advantageous compared to the addition of alloying elements. (Problem to be solved by the invention) In comparison, the strength of the Fe-C based sintered material is inferior. The reason for this is that the sintered material usually has 10 pores.
This is because it contains ~20% of carbon steel, and even if the pore volume is reduced to 1% or less by external force such as forging, it is difficult to obtain a strength equivalent to that of carbon steel. This is because the strength of the sintered material is greatly influenced by the matrix strength and neck strength in addition to the pore content. This is thought to be due to the fact that the strength of the neck is not sufficient, as it is thought to be on the same level as carbon steel.

On the other hand, in the technique described in Japanese Patent Application Laid-open No. 59-38351,
In order to ensure the strength of the sintered material, special high-temperature sintering is performed using low-alloy steel powder as a raw material in a vacuum or reduced pressure atmosphere. Is it bad performance and high equipment costs?
Sintering at a high temperature of over 1200° C. is required, which increases running costs.

In order to solve the above problems, the present inventors added sintering activated powder and graphite powder to iron-based alloy powder to create a sintered material with high strength without high-temperature sintering. We have developed a manufacturing method (%Gan Sho 61-18642), but since graphite powder is added at the same time, this graphite powder eliminates the activation effect that the sintered activated powder originally has by t-100%. I wasn't able to show my full potential.

The present invention is intended to solve the above problems, and aims to provide a method for producing a sintered material with high strength without using graphite powder, which is usually added to strengthen the matrix. (Means for Solving the Problems) The present invention provides a sintered product comprising iron or iron-based alloy powder, a composition of which is the same as or similar to that of the iron-based metal powder, and tciI (5 to 7 carbon atoms) added thereto. Activated powder α5 to 10 weight L4t is added and mixed, and this mixed powder is molded, sintered, and subjected to carburizing, quenching, and tempering treatment or carbonitriding, quenching, and tempering treatment.Used in the present invention. The iron or iron-based alloy powder that is the pace powder is mainly commercially available 5AE411:10 series or 5AEJ600 series powder, but is not limited to these. The above powder usually has a weight of α1 to α5 (
Hereinafter, it will simply contain (i) oxygen.

The inventors have developed a conventional sintering method by adding to the pace powder and 90% low alloy steel powder a sinter-activated powder containing sufficient carbon to reduce the oxides in the powder. We have discovered that the sintering of the above powder can be promoted and activated without requiring high-temperature sintering of 1200° C. or higher by using a reducing gas such as decomposed ammonia gas, N, or pace gas used for sintering.

The composition other than carbon in the sintered activated powder is not directly involved in activation, but in order to give the same structure and strength as the paste powder after sintering, it is necessary to approximate the composition of the paste powder. Therefore, it is preferable to use a sintering activated powder that matches the composition of the paste powder.

When the particle size of the sintered activation powder is constant, the finer the particles, the more contact points with the pace powder and the better the activation efficiency. In addition, the coarser the grain, the higher the rate of negative impact on compressibility, so -10
It is preferable to use a powder for zero mesh. The sintered activated powder according to the present invention has an effective activation effect regardless of the manufacturing method, such as water atomization method, gas atomization method, pulverization method, Alternatively, the sintered activated powder, which is produced by an oxide reduction method, contains carbon as a basic composition, and 1 usually contains Cr, Mn, Mo, Ni, Cu, etc. to have a composition similar to that of the paste powder.
Co, 8i, P.

It contains one or more alloying elements such as B, and the remainder consists essentially of Fe.

The carbon content of this sintered activated powder is 15 to 7.0%, which means that if it is less than L5%, the activation effect is small or no activation effect is evident, and if it exceeds ZO This is because the effect of sintering will not be saturated and it will be difficult to manufacture the powder.Also, the amount of sintering activated powder added should be α5 to 10.
%, this is because if it is less than α5, the number of areas where the effect occurs is small and the total activation effect is small, and if it is more than 10, it will have a negative effect on compressibility.

In the present invention, sintering activated powder is added to and mixed with the above-described paste powder, and the mixture is molded and then sintered.

After that, carburizing and quenching and tempering treatment or carburizing and nitriding and quenching and tempering are performed. This carburizing and quenching and tempering treatment is carried out at 850 to 1000°C for 30 to 180 minutes in an atmosphere with an equilibrium carbon content of α5 to 1.5. After holding, quench in water or oil, or F1a5
After holding at o~1000℃ for 30~180 minutes, further 750℃
After holding at ~950℃ for 5 to 60 minutes, quenching in water or oil and further tempering as necessary, to a temperature of 150~
After heating and maintaining at 500°C, it is cooled.

The carburizing, nitriding, quenching and tempering treatment is carried out in an atmosphere with an equilibrium carbon content of α2 to 1.0 and an equilibrium nitrogen content of α1 to α7.

After being held at 820 to 960°C for 30 to 180 minutes, it is rapidly cooled in oil or water. Tempering is further performed as necessary, and after being heated and held at 150 to 500°C, it is cooled.

If the quenching temperature is lower than the above range, the quenching will be insufficient, and if the temperature is higher than the range, the strength will not be sufficiently improved due to coarsening of crystal grains. Since the sintered material of the invention is made from powder, the bond between the powders is the most important element. This means that even if the matrix, that is, the individual powders themselves, are strengthened, if the powders are not bonded to each other, This is because the desired strength and abrasion resistance cannot be obtained.

For this reason, strengthening the bonding force between powders, that is, strengthening the neck, is the most important factor in improving the properties of sintered materials.Q The present invention improves the strength of the neck by adding and mixing sintering activated powder to the base powder, and sintering it after molding. After promoting the formation and growth of carbon fibers and strengthening the neck, the next process of carburizing or carbonitriding removes the carbon necessary to strengthen the matrix in the atmosphere, thereby strengthening the matrix.

In addition to strengthening the neck, the strength of the sintered material was also increased.

Further, the present invention attempts to improve the strength of the sheath layer by performing quenching using heating during carburizing or carbo-nitriding treatment, and further tempering as necessary. Even if the sintered body is slowly cooled after carburizing or carbo-nitriding without any initial treatment, it is possible to achieve high strength because strengthening the neck is the most important factor in improving the properties of sintered materials, as described above. it is obvious.

(Function) In the process of manufacturing sintered materials, necks are formed during the temperature raising process during sintering, and the necks further grow during the soaking process. The present inventor has discovered that the presence or absence of an oxide layer on the powder surface has a significant effect on the formation of this neck. In other words, the presence of an oxide layer on the powder surface prevents the formation of a neck, and Neck formation begins only when the layer is removed. In normal sintering, oxides on the powder surface are reduced and removed by using a reducing atmosphere, but the density of the powder compact is high. In this case, it is difficult for gas to penetrate into the compact, and a reducing effect cannot be expected.

In the case of high-strength sintered materials, it is common to use them at high densities, which is disadvantageous because the formation of necks is delayed. Therefore, in order to promote the formation of necks, oxidation methods other than the atmosphere must be used. It is necessary to remove the object.◇The present invention actively performs this action using the sintered activated powder, thereby accelerating the formation of necks, which also promotes the growth of necks by traps. It is. That is, carbon in the sintered activated powder promotes the formation of necks by reducing and removing the oxide layer on the surface of the base powder in the low temperature range of the heating process. This reaction is approximately 6
Since this occurs from around 00℃, the neck will grow by the time the soaking temperature is reached.This means that the neck will be sufficiently strengthened without the need for high temperature sintering at temperatures above 1200℃. By subsequently carrying out a carburizing, quenching and tempering treatment or a carburizing, nitriding, quenching and tempering treatment, the matrix is strengthened and does not require the addition of graphite powder, which has a negative effect on neck formation.

(Example) Next, specific examples of the present invention will be explained while comparing them with comparative examples. Note that the weight range is simply written as "related".

Example 1 Commercially available low Cr alloy powder (Fe-1, 1% Cr-174M
n-α25%Mo, Kawasaki Steel M4) and sintered activated powder (
Fe-1,04Cr-175%Mn-α28%Mo-A
61C) 5% and the lubricant zinc stearate powder (hereinafter referred to as lubricant) 1169G were mixed in a V-type mixer, and the green compact density was 7.05f using a JSPM standard tensile test piece-shaped mold.
/- test pieces were molded. This green compact was sintered at 1150° C. for 80 minutes in a decomposed ammonia atmosphere. Next, this sintered body was held at 900°C for 120 minutes in an atmosphere with an equilibrium carbon content of 18%, and after carburizing, it was put into oil at 60°C and rapidly cooled. 60
After holding for a minute, it was allowed to cool in the atmosphere. The carbon content of the obtained test piece was α59.

Example 2 A sintered body was manufactured using basically the same composition and method as in Example 1. The zero treatment in which carburizing, nitriding, quenching and tempering was performed was carried out using equilibrium carbon ii [L7], equilibrium nitrogen 1 ( After being held at 890° C. for 120 minutes in an atmosphere of 14° C., the material was put into oil at 60° C. to be rapidly cooled and tempered in basically the same manner as in Example 1.

The carbon content Vi of the obtained test piece was 14 times. Example 3 Commercially available low Ni alloy powder (Fe-1,9%Ni-a46
c4Mo, Kobe Steel) and sintered activated powder (Fe-1,
81Ni-α5-chi MO-me 1 C) 3-chi and lubricant α6%
The mixed powder was mixed in a V-type mixer. This mixed powder was formed into a tensile test piece, and then sintered at 1150° C. for 80 minutes in a decomposed ammonia atmosphere. Next, carburizing, quenching and tempering treatment was performed basically in the same manner as in Example 1.

Comparative Example 1 The same low Cr alloy powder and sintered activated powder as in Example 1 were mixed with graphite powder (Japanese graphite &! A, C, P,) (L 4 and lubricant α6 in a V-type mixer After mixing at 7.05r/
A tensile test compact of -
I did it for a minute. Next, vacuum hardening was performed. Using a vacuum heat treatment furnace, it was held at 900°C for 30 minutes, then put into oil at 60°C to be rapidly cooled and hardened. ◎ Tempering was performed at 185°C for 60 minutes, the same as in Example 1. The carbon content of the obtained test piece was 141%.

Comparative Example 2 Except for adding graphite powder α4 to the composition of Example 3, the powder was mixed, molded, and sintered in basically the same manner as in Example 3, followed by zero-order vacuum quenching. Quenching and tempering was performed basically in the same manner as in Comparative Example 1. The carbon content of the obtained test piece was 145%.

Comparative Example 3 Low Cr alloy powder of Example 1, graphite powder α5 and lubricant (
After mixing with 16% in a V-type mixer, a tensile test piece was molded. The sintering process was basically the same as in Example 1, and the heat treatment was performed at 1150° C. for 80 minutes in an atmosphere of 1 decomposed ammonia, and the conditions were the same as in Comparative Example 1. The carbon content of the obtained test piece was α4.

Using the test pieces obtained in Examples 1 to 3 and Comparative Examples 1 to 3, a tensile test was conducted to compare the strength and comparative evaluation was performed.

Tensile strength was measured at room temperature with a crosshead speed of 2
This was done under extreme conditions.

The results are shown in the drawing.

Although Example 1 and Comparative Example 1 have almost the same composition, the tensile strength of Example 1 is about 100 N/- higher than that of Comparative Example 1, and is superior in strength. Further, although Example 2 has the same composition as Example 1 and the heat treatment method is different, it also shows the same strength.

Furthermore, Comparative Example 3 has almost the same composition as Comparative Example 1 except that it does not contain sinter-activated powder, but the tensile strength is significantly lower. Example 3 and Comparative Example 2 are also almost the same. Regarding the composition, the tensile strength of Example 3 is approximately 8 ON/- higher than that of Comparative Example 2.

These results show that the present invention is effective in improving the strength of sintered materials.

(Effects of the Invention) As described above, according to the present invention, during sintering, oxides in the base powder are 1200 under special sintering atmosphere conditions as in conventional
Even without performing high-temperature sintering at temperatures above ℃, it is possible to obtain strength equal to or higher than that of materials subjected to high-temperature sintering.O This sintered body can be further carburized or carbonitrided to strengthen the matrix. As a result, the sintered material has higher strength without adding graphite powder as in the conventional method.◎ From these facts, according to the present invention, high-strength sintered material can be manufactured without high-temperature sintering, so the equipment The cost and manufacturing cost can be reduced.

[Brief explanation of drawings]

Claims (1)

[Claims] Add and mix 0.5 to 10% by weight of sintered activated powder, which is made by adding 0.5 to 7% by weight of carbon to the same or similar composition as the iron or iron-based alloy powder, to iron or iron-based alloy powder, and mix this powder. A method for producing a high-strength sintered material, which comprises molding a mixed powder, sintering it, and subjecting it to carburizing, quenching and tempering treatment or carburizing, nitriding, quenching and tempering treatment.