JPH05117819A - High strength alloy steel for injection molding and powder metallurgy - Google Patents

Abstract

PURPOSE:To provide alloy steel for injection molding and powder metallurgy having much higher strength and slightly lower elongation than a conventional Fe-Ni-C alloy. CONSTITUTION:A blend having a compsn. consisting of 1-10wt.% Cu, 1-10wt.% Ni, 0.3-1wt.% C and the balance Fe is kneaded with an org. binder and injection molded. The resulting compact is freed of the binder and sintered to obtain a sintered compact having 93.2kg/mm<2> tensile fracture strength and 10.6% elongation. The elongation is slightly lower than that (15.7%) of an Fe-Ni-C alloy but the tensile fracture strength is much higher than that (51.3kg/mm<2>) of the Fe-Ni-C alloy.

Description

Detailed Description of the Invention

[0001]

The present invention relates to OA equipment, precision equipment,
The present invention relates to a high-strength alloy steel for injection-molding powder metallurgy used for manufacturing products having complicated shapes such as automobile parts.

[0002]

2. Description of the Related Art Many steel members used in office automation equipment, precision equipment, automobile parts, etc. have a three-dimensionally complicated shape, and as a method for manufacturing these products,
Injection molding powder metallurgy is a method of injection-molding a kneaded product obtained by kneading a metal powder such as carbonyl Fe powder, carbonyl Ni powder, ultra-high pressure water atomized fine powder and a binder, and then debinding and sintering. Are known.

However, the types of raw material alloys for products obtained by this method are small in number because the types of raw material metal powders suitable for injection molding powder metallurgy on the market are limited. Among them, Fe-Ni-C alloy is known and has been conventionally used as a material capable of obtaining the strongest product.

[0004]

However, this F
Since the e-Ni-C alloy has a tensile strength of only about 50 kg / mm ² at the time of completion of the sintering treatment, it is miniaturized,
As a high-strength alloy steel that is strongly required to be thinned, it has an unsatisfactory tensile strength and is one step closer.

The present invention compares the elongation of a product with that of conventional Fe-
It is an object of the present invention to provide an excellent high strength alloy steel for injection molding powder metallurgy, which is not so much reduced as compared with a Ni-C alloy.

[0006]

[Means for Solving the Problems] The inventors of the present invention have made extensive studies to solve the above problems and achieve the above objects,
The present invention has been completed by finding that the object can be achieved by using an Fe-Cu-Ni-C alloy having a specific composition range. That is, the present invention is 1-10 wt% Cu,
It is a high-strength alloy steel for injection molding powder metallurgy consisting of 1 to 10 wt% Ni, 0.3 to 1 wt% C, the balance Fe and inevitable impurities.

As raw materials for obtaining the high-strength alloy steel of the present invention, Cu is pure Cu powder having an average particle size of 12 μm or less produced by an ultra-high pressure water atomizing method, and Ni is carbonyl Ni, C having an average particle size of 8 μm or less. In addition to carbonyl Fe, natural graphite is preferable, because natural graphite is scaly, and because it is essentially gasified at a high temperature and then carburized and diffused into the product, and then its composition is obtained. Although it is necessary to reduce the amount, it is not necessary to limit the particle size, and it is preferable to use carbonyl Fe having an average particle size of 8 μm or less.

As the binder, for example, an organic binder prepared by appropriately mixing polyethylene, paraffin wax, stearic acid and the like is used.

Injection molding is carried out by
10 wt% Cu, 1 to 10 wt% Ni, 0.3 to 1 wt% C, the balance Fe and inevitable impurities are mixed to make 91.5 to 92.5 wt% of this metal raw material. On the other hand, 7.5 to 8.5% by weight of the binder as described above is added and kneaded by a kneader, and the kneaded product may be injection-molded into a predetermined mold under normal injection conditions. The obtained compact was heated at a temperature of up to 300 ° C. in an inert atmosphere to remove the binder from the compact, and then the vacuum degree was 0.005 to 0.1 Torr and the sintering temperature was 120 in a vacuum sintering furnace.
A sound product can be obtained by sintering at 0 to 1250 ° C.

[0010]

In the present invention, Cu is an element added to strengthen the Fe matrix in the sintered body structure, and N
i is an element added to enhance sinterability and toughness, and C is an essential element to promote sinterability.

Therefore, the composition of the high-strength alloy steel of the present invention is defined as described above because the Cu content is less than 1% by weight and / or the Ni content is less than 1% by weight, and / or
Alternatively, if the content of C is less than 0.3% by weight, the strength of the alloy steel is not sufficiently strengthened. On the other hand, the Cu content is 10% by weight
When the content of Ni exceeds 10% by weight and / or the content of Ni exceeds 10% by weight, and / or the content of C exceeds 1% by weight, the elongation of the alloy steel decreases remarkably.

In the injection molding of the raw metal powder blended in such a range, it is preferable that the binder is blended within the above range because the blending amount of the binder is less than 8% by weight. Then, when injection molding raw materials,
If the fluidity of the raw material is insufficient and the moldability of the product is often decreased, conversely, if the blending amount exceeds 8.5% by weight,
This is because defects such as foamed portions and cracks are likely to occur on the product surface after the binder removal treatment.

Further, the debinding process temperature is 300 ° C.
However, if the binder removal process is performed at a temperature higher than 300 ° C., the binder will pass through too much and the handling strength will decrease, and the handling failure rate will be high during transfer to the next step after the binder removal process. Because it will be.

[0014]

EXAMPLES Next, examples of the present invention will be described. Example 1 Pure Cu fine powder (average particle size 8 μm) and carbonyl Ni powder (average particle size 5 μm) made by ultra-high pressure water atomization method
And carbonyl Fe containing 0.05% by weight of carbon
Powder (average particle size 5μm) and natural graphite (average particle size 22μ
m), 2.0 wt% Cu, 2.0 wt% N
i, 0.5% by weight C, the remaining Fe was blended, and an organic binder (30% by weight of polyethylene, 60% by weight of paraffin wax, 10% by weight of stearic acid) was added.
The metal raw material mixture was added at a ratio of 8% by weight to 92% by weight, and 5 kg thereof was rotated by a planetary mixer having a diameter of 300 mm at a rotation speed of 20 r. p. m. A kneading treatment was performed at 100 ° C. for 1 hour, and the kneaded product was granulated into pellets having a diameter of 5 mm to obtain a forming raw material.

The injection pressure of this molding raw material was 600 kg / c.
It was injection molded into a mold for obtaining a powder sintered compact tensile test piece based on JSPM standard 2-64 under the conditions of m ² , injection speed of 30 mm / sec, and injection temperature of 90 ° C. Then, the injection molded body was heated to 300 ° C. in a nitrogen atmosphere to remove the binder, and then in a semi-continuous vacuum sintering furnace with a vacuum degree set to 5 × 10 ⁻² Torr, at a sintering temperature of 1250 ° C. Sintering was performed to obtain a healthy sintered body. In this way, 10 sintered body test pieces were obtained.

The breaking strength and the elongation of each of the 10 test pieces obtained were measured by using Shimadzu Autograph AE-5000 under the conditions of a load cell of 5000 kg and a pulling speed of 5 mm / min. These results are shown in Table 1 as an average value of 10 measured values. Example 2 The composition was 2.0% Cu, 10.0% Ni, 0.1% by weight.
Ten sintered bodies were obtained in the same manner as in Example 1 except that 5% C and the remaining Fe were used, and each test was performed in the same manner as in Example 1. The results are also shown in Table 1. Example 3 Composition by weight% 5.0% Cu, 2.0% Ni, 0.5
% C and 1 except that the balance is Fe.
0 sintered bodies were obtained and various tests were conducted in the same manner as in Example 1. The results are also shown in Table 1. Example 4 The composition was expressed in weight%, 10.0% Cu, 2.0% Ni, 0.1%.
Ten sintered bodies were obtained in the same manner as in Example 1 except that 5% C and the remaining Fe were used, and various tests were performed in the same manner as in Example 1. The results are also shown in Table 1. Comparative Example 1 The composition is 0.5% by weight, 0.5% Cu, 2.0% Ni, 0.5
% C and 1 except that the balance is Fe.
0 sintered bodies were obtained and various tests were conducted in the same manner as in Example 1. The results are also shown in Table 1. Comparative Example 2 The composition was 2.0% Cu, 0.5% Ni, 0.5% by weight.
% C and 1 except that the balance is Fe.
0 sintered bodies were obtained and various tests were conducted in the same manner as in Example 1. The results are also shown in Table 1. Comparative Example 3 The composition was 2.0% Cu, 12.0% Ni, 0.1% by weight.
Ten sintered bodies were obtained in the same manner as in Example 1 except that 5% C and the remaining Fe were used, and various tests were performed in the same manner as in Example 1. The results are also shown in Table 1.

[0017]

[Table 1] Comparative Example 4 Carbonyl Fe powder (average particle size 5 μm) containing carbon in an amount of 0.9% by weight and carbonyl Ni powder (average particle size 5
.mu.m) and the composition is 2.0% Ni by weight%,
9% C, the rest Fe, except that Cu was not added,
Ten sintered bodies were obtained in the same manner as in Example 1, and various tests were performed in the same manner as in Example 1. The results are also shown in Table 1. The relative density ratios of all the sintered bodies obtained in the examples and the comparative examples were determined and found to be in the range of 92 to 95%.

[0018]

INDUSTRIAL APPLICABILITY According to the present invention, Fe-Cu-with a specific composition range
Since it is a Ni-C alloy, it does not reduce the elongation,
The tensile rupture strength was improved, and a high-strength alloy steel excellent for injection molding powder metallurgy was obtained, and a remarkable effect is recognized.

Claims (1)

[Claims] 1. 1 to 10 wt% Cu, 1 to 10 wt% N
A high-strength alloy steel for injection molding powder metallurgy, which comprises i, 0.3 to 1 wt% C, the balance Fe, and unavoidable impurities.