CN1660527A - Warm press forming method in high density and low temperature for powder of stainless steel - Google Patents

Abstract

The invention provides a high-density low-temperature warm-press forming method for stainless steel powder. In this method, the domestic 304L, 316L, 410L, 430L stainless steel powder of ≤147μm is evenly mixed with 0.1-0.3% of the total mass percentage of low-temperature lubricant, the mold is heated to 80-100°C, and the EBS wax powder is sprayed by electrostatic spraying method. Spray on the inner cavity of the mold, then preheat the stainless steel powder mixed with lubricant to 70-90°C, put it into the mold cavity and press it under the pressure of 600-800MPa. The density of the green body is 0.12-0.30g/cm ³ higher than that of the conventional cold-pressed green body, and the strength of the green body is 10-38% higher than that of the cold-pressed body. The method has the characteristics of energy saving, high density, low cost, wide temperature control range, and easy operation, and can greatly improve the density and performance of stainless steel powder metallurgy parts. The high-density powder metallurgy stainless steel parts produced by the invention can be widely used in machinery , chemical industry, instrumentation, medical equipment, office machinery, food and automobile industries.

Description

High-density low-temperature warm-press forming method for stainless steel powder

Technical field

The invention relates to powder metallurgy technology, in particular to a high-density low-temperature warm-press forming method of stainless steel powder.

Background technique

The advantage of using the traditional powder metallurgy method to produce stainless steel parts is that it can produce final shape or near-net shape powder metallurgy parts at a lower cost, which can realize less cutting and no machining, but the disadvantage is that the density of the parts is not high, and the corrosion resistance and mechanical properties are reduced. . Although the stainless steel parts produced by isostatic pressing and injection molding have high density, their application is greatly limited due to the complicated process and high cost. The warm-pressing process, which was successfully developed in the 1990s and has been industrialized, not only overcomes the shortcomings of low part density, but also has the advantages of low cost. It is the latest advanced powder metallurgy technology. At present, there are many technologies related to temperature pressing, mainly ANCORDENSE ^TM process of North America Hoeganaes Company in the United States, DENSEMIX ^T process ^M of Sweden HOEGANAES Company and FLOWMET ^TM process of Canada QMP METAL POWDERS Company and other powder series manufacturing methods. The process of the above-mentioned warm-pressing process is mainly to heat the warm-pressed powder added with a special type of lubricant and binder to about 150°C, and press it in a mold heated to the above-mentioned temperature at a pressure of 400-700MPa. After sintering at 1120-1260°C, the density of the parts can reach 7.25-7.4g/cm ³ . However, the above-mentioned warm-pressing process is mainly based on pure iron powder or partially pre-alloyed iron-based powder, while the low-temperature warm-pressing process of stainless steel powder has not been officially reported at home and abroad. Xiao Zhiyu et al once wrote an article titled "Warm compacting behavior of stainless steel powders" on pages 756-761 of Transaction of Nonferrous Metals Society of China (English version Transaction of Nonferrous Metals Society of China) 2004, 14 (4). ") mentioned in the article that the temperature and pressure temperature range of stainless steel is 100-120°C. In addition, there are only a handful of manufacturers in the world that can supply warm-pressed powders, mainly including HOEGANAES in Sweden, NORTH AMERICA HOEGANAES in the United States, and QMPMETAL POWDERS in Canada. These patent-protected powders are not only very expensive, but also have very strict requirements on the operating temperature, that is, the temperature range is required to be controlled at ±2°C, which requires a specific temperature-pressure system to complete, and these temperature-pressure systems are subject to Patent protection, so the equipment investment of the warm-pressing production line is very large.

Contents of invention

The purpose of the present invention is to overcome the deficiencies in the application of the existing warm-press technology, and provide a high-density low-temperature warm-press forming method for stainless steel powder that can use domestic stainless steel powder, low energy consumption, low investment, low cost, and is easy to operate and control .

The purpose of the present invention can be achieved through the following measures:

A high-density low-temperature warm-press forming method for stainless steel powder, characterized in that the process and conditions are as follows:

1. Add 0.1-0.3% lubricant in the total mass percentage to the stainless steel powder with particle diameter ≤ 147μm and mix thoroughly;

2. Heat the above-mentioned stainless steel powder mixed with lubricant to 70-90°C;

3. Heat the mold to 80-100°C, and spray the EBS wax powder used for mold wall lubrication on the inner cavity of the mold by electrostatic spraying;

4. Fill the mold cavity with the above-mentioned heated stainless steel powder, and press it under 600-800MPa;

5. Sinter at 1250-1300°C for 1-1.5 hours in a decomposed ammonia atmosphere or in a vacuum state to manufacture high-density stainless steel powder metallurgy parts.

The stainless steel powder used above includes 304L, 316L, 410L, 430L stainless steel powder, and the low-temperature lubricant used refers to polyethylene wax powder, long-chain fatty acid diamide wax powder or their mixture. The temperature control accuracy of the above-mentioned low-temperature temperature and pressure is as wide as ±5°C.

Compared with the prior art, the present invention has the following outstanding advantages:

1. For the first time, the present invention successfully applies the low-temperature warm-pressing process to the forming of stainless steel powder metallurgy parts, realizing the low-cost and high-densification of stainless steel powder press-forming.

2. Since the present invention has relatively lower requirements for temperature control accuracy, the temperature fluctuation range only needs to be controlled at ±5°C, while foreign special powders require that the warm-pressing temperature must be controlled at ±2°C. Therefore, the present invention can be realized on the basis of existing equipment with a little modification, and does not need to rely on expensive patented temperature and pressure systems abroad, and has the characteristics of less investment and quick results.

3. The invention adopts domestic water atomized stainless steel powder, which has low cost, good formability and compressibility of the powder, and does not need to rely on expensive foreign patent powder. Can be widely used in various industries such as machinery, chemical industry, instrumentation, medical equipment, office machinery, food and automobiles.

4. The warm-pressing temperature of the present invention can be as low as 70-90°C, so it has the characteristics of low energy consumption and long service life of the mold. Low temperature and warm pressing is not only beneficial to the flow of powder, but also solves the shortcoming of easy agglomeration of powder under high temperature.

5. Compared with the stainless steel products produced by the traditional powder metallurgy method, the stainless steel powder metallurgy products produced by the present invention have different degrees of improvement in green density, green strength, sintered density and sintered material tensile strength.

Detailed ways

The present invention will be further described by following examples:

Embodiment 1: Low-temperature warm-press forming method of 316L stainless steel powder

Its warm-pressing process and its conditions include:

1. Use domestic ≤147μm water to atomize 316L stainless steel powder, add 0.1% polyethylene wax powder as a low-temperature lubricant according to the total mass percentage, and then dry mix it on a V-type mixer for 15 minutes;

2. Heat the above-mentioned 316L stainless steel powder mixed with lubricant to 90°C;

3. Heat the mold to 100°C, and electrostatically spray EBS wax powder on the inner cavity of the mold;

4. Fill the mold with heated 316L stainless steel powder mixed with lubricant, and press it at 800MPa;

5. Sinter at 1300°C for 1 hour in an atmosphere of decomposed ammonia.

The green body density of 316L stainless steel can reach 7.15g/cm ³ , which is 0.30g/cm ³ higher than that of conventional cold-pressed green body; the green body strength can reach 35MPa, which is 38% higher than that of cold-pressed body; the sintered density can reach 7.5g/cm 3 cm ³ , which is 0.12g/cm ³ higher than that of cold pressing; the tensile strength of the material reaches 540MPa, which is 16% higher than that of cold pressing.

Embodiment 2: Low-temperature warm-press forming method of 304L stainless steel powder

Its warm-pressing process and its conditions include:

1. Use domestic ≤147μm water atomization 304L stainless steel powder, and add 0.3% long-chain fatty acid diamide wax powder as a low-temperature lubricant according to the total mass percentage, and then dry mix it on a type mixer for 25 minutes;

2. Heat the 304L stainless steel powder mixed with lubricant to 70°C;

3. Heat the mold to 80°C, and electrostatically spray EBS wax powder on the inner cavity of the mold;

4. Fill the mold with heated 304L stainless steel powder, and press it under 600MPa;

5. Sinter at 1300°C for 1.5 hours in an atmosphere of decomposed ammonia.

The green body density of 304L stainless steel can reach 7.05g/cm ³ , which is 0.22g/cm ³ higher than that of conventional cold-pressed green body; the green body strength reaches 28MPa, which is 18% higher than that of cold-pressed body; the sintered density reaches 7.38g/cm 3 cm ³ , which is 0.13g/cm ³ higher than that of cold pressing; the tensile strength of the material reaches 510MPa, which is 6% higher than that of cold pressing.

Embodiment 3: Low-temperature warm-press forming method of 410L stainless steel powder

Its warm-pressing process and its conditions include:

1. Use domestic ≤147μm water atomization 410L stainless steel powder, and add 0.1% polyethylene wax powder and 0.1% long-chain fatty acid diamide wax powder as low-temperature lubricant according to the total mass percentage, and then mix in the V-type Dry mixing on the feeder for 30 minutes;

2. Heat the 410L stainless steel powder mixed with lubricant to 80°C;

3. Heat the mold to 100°C, and electrostatically spray EBS wax powder on the inner cavity of the mold;

4. Fill the mold with heated 410L stainless steel powder, and press it under 700MPa;

5. Sinter in a vacuum furnace at 1250°C for 1 hour.

The green body density of 410L stainless steel can reach 6.80g/cm ³ , which is 0.12g/cm ³ higher than that of conventional cold-pressed green body; the green body strength can reach 32MPa, which is 25% higher than that of cold-pressed body; the sintered density can reach 7.48g/cm 3 cm ³ , which is 0.15g/cm ³ higher than that of cold pressing; the tensile strength of the material reaches 410MPa, which is 8% higher than that of cold pressing.

Embodiment 4: Low-temperature warm-press forming method of 430L stainless steel powder

Its warm-pressing process and its conditions include:

1. Use domestic ≤147μm water atomization 430L stainless steel powder, and add 0.2% long-chain fatty acid diamide wax powder as a low-temperature lubricant according to the total mass percentage, and then dry-mix on a V-type mixer for 30 minutes;

2. Heat the 430L stainless steel powder mixed with lubricant to 80°C;

3. Heat the mold to 90°C, and electrostatically spray EBS wax powder on the inner cavity of the mold;

4. Fill the mold with heated 430L stainless steel powder and press it under 800MPa;

5. Sinter in a vacuum furnace at 1250°C for 1 hour.

The green body density of 430L stainless steel can reach 6.73g/cm ³ , which is 0.12g/cm ³ higher than that of conventional cold-pressed green body; the green body strength reaches 30MPa, which is 10% higher than that of cold-pressed body; the sintered density reaches 7.45g/cm 3 cm ³ , which is 0.15g/cm ³ higher than that of cold pressing; the tensile strength of the material reaches 422MPa, which is 5% higher than that of cold pressing.

Claims (3)

1, a kind of warm press forming method in high density and low temperature of powder of stainless steel is characterized in that: its technology and condition are as follows:

(1) low temperature lubricant that adds by gross mass percentage 0.1-0.3% in the powder of stainless steel of≤147 μ m at grain fully mixes;

(2) the above-mentioned powder of stainless steel that is mixed with lubricant is heated to 70-90 ℃;

(3) mold heated is arrived 80-100 ℃, and will adopt electrostatic spraying as the EBS wax powder that die wall lubrication is used in dies cavity;

(4) powder of stainless steel after the above-mentioned heating is filled in the die cavity, and under 600-800MPa press forming;

(5) under cracked ammonium atmosphere or vacuum state in 1250-1300 ℃ of sintering 1-1.5 hour, promptly manufacture high density stainless steel powder metallurgical part.

2, according to the warm press forming method in high density and low temperature of the described a kind of powder of stainless steel of claim 1, it is characterized in that, used powder of stainless steel comprises 304L, 316L, 410L, 430L powder of stainless steel, and used low temperature lubricant is meant PEF wax powder, LCFA diamide waxes powder or their mixture.

According to the warm press forming method in high density and low temperature of the described a kind of powder of stainless steel of claim 1, it is characterized in that 3, the accuracy of temperature control of lower temperature warm compaction is wide to ± 5 ℃.