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(11) | EP 0 050 969 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Alloy steel powder |
| (57) A corrosion resistant alloy steel powder is described, containing, byweight:
16-19% chromium, 12-13% nickel, upto2% manganese upto 4% molybdenum, upto 0.2% carbon, 1.7 -3.0% silicon and 0.04-0.24% phosphorus, the balance being essentially iron. The alloy powder is a modification of 300 series stainless steels and includes increased amounts of silicon and phosphorus. The alloy powder is useful in making fully dense, corrosion resistant products using powder metallurgytechniques. |
[0001] The present invention provides a corrosion resistant alloy steel powder and a method of producing final products using the same. More specifically, the alloy powder is a modification of a type 300 series stainless steel, with increased percentages of silicon and phosphorus. The alloy powder is useful for producing fully dense metal products by powder metallurgy techniques.
[0002] Type 300 series stainless steels are common stainless steels used in numerous industrial applications. In attempting to make fully dense products from the atomized powder of the alloys of this type of stainless steel using powder metallurgy techniques, it is known that powder alloys of the typical compositions of the alloy series, i.e. type 304 and type 316, are difficult to sinter to full density.
[0003] It is believed that the difficulty in sintering is due to the narrow difference between the solidus and liquidus temperatures of these alloys. This difference is approximately 10F° (5°C). Accordingly, the width of the liquid phase sintering range of such an alloy would be so narrow that it would be economically impractical to control the sintering temperature accurately enough in a commercial production operation.
[0004] Accordingly, it is necessary to increase the difference between the liquidus and solidus temperatures in order that liquid phase sintering can be commercially performed.
[0005] The present invention provides a high alloy steel powder useful in forming fully dense, corrosion resistant products by powder metallurgy techniques. A method of producing final products from the steel powder is also provided.
[0006] In the method of producing the alloy powder of the present invention, the typical composition of the type 300 series stainless steel is changed to provide additional silicon and phosphorus. Thus the invention provides an alloy steel powder containing, by weight:
the balance being essentially iron.
[0007] The difference between the solidus and liquidus temperatures is increased to greater than 25°F (14°C) by the addition of the silicon andphosphorus, and sintering can be commercially performed within the temperature range. The additional silicon is usually added in a pre-alloy operation prior to atomization of the molten alloy to form a powder. The phosphorus can be added in the pre-alloy operation, but can also be added in an ad-mix operation. In such an ad-mix operation, the phosphorus is added in powder form to the alloy powder, usually in the form of ferro-phosphorus powder.
[0008] The nickel content of the alloys is preferably about 12%. The silicon content may for example be 2-3% and is preferably about 3%. The phosphorus content is preferably 0.08-0.1%.
[0009] The maximum carbon content of the alloys is typically about 0.1%, and if desired carbon, manganese and molybdenum can be absent from the compositions.
Example 1
[0011] One iron base alloy that was water atomized and screen at -88 mesh to provide a powdered metal had the following initial analysis by weight:
[0012] The powdered metal was blended with about 1% by weight Acrawax (Trademark) for die lubrication purposes. Any similar lubricant may also be used. The sample was compacted in a die at 50 TSI (7047 Kg/cm2), the lubricant was removed in a burn off process and then the compacted sample was vacuum sintered at 2420°F (1327°C) for 90 minutes. A final product of over 97% theoretical density, ultimate tensile strength of 100,000 lb/in2 (7047 Kg/cm2), yield strength of 49,000 lb/in2 (3452 Kg/cm2), elongation of 10% and unnotched impact strength of 32 ft-lb (43 joules) was produced. In addition, the corrosion rate of the final product was 0.1 inch per year (0.25 cm/year). The corrosion test was performed according to practice B of ASTM A 262. The product was also found to be rust free in a 5% salt fog environment according to ASTM B 117-63.
[0013] If desired, the final products can be water quenched to improve corrosion resistance, ductility, toughness and other properties. In the above example, the final product when water quenched from a solution treatment temprature of 2100°F (1150°C) has an elongation of 40% and an unnotched impact strength of greater than 120 ft-lb (163 joules). The corrosion rate of the final product was 0.04 in/yr (1 mm/yr) in boiling sulfuric acid according to practice B of ASTM A 262.
[0014] Other samples of similar composition were successfully sintered at temperatures between 2380-2460°F (1305-1350°C).
Example 2
[0015] Another iron base alloy that was water atomized and screened at -88 mesh to provide a powdered metal had the following initial analysis by weight:
[0016] The powdered metal was compacted and sintered in a manner similar to Example 1. The final product had properties similar to the final product in Example 1, except that elongation improved to 26%. The corrosion rate was 0.047 in/yr (1.2 mm/yr).
Example 3
[0017] Another iron base alloy that was water atomized and screened at -88 mesh to provide a powdered metal had the following initial analysis by weight:
[0018] The powdered metal was blended with about 1% by weight Acrawax (Trademark) for die lubrication purposes. Any similar lubricant may also be used. The sample was compacted in a die at 50 TSI (7047 Kg/cm2), the lubricant was removed in a burn off process and then the compacted sample was vacuum sintered at 2430°F (1332°C) for 90 minutes. A final product of 99% theoretical density, ultimate tensile strength of 93,000 lb/in2 (6553 Kg/cm2), yield strength of 37,000 lb/in2 (2607 Kg/cm2), elongation of 45%, unnotched impact strength of greater than 120 ft-lb (161 joules) and notched impact strength of 17 ft-lb (23 joules) was produced.
[0019] In this example, when the final product was gas fan cooled from a solution treatment temperature of 2100°F (1150°C) it has an elongation of 57% and a notched impact strength of 38 ft-in (51 joules). The corrosion rate was 0.16 in/yr (4 mm/yr).
Example 4
[0020] Another iron base alloy that was water atomized and screened at -88 mesh to provide a powdered metal had the following initial analysis by weight:
[0021] The powdered metal was compacted and sintered in a manner similar to that set forth in Example 1. The final product had properties similar to the final product in Example 1, except that the corrosion rate was 0.05 in/yr (1.27 mm/yr).
Example 5
[0022] Another iron base alloy that was water atomized and screened at -88 mesh to provide a powdered metal had the following initial analysis by weight:
[0023] The powdered metal was compacted and sintered in a manner similar to that set forth in Example 1. The final product had properties similar to the final product in Example 1, except that the corrosion rate was 0.037 in/yr (0.94 mm/yr).
Example 6
[0024] Another iron base alloy that was atomized and screened at -88 mesh to provide a powdered metal had the following initial analysis by weight:
[0025] The powdered metal was compacted and sintered in a manner similar to that set forth in Example 1. The final product had properties similar to the final product in Example 1, except that the corrosion rate was 0.049 in/yr (1.25 mm/yr).
Example 7
[0026] Another iron base alloy that was water atomized and screened at -88 mesh to provide a powdered metal had the following initial analysis by weight:
[0027] The powdered metal was compacted and sintered in a manner similar to that set forth in Example 1. The final product had properties similar to the final product in Example 1.
Example 8
1. An alloy steel powder containing, by weight:
16 - 19% chromium,
12 - 13% nickel,
up to 2% manganese,
up to 4% molybdenum,-
up to 0.2% carbon,
1.7 - 3.0% silicon and
0.04 - 0.24% phosphorus, the balance being essentially iron
2. An alloy powder as claimed in claim 1 which contains about 12% nickel.
3. An alloy powder as claimed in claim 1 or claim 2 which contains 2-3% silicon.
4. An alloy powder as claimed in any one of the preceding claims which contains about
3% silicon.
5. An alloy powder as claimed in any one of the preceding claims which contains 0.08
- 0.1% phosphorus.
6. An alloy powder as claimed in any one of the preceding claims which contains up
to about 0.1% carbon.
7. An alloy powder as claimed in claim 1 having, approximately, any one of the compositions
set out below (weight percentage basis):
the balance in each case being essentially iron.
the balance in each case being essentially iron.
8. Products produced by compacting and sintering a powder as claimed in any one of
the preceding claims.