Kobe Kobelco Process

Kobe Steel Company and Kobelco Metal Powders produce water-atomized iron powder using a special V-jet water atomization process. Typical properties of four Kobelco water-atomized ferrous powders are summarized in Tables 9 and 10. Grades 500MA, 300MA, and 300ME achieve green densities of 6.8 g/cm3 at 415 MPa (60 ksi). Grade 300MC has the highest compressibility, achieving a 6.90 g/cm3 and 9.6 MPa (1.4 ksi) green strength at 415 MPa (60 ksi) with 0.75% zinc stearate (Fig. 16). Kobelco has also produced a 300MS grade iron powder with lower compressibility and green density (6.7 g/cm3 at 415 MPa, or 60 ksi) but improved cleanliness, that is, low inclusion level (size: 50 /'m max and area ratio: 0.03% max), which finds successful applications in hot powder forging of connecting rods and other automotive parts.

Table 9 Typical chemical and sieve analysis of Kobe ferrous water-atomized powder grades

Property

Kobe grade

500MA

300MA

300MC

300ME

Chemical analysis, %

Carbon

0.001

0.001

0.001

0.001

Silicon

0.01

0.01

<0.01

<0.01

Manganese

0.16

0.16

0.16

0.17

Phosphorus

0.004

0.004

0.004

0.004

Sulfur

0.009

0.009

0.009

0.009

Nickel

0.01

Chromium

0.02

Oxygen

0.14

0.13

0.09

0.13

Sieve analysis, %

+60

0.2

0.2

-60/+100

14

5

16

5

-100/+325

61

68

66

68

Table 10 Typical properties of Kobe water-atomized ferrous powders

Property

Kobe grade

500MA

300MA

300MC

300ME

Powder properties

Apparent density, g/cm3

2.92

2.91

2.87

2.93

Flow rate, s

25.1

24.7

25.8

24.6

Green density(a), g/cm3

6.82

6.82

6.90

6.82

Green strength, MPa (psi)

8.3 (1200)

8.3 (1200)

9.7 (1400)

7.9 (1150)

Sintered properties1-1'"1

Dimensional change(c),%

+0.21

+0.23

+0.33

+0.23

(a) Green strength and density with 0.76% zinc stearate lubricant.

(b) Sintered at 1120 °C (2048 °F) for 30 min in 75% H2 + 25% N2 gas.

(c) 2% Cu and 0.90% graphite added with zinc stearate

(a) Green strength and density with 0.76% zinc stearate lubricant.

(b) Sintered at 1120 °C (2048 °F) for 30 min in 75% H2 + 25% N2 gas.

(c) 2% Cu and 0.90% graphite added with zinc stearate

0.5

Compacting pressure

with Acrawax -

1

*

120-

- 3QDMC y''"'

90-

60 -

- 300MA

----0.75% Acra wax

- 0.75% ZnSt i i i i

120 90

Vi tn c

Compacting pressure

with Acrawax -

1

120-

3Q0MC

90-

\

60

500MA

----0,75% Acra wax

- 0.76% ZnSt i i i i

120 90

Vi in fZ

Fig. 16 Green strength and density comparison of high compressibility 300MC powder grade with (a) 300MA grade and (b) 500MA grade of Kobelco. ksi x 6.8947 = MPa

Kobe Steel Company also produces water-atomized iron powder grades such as:

• 300M offering high compressibility (6.9 g/cm3 at 440 MPa, or 64 ksi)

• 300MH offering slightly higher purity and compressibility level (7.0 g/cm3 at the same compacting pressure)

• 300NH achieving 7.1 g/cm3 green density after extended reduction/annealing treatment (Ref 24)

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