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Ductile Cast Iron Hardness Requirements

1. Ductile iron castings (ASTM A536-84)

Ductile iron is a very good material for metal castings, this kind of cast iron has globular graphite, and basically has no other form of graphite. The iron casting grade is represented by "tensile strength - yield strength - elongation", For example:

Grade: 80-55-06. It means the tensile strength is 80,000 pounds / inch 2 (552MPa), the yield strength is 55,000 pounds / inch 2 (379MPa), and the elongation is 6.0% (2 inches or 50mm).

The ductile iron castings should be heat-treated appropriately, such as annealed, normalized, quenched and tempered. There are certain provisions in the contract or purchase order, the castings should meet the requirements as hardness, chemical composition, and microstructure and so on.

2. Austenitic ductile iron castings (ASTM A439-89)

They are mainly used as heat resistance, corrosion resistance and wear resistance castings. The castings should be stress-eliminated, stabilized, heat treated or annealed. The casting hardness requirements are as follows:  

Property

Grade

D-2

D-2B

D-2C

D-3

D-3A

D-4

D-5

D-5B

D-5S

Property

Tensile strength, not less than thousands of pounds / inch 2 (MPa)

58 (400)

58 (400)

58 (400)

55 (379)

55 (379)

60 (414)

55 (379)

55 (379)

65 (449)

Yield strength (0.2% residual elongation), no less than thousands of pounds / inch 2 (MPa)

30 (207)

30 (207)

28 (193)

30 (207)

30 (207)

30 (207)

30 (207)

30 (207)

2 inches or 50mm elongation, no less than, %

8.0

7.0

20.0

6.0

10.0

20.0

6.0

10

Brinell hardness HB (3000 kg)

139-202

148-211

121-171

139-202

139-193

202-273

131-185

139-193

131-193

 

3. Austempered ductile iron castings (ASTM A897M-90)    

They are used for ductile iron castings which need austempering heat treatment. Austempering can narrow the mechanical properties between different parts of the same area or castings cast from the same furnace hot metal.

The application of austempering heat treatment can increase the performance range available on the ductile iron parts. The mechanical property requirements of different grades of castings are as follows:

 

Grade
850/550/10

Grade
1050/700/7

Grade
1200/850/4

Grade
1400/1100/1

Grade
1600/1300/-

Minimum tensile strength, MPa

850

1050

1200

1400

1600

Minimum yield strength, MPa

550

700

850

1100

1300

Elongation (50 mm) minimum,%

10

7

4

1

Impact energy, Bajaur

100

80

60

35

Typical hardness, Brinell hardness HB

269-321

302-363

341-444

388-477

444-555

4. The ferrite ductile iron castings used for high pressure (ASTM A395 M-88)  
 
They are
used for high pressure ductile iron valves, flanges, pipe fittings, pumps and other pipe fittings. The order contract should include the heat treatment requirement.

The hardness of castings and the specimen should be within the following range: Brinell hardness, 3000kg force / 10mm ball, HB143-187.

The casting hardness requirements are as follows: 

1

1

1

1

2

2

2

3

A

B

C

D

A

B

C

A

Ni-Cr-HiC

Ni-Cr-LoC

Ni-Cr-GB

Ni-HiCr

12%Cr

15% Cr-Mo

20% Cr-Mo

25% Cr

550

550

550

500

550

450

450

450

600

600

600

600

600

600

600

600

650

650

650

650

650

650

650

650

600

600

600

550

550

400

400

400

400

400

8(200)

8(200)

3(75) ball diameter

12 (300)

1 (25) ball diameter

4 (100)

8 (200)

8 (200)

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