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Gietijzer
Lamellair gietijzer onder microscoop 100x vergroot

CAST IRON (EN-GJL)

Gray iron, or grey cast iron, is a type of cast iron that has a graphite microstructure. It is named after the gray color of the fracture it forms, which is due to the presence of graphite. It is the most common cast iron and the most widely used cast material based on weight.

It is used for housings where the stiffness of the component is more important than its tensile strength, such as internal combustion engine cylinder blocks, pump housings, valve bodies, electrical boxes, and decorative castings. Grey cast iron's high thermal conductivity and specific head capacity are often exploited to make cast iron cookware and disc brake rotors.

Structure

A typical chemical composition to obtain a graphitic microstructure is 2.5 to 4.0% carbon and 1 to 3% silicon by weight. Graphite may occupy 6 to 10% of the volume of grey iron. Silicon is important to making grey iron as opposed to white cast iron, because silicon is a graphite stabilizing element in cast iron, which means it helps the alloy produce graphite instead of iron carbides; at 3% silicon almost no carbon is held in chemical combination with the iron. Another factor affecting graphitization is the solidification rate; the slower the rate, the greater the time for the carbon to diffuse and accumulate into graphite. A moderate cooling rate forms a more pearlitic matrix, while a fast cooling rate forms a more ferritic matrix. To achieve a fully ferritic matrix the alloy must be annealed. Rapid cooling partly or completely suppresses graphitization and leads to the formation of cementite, which is called white iron.

The graphite takes on the shape of a three-dimensional flake. In two dimensions, as a polished surface will appear under a microscope, the graphite flakes appear as fine lines. The graphite has no appreciable strength, so they can be treated as voids. The tips of the flakes act as preexisting notches; therefore, it is brittle. The presence of graphite flakes makes the Grey Iron easily machinable as they tend to crack easily across the graphite flakes. Grey iron also has very good damping capacity and hence it is mostly used as the base for machine tool mountings.

Technological and physical values

Item according to DIN EN 1561 Measure Unit EN-GJL-150 EN-GJL-200 EN-GJL-250 EN-GJL-300 EN-GJL-350
EN-JL 1020 EN-JL 1030 EN-JL 1040 EN-JL 1050 EN-JL 1060
Tensile Strength Rm MPA 150-250 200-300 250-350 300-400 350-450
0.1% Yield Strength Rp0,1 MPA 98-165 130-195 165-228 195-260 228-285
Elongation Strength A % 0,3 - 0,8 0,3 - 0,8 0,3 - 0,8 0,3 - 0,8 0,3 - 0,8
Compressive Strength σdB MPa 600 720 840 960 1080
0,1% Compressive Strength σd0,1 MPa 195 260 325 390 455
Flexural Strength σbB MPa 250 290 340 390 490
Schuifspanning σaB MPa 170 230 290 345 400
Shear Stress TtB MPa 170 230 290 345 400
Modules of elasticity E GPa 78 - 103 88 - 113 103 - 118 108 - 137 123 - 143
Poisson number v - 0,26 0,26 0,26 0,26 0,26
Brinell hardness HB 160 - 190 180 - 220 190 - 230 200 - 240 210 - 250
Ductility σbW MPa 70 90 120 140 145
Tension and pressure change σzdW MPa 40 50 60 75 85
Breaking Strength Klc N/mm3/2 320 400 480 560 650
Density g/cm3 7,10 7,15 7,20 7,25 7,30

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Casting involved mechanical properties

Item according to DIN EN 1561 Tensile Strength cast in apart test piece [MPa] Wall thickness [mm] Tensile Strength in moded test piece

[MPa] Min.
Expectaition Values in the casting
from to TensileStrength [MPa] min. Values Brinell hardness [HB] Max. Values
EN-GJL-150
EN-JL 1020
150 - 250 2,5
5
10

20
5
10
20

40
-
-
-
120
180
155
130
110
250
225
205
185
EN-GJL-200
EN-JL 1030
200 - 300 2,5
5
10
20
5
10
20
40
-
-
-
170
230
205
180
155
270
245
220
200
EN-GJL-250
EN-JL 1040
250 - 350 5
10
20
40
10
20
40
80
250
-
210
190
270
225
195
170

250
230
215
EN-GJL-300
EN-JL 1050
300 - 400 10
20
40
80

150
20
40
80
150

300
-
250
220
210
190 5)
270
240
210
195
-
260
240
230
215
205
EN-GJL-350
EN-JL 1060
350 - 450 10
20
40
80
150
20
40
80
150
300
-
290
260
230
210 5)
315
280
250
225
-
275
260
240
225
215

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