Fe3C carbides in electrical sheet steel

Figure 10: 0.018% C, 2.02% Si, 0.225% Al, 1000 C 1 h + 200 C 24 h/air, extraction replica. Scale bar: 2 µm.

Figure 11: 0.018% C, 2.02% Si, 0.225% Al, 1000 C 1 h + 200 C 24 h/air, extraction replica. Scale bar: 0.25 µm.

Figure 12: 0.012% C, 3.66% Si, 0.225% Al 1000 C 1 h + 450 C 24 h/air, extraction replica. Scale bar: 1 µm.

Figure 13: 0.012% C, 3.66% Si, 0.225% Al, 1000 C 1 h + 500 C 24 h/air, extraction replica. Scale bar: 1 µm.

Carbide name: Fe3C
Record No.: 1499
Carbide formula: Fe3C
Carbide type: M3C
Carbide composition in weight %: No data
Image type: TEM
Steel name: Electrical sheet steel
Mat.No. (Wr.Nr.) designation: No data
DIN designation: No data
AISI/SAE/ASTM designation: No data
Other designation: No data
Steel group: Electrical sheet steels
Steel composition in weight %: 0.018% C, 2.02% Si, 0.225% Al. 0.012% C, 3.66% Si, 0.225% Al.
Heat treatment/condition: See the text
Note: Electrical sheet materials are used for magnetic cores in generators and transformers. Of this core (about 2 to 4% Si, carbon content es low as possible) it is required that the magnetic hysteresis losses should be as low as possible.

Grain boundaries and precipitates similar in size to the thickness of the Bloch domain boundaries (approx. 100 nm) increase the hysteresis losses. The finished product should therefore be coarsegrained and free of fine precipitates. The main precipitates are MnS and, in some materials AlN. During the production process they limit grain growth and, in grain orientated sheets, also produce a particular texture. The carbon is usually in solution in these materials. Precipitation of carbides leads to magnetic aging.

The precipitation behaviour of carbides in electrical sheet materials has been investigated frequently. After a solution treatment at 1000 C and subsequent heat treatment in the range 200 to 400 C, Fe3C is precipitated in the form of platelets within the grains (Fig. 10 and Fig. 11). Raising the aging temperature to 400 to 500 C leads to the precipitation of carbides on the grain boundaries and only at high silicon contents (3.66 %) within the grains (Fig. 12). This is an iron-silicon carbide, known µ-carbide. The structure has not yet been finally determined. An additional heat treatment at 200 C has no effect on the state of precipitation (Fig. 13) and does not lead to higher hysteresis losses.
Links: No data
Reference: Not shown in this demo version.

Copyright © 2018 by Steel Data. All Rights Reserved.