Oxide stringers in high carbon wire rod steel

Oxide stringers in high carbon wire rod steel

Figure 1: X-ray map of constituent elements of oxide and sulfide stringers in wire rod sample. SEM, scale bars: 20 µm.

Inclusion name: Oxide stringers
Record No.: 850
Inclusion formula: MnO x SiO2 x Al2O3
Inclusion type (Macro/Micro/Nano): Macro
Inclusion type (Exogenous/Indigenous): No data
Inclusion classification: Oxide
Inclusion composition in weight %: 35–40% MnO, 55–65% SiO2, 1–2% Al2O3 and traces of CaO and TiO2.
Sample: High carbon wire rod steel
Steel composition in weight %: 0.70-0.80% C, 0.65-0.70% Mn, 0.16-0.30% Si, max. 0.020% P, max. 0.020% S, max. 60 ppm N.
Note: Oxide Stringers: This type of inclusion appeared as bulky stringers composed of several closely spaced fragments, which were aligned along the rolling direction of wire rod. Such stringers were found in almost all pre up-gradation wire rod samples. In the post up-gradation samples they were observed relatively less frequently. SEM image of one of such oxide stringers is shown in Fig. 1 along with the X-ray map of its constituent elements. These inclusions have been classified as B-type non-deformable inclusion that exhibited variable deformability due to variations in their chemical composition. From their composition, those oxide stringers were identified as the rhodonite phase of the MnO–SiO2–Al2O3 system which contained 35–40% MnO, 55–65% SiO2, 1–2% Al2O3 and traces of CaO and TiO2. This type of inclusion has been found to be largely responsible for impairing the cleanliness of wire rod samples of the given steel samples. Presence of rhodonite has also been identified in the corresponding liquid steel samples from the ladle as well as the tundish.
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