Multiphase inclusions in C-Mn-B steel

Multiphase inclusions in C-Mn-B steel

Figure 1: Inclusions in the sample neck (sample deformed at 1200 C with strain rate 6.5s-1). SEM, scale bar: 5 µm.

Figure 2: The EDX spectra of inclusions showed in upper Fig., taken with 10 kV energy.

Inclusion name: Multiphase inclusion
Record No.: 862
Inclusion formula: No data
Inclusion type (Macro/Micro/Nano): Micro
Inclusion type (Exogenous/Indigenous): Indigenous
Inclusion classification: Sulfide, oxide
Inclusion composition in weight %: See the EDX spectra
Sample: C-Mn-B steel
Steel composition in weight %: 0.10% C, 0.47% Mn, 0.08% Si, 0.014% P, 0.023% S, 0.08% Cr, 0.05% NI, 0.17% Cu, 0.014% Mo, 0.009% Sn, 0.006% B, 0.009% N.
Note: Microstructure investigations after hot deformation carried out on the low carbon-manganese steel with addition of boron was presented in this work. The non-metallic inclusion influence on the microstructure and type of crack mechanism was shown.
The Fig. 1 present the etched sample. The inclusions which were analyzed are in different sizes from 0.6 to 4 µm and mostly there are: MnS with round shape and SiO2 in different shapes but always with some other elements like Al2O3 and MnO.
In the Fig. 2 MnS inclusion with other elements like Al and Si can be seen. Si could form oxides around the MnS phase – light ring around the inclusion – or some parts of the inclusion – black part on the bottom. Inclusion with 4 µm in diameter occurs with a not very big void – 8 µm in length – but in the neighborhood under the surface there is a bigger microcrack on the grain boundary. There is silicate oxide with diameter 0.65 µm inside a ferrite grain (2) and no void around that inclusion. Fe peaks in the EDX spectra originate from the matrix. MnS inclusion with some silicate oxide around with diameter 1.3 µm occurs on the grain boundary inside a 4 µm long void (3). There was also indicated silicate oxide inside 4 µm long void with a diameter of 1.3 µm within a ferrite grain. The surface is covered by many microvoids, which occurs inside grains as well as on the grain boundary.
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