The iron sulfide coexisted with silicon oxide with different morphologies in sample H13L

The iron sulfide coexisted with silicon oxide with different morphologies in sample H13L

Figure 1: The iron sulfide coexisted with silicon oxide with different morphologies. Scale bars: 100, 500 nm.

Table 1: The detail heat treatment history of samples.

Inclusion name: Iron sulfide and silicon oxide
Record No.: 867
Inclusion formula: FeS, SiO2
Inclusion type (Macro/Micro/Nano): Nano
Inclusion type (Exogenous/Indigenous): Indigenous
Inclusion classification: Sulfide, oxide
Inclusion composition in weight %: No data
Sample: Steel
Steel composition in weight %: 0.005% C, 0.25% Cu, 0.024% S, 0.0080% P, 0.0012% N.
Note: Copper and sulfur are typical residual elements or impurity elements in steel. Sufficient removal of them during steelmaking process is difficult for copper and costly for sulfur. Utilization of copper and sulfur in steel, especially in steel scrap, has been an important issue for a long period for metallurgists. Copper and sulfur may combine to form a copper sulfide, which may provide a prospect to avoid the detrimental effects of copper and sulfur in steel. Unfortunately the formation mechanism of a copper sulfide in steel has not been completely clarified so far. In the present paper, solution treatment of samples containing copper and sulfur are firstly performed at 1623 K for 2.7 x exp10(3) s followed by quenching into water. The samples are then isothermally heat-treated at 673 K, 873 K, 1073 K, 1273 K and 1373 K for different time followed by quenching into water again. The size, morphology, constituent and crystallography of sulfide precipitates in these samples are investigated by SEM and TEM equipped with EDS. Fine copper sulfides (less than 100 nm) are observed to co-exist with silicon oxide in samples even isothermally heattreated at 1373 K for 1.44 x exp 10(4)s. Film-like copper sulfides are generally observed to co-exist with iron sulfide in all samples; Plate-like copper sulfides are observed especially in sample isothermally heat-treated at 1073 K for 1.44 x exp10(4) s. The formation mechanisms of these copper sulfides have been discussed in detail.
In sample H13L another typical precipitate is sulfide with size from 0.2 to 1.5 µm. The EDS spectrums show that these large sulfides are mainly iron sulfide and they are always accompanied with a little of copper sulfide (thereafter named as “free-standing” iron sulfide since it is not coexisted with oxide) as shown in inclusion No. 865.
The iron sulfide coexisted with silicon oxide is also observed in sample H13L. In the case that if iron sulfide and silicon oxide are just contacted with each other (Fig. 1(a)), its size is usually smaller than “free-standing” iron sulfide while larger than the CuxS coexisted with silicon oxide; while if silicon oxide is hugged or covered by iron sulfide (Fig. 1(b)), its size is similar to the “free-standing” iron sulfide.
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