The copper sulfide coexisted with silicon oxide in sample H13L

The copper sulfide coexisted with silicon oxide in sample H13L

Figure 1: The typical two kinds of precipitates in sample H13L (Ti grid). (a) TEM image; EDS spectra for free standing sulfide (b) and sulfide coexisted with silicon oxide (c). Scale bar: 1 µm.

Table 1: The detail heat treatment history of samples.

Inclusion name: Copper sulfide + silicon dioxide
Record No.: 865
Inclusion formula: CuxS + 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.

There are two kinds of typical precipitates observed in sample H13L, as shown in Fig. 1. One is fine sulfide with size less than 100 nm, and it is always coexisted with silicon oxide. The EDS spectrums show that these fine sulfides are mainly copper sulfide (CuxS) and usually include a little of iron or iron sulfide. The atomic rations of these sulfides, (Cu+Fe)/S, are among a wide range, that is from 0.6 to 1.8, although most of it is closed to 1.1.
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