Fig. 10 shows the cross section of the rust layer. The thickness of the
rust layer of the tin-containing steel is thinner than that of tin-free steel.
Fig. 10(a) shows that the rust layers is porous. As time elapses, the rust
layers formed during immersion grow and become more compact,
which could attribute to the compaction and agglomeration of the rust
layer. The rust layer shown in Fig. 10(e) has some cracks and pores,
but the rust layer shown in Fig. 10(f) is dense and compact. This differentia
indicates that the tin-containing steel has a more protective rust
layer than tin-free steel.