Authors reported already that a precoat-heated stainless steel plate with mixed salt fluexs which were made by adding NiCl
2 or FeCl
3 to KCl-LiCl system eutectic salt showed a good property for spreading of BAg-5 using KCI-LiCl system eutectic salt flux.
In this paper, after a stainless steel plate pre-coated with the mixed salt fluxes which were made by adding CuCl or CoCl
2 to KCI-LiCl system eutectic salt flux was heated, corrosion products formed on the plate surface were analyzed by SEM and X-ray diffractometer. On the other hand, spreading tests with KCl-LiCl eutectic salt flux were carried out to know the effect of corrosion products for spreading of BAg-5 on the precoat-heated plates. Moreover, to clarify the flux action of used eutectic salt, the extents of spread area obtained on several pure metals which have the same property as corrosion products were considered by thermochemical calculations based on the reducing reaction heat of each pure metal oxide.
The results are summarized as follows;
1) The spreading of BAg-5 on the precoat-heated stainless steel plate increased similarly to that of the case of previous NiCl
2 or FeCl
3. In the CuCl mixed salt flux, the increasing of spreading depended on the increasing of plate surface area due to Cu particles precipitated on the original stainless steel surface. On the other hand, in the CoCl
2 mixed salt flux, the precipitated Co particles alloyed rapidly with Fe of the stainless steel plate compositions and converted into Co-Fe alloy layer. This phenomenon was the same as that in the FeCl
3 mixed salt flux. Accordingly, the improved spread area in this case may be attributed to the formation of this alloy layer, namely, "De-chromiumnization" phenomenon on the surface of stainless steel plate.
2) The spreading of BAg-5 using KCl-LiCl system eutectic salt flux on the pure metals such as Cu, Co, Ni and Fe base plates depended on the reducing power of used flux for the formed oxide film on the base plate and was not affected by the wetting force of both each base plate and BAg-5.
View full abstract