The special low calcium inoculant containing strontium produces such a powerful inoculating effect that cast irons of very thin section can be made free from mottle even when they are not annealed. This is particularly important when the castings are for nodular graphite gray and flake graphite irons.
The inoculant alloy according to the present invention also suppresses the precipitation of carbide, which is a major disadvantage of other known inoculants.
Inoculation helps to reduce chill in ductile cast iron. This is important because the more chill in a casting, the more it will tend to form pearlite and carbides. Inoculation can take place at many stages in the production process, but is most effective just before or during pouring.
The inoculant alloy consists of a mixture of metallic barium and zirconium which is added to the ferrosilicon or silicon melt. It can be prepared in conventional equipment. The inoculant alloy has good nucleating properties and can suppress the precipitation of carbide. It is also industrially simple to prepare at favorable costs.
Inoculant alloys with a high percentage of barium and calcium can remarkably reduce the chill phenomenon, generating very little residue. This is more than the case with inoculants that only contain calcium. In addition, a high level of strontium in the inoculant helps to significantly lower the amount of calcium present in the molten metal.
IM SR inoculates ductile cast iron well, but with much less calcium and aluminum than most complex inoculants. This allows the inoculant to get into the liquid iron with minimal interference from calcium and aluminum, thereby improving nucleation effectiveness.
In addition, the high proportion of strontium in IM SR can reduce the number of eutectic groups and thus help to improve the ductility of the cast. This effect is especially noticeable when large undercoolings are experienced.
The inoculant alloy according to the invention is distinguished by particularly good suppression of the precipitation of carbide, and by a preparation process that is industrially simple and favorable in terms of costs. It is based on ferrosilicon and can be introduced into the iron at the ladle or directly during pouring. Inoculation can therefore take place at any point during the casting process, but it is most effective just before or during pouring. In this way, inoculation can counteract the negative effects of magnesium treatment on the cast iron, such as inoculant fade and uneven nodule count.
Many foundries struggle with poor nucleation during the solidification process which can lead to chill, carbidie formation and chunky graphite. Inoculants increase the number of nucleation sites to help ensure adequate solidification and to avoid these common metallurgical defects.
Research has shown that controlled amounts of sulfur and oxygen in molten iron can drastically reduce undercooling, chilling and carbide formation. Unlike classic inoculants that use calcium containing 75% ferrosilicon, our patented technology uses mechanically blended alloys of specific sized particles to achieve high levels of oxygen and sulfur without the detrimental effects of the ferrosilicon.
Our alloys are based on barium, strontium or zirconium with a low level of calcium and aluminum to ensure they react with liquid iron in the best possible manner. These alloys are available globally and our technical experts can help you select the right one for your application. They are designed to be added in the ladle as inoculant blocks, or can be used as a cored wire injection process.
The inoculant alloy according to the invention can be prepared industrially by adding a master alloy comprising preferably 5-40% metallic barium and zirconium to a ferrosilicon or silicon melt. This inoculant is particularly suitable for the manufacture of chromium white cast iron and steam and water pressure gray cast iron, which have specific requirements with regard to the structure and durability of the castings.
It has been found that the addition of strontium significantly modifies the microstructure of chromium white cast iron. In particular, the values for carbide area and length decrease as the amount of strontium added increases.
In addition, the stereological parameters of the chromium carbides improve with increasing amounts of strontium. This can be explained by the fact that the strontium is adsorbing at the boundaries of the chromium carbides and thus inhibits their growth. The abrasive-resistant properties of the modified cast irons are also enhanced as a result of this. The impact strength is also improved, although not to the same degree as in a pure hypoeutectic cast iron.
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