Method of melting tinned iron scrap

Details Method of melting tinned iron scrap Method of melting tinned iron scrap

1997-06-16

1999-05-11

Andrews, Melvyn

Specialized metallurgical processes, compositions for use therei

Processes

Producing or treating free metal

75576, 75581, 75690, 423 96, 423618, C21B11/02

Patent

active

059023759

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

The present invention concerns a method of steel scrap or scrap iron (hereinafter merely referred to as "scrap") melting by using a vertical furnace having tuyeres, and using fossil fuels without using electric power for melting and, more in particular, it relates to a method of tinned iron scrap melting capable of producing molten iron with less tin content that can be used for the production of high quality steels corresponding to converter steels or special steels and capable of recovering tin in a reclaimable manner, by utilizing tin-plated iron scrap of low bulk density (for example, tin-plated steel sheets).


BACKGROUND ART

According to the report of Nippon Gakujutsu Shinkokai, 69th Material Processing Committee, First and Second section Joint Research Meeting (1990, August), generation amount of steel scrap as iron type scrap has increased with accumulation amount of steel materials at a rate of about 1,000,000 tons year by year and it is expected that the generation amount of market scrap (obsolete scrap) will be about 40,000,000 ton/year at the year of 2,000, which amounts to 45% for the production quantity of crude steel.
At present, most of market scrap is melted in electric furnaces. Particularly, in recent years, for making the varied kinds of products and for reducing the cost, a so-called mini-mill method has been adopted in which scrap or direct reduced iron for dilution of impurities are melted in electric furnaces, continuously casted and rolled.
On the other hand, in an integrated steel work, a technique of scrap melting without electric power for melting has been developed in order to cope with the increase of the scrap and to ensure iron sources corresponding to diversification of the production quantity of crude steel in the trend of concentration of blast furnaces.
In recent years, along with the trend of consumption intended for higher quality, market scrap of surface treated steel has increased more and one of them includes tinned iron scrap (referred to "can scrap" as market scrap).
Tin (hereinafter referred as Sn) is an element that can not be removed in the steel making step and if Sn remains by more than about 0.04% in the steel, the hot workability or toughness is reduced, so that several proposals have been made for Sn removing technique upon re-utilizing Sn plated steel sheet scrap as the iron source as described below.
For removing plated portions on the surface of steel sheets, Sn-plated steel sheet scrap is heated to 300-1200.degree. C. and treated in a sulfurizing atmosphere thereby transforming Sn into SnS and SnS is mechanically separated or evaporated. Then, using a furnace of a top and bottom blowing converter type, slag is formed on an iron bath such that the top blowing oxygen jet is not in direct contact with the iron bath and oxygen is top blown, in which carbon material containing an appropriate amount of S (sulfur) and the Sn-plated steel sheet scrap treated in the sulfurizing atmosphere are continuously charged and melted. Since the S potential at the oxygen blowing point is increased and SnS of a low boiling point (about 1230.degree. C.) is formed, evaporation of Sn preferentially to Fe (iron) is enabled to obtain a molten metal containing less than 0.05% by weight of the Sn content and, subsequently, low Sn molten steel is manufactured by the usual steel making processes.
Using a method of packing coke and scrap or scrap and iron ore in a layerous form into a vertical furnace, blowing a combustion sustaining gas from primary tuyeres and secondary tuyeres to each of packed layers thereby conducting melting and reduction (method disclosed in Japanese Patent Laid-Open Hei 1-290711), producing molten iron of low impurity content in a vertical furnace charged with scrap containing less impurities, producing molten iron of high impurity contents in another vertical furnace charged with scrap of high impurity contents such as can scrap (for example, 0.63 wt % Sn content). Then, molten iron manufactured by the two furnaces are mixed to obtain pig

REFERENCES:
patent: 5588982 (1996-12-01), Hendrix

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