Metal treatment – Process of modifying or maintaining internal physical... – Heating or cooling of solid metal
Patent
1996-09-06
1998-07-21
Yee, Deborah
Metal treatment
Process of modifying or maintaining internal physical...
Heating or cooling of solid metal
148606, 148591, 148592, C21D 908, C21D 600
Patent
active
057830002
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of heat treating steel pipes, steel tubes, and cold-rolled or hot-rolled steel band-like or rod-like material, such as steel bands, steel strip, steel sheets, steel rods or steel wire which are subsequently heated for soft-annealing purposes.
The invention also relates to steel products that have been treated by means of the inventive method.
2. Description of the Related Art
With the intention of improving the ductility of rod-like or flat, cold- rolled or hot-rolled band-like steel products, the products are heated in an oven to a surface temperature of about 900 degrees C. or higher, normally to a temperature of about 1100 degrees C., and in some cases up to 1300 degrees C. The products are then cooled, normally in air. After cooling the products, it is necessary to remove the oxidation products that form on the surfaces of the cooled products. This is effected in different types of baths, normally an electrolyte bath and/or oxygen bath.
The products are advanced continuously and in succession through the heating oven or furnace, said products being introduced at one end of the oven or furnace and discharged at the other end thereof. The oven is heated with a liquid or gaseous fuel, which is burned with the aid of air. The products may also be heated in batches.
One process stage which determines the speed at which the method can be performed is often the treatment of the heated products in an electrolyte bath and/or an acid bath, i.e. pickling of the products.
Heating of the products in the heating oven also determines the rate at which the method can be performed.
These two rate determining stages of the method greatly limit the capacity of known production plants for the heat treatment of steel products.
Furthermore, the aforesaid baths must be handled in an environmentally friendly manner, resulting in large costs.
Another problem is that fuel combustion in the oven results in large emissions of nitrogen oxides. Large quantities of nitrogen oxides are also emitted to the ambient air when pickling the products. Pickling also results in large quantities of sludge and slime, which must be dumped.
SUMMARY OF THE INVENTION
The present invention solves the aforesaid problems. The invention enables the capacity of a given heat-treatment oven or furnace to be increased. The invention also enables treatment of products in said baths to be markedly reduced, and in certain cases omitted, therewith reducing both the emissions of nitrogen oxides and the production of sludge. The emission of nitrogen oxides from the combustion process is also reduced.
The present invention thus relates to a method of heat-treating steel objects, primarily pipes, tubes, strip, rod and wire-like steel material, such as steel band, strip, sheet, rod or wire of steel which have been rolled and heated in a furnace to a surface temperature above about 900 degrees C. and thereafter cooled and possibly treated in an electrolyte bath and/or acid bath, and includes firing the burners present in the oven with a liquid or a gaseous fuel which is caused to burn with the aid of a gas that contains at least 85 percent by volume oxygen and at most 10 percent by volume nitrogen.
The invention also relates to steel products primarily pipes, tubes, strip-like or rod-like materials made of steel, such as steel strip, steel sheet, steel rod or steel wire, which have been rolled and heated in an oven to a surface temperature above about 900 degrees C. and thereafter cooled and optionally treated in an electrolyte bath and/or acid bath, wherein the product has been heat-treated in the oven while firing the oven burners with a liquid or a gaseous fuel which has been burned with the aid of a gas that contains at least 85 percent by volume oxygen and at most 10 percent by volume nitrogen.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will now be described in more detail with reference to an exemplifying embodiment of the inventive method and also with
REFERENCES:
patent: 1815505 (1931-07-01), Guthrie et al.
patent: 4397451 (1983-08-01), Kinoshita et al.
patent: 4713154 (1987-12-01), Ohta et al.
Axelsson Carl-Lennart
Brannvall Sten-.ANG.ke
Ljungars Sten
Lunner Sven-Eric
Saltin Lars Folke
AGA Aktiebolag
Avesta Sheffield Aktiebolag
Mangels Alfred J.
Yee Deborah
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