DE1244217B - Process for the production of slag-free, segregation-free and void-free blocks from unkilled mild steel with a high yield - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Int. CL:

C21c

German class: 18 b-7/08

Number: 1244217

File number: H 37355 VI a / 18 b

Filing date: September 5, 1959

Open date: 13th Wed 1967

The invention relates to a method of manufacture of slag-free, segregation-free and void-free blocks made of non-calmed mild steel with a high yield by pouring jet degassing at a negative pressure <[10 Torr and subsequent mold degassing at negative pressure.

The casting and manufacturing processes for steel blocks, preferably mild steel blocks, used in Developed over the past few years, deal with the reduction of segregation and segregation Void zones that form in the cast blocks when they solidify. The extent of these zones determines the amount of scrap, which under normal casting conditions can be up to 30% of the block weight can be.

By applying vacuum casting technology to mass steel production, it was possible to eliminate the rejects with restriction of the use of deoxidizing agents such as silicon, aluminum and the like. These deoxidizing agents cause oxidic inclusions in the ingots and, if the permissible concentration limit is exceeded, affect their technological Properties.

The vacuum degassing in the falling pouring stream, which initially only occurs when casting forged steels has been applied, can recently also with success after the development of suitable devices apply when casting bulk steels. It is also already known to use a pouring jet degassing To connect post-degassing in the mold. To suppress block segregation and under certain circumstances it is also necessary to reduce the nitrogen content as in the previous one Pouring jet degassing is also low for post-degassing, preferably to 15 Torr and less to hold. A post-degassing while maintaining such a high negative pressure leads however, especially as a result of the formation of large head voids, to a high attack Scrap. The low output due to this is with quality steels, for example for forging blocks, but not for bulk steels, justifiable.

The object of the invention is to develop an aftertreatment process which can be used for mass jet production in an economically justifiable manner. The aim is to reduce the crop scrap by preventing block segregation and to achieve a bubble-free block surface. For this purpose, the negative pressure during the post-degassing in the mold should be higher than the negative pressure in the process for the production of slag,
Segregation-free and void-free blocks
unkilled mild steel with high yield

Applicant:

Hoesch Aktiengesellschaft,

Dortmund, Eberhardstr. 12th

Named as inventor:

Dr.-Ing. Georg Henke,

Dr.-Ing. Hubert Hoff, Dortmund;

Dr. rer. nat. Hermann-Joseph Kopineck,

Dortmund-Hörde

Pouring jet degassing, so that the CO gases that are still formed during cooling and solidification can no longer rise to the surface.

According to the invention, slag-free, segregation-free and void-free blocks are made from non-calmed soft stabilizers

as with high output by pouring jet degassing at a negative pressure <^ 10 Torr and subsequent mold post-degassing at negative pressure as follows: The negative pressure in the casting jet degassing is only maintained during the post-degassing time t _N , where t _{N is} equal to or less than the pouring jet degassing time t _G and up to to a maximum of 5 min / i of the casting weight of the cast block. After the end of the post-degassing time t _N , a negative pressure ρ of ρ = 40 and 100 Torr is set above the cast block and this negative pressure is maintained until the cast block has largely solidified.

In this way, segregation-free cast ingots with a bubble-free surface are obtained which form sheets be rolled out with a perfect surface quality, for example into body sheet can.

The method according to the invention is explained, for example, using the pressure-time diagram of the illustration of a 10 t mild steel slab which has been cast and vacuum-treated according to the method. At the start of casting, there was an underpressure of lTorr, which was maintained during the casting time t _a = 2 minutes and the post-degassing time t _N = 0.5 minutes.

So ten stayed. Thereafter, the pressure was increased by adding of nitrogen increased to 100 torr over a period of 0.5 minutes. This pressure

709 610/359

Claims (1)

was maintained until the external solidification of the block, which is the case after about 22 minutes was. The pressure above the block was then brought to atmospheric pressure by adding air. Claim: Process for the production of slag-free, segregation-free and void-free blocks from non-calmed mild steel with high output by pouring jet degassing at a negative pressure <Ξ 10 Torr and subsequent mold post-degassing at negative pressure, characterized in that the negative pressure of the pouring jet degassing is only maintained during the post-degassing time t _N , where t _N = t _G (casting jet degassing time) and is up to a maximum of 5 min / t of the casting weight of the cast block and after completion a vacuum of 40 to 100 Torr is set over the cast block and is maintained until the cast block solidifies. Considered publications:
ίο Belgian patent specification No. 552160;
British Patent No. 598,311;
Journal "Stahl und Eisen", 1959, pp. 472 to 477; "Blast Furnace and Steel Plant" magazine, 1958, pp. 595 to 605. 1 sheet of drawings 709 610/359 7.67 © Bundesdruckerei Berlin