JP2003138351A - Alloying-element additive - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide easy-handling low-cost additives used for adding alloying elements at low-alloy steel manufacture because component additives for use in operations subsequent to a deoxidation operation in a converter should be pure and have minimal impurity content to prevent molten steel from recontamination. SOLUTION: The alloying-element additives can be obtained by subjecting sheet-like or slit-like scraps of Cr-based stainless steel, Ni-based stainless steel and Ni steel to shearing into small pieces using a shredder and are used when manufacturing low-alloy steel.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an alloying element additive used in the production of alloy steel such as low alloy structural steel. More specifically, it is a material that replaces a Ni cathode or low carbon ferrochrome (hereinafter referred to as LCFeCr) that is usually used for adding Ni or Cr, is easy to handle, and is inexpensive.

A nickel-chromium steel for machine structure will be described below as an example. The hot metal taken out from the blast furnace is desulfurized (S), desiliconized (Si) and dephosphorized (P), and then charged into a converter. In the converter, high-pressure, high-speed gaseous oxygen is blown into the hot metal, and decarburization (C) is performed until a predetermined carbon (C) value is reached to form molten steel. Then, a coolant is added to bring the mixture to a predetermined temperature and the mixture is transferred to a ladle.

However, since the molten steel at this point contains a large amount of oxygen (O), it cannot be filled with aluminum (A
l) or ferrosilicon (FeSi) is added and deoxidation (O) is performed. When the injection into the ladle is completed, it is lifted up by a crane and is the degassing device in the next step (hereinafter referred to as RH
It is carried to refining work under reduced pressure. The refining work mainly aims to remove the non-metallic inclusions generated by the above-mentioned deoxidation work with Al or FeSi by floating, and to remove the gas (hydrogen, nitrogen, oxygen) contained in a trace amount in the molten steel. At the same time, the molten steel Si, Mn, C
The components such as r and Ni are also adjusted. Additives for these components used in RH are pure and do not contain any impurities because they are added to molten steel that has already been refined. Finally, the molten steel adjusted to a predetermined temperature with a coolant or the like is conveyed to a continuous casting machine (hereinafter referred to as CC) in the next step and formed into a slab.

[0004]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention As described above,
As the additive material used after the deoxidation work in the converter, a pure material with very few impurities is used to prevent the molten steel from being recontaminated. For example, LCFeCr, which is usually used as a Cr addition material, is manufactured from Cr ore as a raw material through a complicated and long working process, but the amount of energy used, labor costs, etc. are high and expensive. The same can be said for Ni, and the commonly used Ni cathode is also extremely expensive. Therefore, the present inventors propose a component additive which is easy to handle and inexpensive to replace the expensive LCFeCr, Ni cathode with high purity.

[0005]

[Means for Solving the Problems] First, non-metals such as mud, plastic, paper, wood chips, and zinc (Zn), copper (C)
u) A clean plate-shaped or slit-shaped scrap of Cr-based stainless steel, Ni-based stainless steel or nickel steel on which non-ferrous metal such as u) is not attached is selected, and each is shredded and shredded by a shredder. The scrap thus crushed is conveyed to a converter or an RH furnace, stored in a furnace bunker, cut out from the bunker at the time of adjusting the molten steel composition, and is fed with LCFeCr and / or N.
It is put into molten steel as an alternative to the i cathode.

As described above, these small scraps must be pure without any impurities because they are used after decarburization and deoxidation in the converter or after refining in RH. . Also, it goes without saying that the component values must be clear and constant. Further, it is desirable to have a rounded shape with corners so that it can be stored in a furnace bunker and can be automatically cut out smoothly.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be specifically described below with reference to embodiments. The target steel type was nickel chrome steel, more specifically SNC415M was tested. The manufacturing process from hot metal is (pre-treatment of hot metal)-(converter)-(RH)
-(CC), and the amount of molten steel per charge is about 3
It was 00 tons. For reference, the component specifications of SNC415M are shown in Table-1.

The small piece scrap used in this test was a piece of SUS304 thin plate scrap having a thickness of about 0.8 mm produced as a by-product from a cold rolling mill for stainless steel at a steel mill, which was processed into a small piece with a shredder. When the collected sample was analyzed, the chemical composition was as shown in Table-2.

[0009]

[1st test status and results] From the hot metal pretreatment process to the completion of the work in the converter, there was no difference from normal. After the converter work was completed, the molten steel composition was checked and then the temperature was checked. When the ladle was set under the converter, the converter was tilted and molten steel was poured into the ladle, but about 2 minutes after the start of pouring, aluminum (Al) was charged and deoxidation was performed. Furthermore, when the deoxidation reaction was completed, the SUS30 stored in the bunker above the furnace also served to cool the molten steel.
4,500 kg of four small pieces of scrap were put on the molten steel in the ladle. After the molten steel injection from the converter to the ladle was completed, the ladle was transferred to the next step, RH.

Immediately after reaching the RH, the molten steel was sampled and sent to the analysis room. The molten steel composition before the refining treatment was as shown in Table-3. Therefore, in order to match the component values to the SNC415M standard,
The following ferroalloys and SUS304 small piece scraps were charged from the furnace bunker, and the amounts were as follows. FeSi 870 kg LCFeMn 1,660 kg SUS304 small piece scrap 970 kg Refining work with RH is carried out by a usual method.
When it was sampled again and analyzed, it had the composition shown in Table 4. After that, the temperature was adjusted and transferred to the next step, CC.

[0011]

[Second test status and results] The same operation as the first test was performed up to the converter operation and the injection of molten steel into the ladle, but about 2 minutes after the start of injection, ferrosilicon (FeSi) was added and deoxidation was performed. It was conducted. In addition, when the deoxidation reaction was completed, SUS304 small piece scrap 5,000 from the furnace bunker
kg was put into the molten steel in the ladle. After the molten steel injection was completed, the ladle was transferred to the RH in the next step.

After arrival at the RH, sampling was performed and sent to the analysis room. The composition of the molten steel before the refining work was as shown in Table-5. Immediately after the analysis value was determined, the following ferroalloys and SUS304 small piece scraps were charged from the furnace bunker, but the amounts used were as follows. FeSi 870 kg LCFeMn 1,650 kg SUS304 small piece scrap 520 kg After that, the refining work was performed by the usual method, but after the work was completed, the analysis of molten steel components was as shown in Table-6. Since it satisfied the standard sufficiently, it was transferred to CC, which is the next step, after normal operations such as temperature adjustment were performed.

[0013]

[Third test status and results] The same work as the second test was performed until the converter work and deoxidation in the ladle. After the completion of the deoxidation reaction, 6,000 kg of SUS304 small piece scrap was thrown into the molten steel from the furnace bunker. After the molten steel transfer to the ladle was completed, it was transferred to the RH in the next process.

After the arrival of the RH, the analysis of molten steel components was conducted as usual. The molten steel composition was as shown in Table-7. Immediately after the analysis value was found, the following ferroalloys were cut out from the furnace bunker and put into molten steel. The amount of iron alloy used was as follows. FeSi 870 kg LCFeMn 1,670 kg SUS304 small piece scrap 120 kg After that, normal work was carried out, but the molten steel components before CC transfer were as follows, which satisfied the standards sufficiently.

[0015]

As described above, if the small piece scrap of the present invention is subjected to the normal work by using the normal equipment, the steelmaking cost can be easily and significantly reduced.

Claims (5)

[Claims] 1. A plate-shaped or slit-shaped scrap containing Ni and Cr is sheared by a shredder.
A small piece of alloying element additive for steelmaking. 2. The plate-shaped or slit-shaped scrap is Cr-based stainless steel containing 15% or more of Cr. The alloying element-added material described in. 3. The plate-shaped or slit-shaped scrap is Ni-based stainless steel containing Cr of 16% or more and Ni of 6% or more. Element addition material described in. 4. The plate-shaped or slit-shaped scrap is Ni steel containing 8% or more of Ni. The alloying element-added material described. 5. The maximum length is 300 mm or less, 2.3. And 4. The alloying element-added material described.