JPS6274047A - Method for refining stainless steel - Google Patents

Abstract

PURPOSE:To manufacture an extremely low-N dead soft stainless steel by feeding oxygen to a furnace contg. molten pig iron, scraps chrome ore, a carbonaceous material and a flux to obtain molten pig iron contg. Cr, removing produced slag, evacuating the furnace and introducing oxygen into the furnace to decarburize and denitrify the molten pig iron. CONSTITUTION:Molten pig iron, scraps, chrome ore, a carbonaceous material and a flux are charged into a reaction furnace 1 and oxygen is fed from a lance 2 to obtain molten pig iron contg. Cr. After produced slag 6 is removed, a cover 8 is placed over the furnace 1, the furnace 1 is evacuated and oxygen is fed by about 1-4Nm<3>/min.ton under about 760Torr pressure. At the same time, gas is blown from a bottom tuyere by 0.5-1Nm<3>/min.ton to carry out degassing. Thus, an extremely low-N dead soft stainless steel is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a novel manufacturing method for manufacturing low C1, low N stainless steel at low cost.

[Conventional technology]

As the demand for high-purity stainless steel with low C1 and low N increases, various methods for manufacturing high-purity stainless steel are currently being proposed in the steel industry.

Specifically, for example, vacuum converter method (VODC+), vacuum oxygen decarburization method (VOD), argon oxygen dilution decarburization method (AOD)
and so on.

All of these methods have their own characteristics, and it goes without saying that the accompanying M-methods also come in various forms, each with its own characteristics.

For example, among the VODClVODs in which the converter is kept in a vacuum state, the former uses a vacuum level of about 1 OTorr r, an oxygen flow rate of I N m' 7 min.l. 0.01~0.05Nm/min・
)・In the latter case, the vacuum level and oxygen supply rate are the same, but the argon blowing from the bottom is 0.01 Nr.
It is operated at n'/min/ton.

In addition, the AOD is operated under conditions of 1 atm and a flow rate of oxygen and argon blown from the bottom at 2 N m' 7 minutes or more.

On the other hand, the manufacturing of crude molten stainless steel to be supplied to these de-C1 de-N goro processes involves the production of ferrochrome using existing electric furnaces, and research conducted at the Nashopur Go Ljjiect, which utilizes energy from carbonaceous material and oxygen without using electricity. As in the production of ferrochrome, the chromium source is solidified to produce iron alloys, and is then produced in electric furnaces (EF), converters (LD) - AOD, VO.
In methods such as D, it is common to reuse the chromium source in 17.3 In addition, in another example, the molten ferrochrome produced by reducing ore in EF is directly used in another furnace to produce stents. Some are used to guide the process.

Chromium ore, carbonaceous material, flux, and oxygen are sent to the hot metal to create molten chromium metal. After the slag is removed, carbon is removed in the presence of oxygen and the composition is adjusted to produce a chromium content of approximately 12%.
In some cases, stainless steel has been obtained.

[Problem that the invention seeks to solve]

However, these technologies have potential or actual problems such as the following:
No.

In other words, in the case of the method VODC, VOl,), since the bottom blowing gas i & speed and oxygen supply expansion are insufficient,
Low N:2. '9-L steel manufacturing is difficult.
two.

On the other hand, in the AOD method, the flow rate of the bottom-blown gas and the oxygen supply rate are 100%, but since it does not have a vacuum evacuation device, there is a limit to its effectiveness just by diluting the gas, and in the end, even in this case, the reaction The effect of reducing nitrogen partial pressure (PN2) at the interface is insufficient, making it difficult to manufacture low-N stainless steel.
:4. The production of stainless steel melting and drying is quick and low energy/L.
However, the method of solidifying molten metal of 1 μm as a chromium source to make a ferroalloy, and then melting it again when stainless steel is produced, has high energy consumption. It's raining.

Also, regarding the ferrochrome manufacturing process itself,
When electricity is used, it is difficult to reduce costs.

[Failure to solve the problem]

Invention 1, in this situation, low C1 low N
As a result of various studies on how to produce stainless steel and stainless steel at low cost, we created chromium-containing hot metal using hot metal, scrap, chromium ore, carbonaceous material, flux, and oxygen. They introduced a stainless steel refining method that involves direct production of sulfur by removing C1 and removing N.

[For production]

According to general considerations, if the partial pressure of nitrogen in the solution is 1, it can be expressed by the following formula:

In the formula, P92 is nitrogen partial pressure, Pr is total gas pressure in the system, QN
2 is nitrogen gas flow, Q co is CO gas flow rate, Q A?
indicates Argonogas 24M.

According to this formula, in order to lower the nitrogen partial pressure, the total gas pressure in the system must be lowered, or the CO gas flow and the nitrogen partial pressure can be lowered. It turns out that if you increase both or either of the gono gas flow rates, it will be better.

Then, to lower the total gas pressure in the system, perform vacuum evacuation (-A, OK), and to increase the QAT, increase the bottom blowing gas.
Increasing θ is also self-effective.
For this purpose, it is understood that it is sufficient to increase the amount of acid A supplied to the reaction site.

From this, in order to process the molten metal, the outline of the reaction vessel is changed from the molten metal production site shown in Figure 1 to the de-C1 theory N as shown in Figure 2. Second, the upper part of the furnace is vacuumed. #JiE, which can hold up to 7G, uses a lid-like part or something that can be covered with a sealed JAW construction.

In the figure, l is a reaction vessel, 2 is:>cis, 3 is a material,
4 is a hula Jji, 5 is a bottom blower! Go 7.6 is slap,
7 is hot metal, 8 is a lid, 9 is a vacuum.
At a pressure of 0 T or r, the bottom blowing gas pressure from the tuyere is set to about 0.5 to 1 N m 7 min.)-ton, and the oxygen supply is about 1 to 4 N m' 7 min. As a result, it is possible to obtain a stainless steel with extremely low C1 and extremely low N, with C<15ppm and N<2'Oppm.

〔Example〕

Approximately 33 tons of hot metal whose P content had been reduced through a pretreatment process to the components shown in column A of the following table was charged into the reaction vessel shown in FIG.

Oxygen is supplied from a lance at a rate of approximately 20,000 Nrn'/h, and 33 tons of chromium ore and 25 tons of coke are supplied.
Approximately 10 tons of flux containing 1 lime and silica sand as main components was charged at the top, and added for about 30 minutes using injection from the upper lance and injection from the bottom tuyere at an addition ratio of 1:1:1.

Note that the bottom-blown Ar gas was 17 Nrn'/min, and the metal temperature at the end was 1645°C.

After 25 minutes had passed after the completion of the addition, the components were as shown in column B in the table.

C a O-3i 02 A l which produced approx.
After removing the slag containing 203-Mg0 using a vacuum suction device, a sealable lid was attached to the top of the furnace as shown in FIG. 2, and oxygen supply was started.

Oxygen supply from upper lance lit 11500 N m'
/h After heating for 13 minutes, turn on the oxygen at 120Nm.
'/h, and the degree of vacuum was increased to 10Torr.
The temperature was then lowered and treated for about 12 minutes.

During this time, the bottom-blown Ar gas was 15 to 25 Nm" 7
It was a minute.

Thereafter, reduction and composition adjustment were performed, and the steel was tapped into a ladle from the taphole in the furnace belly, and then led to the continuous casting process.

The components after C1 removal and N removal (before reduction and component adjustment) and in the continuous casting product are shown in columns C and D of the table, respectively.

Metal component (wt%) [Effects of the invention] By implementing the present invention, it has become possible to easily obtain low C1 and low N stainless steel, which was complicated and could not be easily produced using conventional methods. Ta.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram for explaining the production of molten stainless steel, and FIG. 2 is a schematic diagram of a furnace equipped with vacuum equipment for performing vacuum decarburization treatment on the same furnace after producing the molten metal. 1 is a reaction vessel, 2 is a lance, 3 is a raw material, 4 is a flange,
5 is bottom blowing argon, 6 is slap, 7 is hot metal, 8 is lid, 9 is vacuum line.

Claims (2)

[Claims] (1) Make chromium-containing hot metal from hot metal, scrap, chromium ore, carbonaceous material, flux, and oxygen, and after removing slag, introduce oxygen under vacuum conditions in the same furnace to remove C and N to directly manufacture stainless steel. A stainless steel refining method consisting of: (2) Under vacuum conditions from 10 to 760 Torr or less,
The method for refining stainless steel according to claim 1, which comprises producing the stainless steel at an oxygen supply rate of 1 to 4 Nm^3/min/ton.