JPH0488114A - Method for producing high manganese steel - Google Patents

Abstract

PURPOSE:To attain production of a high manganese steel, in which high decarburizing velocity is attained and a producing cost can stably be reduced, by tapping the molten steel under undeoxidizing condition from a converter, charging high carbon Mn alloy in a ladle to execute adjustment of a Mn content and a top-blowing oxygen in a vacuum degassing vessel to execute vacuum secondary refining. CONSTITUTION:By using a pre-treated molten iron beforehand desulfurized and dephosphorized, a raw decarburized low carbon steel is refined and tapped under the condition of having a little higher blowing-up C content than that in the ordinary method. During the tapping molten steel, the high carbon manganese alloy in a low cost is charged to execute adjustment of the Mn component. After that, by charging Al slag, slag reduction is executed as the aim of a Mn yield improvement. After executing the slag reduction, by top-blowing the oxygen in the vacuum degassing vessel, what is called, by rimmed-treatment, the decarburization is executed for about 10 min and after that, by killed- treatment, the decarburization and the degassing treatment are executed and adjustment of a component is executed to complete the refining.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for producing high manganese steel, and particularly relates to a method for producing high manganese steel that can reduce production costs by using a high carbon manganese alloy.

[Prior Art] Low carbon high manganese steels are used in large quantities today as linepipe materials. The typical conventional manufacturing method for high manganese steel, which has a very narrow carbon tolerance range of 0.05±0.01%, is to smelt it in an oxygen blowing converter, where decarburization is very easy. Steel was tapped at a concentration of about 0.05% C, and a low carbon manganese alloy was added to the ladle during tapping to adjust the amount of manganese, followed by secondary vacuum refining and continuous casting into slabs. . However, in this method, it is necessary to prevent an increase in the amount of C after steel is tapped in a converter, so an expensive low carbon manganese alloy must be used, which has the disadvantage of increasing the melting cost.

Many proposals have been made in the past as methods for manufacturing high Mn steel in an attempt to reduce the above-mentioned melting costs. An overview of the conventional technology will be explained.

JP-A-62-192519: This method uses dephosphorized pretreated hot metal, and performs less slag blowing to reduce the amount of slab in the converter.

A method is disclosed in which a Mn-containing substance is added to a furnace, steel is tapped in a relatively high C state, and decarburized in a vacuum degassing tank, but the type of gas used is not disclosed.

JP-A-63-293109: In this method, C: 0.15 to 0 in converter blowing.
A method is shown in which steel is tapped at a molten steel temperature of 1640° C. or higher, Mn ore is added in a vacuum degassing tank, and decarburization is performed to a C content of 0.1% or less.

JP-A-1-92312: The gist of this method is as follows.

That is, in the molten steel in the vacuum chamber of the rRH vacuum degassing device,
The manganese ore powder is injected through a nozzle provided on the side wall of the vacuum chamber using an inert gas as a carrier gas, and the molten steel is decarburized by the oxygen in the manganese ore, and the manganese concentration in the molten steel is increased. A method for manufacturing high manganese steel. ”.

In this method, the Mn ore is a high carbon manganese ore with a Mn content of 45-55%, the amount of injection is 1-5 kg per ton of molten steel, and the carrier gas is Ar 0.003-0. It is described that 04ONm/min, - is used.

However, in these conventional methods, the decarburization reaction is not necessarily carried out sufficiently, and therefore, efficient treatment cannot be carried out, and it is considered that cost reduction is not sufficient.

[Problem to be solved by the invention]

An object of the present invention is to provide a high manganese steel melting method that solves the problems of the prior art described above and can stably reduce melting costs.

[Means and operations for solving the problems] The gist of the present invention is as follows. That is, a process of adjusting the composition of manganese by adding a high carbon manganese alloy when raw decarburized low carbon steel melted in a refining furnace such as a converter is tapped into a ladle without being deoxidized; a step of decarburizing by top-blowing oxygen in a vacuum degassing tank after adjusting the components; a step of degassing in a vacuum degassing tank after the decarburization;
A method for melting high manganese steel, characterized by comprising the following steps.

The details of the invention will now be described with reference to the accompanying drawings.

In the present invention, crudely decarburized low carbon steel is refined using pretreated hot metal that has been desulfurized and dephosphorized in advance, and is released from the converter without being deoxidized and with a slightly higher blowout C content than before. Steel. During tapping, an inexpensive high-carbon manganese alloy is added to adjust the manganese composition. Thereafter, AQ slag is introduced to perform slag reduction for the purpose of improving the Mn yield. After slab reduction, oxygen is top-blown in a vacuum degassing tank to decarburize for about 10 minutes in a so-called rimmed process, and then decarburize and degas in a quilt process for about 20 minutes to adjust the components and refine. complete.

In the present invention, since oxygen top-blowing is performed in the vacuum secondary refining, the supply of oxygen is sufficient, and as shown in FIG. 1, decarburization is actively carried out and stagnation does not occur.

FIG. 1 shows changes in carbon and oxygen in molten copper during vacuum secondary refining in an example of the present invention. Figure 2 also shows that molten steel with a carbon content of 0.14% before vacuum secondary refining is subjected to vacuum secondary refining by changing the Mn content with and without oxygen top blowing. The decarburization coefficient was investigated and shown.

From FIG. 2, in the present invention which performs oxygen top blowing,
It was found that the decarburization rate is almost constant even when the Mn content is high, and that high decarburization rates can be obtained even with high Mn steel.

Also, the changes in the Mn component during the RH treatment are as shown in Figure 3, and for about 5 minutes during the oxygen top blowing section,
Although some oxidation was observed from Mn: 12.5% to approximately 12.0%, almost no change was observed in other degassing sections, and the Mn yield was good.

Therefore, in the present invention, the blow stop C of the converter is made high,
It has become possible to lower the total iron content (T, Fe) of the slag, increase the Mn yield, and use a cheaper high-carbon Mn alloy.

〔Example〕

An embodiment of the present invention will be described in comparison with a conventional example. Steel was tapped into a ladle under the converter blowing conditions shown in Table 1, and subjected to Mn adjustment and vacuum secondary refining according to the method of the present invention and the conventional method as shown in Table 2, under the same conditions. Continuous casting was performed on the slab.

As a result, in addition to using an inexpensive high-carbon Mn alloy, the embodiment of the present invention has a good Mn yield, so as shown in Table 2, the melting cost was reduced by 400 yen/ compared to the conventional example. We were able to.

〔Effect of the invention〕

As is clear from the above examples, in the present invention, steel is tapped from a converter without being deoxidized, a high carbon Mn alloy is charged into a ladle, manganese is adjusted, and oxygen is top-blown in a vacuum degassing tank. A high decarburization rate was obtained by performing vacuum secondary refining. It was found that this decarburization rate was almost constant regardless of the Mn concentration. As a result, conventional expensive low carbon F
It is possible to eliminate e-Mn and effectively use relatively cheap high carbon Fe-Mn, reducing the melting cost of low C high Mn steel to about 4.
00 yen/ was reduced.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the changes in carbon and oxygen in molten steel in the vacuum secondary refining of the embodiment of the present invention, and Fig. 2 is a diagram showing the changes in Mn in molten steel with and without top-blowing of oxygen in the vacuum secondary refining. Figure 3 is a diagram showing the relationship between Mn content and decarburization coefficient.
) is a diagram showing the relationship between Rod / 1”

Claims (1)

[Claims] (1) A step of adjusting the composition of manganese by adding a high carbon manganese alloy when tapping crude decarburized low carbon steel melted in a refining furnace such as a converter into a ladle without deoxidizing; It is characterized by comprising the steps of decarburizing by top-blowing oxygen in a vacuum degassing tank after adjusting the manganese composition, and decarburizing the gas in a vacuum degassing tank after the decarburization. A method for producing high manganese steel.