JP3023645B2 - Continuous casting method of Pb-containing steel - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating Ca in molten steel when producing a Pb-containing steel containing Al by continuous casting, thereby harmless nonmetallic inclusions present in the molten steel. It is related to the method of conversion.

[0002]

2. Description of the Related Art In recent years, the continuous casting technique has been developed into a casting technique in a form closer to a product by reducing the cross section of a billet continuous casting machine or the like. In such continuous casting, the diameter of the tundish nozzle also becomes smaller,
It is known that in Al-killed steel, Al-Si-killed steel, etc., nozzle blockage due to non-metallic inclusions containing Al ₂ O ₃ as a main component is more likely to occur than in conventional bloom-slab continuous casters.

As means for preventing such nozzle blockage, a technique of adding Ca to molten steel for the purpose of lowering the melting point of Al ₂ O ₃ inclusions in molten steel (for example, Japanese Patent Application Laid-Open No. 63-73)
22. Japanese Patent Application No. 63-131999 / Japanese Patent Application No. 1-3018
90) has been implemented and the effect has been raised.

Japanese Patent Publication No. Sho 64-10310 discloses a method for preventing nozzle clogging by slag control.

[0005]

As described above, there have been many reports on the morphology control technology of Al ₂ O ₃ (non-metallic inclusions) by adding Ca, and there is no effect from the viewpoint of preventing continuous casting nozzle clogging. I have. However, there is no report on Pb-containing steel.

The present inventors have found that Pb-containing molten steel contains C
It has been found that even if the addition of a is performed to control the form of Al ₂ O ₃ (non-metallic inclusions), the effect is extremely small, and as a result, it is impossible to prevent nozzle clogging and quality defects in continuous casting. are doing.

[0007] The present invention has been made in view of such a situation, and when Ca is added to molten steel to lower the melting point of non-metallic inclusions in the molten steel and continuously cast, the Pb-containing steel is continuously cast. The present invention provides a method for continuously casting Pb-containing steel, which prevents nozzle blockage and quality defects caused by Al ₂ O ₃ .

[0008]

According to the present invention, in continuously casting Pb-containing steel, after adding Ca to molten steel not containing Pb in a ladle, a Pb-containing substance is added so as to be a predetermined component. Continuous casting of Pb-containing steel.

[0009]

In order to confirm the effect of Pb content on the Ca treatment, the present inventors first added Pb to molten steel and cast it by adding Ca to molten steel in S45C equivalent steel in actual equipment. The composition of inclusions in a tundish molten steel in a case where only Ca was added to molten steel containing no and cast was compared (FIG. 1).

As a result, when Ca is added and cast after adding Pb, Al ₂ O ₃ is significantly modified by adding Ca as compared with the case where only Ca is added to molten steel not containing Pb and cast. It was found that calcium aluminate, which is insufficient, that is, a modified product of Al ₂ O ₃ , was hardly formed.

[0011] Further, as a result of further investigation of tundish molten steel in the case of casting with addition of Ca after addition of Pb,
Pb grains are crystallized with MnS and oxides as nuclei during the solidification process. Pb grains contain about 1% Ca, and Pb-Ca alloying estimated from the Pb-Ca phase diagram. It turned out to correspond.

From the above investigation results, the presence of Pb in molten steel directly inhibits the reforming reaction of Al ₂ O ₃ by the addition of Ca,
The mechanism, Ca stronger chemical interaction between Pb and Ca can not participate in the reforming reaction of _{Al 2 O 3, Al 2 O} 3 and the Ca for physical affinity is large and Pb Al ₂ O ₃ It was speculated that the frequency of contact with was significantly reduced.

From the above, the present inventors have found that when adding Ca to Pb-containing steel and controlling the form of Al ₂ O _{3 in} the molten steel, Pb in the molten steel present at the time of adding Ca is directly changed to Al.
_It could be found that the reforming reaction of ₂ O ₃ was inhibited.

Next, in order to confirm the above-mentioned mechanism, the present inventors have found that the effect of P on the effect of Ca to modify Al ₂ O ₃ is considered.
The effect of the order of addition of b and Ca was investigated by experiments.

As a result, when Ca was added after adding Pb, only about 15% of calcium aluminate was observed. On the other hand, when Pb was added after adding Ca, the content was about 85%, confirming the above mechanism.

Further, the present inventors investigated the composition of inclusions in molten steel to which Pb was added after adding Ca to molten steel not containing Pb for the purpose of establishing an appropriate level in actual operation.

FIG. 2 shows the result. The modification of Al ₂ O ₃ was almost the same as that when Pb was not added, and the amount of Pb was changed (Pb content in molten steel: 0.052%, 0.2%).
12%), the same result was obtained.

From the above, the present inventors have found that the mechanism for inhibiting the reforming reaction of Al ₂ O ₃ in Pb-added molten steel is based on P in molten steel.
It has been confirmed that the presence of b is caused by the fact that it acts as a reaction inhibitor for the reforming reaction of Al ₂ O ₃ during the addition of Ca, and is solved by adding Pb after adding Ca.

In the practice of the present invention, the method of adding Ca and Pb is not limited at all, and at least when Ca is added to the molten steel to lower the melting point of nonmetallic inclusions in the molten steel to perform continuous casting. The above problem can be solved only when Ca is added to molten steel not containing Pb in a pot and then a Pb-containing substance is added to the molten steel for continuous casting.

The Pb-containing substance may be added at either a ladle or a tundish.

[0021]

EXAMPLES The effects of the method of the present invention are shown in Table 1 in comparison with the conventional method, using a steel grade equivalent to S45C as an example.

In Example 1, bubbling treatment was performed for 3 minutes after adding Ca to molten steel not containing Pb in a ladle,
This is a charge obtained by adding Pb particles to a ladle. The UT defect rate of the product rolled to the steel bar after casting was 0.1%.

When the inclusions in the molten steel in the tundish were analyzed, the weight ratio of angular Al ₂ O ₃ was 10% or less, and the others were modified to calcium aluminate.

Example 2 is a charge in which Pb particles were added to a tundish during continuous casting by performing bubbling treatment for 3 minutes after adding Ca to molten steel not containing Pb in a ladle. The product UT failure rate was 0.3%.

When the inclusions in the molten steel in the tundish were analyzed, the weight ratio of angular Al ₂ O ₃ was 10 as in Example 1.
% Or less.

Comparative Example 1 is a charge obtained by adding a Pb particle to a ladle and then performing a Ca treatment. The clogging and peeling of the immersion nozzle was large during continuous casting. Product UT failure rate is 1
0.5%.

When the inclusions in the molten steel in the tundish were analyzed, the weight ratio of angular Al ₂ O ₃ was as high as 85%, and almost no calcium aluminate was observed.

Comparative Example 2 is also a charge obtained by adding a Pb particle to a ladle and then performing a Ca treatment. During continuous casting, clogging of the immersion nozzle was severely stopped.

[0029]

[Table 1]

[0030]

According to the present invention, Ca in Pb-added steel
Makes it possible to enhance the effect of reforming Al ₂ O ₃ ,
By stabilizing the operation and improving the quality by avoiding the nozzle clogging, the product UT failure rate can be suppressed to the same level as that of steel not adding Pb.

[Brief description of the drawings]

FIG. 1 shows molten steel containing only Ca and Pb after addition of Ca
FIG. 4 is an explanatory view showing the results of comparing the inclusion compositions in steel of molten steel in which the lead concentration in steel was determined by adding iron.

FIG. 2 shows molten steel containing only Ca and Pb after addition of Ca
FIG. 3 is an explanatory diagram showing the results of comparing molten steel with added steel from a tundish at the time of continuous casting and comparing the composition of inclusions in each steel.

──────────────────────────────────────────────────の Continued on the front page (72) Inventor Masashi Yoshida 12 Nakamachi, Muroran City Nippon Steel Corporation Muroran Steel Works (72) Inventor Yuji Kawachi 12 Nakamachi, Muroran City Nippon Steel Corporation Muroran Steel (56) References JP-A-3-47663 (JP, A) JP-A-60-158962 (JP, A) JP-A-60-158961 (JP, A) JP-A-64-39345 (JP, A) JP-A-61-276756 (JP, A) JP-A-3-165952 (JP, A) JP-A-1-299742 (JP, A) JP-A-61-202748 (JP, A) JP-B-46-21818 (JP, B1) (58) Fields investigated (Int. Cl. ⁷ , DB name) B22D 11/00 B22D 1/00 B22D 11/108 C21C 7/04

Claims (1)

(57) [Claims] In a continuous casting of Pb-containing steel, after adding Ca to molten steel not containing Pb in a ladle, P is added to the molten steel.
A continuous casting method for Pb-containing steel, characterized by adding a b-containing substance to a predetermined component and continuously casting.