JPS59129714A - Method for controlling form of inclusion in aluminum killed steel for cold rolled sheet - Google Patents

Abstract

PURPOSE:To obtain an aluminum killed steel for a cold rolled sheet which can avert advantageously various cracks in the stage of severe plastic working by adding a flux composed specifically of MgO, CaO and/CaF2 at a specific ratio to a molten steel subjected to a component adjustment in the stage of tapping, stirring forcibly the steel and controlling the form of the inclusion therein. CONSTITUTION:A low carbon aluminum killed steel contg. generally, by weight %, 0.01-0.08% C, <0.08% Si, 0.15-0.35% Mn, and 0.020-0.15% Sol.Al is melted in a steel making furnace. The molten steel is subjected to a required component adjustment according to a conventional method in the stage of tapping the same from the steel making furnace, for example, a converter. A flux consisting of 10-30% MgO basing on the molten steel and the balance CaO and/ or CaF2 is added to such molten steel at a ratio of 1-4kg/molten steel ton and the molten steel is forcibly stirred by the inert gas blown thereto. As a result, the Al2O3 cluster and CaO-Al2O3 inclusion of high m.p. formed in the molten steel are component-adjusted to the CaO-Al2O3-MgO inclusion of low m.p. with the target components of CaO/Al2O3 0.6-1.2, MgO=8-15%, whereby the component adjustment of the molten steel is accomplished.

Description

Detailed Description of the Invention (Technical Field) The present invention relates to a method for controlling the form of inclusions in cold-rolled aluminum-killed steel.
It occupies a position in the technical field of out-of-furnace refining, which is a secondary treatment prior to continuous casting.

(Problem) Among the conventional general tinplate materials and can materials, so-called DI cans (
low-carbon aluminum killed cold-rolled steel sheets used for deep-drawn steel sheets for automatic production, etc., contain inclusions in the steel, especially AI! .

2 δ-based and Cj aOAl s Oa-based nonmetallic inclusions tend to cause cracks and linear scratches on the surface of the steel sheet, and press cracks and 7-lunge cracks occur during severe plastic deformation due to deep drawing or ironing. However, there was a problem in that it was prone to ion cracking.

On the other hand, the conventional method is to first remove the A
The components of / are adjusted, and the A/, 08-based inclusions generated accompanying this component adjustment are removed from OaO- derived from the blowing operation.
Together with Al2O8 inclusions, they are floated and separated by Ar bubbling in a ladle or RH vacuum stirring treatment.
In addition to going through the so-called out-of-furnace refining process, the generation of Al2O8-based inclusions due to air oxidation of the molten steel during the process from the ladle to the tundish to the continuous casting mold is prevented by an atmosphere Ar seal, or by the tundish. Even if passive measures are taken, such as creating a weir inside the molten steel and promoting the flotation and separation of inclusions in the molten steel, it is not always possible to achieve a satisfactory casting condition. However, disadvantages were often experienced, such as:

In other words, AI in molten steel whose composition was adjusted at the time of tapping! However, due to the subsequent Ar bubbling and RH vacuum treatment, the target value was lowered, and therefore, during the treatment, it was necessary to adjust the composition of 1' in the steel again, and at this time, a large amount of A was newly added.
I! In addition, the Ar seal for the flow path of molten steel to the continuous casting mold has deteriorated beyond the control limit, and the level of the molten metal in the tundish has decreased due to weirs. There is a concern that promotion of flotation and separation of inclusions may be impaired.

Conventionally, it has been difficult to consistently and stably reduce linear flaws and cracks on product boards in this way.

(Motivation for the Invention) By the way, in DI cans, cracks caused by can-making processing are induced by AI of 50 μm or more, GaO-based composite inclusions, or irregularly shaped A/', 0. Based on the fact that system inclusions are said to be the main cause of these inclusions, the inventors conducted development research with an eye toward solving the above problems by changing the inclusion composition. , arrived at this invention.

(Structure of the Invention) This invention provides molten steel that has been subjected to necessary composition adjustment when tapped from a steelmaking furnace, with 10 to 80% by weight of MO and the remaining O.
A flux having a composition of aO and/or Qa'i's is added at a rate of 1 to 4 particles per ton of molten steel, and stirring is forced to make the inclusions in the steel extensible, broken, and dispersed. By adjusting the composition to a simple composition, we have made it possible to effectively solve the problems associated with particularly severe deformation of the above-mentioned low carbon aluminum guild steel strips.
This is a method for controlling the morphology of inclusions in aluminum killed steel for cold rolled sheets.

The general composition range of low carbon aluminium-killed steel suitable for inclusion morphology control according to this invention is approximately as follows.

0 + 0.01-0.08 multiplication factor s1; <o. 080 7Mn; 0.15
~Sail 85#SO/At; o, ozo~0.15wt Low carbon aluminum killed steel for cold-rolled sheets produced by melting in a steelmaking furnace, for example, a converter, has the above-mentioned composition. At the time of tapping, necessary compositional adjustment is carried out according to a conventional method, and then a flux having a composition of 10 to 80% by weight of M and O with the remainder being mainly 0, aO and/or OaFg is added to the molten steel bath in tons. The high melting point At20 produced in the molten steel after the above composition adjustment is preferably injected and stirred with an inert gas such as Ar or N2 at a ratio of 1 to 44%. ．．
Clusters and OaO-kl, 08-based inclusions are removed by OaO
,i,. Medium 0.6-1.2, MyO=8-15 I
Target 8 Low melting point GOOaO-At208-My with target component
The composition of O-based inclusions is adjusted, and in this way,
The inclusions in the steel become highly extensible, and after the above-mentioned treatment according to the present invention, continuous casting according to the conventional method, hot rolling using the resulting slab as raw material, and cold rolling steps are performed to produce a cold rolled sheet. In the condition, the inclusion thickness ratio to the plate thickness is
The size of the inclusions becomes significantly smaller, and the inclusions are destroyed during the rolling process.
As a result of dispersion, there are no linear scratches that often occur on the surface of cold-rolled sheets, and even when the cold-rolled sheets are subjected to harsh drawing or graining conditions later on. , the risk of cracking and other defects is drastically reduced.

In carrying out the present invention, effective flotation separation of inclusions can be fully expected by the above-mentioned stirring process, and the conventional A
Although the steps of r bubbling and RH vacuum stirring treatment are unnecessary, they can of course be applied within these steps.

In this invention, the flux composition is limited as described above because M and O exceed 80% by weight, and OaO and Oa
AI in molten steel when the total amount of Fp and Fp is less than 70% by weight! , O, and aao-AI! OaO-A7, which has a slow reactivity with 208-based inclusions and a low melting point?
208- It is difficult to adjust the M, O system composition, and on the contrary, it worsens the extensibility of inclusions.
If the total weight of OaO and Q al” 2 exceeds 90 weight 11, Al in the steel, 08 OaO
-Al2O8-based inclusions are OaO-14208-MyO
This is because even if the composition is adjusted in the system, the MfO amount will be less than 8% by weight, so the melting point will not be low, and the necessary improvement in extensibility cannot be expected. Regarding flux formulation, Oa
O and OaF have the same effect on adjusting the composition of the inclusions.

Next, the flux must be in the range of 1 to 4 to 9 per ton of molten steel, and if it is less than this range, the necessary form control should be determined for the total amount of the harmful inclusions in the molten steel. If you are unable to do so and the amount exceeds the above range,
Due to excessive adjustment of the inclusion composition, undesirable high-melting point inclusions are generated and their flotation separation is hindered, and flux components remain in the molten steel, resulting in defects in cold-rolled sheets. leading to occurrence.

When a suitable amount of flux with a composition suitable for the above-mentioned composition is applied to the stirring treatment of the present invention, nonmetallic inclusion particles agglomerate and become large particles due to mutual contact in the molten steel bath, thus increasing the floating speed in the steel bath. It was found that the molten steel was advantageously separated and removed from the molten steel by a short stirring process, and the cleanliness of the molten steel was significantly improved.

Example 1 Using a vacuum induction melting furnace with a furnace capacity of 50 yen, low carbon aluminum killed m (G = 0.05, Si = 0.02, Mn = 0.
21, Al = 0.054, S = 0.009, P
= 0.0101) i 50kpw at 1650℃
60 prepared by pre-melting with i15
100 fw of fine flux powder with a composition range of 40a0 20% OaF -20% MyO was added at a rate of 2 kp per ton of molten steel, stirred by Ar bubbling to suspend it, and then immediately poured into the mold. Cast, OJmm coated rolled steel plate, surface.

The number of linear flaws that occurred was investigated.

The results are shown in Table 1, and it can be seen that the linear scratches are reduced to less than h compared to the conventional method (when melting is performed by atmospheric melting and only the usual component adjustment is performed, and no inclusion composition adjustment is performed). The effectiveness of reducing and preventing defects caused by inclusions in cold rolled sheets of killed steel is clear.

be.

Table 1 Example 2 Low carbon aluminum killed steel (OiO, 06%
, Si HO, 024, In; 0.024. Al
; 0.074%S; 0.010%, P;
After melting 0.012%), heat (referred to as method A) was added in an RH vacuum chamber at a rate of 2 parts W per ton of flux molten steel as described in Example 1, and the flux was added in a ladle. The heat was injected into the top-blown injection tube (
(referred to as Method B) and normal heat without flux addition (
The number of non-metallic inclusions in cold-rolled plates (referred to as the c method) and the cracking of can edges when these plates are processed into cans and then a stress equivalent to the flanging strain of the can is applied to the can edges. Table 2 shows the degree of comparison.

Table 2 As a result, it is clear that nonmetallic inclusions are reduced in methods A and B compared to the conventional method (method C).

However, an even greater effect than the reduction in non-metallic inclusions is the reduction in the incidence of can cracking.

The crack occurrence rates in Method A and Method B indicate that the improvement effect is greater than the effect of reducing nonmetallic inclusions.

This is thought to be because the non-metallic inclusions were adjusted to be extensible, resulting in a decrease in the ratio of the thickness of the inclusions to the thickness of the can, resulting in a reduction in the susceptibility to cracking due to stress strain during processing.

As described above, by controlling the inclusion morphology according to the present invention, in addition to reducing linear flaws in cold-rolled low-silicon aluminum guild steel sheets, severe plasticity such as drawing or ironing using this material can be reduced. It is possible to advantageously avoid the ridge cracks that conventionally often occur during processing.

Liability applicant: Kawasaki Steel Corporation

Claims (1)

[Claims] L: To the molten steel that has been subjected to the necessary composition adjustment during tapping from the steelmaking furnace, 7 lux having a composition of □10 to 30 weight ratios of M and O and the remaining CaO and/or OaF is added per ton of molten steel. Cold gong plate direction is a method for controlling the form of inclusions in aluminum-killed steel, which is characterized by adding nicotine in a proportion and forcing stirring to adjust the inclusions in the steel to a composition that is extensible and easy to break and disperse. Method.