JPH0742546B2 - Hot slab width sizing mold - Google Patents

Description

The present invention relates to a width sizing of a hot slab used when a hot slab is width-reduced over its entire length by a press working method to produce a slab of a predetermined width. For molds.

(Prior Art) In recent years, the types and sizes of steel plates demanded by customers are extremely large, and in particular, there are many sizes. If a slab having a width commensurate with the manufacturing process of steel plates having different sizes can be easily supplied, the process can be simplified and the yield can be improved. Therefore, recently, a slab having a width most suitable for the steel sheet size is manufactured by changing the width during continuous casting, reducing the width by a vertical rolling mill, width sizing by a press, and the like.

In the slab manufacturing method described above, the pressing method is used to press down the side surface of the slab S with a mold 1 having a surface 2 parallel to the surface and an inclined surface 3 to form a slab of a predetermined width. It is manufactured. This method has been recently implemented because it is more efficient than the method of changing the width of the mold and the method of using the vertical rolling mill. However, in this method, since the contact time between the mold and the slab is long, the mold temperature rises abnormally and wear or heat crack occurs on the pressure surface.

Conventionally, hot die tool steels (such as SKD61) and spheroidal graphite cast iron have been used as materials for width sizing dies.
Since the hot die tool steel has martensite as the matrix structure, it has excellent wear resistance, but has low heat crack resistance. Since the spheroidal graphite cast iron can have its matrix structure freely set to ferrite, martensite, etc., it has the advantage that it is easy to adjust the balance between strength and toughness, but according to the investigation of the present inventors, However, the heat crack retention effect of spheroidal graphite cannot be expected,
On the contrary, it was found to promote the development of heat cracks.

Therefore, the die is cooled by the following method to extend its life.

a. Method of spraying cooling water on the die pressure lower surface This method is to spray a large amount of cooling water on the die pressure lower surface during pressing. However, in this method, the slab is locally supercooled, which may deteriorate the quality. Another method is to spray the previous slab and then spray it until the next one.However, since the mold is heated not only to the surface but also to the inside by the previous pressing, the Sufficient cooling cannot be achieved by sprinkling water for hours. In this sprinkling cooling method, there is a problem that only the mold surface is rapidly cooled, the temperature difference between the inside and the inside becomes large, and heat cracks due to thermal stress occur.

b. Method of passing cooling water inside the mold This method is to provide cooling water by providing a water channel inside the mold. However, in this method, since water is passed through a mold that reciprocates in a high cycle, the apparatus becomes large, equipment costs are high, maintenance is troublesome, and cooling efficiency is low.

(Problems to be Solved by the Invention) Significant wear and heat cracks occur on the pressure surface of a mold used for width sizing a high temperature slab.
Sprinkling water to prevent it not only promotes heat cracking, but may even adversely affect slab quality. It is an object of the present invention to provide a die for hot slab width sizing, which has excellent abrasion resistance and heat cracking resistance in a die by improving the die material itself and can withstand long-term use.

(Means for Solving the Problem) As a result of various studies conducted on the improvement of the wear resistance and heat crack resistance of the width sizing die of the hot slab, the inventors obtained the following findings. It was That is, (1) In order to improve wear resistance and heat crack resistance, it is preferable to select a mold material having an appropriate chemical composition and to make the matrix a bainite structure.

(2) In order to have both abrasion resistance and heat crack resistance, the mold hardness should be in the range of HS30-50.

The present invention has been made based on the above findings, and the summary thereof is as follows. That is, in wt%, C: 0.10 ~ 0.35%, Si: 0.1 ~ 1.5%, Mn: 0.2 ~ 1.5%, Ni: 2% or less, Cr: 1.0 ~ 3.0%, Mo: 0.2 ~ 1.0%, V: 0.1 ~ 0.6%, the balance consisting of Fe and unavoidable impurities, the matrix structure is bainite, and the HS hardness is 30 to 50, in the width sizing mold of the hot slab, is there.

(Function) Hereinafter, the chemical composition (% by weight) of the width die casting mold of the present invention
And the reason why the matrix structure and hardness are set as described above.

C: 0.10 to 0.35% C is a carbide forming element, which increases the wear resistance by combining with Cr and V. If the content is less than 0.1%, the amount of carbide produced is insufficient, resulting in low wear resistance. On the other hand, it is 0.
If it exceeds 35%, carbides are coarsened and heat crack resistance is deteriorated. Therefore, C is 0.01 to 0.35%.

Si: 0.1-1.5% Si is contained to improve the deoxidation of molten metal and the flow of molten metal. If it is less than 0.1%, the effect cannot be obtained.
If it exceeds 1.5%, the matrix structure becomes brittle and the heat crack resistance deteriorates, so the content is made 0.1 to 1.5%.

Mn: 0.2-1.5% Mn is contained together with Si for deoxidation. It is 0.2
If it is less than 0.1%, a sufficient deoxidizing effect cannot be obtained, and if it exceeds 1.5%, the toughness decreases, so its content is made 0.2 to 1.5%.

Ni: 2.0% or less Ni functions to improve the organization of the base. However, if the content exceeds 2%, the stability of the matrix structure at high temperature deteriorates, so it is made 2.0% or less.

Cr: 1.0 to 3.0% Cr combines with C to form a high hardness chromium carbide to enhance wear resistance, and also serves to form a matrix into a bainite structure. If its content is less than 1.0%, its effect is small, while if it exceeds 3.0%, a brittle eutectic carbide is crystallized to deteriorate heat crack resistance. Therefore, its content should be 1.0 to 3.0%.

Mo: 0.2-1.0% Mo dissolves in the matrix to enhance high temperature characteristics such as high temperature softening resistance. Also, like Cr, it is useful for forming a base bainite structure. However, if less than 0.2%, the effect is small, while
Even if the content exceeds 1.0%, the corresponding effect cannot be obtained, so the content should be 0.2-1.0%.

V: 0.1 to 0.6% V not only makes the crystal grains finer to improve the heat crack resistance, but also forms fine VC carbides in the matrix to improve the abrasion resistance. If the content is less than 0.1%, the effect is small, and if it exceeds 0.6%, the carbides are coarsened and the mechanical properties are deteriorated.

Next, the reason why the mold base has a bainite structure is described.
Abrasion resistance and heat crack resistance of the mold vary greatly depending on the structure of the base. The wear resistance of the mold increases as the high temperature strength increases, and the heat crack resistance increases as the high temperature strength and high temperature toughness increase. And that is achieved because the base has a bainite texture. When the matrix has a martensite structure, the high temperature strength is large and thus the wear resistance is high, but the high temperature toughness is small, and thus the heat crack resistance is lowered. When the matrix has a ferrite / pearlite structure, the high temperature toughness is high, but the high temperature strength is low, so the wear resistance is reduced.

The reason for setting the hardness of the mold to HS (Shore hardness) 30 to 50 will be explained. The wear resistance and heat crack resistance of a mold are greatly affected by its hardness. If the HS of the mold is less than 30, the hardness is insufficient and the wear resistance is reduced, and if the HS is more than 50, the toughness is reduced and the heat crack resistance is lowered. In order to have both wear resistance and heat crack resistance, the mold HS should be 30-
Must be in the 50 range.

By the way, the base structure is bainite and the hardness is HS30.
Molds of -50 are produced by cooling the composition to the above range and water-cooling or oil-cooling the austenite temperature (1,050 to 950 ° C). A more stable structure can be obtained by further tempering at 500 to 650 ° C several times.

(Example) Hereinafter, the metal mold | die for width sizing of this invention is demonstrated based on an Example. Mold 1 having the chemical composition, matrix structure and hardness shown in Table 1 and having a shape as shown in FIG. 1 (parallel part length L:
500mm, thickness T: 500mm, width W: 450mm, taper angle θ: 12 degrees)
Produced by continuous casting, width 1,000-1,600mm, thickness
A slab having a length of 270 mm, a length of 7 to 10 m, and a temperature of about 1,200 ° C. was sized by 3,000 pieces in each mold with a maximum width reduction amount of 350 mm. Then, the wear amount and the maximum crack depth of the die pressing surface were examined.

The results are shown in Table 2. As is clear from this, in the case of the present invention examples (No. 1 to 10) having the chemical composition, matrix structure and hardness defined by the present invention, the wear amount (allowable amount 2 mm)
Is less than 1 mm and the maximum crack depth is less than 16 mm. On the other hand, the chemical composition, base structure, and
Comparative example (No. 11 to 2) that does not satisfy any one or more of hardness
In the case of 0), the maximum crack depth is significantly deeper than that of the examples of the present invention, and there are some in which the wear amount is significantly large. From this, it is understood that the mold of the present invention has both excellent wear resistance and heat crack resistance.

(Effects of the Invention) As described above, the mold of the present invention has excellent wear resistance and heat crack resistance, so that it can be used for a long period of time, reducing the mold cost and improving the slab width sizing efficiency. Can greatly contribute to

[Brief description of drawings]

FIG. 1 is a diagram showing a state in which a hot slab is pressed down by a mold. 1 is a mold, 2 is a parallel surface, 3 is an inclined surface, and S is a slab.

Continuation of the front page (56) Reference JP-A-57-82458 (JP, A) JP-A-54-118323 (JP, A) JP-A-63-252633 (JP, A) JP-A-63-252634 (JP , A) JP 63-212029 (JP, A) JP 39-3556 (JP, B1)

Claims (1)

[Claims] 1. By weight%, C: 0.01 to 0.35%, Si: 0.1 to 1.5%, Mn: 0.2 to 1.5%, Ni: 2% or less, Cr: 1.0 to 3.0%, Mo: 0.2 to 1.0%, V: 0.1 to 0.6%, the balance consisting of Fe and unavoidable impurities, the base structure is bainite, and the HS hardness is 30 to 50. Type.