JPH03403A - Die for sizing width of hot slab - Google Patents

Abstract

PURPOSE:To prolong the life of a die without using cooling water and to give excellent wear resistance and heat cracking characteristic by specifying the contents of C, Si, Mn, Ni, Cr, Mo, Nb, N in the composition of the die and the hardness. CONSTITUTION:The chemical composition by weight % of a width sizing die for a hot slab is composed of 0.10-0.35% C, 0.1-1.5% Si, 0.2-1.5% Mn, <=1.0% Ni, 0.8-2.5% Cr, 0.2-1.5% Mo, 0.1-0.8% Nb, 0.01-0.10% N, the sum of more than one of V, Ti, <=0.8% Zr and the balance Fe and inevitable impurities. An adequate heattreatment is given to this die to obtain Shore hardness HS 37-48. If necessary, <=0.2% Ce, and <=0.2% B are contained. Since this die has a long life without cooling such as watering, etc., the sizing cost can be reduced.

Description

Detailed Description of the Invention (Industrial Application Field) This invention is for sizing hot slabs used when manufacturing slabs of a predetermined width by reducing the width of hot slabs over their entire length using a press working method. Regarding molds.

(Prior Art) Recently, there are many types and sizes of steel sheets, and in particular, there are many different sizes. If a slab suitable for the size of the steel plate can be easily supplied to the steel plate rolling process, the process can be simplified and the yield can be improved.

Therefore, various methods of manufacturing slabs with different widths have been proposed. For example, how to change mold convergence during continuous casting,
This method includes width reduction using a vertical rolling mill. Among these methods, the press method, as shown in Fig. 1, involves moving a mold 1, which has a surface 2 parallel to the side surface of the slab S and a surface 3 inclined thereto, back and forth, and presses the side surface of the slab S for sizing. It is. Since this method is more efficient than methods that involve changing the width of the mold or using a vertical rolling mill, it has recently come into widespread use. However, in this method, the contact time between the mold and the slab is long, which causes the mold temperature to rise abnormally, causing wear and heat cracks on the pressing surface of the slab, significantly shortening its life. As a result, there are problems in that the mold cost increases, the sizing cost increases, and the frequency of mold replacement increases, making it difficult to improve sizing efficiency.

Therefore, the mold is cooled with cooling water to extend its life. For example, a. Cooling method by spraying water on the pressing surface of the mold This is a method of spraying a large amount of cooling water on the pressing surface of the mold during pressing. However, with this method, the slab is locally supercooled, which has a negative effect on its quality.Also, there is another method of spraying water after pressing the previous slab and before the next pressing. Since the temperature of not only the surface but also the inside of the object has been raised by the previous pressing, it is not possible to cool it sufficiently with water sprinkling in a short time, and with this method, only the surface is rapidly cooled and the temperature difference with the inside becomes large , there is a problem that heat cracks occur due to thermal stress.

b. Cooling method by passing water inside the mold This is a method in which a water channel is created inside the mold and cooling water is passed through it. However, with this method, water is passed through a mold that reciprocates at high cycles, which increases the equipment cost and increases the size of the equipment.
The problem is that maintenance is time-consuming and cooling efficiency is poor.

(What the invention is trying to solve!i!II) The purpose of this invention is to extend the life of a mold by improving the mold material itself, without relying on cooling water, to achieve excellent wear resistance and heat crack resistance. An object of the present invention is to provide a mold for sizing the width of a slab.

(Means for solving the problem) When width sizing a hot slab by pressing, abrasion and cracks occur on the mold surface. As a result of various studies on how to prevent this, the inventor has found the following knowledge. I got it. In other words, (1) In order for molds that are subjected to high heat loads with surface temperatures as high as 700°C to have both wear resistance and heat crack resistance, the material must be low-alloy steel with high high-temperature strength. be.

(2) Strengthening grain boundaries is the most effective way to increase the high-temperature strength of low-alloy steel, and this can be achieved by precipitating NbN at grain boundaries.

(3) In order for the mold to have high performance and well-balanced wear resistance and heat crack resistance, the Shore hardness HS needs to be 37 to 4 days.

This invention was made based on the above findings, and the gist thereof is as follows.

That is, the first invention is a mold for sizing the width of a hot slab, the chemical composition of which is C:O, lO~0 by weight%.
．． 35%, Si: 0.1-1.5%, Mn: 0.
2 to 1.5%, Nt: t, o% or less, Cr: 0
．． 8-2.5%, Mo: 0.2%-1.5%,
Nb: 0.1-0.8%, N: 0.01-0.
10%, and the total of one or more of V, TI, and Zr is 0.8% or less, the balance is Fe and unavoidable impurities, and the width of the hot slab has a Shore hardness HS of 37 to 48. A mold for sizing, the second invention further contains 0.2% by weight in addition to the components of the mold described above.
This is a mold for sizing the width of a hot slab containing one or both of the following Ce and 0.2% by weight or less of B.

(Function) The reason for limiting the chemical composition of the mold of the present invention and the reason for keeping its hardness within a predetermined range will be explained below.

c: o, to ~0.35% C is a carbide-forming element, and combines with Cr and V to enhance wear resistance. If the content is less than 0.1%, the amount of carbide produced is insufficient and the wear resistance is low, while if it exceeds 0.35%, the carbide becomes coarse and the heat crack resistance is reduced.

Therefore, C should be 0.10 to 0.35%.

Si: 0.1 to 1.5% St is contained in order to deoxidize the molten metal and improve swirling flow. However, if it is less than 0.1%, the effect cannot be obtained, and if it exceeds 1.5%, the base will become weak and the heat crank resistance will deteriorate, so the content should be 0.1 to 1.5%. do.

Mn: 0.2-1.5% Mn is contained together with Si for deoxidation, but 0.2%
If it is less than 1.5%, sufficient deoxidizing effect cannot be obtained, and if it exceeds 1.5%, brittleness will decrease, so the content should be 0.2 to 1.5%.
%.

Ni: 1.0% or less Ni has the effect of improving the matrix structure even with a small amount of content. However, if the content exceeds 1.0%, the structure stability at high temperatures will deteriorate, so the content should be 1.0% or less.

Cr: 0.8 to 2.5% Cr combines with C to form a highly hard chromium carbide to improve wear resistance. However, if the content is less than 0.8%, the effect will be small, and if the content exceeds 2.5%, brittle eutectic carbides will crystallize, impairing heat crack resistance. Therefore, its content should be 0.8 to 2.5%.

Mo: 0.2-1.5% Mo is dissolved in the matrix and improves high-temperature properties such as high-temperature softening resistance. However, if it is less than 0.2%, the effect is small;
On the other hand, even if the content exceeds 1.5%, a corresponding effect cannot be obtained, so the content is set to 0.62 to 1.5%.

Nb: 0.1 to 0.8% Nb is an important element that characterizes this invention, and combines with N to precipitate at grain boundaries as nitride, thereby strengthening the grain boundaries. It works to significantly increase strength, especially at high temperatures. In addition, it combines with C to precipitate high-hardness carbides to improve wear resistance, and also improves heat crack resistance by making crystal grains finer.

However, if it is less than 0.1%, these effects are small;
．． If it exceeds 8%, nitrides and carbides become coarse and deteriorate wear resistance and heat crack resistance, so the content is set to 0.1 to 0.8%.

N: 0.01 to 0.10% N combines with C and Nb to form carbonitrides and increases high-temperature strength. If the content is less than 0.01%, the effect will be small, and if it exceeds 0.1%, carbonitrides will increase and become coarse, deteriorating heat crack resistance.
．． Make it 10%.

V, Tl, Zr: The total content of one or more of these is 0.8% or less. These elements not only refine crystal grains and improve heat crack resistance, but also precipitate fine carbides in the matrix to improve wear resistance. However, if the total amount exceeds 0.8%, the carbides become coarse and mechanical properties deteriorate.

Ce: 0.2% or less Ca, when contained in a small amount, significantly increases the high-temperature strength, but if it is contained in an amount exceeding 0.2%, mechanical properties are degraded, so the content should be lower than that.

B: 0.2% or less B segregates at grain boundaries, strengthens the grain boundaries, and increases high-temperature strength. However, if it exceeds 0.2%, the heat crack resistance decreases, so it should be set to 0.2% or less.

P and S: Both of these are unavoidably contained and lead to embrittlement of the material, so it is better to have less of them.However, if the content of either of them is 0.8% or less, it will not have such a negative effect, so it should be avoided. It is preferable to do the following.

The mold of the present invention is characterized by having a Shore hardness (HS) of 37 to 48.

The explanation will be given below. FIG. 2 is a graph showing the relationship between Shore hardness, wear amount, and heat crack of each test material in Examples described later. As is clear from this figure, if the Shore hardness is in the range of 37 to 4 days, the amount of wear (marked by O) is small and the heat cracks (marked by Δ) are shallow, that is, both wear resistance and heat crack resistance are excellent. ing.

By the way, the Shore hardness is within the above range (HS: 37-48
), it is sufficient to apply appropriate hot rolling and processing to a mold having the above chemical composition, specifically, 900'C to 1.05
The HS can be kept within the above range by quenching at 0°C and tempering at 400°C to 670°C to make the base structure pearlite, bainite, martensite, or a mixed structure thereof.

(Example) Hereinafter, the mold of the present invention will be explained based on an example. 1st
A mold having the chemical composition shown in the table is quenched (oil-cooled from 950°C) and tempered (air-cooled from 650°C).
The hardness (HS) shown in the table was made, and this mold (parallel length: 50 Chgm, thickness = 40 axis - 1 slope angle =
12 degrees) manufactured by continuous casting
0 ■ Laying thickness 250~270a+m, length 6.9~9.4
50 slabs of carbon steel with m% temperature of approximately 1,200"C
0 toshi was sized with a width reduction of 100 to 350 cm, and the amount of wear on the pressing surface of the mold and the depth of heat cracks were examined. The results are shown in Table 2. As is clear from this table, the molds of the invention examples (Nos. 1 to 8) have a small amount of wear and a shallow heat crack depth, that is, they have excellent wear resistance and heat crack resistance. Both properties are very good. On the other hand, a comparative example (9) whose chemical composition deviates from the scope of the present invention
- 17), one or both of the wear resistance and heat crack resistance is poor, and the comparative example N
o. In 9.10.17, the Shore hardness is within the range specified by the present invention, but the chemical composition is out of range, so the wear resistance or heat crack resistance is poor. As a result, both the chemical composition and the Shore hardness are Excellent wear resistance and heat crack resistance can only be obtained by satisfying the following.

(Hereinafter, blank spaces) (Effects of the Invention) As explained above, the mold of the present invention has extremely excellent wear resistance and heat crack resistance. Therefore, it has a long service life even without cooling such as water sprinkling, so it is possible to reduce sizing costs and significantly increase productivity.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the state in which a slab is pressed by a mold, and FIG. 2 is a diagram showing the relationship between the Shore hardness of the mold, the amount of wear, and the depth of heat cracks.

Claims (2)

[Claims] (1) A mold for sizing the width of hot slabs, the chemical composition of which is in weight percent: C: 0.10 to 0.35%, Si: 0.1 to 1.5%,
Mn: 0.2 to 1.5%, Ni: 1.0% or less, Cr:
0.8-2.5%, Mo: 0.2%-1.5%, Nb:
0.1 to 0.8%, N: 0.01 to 0.10%, and further 0.8% in total of one or more of V, Ti, and Zr
Hereinafter, a mold for sizing the width of a hot slab is characterized in that the remainder consists of Fe and unavoidable impurities, and has a Shore hardness HS of 37 to 48. (2) In addition to the components of the mold for sizing the width of a hot slab as described in claim 1, one or more of Ce in an amount of 0.2% by weight or less and B in an amount of 0.2% by weight or less. A mold for width sizing of hot slabs characterized by containing seeds.