KR20100124517A - Press roll strengthened by carbide - Google Patents

Abstract

PURPOSE: A carbide strengthened press roll which has excellent abrasion resistance and anti-corrosion is provided to secure the abrasion resistance of a rolling roll by heat-treating expensive alloy elements. CONSTITUTION: A carbide strengthened press roll comprises an outer layer material. The outer layer material made from C of 2.8-3.5wt%, Ni of 3.5-5.0wt%, Mn of 0.3-1.5wt%, Si of 0.5-2.0wt%, Cr of 0.5-2.5wt%, V of 0.001-6.0wt% and the residue part Fe. The phase configuration of the outer layer material is cementite of 25-35% and graphite of 2-4%.

Description

Press roll strengthened by carbide

The present invention relates to a carbide reinforced rolling roll, and more particularly to a carbide reinforced rolling roll having excellent toughness and wear resistance.

Hot rolled rolling rolls in hot rolling mills have a direct impact on the quality of the rolled product and the manufacturing cost. Especially, the surface roughness and wear damage of the rolled roll directly affect the surface quality, dimensions and shape of the product. In addition, wear resistance is required.

The material of rolling rolls is constituent graphite cast iron roll (DCI roll, Ductile cast iron roll), Adamite roll, Ni-grain cast iron roll, high chromium cast iron roll, high speed steel roll (HSS roll, high speed steel roll).

Among them, high-speed steel roll is mainly used for hot rolling because of its excellent wear resistance and roughness. However, high-speed steel rolls have a problem in that sticking phenomenon occurs frequently due to deterioration of lubricity and adsorption of the rolled material on the roll surface.

In addition, even if the high speed steel roll solves the sticking phenomenon, the manufacturing cost increases due to the securing of thermal fatigue resistance and abrasion resistance by adding expensive alloy elements such as Mo and V.

Therefore, in recent years, in order to improve the physical properties of rolling rolls, the base structure is made into austenite single phase and then rapidly cooled to the martensite transformation temperature, and then the constant temperature heat treatment is performed at this temperature to martensify the base structure and cool it to room temperature The method of securing wear resistance is applied.

However, the method also improves the mechanical properties, but the manufacturing cost is increased by performing a complex heat treatment, there is a problem that is not effective for practical application in the field.

The present invention is to solve the conventional problems as described above, it is an object of the present invention to provide a carbide reinforcement rolling roll that satisfies abrasion resistance and toughness at the same time through the optimum alloy design.

According to a feature of the present invention for achieving the above object, the present invention is C: 2.8 ~ 3.5wt%, Ni: 3.5 ~ 5.0wt%, Mn: 0.3 ~ 1.5wt%, Si: 0.5 ~ 2.0wt%, Cr : 0.5 to 2.5 wt%, V: 0.001 to 6.0 wt% and the outer layer material having an alloy composition of the balance Fe and other unavoidable impurities.

In the phase structure of the outer layer material, 25 to 35% of cementite and 2 to 4% of graphite are produced in the martensite matrix.

The content of Si and Cr satisfies the formula Si / Cr = a * V (%) + b.

A is 0.34 to 0.7.

B is 0.4 to 0.7.

The present invention solves the problem that the amount of graphite decreases when carbide is increased in the alloy designing the content of Si and Cr in the range satisfying the formula Si / Cr = a * V (%) + b. Therefore, there is a useful effect to ensure both wear resistance and toughness of the rolling roll.

In addition, the present invention can secure the wear resistance of the rolling roll without adding an expensive alloy element or a separate heat treatment to ensure wear resistance. Therefore, there is a useful effect of reducing the manufacturing cost of the rolling rolls.

Hereinafter, a preferred embodiment of the carbide reinforcement rolling roll according to the present invention will be described in detail.

Rolling roll of the present invention is C: 2.8 ~ 3.5wt%, Ni: 3.5 ~ 5.0wt%, Mn: 0.3 ~ 1.5wt%, Si: 0.5 ~ 2.0wt%, Cr: 0.5 ~ 2.5wt%, V as the outer layer material : 0.001 ~ 6.0wt% and remainder alloy composition of Fe and other unavoidable impurities.

The phase composition produces 25-35% of cementite and 2-4% of graphite in the martensite matrix.

Cementite aims at improving wear resistance. If cementite is less than 25%, the effect of improving the wear resistance is insufficient, and if it exceeds 35%, the occurrence of thermal fatigue crack may increase.

Graphite acts as a hole to stop surface cracks when cracking occurs, and as a lubrication to prevent sticking phenomenon that a part of the rolled material adheres to the roll surface, and has an effect of suppressing thermal cracking phenomenon due to thermal shock.

The principle that graphite is produced in the martensite matrix is shown in FIG. 1. That is, a molten metal having a carbon content of 2.8 to 3.5 wt% solidifies from L (liquid) to L (liquid) + γ (austenite), and then L (liquid) + γ (austenite) to L (liquid) MC carbide forms in the austenite matrix by solidifying part of the liquid phase with) + γ (austenite) + MC. After the process reaction, L (liquid phase) + γ (austenite) + MC is finally solidified into L (liquid phase) + γ (austenite) + MC + Fe ₃ C (cementite) + Gr (graphite). Graphite is crystallized by cementite and graphite depending on Si and Cr content.

If the Si content is high, the crystallization amount of graphite is increased, on the contrary, if the Cr content is high, the cementite crystallization amount is high and the graphite amount is relatively low. After the final solidification is completed, austenite is transformed to martensite during cooling to room temperature under the influence of Ni.

As a result, the solidified tissue is a structure in which cementite, graphite, and carbide are defined on the martensite base as shown in FIG. 1.

 Specifically, in the present invention, V is added to improve wear resistance, and Si and Cr are added as alloying elements to induce graphite production.

V extracts fine VC carbide (= MC carbide) into the matrix to improve wear resistance. However, as V increases, the amount of graphite decreases relatively. Reducing the amount of graphite decreases the toughness of the rolling rolls, thereby increasing the amount of excessive thermal fatigue cracks, thereby increasing the risk of roll breakage.

Therefore, Si and Cr are added to the inoculant to secure the graphite area. Graphite is produced in 2-4% to ensure lubrication and crack resistance.

If graphite is produced at less than 2%, the effect is insignificant, and it is virtually difficult to exceed 4% in the steel to which V is added, and to exceed 4%, the content of V must be reduced, leading to a decrease in wear resistance.

Abrasion resistance is ensured by adding V, but the content of Si and Cr is added in a range satisfying the formula Si / Cr = a * V (%) + b so that the amount of graphite is generated 2-4%. Here, a is set as a variable value between 0.34 and 0.7, and b is set as a constant value between 0.4 and 0.7.

As Si content increases, graphite amount increases, and when Cr content increases, graphite amount decreases. As a result, the relation between the Si / Cr ratio and V is derived in a range in which the graphite amount is 2% or more. As shown in FIG. 3, the relational expression is obtained by experiment.

In the relational expression, the slope a, which is a variable value, is less than 0.34, and the graphite content is less than 2%.

b is a constant value considering the cooling rate according to the thickness of the rolling roll is less than 0.4, the rolling roll can be easily broken during rapid cooling and the amount of graphite is also produced less than 2%. In addition, when b exceeds 0.7, graphite is produced by 2% or more, but it is difficult to secure martensite base during slow cooling.

In addition, in the present invention, Ni is added in the range of 3.5 to 5.0 wt% to shift the CCT curve to the right. This makes the martensite transformation easy by delaying the transformation even when the rolling roll is cooled at room temperature to suppress pearlite growth.

As described above, the molten metal for the outer layer material which is optimized in the alloy composition and satisfies the formula Si / Cr = a * V (%) + b is injected into the centrifugal casting mold, and then the molten metal for the inner layer material of the outer layer material is injected to roll the roll. Manufacture. At this time, the molten metal is injected into the centrifugal casting mold, and when the injection is completed, the centrifugal casting mold is separated from the centrifugal casting apparatus and cooled at room temperature.

For reference, the cooling rate of the above-mentioned rolling roll refers to the cooling rate according to the thickness of the rolling roll, and the cooling rate is slow when the rolling roll is thick, and the cooling rate is fast when the thickness of the rolling roll is thin, so The a value and the b value of Si / Cr = a * V (%) + b are set.

In this case, as the inner layer material, spherical graphite cast iron may be used, and a detailed description thereof will be omitted since its components are well known.

Hereinafter, the function and content of the alloying elements of the present invention are as follows.

2.8 ~ 3.5wt% of carbon

Carbon is an essential element that improves wear resistance mainly by bonding with alloying elements of V and forming VC carbides. Carbon that does not bond with alloying elements is mainly dissolved in the base or extremely finely precipitated to strengthen the base.

When carbon is less than 2.8 wt%, sufficient abrasion resistance cannot be obtained due to insufficient amount of VC carbide. When carbon is more than 3.5 wt%, carbides become excessive and heat cracking resistance of the outer portion of the roll deteriorates. Therefore, the content of carbon is preferably 2.8 to 3.5 wt%.

Nickel (Ni) 3.5 ~ 5.0wt%

Nickel has the effect of increasing the hardenability and stabilizing the strength after quenching. In particular, in the present invention, the transformation is delayed so that pearlite formation is suppressed.

If the nickel is less than 3.5wt%, these effects are inadequate. If the nickel is more than 5.0wt%, the residual austenite phase increases, causing cracking and poor roughness.

Manganese (Mn) 0.3 ~ 1.5wt%

Manganese has a function of fixing deoxidation of molten metal and sulfur, which is an impurity, with MnS. If the manganese is less than 0.3 wt%, these effects are not sufficient. If the manganese is more than 1.5 wt%, residual austenite tends to be formed, and the hardness is not kept stable, and wear resistance tends to deteriorate.

Silicon (Si) 0.5 ~ 2.0wt%

Silicon makes iron and solid solution and promotes graphite production. That is, silicon decomposes cementite (Fe ₃ C) to promote graphitization. If silicon is less than 0.5wt%, graphite is insufficient, and if it is more than 2.0wt%, graphite is excessively produced, making it difficult to secure high hardness of the outer layer of the rolling roll.

Chromium (Cr) 0.5 ~ 2.5wt%

Not only is chromium dissolved in the base to increase hardenability, but also some bond with carbon to precipitate as an extremely fine carbide and strengthen the base.

If the amount of chromium is less than 0.5 wt%, the effect is insignificant. If it exceeds 2.5 wt%, carbides other than VC carbides (for example, M7C3) are formed in excess, resulting in a small volume of hard VC carbides. Since M7C3 is softer than VC, the wear resistance of the outer layer is reduced.

Vanadium (V) 0.001 ~ 6.0wt%

Vanadium is an element that combines with carbon to form VC carbides. Vanadium produces a large amount of VC carbide in the outer layer of the rolling roll to improve wear resistance.

If the vanadium is less than 0.001 wt%, its effect is insignificant. If it exceeds 6.0 wt%, the VC carbide is crystallized as a primary tablet, so that the amount of carbide is increased, resulting in deterioration of rough resistance. In addition, since the specific gravity of the VC carbide is much smaller than that of the molten metal, the distribution is biased on the inner surface of the outer layer, resulting in a heterogeneous material.

The present invention includes the components of the alloy steel, the remainder is Fe and unavoidable elements, which are contained according to the situation of raw materials, materials, manufacturing facilities, etc., allowing fine incorporation of inevitable impurities such as oxygen of 0.01 wt% or less. Can be.

Hereinafter, the above-described carbide reinforcement rolling roll will be described in comparison with Examples and other comparative examples.

Table 1 shows the component ratio and the graphite area according to the embodiment of the present invention and the comparative example.

The molten metal having the components of Examples and Comparative Examples of Table 1 was injected into a centrifugal casting mold, and another molten metal for preparing an inner layer material (component not shown) was additionally injected and then solidified at room temperature to prepare a rolling roll. Then, the graphite area of the outer layer material was measured.

In alloy composition, carbon is 2.8 ~ 3.5wt%, nickel is 3.5 ~ 5.0wt%, manganese is 0.3 ~ 1.5wt%, and the balance is composed of Fe. In this case, since it is to measure the amount of graphite produced according to the relationship between Si, Cr, and V, specific contents of the remaining compositions are not presented.

division
Chemical composition (wt%)
Indices
Si Cr V Si / Cr Graphite area (%) Hardness
(HsD) Wear resistance
(ship) Remarks Comparative Example 1 0.85 1.88 0.00 0.45 3.50 80 One Abrasion Resistance ↓ Comparative Example 2 0.85 1.88 0.50 0.45 1.90 80 1.1
Graphite area
Less than 2%
Comparative Example 3 1.10 1.70 1.00 0.65 1.50 78 1.2 Comparative Example 4 1.60 1.60 3.00 1.00 1.20 81 1.5 Comparative Example 5 1.80 1.50 4.00 1.20 1.10 82 2 Example 1 1.10 1.75 0.50 0.63 3.50 78 1.1
Graphite area
2-4%
Si / Cr = a * V + b
a = 0.35
b = 0.46 Example 2 1.30 1.60 1.00 0.81 3.10 79 1.2 Example 3 1.60 1.40 2.00 1.14 3.20 80 1.3 Example 4 1.80 1.20 3.00 1.50 2.80 81 1.5 Example 5 2.05 1.11 4.00 1.84 2.70 82 2 Example 6 2.40 1.10 5.00 2.18 2.60 83 2.5

[HsD: Measured by Shore Hardness Tester, Hardness Range of Roll: HsD 77 ~ 83]

Here, the wear resistance is measured by using an abrasion resistance tester to determine how many times the wear resistance of Comparative Examples 2 to 5 and Examples 1 to 6 based on Comparative Example 1.

Referring to Table 1, Comparative Example 1 has a graphite area of 3.50%, which satisfies 2% or more, but has low abrasion resistance due to no carbide formation due to V addition.

In Comparative Examples 2 to 5, the graphite area was less than 2%, but the wear resistance of V was increased, but graphite was less than 2%.

Examples 1 to 6 had a graphite area of 2% or more, and were also excellent in wear resistance. Deriving a relational expression based on the results of Examples 1 to 6 yields Si / Cr = a * V (%) + b (a is 0.35, b is 0.46).

That is, it can be seen that graphite area and wear resistance are related to the relationship between Si, Cr, and V.

2 and 3, the graphite area decreases as the content of V increases, and the content of V and the formula Si / Cr = a * V (%) + b (a is 0.34 ~ 0.7, b is 0.4 ~ 0.7), it can be seen that the graphite is divided into a region of less than 2% and a region of 2% or more.

Accordingly, referring to the tissue photograph of FIG. 4, in Comparative Example 3 and Comparative Example 5, graphite is produced in less than 2%, whereas the tissue photographs of Examples 1, 2, and 5 satisfying the above-described relational expressions. In more than 2% of the graphite produced.

That is, it can be seen that both the wear resistance and toughness of the rolling roll can be secured by designing the alloy in a range in which the Si and Cr contents satisfy the formula Si / Cr = a * V (%) + b.

Within the scope of the basic technical idea of the present invention, many other modifications are possible to those skilled in the art, and the scope of the present invention should be interpreted based on the appended claims. will be.

1 is a schematic view showing the principle of the production of graphite in the martensite matrix.

2 is a graph showing the graphite area according to V addition.

3 is a graph showing graphite area according to the relationship between V addition and Si / Cr ratio.

Figure 4 is a 30 times microscope micrograph showing the microstructure of the rolling roll outer layer material prepared by the alloy composition of Table 1.

Claims (5)

C: 2.8-3.5wt%, Ni: 3.5-5.0wt%, Mn: 0.3-1.5wt%, Si: 0.5-2.0wt%, Cr: 0.5-2.5wt%, V: 0.001-6.0wt% and balance Fe Carbide reinforced rolling rolls, characterized in that the outer layer having an alloy composition of the other unavoidable impurities. The method according to claim 1, The phase structure of the outer layer material is carbide reinforcement rolling roll, characterized in that 25-35% cementite, 2-4% graphite is produced in the martensite matrix. The method according to claim 1 or 2, Carbide-reinforced rolling rolls, characterized in that the content of Si and Cr satisfies the formula Si / Cr = a * V (%) + b. The method according to claim 3, Carbide reinforced rolling roll, characterized in that a is 0.34 ~ 0.7. The method according to claim 3, B is a carbide reinforcement rolling roll, characterized in that 0.4 ~ 0.7.

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