JPH02232338A - Roll material having excellent wear resistance - Google Patents

Abstract

PURPOSE:To obtain the roll material having excellent wear resistance at the time of hot rolling by using a steel material or a cast iron material contg. specified amounts of Mo, V and Cr as the outer layer material of a composite roll for hot rolling. CONSTITUTION:Alloy iron having the compsn. contg., by weight, 1.5 to 2.5% C, 0.2 to 1.5% Si, <1.5% Mn, 6 to 10% Mo, 3 to 10% V, 3 to 8% Cr and the balance Fe is used as the outer layer material of a composite rolling roll used at the time of subjecting a steel material or the like to hot rolling. Since the content of C is reduced as compared with that in a roll material made of high alloy cast iron which has conventionally been used, the brittleness in the matrix structure is reduced, toughness is made excellent and chipping is not generated in the use, and since hard double carbide of V, Mo, Cr, etc., is dispersedly present in the matrix having toughness, the composite roll for rolling having high hardness and excellent wear resistance and having prolonged service life can be obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a roll material that is applied to a rolling layer of a rolling composite roll that is mainly subjected to hot rolling.

(Prior art) Composite rolls are used for hot rolling rolls, especially work rolls in the first stage of hot strip mill finishing, in which a high chromium roll material with good wear resistance is used for the outer layer used for rolling. . However, in recent years, demands on the cross-sectional shape and dimensional accuracy of hot-rolled steel sheets have become stricter, and in order to meet these demands, it is necessary to further improve the wear resistance of the rolls.

(Problem to be solved by the invention) The high chromium roll material has a C: 2.0 to 3.2 w
t%, Cr:1O to 30 wt%, and a large amount of highly hard MtCz type chromium carbide is produced in the structure, and has good wear resistance and roughness resistance. However, as mentioned above, since the carbon content is high and the amount of carbon in the base structure is also high, the base structure is relatively brittle and has the disadvantage of being prone to chipping. The chipping occurs when a small piece with a width and length of about 1 m and a depth of about 1 m peels off from the roll surface during rolling. When such chipping occurs, the peeled portions are transferred to the surface of the rolled material (steel plate) as convex portions at regular intervals, and are rolled down by the next roll, which not only deteriorates the surface quality of the steel plate but also deteriorates the coiling process. During processing or processing of a steel plate, the convex rolled portion becomes a starting point for cracking, resulting in the occurrence of defective products. In addition, the life of the roll will be significantly shortened. The present invention was made in view of the above-mentioned problems, and an object of the present invention is to provide a roll material having superior wear resistance compared to high chromium roll materials.

(Means for Solving the Problems) The roll material of the present invention made to achieve the above object has a chemical composition of C: . 1.5-2.5%, Mo: 6-10
%Si: 0.2-I. 5%, v: 3~
IO %Mn: 1.5% or less, Cr: 3
The composition of the invention is such that the balance of ~8% consists essentially of Fe.

(Function) The chemical composition of the roll material of the present invention is limited for the following reasons. The unit is weight%. C:I. 5 to 2.5% C combines with Crs Mo and V to form various carbides with high hardness and improve wear resistance. If it is less than 1.5%, the amount of carbide will be too small and the wear resistance will be insufficient;
If it exceeds this value, a large amount of primary carbide crystallizes directly from the molten state during casting, resulting in a decrease in toughness.

Si: 0.2-1.5% Si is an element necessary for deoxidizing the molten metal, and also improves the flow of the molten metal, so it is added to improve castability. Furthermore, it has the function of reducing the quenching temperature sensitivity and improving the secondary hardenability due to the precipitation of Mo and ν special carbides. on the other hand,
If it exceeds 1.5%, the material becomes brittle.

Mn: 1.5% or less Mn is added to deoxidize and desulfurize the molten metal.

It also improves hardenability and wear resistance, but 1
．． If it exceeds 5%, the austenite crystal grains become coarse, which may cause cracking during hardening, which is not preferable.

Cr: 3-8% Cr partially forms a solid solution in the base structure, improves the hardenability of the base, and improves wear resistance. It also combines with C to form a highly hard carbide, further improving wear resistance. If it is less than 3%, the amount of carbide is small and wear resistance is poor, and if it exceeds 8%,
Since the amount of carbides becomes excessive, toughness decreases.

Mo: 6-10% Mo improves the hardenability of the matrix structure. Particularly when added in a large amount as in the material of the present invention, it combines with C to form fine MozC-type carbides, improving wear resistance. If it is less than 6%, the amount of carbide is small, resulting in poor wear resistance, and if it exceeds 10%, the amount of carbide becomes saturated, resulting in a cost disadvantage. Furthermore, supersaturated dissolved No stabilizes the retained austenite in the matrix, making it difficult to obtain sufficient hardness. ■ = 3~1O% V makes the casting structure fine and dense and strengthens the matrix. It also combines with C to form high hardness glue carbide. Since the carbide is formed in finely dispersed form in the structure, it improves wear resistance. The range of C content of the present invention (1.5 to 2.
In order to obtain the above effect of V at 5%), it is desirable to add 3% or more of V. On the other hand, if it exceeds 10%, the effect is saturated and the material becomes brittle. In addition to the above-mentioned components, the roll material of the present invention contains substantially Fe.
is formed. Incidentally, P1S makes the material brittle, so it is desirable to have less P1S. P: less than 0.05%, S
: o. It is best to keep the os% drop.

The roll material of the present invention has excellent wear resistance by actively adding Mo, Cr, ν, etc., which improve the hardenability of the base structure and form highly hard carbides while keeping the C content low. It is a high alloy cast material.

Therefore, this roll material has a lower C content than conventional high chromium roll materials, but while conventional rolls have a structure mainly composed of Cr carbide, this roll material has a structure mainly composed of Cr, MoS.
V produces various forms of high-hardness double carbide in the base fibers, thereby improving wear resistance.
On the other hand, since the above-mentioned base structure also has a low C content, its toughness is improved, and together with the formation of the above-mentioned double carbide, the occurrence of the above-mentioned structure chipping is prevented, and as a result, the roll life can be significantly improved. can.

In addition, since the cast material does not contain particles with particularly high specific gravity, gravitational segregation of single-series carbides does not occur during centrifugal casting, and after melting, fine carbides are produced without the need for a forging process. It is possible to obtain a cast structure in which the particles are uniformly dispersed.

(Example) The roll material of the present invention described above is mainly used as a cast material for the outer layer, which is the layer used in composite rolls for hot rolling. A tough cast iron material such as cast iron or a cast steel material such as graphite cast steel is used as appropriate.

In addition, as a manufacturing method for the composite roll, after casting the outer layer by centrifugal force casting, a centrifugal force casting mold containing the outer layer is stood up to form a stationary mold, and the inner layer material molten metal is placed inside the stationary mold. There is a method of pouring molten metal and welding the outer layer and the inner layer together, and this method is commonly used because it is simple.

In addition, when welding the outer layer and the inner layer, the C from the outer layer to the inner layer
In order to prevent mixing of alloying elements such as r, Mo, and V, it is preferable to provide an intermediate layer between the outer layer and the inner layer. By providing the intermediate layer, Cr, M is transferred from the outer layer to the inner layer.
In addition to preventing the mixing and diffusion of alloying elements such as O and V,
This is because embrittlement at the boundary between the outer layer and the inner layer can be effectively prevented.

After casting, the composite roll is usually subjected to the following heat treatment. First, after heating and holding at a high temperature above point A, a quenching treatment is performed to remove the coarse and low strength austenite structure.
Fine and strong base structure (martensite and paynite)
transform into. Further, secondary hardening is performed by precipitation of special carbides from the base structure, and tempering treatment is performed to decompose residual austenite. By performing the above heat treatment, a predetermined hardness can be imparted to the roll outer layer.

The roll material in the present invention refers not only to the hot rolling roll described above, but also to outer layer materials such as cold rolling rolls, hot skin pass rolls, and rolls for H-shaped steel, as well as rollers in rolling equipment. is also an applicable material. For example, it can be applied as an outer layer material of a hollow cylindrical roller such as a hot run table roller.

Next, a specific manufacturing example of a composite roll in which the roll material of the present invention is applied to the outer layer, which is the layer used for rolling, will be described. still,
For comparison, we also manufactured a composite roll using a conventional high chromium cast iron material for the outer layer as a conventional example.

(2) A Mo-based high alloy material shown in Table 1 was used as the outer layer molten metal, and this was cast into a cylindrical mold rotating on a centrifugal casting machine to a casting thickness of 60 cylinders. At this time, the inner surface of the mold is coated with a coating material made of zircon sand to a thickness of 3 cylinders, and the rotation speed of the mold is GNO. So 1401 pouring temperature is 1500
It was °C.

Table 1 ■ Outer layer The outer layer was completely solidified 9 minutes after the start of casting.

Thereafter, a centrifugal casting mold having an outer layer therein was vertically erected, and an upper mold and a lower mold for roll shaft casting were connected to both ends of the mold to form a stationary casting mold. After filling the inside completely with molten ductile cast iron as core material,
The upper part was covered with a riser heat insulator. ■ Three days after casting, the mold was dismantled, the roll material was taken out and machined, and then held at 1050"C for 2 hours, rapidly cooled and quenched to 280°C, and kept at that temperature for 10 hours. After the paynite transformation, it was cooled to room temperature.Furthermore, it was kept at 550'C for 15 hours for tempering treatment, and then cooled from the same temperature to 200°C,
Paynite tempering treatment was carried out by holding for 0 hours and transforming the retained austenite into secondary paynite again.

■ After finishing processing, body diameter 400Mφ, body length 700mmf,
A product with a total length of 1500 mmj2 was obtained. Further, when the hardness of the outer layer of the product was measured, Hs was 86 to 89. On the other hand, the hardness of the outer layer of a roll using conventional high chromium cast iron material was Hs 74-76.

(2) Test piece 1 for wear test was taken from the outer layer of the roll obtained above and subjected to the wear test as schematically shown in FIG. At a test temperature of 25°C, the test bead 1 has a body diameter of 10
A roller 2 made of SS material with a zero body and a body length of 5 mm was rotated at a high speed of 12,000 rpa+ while applying a load of 6 kg and was pressed, and after 30 minutes, the depth of wear on the surface of the test bead 1 was measured. Test beads were also taken from the outer layer of the conventional high-chromium cast iron material and subjected to the same wear test.

As a result of the above wear test, it was confirmed that the roll material of the example was about 3.8 to 4.1 times more excellent in wear resistance than the high chromium cast iron material.

(Effects of the Invention) The roll material of the present invention suppresses C, improves the hardenability of the matrix structure, and forms high hardness carbides.
, Cr, and V are actively added to the cast material, so Mo, C are added to the strong matrix structure with low C content.
It has a structure in which various forms of high-hardness double carbide consisting of r, v, etc. are formed. Therefore, the occurrence of chipping is prevented, and the roll material has extremely superior wear resistance compared to conventional high chromium cast iron roll materials. Incidentally, since the cast material does not include spines, even if it is cast by centrifugal force casting, a healthy cast structure with little segregation and uniformly dispersed fine carbides can be obtained.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing the wear test of this example.

Claims (1)

[Claims] (1) Chemical composition in weight percent: C: 1.5-2.5%, Mo: 6-10%, Si: 0.2-1.5%, V: 3-10% Mn: 1.5% or less , Cr: 3 to 8%, and the remainder substantially consists of Fe. A roll material with excellent wear resistance.