DE2744377C2 - Composite roll, especially for guiding slabs in a continuous casting plant - Google Patents

Description

The invention relates to a composite roll, in particular od for slab guidance in a continuous caster. Like., With two concentric metal layers, of which the outer layer is made of a chrome steel and the Core layer consists of a cast steel and the metal of the outer layer has a lower coefficient of expansion than the metal of the core layer.

The rollers used in a continuous casting plant are in direct contact with the slab, is the temperature of 1000-1300 ⁰ C. The rollers are also exposed to strong radiation in a humid atmosphere for a relatively long time. For this reason, in certain areas of the continuous casting plants, rollers are usually used, the jacket of which is applied and fastened to the journals by welding. These rollers are hollow and are cooled by circulating water. In other areas of the same continuous caster, the roll bodies are also cooled by spray water, the surface temperature of which is lower, which is why the rolls can be made solid.

A major problem with these solid or hollow rolls is the occurrence of circumferential thermal cracks. These cracks arise in the network of thermal fatigue, which the roll surface inevitably already has the very first revolution of the roller. This network, which in the consequence changing bending stresses is subject to the operation of the plant, leads mainly to the formation of circumferential cracks, which become evenly deeper and inevitably lead to breakage of the casing from which the roll barrel consists.

The formation and propagation of the circumferential cracks is due to the almost complete lack of counteracting Internal tensions in the coat back. This jacket, which is made by welding on the hollow tenon is applied, must namely experience a relaxation at high temperature, so that the unfavorable Tensile stresses that always occur in the connection area of the roll projections are relieved.

Another serious problem is the risk of sticking between the product to be processed and the roller. This adhesive effect, which is mainly due to the high slab temperature, 45 can arise from the fact that it is on the roller surface as a result of the humid and warm atmosphere

forming scale adheres only slightly and is not resistant, so that there is sticking between the metal

|| the roller and the product cannot be prevented.

ά From DE-OS 18 14 112, a composite roll is already known, in which the outer layer of a

§ Chrome steel and the core layer consists of a cast steel. This composite roller is used for the purpose of

50 Increase in wear resistance produced in such a way that wires or wires on a cylindrical roller core

jf strips are welded on, which form the chromium steel outer layer, whereupon using

H annealing process can be cut into the roll surface caliber. The by means of build-up welding

applied chrome steel has a coefficient of expansion that differs from that of a

I 'unalloyed steel, of which the core of the composite roll is made, does not differ significantly. Also at

& 55 of this known composite roller, circumferential thermal cracks occur in the roller surface when the

■ The outer layer is exposed to tensile stresses.

The present invention is based on the object of providing a composite roll of the type under consideration in the

Ϊ? Way to improve that the formation and expansion of heat cracks in the roll surface or

fl their outer layer as well as a gluing between the products to be guided by the roller and the

1 * 60 roller surface are reliably prevented.

|: This object is achieved according to the invention by the features specified in the characterizing part of claim 1 solved. Advantageous further developments of the invention are characterized in the subclaims.

As a result of the special material composition of the two concentric metal layers of the invention Composite roller with their significantly different coefficients of expansion and their manufacture of the roller body in the centrifugal casting process, such a compressive prestress is created in the outer layer, that the formation of heat cracks in the outer layer is reliably prevented.

It is true that AT-PS 2 63 835 already deals with the problem of the resistance of a roller to Heat cracks, for which it is proposed to produce a cast iron body and to convert it into a roller shape

forge, which is known in practice under the designation "cylinder NT". It can be next to the Chill and sand casting are also centrifugal casting. However, the roller produced in this way always consists of a single metal layer, with which it is not comparable with the subject of the application.

The composite roll according to the invention «; has the following compared to the previously known rollers of a comparable type Advantages:

- Improved thermal behavior due to the prestress in the outer layer;

- generally higher strength, especially higher resistance to thermal fatigue;

- Presence of an approximately constant pre-tension on the entire roll thickness due to the different expansion coefficients of the core and cladding, from which the desired better ι ο Durability results;

- Ensuring the desired result through the structure achieved by centrifugal casting Metal and the connection of the two adjacent layers;

- low oxidation of the roll barrel at temperatures above 600 ° C, resulting in excellent abrasion resistance leads and prevents sticking to the hot product and

- Problem-free welding of hollow rolls to the journal due to the composition of the inner jacket.

The invention is described below with reference to the drawing. It shows F i g. 1 a hollow roller according to the invention and FIG. 2 shows a solid roller according to the invention.

Fig.! shows a slab guide roll 1, which is provided for a continuous caster and consists of a

Outer layer 11 consists, which forms the roll barrel, and a core layer 12, which is on the two journals

13 is secured by welded joints 14 which run on the roll end faces. The outer layer can make up 20 to 50% of the total thickness.

The two materials a and b, of which the outer layer and core layer are made, have very specific ones

Properties. These two materials that are cast using the centrifugal casting process and are good at the same time Should have adhesive properties, are characterized by the following features:

Metal a: expansion coefficient Aa metal b: expansion coefficient AB

Aa <Ab

Since the heat shrinkage of a on cooling is less than that of b, compressive stresses always occur in the outer rolling zone - regardless of thermal treatment or relaxation - which, if they are sufficiently strong, prevent the formation of circumferential cracks.

Another important feature: metal a does not oxidize up to about 65O ^{0 C;} this temperature can be reached during operation of the roll in the cooling area of a continuous casting device. In addition, the metal b must be excellently weldable with ordinary steel pins.

These characteristics can be achieved simultaneously if a composition with the following percentage Content is chosen, with iron and impurities from the melting process making up the remainder:

C. Si. Mn. Cr. Ni. Mon

a 0.10 to 0.30 0.3 to 1 0.3 to 1 11.5 to 4.5 Obisl 0.50 to 50

b 0.10 to 0.30 0.3 to 0.6 0.3 to 0.6 - - -

Thanks to its high chromium content, metal a does not oxidize and is therefore very resistant to corrosion in the warmth; at the same time it has excellent elastic and plastic properties. The remaining Elements make the metal a sufficiently hardenable that ferrite is avoided. These characteristics represent one special advantage and make the Waize resistant, especially against the effects of strong bending loads or shock load.

The average linear expansion coefficient for a metal at 20 ° C to 600 ⁰ C in the order of 11.5 χ 10- ⁶ mm / mm / ° C. Metal b has a coefficient of linear expansion on the order of 14.2 × 10 ~ ⁶ mm / mm / C in the same temperature range. If the two metals shrink, the minimum shrinkage at medium temperature on a roll barrel with a diameter of 440 mm is approximately - 150 to - 200 N / mm ² , i.e. approximately three to four times the tensile stress due to different bending stress, which ensures excellent resistance to cracking .

As shown in FIG. 1, the welds 13 run in the non-alloyed metal b with a low C content and can therefore be easily carried out. These welded connections withstand relaxation in the plastic area.

F i g. 2 shows a solid roller 2, which consists of an outer layer 21 and a solid core 22. The metal of the outer layer consists of the same material as the metal a of the hollow roller from FIG. 1. In this case, the metal does not necessarily have to be easily weldable as in the case of metal b, so that finely spherulitic cast iron can be used as the metal. The coefficient of expansion of spherulitic cast is somewhat

below that of steel (13.7 χ 10- ⁶ mm / mm / C °). However, this is acceptable since the different bending stresses are less due to the greater rigidity of the roll. The percentage composition of the iron-based metals used here:

5

C. Si. Mn. Cr. Ni. Mon

Metal a 0.10 to 0.30 0.3 to 1 0.3 to 1 11.5 to 14.5 Obisl 0.50 to 1.50

10 metal 3.00 to 3.50 1.50 to 2.50 0.30 to 1.00 - - -

1 sheet of drawings

Claims (3)

Patent claims: 1. Composite roll, in particular for guiding slabs in a continuous caster or the like, with two concentric metal layers, of which the outer layer is made up of a chrome steel and the core layer a cast steel and the metal of the outer layer has a lower coefficient of expansion than having the metal of the core layer, characterized in that the outer layer consists of a Chromium steel consists of 0.10 to 0.30% C, 0.3 to 1% Si, 03 to 1% Mn, 11.5 to 14.5% Cr, 0 to 1% Ni, 0.5 to Contains 1.50% Mo and iron with impurities from the melting process as the remainder and the two metal layers (11,12 or 21,22) are produced by centrifugal casting in such a way that in the outer layer (11,21) ίο there is a pressure pre-tension 2. Composite roll according to claim 1, characterized in that it is designed as a hollow roll and the core layer (12) made of a non-alloy steel with a low carbon content of the following composition consists of: 0.10 to 0.30% C, 03 to 0.6% Si, 0.3 to 0.6% Mn and iron with melting-related Impurities as the remainder 3. Composite roll according to claim 1, characterized in that it is designed as a solid roll whose Core (22) consists of spherulitic cast iron of the following composition: 3.00 to 3.50% C, 1.50 to 2.50% Si, 0.30 to 1.00% Mn and iron with impurities from the melting process as the remainder