DE2415044A1 - LARGE FORMAT COMPOSITION AND LARGE THICKNESS - Google Patents

Description

Patent attorneys

Dipl.-inq. R. Π Ε £ T Z sen. '

Ur.-Sng. ? ϊ. 15 - * ■ '* - J ^r - Z 4 I 5 U 4

Munich 22, Siümiscrrstr. 10

8l-22.422P (22.425H)

March 28, 1974

HITACHIMETALS, LTD., Tokyo (Japan )

Large format and thick composite sheaths

The invention relates to large format, large thickness composite shells which are suitable for use with horizontal rolls and assembly type vertical rolls are suitable for a universal rolling mill for manufacturing H-shaped beams in which Type on the shaft as the core coats large format with a relatively to be mounted to the diameter small width.

Rollers of the composite type have been used a long way Extent used because the core shaft can be reused, in-

81- (A 88-03) -T-r (8)

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where one coat is replaced by another, and the rollers of the composite type are of low rolling cost, making them more economical to use than rolls of the one-piece type can. Up until now it was common to use cast steel jackets with a medium carbon content and a Shore hardness number of less than 50 for composite type rolls of a universal rolling mill for producing Use H-shaped straps. There are several disadvantages associated with such coats. There is wear and tear on the side surface every such jacket, scratches occur on the flange due to impact, and the jacket is unable to withstand pressure, which acts on it by bending the metal to be rolled or for other reasons.

On the other hand, with the advancement of the rolling technique and the increase in the efficiency in performing rolling, in recent years Years ago there was a growing need for such jackets for use in rolls of a universal rolling mill for production of H-shaped beams should have the following properties:

(1) The coats should be tough and free from the possibility of breakage;

(2) the jackets should be very resistant to wear and tear be and show no surface roughness;

(3) the jackets should be very resistant to cracking when heated be; and

(4) the defects are said to be deep-hardening or of little internal origin

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Be hardness drop if the diameter range for the effective use is great.

However, it has been found in the manufacture of large thickness jackets with all of the properties mentioned from a single material Trouble. In particular, it was impossible to manufacture such jackets by casting in a mold, as the material was of low strength was.

To overcome this problem, methods have been developed to make jackets of the composite or composite type, each jacket having an outer and an inner layer of the same thickness made of different materials. In detail such defects from a high-performance surface or outer layer made of a high hardening alloy or alloy with high Carbon content, which is very resistant to wear and tear, the appearance of surface roughness and cracking when heated, as well as strong is deep-hardening, and an inner layer made of a soft and ductile Low hardness material that is so tough that it will not fail when subjected to shrink-fit stress during manufacture or when subjected to rolling and thermal stresses act on the jacket during operation at the same time, and which has a reduced internal residual stress.

The known composite jackets have heretofore been made by casting two types of metals using a solid mold that is associated with a Partition made of a steel plate is provided (DT-PS 1 937 974), or

40 9 8 A 37 0 7 4 6 ". · ■.

prepared in such a way that you first a metal melt for the outer layer poured into the mold and the inner part of the poured molten metal by another molten metal for the inner Layer replaced after the outer layer solidified to a certain distance from the surface. The former method may have the disadvantage that the outer layer and the inner layer sometimes do not weld properly to one another, whereby a heating hood shows little effect, since the outer and inner layers are separated by the partition, and the degassing the poured metal melt is not sufficiently achieved. The latter method has disadvantages in that the molten metal for the inner and outer layers tend to be strongly mixed with one another, so that it is impossible to carry out the operation to be carried out under stable conditions because of difficulties in controlling the thickness of both layers and the amount of Molten metal result for each of the layers. For this reason, the latter method in particular has not been able to establish itself in practice.

A tube of small thickness, which is formed in two layers and composed of an iron or non-ferrous material, can can be easily produced by centrifugal casting, and the two layers form v / ohl-defined concentric circular rings Zones, since such a pipe is only thin and the outer and inner layers solidify quickly. Because this tube is not exposed to excessive mechanical or thermal stress, as is the case with rollers, occurs in the manufacture of a such a small-thickness pipe does not pose a serious technical problem.

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However, if composite sheaths of large format and large thickness, which have an outer diameter of more than 900 mm and where the ratio of the thickness T to the diameter D, d. H. T / D is over 0.20, made by centrifugal casting for use in a rolling mill are to be, one encounters considerable difficulties, since the jacket should have the properties mentioned above.

The problems to be solved in making such composite shells by centrifugal casting are as follows:

(a) It takes a long time for both the outer and inner layers to solidify and differences in the The rate of solidification of the molten metal increases from area to area, making it difficult to produce a composite shell with concentric To produce circular layers, each of which consists of a homogeneous material and which are formed by a cylindrical Boundary layer are separated. The outer and inner layers either mix too much with each other, so that none are well-defined outer or inner layer is formed, or the outer and inner layers only insufficiently weld to one another.

(b) It is difficult to minimize the residual stress that exists on the inside of the boundary layer through which the metals are responsible the outer and inner layers penetrate from one layer to the other, so that it is difficult to form a satisfactory boundary layer without defects throughout the entire cladding.

(c) A coat in which the thicknesses of the outer layer and the

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If the inner layer is not properly adjusted, it may fail during manufacture or in operation

(d) The rate of solidification of molten metals is slow, and adverse segregation easily occurs in the outer and lower the inner layer.

Therefore, it has been extremely difficult to manufacture high hardness, large size, large thickness composite shells by centrifugal casting.

The invention is based on the object of ideally large-format and very thick composite sheaths with certain properties and the Suitability for use in composite type rolls for making H-steel parts that extend through Centrifugal casting can be produced without the disadvantages mentioned occurring.

The subject of the invention, with which this object is achieved, are for rolls of a universal rolling mill for the production of H-shaped Profile rails suitable composite sheaths large format and large thickness, which are produced by centrifugal casting and an outer diameter of over 900 mm, characterized in that each composite jacket has an outer layer of high carbon cast alloy steel with a carbon content of 1.6 to 2.2% by weight and a Shore hardness number over 55 and an inner layer made of high-carbon cast steel with a Shore hardness number of 35 to 42 and that a crystallization of spheroidal graphite is produced in the inner layer.

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Preferably, in these composite jackets according to the invention, the ratio of the thickness of the outer layer to the thickness of the Inner layer in a range from 0.5 to 2.6.

The ratio of the total thickness of the two cladding layers is advantageous to the outer diameter of the composite jacket in a range from 0.2 to 0.4.

The invention therefore gives large-format and very thick composite ones Jacket suitable for use in rolls of a universal rolling mill for the production of M-shaped beams and with a small width in relation to the diameter. The coats have each have an outer diameter of over 900 mm and have an outer layer made of high-carbon cast alloy steel with a carbon content in the range from 1.6 to 2.2% by weight and a Shore hardness number of over 55 and an inner layer of high carbon cast steel with a Shore hardness number in the range from 35 to 42, a crystallization of graphite having taken place in this inner layer. The outer and inner layers become both produced by centrifugal casting in such a way that the ratio of Thickness of the outer layer to that of the inner layer ranges from 0.5 to 2.6.

The invention is explained in more detail with reference to the drawing; show in it:

Fig. 1 is a front view of a composite jacket according to the invention ;

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FIG. 2 is a vertical sectional view of the composite jacket according to FIG Fig. 1; and

3 shows a diagram to illustrate the hardness curve from the mantle surface inwards.

The invention is now to be illustrated with reference to one in the drawing Exemplary embodiment will be explained in more detail. Fig. 1 shows the structure of a composite jacket of great thickness, which is to It is suitable for use with a horizontal roll of large thickness and narrow width of the composite type, that of a universal rolling mill is used to produce H-shaped beams or profile rails. The jacket comprises an outer layer 1 large Thickness made from a high carbon alloy steel, an inner one Layer 2 of tough high carbon cast steel in which crystallization occurs of graphite has taken place and which has a low Shore hardness number, as well as a boundary layer 3, which consists of a mixture the materials for the outer and inner layers 1 and 2, respectively. A shrink connection surface can also be seen on the inside of the inner layer 2.

Large format and large thickness composite jackets with a diameter greater than 900 mm, in which the ratio of the thickness T to outside diameter D, d. H. T / D in the range of 0.20 and 0.40 are made as follows: A certain amount of melted Alloy steel with high carbon content is used in a metallic mold for centrifugal or centrifugal casting

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poured at high speed on a horizontal centrifugal casting machine rotates to form the outer layer 1, which after completion of the casting has a Shore hardness number of over 55 and a Should have carbon content in the range from 1.6 to 2.2%. Direct before the inner surface of the melt for the outer layer 1 completely solidifies after a certain time has elapsed, a certain amount of molten high carbon cast steel is used for the inner layer 2, in which graphite crystallization occurs after solidification can cause, poured into the mold in such a way that the ratio of the thickness 11 of the outer layer 1 to the thickness 12 the inner layer 2, d. H. tl / t2 in the range of 0.50 and 2.6 and the Shore hardness number of the inner layer 2 after completion of the casting are in the range from 35 to 42. So find one from the metallurgical Desired mixing and fusing of the two types of metal melts in the boundary layer 3 between the outer layer 1 and the inner layer 2 instead of without excessive diffusion of the metals occurring, so that the produced Composite jacket has no cracks in the finished cast state. After the casting or the composite jacket has completely solidified, the rotation of the mold is interrupted and the casting process is ended.

The reason why the diameter of the jackets according to the invention to over 900 mm and the ratio of the thickness T to the outer diameter D, i.e. H. T / D preferably to a range of 0.20 to 0.40 is as follows: The invention aims to provide large-format and very thick composite sheaths with an outside diameter of over 900 mm. In the case of coats

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small thicknesses where the T / D ratio is less than 0.20, there is practically no problem to be overcome, since the cooling of the coats takes place relatively quickly. Hence the lower limit of the ratio T / D is set to 0.20. On the other hand, when the ratio T / D is over 0.40, the casting has an unusual one great thickness and is therefore no longer generally referred to as a coat. In addition, it takes an extremely long time Time to achieve a complete solidification and cooling of the metals, so that it does not matter how the thickness of the outer and the inner layer being controlled, it is impossible to produce composite shells by centrifugal casting which meet the aforementioned requirements fulfill.

According to the invention, the carbon content of the alloy steel for the outer layer 1 is in a range from 1.6 to 2.2 Weight% limited because the carbon content exceeds 2.2% the material is brittle and surface cracking tends to occur when the jacket is subjected to heat treatment becomes, and there in the case of a carbon content below 1.6 wt .-% a Hot rolling causes wear and pitting of the jackets.

The ratio of the thickness 11 of the outer layer 1 to the thickness the inner layer 2, d. H. tl / t2 of the coats, is according to the invention preferably to a range of 0.50 to 2.6 from the following Reason limited: So that the boundary layer 3 is in a perfect state for the mutual connection of the outer layer 1 and the inner layer 2 is by fusing the two metals, is said to be a

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Part of the inner surface of the outer layer 1 after solidification melt again by pouring in the melt for the inner layer 2 and then solidify again. For this it is necessary that the amount of melt for the inner layer 2 is so large that the ratio tl / t2 is not more than 2.6, so that the melt for the inner layer has a heat capacity which is high in relation to the volume of the outer layer 1, so that a part (with a thickness between about 15 and 20 mm) on the inner surface of the outer layer just before the completion of solidification can be melted again. When the ratio tl / t2 is less than 0.5, the thickness of the outer layer is 1 in comparison with the thickness of the inner layer 2 is extremely small. In this case the heat capacity of the melt for the inner layer 2 is excessively high in relation to the volume of the outer layer 1, so that the inside of the outer layer 1 is too light or too far again melts and diffuses, so that you produce the outer layer 1 with a certain thickness and the boundary layer 3 in the mold could form a circular cylinder free of eccentricities.

In connection with the ratio tl / t2, difficulties arise in the production of a casting in which the outer layer has a desired thickness and the outer and inner layers are separated by a boundary layer that really is circular and not eccentric.

The reason why the Shore hardness number of the outer layer should be over 55 is that the coats must be sufficiently hard

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sen to be wear-resistant and resilient to emergence to be of surface roughness. When the Shore hardness number the inner layer 2 is over 42, the sheaths become excessively brittle, leaving opportunities for failure during manufacture and arise in the company. If the Shore hardness number of the inner layer is below 35, then the shrink joint surface is absent the jacket sufficient rigidity after completion of the shrink connection and assembly, so that problems the slip and detachment of the jacket from the supporting core cylinder. So to eliminate this problem is the Shore hardness number the inner layer 2 is limited to the range from 35 to 42, and in the inner layer 2 the tendency to crystallize of spheroidal graphite is present. It should be noted that the hardness of the inner layer 2 is closely related to the range of the ratio tl / t2 of 0.5 related to 2.6 and that the Shore hardness number of the inner Layer 2 is preferably in the vicinity of 35, at which the steel has a high toughness and crystallization readily in it of spheroidal graphite form takes place.

Fig. 3 illustrates the course of the penetration of the hardness in a Composite jacket according to the invention. It shows that, since the outer layer is very deep hardening, that from the outer layer to the inner one The residual tensile stress acting on the layer becomes very large if the thickness of the outer layer with a Shore hardness number of over 55 is so is large that the ratio tl / t2 of the composite shell is over 2.6. This increases the chances of breaks.

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A composite jacket produced in accordance with the above explanations and meeting the requirements is, if necessary considered, subjected to homogenization and spheroidization. Then it turns into coats of smaller size, i. H. smaller width which are subjected to heat treatment such as quenching and tempering to produce the final products, i.e. H. the final To obtain composite jackets whose ratio tl / t2 is in a range from 0.5 to 2.6.

The finished composite sheaths are firmly mounted on shafts as cylindrical cores by means of a shrink fit. That's how you accomplish the manufacture of a roller with a composite shell of large format and great thickness.

example

Table 1 shows the chemical composition of the metals used to produce a composite jacket for a horizontal pre-pass roll which had an outer diameter of 1390 mm, an inner diameter of 650 mm and an overall length were used of 1600 mm and in which the required thickness of the outer layer was over 245 mm.

Table 1

Chemical composition (%) __

C Si Mn P S Ni Cr Mo

Outer layer 2.07 0.78 0.81 0.020 0.003 2.32 0.94 0.89

Inner layer 1.45 1.56 0.77 0.018 0.005 0.42 0.23 0.15

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12,200 kg of melt for the outer layer at 1450 C were poured into a metallic mold which was placed on a horizontal centrifugal casting device rotated at 120 G to produce large-format defects. After a certain amount of time and immediately Before the completion of the solidification of the inner surface of the melt for the outer layer, a further 3500 kg of melt were added for the inner layer of 1500 C poured into the metallic mold. the Rotation of the mold was stopped when the solidification of the two melts was completed in about 5 hours.

The outer layer was particularly thick and made of high carbon alloy steel, which is brittle when it is after production by casting in a mold is not subjected to any post-treatment. Therefore the casting was held removed from the metallic mold at a temperature above 600 ° C. and subjected to homogenization and spheroidization. The casting was then divided into smaller parts by turning, each part having a required width. After each jacket was roughed, it was quenched and tempered. Then every coat was processed further, until it had the precisely determined dimensions, and finally mounted on a shaft by shrink fitting.

The results of an inspection carried out by coloring the entire surface and supersonic crack detection methods applied, show that the jackets so produced are free of cracks. The Shore hardness number of the surface of the jackets was

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between 60 and 61, while the Shore hardness number of the inner surface was between 38 and 41. The high degree of deep hardening of the jackets was as illustrated by FIG. It is found that despite the fact that the coats'of large format and large Thickness, the reduction in hardness within the outer layer is very small and the outer layer and the inner layer are separate, Form layers separated by a clear boundary layer. The jackets each had an outer layer 250 mm thick, while the total thickness of each jacket was 350 mm. Variations in the thickness of the outer layer were less than 6 mm. The relationship T / D was 0.25 and the ratio tl / t2 was 2.5, i.e. H. Values that are in the predetermined ranges.

layer Tabel 2 Ductility Charby-Strikes layer tensile strenght «) (kg-m / cm) . (kg / mm) 0.3 0.2 Outer 63 3.2 1.2 Inner 80

Horizontal rolls for the production of H-shaped beams using the composite shells according to the invention were found to be suitable for the production of H-shaped girders of 1980 t by rolling in one pass compared with H-shaped girders of only 1000 t, which could be produced by rolling in one pass with conventional rollers with a Shore hardness number below 50.

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The extent of the wear caused on the side wall was between 0.15 and 0.20 mm for a roll pass and was therefore lower than the amount of wear caused on the known rolls, which was 0.4 mm.

From the foregoing description it can be seen that the invention Large format and large thickness composite jackets that meet the requirements of the material being used Meet hardness and the thickness of the outer layer and which are free from casting cracks, durable and of excellent performance - The composite jackets according to the invention have no risk of breakage and can have an operating life of about twice as long like that of the well-known coats. The use of the composite jackets of the invention is also very great economical as the material costs required to manufacture the rollers are low.

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Claims (4)

Claims ( 1. yFor rolls of a universal rolling mill for the production of H-shaped profile rails suitable composite shells of large format and great thickness, which are produced by centrifugal casting and have an outer diameter of over 900 mm, characterized in that each composite shell has an outer layer (1) Made of high carbon cast alloy steel with a carbon content from 1.6 to 2.2% by weight and a Shore hardness number over 55 and an inner layer (2) made of high-carbon cast steel with a Shore hardness number of 35 to 42 and that in the inner layer (2) crystallization of spheroidal graphite is generated. 2. composite sheaths according to claim 1, characterized in that that the ratio of the thickness (ti) of the outer layer (l) to the thickness (t2) of the inner layer (2) is in a range from 0.5 to 2.6. 3. Composite jackets according to claim 1 or 2, characterized in that the ratio of the total thickness (T) of the two jacket layers (1.2) to the outer diameter (D) of the composite shell is in a range from 0.2 to 0.4. 4 09843/0746 .Blank