JPH02149638A - Composite roll for rolling and its manufacture - Google Patents

Abstract

PURPOSE:To obtain the title composite roll having excellent wear resistance, resistance to roughening of surface, heat cracking resistance, strength and toughness, at the time of manufacturing a composite roll for hot rolling, by using cast iron having the structure in which eutectic carbide is aggregated into the shape of grains as an outer shell layer and a ferrous material having a solidus temp. higher than that of the cast iron of the outer shell layer as an internal layer. CONSTITUTION:As a work roll used at the time of subjecting a steel material or the like to hot rolling, a composite roll constituted of an outer shell layer 1 and an internal layer 2 is used. The outer shell layer 1 is manufactured by high Cr cast iron or the like contg. >2.0wt.% C and having the structure contg. netlike eutectic carbide; the surface is held by heating to the solidus temp. of the cast iron as an outer shell layer or higher than that by 80 deg.C and the netlike eutectic carbide is aggregated into the shape of grains, by which the wear resistance, resistance to roughening of surface and heat cracking resistance can be improved. At this time, as the material for an internal layer, the ductile cast iron or the like having a solidus higher than that of the above heating temp. and having excellent strength and toughness are used.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a rolling composite roll suitable as a work roll for hot rolling, and a method for manufacturing the same.

(Prior art and its issues) In general, rolling rolls have sufficient hardness to achieve excellent wear resistance and surface roughness resistance, and sufficient hardness to withstand bending due to rolling loads and torsion due to driving force transmission. It is required to have properties such as strength and toughness, which are incompatible with each other in terms of material properties. A composite roll consisting of an inner layer (arm) 2 is adopted.In this case, a material with excellent wear resistance, roughness resistance, and heat cracking resistance is used for the outer shell layer that comes into contact with the unrolled material during the rolling process. It goes without saying that the inner layer is made of a material with high strength and toughness that can support the bending caused by rolling loads and the torsion caused by drive transmission. Conventionally, high chromium cast iron or high-base metal grain was used as the material for the outer shell layer. Cast iron, etc., and high-grade ordinary cast iron or ductile cast iron were generally used for the inner layer material.

In addition, known composite technologies such as centrifugal force casting method and hollow casting method are applied to manufacture such a composite roll for rolling.

However, in recent years, rolling has become more and more severe due to the thermal and mechanical loads on the rolls, so conventional rolling rolls have not had the wear resistance and heat cracking resistance required under the above conditions. The problem has arisen that the properties such as roughness resistance and rough skin resistance cannot be fully satisfied.

Therefore, the present applicant first proposed a method for improving the properties of high-chromium cast iron, high-base metal grain cast iron, etc. as rolling roll outer shell layer material (means for improving wear resistance, roughness resistance, and heat cracking resistance). We proposed a treatment method in which the above-mentioned cast iron, in which network-like eutectic carbides have crystallized, is heated and held in a temperature range of [solidus temperature] to [solidus temperature +80°C] to agglomerate and granulate the carbides. (Unexamined Japanese Patent Publication No. 62-267413).

Furthermore, the present applicant has discovered that when the above-proposed carbide aggregation technology is applied to a rolling roll, the temperature of the roll surface sometimes rises too much, resulting in a coexistence state of a liquid phase and a solid phase. In response to the fact that the rolls were found to be prone to wrinkles and deformation, the best of conventional composite rolls (for example those with an outer shell layer made of high chromium cast iron and an inner layer made of ductile cast iron) After covering the outer periphery with "a material with a higher melting point than the conventional outer shell layer material" [the solid phase of the outer shell layer material yA?] J1 degree]～
By heating and maintaining the temperature in the [solidus temperature of the outer shell layer material + 80°C], it is possible to solve the problem of deformation of the roll surface and achieve agglomeration and granulation of network-like eutectic carbide. He also proposed a method of rolling after removing the high melting point material covering the steel (Japanese Patent Laid-Open No. 63-203206).

However, the temperature range of [solidus temperature of the outer shell layer material] to [solidus temperature of the outer shell layer material + 80°C] is Subsequent studies by the present inventors, which continued while applying the technology to agglomerate and granulate by heating and holding the carbide to actual composite rolls of various diameters, revealed that the technology could be applied to composite rolls for rolling. If applied simply to modify the shell layer, it may indeed cause the problem of deformation of the roll surface, but more importantly, depending on the heat treatment conditions, it may cause deformation of the inner layer material, making roll manufacturing difficult. It has become clear that there is a risk of an accident. It has also been found that this situation tends to manifest itself as significant deformation of the neck and shaft portions of the inner layer of the roll.

Therefore, the object of the present invention is to reduce the temperature of the rolling composite roll having an outer shell layer in which network-like eutectic carbides crystallize from [solidus temperature of the outer shell layer] to [outer shell temperature]. The solidus temperature of the layer + 80°C] is heated and maintained to cause agglomeration and agglomeration of the eutectic carbides.
Excellent toughness without causing deformation of the inner layer material during granulation.

It is an object of the present invention to provide a means for industrially stably manufacturing a composite roll for rolling that has wear resistance, roughness resistance, heat crack resistance, etc.

Means for Solving the Problems> As a result of conducting research through numerous experiments in order to achieve the above object, the inventor was able to obtain the knowledge shown in the following (a) to (c). Ta. That is, (a) the network-like eutectic carbide crystallized in the outer shell layer of the rolling composite roll is aggregated and
The reason why the inner layer of the roll is deformed by heat treatment for granulation is that due to its composition, the inner layer material has a lower solidus and liquidus temperature than the outer shell layer, and when the roll is heated, the inner layer material deforms first. It is due to some melting. That is, when a composite roll is heated, for example, by high-frequency induction heating in order to agglomerate the eutectic carbide in the outer shell layer, the temperature of the roll surface increases at the beginning of heating, but the temperature of the inner layer material does not rise to a high temperature.
If heating is continued until the eutectic carbide coagulates, heat will be transmitted to the inside, and the inner layer material will eventually reach almost the same temperature as the surface. As a result, the inner layer material of the roll melts and deforms (as described above, the deformation from the roll neck to the shaft is significant), making it unusable as a rolling roll.

Table 1 below shows examples of chemical composition and solidus temperature of high chromium cast iron and high alloy grain cast iron used as the outer layer material of composite rolls for rolling, and ductile cast iron used as the inner layer material. Table 1 also shows that the inner layer material has a lower solidus temperature and liquidus temperature than the outer shell material, and when heated to the same temperature, It can be seen that the inner layer material melts first.

Figure 2 shows a composite roll (body diameter near 70m, body length: 178Qmm, total length: 3900mm) whose outer shell layer is made of high chromium cast iron and inner layer made of ductile cast iron.
2 is a graph showing the internal temperature of the roll when subjected to granulation heat treatment (in FIG. 2, the liquid phase temperature and solid phase temperature of the outer layer material and the inner layer material are also shown). In the carbide aggregation/granulation heat treatment, conditions were adopted in which the roll surface temperature was maintained at 1210° C. for 5 hours by high-frequency induction heating.

Also from FIG. 2, it can be seen that the inner layer temperature during the heat treatment for carbide aggregation and granulation eventually becomes approximately the same temperature as the surface and exceeds the liquid phase temperature of the inner layer material.

(b) Therefore, if the material to be applied as the inner layer material of the rolling composite roll is ``a material that has a solidus temperature that does not melt and deform even when the outer shell layer material is heated for a long time'', it is necessary to deformation of the inner layer is stably prevented.

(c) For example, if the carbide agglomeration/granulation heat treatment is performed as it is under the "conditions of heating and holding the roll surface at 1210°C", which gave the results shown in Figure 2,
It is true that scale occurs on the composite roll surface and some wrinkle-like deformation occurs, but these situations are actually not that serious, and rolling can be done satisfactorily with relatively simple maintenance. It is possible to make a composite roll product for use.

The present invention has been made based on the above-mentioned findings, etc., and provides a rolling composite roll with an outer shell layer having a carbon content of 2.0% or more (hereinafter, % representing the component ratio is % by weight), By constructing the cast iron having a structure in which eutectic carbides are agglomerated and granulated, and the inner layer being made of an iron-based material having a solidus temperature higher than [the solidus temperature of the outer shell layer material + 80°C], It is characterized by having the necessary properties such as excellent toughness, wear resistance, roughness resistance, and heat cracking resistance, and is further characterized by ``cast iron with an outer shell layer of carbon i1:2.0% or more, Then, a composite roll whose inner layer is made of an iron-based material having a solidus temperature higher than [the solidus temperature of the outer shell layer material +80°C] is used.
[Solidus temperature of outer shell layer material] ~ [Solidus temperature of outer shell layer material +
By heating and maintaining the roll at a temperature of 80°C, it is possible to stably produce a rolling composite roll having an outer shell layer of agglomerated and granulated eutectic carbides. It is something.

Next, the reason why the configuration of the roll and the manufacturing conditions thereof are limited as described above in the present invention will be explained together with the effects that underpin this.

First of all, the reason why the outer shell layer of the rolling composite roll according to the present invention is made of "cast iron having a structure in which eutectic carbides are aggregated and granulated" is that the outer shell layer can be obtained as cast. This is because the conventional structure in which network-like eutectic carbides exist has insufficient wear resistance, heat cracking resistance, and roughening resistance, and cannot withstand use under relatively severe rolling conditions. In addition, the carbon content of the cast iron constituting the outer shell layer is set to 2% or more because a eutectic reaction is observed in cast iron with a carbon content of 2% or more, and eutectic carbides crystallize. This is because by performing the carbide aggregation heat treatment, it becomes possible to realize an outer shell layer Mi fabric in which eutectic carbides are agglomerated and granulated.

By the way, the carbide aggregation heat treatment must be carried out in a temperature range of [solidus temperature of the outer shell layer material] to [solidus temperature of the outer shell layer material +80'c]. This is because if the heat treatment temperature is lower than the solidus temperature of the outer shell layer material, it is difficult to change the shape of the network-like eutectic carbide. +80°C], it becomes impossible to prevent the composite roll from partially melting, and the shape cannot be maintained.

In addition, in order to agglomerate and granulate the network-like eutectic carbide, the holding time during the heat treatment is preferably 4 hours or more. If this heating and holding time is short, for example within 30 minutes, the inner layer material will not be heated to a high temperature. does not aggregate. However, if heated and held for a long time, the inner layer material will also be heated to a high temperature, causing melting and deformation. Therefore, in order to prevent such inconveniences, an inner layer material whose solidus temperature is higher than the upper limit temperature of the carbide aggregation/granulation heat treatment [solidus temperature of the outer shell layer material + 80°C] is used. This is why we decided to do so.

If a material under the above conditions is used as the inner layer material, the rolling composite material will have an outer shell layer with a structure in which eutectic carbides are agglomerated and granulated, and exhibit extremely excellent wear resistance, heat cracking resistance, and surface roughness resistance. Rolls can now be obtained practically stably and reliably.

Note that the specific material of the inner layer material has a carbon content of 0.
Cast steel or forged steel with a content of 8% or less (SC according to JIS standards).

(represented by symbols such as SCM, SNCM, etc.) may be selected. These are iron-based materials that not only have a solidus temperature that satisfies the above conditions, but also sufficiently satisfy the required strength and toughness as shaft materials for rolling rolls, and have extremely good bondability with the outer shell layer.

In addition, the specific material for the outer shell layer material is high chromium cast iron, high alloy cast iron, etc., which have been conventionally used for the outer shell layer material of composite rolling rolls, and have a carbon content of 2.0% or more. You can use any of them.

Next, the effects of the present invention will be explained in more detail with reference to Examples.

<Example> SC standardized by JIS as roll shaft material (inner layer material)
A forged steel material equivalent to M430 (hardness: Hs40) is used, and a high chromium cast iron having the composition shown in Table 2 is overlaid with a thickness of 100 mm as an outer shell layer around it to form a composite material as shown in Fig. 1 above. I made it into a roll.

Subsequently, the resulting composite roll is heated and held for 5 hours using high-frequency induction heating so that the roll surface reaches 1210°C in a roughly finished state with a machining allowance of 20 mm around the entire circumference to form a network-like eutectic carbide agglomerate. - Granulation heat treatment was performed, followed by slow cooling.

The entire surface of the rolling composite roll manufactured in this way was covered with scale, and wrinkle-like deformation was observed, but the deformation was small and there was no deformation of the inner layer material, so machining Body diameter near 70 iris x body length: 1780
nx full length: 3900 No defects were observed when the crane was finished.

It was also confirmed that the outer shell layer, which had a net-like carbide shape when it was built up, had a structure in which the carbides aggregated and became granular after heat treatment.

Separately, for comparison, high chromium cast iron shown in Table 2 above was applied as the outer shell layer material, and ductile cast iron shown in Table 1 above was applied as the inner layer material, and the centrifugal casting method was used. A rolling composite roll of similar dimensions (without heat treatment for agglomeration and granulation of reticulated eutectic carbide) was also manufactured.

Then, each of the above composite rolls was applied to the upper and lower work rolls of a hot finishing rolling mill (F5 stand), and each JTS
When SPHC-equivalent steel materials were test rolled, the results shown in Table 3 were obtained.

In addition, in Table 3, the breakdown of the number of rolls used is divided into "normal rolling" and "rolling accident rolling" and the results of each roll are compared.

Table 3 As is clear from the results shown in Table 3, it can be seen that the composite roll according to the present invention can improve the wear resistance by as much as 20% in terms of wear amount compared to the comparative (conventional) composite roll.

In addition, since the composite roll according to the present invention has excellent surface roughness resistance, the average durability of the roll is also small. It can also be confirmed that this is an improvement of 40%.

Furthermore, the damage (depth of flaws) to the roll caused by squeezing of the material to be rolled is 7 for the comparative (conventional) composite roll, but 3 for the composite roll according to the present invention.
It is also clear that the distance can be halved to 1 m or less.

Summary of Effects> As explained above, according to the present invention, it is possible to stably and reliably provide a rolling composite roll with significantly improved wear resistance, roughness resistance, heat cracking resistance, strength and toughness. This makes it possible to bring about extremely useful effects industrially, such as greatly contributing to the promotion of higher efficiency and lower costs in rolling operations.

is a graph showing the temperature inside the roll when a composite roll made of ductile cast iron is subjected to carbide aggregation/granulation heat treatment.

Claims (2)

[Claims] (1) Cast iron in which the outer shell layer has a carbon content of 2.0% by weight or more and a structure in which eutectic carbides are agglomerated and granulated, and the inner layer is made from [solidus temperature of the outer shell layer material + 80°C] A composite roll for rolling, characterized in that it is made of an iron-based material having a high solidus temperature. (2) The outer shell layer is made of cast iron with a carbon content of 2.0% by weight or more, and the inner layer is made of iron-based material with a solidus temperature higher than [the solidus temperature of the outer shell layer material + 80°C] According to claim 1, the composite roll is heated and maintained in a temperature range of [solidus temperature of the outer shell layer material] to [solidus temperature of the outer shell layer material +80°C]. A method for manufacturing a composite roll for rolling.