JPS61232009A - Work roll for rolling mill - Google Patents

Abstract

PURPOSE:To make a work roll consisting of a body part and shaft parts usable for the other stand after the use in the 1st stand by providing a high-temp. tempered region only to the initial surface layer of the work roll thereby providing a good biting characteristic to the roll when used in the 1st stand in the initial period of use when the body diameter of the roll is large. CONSTITUTION:The body part 1 of the work roll for a cold rolling mill having 620 mm initial body diameter, 530 mm discarding diameter and 90 mm total utilizing body diameter is subjected to quick heating-up only in the surface layer part once or plural times in an electromagnetic induction heating coil 5 of a high-frequency and is then allowed to cool by which the primary tempering is executed in said part. The entire part of the body part is thereafter subjected to tempering once or plural times and the hardness distribution curve in the depth direction shown by a solid line A is obtd. Such roll is used in the 1st stand. The layer having the performance of the hardness distribution curve in the depth direction shown by a dotted line B is exposed after the roll is used to the intermediate point of the total utilizing body diameter of 90 mm, i.e., the point of the time when the Shore hardness decreases approximately to 87 Hs. The roll is therefore usable for an optional stand except in the 1st stand.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a work roll for a rolling mill, and is particularly suitable for use in a first stand that requires good biting resistance and accident resistance in the initial stage of use when the roll has a large body diameter.

The present invention also relates to a work roll that has the ability to be used for other stands from the middle of its diameter.

[Background of the invention]

In general, work rolls for cold rolling mills include, for example, "Tetsu to Hagane J
As shown in VO7, 57, 翫5, after hardening the body of the roll material that has been subjected to spheroidization treatment in advance, it has a predetermined surface hardness, hardness distribution in the depth direction, stable martensitic structure, and desirable residual application distribution. The entire body is tempered once or multiple times in order to obtain the desired properties. The heating temperature during quenching and the heating temperature during tempering differ depending on the chemical component ratio of the material, the heating method, and the specifications to be obtained. For example, if the weight ratio is C = 0.8%, 5i
=0.6%, 'Mn=0.5%, N1=0.2%, Cr
In the case of a material in which Mo = 3.0% and Mo = 0.2% with some impurities and the balance being Fe, the general temperature is around 950°C for the former and around 120°C for the latter. The depthwise hardness distribution of the roll body heat-treated in this manner shows the highest value on the surface side, and shows a form in which the hardness gradually decreases as the depth increases.

On the other hand, in a cold tandem rolling mill that has multiple stands and rolls continuously, the rear stands need to have wear resistance and surface roughness resistance in order to finish the rolled material beautifully and with high precision dimensions. Become. From this point of view, the work roll is placed in the final stand at the beginning of use when its hardness is high, then as the diameter of use progresses and the hardness decreases, it is placed in stages before and after the stand, and then in the stand with the lowest hardness. It is desirable to use it for the first stand at the point when the

Tosero is the work roll used for the first stand,
It is extremely important to have good so-called biting properties that allow the material to be rolled to be rolled smoothly. For this reason, in reality, there are many cases in which the stand is used as the first stand in the initial stage of use when the body diameter is large.

This means that when the contact angle between the roll and the rolled material is θ, and the coefficient of friction between the roll and the rolled material is p, the rolled material will be bitten by the roll unless μ〉tan θ. It is publicly known that there is no such thing. Here, the roll radius is R9 and the reduction amount is Δh.
It can be approximated as tanθ and sinθ. Therefore, it is clear that the larger the roll radius R and the larger the friction coefficient μ, the more advantageous it is to the biting property.

Also, during grinding, the harder the roll is, the more likely the grinding wheel will become clogged, making it difficult to grind.

The roughness of the ground roll surface becomes smaller, resulting in a lower friction coefficient μ. Therefore, from the viewpoint of ensuring the friction coefficient μ and maintaining the advantageous biting property, it is advantageous that the roll hardness is lower.

On the other hand, since the rolled material subjected to cold rolling has undergone hot rolling, it is common for the material to have a relatively large variation in thickness in both the width direction and the rolling direction. It is a fact that due to this plate thickness variation, the biting property is reduced in the first stand, resulting in partial slippage between the rolled material and the roll surface with some frequency. This type of slip may also occur when rolling conditions suddenly change, such as during rolling when rolled materials of different thicknesses, widths, or materials are connected by welding or the like. Such slipping results in not only plastic deformation heat of the material to be rolled, but also a break in the rolling oil film between the roll surface and the material to be rolled, resulting in frictional heat due to direct contact. Regarding thermal shock caused by such slipping, there is also a well-known fact ("Hitachi Hyoron" Vol. 58, No. 9 (19
76-91)) However, as shown in the experimental results shown in Figure 4, the higher the hardness, the more likely a heat rack is to occur, and the lower the hardness, the less likely it is to occur. is advantageous.

When poor biting or slipping occurs, tissue changes and heat racks occur on the roll surface, but the structure change area is inferior in strength to the surrounding normal area, and is also susceptible to local thermal residual stress. Due to the redistribution, cracks are likely to occur during operation due to the Hertzian pressure of contact with the rolling material and the reinforcing rolls that support the work rolls, and once cracks occur, they propagate below the surface layer and eventually As shown in FIG. 5, large peeling occurs in the body of the work roll, which often results in a significant reduction in the life of the roll.

Work rolls with a high initial diameter are often used in the stand of the cold rolling mill tube 1 to ensure good biting properties, but in this stand, slipping frequently occurs in the rolled material and the rolls are damaged. In addition to causing damage, it also causes great damage to rolling production efficiency.The higher the tempering temperature, the lower the heat sensitivity of the roll, and the greater its toughness. By applying conventional tempering, we created a high-temperature tempering region in the initial surface layer, and focused on achieving good biting properties and performance that could be used in other stands.

These phenomena have the disadvantage that when the hardness is high, the toughness is poor and the residual stress of the conventional roll itself tends to become noticeable in the early stages of use.

In addition, since it is the first stand, the front and back sides of the rolled product that have passed through all the stands and completed cold rolling! According to the inspector, early detection of slip marks and cracks on the surface of the body of the work roll used in the first stand is difficult.
Although there is a view that the slipping phenomenon on stands is unavoidable to some extent, these troubles in the early stages of use of work rolls result in a significant deterioration of the roll consumption rate, and require a great deal of effort and time for inspection and removal work. There was a serious drawback that it was costly and caused a significant drop in the yield and production efficiency of rolled products. Furthermore, if a work roll that has performance suitable for the first stand from the time of new is manufactured using the conventional tempering treatment method, the hardness will decrease too much as the diameter of use increases, and if only the first stand is used. However, it had the disadvantage that it could not be used with any other stand.

In addition, as a manufacturing method for rolls with a deep hardened layer, it is possible to make it possible by co-locating a low frequency induction heating coil.
It is discussed by Kubo, Nakano et al. in Tetsu to Hagane, No. 5, 1957, entitled "Quenching Roll Using Dual Frequency Transfer Type Induction Heating." It also states that the higher the tempering temperature is, the more advantageous it is in the event of a rolling accident. The statement that the higher the tempering temperature is, the better it is, also describes a known concept regarding general tempering of the entire body.

[Purpose of the invention]

The purpose of the present invention is to
Used in stands, it has good biting properties, and also has heat resistance against slippage, thermal shock resistance, and toughness.
Another object of the present invention is to provide a work roll for an e-Teko rolling mill that can be used in other stands after being used in the first stand.

[Summary of the invention]

The outline of the present invention is as follows. That is, in the contact width portion between the roll body surface and the rolled material during steady rolling, the rolled material exceeds the tempering temperature of the roll due to the plastic deformation heat of the rolled material and the friction heat between the two sides. 2
However, due to the cooling liquid that also serves as a lubricant, the surface of the roll body other than the contact width area is approximately 50 to 80 degrees Celsius.
℃, and due to the presence of a lubricating film of the cooling liquid, the contact width of the roll body surface is approximately 150℃ to 250℃ due to heat conduction to the surroundings and inside of the contact width. The reality is that the temperature increase has been suppressed to 2/2. In other words, it can be assumed that during rolling in a steady state, the surface of the roll body can withstand the temperature rise of the rolled material approximately twice the tempering temperature of the roll due to the effect of the cooling fluid on the roll.

Therefore, 150 to 2 of the rolled material during steady rolling.
The heating temperature of 50° C. can be said to be approximately equal to or slightly higher than the upper limit temperature that conventional rolls can tolerate.

From this, if you encounter a slip that generates significant heat,
The roll surface will be exposed to an acceptable temperature,
That part will undergo a tempering effect with a rapid cooling rate (a re-quenching effect if the temperature at this time exceeds the quenching temperature of the roll) for an extremely short period of time.

For these reasons, by applying a tempering temperature as high as possible to only the surface layer of the roll body, we have created a property that can withstand localized temperature increases during slips caused by plate thickness fluctuations, which are most often encountered. This study focuses on the fact that it is possible to give The method is to heat the surface layer of the roll body before applying conventional tempering and in a medium- or high-frequency electromagnetic induction heating coil that makes it easy to electrically control the heating temperature, heating depth, and heating rate. The above-mentioned performance is imparted by rapidly raising the temperature once or multiple times and then cooling it for primary tempering, and then subjecting the entire body to tempering once or multiple times in the same way as conventional rolls. We focused on the fact that it is suitable for use in the first stand at the initial stage of roll use, and can be imparted with performance that can be used in other stands after it has been used.

That is, the present invention is characterized in that a high-temperature tempering region is provided only in the egg surface layer in a work roll for a cold rolling mill consisting of a body portion and a shaft portion.

[Embodiments of the invention]

Examples of the present invention will be described below.

Figure 1 shows the initial barrel diameter of 620 mm and the waste diameter of 530 mm.

The schematic shape of a work roll for a four-tandem cold rolling mill with a body length of 1420 m and a total length of 3450 mm is shown. The roll shown in Figure 1 is used until the middle point of the total usable diameter of 90 m, that is, when the shore hardness has decreased to approximately H887, and then it is heat treated again and reused to the scrap diameter. be.

The tempering process according to this embodiment is performed as follows.

First, as shown by the dotted line in Figure 1, attach the 25mm
Figure 2 shows the body of the roll material that has been hardened with an extra length of 0.0 mm and deep-cooled before tempering.
It is placed inside an electromagnetic induction coil of 00 hertz intermediate wave, and the electromagnetic induction coil is energized while rotating and moving the roll material up and down to prevent uneven temperature rise.The aim is to reach a depth of about 5m on the surface side of the roll body. The temperature was rapidly raised to 210° C.±10° C., held for 1 minute, and then allowed to cool to room temperature for primary surface tempering. At this point, the surface layer is in an incompletely tempered structure, but first, the entire roll material is immersed in an oil bath.
By repeating tempering once at a roll material temperature of 120°C ± 5°C for 30 hours and then twice at the same temperature for 25 hours, a sufficient tempering effect is achieved overall. did. After completing these heat treatments, the extra length that had been attached to one end of the body was shaved off in several steps.
A depth-wise hardness distribution curve as shown by solid line A in FIG. 3 was obtained. In other words, the Shore hardness is approximately Hs 88 from the surface to a depth of approximately 5 m, and then the Shore hardness rapidly increases to Hs 92 from the surface to a depth of approximately 8 m, after which the conventional tempering method shown by the dotted line B in the figure is applied. This shows that a distribution form equivalent to the depth direction hardness distribution curve was obtained.

Note that the dimensions of one work roll, the total amount of body diameter used, and the amount of body diameter desired for the first stand vary depending on the rolling mill, so a system that can convert the frequency is used as the power source for the electromagnetic induction heating coil. You can deal with it by doing this.

〔Effect of the invention〕

As explained above, according to the present invention, the heat sensitivity of the surface layer is reduced by providing a high-temperature tempering region on the surface layer side of the roll at the initial stage of use when the roll has good biting properties due to its large diameter. To avoid 50 to 70% of the occurrence of thermal effects caused by frequent slips caused by the plate thickness slightly exceeding the limit of biting property in the first stand, which is dull and would normally occur in the case of conventional rolls. However, even if a relatively severe slip is encountered, it can be reduced to 30 to 50% in terms of area and 50 to 70% in depth compared to conventional rolls. At the same time, even if a heat crack were to occur due to a fairly severe slip, the degree of damage would be milder than with conventional rolls for the reasons mentioned above, and the rate of crack growth would be slower than with conventional rolls. This is clear from the fact that the surface layer is endowed with a property rich in toughness.As a result, the roll consumption rate has been reduced to about 70% of the conventional level, and inspection and removal work associated with roll troubles has been reduced to about 70%. It can be reduced to 50%. After the high-temperature tempering area on the surface side is consumed in the first stand, a layer with the same performance as the conventional roll is exposed, so the same roll can be used in any stand other than the first stand. It is possible to use.

As a result, it is possible to significantly reduce troubles caused by roll damage caused by the slip phenomenon that occurred quite frequently on the first stand in the early stages of use of conventional large-diameter machines. The labor and time spent on inspection and deletion work, as well as the roll unit consumption, can be significantly reduced.
Indirectly, both the yield and production efficiency of rolled products can be significantly improved.

In addition, the method of the present invention is applicable not only to cold tandem rolling mill work rolls but also to general cases where the size of the body diameter is determined from the relationship of the pass line for each stand, and it is desirable to select the appropriate hardness for each stand. Another great advantage is that it can be applied to various rolls for tandem rolling mills.

[Brief explanation of the drawing]

FIG. 1 is a front view showing the general dimensions and shape of a work roll to which an embodiment of the present invention is applied and the shape with extra length added to one end of the body;
The figure is a front view showing the heating method during primary tempering according to the present invention, Figure 3 is a graph showing the hardness distribution curve in the depth direction according to the present invention in comparison with the conventional method, and Figure 4 is a roll A graph of experimental results showing the relationship between the hardness of the material and cracks generated by thermal shock. Figure 5 shows an example of a surface crack that occurred due to slipping and progressed below the surface layer due to continued use, leading to spalling. FIG. 1... Trunk part, 2... Shaft part, 3... Usage layer, 4...
- Excess length, 5... Electromagnetic induction heating coil, 6... Medium frequency (or high frequency) power supply.

Claims (1)

[Claims] 1. A work roll for a rolling mill consisting of a body and a shaft, characterized in that a high-temperature tempering region is provided only in the initial surface layer.