JPH078367B2 - Method for manufacturing work roll for rolling mill - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a work roll for a rolling mill, and is particularly suitable for use in a first stand that requires biting property and accident resistance at the beginning of use with a large cylinder diameter, and is used. The present invention relates to a method for manufacturing a work roll for a rolling mill, which has a performance that can be used for other stands from the middle of the diameter.

[Background of the Invention]

Generally, work rolls for cold rolling mills include, for example, "iron and steel".
As shown in VO7,57, No.5, after quenching the body of the roll material that has been pre-spheroidized, the surface hardness and hardness distribution in the depth direction, stable martensite structure, desirable residual application In order to obtain distribution and the like, the entire body is tempered once or multiple times. The heating temperature at the time of quenching and the heating temperature at the time of tempering differ depending on the chemical composition ratio of the material, the heating method, or the specifications to be obtained. For example, the weight ratio is C = 0.8%, Si = 0.6%. , Mn = 0.
For materials with 5%, Ni = 0.2%, Cr = 3.0%, Mo = 0.2%, some impurities and the balance being Fe, the former is around 950 ° C and the latter is around 120 ° C at general temperature. is there. The hardness distribution in the depth direction of the roll body thus heat-treated is
The highest value is shown on the surface side, and the hardness gradually decreases as the depth increases.

On the other hand, in a cold tandem rolling mill that has a plurality of stands and continuously rolls, the latter stand is required to have wear resistance and rough surface resistance in order to finish the material to be rolled into beautiful and accurate dimensions. . From this point of view, the work roll has a high hardness and is used as the last stand in the early stage of use, as the diameter of the work roll increases and as the hardness decreases, the work rolls gradually move to the front and rear stands, and the hardness becomes the lowest. It is desirable to use it for the first stand up to the point when it comes to rest.

However, in the work roll used for the first stand,
It is extremely important that the so-called biting property, which leads to smooth rolling of the material to be rolled, is good. Therefore, in many cases, the first stand is actually used in the early stage of use when the body diameter is large. This means that if the contact angle between the roll and the material to be rolled is θ and the friction coefficient between the roll and the material to be rolled is μ, the material to be rolled is caught in the roll unless μ> tan θ. It is known that there is no. Where the roll radius is
If R and the amount of reduction are Δh, and tan θ ≈ sin θ is approximately considered, Can be shown as Therefore, it is clear that the larger the roll radius R and the larger the friction coefficient μ are, the more advantageous the biteability is. Also, during grinding, the higher the hardness of the roll, the more likely the grinding wheel is to become clogged and difficult to grind, so the roughness of the ground roll surface becomes a small value and the friction coefficient μ is lowered. Becomes Therefore, from the viewpoint of securing the friction coefficient μ and maintaining the advantageous biting property, it is advantageous that the hardness of the roll is low.

On the other hand, since the pressure to be cold-rolled is that which has been subjected to hot-rolling work, it is normal for the plate thickness to fluctuate relatively in both the width direction and the rolling direction. It is a fact that, due to the variation in the plate thickness, the biting property of the first stand is lowered, and a partial slip occurs between the material to be rolled and the surface of the roll with considerable frequency. This type of slip may occur even when the rolling conditions change suddenly, such as during rolling when the materials to be rolled having different thicknesses, widths or materials are connected by welding or the like. In the case of such a slip, in addition to the plastic deformation heat of the material to be rolled, the rolling oil film between the roll surface and the material to be rolled is broken to cause frictional heat due to direct contact. Against such thermal shocks from slips, it is a well-known fact ("Hitachi critique" Vol.58, No9 (1976-91), but as shown in the experimental results shown in Fig. 4, the higher the hardness, the more the heat rack. It is advantageous that the roll has a low hardness because it has a characteristic that it easily occurs, and the lower the hardness, the less likely it is to generate heat rack.

When the biting property is poor or slip occurs, the roll surface undergoes a microstructure change or heat lag, but the microstructure change part is inferior in strength as compared with the normal part around it, and the local residual thermal stress is not regenerated. Depending on the distribution, the contact Hertz pressure with the material to be rolled or the reinforcing roll supporting the work roll is likely to overlap with each other to cause a crack during operation, and the crack once generated progresses below the surface layer and finally reaches the As shown in FIG. 5, large peeling of the body of the work roll often results in a significant reduction in roll life. The first stand of the cold rolling mill is often equipped with a work roll having a high hardness at the initial diameter in order to secure the biting property.
With this stand, slips occur frequently on the material to be rolled, the rolls are damaged, and the rolling production efficiency is also greatly damaged.

These phenomena have a drawback that the higher the hardness is, the poorer the toughness is, the larger the residual stress of the conventional roll itself is, and the more prominent it is at the beginning of use. At the same time, since it is the first stand, observation of the front and back surfaces of the rolled product that has passed through all the stands and completed the cold rolling shows that there are traces of slips and cracks on the surface of the work roll body used in the first stand. Early detection is difficult, and there is the idea that the slip phenomenon at the first stand is unavoidable to some extent, but troubles in the early stages of using these work rolls result in a marked deterioration of the roll unit and inspection / inspection. There has been a serious drawback in that a great deal of labor and time are spent on the deletion work and that the yield of rolled products and the production efficiency are greatly reduced. Further, if a work roll having a performance suitable for the first stand is manufactured from a new product by the conventional tempering treatment method, the hardness is excessively lowered from the middle of the progress of the use diameter, and only the first stand is used. However, it has a drawback that it cannot be used with any other stand.

The higher the tempering temperature, the lower the heat sensitivity of the roll, and the more tough it is. Therefore, high-temperature tempering is applied only to the surface layer of the roll, and then tempering in the conventional manner provides good biting properties. , Focused on having the performance that can be used with other stands.

As a method of manufacturing a roll having a deep hardened layer, it is possible to make it possible by arranging low-frequency induction heating coils side by side. Kubo, Nakano et al. It is also described that the higher the tempering temperature is, the more advantageous it is when a rolling accident is encountered. However, this paper not only describes the technology of the heating method during quenching, but also states that the higher the tempering temperature is, the better the general idea of general tempering for the entire body is. It is a thing.

[Object of the Invention]

The object of the present invention is to make the first
Used as a stand and has good biteability, and has heat resistance to slip, heat shock resistance and toughness.
Another object of the present invention is to provide a method for manufacturing a work roll for a rolling mill that can be used for other stands after being used for the first stand.

[Outline of Invention]

The outline of the present invention is as follows. That is, in the contact width portion of the roll body surface and the material to be rolled in the steady rolling, the material to be rolled exceeds the tempering temperature of the roll by the plastic deformation heat of the material to be rolled and the relative sliding friction heat.
Causes a fever of ℃. However, due to the cooling liquid that also serves as a lubricant, the surface of the roll body other than the contact width part is cooled to about 50 to 80 ° C., and due to the existence of a lubricating film of the cooling liquid,
Due to heat conduction to and around the contact width portion, the contact width portion on the surface of the roll body is actually kept at a temperature rise of about 1/2 of 150 to 250 ° C. In other words, this is due to the effect of the cooling liquid on the roll during rolling in the steady state, so that the surface of the roll body has a temperature of about 2 times the tempering temperature of the roll.
It can be considered that it withstands the temperature rise of the rolled material which is doubled.

Therefore, the material to be rolled during steady rolling is 150 to 250 ° C.
It can be said that the temperature rise temperature is substantially equal to or slightly lower than the upper limit temperature that the conventional roll can tolerate.

However, if a slip such as a remarkable heat generation during unsteady rolling is encountered, the roll surface will be exposed to an allowable temperature or higher, and that part will be tempered for a very short time but with a high cooling rate (temperature at this time). If the temperature exceeds the quenching temperature of the roll, it will be re-quenched).

From these facts, by applying the tempering temperature as high as possible to the surface side of the roll body only, it is possible to withstand the local temperature rise during the slip caused by the variation in plate thickness that is most often encountered. The focus is on the ability to add. And, as a method, before applying the conventional tempering, use of the roll body in the medium frequency or high frequency electromagnetic induction heating coil in which the temperature rising temperature, the temperature rising depth and the temperature rising rate are easily controlled electrically. By rapidly raising the temperature of only the outer layer of the radial layer and then allowing it to cool to the primary tempering, and then performing the entire tempering of the body like the conventional roll once or multiple times, the above-mentioned performance is obtained. It has been noted that the performance of the same roll is suitable for use in the first stand in the initial stage of use with the same roll, and that the performance that can be used for other stands can be imparted from the stage where the use diameter has progressed.

That is, the present invention is a method for manufacturing a work roll for a rolling mill, wherein a work roll including a body portion and a shaft portion is tempered by heating and cooling the entire work roll after the quenching treatment is performed. After the heat treatment, only the surface layer of the body is heated at 210 ℃ ± 10 ℃, which is higher than the tempering temperature, and then cooled at high temperature. After the high temperature tempering, the entire work roll is kept at 120 ℃ ± 5 ℃. It is characterized in that it is tempered by heating and cooling at a temperature to secure a hardness distribution of a predetermined hardness or less in the depth direction of the surface layer portion.

Example of Invention

 Examples of the present invention will be described below.

Figure 1 shows the initial body diameter of 620 mm, scrap diameter of 530 mm, body length of 1420 mm, total length of 3
A schematic shape of a work roll for a 450 mm 4 tandem cold rolling mill is shown. The roll shown in Fig. 1 is the total diameter
After being used until the middle point of 90 mm, that is, when the Shore hardness has decreased to about HS87, it is heat-treated again and reused to the discarded diameter.

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

First, as shown by the dotted line in Fig. 1, 250m at one end of the body
As shown in Fig. 2, the main body of the roll material, which has been subjected to quenching treatment with extra length of m and deep cooling treatment before tempering, is placed in an electromagnetic induction coil with an intermediate wave of 1000 hertz to prevent uneven heating. Energize the electromagnetic induction coil while rotating the roll material up and down so that it does not come in, making the surface side of the roll body about 5 m deep
The temperature was rapidly raised to 210 ° C ± 10 ° C up to m, held for 1 minute, and then allowed to cool to room temperature for primary surface layer tempering. At this point, the surface layer is in an incompletely tempered structure, but then the entire roll material is immersed in an oil bath and the roll material temperature is
A tempering effect of holding for 30 hours at 120 ° C. ± 5 ° C. once and a tempering operation of holding for 25 hours at the same temperature were repeated twice to give a sufficient tempering effect as a whole. After the completion of these heat treatments, the surplus length portion previously attached to one end of the body portion was carved in several times, and the high temperature tempering having the depth-direction hardness distribution curve as shown by the solid line A in FIG. The area was obtained. That is, the Shore hardness is H up to a depth of about 5 mm from the surface.
At about s88, then at about 8mm depth, after the shear hardness rapidly increased to Hs92, a distribution form equal to the depth direction hardness distribution curve in the conventional tempering method shown by the dotted line B in the figure is obtained. Has been shown. That is, the hardness distribution in the depth direction of the surface layer portion is formed to be at least equal to or less than the predetermined hardness of Hs92 that secures the biting property of the material to be rolled.

Since the size of the work rolls, the total amount of cylinder diameter used, or the amount of cylinder diameter desired to be used for the first stand vary depending on the rolling mill, a frequency conversion method can be used as the power source for the electromagnetic induction heating coil. Can be dealt with.

〔The invention's effect〕

As described above, according to the present invention, after subjecting the work roll to the quenching treatment, the tempering temperature higher than the tempering temperature of the entire work roll is applied to the surface layer portion of the body before tempering the whole work roll. High temperature tempering, then the whole work roll is tempered, so a sufficient tempering effect can be obtained, and the hardness distribution in the depth direction of the surface layer part becomes less than a predetermined hardness and the heat sensitivity of the surface layer part becomes It becomes dull, and troubles due to roll damage caused by the slip phenomenon that occurred in the first stand in the early stage of use with a large body diameter in the early stage of use can be greatly reduced. As a result, direct inspection and inspection can be performed. The labor and time spent for the deletion work and the roll unit can be significantly reduced, and indirectly, both the yield of rolled products and the production efficiency can be significantly improved. In the first stand, it is possible to avoid the occurrence of heat effect due to a considerable frequency of slips caused by the plate thickness part slightly exceeding the biteability limit in the first stand by 50 to 70% of the case of the conventional roll. In addition, even if a relatively severe slip is encountered, the area ratio of the conventional roll is 30 to 50%, and the depth ratio is 50 to 70%.
Can be reduced. At the same time, even if a fairly severe slip is encountered and a heat crack is generated, the degree of damage is more frequent than that of the conventional roll due to the above-mentioned reason, and the progress speed of the crack can be slower than that of the conventional roll. It is also clear from the fact that the surface layer is given toughness, and as a result, it is possible to directly reduce the roll unit consumption to about 70% of the conventional level, and to perform inspection / deletion work related to roll troubles about 50%. % Can be reduced. After the high temperature tempering area on the surface side is consumed by the first stand, a layer having the same performance as that of the conventional roll is exposed. It is possible to use.

Further, the method of the present invention is not limited to cold tandem rolling mill work rolls, but the size of the barrel diameter is determined from the relationship of the pass line for each stand, and it is generally used when it is desirable to select a suitable hardness for each. It is also a great advantage that it can be applied to various rolls for various tandem rolling mills.

[Brief description of drawings]

FIG. 1 is a front view showing schematic dimensions of a work roll to which an embodiment of the present invention is applied and a shape in which an extra length is added to one end of a body,
FIG. 4 is a front view showing a heating method in the primary tempering according to the present invention, FIG. 3 is a graph showing a hardness distribution curve in the depth direction according to the present invention in comparison with a conventional method, and FIG. 4 is a roll. Fig. 5 is a graph of the experimental results showing the relationship between the hardness of the material and the cracks generated by thermal shock. Fig. 5 shows the surface cracks generated by encountering the slip that continue to be used under the surface layer and then spall. It is an external view showing a reached example. 1 ... Body part, 2 ... Shaft part, 3 ... Use layer, 4 ... Extra length part, 5 ... Electromagnetic induction heating coil, 6 ... Medium frequency (or high frequency) power supply.

Continuation of front page (56) Reference JP-A-61-165211 (JP, A) JP-A-56-65929 (JP, A) JP-B-1-19444 (JP, B2)

Claims (1)

[Claims] 1. A method of manufacturing a work roll for a rolling mill, wherein a work roll including a body portion and a shaft portion is subjected to quenching treatment and then tempered to heat and cool the entire work roll. After the treatment, only the surface layer of the body is subjected to high temperature tempering of heating and cooling at a temperature higher than the tempering temperature of 210 ° C. ± 10 ° C., and after the high temperature tempering,
For a rolling mill, characterized in that the work roll as a whole is subjected to the tempering of heating and cooling at a temperature of 120 ° C ± 5 ° C to secure a hardness distribution of a predetermined hardness or less in the depth direction of the surface layer portion. Method of manufacturing work rolls.