JPS6132382B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a spheroidal graphite cast iron Kariba roll made by Kariba cutting and forming. Concerning the provision of spheroidal graphite cast iron Caliva roll.

In a rough stand during hot rolling, the rolled material is at a high temperature and the rolling speed is slow, so the degree of thermal influence on the rolls is extremely large. Therefore,
The rolls used at this location are prone to cracks due to thermal fatigue, and the cracks often develop and cause breakage accidents.

In general, spheroidal graphite cast iron rolls (hereinafter referred to as DCI rolls) have good crack resistance due to the presence of spheroidal graphite, but even when used in stands with the above-mentioned severe thermal conditions, breakage accidents still occur. Is recognized. On the other hand, since the rolling time on a rough stand is long and the DCI roll has a large drop in hardness, this type of roll with a deep caliber is often unable to achieve satisfactory results in terms of wear resistance.

DCI Caliba rolls used in rough stands are required to be excellent in both accident resistance and abrasion resistance, but the currently commonly used DCI Caliba rolls do not satisfy both of these properties. I am unable to do so due to circumstances.

In the past, this problem was solved by the so-called Kariba casting method, but on the other hand, the Kariba casting method has the disadvantage of high casting costs and the tendency to produce defects due to casting defects. Not implemented.

The present invention was made in view of the above problems, and
The purpose is to provide a DCI Kariba roll that is excellent in both wear resistance and accident resistance.The feature is that in the DCI Kariba roll made by Kariba cutting and forming, the hardness of the Kariba bottom is lower than the flange part. The hardness is Hs2 to 10 higher than the hardness at the same depth in the bottom of the caliber, and the amount of spheroidal graphite at the bottom of the caliber is approximately the same as the amount of spheroidal graphite at the same depth at the flange.

The DCI calibarol of the present invention will be explained below along with its manufacturing method.

First, the component range of the DCI roll material according to the present invention will be explained below along with the reasons for its limitation.

C: 3.0 to 3.7% If C is less than 3.0%, the amounts of both cementite and graphite will decrease, and the characteristics of the DCI roll material cannot be fully exhibited. On the other hand, if it exceeds 3.7%, the material becomes brittle.

Si: 1.5-2.5% If Si is less than 1.5%, the amount of cementite is too large and becomes hard and brittle. On the other hand, if it exceeds 2.5%, the amount of graphite becomes too large and becomes soft and the base structure becomes weak.

Mn: 0.2-1.0 Mn is effective in suppressing the harm of S, but 0.2%
If it is less than that, the effect will be small. Furthermore, Mn easily increases base hardness, but if its content increases too much, it makes the material brittle, so the limit is set at 1.0%.

P: 0.01-0.2% P increases the fluidity of the melt, but it makes the material brittle, so it should be kept at 0.2% or less. The lower the P content, the more desirable it is, but if it is less than 0.01%, the above-mentioned effects are slight, and in practice it is difficult to control the content to less than 0.01%, so 0.01% is set as the lower limit.

S: 0.06% or less S, like P, makes the material brittle and also inhibits the spheroidization of graphite, so it needs to be as low as possible.
0.06% or less.

Ni: 0.7 to 3.0% Ni is an element related to graphitization and base hardness, and if it is less than 0.7%, graphitization is insufficient and base hardness is also low. On the other hand, if it exceeds 3.0%, the amount of cementite decreases and the base tends to become thermally unstable bainite or martensite, making it unsuitable for hot rolling.

Cr: 0.05-0.6% Cr is mainly related to the amount of cementite, and if it is less than 0.05%, hardly any cementite will crystallize, causing a problem in terms of wear resistance. the other 0.6%
If it exceeds , there will be too much cementite and it will become brittle.

Mo: 0.1 to 0.6% Mo is related to the amount of cementite and base hardness, and if it is less than 0.1%, the amount of cementite decreases and the base hardness decreases. But 0.6%
If it exceeds , the amount of cementite becomes too large and at the same time the effect of increasing base hardness decreases, which is not economical.

Mg: 0.02-0.1% Mg is necessary for graphite spheroidization, but
If it is less than 0.02%, the effect is insufficient, and if it exceeds 0.1%, casting defects are likely to occur.

The DCI material used in the present invention contains each of the above components in weight percent, with the remainder being Fe and normal impurities.

However, the present invention made of such materials
DCI Calibarol will be explained in detail in the order of its manufacturing process.

Processing before heat treatment One feature of the present invention is that, prior to heat treatment, the DCI caliber roll material obtained by casting is subjected to rough processing in which the caliber portion is cut and formed. FIG. 1 shows, as an example, the rough processing state of a Caliba roll having Diamond Caliba, where the solid line in the figure shows the rough processing state before heat treatment, and the dotted line in the figure shows the product dimensions after heat treatment. in this case,
Of course, the portion a shown in the figure corresponds to the caliber portion, and the portion b corresponds to the flange portion. When rough machining this caliber part, leave 1 to 20 mm (on one side) of its extra thickness (dimension d in the figure). That is,
The smaller this extra thickness is, the more effective it is, but if it is less than 1 mm, the surface decarburized layer during heat treatment cannot be completely removed during the final Caliba finishing process, while if it exceeds 20 mm, the surface cutting allowance will be excessive, and the effect of the present invention will be reduced. This is because it becomes smaller. Although it is not necessary to specifically specify the extra thickness of the flange portion and the extra thickness of the body length, for the purpose of the present invention, the flange portion is generally about 3 mm thick on one side, and the body length is about 5 mm on one side, as an example. Further, the excess thickness of the neck portion and metal portion is not an important issue, and in some cases, the flange portion, body length, neck portion, and metal portion may be heat treated without being processed.

Heat Treatment The present invention is characterized in that the cast material subjected to rough processing as described above is subjected to heat treatment as shown in FIG. That is, FIG. 3 shows the heating and cooling curves of the heat treatment according to the present invention, of which the B zone is particularly important. First, let's talk about the heating temperature.The appropriate temperature is 800℃ for the following reasons, while also referring to the test results in Figure 2.
Determined to be in the range of ~900℃. In other words, the main reason is that when the heating holding temperature exceeds 900℃,
This is because the elongation becomes smaller, causing problems in terms of crack resistance, and conversely, if the temperature is lower than 800°C, the base will not be sufficiently austenitized and the hardness will be low.

In addition, to explain the reference test in Figure 2, this is roll size: 600φ x 1800 (body), chemical composition: C3.42, Si1.98, Mn0.51,
P0.078, S0.012, Ni1.45, Cr0.22, Mo0.18,
The heat treatment temperature was changed for each sample of Mg0.052 (each weight %), and each sample was heat treated under the conditions of a holding time of 6 hours and a cooling rate of 230℃/hour. The elongation was measured at a position of 120 mm from the surface of the part, and this is shown in a graph.

Next, the retention time must be limited to 10 hours or less. This heating holding time is the time required to austenitize the matrix, but the heating rate is 800-900℃ (generally 20-100℃).
If you also take into account the temperature (°C/Hr), instantaneous (OHr) may be sufficient. However, the retention time is 10 hours.
If it exceeds this, unfavorable effects will appear in terms of graphitization of cementite and coarsening of the structure.

Next, cooling treatment after heating and holding is also a particularly important factor in the present invention, and the cooling rate is limited to 50 to 300°C/Hr. This is 50℃/Hr
This is because, if the cooling rate is less than
This is because a cooling rate exceeding 300°C/Hr is practically difficult to achieve using a normal cooling method that cools only the surface of the casting material, and this is a practical upper limit.

In Fig. 3, zone A shows the temperature rising process, and zone C shows the strain relief annealing process after cooling treatment, but neither is particularly special, and the strain relief temperature is generally 400 to 650℃. be done.

The DCI Caliba roll material, which has been subjected to a predetermined heat treatment after rough processing in this manner, is finally finished into a product Caliba roll by cutting off the excess thickness of the Caliba portion and other parts.

The present invention obtained by the above manufacturing method
In addition to improving the toughness of the DCI Caliba roll, it is possible to increase the hardness of the Caliba part, especially the Caliba bottom, and to reduce the amount of spheroidal graphite at the same depth in the flange part without reducing the amount of spheroidal graphite in the Caliba bottom. It can be made equivalent. Next, an explanation will be given based on the actual results. FIG. 4 shows, as an example, the hardness distribution measurement results of Calibarol manufactured under the following conditions in comparison with the corresponding conventional example.

However, test material: Same as the test material shown in Figure 2 above Shape of caliber: Box (width 160, depth 80) Rough processing: Excess thickness of caliber part before heat treatment 8 mm Heat treatment conditions: Heating and holding 850℃ x 2 hours Cooling rate 180℃/Hr From this figure, it can be seen that the hardness of the DCI caliber roll according to the present invention at the caliber part is higher than the hardness at the same depth of the flange part, or in other words, compared to the hardness at the caliber part of the conventional product. and target Hs2~
It can be seen that a hardness increase of 10 is easily achieved. In addition, for the roll of the present invention, the target hardness increase is Hs2 to 10, but this is because an increase in hardness below Hs2 will hardly improve the rolling performance. On the other hand, this is due to the fact that it is difficult to increase the hardness beyond Hs10 using the manufacturing method of the present invention.

Further examples of the present invention are listed below.

Example roll dimensions: 600φ×1600 Hardness: Specified Hs50~55 Chemical composition (weight%): C3.32, Si2.01, Mn0.62, P0.011, S0.005, Ni1.83, Cr0.22, Mo0.31, Mg0.48 Hardness: Hs46 at Kariba bottom (approximately Hs42 for conventional products) Rolling performance: 25% reduction in wear compared to conventional products As described in detail above, the DCI Kariba roll of the present invention has DCI is used as the Caliba roll material, and the hardness of the Caliba bottom is Hs2~10 higher than the hardness at the same depth in the flange, so when hot rolling shape steel, the Caliba bottom has particularly severe thermal conditions during forming process. It has excellent abrasion resistance, and the amount of spheroidal graphite in the bottom of the caliber is approximately the same as the amount of spheroidal graphite at the same depth in the flange, so even if a crack occurs on the bottom of the caliber, a large amount will be present in the bottom of the caliber. Due to the action of spheroidal graphite, its progress can be prevented as much as possible, and it also has excellent accident resistance. Thus, the DCI carivalol of the present invention is
Its useful value as a roll used in a roughing stand in hot rolling is significant.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing an example of a rough processing state of a Caliba roll. FIG. 2 is a diagram showing the relationship between heat treatment temperature and elongation of DCI roll material. FIG. 3 is a diagram showing an example of a heating/cooling curve of heat treatment according to the present invention. FIG. 4 is a diagram showing the hardness distribution of the roll body of a roll according to an embodiment of the present invention in comparison with that of a conventional product.

Claims (1)

[Claims] 1% by weight: C: 3.0~3.7% Si: 1.5~2.5% Mn: 0.2~1.0% P: 0.01~0.2% S: 0.06% or less Ni: 0.7~3.0% Cr: 0.05~ 0.6% Mo: 0.1~0.6% Mg: 0.02~0.1% The balance is Fe and normal impurities, and in the spheroidal graphite cast iron Kariba roll made by Kariba cutting processing, the hardness of the Kariba bottom is higher than the hardness at the same depth position in the flange part. A spheroidal graphite cast iron Karivar roll having a high hardness of Hs2 to 10, and characterized in that the amount of spheroidal graphite in the Kariba bottom is approximately equal to the amount of spheroidal graphite at the same depth position in the flange part.