JPS6035968B2 - Manufacturing method for forged white cast iron caliber roll - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a forged white cast iron caliber roll.

The present inventors first developed a strong cast iron roll (Hakama Kosho 42-16).
No. 871) was invented.

This strong cast iron roll is made of high-purity cast iron with a structure similar to that of white pig iron, and is given toughness by hot working, and is a high-carbon, strong rutting roll comparable to forged steel rolls. The caliber roll made of forged white cast iron according to the above-mentioned earlier invention, which is used for hot rolling of various shaped steels such as H-shaped, sheet pile, channel, or billet for green material, has a caliber roll made of forged white cast iron according to the above-mentioned earlier invention. The wear resistance, heat cracking resistance, and roughening resistance of this material are significantly improved due to the fine distribution of carbides.

However, conventionally, such caliber rolls have been caliber-processed by turning from the forged white cast iron plain rolls of the previous invention. In other words, all caliber rolls for hot rolling have a deep caliber shape, so in the normal manufacturing method of machining holes by turning from a plain forged white cast iron roll, carbides existing from the outer periphery toward the center, Also, due to the coarsening of the crystal grains, the properties of the side walls of the caliber become non-uniform, and in particular roughness at the bottom of the caliber or heat cracks are likely to occur near the bottom of the side walls.
The present invention is a method for manufacturing a caliber roll, which strengthens the caliber part in order to improve the abrasion resistance, heat crack resistance, and roughness resistance of the caliber part.

An object of the present invention is to provide a method for manufacturing a forged white cast iron caliber roll that has excellent abrasion resistance, heat crack resistance, and roughening resistance in the caliber portion, and also has excellent grain quality.

The present invention confirms that the cause of rough skin and deep heat cracks in a part of Kariba is the coarsening of the carbide structure inside the cast iron. This improves the structure of the caliber part, which was not included in the previous model.

That is, the present invention contains 1.7 to 3.8% carbon and 0.3% silicon.
~2.5%, manganese 0.4-1.0%, plus chromium 0.5-2.0%, molybdenum 0.15-2.0%
, vanadium 0.1-1.0%, tungsten 0.15
Contains ~1.0% of one or more types, P, S, C↓
A smooth shape is obtained by hot forging cast iron with a structure similar to white cast iron, with a total content of harmful elements of Trillion, Sn, Pb, Zn, Sb, and Bi of 0.2% or less, and the balance being substantially Fe. After making it into a roll shape of forged white mirror iron, 800qo~950qo
The gist of the present invention is a method for manufacturing a forged white cast iron caliber roll, which is characterized in that a portion of the caliber is formed by low-temperature forging in a temperature range of .

Cast iron having the composition range according to the present invention is easily hot-worked and is a strongly rutted cast iron roll material, that is, forged white cast iron, and by hot working according to the present invention, the forged structure is destroyed and the carbide is a fine structure. Because it is dispersed throughout the base, the brittleness characteristic of cast iron disappears, and it provides revolutionary plowing properties, as well as excellent abrasion resistance, heat crack resistance, and roughness resistance in some parts of the cast iron.

The reason why the forged white cast iron, which is the starting material of the present invention, is limited to the above-mentioned range of ingredients is as follows.

According to the inventor's tests, the carbon content is close to the eutectic point.
．． It was found that when the temperature exceeds 8%, the high temperature deformation property decreases significantly. On the other hand, when the carbon content is 1.7%, as is clear from the Fe-C equilibrium diagram, the amount of cementite precipitated is small and the roll cannot be given the abrasiveness characteristic of white cast iron. Silicon is added to improve the strength of the matrix and castability, but if it exceeds 2.5%, the strength of the product after heat treatment will decrease, while if it is less than 0.3%, these effects cannot be expected. The content should be in the range of 0.3 to 2.5%. However, the desirable silicon content range for forged white cast iron is 0.4
~1.5%. Manganese chemically combines with sulfur and has the effect of stabilizing austenite and cementite, but if it is less than 0.4%, the effect is weak and if it is contained more than 1.0%, the mechanical strength of the product after heat treatment is lost. Therefore, the upper limit is set at 1.0%.

The alloying elements of chromium, molybdenum, vanadium, and tungsten contained one or more in the forged white cast iron according to the present invention not only prevent the generation of free graphite as much as possible in the cast state, but also , is an element that stabilizes austenite and cementite at high temperatures in a pongee-like manner even during hot working and heat treatment, and in particular, the forged white cast iron according to the present invention has an extremely low content of harmful elements as described above, so graphitization is possible. progresses quickly,
Addition of one or more of the above-mentioned alloying elements is an essential condition.

However, as the amount of these alloying elements increases, they significantly inhibit the high-temperature deformation of the cast object or deteriorate the mechanical properties after heat treatment. It is contained in a minimum amount so that it has a structure similar to a white gun based on iron-carbon binary carbide in the cast state.
That is, chromium is a strong carbide-forming element and at the same time enters into the matrix and densifies the structure, but in order to prevent graphitization it is necessary to add 0.5% or more.

On the other hand, within the composition range of the forged white cast iron alloy according to the present invention, if the chromium content exceeds 2.0%, it becomes extremely difficult to refine carbides, so the chromium content should be 0.5 to 2.0%.
A value within the range of 0% must be selected. Molybdenum needs to be added in an amount of 0.15% or more in order to increase the high-temperature strength of the matrix with a small amount of alloy, but adding more than 2.0% does not improve the effect, and the high-temperature deformation deteriorates.

Molybdenum is usually not used alone but is added together with chromium. Preferably, the combined addition of 0.8 to 1.5% chromium and 0.2 to 0.6% molybdenum significantly improves the heat treatment properties. Like chromium, vanadium is an element that stabilizes carbides, and when added in an amount of 0.1% or more, it exhibits this effect, making the crystal grains of the base finer and the structure denser. In the component range, if the vanadium content exceeds 1.0%, the high temperature deformability will be significantly reduced.

The function of tungsten as an alloying element is almost the same as that of molybdenum, and its effect is exhibited when it is added in an amount of 0.15% or more, but the effect does not improve even if it is added in an amount exceeding 1.0%, and the high-temperature deformability decreases. to degrade. As mentioned above, the forged white cast iron alloy has an extremely low content of harmful elements, and these complex compounds are less likely to precipitate at grain boundaries as impurities.
Hot processing is easy. Furthermore, the fact that there are fewer harmful elements means that even if brittle cementite exists in a network, the grade of the matrix is large, so it is highly likely that the cementite will be easily refined by hot working and dispersed uniformly in the matrix. did. In the forged white cast iron alloy according to the present invention, the maximum permissible phosphorus content is 0.030% when each of the harmful elements is present individually. Exceeding this will reduce the rutting properties of the product.

Sulfur has a particularly large effect on high temperature deformability.0.015
% or less, preferably 0.01% or less. Further, in the forged white cast iron alloy according to the present invention, it has been found through many tests by the inventor that the total content of copper and tin is preferably 0.10% or less, and the content of tin is preferably 0.03% or less.

It has also been found that the total content of the various elements listed as harmful in the present invention is 0.20% or less, particularly 0.15% or less, within a range that does not impair high temperature deformability. In other words, when the content of these harmful elements is high, oxides,
This is because sulfurizing agents form compounds called nitrides, which adversely affect high-temperature deformability. The present invention uses the above-mentioned forged white cast iron alloy for rolling.

It is used as a tool. The temperature range at which white cast iron can be forged is 1,125°C to 90,000°C, but after it has been forged to a plain state, it can be processed at even lower temperatures. becomes effective.

If the depth of the caliber forging is deep, a relatively high temperature range will be required because the center part, where the effect of the break-in forging is relatively small, will be hot worked. On the other hand, in the case of shallow calibers, low-temperature forging in a lower temperature range is effective. When forging at a low temperature of less than 800 qo, fairly deep surface flaws are likely to be formed due to cracks generated from residual redeprite, so in the caliber forging method to improve the properties of the caliber part, a forging temperature of 80 qo or higher is required. do.

Further, when the weight exceeds 950 qo, the deformability of the base is large, so even if local hot working is performed, the coarse residual carbides will not be fragmented. When forged in the temperature range from 800 qo to 95 qo and 0 qo, coarse carbides are mechanically destroyed and the structure becomes finer even though there is no major dimensional change.

In order to obtain a fine surface layer, if the caliber shape is shallow, a temperature range of 800° to 85° is best;
~200 If the surface layer of the river is required,
Higher temperature ranges up to 950 oo are useful. In the present invention, since low-temperature forging is performed after normal forging, special jigs and tools are required to easily perform plastic deformation. Special jigs and tools are determined based on the forging caliber diagram, and must be one-third or less of the medium size of the caliber. This is to reduce deformation stress and prevent surface cracks from occurring. As described above, the caliber forging method of the present invention improves sidewall wear and heat cracking, which have been considered weak points of rolls with holes, and makes it possible to manufacture rolls with higher performance.

Figure 1 shows the difference between the metal flow of the caliber when forging the caliber of the roll after forging and the metal flow opening of the normal turning caliber, and Figure 2 shows the heat resistance sample taken from the caliber surface. 55 when using a crack test piece
This shows the crack distribution of forged Calivar and turned Calivar after the 0oo and 100m test runs, and shows that due to the low-temperature forging of Calibar, the distribution of heat cracks is mainly shallow. .

Table 1 shows the mechanical properties of the side wall of the caliber and the fatigue strength of the bottom of the caliber.By strengthening the caliber in exchange for improving the thermal properties, the strength can be increased by 30%.
%, which means that it will be effective in preventing breakage starting from a part of Caliba. Table 1 Material strength value - U (C: 1.8) The present invention will be explained based on examples.

Example 1 After degassing the molten metal melted and refined in the Eru type electric furnace, 52
It is cast into a mold and heated to a rough roll for billet hot rolling (body diameter 5650, body length 150, total length 2,500, diamond caliber K1, K2, K3, K4 maximum 1150) at a processing temperature of 1080 to pseudo 0℃. After forging and finishing 8 parts in a plane shape, caliber forging was performed at a temperature of 85 to 80 pi.

This mirror block is similar to the white gun and has the following IG chemical components (wt%).

Comparing the usage results of this roll when the roll was subjected to caliber forging and the hole pattern was machined by turning using the conventional method, the results were 180% higher than the conventional roll as shown below.

Example of the present invention Conventional example Turning after forging force lever Forging force lever Forged white cast iron.

-Le White cast iron. -Rolling result: 241 ot.

Example 2 of 1359 (same steel ratio) Rakuyo smelted and refined in a ferret electric furnace was degassed and cast in a 3-hikiku type mold to make a rough roll for H type steel (arm diameter 11500)
After hot forging at a processing temperature of 0 to 0 degrees Celsius to finish the plain-shaped chest, caliber forging at a temperature of 950 to 900 degrees Celsius. I did this.

The original lump is Liu Ori, which is similar to white pig iron, and has the following chemical components (wt%).
)have.

Comparing the usage results of this roll when the caliber forging was carried out and the conventional method when the hole was machined by turning, it was found that the forged white of the turned caliber was improved due to the improved side wall wear resistance due to the caliber forging. The performance was 150% higher than that of cast iron rolls.

Example of the present invention Conventional example: Rikiriba - Turning after casting - Forging white cast iron roll White cast iron.

-Rolling result: 448t.

n/object 299 n-rib *(same steel type ratio) Example 3 After degassing the molten metal smelted in a ferro type electric furnace, 52
Intermediate for billet casting in a chrysanthemum mold.

(arm diameter 6100, body length 120, total length 3550, with 4 calibers up to 200) and processing temperature 1080 ~
After hot forging at 980℃ and finishing the plain-shaped body 9
Caliber forging was carried out at temperatures of 50-900°C. The original lump has a structure similar to that of white pig iron, and has the following chemical components (wt%):
have. Comparing the usage results of this roll when the roll was subjected to caliber forging and the hole pattern was machined by turning using the conventional method, the results were 165% higher than the conventional roll as shown below.

Example of the present invention Conventional example Forging of power lever - turning after casting Forged white cast iron.

-Ru white cast iron o-ru rolling results 9457t.

Comparison of the same steel type that works 5730 tons) Example
4 After degassing the molten metal melted and refined in an Eru-type electric furnace, it was cast into a three-piece chrysanthemum mold and an intermediate roll for H-shaped steel (Tsukioka diameter 110
0◇, body length 2300, total length 5000 and has 4 calibers), hot forged at a processing temperature of 1080 to 980℃, and after finishing the plain-shaped body, 850 to 80000. E
- Caliber forged at temperature.

This coin has a structure similar to that of white pig iron, and has the following chemical components (wt%).
)have. A comparison of the usage results of this roll when the caliber forging was carried out and the hole molded by the secondary method was performed, and as shown below, the performance was 145% compared to the secondary method.

Example of the present invention Conventional example The turning process after forging the J bar is Forged white cast iron roll Forged white cast iron.

-Rolling results 673tons 464to~
Nori (same steel type ratio)

[Brief explanation of drawings]

Figure 1 is a diagram showing the metal flow of a roll caliber, A is a diagram showing the metal flow of a forged caliber, and Figure 2 is a diagram showing the metal flow of a turned caliber. Figure 2 shows cracks in a forged caliber and a turned caliber after a heat crack resistance test. It is a schematic diagram showing a distribution situation. Kayanozuta 2

Claims (1)

[Claims] 1 1.7-3.8% carbon, 0.3-2.5% silicon, 0.4-1.0% manganese, plus 0.5-2.0% chromium
%, molybdenum 0.15-2.0%, vanadium 0.1
~1.0%, tungsten 0.15~1.0%, P, S, Cu, As, Sn, Pb
, Zn, Sb, Bi, the total content of harmful elements is 0.2
% or less, and the balance is substantially Fe, which has a structure similar to white cast iron, is hot-forged to form a smooth forged white cast iron roll shape, and then by low-temperature forging in a temperature range of 800°C to 950°C. A method for manufacturing a forged white cast iron caliber roll, characterized by forming a caliber part.