JPS6043428A - Production of graphite steel roll - Google Patents

Abstract

PURPOSE:To obtain a graphite steel roll for hot rolling having high resistance to fracture and wear by subjecting a molten metal having a specific compsn. to a spheroidizing treatment, casting a blank material for a roll from said metal and subjecting the blank material to caliber working then to a thermal diffusion treatment, quick cooling and stress relief heat treatment. CONSTITUTION:Ca-Si and Mg+FC-Si are inoculated to a molten metal consisting, by wt%, of 1.2-1.6 C, 1.2-1.7 Si, <=1.0 Mn, 0.5-1.8 Ni, 0.1-0.25 Cr, 0.2-0.8 Mo, <=0.05 P, <=0.03 S, and the balance Fe, by which the molten metal is spheroidized. A blank material for roll is cast from such molten metal and subjected to caliber working. The material is subjected to a diffusion heat treatment at 900-1,100 deg.C and is held at 800-900 deg.C and after the material is subjected to discharge from the furnace air cooling spray water cooling followed by quick cooling, the steel is subjected to a stress relief heat treatment at 550- 620 deg.C. Graphite is thus formed to a number of 5-20 pieces/mm.<2> in the structure and cementite is made <=1.0% in area %. Graphite is formed at 2-6% and ferrite at 1-10% and 45-55 deg. hardness Hs and 55-70kg/mm.<2> 0.2% yield strength are provided to the material.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing graphite steel rolls used for hot rolling rolls such as bloomers for long steel and rough rolling rolls.

Conventionally, as a graphite steel material for rolls used for hot rolling rolls, those having the composition listed in Table 1 and having a hardness adjusted to a hardness of Us 30 to 45° by heat treatment are used. .

Table 1 Chemical composition (W and %) However, the conventional graphite steel rolls mentioned above are not breakage resistant.

It was difficult to say that the abrasion resistance was sufficient6.Therefore, in Japanese Patent Application No. 57-154042, the applicant of the present application
We proposed a new graphite steel roll roll with excellent breakage and wear resistance.

The object of the present invention is to provide a method for manufacturing a graphite steel roll based on the roll material proposed above, which has further improved breakage resistance and wear resistance, and is characterized by:
Oa-Si, M
g + Fe - Perform spheroidization treatment with an inoculant such as Si, cast the molten metal to obtain a roll material, then perform caliber processing on the roll material, and then 900 to 1100 °
After performing diffusion heat treatment at 0°C, holding at 800-900° OK for a predetermined time, rapid cooling with nitrogen cooling and spray water cooling, followed by strain relief heat treatment at 550-620°C. Generates 5 to 20 graphites/fl'' and 1 area % of lump cementite): suppresses it to 1.0% or less, generates graphite: 2 to 6%, ferrite: 1 to 10%, and has mechanical properties. Hardness: Bs 45-55
°, 0.2% crab resistance 55 to 7011/uIx.

Table 2 Chemical Composition (wt%) The present invention will be explained below, starting with the range of components of graphite steel and the reason for its limitation.

C1.2 to 1.6% C is necessary in an amount of 1.2% or more in order to crystallize graphite, but if it exceeds 1.6%, a large amount of massive cementite is generated, which is not preferable.

Si 1.2-1.7% Si is necessary for the purpose of ferrite precipitation and graphite crystallization! +, if it is less than 1.2%, graphite is less than 2% and ferrite is less than 1%, and sufficient toughness cannot be obtained.

This is because the roll material has poor breakage resistance. On the other hand, 1.7
This is because if it exceeds %, the amount of efficence increases (10% or more), leading to a decrease in hardness and resulting in poor wear resistance.

1.0% or less Mn cannot be avoided from mixing raw materials, but it is less than 1.0%.
A small amount below is useful for improving hardenability and ensuring the hardness necessary for wear resistance. However, if it exceeds 1.0%, it becomes too hard and the toughness decreases, which is not preferable.

Ni Q, 5-1.8% Ni is used to improve hardenability like Mtn, to ensure hardness to obtain wear resistance as a roll material, and to make the structure dense and ensure toughness. It is a necessary element, and 0.5% or more is necessary. However, if it exceeds 1.8%, it becomes too hard and the toughness decreases, which is not preferable.

Or 0.1 to 0.25% If too much Or is contained, it will form massive cementite and cause a significant decrease in toughness.
It shall be 25%. On the other hand, if the Or content is too low, the Si-containing water content is high and at the same time the amount of ferrite is too large, which deteriorates the wear resistance, so the lower limit is set to 0.1%.

Mo 0.2-0.8% MO is required to be at least 0.2% in order to improve hardenability and ensure hardness to obtain wear resistance as a low 1v chestnut. However, if it exceeds 0.8%, it becomes too hard and tough.
! +, which is not preferable because it deteriorates.

Po, 0.05% or less, 80.05% or less It is inevitable that some P and S will be included as impurities, but if too much P is present, it will precipitate as impurities at the grain boundaries and reduce toughness, so 0.05% The following shall apply. In the case of S, too, if the content is too bulky, the shape of the graphite will not become round even after the spheroidization treatment, resulting in a decrease in toughness, so the content should be 0.03% or less.

The graphite steel roll material according to the present invention has the above-mentioned specific component range. In addition, when casting this graphite steel, K (3m-8i or Mg + Fe
-8i etc. are added.

(The above description is substantially the same as that in Japanese Patent Application No. 57-134042.) Next, the molten metal of the above components is cast by centrifugal force casting, pouring casting, etc. as usual to obtain a raw A/material.

In contrast to the present invention, which performs rough machining with a finish machining allowance of 5 to 10 mm on an actual rolling caliber, in the previously proposed patent application No. 134042/1987, the outer periphery of the roll material is straight. It was heat-treated under the following conditions.

Next, the rough-processed raw material is
Diffusion heat treatment is performed at 1100°C for 5 to 30 hours.

This is done to diffuse impurities that segregated during as-casting, and to dissolve some of the massive cementite into a solid solution to form a uniform gas structure. Here, if the temperature range is below 90,000°C, the temperature is too low and there is little effect on diffusion, and if it is above 1,100°C, the bulk cementite partially melts and becomes brittle.

Next, the mold is baked by holding at 800°0-900'0 for 5 to 15 hours. In the present invention, in order to make the base structure dense pearlite and high hardness, it is taken out from the furnace and rapidly cooled by air cooling or spray water cooling while rotating on rollers.

The above-mentioned maintenance of 800 to 900°0 is carried out in order to uniformly disperse ferrite in the pearlite base structure and to ensure the hardness necessary for the wear resistance of the roll material after baking heat treatment. Here, the temperature control is because ferrite does not become uniform at temperatures below 800°C, and solid solution of pearlite progresses at temperatures above 900°C, causing ferrite to disappear.

Finally, strain relief heat treatment is performed at 550°C to 620°C for 5 to 50 hours.

By performing the above heat treatment, the number of graphites in the structure is 5 to 2.
0 pieces of Arm"k are generated, and the area percentage of block cementite) is kept below 1.0%. Graphite: 2 to 6% and ferrite: 1 to 10% are all generated. Also, as mechanical properties, Hardness: 1-1s45~55°, 0.2%
Resistance? 55 to 70 Kt/run".

Next, embodiments of the present invention will be explained by comparing them with those of Japanese Patent Application No. 154042/1982.

Example 6 Graphite steel rolls having a diameter of 600 mm and a diameter of 5007 mm were manufactured under the conditions shown in Table 3. Table 4 lists the test results for its mechanical properties.

In addition, the graphite number at the 7Qtsx position from the roll surface,
Table 5 shows the results of measuring the area ratio of graphite, ferrite, and massive cementite using an image analyzer.

Table 5 As is clear from the above test results, the structure of the roll according to the present invention is almost the same as that of Japanese Patent Application No. 57-1.154042 and has excellent crack resistance, and the roll according to the present invention has slightly inferior elongation. It has high tensile strength and 0.2% strength, so it has high fatigue strength and excellent breakage resistance. In addition, it has high hardness, so it has excellent wear resistance.

As described above, according to the present invention, Japanese Patent Application No. 57'-1
Compared to No. 34042, it has a dense pearlite structure, higher hardness, and higher yield strength, so it is possible to provide a graphite steel roll with improved wear resistance and breakage resistance.

Patent applicant: Kubota Iron Works Co., Ltd.

Claims (1)

[Claims] 1.0% by weight: 1.2-1.6% 8i: 1.2-1.7% Mn: 1.0% or less Ni: 0.5-1.8% Or : 0.1-0.25% Mo: 0.2-0.8% P: o, os% or less 8: 0.03% or less, with the balance consisting of Fe and inevitable impurities, into the molten metal
A-8i, Mg+Fe-8i or other inoculants are used to spheroidize the molten metal, the molten metal is cast to obtain a roll material, and the roll material is then potash-processed.
Perform diffusion heat treatment at 1100'OK, 800~900°
After holding at 0 for a predetermined time, the sample is taken out of the furnace, rapidly cooled by air cooling and then sprayed with water, and then subjected to strain relief heat treatment at 550 to 620° 0 to generate blood 2 containing 5 to 20 graphites in the tissue. and bowl-shaped cementite (area%): 1.0%
Graphite: 2-6%, ferrite: 1-10% are produced below, and mechanical properties include hardness: Hs45-55
A method for manufacturing a graphite steel roll, characterized by imparting a 0.2% proof stress of 55 to 70 K14m.