JPS5952930B2 - Manufacturing method for spheroidal graphite cast iron rolls for hot rolling - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a spheroidal graphite cast iron roll for hot rolling, and more specifically to a method for manufacturing a spheroidal graphite cast iron roll for hot rolling, which can prevent cracks from occurring due to thermal fatigue during hot rolling. Concerning a method of manufacturing cast iron rolls.

Generally, in a rough stand during hot rolling, the rolled material is at a high temperature, the rolling speed is slow, and the thermal effect is extremely large.

As a result, cracks occur in the rolls used due to thermal fatigue, and in severe cases, the cracks propagate, leading to roll breakage accidents.

Further, spheroidal graphite cast iron rolls for hot rolling have good crack resistance due to the presence of spheroidal graphite, but roll breakage accidents still frequently occur in stands with severe thermal conditions.

Therefore, in conventional spheroidal graphite cast iron rolls for rough stands, the amount of cementite has been suppressed.

However, since cementite improves wear resistance at high temperatures, there is a problem in that reducing the amount of cementite deteriorates wear resistance.

The present invention solves the drawbacks and problems of the rolls with rough stands in the conventional hot rolling described above, and improves the crack resistance by improving the structure with a sufficient amount of cementite present. This is a method for manufacturing a spheroidal graphite cast iron roll for hot rolling with improved breakage resistance.

The manufacturing method of the spheroidal graphite cast iron roll for hot rolling according to the present invention is characterized by: C3.0 to 3.7%, Si1.5
~2.5%, MnO32~1.0%, Ni0.7~3.
0%, Cr0.1-0.5%, MOo, 1-1.0%,
A spheroidal graphite cast iron roll consisting of 002 to 0.1% MgO, balance Fe and unavoidable impurities is heat treated at a temperature of 780° to 840°C.

The roll manufactured by the method for manufacturing a spheroidal graphite cast iron roll for hot rolling according to the present invention has a mixed structure of ferrite and pearlite, which can be obtained by heat treatment at a temperature of 780° to 840°C. It is something that can be obtained.

More specifically, the roll manufactured by the method for producing a spheroidal graphite cast iron roll for hot rolling according to the present invention has a structure that is transformed into ferrite 1 near the cementite, and a mixed structure of ferrite and pearlite in the area away from the cementite. There is.

Hereinafter, a method for manufacturing a spheroidal graphite cast iron roll for hot rolling according to the present invention will be explained in detail.

The components and component ratios of the roll material in the method for manufacturing a spheroidal graphite cast iron roll for hot rolling according to the present invention will be explained.

If the C content is less than 3.0%, the amount of cementite and graphite will be small, and the characteristics of a DCI roll cannot be fully demonstrated, and if the C content exceeds 3.7%, graphitization will be promoted. The material becomes brittle.

Therefore, the C content is set to 3.0 to 3.7%.

Si is an element that affects graphitization, and the content is 1.
If it is less than 5%, the amount of cementite will be too large, and
When the content exceeds 2.5%, graphitization progresses and the amount of graphite becomes too large, making the material brittle.

Therefore, the Si content is set to 1.5 to 2.5%. Mn combines with S to suppress the negative effects of S, but when the content is 0.
If it is less than 2%, the effect is small, and although Mn increases hardness, if it is contained in more than 1.0%, the material becomes brittle.

Therefore, the Mn content is set to 0.2 to 1.0%.

Ni increases the hardness of the material without making it brittle, but if it is less than 0.7%, this effect cannot be expected, and if the content exceeds 3.0%, the structure becomes thermally unstable. It becomes bainite and becomes unusable.

Therefore, the Ni content is set to 0.7 to 3.0%.

Cr is an element that promotes the crystallization of cementite, and if the content is less than 0.1%, the amount of graphite becomes too large, the amount of cementite decreases too much, and the wear resistance deteriorates. When the content exceeds 0.5%, the amount of cementite becomes too large and the toughness decreases.

Therefore, the Cr content is set to 0.1 to 0.5%.

Like Ni, Mo has the characteristics of increasing the hardness of the material without making it brittle, and does not reduce the hardness at high temperatures, and it cannot be expected that Mo will exhibit these characteristics if the content is less than 0.1%. Moreover, if it is contained in an amount exceeding 1.0%, the increase in the characteristic will be reduced and it will become unnecessary.

Therefore, the Mo content is set to 0.1 to 1.0%.

Mg is an element that makes graphite spheroidized, and the content is 0.0
If the content is less than 2%, no effect will be observed, and if the content exceeds 0.1%, casting defects will likely occur.

Therefore, the Mg content is set to 0.02 to 0.1%.

The roll material used in the method for producing a spheroidal graphite cast iron roll for hot rolling according to the present invention has the above-mentioned components and component ratios, and can be heat-treated at a temperature of 780° to 840°C. , the area near the cementite can be turned into ferrite, and the area away from the cementite can have a mixed structure of ferrite and pearlite, resulting in excellent performance as a spheroidal graphite cast iron roll for hot rolling.

To explain in more detail, if the heat treatment temperature is lower than 780℃, it is difficult to obtain a mixed structure of ferrite and pearlite, resulting in granular pearlite, which reduces the elongation of the material and at the same time reduces the hardness. As the amount decreases, the hardness increases, the elongation of the material decreases, and the crack resistance deteriorates.

In addition, at a heat treatment temperature exceeding 840° C., the vicinity of cementite tends to turn into pearlite.

Therefore, it is desirable that the heat treatment temperature be in the range of 780° to 840°C.

Next, the relationship between heat treatment temperature and elongation, and the heat treatment temperature and structure in the method for manufacturing a spheroidal graphite cast iron roll for hot rolling according to the present invention will be explained.

C3.31%, Si2.02% by normal melting method
, Mn0.51%, Po, 076%, So, 008
%, Ni 1.86%, Cry 22%, Mo 0.38%
, MgO, 048%, and the balance was Fe to form a molten metal containing impurities, and a roll having roll dimensions of 800φ x 20,001 mm was manufactured.

Next, heat treatment was performed, and the results are shown in FIG.

That is, when the heat treatment temperature is 780°C, the elongation rapidly increases to 2.5% or more, and it shows the highest elongation at 840°C, and when the temperature exceeds 840°C, the elongation rapidly decreases.

Moreover, FIG. 2 is a microscopic photograph of the product heat-treated at a temperature of 720° C., and FIGS. 3 to 6, which will be explained below, show completely different structures in the two-phase mixed structure of ferrite and pearlite.

Figure 3 shows heat treatment at a temperature of 780°C, Figure 4 shows temperature of 800°C.
℃ and 820℃, respectively. As can be seen from the micrographs of FIGS. When the cementite is surrounded by ferrite, cracks that occur in the cementite are difficult to propagate, resulting in greater elongation of the material and better crack resistance.

Figure 6 is a microscopic photograph taken after heat treatment at a temperature of 860°C. Since the ferrite is located away from the cementite, although the mixed structure of ferrite and pearlite itself has a large elongation, the elongation as a whole decreases. .

Next, an embodiment of the method for manufacturing a spheroidal graphite cast iron roll for hot rolling according to the present invention will be described.

Example A roll material in the method for manufacturing a spheroidal graphite cast iron roll for hot rolling according to the present invention is melted by a normal method, and the body part 65 is
0φx15001. A roll of Hs48±2 was made.

Caliber dimensions are 100φ9160φ. Then, the round steel was rolled.

(1) When the heat treatment temperature was 720° C. or lower, 40% of the samples were broken.

(2) When the heat treatment temperature was in the range of 780° to 840°C, 30 pieces were used immediately after the heat treatment, but no breakage occurred.

Therefore, although the mixed structure of ferrite and pearlite itself has a large elongation, the elongation as a whole decreases.

As explained above, since the method for manufacturing a spheroidal graphite cast iron roll for hot rolling according to the present invention has the above configuration,
The manufactured rolls do not develop cracks due to thermal fatigue, and even if cracks do occur, they do not develop any further. Therefore, they have excellent performance as hot rolling rolls that do not cause roll breakage accidents. It has the following.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the relationship between heat treatment temperature and elongation, and FIGS. 2 to 6 are micrographs at each heat treatment temperature.

Claims (1)

[Claims] IC3, 0-3.7%, Si1.5-2.5%, M
n0.2-1.0%, NiO, 7-3.0%, Cr0.
1-0.5%, Mo0.1-1.0%, Mg0.02-
1. A method for producing a spheroidal graphite cast iron roll for hot rolling, which comprises heat-treating a spheroidal graphite cast iron roll comprising 0.1% Fe, the balance being Fe and unavoidable impurities at a temperature of 780° to 840°C.