JPS5923842A - Graphite steel material for roll for hot rolling - Google Patents

Abstract

PURPOSE:To improve the breaking resistance of a roll for hot rolling by spheroidizing graphite in a molten high carbon steel contg. a specified amount of Cu, and using the resulting steel as the material of the roll. CONSTITUTION:In the manufacture of a roll for hot rolling, Ca-Si or Mg and Fe-Si are inoculated into a molten steel contg. 1.2-1.6% C, 1.2-1.7% Si, <1.0%, Mn, 0.5-1.8% Ni, 0.1-0.25% Cr, 0.2-0.5% Mo, 1.0-3.0% Cu, <0.05% P and <0.03% S to spheroidize graphite in the steel, and the resulting steel is cast into a roll. By the spheroidizing treatment and the addition of Cu as a carbide precipitating element, a roll contg. 5-20 pieces/mm.<2> and 2-6% graphite, <=1.0% by area of massive cementite and 1-10% by area of ferrite is obtd. The roll has high yield strength and superior breaking resistance.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to improvements in graphite steel roll materials used in hot rolling rolls such as bloomers for long steel and rough rolling rolls.

Conventionally, graphite steel materials for rolls used for hot rolling rolls include C1.2 to 1.5% and 8i 1.0 to 1.
．． 7 Excellent, Mn 0.6-1.0%, NiO,5
~1. a*, Or 0.4-1.2%, Mo Q, 3
~0.5%, the balance being Fe, and the hardness adjusted to Hs 30 to 45 by heat treatment is used.

The present invention has been made for the purpose of providing graphite steel that exhibits even better breakage resistance as a roll material than this conventional one. That is, 1. the present invention is a graphite steel roll material for hot rolling, 01.2~1.6.8i 1.2~L
7, Mn 1.0 or less, Ni o,s ~1. s
, Cro, 1-0.25, No. 0.2-0.5
, C! u1. [] ~ 3.0, P O, [ ] 5 or less, 80.03 or less, respectively, by weight%, the balance substantially consists of Fe, and 0a-8i or Mg4 at or after tapping the hot water
- A roll material formed by spheroidizing treatment with Fe-8i etc., containing graphite number 5-20 @/1xa, graphite 2-6 excellent, massive cementite 1.043f or less, ferrite 1-10 % at each area ratio.

In the graphite steel roll material according to the present invention, the chromium content is kept low at 0.1 to 0.25% compared to conventional products, and a new technology has been developed for the purpose of precipitating particularly fine carbide to obtain high yield strength. By adding 0 to 3.0% of Oul to the material and subjecting it to a special heat treatment, the massive cementite that was often found in conventional graphite steel roll materials can be reduced or eliminated as much as possible. While promoting the crystallization of graphite, the crystallization process promotes the precipitation of fine graphite and has a ferrite-phytonite phase structure as a matrix structure. In other words, by forming a υ two-phase structure due to the precipitation of 7E, it is made stronger than conventional graphite steel, and the Ou
Due to the precipitation of fine carbide due to the inclusion of Cu, the present invention provides a material having particularly high yield strength and superior breakage resistance compared to a material without Cu.

The present invention will be explained below, starting with the range of components of graphite steel and the reason for its limitation.

C1.2~1.6% C is 1.2% to crystallize graphite through spheroidization treatment
The above is necessary, but if it exceeds 1.6%, it will cause a lot of lumpy cementite, which is undesirable. , improves heat crack resistance.

st 1.2~1.7*8i is necessary for the purpose of ferrite precipitation and graphite crystallization, and if it is less than 1.296, the graphite will be less than 296 and the ferrite will be less than 1%, and sufficient toughness will not be obtained. This is because the roll material has poor breakage resistance.

On the other hand, if it exceeds 1.796, there is a lot of ferrite (10%
(above), resulting in a decrease in hardness and poor wear resistance.

Mn of 1.0% or less is unavoidable from being mixed in from the blended raw materials, but a small amount of 1.0% or less is useful for improving hardenability and ensuring the hardness necessary for wear resistance. However, if it exceeds 1.0%, it is not preferable because it becomes too hard and the toughness decreases.

Ni O, 5-1.8% Ni is used to improve hardenability as in kites, to ensure hardness to obtain wear resistance as a roll material, and to make the structure dense and ensure toughness. Necessary elements, 0.
54 or more is required. However, if it exceeds 1.8%, it is not preferable because it becomes too hard and the toughness decreases.

Or 0.1 to 0.25 * If too much Or is contained, massive mentite is formed and a significant decrease in toughness is caused, so in the present invention, the upper limit is particularly set to 0.
It shall be 25%. On the other hand, if the Or content is too low, the amount of ferrite will be too large and the wear resistance will deteriorate, as in the case where the 81 content is high, so the lower limit is set to 0.1%.

no□, 2 to 0.5% MO is required to be 0.2% or more in order to improve hardenability and ensure hardness to obtain wear resistance as a roll material. However, if it exceeds 0.596, it becomes too hard and the toughness deteriorates, which is not preferable.

Cu 1.0-3.0% On is an element necessary to obtain high proof strength, and is
Fine Cu carbides are uniformly precipitated in the matrix by strain relief heat treatment at 0 to 600°C. That is, the graphite steel roll material of the present invention has high hardness and high yield strength by particularly containing an appropriate amount of O. This is because if Oul is less than 0%, the amount of carbide precipitated will be small, and if it exceeds 3.0%, no further effect can be expected.

P O, 05% or less, 80.03% or less It is inevitable that P and 8 are contained to some extent as impurities, but if too much P is present, it will precipitate as impurities at the grain boundaries and reduce toughness. The following shall apply. In the case of No. 8, if the content is too high, the shape of the graphite will not be rounded even by the spheroidization treatment and the toughness will decrease, so the content should be 0.03% or less.

The graphite steel roll material according to the present invention has the above-mentioned specific limitation range. In addition, when casting this graphite steel, Oa -81 or Mg + Fe is used as a necessary spheroidizing treatment during or after tapping the metal, as in the past.
-8i etc. are added.

However, in the graphite steel roll material of the present invention, by adjusting the composition as described above and applying a special heat treatment described later, the graphite steel roll material contains 5 to 20 graphites and 2 to 6 graphites.
%, massive cementite 1.0% or less, ferrite 1~
It is characterized in that it contains 109S in various area ratios, that is, it has a ferrite-burfitoni phase structure.

The manufacturing means for realizing such a specific structure is carried out by heat treatment under the following conditions.

That is, the graphite steel roll material having the above components is first 9
It is subjected to diffusion heat treatment at 00 to 1100°C. 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 structure. Here, the temperature range is such that if the temperature is below 900°C, the temperature is too low and the effect for diffusion is small, and if it is above 1100°C, the bulk cementite partially melts and becomes brittle. Next 740-8
Subjected to homogenization and standardization of ferrite at 40°C.

This is done in order to uniformly disperse a small amount of ferrite into the base structure of the panifite for toughening, and to ensure the hardness necessary for the wear resistance of the roll material by air cooling after the standard heat treatment. Here, the temperature range is such that at temperatures below 740°C, ferrite does not become uniform, and at temperatures above 840°C, solid solution of pearlite progresses and ferrite disappears.

Finally, strain relief heat treatment is performed at 500 to 600°C. This is done to precipitate Cu carbides and remove strain from the rolls, but below 500°C the amount of carbide precipitated is too small to achieve high yield strength, and above 600°C the precipitation becomes difficult to occur. .

The graphite steel roll material of the present invention, which has a specific component range in which the Or content is adjusted in this way and contains Cu in particular, and is also obtained by heat treatment under specific conditions, has the following properties: As shown in the example, it has graphite, carbide, and the structure described above.

Next, examples of the present invention are listed below along with conventional examples and comparative examples (those not containing Cu).

Example 6 Graphite steel rolls of 000 x 500 f were manufactured under the conditions indicated. The test results are listed in the attached table.

However, massive cementite, ferrite content, graphite number, and graphite area ratio are measured using an image analyzer.

As confirmed from the above examples, in the graphite steel raw μ material of the present invention, crystallization of graphite is promoted compared to the conventional material, so the lumps generated on the raw μ surface are dispersed. , and cracks are difficult to propagate inside the low μ. In addition, since it has a pearlite phase structure, it has improved mechanical properties, and is characterized by high yield strength and excellent toughness compared to those that do not contain copper. Therefore, according to the present invention, there is provided a low μ material of this type that is resistant to cracking and particularly has excellent breakage resistance.

Patent applicant: Kubota Iron Works Co., Ltd.

Claims (1)

[Claims] +01.2-1.6, 8i 1.2-j, 7
, Mnj, Q or less, NiO, 5-1.8, C! r O
,1~0.25,MoO,2~0.5,Cu
1. o ~ 3.0, P O, 05 or less, 80.03 or less by weight, the remainder is substantially free of Fe, and is spheroidized with 0a-81 or Mg + Fe-8i, etc. during or after tapping. It is a roll material consisting of 5 to 20 graphites (including @/xa and 2 to 6 graphites).
%, massive cementite 1.0% or less, ferrite 1~
A graphite steel roll material for hot rolling, characterized in that it has a structure containing 10% in each area ratio.