JPS6333543A - Graphite-crystallized high-chromium roll material - Google Patents

Abstract

PURPOSE:To combine superior seizure resistance with wear resistance, by incorporating specific amounts of Mo in a high-chromium roll material with the prescribed composition so as to crystallize graphite and prevent the deterioration in rollability. CONSTITUTION:The high-chromium roll material is constituted of, by weight, 2.4-3.4% C, 2.0-3.4% Si, 0.5-1.5% Mn, <=0.1% P, <=0.08% S, 4.5-10% Ni, 5-9% Cr, 1.5-3.0% Mo, and the balance essentially Fe, or, in place of a part of Fe, <=1.0% Nb or <=1.0% V is incorporated. Owing to the above composition, crystallization of graphite, temper softening resistance of matrix structure, and resistance to plastic flow can be improved, so that, combined with the formation of high-hardness chromium carbide, superior seizure resistance can be provided together with wear resistance.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to an outer layer material of a rolling composite roll mainly used for hot rolling. Regarding chrome roll materials.

(Prior Art) Metallurgically speaking, high chromium roll materials contain fine high-hardness carbides in their matrix structure, and are characterized by excellent wear resistance. A composite roll in which the outer layer of a rolling roll is formed of such a high chromium roll material is used as a work roll in the front stage of a hot strip mill finishing row.

However, high chromium roll material has low thermal conductivity, so when used for hot rolling under the same rolling conditions, it is more likely to contact the rolled material than a work roll whose outer layer is formed of other roll materials with good thermal conductivity. The drawback is that the temperature rise on the surface of the shell is large.

If the temperature rise on the cylinder surface is large (or the temperature difference with the inside of the cylinder is large), the roughness resistance, abrasion resistance, and crank resistance of the roll will be adversely affected, leading to deterioration of rolling characteristics.

Therefore, as disclosed in Japanese Patent Application No. 57-73947, the present inventor succeeded in improving the thermal conductivity of the outer layer high chromium material by crystallizing graphite in the high chromium structure. This effectively prevented the deterioration of the rolling properties and significantly improved the seizure resistance.

(Problems to be Solved by the Invention) However, recently, rolling conditions have become increasingly severe, and further improvements in wear resistance and seizure resistance are desired. On the other hand, with the graphite crystallized high chromium roll material mentioned above, it is difficult to obtain high hardness due to its chemical composition, and even if a high hardness material is obtained by casting under strict control of the composition. , resistance to softening due to temperature rise during rolling is low, and therefore plastic flow is likely to occur on the work roll surface, making it difficult to provide both excellent wear resistance and seizure resistance.

The present invention was made in view of this problem, and an object of the present invention is to provide a graphite crystallized high chromium roll material that easily obtains high hardness and is less likely to cause plastic flow during hot rolling.

(Means for Solving the Problems) The graphite-crystallized high-chromium roll material of the present invention, which was taken to achieve the above-mentioned objects, is characterized by a chemical composition of C:2. 4~3.4% Si: 2°O~3.4%Mn
: 0.5-1.5% P: 0.1% or less S
: 0.08% or less Ni: 4.5-10% Cr
: 5% to 9% Mo: 1.5% to 3.0% The balance is substantially made of Fe. In addition, in place of a part of the Fe, Nb: 1.0% or less or V:t, O
%% or less.

(Example) Hereinafter, the reason for limiting the components of the roll material of the present invention will be described, and the application to a composite roll will be mentioned.

The chemical composition (unit weight %) of the graphite crystallized high chromium roll material of the present invention is limited for the following reasons.

C: 2.4-3.4% C combines with Cr to form chromium carbide, and
It crystallizes into fine graphite due to graphitization forming elements such as Si and Ni, which will be described later. When C is less than 2.4%, chromium carbide decreases and graphite crystallization also disappears, resulting in a significant decrease in seizure resistance. When C exceeds 3°4%, Cr%
Although there is a relationship with Mo%, in the present invention, Cr is 9.0%.
Below, since MO is limited to 3.0% or less, supersaturated C becomes graphitized due to high St% and Ni%, and a large amount of graphite crystallizes, resulting in poor wear resistance and roughness resistance. .

Si: 2.0 to 3.4% Si is necessary to crystallize graphite in high chromium materials, and in balance with Cr% and MO%, which are white ironing elements,
The amount is determined, but if it is less than 2.0%, there is no effect, and if it exceeds 3.4%, graphite crystallization will be excessive and the wear resistance will be poor. Regarding Si, lower Si during tapping,
It is easier to crystallize graphite if inoculation is performed before casting and the components of the final product are within the above range.

Mn: 0.5-1.5% Actively added along with St to deoxidize the molten metal.
[1 must be at least 0.5%; if the content exceeds 1.5%, the mechanical properties, especially the toughness, will deteriorate significantly.

P: 0.1% or less The smaller the amount of P in the roll material, the more desirable it is, and from the viewpoint of preventing embrittlement, it is set to 0.1% or less.

S: o, os% or less S, like P, makes the roll material brittle, so the smaller the content, the more desirable it is, and should be 0.08% or less.

Ni: 4.5-10% Ni is actively included to improve the matrix structure and crystallize graphite. If it is less than 4.5%, graphite will not crystallize, and if it exceeds 10%, it will be the same as Si. There is too much graphite, and
Austenite becomes stable and does not undergo transformation even during subsequent heat treatment, resulting in poor skin roughness resistance.

Cr: 5-9% Cr combines with C to form Cr carbide, but if it is less than 5%, it has no effect, and if it exceeds 9%, in the present invention, MO, which is a white ironing element, is added to 3.0%. Graphite does not crystallize because it contains up to

Mo: 1.5 to 3.0% Mo enters into the matrix, increases resistance to temper softening, and improves plastic flow resistance, and also enters into the carbide and is effective in improving the hardness of the carbide. Furthermore, due to this improvement in softening resistance and plastic flow resistance, seizure resistance is also improved. 1.5%
If it is less than 3.0%, the effect of L will be small, and if it is contained in excess of 3.0%, there will be a strong tendency for whitening, and graphite crystallization will not be obtained.

Incidentally, Mo, together with Cr, is an element that combines with C to form a carbide, but the strength of its carbide-forming action is slightly weaker than that of Cr. This means that the graphitization coefficient KG
It is clear from the fact that is expressed by the following formula.

K G = 1.0$5i-0,25χMn+0.35
χNi-1,0χCr-0,35χM.

Therefore, in the present invention, since the upper limit of the Cr content is set to 9χ compared to Japanese Patent Application No. 57-73947, M.

Even if it is added up to 3.0χ, there is no adverse effect in terms of graphitization.

In addition to the above-mentioned alloy components, the graphite-crystallized high-chromium roll material of the present invention is made of substantially Fe, but in place of a part of Fe, Nb or It can be contained in Both Nb and V have the effect of refining the casting structure when they are 1.0% or less, but when they exceed 1.0%, they combine with C and inhibit the crystallization of graphite.

In order to investigate the seizure resistance of the graphite-crystallized high-chromium roll material mentioned above, the present inventor conducted a Fabry test as described below.

In the Fabry test, as shown in Figure 1, the test pin 1
1 is fixed to a rotating machine 12 by a shear pin 13, and the other end is attached to a pair of V blocks 14.1 under a constant load P.
14 while rotating the test pin 11,
The presence and extent of seizure is determined by the torque required for rotation.

(1) First, the graphite-crystallized high-chromium roll materials of Examples 1 and 2 and the conventional example shown in Table 1 were melted and cast into block bodies, and test pieces for testing were taken from the block bodies.

Table 1 ■ The test conditions for the Fabry test were as follows.

Test piece dimensions: φ6.5 x 40m!
■Block dimensions......φ12 Test bin rotation speed"..."300 rpm (0.1m
/5ec) Applied load...35kgf, 10
0 kgf test environment: In the atmosphere, without lubrication ■Test results At a load of 35 kgf, no sudden increase in torque, that is, occurrence of seizure, was observed in all three samples.

On the other hand, under the applied load toohgr, in Example 1, an increase in torque was observed 100 seconds after the start of the test, but no rapid increase occurred. Further, in Example 2, no increase in torque was observed even after 120 seconds. However, in the conventional example, an increase in torque occurred at 52 seconds, and then a rapid increase was observed.

When we investigated the cross-sectional structure of the test piece after the test, we found that
While no plastic flow was observed in Examples 1 and 2, plastic flow was observed in the conventional example.

From the above results, it was confirmed that the graphite crystallized high chromium material of the present invention has extremely excellent seizure resistance.

The hardness of each sample was as follows.

Example 1-Hs76.0, Example 2-H577.0
Conventional example: Hs76.5 The graphite crystallized high chromium roll material described above is mainly used as a cast material for the outer layer of a rolling composite roll, but as the inner layer (core) material, A cast iron material with toughness such as high-grade cast iron or ductile cast iron, or a cast steel material such as graphite cast steel is used as appropriate.

In addition, as a manufacturing method for the composite roll, after casting the outer layer by centrifugal force casting, a centrifugal force casting mold containing the outer layer is stood up to form a stationary mold, and the inner layer material molten metal is placed inside the stationary mold. There is a method of pouring molten metal and welding the outer layer and inner layer together, and since it is a tube, it is commonly applied.

In addition, the roll material as used in the present invention means a material that can be applied not only to the rolling roll described above but also to rollers in rolling equipment. Therefore, it goes without saying that the roll material of the present invention can be applied not only to the outer layer material of a rolling roll, but also to, for example, a hollow cylindrical roller such as a hot run table roller.

Next, an example of manufacturing a composite roll having the following dimensions to which the graphite crystallized high chromium roll material of the present invention is applied will be described.

(110 dimensions (unit: in) Product body diameter: 680φ Body length: 1800 Overall length:
3800 (2) Manufacturing method■ In a centrifugal casting device, pour the molten metal shown in Table 2 into the rotating roll casting mold (all of which correspond to the roll material of the present invention) as shown in the same table. Cast at temperature.

Casting amount is 80mm thick (casting weight 2Ton 400K)
g).

Table 2 ■ Outer layer The outer layer was completely solidified 19 minutes after the start of casting.

■ After that, the mold containing the outer layer is vertically erected, and an upper mold and a lower mold for forming the roll shaft are installed in series at both ends of the mold to form a stationary mold, and the molten metal for the shaft core material is placed inside the mold. After it was poured and completely filled, it was covered with a riser heat insulator. The type of shaft core material and casting temperature are as follows.

Example A: High-grade cast iron 1380°C Example B: Ductile cast iron 1365°C ■ After the shaft core material has completely solidified and cooled to room temperature, it is taken out of the mold and subjected to the following heat treatment and machining. Obtained the final product. The heat treatment was carried out at 550° C. for the purpose of decomposing the austenite in the base of both the grains.

(Both Examples A and B) (3) Inspection When the roll body was subjected to ultrasonic flaw detection, Examples A and B
In both cases, it was confirmed that the outer layer and the shaft core were completely connected.

Further, when the outer layer structures were observed under a microscope, it was confirmed that both were composed of fine graphite, chromium carbide, and a matrix.

Furthermore, when the hardness of the outer layer was examined, it was found to be high hardness as shown below, suggesting that it has excellent wear resistance.

Example A...Hs81-85 Example B...Hs78-79 (Effects of the invention) As explained above, the graphite crystallized high chromium roll material of the present invention has Cr: 5-9%, Mo: 1 Since it is made of cast iron material with a specific composition containing .5 to 3.0%, it is possible to improve graphite crystallization and tempering softening resistance of the matrix structure and plastic flow resistance, and it is possible to improve the hardness of chromium carbide. Combined with this, it was possible to achieve both excellent seizure resistance and wear resistance.

As described above, the roll material of the present invention has excellent seizure resistance and abrasion resistance, so it is suitable for rolls used in rolling equipment and as the outer layer of rollers, and has great utility value in this industrial field. .

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of the fabry test procedure.

Claims (2)

[Claims] (1) Chemical composition in weight%: C: 2.4-3.4% Si: 2.0-3.4% Mn: 0
．． 5 to 1.5% P: 0.1% or less S: 0.08% or less Ni: 4.5 to 10% Cr: 5 to 9% Mo: 1.5 to 3.0% The remainder substantially consists of Fe A high chromium roll material with crystallized graphite. (2) Chemical composition in weight%: C: 2.4-3.4% Si: 2.0-3.4% Mn: 0
．． 5-1.5% P: 0.1% or less S: 0.08% or less Ni: 4.5-10% Cr: 5-9% Mo: 1.5-3.0% Nb: 1.0% or V: 1.0% or less A high chromium roll material in which graphite crystallizes, characterized in that the remainder substantially consists of Fe.