JPS61199035A - Manufacture of composite roll having tough neck part - Google Patents

Abstract

PURPOSE:To improve the fatigue strength of a composite roll by casting the body core part and the neck parts of the roll in ductile cast iron having a prescribed composition, austenitizing only the neck parts under prescribed conditions, and subjecting them to isothermal transformation so as to toughen remarkably the neck parts. CONSTITUTION:A composite roll is composed of a body shell part 1, a body core part 2 welded to the shell part 1 as one body, and neck parts 3 formed on both sides of the core part 2 as one body. The neck parts 3 and the core part 2 are cast in ductile cast iron contg., by weight, 3-3.8% C, 0.7-3% Ni, 1.5-2.5% Si, 0.1-0.6% Cr and 0.2-1% Mn. The neck parts 3 are heated to 800-950 deg.C, cooled at 150-500 deg.C/hr cooling rate and held at 350-600 deg.C constant temp. to carry out isothermal transformation.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention relates to a method for manufacturing a composite roll with a strong base.

(Prior art) Since rolling rolls are required to have different properties for the shell surface part that contacts the rolled material, the shell core part and the neck part, the shell outer shell 1 corresponding to the rolling layer as shown in Fig. 3, It is often a composite roll in which the body core 2 and the neck 3 are made of different materials. The properties required of the shell 1 include abrasion resistance and cod resistance.

Roll materials such as chilled materials, grain materials, ductile materials, adamite materials, and high chromium materials can be exemplified as materials that satisfy these properties. On the other hand, toughness is required for the core portion 2 and the neck portion 3, and ductile cast iron, high-grade cast iron, graphite steel, etc. are used.

Incidentally, in recent years, various rolling methods have been developed and adopted in hot strip mills in order to save energy and control the shape of the strip. As for the rolling roll used in this new method, the outer shell of the body must of course have the same properties as the layer used for rolling, as mentioned above, and the neck part must have stronger toughness than before. It has come to be demanded.

The method for manufacturing the composite roll is usually as shown in Fig. 4, after centrifugally casting an outer shell 1, a centrifugal casting mold 4 containing the outer shell 1 is erected, and necks are formed at the upper and lower parts of the die. An upper die 7 and a lower die 6 are provided to form a vertical mold 9, and a molten core material for forming a body core and a base is poured into the mold 9. For the upper mold 7 and the lower mold 6, a slow cooling mold such as a sand mold is usually used, but in order to improve the toughness of the neck part, a rapid cooling mold such as a metal mold is used for part or all of the mold. In addition, in FIG. 4, 5 is a sand mold band, and 8 is a weir.

(Problems to be Solved by the Invention) However, the rapid cooling mold has the disadvantage that casting cracks are likely to occur on the surface of the neck portion, and shrinkage holes are likely to be formed inside the neck portion due to the progress of solidification with the body core.

The present invention was made in view of this problem, and an object of the present invention is to provide a means for improving the toughness of the neck portion without using a quenching mold.

(Means for Solving the Problems) The features of the present invention for achieving the above-mentioned objects are as follows: The body core portion and the neck portion have a weight percentage of C: 3. O
~3.8% Ni:0.7~3.0%Si: 1
．． 5-2.5% Cr: 0.1-0.6% Mn
: 0.2~1.0% Mo: 0.1~0.8
%P; 0. Shout~0.2% Mg: 0.02~0.
08% S: 0.06% or less The remainder is substantially formed of Fe, and only one or both of the neck portions are heated to 800 to 950°C to austenite, and then cooled at 150 to 500°C/) lr. Then, the temperature is maintained at 350 to 600° C. to effect constant temperature transformation.

(Example) Regarding the composite roll to which the present invention is applicable, the outer shell of the roll is made of conventionally used roll materials such as chilled material and grain material, but the core part and the neck part A ductile cast iron material having a specific chemical composition shown below is used as the core material for forming the core material. The unit is weight %.

C: 3.0~3.8% Nt: 0.7~3.0%Si
: 1.5-2.5% Cr: o, i ~0
．． 6%Mn: 0.2-1.0% Mo: 0
．． 1-0.8% P: 0.01-0.2% Mg:
0.02 to 0.08% S: 0.06% or less The remainder is substantially Fe or less.The reasons for limiting the components of the ductile cast iron will be explained.

C,: a, O ~ 3.8% If the C content is less than 3.0%, the amount of graphite will be insufficient, the chilling of the material will be promoted, and the toughness will be significantly reduced;
%, excessive graphitization results in brittleness.

5i:t, 5 to 2.5% Si is an element that promotes graphitization, but if it is less than 1.5%, graphitization does not proceed sufficiently and cementite becomes excessive. On the other hand, if it exceeds 2.5%, the amount of graphite becomes excessive, leading to deterioration in strength, and also having a negative effect on toughening during heat treatment, which will be described later. In other words, pearlite transformation is more likely to occur.

Mn20, 2-1.0% Mn is effective in suppressing the harmfulness of S, but 0.2%
If it is less than %, the effect cannot be expected. Furthermore, although Mn is effective in increasing the height of the matrix, too much Mn tends to make the material brittle, so it should be kept at 1% or less.

P: 0.01-0.2% P improves the fluidity of the molten metal and imparts wear resistance. Therefore, the content is 0.01% or more.

However, excessive addition makes the material brittle, so the content should be 0.2% or less.

s: o, oe% or less S combines with Mg to form MgS and prevents graphite spheroidization, so it is set to 0.06% or less.

Ni: 0.7 to 3.0% Ni has the effect of promoting graphitization and improving matrix hardness. If it is less than 0.7%, the effect will be small, while if it exceeds 3.0%, the matrix base will tend to become martensite, which is not preferable.

Cr: 0.1 to 0.6% Cr is an element that inhibits graphitization, but at least 0.1% is necessary for refining the matrix structure or making the structure of thick castings uniform. On the other hand, if it exceeds 0.6%, graphitization is significantly inhibited and the material becomes brittle.

Mo: 0.1-0.8% 0.1% of io is necessary to form a solid solution in the matrix structure, delay pearlite transformation, and facilitate bainite transformation, but if it exceeds 0.8%, graphite This is undesirable as it inhibits the formation of

Mg: 0.02 to 0.08% Mg is included to make graphite spheroidized, but 0.02 to 0.08%
．． If it is less than 0.02%, the effect is small (causing poor spheroidization,
On the other hand, if it exceeds 0.08%, graphitization is inhibited and casting defects are likely to occur.

In addition to the above-mentioned alloy components, the ductile cast iron forming the core material consists essentially of Fe.

The above composite role, as explained in Figure 4,
After centrifugally casting the trunk shell 4, a predetermined vertical mold 9 is constructed, a molten core material is cast, and the trunk core and neck are integrally cast.

Next, the composite roll obtained as described above is appropriately heat treated according to the outer shell material, and then only the neck portion is subjected to austempering treatment.

That is, for example, as shown in FIG. 1, the shell outer shell 1 and the core 2 are exposed to the atmosphere, and only the neck 3 of the composite roll is inserted into the heating furnace 10.

The barrel outer shell 1 is placed on a rotating roller 11, which rotates the composite roll, so that the neck 3 is evenly heated by the heating furnace 10. According to such means, the heating furnace 10 can also be made small, which is superior in terms of energy saving, and furthermore, the neck portion can be heated extremely efficiently.

The heating furnace 10 preferably has a structure capable of rapid heating, such as a so-called DH furnace in which a large number of heating burners directed toward the circumferential surface of the neck portion are provided on its inner surface.

In addition, although FIG. 1 shows both neck portions 3.3 inserted into the heating furnace 10.10, if only one neck portion is to be strengthened, only the neck portion on that side is inserted into the heating furnace 10. Of course you can do it.

The neck portion 3 is austempered in a heating furnace 10 according to the heat treatment diagram shown in FIG. That is, first,
0 which is heated to 800-950℃ and becomes austenitized
In the core material component system according to the present invention, a minimum temperature of 8°C (10°C) is required to austenitize, but too high a temperature will cause coarsening of crystal grains and eventually deterioration of toughness after heat treatment. The upper limit is 0.degree. C. In this temperature range, the holding time is 0.5 to 10 hours, which is a practical range in terms of production.

Moreover, regarding heating, it is preferable to perform rapid heating. This is because it is possible to prevent heat from being conducted from the trunk core 2 to the trunk outer shell 1 as much as possible. If heat is conducted to the shell side, there is a risk that the properties of the outer shell, which have the effect of the heat treatment already applied according to the properties of the outer shell material, will be impaired.

In addition, when heating the entire roll, the temperature is 400 to 500°C.
The reason why it is desirable to preheat the neck part is to prevent thermal stress cracking from occurring due to the temperature difference between the neck part and other parts when only the neck part is heat treated.

After being austenitized, the constant temperature holding temperature (3
50-600°C) at a cooling rate of 150-500°C/llr. In order to prevent the matrix structure from transforming into pearlite up to the temperature at which the constant temperature is maintained, at least 1.
50℃/Hr is required, and the maximum is 500℃/ll
r is sufficient, and even if the cooling rate is increased further, the effect on the structure remains the same and it is meaningless.

Such a cooling rate can be easily obtained by forced air cooling using an electric fan or the like or spray water cooling.

The constant temperature maintenance temperature was set at 350 to 600°C.
This is because martensitic transformation may occur at temperatures below 50°C, and if this transformation occurs, toughness will be impaired.
On the other hand, if the temperature exceeds 600°C, coarse pearlite transformation occurs, which also deteriorates toughness. At such temperatures, usually 1 to 10
) The temperature is kept constant for 1r.

After the isothermal transformation treatment, the composite roll is air-cooled to obtain a composite roll with the desired tough neck portion. Then, it is processed into the desired roll shape and becomes the final product.

Next, more specific examples will be described together with comparative examples.

+11 Using grain material for the outer shell and ductile cast iron shown in Table 1 for the core and neck parts, a hot strip mill finished work roll having the following dimensions was cast as shown in Figure 4. The upper and lower molds that form the neck were both sand molds.

Body diameter φ7701■×Body length 1750m1 Neck diameter φ450 Dragon, total length 4300 Dragon No. 1 Table (2) After casting Examples and Comparative Examples, strain relief annealing was performed at 420° C. As shown in the figure, only the neck portion was austempered under the following heat treatment conditions.

Austenitization treatment 880℃X1llr Cooling rate from austenite region 200℃/Hr Constant temperature transformation treatment
400°C x 2 hours (3) The rotational bending fatigue strength of the neck portion of the obtained roll was investigated. The sample collection positions (all dimensions from the cast skin condition) are as follows.

Upper neck...800 mj from the torso end! Lower neck taken in the axial direction at a depth of 40 mm...800 wm6 from the body end, 40 mm deep
The test equipment used was an Ono rotary bending fatigue tester, and the test piece was a 10 dragon diameter smooth test piece.

As a result, at the N=107 level Example: 25kg/wm2 Comparative example: 18kg/2 kg Met.

(Effects of the Invention) As explained above, according to the method of the present invention, the core and neck portions of the composite roll are formed of ductile cast iron of a specific composition, and only the neck portion, which is desired to be strengthened, is rapidly heated to 800 to 950°C. After heating to austenite, it is kept at a constant temperature of 150 to 350 to 600 °C to undergo constant temperature transformation.
The neck structure can be made into a bainite structure without producing martensite or coarse pearlite.
The neck portion can be significantly strengthened and fatigue strength can be significantly improved. Also, when casting the neck portion of the composite roll, a slow cooling mold can be used, and casting quality can be maintained favorably.

[Brief explanation of drawings]

Fig. 1 is a partial cross-sectional explanatory diagram showing a heat treatment means according to the present invention, Fig. 2 is an austempering heat treatment diagram according to the present invention, Fig. 3 is a cross-sectional view showing the structure of a composite roll, and Fig. 4 is a cross-sectional diagram showing a composite roll. FIG. 3 is an explanatory cross-sectional view showing a roll manufacturing means. 1... Torso outer shell, 2... Torso core, 3... Neck part,
IO...Heating furnace. 7th figure 2 figure 3rd member R4FA

Claims (1)

[Claims] 1. For a composite roll consisting of an outer shell corresponding to the layer used for rolling, a core part integrally welded to the outer shell, and neck parts integrally formed on both sides of the core part, The weight percentage of the trunk core portion and neck portion is C: 3.0 to 3.8%, Ni: 0.
7-3.0% Si: 1.5-2.5% Cr: 0.1
~0.6% Mn: 0.2~1.0% Mo: 0.1~
0.8% P: 0.01~0.2% Mg: 0.02~
0.08% S: 0.06% or less The remainder is substantially made of Fe, and only one or both of the neck portions are made of 800 to 9
After heating to 50℃ and austenitizing, 150~5
Cooled at 00℃/Hr, then 350-600℃
A method for producing a composite roll with a strong neck part, which is characterized by constant temperature maintenance and constant temperature transformation.