JPS5835576B2 - Manufacturing method of chilled material for rolling rolls - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a chilled material for a mill roll, and more particularly to a method for producing a chilled material for a mill roll having excellent wear resistance.

In general, when the hardness of finishing rolls for rolling shaped steel, such as angle channels, is low, the material for rolling rolls is low, the wear resistance is poor and the amount of rolling is small.If the hardness is increased to improve the wear resistance, the top roll ( In the case of a concave roll, there are various problems such as cracks occurring on the circumference of the caliber seat and crescent-shaped cracks occurring inside the caliber.

Therefore, rolling rolls are made by casting chilled molten metal into a mold by vertical blowing or centrifugal casting, and after cooling,
It was manufactured by removing strain at a temperature of ~550°C.

In addition, the chilled material of this rolling roll contains a large amount of cementite in the microstructure, and the base structure is also tempered martensite mainly composed of sorbite, and the toughness of the entire structure is σB-60 to 70 kg/ myj, which is a small value, and therefore the material that can be matched with the applicable rolling stand is only within a narrow range, and the rolls were produced using a manufacturing method suited to each individual case.

Incidentally, as shown in the micrograph in Figure 1, the microstructure of conventional rolling rolls made of chilled material is mainly composed of sorbite and tempered martensite. Decomposition and the formation of graphite lead to a significant decrease in hardness.

The present invention solves the various problems with the conventional chilled materials for rolling rolls described above, and manufactures chilled materials for rolling rolls that have excellent wear resistance, high bending strength, and high hardness. It is the law.

The characteristics of the manufacturing method of the chilled material for rolling rolls according to the present invention are as follows: C2.8 to 3.5%, Si0.3 to 0.9%.
%, Mn 0.3-1.2%, Ni 1.5-3.5%
, Cr2. After forming a molten cast iron consisting of O ~ 5.0%, Mo 0.2 ~ 1.0%, and the balance substantially Fe into a roll shape by vertical blowing or centrifugal casting, 95
Heating to 0°C or higher and -50°C/deg below the solidus line, then rapidly cooling and holding in a temperature range of 450°C to 550°C,
After that, it is heated again to 7800-860°C and then cooled.

The method for producing a chilled material for rolling rolls according to the present invention will be described in detail below.

In the method for producing chilled material for rolling rolls according to the present invention,
-50'C/deg below the solidus line at 950°C or higher (described later)
In order to prevent graphitization when heated to a temperature of 1, the content of graphitization-promoting elements such as Si and Ni should be low, and the content of graphitization-inhibiting elements such as Mn should be reduced.

It is preferable to have a high content of Cr, Mo, etc.

Next, each component and component ratio of the chilled material used in the method for producing a chilled material for a roll according to the present invention will be explained.

C is an element that determines the ratio of cementite and graphite together with Si, and if the C content is less than 2.8%, the amount of cementite is too small and the wear resistance is poor;
If it exceeds %, the amount of cementite will be too large and the toughness will be significantly reduced, and furthermore, the effect of high temperature treatment will be reduced.

Therefore, the C content is set in the range of 2.8 to 3.5%.

Si is an element that determines the ratio of cementite and graphite together with C, and up to 0.3% is introduced from the raw material, but at this content there is no graphite and there is only cementite, and the Si content is 0.3%. If the amount exceeds 9, the graphitization effect becomes too large.

Therefore, the Si content is set to 9.3 to 0.9%.

Particularly desirable is a Si content of 0.7% or less.

Up to 0.3% of Mn is mixed in from raw materials, but if it is less than 0.3%, it has no deoxidizing effect, and if the C content exceeds 1.2%, it delays Ar1 transformation, making it fragile. Becomes a material.

Therefore, the Mn content is in the range of 0.3 to 1.2%.

Ni is an element that increases the strength of the matrix, but if the Ni content is less than 1.5%, the matrix strength decreases, and
If the Ni content exceeds 3.5%, Ar1 transformation will be delayed, making it difficult to obtain a pearlite-based material.

Therefore, the Ni content is set to 1.5 to 3.5%.

If the Cr content is less than 2.0%, graphitization cannot be prevented, although it has a relationship with Si, and if the content exceeds 5.0%, a large amount of Cr carbide will be produced, making it difficult to heat treatment. less effective.

Therefore, the Cr content is set to 2.0 to 5.0%.

Mo is an element that inhibits graphitization, but its content is 0.2%.
If the content is less than 1.0%, the effect will not be achieved. If the content exceeds 1.0%, the material becomes brittle, as in the case of Mn.

Therefore, the MO content is set in the range of 0.2 to 1.0%.

Furthermore, in the method for manufacturing a chilled material for rolling rolls according to the present invention, heat treatment thereof will be explained.

The above-mentioned chilled material is 950℃ or above solidus line -500C/
When heated to 100°C, two phases of cementite and γ are formed, and the state of diffusion between these two phases appears as a slight decrease in cementite.

At temperatures below 950°C, the diffusion rate is low and there is little effect on thermal stability, and at temperatures above -50°C/deg below the solidus, partial melting begins, resulting in a completely different structure. be.

Therefore, the heating temperature after casting into a roll is set at 950°C or higher and -50'C/deg below the solidus line.

In addition, the reason for cooling to 450°-550°C after the above heating is to prevent the generation of residual stress and save energy.
This is because below 450°C, a yield point occurs, and above 550°C, untransformed γ remains.

This cooling is done rapidly by spray water cooling. However, other cooling means may also be used.

After this cooling, the reason for reheating to 7800-860°C is to granulate the matrix; granulation does not occur below 780°C, and granulation is completed in the shortest time at a temperature of 830°C. Above 860°C, the matrix does not become granulated.

Next, an example of the method for manufacturing a chilled material for a rolling roll according to the present invention will be described.

Example 1 As an upper roll for angle finishing of 370ψ×500d,
An outer shell with an inner thickness of 55 mm is cast into a mold that fits these dimensions by centrifugal force casting, and after solidification, the core material is spheroidal graphite cast iron (F
CD50) was welded.

In this case, the components of the outer shell are C3.01%, Si0.54
%, Mn0.68%, Ni2.45%, Cr2.23%
, Mo0.41%, balance Fe.

This obtained roll material is roughly processed, and while both neck parts are rotated by rollers, only the body part is heated to 1050 ° C.
After holding for 90 minutes, cooled to 470°C by spray water cooling,
Immediately thereafter, it was heated to 830°C and held for 10 hours.

Next, it was air-cooled to 650°C and then furnace-cooled to 200°C.

Thereafter, strain relief was performed at 550° C. for 10 hours.

The structure at this time is equivalent to the micrograph shown in Figure 2,
The bending strength was 82.0 to 9/lni, and the Hs was 71.5°.

Incidentally, the structure of the chilled material obtained by the method for manufacturing a chilled material for rolling rolls according to the present invention is as shown in the micrograph shown in FIG. 2, in which the matrix forms granular cementite.

Mechanical properties and bending strength a B = 80-90 kg
/i+j, Hs = 65° to 75°.

It goes without saying that large amounts of graphite are not produced due to the decomposition of cementite.

Example 2 An example applied to a ψ400×1001 round bar roll is shown below.

3.20% CSO, 72% Si, 0 as outer shell material
．． 65%Mn, 2.30%Ni, 2.89%Cr, 0.
A composite roll containing 33% Mo and having a core material of FCD50 was cast.

The obtained material was roughly processed by heating in the same manner as in Example 1, held at 980°C for 120 minutes, and then cooled with blast to 450°C.

Immediately, the mixture was heated to 830°C, held for 5 hours, blast cooled to 650°C, and then cooled in a furnace.

Thereafter, strain relief was performed at 600° C. for 10 hours.

The microstructure at this time is also the same as in Figure 2, and the hardness is Hs
66.5°, bending strength cyB=85.6ky/m
It showed a.

As explained above, since the method for manufacturing a chilled material for rolling rolls according to the present invention has the above configuration,
By strengthening the matrix structure of chilled materials and treating them at high temperatures, heat resistance stability can be improved.When applied to rolling rolls as chilled materials, wear resistance and crank resistance are improved, compared to conventional chilled materials. This has the effect of obtaining rolling results that are more than twice as good.

[Brief explanation of drawings]

FIG. 1 is a microscopic photograph of a conventional chilled material, and FIG. 2 is a microscopic photograph of a chilled material obtained by the method for producing a chilled material for rolling rolls according to the present invention.

Claims (1)

[Claims] IC2: 8-3.5%, SiO: 3-0.9%,
Mn0, 3-1.2%, Ni1.5-3.5%, Cr2
．． After forming a molten cast iron consisting of 0 to 5.0% Mo, 0.2 to 1.0% Mo, and the balance substantially Fe into a roll shape by vertical blowing or centrifugal casting, the solidus temperature is 950°C or higher. Heat to below -50 °C/deg, then 45
0 (quickly cooled and held in the temperature range of 550°C, then cooled again to 780°C)
A method for producing a chilled material for rolling rolls, which comprises heating to -860°C and then cooling.