JPS5810983B2 - Tough and wear-resistant composite roll - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a composite roll whose outer shell is made of a chilled material having high strength and superior wear resistance to conventional materials.

Traditionally, rolls for hot steel rolling that require both strength and wear resistance include single chilled rolls with an outer shell made of white iron and an inner shell made of gray iron, and outer shells made of chilled material that has become white. Composite chilled rolls whose inner shells are formed by casting ordinary cast iron or strong cast iron are often used.

The chemical composition of the chilled material used for the outer shell material of this single roll or composite roll is C:3. O~4.0%, Si:0
．． 2-0.6%, Mn: 0.2-0.6%, Ni: O~
4.0% (0 to 4.5% for composite rolls), Cr: 0 to
1.2% (0.2-1.2% for composite rolls), Mo:
0-0.3% (O-0.5% for composite rolls), P: 0
．． 4%, S: around 0.06%, but one characteristic of this type of conventional chilled material is that Cr is generally 1.
The content should be 2% or less, because chilling can be achieved sufficiently at this level.

Also, in the case of composite rolls, the P content is high, but this is due to reasons such as melt flow, but it is also because it increases the amount of steadite produced and contributes to improving wear resistance together with cementite. be.

Therefore, if the P content is lowered to avoid embrittlement of the material, the wear resistance will be poor.

By the way, in order to improve the wear resistance of chilled materials,
It is thought that this is mainly achieved by increasing the amount of cementite, increasing the hardness and strength of the cementite itself, and increasing the hardness of the matrix. Merely increasing the hardness of the material not only makes it difficult to manufacture as it cracks easily during casting, but also tends to cause cracks, chipping, and chipping during use, resulting in problems with accident resistance.

That is, in order to provide a chilled material with excellent wear resistance, high toughness is also required.

The present invention has succeeded in developing a composite chilled roll with particularly excellent wear resistance by using a chilled material improved to be strong and with excellent wear resistance for the outer shell. The characteristics of the composite roll are that the outer shell contains C: 3.4 to 3.9%, Si: o, 2 to i
, o%, Mn: 0.2-0.8%, Ni: 3.
0 to 5.0%, Mo: 0.2 to 0.8%, Cr: 1
．． 3 to 2.2%, P: 0.06% or less, S: O, O% or less, and the total residual of rare earth elements such as Mg and Ce is 0.0
It is made of a chilled material consisting of 15 to 0.05% with the balance being Fe and has a Shore hardness of 80° to 90°,
The inner shell is made of ordinary cast iron, alloy cast iron, or ductile cast iron.

In describing the present invention in detail below, the main points regarding improvement of the chilled material used for the outer shell of the composite roll will be listed and explained below.

(1) Conventionally, it has been said that when the C content is as high as 3.5 to 3.7%, it becomes brittle and is not desirable as a roll for hot steel rolling, but when P and S are low, = -C content It was found that the strength did not decrease much even when the temperature was high.

(2) P deteriorates the strength of chilled materials,
Conventional rolls contain about 0.4% of this P, and the abrasion resistance is improved by the large amounts of steadite and cementite produced.

However, in the present invention, by increasing the amount of cementite due to the high C content, and by increasing the amount of Cr added,
It has been demonstrated that a product that is strong and has excellent wear resistance can be obtained.

(3) It was found that maximum strength can be obtained with a Cr content of 1.5 to 2.0%.

(4) It has been found that reducing the S content and incorporating an appropriate amount of Mg increases the strength regardless of the presence or absence of graphite due to its desulfurization and deoxidation.

Furthermore, in cases where the presence of graphite was observed, it was confirmed that both the amount of graphite and the number of graphites decreased due to the tendency of Mg to become white.

Each component of the improved chilled material used for the outer shell of the composite roll of the present invention will now be explained in more detail.

C: 3.4-3.9% Rolls other than rolls for hot steel rolling often have a C content of around 8%, but rolls for hot steel rolling ensure their toughness. In this sense, it is customary to have a relatively low value of 03.1 to 3.6%.

On the other hand, in the present invention, the C content is increased, but at the same time the P content is kept low, so that the toughness is not impaired, as will be clear from the test results described below.

Almost no C becomes graphite, and most of it becomes primary cementite, and it is desirable to increase the amount of primary cementite as much as possible in order to improve wear resistance.

However, in the present invention, the lower limit of the C content is set to 3.4% so that primary crystal cementite exceeding 40%, which ensures sufficient wear resistance, can be obtained.

However, if the C content is too high, the cast structure becomes rough inside and becomes an unrestricted structure from the surface to the inside, which is inappropriate, and therefore the upper limit is set at 3.9%.

Si: 0.2-1.0% If Si is less than 0.2%, deoxidation will be insufficient.

However, Si promotes the appearance of graphite, and 1.0
% or more, it is unsuitable because the amount of graphite increases to a certain extent even in relation to other component ranges.

Mn: 0.2-0.8% If Mn is less than 0.2%, deoxidation becomes insufficient.

However, Mn, together with Si and Cr, affects the embrittlement of the hardened structure after strain relief, and in this respect, a problem occurs when Mn is 0.8% or more.

Ni: 3.0-5.0%, Mo: 0.2-0.
8% Ni and Mo are the most effective for obtaining high hardness, and depending on the strain relief heat treatment, in this composition range, the hardness is about Hs 6° for 1% Ni, and about 12° hardness for 1% Mo. This greatly increases the hardness.

The above-mentioned Si and Mn do not significantly affect the hardness within their component ranges.

So, let's talk about Ni first. It is mainly Mo.
In correlation with the upper limit of 0.8%, the lower limit is set at 3.0% in order to obtain the target hardness, but the upper limit is set at 5.0% because of this component range. This is because if the combination exceeds this limit, the austenite will become stabilized and casting cracks will occur.

Next, regarding Mo, 0.2% is the effective lower limit, and about 0.2% also contributes to the toughness of the material.

On the other hand, the upper limit of 0.8% for Mo was determined based on the economic efficiency of Mo, which is expensive in the correlation between the amounts of Ni and Mo.

It should be noted that the most economical amount of Mo is usually about 0.3% in order to obtain the target material structure.

Cr: 1.3 to 2.2% Cr is an element that greatly contributes to improving toughness, as will be clear from the test results described below.

Conventionally, Cr has been used as the main element for chilling.
The amount was determined in balance with the amount of Ni, but in the present invention, the range is set to 1.3 to 2.2% from the viewpoint of maximizing the toughness of the material.

P: 0.06% or less As will be clear from the test results described later, P has a large effect on the deterioration of toughness, and in particular, when treated with rare earths such as Mg, toughness is generally reduced at 0.06% or more. Therefore, Po is set to 0.6% or less.

S: 0.03% or less S is 0.03% or less to stabilize the chilling tendency caused by Mg treatment, etc.
03% or less.

S is usually contained in an amount of about 0.01 to 0.02%, but it is thought that this remains after combining with Mg and the like.

Rare earth elements such as Mg and CeMg or similar rare earth elements such as Ce act to stabilize chilling, but if this residual 4. total is 0.0
The reason why we set it to 15-0.05% is that below 0.015%, S
This is because the chilling tendency tends to become unstable depending on the amount and the balance with other components, and on the other hand, if it exceeds 0.05%, impurities tend to become foreign substances and the material quality changes.

Incidentally, even when Mg is 0.015 to 0.05% in the above-mentioned component ranges, most of the C in the outer shell structure of the used part is cementite, but some lumps of graphite may be included.

The range of each component of the chilled material used for the outer shell of the composite roll is as described above, but in the composite roll of the present invention, the outer shell is formed of such a chilled material, and the inner shell (core material) is made of a conventional material. As in the case of composite chilled rolls, they are made of ordinary cast iron, alloyed cast iron, or ductile cast iron, depending on the field of use.

A specific example of the composite roll of the present invention is as follows.

Example roll dimensions: 330 φ x 5101 mm, thickness used: 20 m, outer shell thickness: 32 mm Next, in order to demonstrate the characteristics of the chilled outer shell material in the composite roll of the present invention, the following tests were carried out.

That is, for each chilled material listed in Table 1, 340
A roll material of φX5801X45t was manufactured and subjected to the tests shown in Table 2.

Here, each roll material was cast by centrifugal force casting using a GNO140 mold, cooled to approximately the same cooling conditions as during roll manufacturing, and further subjected to eggplant heat treatment twice at 300°C for 10 hours. The test piece used for the bending test was taken at a 20φ x 1401 mm centering on a position 15 mm from the outer surface of each roll material, and the part corresponding to the outer surface side of the roll material at 20 mm The test was conducted with the glass facing down, and the test results show the average value of the four pieces.

Based on these test results, C for toughness (transverse rupture strength)
, Cr and P are illustrated in the graphs of FIGS. 1 to 3. According to FIG. 1, the left culm transverse rupture strength is It can be seen that the transverse rupture strength does not decrease, and according to Fig. 2, it can be seen that increasing the amount of Cr greatly contributes to improving the transverse rupture strength, and according to Fig. 3, the increase in P significantly reduces the transverse rupture strength. I understand.

Next, examples in which a rare earth element is contained together with Mg are listed below.

However, the manufacturing conditions and testing conditions for the sample materials are the same as in the previous example.

As is clear from the above test results, the chilled outer shell material used in the present invention has higher strength and strength than conventional materials.
Both the hardness and the strength are significantly improved.

In the composite chilled roll formed from this chilled material, the tensile strength of the conventional chilled shell material is 16
~25kg/mm2, while 40~50kg
/mA, and its hardness is 80° to 90° in terms of Shore hardness.

Therefore, in the composite roll of the present invention, the outer shell material has a high hardness that was virtually impossible in the past, and its wear resistance is dramatically increased. Because of its properties, it does not crack during casting, and there is little risk of cracking, chipping, chipping, etc. during use, and its accident resistance is extremely good.

The composite roll of the present invention maximizes its wear resistance by simultaneously increasing the strength of the chilled outer shell. It is applicable to rolling rolls including rolling rolls, other composite chilled rolls and rollers such as straightening machine rollers and wear-resistant rollers, and furthermore, its excellent outer chilled material alone can be used for various types of durability. It can also be used for wear parts.

[Brief explanation of drawings]

Figure 1 is a graph showing the effect of the amount of C on the transverse rupture strength in chilled materials, Figure 2 is a graph showing the effect of the same amount of Cr on the transverse rupture strength, and Figure 3 is the effect of the same amount of P on the transverse rupture force. It is a graph diagram showing the influence.

Claims (1)

[Claims] 1. The outer shell is made of C: 3.4 to 3.9%, Si: 0.2 to 1
．． 0%, Mn: 0.2-0.8%, Ni: 3.0-
5.0%, M. : 0.2-0.8%, Cr: 1.3-2.2%, P
: 0.06% or less, S: 0.03% or less, and the total residual amount of rare earth elements such as Mg and Ce is 0.015 to 0.
．． 05% with the remainder being Fe, and Shore hardness of 80°~
The inner shell is made of a chilled material having an angle of 90°, and
A tough and wear-resistant composite roll characterized by being formed of ordinary cast iron alloy cast iron or ductile cast iron.