JPH06172927A - High-speed steel series roll material - Google Patents

Abstract

PURPOSE:To produce a high-speed steel series roll material having a fine structure and excellent in surface roughening resistance by preparing steel contg. specified ratios of C, Si, Mn, Cr, Mo, W and V. CONSTITUTION:A high-speed steel series roll material contg., by weight, 1.5 to 2.0% C, 0.2 to 1.5% Si, <=1.5% Mn, 3 to 8% Cr, 6 to 14% 2Mo+W and 5.5 to 7.5% V, and the balance Fe is cast. Heat treatment for this roll material is preferably executed in such a manner that, after the casting, the whole body of the roll is heated to an austenitizing temp., cooling is executed in the temp. range of about 400 to 650 deg.C at about >=300 deg.C/hr cooling rate and tempering is executed at about 500 to 600 deg.C for one or several times. In this way, the high-speed steel series roll material having a good fine structure and improved in surface roughening resistance and high temp. strength can be obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high speed steel roll material having a fine structure and excellent resistance to surface roughening.

[0002]

2. Description of the Related Art As a highly wear-resistant roll material for casting, as disclosed in Japanese Patent Application Laid-Open No. 4-176840, a high speed steel roll material having the following chemical composition (wt%) is known. C: 1.0 to 3.0%, Si: 0.1 to 2.0%, Mn:
0.1 to 2.0%, Cr: 3.0 to 10.0%, Mo: 0.1 to 6.
0%, W: 1.5 to 10.0%, total of one or two kinds of V and Nb: 3.0 to 10.0%, balance substantially Fe As is well known, a finer crystal structure is preferable as a roll material. This is because the finer the crystal structure, the less likely the chipping of the surface structure is to occur, the better the resistance to surface roughening, and the higher the resistance to thermal shock. In order to obtain a fine structure in the cast material, a crystal refining agent may be added, or the material may be rapidly cooled during solidification.

[0003]

However, in the HSS-based roll material, a finely-dividing agent such as V has already been added in a large amount, and even if it is added more than this, the fine-refining effect cannot be expected. Is likely to occur. Further, in the method of quenching during solidification, casting cracks and casting defects are likely to occur in large castings such as rolling rolls.

The present invention has been made in view of the above problems, and is a high speed steel capable of refining crystals while maintaining wear resistance without quenching during solidification and addition of a new crystal refining agent. The purpose is to provide a roll material.

[0005]

The HSS-based roll material of the present invention has a chemical composition of wt%, C: 1.5-2.0%, S
i: 0.2 to 1.5%, Mn: 1.5% or less, Cr: 3 to 8
%, 2 Mo + W: 6-14%, V: 5.5-7.5%
And the balance is substantially Fe.

[0006]

The high-speed roll material of the present invention has an excellent crystal refining effect obtained by selecting a specific component range of the known similar roll material without impairing wear resistance. By miniaturization, it is possible to improve the rough surface resistance and the high temperature strength.

[0007]

EXAMPLES The chemical composition of the HSS-based roll material according to the present invention is limited for the following reasons. Below, all units are wt%
Is. C: 1.5 to 2.0% C combines with carbide forming elements such as Cr, Mo, W, and V to form carbide with high hardness and improve wear resistance.
If it is less than 1.5%, the amount of carbides is small and the wear resistance decreases. On the other hand, if it exceeds 2.0%, it is difficult to obtain a fine structure.

Si: 0.2 to 1.5% Si is added for the purpose of deoxidizing and improving the flowability of molten metal during casting. If it is less than 0.2%, this effect is insufficient, while 1.5
%, The hardenability deteriorates and the material becomes brittle. Mn: 1.5% or less Mn combines with S to form a compound (MnS) and prevents embrittlement due to S. It also has the effect of improving hardenability and wear resistance. However, if it exceeds 1.5%, the material becomes brittle.

Cr: 3-8% Cr dissolves in the matrix to improve the hardenability and
A part of it combines with C to form a carbide, which improves wear resistance. Less than 3% has less effect, while 8%
If it exceeds, the action is saturated and the material becomes brittle. 2 Mo + W: 6-14% Mo and W combine with C to form M ₂ C-type or M ₆ C-type carbides, which improves wear resistance and a part of them dissolves in the matrix. Contributes to secondary curing. Since Mo is twice as effective as W, the component range is defined by the sum of twice Mo content and W content (2 Mo + W). 2 Mo + W is 6
If it is less than%, such an effect is small, while if it exceeds 14%, the amount of carbides increases and the toughness decreases, and the retained austenite is stabilized by Mo and W dissolved in the matrix, making it difficult to obtain high hardness.

V: 5.5-7.5% V combines with C to form a high hardness MC type carbide, and
Has a crystal refining effect. If it is less than 5.5%, the structure is not easily refined, while if it exceeds 7.5%, MC type carbides are likely to segregate. In particular, when cast by the centrifugal force casting method, the segregation tendency becomes large.

In addition to the above components, the roll material of the present invention is formed by the balance of Fe and impurities inevitably mixed. Since P and S both make the material brittle, it is desirable that they are as small as possible. The roll material of the present invention is preferably used as an outer layer material of a two-layer composite roll in which an outer layer and a solid inner layer or a cylindrical inner layer are welded, or a three-layer composite roll in which an intermediate layer is cast between the outer layer and the inner layer. To be done. As the inner layer material, a tough material such as high-grade cast iron, ductile cast iron or graphite steel is used. As a roll casting method, as is well known, a die centrifugal force casting method is used to cast an outer layer, and optionally an intermediate layer, and then a solid inner layer is statically cast therein.

The heat treatment of the roll material according to the present invention is carried out after casting, after the whole roll is heated to the austenitizing temperature, 400 to 650.
By cooling the temperature range up to ℃ at a cooling rate of 300 ℃ / hr or more, a good quenched structure can be obtained. Tempering may be performed at a temperature of 500 to 600 ° C once to several times. The roll material referred to in the present invention is mainly used as an outer layer material of a rolling roll, but can also be used as a roller outer layer material such as a roller in a rolling accessory facility, for example, a hot run table roller.

Next, specific examples will be given. (1) Cylindrical castings were cast from the HSS-based roll molten metal shown in Table 1 by centrifugal die casting. The casting conditions are as follows. In Table 1, Nos. 1 to 3 are examples and No. 4 is a comparative example. Mold size: φ620mm x length 1300mm Mold rotation speed: 140 with GNo. Casting thickness: 60mm

[0014]

[Table 1]

(2) After casting, a structure observation piece was taken from each sample, and the structure was observed with a microscope. The results are shown in FIGS. 1 and 2. The numbers in parentheses in FIG. 1 correspond to the sample numbers (Example: No. 1 to 3) in Table 1, and FIG. 2 corresponds to the comparative example (Sample No. 4). The magnification is 50 times. From the figure, it was confirmed that the crystals of Nos. 1 to 3 according to the example were significantly finer than those of No. 4 of the comparative example. Note that segregation of carbide did not occur in any of the samples.

(3) Next, each sample is heated to 1100 ° C.,
After the quenching, the hardness was measured after tempering at 550 ° C. The results are shown below. From the results below, it is presumed that the Examples and Comparative Examples have the same hardness, and that the material of the present invention has excellent wear resistance.

No. 1 ... H _RC 59.5, No. 2 ... H _RC 58.
1, No. 3 ... H _RC 59.8, No. 4 ... H _RC 60.3

[0018]

As described above, since the high speed steel roll material of the present invention is composed of a specific composition containing C: 1.5 to 2.0%, V: 5.5 to 7.5%, etc., it is special cast for quenching. Even if the method was not adopted, a good microstructure was obtained by the ordinary die casting method, and the roughening resistance and high temperature strength could be improved.

[Brief description of drawings]

FIG. 1 is a drawing substitute metal structure photograph (50 times) of a high-speed steel roll material of an example.

FIG. 2 is a drawing substitute metal structure photograph (50 times) of a high speed steel roll material of a comparative example.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Nagamori Morikawa 64 Nishimukojima-cho, Amagasaki City, Hyogo Prefecture Kubota Amagasaki Plant

Claims (1)

[Claims] 1. The chemical composition is wt%, C: 1.5-2.0%, Si: 0.2-1.5%, Mn:
1.5% or less, Cr: 3 to 8%, 2 Mo + W: 6 to 14%, V:
A high-speed roll material characterized by comprising 5.5 to 7.5% and the balance substantially Fe.