JPH0754095A - Centrifugal cast composite roll - Google Patents

Abstract

PURPOSE:To improve the wear resistance, cracking resistance and processibility by specifying the composition of an outer layer material of roll by centrifugal casting process. CONSTITUTION:A composite roll is made by welding the outer layer material and steel shaft material by centrifugal casting process. The composition of the outer layer material at that time consists of, by wt.%, 0.8-1.2% C, <=1.5% Si, <=1.2% Mn, 4.0-6.0% Cr, 0.5-2.0% V, 1.0-3.0% Co, 0.1-2.0% Nb, further, as necessary, adding <=2% Ni, and the balance Fe and inevitable impurities. By using this composition, segregation due to centrifugation of hard carbide at the time of centrifugal casting is prevented and the inexpensive and high- performance composite roll is manufactured.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a centrifugally cast composite roll for rolling steel materials or non-ferrous metals.

[0002]

2. Description of the Related Art In recent years, with regard to hot rolling and cold rolling of steel, high pressure, high speed continuous rolling, increase of hard-to-roll materials and thinning of products have progressed, and the environment for use of rolls has become severer. Is following. Along with this, the increase of roll wear or the influence on the roll in case of a rolling accident such as slipping or narrowing has become serious.

Such a situation not only increases the unit consumption of rolls, but also hinders schedule-free rolling and reduces the surface quality of rolled products. In addition, in the case of a rolling accident, equipment damage due to roll breakage may be caused, and productivity may be significantly reduced due to mill breaks. Therefore, the roll material is required to have not only wear resistance and crack resistance but also densification of the solidified structure. In addition, since the roll imparts surface roughness and removes the fatigue layer by a grinding operation, good grindability is also an important item.

In hot rolling of steel, the wear of the roll is severe, and there is a particularly high need for improvement in wear resistance. Therefore, in place of the conventionally used high Cr cast iron or Ni grain cast iron, use of high C high V type high speed tool steel has recently been made. {Materials and process: vol: 4 (1991) -442, vol:
4 (1991) -450} are proposed, and it is disclosed that each exhibits excellent wear resistance. Further, as for cold rolling, Japanese Patent Publication No. 56-9323, JP-A No. 54-1593.
No. 23, JP-A-57-47849, etc., a method of adding a hard carbide-forming element has been proposed for the main purpose of improving wear resistance.

However, according to such a method, the carbides crystallized in the solidification process become coarse, which promotes wear due to the falling of the carbides, lowers crack resistance and grindability, and causes the solidified structure to roll. There was a problem that it appeared on the surface and was transferred to the surface of the rolled product, so it was not generally effective. These are problems in the steel ingot melting process, and by increasing the solidification rate, the solidification structure becomes denser, and the carbides that crystallize can also be refined. As a measure to speed up the solidification rate, roll compounding is effective, and as the roll compounding technique, centrifugal casting method, continuous overlay method and compound E method are used.
The SR method and the like have been proposed. In this compounding technology,
The centrifugal casting method is an effective compounding means because it has a simple manufacturing process, can be manufactured at low cost, and has a relatively high solidification rate as compared with other methods.

However, in a component system in which MC (metal carbide) type hard carbide is present, segregation due to centrifugal separation of carbide is a problem due to the difference in specific gravity between molten steel and crystallized carbide.

[0007]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a centrifugally cast composite roll, which is suitable for use with a rolling roll material having a composition which advantageously solves the above-mentioned problems. .

[0008]

[Means for Solving the Problems] Now, the inventors of the present invention have diligently studied toward the realization of the above-mentioned object, and the inventors of the present invention have tried to control the composition of the carbide to crystallize, thereby centrifuging the carbide found in the centrifugal casting method. It was found that segregation associated with separation can be improved. Specifically, by adding Nb, segregation can be improved, and by limiting C, Cr, Mo, V, and Co together, the above problems such as wear resistance, crack resistance, and grindability can be improved. found.

The so-called present invention was developed based on such knowledge, and the first invention comprises an outer layer material and a steel shaft material fusion-integrated with the outer layer material by a centrifugal casting method. A composite roll, wherein the outer layer material is C: 0.8 to 1.2.
wt%, Si: 1.5 wt% or less, Mn: 1.2 wt% or less, Cr: 4.0
~ 6.0 wt%, Mo: 3.0-6.0 wt%, V: 0.5-2.0 wt%
%, Co: 1.0 to 3.0 wt% and Nb: 0.1 to 2.0 wt%, the balance being Fe and unavoidable impurities, which is a centrifugal casting composite roll.

A second invention is a composite roll comprising an outer layer material and a steel shaft material fusion-integrated with the outer layer material by centrifugal casting, wherein the outer layer material is C: 0.8 to 1.2 wt%. ,
Si: 1.5 wt% or less, Mn: 1.2 wt% or less, Cr: 4.0 to 6.0
wt%, Mo: 3.0 to 6.0 wt%, V: 0.5 to 2.0 wt%, Co:
A centrifugally cast composite roll characterized by containing 1.0 to 3.0 wt%, Nb: 0.1 to 2.0 wt% and Ni: 2% or less, and the balance being Fe and inevitable impurities.

[0011]

[Function] First, the research which is the basis for limiting the component range of the outer layer material will be described. Figure 1 shows 1% C-5% Cr-1
It is a figure which shows the relationship between Mo amount and hardness of the steel which 1100 degreeC quenching and 525 degreeC tempering process were performed about% V steel. It can be seen that the hardness increases as the amount of Mo increases, but it is almost saturated at 6%. Further, the steel containing 2% Co tended to have higher hardness than the steel containing no additive.

FIG. 2 shows a contact stress of 200 kgf / mm ² , a slip rate of 5%, and 21 / mi for 1% C-5% Cr-1% V-2% Co steel.
It is the figure which arranged the relationship between the amount of Mo and the wear depth by carrying out a cold wear test 1 × 10 ⁶ times under a 5% mineral oil emulsion lubrication condition of n 2. It can be seen that the wear resistance is excellent in the region where Mo is 3 to 6%. FIG. 3 shows the grindability of the rolls, and is a diagram showing the relationship between the V amount and the grindstone consumption rate. . It can be seen that the grindstone consumption rate increases and the grindability decreases as V increases.

[0013]

[Table 1]

[0014]

[Table 2]

These results suggest that by controlling Mo, Co, and V in appropriate ranges, it is possible to have high hardness and achieve both wear resistance and grindability. However, when the outer layer material is melted by the centrifugal casting method, the VC existing in the steel is
Since the specific gravity of was smaller than that of the molten steel, segregation of carbide was caused by centrifugation. As a solution, we focused on NbC, which is at the same level as the specific gravity of molten steel, and focused on 1% C-5% Cr-4% Mo.
The addition of Nb was investigated for -1% V-2% Co steel. As a result, it was found that the addition of 0.1% or more of Nb formed a double carbide in which Nb was present in VC, and it was found that segregation of the carbide could be suppressed. On the other hand, addition of more than 2% is effective for segregation of carbides, but coarsens the carbides.

In consideration of the points suggested by the above-mentioned examination results, as a result of studying suitable outer layer material components of the centrifugally cast roll capable of achieving the above-mentioned object, it is concluded that the following component composition is necessary. Reached The reasons for limiting the content of alloying elements in the outer layer material of the centrifugally cast composite roll of the present invention will be described below.

C: 0.8 to 1.2 wt% C plays an important role in forming carbides or ensuring hardenability, and 0.8 wt% or more is necessary, but 1.2 wt%
If it exceeds, the carbide will be coarsened and the wear resistance and crack resistance will be deteriorated, so the upper limit is made 1.2 wt%. Si: 1.5 wt% or less Si is necessary to secure deoxidizer and castability, but is added.
If it exceeds 1.5 wt%, the crack resistance is lowered, so the upper limit is made 1.5 wt%.

Mn: 1.2 wt% or less Mn is necessary for the same purpose as Si, but if it exceeds 1.2 wt%, the upper limit is 1.2 wt% in order to reduce crack resistance.
%. Cr: 4.0 to 6.0 wt% Cr is an element necessary to improve wear resistance by forming carbides. It is also an element effective in improving hardenability and temper softening resistance, but if it is less than 4.0 wt% Its effect is small,
On the other hand, addition of more than 6.0 wt% causes Cr carbide to coarsen and causes a decrease in hardness, so the content was determined to be in the range of 4.0 to 6.0 wt%.

Mo: 3.0 to 6.0 wt% Mo effectively contributes to the improvement of hardness after the secondary hardening and tempering treatment, and improves wear resistance and crack resistance. However, if the content is less than 3.0 wt%, the hardness after the secondary hardening treatment is not sufficient. On the other hand, if the content exceeds 6.0 wt%, MC-based V and Nb double carbides, which will be described later, do not contain Mo. Since it becomes a carbide and reduces wear resistance, Mo is 3.0 to 6.0 wt%
It was decided to contain in the range of.

V: 0.5 to 2.0 wt% V is an element that forms hard MC type carbides and contributes most effectively to the improvement of wear resistance, but if it is less than 0.5 wt%, the effect of improving wear resistance is obtained. If it is too small, the addition amount exceeding 2.0 wt% leads to a great decrease in grindability and sufficient hardness cannot be obtained. Therefore, V is included in the range of 0.5 to 2.0 wt%.

Co: 1.0 to 3.0 wt% Co contributes as an element for improving the hardness after the secondary hardening and tempering treatment, and is useful in that the heating temperature during quenching can be suppressed to a low level. It also has the effect of suppressing the formation of oxide scale during forging and heat treatment, and facilitates the forging heat treatment work. However, if it is less than 1.0 wt%, its effect is small, while if it exceeds 3.0 wt%, hardenability is deteriorated. Therefore, Co is included in the range of 1.0 to 3.0 wt%.

Nb: 0.1 to 2.0 wt% Nb coexists as a double carbide in MC type carbide mainly composed of V, increases the specific gravity of MC type carbide and makes it close to that of molten steel. MC type during centrifugal casting It is a useful element that suppresses the segregation of carbides by centrifugation, and is an important element in the present invention. However, if it is less than 0.1 wt%, the effect is not recognized, and if it exceeds 2.0 wt%, the amount of MC type carbides increases, and the grindability and hardness are reduced.
The range was 0.1 to 2.0 wt%.

The centrifugally cast outer layer material of the present invention may contain Ni in addition to the above-mentioned alloy elements. Ni: 2 wt% or less Ni is added to improve the hardenability and strengthen the matrix structure, but the addition of more than 2.0 wt% is preferable because it forms an unstable structure such as the presence of retained austenite. However, the upper limit was set to 2.0 wt%.

In addition, the inevitable impurities are mainly P and S, but P: 0.030 wt% or less and S: 0.010 wt% or less are acceptable. The shaft material is not particularly specified, but it is preferable to use cast iron system of ductile or Ni grain, carbon steel for machine structure, alloy steel, tool steel or bearing steel.

The centrifugally cast composite steel ingot having the outer layer material is subjected to heat treatment and machining in the cast state,
Although it is generally used as a roll, forging can be added as necessary for the purpose of dividing the coarse carbide of the outer layer material, pressing the microcavity of the shaft material, and improving the strength and toughness.

[0026]

[Example] A composite steel ingot having the chemical composition of the outer layer material shown in Table 3 manufactured by centrifugal casting was prototyped. As the shaft material, Japanese Industrial Standard SKD61 or SUJ2 was used. The obtained composite steel ingot was subjected to normalizing treatment at 900 ° C. (cooling was air cooling), macro and microstructures were observed, and segregation of carbide by centrifugation was examined. For the invention steel 1 ′, a forging material having a forging ratio of 2S was also investigated.
The results are also shown in Table 3.

It was confirmed that the outer layer material of the method of the present invention did not have segregation due to centrifugal separation of carbides and was a sound roll. On the other hand, in the steel containing a small amount of Nb, segregation due to centrifugal separation of V carbides was present, and coarsening of carbides was observed in the component system in which Nb exceeds 2%. Regarding the outer layer material shown in Table 3,
Normalizing at 900 ° C (cooling by air) and 950 ° C-
After 4 hours of oil quenching and 700 ° C-6 hours of tempering heat treatment, a small test piece was sampled and subjected to heat treatment simulating actual equipment surface quenching and tempering to perform secondary hardening behavior, wear test, thermal shock test A grindability test was performed. The results are shown in Table 4. The steel of the present invention has high hardness,
This result suggests that the resistance to indentation damage due to the inclusion of foreign matter during rolling is high. In addition, it was confirmed that each of the characteristics of wear, thermal shock and grinding was an excellent component system. On the other hand, in the comparative steel, the hardness and wear resistance were lowered, or the grindability was significantly lowered.

[0028]

[Table 3]

[0029]

[Table 4]

[0030]

As described above, according to the present invention, it is possible to prevent segregation of hard carbide due to centrifugal separation during centrifugal casting,
It is possible to provide a roll that is inexpensive and has excellent performance, and has great industrial effects such as improvement in rolling productivity and reduction in roll unit consumption.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between Mo content and hardness.

FIG. 2 is a graph showing the relationship between Mo content and wear depth.

FIG. 3 is a graph showing the relationship between the V content and the grindstone consumption rate.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location C22C 38/30

Claims (2)

[Claims] 1. A composite roll comprising an outer layer material and a steel shaft material fused and integrated with the outer layer material by centrifugal casting, wherein the outer layer material is C: 0.8 to 1.2 wt% and Si: 1.5 wt. % Or less, Mn: 1.2 wt% or less, Cr: 4.0 to 6.0 wt%, Mo: 3.0 to 6.0 wt%, V: 0.5 to 2.0 wt%, Co: 1.0 to 3.0 wt% and Nb: 0.1 to 2.0 wt% A centrifugally cast composite roll characterized by containing, and the balance being Fe and inevitable impurities. 2. A composite roll comprising an outer layer material and a steel shaft material fused and integrated with the outer layer material by a centrifugal casting method, wherein the outer layer material is C: 0.8 to 1.2 wt%, Si: 1.5 wt. % Or less, Mn: 1.2 wt% or less, Cr: 4.0 to 6.0 wt%, Mo: 3.0 to 6.0 wt%, V: 0.5 to 2.0 wt%, Co: 1.0 to 3.0 wt%, Nb: 0.1 to 2.0 wt% and Ni: A composite roll made of centrifugal casting, containing 2% or less, and the balance being Fe and inevitable impurities.