JPH0532122B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) This invention relates to a composite sleeve used in assembly rolls for hot strip mill roughing stands, etc. (Prior art) A roll assembled by shrink-fitting a rolling sleeve having a rolling layer into an arbor is called an assembled roll, and is used as a work roll for hot strip mill roughing stands, etc. There is. For example, properties required for the rolling layer used in the roughing stand of a hot strip mill include abrasion resistance, accident resistance, roughness resistance, and slip resistance (biting resistance). I can do it. on the other hand,
The inner surface of the sleeve is required to have sufficient toughness to withstand shrink fit stress, stress during rolling, and the like. In order to satisfy these different requirements, the first type of sleeve that is shrink-fitted to the arbor is
As shown in the drawings and FIG. 2, a composite sleeve 1 is used in which an outer layer 2 and an inner layer 3, which are layers used for rolling, are made of different materials. 4 in FIG. 1 is an arbor into which the composite sleeve is shrink-fitted. Conventionally, the outer layer materials include special cast steel, adamite material, hardened forged steel material, graphite steel, spheroidal graphite cast iron,
Grain wood etc. are used. (Some are also used as single roll materials). Furthermore, recently, in some mills, high chromium cast iron rolls used as rolling rolls before the finishing stand are used as they are in the roughing stand. On the other hand, as the inner layer material, high-grade cast iron, ductile cast iron, etc., which have excellent toughness, are used. (Problems to be Solved by the Invention) In recent years, there has been a trend towards higher quality and energy saving in thin plate rolling, and rolling conditions have also become more severe. Therefore, as an outer layer material, it has wear resistance,
Improvements in surface roughness resistance have led to demands for higher toughness for inner layer materials. However, the adamite material and the steel-based outer layer material have a hardness of Hs55 or less and have good slip resistance, but have problems in wear resistance and roughness resistance. In addition, some places use Hs50 to 75 for spheroidal graphite cast iron, but it has poor wear resistance and crack resistance, and furthermore, some places use Hs65 to 75 for grain materials. Yes, but
There are problems with crack resistance and rough skin resistance. On the other hand, high chromium cast iron rolls used as rolling rolls in the front stage of the finishing stand have problems in that they tend to slip against the rolled material, have poor bite into the rolled material, and are also prone to fatigue cracks. Furthermore, sufficient toughness is not obtained as an inner layer material. The present invention was devised in view of these problems, and includes an outer layer that has superior wear resistance and roughness resistance without reducing slip resistance and crack resistance, and an inner layer that has extremely high toughness. The purpose of the present invention is to provide a composite sleeve consisting of: (Means for Solving the Problems) In order to achieve the above object, the outer layer of the composite sleeve has a specific composition of Hs65-80 having a specific composition of C: 0.8-1.2% and Cr: 10-14% in weight%. Centrifugally cast with C high chromium cast iron, while the inner layer is C: 0.3~1.0
%, Ni: 0.5~2.0%, Cr: 0.5~3%, Mo: 0.1~
Cast with special cast steel material with specific composition having 0.8%,
Welded and integrated to the inner surface of the outer layer. (Example) First, the reason for limiting the components of the outer layer material of the present invention will be described. Hereinafter, the unit is weight %. C: 0.8 to 1.2% C is a high hardness (Fe, Cr) ₇ C It is determined by the desired amount of carbide while maintaining a balance with the Cr content within the range that stabilizes the type ₃ carbide.
If the amount of carbide is less than 0.8%, the amount of carbide will be too small, resulting in insufficient wear resistance, while if it exceeds 1.2%, the amount of carbide will be too large, resulting in a decrease in slip resistance, roughness resistance, and toughness resistance. Si: 0.5-1.2% Si is an element necessary for deoxidizing the molten metal, and must be contained at least 0.5%. However, Si
Since C lowers the solubility of C in austenite, excessive content will result in insufficient carbide formation, making it difficult to obtain hardness and deteriorating mechanical properties, so it should be kept at 1.2% or less. Mn: 0.5-1.2% Mn is required at least 0.5% for deoxidizing the molten metal and removing harmful S. However, if it exceeds 1.2%, mechanical properties, especially toughness, will deteriorate significantly. P: 0.03% or less P is an element that is preferably as small as possible in the roll material, and should be kept at 0.03% or less in order to prevent the material from becoming brittle. S: 0.03% or less Like P, the lower the S content, the better, and the content should be 0.03% or less to prevent embrittlement. Ni: 0.5-2.0% Ni is contained to improve hardenability and actively adjust hardness, and its content is 0.5%.
If the content is less than 2.0%, there will be no sufficient effect, while if the content exceeds 2.0%, it will stabilize austenite and increase residual austenite, making it difficult to adjust the hardness by heat treatment after casting. Cr: 10-14% Cr is contained to improve toughness and wear resistance, but in order to obtain high hardness (Fe, Cr) ₇ C ₃ type carbide, it is necessary to balance it with the C content. There is. Regarding the C content of the present invention, if the C content is less than 10%, it is not possible to sufficiently obtain the above-mentioned M ₇ C ₃ type carbide, whereas if the C content exceeds 14%, M ₂₃ C ₆
The amount of carbide in the mold increases. Since this carbide has a lower hardness than the M ₇ C ₃ type carbide, it becomes difficult to obtain sufficient wear resistance. By the way, M ₇ C ₃ is Hv2300 ~
2400, _{M23C 6} type is Hv1500-1600. Mo: 1.0-2.5% Mo is effective in increasing quenching and tempering resistance and at the same time stabilizing carbides, but its content is
If it is less than 1.0%, there is no such effect; on the other hand, if the component system of the outer layer material of the present invention (C: 0.8 to 1.2%, Cr: 10 to
14%), below 2.5% is sufficient to obtain Hs65-80. In addition to the above components, the outer layer material according to the present invention contains the remaining components.
Formed by Fe and unavoidably mixed impurities. Incidentally, the outer layer material of the present invention hardly contains V except for a trace amount of V present as an impurity. This is because V has a strong affinity with C, and is generated as VC in the molten metal, which is deflected into layers during centrifugal casting, resulting in a deterioration in the quality of the composite sleeve. Next, the reason for limiting the components of the inner layer material will be described.
Hereinafter, the unit is weight %. C: 0.3 to 1.0% If the C% is too low, it is necessary to increase the melting temperature, which poses a cost problem. Furthermore, if the difference in C% between the outer layer and the inner layer becomes large, defects may occur in the welded portion. For the above reasons, it is set at 0.3% or more.
On the other hand, the content is set at 1.0% or less as a range that does not form cementite and imparts toughness. Si: 0.2~1.0% 0.2% or more 1.0% for the same reason as the outer layer
The following shall apply. Mu: 0.2-1.5% Mn combines with S and eliminates the negative effects of S, but
If it is less than 0.2%, this effect will not be achieved, while if it exceeds 1.5%, the toughness of the material will deteriorate significantly. P: 0.1% or less P is an impurity element and makes the material brittle, so it should be kept at 0.1% or less to avoid causing problems. S: 0.1% or less Like P, S is an impurity element and makes the material brittle, so it is set to 0.1% or less as a range where the effect is minimal. Ni: 0.5 to 3.0% Ni increases hardenability and is effective for toughness, but 0.5 to 3.0%
If it is less than 3.0%, there will be little effect, but from the economic point of view it should be kept at 3.0% or less. Cr: 0.5 to 5.0% Cr increases hardenability and is effective for toughness, but Cr: 0.5 to 5.0%
If it is less than 5.0%, there is almost no effect, while if it exceeds 5.0%, it becomes chilled and becomes brittle. Mo: 0.1 to 0.8% Mo, like Ni and Cr, increases the hardenability of the material and contributes to toughness. If it is less than 0.1%, the effect is small;
On the other hand, if it exceeds 0.8%, it becomes too hard and brittle. In addition to the above ingredients, the inner layer material is essentially composed of Fe, but in order to improve the quality of the inner layer, part of the Fe may be replaced with the following ingredients as needed:
It can contain one kind or two or more kinds. Nb: 0.1 to 0.8% Nb contributes to the refinement of the structure, and if it is less than 0.1%, the effect is small, while if it exceeds 0.8%, the effect is saturated, which is disadvantageous from an economic point of view. Ti, Al, Zr: The total of one or more types is 0.2% or less. The inner layer has a lower C% than the outer layer, so defects are likely to occur. Therefore, add 0.2% or less. The composite sleeve according to the present invention is composed of an outer layer and an inner layer containing the above-described components, and the sleeve has the toughness of the material and the targeted qualities such as hardness, abrasion resistance, roughness resistance, and crack resistance. In order to obtain this, the sleeve material cast by the manufacturing method described below is heat treated to raise the temperature to the austenite region, and incidentally subjected to heat treatment below the reciprocal transformation temperature for the purpose of tempering, isothermal transformation, and strain relief. That is, in high-chromium steel with a high C content, the matrix exhibits an austenitic structure when as cast, but it is not suitable as a roll material in terms of wear resistance. In order to change this austenite structure into a martensite or bainite structure, it is necessary to destabilize this austenite. That is, by maintaining the temperature at the A _C1 point or higher, C _r carbide is precipitated in the matrix, and the C and C _r concentrations in the matrix decrease. The form of C _r carbide varies depending on the holding temperature and tends to take the form of M ₇ C ₃ at temperatures above 950°C. In order to obtain a hardened structure, the cooling rate should be CCT.
A critical cooling rate or higher that does not intersect the Ps′ line is required. In the case of high chromium systems, Ps even with relatively slow cooling
Although it does not cross the line, a cooling rate of 250°C/Hr or higher is required. In addition, tempering obtains a thermally stable structure and at the same time, from a balance with product hardness,
600℃ is suitable. In addition, the appropriate temperature for the strain relief treatment is 400 to 600°C in order to reduce the residual stress of the roll in balance with the thermal stress generated in the roll. As a result of the above heat treatment, the structure of the outer layer material becomes a mixed structure of matrix and eutectic carbide (M ₇ C ₃ type), and the matrix structure is composed of precipitated secondary carbide (M ₇
C ₃ type) and a tempered martensite and bainitic structure, with a hardness of Hs65 to 80. In addition, due to the heat treatment, the structure of the inner layer material becomes a mixed structure consisting mainly of barite and some bainite, and the tensile strength becomes 80 to 120 Kg/ ^mm2 , compared to that of conventional ductile cast iron (40 to 45 Kg/ ^mm2 ). The strength is more than twice as strong as that of the previous one. Therefore, resistance to breakage is increased, it becomes possible to firmly shrink-fit to the arbor, and a large rolling torque can be transmitted from the arbor. Next, a method for manufacturing the composite sleeve will be described. Generally, it is convenient to use a centrifugal casting method as a method for manufacturing a composite sleeve. Fig. 3 shows the case where both the outer layer 2 and the inner layer 3 are centrifugally cast, and Fig. 4 shows that after centrifugally casting the outer layer 2, the mold in which the outer layer was cast is stood upright to form a stationary mold. This figure shows the case of statically casting an inner layer casting material into a mold. In the same figure, 5 is a centrifugal force casting mold, 6
7 is a rotating roller; 8 is a molten metal ladle; 9
indicates the pouring gutter. Although Fig. 3 shows a centrifugal casting method with a rotating shaft in the horizontal direction (so-called horizontal centrifugal casting method), it also shows a centrifugal casting method with a rotating shaft in an oblique or vertical direction (so-called oblique centrifugal casting method). It goes without saying that it can also be manufactured using a casting method or a vertical centrifugal casting method. Moreover, in the case of FIG. 4, it is natural to form a shaft-fitting hole in the center of the material after casting. Next, specific examples will be explained. Manufacturing example of a composite sleeve with a body diameter of 900 mm x body length of 2000 mm x wall thickness of 140 mm (1) As shown in Figure 3, a centrifugal casting mold was made with C _NO.
140°C, and the molten metal for the outer layer shown in Table 1 was cast at a casting temperature of 1400°C to a wall thickness of 100mm (4T 900Kg). (2) Immediately before or immediately after the inner surface of the outer layer solidifies (from the outer layer casting)
20 minutes later), pour the molten metal of the inner layer material as shown in the table at the casting temperature.
Cast at 1550℃ with a wall thickness of 40mm (1T 700Kg). (3) After complete solidification, the composite sleeve material is removed from the mold, heated to 1000℃, held for 5 hours, and then sprayed with water (250℃) to 400℃.
℃/Hr), and then kept at 500℃ for 15 hours and then cooled in the furnace. (4) After machining the obtained composite sleeve, ultrasonic flaw detection revealed that the boundary between the outer layer and the inner layer was metallurgically welded and integrated. Further, the body surface hardness was Hs73, and the inner layer strength was extremely strong with a tensile strength of 93 Kg/mm ² and an elongation of 7%. Table 1 also shows the results of investigating the composition of the product.

[Table] (Effects of the invention) As explained above, the low C high chromium cast iron for the outer layer of the composite sleeve of the present invention has sufficient (Fe, Cr) ₇
Other ingredients are regulated within a specific range so that _C3 type high hardness carbide can be crystallized, so it is possible to improve slip resistance without compromising wear resistance and roughness resistance. Furthermore, since the amount of carbide is not excessive, crack resistance can also be improved. Further, since the outer layer of the composite roll of the present invention is formed by centrifugal casting, it is easy to manufacture and has excellent productivity. Moreover, during centrifugal force casting, only a small amount of V, which causes layered deflection, is present as an impurity, so that deflection of VC is less likely to occur and the quality is good. In addition, since the inner layer is made of special cast steel with a specific chemical composition, it can have a high tensile strength of 80 kg/mm ² or more, exhibiting extremely high toughness and significantly improving the breakage resistance of the sleeve. As described above, in the composite sleeve according to the present invention, the inner layer has extremely high toughness, while the outer layer has excellent wear resistance and roughness resistance, as well as good slip resistance and crack resistance. Therefore, it has great utility in the field of rolling where both of these properties are required, for example as a sleeve for assembled rolls used in the roughing stand of hot strip mills.

[Brief explanation of the drawing]

Figure 1 is a vertical cross-sectional view of the main parts of the assembled roll, Figure 2 is a cross-sectional view of the composite sleeve, Figure 3 is a cross-sectional view of the centrifugal casting mold showing the centrifugal casting state of the inner layer, and Figure 4 is a cross-sectional view of the centrifugal casting mold. FIG. 3 is a cross-sectional view of the same mold showing the static casting state of the inner layer. 1...Composite sleeve, 2...Outer layer, 3...Inner layer.

Claims (1)

[Claims] 1. In a composite sleeve in which an inner layer made of a tough material is integrally welded to the inner surface of an outer layer which is a rolling layer that is centrifugally cast and used for rolling, the outer layer has a weight percentage of
So, C: 0.8~1.2% Ni: 0.5~2.0% Si: 0.5~1.2% Cr: 10~14% Mn: 0.5~1.2% Mo: 1.0~2.5% P: 0.03% or less S: 0.03% or less balance Fe Hs65~80 consisting of and unavoidable impurities
Made of low carbon high chromium cast iron material, the inner layer is weight% C: 0.3~1.0% Ni: 0.5~3.0% Si: 0.2~1.0% Cr: 0.5~5.0% Mn: 0.2~1.5% Mo: 0.1 ~0.8% P: 0.1% or less S: 0.1% or less A composite sleeve characterized by being made of special cast steel with extremely excellent toughness, the remainder being Fe and unavoidable impurities.