JPH0250977B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a composite sleeve for an assembly roller for a hot run table, which requires corrosion resistance, wear resistance, and crack resistance. (Conventional technology and its problems) Conventionally, as a roller for a hot run table,
Single rollers made of ordinary steel, ordinary cast iron, etc., and assembled rollers whose sleeves are made of Cr-Mo steel and are shrink-fitted to a tough arbor are used. The rollers are in contact with the high-temperature strip and are also exposed to cooling water, so they are placed in a strongly corrosive environment and are required to have excellent corrosion resistance, and also have strong requirements for wear resistance. Furthermore, in the case of assembled rollers, crack resistance (split damage resistance) is required for sleeves.
is also required. However, ordinary cast iron has poor corrosion resistance, and when ordinary steel and Cr-Mo steel are hardened to improve wear resistance, their toughness deteriorates and crack resistance decreases due to factors such as residual stress. There is a problem. The present invention was made in view of such problems,
The purpose of the present invention is to provide a sleeve that has the performance required for a sleeve for an assembly roller for a hot run table, that is, corrosion resistance, wear resistance, and crack resistance. (Means for Solving the Problems) The means of the present invention for achieving the above object is a composite sleeve having a two-layer structure of an outer layer and an inner layer, the outer layer having a C: 0.8 to 1.2. %,
Made of low carbon, high chromium cast iron material with Hs70 to 80 containing Cr: 14 to 25% (excluding 14% Cr).
On the other hand, the inner layer is C: 0.3-1.0%, Ni: 0.5-3.0%,
It is made of special cast steel with extremely high toughness containing 0.5-7.0% Cr and 0.1-0.8% Mo. (Example) FIG. 1 shows the structure of an assembly roller in which a composite sleeve 1 according to the present invention is shrink-fitted to an arbor 4. As shown in FIG. 1 and FIG. An inner layer 3 having toughness is welded and integrated. First, the reasons for limiting the components of the outer layer material of the present invention will be described. Hereinafter, the unit is % by weight. C: 0.8 to 1.2% C (Fe, Cr) ₂₃ C It is determined by the desired amount of carbide while keeping a balance with the Cr content within the range that stabilizes type ₆ carbide, but if C is less than 0.8%, If the amount of carbide is too small, wear resistance will be insufficient, while if it exceeds 1.2%, the amount of carbide will be too large, resulting in decreased corrosion resistance and poor wear resistance (Fe, Cr) ₇ C ₃ type carbides will be formed. do. 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%, it will stabilize austenite and make it difficult to obtain a heat-treated transformed structure. 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 included 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: 14-25% (excluding 14% Cr) Excellent corrosion resistance and moderate hardness (Fe,
Cr) ₂₃ C In order to obtain type ₆ carbide, it is necessary to balance it with the C content. Regarding the C content of the outer layer according to the present invention, if the C content is less than 14%, it becomes M ₇ C ₃ type carbide, which has high hardness but has poor corrosion resistance.On the other hand, if it exceeds 25%, it becomes a single phase of ferrite and carbide. No more crystallization. In addition, Cr in the outer layer inevitably mixes into the inner layer when welding and integrating the inner layer, increasing the Cr% of the inner layer.
In order to keep Cr% within the specified range, the Cr of the outer layer must be
It is considered to be 25% or less. In addition, the hardness of carbide is
_{M23C 6} type is Hv1500 _~ 1600, _M7C3 type is Hv2300~
It is 2400. 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%, such an effect will not be obtained.On the other hand, in the component system of the outer layer material of the present invention, 2.5% or less is sufficient to obtain Hs70 to 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. 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. Mn: 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 as long as it does not cause any problems. S: 0.1% or less S, like P, is an impurity element and makes the material brittle, so it is set to 0.1% or less as a range where its influence is small. Ni: 0.5 to 3.0% Ni increases hardenability and is effective for toughness, but 0.5
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 7.0% Cr increases hardenability and is effective for toughness, but 0.5 to 7.0%
If it is less than 7.0%, there is almost no effect, whereas if it exceeds 7.0%, 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 making it tougher. 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-mentioned components, the remaining material of the inner layer is substantially made of Fe. The composite sleeve according to the present invention is composed of an outer layer and an inner layer containing the components described above, and ensures the toughness of the material and achieves the target qualities such as hardness, abrasion resistance, corrosion resistance, and crack resistance. For this purpose, 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 tempering and heat treatment below the reciprocal transformation temperature for the purpose of removing distortion. That is, high chromium steel with a high C content is as cast and has an austenitic matrix, but it is not suitable as a roll material in terms of wear resistance. In order to change this austenite structure to martensite or bainite structure, it is necessary to destabilize this austenite. That is, by maintaining the temperature at Ac ₁ point or higher, Cr carbide precipitates in the matrix, and the C and Cr concentrations in the matrix decrease. The form of Cr carbide varies depending on its holding temperature, and it tends to take the form of M ₂₃ C ₆ at 1000°C to 800°C. In order to obtain a hardened structure, the cooling rate should be CCT.
A disjunction 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 achieves a thermally stable structure and at the same time, from a balance with product hardness.
A temperature of 400 to 600°C is appropriate. Further, the heat treatment for strain relief is suitably carried out at a temperature of 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 becomes a mixed structure of matrix and eutectic carbide (M ₂₃ C ₆ type), and the matrix structure consists of precipitated secondary carbide (M ₂₃ C ₆ type), tempered martensite, and bainite. It becomes a structure with a hardness of Hs70-80. Furthermore, due to the heat treatment, the structure of the inner layer becomes a mixed structure consisting mainly of pearlite structure and partly bainite structure, and the tensile strength becomes 80 to 120 Kg/ ^mm2 ,
The strength is more than twice as strong as that of conventional ductile cast iron (40 to 45 kg/mm ² ). Therefore, the resistance to breakage is increased and it becomes possible to firmly shrink-fit to 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 shows a case where the inner layer casting material of the mold is statically cast. In the same figure, 5 is a centrifugal force casting mold, 6
is a band for stopping hot water formed from a metal mold, sand mold or firebrick, 7 is a rotating roller, 8 is a molten metal ladle,
9 indicates a pouring gutter. Although Fig. 3 shows a centrifugal force casting method with a rotation axis in the horizontal direction (so-called horizontal centrifugal force casting method), there is also a centrifugal force casting method with a rotation axis in an oblique or vertical direction (so-called oblique centrifugal force casting method). It goes without saying that it can also be manufactured using a force casting method or a vertical centrifugal force 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 listed and explained. Example A Manufacture example of a composite sleeve with body diameter of 310 mm x body length of 1800 mm x wall thickness of 80 mm (1) As shown in Figure 3, a centrifugal force casting mold is made with G 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 thickness of 40 mm (500 kg). (2) Immediately before or immediately after the inner surface of the outer layer solidifies (6 minutes after casting the outer layer), the molten metal for the inner layer shown in the table is poured at the casting temperature.
Cast at 1550℃ with a wall thickness of 40mm (360Kg). (3) After complete solidification, the composite sleeve material is removed from the mold, heated to 900°C, held for 5 hours, and then sprayed with water (500°C) to 400°C.
℃/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. The body surface hardness was Hs73, and the inner layer strength was extremely strong with a tensile strength of 102 Kg/mm ² and an elongation of 7%. Additionally, Table 1 shows the results of investigating the composition of the product.

[Table] Example B Body diameter 300mm x body length 1800mm x wall thickness 70mm (outer layer 25mm,
Manufacturing Example of a Composite Sleeve with an Inner Layer of 45 mm (1) A composite sleeve having the product composition shown in Table 2 below was manufactured in the same manner as in Example A. For comparison, a single roller made of ordinary cast iron was cast as Conventional Example 1.
In addition, as Conventional Example 2, a single-layer sleeve with holes formed by forging Cr-Mo steel was manufactured. After rough processing, the single layer sleeve was kept at 850℃ for 5 hours, cooled in oil,
After holding at 550°C for 20 hours, heat treatment was performed by rapidly cooling. The compositions of conventional roller materials are also shown in Table 2.

[Table] (2) During production of the roller, samples of 10 x 20 x thickness 5 (mm) were taken from the outer layer of the example and conventional examples 1 and 2 and subjected to a corrosion resistance test. The test method was to immerse the sample in water in step 1, take it out after a predetermined period of time, polish the surface of the sample with emery paper (#600) to remove rust, and then weigh it to determine the corrosion loss. The result is the third
Shown in the table.

[Table] (Note) Values indicate corrosion loss per ^cm2 .
From Table 3, it can be seen that the corrosion of the ordinary cast iron of Conventional Example 1 is significant, and the corrosion resistance of the Cr--Mo steel of Examples and Conventional Example 2 is good. (3) In addition, when manufacturing the roller, tensile test pieces were taken from the inner layer of Example and Conventional Example 2, and the same test was conducted, and the tensile strength was as follows: Example: 98 Kg/mm ² Conventional Example 2: 95 Kg/mm ² , and although the C% was the same, it was recognized that the Example had higher strength. (4) The rollers of the example and the conventional example were installed on a hot run table in front of a hot strip mill finishing stand, and the amount of wear (diameter reduction) and the depth of heat cracks were measured after a predetermined period of time had elapsed.
The results are shown in Tables 4 and 5.

[Table] (Note) Unit: mm

[Table] (Note) Unit: mm
From Tables 4 and 5, it is recognized that the sleeves of the Examples are superior in both abrasion resistance and heat crack resistance compared to Conventional Examples 1 and 2. In particular, it can be seen that the improvement is more than twice that of Conventional Example 2. (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) _23C Since the other components are regulated within a specific range to crystallize _6- type carbide, which has excellent corrosion resistance, it imparts corrosion resistance and improves the matrix structure without compromising wear resistance. It is possible to improve oxidation resistance, and since the amount of carbide is not excessive, it is also possible to improve corrosion resistance and crack resistance. In addition, since the inner layer is made of special cast steel with a specific chemical structure, 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, the composite sleeve according to the present invention has an inner layer with extremely high toughness, and an outer layer with excellent wear resistance, as well as good corrosion resistance and crack resistance. It has great utility as a sleeve for assembly rollers used in hot run tables that require both.

[Brief explanation of drawings]

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

Claims (1)

[Claims] 1. In a composite sleeve in which an outer layer used as a layer and an inner layer with excellent toughness are welded and integrated, the outer layer has the following content in weight%: C: 0.8 to 1.2% Ni: 0.5 to 2.0% Si: 0.5 to 1.2% Cr: 14 to 25% Mn: 0.5 to 1.2% (excluding 14% Cr) P: 0.03% or less Mo: 1.0 to 2.5% S: 0.03% or less The balance consists of Fe and inevitable impurities and
Made of low carbon high chromium cast iron material with Hs70~80, the inner layer is weight% C: 0.3~1.0% Ni: 0.5~3.0% Si: 0.2~1.0% Cr: 0.5~7.0% Mn: 0.2~1.5 % Mo: 0.1 to 0.8% P: 0.1% or less S: 0.1% or less A composite sleeve characterized in that it is made of special cast steel with extremely excellent toughness, the balance being Fe and unavoidable impurities.