JPS6157083B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to the provision of a new type of composite sleeve having higher performance, which is mainly used in the rolling field of H-beam steel, and a preferable method for manufacturing the same. When rolling H-shaped steel, it is common to use a universal mill from the standpoint of productivity and quality assurance, but most of the rolls used in this universal mill, namely horizontal rolls, vertical rolls, and edge rolls, are It is a sleeve type. In other words, horizontal rolls are assembled by shrink-fitting a sleeve into an arbor, and are used for rolling by applying torque to the arbor and taking the rolling load, while vertical rolls have bearings installed in the inner hole of the sleeve. It is installed and receives rolling load. In casting the sleeve, the method shown in FIG. 1 is generally adopted from the viewpoint of improving the quality of the material and improving the casting yield. That is, first, the outer shell is centrifugally cast, and the inner shell is centrifugally cast when it is unsolidified or after solidification, and the two are welded together. In this case, since the inner shell material reinforces the sleeve, special attention must be paid to its toughness.
That is, for example, in sleeves for horizontal rolls,
Rolling load, thermal stress during rolling, thermal stress during shrink fitting, and residual stress associated with sleeve manufacturing act on the inner surface as tensile stress, so it is necessary to withstand this inner surface tensile stress. required. On the other hand, since the outer shell material is in contact with the rolled material and is directly linked to rolling performance such as wear resistance and roughness resistance, improving the outer shell material is most important. Especially for horizontal rolls, H
Sliding wear on the flange of the shaped steel is severe, and of the properties generally required in hot rolling (crack resistance, seizure resistance, roughening resistance, wear resistance), wear resistance is especially important. . Further, as for vertical rolls and edge rolls, with the recent increase in the number of rolling tons, there is a growing demand for improved wear resistance. Conventionally, adamite material with Hs55 to 65 has been used for this kind of outer shell material, but it has problems in terms of seizure resistance and roughness resistance, and it is difficult to set the hardness to Hs65 or higher due to manufacturing technology. It is also difficult due to the problem of accidents during use. Furthermore, the welding of the outer shell and inner shell must be sound in order to prevent accidents when using the rolls, and composite technology is also an important issue. Based on this background of the prior art, the present invention has created a new composite sleeve of this type that has superior wear resistance than conventional sleeves, and has sufficient accident resistance and resistance to breakage accidents. The present invention also provides a suitable method for producing the same. That is, the present invention includes an outer shell made of a high chromium material, an inner shell made of spherical graphite steel, and
The present invention provides a new composite sleeve having an outer shell hardness of Hs70 or more, which is formed by welding and integrating the intermediate layer interposed between the outer and inner shells, and at the same time provides a manufacturing method thereof using a centrifugal casting method. It is something to do. The composite sleeve for rolling H-shaped steel of the present invention will be described in detail below with respect to the materials of its outer shell, intermediate layer, and inner shell. First, the outer shell material is made of a high chromium material with a hardness of Hs70 or higher, and the range of each component and the reasons for the limitations are explained as follows. C should be determined based on the desired amount of carbide while keeping a balance with Cr within the range that stabilizes (Fe-Cr) ₇ C type ₃ carbide, but if it is less than 2.0%, the amount of carbide is small and wear resistance is improved. lack of sex, while
If the content exceeds 3.2%, the amount of carbides becomes too large, resulting in significant deterioration in mechanical strength, especially toughness. Therefore, C is defined as 2.0 to 3.2%. Si is necessary for deoxidizing the molten metal, and if it is less than 0.5%, it has no effect; on the other hand, if it is contained in more than 1.5%, it causes deterioration of mechanical properties, and also lowers the Ar ₁ transformation point and improves hardness. It becomes difficult to get caught. Therefore, the Si content is in the range of 0.5 to 1.5%. Mn is required to have a content of at least 0.5% as an aid to deoxidizing Si, and if it is less than 0.5%, there is no deoxidizing effect. However, if the content exceeds 1.5%, the mechanical properties, especially the toughness, will deteriorate significantly.
Therefore, the Mn content is also in the range of 0.5 to 1.5%. The less P is an element, the more desirable it is, especially in roll materials, and it also makes the material brittle.
0.1% or less. S, like P, makes the roll material brittle, so the smaller the content, the more desirable it is, and the content should be 0.1% or less. Ni is contained to improve hardenability and actively adjust hardness. If it is less than 0.8%, it has no effect, while if it is contained more than 2.5%, retained austenite increases and hardness increases. Become.
Therefore, in the present invention, in order to obtain the target hardness Hs70 or higher, the Ni content is set in the range of 0.8 to 2.5%. Cr is used to improve toughness and wear resistance, but if its content is less than 10%, many M ₃ C type carbides will crystallize, making it impossible to obtain toughness and fine uniformity of carbides. Moreover, when the content exceeds 25%, the amount of M ₂₃ C ₆ type carbide increases. This carbide has lower hardness than the M ₇ C ₃ type carbide and cannot provide sufficient wear resistance. In the present invention, the Cr content is defined as a range of 10 to 25%, in balance with the above-mentioned range of the C content, as the range in which M ₇ C ₃ type carbide occurs. Mo increases the quenching and tempering resistance and at the same time enters into the carbide, increasing the hardness of the carbide and promoting tempering softening resistance, and its content is
Below 0.5%, this effect is small;
If the content exceeds %, the residual austenite in the matrix becomes stabilized, and on the contrary, the hardness decreases. Therefore, the Mo content should be in the range of 0.5 to 2.0%. The outer shell material contains each of the above components in weight percent, with the remainder essentially consisting of Fe, but other components other than the above, which are added as supplements and have been found to be particularly effective, include the following: Examples include Nb and V. Nb is effective in refining the casting structure, and the inclusion of Nb promotes precipitation hardening and improves wear resistance, especially in the range of target hardness Hs70 or higher.
This effect exists when the Nb content is less than 1.0%, and when it exceeds 1.0%, this effect is saturated and costs increase. Therefore, the Nb content should be 1.0% or less. V is contained for the same purpose as Nb, and especially in the range of target hardness Hs70 or higher, the V content is 1.0%.
If the content exceeds 1.0%, V carbide increases and the toughness deteriorates. Therefore, V
The content shall be 1.0% or less. The cast structure of the outer shell high chromium material composed of the above component range is hard (Fe, Cr) ₇ C ₃ type carbide,
It consists of a base of retained austenite and some martensite. Regarding retained austenite, it is designed to suppress its increase and stabilization.
Although the outer shell components are prepared by suppressing the amount of Ni and Mo added, in spite of this, in a structure in which retained austenite exists, some retained austenite in the matrix may come into contact with the hot rolled material during rolling. Because it begins to undergo transformation, its structure is extremely unstable, and as a result, it has poor roughness and abrasion resistance as a sleeve. Therefore, in order to stabilize the cast structure of this type of high chromium material, it is customary to perform heat treatment during the manufacturing process. In this case, there are two heat treatment methods that can be applied. In other words, the casting stress is removed by heating to a temperature below the transformation point, and the retained austenite generated in the casting state is transformed into a martensite or pearlite structure, thereby stabilizing the structure so that no structural transformation occurs during rolling. There are two methods: one method is to heat the material to a temperature higher than the transformation point, and the subsequent cooling rate is further accelerated to obtain a structure that cannot be obtained by the cooling rate after casting. The present invention utilizes this latter heat treatment method. That is, after welding and casting the high chromium outer shell material and the inner shell material described later,
This is heated to a temperature range of 900 to 1100°C and maintained to precipitate secondary carbide in the matrix, destabilize austenite, and raise the martensitic transformation start point (Ms point) to 150 to 300°C. In the subsequent cooling process, the cooling rate is accelerated to 100°C/Hr or more to prevent pearlite transformation and cause martensitic transformation to occur near room temperature, thereby forming the (FeCr) ₇ C ₃ type main body. It consists of a base mainly composed of primary and secondary carbide and martensite,
The present invention also provides a composite sleeve that has an outer shell hardness of Hs70 or higher, has high wear resistance and roughness resistance, and has reduced residual stress. The reason why the heating temperature is kept between 900 and 1100°C during the above heat treatment conditions is that although secondary carbide precipitates at temperatures below 900°C, its form becomes (FeCr) ₂₃ C ₆ type, which is a feature of the present invention. This is because (Fe, Cr) _7C3 type carbide, which pursues _high wear resistance, cannot be obtained. That is, even when comparing the hardness of the carbide itself, the (Fe, Cr) ₂₃ C ₆ type is approximately Hv400 softer than the (Fe, Cr) ₇ C ₃ type. Therefore, in the present invention, the heating temperature is limited to 900° C. or higher in order to precipitate (Fe, Cr) ₇ C ₃ type secondary carbide in the matrix. On the other hand, the upper limit of the heating holding temperature is limited to 1100°C or higher based on the viewpoint of preventing tissue enlargement and saving energy for long-term heating holding.
From the viewpoint of raising the Ms point and reducing the transformation stress
It is best to keep the temperature below 1100℃. In addition, the reason for limiting the cooling rate after heating and holding is that when cooling from the temperature range of 900 to 1100°C mentioned above, if it is not rapidly cooled to 100°C/Hr or more, pearlite transformation will occur during cooling, and the desired martensite This is because it becomes impossible to obtain a base organization. This cooling rate of 100°C/Hr or higher is achieved by forced air cooling in the atmosphere or spray water cooling. As is well known, sleeves for rolling H-shaped steel are used by shrink-fitting the sleeve onto an arbor, but in this case, there are many cases in which cracks occur at the shrink-fitting portion with the arbor, that is, from the inner surface of the sleeve, resulting in breakage.
Although the inner shell material will be described in detail later, the above heat treatment not only modifies the outer shell material but also graphitizes the eutectic cementite in the inner shell material that is integrated with the outer shell. A great effect can also be obtained on the modification of the inner shell material by promoting its toughness. After the heat treatment, strain relief annealing is of course performed at an appropriate temperature in order to reduce residual stress that is closely related to breakage of the sleeve. In the above description of the outer shell material, each component and its heat treatment conditions have been explained in relation to its target hardness Hs70 or higher, and this is based on the following reasons. In general, sleeves for rolling H-type steel are required to have resistance to wear between the side wall and H-type steel flange, roughening of the side wall, resistance to cracking, and resistance to flange breakage, but the wear resistance of the sleeve depends on hardness. There is a strong correlation between the two, and if the hardness is less than Hs70, sufficient roughness resistance and wear resistance cannot be ensured. In other words, in order to ensure excellent roughness resistance, abrasion resistance, accident resistance, and crack resistance, high chromium materials must have a hardness of Hs70.
This is because the above is required. The upper limit of the hardness of the outer shell material is not specified separately, but depending on the above component range and heat treatment,
In addition, when considering accident resistance, it is generally difficult to make the outer shell material have a hardness of Hs90 or higher. Next, the middle layer will be explained. This intermediate layer is interposed between the first outer shell and the second inner shell, and is formed from the outer shell mainly made of high chromium material to the inner shell (shaft core).
The purpose of this is to prevent the inner shell material from deteriorating its toughness due to its high Cr content due to mixing and diffusion of Cr. The range of each component of the intermediate layer material and the reason for its limitation will be explained as follows. First, regarding the C content, it is a molten metal component at the time of casting and is specified in the range of 1.0 to 2.0%, and in the state where it is partially mixed with the outer shell after casting, that is, in the product state, it is in the range of 1.3 to 2.5%. be done. In other words, when the intermediate layer molten metal is cast on the inner surface of an already cast outer shell, a part of the inner surface is melted and the C content of the intermediate layer material changes (increases), and it is 1.0 to 2.0% relative to the above outer shell material. When using an intermediate layer molten metal with a C content of
When the dissolved amount of the outer shell is completely and uniformly mixed into the intermediate layer, the C content increases to 1.3 to 2.5%. The reason for this composition restriction is that when the molten metal composition is C1.0% or less, the casting temperature of the intermediate layer becomes high, the outer shell becomes easier to melt, and the amount of Cr mixed into the intermediate layer further increases. This is because the reason for the existence of the intermediate layer is lost because it prevents the diffusion of carbon into the inner shell (shaft core).Also, if the carbon content exceeds 2.0%, the amount of carbides increases, and the toughness of the intermediate layer itself deteriorates. Moreover, the reason for the existence of the middle class will be lost. Si has the effect of deoxidizing the molten metal, and 0.2% or more is necessary, but if it exceeds 2.0%, it becomes brittle and deteriorates the mechanical properties of the intermediate layer, so 0.2% or more
The range shall be 2.0%. Mn also has the same effect as Si, and
0.3% or more of MnS is necessary to eliminate the negative effects of S, but if it exceeds 2.0%, the effect will be saturated and the mechanical properties will also deteriorate.
It should be in the range of 0.3% to 2.0%. P increases the fluidity of the molten metal, but in roll materials it reduces the toughness of the material, so it is kept at 0.1% or less. Like P, S also makes the roll material brittle, so it should be kept at 0.1% or less without causing any actual damage. Regarding Ni, even if it is not added separately, it is contained at 0.2% or more due to contamination from the outer shell material.
A content of 2.5% is not a problem. But 2.5%
If it exceeds 2.5%, the hardenability will improve, but the matrix will become too hard, which is not desirable from the standpoint of toughness, and will also increase residual stress, so it is necessary to limit it to 2.5% or less. Regarding the molten metal in the intermediate layer before casting, the amount of contamination from the outer shell is anticipated, and the
It is necessary to suppress the Ni amount to 2.0% or less. As for Cr, it is desirable to have a low content because of the significance of casting the intermediate layer, and the content of the molten metal for casting is regulated to 3.0% or less, which is easy to control industrially. In other words, when Cr is contained in excess of 3.0%, the content of the intermediate layer increases when combined with the amount of Cr mixed in from the outer shell after casting, and the amount of Cr mixed in the inner shell (shaft core) increases. In order to prevent this, the Cr content of the molten metal should be increased to 3.0.
% or less. Incidentally, the Cr content
When an intermediate layer molten metal containing 3.0% or less is cast, the Cr content after casting is in the range of 0.5 to 9.0%. Mo has the same effect as Ni, but at 1.5%
If the content is more than that, the intermediate layer will become too hard.
Limit it to 1.5% or less as a range that does not cause any real harm. The intermediate layer material contains each of the above components by weight%, and the balance is basically composed of Fe, but other components other than the above, and if necessary, the following Ti, Al, Zr as a deoxidizing agent. These can be added singly or in combination. In other words, since the above-mentioned intermediate layer material is a material that is relatively easily oxidized, Ti,
One or more of Al and Zr in total weight% 0.1%
By adding less than 10% and deoxidizing, an intermediate layer that is more sound in terms of material can be obtained. Regarding the upper limit of the added content above, all of the above elements are strong deoxidizers, so if they are used alone or in combination,
If it is contained in an amount of 0.1% or more, it will become overoxidized, which is undesirable, and at the same time, it will also contain oxides as various reaction products, leading to deterioration in the mechanical properties of the material. Next, the inner shell material of the sleeve according to the present invention will be explained. This inner shell is made of a so-called spherical graphite steel material, and the range of each component and the reason for the limitation will be explained as follows. As for the inner shell material, during casting, part of the inner surface of the previous intermediate layer is washed and welded, so it is necessary to take into consideration the amount of washing when determining the molten metal composition during casting of the inner shell. In the case of graphite steel material, C dissolves into the matrix and becomes graphite (in some cases, a portion becomes eutectic cementite). If the C content is less than 1.0%, melting and casting temperatures will be high, resulting in increased costs. On the other hand, if it exceeds 2.0%, graphite tends to lose its spherical shape and its toughness deteriorates. Therefore, C is defined as 1.0 to 2.0%. Si has a close relationship with graphite crystallization,
If it is less than 0.6%, it is almost difficult to crystallize graphite. However, if it exceeds 3.0%, Si dissolved in ferrite tends to deteriorate the toughness of the material. Therefore, the Si content is
It should be in the range of 0.6 to 3.0%. In addition, it is generally known that inoculating Si with CaSi, etc. immediately before casting brings about good results in order to promote graphitization.
In the present invention, this technology is also applied during production, and CaSi is added at a Si content of 0.1 to 1.0% immediately before casting.
Can be added. In this case, if it is less than 0.1%, the effect of graphitization is small, while if it exceeds 1.0%, the effect is saturated and it is not economical. Even in the case of inoculation, the above Si component range is regulated by the content after addition of CaSi, etc. Mn combines with S to form MnS, which has the effect of eliminating the negative effects of S. However, if it is less than 0.2%, this effect cannot be obtained, while if it exceeds 1.0%, the toughness of the material will deteriorate significantly, so its content should be controlled. It should be in the range of 0.2 to 1.0%. P increases the fluidity of the molten metal, but since it makes the material brittle, it is preferably as low as possible, and should be 0.1% or less. Like P, S makes the material brittle, so the lower the content, the better, and should be 0.1% or less. Note that when CaSi is added, the S content is generally 0.04% or less because it is desulfurized by Ca. Ni is effective in slowing down the transformation of the material and making it tougher, but 0.1% or more
% or less is necessary and sufficient. Note that if the Ni content is less than 0.1%, the above effects will be insufficient, but because roll waste pig iron is generally used as the raw material for melting, in practice the Ni content is 0.1%.
It is difficult to obtain materials with less than %. Since the outer shell of Cr is a high chromium material, it is unavoidable that some amount of Cr will be mixed into the inner shell when the outer and inner shells are welded together, and care must be taken especially when determining the molten metal components of the inner shell. This varies depending on the outer shell component, inner shell component, and casting conditions, but the Cr of the inner shell material
The content increases by 0.2 to 1.0% compared to the time of casting.
The appropriate Cr content of the inner shell as a product is in the range of 0.3 to 2.0%. In other words, Cr is effective in toughening the material, but if it is less than 0.3%, it has no effect.
On the other hand, if it exceeds 2.0%, it becomes difficult for graphite to crystallize, resulting in deterioration of toughness instead. On the other hand, in order to regulate the Cr content of this inner shell material within a predetermined range, it is necessary to
Taking the Cr content into consideration, it is necessary to specify the Cr content of the inner shell molten metal during casting within the range of 0.1 to 1.0%. Like Ni, Mo is an important element in terms of ensuring toughness, but if it is less than 0.1% it has no effect;
If it exceeds 1.0%, it becomes hard and rather brittle, so the Mo content should be in the range of 0.1 to 1.0%. The inner shell material contains each of the above components in weight percent, and the remainder is essentially Fe, but other components other than the above, and if necessary, the following Ti, Al, Zr as deoxidizers. These can be added singly or in combination. That is, the inner shell material is C
Since the content is within the range of 1.0 to 2.0%, Ti,
0.1% total weight of one or more of Al and Zr
By adding less than 100% and deoxidizing, a roll with more sound material and no cavities can be obtained. Regarding the upper limit of the added content, all of the above elements are strong deoxidizing agents, so if they are contained alone or in combination at 0.1% or more, the molten metal will become overoxidized and the molten metal will become overoxidized. This is because it reduces liquidity. The composite sleeve for rolling H-type steel according to the present invention has the above-described structure, and a method for manufacturing this sleeve by centrifugal casting will be explained with reference to the example shown in FIG. That is, a rotary mold 1 with sleeves 2, 2 made of sand mold or heat-resistant bricks fixed to both ends of the inner surface is installed on the rotary rollers 6, 6 of a centrifugal casting machine.
While the mold 1 is rotating, the molten metal to form the outer shell 3 is first poured into it from the molten metal ladle 7 through the pouring gutter 8 etc., and then the inner surface of the outer shell 3 is partially or completely unsolidified. In between, pour the molten metal to form the intermediate layer 4,
Furthermore, the molten metal which is to form the inner shell 5 is cast after solidification or while still unsolidified. In this way, these three parts, ie, the outer shell 3, the intermediate layer 4, and the inner shell 5, are completely metallurgically combined to form an integral sleeve. Note that although the illustrated casting method is exemplified in which the rotating shaft is horizontal, this does not, of course, preclude casting with the rotating shaft changed to a vertical or inclined state. Also, when casting the inner shell 4,
The casting side can be changed from the case of the outer shell 3 and the casting can be performed from the opposite side, which is effective in ensuring a uniform thickness of the outer shell. As described above, the composite sleeve thus cast is further subjected to a predetermined heat treatment. The composite sleeve manufactured as described above is
When used as a horizontal roll, it is shrink-fitted into an arbor and used as a sleeve roll. Conventionally, the materials used for the arbor are SCM-4, SF-60, cast steel, ductile cast iron, etc., and the diameter is usually 500 to 850 mm. In addition, the shrink fit rate is 0.8×
10 ^-3 , but a lubricant or adhesive may be used during shrink fitting. The material of the arbor is appropriately selected depending on the design of the rolling stand and rolling conditions (rolling load, motor output, etc.). The material of the arbor does not affect the abrasion resistance, which is a rolling characteristic of sleeve rolls, and the accident resistance (resistance to breakage accidents) depends on the tangential direction (circumference) of the inner surface of the sleeve. direction)
It is determined by the strength and residual stress of the arbor, and is not directly related to the material of the arbor. Incidentally, from past experience, the tensile strength (tangential direction) of the inner surface of the sleeve is 45
Kg/ ^mm2 or more, residual tensile stress (tangential direction) is 15Kg/
It is known that there is no problem if it is less than mm ² .
In other words, in the case of horizontal rolls, the tensile stress in the tangential direction (circumferential direction) acting on the inner surface of the sleeve is the rolling load 2
Kg/mm ² , thermal stress during rolling 6Kg/mm ² , maximum shrink-fitting stress 12Kg/mm ² (past results) and maximum residual stress
Considering the safety factor based on 15Kg/mm ² , the inner surface of the sleeve needs to have a strength of 45Kg/mm ² or more. Next, examples and reference examples of the present invention will be described. Table 1 shows the chemical compositions of the molten metals of Examples 1 and 2 of the present invention and Reference Examples. Using these molten metals, a sleeve material in which the outer shell, middle layer, and inner shell were welded and integrated was cast by the centrifugal casting method shown in Figure 1 under the manufacturing conditions shown in Table 2. After solidification was completed, After performing the heat treatment shown in Table 2, composite sleeves with predetermined dimensions were collected.

【table】

[Table] The product chemical composition of the obtained composite sleeve is shown in Table 3.
Shown in the table. The composition of the outer shell is omitted because it is almost the same as the composition of the molten metal. The sample sampling position (mm) from the outer surface of the product is as follows. Examples 1 and 2 Reference example Middle layer 170 90 Inner shell 250 200

[Table] The results of measuring the outer surface hardness of the obtained composite sleeve are shown below. Example 1...Hs72 Example 2...Hs75 Reference example...Hs74-76 Material tests were conducted using the obtained composite sleeves. (i) Wear resistance It is determined by the test results of the Ohkoshi type wear test, and it is known that if judged as a trend value, it will show the same trend as the actual rolling results. Thickness 10mm from center of sleeve outer shell, width 20
A test piece with a length of 50 mm was taken in the axial direction, and the specific wear amount without lubrication was measured under the following test conditions. Sliding speed: 3.4m/sec Sliding distance: 200m Final load: 17.6~18.5Kg Rotating ring: SUJ2 (H _RC 60~63) (ii) Accident resistance (resistance to breakage accidents) Sleeve inner surface (inner shell inner surface) The tensile strength and residual stress in the tangential direction (circumferential direction) were measured. The measurement results for (i) and (ii) are shown in Table 4. In addition, when measuring the specific wear amount, measurements were also made on adaite materials (hardness Hs 62 to 64) having the following components for comparison. C: 2.12%, Si: 0.61%, Mn: 0.99%, P:
0.19%, S: 0.008%, Ni: 1.72%, Cr: 1.43
%, Mo: 1.02%, remainder substantially Fe (unit weight %)

From [Table] and Table 4, it can be seen that the outer shell of the composite sleeve of the present invention has high hardness and extremely excellent wear resistance. Furthermore, the strength of the inner surface of the sleeve (inner shell inner surface) is excellent, the residual stress is also low, and the accident resistance is also found to be good. The present invention has been described in detail above, and the composite sleeve for rolling H-shaped steel according to the present invention suppresses the increase and stabilization of retained austenite in its outer shell and has a high hardness of (Fe, Cr) ₇ C ₃ type. In order to generate a large amount of carbide, the outer shell is made of Ni: 0.8 to 2.5%,
It is made of a high chromium material with a specific chemical composition of Mo: 0.5 to 2.0%, and its inner shell is made of a spheroidal graphite cast iron material with a specific chemical composition, which are welded together and maintained at 900 to 1100°C. Then, by precipitating (Fe, Cr) ₇ C ₃ type secondary carbide in the matrix and raising the Ms point, and then cooling at a rate of 100°C/Hr or more, it is possible to generate pearlite with low hardness. The outer shell is mainly composed of a martensite base containing a large amount of primary and secondary carbides of the (Fe, Cr) ₇ C ₃ type, and the desired target is achieved. It is possible to reliably achieve an outer shell hardness of Hs70 or higher, which provides excellent wear resistance and roughness resistance, and contributes significantly to reducing uneven wear during actual rolling. The transformation stress can be reduced by the increase in the stress, and the residual stress on the inner surface of the sleeve can be reduced. On the other hand, the graphite steel material that forms the inner shell has excellent material toughness, and the presence of the intermediate layer reliably solves the problem of material embrittlement caused by Cr contamination from the outer shell. As the additional effect of improving shell toughness is exhibited, it has excellent resistance to breakage accidents without compromising toughness.The synergistic effect of these excellent properties of the outer and inner shells makes this sleeve Compared to conventional products, the rolling performance and sleeve life are significantly improved, and it can be extremely useful especially in the field of H-type steel rolling. Furthermore, according to the manufacturing method of the present invention using centrifugal force casting, the intermediate layer and inner shell are also formed by centrifugal force casting following the outer shell, so there is little mixing between each layer, and especially the inner shell molten metal. The amount of Cr is regulated to a low content in advance, taking into consideration the amount of contamination from the outer shell, so that the inner shell material does not become high in Cr due to the presence of the intermediate layer and deteriorate its toughness. In addition, good results were obtained in terms of weldability, and furthermore, by implementing the high-temperature heat treatment, the above-mentioned remarkable improvement effect on the outer and inner shells was obtained, and it can be used as a technical means to obtain the desired composite sleeve. This is particularly useful. In addition, in the case of the sleeve according to the present invention, since the C content of the inner shell is lower than that of the outer shell, if an intermediate layer is not provided, the final solidified part will be inside the outer shell, so that it will be pulled toward the outside of the welded part. Although there is a high risk of generating nested defects, by interposing the intermediate layer,
It also has the advantage of reliably eliminating this drawback.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view showing one example of the manufacturing method according to the present invention.

Claims (1)

[Claims] 1 C: 2.0 to 3.2%, Si: 0.5 to 1.5%, Mn: 0.5 to 1.5%, P: 0.1% or less, S: 0.1% or less, Ni: 0.8 to 2.5%, Cr: 10 ~25%, Mo: 0.5~2.0%, and the remainder essentially consists of Fe, and mainly consists of primary and _secondary carbides mainly of the (Fe, Cr) _7C3 type and martensite. and an outer shell made of a high chromium material consisting of bases; 2.5%, Cr: 0.5 to 9.0%, Mo: 1.5% or less, and an intermediate layer containing each weight% of the following, with the remainder substantially consisting of Fe; C: 1.0 to 2.0%, Si: 0.6 to 3.0%, Mn: 0.2 ~1.0%, P: 0.1% or less, S: 0.1% or less, Ni: 0.1 to 1.0%, Cr: 0.3 to 2.0%, Mo: 0.1 to 1.0%, and the remainder essentially consists of Fe. 1. A composite sleeve for rolling H-type steel, characterized in that an inner shell made of spherical graphite steel is integrally welded to prevent the occurrence of nest-like defects, and the outer shell has a hardness of Hs70 or more. 2 C: 2.0-3.2%, Si: 0.5-1.5%, Mn: 0.5-1.5%, P: 0.1% or less, S: 0.1% or less, Ni: 0.8-2.5%, Cr: 10-25%, Mo: The _{primary and} An outer shell made of a high chromium material consisting of a base mainly composed of secondary carbide and martensite; C: 1.3 to 2.5%, Si: 0.2 to 2.0%, Mn: 0.3 to 2.0%, P: 0.1% or less, S: 0.1% or less, Ni: 0.2 to 2.5%, Cr: 0.5 to 9.0%, Mo: 1.5% or less, and an intermediate layer containing each weight% of the following, with the balance substantially consisting of Fe; C: 1.0 to 2.0%, Si: Contains each weight% of 0.6 to 3.0%, Mn: 0.2 to 1.0%, P: 0.1% or less, S: 0.1% or less, Ni: 0.1 to 1.0%, Cr: 0.3 to 2.0%, Mo: 0.1 to 1.0%. , an inner shell made of spherical graphite steel, the remainder of which is substantially composed of Fe, are welded and integrated to prevent the occurrence of nest-like defects, and the outer shell has a hardness of Hs70 or more. Composite sleeve for rolling H type steel. 3 By centrifugal casting method, C: 2.0-3.2%, Si: 0.5-1.5%, Mn: 0.5-1.5%, P: 0.1% or less, S: 0.1% or less, Ni: 0.8-2.5%, Cr: 10 ~25%, Mo: 0.5~2.0%, each weight%, after casting a high chromium outer shell molten metal with the remainder substantially Fe, while the inner surface is partially or completely unsolidified, C: 1.0-2.0%, Si: 0.2-2.0%, Mn: 0.3-2.0%, P: 0.1% or less, S: 0.1% or less, Ni: 2.0% or less, Cr: 3.0% or less, Mo: 1.5% or less , and the remainder substantially consisting of Fe is cast, and the inner surface is further solidified or unsolidified, C: 1.0 to 2.0%, Si: 0.6 to 3.0%, Mn: 0.2 ~1.0%, P: 0.1% or less, S: 0.1% or less, Ni: 0.1 to 1.0%, Cr: 0.1 to 1.0%, Mo: 0.1 to 1.0%, and the balance is substantially Fe. After pouring the molten graphite steel inner shell and welding the outer shell, middle layer, and inner shell together to prevent the occurrence of nest-like defects, the temperature was maintained at 900 to 1100°C and heated at 100°C/Hr.
A method for manufacturing a composite sleeve for rolling H-type steel, characterized by performing heat treatment for cooling at a cooling rate above.