JPS6154087B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an improvement of a composite sleeve used in a grooved rolling roll for rolling steel pipes, and more particularly to a manufacturing method for obtaining a composite sleeve with improved wear resistance in the grooved portion thereof. Conventionally, in this type of rolling roll with grooves, as shown in FIG. 1, a sleeve 2 having a groove 5 in an arbor 1 is fixed to a body part 6 by mechanical coupling means such as shrink fitting or keying. A sleeve assembly structure is used. At this time, sleeve 2 has
A chilled material or grain material having a hardness of Hs 65 to 75 is used, and the hole 5 is formed by cutting or during casting. By the way, the sleeve outer layer 3 in which the hole portion 5 is provided needs to have wear resistance, so it needs to be made of a high hardness material such as the above-mentioned high hardness chilled material. The stress is large, and problems such as cracking from the inner layer may occur during shrink fitting. Therefore, conventionally, this type of roll has
As shown in the figure, the outer layer 3 is made of the above-mentioned high hardness material, while the inner layer 4 is often a composite sleeve made of a material with excellent toughness. Therefore, when using such a composite sleeve, the wall thickness t ₁ of the outer layer 3 is thin and the wall thickness t ₂ of the inner layer 4 is thin.
When the outer layer 3 is thick, the residual stress is small and there is no problem even if the outer layer 3 has high hardness. However, if the outer layer 3 has a thick wall thickness t ₁ and the inner layer 4 has a thin wall thickness t ₂ , the residual stress in the sleeve becomes large and tends to lead to a broken line, causing the sleeve outer layer 3 and the hole 5
There is a limit to the increase in hardness. In order to solve these problems, the present invention selects and improves the sleeve material and structure for a composite sleeve that is used in a grooved rolling roll and has a thick outer layer compared to the wall thickness, and also improves the sleeve material and structure after casting. By improving heat treatment methods such as quenching, we have been able to reduce the residual stress in the sleeve while increasing the hardness of the outer layer, especially the necessary hole-shaped layer. This has succeeded in improving the usability of the system. That is, the present invention provides a method for manufacturing a composite sleeve for a mill roll with grooves, in which an outer layer of high chromium cast iron is cast by centrifugal force casting, and then an inner layer of graphite cast steel is cast therein by centrifugal force casting or static casting. A cylindrical composite sleeve is cast in which the outer layer and the inner layer are welded and integrated, the outer layer is thicker than the inner layer, and then the composite sleeve is heat treated and the outer layer is precast or cut. In the method for manufacturing a composite sleeve for a rolling roll with grooves, the heat treatment is performed at a temperature of 800 to 950°C.
After softening annealing at 600-700℃, 900-1100
Quenching only the layer used in the hole molding at ℃ and 400 to 600℃
It is characterized in that the hardness of the hole portion is made Hs75 or higher by tempering at . The present invention will be explained in detail below. The composite sleeve according to the present invention is formed by welding an outer layer 7 made of high chromium cast iron and an inner layer 8 made of graphite cast steel by casting, and as shown in FIG. It is made by forming a hardened layer on the. When casting this composite sleeve, the outer layer 7 is cast to a predetermined thickness by centrifugal force casting. That is, first, an outer layer molten metal of high chromium cast iron as exemplified is poured into a rotary mold set on a centrifugal casting machine, and a cylindrical body of the outer layer material is formed on the inner surface of the mold. In this case, the hole shape required for the outer layer can be formed directly during casting by providing a chiller that protrudes on the inner surface of the mold, or it can be formed by cutting separately after casting the composite sleeve. It's okay. Then we move on to casting the inner layer. The inner layer may be subsequently centrifugally cast at a predetermined timing after the outer layer is cast, or the mold may be left standing upright, cast by pouring, and the inner diameter of the sleeve may be bored to obtain the desired composite sleeve. . The inner layer is made of strong graphite cast steel, but since a part of the inner surface of the outer layer is washed during casting and mixed into the inner layer, the inner layer is ultimately formed of a material containing some Cr as exemplified later. In this way, a composite sleeve is cast in which the outer layer and the inner layer, each made of a predetermined material, are welded and integrated. The material of each layer of the composite sleeve according to the present invention will be specifically explained. [Outer layer] The outer layer of the sleeve is made of high chromium cast iron with the aim of achieving a hardness of Hs75 or higher at the bottom of the hole. The high chromium cast iron preferably has C1.6 to 3.4, Si0.3 to 1.5,
Mn0.3~1.5, Ni0.1~2.0, Cr10~25, Mo0.5~3.0
% by weight, and the remainder consists of Fe and impurities. The reason for limiting the range of each component is as follows. C should be determined according to the desired amount of carbide by keeping a balance with the amount of Cr within the range that stabilizes the (Fe-Cr) ₇ C type ₃ carbide, but C1.6%
If the content is less than 3.4%, the carbide content is too small and wear resistance is insufficient, and if it exceeds 3.4%, the carbide content is too large, resulting in significant deterioration in mechanical strength, particularly toughness. Si is necessary in an amount of 0.3% or more to deoxidize the molten metal, but if it is contained in an amount exceeding 1.5%, the mechanical properties will deteriorate and at the same time the Ar ₁ transformation point will be lowered, making it difficult to obtain hardness. be. Mn is still necessary in an amount of 0.3% or more as an aid to deoxidizing the molten metal, but if it is contained in an amount exceeding 1.5%, the deterioration of mechanical properties, particularly toughness, becomes significant. Ni is included to improve hardenability and actively adjust hardness, and 0.1% or more is required, but 2.0%
This is because if the content exceeds the amount, retained austenite increases and hardness cannot be increased. Cr is contained in large amounts for the purpose of improving toughness and wear resistance, but its content is 10%.
If it is less than 25%, many M ₃ C type carbides will crystallize and the toughness will decrease and fine uniformity of the carbides will not be obtained.
If the content exceeds %, the amount of M ₂₃ C ₆ type carbide increases, which is undesirable. This M ₂₃ C ₆ type carbide is
Compared to _{the M7C3} type carbide, the hardness is lower and sufficient wear resistance cannot be obtained, and the Cr content is 10 _to 25% in balance with the above C content as the range in which the _M7C3 type carbide occurs. %. Mo is useful for increasing quenching and tempering resistance, and at the same time entering into carbides to increase carbide hardness and promoting tempering softening resistance.When the content is less than 0.5%, the effect is small, and when the content exceeds 3.0%, Mo is effective. This is because, if it is contained, the retained austenite in the matrix becomes stable, which in turn causes a decrease in hardness. The high chromium cast iron in the outer layer is made of iron with the remainder being Fe other than the above components.
and impurities, but this does not preclude further addition of V, W or Co as necessary. These elements are added for the same purpose as Mo, but
If too large amounts are added, it will be uneconomical and the material will become brittle, so the upper limits are V2.0%, W5.0%, respectively.
Co3.0%. [Inner layer] The inner layer is made of tough graphite cast steel, and a part of the inner surface of the outer layer is melted and mixed into the inner layer. Considering this compositional variation, the inner layer of graphite cast steel should preferably have C1.0~2.0, Si1.0~2.5, Mn0.3~
1.2, 0.2 to 2.5 Ni, 1.0 to 3.0 Cr, and 0.05 to 1.5% by weight, with the balance consisting of Fe and impurities. In addition, when casting the inner layer, it is also possible to divide the process into multiple steps to form a composite sleeve having a structure of substantially three or more layers. The reason for limiting the range of each component is as follows. C is required at 1.0% or more for graphite precipitation, but
This is because if the content exceeds 2.0%, the mechanical properties will deteriorate. 1.0% or more of Si is required for graphite precipitation, but
This is because if the content exceeds 2.5%, the mechanical properties will deteriorate. Mn is required at least 0.3% for deoxidation, but
This is because if the content exceeds 1.2%, it becomes brittle. Ni is required to be at least 0.2% for both the purpose of improving mechanical properties and eliminating the harm caused by Cr, but if it is included in a large amount, it becomes bainite and is also uneconomical, so the upper limit is set at 2.5%. . It is desirable that Cr be low, and although Cr is not added during casting, it is inevitably included in the range of 1.0 to 3.0% when the outer layer is washed. Mo is required at 0.05% or more to improve mechanical properties, but the upper limit may be exceeded due to washing of the outer layer.
The rate shall be 1.5%. The inner layer graphite cast steel after being welded to the outer layer has the above composition range, with the remainder consisting of Fe and impurities. In addition,
When the outer layer contains V and W contains Co, some of them will be diffused and mixed into the inner layer as well. The present invention is characterized in that after a composite sleeve is cast by integrally welding the outer and inner layers of respective predetermined materials as described above, the composite sleeve is further subjected to the following heat treatment. That is, after casting the composite sleeve and slowly cooling it, it is preferable to first
Subjected to diffusion heat treatment at ~1100℃, then 800-950℃
The inner layer is subjected to granulation treatment at 600 to 700°C, and the outer layer is subjected to softening annealing to undergo pearlite transformation. This heat treatment softens the high chromium cast iron of the outer layer, while increasing the toughness of the graphite cast steel of the inner layer, which prevents cracking during the subsequent local hardening of the outer layer and accidents during use. After the required heat treatment has been applied to the entire composite sleeve, in the present invention, as shown in FIG. The hardness of the layer 9 used in the hole part is made to be Hs75 or higher by hardening. That is, specifically, this hardening treatment is performed at a temperature of 900 to 1100 on only the layer 9 used in the hole portion 5.
After hardening and annealing the entire sleeve,
The heat treatment method of the present invention, in which local hardening is applied to the hole portion 5, is characterized in that it is possible to impart the desired high hardness to the layer 9 used in the hole portion without increasing residual stress in the sleeve. . This is done by heating the entire sleeve and quenching it uniformly to remove all the outer layers.
When using a material with a high hardness of Hs75 or higher, if the wall thickness t ₁ of the outer layer 7 is larger than the inner thickness t ₂ of the inner layer 8, the residual compressive stress generated on the entire surface of the outer layer 7 with the wall thickness t ₁ will be This is because a residual tensile stress greater than the material strength of the inner layer 8 is generated, which may lead to sleeve breakage. Therefore, the method of the present invention is most effective for those with a large outer layer thickness _t1 , such as grooved rolls for rolling steel pipes, and in addition, compared to conventional chilled and grain materials, Since the outer layer high chromium cast iron has good hardenability and is less likely to crack during hardening, the hardness of the layer 9 used for the hole portion of the outer layer 7 can be easily increased to the desired target hardness. In addition, in conventional composite rolls, when the outer layer is made of chilled or grain material, the inner layer is made of ordinary cast iron or ductile cast iron, but graphite cast steel is stronger and safer than these materials. Therefore, according to the manufacturing method of the present invention, for a composite sleeve in which the wall thickness t ₁ of the outer layer 7 is larger than the wall thickness t ₂ of the inner layer 8, a composite sleeve having excellent wear resistance is used in the hole-shaped layer. Sleeves can be manufactured safely. Note that the graphite cast steel of the inner layer 8 contains a large amount of chromium from the high chromium cast iron of the outer layer 7, but if the inner layer is made of a cast iron material, it becomes brittle and the safety level decreases, whereas in the case of graphite cast steel. By absorbing this chromium, it is possible to maintain and utilize its original properties, and there is no need to worry about the problem of material deterioration due to diffusion of chromium. After processing, the sleeve manufactured in this manner is shrink-fitted into the arbor and used. Next, specific examples of the present invention will be described. Example 1 Product dimensions 800〓×500, inner diameter 350〓, hole depth
A 110 mm composite slave was manufactured as follows. First, the outer layer was cast to a predetermined thickness by centrifugal casting, followed by the inner layer to a predetermined thickness, and both were welded together to manufacture a composite sleeve. The composition of each layer after casting is as follows.

[Table] This composite sleeve was subjected to diffusion heat treatment at 1000℃,
As a result of granulation and hardening annealing at 860°C and 650°C, the outer layer had a hardness of Hs40 to 43. Then, only the hole part was medium frequency hardened at 1030℃, and then heated to 500℃.
As a result of tempering, a hardness of Hs81 was obtained in the hole part. Example 2 A composite sleeve having the same dimensions and shape as Example 1 was manufactured as follows. First, the outer layer was cast to a predetermined thickness by centrifugal casting, and then a mold was erected at an appropriate timing, the core material forming the inner layer was cast, and the two were welded together to form a composite sleeve. The composition of each layer after casting is as follows.

[Table] This casting was subjected to diffusion heat treatment at 950℃, 850℃,
A hardness of Hs47 to 49 was obtained for the boundary and outer layer that was granulated and hardened and annealed at 650°C. However, after adding hole machining and boring to the casting of the lever and forming it into a composite sleeve, only the hole portion was medium-frequency quenched at 1000℃ and then tempered at 500℃.
A hardness of Hs87-88 was obtained. As described above, according to the manufacturing method of the present invention, after casting a composite sleeve in which the outer layer is made of high chromium cast iron and the inner layer is made of graphite cast steel, after the required hardening annealing, only the layer used in the hole portion of the outer layer is coated. Because of the quenching and tempering treatment, for composite sleeves where the outer layer is thicker than the inner layer, it is possible to increase the hardness of the layer used in the hole without increasing residual stress in the sleeve. Furthermore, it is now possible to easily impart a hardness of Hs75 or higher to the hole, which was virtually impossible due to residual stress using conventional methods. Furthermore, since the inner layer of this composite sleeve is made of graphite cast steel to ensure toughness, it is safe without cracking during both hardening and use. Therefore, if the composite sleeve obtained by this method is assembled into an arbor and subjected to rolling, it is possible to significantly improve its use characteristics such as wear resistance without compromising safety.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing the structure of a conventional mill roll with grooves. FIG. 2 is a sectional view showing the structure of the grooved mill roll according to the present invention. 1... Arbor, 3, 7... Outer layer, 4, 8...
Inner layer, 5...Hole type (part), 6...Shrink fit fixing surface,
9...Layer used in the hole mold section (quenched layer).

Claims (1)

[Scope of Claims] 1. After forming an outer layer of high chromium cast iron by centrifugal force casting, an inner layer of graphite cast steel is cast inside it by centrifugal force casting or static casting, and the outer layer and inner layer are welded and integrated, A cylindrical composite sleeve whose outer layer has a wall thickness larger than that of the inner layer is cast, and then the composite sleeve is heat-treated to harden the hole molded in the outer layer in advance by casting or cutting. In the method for manufacturing a composite sleeve for shaped rolling rolls, the heat treatment involves heating the composite sleeve at 800 to 950°C.
After hardening annealing at 600-700℃, 900-1100
Quenching only the layer used in the hole molding at ℃ and 400 to 600℃
1. A method for manufacturing a composite sleeve for a mill roll with grooves, characterized in that the hardness of the groove portion is made Hs75 or higher by tempering the sleeve.