JPS6116335B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a hollow composite roller that has both excellent wear resistance and accident resistance. Generally, wear-resistant rollers are required to have the following characteristics. (1) Abrasion resistance This type of roller usually crushes a large amount of materials, and the materials to be crushed vary from relatively hard materials to highly corrosive materials. When grinding hard materials, the rollers are worn out and mixed into the material to be ground. On the other hand, when pulverizing highly corrosive materials, the highly corrosive nature leads to accelerated wear and contamination of the material to be pulverized. Therefore, due to such usage conditions, the roller must have a uniform structure with high corrosion resistance and excellent wear resistance. (2) Accident resistance In abnormal situations, such as when the material to be crushed flows into the rollers, sudden stress is applied to the rollers, which can easily lead to roller accidents. For this reason, if the roller has poor accident resistance, it will wear abnormally and the life of the roller will be significantly reduced. On the other hand, the roller as a whole needs to have sufficient toughness to withstand a large amount of crushing treatment. In addition, since rollers are usually used by shrink-fitting onto a shaft, crushing loads, thermal stress during shrink-fitting, residual stress associated with roller manufacturing, etc. act as tensile stress on the inner surface of the roller, so this inner surface tensile stress The inner surface of the roller must be especially tough. Due to the above-mentioned required characteristics, so-called high chromium rollers have conventionally been used as rollers for this type of application. In other words, the outer layer is made of a high-chromium cast iron material with excellent wear and corrosion resistance, while the inner layer is made of a strong material such as ductile cast iron to ensure accident resistance, and the two are welded together to form a hollow composite. It is configured as a roller. As a manufacturing method for this composite roller, centrifugal casting has been established as the most suitable method from the viewpoints of ease of controlling the thickness of the outer layer, prevention of Cr diffusion into the inner layer, economical efficiency, etc. However, the problem with this type of composite roller is that since the outer layer is made of a high chromium material, it is unavoidable that a certain amount of Cr will mix and diffuse into the inner layer during manufacturing. It is difficult to obtain a tensile strength of 30 kg/mm ² or less, which is comparable to ordinary cast iron, and it cannot satisfy the desired toughness and accident resistance for a composite roller. The present invention has been made with the aim of solving the above-mentioned problems when forming a cast composite roller with the outer layer made of high chromium cast iron and the inner layer made of ductile cast iron. The present invention provides a hollow cast composite roller having a novel two-layer structure formed by integrally welding an outer layer and an inner layer. In the specification, all values of chemical components mean % by weight. The heat treatment conditions for each layer of the composite roller according to the present invention will be explained below. [Outer layer] The outer layer is C2.0~3.2, Si0.5~1.5, Mn0.5~1.5,
P0.08 or less, S0.06 or less, Ni1.0~2.0, Cr10~30,
Contains Mo0.5~1.5, the remainder is substantially Fe and hardness
Formed from high chromium cast iron with Hs70 or higher. In addition, for the purpose of further increasing the hardness of the outer layer, one or two types of Nb 1.0 or less and V1.0 or less may be contained in place of a part of the Fe. The reason for limiting the range of components of the outer layer is as follows. C: 2.0 to 3.2 C is within the range that stabilizes the (Fe, Cr) ₇ C ₃ type carbide and is balanced with the subsequent Cr amount, and is determined by the target carbide amount. However, below C2.0, the amount of carbide is small and wear resistance is insufficient;
If it exceeds 3.2, the amount of carbide becomes excessive, and mechanical strength, especially toughness, deteriorates significantly. Si: 0.5 to 1.5 Si is necessary for deoxidizing the molten metal, but if it is less than 0.5, the effect is not sufficient. However, when the content exceeds 1.5, mechanical properties deteriorate,
At the same time, it lowers the Ar ₁ transformation point, making it difficult to obtain hardness. Mn: 0.5 to 1.5 Mn needs to be contained in an amount of at least 0.5 to assist in deoxidizing Si, and if it is less than 0.5, a sufficient deoxidizing effect cannot be obtained. However, if the content exceeds 1.5, the mechanical properties, particularly the toughness, will deteriorate significantly. P: 0.08 or less P is preferably as low as possible especially in roll materials, and from the viewpoint of making the material brittle, it is suppressed to 0.08 or less. S: 0.06 or less For the same reason as P, the smaller the amount of S, the more desirable it is, and its content should be 0.06 or less. Ni: 1.0 to 2.0 Ni is added to improve hardenability and actively adjust hardness. If it is less than 1.0, the effect is insufficient, while if it is contained more than 2.0, retained austenite increases. Hardness is difficult to increase, especially hardness
From the standpoint of achieving Hs70 or higher, the content should be 1.0
~2.0. Cr: 10-30 Cr is contained to improve toughness and wear resistance, but if the content is less than 10, a large amount of M ₃ C type carbides will crystallize, resulting in a decrease in toughness and fine uniformity of carbides. On the other hand, if it exceeds 30, 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. Therefore, the Cr content is defined to be in the range of 10 to 30, in balance with the C content, as a range in which an appropriate M ₇ C ₃ type carbide can be obtained. Mo: 0.5 to 1.5 Mo forms carbides at the same time as increasing resistance to tempering and tempering, and is effective in increasing hardness and promoting resistance to softening in tempering. However, if the content is less than 0.5, this effect will not occur. On the other hand, if the content exceeds 1.5, retained austenite will become stabilized in the matrix, which may even lead to a decrease in hardness. The high chromium cast iron material that forms the outer layer contains the above components, with the remainder consisting of Fe after removing impurities, but the outer layer material contains the following Nb,
One or two types of V can be contained as necessary. Nb: 1.0 or less Nb is effective in refining the casting structure, and the inclusion of Nb promotes precipitation hardening and improves wear resistance, but especially when the hardness is Hs70 or higher, the Nb content is required to be 1.0 or less. It is enough. That is, Nb
This is because even if the content exceeds 1.0, the improvement effect will be saturated and the cost will increase. V: 1.0 or less V is contained for the same purpose as Nb, and from the same standpoint, a content of 1.0 or less is necessary and sufficient. That is, even if it exceeds 1.0, the effect is saturated, and rather the V carbide increases and the toughness deteriorates. The cast iron structure of the outer layer high chromium material consisting of the above component range is hard (Fe, Cr). ₇ C Type ₃ carbide and matrix are composed of retained austenite and some martensite, but the outer layer has excellent wear resistance and accident resistance. In order to improve this, it is customary to heat treat the material during the manufacturing process. In this case, heat treatment methods include heating to a temperature below the transformation point to remove casting stress and transforming retained austenite generated in the casting state into martensite or pearlite structure, and heating to a temperature higher than the transformation point There is a method of obtaining a structure that cannot be obtained only by the cooling rate after casting by changing the subsequent cooling rate. In the application of wear-resistant rollers, a hollow roller body is assembled by shrink-fitting into an arbor, but in this case, the roller often breaks due to cracks from the shrink-fit portion with the arbor, that is, from the inner surface of the sleeve. The inner layer of the hollow roller body will be described in detail below, but the above heat treatment contributes to reducing residual stress and improving the toughness of the inner layer material, and is highly effective in improving not only the outer layer material but also the inner layer material. After the above-mentioned heat treatment, it is of course necessary to perform strain relief annealing 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 layer, we have mentioned a hardness of Hs70 or higher, but this is because this type of roller requires wear resistance, crack resistance, etc., and wear resistance has a strong correlation with hardness. This is because if it is less than that, sufficient wear resistance cannot be obtained. Although the upper limit of the hardness of the outer layer is not specified, it is generally difficult to obtain a material with Hs90 or higher using the above-mentioned outer layer chemical composition and heat treatment, taking into account accident resistance. [Inner layer] Inner layer is C2.0~3.0, Si2.0~3.0, Mn0.5~1.5,
P0.06 or less, S0.04 or less, Ni13~25, Cr5 or less,
Contains Mo1.0 or less, Mg0.02~0.1, and the remainder is substantially
Formed from ductile cast iron with a particularly high Ni content of Fe. Since this inner layer is welded after a part of the inner surface of the outer layer is washed, it is necessary to determine the inner layer casting components in consideration of the amount of washing. The reason for limiting the range of components of the inner layer is as follows. C: 2.0 to 3.0 C is contained to impart toughness and strength, but if the content is less than 2.0, the material will become chilled and the toughness as an inner layer material will significantly decrease. On the other hand, if the content exceeds 3.0, graphitization will be excessive, resulting in insufficient strength as an inner layer material. That is,
In applications where wear-resistant rollers are used, if the strength is insufficient when mechanically connecting the hollow roller and arbor that are normally used (usually by shrink fit), a large fitting allowance cannot be achieved, resulting in axial displacement of the roller and internal damage. Leads to defects. Si: 2.0 to 3.0 Si is effective in preventing the inner layer material from becoming brittle due to contamination with Cr in the outer layer, but if it is less than 2.0, graphitization is poor and a large amount of cementite crystallizes, resulting in decreased strength and residual Stress makes it more likely to crack during casting.
Moreover, if it exceeds 3.0, graphitization is promoted too much and strength deteriorates, which is not preferable. In order to prevent material deterioration due to Cr contamination in the inner layer, it is an effective method to inoculate with Ca-Si or Fe-Si when casting the inner layer, and in this case, the amount of inoculation should be 0.2 to 0.5.
(in terms of si content), and it is necessary to set the Si content after inoculation to the above range of 2.0 to 3.0. Mn: 0.5-1.5 Combines with MnS to form MnS and removes the harmful effects of S, but if it is less than 0.5, this effect is not sufficient, while if it exceeds 1.5, the material deteriorates rather than removing the harmful effects of S. This is not preferable because the effect becomes significant. P: 0.06 or less 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 0.06 or less. S: 0.04 or less Similar to P, S makes the material brittle, so the lower it is, the better, and in the case of inner layer ductile cast iron, S
Since S combines with Mg and inhibits the spheroidization of graphite as MgS, from this point of view as well, the content of S needs to be low, and is set at 0.04 or less. Ni: 13-25 Ni is contained in balance with the amount of Cr to ensure the toughness of the inner layer. In other words, Ni is an element that is actively added to prevent Cr from mixing in from the outer layer and turning the inner layer into white metal, and by increasing its content, it promotes graphitization and strengthens the matrix structure. It is effective in making the material tough. However, from the balance with the amount of Cr mixed in the inner layer, 13
If it is less than 25, the effect is not certain, while if it exceeds 25, the effect becomes saturated and becomes uneconomical. In addition, the inner layer
In cases where the Cr content can be suppressed to around 1.0, the Ni content may be around 15, and in cases where the outer layer has a high Cr content and the inner layer also contains close to 5 Cr, the Ni content should be set at the upper limit. It is desirable to increase it to near 25. However, when the Cr content of the inner layer exceeds 5, the chilling effect is large, and the material quality cannot be adjusted only by increasing Ni and Si, and the entire inner layer becomes white. Generally, it is appropriate that the inner layer has a Cr content of about 3 and a Ni content of about 20. Cr: 5 or less As mentioned above, in order to prevent whitening and brittleness of the inner layer, it is necessary to suppress the Cr content to 5 or less. Note that since a certain amount of Cr is unavoidably mixed into the inner layer from the outer layer, it is desirable that the Cr content of the molten metal cast in the inner layer is as low as possible, and it is preferably suppressed to about less than 1.0. Mo: 1.0 or less Mo content exceeding 1.0 is not preferable because the material becomes too hard. Mg: 0.02 to 0.1 Mg is an element necessary for spheroidizing graphite, and if the content is less than 0.02, spheroidization will occur and the inner layer may not be made of strong ductile cast iron. However, if the content exceeds 0.1, it is unfavorable in terms of the chilling effect of Mg and the formation of dross. The ductile cast iron material forming the inner layer contains the above components, with the remainder consisting of Fe after removing impurities. The composite roller according to the present invention is formed by metallurgically welding and integrating the above-mentioned outer layer and inner layer, and is preferably manufactured using a centrifugal casting method. A concrete usage structure example of the composite roller manufactured in this way is as shown in the figure.
In the figure, 1 and 2 indicate an outer layer and an inner layer forming a hollow roller, and 3 indicates an arbor into which this hollow roller is shrink-fitted. In addition, the material of the arbor is SCM-4, SF-
60, cast steel, ductile cast iron, etc. are used as appropriate.
However, the performance of the grinding roller does not depend on the degree of shrink-fitting of the material of the arbor, but is solely determined by the hardness of the outer layer and the strength of the inner layer of the roller. Next, embodiments of the present invention will be described together with reference examples and conventional examples. Example An example of manufacturing a hollow roller with a product body diameter of 630φ and a body length of 840L. [Manufacturing process] (1) As the outer layer, high chromium cast iron molten metal with a wall thickness of 65 mm (casting weight 955 kg) is placed in a rotating mold on a centrifugal casting machine.
It was cast at 1400℃. (2) Nine minutes after the start of casting of the outer layer, the thickness of the inner layer is increased.
Molten ductile cast iron of 100mm (casting weight 1 ^T 200Kg) was cast into a rotating mold at 1400℃. (3) Forty minutes after the start of casting of the outer layer, the outer layer and the inner layer were completely solidified. (4) After that, disassemble the mold and take out the hollow roller.
This was charged into the furnace and heated to 1000℃, held for 5 hours, then taken out of the furnace and forced air cooled until the surface reached 500℃, then kept at 500℃ in the furnace, and then cooled in the furnace. did. [Test Results] After the composite roller obtained in the above manufacturing process was machined, it was subjected to an ultrasonic test from the surface and a fracture investigation. As a result, the thickness of the outer layer was 50 mm because it was washed away by the inner layer. On the other hand, the Cr content in the inner layer had increased to 2 to 3%. In addition, the outer layer and inner layer were completely connected, and structural continuity was observed. The chemical components of the outer layer and inner layer are as follows.

【table】

[Table] The mechanical properties of the inner layer of the above composite roller were investigated and found to be as follows. Tensile strength: 48.5Kg/mm ² Elongation: 14% Next, the outer and inner surfaces of this composite roller were processed to form an inner diameter of 370φ, and then assembled into an arbor with a shrinkage fit of 6/10000. As a result of measuring the hardness of the body, a hardness of Hs73 was obtained (however, heat treatment at 550°C x 10 hours was performed twice). As a result of using the composite roller assembled in the arbor for coal pulverization, no dents, abnormal wear, or corrosion cracks occurred in the outer layer. Further, there was no misalignment between the arbor and roller due to the driving of the arbor, and no breakage of the inner surface of the roller. Reference Example A composite roller was manufactured in the same manner as in Example 1 using the following outer layer and inner layer.

【table】

[Table] The mechanical properties of the inner layer of the above composite roller were investigated and found to be as follows. Tensile strength: 50Kg/ ^mm2 Elongation: 14.8% The outer and inner surfaces of this composite roller are processed, and the inner diameter
After forming it to 370φ, it was assembled into an arbor with a shrinkage fit of 6/10000. As a result of measuring the hardness of the body, a hardness of Hs76 was obtained (However, as a result of heat treatment,
After holding at 1000° for 5 hours, spray with water and then cool at 550°C.
(10 hours of distortion removal was performed). Conventional Example Similar to the example, a composite roller was centrifugally cast using a molten metal containing the following components (unit weight %, the remainder being essentially Fe). ●Chemical composition of outer layer molten metal (high chromium cast iron) C: 2.79%, Si: 0.69%, Mn: 0.84% P: 0.032%, S: 0.25%, Ni: 1.76% Cr: 18.00%, Mo: 1.14% ●Inner layer molten metal Chemical composition (low Ni ductile cast iron) C: 3.53%, Si: 2.56%, Mn: 0.43% P: 0.070%, S: 0.010%, Ni: 0.71% Cr: 0.17%, Mo: 0.09%, Mg: 0.050% The inner layer chemical components (unit weight %, remainder Fe) of the obtained composite roller were as follows. C: 3.52%, Si: 2.43%, Mn: 0.50% P: 0.071%, S: 0.012%, Ni: 0.70% Cr: 3.35%, Mo: 0.29%, Mg: 0.049% The strength of the inner layer is as follows It is as follows,
It had the strength level of FC cast iron. Tensile strength: 26.8Kg/ ^mm2 Elongation: 0.16% Furthermore, the graphite shape at the boundary between the outer layer and the inner layer is poor;
Poor welding occurred. Although centrifugal casting has been described as the manufacturing method of the present invention, there are other methods such as a pouring method using a thin partition plate. In the composite roller of the present invention described above, the outer layer is formed of high chromium cast iron material, while the inner layer is particularly
Since it is made of a ductile cast iron material with a high Ni content, it has abrasion resistance, toughness, and accident resistance suitable for applications such as wear-resistant rollers. In other words, conventional single-piece high chromium rollers have a fatal drawback of inferior toughness, and are not suitable for mechanical assembly such as shrink fitting. Even in the case of rollers, deterioration due to the inclusion of Cr in the inner layer was an unavoidable problem, but
In the case of the present invention, by improving the material of the inner layer, it is possible to reliably prevent the inner layer from becoming brittle even when Cr is mixed therein. Therefore, if the hollow composite roller according to the present invention is assembled and used in an arbor by shrink-fitting, since the inner layer has high toughness, it is easy to increase the shrink-fitting amount, which improves the service life and safety of the assembled roller. can be doubled. Although the present invention is most suitable for use as a wear-resistant roller as described above, it can also be used for rolls such as wire finishing rolls and hot strip mill rough rolling rolls.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal cross-sectional view showing an example of a structure in which a composite roller according to the present invention is used, and FIG. 2 is a cross-sectional view thereof. 1...outer layer, 2...inner layer, 3...arbor.

Claims (1)

[Claims] 1 C2.0~3.2, Si0.5~1.5, Mn0.5~1.5, P0.08
Below, S0.06 or below, Ni1.0~2.0, Cr10~30, Mo0.5
An outer layer made of high chromium cast iron containing ~1.5% by weight, the remainder being substantially Fe, and having a hardness of Hs70 or more; C2.0~3.0, Si2.0~3.0, Mn0.5~1.5, P0.06 or less , S0.04 or less, Ni13~25, Cr5 or less, Mo1.0 or less, Mg0.02~0.1 in each weight%, the balance being substantially
A hollow composite roller characterized by a welded and integrated inner layer made of Fe ductile cast iron.