JPS5890363A - Production of composite roll of high alloy cast iron - Google Patents

Abstract

PURPOSE:To prevent the generation of defects in the melt stuck part of both inside and outside layers, and to improve the mechanical strength in the melt stuck parts in the stage of producing a composite roll by constituting an inside layer material of as-cast high-carbon cast steel having spheroidal or massive graphite. CONSTITUTION:In producing a composite roll of which the outside shell is formed of high alloy gray cast iron by a centrifugal casting method, the melt of the high carbon cast steel which consists of 1.0-1.8% C, 1.0-2.0% Si, <=0.020% S, and the balance Fe and <=2% impurities and is subjected to a molten metal treatment by an Mg alloy, a Ca alloy or an alloy contg. both of Mg and Ca is charged as molten metal for the inside layer material after the outside shell is solidified to prescribed thickness. After the melt is filled in a mold, the melt is allowed to solidify, whereby the composite roll of the high alloy cast iron wherein the inside layer is formed of the as-cast high-carbon cast steel deposited with spheroidal or massive graphite is produced.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a high-alloy cast iron composite roll used as a work roll of a hot rolling mill, etc., in which the outer shell layer is made of high-alloy grain cast iron using the 4IK centrifugal casting method. The present invention relates to a manufacturing technology for the inner layer of a roll.

As is well known, work rolls in hot rolling mills are used under extremely severe conditions and are required to meet various conditions such as toughness, wear resistance, heat cracking resistance, and spalling resistance. It is difficult to fully satisfy these conditions with a single material, so recently, centrifugal casting has been used to create an outer shell layer made of a material that satisfies the characteristics required for the outer surface, such as wear resistance. In many cases, a so-called composite roll is used, which has an inner layer of tough material formed on the inside.In other words, this composite roll injects the molten shell material into a mold that is rotating at a predetermined speed. However, when the outer shell material has solidified to a predetermined thickness, the molten metal for the inner layer material is injected and solidified.

By the way, cast iron rolls used for hot rolling work rolls have recently been made of high-alloy grain cast iron with a C2.8 to 3.8 degree, which has increased hardness and strength and has graphite precipitated to the surface, which is different from cast iron. However, this high-alloy grain cast iron is extremely hard and contains a large amount of carbide crystallization, so it lacks toughness, so it is not suitable as an outer shell material for composite rolls (as mentioned above). It is usually used in combination with a tough inner layer material. Conventionally, the inner layer material of a composite roll using high-alloy grain cast iron as the outer shell material has a chemical composition of C3.0 to 3.6 and Si 1.0 to 2.0.
Ordinary cast iron with flaky graphite or strong cast iron containing a small amount of alloying elements is often used, and in this case, the strength of the inner layer material is about 15 to 301 in tensile strength and 10 in Young's modulus.
However, it is known that this level of strength cannot withstand the blue oxidation of recent rolling conditions, so recently the strength has been further improved, especially in terms of toughness and flatness resistance. In order to increase the
Spheroidal graphite cast iron, in which graphite is made spheroidal by adding alloys, is now being used. This type of inner layer material has a tensile strength of about 30 to 50, and a Young's modulus of about 16,000 to IS.
It is about ookg/ii, which is a considerable improvement compared to the case of ordinary cast iron.

However, as mentioned above, when ductile cast iron is used as the inner layer material for the purpose of improving the strength of a composite roll in which high-alloy grain cast iron is used as the outer shell material, a flaky graphite layer is formed at the welded part with the outer shell layer. As a result, when used for rolling, there is a risk that cracks may occur from the welded portion and the outer shell layer may peel off. In order to prevent the formation of a flaky graphite layer at the weld between the outer shell layer and the inner layer, it is possible to reduce the S content of the outer shell layer, or add Mg alloy, etc. to the outer shell material. There are methods such as making the outer shell layer also ductile, or casting an intermediate layer as a third phase between the outer shell layer and the inner layer, but all of these methods complicate the production process. There are problems such as an increase in costs.

Furthermore, as mentioned above, ordinary cast iron and ductile cast iron, which are used for the purpose of strengthening the inner layer, have almost the same or similar C content as the high-alloy grain cast iron, which is the outer shell material. Solidification temperature is almost the same. Therefore, even if composite casting is performed, solidification progresses almost continuously from the outer periphery of the roll toward the center, and the width of the transition region from the outer shell layer to the inner layer, that is, the mixing region of both the inner and outer molten metal at the weld zone, is narrow; As a result, when used for rolling, stress concentration tends to occur in the transition region, that is, near the weld, and this is also a cause for cracks to occur in the weld. Ta.

This invention was made in view of the above circumstances, and is intended to prevent the welded parts of the inner and outer layers from becoming areas of deterioration in mechanical properties when high-alloy grain cast iron is used as the outer shell material, and to prevent the welds between the outer shell layer and the inner layer. By gently changing the material properties in the transition region, it improves the metallurgical bond between the inner and outer layers, thereby preventing cracks in the welded area and peeling of the outer shell layer when used for rolling. The purpose is to obtain a composite roll having an inner layer of ductile cast iron with even higher strength and toughness.

That is, the method for manufacturing a composite roll of the present invention is basically to manufacture a composite roll whose outer shell is made of high-alloy grain cast iron using a centrifugal casting method. The inner layer is made of cast steel.

Specifically, after the outer shell has solidified to a predetermined thickness, C1.0 to C1.
8%, S11. A high carbon cast steel molten metal consisting of O ~ 2.0%, 80.020% or less, the balance F, and 2% or less impurity elements is injected, filled into the mold, solidified, and cast to form a spherical or block-shaped The present invention is characterized by manufacturing a high-alloy cast iron composite gas tube whose inner layer is high-carbon cast steel on which graphite has been precipitated.

In carrying out the method of the invention in ξ, which will be described in more detail below, an inner layer is first formed.

That is, the molten outer shell material is injected into a rotating mold, and when the outer shell layer has solidified to a predetermined thickness, the molten inner layer material is injected, and the molten inner layer material fills the mold and solidifies. Here, the outer shell material is known high-alloy grain cast iron, that is, c2.8~
3.8chi 1.8i0.8~1.8-1Kn 0.3~1
．． 0 To, P 0.3 or less, 80.06% or less,
Cr 0.5-2. Contains O4%Ni5, 0- or less, and if necessary a small amount (about 0.3%) of Mo, with the balance containing Fe and unavoidable impurities (cast iron with a better composition is used.On the other hand, the inner layer As for the material, the above-mentioned Noyo K C1,0~1
．． 8%, Si1. A high carbon cast steel molten metal consisting of 0~2.0%, 80.020- or less, the balance pe, and 2 or less impurity elements is treated with an alloy containing one or two of KMg and Cm before casting. use.

Here, to explain the reasons for limiting the chemical composition of the inner layer material, if the C content is less than 1.0%, it will be difficult to spread if graphite is precipitated by as-casting, and if the cooling rate is fast, it will be chilled. This results in material deterioration. Moreover, the molten metal injection temperature is 15
Since a temperature of 50'C or more is required, there is a risk that the already formed outer shell layer will be significantly remelted and the necessary outer shell thickness will not be secured, and there will be shrinkage cavities in the roll shaft core. There is a risk of forming internal defects such as shrinkage nests. On the other hand, if the C content exceeds 1.81, the graphite shape becomes coarse and spherical graphite cannot be obtained, and the graphite becomes almost flaky, resulting in a decrease in strength.

Another element is known as a graphitization promoting element, but in the 1C content range in this invention, the Si content is 1.
If it is less than 0.01, the amount of graphite precipitated is small, and the graphite shape becomes fine granular, so that the effect of preventing the occurrence of defects due to volume expansion due to graphite precipitation cannot be expected. On the other hand, if the Si content exceeds 2.0%, graphitization is promoted too much, making it difficult for the graphite to become spherical and causing the precipitation of coarse blocky graphite, which is undesirable in terms of strength.

Limiting the S content to 0.020 mm or less allows the action of Mg or ice to be perfected in molten metal processing using Mg alloys or Ca alloys. For this reason, if the S content exceeds 0.020%, Mg or Ca will combine with S to form sulfide, that is, MgS or CaS, and will no longer contribute to graphite spheroidization.

Other chemical components include Mn, P, Cr
, M.

etc. may be added in a range of 0.3 to 2.0% as necessary.

In this invention, Mg alloy, Ca alloy,
Alternatively, processing the molten metal by adding an alloy containing both Mg and -Cm is a rounding process in which spherical or nearly spherical lump graphite is precipitated in the high carbon cast steel that forms the inner layer in the as-cast state. If the treatment is not performed, the graphite shape will not be spherical or similar to a block shape, so the graphite will become notches and high strength will not be obtained.

Next, the progress of solidification from the outer shell layer to the inner layer using the above-mentioned outer shell material and inner layer material will be explained. In the case of tatami overcast iron or ductile cast iron, which has been used as the inner layer material since theft, the C content range is similar to the above-mentioned high-alloy grain cast iron of the outer shell, so the outer shell material is The solidification temperatures of the molten metal and the molten metal of the inner layer material are almost the same, so even if composite casting is performed, solidification progresses almost continuously from the outer periphery of the roll toward the center, resulting in a transition from the outer shell layer to the inner layer. The width of the region, that is, the mixing region of both molten metals is narrow. On the other hand, in this invention, high carbon cast steel whose C content is in the hypereutectoid steel range, which is lower than that of grain cast iron as the outer shell material, is used as the inner layer material, and its solidification initiation temperature is 1350.
Since the temperature is as high as ~1450°C, the injection temperature of the molten metal for the inner layer material also becomes high.

Therefore, when pouring the molten inner layer material, the unsolidified molten outer shell material inside the outer shell part and the molten inner layer material are sufficiently mixed, and a part of the inner wall of the outer shell layer that has already solidified is remelted. Therefore, welding defects do not occur at the boundary between the outer shell layer and the inner layer, and the width of the mixing area of both the inner and outer molten metals is wide. A healthy composite roll with no material changes can be obtained.

When pouring the high carbon cast steel molten metal as the inner layer material, the entire amount of the inner layer molten metal may be poured at once, but it may also be poured in several directions. When injecting in small quantities, it is possible to avoid applying unnecessary high-temperature heat to the already solidified outer shell layer, and to appropriately control the progress of solidification from the outer circumference of the roll to the center. can do.

As mentioned above, in the method of this invention, spheroidal or massive graphite is precipitated by as-casting into the high carbon cast steel of the inner layer material, and the purpose is 1) to obtain high strength, and 2) to reduce volume expansion due to graphitization. and 3) to omit the heat treatment step. To explain these in more detail, as-cast high carbon cast steel with spheroidal graphite or nearly spheroidal massive graphite has a tensile strength of 50 to 7 Q AII/4w1t and an elongation of 1 to 5.
%, and the strength is 2.5 to 3 times stronger than ordinary cast iron, which has traditionally been used as an inner layer material, and about 1.5 times stronger than Daretile cast iron. .

In addition, during solidification and cooling, carbon atoms that were dissolved in high carbon cast steel form graphite and precipitate, causing volumetric expansion, which offsets the volumetric decrease caused by solidification contraction, and as a result, the center of the inner layer The occurrence of internal defects such as shrinkage nests and shrinkage nests can be effectively prevented, and a composite sole with a sound interior can be obtained. Furthermore, regarding graphitization of high carbon cast steel, in addition to precipitating as-cast as in the method of this invention, it is once chilled during solidification and precipitated as cementite.
Although it is possible to graphitize it later by heat treatment,
In that case, heat treatment at high temperatures and for a long time is required, which is not only disadvantageous in terms of energy and cost, but also increases the hardness of the high-grade grain cast iron of the outer shell.
There is a risk that the amount of carbides, etc. will decrease and the outer shell properties required for rolling rolls will not be satisfied.For these reasons, it is essential to precipitate graphite by as-casting high carbon cast steel as the inner layer material.

Next, a practical example in which the method of the present invention was applied to the production of a post-hot-rolled work roll, and a comparative example in which the same work sail as described above was produced using conventional ordinary cast iron as the inner layer material will be described.

Example Roll size - 700wc x 7 with outer shell made of high alloy grain cast iron and inner layer made of high carbon cast steel by centrifugal casting method
A composite of 1 j Q Q m was prepared. The production content of high alloy grain cast iron of the outer shell is 03.26%, sto
, 7(NG, Mn 0.61%, Po, 051%, S
Q, 017%, y14.35%, Or 1-81%,
M.

0.38%, the rest is practically!・The chemical composition of the high carbon cast steel in the inner layer is 01.27%, 611.53%, M
u 0.49%, Po, 030%, 50.012%, N
i0004%, Or 0.07%, No O, 029g
, CaO 1004%, the balance substantially lPe, and the high carbon cast steel infiltration was performed with Fe-45% 5l-25% before casting.
The molten metal was treated by adding 1.5% of Oa alloy. The injection temperature of the high carbon cast steel molten metal that forms the inner layer is 1480"C.
In addition, the entire amount of the molten metal was injected at one time. Comparative Example A composite roll of the same roll size as described above was manufactured by using a centrifugal casting method, with an outer shell made of high-grade gold grain cast iron and an inner layer made of ordinary cast iron. The chemical composition of the high alloy grain cast iron of the outer shell is the same as in the example, and the ordinary cast iron of the inner layer is the same as that conventionally used for the inner layer, and its chemical composition is 03.31%, 811%. .23%, Mn0.45%
, Po, 086%, 80.012%, Ni o, 75%
, Qro, 50%, Mo 0.14%, remainder substantially F
It was set as e.

Note that the injection temperature of the ordinary cast iron forming the inner layer was 1330°C, which was 150°C lower than that in the example. Further, as the injection method for the inner layer material molten metal, a method was adopted in which the entire amount was injected at one time, similar to the example.

FIG. 1 shows a photograph of the internally welded macrostructure in a cross section perpendicular to the axial direction of the roll obtained in the above example. In FIG. 1, l indicates an outer shell layer made of high-alloy grain cast iron, 2 indicates a welded mixed region of the outer shell material and inner layer material, and 3 indicates an inner layer made of high carbon cast steel. For example, it is clear that there are no internal defects such as poor welding near the boundary between the outer shell layer and the inner layer, and that the bonding is good metallurgically. Furthermore, the width of the mixed region of the outer shell material and the inner layer material was as wide as 3.0 sII or more, and it was confirmed that the material quality changed continuously and gradually from the outer shell structure to the inner layer structure. Furthermore, the microstructure of the inner layer of the four bars obtained according to the embodiment of the present invention is as shown in the photograph in FIG. Totally unacceptable.

On the other hand, FIG. 3 shows a photograph of an internally welded structure in a cross section perpendicular to the axial direction of a steel obtained in a comparative example using ordinary cast iron as the inner layer material.

In Fig. 3, 4 is an outer shell layer made of high-alloy grain cast iron;
5 shows the welded part between the outer shell material and the inner layer material, and 6 shows the inner layer made of ordinary cast iron. In this case, there are no defects such as poor welding in the welded part, but there is a difference between the outer shell material and the inner layer material. It is clear that the width of the transition region is extremely narrow, and the material change is rapid.

In this way, in the case of the example in which ordinary cast iron was used as the inner layer material, the material change from the outer shell layer to the inner layer was rapid;
According to the embodiment of the present invention in which high carbon cast steel was used as the inner layer material, as described above, the material change from the outer shell layer to the inner layer was gradual, and a good structural change could be obtained. The reason why we were able to obtain such a gradual and continuous material change was
This is because by using high carbon cast steel as the inner layer material, it becomes possible to inject the molten inner layer material at a high temperature, and it becomes possible to maintain an appropriate solidification form.

Furthermore, as described above, it is clear from the hardness measurement results shown below that the embodiment of the present invention was able to achieve a gradual and continuous change in material quality from the outer shell layer to the inner layer. That is, FIG. 4 shows the change in hardness in the radial direction from the outer surface toward the inside of the composite wool 1 according to the embodiment of the present invention in which the inner layer is made of high carbon cast steel, and the composite roll according to the comparative example in which the inner layer is made of ordinary cast iron. In FIG. 4, 7 shows the hardness change of the composite roll according to the embodiment of the present invention', and 8 shows the hardness change of the composite roll according to the comparative example.

From FIG. 4, it can be seen that even in the composite seal according to the embodiment of the present invention in which high-carbon molten steel was injected at high temperature as the inner layer material, the hardness of the outer layer did not decrease and showed the same value as the composite roll according to the comparative example. However, there is a significant difference in the form of change in hardness in the transition region from the outer shell layer to the inner layer. That is, in the composite reel of the comparative example in which the inner layer material is ordinary cast iron, the transition region is formed with a width of about 110 l1, and the hardness decreases rapidly from the outer shell layer to the inner layer, whereas in the case of the present invention In the composite roll of the example, the width of the transition region is 30 mm or more, and the gradient of the decrease in hardness from the outer shell layer to the inner layer is said to be gentle, and there is no sudden change in material quality. It is clear that this is being prevented.

Furthermore, when the mechanical strength of each welded part and inner layer of the composite seal according to the embodiment of the invention and the composite roll according to the comparative example was examined, the following results were obtained. In other words, the tensile strength of the welded part of the composite seal is 15 to 187 in the comparative example Nyorori Ichiru, which uses ordinary cast iron as the inner layer material.
9/&ll'', whereas in the seal according to the embodiment of the present invention using high carbon cast steel as the inner layer material, the seal was about 40/&ll''.
A value of ~43 kg7hm' was obtained. As described above, it has been confirmed that according to the examples of the present invention, the strength of the welded part is more than doubled, and that accidents such as cracking in the welded part and peeling of the outer shell layer do not occur during rolling use. Ta.

In addition, the strength of the inner layer part is 18 to 2811 g in the roll according to the comparative example in which the inner layer material is ordinary cast iron.
/41m2 myank rate 11000~14000319,
The tensile strength was only about 4', but the tensile strength was 50.9 to 56 for the comparative roll using high carbon cast steel as the inner layer material.
．． An excellent value of 6 kg 7 M Young's modulus of 18100 peak-2 was obtained. At the same time, an impact test was conducted on the inner layer of the composite roll, and the results showed that the composite roll according to the example of the present invention was about 5% lower than the composite roll according to the comparative example.
It was recognized that the impact value had improved to a certain extent.

Although not listed as a comparative example, the tensile strength of the inner layer portion of conventional composite steel using ductile cast iron as the inner layer material is approximately 30 to 50 mm, and even compared to this, the present invention A high-strength, tough cast iron roll can be obtained in which the composite roll according to the embodiment has excellent strength, and there is no abnormal structure layer or internal defects between the outer shell layer and the inner layer, and there is no sudden material change. This was confirmed.

As is clear from the above description, according to the present invention, when producing a four-ring in which high-grade grain cast iron is used as the outer shell material, the inner layer material is replaced with conventional ordinary cast iron or ductile cast iron, and cast iron is used as the inner layer material. By using high-carbon cast steel that has spherical or nearly spherical lump graphite, it is possible to prevent defects from occurring at the welds of both the inner and outer layers, and to widen the mixing area of the materials of both the inner and outer layers, thereby preventing sudden damage. In addition to eliminating material changes, it improves the mechanical strength of the welded part, eliminating problems such as cracks from the welded part and peeling of the outer shell layer, and the strength of the inner layer is also higher than before. can be significantly improved.

In addition, as for the manufacturing process, it is a simple method of applying high carbon cast steel that has spherical or nearly spherical lump graphite in the as-cast state without modifying the conventional casting method or equipment or applying heat treatment. It has become possible to easily manufacture composite rolls with high strength, soundness, and high durability. As described above, according to the method of the present invention, it is possible to easily produce a composite roll having sufficiently good usability even under severe rolling conditions, and it can be implemented industrially to bring great benefits.

[Brief explanation of drawings]

Figure 1 is a macrostructure photograph showing the welded part structure of a composite roll obtained by an example of the present invention, Figure 2 is a microstructure photograph of the inner layer of the same composite roll, and Figure 3 is a photograph obtained by a comparative example using a conventional method. Fig. 4 is a macrostructure photograph showing the structure of the welded part of the composite roll obtained by the present invention, and Fig. 4 is a line showing the hardness distribution of the composite roll obtained by the example of the present invention and the composite roll obtained by the comparative example using the conventional method. It is a diagram. 1... Outer shell layer, 2... Welding mixed area, 3... Inner layer. Applicant Kawasaki Steel Co., Ltd. Agent Patent attorney Takehito Toyota (1 idiot) Figure 1 Figure 3 Figure 4 Row 1 Length 1 v Uno distance (mm)

Claims (1)

[Claims] When manufacturing a composite roll whose outer shell layer is made of high-alloy grain cast iron using the centrifugal casting method, when the outer shell layer has solidified to a predetermined thickness, Mg alloy or Cm alloy is used as the molten inner layer material.
C1. alloy or alloy containing both Cm and Mg. O~1.8chi, S! 1.0-2.
0'lks S 0.020% or less, balance Fe >
A composite material in which molten high carbon cast steel containing impurity elements of λ0 or less is injected, filled into the mold, solidified, and left to cast to precipitate spherical or expanded graphite, forming the inner layer of high carbon cast steel. A method for manufacturing a high-alloy cast iron composite roll, which is characterized by obtaining a roll.