JPH0353043A - High chromium cast iron roll material with excellent crack and slip resistance - Google Patents

Abstract

PURPOSE:To produce a roll stock improved in cracking resistance and slip resistance while maintaining wear resistance by preparing a high chromium cast iron roll stock having a specific composition in which C content is reduced. CONSTITUTION:A high chromium cast iron roll stock which has a chemical composition consisting of, by weight, 1.3-2.0% C, 0.3-1.5% Si, 0.3-1.5% Mn, 0.5.2.4% Ni, 11-19% Cr, 0.8-3.0% Mo, and the balance essentially Fe and containing, if necessary, 0.1-1.0% Ti or 0.1-1.0% Nb in place of a part of Fe is prepared. By this method, the high chromium cast iron roll stock excellent in cracking resistance and slip resistance while maintaining wear resistance can be obtained. This stock can be used mainly for the outer layer of a composite roll for hot rolling.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a roll material that is applied to a rolling layer of a rolling composite roll that is mainly subjected to hot rolling.

(Conventional technology) Adamite rolls have traditionally been used for hot rolling rolls, especially work rolls in the first stage of hot strip mill finishing, but in recent years, hot rolled steel sheets have been improved in quality, thinner gauges, and special steels have been used. In response to increases in rolling ratios, composite rolls are being used in which a high chromium roll material with excellent wear resistance is applied to the outer layer used for rolling.

(Problem to be solved by the invention) The high chromium roll material has a C: 2.0 to 3.2 w
t%, Cr: 10-30-t%, and has high hardness M? It is produced in large amounts of C3 type chromium carbide, and has excellent wear resistance, but has the problem of poor slip resistance and crack resistance. In particular, a serious accident caused by insufficient tarac resistance is a so-called chipping accident. The chipping accident occurs when a small piece with a width and length of several strokes and a depth of about 1 mm is peeled off from the roll surface during rolling. When such an accident occurs, the peeled portions are transferred to the surface of the material to be rolled (steel plate) as convex portions at regular intervals, and are rolled down by the next roll, which not only deteriorates the surface quality of the steel plate but also causes damage during coiling. When processing a steel plate or a steel plate, the convex rolled portion becomes a starting point for cracking, resulting in the occurrence of defective products.

The present invention was made in view of these problems, and an object of the present invention is to provide a high chromium cast iron roll material having excellent slip resistance and crack resistance.

(Means for Solving the Problems) The high chromium cast iron roll material of the present invention, which has been made to achieve the above object, has a chemical composition of C: 1.3 to 2.0 in weight percent.
%, Cr: 11-19%Si: 0.3
~1.5%, Mo: 0.8~3.0% Mn:
0.3-1.5%, Ni: 0.5-2.4%, and the remainder substantially consists of Fe.

Furthermore, in place of some of the Fe in the roll material of the above assembly, T
i: O. l=1.0 heavy background%, or Nb:0.1
It is preferable to contain up to 1.0% by weight.

(Function) The chemical composition of the high chromium cast iron roll material of the present invention is limited for the following reasons. The unit is weight %.

C: 1.3 to 2.0% C combines with Cr or Mo to form carbide. In the present invention, Cl is contained in the above range in order to reduce Cl compared to conventional high chromium cast iron materials, suppress the amount of carbide in the structure, and stably crystallize tough M23C& type carbides. That is, if it is less than 1.3%, the amount of carbide will be too small and the wear resistance will be insufficient, and if it exceeds 2.0%, the amount of carbide will be excessive and the M. C. Type carbides crystallize, resulting in deterioration of crack resistance and slip resistance.

Si: 0.3-1.5% Si is an element necessary for deoxidizing molten metal, and 0.3%
The above is necessary. However, if it exceeds 1.5%, the base will collapse.

Mn: 0.3 to 1.5% Mn is required to be 0.3% or more for deoxidizing and desulfurizing the molten metal. However, if it exceeds 1.5%, mechanical properties, especially toughness, deteriorate significantly.

Ni: 0.5 to 2.4% Ni is dissolved in the base without forming carbides, improving the strength of the base and improving quench hardenability.

If it is less than 0.5%, base reinforcement will not be sufficient. On the other hand, 2.4
Even if it exceeds 5%, the effect of strengthening the base can be recognized up to about 5%, but the drawback is that the manufacturing cost is high. Furthermore, if added in a large amount, residual austenite becomes stable, making it difficult to adjust the hardness in subsequent heat treatment.

Cr: 11 to 19% Cr is added mainly to form an appropriate amount of L3C6 type carbide. If it is less than 11%, the amount of Cr carbide produced will be too small and the wear resistance will deteriorate.

On the other hand, if the content exceeds 19%, the Cr carbon
The amount of byd becomes excessive, which inhibits the improvement of crack resistance, which is the objective of the present invention.

Mo: 0.8 to 3.0% Mo, like Fe, Cr, etc., is effective in suppressing carbides and increasing resistance to temper softening. If the content is less than 0.8%, the above effects will not be obtained, while if the content exceeds 3.0%, retained austenite will be stabilized, making it difficult to obtain sufficient hardness.

In addition to the above precepts, the high chromium cast iron roll material of the present invention has T
It is also possible to contain i or Nb in the following range.

Ti: 0.1 to 1.0% Ti forms a high hardness carbide that has about twice the hardness of Mo carbide, and has the effect of improving wear resistance. Further, like Mo, it is effective in increasing resistance to temper softening. 0.1
If it is less than 1.0%, it will not have the above effect, while if it exceeds 1.0%, segregation will occur due to the difference in specific gravity when the outer layer of a roll is produced by centrifugal casting, which is not preferable.

Nb: o. t~1.0% Nb makes the cast structure fine and dense, strengthens the matrix, and improves resistance to temper softening. If it is less than 0.1%, the above effect will not be observed, while if it exceeds 1%, the manufacturing cost will increase.

The high chromium cast iron roll material of the present invention has the above-mentioned precepts.
and impurities. It should be noted that both P and S make the material brittle, so it is preferable to have as little as possible.P: 0.08%
S: It is better to keep it below 0.06%.

The high chromium cast iron roll material of the present invention suppresses the amount of carbide produced within a range that does not impair wear resistance by particularly suppressing the C content, and also has MtzC which has toughness.
Crystallize h-type carbide. It is characterized by a structure in which the carbide is supported by a matrix structure strengthened by Ni as a solid solution, which improves crack resistance and slip resistance while maintaining wear resistance.

In addition, Ti is actively added to the above structure to form a highly hard Ti carbide in addition to the tough Mz3Cb type carbide, and both carbides are supported by the Ni solid solution strengthened structure. It is also possible to do this. This makes it possible to particularly improve wear resistance.

Alternatively, it is also possible to actively add Nb to the structure to make the base structure fine and dense, thereby further strengthening the base structure. As a result, the 1'lzsC6 type carbide is supported by a stronger base structure, and it is possible to particularly improve crack resistance while maintaining wear resistance.

(Example) The high chromium cast iron roll material explained above is mainly used as a casting material for the outer layer, which is the layer used in composite rolls for hot rolling. A tough cast iron material such as cast iron or a cast steel material such as graphite cast steel may be used as appropriate.

＼Also, as a manufacturing method for the composite roll, after casting the outer layer by centrifugal force casting, a centrifugal force casting mold containing the outer layer is erected to form a stationary mold, and the inner layer material is placed inside the mold. There is a method of pouring molten metal and welding the outer layer and the inner layer together, and this method is commonly used because it is simple.

When welding the outer layer and the inner layer, the C from the outer layer to the inner surface
In order to prevent mixing of r, it is preferable to provide an intermediate layer between the outer layer and the inner layer. This is because by providing the intermediate layer, it is possible to prevent Cr from mixing and diffusing from the outer layer to the inner layer, and also to effectively prevent embrittlement of the boundary between the outer layer and the inner layer.

After casting, the composite roll is usually subjected to the following heat treatment. First, Cr and C dissolved in austenite are precipitated as secondary carbides by heating and held at a high temperature above point A to lower the Cr and C concentrations in austenite, and then undergo transformation in the subsequent cooling (quenching) process. A so-called destabilizing heat treatment of austenite 1~ is performed to convert it into austenite, which is easy to form. Then, austenite is transformed into martensite through a quenching treatment, and subsequently, a tempering heat treatment is performed at a temperature of 400 to 600°C in order to create a thermally stable structure and reduce residual stress generated during transformation.

By applying the above heat treatment, the outer layer of the roll has Hs75
A hardness of ~85 can be imparted.

The roll material in the present invention refers not only to the hot rolling roll described above, but also to outer layer materials such as cold rolling rolls, hot skin bath rolls, and rolls for H-shaped steel, as well as rollers in rolling equipment. It is also a material that can be applied to For example, it can be applied as an outer layer material of a hollow cylindrical roller such as a hot run table roller.

Next, a specific manufacturing example of a composite roll in which the high chromium cast iron roll material of the present invention is applied to the outer layer used for rolling will be described. For comparison, a composite roll using a conventional high chromium cast iron material for the outer layer was also manufactured as a conventional example.

<Example A> (1) High chromium cast iron shown in Table 1 was used as the outer layer material molten metal, and this was poured into a cylindrical mold rotating on a centrifugal casting machine to a casting thickness of 100 Ill. At this time, a coating agent made of resin sand was applied to the inner surface of the mold to a thickness of 3111 mm.
The number of revolutions of the mold was 140 GNα, and the pouring temperature was 1510'C.

Table 1 (2) Outer layer The outer layer was completely solidified 20 to 22 minutes after the start of casting. Thereafter, a centrifugal casting mold having an outer layer therein was vertically erected, and an upper mold and a lower mold for roll shaft casting were connected to both ends of the mold to construct a stationary casting mold. The ductile cast iron molten metal shown in Table 2 was poured into the inside as a shaft core material molten metal to completely fill the inside, and the upper part was covered with a riser heat insulator.

Next Leaf No. 2 table Housing D unit, weight%. The remainder is essentially Fe (3) 3 days after casting, Dismantle the above mold, Low After extracting and machining the raw material, That's it The heat treatment shown in Table 3 was then performed.

No. 3 table (4) After finishing processing, The outer layer of the product is as shown in Table 4. there were.

Table 4 (5) Each of the above rolls was installed in an actual hot strip mill finishing stand and subjected to rolling.

The rolling results of each roll are shown in Table 5 as the number of tons of material to be rolled passing during the time when the outer layer of the roll wears 1 mm.

Table 5 From Table 5, it was confirmed that the wear resistance of each roll of this example was improved compared to the conventional example.

In addition, in conventional rolls, the average pitch of fine cracks that cause chipping accidents on the roll surface is 0.5.
ytm, whereas in the roll of this example, the average pitch of fine cracks in Example A1, Example A-2, and Example A-3 was 1 mm. This shows that the roll is insensitive to heat cycles, which is advantageous for crack resistance.

Needless to say, there were no accidents resulting from the use of this roll. Furthermore, improvements in slip resistance (biting property) and roughening resistance were observed compared to conventional rolls.

Example B> (1) Example B shown in Table 6 under the same conditions as Example A.
A certain outer layer material molten metal from Example B-1, Example B-2 and Example B-3 was cast into a centrifugal casting mold to a casting thickness of 100 mm. Approximately 14 minutes after the start of casting of the outer layer, when a part of the inner peripheral surface of the outer layer is in an unsolidified state, the intermediate molten metal shown in Table 6 is poured onto the inner peripheral surface of the outer layer to a casting thickness of 25 m. Cast in.

(2) Outer layer Approximately 30 minutes after the start of casting, the outer layer and intermediate layer were completely solidified. Thereafter, a centrifugal casting mold containing an outer layer and an intermediate layer was vertically erected, and an upper mold and a lower mold for roll shaft casting were connected to both ends of the mold to construct a stationary casting mold. The ductile cast iron molten metal shown in Table 6 was cast into the inside as the core material molten metal to completely fill it, and then the upper part was covered with a riser heat insulating material.

Next Leaf (3) 3 days after casting, Dismantle the above mold, That's it The heat treatment shown in Table 7 was then performed.

No. 7 table (4) The thickness of the outer layer and middle layer of the product roll after finishing processing, The surface hardness of the outer layer is as shown in Table 8. It was.

Table 8 Also, in the intermediate layer and inner layer of each roll, an increase in Cr content due to mixing and diffusion of Cr from the outer layer was observed. This is shown in Table 9.

Table 9 (Note) Units, weight % (5) Round bar test pieces were taken from each of the rolls so that the interface between each layer was at an angle of 45 degrees to the axial direction, and the compressive strength was examined. The results are shown in Table IO.

Table 10 For comparison, a two-layer composite roll was cast using each of the outer and inner molten metals and directly welded together. In this case, the compressive strength in the 45-degree direction at the boundary between the outer layer and the inner layer The compressive strengths were all about 120 kg/ton'', which were considerably lower values than the compressive strengths of the previous examples.

Further, during the strength test, in both examples, no reduction in slippage at the boundary due to the embrittlement of the boundary observed due to direct welding of the outer layer and the inner layer was observed.

(Effects of the Invention) The high chromium cast iron roll material of the present invention suppresses the amount of carbide generated by suppressing the C content and adding Ni, and at the same time crystallizes L!C& type carbides having toughness. It was possible to create a structure in which the carbide was supported by a strong base structure.Therefore, the crack resistance was improved while maintaining the wear resistance, and the occurrence of chipping accidents was prevented.

Furthermore, since the amount of carbide was suppressed, the coefficient of friction between the roll and the rolled material increased, resulting in improved slip resistance. moreover,
Since the matrix structure was strengthened, plastic flow resistance was also improved, and roughness resistance was improved.

Further, by actively adding Ti, a highly hard Ti carbide was crystallized together with a tough Mz3Ch type carbide, and a structure was created in which both carbides were supported by a strong base structure. Therefore, in addition to the above-mentioned effects, it was possible to particularly improve wear resistance.

Alternatively, by actively adding Nb, the base structure was finely and densified, and the base structure was further strengthened, so that the FIzzCb type carbide could be supported by a stronger base structure. Therefore, in addition to the above-mentioned effects, it was possible to particularly improve crack resistance and roughness resistance.

Therefore, the high chromium cast iron roll material of the present invention was able to maintain or improve the conventional excellent wear resistance while also having excellent crack resistance and slip resistance.

Claims (3)

[Claims] (1) Chemical composition in weight percent: C: 1.3-2.0%, Cr: 11-19%, Si: 0.
3-1.5%, Mo: 0.8-3.0% Mn: 0.3-
1.5%, Ni: 0.5 to 2.4%, and the balance substantially consists of Fe. A high chromium cast iron roll material with excellent crack resistance and slip resistance. (2) A roll material with excellent crack resistance and slip resistance characterized by containing 0.1 to 1.0% by weight of Ti in place of a part of Fe in the roll material according to claim (1). Chrome cast iron roll material. (3) A roll material with excellent crack resistance and slip resistance characterized by containing 0.1 to 1.0% by weight of Nb in place of a part of Fe in the roll material according to claim (1). Chrome cast iron roll material.