JPH02290942A - High chromium cast iron roll material having excellent crack resistance, slip resistance and seizure resistance - Google Patents

Abstract

PURPOSE:To improve the crack resistance, slip resistance and seizure resistance of the high chromium cast iron roll material by specifying the contents of C, Cr, Si, Mo, Mn, V and Ni. CONSTITUTION:The high chromium cast iron roll material is formed from the compsn. contg., by weight, 1.3 to 2% C, 11 to 19% Cr, 0.3 to 2% Si, 0.8 to 3% Mo, 0.3 to 2% Mn, 0.5 to 3% V, 0.5 to 5% Ni and the balance Fe. In the roll material, the content of C is suppressed and Ni and V are positively added. Thus, the amt. of carbide to be formed is suppressed to crystallize out M23C6 carbide having toughness; the carbide is given in a rigid base structure.

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 made with higher quality, thinner gauges, and special copper rolling ratios. In response to the increasing number of rolls, 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.

(Problems to be Solved by the Invention) The high chromium roll material has a C:2. O~3.2wt
%, Cr: 10 to 30 iyt%, and has high hardness M, Cr in the structure. It is made of a large amount of mold 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 crank resistance is a so-called chipping accident. The chipping accident occurs when a small piece with a width and length of several mm and a depth of about 1 mm peels off from the roll surface during rolling. When such an accident occurs, the peeled portions are transferred to the surface of the rolled material (copper 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 steel sheets or steel sheets, the convex rolled portion becomes the starting point for cracking, leading to the occurrence of defective products. The present invention was made in view of such problems, and an object of the present invention is to provide a high chromium roll material having excellent slip resistance, crank resistance, and seizure resistance.

(Means for Solving the Problems) The high chromium cast iron roll material of the present invention made to achieve the above object has a chemical composition of C: 1.3 to 2.0 in weight%.
%, Cr: 11-19%Si: 0.3-2.0
%, Mo: 0.8-3.0% Mn: 0.
3-2.0%, V: 0.5-3.0% Ni: 0.5-
5.0% The balance is substantially composed of Fe.

(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: 1.3-2.0% C is Cr. It combines with Mo or V to form carbide. In the present invention, C is contained in the above range in order to reduce the amount of C compared to conventional high chromium cast iron materials, suppress the amount of carbide in the structure, and stably crystallize MtxCb type carbides having toughness. That is, if the amount of carbide is less than 1.3%, the amount of carbide will be excessive and wear resistance will be insufficient, and if it exceeds 2.0%, the amount of carbide will be excessive and MrCz type carbide with high hardness will crystallize, resulting in poor crack resistance and slip resistance. deteriorates.

Si: 0.3-2.0% St is an element necessary for deoxidizing molten metal, and 0.3%
The above is necessary. However, if it exceeds 2.0%, the base becomes brittle.

Mn: 0.3 to 2.0% Mn is required to be 0.3% or more for deoxidizing and desulfurizing the molten metal. However, if it exceeds 2.0%, mechanical properties, especially toughness, deteriorate significantly.

Hardness adjustment tends to be difficult during subsequent heat treatment.

(1: 11 to 19% Cr is added mainly to form an appropriate amount of Mt3Ch 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, 19
If the content exceeds %, the amount of Cr carbide produced will be excessive, and the improvement in crack resistance, which is the objective of the present invention, will be inhibited.

Mo: 0.8 to 3.0% Mo, like Fe, Cr, etc., forms carbides and is effective in increasing temper softening resistance. 0.8%
If the content is less than 3.0%, the above effects will be small, while if the content exceeds 3.0%, it will be difficult to stabilize retained austenite and obtain sufficient hardness.

Ni: 0.5 to 5.0% Ni is actively added to improve the strength of the base as well as quench hardenability by solidly dissolving in the base without forming carbides. In the range from .5% to 5%, the base is strengthened as Ni increases. 0.5%
If it is less than 5%, sufficient base reinforcement cannot be achieved, and if it exceeds 5%, retained austenite becomes stable, making it difficult to adjust the hardness in subsequent heat treatment.

V: 0.5-3.0% (1) is actively added to make the cast structure fine and dense and strengthen the matrix. In addition, since the generated ① force-bide is finely dispersed in the structure, it is also effective in improving wear resistance and seizure resistance. If it is less than 0.5%, sufficient base reinforcement will not be obtained, and if it exceeds 3%, it will become brittle, and when the outer layer of a roll is produced by centrifugal casting, segregation will occur due to the difference in specific gravity.

In addition to the above-mentioned components, the high chromium cast iron roll material of the present invention is made essentially of Fe. Incidentally, since both P and S make the material brittle, it is desirable to have as little as possible, and P: less than 0.08% and S: less than 0.06% are preferred.

The high chromium cast iron roll material of the present invention suppresses the amount of carbide generated within a range that does not impair wear resistance and has toughness by particularly suppressing the C content.
C6 type carbide is crystallized. Then, Ni is actively added to strengthen the base structure as a solid solution, and at the same time, (2) is also actively added to make the base structure fine and dense, strengthening the base structure and improving seizure resistance. ! It is characterized by having a structure in which the hjc6 type carbide is supported by a strong base structure, which improves wear resistance, slip resistance, and seizure 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 is used as appropriate.

In addition, 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 stood up to form a stationary mold, and the inner layer material molten metal is placed inside the stationary 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.

In addition, when welding the outer layer and the inner layer, the C from the outer layer to the inner layer
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 holding at a high temperature of A3 point or higher to lower the Cr and C concentration in austenite, and then transform in the subsequent cooling (quenching) process. A so-called austenite destabilization heat treatment is performed to transform it into a more stable austenite. Then, the austenite is transformed into martensite through quenching treatment, and subsequently, in order to create a thermally stable structure and reduce the residual stress generated during transformation,
Tempering heat treatment is carried out at a temperature of 400-600'C.

By applying the above heat treatment, the outer layer of the roll has Its7
A hardness of 5 to 85 can be imparted.

The roll material used in the present invention refers not only to the above-mentioned hot rolling rolls, but also to outer layer materials such as cold rolling rolls, hot skin pass rolls, H-type FI rolls, and 82 material rolling rolls. It is also a material that can be applied to rollers in rolling equipment. 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 cast to a casting thickness of 100 mm into a cylindrical mold rotating on a centrifugal casting machine. . At this time, a coating agent made of resin sand is applied to the inner surface of the mold to a thickness of 3ffllI.
+ coating, and the rotation speed of the cough mold is G No. So 140
The pouring temperature was 1520°C in each example.

Table 1 (2) Outer layer Approximately 22 minutes after the start of casting, the outer layer solidified completely. 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 form 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 then the upper part was covered with a riser heat insulator.

Next Leaves Table 2 Table 3 Table (3) The following heat treatments were applied to each leaf. The roll of Example A-1 was heated at 150°c/h after being maintained at 1030°C for 8 hours.
It is cooled and quenched at a cooling rate, and further heated at 500°C for 30°C.
H tempering treatment was performed.

After holding the roll of Example A-2 at 950°C for 10 hours,
Cool and harden at a cooling rate of 200°C/h, and then
It was tempered at 00℃ for 15 hours. The roll of Example 813 was held at 1100°C for 10 hours, then cooled and quenched at a cooling rate of 150°C/h, and further heated at 510°C for 15 hours.
H-tempered. (4) After finishing, the outer layer of the product was as shown in Table 3. (5) Each of the rolls described above was installed on an actual hot strip mill finishing stand and subjected to rolling. As a result, the rolling results are shown in Table 4 as the number of passing tons of the rolled material rolled while the outer layer of the roll was worn by 1 mm.

Table 4 From Table 4, it was observed that the wear resistance of each example was significantly improved compared to the conventional example.

In addition, in conventional rolls, the average pitch of fine cracks on the roll surface, which can cause chipping accidents, is 0.5 m.
In contrast, in the rolls of this example, the pitch of the fine cranks was 1 mm on average in each example. 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 resistance) and roughening resistance were observed compared to conventional rolls, and no seizure accidents were observed.

Furthermore, after the above-mentioned rolling, the surface of the roll body of each example and the conventional example was modified and leveled, and then placed again on the hot strip mill finishing stand and subjected to rolling of stainless steel. Although there were many incidents of co-seizing of both rolls, there were no incidents of seizing of the roll of this example, and improvement in anti-seizure property was observed.

Example B> (1) Under the same conditions as Example A, the molten outer layer material shown in Table 5 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 5 is poured onto the inner peripheral surface of the outer layer to a thickness of 25IIIl. is.

(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 form a stationary casting mold. The ductile cast iron molten metal shown in Table 5 was poured into the inside as the core material molten metal, and the ductile cast iron metal shown in Table 5 was completely filled, and then the upper part was covered with a riser heat insulator.

Next Leaf (3) Three days after casting, the molds were disassembled and each was subjected to the following heat treatment.

Example B-1 was held at 1030°C for 8 hours, then cooled and hardened at a cooling rate of 150°C/h, and further tempered at 500°C for 30 hours.

Example B-2 was held at 950°C for 10 hours, then cooled and hardened at a cooling rate of 200°C/h, and further tempered at 500°C for 15 hours.

In Example B-3, after holding at l100°C for 10 hours,
It is cooled and quenched at a cooling rate of °C/h, and further heated to 510°C.
Tempering treatment was performed at °C for 15 hours.

(4) Table 6 shows the outer layer thickness, intermediate layer thickness, and surface hardness of the outer layer of the finished product roll.

Table 6 Furthermore, the Cr content in the intermediate layer and inner layer of each example increased due to the mixing and diffusion of Cr from the outer layer.

Table 7 shows the Cr content of each layer.

Table 7 (5) Round bar test pieces were taken from each of the rolls so that the boundary surface of each layer was at an angle of 45 degrees with respect to the axial direction, and the compressive strength was examined. The results are shown in Table 8.

Table 8 For comparison, a two-layer composite roll was cast using each outer layer molten metal and inner N molten metal shown in Table 5 above, and the two were directly welded. In this case, the boundary between the outer layer and the inner layer The compressive strength in the 45 degree direction of the three samples was approximately 120 kg/+nm2, which was a considerably lower value than the compressive strength of the Examples shown in Table 8 above.

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

(Effects of the Invention) The high chromium cast iron roll material of the present invention suppresses the amount of carbide produced by suppressing the C content and actively adding Ni and ■.
It was possible to crystallize 23C6 type carbide and create a structure in which the carbide is supported by a strong matrix structure.

As a result, crank resistance has been improved while maintaining and improving wear resistance, and chipping accidents have been prevented. Furthermore, since the amount of carbide was suppressed, the friction coefficient between the roll and the rolled material increased, resulting in improved slip resistance. Furthermore, since the produced carbide contains finely dispersed carbide, the seizure resistance is improved. Furthermore, since the matrix structure was strengthened, the plastic flow resistance was improved, and the roughness resistance was improved.

Therefore, the high chromium cast iron roll material of the present invention was able to have excellent crack resistance, slip resistance, seizure resistance, and roughening resistance in addition to the conventional excellent wear resistance.

Claims (1)

[Claims] (1) Chemical composition in weight percent: C: 1.3-2.0%, Cr: 11-19%, Si: 0.
3-2.0%, Mo: 0.8-3.0% Mn: 0.3-
2.0%, V: 0.5-3.0% Ni: 0.5-5.0
% A high chromium cast iron roll material with excellent crack resistance, slip resistance and seizure resistance, characterized in that the remainder essentially consists of Fe.