JPH0214415B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a composite roll having excellent wear resistance, crack resistance, etc. and used as a roll for hot rolling striped plates. [Prior Art] Conventionally, rolls for striped plate hot rolling have had cores made of ordinary cast iron, spheroidal graphite cast iron, etc.
The outer peripheral surface of the core is made of high-alloy nickel grain cast iron (C: 3.2-3.5%, Si: 0.5-1.5%, Mn: 0.5-1.0
%, Ni: 4.0~4.5%, Cr: 1.5~2.0%, Mo: 0.2
Composite roll coated with a shell consisting of ~0.7%, balance Fe) or Adamite roll (C:
1.4-2.2%, Si: 0.3-0.6%, Mn: 0.5-1.0%,
Ni: 0.5~1.5%, Cr: 0.9~1.3%, Mo: 0.3~0.6
%, balance Fe) is used. [Problems to be solved by the invention] A composite roll whose shell is made of high-alloy nickel grain cast iron (hereinafter referred to as a "composite high-alloy grain roll") has a high hardness _HSD of 75 to 82 and has excellent wear resistance. It is excellent, but on the other hand, the fracture toughness value K _I C
(ASTM E399-79) is low at 70-80Kgmm ^3/2 , and has poor crack resistance. For this reason, the shell of the roll has grooves for stripe transfer (groove depth: e.g. 3 to 5 mm).
mm) and used as a work roll for rolling striped plates, cracks tend to form at the corners of the grooves, and the cracks progress and chipping occurs at the corners of the grooves, resulting in uneven peaks of striped stripes on the product stripes. In the worst case, this may lead to roll spalling or breakage. On the other hand, Adamite roll has a fracture toughness value K _I C
is high at 100-120Kgmm ^3/2 and has excellent crack resistance, but the altitude _HSD is low at 50-55,
When used as a work roll for rolling a striped plate, the corners of the grooves for stripe transfer rapidly wear out, causing the so-called sagging phenomenon in which the corners become rounded. When this crest sag becomes large, it causes a defect in the shape of the ridges of the striped pattern on the product striped plate. In view of the above, it is an object of the present invention to provide a composite roll with excellent wear resistance, crack resistance, etc., which is useful as a roll for hot rolling striped plates. [Means for Solving the Problems] The composite roll for striped plate hot rolling of the present invention has a shell covering the core containing C: 1.8 to 2.5% and Si: 0.5 to 2.
1.5%, Mn: 0.85~1.5%, Ni: 4.0~6.0%, Cr:
It has a chemical composition of 1.0 to 3.0% Mo, 0.3 to 1.5% Mo, and the balance substantially Fe, and is characterized by being formed of cast iron having a structure in which carbides are dispersed in a bainite matrix. The shell made of cast iron of the composite roll according to the present invention has the above chemical composition and a structure in which fine carbides are dispersed and crystallized in a bainite matrix, and as shown in the examples below, the shell has a high altitude H _S D is approximately 70 or more, surpassing Adamite, and the fracture toughness value K _I C is approximately 90.
Kgmm ^3/2 or higher, higher than that of high alloy nickel grain cast iron. In addition, the tensile strength is approximately 50 Kgmm ² or more, which is comparable to that of adamite. The core material of the composite roll of the present invention can be selected from various cast irons and cast steels known as core materials for this type of composite roll, such as ordinary cast iron and spheroidal graphite cast iron, depending on the purpose of the roll, usage conditions, etc. Just choose as appropriate. FIG. 1 shows an example of the cross-sectional structure of the composite roll of the present invention. 1 is a core, and 2 is a shell covering the outer peripheral surface of the core 1. The core 1 and shell 2 are metallurgically fused and integrated at their interface. The composite roll of the present invention is manufactured using a general manufacturing method for this type of roll. First, a molten shell material is injected into a centrifugal casting mold to form a shell having a predetermined wall thickness, and then a core material is placed inside the shell. After casting the molten metal and solidifying it to form a cast body in which the shell and core are fused at the interface, the cast body is taken out of the mold and subjected to quenching heat treatment and structure stabilization heat treatment to form a shell and a bainite base. It is manufactured by providing a structure in which carbide is finely dispersed, and then performing machining to form a roll surface having grooves for stripe transfer. The heating temperature in the above-mentioned quenching heat treatment is preferably 900° C. or higher to uniformly form austenite, and the upper limit is preferably 1000° C. to avoid coarsening of austenite grains.
The structure stabilizing heat treatment is preferably carried out at a temperature range of 400 to 650° in order to form a homogeneous and complete bainite base. If the temperature is lower than 400℃, there is a risk of martensanth transformation or residual austenite phase, while if the temperature exceeds 650℃, layered pearlite will form, and in either case, it will be difficult to secure a complete bainite base. Because it will be. Next, the reasons for limiting the components of the shell material of the composite roll of the present invention will be explained. C: 1.8 to 2.5% C combines with Cr to form chromium carbide, thereby increasing wear resistance. When the amount of C is less than 1.8%, the amount of carbide is insufficient, and the above effects cannot be achieved. On the other hand, if the C content exceeds 2.5%, the amount of carbides becomes excessive, resulting in a decrease in toughness and poor crack resistance. Therefore, 1.8 to 2.5
%. Si: 0.5-1.5% Si needs at least 0.5% as a deoxidizing agent. As the amount added increases, the deoxidizing effect increases, but if it exceeds 1.5%, a graphitization effect appears, leading to a decrease in strength. Therefore, it is set at 0.5 to 1.5%. Mn: 0.85 to 1.5% Mn is added for deoxidation, stabilization of the base structure, and improvement of hardenability (increase of hardening depth). Stabilization of the base is necessary for stabilizing high toughness (cracking resistance) and high hardness (wear resistance).
In addition, due to the increase in hardening depth due to improved hardenability,
High hardness is ensured down to the bottom of the striped grooves formed after heat treatment, and during actual machine use, friction and
In addition to suppressing deformation, it is possible to ensure surface hardness when re-cutting a surface that has deteriorated due to use for a certain period of time and repeatedly reusing it. It takes at least 0.85% to achieve this effect. but,
When it exceeds 1.5%, the effect is almost saturated, so
Set at 0.85-1.5%. Ni: 4.0-6.0% Ni makes the base structure highly hard bainitic,
Added to increase wear resistance. By adding 3.0%, it is possible to avoid the formation of pearlite in the base structure and the resulting lack of wear resistance, but in order to make the base structure a homogeneous and complete bainite without mixed phases such as pearlite, it is necessary to add 4.0% or more. shall be.
Complete bainiticization of this base structure makes it possible to improve toughness (crack resistance) and maintain and stabilize high hardness (wear resistance). Furthermore, the bainite structure does not undergo transformation like martensite even when used at high temperatures and is stable, so high toughness and high hardness are maintained during high temperature use. On the other hand, if it exceeds 6.0%, the amount of retained austenite increases, and in this case too, the hardness decreases and wear resistance becomes insufficient. Therefore, it is set at 4.0 to 6.0%. Cr: 1.0-3.0% Cr increases hardness and improves wear resistance by forming carbides. If it is less than 1.0%,
Due to insufficient amount of carbide, sufficient wear resistance cannot be ensured. Wear resistance improves as the amount added increases, but if it exceeds 3.0%, the amount of carbide becomes excessive, leading to deterioration of crack resistance due to a decrease in toughness. Therefore, it is set at 1.0 to 3.0%. Mo: 0.3 to 1.5% Mo is an element that is effective in strengthening the matrix structure and improving high-temperature strength. If it is less than 0.3%, the effect is insufficient, and if it exceeds 1.5%, the effect is almost saturated, and as the whitening progresses, the amount of retained austenite increases, resulting in a decrease in strength, wear resistance, etc. View. Therefore, it is set at 0.3 to 1.5%. Incidentally, P, S, and other impurities are allowed to mix unavoidably in normal refining technology. For example, P
As long as S is within the range of 0.05% or less and S is within the range of 0.04% or less, the spirit of the present invention will not be impaired. [Example] [] Manufacture of composite roll: Molten shell material was poured into a rotating mold held horizontally on a centrifugal casting machine at a casting temperature of 1450°C.
After solidifying to the inner surface of the shell, the mold is stood vertically and left standing, and the molten core material is poured into the shell at a casting temperature of 1410℃. After solidification, the cast body is taken out of the mold, quenched at 930°C, and then subjected to structure stabilization heat treatment at 500°C for 40 hours to form a structure in which carbides are finely dispersed in the bainite matrix, and then subjected to rough machining and Finish machining was performed to form grooves for stripe transfer. Through the above steps, sample work rolls (A) to (D) for striped plate hot rolling having the cross-sectional structure shown in Fig. 1 (the striped transfer grooves on the surface of the shell 2 are not shown) were obtained. Ta. All roll sizes are
Body diameter: 1000〓, body length: 4800 ^l , shell thickness: 100 ^t
(mm), the groove depth of the stripe transfer groove is 3 ^d , and the groove width is 3 ^w (mm). First, the chemical composition of the shell of each test roll was determined.
Shown in the table. Rolls (A) and (B) are invention examples, rolls
(C) is a composite high-alloy nickel grain roll, and roll (D) is an adamite roll. The core material of each test roll is ordinary cast iron (C: 3.5%,
Si: 2.5%, Mn: 0.5%, P: 0.03%, S: 0.01
%, Ni: 1.0%, Cr: 0.3%, balance Fe). In addition, microscopic observation of test pieces cut from each roll revealed that rolls (A) and (B) of the invention example had a structure consisting of a homogeneous and complete bainite base and fine carbides dispersed in the base. , Roll (C) (high alloy nickel grain roll) has a structure in which carbide and graphite are dispersed in a bainite base, and Roll (D) (adamite roll)
In each case, a structure in which carbides were dispersed in a layered pearlite base was observed. [] Mechanical properties: A test piece was cut out from each shell of each of the above sample rolls (A) to (D) and subjected to a mechanical test. Second
The results shown in the table were obtained. It can be seen that the rolls (A) and (B) of the invention examples have both high levels of hardness and fracture toughness, and also have sufficient tensile strength, making them excellent rolls for hot rolling striped plates. In addition, the hardness (H _S D) at a depth of 50 mm from the surface of rolls (A) and (B), which are invention examples, is 72.0 for roll (A) and 72.5 for roll (B), indicating that the hardness is sufficiently hardened to the deep part. This ensures sufficient reusability over many times through re-cutting of the surface during actual use.

【table】

〔Effect of the invention〕

The composite roll of the present invention has both a fracture toughness value that exceeds that of conventional composite high alloy grain rolls and a high hardness that exceeds that of Adamite rolls, and has excellent crack resistance and abrasion resistance, as well as sufficient strength. Because of this, during hot rolling of striped plates, corner cracks in the striped grooves, chipping, spalling, etc. caused by the cracks are less likely to occur, and the phenomenon of groove crests sagging due to wear is also less likely to occur. . Therefore, the useful life of the roll is improved, and at the same time, defects in the shape of the striped plate are prevented, and the quality of the striped plate is improved.

[Brief explanation of drawings]

FIG. 1 is a partially cutaway front view showing the cross-sectional structure of the composite roll. 1: Core, 2: Ciel.

Claims (1)

[Claims] 1. In a composite roll for striped plate hot rolling, which consists of a core and a shell covering the core, and in which grooves for stripe transfer are formed in the shell, the shell is C:
1.8~2.5%, Si: 0.5~1.5%, Mn: 0.85~1.5%,
Ni: 4.0-6.0%, Cr: 1.0-3.0%, Mo: 0.3-1.5
%, the remainder having a chemical composition consisting essentially of Fe,
A composite roll for hot rolling striped plates having excellent wear resistance and crack resistance, characterized by being made of cast iron having a metal structure in which carbides are dispersed in a bainite base.