JP3320547B2 - Manufacturing method of high carbon content stainless steel sheet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a JIS standard SUS4
C: 0.60 to 1.20 mass as specified in 40
%, Cr: 16.0 to 18.0 mass%, Si: 0 to 1.0 mas
s%, Mn: 0 to 1.0 mass%, Mo: 0 to 0.75 mass%
The present invention relates to a method for producing a high-carbon-containing stainless steel thin plate having a composition containing Fe and the unavoidable impurities with the balance being Fe by a twin-roll method.

[0002]

2. Description of the Related Art C: 0.60 to 1.20 mass%, Cr: 1
6.0 to 18.0 mass%, Si: 0 to 1.0 mass%, Mn:
0-1.0 mass%, Mo: 0-0.75 mass%,
A high carbon content martensitic stainless steel (hereinafter referred to as "the present alloy") having a composition consisting of Fe and inevitable impurities has been conventionally known as SUS440 specified in JIS standards. This alloy has high quenching hardness, the highest hardness among stainless steels, and extremely excellent wear resistance.
Widely used as medical scalpel material.

Conventionally, as a method for producing the present alloy, an ingot obtained by melting, casting, and solidifying an alloy having the above composition is repeatedly subjected to hot rolling until a hot-rolled sheet having a desired thickness is obtained. A method of obtaining a cold rolled sheet as a final product by repeating cold rolling has been performed. The cross section of the ingot before hot rolling has an area of 10 ⁴ mm ² or more.

[0004]

However, a martensitic stainless steel containing a high carbon content, such as the present alloy, is once obtained as an ingot having a cross-sectional size of 10 ⁴ mm ² or more, and is cast. In the solidification process, a large amount of eutectic carbide of Cr is crystallized at primary grain boundaries, thereby producing a network carbide. If such coarse carbides remain in the final product, the properties of the product are significantly impaired. For example, in the case of razor blades that require delicate sharpness such as razor replacement blades, if large carbides appear on the cutting edge, the blades will spill and the sharpness will be impaired.

[0005] Therefore, in order to obtain a thin plate of the present alloy by a conventional manufacturing method, a small ingot must be used in order to suppress the eutectic carbide from becoming coarse during solidification as much as possible. Productivity decreases. In addition, a high-temperature and long-time hot rolling or annealing step is required in order to dissolve and eliminate the eutectic carbide. However, C
r Carbide remains partially undissolved even when heated at high temperature, and it does not become fine even after hot rolling and spheroidizing treatment, and may conversely become coarse. .
As described above, the conventional manufacturing method requires a remarkably large number of steps and a large amount of energy, and has extremely low productivity.
This has led to high manufacturing costs and also had quality problems.

Here, the twin-roll method is known as a means for producing a thin plate directly from a molten metal. The twin-roll method has a much higher solidification rate than the normal ingot-making method. If a thin plate of this alloy is manufactured by the twin-roll method, the eutectic carbide, which has become a problem during solidification in the ordinary continuous casting method, etc., can be extremely reduced. The material can be improved by miniaturization, and the hot rolling process is not required, so that the process can be saved at the same time.
However, when a thin plate is continuously cast by applying the conventional twin-roll method to a high-carbon stainless steel with a very wide range of liquidus temperature and solidus temperature like this alloy, the thickness of the obtained thin plate There is a problem that a two-piece crack is likely to occur at the center, and a sound thin plate cannot be manufactured.

An object of the present invention is to provide a JIS standard SUS44.
The continuous rolling of high-carbon stainless steel as specified in series 0 from the molten metal by the twin roll method directly eliminates the hot rolling process, greatly reducing the number of steps and reducing costs. It is an object of the present invention to provide a method capable of producing a thin plate having a sound internal quality without a double crack defect.

[0008]

According to the present invention, C:
0.60 to 1.20 mass%, Cr: 16.0 to 18.0 mass
%, Si: 0 to 1.0 mass%, Mn: 0 to 1.0 mass%, M
o: A melt of a high carbon content stainless steel containing 0 to 0.75 mass%, with the balance being Fe and unavoidable impurities, is melted, and the melt is cooled by a pair of internal water cooling rotating in opposite directions. Twin rolls that feed from the upper part of a copper or copper alloy roll and apply a pressing load by the roll pair to press the solidified shells of molten steel formed on both circumferential surfaces of the roll pair together to continuously cast thin sheets. In the law,
The crimping load P applied by the roll pair is calculated as follows: 2.36 × 10 ^-4 · r ^1/2 · b ≤ P ≤ 3.54 ×
^10-3 · r1 ^{/ 2} · b P: Compression load (kN) r: Initial roll radius (mm) b: Sheet width (mm) Is provided.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present inventors first filed a patent application from the Japanese Patent Application No.
Various high-carbon stainless steels are melted and cast using a twin-roll continuous caster that can control the magnitude of the pressure bonding load, as proposed in Japanese Patent Application No. 2-114041 and Japanese Patent Application No. 2-214042, and the obtained thin plate is obtained. The quality was investigated. As a result, it was found that two cracks may or may not occur even under the same casting conditions. When observing the surface of the thin plate where two cracks occurred, as shown in Fig. 1, a streak pattern 1 in the thin plate width direction corresponding to the strong cooling portion and a streak pattern in the thin plate width direction corresponding to the slow cooling portion were observed. The pattern 2 was alternately observed with a certain periodicity. In addition, swelling occurred on the surface of the portion where the pattern 1 corresponding to the strongly cooled portion occurred. When the cross section of the thin plate was examined at the swelled position, a so-called double crack, in which the upper shell and the lower shell were not joined at the center of the plate thickness, was observed. On the other hand, in the thin plate in which the two-piece crack did not occur, the streak pattern 1 corresponding to such a strong cooling portion and the streak pattern 2 corresponding to a gentle cooling portion were not substantially observed.

[0010] Therefore, as a result of a detailed investigation of the fluctuation of the pressing load during casting and the interval of the pattern generation during the casting of a thin plate having a striped pattern, the striped pattern that appears alternately with periodicity was found to be twin-roll continuous cast. It has been found to be caused by fluctuations in the crimping load applied by the roll pairs of the machine. That is,
On the surface of the plate where the change in the crimping load applied by the roll pair occurred, a strong cooling part corresponding to the area continuously cast when the crimping load was increased, and continuous casting when the crimping load was reduced Slow cooling portions corresponding to the areas alternated.
Then, due to such a change in the crimping load, a two-piece crack occurred in the strong cooling part.

A crocodile crack in hot rolling has been reported as a phenomenon similar to double cracking in continuous sheet casting [Lecture: Modern Metallurgy, Materials 11 Metalworking: The Japan Institute of Metals (1986) p192] ]. According to this report, crocodile cracks in hot rolling occur as a result of the preferential deformation of the center of the sheet thickness, which has low deformation resistance, when rolled, and the tensile stress acting in the thickness direction. ing. The double cracks in continuous casting of thin sheets are scattered inside the plate without opening like the crocodile cracks in hot rolling, but the crocodile cracks and the double cracks are formed by the same mechanism. It is inferred.

[0012] High carbon stainless steel has a wide solid-liquid coexistence temperature range compared to ordinary stainless steel because cracks are likely to occur when continuous casting of high carbon stainless steel in thin sheets.
The segregation of components occurs in the final solidified part, and the concentrated molten metal tends to remain in the film shape at the center of the sheet thickness even near the roll kiss point. Therefore, the joint surface of the solidified shells grown from the upper shell and the lower shell This is considered to be due to the lack of ductility and low bonding strength.

On the other hand, when the pressure is reduced so as not to cause splitting of the two sheets, the above-mentioned streak-like pattern disappears, but bulging tends to occur. In other words, when the pressing load is small, in the region where the growth of the solidified shell from both roll surfaces is the slowest, a large amount of unsolidified molten steel still exists in the center of the plate thickness even after the plate is released from the roll, and reheating occurs. It is presumed that bulging occurs due to this. If the bulging becomes extremely apparent, the cast plate may be broken.

Therefore, the present inventors cast the present alloy using a twin roll continuous caster while variously changing the pressing load at the time of casting, and examined in detail the relationship between the frequency of occurrence of cracks and bulging. . The radius of the roll used for casting was 200 mm at the center in the width direction, and the obtained plate width was 300 mm.

After the investigation, the results shown in FIG. 2 were obtained. In other words, the larger the crimping load, the higher the frequency of cracks
In addition, the above-described result that bulging occurs when the crimping load is excessively small was obtained. As described above, a line-shaped periodic pattern and swelling were observed on the plate surface in which two cracks occurred, and a large variation in the strength of the pressure load was recognized. On the other hand, when no two-piece cracks occurred, no streak-like pattern was observed, and the change in the crimping load during casting was small and stable. As described above, it has been found that the change in the crimping load that causes the splitting of the two pieces is basically more likely to occur as the crimping load during casting increases. After all, in order to obtain a stable sheet with no cracks and no bulging defects for this alloy using a twin-roll continuous caster, the rolls used in the investigation must be press-bonded during casting. It was found that the load should be controlled in the range of 1 kN or more and 15 kN or less.

Therefore, when the roll radius is 200 mm and the sheet width is 3
In the case of 00 mm, the pressure applied by the roll pair may be controlled within a range of 1 kN or more and 15 kN or less, but this range varies depending on the roll diameter and the sheet width.

Here, the rolling load P in rolling is expressed by the following equation (1). The press load in continuous casting of thin sheets is basically the same as the rolling load in rolling. P = km · ld · b (1) where km: average deformation resistance, ld: contact length, b: plate width, and the contact length ld is expressed by the following equation (2). l d = (r · Δh) ^1/2 (2) where, r: roll radius, Δh: reduction amount Therefore, from the expressions (1) and (2), the following expression (3) is obtained. . P = km · (r · Δh) ^1/2 · b (3)

In the twin-roll method, km · (Δh) ^1/2 is unknown, but as shown in the results of the above investigation, when the radius r is 2
Since the lower limit of the appropriate crimping load is 1 kN and the upper limit is 15 kN when a thin plate having a width b of 300 mm is cast using a twin-roll experimental apparatus equipped with a 00 mm roll,
Substituting each value into equation (3), when the lower limit is 1 kN, km · (Δh) ^1/2 = 2.36 × 10 ^-4 (kN / mm ^3/2 ) Upper limit (15 kN) In the case of, km · (Δh) ^1/2 = 3.54 × 10 ⁻³ (kN / mm ^3/2 ).

Thus, in the present invention, when a high carbon content stainless steel of the width plate b is cast by a twin roll machine having a roll radius r, the crimping load P during casting is controlled to the following range. It was decided to prevent occurrence of cracks and bulging. 2.36 × 10 ^-4 · r ^1/2 · b ≤ P ≤ 3.54 × 10 ^-3 · r ^1/2 · b (4)

[0020]

Examples of the present invention will be specifically described below. Table 1
Examples (Heat Nos. 1 to 5) used in Examples
And Comparative Examples (Heat Nos. 6 to 7) are shown in Table 2.
The casting conditions and measurement results are shown in FIG. Note that, as each steel type, those equivalent to SUS440A and SUS440C, which are typical examples of the high-carbon-containing stainless steel to be used in the present invention, were used.

[0021]

[Table 1]

[0022]

[Table 2]

(Examples of the present invention: Heat Nos. 1 to 3) A twin-roll type continuous casting machine equipped with a precipitation hardening type copper alloy-based internally water-cooled casting roll was used to melt the steel in a vacuum induction furnace.
Average casting speed of 2kg of 0kg high carbon content stainless steel melt
It was continuously cast at 5 m / min. Roll radius r is 200m
m, the effective body length (board width b) was 300 mm. Under these conditions, the crimping load during casting was set such that 1 kN ≦ P ≦ 15 kN so that the crimping load P during casting satisfied the above equation (4). Then, as heat Nos. 1, 2, and 3, the thicknesses are 2.4 mm, 2.2 mm,
2.5 mm thin plates (each having a width b of 300 mm) were manufactured.

Heat Nos. 1 to 3 manufactured under the above conditions
With respect to the thin plate of (Example of the present invention), the presence or absence of a streak pattern on the plate surface and the occurrence of split cracks were investigated. The occurrence of double cracks is based on a survey using an ultrasonic flaw detector and a survey in which a thin plate is randomly cut in the longitudinal direction and a cross section is observed. As a result, as shown in Table 2, in each case, except for the unsteady region at the beginning of casting,
No streak pattern and cracks were found at all. No bulging occurred in any case.

(Example of the present invention: Heat No. 4)
In the same manner as in steps 1 to 3, using a twin-roll continuous caster equipped with a precipitation-hardened copper alloy internal water-cooled casting roll, melted 500 kg of high-carbon stainless steel melt in a vacuum induction furnace. It was continuously cast at an average casting speed of 48 m / min. The roll radius is 400mm, effective body length (board width b)
Was 300 mm. Under these conditions, the crimping load during casting was set such that 1.4 kN ≦ P ≦ 21 kN so that the crimping load P during casting satisfied the above equation (4). Then, a thin plate having a thickness of 2.6 mm and a width of 300 mm was manufactured.

With respect to the thin plate of Heat No. 4 (Example of the present invention) manufactured under the above conditions, the presence or absence of a streak pattern on the plate surface and the occurrence of splitting were examined in the same manner as above. As a result, as shown in Table 2, except for the unsteady region in the early stage of casting, neither a streak pattern nor a two-ply crack was observed at all. In addition, no bulging occurred.

(Example of the present invention: Heat No. 5)
In the same manner as in Examples 1 to 4, using a twin-roll continuous caster equipped with a precipitation-hardened copper alloy-made internal water-cooled casting roll, 500 kg of a high carbon content stainless steel melt produced in a vacuum induction furnace was melted. It was continuously cast at an average casting speed of 48 m / min. The roll radius is 400mm, effective body length (board width b)
Was set to 600 mm. Under these conditions, the crimping load during casting was set so that 2.8 kN ≦ P ≦ 42 kN so that the crimping load P during casting satisfied the above equation (4). Then, a thin plate having a thickness of 2.3 mm and a width of 600 mm was manufactured.

With respect to the thin plate of Heat No. 5 (Example of the present invention) manufactured under the above conditions, the presence or absence of a streak pattern on the plate surface and the occurrence of splitting were examined in the same manner as above. As a result, as shown in Table 2, except for the unsteady region in the early stage of casting, neither a streak pattern nor a two-ply crack was observed at all. In addition, no bulging occurred.

(Comparative Example: Heat No. 6) Compression load during casting using the same rolls (plate width b: 300 mm, roll radius r: 200 mm) as the rolls used in Heat Nos. 1 to 3 of the present invention. Exceeds 15 kN which is the upper limit of the present invention.
Cast at 8kN, thickness 2.4mm, board width 300m
m sheets were produced.

With respect to the thin plate of Heat No. 6 (Comparative Example) manufactured under the above conditions, the presence or absence of a streak pattern on the plate surface and the occurrence of double cracks were examined in the same manner as above. As a result, as shown in Table 2, a clear streak pattern was observed,
A large number of two-piece cracks were found at the location corresponding to the strong cooling part.
However, no bulging had occurred.

(Comparative Example: Heat No. 7) Using the same rolls (plate width b: 300 mm, roll radius r: 200 mm) as the rolls used in Heat Nos. Is less than 1 kN which is the lower limit of the present invention.
Casting was performed at a setting of 6 kN.

With respect to the thin plate of Heat No. 7 (Comparative Example) manufactured under the above conditions, the presence or absence of a streak pattern on the plate surface and the occurrence of cracks were examined in the same manner as described above. As a result, as shown in Table 2, no streak pattern or split crack was observed, but bulging was observed almost continuously.

(Comparative Example: Heat No. 8) Compression load during casting using the same rolls (plate width b: 300 mm, roll radius r: 200 mm) as the rolls used in Heat Nos. 1 to 3 of the present invention. Is the lower limit of 1 kN of the present invention,
Casting was carried out at a setting of 0.2 kN, which is even lower than that of the case of o.7.

As a result, large bulging occurred in the thin plate during casting, the plate was broken during casting, and a product could not be obtained.

[0035]

According to the present invention, the JIS standard SUS4
A thin plate can be directly produced from a molten metal by continuously casting a high carbon content stainless steel specified as Series 40, and a thin plate free of cracks and bulging defects can be obtained. Therefore, in the production of the present alloy, remarkable process saving, energy saving and labor saving are achieved.

[Brief description of the drawings]

FIG. 1 is a view showing a surface state of a thin plate in which a streak-like cooling pattern is generated due to a change in a pressing load.

FIG. 2 is a graph showing the relationship between the pressure applied during casting and the frequency of occurrence of cracks and bulging in two pieces.

[Explanation of symbols]

 1 Streaked pattern in the thin plate width direction corresponding to the strong cooling part 2 Streaked pattern in the thin plate width direction corresponding to the slow cooling part

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-5-212505 (JP, A) JP-A-2-182397 (JP, A) JP-A-5-115946 (JP, A) JP-A-4-112 323349 (JP, A) JP-A-5-209252 (JP, A) JP-A-6-65639 (JP, A) JP-A-4-94845 (JP, A) JP-A-4-94846 (JP, A) (58) Field surveyed (Int.Cl. ⁷ , DB name) B22D 11/06 330 B22D 11/00 C22C 38/00 302 C22C 38/22

Claims (1)

(57) [Claims] 1. C: 0.60 to 1.20 mass%, Cr: 1
6.0 to 18.0 mass%, Si: 0 to 1.0 mass%, Mn:
0-1.0 mass%, Mo: 0-0.75 mass%,
A melt of high carbon content stainless steel having a balance of Fe and unavoidable impurities is melted, and the melt is supplied from above a pair of internally water-cooled copper or copper alloy rolls rotating in opposite directions. In the twin-roll method in which the solidified shells of molten steel formed on both circumferential surfaces of the pair of rolls are pressed together by applying a compression load by the pair of rolls, and the thin plate is continuously cast, the pressing load P applied by the pair of rolls is determined. , 2.36 × 10 ^-4 · r ^1/2 · b ≤ P ≤ 3.54 ×
10 ^-3 · r ^1/2 · b P: Crimping load (kN) r: Initial roll radius (mm) b: Plate width (mm) .