JP2005082838A - Method for manufacturing high-carbon hot-rolled stainless steel plate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a high-carbon hot-rolled stainless steel plate in which large-sized carbides are made finer or vanished. <P>SOLUTION: A method for treating a high-carbon stainless steel slab includes soaking the slab preferably having a composition containing 0.3-1.2% C and 10-20% Cr, at a soaking temperature of T (°C), for such a period of time t(s) as to satisfy t>δ<SP>2</SP>/(4D<SB>Cr</SB>), (wherein t is a soaking period of time (s); δ is the maximum particle size (cm) of segregated particles which contain Cr not less than 1/ke of the representative Cr content, in a segregation part in the central part of the slab in the thickness direction; ke is equilibrium distribution coefficient (=0.85) between the liquid phase and γ-phase of Cr; and D<SB>Cr</SB>is a diffusion coefficient (cm<SP>2</SP>/s) of Cr in the γ-phase at T (°C)), to make the carbides finer. The method for manufacturing the hot-rolled stainless steel plate includes hot-rolling this high-carbon stainless steel slab. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for producing a high-carbon stainless steel hot-rolled steel sheet suitable as a material for a blade such as a razor or a wear-resistant member such as a bearing, and a large-size due to segregation of alloy elements during casting, particularly Cr. It relates to the reduction of carbides.

High carbon stainless steel is generally used as a material for various wear-resistant members such as razors, high-grade knives, knives, cutters, and bearings, cams, rollers, etc. because of its high quenching hardness and excellent wear resistance. ing. When these high carbon stainless steels are cast into slabs by a general casting method with a slow cooling rate such as ingot casting or continuous casting, huge primary carbides (Cr _m C) of several μm to several tens of μm in the solidification process. _n ) is easy to generate. This huge primary carbide is difficult to be dissolved by heating during hot rolling or quenching, and remains partially undissolved as coarse carbide, resulting in a fine distribution of carbide and a uniform distribution of carbide. It is inhibiting. If such coarse carbides remain in the material after quenching treatment, a surface pattern will appear in the processing stage of the product, or blade spillage may occur during use for blades, or it may be used for wear-resistant parts. This causes one cause such as peeling at the contact surface.

  For such a problem, for example, in Patent Document 1, molten steel containing C: 0.15 to 1.2% and Cr: 15 to 20% is used, and the temperature range from the liquidus to the solidus is 50 ° C./s or more. There has been proposed a method for producing a high carbon content stainless steel having a uniform and fine carbide structure which is cast at a cooling rate of 1 and then spheroidized and annealed.

  Patent Document 2 discloses a molten steel containing C: 0.15 to 1.2%, Cr: 15 to 20%, N: 0.01 to 0.30%, and the temperature range from the liquidus to the solidus is 50 ° C./s or more. After cooling at a cooling rate of 2 ° C / s, the temperature range from solidus to 500 ° C is cooled at 2 ° C / s or higher, pickling, cold rolling, and holding for 10 min at 700 ° C to 850 ° C. A method for producing a high carbon-containing martensitic stainless steel strip having a uniform fine carbide structure and excellent impact toughness has been proposed.

  Patent Document 3 contains C: 0.6 to 1.0%, Cr: 10 to 14%, in which an ingot is manufactured by using an ingot casting method so that the minimum side width of a cross-sectional dimension is 200 mm or less. A method for producing stainless steel has been proposed.

Further, Patent Document 4 proposes a method of obtaining a billet of martensitic stainless steel with a small amount of eutectic carbide that is heat-treated under a temperature and time that satisfy specific conditions.
JP-A-5-209252 JP-A-6-65639 Japanese Patent Laid-Open No. 10-30107 Japanese Patent Publication No.1-14967

  In the techniques described in Patent Document 1 and Patent Document 2, it is necessary to rapidly cool the temperature range from the liquidus to the solidus at a cooling rate of 50 ° C./s or more during the solidification process. However, even if a special device such as a strip caster is used, adjusting the cooling rate in the temperature range from the liquidus to the solidus of the molten steel to the above-mentioned speed itself is accompanied by great difficulty and solidification. Such rapid cooling in the process has a risk of promoting surface cracking of the slab, and is problematic from the viewpoint of the quality stability of the slab.

  In the technique described in Patent Document 3, a thin ingot is used. However, since casting is performed by a so-called ingot-making method, there is a problem that a cooling rate is slow and productivity is lowered.

  In addition, high carbon stainless steel has a wide temperature range between the liquidus and solidus, the so-called solid-liquid coexistence temperature range. However, depending on the molten steel composition and casting method, when the slab thickness is 180 mm or more, center segregation and V segregation are likely to occur in the slab, and large carbides are easily crystallized. Such a large carbide, as in the technique described in Patent Document 4, is not refined to the extent that the soaking process is performed at a high temperature of 1200 to 1300 ° C. for 10 to 22 hours. In addition, it does not become fine at the time of heating such as hot rolling or quenching, but conversely becomes coarse and coarse. Therefore, in the high carbon stainless hot-rolled steel sheet manufactured using a slab manufactured by a continuous casting method, the carbide cannot be refined, which is a serious problem in quality.

  The present invention advantageously solves such problems of the prior art, and can produce a hot rolled steel sheet in which large carbides produced in the casting stage have been refined or lost, simply, reliably, and inexpensively. It aims at providing the manufacturing method of a high carbon stainless steel hot-rolled steel plate. In the present invention, the “steel plate” includes a steel strip.

  In order to achieve the above-described problems, the present inventors diligently studied the shape change during the heat treatment of the large carbide generated during casting. As a result, the large carbides produced during casting continue to grow as the heat treatment time elapses, but after a certain period of time the growth stops and finally decreases to a size that does not cause a problem in the product. It was found that it disappeared when heat treatment was continued. Further, the present inventors, when the segregation is significant and the slab thickness is large, are not controlled by the diffusion rate of carbon but controlled by the diffusion of Cr, as described in Patent Document 4. I also found out.

  FIG. 1 shows the results of basic experiments conducted by the present inventors. FIG. 1 shows steel A (mass% 0.45% C-0.39% Si-0.50% Mn-0. 17% P-0.0030% S-14.35% Cr-0.53% Mo-0. 1717% V-0.49% Ni-0.359% N Stainless steel with composition of balance iron) and steel B (mass% 0.66% C-0.29% Si-0.66% Mn-0.015% P-0.0014% S-13.06% Cr-0. 28% V-0. 13% Ni-0.0286 % N, stainless steel with a balance iron composition) was subjected to soaking treatment up to 300h at 1220 ° C using high-carbon stainless steel slabs (thickness: 200mm) made of continuous casting. About the slab, the carbide particle size in the segregation part observed in the thickness center part is measured, and is illustrated in the relationship between the maximum particle diameter of carbide and the soaking time.

  From FIG. 1, the large carbide in the segregation part grows with the lapse of soaking time up to about 70 h and continues to increase in particle size, but after that it decreases to a particle size of about 2 to 3 μm, which is not a problem in the product. It turns out that it disappears at last.

The present inventors further studied the mechanism of the phenomenon of disappearance of this carbide. As a result, we found that in high carbon stainless steel with high Cr content, this phenomenon was not rate of carbon diffusion but a rate-limited phenomenon mainly by Cr diffusion. And the loss | disappearance of the large carbide | carbonized_material produced | generated in the slab made from a continuous casting of high carbon stainless steel is in the segregation part of the diffusion coefficient DCr (cm < ² > / s) of _{Cr in} soaking temperature T (degreeC), and a slab thickness center part. In order to eliminate large carbides, it is considered that it depends on the maximum grain size δ (cm) of the segregated grains from which Cr has segregated, and the following equation (1):
t> δ ² / (4D _Cr ) (1)
It was found that it is necessary to perform soaking with a soaking time t (s) satisfying Here, t: maximum heat treatment time (s), δ: maximum segregated grain size (cm) having a Cr concentration of 1 / ke or more of the representative (molten steel) Cr concentration in the segregated portion at the center of the slab thickness , Ke: equilibrium distribution coefficient (= 0.85) between the γ phase and liquid phase of _Cr , and D _Cr : diffusion coefficient (cm ² / s) of Cr in the γ phase at T (° C.). Note that D _Cr is the following formula: D _Cr = D ₀ exp {−Q / (R (T + 273))},
Here, D ₀ : constant (= −0.0853Cr + 1.706) (cm ² / s),
Q: Activation energy of diffusion of Cr (= −406.5Cr + 59487) (cal / mol),
R: gas constant (= 1.986 cal / mol / K),
T: Soaking temperature (° C)
Cr: Cr (chromium) concentration in steel (mass%)
Defined by

The present invention has been completed based on the above findings and further studies. That is, the gist of the present invention is as follows.
・ For high carbon stainless steel slabs, set soaking temperature to T (° C) and set soaking time to the following formula (1)
t> δ ² / (4D _Cr ) (1)
(Where t: soaking time (s), δ: maximum segregated grain size (cm) of the segregated part at the center of the slab thickness with a Cr concentration of 1 / ke or more of the representative Cr concentration, ke : Equilibrium partition coefficient between γ phase and liquid phase of Cr (= 0.85), D _Cr : Diffusion coefficient of Cr in γ phase at T (° C) (cm ² / s))
A method for treating a high-carbon stainless steel slab, characterized by performing soaking for a time t (s) that satisfies the above.
(2) The high carbon stainless steel casting according to (1), wherein the high carbon stainless steel slab has a composition containing mass%, C: 0.3 to 1.2%, and Cr: 10 to 20%. How to handle pieces.
(3) When hot rolling a high carbon stainless steel slab to obtain a high carbon stainless hot rolled steel sheet, prior to the hot rolling, the soaking temperature of the high carbon stainless steel slab is set to T (° C. ) And the soaking time is expressed by the following formula (1)
t> δ ² / (4D _Cr ) (1)
(Where t: soaking time (s), δ: maximum segregated grain size (cm) of the segregated part at the center of the slab thickness with a Cr concentration of 1 / ke or more of the representative Cr concentration, ke : Equilibrium partition coefficient between γ phase and liquid phase of Cr (= 0.85), D _Cr : Diffusion coefficient of Cr in γ phase at T (° C) (cm ² / s))
A method for producing a high-carbon stainless steel hot-rolled steel sheet, characterized by performing soaking for a time t (s) that satisfies the above.
(4) In (3), the high-carbon stainless steel slab has a composition containing mass%, C: 0.3 to 1.2%, and Cr: 10 to 20%. A method of manufacturing a steel sheet.
(5) In (3) or (4), the high-carbon stainless steel slab is a continuous-cast high-carbon stainless steel slab having a slab thickness of 180 mm or more, and the following (2) formula
t> 32126 exp {0.0124 (Ts−T)} {(Tl−Ts) / 76} ^1.4 (2)
(Where, t: soaking time (s), Tl: liquid phase temperature (° C.) of representative components of steel, Ts: solid phase temperature (° C.) of representative components of steel, T: soaking temperature (° C.))
The manufacturing method of the high carbon stainless steel hot-rolled steel sheet characterized by using this.

  According to the present invention, there is no need to newly install special equipment, and the large carbides of the high carbon stainless steel slab are refined or eliminated by a simple method, and the Cr-based carbides are refined or eliminated. High-quality high-carbon stainless steel hot-rolled steel sheet can be manufactured at low cost, and it has a remarkable industrial effect. In addition, according to the present invention, a high carbon stainless steel slab manufactured efficiently using a slab continuous casting machine having higher productivity than the strip caster method (thin slab caster) or the ingot casting method is used as a material. In addition, the productivity can be remarkably improved and the manufacturing cost can be reduced.

In the present invention, when hot rolling a high carbon stainless steel slab to obtain a high carbon stainless hot rolled steel sheet, prior to hot rolling, an appropriate soaking treatment is performed on the high carbon stainless steel slab to refine the carbide. To do. Appropriate soaking treatment for high-carbon stainless steel slabs is performed by setting soaking temperature to T (° C) and soaking time to the following formula (1)
t> δ ² / (4D _Cr ) (1)
(Where t: soaking time (s), δ: maximum segregated grain size (cm) of the segregated part at the center of the slab thickness with a Cr concentration of 1 / ke or more of the representative Cr concentration, ke : Equilibrium partition coefficient between γ phase and liquid phase of Cr (= 0.85), D _Cr : Diffusion coefficient of Cr in γ phase at T (° C) (cm ² / s))
The time t (s) is satisfied.

  This equation (1) is derived by analyzing the phenomenon of the shape change of the large carbide shown in FIG. The phenomenon shown in FIG. 1 can be explained as follows. That is, at the beginning of soaking, Cr-based carbide particles that have almost reached equilibrium with the segregation part concentration become Ostwald due to diffusion of solute atoms (C, Cr, etc.) with interfacial energy as the driving force as soaking time increases. The growth coarsens to an equilibrium state, and the growth of Cr-based carbide particles stops. Even in this state, segregation of solute elements such as C and Cr exists around the carbide particles. For this reason, when the soaking time is further increased, Cr and C in the segregation part around the carbide continue to diffuse to the matrix side (non-segregation part side), so the concentration further decreases, and Cr and C in the carbide. As a result, the carbide particle size gradually decreases as a result of dissolution and diffusion into the matrix, and finally, only carbides that are in equilibrium with the concentration and temperature of the matrix are present, and in some cases disappear. Thus, the change in the shape of the carbide shown in FIG. 1 is mainly due to the diffusion of Cr because the elements constituting the carbide, particularly the high carbon stainless steel targeted by the present invention, has a high Cr content and is highly segregated. It is considered that the rate is determined by the carbide particle diameter, and the processing time required for the disappearance of the large carbide (Cr carbide) in the slab can be determined by the equation (1).

  Δ on the right side of equation (1) is determined as follows. For the segregated grains at the center of the slab thickness, the Cr concentration of each segregated grain is measured by an X-ray microanalyzer, and the grain sizes of the segregated grains having a Cr concentration of 1 / ke or more of the representative Cr concentration are obtained. Let the maximum value be δ. It is preferable that δ is measured in advance for each casting condition and tabulated. The particle diameter of the segregated grains is a value converted into an equivalent circle diameter from the area of each segregated grain obtained by image analysis. The measurement surface should be a cross section parallel to the casting direction of the slab, and the measurement range should be about 30 to 40 mm wide across the thickness center line of the slab and about 30 to 40 mm long in the casting direction. Is preferred. Needless to say, the measurement surface is a buffed surface. The beam diameter of the X-ray microanalyzer is related to the segregated particle diameter, but is preferably about 50 to 200 μm. Here, ke is an equilibrium partition coefficient between the γ phase and the liquid phase of Cr, specifically 0.85. The “representative Cr concentration” in the present invention uses the molten steel in the tundish for the continuous casting method, and the molten steel in the ladle for the ingot casting method.

Further, D _{Cr on} the right side of the equation (1) is a diffusion coefficient (cm ² / s) of Cr in the γ phase at the soaking temperature T (° C.), and the following equation: D _Cr = D ₀ exp {−Q / (R (T + 273))},
Here, D ₀ : constant (= −0.0853Cr + 1.706) (cm ² / s),
Q: Activation energy of Cr diffusion
(= -406.5Cr + 59487) (cal / mol),
R: gas constant (= 1.986 cal / mol / K),
Cr: Cr (chromium) concentration in steel (mass%)
T: Soaking temperature (° C)
Defined by D ₀ is a constant depending on the steel type, and is (−0.0853Cr + 1.706) cm ² / s in the high carbon stainless steel targeted by the present invention. Therefore, D _Cr can be determined by the soaking temperature T and the Cr concentration.

  In the present invention, from the soaking temperature T and the formula (1), the soaking time t is determined so as to satisfy the formula (1), and the soaking of the high carbon stainless steel slab is performed.

  It is preferable that the soaking temperature T is determined in consideration of a range in which the operation is not disturbed or the maximum heating temperature of the furnace. However, if the soaking time is too long, such as 100 hours or more, the slab surface is decarburized and adversely affects the product characteristics. Therefore, it is preferable to determine the soaking temperature T so that it is within 100 hours. The cooling after soaking is preferably furnace cooling from the viewpoint of preventing slab breakage.

  When the soaking time t does not satisfy the formula (1), large carbides (Cr carbides) remain in the slab without disappearing, and are not lost by subsequent hot rolling and quenching treatments. Coarse carbides remain in the hot-rolled steel sheet, resulting in poor product quality.

Steel A (mass%, 0.45% C-0.39% Si-0.50% Mn-0.017% P-0.0030% S-14.35% Cr-0.53% Mo-0.117% V-0.49% Ni-0.0359% N, balance iron And steel B (mass%, 0.66% C-0.29% Si-0.66% Mn-0.015% P-0.0014% S-13.06% Cr-0.028% V-0.13% Ni-0.0286% N 2 types of continuous cast high carbon stainless steel slabs (thickness: 200 mm) with a uniform temperature treatment at varying temperatures and times, and the large carbide in the slab The presence or absence of the residual is investigated, and the relationship between soaking temperature and soaking time is shown in FIG. The curve in FIG. 2 is a line that satisfies t = δ ² / (4D _Cr ). With this line as a boundary, large carbides in the slab disappear in a region that satisfies the formula (1) (particle size less than 2 μm). It is clearly shown that it remains (particle size of 2 μm or more) in other regions. It can be seen that equation (1) is effective in determining the processing time for the disappearance of large carbides.

In the case of high carbon stainless steel slabs (slabs) manufactured by the continuous casting method, the soaking time t for the disappearance of large carbides is based on the formula (1), with variations in δ and the generation of segregated grains. Considering the dependence of the steel type on ease, the following equation (2) is simpler instead of equation (1)
t> 32126 exp {0.0124 (Ts−T)} {(Tl−Ts) / 76} ^1.4 (2)
(Where, t: soaking time (s), Tl: liquid phase temperature (° C.) of representative components of steel, Ts: solid phase temperature (° C.) of representative components of steel, T: soaking temperature (° C.))
Can be used. Incidentally, Tl has the formula Tl = 1494 - (- 21C + 52C 2 + 13Si + 8.3Mn + 34.4P + 38S + 3.1Ni + 1.5Cr + 3.3Mo + 9.5Nb + 4.0V + 72N)
Ts is the following formula: Ts = 1515− (132.8C + 32.2C ² + 40.5Si + 3Mn + 500P + 700S + 4.3Ni + 2Cr + 7.1Mo + 50Nb + 5.5V + 186N)
(Here, C, Si, Mn, P, S, Ni, Cr, Mo, Nb, V, N: representative values of each element content (mass%))
It is a value defined by. In the present invention, the content of each element is a typical value using the molten steel in the tundish in the case of the continuous ingot-making method and the molten steel in the ladle in the case of the ingot-making method. In addition, in the calculation of the above formula, the elements not contained are calculated as zero.

  In the present invention, “high carbon stainless steel” generally includes steel types classified into the category of high carbon martensitic stainless steel. Among them, 0.3 mass% or more of C and 10 mass% or more of Cr are included. High carbon martensitic stainless steel that contains Cr-based carbonitrides is supported. The preferable composition of the high carbon stainless steel slab conforming to the present invention is mass%, including C: 0.3 to 1.2%, Cr: 10 to 20%, Si: 0.2 to 0.8%, Mn: 0.2 to It contains at least one of 0.8%, or Mo: 1% or less, V: 1% or less, Ni: 1% or less, preferably the balance Fe and unavoidable impurities.

  Next, the reasons for limiting the composition of the high carbon stainless steel cast used in the present invention will be described. Hereinafter, mass% in the composition is simply referred to as%.

C: 0.3-1.2%
C is an element that increases strength and hardness, and is preferably contained in an amount of 0.3% or more in the present invention in order to ensure necessary hardness and wear resistance. On the other hand, if it exceeds 1.2%, corrosion resistance and toughness deteriorate. For this reason, it is preferable to limit C to 0.3 to 1.2% of range.

Cr: 10-20%
Cr is an element that improves corrosion resistance, and is preferably contained in an amount of 10% or more in the present invention in order to maintain good corrosion resistance. On the other hand, if the content exceeds 20%, the crystallization amount of the eutectic carbide increases, the coarsening of the carbide becomes remarkable, and the quenching hardness is reduced. For this reason, it is preferable to limit Cr to the range of 10 to 20%.

  In addition to C and Cr, it is preferable to contain Si: 0.2 to 0.8% and Mn: 0.2 to 0.8%.

Si: 0.2-0.8%
Si is an element effective for deoxidation and increases strength and hardness. In order to obtain such effects, it is preferably contained in an amount of 0.2% or more. On the other hand, when it contains exceeding 0.8%, ductility and workability will fall. For this reason, it is preferable to limit Si to 0.2 to 0.8% of range.

Mn: 0.2-0.8%
Mn is an element that is effective for deoxidation and increases strength and hardness. In order to obtain such effects, it is preferably contained in an amount of 0.2% or more. On the other hand, if the content exceeds 0.8%, retained austenite is generated during quenching, and the quenching hardness is decreased. For this reason, it is preferable to limit Mn to the range of 0.2 to 0.8%.

  In addition to the composition described above, one or more of Mo, V, and Ni can be contained depending on the application.

Mo: 1% or less
Mo is an element that improves the corrosion resistance, and is preferably contained in an amount of 0.3% or more. However, if it exceeds 1%, ductility and workability deteriorate. For this reason, it is preferable to limit Mo to 1% or less.

V: 1% or less V is an element that improves the toughness after quenching, and is preferably contained in an amount of 0.05% or more. However, if it exceeds 1%, ductility and workability deteriorate. For this reason, it is preferable to limit V to 1% or less.

Ni: 1% or less
Ni is an element that improves corrosion resistance and also improves ductility and toughness, and can be contained if necessary. Inclusion exceeding 1% deteriorates ductility and workability.

  The balance other than the above components is Fe and inevitable impurities. Inevitable impurities include P: 0.035% or less, S: 0.010% or less, and N: 0.05% or less.

  In the present invention, the method for producing the high carbon stainless steel slab is not particularly limited. The high-carbon stainless steel molten steel having the composition described above can be melted by a generally known melting method to obtain a slab having a predetermined size by a generally known method such as an ingot-bundling method or a continuous casting method.

  The slab that has been soaked under the above conditions is then reheated and hot rolled. In the present invention, the hot rolling is not particularly limited as long as it can be a hot rolled steel sheet (steel strip) having a desired size and shape. In the present invention, any known hot rolling method for high carbon stainless steel can be applied.

  Slabs (thickness: 180-260 mm, width 1000-1200 mm) having the compositions (representative component concentrations) shown in Table 1 were produced by a continuous casting method. In addition, the tundish molten steel superheat degree (molten steel temperature -Tl) in the case of continuous casting was 20-60 degreeC. The obtained continuous cast slab was subjected to soaking treatment under the conditions shown in Table 2.

Table 2 also shows the value on the right side of equation (1). Δ in the obtained continuous cast slab was obtained by collecting a slab sample from each slab. For the segregated grains at the center of the slab thickness, the Cr concentration of each segregated grain is measured by an X-ray microanalyzer (beam diameter: 100 μm), and the segregated grain is 1 / ke (= 1.18) or more of the representative Cr concentration. The grain size of each grain was determined, and the maximum value was taken as δ. The particle diameter of the segregated grains was a value converted to an equivalent circle diameter from the area of each segregated grain determined by image analysis. The measurement range was 30 mm in width and 30 mm in length in the casting direction across the thickness center line of the slab. The ke which is the equilibrium partition coefficient between the γ phase and the liquid phase of Cr was 0.85. Further, D _Cr is represented by the following formula: D _Cr = D ₀ exp {−Q / (R (T + 273))},
Was used to determine. Here, D ₀ = −0.0853Cr + 1.706 cm ² / s, Q = −406.5Cr + 59487 cal / mol, R = 1.986 cal / mol / K were used.

  Table 2 also shows the value on the right side of equation (2). Tl and Ts were calculated using the above-described formulas and listed in Table 1.

  The slabs subjected to soaking treatment under the conditions shown in Table 2 were examined for the disappearance of carbides.

  The Cr-based carbide is colored and corroded with Murakami reagent for the range of 30mm width and 30mm length in the casting direction across the thickness center line at the thickness center of the obtained slab, and photographed with an optical microscope (1000x) The carbide particle size was measured. The case where the maximum value of the carbide particle size in each slab was less than 2 μm was evaluated as carbide disappearance, and the case where the maximum value was more than that was evaluated as carbide residue. The obtained results are shown in Table 2.

  In all of the examples of the present invention in which the soaking time t satisfies the formulas (1) and (2), the carbides disappear, but the carbides remain if they are outside the scope of the present invention.

  The slab subjected to soaking treatment under the conditions shown in Table 2 was then hot-rolled to form a hot-rolled steel strip. Further, these hot-rolled steel strips were cold-rolled to obtain 1.0 mm-thick cold-rolled steel strips. A razor blade was produced using a part of the obtained cold-rolled steel strip as a raw material, and the presence or absence of spilling of the cutting edge due to Cr carbide and pattern defects was examined with the naked eye. In any of the inventive examples, no occurrence of defects was observed. On the other hand, in the comparative example outside the scope of the present invention, 1 to 5% of defects were observed.

It is a graph which shows the relationship between the carbide particle size in the high carbon stainless steel continuous casting slab, and soaking time. It is a graph which shows the influence of soaking time and soaking temperature on disappearance of a large carbide.

Claims (5)

The high carbon stainless steel slab is subjected to soaking treatment with a soaking temperature of T (° C) and a soaking time of t (s) satisfying the following formula (1). Processing method for stainless steel slabs.
Record
t> δ ² / (4D _Cr ) (1)
Where t: soaking time (s),
δ: The maximum particle size (cm) of segregated grains having a Cr concentration of 1 / ke or more of the representative Cr concentration in the segregated portion at the center of the slab thickness,
ke: Equilibrium partition coefficient (= 0.85) between γ phase and liquid phase of Cr,
D _Cr : Diffusion coefficient of Cr in γ phase at T (° C) (cm ² / s) The high-carbon stainless steel slab according to claim 1, wherein the high-carbon stainless steel slab has a composition containing C: 0.3 to 1.2% and Cr: 10 to 20% in mass%. Processing method. When hot rolling a high carbon stainless steel slab to obtain a high carbon stainless hot rolled steel sheet, prior to the hot rolling, the soaking temperature of the high carbon stainless steel slab is T (° C.), A method for producing a high-carbon stainless steel hot-rolled steel sheet, characterized in that a soaking treatment is carried out with a soaking treatment time t (s) satisfying the following formula (1).
Record
t> δ ² / (4D _Cr ) (1)
Where t: soaking time (s),
δ: The maximum particle size (cm) of segregated grains having a Cr concentration of 1 / ke or more of the representative Cr concentration in the segregated portion at the center of the slab thickness,
ke: Equilibrium partition coefficient (= 0.85) between γ phase and liquid phase of Cr,
D _Cr : Diffusion coefficient of Cr in γ phase at T (° C) (cm ² / s) The high-carbon stainless steel hot-rolled steel sheet according to claim 3, wherein the high-carbon stainless steel cast slab has a composition containing C: 0.3 to 1.2% and Cr: 10 to 20% in mass%. Production method. 5. The high carbon stainless steel slab is a continuous cast high carbon stainless steel slab having a casting thickness of 180 mm or more, and the following formula (2) is used instead of the formula (1). The manufacturing method of the high carbon stainless steel hot-rolled steel plate as described in 2.
Record
t> 32126 exp {0.0124 (Ts−T)} {(Tl−Ts) / 76} ^1.4 (2)
Where t: soaking time (s),
Tl: Liquidus temperature (° C) for typical steel components
Ts: solid phase temperature (° C.) of typical components of steel,
T: Soaking temperature (° C)

Images