JPH0414181B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to a Cr carbide-dispersed stainless steel sheet for cutlery and a method for manufacturing the same.

Razors and knives require high hardness for sharpness, so steel containing 0.3% or more of C is generally used. Furthermore, stainless steel is also widely used because it is undesirable for it to rust or corrode in a short period of time for sanitary purposes. However, in the case of stainless steel, C
Even if a large amount of Cr is added, coarse Cr carbides will precipitate, and the amount of C that contributes to the hardening effect will not increase. For this reason, as is clear from the rumor that stainless steel is generally inferior in sharpness, its hardness is not as high as that of carbon steel. Therefore, if hardness is emphasized, corrosion resistance must be abandoned and carbon steel is used, and if corrosion resistance is emphasized, stainless steel must be used, although the hardness remains unsatisfactory. As described above, there is currently no material that satisfies both internal hardness and corrosion resistance for use in cutlery.

The present invention relates to a Cr carbide-dispersed stainless steel plate for cutlery which needs to satisfy both hardness and corrosion resistance.

(b) Conventional technology As a material that satisfies hardness and corrosion resistance at the same time,
Clad steel is used, which uses high carbon steel as the base material and stainless steel as the cladding material. The use of clad steel has reduced the area of rust and corrosion, so it cannot be said that there is no effect in this respect. However, when used as a knife, at least a small portion of the cutting edge is not covered with stainless steel and the carbon steel has to be exposed on the surface. Furthermore, the condition of the cutting edge has a sensitive effect on so-called sharpness, so even slight rust or corrosion can lead to a decline in quality. For this reason, even if clad steel is used, which uses high carbon steel as the base material and stainless steel as the cladding material, it cannot be said that both hardness and corrosion resistance are satisfied at the same time.

As mentioned above, there is a limit to increasing the hardness of stainless steel by increasing the amount of C. Therefore, it has been proposed that only the cutting edge be carburized and quenched or nitrided, or that only the cutting edge be hardened by ion implantation. These methods yield satisfactory results in terms of hardening, but as in the case of clad steel, the amount of solid solute Cr in the hardened part of the cutting edge, which is sufficient to maintain basic corrosion resistance, is significantly reduced. The reality is that the corrosion resistance deteriorates and the cost increases significantly. Therefore, it cannot be said that the problem of corrosion resistance has been solved.

On the other hand, there is a technology for strengthening steel by dispersing particles therein, which is used as precipitation-strengthened stainless steel, but in this case, the particles are precipitated in the steel through heat treatment. However, as the base steel for strengthening, low C steel is usually used with emphasis on workability, but the principle of precipitation strengthening has never been utilized in the high hardness material used in the present invention.

In addition, there are already known methods (FRM,
PRM) and is already widely used in structural materials and carbide tools (A.Kelly
Author, translated by Yotaro Murakami: Composite Materials (1971). Such). However, these metal matrix composite materials (MMC) are extremely difficult to roll into plates or strips.
It could not be applied to applications that require a plate-like shape, such as a cutlery.

Thus, there is no material for cutlery that satisfies both hardness and corrosion resistance at the same time.

(c) Problems to be solved by the invention The present invention uses stainless steel as a base to ensure corrosion resistance, and uses a hardening method using fine particle dispersion, which has not been used in conventional cutlery steels, to ensure high hardness. I was oriented toward that. By using Cr carbide, which is normally contained in stainless steel, as the particles, we aimed to achieve the same effect as using stainless steel with a high C content. However, it is clear that coarse carbides such as those produced by conventional manufacturing methods do not have the characteristics of a cutlery. The key points of the present invention are to limit the amount and size of dispersed particles in stainless steel to a level suitable for use in cutlery,
Invented a method of rolling into plate shapes and used them for cutlery.
The point is that hardened stainless steel is applied by dispersing a large amount of Cr carbide.

(d) Means for solving the problem The inventors deduced from the deformation characteristics of the low melting point portion such as center segregation that in order to roll steel with dispersed particles, it is necessary to completely solidify the steel. Although it is extremely difficult in this state, the present invention was achieved by discovering that it is possible if it is locally melted.

In other words, in the case of stainless steel, the melting start temperature decreases as the C content increases, and in 17Cr steel, the melting start temperature is approximately 1250°C when the C content is 0.5% or more.
It is recognized that it becomes a semi-molten state. They thought that by rolling the material in this semi-molten state, it would be possible to disperse particles such as oxides.

Conventionally, it was thought that processing such as rolling in a semi-molten state was impossible because surface flaws and various cracks would occur, but the present inventors previously developed a method to convert semi-molten materials into materials that do not exhibit a molten state. By covering the material, rolling can be carried out without any problems, and they have found advantages such as significantly reducing the rolling load. The present invention also utilizes this technique.

Below, the behavior of the manufacturing process of the Cr carbide particle dispersed stainless steel according to the present invention will be explained using A and B of FIG.

Two or more high carbon stainless steel plates 1 exhibiting a semi-molten state are stacked together and a reinforcing material is applied to the stacked surfaces.
Sandwich particles 2 such as Cr carbide. Furthermore, these are covered with a packing material 3 made of a material that does not exhibit a molten state, such as carbon steel or low C stainless steel. The steel pieces assembled in this manner are heated to a temperature at which the high carbon stainless steel plate 1 is in a semi-molten state, and rolled in the semi-molten state. Cr mixed in as a result of this
The carbide enters the molten part (see figure 1) and makes it possible to roll the particle dispersion strengthened steel. Furthermore, since the Cr carbide particles are mixed into the lapped surfaces, there is a possibility that they become layered, but since rolling in a semi-molten state causes movement in the thickness direction,
It was observed that rolling in a semi-molten state resulted in uniformity in the thickness direction (FIG. 2B).

Since the Cr carbide dispersion-strengthened high carbon stainless steel produced in this way has a plate shape, it can be easily processed into cutlery.

Next, the influence of particle size on the characteristics when used in cutlery will be explained. It was found that when the size of the Cr carbide particles exceeded 10 μm, the shape of the cutting edge became unstable and caused the blade to chip, and the size was found to be inappropriate for the intended use. It is believed that the steel according to the present invention can be easily produced by adding a large amount of C in the normal stainless steel manufacturing process. However, the conventional method not only makes the structure difficult, but also causes the Cr carbide to become extremely coarse (the maximum size can reach 50 μm or more), making it unsuitable for use in cutlery.

Next, the limiting conditions of the present invention will be explained.

The amount of C in the stainless steel for cutlery according to the present invention is:
This is the average value of C in the base material and C in the dispersed Cr carbide. A higher C content is desirable from the viewpoint of hardness, but since processing into a steel plate or cutting a blade becomes impossible, the upper limit was set at 1.5%. In addition, the lower limit was set at 0.6% or more since it is necessary to exhibit a semi-molten state.

If the amount of Si is less than 0.01%, deoxidation will be incomplete,
The lower limit was set at 0.01% because coarse oxide inclusions are generated and cause the blade to chip, and the upper limit was set at 1.0% because if it exceeds 1.0%, hot workability deteriorates and manufacturing becomes extremely difficult. .

If the amount of Mn is less than 0.01%, it will be impossible to fix the inevitable impurity S, which will cause surface cracks during hot working and reduce productivity.
% was set as the lower limit, and if it exceeded 1.0%, the γ phase remained even after quench hardening, resulting in microscopically low hardness areas, so 1.0% was set as the upper limit.

Cr also consists of Cr in the base metal and Cr in the dispersed Cr carbide.
is the average value. If the Cr content is less than 10%, stainless steel lacks the basic corrosion resistance, so the lower limit is set. A higher Cr content is better in terms of corrosion resistance, but the toughness deteriorates and workability is significantly reduced, so the upper limit is 25%. And so.

If the amount of Al is less than 0.02% in terms of acid-soluble Al content, deoxidation will be incomplete and coarse oxide inclusions will be generated, causing the blade to chip, so the lower limit is set at 0.002%,
If it exceeds 0.2%, not only will hot workability deteriorate and production becomes extremely difficult, but also descaling properties will deteriorate and production becomes difficult, so 0.2% was set as the upper limit.

In addition, in the second invention, the lower limit of the amount of C and Cr in the stainless steel before mixing with Cr carbide is 0.6% or more for C and 0.6% or more for Cr since it is necessary to exhibit a semi-molten state.
must be 10% or more. Also, the upper limit is Cr
The amount of Cr needs to be lower than the amount of Cr in the product after the carbide is mixed in, but since this is only regulated by the upper limit of the product, it is set to be 1.5% or less for C and 25% or less for Cr.

Cr carbide particles dispersed in steel for strengthening are
The lower limit was set at 10%, at which the effect of dispersion begins to be recognized, and the upper limit was set at 30%, at which rolling becomes difficult even in a semi-molten state.

In addition, the size of the particles to be dispersed was set at the upper limit of the maximum size because if it exceeded 10 μm, it would cause the blade to spill. Formally, the lower limit is the molecular size of the Cr carbide, but such a limit is practically meaningless, so the minimum size is not limited. However, if the size is small, although there is no particular adverse effect on the quality after mixing, it becomes extremely difficult to handle before mixing, so in the second invention, the lower limit of the average size is set to 0.1 μm.

The rolling temperature in the second invention is set at 1250° C. or higher and 1450° C. or lower since it is necessary to perform rolling at least one pass in a semi-molten state.

In addition, rolling in a fully solidified state below 1250°C combined with rolling in a semi-molten state is no different from rolling in the normal process, but below 750°C the strength of the material increases rapidly and is required for rolling. The lower temperature limit was set at 750°C because the rolling force increases dramatically.

Similarly, the lower limit of the rolling reduction ratio in the semi-molten state in the second invention was set to 10% because the rolling reduction effect cannot be obtained if it is less than 10%.

In order to mix powder particles into the matrix by rolling in a semi-molten state, it is thought that the higher the rolling reduction rate, the more effective it is, but if the rolling reduction rate per pass exceeds 70%, the molten part will be squeezed out. The upper limit was set at 70% because of the risk of

Further, although the upper limit of the total rolling reduction ratio is not technically limited, it is limited by the thickness of the rolled plate from the viewpoint of manufacturability including the next process. 1.5 because a rolling mill with extremely high rolling force is required to reduce the thickness of the plate after rolling to less than 1.5 mm.
The lower limit for rolling was set to mm, and the upper limit was set to 8 mm because it would be difficult to manufacture cutlery in the next process if the plate thickness exceeded 8 mm.

(E) Function As shown above, since the base material including the cutting edge is stainless steel, it has excellent corrosion resistance, and the cutting edge has hardening substances such as oxide particles dispersed, so it has a high hardness as a cutting tool. It has become possible to supply stainless steel for cutlery with sufficient sharpness and excellent sharpness. With this material, the sharpness of the cutting edge does not depend solely on the hardness of the steel itself, but rather is based on dispersed fine particles, so there is less wear on the cutting edge and maintenance is easier than with carbon steel as well as stainless steel. This is significantly better than the previous model.

(F) Example C: 1.1%, Si: 0.46%, Mn: 0.60%, Cr:
1mm containing 16.7%, acid-soluble Al: 0.012%, and consisting essentially of Fe excluding other unavoidable impurities.
25 thick stainless steel plates with an average grain size of 5 μm between them.
Cr ₂₃ C ₆ powder with a maximum particle size of 8 μm was sandwiched and stacked at a density of 50 to 100 g/m ² . Furthermore, the whole is C:
Contains 0.06%, Si: 0.52%, Mn: 0.53%, Cr: 16.3%, excluding other inevitable impurities.
It was packed with a 1.2 mm thick SUS430 stainless steel plate made of Fe, and the internal pressure was reduced to 10 Torr or less. That,
It was heated to 1400℃ and rolled down to a total of 15mm in 3 passes in the temperature range up to 1250℃. Subsequently, after rolling down to 5 mm at a temperature range of 1250 to 850℃, both sides were
The blade was manufactured by grinding it to 0.5mm. The average chemical composition of this material is C: 1.3%, Si: 0.47%, Mn:
0.58%, Cr: 21.4%, which was substantially Fe except for other unavoidable impurities, the amount of dispersed Cr carbide was 21.8%, and the maximum particle size was 8 μm. Cutlery manufactured using this material has a hardness
It has a hardness of approximately 745 in HV, which is higher than that of conventional stainless steel and carbon steel cutlery. Furthermore, after soaking in tap water, it was left in an environment with a humidity of about 90% for 24 hours, but no rust was observed. In the case of the carbon steel cutlery tested for comparison, red rust began to form in about 10 minutes, and rusting occurred on almost the entire surface within 24 hours, confirming the extremely excellent rust resistance of the cutlery of the present invention. .

C: 0.68%, Si: 0.43%, Mn: 0.55%, Cr:
13.5%, acid-soluble Al: 0.033%, and excluding other unavoidable impurities, 25 1 mm thick stainless steel plates consisting essentially of Fe, with an average grain size of 5 μm between them.
Cr ₂₃ C ₆ powder with a maximum particle size of 8 μm was sandwiched and stacked at a density of 50 to 100 g/m ² . Furthermore, the whole is C:
Contains 0.06%, Si: 0.52%, Mn: 0.53%: Cr: 16.3%, and excluding other unavoidable impurities, substantially
It was packed with a 1.2 mm thick SUS430 stainless steel plate made of Fe, and the internal pressure was reduced to 10 Torr or less. That,
It was heated to 1420°C and rolled down to a total of 20mm in 4 passes in the temperature range up to 1250°C. Subsequently, after reducing the temperature to 3mm in the temperature range of 1250 to 850℃, both sides were
The blade was manufactured by grinding it to 0.5mm. The average chemical composition of this material is C: 1.0%, Si: 0.44%, Mn:
0.50%: Cr: 19.7%, substantially Fe except for other unavoidable impurities, the amount of dispersed Cr carbide was 18.4%, and the maximum particle size was 8 μm. Cutlery manufactured using this material has a hardness
The HV was approximately 718, which is higher than the hardness of conventional stainless steel and carbon steel knives. Furthermore, after soaking in tap water, it was left in an environment with about 90% humidity for 24 hours, but no rust was observed. In the case of the carbon steel cutlery tested for comparison, red rust began to occur in about 10 minutes, and rusting occurred on almost the entire surface after 24 hours, confirming the extremely excellent rust resistance of the cutlery of the present invention.

(a) Effects of the Invention According to the present invention, a material for cutlery having corrosion resistance and high hardness was obtained. As a result, it has become possible to supply blades with excellent performance that require less maintenance at low cost.

[Brief explanation of drawings]

FIG. 1 is a diagram illustrating the behavior of the manufacturing process of a Cr carbide particle dispersed stainless steel for cutlery according to the method of the present invention.

Claims (1)

[Claims] 1 C: 0.6% or more and 1.5% or less, Si: 0.01% or more and 1.0
% or less, Mn: 0.01% or more and 1.0% or less, Cr: 10% or more and 25% or less, and acid-soluble Al: 0.002% or more and 0.2% or less, the remainder consists of Fe and inevitable impurities, of which Cr carbide is the weight A Cr carbide-dispersed stainless steel sheet for cutlery, characterized in that the Cr carbide has a maximum diameter of 10% or more and 30% or less, and is strengthened by particle dispersion so that the maximum diameter of the Cr carbide is less than 10 μm. 2 C: 0.6% or more and 1.5% or less, Si: 0.01% or more and 1.0
% or less, Mn: 0.01% or more and 1.0% or less, Cr: 10% or more and 25% or less, and acid-soluble Al: 0.002% or more and 0.2% or less, with the balance consisting of Fe and unavoidable impurities. , the maximum diameter on each overlapped surface is less than 10 μm, and the average size is 0.1 μm
Sandwiching Cr carbide that is above 1250℃
Perform one pass or more of rolling at a temperature of 1450°C or lower with a reduction rate of at least 10% or more and 70% or less per pass, and in combination with rolling at a temperature of 750°C or more and less than 1250°C to a thickness of 1.5 mm or more and 8 mm or less. Apply pressure,
Contains 0.6% to 1.5% of C and 10% to 25% of Cr in the average composition, of which Cr carbide accounts for 10% to 30% by weight, and the maximum diameter of the Cr carbide is less than 10 μm. A method for manufacturing a Cr carbide-dispersed stainless steel sheet for cutlery, characterized by: