JP2000273587A - Stainless steel for cutting tool, excellent in corrosion resistance, durability of cutting quality, and workability - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a stainless steel for cutting tool, excellent in corrosion resistance, durability of cutting quality, and workability. SOLUTION: The stainless steel has a composition consisting of, by weight, 0.70-1.10% C, <=1.00% Si, <=1.00% Mn, 16.00-19.00% Cr, 1.00-2.50% Mo, 0.05-0.50% V, and the balance Fe with inevitable impurities. By forming hard and fine <=5 μm carbides composed essentially of Cr, Mo, and V, the edge line roughness of a cutting tool can be maintained at about 10 μm, that is, in a state of the edge of an unused cutting tool, without causing edge breakage, nicks in the edge, etc. In this way, deterioration in the durability of cutting quality can be prevented and the state of excellent cutting quality can be maintained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a knife having excellent corrosion resistance, sharpness persistence and workability, which can be used for various household, industrial and medical knives such as knives, scissors, razors, knives and cutters. For stainless steel.

[0002]

2. Description of the Related Art Higher carbon content martensitic stainless steels such as SUS440, which have a higher C and Cr content, are required for cutting tools which require higher hardness and excellent wear resistance. Is used.

[0003] However, these conventional steels have the following problems. Since these conventional steels have a high Cr content, they are passivated in a relatively weakly corrosive environment and have good corrosion resistance. However, in an environment having relatively strong corrosiveness such as, for example, containing sea salt particles, pitting occurs and the corrosion resistance is poor. Further, as represented by SUS440C, as C becomes higher, the hot workability becomes poorer, and cracks and the like tend to occur particularly in hot rolling.

On the other hand, as one method of evaluating the performance of a blade, there is a method of sharpening the blade. However, starting with cooking,
Evaluation mainly depends on human senses, which is one of the difficulties of quantitative evaluation.

[0005] As a quantitative evaluation of the sharpness of the blade, the present multi-type sharpness test is mainly performed among many evaluation methods. In general, the polynomial uses a paper bundle of a predetermined size at a substantially constant humidity, under a predetermined load and a cutting speed, and quantitatively evaluates the sharpness of the blade by the number of papers cut by one reciprocation or one pass. I do.

[0006] However, the following problems exist in the conventional steel for cutting tools. In such a sharpness test, in general, the number of cuts, that is, sharpness sharply decreases as the number of cuts increases from the first number of cuts (initial sharpness) to about 20 cuts. After that,
The number of cuts gradually decreases, and the number of cuts (convergent sharpness) becomes almost constant after about 80 times.

[0007] Conventionally, as steel for cutting tools excellent in sharpness, for example, there is one disclosed in Japanese Patent Application Laid-Open No. 10-1703. This conventional steel is an alloy steel for blades obtained by sintering and densifying steel powder by hot isostatic pressure treatment.To obtain sufficient sharpness as a blade, quenching hardness is considered to be a main factor, It is described that a high quench hardness of HRC 62 or more is essential.

[0008]

In general, it is known that the sharpness of a blade is higher as the hardness is higher, but the sharpness in this case mainly refers to convergent sharpness. The relationship with the initial sharpness was not considered. Also in Japanese Patent Application Laid-Open No. 10-1703, the sharpness of the material is determined by the number of cuts for the 40th time, and it is not possible to judge whether the sustainability of the sharpness is good or bad by this evaluation method. Therefore, there has not been proposed any knife having excellent sharpness persistence that can maintain the sharpness from the initial sharpness forever.

The present invention has been made in view of the above-mentioned conventional problems, and has excellent cutting durability, corrosion resistance, and good workability, and is excellent in corrosion resistance, sharpness persistence, and workability. It is intended to provide stainless steel for use.

[0010]

In order to solve the above problems,
The present inventors have conducted intensive studies particularly on the factors affecting the sharpness persistence. As a result, quenching hardness is not the main factor, and C, Cr,
It was newly found that the content of Mo and V and the size of hard and fine carbides mainly composed of Cr, Mo and V in the matrix greatly affected the sharpness persistence of the cutting tool, in particular,
The present invention has been made.

That is, the stainless steel for cutting tools described in claim 1 of the present invention has a C: 0.70 to 1.
10%, Si: 1.00% or less, Mn: 1.00% or less, Cr: 16.00 to 19.00%, Mo: 1.00
-2.50%, V: 0.05-0.50%, and the balance consists of Fe and unavoidable impurities, and the size of carbides in the parent phase is 5 μm or less. And

[0012] Cr, Mo, and V are added in combination to form a hard and fine carbide of 5 µm or less mainly composed of Cr, Mo, and V, thereby obtaining a stainless steel for blades having excellent sharpness persistence. Further, the content of Mo is set to 1.00.
When the content is relatively large, such as ~ 2.50%, the content of Mo dissolved in the base tissue increases, so that the occurrence of pitting corrosion is suppressed,
Corrosion resistance is improved. Furthermore, the hot workability is improved by not excessively increasing the contents of C, Mo, and V, and the hardness at the time of punching of the product shape is reduced by strain relief annealing after cold rolling. Thereby, the punching workability is also improved.

[0013] That is, by setting the alloying component and content of the stainless steel for the cutting tool as described above and setting the size of the carbide in the parent phase to 5 µm or less, the cutting performance of the cutting tool is improved and It has excellent corrosion resistance and workability. Therefore, a blade made of such an alloy steel hardly causes chipping or spilling even when used for a long period of time, and can be provided as a blade excellent in corrosion resistance, durability of sharpness, and workability.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below. The stainless steel for a cutting tool of the present embodiment has, in terms of% by weight, C: 0.70 to 1.10%, and Si: 1.0%.
0% or less, Mn: 1.00% or less, Cr: 16.00 to
19.00%, Mo: 1.00 to 2.50%, V: 0.
It is a stainless steel for blades containing 0.55% to 0.50%, with the balance being Fe and unavoidable impurities and having a carbide size of 5 μm or less in the parent phase.

The most notable aspect of the present invention is that C
The purpose is to add a complex of r, Mo, and V to form a hard, fine carbide of 5 μm or less mainly composed of these.

The fine carbides mainly composed of Cr, Mo and V are uniformly dispersed in the matrix, and realize excellent cutting durability as a blade as shown in Examples described later. Can do things.

These alloy components and contents are set so as to be excellent in corrosion resistance, sharpness persistence and workability as stainless steel for cutting tools as in the inventions of claims 1 and 2. The reasons for limiting the chemical components will be described.

C: 0.70 to 1.10%; C is an element for increasing the hardness after quenching and tempering, and is Cr, Mo, V
To form high hardness carbides such as M ₂₃ C ₆ type and M ₇ C ₃ type to secure hardness. If the addition amount is too large, coarsening of carbides, reduction of specularity, reduction of hot workability, deterioration of corrosion resistance, and the like are caused. Therefore, 1.10% or less, preferably 0.1% or less.
95% or less. On the other hand, if the addition amount is too small, the strength and hardness after quenching and tempering cannot be obtained, so that 0.70%
Or more, preferably 0.80% or more.

Si: 1.00% or less; Si is added because it is an element that improves the resistance to tempering and softening and is also effective as a deoxidizing agent. However, if the addition amount is too large, the effect is saturated and the cost is increased. Therefore, the addition amount is set to 1.00% or less, preferably 0.50% or less.

Mn: 1.00% or less; Mn is added because it is an element that improves hardenability and is also effective as a deoxidizing agent. However, if the addition amount is too large, the effect is saturated and the cost is increased, so the addition amount is 1.00%.
Or less, preferably 0.50% or less.

Cr: 16.0 to 19.00%; Cr
Is an element that is present in the base structure and carbides to improve corrosion resistance and hardenability, and to impart temper hardness, high temperature hardness and wear resistance. If its content is less than 16%,
Since sufficient corrosion resistance cannot be obtained, the lower limit was set to 16%.
On the other hand, if the content is too large, these effects are saturated, leading to an increase in cost, as well as an increase in annealing hardness and deterioration in machinability, so that the content is 19% or less, preferably 18% or less. % Or less.

Mo: 1.00 to 2.50%; Mo is present in the base structure and carbide to suppress the occurrence of pitting corrosion, improve the corrosion resistance, and increase the hardness after tempering. Element. In addition, hardenability, wear resistance, toughness,
In order to improve tempering softening resistance and the like, it is necessary to add 1.00% or more. On the other hand, when the addition amount exceeds 2.50%, there are problems such as a decrease in hot workability, a decrease in toughness, and an increase in cost, and the addition amount is 2.50% or less, preferably 1.50% or less. I do.

V: 0.05 to 0.50%; V is present in the base structure and carbide to improve hardenability, wear resistance, toughness, temper softening resistance and the like.
% Must be added. On the other hand, the addition amount is 0.50%
If the ratio exceeds 1, there are problems such as a decrease in hot workability, a decrease in toughness, an increase in cost, and a decrease in cold workability.

The stainless steel for the cutting tool comprises the above-mentioned alloy components and the balance of Fe and impurities unavoidably mixed. The impurities may include P and S. However, since these elements make the material brittle, the smaller the number, the better. The content of each element is set to 0.10% or less. In some cases, Ni and Cu are inevitably mixed from the raw material. These elements contribute to the improvement of corrosion resistance, but when contained in large amounts, the quenching hardness is reduced, so the upper limit is set to 1%.

Next, the operation of the present invention will be described. In the stainless steel for blades of the present invention, the above-mentioned hard, mainly composed of Cr, Mo, and V, and fine carbide of 5 μm or less are dispersed in the matrix by composite addition of Cr, Mo, and V. . Therefore, as shown in Examples described later, it is possible to realize excellent sharpness persistence as a blade.

In the steel of the present invention, C is set to 0.70 to 1.1.
0%, Cr: 16.00 to 19.00%, Mo: 1.0
By limiting 0 to 2.50% and V to 0.05 to 0.50%, excellent corrosion resistance and workability can be exhibited as shown in Examples described later.

As described above, according to the present invention, it is possible to provide a stainless steel for cutting tools which is excellent in sustainability of sharpness, corrosion resistance and workability.

Next, as in the third aspect of the present invention, the stainless steel for a cutting tool further comprises W: 0.02 to 1.50.
%, Ti: 0.02 to 0.50%, Nb: 0.02 to
It is preferable to contain one or more of 0.50% and Zr: 0.02 to 0.50%. Hereinafter, the reasons for limiting these components will be described.

W: 0.02 to 1.50%; W must be added in an amount of 0.02% or more in order to further improve the wear resistance. On the other hand, when the addition amount exceeds 1.50%, there are problems such as a decrease in hot workability, an increase in cost, and a decrease in toughness.

Ti: 0.02 to 0.50%; To further improve the wear resistance, it is necessary to add 0.02% or more of Ti. On the other hand, when the addition amount exceeds 0.50%, there is a problem that hot workability is impaired.

Nb: 0.02 to 0.50%; Nb is used in an amount of 0.02% to further refine crystal grains and improve toughness.
It is necessary to add 2% or more. On the other hand, the addition amount is 0.50
%, There is a problem that the effect is saturated and the effect is rather reduced.

Zr: 0.02 to 0.50%; In order to further refine crystal grains and improve toughness, Zr is used in an amount of 0.1 to 0.5%.
It is necessary to add at least 02%. On the other hand, when the addition amount is 0.5
If it exceeds 0%, there is a problem that the above effect is saturated and the effect is rather reduced.

[0033]

EXAMPLES Here, in order to evaluate the material properties of the stainless steel for cutting tools described above, evaluation of workability and corrosion resistance and a sharpness test of a knife were performed under the following conditions.

In producing the stainless steel for cutting tools of this example, about 41 cm × melted in a 1.6 ton melting furnace.
A 41 cm × 126 cm steel ingot is prepared and used as a material. Next, this material is hot-rolled to produce a hot-rolled steel sheet having a thickness of 22 mm. Further, a hot-rolled steel sheet having a thickness of 4.0 mm is produced, and after heating and holding at 840 ° C. for 90 minutes, complete annealing is performed by slow cooling. Further, a cold-rolled steel sheet having a thickness of 2.5 mm is prepared, heated and held at 780 ° C. for 15 minutes, and then subjected to strain relief annealing by air cooling. Thereafter, the steel sheet was punched into a product shape, heated and held at 1050 ° C. for 20 minutes, quenched by air cooling, heated and held at 150 to 200 ° C. for 60 minutes, and then tempered by air cooling. In order to quantitatively evaluate the excellent properties of the steels of the present invention (E1 to E8) thus obtained, comparative steels (C9 to C13) and conventional steels (C14 to
Various tests were performed together with C16). First, the composition and the like of the prepared steel are shown in Table 1.

[0035]

[Table 1]

The steels of the present invention (E1 to E8) all have compositions within the composition range of the present invention, and the size of carbides in the parent phase is 5 μm or less. Further, among the steels of the present invention, E4 to E8 are steels to which one or more of W, Ti, Nb, and Zr are added.

Among the comparative steels (C9 to C13), C9 is one in which the individual chemical components are within the scope of the present invention, but the size of carbide in the matrix is not less than 5 μm. Also, C10
To C13 are those in which any of the chemical components fall outside the scope of the present invention. Conventional steels (C14 to C16) are SUS440A and SUS4 which are used as steel plates for cutting tools.
40B and SUS440C, in particular, the contents of Mo and V are out of the range of the present invention.

Each of these steels (E1-E8, C9-
C16) was subjected to hot rolling and complete annealing in the same manner as above, followed by cold rolling and strain relief annealing. Then, a hardness test piece and a salt water spray test piece were cut out from the steel sheet. The size of the hardness test piece is 50 mm with a thickness of 2.5 mm
m square, salt spray test specimen size is 2.5mm
× 100 mm. Next, for the salt spray test piece,
After heating and holding at 1050 ° C. for 20 minutes, quenching was performed by air cooling. After heating and holding at 200 ° C. for 60 minutes, tempering was performed by air cooling. For hardness test and salt spray test,
The scale of each test piece was dropped in advance, and # 600 finish polishing was performed. Thereafter, punchability by a hardness test and corrosion resistance by a salt spray test were evaluated. As for the evaluation of the sustainability of sharpness, a knife was trial-produced and evaluated as described later. Table 2 shows the evaluation results.

[0039]

[Table 2]

The hot workability was evaluated by the presence or absence of cracks or the like in a steel sheet obtained by hot rolling a material to a thickness of 22 mm. When no cracks or the like were observed, it was evaluated as ○, when slight edge cracks, etc. were observed, as Δ, and when harmful edge cracks, tip cracks, etc., were evaluated as x. The hot rolling in the steel of the present invention could be performed smoothly without cracking or the like. As can be seen from Table 2, the hot workability evaluation was good without any cracks or the like except for C11 and C16. It is considered that the reason why the hot workability of C11 and C16 was inferior was that the content of C was high.

The punching workability was evaluated by a hardness test. The hardness at the time of punching the steel sheet into the product shape was measured using a Rockwell hardness tester. Hardness is HRB
○: 100 or less, △: 100 to 105
106 or more were evaluated as x. All the punching processes to the product shape in the steel of the present invention have hardness of HRB1.
It was less than 00 and could be easily punched. As is known from Table 2, the evaluation of the punching workability was C9, C1.
1, except for C16. C9, C11, C1
It is considered that the cold workability of No. 6 was inferior due to the particularly high contents of C and V.

The corrosion resistance was evaluated by a salt spray test. The salt spray test was performed at a salt concentration of 1% and a test time of 24 hours. The test was evaluated by the rating number method based on JIS Z2371. A rating number of 10 was evaluated as ○, a rating number of 9 was evaluated as Δ, and a rating number of 8 or less was evaluated as x. The rusting state of the steel of the present invention in the salt spray test showed that there was no rusting that could be discerned with the naked eye, and that the steel exhibited excellent corrosion resistance. This is considered to be due to the fact that a sufficient amount of Cr and Mo are dissolved in the base structure with respect to the C content, thereby suppressing the occurrence of pitting corrosion. As known from Table 2, the evaluation of the corrosion resistance was C11, C12, C1.
4-C16 was inferior. It is considered that this is because the contents of Cr and Mo are insufficient with respect to the content of C.

The evaluation of the sustainability of sharpness was evaluated by the present polymorphic sharpness test. A knife was prototyped from the test materials, and the sharpness was evaluated using the multi-type sharpness tester. That is, the sharpness of the blade was quantitatively evaluated based on the number of sheets cut by one passage of the blade under a predetermined load and a cutting speed under a predetermined load at a substantially constant humidity. In this test, the cutting load was 3267 gf, the cutting method was cut through one pass, the cutting stroke was 50 mm, and the material to be cut was tested on PPC paper (15 mm × 60 mm with a thickness of 0.1 mm). The paper bundle was replaced every time, and the cutting was repeated 100 times under the same conditions. However, in order to remove the influence of the hardness of the knife on the number of cut pieces, the hardness of the knife is adjusted to the HRC 59 by changing the tempering temperature. Generally, from the first number of cuts (initial sharpness) to about 20 cuts, the number of cuts, that is, sharpness sharply decreases as the number of cuts increases. After that,
The number of cuts gradually decreases, and the number of cuts (convergent sharpness) becomes almost constant after about 80 times. Therefore, the evaluation of the sharpness persistence is based on the ratio of the number of cuts of the first and 100th times, that is, (100th cut number) / (first cut number).
Was evaluated. The first cutting number is the steel of the present invention,
Both the comparative steel and the conventional steel are between 44 and 46 sheets, and the initial sharpness is equivalent.比, 0.80 to 0.90, Δ, 0.80
The following were evaluated as x.

The sharpness persistence of the knife of the steel of the present invention showed excellent sharpness persistence with almost no decrease in the sharpness from start to finish as the number of cuts increased. This is good because the content of C is appropriate and coarse primary carbides are not seen, and the ratio of carbides in the matrix is sufficiently large. Furthermore, by forming a hard and fine carbide of 5 μm or less mainly composed of Cr, Mo, and V,
The cutting edge roughness (maximum line roughness value of the cutting edge line) of the cutting edge can be maintained in the state of a cutting edge of about 10 μm without using the cutting edge without causing chipping or spilling of the cutting edge. It is considered that the sharpness was maintained without deterioration in the sharpness.

As can be seen from Table 2, there was no favorable evaluation of sharpness persistence except for the steel of the present invention. As a cause of this, first, although the individual chemical components of C9 are within the scope of the present invention, the size of the carbide in the mother phase is not less than 5 μm and is slightly large, so the carbide exposed near the cutting edge of the blade is It is considered that some of the particles fell off due to the mechanical action during cutting, and the sharpness was reduced. Further, C14 of the conventional steel has a relatively low C content, and thus is good without showing coarse primary carbides. However, the proportion of carbides in the parent phase is small, and furthermore, the carbides mainly composed of Cr Therefore, it is considered that the hardness of the carbide was reduced, the cutting edge was worn during cutting, and the sharpness persistence was reduced. Further, in the conventional steel C16, since the content of C is relatively high, the ratio of carbide in the matrix is good and good. However, similarly to C14, since the carbide mainly contains Cr, the hardness of the carbide is high. Lower, and some coarse primary carbides are seen,
It is considered that blade spillage and the like occurred, and the sharpness persistence was reduced. That is, as can be seen from the results of C10 to C16, if any one of the individual chemical components of C, Cr, Mo, and V deviates from the range of the present invention or generates a carbide larger than 5 μm, the sharpness decreases. Good sharpness persistence cannot be obtained.

[0046]

As described above, according to the present invention, the composition range is limited to the above-mentioned specific range, and the size of the carbide in the mother phase is set to 5 μm or less, whereby the sharpness is maintained and the sharpness is maintained. It is possible to provide stainless steel for cutting tools excellent in corrosion resistance, good workability, excellent in corrosion resistance, sharpness persistence, and workability.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Mankei Goto 1 Wanowari, Arao-cho, Tokai-shi, Aichi Prefecture Inside Aichi Steel Co., Ltd. Deep Sea Metal Co., Ltd.

Claims (3)

[Claims] C. 0.70 to 1.1% by weight.
10%, Si: 1.00% or less, Mn: 1.00% or less, Cr: 16.00 to 19.00%, Mo: 1.00
-2.50%, V: 0.05-0.50%, and the balance consists of Fe and unavoidable impurities, and the size of carbides in the parent phase is 5 μm or less. Stainless steel for cutting tools with excellent corrosion resistance, sharpness persistence and workability. 2. C: 0.80 to 0.1% by weight.
95%, Si: 0.50% or less, Mn: 0.50% or less, Cr: 17.00 to 18.00%, Mo: 1.00
-1.50%, V: 0.05-0.25%, and the balance consists of Fe and unavoidable impurities, and the size of carbides in the parent phase is 5 μm or less. Stainless steel for cutting tools with excellent corrosion resistance, sharpness persistence and workability. 3. The method according to claim 1, further comprising:
W: 0.02 to 1.50%, Ti: 0.02 to 0.50
%, Nb: 0.02-0.50%, Zr: 0.02-
A stainless steel for cutting tools excellent in corrosion resistance, durability of sharpness and workability, characterized by containing one or more of 0.50%.