UA120119C2 - Martensitic stainless steel, method for the production of a semi-finished product from said steel, and cutting tool produced from the semi-finished product - Google Patents

Abstract

The invention relates to a martensitic stainless steel characterised in that its composition consists of, by weight percent: 0.10 % 0 С 0.45 %; traces t Mn 1.0 %; traces t Si S 1.0 %; traces t S S 0.01 %; traces t P P 0.04 %; 15.0 % Cr C 18.0 %; traces e Ni N 0.50 %; traces t Mo M 0.50 %; traces t Cu C 0.50 %; traces t V V 0.50 %; traces t Nb N 0.03 %; traces t Ті 0.03 %; traces t Zr Z 0.03 %; traces t Al A 0.010 %; traces t О 0.0080 %; traces t Pb P 0.02 %; traces t Bi B 0.02 %; traces t Sn S 0.02 %; 0.10 % 2 N 0.20 %; С + N + 0.25 %; Cr+16 N-5 С 16.0 %; preferably 17 Cr+500 С + 500 N + 570 %; the remainder being iron and impurities resulting from production. The invention also relates to a method for the production of a semi-finished product from the aforementioned martensitic stainless steel, and a cutting tool produced from said semi-finished product.

Description

oda i I u zeve AN i Ayannia b goty DYKO NI i nn "OM di 64040000 mo pontirennya 630.4. PP Mon MO, Wro prnnnnnnnnnnnnnttnnttrnnnnnia pria - at 10. 20 z 40

Martensite level (95)

Fig.

The invention relates to martensitic stainless steel. Such steel is primarily intended for the production of cutting tools, in particular parts of knife products such as scalpels, scissor blades or blades of knives or household food processors.

Steels intended for knife products must have high corrosion resistance, polishability and hardness.

Martensitic stainless Steels currently used for the production of cutting tool blades, such as steel grades EM 1.4021, EM 1.4028 and EM 1.4034, have levels of St content equal to or less than 14 or 14.5 wt.bOb and different levels of C content , namely, 0.16 - 0.25 wt. 956 for EM 1.4021, 0.26 - 0.35 wt. 95 for EM 1.4028 and 2.43 - 0.50 wt. 95 for EM 1.4034. The level of steel hardness primarily depends on this level of C content.

When even higher corrosion resistance is required, the EM 1.4419 brand with 0.36 - 0.42 wt. 95.0, 13.0 - 14595 Sti 0.60 - 1.00 wt. 95 Mo.

In the production process, these steels are usually melted in an argon-oxygen (AOI) or vacuum-oxygen (VOC) decarburization converter, then poured continuously in the form of slabs, blooms or billets and further subjected to hot rolling to obtain a roll, rolled bar or wire rod. They are then annealed to obtain a ferritic structure containing carbides which is soft enough to be suitable for cold rolling into flats or to facilitate the sputtering prior to forging of hot-rolled semi-finished products in the case of long gauges.

Then the product is subjected to recrystallization annealing. In this softened state of recrystallized ferrite containing carbides, the product is cut to give it its final shape, such as a knife blade, before undergoing a heat treatment involving high-temperature austenizing, typically between 950 °C and 1150 °C, followed by quenching to the ambient temperature, which leads mainly to the martensitic structure.

In this martensitic state, the product has high hardness, which is high when the carbon content is high, but is also very brittle. Annealing is then performed, typically at temperatures between 100C and 300C, to reduce brittleness without greatly reducing hardness. Next, the blade is subjected to various operations, including sharpening and

From polishing to give it cutting ability and aesthetic appearance.

None of the four steel grades mentioned above can simultaneously provide good corrosion resistance, good surface condition and high hardness at an acceptable cost.

The EM 1.4419 grade has good corrosion resistance and high hardness, but due to the addition of a large amount of Mo, it is very expensive.

The EM 1.4034 grade has high hardness, but also has a mediocre surface appearance after polishing due to the presence of a large amount of carbides that do not dissolve in the austenization process due to the high level of C content in this grade of steel. Its corrosion resistance is insufficient, since the level of St content in the matrix is insufficient high, taking into account in particular that part of Cg is captured in undissolved carbides. In addition, the cutting edge of the blade is often subject to crevice corrosion, which occurs due to the delamination along cleavage planes of large primary carbides that appear at the end of solidification during continuous casting.

Grades EM 1.4021 and 1.4028, which contain less C, have lower hardness, but do not have sufficient corrosion resistance due to very low levels of St content.

This invention pursues the goals of solving the above-mentioned problems. In particular, it aims to offer a martensitic stainless steel for cutting tools that is as cost-effective to manufacture as possible, yet has good corrosion resistance, good polishability and high hardness.

Based on this, the present invention relates to martensitic stainless steel, which is distinguished by the fact that its composition is in mass percentage parts: - 010965 "хСк0.45; preferably 0.20хХ0.38; better 0.20:хС:0.35; optimally 0.30:0:0.35; - trace amounts "Mp: 1.0; mostly trace amounts of "Mp:x0.6; - trace quantities x5ik1.0; - trace amounts x5:0.01; mainly trace amounts x5:0.005; - trace amounts of хР«:0.04; - 15.0:Stg«:18.0; mostly 15.0:Sti:17.0; better 15.2:St:17.0; optimally 15.55Сg:16.0; - trace amounts of "MihO,50; - trace amounts of "Moh 0.50; mostly trace amounts of "Mo:x0.01; trace amounts of "Moh0.05" are better; 60 - trace amounts of "Sikh0.50; mainly trace amounts of хСихО0.3;

- trace amounts: uUx0.50; mainly trace amounts of hooks0.2; - trace amounts of "Мхх0.03; - trace amounts of "Tikh0.03; - trace amounts 570.03; - trace amounts of хАЙКО, 010; - trace amounts x0:0.0080; - trace amounts of хПХх0.02; - trace amounts "Vih0.02; - trace amounts x5p:0.02; -0.10:M:0.20; preferably 0.15:M:0.20; - b-M20,25; mainly С-М20,30; better SyaM20.45; - St4-16M-5S216.0; - mostly 17Sgt-5000-500M2570; the rest, which is iron and impurities that are formed during melting.

Its microstructure mainly includes at least 7595 martensite. The present invention also relates to the method of production of blanks made from this martensitic stainless steel, which is characterized by the fact that: - the billet is melted and cast from steel having the composition presented above; - the specified workpiece is heated to a temperature higher than or equal to 1000 "C; - it is subjected to hot rolling to obtain a sheet, rod or wire rod; - the specified sheet, rod or wire rod is annealed at a temperature between 700 and 900 "C; and - a forming operation is performed on the specified sheet, rod or wire rod.

Said blank may be a sheet, and said forming operation may be cold rolling.

Said blank may be a bar, and said forming operation may be stamping.

The indicated workpiece has undergone formation, if the level of Cg content in it is between 15 and 17 wt. 95, may then be austenitized between 950 and 1150 "C, then cooled at a rate of at least 15 "C/s to a temperature less than or equal to 20 "C, then subjected to

From annealing at a temperature between 100 and 300 "С.

Said molded billet can then be austenitized at a temperature between 950 and 1150 "C, then cooled at a rate of at least 15 "C/s to a temperature below or equal to 20 "C, and then cryogenically treated at a temperature of -220 to -50 C and then annealing at a temperature between 100 and 300 "C.

The invention also relates to a cutting tool, which is distinguished by the fact that it is made from a workpiece prepared according to the previous method.

This cutting tool can be a knife item, such as a knife blade, a food processor blade, a scalpel or a scissor blade.

It will be clear to anyone that the present invention consists in the use (for the purpose of manufacturing a cutting tool) of a martensitic stainless steel of a special composition, which does not contain expensive elements with high content levels, but which contains relatively large amounts of nitrogen, which is in a clearly limited range . A certain balance in the levels of St, C and M content is also required.

Other features and advantages of the invention will become apparent after reading the following description, which is provided by way of example and presented with reference to the attached figure 1, which shows the changes in Vickers hardness of steel under a load of 1 kg, martensite content, due to changes in level, after austenization, hardening and annealing of steel according to the invention.

As for the chemical composition of the steel according to the invention, the following reasoning is presented. It should be understood that the ranges of content levels of the various elements considered to be preferred are independent of each other, and that any combination of the ranges limited to the following description may be contemplated in the context of the present invention, provided that the individual content levels of C, M and Sg, which are allowed at the same time, may correspond to the dependencies that must exist between them according to the invention.

C increases the hardness in the martensitic state after austenization, hardening and annealing. However, it also contributes to the precipitation of primary M7Cz carbides during the hardening process, which can be revealed during polishing or sharpening of the blade, which deteriorates the appearance of the product surface. Areas where they are exposed before polishing can also become sources of crevice corrosion. An excessive level of C content also leads, depending on the austenization temperature, to either an excessively high level of C content in the austenite matrix, which no longer allows obtaining a sufficient fraction of martensite after annealing, or to the constant presence of undissolved carbides

MezSv, which extract Cg from the austenite matrix. Thus, they reduce corrosion resistance and are unfavorable from the point of view of polishing.

Therefore, the level of C content should be at least 0.10 wt. 95 to provide sufficient hardness, and not to exceed 0.45 wt.95 to obtain good corrosion resistance and a satisfactory surface appearance after polishing. However, depending on the method of casting and hardening used, it may be useful to slightly limit the maximum level of C content in the case where there are risks that the method will not be able to guarantee such homogeneity of the steel during the hardening process, which would be sufficient to avoid the precipitation of primary carbides M7C3 . In this case, it is desirable to limit the level of C content to 0.38 wt. 9, preferably 0.20 wt. UochCx0.38 wt. 90; better 0.20 wt. UochCx0.35 wt. 90; optimally 0.30 wt. 60.35 wt. 9.

The optimal range allows, in particular, to avoid high hardness by limiting the formation of carbide within acceptable ratios, a possible loss of hardness due to a decrease in the maximum level of C content relative to the more general range, which, as will be shown later, can be compensated by the presence of sufficient nitrogen for this purpose.

In addition, the level of content C must satisfy the formulas relating it to the level of content M and to the levels of content M and C, as will be explained later.

Mp is a so-called gamma-forming element because it stabilizes the austenite structure.

An excessive level of Mn content leads to an insufficient level of martensite after austenization and quenching, which results in a decrease in hardness. In this regard, the level of Mn content should be between the trace amounts that appear as a result of melting and 1.0 wt. 9 juo. To help achieve optimally low M5 temperature, the level of its content is preferably limited to 0.6 wt. 95. 5i is a useful element in the production of steel. It has pronounced reductive properties and therefore allows the reduction of St oxides in the steel reduction phase, which follows the decarburization phase in the AOU or MOU-converter. However, the level of 5i content in the final steel should be between trace amounts and 1.0 wt. 95, because this element has a hot-set effect that limits the possibilities for hot deformation during

From hot rolling or stamping. To help achieve the optimally low temperature of M5, the level of its content is preferably limited to 0.695.

Z and R are impurities that reduce plasticity in the hot state. P easily segregates at grain boundaries and contributes to their delamination along cleavage planes. In addition, Z reduces resistance to pitting corrosion by forming compounds with Mn that act as initiating sources for this type of corrosion. In this regard, the content levels of 5 and P should, respectively, be between trace amounts and, respectively, 0.01 wt.9o and 0.04 wt.95. Preferably, the content level of 5 does not exceed 0.00595 to even more reliably ensure sufficient corrosion resistance.

Cg is a necessary element to ensure corrosion resistance. However, the level of its content must be limited, since a very high content leads to the risk of lowering the MI temperature (the temperature at the end of the martensitic transformation) below the ambient temperature. This would lead to too incomplete martensitic transformation and insufficient hardness after austenizing and quenching to ambient temperature. For these reasons, the level of St content should be between 15.0 wt.9o and 18.0 wt.95.

However, it is desirable to limit the level of St content to 15.0 - 17.0 wt. 95, better 15.2 - 17.0 wt. 956, even better 15.5 - 16.0 wt. 95, primarily in cases of non-cryogenic processing of steel, in order not to have a very high temperature M5 at the beginning of the martensitic transformation and not to leave as a result a very large amount of residual austenite, which would limit the hardness and, accordingly, the tensile strength Kt , which is undesirable for martensitic steel. If necessary, the reduced corrosion resistance caused by a decrease in the maximum level of St content can be compensated by a high level of M content, which is limited to the limits expected by some other reasons.

However, the solubility of M in liquid metal decreases with a decrease in the level of St content, as a result of which, when the St content is below 15 wt. 95, it already turns out to be impossible to preserve in the liquid metal sufficient quantities of steel M dissolved at the hardening temperature, which leads to the formation of M2 bubbles during the hardening process and no longer allows to compensate with the help of M the decrease in the amount of St from the point of view of corrosion resistance. At the same time, such a reduced limit on Cg relative to the solubility of M increases when the ferrostatic pressure during solidification decreases.

It may be preferable to increase the minimum level of St content from 15.0 wt. 95 to 15.2 wt. 95 or 15.5 wt. 95 depending on the type of casting method and casting conditions used to protect 60 against any risk of Me bubble formation.

The content level of St must also satisfy the formula connecting it with the content levels of M and

C, as will be explained below.

The elements Mi, Si, Mo and M are expensive and also reduce the temperature of the MI. Therefore, the content level of each of these elements should be limited between trace amounts and 0.50 wt.95, for

Mo preferably not exceeding 0.10 wt. 95. Therefore, there is no need to add any of them after melting the starting materials. Even more favorable from the point of view of helping to achieve the optimally low temperature of M5 is the level of Mo content, which does not exceed 0.05 wt. 95. For the same reason, it is preferable that the level of C content does not exceed 0.3 wt. 95 and the M content level did not rise above 0.2 wt. 95.

MB, Ti and 7 are so-called "stabilizing" elements, which means that in the presence of MiC and at high temperatures they form carbides and nitrides, which are more stable than carbides and nitrides of Sg. These elements, however, are undesirable because their respective carbides and nitrides, having been formed during the production process, can no longer be easily dissolved during austenization, which limits the levels of C and M content in the austenite and therefore the corresponding hardness of the martensite after quenching. Therefore, the content level of each of these elements should be between trace amounts and 0.03 wt. b.

Similarly, the AI content level should be between trace amounts and 0.010 wt. 96 in order to avoid the formation of AI nitrides, the dissolution temperature of which would be very high and would lead to a decrease in the level of M content in austenite and, as a result, the hardness of martensite after quenching.

The level of O content is a consequence of the method of obtaining solidite and its composition. It should be between trace amounts and a maximum of 0.0080 wt. 95 (80 ppm) in order to avoid the formation of a very large number and/or very large oxide inclusions, which due to pitting can be areas that contribute to the occurrence of corrosion, as well as being painted during the polishing process, as a result of which the appearance of the surface the product will not be satisfactory. The level of O content also affects the mechanical properties of steel and, if necessary, it is possible to set a standard limit below 80 parts per million, which cannot be exceeded regardless of the requirements of the users of the final product.

The levels of RB, Vi, and p may be limited by trace amounts formed in

As a result of melting, and the amount of each of them should not exceed 0.02 wt. 95, so as not to complicate the implementation of transformations in a hot state.

Control of the content of M within a clear limited level is an essential object of this invention.

Just like C, it allows, when it is in a solid solution, to increase the hardness of martensite, without having the disadvantage associated with the formation of precipitates during solidification.

If the presence of an excessively high level of C content is undesirable from the point of view of avoiding the formation of a very large amount of secretions, the addition of M allows to compensate for the loss of hardness. Nitride is formed at temperatures lower than the temperature of the formation of carbides, which makes their introduction into the solution during austenization easier. The presence of M in solid solution also improves corrosion resistance.

However, a very high level of M content no longer allows its complete dissolution during the hardening process and leads to the formation of M bubbles, which form voids (pores) during steel hardening, which are harmful to the internal state of the metal.

For these reasons, the M content level should be between 0.10 wt.95 and 0.20 wt.9o, preferably between 0.15 and 0.20 wt.9b5.

The level of content M must also satisfy the formula connecting it with the levels of content Сg |i b.

Indeed, the hardness of martensite depends on the levels of C and M content in it. The authors of this invention showed that the strengthening effects of these two elements are similar and therefore the hardness of martensite depends on the overall level of C and M content in it. The authors of the invention found that the hardness after quenching and annealing will be sufficient provided the following formula is followed:

C - M 2 0.25 wt. 95, mainly С « M 2 0.30 wt. 9.

In an even more preferred embodiment of the invention, an even higher hardness is achieved after quenching and annealing if the following formula is satisfied:

С M 2» 0.45 wt. 9.

Corrosion resistance is influenced by three elements. Cg and M have a beneficial effect, while C has a negative effect, since it is usually impossible to dissolve all Cg carbides during austenization, since the requirements of ensuring productivity and reducing costs limit the processing time and temperature in industrial practice. Undissolved Cg carbides reduce the level of Cg content of the austenite matrix and thus reduce the level of corrosion resistance.

Based on the study of corrosion resistance of martensitic steels with different mass content

St, M and C, the authors of this invention derived a formula that binds these elements, which allows to provide very good corrosion resistance.

Art 16M - 50 2 16.0 wt. 95.

One preferred, but not mandatory, condition is that 17St - 5000 - 500M 2 570 wt. 95.

This condition makes it possible to guarantee that the temperature of M5 will not be too high, since compliance with it will mean a decrease in the value of M5 by about 60 "С in comparison with what would be allowed if the selected upper limit of the content level of C, M and Cg were simultaneously met.

Steels according to the invention were tested for the degree of austenization at various temperatures before quenching in water at 20 C with a cooling rate of more than 100 "C/s, accompanied by annealing at 200 "C to vary the proportion of dissolved carbides and, therefore, the level of carbon content in austenite, and then in martensite after quenching. Measurements of martensite level as well as Vickers hardness were carried out to trace the process of change of hardness as a function of martensite content level, and the results obtained for the steel having the composition of Example 14 of Table 1 are shown in Fig. 1.

Fig. 1 shows that the hardness begins to increase with a decrease in the level of martensite content, since martensite is strengthened under the influence of carbon enrichment. The hardness reaches a maximum and then decreases when the level of martensite content becomes very low. Below 7595 martensite content, martensite strengthening no longer compensates for the strengthening due to the presence of residual austenite, which has a lower hardness. Therefore, in one preferred embodiment of the invention adapted to the production of a steel casting for a cutting tool, the level of martensite in the steel after austenizing, quenching at a rate of at least 15 "C/s to a temperature lower than or equal to 20 "C, and then annealing at a temperature of 100 to 300 "C, which in a typical case is 200 "C, is greater than or equal to 7595.

Obtaining a high level of martensite content capable of reaching 10095 can be better ensured if after quenching to 20 "C or below before performing

From annealing at 100-300 "C, cryogenic treatment is performed, that is, hardening in an environment with a very low temperature from -220 to -50 "C, usually in liquid nitrogen at -196 C or in carbon dioxide snow at -80 "C.

When the martensite content level does not reach 10095, the rest of the microstructure is typically essentially residual austenite. Ferrite may also be present.

Presented as non-limiting examples, the following results demonstrate the preferred features provided in accordance with the present invention.

The compositions of the various steel samples that were investigated are shown in Table 1 in terms of mass percentages. Values that do not meet the requirements of the invention are underlined. Also, for each sample, the values of C and M, St - 16M - 5C and 17St and - 500C and 500Ω are presented.

Table 1

Compositions of the studied samples 777777.71юЮМЮМ7 | with | Mp | 5 | R | 5 | m | Si | Si | mo | HM r |ol12| 047 | 043 |0ой21|0003| 034 | 16.7 | 016 | 003 | 0.09 16 0410 039 | oh |0bo07|0001| 041 | 16.68 | ov | 002 | 0.09 twist- 7 10432| 0.39 | 042 0.007|0001) 041) 179 | 08 | 002 | 0.09 by move 9 05345 0.31 | 0.38 000101 0.001| 025 | 1535 | ol8 | 002 | 0.07 pe 0.332) 0.38 | 027 | 0бо0о6|0002| 0.34 | 15.8 | 023 | 003 | OO on 00340) 026 | 032 |bo0e|0001| 028 | 163 | 023 | 002 | 0.09 4 0442) 038 | 029 |0boto|0002| 096 | 160 | 014 | 003 | 0.06

Table 1

Compositions of the studied samples 7777.7юЎМЮрюмМмМКЕф с | Mp | 5 | R | 5 | mi | St | Si | Mo | UM 8 |ol63| 027 | 040 |001110,001| 033 | 160 | 020 | 003 | 006 2 (0312) 033 | 042 |000810,001| 0.35 | 13.8 | 008 | 003 | 0.09 b |0465)| 027 | 043 |00071|0.002| 028 | 163 | 028 | 002 0.08

Comparison |В /0.520)| 0.30 | 024 |00181| 0001) 041 | 164 | 09 | 003 | 04 neo |0448)| 039 | 029 |002410,001| 026 | 185 | 04 | 002 009 17Sg- i210)0) 9; mo) background | doЙ|Й 7) vp mo | cm RM uBOom (more important 16 |0003|00002| 00021 0.001 | 0.007 | 0.003 | 0.184 | 0.594 | 17.69 | 582.6 8 |0003|00005| 000021 0.001 | 0.006 | 0.001 | 0.629 | 0.17 44 | 52241

According to M |0bo02 | o0o021|0.003| 0.001 | 0010 | 0.003 | 0.176 | 0.508 | 16.96 | 522.6 by invention

17Sg- i210)0) 9; me | those | li | 7 | vp mo | cm RM uBOom

And (more important b |0004| 0.002 0.001 | 0.001 | 0.013 | 0.003 | 0.032 | 0.497 | 14.51 | 525.6

Comparison |B88 / 000051 0.002 0.002 0.002 | 0.012 | 0.003 / 0198 | 0.718 | 16.97 | 637.8 in |0002| 0.001 0.001 | 0.001 | 0.008 | 0.002 | 0.195 | 0.643 | 19.38 | 636.0

After pouring, these steels were heated to a temperature above 1100 °C, subjected to hot rolling to a thickness of 3 mm, annealed at a temperature of 800 °C, and then subjected to etching and cold rolling to a thickness of 1.5 mm.

The steel sheets were then annealed at a temperature of 800 °C.

The annealed sheet steel was then subjected to austenizing treatment for 15 minutes at 1050 °C, accompanied by quenching in water to a temperature of 20 °C.

After cutting the sheets into two parts, one of these parts was then immersed for 10 minutes in a thermostatic bath at -80 "C in order to be able to evaluate the effect of cryogenic treatment in addition to simple hardening in water.

After that, all parts of the sheets were annealed for 1 hour at 200 °C.

Table 2 shows the results of tests and observations made on these steels.

Underlined values correspond to the levels of indicators that are considered insufficient.

The internal state is evaluated in the raw hardened state after pouring, in the understanding that the operations of further transformations will not disturb it.

The level of martensite is measured after quenching in water at 20 "C and after cryogenic treatment, which is quenching at -80 "C, while this quenching, or the second of these quenching operations, is accompanied by annealing at 200 "C. When after quenching in water at At 20 "С, the level of martensite is equal to or exceeds 75 95, the other data presented in Table 2 belong to the state after quenching at 20 "С, accompanied by annealing at 200 "С. When the level of martensite is lower than or equal to 75 95 after quenching in water at 20 "С, the other results presented in Table 2 belong to the state after cryogenic treatment (hardening at a very low temperature, for example, in carbon dioxide snow) at -80 "С, accompanied by annealing at 200 "С.

Corrosion resistance is evaluated using the corrosion test in electrolytes, which evaluates the formation of pits of pitting corrosion in a medium composed of 0.02M mass at 23 "Si pH 6.6. An electrochemical test performed on 24 samples allows to determine the potential

Aeolian, for which the elementary probability of the formation of pits is 0.1 cm. Corrosion resistance

Zo is considered unsatisfactory if the Eoi potential is lower than 350 mV according to the results of measurements on a saturated KSI calomel electrode (350 mV (NKE)). It is considered satisfactory if the value of the EO,1 potential is between 350 mV (NKE) and 450 mV (NKE). And it is recognized as very satisfactory if the potential EO,1 exceeds 450 mV (NKE).

Vickers hardness is measured according to the EM ISO 6507 standard in thickness on a section polished to a mirror shine, under a load of 1 kg with a diamond pyramid with a square base. The average value of the obtained hardness is calculated from 10 prints.

The hardness is considered insufficient if the average hardness is less than 500 NM. It is considered satisfactory if the average value of hardness is between 500 NM and 550

WELL. It is considered very satisfactory if its average value is between 551 NM and 600 NMU. And it is recognized as excellent if the average value of hardness exceeds 600 NU.

Suitability for polishing is evaluated by flat polishing of the middle part of the sample with successive application with a force of 30 N of sanding paper based on 5IS with grits of 180, 320, 500, 800 and 1200, then polishing the sheet with diamond paste with a particle size of 3 μm and further 1 μm with a force of 20 N. After that, the surface is examined under an optical microscope at a magnification of x100. Polishability is considered insufficient if the density of defects, traditionally called the "comet tail", is equal to or greater than 100/cm". Polishability is considered satisfactory if the value of this density is between 10/cm? and 99/cm" . Polishing is considered very satisfactory if the value of this density is between 1/cm: and 9/cm2. Polishing is recognized as excellent if the value of this density is less than 1/cm?.

The internal condition is evaluated when considering the cross-section of raw hardened steel by the method of optical metallography at a magnification of x25. The internal condition is unsatisfactory and is marked in Table 2 with the value "0" if spherical cavities (voids) are observed, indicating the formation of nitrogen bubbles during solidification. In other cases, the internal condition is considered satisfactory and is indicated in table 2 by the value "1".

The level of martensite is determined by X-ray diffraction by measuring the intensity of the characteristic rays of martensite in comparison with the intensity of the characteristic rays of austenite, meaning that in all the samples examined, they are the only two phases present. In general, it should not be possible to observe small amounts of other phases in the samples according to the invention. The first thing to pay attention to in the context of the invention is the level of martensite.

The level of martensite exceeding or equal to 75 95 after quenching at 20 "C and annealing at 200 "C, or exceeding or equal to 75 95 after annealing at 20 "C, cryogenic treatment at - 80 "C and annealing at 200 "C, is Satisfactory If a martensite level of 75 95 or more cannot be achieved by any of these treatments, the specimen is considered unsatisfactory.

Table 2

Results of tests performed on samples from Table 1.

Eol (MVV Hardness Polishing Internal Martensite | Martensite (NKE) NU (tail condition (95) hardness at | (Us) hardness at comet/sme 207 -807С m | 60 | 55 | 0 | 1 | 00 | 00 2 | 695 | 536 | 0 | 1 | 97 | 00 / from | 570 | 650 | 0 | 1 | 95 | 00

B | 50 | 689 | 36 | 1 | 7 | 86 16 | 60 | 648 | 43 | 1 | 76 | 85 7 | 660 | 687 | 51 | 1 | 69 | 8 8 | 55 | 70 | 08 | 1 | 97 | 00

For pe | 565 | 690 | 06 | 1 | 96 | 100 by invention |MP1 / 690 | 680 | 05 | 1 | 90 | 94 2 | 565 689. And | 8 | 1 | 92 | 98 / mpa4a | 550 | 628 | 49 | 1 | 76 | 86 5 | 535 5 | 0 | 1 | 98 | 00 MB | 520 | 682 | Sh Z | 1 | 90 | 97 8 | 565 | 520 | 0 | 1 | 00 | 00 Fri | 585 | b | 0 | 1 | 96 | 00 /

Table 2

Results of tests performed on samples from table 1. Polirovanist 2000. | Martensite | Martensite comet/sme 207 -807C in | 240 | 488 0 | 1 | 00 | 00 | 490 | 680 | 02 | 0 | 93 | 99 b | 400 | 686 | 109. sh1 | 93 | 98

Porov-|V? | 630 | 650 | 24 | 0 | 63 | 79 nanny |В | 50 | 699 | 215 | 1 | 48 | 70 not | 705 615 | 56 | 1 | 50 | 72 howls 510 | 479 | 0 | 1 | 00 | 00 eyelashes; 445 | 583 | 68 | 1 | 00 | 00 o'clock! 390 | 708 0 | 1 | 92 | 9

VIZ 605 | 489 | 0 | 1 | 00 | 00 in4| 655 | 632 | 0 | 0 | 95 | 00 /

Steels according to the invention from I1 to Ib, as well as Steels from I8 to I0 combine the properties of good corrosion resistance, hardness and polishability and have a good internal condition, as well as level 5 of martensite after hardening at 20 "С, which is equal to or exceeds 75 95.

Steel 17 according to the invention combines the properties of good corrosion resistance, hardness and polishability and has a good internal state, as well as a level of martensite equal to or exceeding 7595, but on the condition that cryogenic treatment is carried out at -80 C. Indeed, after simple quenching in water at 20" C level of martensite is still insufficient, which correlates with the presence of St in an amount higher than in other samples according to this invention.

It can be seen that at the comparative level of M, the hardness increases between samples I, I2, where C is between 0.10 and 0.20 wt. 95, on the one hand, and sample IZ, in which C is 0.20 and 0.30 wt. 9o, and above all I8, IZ, 110, where C is between 0.30 and 0.35 wt. 95, on the other hand.

I14, where the C content is still high and M is at the same level as in the previous cases, has a lower hardness than theirs, since the martensite fraction after quenching begins to decrease due to a decrease in the Mi temperature associated with a high by the amount of 17St-500S-500M (see table 1). It can also be seen that with comparable levels of M and other essential elements, an increase in the content of St allows to improve corrosion resistance (see samples I8 and 19). On the contrary, an increase in the level of St content leads to a tendency to decrease hardness; see samples I8, I10 and I11, the compositions of which differ significantly only in relation to Sg.

Exceeding Cg 18 wt.9o could increase corrosion resistance, but in order to maintain a satisfactory M5 indicator, it would cause a decrease in the levels of C and M content, and proper hardness would no longer be provided.

Comparative steels from K1 to KZ have the levels of Sg and M content, as well as the sum values of SEM and/or

St--16M-5C, which are unsatisfactory, which does not allow to achieve sufficient corrosion resistance.

Comparative steels KA and K5 have insufficient levels of St. content. Without provided addition

M compensation in K4 steel also turns out to be insufficient value of the aggregate St-16M-5S, which leads to unsatisfactory corrosion resistance. For K5 steel, compensation for the lack of Cg by adding M restores satisfactory corrosion resistance, but no longer allows to ensure

З is a good internal state, since the level of С content is insufficient to ensure the complete dissolution of M in the liquid metal.

Comparative steel Kb has a very high level of C content and an insufficient level of M content.

An excessively high level of C content does not allow to demonstrate sufficient suitability for polishing due to excessive formation of carbides.

The comparative steel K7 has a very high level of M content, which disturbs the internal state. The same applies to the comparative steel K14. The reference steel K8 has an excessive level of C content, which leads to insufficient polishability and a very low level of martensite content even after cryogenic hardening at -80 "С. -80 "S.

Comparative steels K10 and K11 have very low levels of C content, as well as an insufficient amount of CM, which leads to excessively low hardness. Comparative steels K12 and K13 would have compositions according to the invention relative to the individual levels of the content of each element, but their indicators

St-16M-5S, which are less than 16.0 wt. 95, are insufficient to achieve corrosion resistance as high as that of steels that conform to the present invention in all respects, including those that only slightly exceed 16.0 wt. 95 to secure this amount

St--16M-50.

For obvious reasons, steels according to the invention are used for the production of cutting tools, for example, scalpels, scissors, knife blades or disk-shaped knives for food processors.

Claims (25)

FORMULA OF THE INVENTION 15 1. Martensitic stainless steel, characterized by the fact that its composition in mass percentages contains: 0 10-сС50.45, trace amounts «Мп1.0, 20 trace amounts «5и»к1.0, trace amounts «550.01, trace amounts of хР-е0.04, 15.0"5St"с18.0, trace amounts of "Mi"сО0.50, 25 trace amounts of "Moh 0.50, trace amounts of "Сис0О0.50, trace amounts of "M-0.50 , trace amounts of Moss 0.03, trace amounts of Tis 0.03, 30 trace amounts of k2ii: 0.03, trace amounts of хАЙх 0.010, trace amounts of хО-: 0.0080, trace amounts of Пр«0.02, trace amounts "VisO0.02, 35 trace amounts "x5x0.02, 010 -M0.20, Xia-Mm"0.25, St-16M-5С16.0, the rest are iron and impurities formed during melting. 40 2. Steel according to claim 1, which is characterized in that its microstructure includes at least 75 95 martensite. 3. Steel according to claim 1 or 2, which differs in that 0.20 wt. 95 "C" 0.38 wt. 905. 4. Steel according to claim 3, which differs in that 0.20 wt. 956 -C-0.35 wt. 905. 5. Steel according to claim 4, which differs in that 0.30 wt. 95 "С-0.35 wt. 95. 45 6. Steel according to claim 1 or 2, which differs in that trace amounts of "Mp0.6 wt. 905. 7. Steel according to claim 1 or 2, which differs in that trace amounts of x5:50.005 wt. 95. 8. Steel according to claim 1 or 2, which differs in that 15.0 wt. 95 "St" with 17.0 wt. 95. 9. Steel according to claim 8, which differs in that 15.2 wt. 95 "St-17.0 wt. 95. 10. Steel according to claim 9, which differs in that 15.5 wt. 95 "St-16.0 wt. 905. 50 11. Steel according to claim 1 or 2, which differs in that trace amounts of "Mo" 0.1 wt. 905. 12. Steel according to claim 11, which differs in that trace amounts of "Mo-0.05 wt. 905. 13. Steel according to claim 1 or 2, which differs in that trace amounts of "Су"сО0,З mass. 90. 14. Steel according to claim 1 or 2, which differs in that trace amounts of "M" 0.2 wt. 95. 15. Steel according to claim 1 or 2, which differs in that 0.15 wt. 95 "M" 0.20 wt. 90. 55 16. Steel according to claim 1 or 2, which differs in that С--М20,30 wt. 95. 17. Steel according to claim 16, which differs in that С-я-М20.45 wt. 95. 18. Steel according to claim 1 or 2, which differs in that 17С/-5000-500М-570 wt. 95. 19. The method of production of blanks obtained from martensitic stainless steel, which differs in that: the billet is obtained and cast from steel having a composition according to any of claims 1-18; the specified workpiece is heated to a temperature higher than or equal to 1000 "C; the specified workpiece is subjected to hot rolling to obtain a sheet, rod or wire rod; the specified sheet, rod or wire rod is annealed at a temperature of 700-900 "C; and perform the operation of forming the specified sheet, rod or wire rod. 20. The method according to claim 19, characterized in that said blank is a sheet and said forming operation is cold rolling. 21. The method according to claim 19, which is characterized by the fact that the specified workpiece is a rod or wire rod and the specified forming operation is stamping. 22. The method according to any of claims 19-21, which is characterized by the fact that the steel has a composition according to claim 2, while the specified molded blank is further subjected to austenization at a temperature of 950-1150 "C, then cooled at a rate of at least 15 "C/ c to a temperature less than or equal to "C", after which it is subjected to annealing at a temperature of 100-300 "C. 23. The method according to any one of claims 19-21, which is characterized by the fact that the steel has a composition according to claim 1 or 2, while the specified molded blank is further subjected to austenization at a temperature of 950-1150 "C, then cooled at a rate of at least 15 " C/s to a temperature less than or equal to 20 C, after which it is subjected to cryogenic treatment at a temperature from -220 to -507 C and then annealed at a temperature of 100-300 "C. 24. A cutting tool, which is characterized by the fact that it is obtained from a workpiece produced by the method according to any of claims 19-23. 25. A cutting tool according to claim 24, characterized in that it is an element of knife products, such as a knife blade, a food processor blade, a scalpel or a scissor blade. 710 BC; F ny, 620 str g sn o; 10 20 of 40 Martensite level (95) Fig. 000 KomputernaverstkaL.Tsikhanovska.d (00000000 Ministry of Economic Development, Trade and Agriculture of Ukraine, St. M. Hrushevskyi, 12/2, Kyiv, 01008, Ukraine SE "Ukrainian Institute of Intellectual Property", str. Glazunova, 1, Kyiv - 42, 01601