KR20170141250A - Martensitic stainless steel, a method for producing a semi-finished product from the above steel, and a cutting tool manufactured from the semi-finished product - Google Patents

Abstract

By weight percentage: 0.10%? C? 0.45%; Trace amount? Mn? 1.0%; Trace amount? Si? 1.0%; Trace amount? S? 0.01%; Trace amount? P? 0.04%; 15.0%? Cr? 18.0%; Trace amount Ni < = 0.50%; Trace amount? Mo? 0.50%; Trace amount? Cu? 0.50%; Trace amount? V? 0.50%; Trace amount? Nb? 0.03%; Trace amount? Ti? 0.03%; Trace amount? Zr? 0.03%; Trace amount? Al? 0.010%; Trace amount? O? 0.0080%; Trace amount? Pb? 0.02%; Trace amount? Bi? 0.02%; Trace amount? Sn? 0.02%; 0.10%? N? 0.20%; C + N? 0.25%; Cr + 16 N - 5 C ≥ 16.0%; Preferably 17 Cr + 500 C + 500 N < = 570%;
And a composition of impurities resulting from development and a remnant of iron.
A method of manufacturing an intermediate product from such a martensitic stainless steel, and a cutting tool manufactured from such a semi-finished product.

Description

Martensitic stainless steel, a method for producing a semi-finished product from the above steel, and a cutting tool manufactured from the semi-finished product

The present invention relates to a martensitic stainless steel. Such steels are mainly for producing cutter pieces, such as cutting tools, especially scalpels, scissor blades, or knife blades or domestic food processors.

Cutlery steels should have high corrosion resistance, ability to be polished and hardness.

Martensitic stainless steels currently used for producing blades of cutting tools such as steels of the type EN 1.4021, EN 1.4028 and EN 1.4034 have Cr content levels of up to 14% or 14.5% by weight and various C content levels, namely EN 1.4021 0.16% -0.25% for EN 1.4028, 0.26-0.35% for EN 1.4028 and 2.43-0.50% for EN 1.4034. The hardness level of the steel mainly depends on this C content level.

If better corrosion resistance is required, EN 1.4419 grades with 0.36-0.42% C, 13.0-14.5% Cr and 0.60-1.00% Mo can be used.

During the manufacturing process, these steels are generally melted in AOD or VOD converters and then continuously injected in the form of slabs, blooms or billets, Or hot rolled to obtain a wire rod. They are then subjected to cold rolling for flat products, or to cold rolling for flat products, or for sufficient long enough to facilitate sawing before forging hot rolled semi-finished products for long products And undergoes annealing to obtain a soft, ferrite structure containing carbide.

The product then undergoes recrystallization annealing. In this softened state of the recrystallized ferrite-containing carbide, the product is cut to have a final shape such as, for example, a knife blade, before undergoing a heat treatment comprising a high temperature austenitization, generally between 950 ° C and 1150 ° C , Followed by quenching at ambient temperature to induce a mainly martensitic structure.

In this martensitic state, the product has a high hardness, which is higher when the carbon content is higher, but is also more brittle. In general, annealing treatments between 100 [deg.] C and 300 [deg.] C are performed later to reduce brittleness without too low a hardness. The blade then undergoes various tasks, including sharpening and polishing, to provide cutting quality and aesthetic appearance.

None of the four grades quoted simultaneously tolerates good corrosion resistance, good surface condition and high hardness at a reasonable cost.

EN 1.4419 grades have excellent corrosion resistance and high hardness, but the addition of large amounts of Mo is very costly.

The EN 1.4034 grade has a high hardness but also has a mediocre surface appearance after polishing because of the presence of large amounts of carbides that do not dissolve during the austenitization due to the high C content level of this grade. Particularly in consideration of the fact that a part of Cr is entrapped in the undissolved carbide, the corrosion resistance is insufficient because the Cr content level is not sufficiently high in the matrix. In addition, the cutting edge of the blade often undergoes crevice corrosion resulting from the large cleavage of the primary carbide at the end of solidification during continuous casting.

EN 1.4021 and 1.4028 grades, which contain small amounts of C, have low hardness but do not have sufficient corrosion resistance due to excessively low Cr content levels.

The present invention aims at solving the above-mentioned problems. In particular, a martensitic stainless steel for cutting tools having high corrosion resistance, excellent abrasion resistance and high hardness, which is as cost effective as possible, is proposed.

For this purpose, the present invention relates to a composition comprising, by weight percentage:

- 0.10%? C? 0.45%; Preferably 0.20%? C? 0.38%; More preferably 0.20%? C? 0.35%; Optimally 0.30%? C? 0.35%;

- trace amount? Mn? 1.0%; Preferably a trace amount? Mn? 0.6%;

- trace amount? Si? 1.0%;

- trace amount? S? 0.01%; Preferably, the trace amount? S? 0.005%;

- trace amount? P? 0.04%;

- 15.0%? Cr? 18.0%; Preferably 15.0%? Cr? 17.0%; More preferably 15.2%? Cr? 17.0%; Optimally 15.5% < = Cr < = 16.0%;

- trace amount Ni < = 0.50%;

- trace amount? Mo? 0.50%; Preferably a trace amount? Mo? 0.01%; More preferably a trace amount? Mo? 0.05%;

- trace amount? Cu? 0.50%; Preferably a trace amount? Cu? 0.3%;

- trace amount? V? 0.50%; Preferably a trace amount? V? 0.2%;

- trace amount? Nb? 0.03%;

- trace amount? Ti? 0.03%;

- trace amount? Zr? 0.03%;

- trace amount? Al? 0.010%;

- trace amount? O? 0.0080%;

- trace amount? Pb? 0.02%;

- trace amount? Bi? 0.02%;

- trace amount? Sn? 0.02%;

- 0.10%? N? 0.20%; Preferably 0.15%? N? 0.20%;

- C + N? 0.25%; C + N > = 0.30%; More preferably C + N > = 0.45%;

- Cr + 16 N - 5 C ≥ 16.0%;

- 17 Cr + 500 C + 500 N < = 570%;

And a composition of an impurity and a rest of iron which is a result of melting. The present invention relates to a martensitic stainless steel.

Preferably, its own microstructure contains at least 75% of martensite. The present invention also relates to a process for the production of semi-finished products comprising martensitic stainless steels characterized by:

- molten and casting the semi-finished product from the steel with the composition described above;

The semi-finished product is heated to a temperature of 1000 캜 or higher;

The semi-finished product is hot-rolled to obtain a sheet, a bar or a wire rod;

The sheet, bar or wire is annealed at a temperature comprised between 700 [deg.] C and 900 [deg.] C;

A shaping operation is performed on the sheet, bar or wire.

The semi-finished product may be a sheet, and the molding operation may be cold rolling.

The semi-finished product may be a bar or a wire rod, and the molding operation may be forging.

The molded semi-finished product can then be austenitized between 950 ° C and 1150 ° C, if its Cr content level is between 15% and 17%, and then at 20 ° C / s at a rate of at least 20 ° C / RTI ID = 0.0 > 100 C < / RTI > and < RTI ID = 0.0 > 300 C. < / RTI >

The shaped semi-finished product can then be austenitized between 950 ° C and 1150 ° C and then cooled to a temperature of 20 ° C or less at a rate of at least 15 ° C / s and then cooled to a temperature of -220 ° C to -50 ° C After undergoing a cryogenic treatment at a temperature of between < RTI ID = 0.0 > 100 C < / RTI >

The present invention also relates to a cutting tool characterized in that it consists of a semi-finished product manufactured according to the above-described method.

The cutting tool may be a cutlery item such as a knife blade, a food processor blade, a scalpel, or a scissor blade.

As will be appreciated, the present invention utilizes martensitic stainless steels having a specific composition to produce cutting tools, so that there is no expensive element with a high content level, but a relatively large amount of nitrogen . Specific balancing of Cr, C and N content levels is also required.

Other features and advantages of the present invention will be better understood when reading the following description, which is given by way of example and made with reference to the accompanying FIG. 1, which shows that austenitization, And the evolution of the Vickers hardness of the steel under a load of 1 kg, based on the martensite level after the addition.

With respect to the chemical composition of the steel according to the present invention, the following support is submitted. As long as the content level ranges of the various elements considered to be priorities are independent of each other and any combination of the ranges defined in the following description can be considered in the context of the present invention, It is clear that the content levels can take into account the relevance that must exist between them in accordance with the present invention.

C increases the hardness in a martensitic state after austenitization, crystallization and annealing. However, this means that M ₇ C ₃ It also promotes the precipitation of primary carbides, which can be stripped during polishing or sharpening of the blades, degrading the surface appearance of the product. Sites found before polishing can also be places of crevice corrosion. Austenite in accordance with nitro change temperature, excessive C content level is not dissolved depletion of Cr in an excessively high C content level or austenitic matrix in the austenitic matrix, it can not be obtained any longer sufficient martensite section after annealing M ₂₃ C ₆ carbide. ≪ / RTI > They therefore reduce corrosion resistance and are detrimental to polishability.

Therefore, the content level of C should be at least 0.10% to obtain sufficient hardness, 0.45% or less to obtain excellent corrosion resistance and satisfactory surface appearance after polishing. Depending on the casting and solidification methods used, however, if there is a risk that this method will not ensure sufficient homogeneity of the steel during solidification to prevent precipitation of the M ₇ C ₃ primary carbides, a slight further limitation of the maximum C content level It can be useful. In this case, the content level of C is 0.38%, preferably 0.20%? C? 0.38%; More preferably 0.20%? C? 0.35%; It is preferable to limit it to 0.30%? C? 0.35% optimally.

Particularly, the optimum range makes it possible to prevent high hardness while limiting the formation of carbides within an acceptable range, and as will be seen later, the possibility of loss of hardness due to reduction at the maximum C content level relative to the more general range, Can be compensated for by the presence of sufficient nitrogen in order to achieve < RTI ID = 0.0 >

Further, as will be described later, the content level of C must satisfy the expression relating to the content level of N and the content level of N and Cr.

Mn is a so-called gammagenous element because it stabilizes the austenitic structure. Excessive Mn content levels result in insufficient martensite levels after austenitizing and casting treatment, which leads to a decrease in hardness. For this reason, the Mn content level should be included between the trace amount which is the result of melting and 1.0%. Preferably, its own level of content is limited to 0.6% to help optimally achieve a low Ms temperature.

Si is a useful element in the steelmaking process. It is highly reduced, thus making it possible to reduce Cr oxides on reduction of the steel in the AOD or VOD converter following the decarburization phase. However, the level of Si content in the final steel should be between trace and 1.0%, since these elements have a hot hardening effect which limits the possibility of hot deformation during hot rolling or forging. Preferably, its own level of content is limited to 0.6% to help optimally achieve a low Ms temperature.

S and P are impurities that reduce high temperature ductility. P easily separates at the grain boundaries and promotes its cleavage. In addition, S forms a compound with Mn that serves as a starting point for this type of corrosion, thereby reducing corrosion resistance due to pitting. For this purpose, the S and P content levels should be included between trace amounts, respectively, between 0.01% and 0.04% by weight, respectively. Preferably, the content level of S does not exceed 0.005% and ensures even more excellent corrosion resistance.

Cr is an essential element for corrosion resistance. However, since the high content level is at risk of lowering to a temperature Mf (the temperature at the end of the martensitic transformation) below the ambient temperature, its own content level should be limited. This will lead to an excessively incomplete martensitic transformation and insufficient hardness after the austenitization and the application to ambient temperature. For these various reasons, the Cr content level should be included between 15.0 wt.% And 18.0 wt.%. However, if the cryogenic treatment of the steel is not carried out, it is more preferable to have 15.0-17.0%, more preferably 15.2-17.0%, even more preferably 15.5-17.0%, in order to avoid having an excessively hot Ms at the beginning of the martensitic transformation. It is desirable to limit the Cr content level to 16.0% and thus not leave too much of the austenite remaining to limit the hardness, and thus the tensile strength Rm is undesirable in martensitic steels. If necessary, the reduced corrosion resistance due to reduction in the maximum Cr content level can be compensated by a high N content level within the limits specified elsewhere.

However, Cr if the reduced content level, and the N-solubility in the liquid metal decreases, no longer possesses the Cr is less than 15% of the liquid metal, is sufficiently dissolved in a river solidification temperature N is N ₂ bubbles during solidification bubbles and does not allow N to compensate for the reduction of Cr with respect to corrosion resistance. If the ferrostatic pressure decreases in the solidification, this low Cr limit for solubility of N also increases. It may be desirable to increase the minimum Cr content level from 15.0% to 15.2% or 15.5% depending on the casting conditions and type of casting method used to protect against any risk of N ₂ bubble formation.

As described below, the content level of Cr must also satisfy an expression relating to the content levels of N and C.

The elements Ni, Cu, Mo and V are expensive and also reduce the temperature Mf. Therefore, the content level of each of these elements should be limited to a trace amount of 0.50 wt%, preferably 0.10% or less in the case of Mo. Therefore, it is not necessary to add anything after melting the raw material. To help obtain the optimum low temperature Ms, it is more preferred that the Mo content level does not exceed 0.05%. For the same reason, it is preferable that the content level of Cu does not exceed 0.3%, and the content level of V should not exceed 0.2%.

Nb, Ti and Zr are so-called "stabilizing" elements, which means to form carbides and nitrides that are more stable than carbides and nitrides of Cr in the presence of N and C and at high temperatures. However, once each of these carbides and nitrides formed during the production process is no longer readily soluble during austenitization, this limits the level of C and N content in the austenite and therefore the corresponding hardness of the martensite after casting , These elements are not preferable. Therefore, the content level of each of these elements should be between trace and 0.03%.

Likewise, the content level of Al must be between a trace amount and 0.010% in order to prevent the formation of Al nitride, its melting temperature may be too high, and the level of N content of austenite and therefore the hardness of martensite after casting .

The content level of O depends on the method of manufacturing the steel and its own composition. To prevent the formation of too much and / or too large an oxide inclusions, it must be contained between a trace amount and a maximum value of 0.0080% (80 ppm), which can constitute a preferred starting point in the case of corrosion by fitting, And can also be stripped during polishing if the surface appearance of the product is unsatisfactory. The content level of O also affects the mechanical properties of the steel, and traditionally, it may set limits below 80ppm, which can not be exceeded, depending on the requirements of the end user, optionally.

The Pb, Bi and Sn content levels may be limited to trace amounts resulting from melting and each should not exceed 0.02% so as not to make hot transformations too difficult.

Controlling the content level of N for a well-defined level is an essential aspect of the present invention. C, it is possible to increase the hardness of martensite without having the drawback of forming a precipitate during solidification, when it is present as a solid solution. If it is not desired to have an excessively high C content level to prevent too much precipitate from forming, N can be added to compensate for the loss of hardness. Since the nitride is formed at a lower temperature than the carbide, it is easier to inject it into the solution during the austenitization. The presence of N in the solid solution also improves the corrosion resistance.

However, excess N content levels do not allow for its complete dissolution during solidification, but form blowholes during the solidification of the steel and lead to the formation of N ₂ bubbles which are detrimental to the internal health of the metal.

For these various reasons, the N content level should be between 0.10 wt.% And 0.20 wt.%, Preferably between 0.15 wt.% And 0.20 wt.%.

The content level of N should also satisfy an expression related to the content levels of Cr and C.

Indeed, the hardness of martensite depends on its own C and N content levels. The present inventors have shown that the hardening effects of these two elements are similar and thus the hardness of the martensite is dependent on its own total C + N content level. It has been clarified by the present inventors that, considering the following equations, the hardness after crystallization and annealing will be sufficient:

C + N? 0.25%, preferably C + N? 0.30%

In a further preferred embodiment of the present invention, higher hardness is obtained after the etching and annealing, when the following formula is taken into consideration:

C + N? 0.45%.

Three elements affect corrosion resistance. Cr and N are beneficial, while C has a negative effect, since in general it is not possible to dissolve all of the carbides of Cr during austenitization, since this limits the duration and temperature of the process in the industrial field in terms of productivity and cost. The undissolved Cr carbide decreases the level of Cr content of the austenitic matrix and thus reduces the level of corrosion content.

From the corrosion resistance studies of martensitic steels with different weight contents of Cr, N and C, the present inventors have found a combination of these various elements which can guarantee very good corrosion resistance.

Cr + 16 N - 5 C ≥ 16.0%

One preferred condition (but not necessarily) is as follows:

17Cr + 500C + 500N ≤ 570%

This condition can ensure that the temperature Ms is not too high, which, in turn, is about 60% higher than what compliance can be tolerated by the simultaneous satisfaction of the limits of the content levels of the selected higher C, N and Cr Lt; 0 > C.

The steel according to the present invention undergoes austenitization tests at different temperatures prior to casting in water at 20 DEG C at a cooling rate of greater than 100 DEG C / s and then annealed at 200 DEG C so that the ratio of dissolved carbides, The carbon content level in the austenite, and the carbon content level in the post-martensite. The results, as well as the martensite level as well as the Vickers hardness, were measured to track the change in hardness as a function of martensite level and for the steels having the composition of Example I4 of Table 1, the results of which are shown in FIG.

Figure 1 shows that the hardness begins by increasing with the drop of the martensite level since the martensite is cured by carbon enrichment. The hardness decreases after reaching the maximum value, until the martensite level becomes too low. Less than 75% martensite no longer compensates for the softening of the martensite associated with the presence of residual austenite with lower hardness. For this reason, in one preferred embodiment of the present invention, suitable for producing cutting tools from cast steel, after austenitization is carried out at a temperature of at least 15 [deg.] C / s and no more than 20 [deg.] C, The martensite level of the steel annealed at a temperature of 100 占 폚 to 300 占 폚, typically 200 占 폚, is 75% or more.

Acquisition of a high martensite level that can reach 100% can be better ensured if the cryogenic treatment is carried out after 20 ° C or below, annealing is carried out at a very low temperature of -220 ° C to -50 ° C, generally at -196 ° C in liquid nitrogen or in a carbon dioxide snow at -80 ° C, at 100-300 ° C Before it is done.

If the martensite content level does not reach 100%, the remaining microstructure is essentially made up of the residual austenite. Ferrite may also be present here.

By way of non-limiting example, the following results will show advantageous properties imparted by the present invention.

The compositions of the different tested steel samples are shown in Table 1, expressed as weight percentages. The underlined values are those that do not comply with the present invention. We have also reported values of C + N, Cr + 16N-5C and 17Cr + 500C + 500N for each sample.

Table 1: Composition of tested samples

After casting, these steels were heated to a temperature exceeding 1100 占 폚, hot rolled to a thickness of 3 mm, annealed at a temperature of 800 占 폚, pickled and cold-rolled to a thickness of 1.5 mm.

The steel sheet was then annealed at a temperature of 800 ° C.

The annealed steel sheet then underwent austenitization treatment at 1050 占 폚 for 15 minutes, followed by quenching in water at a temperature of 20 占 폚.

After cutting the plates into two parts, one of them was immersed in a thermostated bath at -80 DEG C for 10 minutes and then a simple addition of water was added so that the effect of the cryogenic treatment could be evaluated Respectively.

Annealing for 1 hour at < RTI ID = 0.0 > 200 C < / RTI > was then performed on each sheet portion.

Table 2 shows the tests and observations performed on these steels. The underlined values correspond to performance levels that are considered insufficient.

The internal health state is assessed for the raw solidification state after injection and is known not to damage it due to subsequent deformation work.

The martensite level is measured after being cured in water at 20 ° C and then cryogenically treated at -80 ° C, and the second of these crystallization operations is followed by annealing at 200 ° C It goes through. Other results given in Table 2 when the martensite level is greater than 75% after being implanted in water at 20 ° C relates to a state at 20 ° C followed by an annealed state at 200 ° C. If the martensite level is less than 75% after being treated in water at 20 ° C, the other results given in Table 2 are cryogenic at very low temperatures (performed at very low temperatures, for example in dry ice) RTI ID = 0.0 > 200 C. < / RTI >

The corrosion resistance was evaluated by an electrochemical corrosion test by fitting in an environment of 0.02M NaCl, 23 DEG C and pH 6.6. The electrochemical tests performed on 24 samples enable the elementary pitting probability to determine a potential E _0.1 equal to 0.1 cm ^-2 . Corrosion resistance is considered unsatisfactory when the measured potential E _0.1 is less than 350 mV compared to a KCl saturated calomel electrode (350 mV / ECS). If the potential E _0.1 is included between 350 mV / ECS and 450 mV / ECS, it is considered satisfactory. When the dislocation E _0.1 is greater than 450 mV / ECS, it is considered very satisfactory.

The Vickers hardness is measured in terms of the thickness for a mirror polished cut under a load of 1 kg with a diamond pyramidal tip having a square base according to standard EN ISO 6507. The average of the hardness obtained is calculated by performing 10 imprints. If the average hardness is less than 500 HV, the hardness is considered to be insufficient. If the average hardness is included between 500 HV and 550 HV, this is considered to be satisfactory. If the average hardness is between 551 HV and 600 HV, this is considered very satisfactory. If the average hardness is greater than 600 HV, it is considered good.

The abrasivity was evaluated by flat polishing at a medium thickness of the sample using SiC 180, 320, 500, 800 and 1200 paper continuously with a force of 30 N, On an imbibed sheet with a diamond paste having a particle size of 1 mu m. The surface was then observed with an optical microscope at a magnification of x100. If the flaw density traditionally referred to as "comet-tail " is greater than 100 / cm2, then the abrasiveness is considered insufficient. When such a density is included between 10 / cm < 2 > and 99 / cm < 2 >, the abrasiveness is regarded as satisfactory. When such a density is included in the range of 1 / cm2 to 9 / cm2, the abrasiveness is considered to be very satisfactory. When the density is smaller than 1 / cm 2, the abrasive property is considered to be excellent.

Internal health status is assessed by observing the cleavage of raw solidification steel by optical metallography at a magnification of x25. When globular cavities (blowholes) are observed that reflect the formation of nitrogen bubbles at the time of solidification when the internal health condition is not satisfactory, the value "0" Otherwise, the internal health condition is deemed satisfactory and is indicated by the value "1 " in Table 2.

The martensite level is determined by X-ray diffraction by measuring the intensity of the characteristic radiation of the martensite as compared to the intensity of the characteristic ray of the austenite, and it is the only two phases present in all the samples tested It is known. In general, it can not be excluded that other phases in a sample according to the invention can be observed marginally. In the context of the present invention, it is the martensite level that should be considered more than anything else.

A martensite level of 75% or more after annealing at 200 占 폚, annealing at 20 占 폚 or at a cryogenic temperature of -80 占 폚 and annealing at 200 占 폚 is satisfactory. If at least 75% martensite levels can not be obtained by either of these treatments, the sample is considered unsatisfactory.

Table 2: Results of tests performed on the samples in Table 1

The steels I8 to I9 as well as the steels I1 to I6 according to the present invention have excellent corrosion resistance, hardness and abrasion resistance, and have an excellent internal health condition as well as a martensite level of 75% or more after being called at 20 deg.

The steel I7 according to the present invention is characterized by excellent corrosion resistance, hardness and abrasion characteristics and has excellent internal health conditions as well as martensite levels of 75% or more, but under conditions where cryogenic treatment is carried out at -80 캜. Indeed, after simple quenching in water at 20 占 폚, the martensite level is still insufficient, which is associated with the presence of Cr at higher levels than other samples according to the invention.

At a similar level of N, samples I1 and I2 (where C is between 0.10 and 0.20%), on the one hand, and sample I3 (where C is between 0.20 and 0.30%) and in particular samples I8, I9 and I10 (Where C is between 0.30% and 0.35%).

C is still high and I14, which is the same level as the previous cases, has a lower hardness because of the decrease in temperature Mf associated with the high value of the sum of 17Cr + 500C + 500N (see Table 1) This is because the fraction of martensite begins to decrease. It can also be seen that, at similar levels of N and other essential elements, an increase in Cr can improve corrosion resistance (see Samples I8 and I9). Conversely, an increase in the Cr content level tends to decrease the hardness; See samples I8, I10 and I11, the composition of which is significantly different for Cr only. More than 18% Cr may increase corrosion resistance, but will result in reduced levels of C and N content to maintain a satisfactory Ms, and correct hardness will no longer be assured.

Reference steels R1 to R3 have unsatisfactory levels of Cr and N content, as well as the sum of C + N and / or Cr + 16 N - 5 C, which does not allow sufficient corrosion resistance.

Reference steels R4 and R5 have insufficient Cr content levels. In the absence of compensation by the addition of N, the steel R4 also has an insufficient Cr + 16N-5C combination which results in unsatisfactory corrosion resistance. Compensation for the shortage of Cr by adding N to the steel R5 restores satisfactory corrosion resistance, but since the content level of Cr is no longer sufficient to allow complete dissolution of N in the liquid metal, Can not be guaranteed.

The reference steel R6 has too high a C content level and an insufficient N content level. Excessively high C content levels do not have sufficient abrasive properties due to excessive carbide formation.

Reference steel R7 has too high an N content level, thus impairing internal health. The same applies to the reference river R14. The reference steel R8 has an excessive C content level, which results in poor abrasive properties and even too low a martensite level after cryogenic heating at -80 ° C. The reference steel R9 contains too much Cr, which results in insufficient martensite levels even after cryogenic heating at -80 占 폚.

The reference rivers R10 and R11 have too low C content levels as well as insufficient C + N sums, resulting in too low a hardness. The reference rivers R12 and R13 may have a composition according to the invention for the individual content levels of each element, but their Cr + 16N-5C content levels below 16.0% are 16.0% for Cr + 16N-5C It is insufficient to ensure corrosion resistance as high as corrosion resistance of the steel according to the present invention for all the points, including only slightly exceeding the value.

The steel according to the present invention is used for reasonable reasons to manufacture cutting tools, for example, scalpels, scissors, knife blades or circular blades for food processors.

Claims (9)

By weight percentage:
- 0.10%? C? 0.45%; Preferably 0.20%? C? 0.38%; More preferably 0.20%? C? 0.35%; Optimally 0.30%? C? 0.35%;
- trace amount? Mn? 1.0%; Preferably a trace amount? Mn? 0.6%;
- trace amount? Si? 1.0%;
- trace amount? S? 0.01%; Preferably, the trace amount? S? 0.005%;
- trace amount? P? 0.04%;
- 15.0%? Cr? 18.0%; Preferably 15.0%? Cr? 17.0%; More preferably 15.2%? Cr? 17.0%; Optimally 15.5% < = Cr < = 16.0%;
- trace amount Ni < = 0.50%;
- trace amount? Mo? 0.50%; Preferably a trace amount? Mo? 0.01%; More preferably a trace amount? Mo? 0.05%;
- trace amount? Cu? 0.50%; Preferably a trace amount? Cu? 0.3%;
- trace amount? V? 0.50%; Preferably a trace amount? V? 0.2%;
- trace amount? Nb? 0.03%;
- trace amount? Ti? 0.03%;
- trace amount? Zr? 0.03%;
- trace amount? Al? 0.010%;
- trace amount? O? 0.0080%;
- trace amount? Pb? 0.02%;
- trace amount? Bi? 0.02%;
- trace amount? Sn? 0.02%;
- 0.10%? N? 0.20%; Preferably 0.15%? N? 0.20%;
- C + N? 0.25%; C + N > = 0.30%; More preferably C + N > = 0.45%;
- Cr + 16 N - 5 C ≥ 16.0%;
- preferably 17Cr + 500C + 500N < = 570%;
And the impurities and the rest of the iron resulting from the development,
By weight of a martensitic stainless steel. The martensitic stainless steel according to claim 1, characterized in that its microstructure contains at least 75% of martensite. - semi-finished products are developed and poured from a steel having the composition according to claim 1;
The semi-finished product is heated to a temperature of 1000 캜 or higher;
The semi-finished product is hot-rolled to obtain a sheet, a bar or a wire rod;
The sheet, bar or wire is annealed at a temperature comprised between 700 [deg.] C and 900 [deg.] C;
Characterized in that a shaping operation is carried out on the sheet, bar or wire, the semi-finished product being made of martensitic stainless steel. 4. The method of manufacturing a semi-finished product according to claim 3, wherein the semi-finished product is a sheet and the forming operation is cold-rolling. 4. The method according to claim 3, wherein the semi-finished product is a bar or a wire rod, and the forming operation is forging. The steel according to any one of claims 3 to 5, wherein the steel has a composition according to claim 2 and the shaped semi-finished product is then austenitized between 950 ° C and 1150 ° C, gt; 20 C < / RTI > at a temperature of between about < RTI ID = 0.0 > 100 C < / RTI > and < RTI ID = 0.0 > 300 C. < / RTI > The steel according to any one of claims 3 to 5, wherein the steel has a composition according to claim 1 or claim 2, wherein the shaped semi-finished product is then austenitized between 950 ° C and 1150 ° C, s and then undergoes a cryogenic treatment at a temperature of -220 ° C to -50 ° C and then undergoes annealing at a temperature comprised between 100 ° C and 300 ° C By weight based on the total weight of the martensitic stainless steel. A cutting tool comprising a semi-finished product produced according to the method of any one of claims 3 to 7. The cutting tool according to claim 8, characterized in that it is a cutlery item such as a knife blade, a food processor blade, a scalpel, or a scissor blade.

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