JP2018521215A - Martensitic stainless steel, method for producing a semi-finished product from the steel, and cutting tool produced from the semi-finished product - Google Patents

Abstract

  The composition is 0.10% ≦ C ≦ 0.45% by mass percentage; trace amount ≦ Mn ≦ 1.0%; trace amount ≦ Si ≦ 1.0%; trace amount ≦ S ≦ 0.01%; ≦ P ≦ 0.04%; 15.0% ≦ Cr ≦ 18.%; Trace amount ≦ Ni ≦ 0.50%; Trace amount ≦ Mo ≦ 0.50%; Trace amount ≦ Cu ≦ 0.50%; Amount ≦ V ≦ 0.50%; trace amount ≦ Nb ≦ 0.03%; trace amount ≦ Ti ≦ 0.03%; trace amount ≦ Zr ≦ 0.03%; trace amount ≦ Al ≦ 0.010%; 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 + 16N−5C ≧ 16.0%; preferably 17Cr + 500C + 500N ≦ 570%; the balance being iron and manufacturing-derived impurities Martensite stainless steel characterized by The manufacturing method of the semi-finished product from this martensitic stainless steel, and the cutting tool manufactured from this semi-finished product.

Description

  The present invention relates to martensitic stainless steel. This steel is primarily intended for the manufacture of cutting tools, in particular blades such as scalpels, scissors or knife blades or household food processors.

  Steel intended for cutlery is required to have high corrosion resistance, polishing performance, and hardness.

  The martensitic stainless steel currently used in the manufacture of cutting tools blades such as steel of type EN1.4021, EN1.4028 and EN1.4034 has a Cr content of 14 or 14.5% by weight and variable C content, ie 0.16% to 0.25% for EN1.4021, 0.26 to 0.35% for EN1.4028, and 2.43 to 0.50% for EN1.4034 Have. The hardness level of steel depends mainly on this C content.

  If even better corrosion resistance is sought, grade EN1.4419 containing 0.36 to 0.42% C, 13.0 to 14.5% Cr and 0.60 to 1.00% Mo can be used. .

  During manufacturing, these steels are typically melted in an AOD or VOD converter, then poured continuously in the form of slabs, blooms or billets and then hot so as to obtain coils, rolled bars or wire rods. Roll. It is carbide that is soft enough that it can then be annealed to facilitate cold rolling on flat products or to facilitate sawing before forging hot rolled semi-finished products on long products A ferrite structure containing is given.

  The product is then subjected to a recrystallization anneal. In this softened state of the recrystallized carbide-containing ferrite, prior to undergoing a heat treatment including high temperature austenitization (typically 950 ° C. to 1150 ° C., followed by quenching to an ambient temperature that mainly results in a martensite structure) The product is cut to give its final shape, for example the shape of a knife blade.

  In this martensitic state, the product has a higher and higher hardness when the carbon content is high, but it is also very brittle. An annealing treatment (typically 100 ° C. to 300 ° C.) is then performed to reduce brittleness without unduly reducing the hardness. The blade is then subjected to various operations such as grinding and polishing, giving it a cutting quality and an aesthetic appearance.

  None of the four quoted grades simultaneously allow good corrosion resistance, good surface condition and high hardness for reasonable cost.

  Grade EN1.4419 has good corrosion resistance and high hardness, but is expensive due to the addition of large amounts of Mo.

  Grade EN1.4034 has a high hardness but also has a poor surface appearance after polishing due to the presence of large amounts of carbides that do not dissolve during austenitization due to the high C content of this grade. In particular, considering that a part of Cr is trapped by undissolved carbides, the Cr content is not sufficiently high in the matrix, so that the corrosion resistance is insufficient. In addition, the cutting edge of the blade is often subject to crevice corrosion resulting from cleavage of large primary carbides that appear at the end of solidification during continuous casting.

  Grades EN 1.4021 and 1.4028 with low C content have lower hardness but do not have sufficient corrosion resistance due to excessively low Cr content.

  The present invention aims to solve the above-mentioned problems. In particular, it seeks to propose a martensitic stainless steel for cutting tools that is as cost effective as possible with good corrosion resistance, good polishing performance and high hardness.

To that end, the present invention has a composition in weight percent:
-0.10% ≦ C ≦ 0.45%; preferably 0.20% ≦ C ≦ 0.38%; better 0.20% ≦ C ≦ 0.35%; optimally 0.30% ≦ C ≦ 0.35%;
-Trace amount ≤ Mn ≤ 1.0%; preferably Trace amount ≤ Mn ≤ 0.6%;
-Trace amount ≤ Si ≤ 1.0%;
-Trace amount ≤ S ≤ 0.01%; preferably Trace amount ≤ S ≤ 0.005%;
-Trace amount ≤ P ≤ 0.04%;
-15.0% ≦ Cr ≦ 18.0%; preferably 15.0% ≦ Cr ≦ 17.0%; better 15.2% ≦ Cr ≦ 17.0%; optimally 15.5% ≦ Cr ≦ 16.0%;
-Trace amount ≤ Ni ≤ 0.50%;
-Trace quantity ≤ Mo ≤ 0.50%; preferably trace quantity ≤ Mo ≤ 0.01%; better trace quantity ≤ Mo ≤ 0.05%;
-Trace amount ≤ Cu ≤ 0.50%; preferably Trace amount ≤ Cu ≤ 0.3%;
-Trace amount ≤ V ≤ 0.50%; preferably 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%; preferably C + N ≧ 0.30%; better C + N ≧ 0.45%;
-Cr + 16N-5C ≧ 16.0%;
-Preferably 17Cr + 500C + 500N ≦ 570%;
The remainder relates to martensitic stainless steel characterized by iron and melt-derived impurities.

The microstructure preferably contains at least 75% martensite. The present invention is:
-Melting and casting a semi-finished product from steel having the above composition;
-Heating said semi-finished product to a temperature above 1000 ° C;
-Hot rolling it to obtain a sheet, rod or wire rod;
-Annealing the sheet, rod or wire rod at a temperature of 700-900 ° C; and
-It also relates to a method for producing a semi-finished product made from martensitic stainless steel, characterized in that a molding operation is carried out on said sheet, rod or wire rod.

  The semi-finished product can be a sheet and the forming operation can be cold rolling.

  The semi-finished product can be a rod or a wire rod, and the forming operation can be forging.

  The molded semi-finished product can then be austenitized at 950-1150 ° C. if its Cr content is 15-17%, then 20 ° C. at a rate of at least 15 ° C./sec. It can be cooled to the following temperature and then subjected to annealing at a temperature of 100-300 ° C.

  The molded semi-finished product can then be austenitized at 950-1150 ° C., then cooled to a temperature of 20 ° C. or less at a rate of at least 15 ° C./second, and then −220 to A low temperature treatment is performed at a temperature of −50 ° C., followed by annealing at a temperature of 100 to 300 ° C.

  The present invention also relates to a cutting tool manufactured from a semi-finished product prepared by the above method.

  The cutting tool can be a knife such as a knife blade, a food processor blade, a scalpel or a scissors blade.

  As will be appreciated, the present invention provides a martensitic stainless steel having a specific composition that contains a relatively high amount of nitrogen that is in a well-defined range, but does not contain high content and costly elements. Consisting of use for manufacturing cutting tools. In particular, a balance of Cr, C and N content is also necessary.

  Other features and advantages of the present invention are the accompanying figures showing the Vickers hardness evolution of steel under a load of 1 kg based on the amount of martensite after austenitizing, quenching and annealing of the steel according to the present invention. It will be apparent upon reading the following description which is given as an example with reference to 1 and made.

(No original text)

  The following support is submitted for the chemical composition of the steel according to the invention. The content ranges of the various elements that are considered to be preferential are independent of each other and the individual contents of C, N and Cr that are possible at the same time must exist between them according to the invention. It should be clear that any combination of the ranges defined in the following description can be considered in the context of the present invention as long as the relationship can be observed.

C increases the hardness in the martensite state after austenitization, rapid cooling and annealing. However, it also tends to precipitate M ₇ C ₃ primary carbides that can be scraped off during blade grinding or grinding during solidification, which degrades the surface appearance of the product. The location where it is found before polishing can also be a seat for tear corrosion. Excessive C content, depending on the austenitizing temperature, drastically reduces the excessively high C content in the austenite matrix that no longer makes it possible to obtain a sufficient martensite fraction after annealing, or Cr in the austenite matrix It also provides the persistence of undissolved M ₂₃ C ₆ carbide. It thus reduces corrosion resistance and adversely affects polishing performance.

The C content must therefore be at least 0.10% to obtain a sufficient hardness, and 0.45% or less to obtain good corrosion resistance and a satisfactory surface appearance after polishing. However, depending on the casting and solidification method used, this method takes the risk of not guaranteeing sufficient uniformity of the steel during solidification so as to avoid M ₇ C ₃ primary carbide precipitates, It may prove useful to limit the maximum C content a little more. In this case, the C content is 0.38%, preferably 0.20% ≦ C ≦ 0.38%; better 0.20% ≦ C ≦ 0.35%; optimally 0.30% It is better to limit it to ≦ C ≦ 0.35%.

  As will be seen later, in particular, the optimal range makes it possible to avoid high hardness while limiting carbide formation within an acceptable proportion, and to reduce the maximum C content over the more general range. The possible loss of hardness due can be compensated by the sufficient nitrogen present for it.

  Furthermore, the C content must satisfy the formula that ties it to the N content, as well as the N and Cr content, as will be explained later.

  Mn is a so-called gamma-generating element because it stabilizes the austenite structure. Excess Mn content results in an insufficient amount of martensite after austenitization and quenching, which results in reduced hardness. For this reason, the Mn content needs to be from trace-derived to 1.0%. Preferably, its content is limited to 0.6% to help obtain an optimally low Ms temperature.

  Si is a useful element in the steel manufacturing process. It is highly reducible and thus allows the reduction of Cr oxides in the steel reduction phase following the decarburization phase in AOD or VOD converters. However, the Si content in the final steel must be trace amount to 1.0% because it has a high temperature hardening effect that limits the possibility of this element being hot deformed during hot rolling or forging. There is. Preferably its content is limited to 0.6% to help obtain an optimally low Ms temperature.

  S and P are impurities that reduce high temperature ductility. P separates easily at the grain boundary and facilitates its cleavage. Furthermore, S reduces the resistance to corrosion caused by pitting by forming a compound containing Mn that serves as a starting point for this type of corrosion. Therefore, S and P contents need to be trace amounts to 0.01% by mass and 0.04% by mass, respectively. Preferably, the S content does not exceed 0.005% in order to better ensure sufficient corrosion resistance.

  Cr is an essential element with respect to corrosion resistance. However, its content needs to be limited because the high content risks reducing the temperature Mf (temperature at the end of the martensite transition) below the ambient temperature. This results in excessively incomplete martensite transition and insufficient hardness after austenitization and rapid cooling to ambient temperature. For these various reasons, the Cr content needs to be between 15.0 mass% and 18.0 mass%. However, the low temperature of the steel does not have an excessively high temperature Ms at the beginning of the martensitic transition, and therefore does not leave an excessive amount of retained austenite that limits the undesirable hardness and thus the tensile strength Rm in the martensitic steel. Limit Cr content to 15.0 to 17.0%, better 15.2 to 17.0%, even better 15.5 to 16.0%, especially when no treatment is performed. It is good. If necessary, the reduced corrosion resistance caused by the reduction of the maximum Cr content can be compensated by the high N content within the limits defined elsewhere.

However, the solubility of N in the liquid metal decreases when the Cr content decreases, and as a result, if it is less than 15% Cr, it will not be possible to retain sufficiently dissolved N in the liquid metal at the solidification temperature of the steel, This results in the formation of N ₂ bubbles during solidification, and N cannot compensate for the decrease in Cr with respect to corrosion resistance. This lower limit of Cr with respect to the solubility of N increases even when the molten steel static pressure during solidification decreases. Depending on the type of casting method and casting conditions used to protect against any risk of formation of N ₂ bubbles increases the minimum Cr content to 15.2%, or 15.5% from 15.0% It may be preferable.

  As explained below, the Cr content must also satisfy the formula that links it to the N and C content.

  Elements Ni, Cu, Mo and V are expensive and also reduce the temperature Mf. The content of each of these elements should therefore be limited to trace amounts to 0.50% by weight, preferably 0.10% or less with respect to Mo. Therefore, it is not necessary to add any after the raw material is melted. It is even more desirable that the Mo content not exceed 0.05% so as to help obtain an optimally low temperature Ms. For the same reason, it is preferred that the Cu content does not exceed 0.3% and the V content does not exceed 0.2%.

  Nb, Ti and Zr are so-called “stabilizing” elements, which means that they form more stable carbides and nitrides than Cr carbides and nitrides in the presence of N and C at high temperatures. . However, these elements can no longer readily dissolve during austenitization once their carbides and nitrides are formed during the manufacturing process, and the content of C and N in the austenite, and thus quenching This is undesirable because it limits the corresponding hardness of the later martensite. The content of each of these elements must therefore be trace amounts to 0.03%.

  The Al content is similarly trace amount to 0.010% so as to avoid the formation of Al nitride which reduces the austenite N content and hence the martensite hardness after quenching, with too high melting temperature. There must be.

  The O content is derived from the manufacturing method of steel and its composition. It constitutes a point where corrosion by pitting is likely to start, where the surface appearance of the product is not satisfactory, and too many and / or too large oxides that can cleave during polishing The trace amount should be up to 0.0080% (80 ppm) maximum to avoid inclusion formation. The O content also affects the mechanical properties of the steel, optionally optionally setting a limit below 80 ppm, which can traditionally not be exceeded depending on the end user's requirements. It may be possible.

  Pb, Bi and Sn content can be limited to traces from melting and each should not exceed 0.02% so as not to make the high temperature transition too difficult.

  Controlling the N content with respect to a clearly defined amount is an essential aspect of the present invention. Like C, it makes it possible to increase the hardness of martensite when it is in a solid solution without the disadvantages of the formation of precipitates during solidification. If it is not desired to have an excessively high C content so as to avoid the formation of too many precipitates, the addition of N can make up for the loss of hardness. Nitride forms at a lower temperature than carbide, thereby making it easier to put into solution during austenitization. The presence of N in the solid solution also improves the corrosion resistance.

However, excess N content no longer completes its dissolution during solidification, leading to the formation of N ₂ bubbles and forming blowholes that adversely affect the internal state of the metal during solidification of the steel.

  For these various reasons, the N content should be 0.10% to 0.20% by weight, preferably 0.15 to 0.20% by weight.

  The N content must also satisfy the formula that links it to the Cr and C content.

Indeed, the hardness of martensite depends on its C and N content. The inventors have shown that the hardening effect of these two elements is smaller and therefore the hardness of martensite depends on the overall C + N content. The following formula:
C + N ≧ 0.25%, preferably C + N ≧ 0.30%
Therefore, the inventors have established that the hardness after quenching and annealing is sufficient.

In one more preferred embodiment of the invention, the following formula:
C + N ≧ 0.45%
According to, higher hardness is obtained after quenching and annealing.

  The three elements affect the corrosion resistance. Although Cr and N are beneficial, in industrial practice, it is generally not possible for all of the Cr carbides to dissolve during austenitization for reasons of productivity and cost limiting process duration and temperature, so C Has a negative effect. Undissolved Cr carbide reduces the Cr content of the austenite matrix and thus reduces the corrosion content.

From the study of the corrosion resistance of martensitic steels with different mass contents of Cr, N and C, we have combined these various elements that make it possible to ensure a very good corrosion resistance. I found.
Cr + 16N-5C ≧ 16.0%
Preferred but not required conditions are:
17Cr + 500C + 500N ≦ 570%
It is.

  This condition represents a decrease in Ms of about 60 ° C., whereas that compliance is made possible by simultaneously satisfying the selected upper limits of C, N and Cr content, so this condition causes the temperature Ms to be excessive. It is possible to ensure that it is not expensive.

  The steel according to the invention is subjected to an austenitization test at different temperatures before quenching in water at 20 ° C. at a cooling rate of more than 100 ° C./second, then the percentage of dissolved carbides, in the resulting austenite and then in the quench In order to change the amount of carbide in the later martensite, annealing was performed at 200 ° C. Martensite content and Vickers hardness were measured for steels having the composition of Example I4 in Table 1 to follow the progress of hardness as a function of martensite content. The result is shown in FIG.

  FIG. 1 shows that as martensite hardens due to carbon enrichment, the hardness begins to increase with decreasing martensite content. The hardness reaches a maximum and then decreases when the amount of martensite becomes too low. At less than 75% martensite, the hardening of martensite no longer offsets the softening associated with the presence of residual austenite with lower hardness. For this reason, in one preferred embodiment of the invention adapted for the production of cutting tools from cast steel, austenitization, quenching at a rate of at least 15 ° C./s to below 20 ° C., followed by 100-300 ° C. Typically, the martensite content of the steel after annealing at a temperature of 200 ° C. is 75% or more.

  The acquisition of a high amount of martensite that can reach 100% is achieved when a low temperature treatment is performed after quenching to below 20 ° C., ie before quenching is performed at an annealing of 100 to 300 ° C. Better results can be achieved when carried out in a medium at a very low temperature of 50 ° C., typically in liquid nitrogen at −196 ° C. or in carbon dioxide snow at −80 ° C.

  If the martensite content does not reach 100%, the remaining microstructure is typically composed essentially of retained austenite. There may also be ferrite.

  As a non-limiting example, the following results show the advantageous properties conferred by the present invention.

  The composition of the various tested steel samples is shown in Table 1 and is expressed in weight percent. Values underlined are not in accordance with the present invention. We also reported C + N, Cr + 16N-5C, and 17Cr + 500C + 500N values for each sample.

  After casting, these steels are heated to a temperature above 1100 ° C., hot rolled to a thickness of 3 mm, annealed at a temperature of 800 ° C., then pickled and cold rolled to a thickness of 1.5 mm. did.

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

  The annealed steel sheet was then subjected to an austenitizing treatment at 1050 ° C. for 15 minutes and then quenched in water to a temperature of 20 ° C.

  After cutting the sheet into two parts, one of them was then submerged in a thermostatic bath at -80 ° C for 10 minutes in addition to mere quenching in water so that the effect of low temperature treatment could be evaluated. .

  A 1 hour anneal at 200 ° C. was then performed on the portions of each sheet.

  Table 2 shows the results of tests and observations performed on these steels. Underlined values correspond to performance levels that are considered inadequate.

  The internal state is evaluated in the raw solid state after injection and it can be seen that subsequent transfer operations do not damage it. The amount of martensite was measured after quenching in water at 20 ° C. and after low temperature treatment by quenching at −80 ° C., followed by annealing at 200 ° C. as the second of this quenching or quenching operation. If the amount of martensite is 75% or more after quenching in water at 20 ° C., the other results given in Table 2 relate to the condition of being quenched at 20 ° C. and then annealed at 200 ° C. If the amount of martensite is 75% or less after quenching in water at 20 ° C., the other results given in Table 2 are: low temperature treatment at −80 ° C. (quenching to very low temperatures, eg in carbon dioxide snow Next, it relates to the state after annealing at 200 ° C.

Corrosion resistance is evaluated by an electrochemical corrosion test by pitting in an environment composed of NaCl 0.02M at 23 ° C. and a pH of 6.6. An electrochemical test performed on 24 samples makes it possible to determine a potential E _0.1 with a basic pitting probability equal to 0.1 cm ⁻² . Corrosion resistance is considered unsatisfactory when the potential E _0.1 measured against a calomel electrode saturated with KCl (350 mV / ECS) is less than 350 mV. It is considered satisfactory when the potential E _0.1 is 350 mV / ECS to 450 mV / ECS. It is considered to be very satisfactory when the potential E _0.1 is 450 mV / ECS greater.

  The Vickers hardness is measured in accordance with the standard EN ISO 6507 with a diamond pyramid tip having a square base under a load of 1 kg and the thickness at a mirror-polished cut. The average of the obtained hardness is calculated by carrying out 10 notches. The hardness is considered insufficient when the average hardness is less than 500 HV. It is considered satisfactory when the average hardness is between 500 HV and 550 HV. It is considered very satisfactory when the average hardness is between 551 and 600 HV. It is considered outstanding when the average hardness is over 600 HV.

The polishing performance was performed by using a SiC 180, 320, 500, 800, and 1200 paper sequentially with a force of 30 N to perform flat polishing at the center thickness of the sample, and then with a force of 20 N, a diamond having a particle size of 3 μm and then 1 μm. Evaluation is performed by polishing with a sheet that has absorbed the paste. The surface is then observed with an optical microscope at a magnification of x100. Polishing performance is considered inadequate when the defect density (previously called “comet tail”) is 100 / cm ² or more. Polishing performance is considered satisfactory when this density is between 10 / cm ^{2 and} 99 / cm ² . The polishing performance is considered very satisfactory when this density is 1-9 / cm ² . Polishing performance is considered superior when this density is less than 1 / cm ² .

  The internal state is evaluated by observing the raw solid steel cuts by optical metallography at a magnification of x25. If a spherical cavity (blowhole) reflecting the formation of nitrogen bubbles upon solidification is observed, the internal state is not satisfactory and is indicated by the value “0” in Table 2. Otherwise, the internal state is considered satisfactory and is indicated by the value “1” in Table 2.

  The amount of martensite is determined by X-ray diffraction by measuring the intensity of the martensite characteristic line compared to the intensity of the austenite characteristic line. In all of the samples tested, it can be seen that only two phases are present. In general, it is not excluded that other phases may be slightly observed in the samples according to the invention. What should be considered in the context of the present invention is firstly the amount of martensite.

  75% or more martensite content after quenching at 20 ° C. and annealing at 200 ° C., or annealing at 20 ° C., low temperature treatment at −80 ° C., and 75% or more martensite content after annealing at 200 ° C. is there. A sample is considered unsatisfactory if one of these treatments fails to obtain a martensite content greater than 75%.

  Steels according to the invention I1 to I6 and steels I8 to I0 combine good corrosion resistance, hardness and polishing performance characteristics, have good internal conditions and a martensite content of 75% or more after quenching at 20 ° C.

  Steel I7 according to the present invention combines good corrosion resistance, hardness and polishing performance characteristics, has a good internal state and a martensite content of 75% or more (provided that the low temperature treatment is performed at -80 ° C). Indeed, after mere quenching in water at 20 ° C., the amount of martensite is still not sufficient, which is related to the presence of Cr in a higher amount than that of other samples according to the invention.

  In comparable amounts of N, the hardness is between samples I1, I2 with C of 0.10 to 0.20%, while sample I3 with C of 0.20 to 0.30%, In particular, it can be seen that C increases between I8, I9, and I10 where 0.30 to 0.35%.

  I14, where C is higher and N is at the same level as before, has a lower hardness because the martensite fraction starts to decrease after quenching due to the decrease in temperature Mf associated with the high value of 17Cr + 500C + 500N in total. (See Table 1). It can also be seen that corrosion resistance can be improved by increasing Cr, even in comparable amounts of N and other essential elements (see samples I8 and I9). Conversely, increasing Cr content tends to reduce hardness (see Samples I8, I10 and I11 whose composition differs greatly only with respect to Cr). Above 18% Cr, corrosion resistance can be increased, but will result in reduced C and N content to maintain satisfactory Ms, and the correct hardness will no longer be guaranteed.

  The reference steels R1 to R3 have an unsatisfactory Cr and N content that does not allow sufficient corrosion resistance, and a sum of C + N and / or Cr + 16N-5C.

  Reference steels R4 and R5 have insufficient Cr content. Without compensation by the addition of N, Steel R4 also has an insufficient Cr + 16N-5C combination that results in unsatisfactory corrosion resistance. For steel R5, the compensation for the Cr deficiency by the addition of N rebuilds satisfactory corrosion resistance, but the Cr content is no longer sufficient to completely dissolve N in the liquid metal, so it is no longer a good internal It does not make it possible to ensure the condition.

  Reference steel R6 has an excessively high C content and insufficient N content. An excessively high C content does not have sufficient polishing performance due to excessive carbide formation.

  Reference steel R7 has an excessively high N content which damages the internal state. The same applies to the reference steel R14. Reference steel R8 has an excess C content that results in poor polishing performance and too low martensite content even after low temperature quench at -80 ° C. Reference steel R9 contains a much excess of Cr that results in an insufficient amount of martensite even after low temperature quenching at −80 ° C.

  Reference steels R10 and R11 have an excessively low C content and insufficient C + N sum resulting in excessively low hardness. The reference steels R12 and R13 have a composition according to the invention with respect to the individual content of each element, but its Cr + 16N-5C content of less than 16.0% has a value of 16.0% with respect to this total Cr + 16N-5C. In all respects, including just over, it is insufficient to guarantee the corrosion resistance of steel according to the present invention.

  The steel according to the invention is used for good reasons in the manufacture of cutting tools such as scalpels, scissors, knife blades or food processor round blades.

Claims (9)

Composition is in weight percent:
-0.10% ≦ C ≦ 0.45%; preferably 0.20% ≦ C ≦ 0.38%; better 0.20% ≦ C ≦ 0.35%; optimally 0.30% ≦ C ≦ 0.35%;
-Trace amount ≤ Mn ≤ 1.0%; preferably Trace amount ≤ Mn ≤ 0.6%;
-Trace amount ≤ Si ≤ 1.0%;
-Trace amount ≤ S ≤ 0.01%; preferably Trace amount ≤ S ≤ 0.005%;
-Trace amount ≤ P ≤ 0.04%;
-15.0% ≦ Cr ≦ 18.0%; preferably 15.0% ≦ Cr ≦ 17.0%; better 15.2% ≦ Cr ≦ 17.0%; optimally 15.5% ≦ Cr ≦ 16.0%;
-Trace amount ≤ Ni ≤ 0.50%;
-Trace quantity ≤ Mo ≤ 0.50%; preferably trace quantity ≤ Mo ≤ 0.01%; better trace quantity ≤ Mo ≤ 0.05%;
-Trace amount ≤ Cu ≤ 0.50%; preferably Trace amount ≤ Cu ≤ 0.3%;
-Trace amount ≤ V ≤ 0.50%; preferably 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%; preferably C + N ≧ 0.30%; better C + N ≧ 0.45%;
-Cr + 16N-5C ≧ 16.0%;
-Preferably 17Cr + 500C + 500N ≦ 570%;
The balance is martensitic stainless steel characterized by iron and manufacturing-derived impurities.   The steel according to claim 1, characterized in that its microstructure comprises at least 75% martensite. The semi-finished product is produced from steel having the composition according to claim 1 and poured;
-Heating said semi-finished product to a temperature above 1000 ° C;
-Hot rolling it to obtain a sheet, rod or wire rod;
-Annealing the sheet, rod or wire rod at a temperature of 700-900 ° C; and
A method for producing a semi-finished product made from martensitic stainless steel, characterized in that a molding operation is carried out on said sheet, rod or wire rod.   The method according to claim 3, wherein the semi-finished product is a sheet and the forming operation is cold rolling.   The method according to claim 3, wherein the semi-finished product is a rod or a wire rod and the forming operation is forging.   The steel has the composition of claim 2 and the shaped semi-finished product is then austenitized at 950-1150 ° C and then cooled to a temperature of 20 ° C or less at a rate of at least 15 ° C / second. Then, it is subjected to annealing at a temperature of 100 to 300 ° C., The method according to claim 3.   The steel has the composition of claim 1 or 2 and the shaped semi-finished product is then austenitized at 950-1150 ° C and then at a rate of at least 15 ° C / second to a temperature of 20 ° C or less. The method according to any one of claims 3 to 5, characterized in that it is cooled and then subjected to a low temperature treatment at a temperature of -220 to -50 ° C and then annealed at a temperature of 100 to 300 ° C. .   A cutting tool manufactured from a semi-finished product prepared by the method according to any one of claims 3 to 7.   The cutting tool according to claim 8, wherein the cutting tool is a knife such as a knife blade, a food processor blade, a knife or a scissors blade.

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