JP2010539325A - Martensitic stainless steel, manufacturing method of parts made from this steel, and parts manufactured by this method - Google Patents

Abstract

  0.05% ≦ N ≦ 0.15%, 10% ≦ Cr ≦ 12.4 in terms of weight percentage, 0.22% ≦ C ≦ 0.32%, 0.33% ≦ C + N ≦ 0.43% %, 0.10% ≦ V ≦ 0.40%, 0.10 ≦ Mo ≦ 1.0%, trace amount ≦ Ni ≦ 1.0%, trace amount ≦ Mn ≦ 1.0%, trace amount ≦ Si ≦ 1.0%, trace ≦ W ≦ 1.0%, trace ≦ Co ≦ 1.0%, trace ≦ Cu ≦ 1.0%, trace ≦ Ti ≦ 0.010%, trace ≦ Nb ≦ 0.050%, trace ≤ Al ≤ 0.050%, trace ≤ S ≤ 0.020%, trace ≤ O ≤ 0.0040%, trace ≤ P ≤ 0.03%, trace ≤ B ≤ 0.0050%, trace amount ≦ Ca ≦ 0.020%, trace amount ≦ Se ≦ 0.010%, trace amount ≦ La ≦ 0.040%, trace amount ≦ Ce ≦ 0.040%, and the balance , Iron and manufacturing work And wherein the result is an impurity caused, martensitic stainless steel.

Description

  The present invention relates to steelmaking, and more precisely to martensitic stainless steel intended for the production of molds that produce plastic materials, for example using injection.

  In order to produce molds for material injection, the industry has a chromium content of 12 to 15% (in weight percent as well as all the contents shown in the rest of the specification), silicon less than 1% Content of manganese less than 1%, carbon content of 0.16% to 0.45%, which is inevitably brought about by manufacturing operations, and generally has a nitrogen content of up to 0.03% Uses AISI 420 group stainless steel. In general, the vanadium content does not exceed 0.1%, which is the result of simple dissolution of the raw materials. Similarly, the molybdenum content is a result of the melting of the raw material and does not exceed 0.2% unless added from 0.2 to 1.0% to improve corrosion resistance. More specifically, the steel using Reference Example X40Cr14, which can exceed a hardness of 50 HRC, due to a carbon content of 0.36 to 0.45%, provides significant wear resistance.

In view of the anticipated applications, the effectiveness of the material must be evaluated by obtaining a good compromise between the following properties:
The abrasion resistance desired in order to be able to produce the maximum number of parts with a guaranteed geometric regularity, including plastic materials rendered wearable by the accumulation of fibers or other reinforcing additives; This wear resistance is provided by a high level of hardness;
-Sufficient toughness to avoid heat treatment, assembly / decomposition processing or crushing during use; in these steels, which are particularly brittle, this property has been found to be in conflict with one of the above, and as the hardness increases, the toughness decreases Do;
-Good polishability that allows the surface polishing quality to be easily achieved on the mold surface to produce parts of plastic material with a smooth and uniform surface appearance; Must be able to maintain a controlled state;
-Sufficient corrosion resistance to avoid drilling, discoloration, mold storage and changes in polishing conditions during use in the context of the production of plastic materials that are slightly or reasonably chemically aggressive; the most active substances are For example, by salting out chloride ions, other groups of steels or alloys are required.

After machining the blank (blank) to near final shape dimensions, the mold is subjected to the following heat treatment operations in a furnace in a controlled atmosphere:
Increase to a quenching temperature in the range of 1000 to 1050 ° C. and then keep in this range for several tens of minutes;
-Quenching in a gas atmosphere to a temperature on the order of 80 ° C;
-Increase to the temperature of the two tempering cycles.

Two temperature ranges are generally proposed for tempering:
-Low temperature tempering: 150 to 250 ° C,
Tempering at 490/530 ° C. in the second hardening zone of the steel.

  Theoretically, both two successive tempering processes are performed in the same range.

  Careful consideration must be given regarding the correct selection of processing parameters.

  With regard to quenching, it is metallurgically recommended to seek a high quenching temperature in order to achieve the preferred martensitic microstructure. However, the high quenching temperature creates a residual stress that can promote deformation and lead to fracture. In particular, the gas pressure is limited to a value of 2 to 4 bar.

  When quenching stops, crushing can occur if cooling continues to drop to the ambient atmosphere before continuing the tempering process. However, the usual choice of stopping cooling at about 80 ° C. is the risk of maintaining residual austenite, especially if the subsequent tempering process is fixed below 500 ° C. and consequently the desired nominal hardness cannot be obtained. With sex.

  In the tempering process, only the low temperature selection allows the restriction to be partially eliminated, and the steel composition and quench cycle eliminate residual austenite with tempering without decomposing residual austenite. If it is possible to maintain, the desired hardness is not achieved. The high temperature tempering treatment decomposes austenite and relieves residual stress, but reduces strength and corrosion resistance.

  There is also a problem with the cost of these steels due to the high content of alloying elements they require that must be able to be minimized without compromising the desired properties.

The object of the present invention is to define an economical steel composition in applications including molds in the manufacture of articles of plastic material having the following properties, for reference examples AISI 420 and X40Cr14:
A preferential equivalent hardness of 49 to 55 HRC in the processing state to withstand abrasion;
-Equivalent wear resistance;
-Improved strength with equal hardness;
-Improved abrasiveness;
-Have these properties under industrial heat treatment conditions comparable to general conditions.

To this end, the present invention is in weight percent,
0.22% ≦ C ≦ 0.32%,
0.05% ≦ N ≦ 0.15% under the condition of 0.33% ≦ C + N ≦ 0.43%,
10% ≦ Cr ≦ 12.4%,
0.10% ≦ V ≦ 0.40%,
0.10 ≦ Mo ≦ 1.0%,
Very small amount ≦ Ni ≦ 1.0%,
Very small amount ≦ Mn ≦ 1.0%,
Very small amount ≦ Si ≦ 1.0%,
Very small amount ≦ W ≦ 1.0%,
Very small amount ≦ Co ≦ 1.0%,
Very small amount ≦ Cu ≦ 1.0%,
Trace amount ≦ Ti ≦ 0.010%,
Very small amount ≦ Nb ≦ 0.050%,
Trace amount ≦ Al ≦ 0.050%,
Very small amount ≦ S ≦ 0.020%,
Very small amount ≦ O ≦ 0.0040%,
Very small amount ≦ P ≦ 0.03%,
Very small amount ≦ B ≦ 0.0050%,
Very small amount ≦ Ca ≦ 0.020%,
Very small amount ≦ Se ≦ 0.010%,
Very small amount ≦ La ≦ 0.040%,
Very small amount ≦ Ce ≦ 0.040%,
Including
Relates to martensitic stainless steel, characterized in that the balance is iron and impurities introduced by manufacturing operations.
Preferably, 0.08% ≦ N ≦ 0.12%.
Preferably, 11.0% ≦ Cr ≦ 12.4%.
Preferably, 0.15% ≦ V ≦ 0.35%.
Preferably, a very small amount ≦ Si ≦ 0.5%.
Preferably, 0.10% ≦ Mo + W / 2 ≦ 1.20%.
Preferably, a very small amount ≦ Ti ≦ 0.003%.
Preferably, a very small amount ≦ Nb ≦ 0.010%.
Preferably, a very small amount ≦ O ≦ 0.0015%.
Preferably, a very small amount ≦ S ≦ 0.003%.
Preferably, a very small amount ≦ Mn + Cu + Co ≦ 1.8%.

The present invention also provides
Producing, casting, forging, or rolling and annealing the steel of the type described above;
Machining the steel to give the surface the shape of the part;
Austenitizing the machined steel at a temperature of 990 to 1040 ° C., preferably 1000 to 1030 ° C .;
Quenching the austenitized steel at a rate of 10 to 40 ° C./min in a temperature range of 800 to 400 ° C .;
Performing two tempering treatments on the quenched steel to give its surface its final hardness;
It relates to a method for manufacturing a martensitic stainless steel part.

  In order to obtain a hardness of 49 to 55 HRC, the tempering process is at a minimum of 200 to 400 ° C., preferably 300 to 380 ° C., respectively, ensuring that the nominal temperature is maintained in the core for at least 1 hour. It can be done for 2 hours.

  In order to obtain a hardness of 42 to 50 HRC, the tempering process can be performed at a temperature of 530 to 560 ° C. for a minimum of 2 hours, respectively, ensuring that the nominal temperature is maintained in the core for at least 1 hour. .

  The invention also relates to a martensitic stainless steel part, characterized in that the element manufactured using said method is manufactured by the method described above.

  This can be a mold element intended for the manufacture of articles of plastic material.

  As will be appreciated, the present invention is located simultaneously at the lower end of the normally required range of carbon and chromium content while imposing precise conditions on other elements that are present or limited or must be avoided. Or, based on the steel composition, which in some cases is less about the chromium content. The manufacturing method is related to this composition.

  The inventor has focused on the actual consideration of the properties of the steel following industrial processing, as described above, rather than following the manufacturing operations, especially laboratory conditions. This study was conducted with the aim of optimizing the behavior of the alloy elements to limit the amount produced.

  The main considerations brought to the present invention are as follows.

Abrasiveness and surface quality of the polished state of steel are degraded by the following:
Non-metal oxides that do not reflect light and that further break down or become exposed to contact with the abrasive and leave streaks or “comet tails” on the mold surface Presence of inclusions;
-Due to the fact that the soft region yields more rapidly than the hard region, it causes vibrations during polishing, spontaneously forms during solidification of the rod, and stiffer regions or lines that alternate with soft regions or lines. Separation in dendritic tissue generated on the surface of the mold;
-Presence of undissolved micrometer chromium carbide during quenching operation.

  In general, its strength is reasonable in this type of steel, but becomes lower at a given hardness as the chromium content increases. It can be improved by balancing the composition and in particular the addition of nickel and manganese that allows the austenite residue to be retained during the quenching operation. However, this solution, which no longer has an effect when the tempering operation is carried out above 500 degrees, is found to be unstable and delays the generation of hardness. It is not retained, especially as it is not compatible with the desired reduction in alloy element content.

To achieve the above objective, it determines:
-On the one hand, producing the steel according to well-known methods that limit the presence of oxidized non-metallic inclusions, thereby giving the steel a low oxygen content,
And, on the other hand, balance between elements to significantly reduce alloy elements, introduce nitrogen, increase strength, reduce intradendritic separation and limit micrometer precipitate density To optimize.

FIG. 2 shows micrographs of a reference steel and two steel samples according to the invention. It is a figure which shows the influence of the temperature of two tempering processes in the corrosion resistance of steel by this invention. It is a figure which shows the influence of the temperature of the tempering process in corrosion resistance. It is a figure which shows interaction with chromium content and the rapid cooling rate in corrosion resistance. FIG. 3 shows the hardness of the steel according to the invention and the reference steel according to the temperature of the tempering treatment.

The invention will be better understood from the following detailed description given with reference to the accompanying drawings in which:
FIG. 1 shows micrographs of samples of a reference steel and two steels according to the invention, showing the density and distribution of micrometer carbides in the state of use of these steels.
FIG. 2 shows the effect of the temperature of the two tempering treatments on the corrosion resistance of the steel according to the invention.
FIG. 3 shows the effect of tempering temperature on corrosion resistance.
FIG. 4 shows the interaction between the chromium content and the quenching rate in corrosion resistance.
FIG. 5 shows the hardness of the steel according to the invention and the reference steel according to the temperature of the tempering treatment.

  Table 1 presents the composition of the samples examined. The sample “reference example” corresponds to a general type of X40Cr14 steel. The samples of Examples 1 to 7 are not according to the invention, but make it possible to eliminate the disadvantages caused by not meeting all the conditions required by the invention. Samples “Invention 1” and “Invention 2” are according to the invention.

  Accordingly, the object of the present invention is to achieve a hardness of 52 HRC with strength and corrosion resistance that is greater than or equal to the reference steel AISI420 or X40Cr14 in its normal use, preferably at low temperatures (less than 400 ° C.) according to the range of industrial quenching rates Is to provide an optimized steel that is intended to be processed according to a subsequent double tempering process.

  Furthermore, the object of the present invention can be to reduce manufacturing costs, avoid the presence of untreated austenite after quenching operations, and reduce the degree of dendritic separation that is detrimental to strength and polishing quality. The limit is to limit the addition of alloying elements, especially metal elements.

  For this reason, the inventor has reached the following results relating to the definition of the steel composition of the present invention.

  The nitrogen content should be from 0.05% to 0.15%, preferably from 0.08% to 0.12%. Therefore, this element is essential for forming type V (C, N) carbonitrides that can avoid grain expansion during austenitization after chromium carbide is dissolved, so Present systematically by content. However, excess content is detrimental when exceeding the solubility limit in the solid state and will be a source of metallurgical defects. Nitrogen combines with carbon to give hardness and is related to corrosion resistance. The nitrogen content can be adjusted by supplying gaseous nitrogen when the molten steel is produced.

  Carbon combines primarily with nitrogen to contribute to the required hardness. Considering the hardness required after tempering at low temperatures, the percentage should be between 0.22% and 0.32%. Furthermore, the sum of C + N must be 0.33% to 0.43% to allow the desired hardness to be achieved after tempering.

  Chromium gives the steel its corrosion resistance. In view of the industrial quenching rate used and the tempering range selected and according to the mechanism explained above, its content is 10 to 12.4%, preferably 11.0 to 12.2. Must be 4%.

  Vanadium should be present in a content of 0.10% to 0.40%, preferably 0.15% to 0.35%. Its presence is essential to form sufficiently dense micro and nano precipitates with carbon and nitrogen that can avoid particle expansion. Excess content is detrimental due to excessive fixation of carbon that would impair curing and due to the formation of carbides during solidification, separate or within clusters, which is undesirable for strength and polishing state quality. I will.

  Molybdenum complements the behavior of chromium with respect to corrosion resistance; it is present in a percentage of 0.10 to 1.0% for reuse operations or by deliberate addition. A higher content would be detrimental due to the increased degree of dendritic separation and because of the risk of forming delta ferrite.

  Nickel may be present in a content of less than 1.0%, especially due to raw material contributions. The beneficial effect of addition within this limit is not seen with respect to toughness. However, higher contents would be able to maintain untreated austenite in the treated state.

  Manganese is an essential element in this type of steel because of the manufacturing method and available raw materials. No beneficial effect is seen, which is found to be necessary to limit its concentration to 1.0% in order to avoid untreated austenite after heat treatment.

  Silicon is inevitably present for steel production and deoxidation. The inclusion of silicon can affect the solidification process and the delta / gamma conversion and, as a result of the presence of this phase at the end of solidification before forging, can result in the presence of delta ferrite or local separation. The amount should be limited to 1.0%, preferably 0.5%.

  Tungsten can be present in a content of less than 1.0% without having any favorable or deleterious effect on the product. Nevertheless, because of its individual operation or synergistic effect with molybdenum, it is a local precipitation due to the presence of delta ferrite in the state of use or the presence of delta ferrite at every stage of thermomechanical processing. May promote the presence of objects or separations. It would be desirable to meet the condition of 0.10% ≦ Mo + W / 2 ≦ 1.20.

  Cobalt and copper do not have a recognized beneficial effect, but may be present at a content of 1.0% or less: higher content may promote the presence of untreated austenite.

  In order to limit the risk of the presence of untreated austenite, the total content of Mn, Cu and Co is desirably 1.8% or less.

  Titanium and niobium are highly reactive elements that form very hard precipitates that are detrimental to the quality of the polished state. Its content must be kept as low as possible: up to 0.010% for Ti, preferably up to 0.003%, up to 0.050% for Nb, preferably up to 0.00. 010%.

  Aluminum added in steel deoxidation may remain present in oxide inclusions that are very detrimental to the polishing conditions. The level of addition must be compatible with the manufacturing method used. The aluminum does not result in the presence of a large amount of aluminum oxide or silico aluminates content that results in an acceptable content of oxygen in excess (0.0040%, preferably 0.0015%) Under conditions, a maximum content of 0.050% is allowed.

  Sulfur is limited to a content of less than 0.003% to avoid the formation of sulfur content. However, optionally, it promotes the formation of spherical sulfides to improve machinability for some damage to the quality of the polished state, preferably other factors (Se up to 0.010% Se, 0 It is possible to choose to make voluntary additions in the range of 0.003 to 0.020% combined with .020% Ca, 0.040% La, 0.040% Ce)) It is.

  The maximum oxygen content is 0.0040%, preferably 0.0015%. This factor is an indicator of inclusion density, which, if too high, is detrimental to the surface polishing condition. This content must be as low as possible, and the method for producing the steel must be selected as a result. In fact, known methods allow values as small as O = 5 ppm under economically acceptable conditions.

  The phosphorus content is limited to 0.03%, which is a common content in this class of steel. The deleterious effects of P are not noted in this range.

  Boron can be added to improve quenching capacity with a content not exceeding 0.0050%.

  The preferred contents indicated in some elements may be given alone, but need not necessarily be combined with the other preferred contents indicated.

  Elements not mentioned may be present at a content level of impurities resulting from manufacturing that does not modify the properties that the present invention seeks to optimize.

  The product is a general technical requirement for special high quality steels intended for use in cast articles of plastic materials in order to limit the content and separation of inclusions in order to obtain a high quality polished state. Must be manufactured according to. This production must have a stage for deoxidation and removal of the contents in the metallurgical reactor after melting. Preferably, the remelting operation with electrodes that can be consumed under the slag improves the purity of the inclusions, especially for the production of large molds and to obtain high quality polishing conditions, In particular, nitrogen may be distributed in a uniform manner throughout the mass.

  A thermodynamic transformation using a forging or rolling finish with an annealing operation must be subsequently performed to complement the uniformity and tightness of the microstructure.

  After machining the part into the final shape and prior to working, the product is about 1020 ° C. to obtain a hardness of about 52 HRC ± 2 HRC, typically 49 to 55 HRC, according to the preferred working method. Austenitization at (990 to 1040 ° C., preferably 1000 to 1030 ° C.), eg controlled cooling operation at a rate of 10 to 40 ° C./min to fit the part size under neutral gas pressure, then 200 Must be subjected to a heat treatment operation comprising two tempering operations at temperatures from to 400 ° C, preferably from 300 to 380 ° C.

  Optionally, in applications that require hardness greater than 50 HRC, the steel defined by the present invention is less than 530 due to the hardness being 50 HRC or less and 42 HRC or more under conditions where corrosion resistance appears to be sufficient. It can be processed using double tempering at 560C to 560C.

In the reference steel, chromium carbide (M ₂₃ C ₆ ) present in the delivery state is dissolved during austenitization preceding the quenching operation and the temperature maintained is 1020 / Limited to 1030 ° C. However, an enormous amount of carbides distributed in a non-uniform manner remains at this melting temperature. Vanadium carbonitride at an appropriate quenching temperature by replacing about 0.10 to 0.15% of the carbon content with nitrogen, reducing the chromium content by about 2%, and simultaneously introducing vanadium. Particles fixed by nanometer deposition of the object V (C, N) do not grow while most of the chromium carbide is dissolved.

  In the three compositions examined, a comparative calculation of the equilibrium at 1030 ° using a thermodynamic simulation with the software THERMOCALC (commonly used by metallurgists) shows this change (see Table 2). .

  The effective density of micrometer carbides observed in the industrial product shown in FIG. 1 is effectively reduced in a considerable manner between the reference composition and the composition of the present invention, which is Constitutes a favorable factor in the quality of the polished state.

In the reference steel, the ability of corrosion resistance is theoretically in accordance with basic knowledge related specifically to the chromium content available in the matrix; theoretical calculations show that carbides that are not dissolved during austenitization It indicates that about 0.9% of chromium is fixed. This chromium content, which is not available in corrosion resistance, will be less than 0.1% in experimental grades alloyed with vanadium and nitrogen. According to the following equation, which allows the composition to be classified according to resistance to pitting and applied to the effective composition of the matrix, the experimental composition according to Table 2 It can be seen that inventions 1 and 2 which are products have coefficients close to the reference example:
P. R. E. (Pitting Resistance Equivalent) =% Cr + 3.3 ×% Mo + 30 ×% N.

In addition to the above discussion describing the potential in the state prior to quenching, it is advantageous to make measurements in the effective state of the metal at the stage of use. The electrochemical method performed in standard ASTM G 108 is to polarize the sample for 15 minutes in an aqueous solution of H ₂ SO ₄ at 1% by weight at −550 mV / ECS and then back and forth at −60 mV / mn from −550 mV to +500 mV. It involves performing a scanning operation. The characteristic line intensity / potential at return may have two peaks, one (peak 1) is due to matrix dissolution and the second (peak 2) is At higher potential, it relates to dissolution in the region of chromium carbide precipitates. Steel becomes more sensitive to corrosion as the melting current increases. Characteristic lines are presented in FIGS.

  Current experiments in the reference steel show that the two parameters of heat treatment have a great influence on the corrosion resistance while obtaining the desired hardness of about 52 HRC: tempering temperature and quenching rate.

  These effects have been demonstrated by laboratory tests.

(A) Temperature effect:
FIG. 2 shows that in casting invention 1, this steel becomes very sensitive to corrosion in the tempering operation performed in the hardening region of about 500 ° C. Low temperature tempering operations are therefore preferred (200 to 380 ° C.) if corrosion resistance is a feature that must be commanded in the expected application.

  This trend was confirmed in all of the compositions tested, as shown in FIG. This shows the effect of a double tempering operation for 2 hours at 380 ° C. or at a temperature close to 500 ° C. in corrosion resistance considering the corrosion current at peak 2 in FIG. The exact temperature of the double tempering at about 500 ° C. is adjusted so that the exact temperature allows the same hardness as after the double tempering operation at 380 ° C. to be obtained. It can be seen in particular that the sample according to the invention has a corrosion resistance very comparable to that of the reference sample in a double tempering operation at 380 ° C.

  It is demonstrated that at low tempering temperatures, the corrosion resistance decreases slightly between 200 ° C. and 380 ° C. and rapidly degrades above 400 ° C.

  In order for the tempering operation to have the desired effect, they must last for at least 2 hours and their nominal temperature must be maintained in the core of the part for at least 1 hour.

(B) Effect of quenching rate Unexpectedly, as shown in FIG. 4 which compares the experimental castings to two that are distinguished from each other only by their chromium content, the increase in content of this element is Corrosion resistance is not improved under industrial quenching conditions using cooling rates on the order of 20 ° C / min in the range of 900/400 ° C. The low quench rate results in the appearance of peak 2, indicating carbide or nitride precipitation, the extent of which increases as the chromium content increases and the matrix corrosion current increases (peak 2).

  These results were confirmed and confirmed in various compositions.

  According to the present invention, a quenching rate of 10 to 40 ° C./min is selected in the temperature range of 800 to 400 ° C., which can be appropriate with technical knowledge of the heat treatment operation.

  Consequently, for industrial quenching operations, the best corrosion resistance is obtained using a low temperature tempering operation, and in this form, a change in chromium content in the range of 10.5 to 15% results for this alloy element. Does not support the normally recognized beneficial effects.

The same undesirable effect of reducing the quench rate and increasing the tempering temperature is found with respect to toughness. This property is generally simply evaluated from the general mechanical properties of region extension and reduction during tensile and impact bending energy testing on V-shaped unscored bars having dimensions of 55 × 10 × 7 mm. Is done. In related tests, a 16 ° C./min quench test was performed on all samples followed by a 2 hour double tempering operation. The results shown in Table 3 indicate the following:
-In composition invention 2 mentioned as an example, the negative effect of reducing the quenching rate;
-Embrittlement effect of double tempering operation at about 550 ° C;
Excellent properties of the hardness / toughness compromise of the two steels of the present invention over the reference example in double tempering at low temperatures (380 ° C.).

  The composition of the present invention, as shown in FIG. 5, is rapidly quenched under industrial conditions and double-baked at 380 ° C., despite softening occurring in this range in this type of steel from an untreated quenched material. It makes it possible to obtain a hardness of 52 HRC or higher after returning.

Claims (16)

By weight percentage,
0.22% ≦ C ≦ 0.32%,
0.05% ≦ N ≦ 0.15% under the condition of 0.33% ≦ C + N ≦ 0.43%,
10% ≦ Cr ≦ 12.4%,
0.10% ≦ V ≦ 0.40%,
0.10 ≦ Mo ≦ 1.0%,
Very small amount ≦ Ni ≦ 1.0%,
Very small amount ≦ Mn ≦ 1.0%,
Very small amount ≦ Si ≦ 1.0%,
Very small amount ≦ W ≦ 1.0%,
Very small amount ≦ Co ≦ 1.0%,
Very small amount ≦ Cu ≦ 1.0%,
Trace amount ≦ Ti ≦ 0.010%,
Very small amount ≦ Nb ≦ 0.050%,
Trace amount ≦ Al ≦ 0.050%,
Very small amount ≦ S ≦ 0.020%,
Very small amount ≦ O ≦ 0.0040%,
Very small amount ≦ P ≦ 0.03%,
Very small amount ≦ B ≦ 0.0050%,
Very small amount ≦ Ca ≦ 0.020%,
Very small amount ≦ Se ≦ 0.010%,
Very small amount ≦ La ≦ 0.040%,
Very small amount ≦ Ce ≦ 0.040%,
Including
Martensitic stainless steel, characterized in that the balance is iron and impurities brought about by manufacturing operations.   The martensitic stainless steel according to claim 1, wherein 0.08% ≦ N ≦ 0.12%.   The steel according to claim 1, wherein 11.0% ≦ Cr ≦ 12.4%.   Steel according to any one of claims 1 to 3, characterized in that 0.15% ≤ V ≤ 0.35%.   The steel according to any one of claims 1 to 4, wherein a very small amount ≤ Si ≤ 0.5%.   Steel according to any one of claims 1 to 5, characterized in that 0.10% ≤Mo + W / 2≤1.20%.   The martensitic stainless steel according to any one of claims 1 to 6, wherein a very small amount ≤ Ti ≤ 0.003%.   The steel according to any one of claims 1 to 7, wherein a very small amount ≤ Nb ≤ 0.010%.   The martensitic stainless steel according to any one of claims 1 to 8, wherein a very small amount ≦ O ≦ 0.0015%.   The steel according to any one of claims 1 to 9, wherein a very small amount ≤ S ≤ 0.003%.   The steel according to any one of claims 1 to 10, wherein a very small amount ≤ Mn + Cu + Co ≤ 1.8%. Producing, casting, forging, or rolling and annealing the steel according to any one of claims 1 to 11;
Machining the steel to give the surface the shape of the part;
Austenitizing the machined steel at a temperature of 990 to 1040 ° C., preferably 1000 to 1030 ° C .;
Quenching the austenitized steel at a rate of 10 to 40 ° C./min in a temperature range of 800 to 400 ° C .;
Performing two tempering treatments on the quenched steel to give its surface its final hardness;
A method of manufacturing a martensitic stainless steel part.   In order to obtain a hardness of 49 to 55 HRC, the tempering process is at a minimum of 200 to 400 ° C., preferably 300 to 380 ° C. respectively, ensuring that the nominal temperature is maintained in the core for at least 1 hour. 13. A method according to claim 12, characterized in that it is performed for a limited time of 2 hours.   In order to obtain a hardness of 42 to 50 HRC, the tempering process is performed at a temperature of 530 to 560 ° C. for a minimum of 2 hours, respectively, ensuring that the nominal temperature is maintained in the core for at least 1 hour. The method according to claim 12, characterized in that:   Martensitic stainless steel part, characterized in that the element manufactured using the method is manufactured according to any one of claims 12 to 14.   16. Part according to claim 15, characterized in that it is a mold element intended for the manufacture of articles of plastic material.