EP2188402A1

EP2188402A1 - Martensitic stainless steel, method for making parts from said steel and parts thus made

Info

Publication number: EP2188402A1
Application number: EP08830336A
Authority: EP
Inventors: André GRELLIER
Original assignee: Aubert and Duval SA
Current assignee: Aubert and Duval SA
Priority date: 2007-09-10
Filing date: 2008-08-25
Publication date: 2010-05-26
Anticipated expiration: 2028-08-25
Also published as: FR2920784A1; CN101861407A; JP2010539325A; CA2698889A1; EP2188402B1; KR20100059965A; FR2920784B1; WO2009034282A1; US20100276038A1; RU2010114173A

Abstract

The invention relates to a martensitic stainless steel characterised in that it comprises in weight percent: - 0.22% < C < 0.32% - 0.05% < N < 0.15%, with 0.33% < C+N < 0.43% - 10% = Cr = 12.4% - 0.10% = V = 0.40% - 0.10% = Mo = 1.0% - traces < Ni = 1.0% - traces < Mn < 1.0% - traces < Si < 1.0% - traces = W = 1.0% - traces < Co < 1.0% - traces = Cu = 1.0% - traces < Ti < 0.010% - traces = Nb = 0.050% - traces = Al = 0.050% - traces < S < 0.020% - traces < O < 0.0040% - traces < P < 0.03% - traces < B < 0.0050% - traces < Ca < 0.020% - traces < Se < 0.010% - traces < La < 0.040% - traces < Ce < 0.040%, the balance consisting of iron and impurities resulting from the production. The invention also relates to a method for producing a part made of such a steel and to the part thus obtained, as a mould element for the production of plastic articles.

Description

Martensitic stainless steel, process for manufacturing parts made of this steel and parts thus produced.

The present invention relates to iron and steel, more specifically, martensitic stainless steels, intended for example for the manufacture of molds for the production of plastics by injection.

For the production of plastic injection molds, the industry uses stainless steels of the AISI 420 family with a chromium content of 12 to 15% (in percentages by weight, like all the contents indicated in the rest of the text). , a silicon content of less than 1%, a manganese content of less than 1%, a carbon content of from 0.16 to 0.45%, and a nitrogen content which is that naturally resulting from the preparation and generally up to 0.03%. Generally, the vanadium content does not exceed 0.1% and results from the simple melting of the raw materials. Similarly, the molybdenum content results from the melting of the raw materials and does not exceed 0.2%, unless 0.2 to 1.0% is added to improve the corrosion resistance. . More specifically, the X40Cr14 nomenclature steel, capable of exceeding a hardness of 50 HRC by virtue of its carbon content of 0.36-0.45%, offers an appreciable abrasion resistance. Given the intended application, the performance of the material must be evaluated by obtaining a good compromise between the following properties:

the desired wear resistance in order to be able to produce the maximum number of parts with a guaranteed geometrical regularity, including with plastics materials made abrasive by integrating fibers or other reinforcing additives; this resistance to wear is conferred by a high hardness;

- sufficient toughness to prevent breaks during heat treatment, assembly-disassembly operations or service; for these notably fragile steels, this property is contradictory with the previous one, the tenacity decreasing when the hardness increases;

- good polishability making it possible to easily obtain a quality polish on the surface of the mold in order to produce plastic parts; with a smooth and uniform surface appearance; the steel must also be able to maintain this polished state as long as possible,

- sufficient corrosion resistance to prevent pitting, tarnishing, polish deterioration during mold storage and during service, in the context of the production of low or medium chemically aggressive plastics; the more active substances, for example by re-release of chloride ions, require steels or alloys from other families.

After machining a blank close to the final shape, the molds undergo in a controlled atmosphere furnace the following heat treatment:

rising to the quenching temperature in the range 1000 to 1050 ° C., followed by holding for a few tens of minutes in this area,

- Quenching under pressure of gas up to a temperature of about 80O;

- rise in temperature for two revenue cycles.

It is usually proposed two income temperature domains:

- low temperature incomes: 150 to 250 ° C - incomes around 490/530 ° C in the secondary hardening zone of steel.

Normally, the two successive incomes are both in the same field.

Arbitrations must be decided for the precise choice of treatment parameters.

For quenching, it is metallurgically recommended to seek high quench rates to benefit from a favorable martensitic microstructure. However, high quenching speeds favor the deformations and generate residual stresses liable to lead to breaks. Practically, the gas pressures are limited to values of 2 to 4 bars.

During quenching, before going back on incomes, breaks are possible if the cooling takes place up to the ambient temperature. ature. But the usual choice to stop the cooling to 80 ° C opens the risk of retaining residual austenite, especially if the subsequent income is set below 500O, and consequently not being able to obtain the desired nominal hardness For the incomes, the choice of the low temperatures allows only a partial release of the stresses, and if the composition of the steel and the quenching cycle left residual austenite, the income does not decompose it, the Target hardness is not achieved High-temperature incomes break down austenite and relax residual stresses, but decrease toughness and corrosion resistance.

There is also the problem of the cost of these steels, due to the high levels of alloying elements they require, and that it should be possible to minimize without degrading the desired properties.

The object of the invention is the definition of an economic composition of steel for mold applications for the manufacture of plastic articles having compared with the references AISI 420 and X40Cr14, the following properties:

- Preferred equivalent hardness of 49 to 55 HRC in the treated state to resist abrasion; - equivalent corrosion resistance;

- improved toughness with equal hardness;

- improved polishability;

all this for industrial heat treatment conditions comparable to the usual conditions. For this purpose, the subject of the invention is a martensitic stainless steel, characterized in that it comprises, in weight percentages:

- 0.22% <C <0.32%

- 0.05% <N <0.15%, with 0.33% <C + N <0.43% - 10% ≤ Cr ≤ 12.4% - 0.10% ≤ V ≤ 0.40%

- 0.10% ≤ Mo ≤ 1.0%

- traces <Ni <1, 0%

- traces <Mn <1, 0% - traces <If <1, 0% - traces ≤ W <1, 0%

- traces <Co <1, 0%

- traces <Cu <1, 0% - traces <Ti <0,010%

- traces <Nb <0,050%

- traces <Al <0.050%

- traces <S <0,020%

- traces <O <0.0040% - traces <P <0.03%

- traces <B <0.0050%

- traces <Ca <0.020%

- traces <Se <0.010%

- traces <<0.040% - traces <Ce <0.040% the rest being iron and impurities resulting from the elaboration.

Preferably 0.08% <N <0.12%.

Preferably 11.0% <Cr <12.4%.

Preferably 0.15% <V <0.35%. Preferably traces <Si <0.5%.

Preferably 0.10% <Mo + W / 2 <1, 20%.

Preferably traces <Ti <0.003%.

Preferably traces <Nb <0.010%.

Preferably <0 <0.0015% traces. Preferably traces <S <0.003%.

Preferably traces <Mn + Cu + Co <1, 8%.

The invention also relates to a process for manufacturing a martensitic stainless steel part, characterized in that:

- one develops, one sinks, one forges or rolls and one anneals a steel of the preceding type;

a machining of said steel is carried out to give it the shape of said part; austenization of said machined steel is carried out at a temperature of 990-1040O, preferably 1000-1030O;

quenching of the austenized steel is carried out at a rate of between 10 and 40OzmJn in the temperature range 800 to 400O; - Two incomes of hardened steel are realized to give it its final hardness.

Said incomes can each be carried out at a temperature of 200 to 400 ° C., preferably 300 to 380 ° C., for a minimum of 2 hours, while maintaining the nominal temperature at least 1 hour at the core, so that obtain a hardness of 49 to 55 HRC.

Said incomes can each be made at a temperature of 530 to 540 ° C for a minimum of 2 hours while maintaining a core temperature of the nominal temperature of at least 1 hour, so as to obtain a hardness between 42 and 50 HRC. The invention also relates to a piece of stainless steel magnetitic, characterized in that the element manufactured by the process is manufactured according to the preceding method.

It may be a mold element for the manufacture of plastic articles. As will be understood, the invention is based on a steel composition whose carbon and chromium contents are simultaneously at the bottom of the ranges usually required, and sometimes even below for the chromium content, with the imposition of conditions. other elements present or to be limited or avoided. A manufacturing method is associated with this composition.

The approach of the inventors has focused on the real consideration of the properties of the steel resulting from the manufacture, and in particular of the industrial treatment as described above, and not according to laboratory conditions. The research was carried out with the aim of optimizing the action of the alloying elements to limit the quantity introduced.

The main considerations leading to the invention are as follows. Polishability and surface quality of the polished state of steel are degraded by:

the presence of nonmetallic inclusions of non-reflective oxides of the light, and which moreover crumble or come loose in contact with the abrasive, and form, by evacuating, stripes or "tails of comets" at the mold surface;

- the interdendritic segregations forming naturally during the solidification of the ingot and generating on the surface of the molds harder zones or lines alternating with softer zones or lines, causing the polishing of undulations because the soft zones are digging faster than hard areas;

the presence of micrometric chromium carbides undissolved in quenching.

In general, the toughness, mediocre for this family of steels, is, for a given hardness, the lower the chromium content is high. It could be improved by balancing the composition, especially with additions of nickel and manganese to maintain a residue of austenite quenching. This solution, which also has no effect if the incomes are made above 500 ° C, proves unstable and handicaps the hardness. as much as it was not compatible with the desired lowering of the content of alloying elements.

To achieve the objectives, it was chosen:

on the one hand, to produce the steel according to known methods limiting the presence of oxidized non-metallic inclusions, thus conferring on the steel a low O content,

- and on the other hand to reduce overall alloy elements, introduce nitrogen, and optimize the equilibrium between elements to increase toughness, reduce interdendritic segregation and limit the density of micrometric precipitates.

The invention will be better understood from the description which follows, given with reference to the following appended figures: FIG. 1, which shows micrographs of samples of a reference steel and of two steels according to the invention, showing the density and the distribution of the micrometric carbides in the state of use of these steels;

FIG. 2 which shows the influence of the temperature of the two incomes on the corrosion resistance of a steel according to the invention;

FIG. 3, which shows the influence of the temperature of the incomes on the resistance to corrosion;

- Figure 4 which shows the interactions of the Cr content and the quenching rate on the corrosion resistance; - Figure 5 which shows the hardness of the steels according to the invention and a reference steel depending on the temperature of the incomes.

Table 1 groups the compositions of the samples studied. The "Reference" sample corresponds to a standard X40Cr14 type steel. The samples Exp.1 to Exp.7 are not in accordance with the invention but make it possible to identify the disadvantages of not complying with all the conditions required by the invention. Samples lnv.1 and lnv.2 are in accordance with the invention.

Table 1: Chemical Composition of the Steels Studied

The object of the invention is therefore to design an optimized steel intended to be treated according to the range of industrial quenching speeds, preferably with a subsequent double low temperature (<400 ° C.) for a hardness of 52 HRC with tenacity and a corrosion resistance equal to or better than that of the reference steel AISI 420 or X40Cr14 in its usual implementation.

In addition, the invention has the objective of minimizing the addition of alloying elements, in particular metal elements, in order to reduce the cost of production, to prevent the presence of residual austenite after quenching, and to reduce the amplitude. interdendritic segregation is detrimental to the tenacity and quality of polish.

For this purpose, the inventors have reached the following results on the definition of the composition of the steels of the invention.

The nitrogen content should be between 0.05% and 0.15% and preferably between 0.08% and 0.12%. This element is therefore systematically present at a high content, because it is essential to form carbonitrides of type V (C ₁ N) able to prevent grain growth after austenization once the dissolved chromium carbides. An excessive content would, however, be detrimental by exceeding the solubility limit in the solid state and would be a source of metallurgical defects. Nitrogen combines with carbon to impart hardness and contributes to corrosion resistance. The nitrogen content can be adjusted by blowing nitrogen gas during the preparation of the liquid steel.

Carbon mainly contributes to imparting the required hardness, associated with nitrogen. Given the hardness sought after low temperature income, the percentage must be between 0.22% and 0.32%. Moreover the sum C + N must be between 0.33% and 0.43% to allow, after income, to obtain the target hardness.

Chrome gives steel its resistance to corrosion. Given the industrial quenching speeds practiced, and the income range chosen, and according to the mechanisms mentioned above, its content must be between 10 and 12.4% and preferably between 11, 0 and 12.4% . The vanadium must be present at a content of between 0.10% and 0.40% and preferably between 0.15% and 0.35%. Its presence is essential to form with carbon and nitrogen a sufficient density of micro- and nanoprepites able to prevent the growth of the grain. Too high a content would be detrimental by the excessive fixation of the carbon which would be lacking for the hardening, and by the formation, during solidification, of isolated carbides or clumps unfavorable to the tenacity and the quality of the polish.

Molybdenum completes the action of chromium for corrosion resistance; it is present, by recycling or by voluntary addition, at percentages between 0.10 and 1.0%. A higher content would be detrimental by increasing the amplitude of interdendritic segregation, and by the risk of forming delta ferrite.

Nickel may be present at levels below 1.0%, particularly because of the input by the raw materials. No favorable action of an addition within this limit for toughness was noted. On the other hand, a higher content would be likely to maintain residual austenite in the treated state.

Manganese is an element naturally present in this family of steel because of the production processes and raw materials available. No beneficial effect has been identified, and it is necessary to limit its concentration to 1.0% to avoid residual austenite after heat treatment.

Silicon is naturally present for the elaboration and deoxidation of steel. Its content must be limited to 1.0% and preferably 0.5%, because it acts on the solidification process and the delta-gamma transformation and can therefore cause the presence of delta ferrite or local segregations consecutive to the presence of this phase at the end of solidification before filling.

Tungsten may be present at levels below 1.0% without having a favorable or detrimental effect on the product. However, by its individual action or by synergy with molybdenum, it can promote the presence of delta ferrite in the state of use, or local precipitation or segregation originating from the presence of delta ferrite at any stage of the production. thermomechanical termination. It will be preferred to meet the condition 0.10% <Mo + W / 2 ≤ 1, 20%.

Cobalt and copper have no identified beneficial effect but may be present at levels less than or equal to 1.0%; higher grades may favor the presence of residual austenite.

It is preferable that the total contents of Mn, Cu and Co is <1, 8%, so as to limit the risk of presence of residual austenite.

Titanium and niobium are very reactive elements that form very hard precipitates harmful to the quality of polishing. Their content must be kept as low as possible: at most 0.010%, preferably at most 0.003% for Ti, and at most 0.050%, preferably at most 0.010% for Nb.

The added aluminum for the deoxidation of the steel can remain present in inclusions of oxides very harmful for the polishing. The level of addition must be adapted to the processing methods used. A maximum level of 0.050% is tolerable, provided that it does not lead to the presence of inclusions of alumina or silico-aluminates in large quantities which would lead to an exceedance of the acceptable O content (0.0040% better, 0.0015%).

The sulfur is preferentially limited to a content of less than 0.003% to prevent the formation of sulphide inclusions. However, optionally, it may be chosen to make a voluntary addition in the range 0.003 to 0.020% preferably associated with another element (SE up to 0.010%, Ca up to 0.020%, La up to 0.040%). %, Ce up to 0.040%) promoting the formation of globular sulphides to improve machinability, to the detriment to a certain extent of the quality of the polish.

The maximum oxygen content is 0.0040%, preferably 0.0015%. Indeed, this element is an index of the inclusion density, harmful to the surface polish when it is too high. This content should be kept as low as possible and the process of making the steel should be selected accordingly. In practice, known methods allow to go down to O = 5 ppm under economically acceptable conditions. The phosphorus content is limited to 0.03% which is a common content in this class of steels. There was no adverse effect of P in this range.

Boron may be added to improve quenchability at a level not exceeding 0.0050%.

The preferred contents indicated for certain elements may be imposed alone, and not necessarily in combination with the other preferred levels indicated.

The elements not mentioned can be present at levels of impurity level resulting from the development, not modifying the properties that the invention seeks to optimize.

The products must be manufactured in accordance with the state of the art for high-quality special steels for plastics molding applications, with the aim of limiting the inclusion content and the segregation of materials. obtaining a quality polish. The preparation must include, after melting, a phase of deoxidation and elimination of inclusions in a metallurgical reactor. Preferably, particularly for the manufacture of large molds and for obtaining the highest amounts of polish, it will be practiced remelting by consumable electrode slag to improve the inclusion cleanliness and distribute the alloy elements, and above all the nitrogen, homogeneously throughout the mass.

A thermomechanical transformation by forging or rolling completed by annealing must follow to complete the homogeneity and compactness of the microstructure. After machining the workpiece to the final shape and before putting into operation, the products must, according to the preferred procedure, undergo a heat treatment comprising austenization at about 1020 ° C (990 to 1040 ° C, preferably 1000 ° C). 1030 ° C), a controlled quenching, for example under a pressure of neutral gas, at a speed of between 10 and 40OZmJn adapted to the size of the workpiece, then two incomes at a temperature of 200 to 400 ° C, preferably between 300 and 380 ° C to obtain a hardness close to 52 HRC _ + 2 HRC, and generally between 49 and 55 HRC. Optionally, for applications that do not require a hardness higher than 50HRC, the steel defined by the invention can be treated with double-feed from 530 "C to 560" C for hardnesses less than or equal to 50 HRC and greater than or equal to at 42 HRC, conditions in which corrosion resistance is sufficient.

For the reference steel, the existing chromium carbides (M ₂₃ C ₆ ) in the delivery state are redissolved during the austenization that precedes quenching, and the holding temperature is limited to 1020/1030 " However, at this solution temperature, a significant amount of heterogeneously distributed carbides remain, with a substitution of about 0.10 to 0.15% of the content of the carbons. carbon by nitrogen, a reduction of about 2% of the chromium content and a simultaneous introduction of vanadium, it is observed at the adequate quenching temperature that the grain, fixed by nanometric precipitates of vanadium carbons; V (C ₁ N) does not increase while most of the chromium carbides have dissolved.

For three of the compositions studied, the comparison of equilibria at 1030 ° by thermodynamic simulation with the logici el THERMOCALC (commonly used by metallurgists) illustrates this mutation (see Table 2).

Table 2: Calculation of thermodynamic equilibria at 1015O for three representative compositions

The effective density of the micrometric carbides observed on industrial products and illustrated in FIG. 1 effectively decreases significantly between the reference composition and the compositions of the invention, which constitutes a favorable factor for the quality of the polished state.

For the reference steel, the corrosion resistance capacity is, theoretically according to the basic knowledge, primarily related to the chromium content available in the matrix; thermodynamic calculations show that carbons undissolved in austenization set about 0.9% chromium. This amount of chromium unavailable for corrosion resistance becomes less than 0.1% for vanadium and nitrogen alloyed experimental grades. According to the following formula:

PRE. (Pitting Equivalent Resistance) =% Cr + 3.3 x% Mo + 3O x% N conventionally allowing to classify the compositions according to their resistance to pitting and applied to the actual composition of the matrix, it is revealed according to the table 2 that the experimental compositions Inv 1 and 2 have a coefficient close to that of the reference.

Beyond the considerations expressed above expressing a potential in the quenched state, measurements should be made in the effective state of the metal at the stage of use. The electrochemical method performed according to the ASTM G 108 standard consists, in a 1% by weight aqueous H ₂ SO ₄ solution, of polarizing the sample for 15 minutes at a potential of -550mV / ECS and then carrying out a forward scan. and back to 60mV / min from -55OmV to + 50OmV. The intensity-potential curves at the return can have two peaks, one (Pic1) due to the dissolution of the matrix, the second (Pic 2), at a higher potential, connected to the dissolution at the right of carbide precipitates of chromium. Steel is all the more sensitive to corrosion as the dissolution current is intense. Characteristic curves are presented in FIGS. 2 and 3. According to the usual practices for the reference steels, while obtaining the desired hardness of 52HRC, two parameters of the heat treatment prove to be influential for the corrosion resistance: the temperature of the income and tempering speed. These effects have been specified by laboratory tests: a) income effect:

Figure 2 shows for the INV1 casting the steel sensitizes strongly vis-à-vis corrosion for revenue generated in the curing zone to 500 ⁰ C. If the corrosion resistance is a characteristic preferable for imperative the applications envisaged, we will therefore favor low-temperature incomes (200-380 ⁰ C).

This trend is confirmed for all the compositions tested, as shown in Figure 3. This shows the influence of a double income of 2 hours at 380 ° C or at a temperature of around 500 ⁰ C, for resistance to Corrosion, considering the corrosion current at peak 2 of Figure 2. The exact temperature of the double income at 500 ⁰ C enviro was adjusted so that it allows to obtain the same hardness after a double income at 380 ⁰ C. It is found in particular that the sample according to the invention has a corrosion resistance very comparable to that of the reference sample for a double income at 380 ^° C.

For the low temperatures of income, it has moreover been verified that the corrosion resistance decreases slightly between 200 ⁰ C and 380 ⁰ C to rapidly degrade above 400 ⁰ C. For the income to have the desired effect They must last at least 2 hours, and their nominal temperature must be maintained in the center of the room for at least 1 hour.

b) effect of the quenching rate: Unexpectedly, as shown in FIG. 4, which compares two experimental streams distinguished from each other by the sole chromium content, the increase in the content of this element does not improve the corrosion resistance under industrial quenching conditions with a cooling rate of the order of 20 ° C./minute in the range 900/400 ^° C. The low cooling rate provokes the development peak 2 revealing the precipitation of carbides or nitrides, and whose amplitude is all the more important that the chromium content is high and amplifies the corrosion current of the matrix (Pic 2). These results are confirmed for the various compositions studied. According to the invention, a quenching speed compatible with the know-how of the heat treatment and between 10 and 40 ° C. in the temperature range 800 to 400 ° C. will be chosen.In conclusion, in the context of industrial quenching, it is with the low temperature incomes that the best resistance to corrosion is obtained, and in this configuration, the variation of the chromium content in the interval 10.5 to 15% does not confirm the usually recognized beneficial effect. for this alloying element, the same adverse effects of the decrease of the quenching rate and the increase of the tempering temperature are found on the toughness.This property is commonly appreciated simply from the conventional mechanical elongation characteristics. and necking in the tensile test and impact bending energy on unscored bars of dimensions 55x10x7 mm. all the samples a quench of 16 ° C / min then a double income of 2h. The results summarized in Table 3 demonstrate:

for the composition Inv. 2 taken as an example, the detrimental effect of lowering the quenching rate; - the weakening effect of double income in the vicinity of 500 ° C;

- For low temperature double income (380 ⁰ C), the superiority of the compromise hardness / toughness of the two steels of the invention compared to the reference.

Table 3: Measured mechanical characteristics for three compositions on representative samples of industrial products

The compositions of the invention make it possible to obtain the hardness of 52 HRC or more after quenching under industrial conditions and double-tempered at 380 ° C., despite the softening experienced in this field for this steel family from crude. quenching, as shown in Figure 5.

Claims

1.- martensitic stainless steel, characterized in that it comprises, in percentages by weight:

- 0.22% <C <0.32% - 0.05% <N <0.15%, with 0.33% <C + N <0.43%

- 10% ≤Cr≤ 12.4%

- 0.10% ≤V≤ 0.40%

- 0.10% <Mo <1.0%

- traces <Ni ≤ 1.0% - traces <Mn <1.0%

- traces ≤ If ≤ 1.0% -traces≤W≤ 1.0%

- traces ≤ Co ≤ 1.0% -traces ≤ Cu ≤ 1.0% - traces ≤ Ti ≤ 0.010%

- traces ≤ Nb ≤ 0.050%

- traces ≤ Al ≤ 0.050%

- traces ≤ S ≤ 0.020%

- traces ≤ O ≤ 0.0040% - traces ≤ P ≤ 0.03%

- traces ≤ B ≤ 0.0050%

- traces ≤ Ca ≤ 0.020%

- traces ≤ Se ≤ 0.010%

- traces ≤ The ≤ 0,040% - traces ≤ Ce ≤ 0,040% the rest being iron and impurities resulting from the elaboration.

2. Steel according to claim 1, characterized in that 0.08% ≤ N ≤ 0.12%.

3. Steel according to claim 1 or 2, characterized in that 11.0% ≤ Cr ≤ 12.4%.

4. Steel according to one of claims 1 to 3, characterized in that 0.15% ≤ V ≤ 0.35%.

5. Steel according to one of claims 1 to 4, characterized in that traces <Si <0.5%.

Steel according to one of Claims 1 to 5, characterized in that

0.10% ≤ Mo + W / 2 ≤ 1, 20%.

7. Steel according to one of claims 1 to 6, characterized in that traces <Ti <0.003%.

8. Steel according to one of claims 1 to 7, characterized in that strokes <Nb <0.010%.

9. Steel according to one of claims 1 to 8, characterized in that ≤ 0 <0.0015%.

10. Steel according to one of claims 1 to 9, characterized in that traces <S <0.003%.

11. Steel according to one of claims 1 to 10, characterized in that traces <Mn + Cu + Co <1, 8%.

12. A method of manufacturing a martensitic stainless steel part, characterized in that:

- is made, cast, forged or rolled and annealed steel according to one of claims 1 to 11;

a machining of said steel is carried out to give it the shape of said part;

austenization of said machined steel is carried out at a temperature of 990-1040O, preferably 1000-1030O; quenching of the austenized steel is carried out at a rate of between 10 and 40OzmJn in the temperature range 800 to 400O;

- Two incomes of hardened steel are realized to give it its final hardness.

13. Process according to claim 12, characterized in that the said incomes are each carried out at a temperature of 200 to 400 ° C, preferably 300 to 380 ° C for a minimum of 2 hours, while maintaining core of the nominal temperature of at least 1h, so as to obtain a hardness of 49 to 55 HRC.

14. The method of claim 12, characterized in that said incomes are each carried out at a temperature of 530 to 560 ° C for a minimum of 2h ensuring a core temperature of the nominal temperature of at least 1 h, so to obtain a hardness between 42 and 50 HRC.

15. martensitic stainless steel part, characterized in that the element manufactured by the process is manufactured according to one of claims 12 to 14.

16. Part according to claim 15, characterized in that it is a mold element for the manufacture of plastic articles.