CN1688734A - Ferritic steel alloy - Google Patents

Abstract

This invention discloses a steel alloy comprising, based on no more than 1.00 weight percent silicon, 18.0 to 22.0 weight percent chromium, 1.80 to 2.50 weight percent molybdenum, 0.01 to 0.10 weight percent nitrogen, no more than 0.01 weight percent titanium, no more than 0.01 weight percent niobium, and no more than 0.01 weight percent aluminum, with the balance being substantially iron. The alloy is ferritic and polishable, and has mechanical properties close to those of standard steel alloy No. 1.4521. The steel alloy of this invention can be processed into watch components, particularly such as the case back, case body, and watch face, thus enabling the manufacture of watch cases that also magnetically shield watchmaking devices.

Description

ferritic steel alloy

The invention relates to the field of high alloy stainless steels used in the watch industry.

Most watches worn today are made of gold, stainless steel and titanium. The development of steel for watches began in 1925, when the British company Firth Vickers Special Steels Ltd. introduced CrNi steel to the market under the designation "DDQ". Almost at the same time, the Krupp company developed steel V2A, but, thanks to steel No. 1.4301, this came into use in the watch industry 50 years later. Then, in the late 1980s, steel "DDQ" was replaced by austenitic stainless steel No. 1.4435, which is now the standard steel, due to the need for improved corrosion resistance in the Swiss watch industry.

Watch cases are usually prepared from metal sheets and plates using die-cutting techniques. In order to achieve the final form they require, they must be cold-extruded to a certain extent, depending on the type of case, and, depending on the thickness of the case, intermediate annealed. The same is true for profiles prepared by cold rolling. Cold hardening behavior is very important for cold block forming. In general, the steels most suitable for this type of deformation are those at low yield strength values, with minimal cooling to harden themselves while increasing the degree of deformation. In the annealed condition during block forming, ferritic stainless steel alloys behave like unalloyed steels.

In order to protect components of horological mechanisms sensitive to magnetic influences from strong magnetic fields, some watchmakers incorporate soft iron boxes (a material that does not itself have magnetic shielding properties) in the above-mentioned titanium or 1.4435 stainless steel case. ). This kind of soft iron box has the function of a protector against magnetic field, which will not allow the magnetic field to penetrate into the watch. Thus, in fact, it is possible to protect the watch from magnetic fields of up to 80,000A/m; but considerable effort is required, as this soft iron case has to be done separately and then incorporated into the actual case, so the total thickness of the watch is limited greatly improved.

For watch steels, the polishability of steel, eg for watch cases, is also required, ie its suitability for producing high-gloss polished surfaces. The austenitic stainless steel No. 1.4435 currently used in the watch industry can only meet this demand to a limited extent. Ferritic stainless steels such as steel No. 1.4521 cannot be polished like austenitic steels: Ferritic steels are almost exclusively stabilized with titanium or Nb against the precipitation of Cr-carbides at the grain boundaries. However, high-hardness titanium carbide or niobium carbide is thus precipitated, impairing the polishability of the ferritic steel. By mechanical polishing, the precipitated carbide particles with a size of 5-10 μm are not removed, and protrude outside as so-called pits, better polishing the surface. So-called polishing marks occur, ie deposits of polishing paste in the polishing shadow of the carbide particles, which are very disturbing to the naked eye. For polishable ferritic chromium steels, it is not practical to stabilize the steel microstructure by adding Ti or Nb due to the negative impact on polishability. However, without Ti or Nb to stabilize the microstructure, the precipitation of chromium carbides at the grain boundaries proceeds so rapidly due to the rate of diffusion that by rapid annealing from solution annealing temperatures is unavoidable, chromium carbides The diffusion rate of ferritic steel is about 2 orders of magnitude higher than that of ferritic steel. In addition, the chromium carbides form hard inclusions, which in turn impair the polishability of the steel.

The polishability of steel is greatly influenced by grain size. Polishing of large grain steel produces an effect known as orange peel, which is unacceptable for polished surfaces. The reason for this is that disordered particles (crystals) behave differently in different orientations. If the grain size measured according to ASTM E 112 is below the value 4 (≥80pm), the human eye can see the crystal surface removed by varying degrees during the polishing process as point-like particles, which exhibit an orange-peel appearance.

In the technical specifications of table steel, another requirement is good processability. Depending on the type of watch case, extensive cold forming operations with intermediate annealing steps must be carried out during the manufacture of the watch case. Furthermore, the preparation of watch straps, for example using drilling and grinding, also requires good machinability of the alloy.

Good corrosion resistance, especially in saline media, is another major requirement for watch steels. Watches are in direct contact with the skin and present a particular risk of corrosion due to wetting through perspiration. The purity of the steel has a considerable effect on corrosion resistance. Rough and linearly precipitated non-metallic inclusions indicate weak spots on the surface where rust marks can initiate and then continue unimpeded. For this reason, in the art steel is usually remelted by the Electro-Slag-Remelting method (ESR method), according to DIN 65602, resulting in a non-metallic, corrosion fostering particle size Down about 2 units or so.

It is known that the chemical and mechanical properties of steel alloys can be controlled by adding metallic and non-metallic elements to the alloy.

The influence of each individual alloying and trace element on the mechanical, chemical and magnetic properties as well as on the microstructure of steels is known per se (cf. Steels-Properties, Processing, Use, Standards] Chapter 2.2 in the second edition, editors "Edelstahl-Vereinigung e.V." Verlag Stahl-Eisen; and C.W. Wegst, Verlag Stahlschlüssel, Wegst GmbH, "Stahlschlüssel" 18th edition, 1998, p. 1 chapter).

The known alloying elements and their effect on the steel if they are added to the alloy respectively are briefly described below.

First, chromium has a passivating effect on steel and thus represents the main alloying element used in all stainless steels.

Molybdenum improves corrosion resistance and, in the presence of halide ions, stability against pitting corrosion.

Silicon is considered by many to be an unwanted impurity in polishable steels because it forms hard oxide inclusions. On the other hand, if the alloy should be magnetically soft, silicon is a required alloying element.

Nitrogen improves corrosion resistance. Since yield strength and work hardening tendency are improved by adding N, the N content is usually strictly limited to 0.2%. It is believed that the addition of N to austenitic steels greatly delays the onset of M ₂₃ C ₆ precipitation (PR Levy, PR, van Bennekom, A., Corrosion 51, 911-921 (1995)). On the other hand, if alloys with soft magnetic properties are desired, the presence of nitrogen is problematic (see, for example, "Ullmann's Encyclopaedia of Industrial Chemistry" 5th Edition, Volume A16, p. 26, left column, second paragraph ).

Manganese is an austenite forming element. Its presence is therefore highly undesirable in ferritic steels.

Trace amounts of sulfur are beneficial for the machinability of the steel, which may be important for the manufacture of certain watch parts, such as watch straps. However, large amounts of it have an adverse effect on the corrosion resistance of steel.

Although the addition of carbon increases the hardness of steel, it is, on the other hand, a very strong austenite former and it reduces machinability and polishability by precipitating chromium carbides at grain boundaries. The presence of carbon is likewise problematic if the alloy is required to have soft magnetic properties (see, for example, "Ullmann's Encyclopedia of Industrial Chemistry" 5th Edition, Volume A16, p. 26, left column, second paragraph).

For the soft magnetic properties of steel alloys, nickel is required as an important alloying element (typically, 30 to 80 weight percent), but, on the other hand, due to its properties as an austenite former is very unnecessary. Furthermore, allergic reactions to Ni-containing alloys have become serious medical problems in industrialized countries. For example, in Europe, more than 20% of young women and more than 6% of young men are impaired by nickel allergy. This is important on watch cases as these rest directly on the skin.

Pure, unalloyed iron (soft iron) is also advantageous as a soft magnetic material, however, it is not known to be corrosion resistant.

The two-dimensional microstructural phase diagram of chrome-nickel steels allows a rough assessment of the microstructure (austenitic, delta-ferrite, martensitic or their mixtures), which will be formed as Cr content (plotted on the x-axis in the figure) and Ni content (plotted on the y-axis in the figure). This microstructural phase diagram can also be expanded by considering the above elements; however, additional elements are only considered in outline and estimated to form as additional nickel or chromium equivalents. In this form, a Schaeffler-graph is known. (A.L. Schaeffler: M.S. Thesis, Univ. of Wisconsin, June 1944; A.L. Schaeffler, The Welding Journal 26/10, 601-620 (1947); A.L. Schaeffler, Metal Progress vol. 56s. 680A, B (1949)). Due to factors determined empirically (Comparison, Briggs, J.Z., Parker, D., Climax Molybdenum Company, pp. 6-7 (1965)), the conversion of the amounts of additional elements into equivalent amounts of chromium and nickel was performed by calculation, as Values are obtained from experiments, so an accurate prediction of the microstructure of a specific alloy is not possible. In particular, from the Schaeffler diagram it is not possible to draw conclusions about the corrosion resistance or the mechanical and magnetic properties of an alloy.

A preliminary estimate of the pitting resistance of Cr/Mo steels can also be obtained from two-dimensional diagrams (Gröfen, H., Chem. Ing. Techn. 54, pp. 108-119 (1982)). In this figure, the limiting potential for the correlation of pitting corrosion initiation (Y-axis) is plotted against the Cr content (X-axis), as determined by the current density/potential curve. The molybdenum content is also considered in terms of chromium equivalents (ibid., and Lorenz, K., Medawar, G., Thyssen-Forschung 1, pp. 97-108 (1969)). A roughly linear correlation between the limiting potential and the Cr(Mo) content was observed. However, this figure does not take into account any additional alloying elements and no conclusions can be drawn as to whether it concerns ferritic alloys, or as to their machinability, polishability and magnetic properties.

The effective total WS defined in the following way:

WS=%wt Cr+3.3×wt% Mo+16×wt% N,

Is a measurement used to roughly estimate the corrosion resistance of steel. Since perspiration from the skin is more corrosive than blood with a 0.9% salt content, the effective total number of implant steels for the watch steel should be at least 26.

An overview of 8 specific, prior art steels (designated by their material numbers) and their weight percentages of important alloying elements is given in Table 1 . Steel No. 1.4521 referred to here is not a watch steel, to the applicant's knowledge.

Table 1 1.4521DIN 10088 1.4523 Steel-Iron-L. Sandvik(Richt)1802 Aichi(IST)YUS 190 Aichi(IST)SUS 444 NAR 445 NARFC3 NTK U-22 C ≤0.025 ≤0.030 ≤0.03(C+N) 0.004 0.025 ≤0.020 ≤0.025 ≤0.025 Si ≤1.00 ≤1.00 0.5 0.06 0.87 ≤0.60 ≤1.00 ≤1.00 Mn ≤1.00 ≤0.50 0.3 0.06 0.21 ≤0.60 ≤1.00 ≤1.00 P ≤0.040 ≤0.040 -- 0.025 0.032 ≤0.040 ≤0.040 ≤0.040 S ≤0.015 0.15-0.35 0.3 0.008 ≤0.002 ≤0.010 ≤0.005 ≤0.030 Cr 17.0-20.0 17.5-19.0 18 18.8 17.8 19.0-21.0 19.0-22.0 21.0-23.0 Mo 1.80-2.50 2.00-2.50 2.3 1.86 2.07 1.70-2.30 0.75-1.25 1.75-2.50 Ni -- -- ≤0.20 -- 0.17 -- -- -- N ≤0.03 -- -- 0.009 ³⁾ 0.025 ³⁾ -- -- ≤0.025 Al -- -- -- -- 0.006 -- -- -- Ti ≤0.081 ⁾ 0.30-0.802 ⁾ 0.6 -- 0.005 -- -- -- Nb -- -- -- 0.15 0.57 -- 0.15 Ca.0.80 Cu -- -- -- -- 0.04 -- 0.08-0.30 -- Fe Surplus Surplus Surplus Surplus Surplus Surplus Surplus Surplus

¹⁾ Ti=4×(C+N)+0.15 to 0.80

²⁾ Ti=0.30 to 0.80, where (C+N)≤0.40

³⁾ N is not explicitly added, it is just an impurity

The object of the present invention is to provide a polishable ferritic steel with soft magnetic properties in which the risk of polishing defects is minimized, which has mechanical properties comparable to steel No. 1.4521, and which is essential for resistance to pitting and crack resistance, same or improved corrosion resistance compared to Steel No.1.4435.

This object is achieved by a steel alloy comprising at most 1.00 weight percent silicon, 18.0 to 22.0 weight percent chromium, 1.80 to 2.50 weight percent molybdenum, 0.01 to 0.10 weight percent nitrogen, based on the alloy, Up to 0.01 weight percent titanium, up to 0.01 weight percent niobium, up to 0.01 weight percent aluminum and the balance essentially iron. Preferred variants are given in the dependent claims.

The steel alloy according to the invention is a soft magnetic CrMoN steel alloy.

Description of drawings

Figure 1 shows the current density/potential diagrams for a) the steel alloy according to the invention and b) the known steel alloy No. 1.4435. Measuring conditions: 3.2% NaCl, pH 4.0, 40°C. x-axis: potential in mV relative to a saturated calomel electrode (SCE) as a reference electrode; y-axis: logarithm of the measured current density. The potential values shown in both figures are the limiting potentials at the onset of pitting corrosion (strong increase in anodic current).

Within the scope of the present application, the term "high alloy" has the usual meaning in the art, ie it designates a steel in which the sum of the amounts of alloying elements is 5% by weight or more.

In the context of the present application, the term "ferrite" means that at least 98% by volume, preferably at least 99.5% by volume, and particularly preferably 100% by volume, of the iron present in the alloy according to the invention is present as ferrite, which is determined by means of metallographic method to proceed.

Within the scope of the present application, the term "soft magnetic" is used for the steel alloy according to the invention, which produces a magnetic shielding effect at least as strong as soft iron.

The metal alloying elements chromium and molybdenum can be added to the alloy of the invention according to conventional methods by adding suitable amounts of pure elements to pig iron or crude steel.

According to the invention, 18.0 to 22.0 percent by weight, preferably 19.5 to 20.5 percent by weight, particularly preferably about 20 percent by weight, of chromium is present, based on the finished alloy.

According to the invention, about 1.80 to about 2.50 percent by weight, preferably about 1.90 to 2.10 percent by weight, particularly preferably about 2 percent by weight, of molybdenum is present, based on the finished alloy.

Nitrogen can be supplied by melting the steel alloy under a nitrogen atmosphere, by blowing nitrogen into the melt or by adding quantitative amounts of a pre-alloy with a high nitrogen content. According to the present invention, the content of nitrogen is about 0.01 to 0.10 weight percent, more preferably about 0.05 to about 0.10 weight percent, and particularly preferably about 0.05 weight percent, based on the alloy.

Silicon can be present in the alloy as _SiO2 (eg, from deoxidation above). Its content can be reduced by mechanically moving or stirring the steel melt in a protective gas. As such, due to the low density, SiO ₂ aggregates and rises to the slag surface. According to the present invention, the content of silicon is at most about 1 weight percent, preferably about 0.7 to 0.9 weight percent, more preferably about 0.8 weight percent, based on the alloy.

As a result of the smelting process, a significant amount (4 to 4.5%) of carbon is present as an admixture in the pig iron, which is then, as is conventional in the art, obtained by adding oxygen or a suitable amount of iron oxide (the carbon to carbon monoxide), this carbon content can be reduced to virtually any desired level. Preferably, according to the invention, carbon is at most 0.025% by weight, particularly preferably at most 0.01% by weight, based on the alloy.

Sulfur originates from the smelting process (iron sulphides are contained in iron ores) and is present in pig iron mainly in the form of manganese sulphide. In the alloy according to the invention, it is preferably present in an amount of at most 0.03 weight percent, more preferably at most 0.002 weight percent. Such low sulfur contents can be achieved by desulfurizing the melt using, for example, a mixture of CaO and metallic magnesium. In another particular embodiment of the steel alloy according to the invention, which has better machinability and acceptable polishability, the upper limit of the sulfur content may be 0.03 based on the alloy (so-called IMA quality) Percent by weight, preferably about 0.015 to 0.03 percent by weight, so that the control of sulfur addition can be performed. For the production of this particular embodiment, fusion metallurgy can be performed with the addition of Ca-Si powder, which converts the hard alumina content into a relatively soft CaSiAl-type mixed oxide and forms finely dispersed manganese sulfides, by It, breaks up the chips formed during machining, thus prolonging the service life of the tool. The controlled addition of sulfur only slightly reduces the corrosion resistance of this embodiment of the steel alloy according to the invention.

According to the invention there is at most about 0.01 weight percent, preferably at most about 0.005 weight percent niobium, based on the finished alloy. This amount can be achieved by the present invention utilizing suitable metal shavings (avoiding niobium-containing steels) during melting of the steel alloy.

According to the present invention, there is preferably at most about 1.00 weight percent, more preferably at most about 0.40 weight percent manganese based on the finished alloy.

Phosphorus originates originally from apatite or other phosphate-containing minerals present in iron ore. During smelting, phosphates can be reduced to iron phosphide (mainly _Fe2P ) and can be present in pig iron or subsequent steel. According to the invention, the preferred low phosphorus content of at most 0.04 wt. % and preferably at most 0.02 wt. Phosphorus minerals are separated from the slag.

According to the invention, an aluminum content of up to about 0.01% by weight and preferably up to about 0.005% by weight is achievable, provided that the deoxidation required during the melting process is done without the use of aluminum but with the use of silicon or in the AOD or VOD process proceed (see below).

Based on the finished alloy, nickel is preferably at most 0.10 weight percent, more preferably at most 0.05 weight percent.

Refinement by addition of gaseous oxygen (conversion to oxides) and addition of CaO, preferably simultaneously remove excess carbon, silicon and phosphorous, as is conventional in the art. It is then refined by means of VOD (Vacuum Oxygen Decarburization) or AOD (Argon Oxygen Decarburization) (excess oxygen is removed by degassing in vacuum or by blowing it out with argon), Excess oxygen can be removed by conventional methods.

By controlling the use of chips (avoiding Ti-containing chips, such as Ti-containing steel No. 1.4571 known in the European range), the titanium content according to the invention can be set up to about 0.01% by weight, preferably up to about 0.005% by weight, especially Up to about 0.002 weight percent is preferred. As a further measure, Ti impurities can be avoided in the refractory lining of the converter used during melting.

In the scope of the present application, the term "substantially the balance of iron" shall refer to the remaining weight percentage of the alloy according to any one of claims 1 to 7, that is, the weight percentage of the balance is not defined by the corresponding claim The elements mentioned by name are composed, but are derived almost exclusively from iron (typically to the extent of at least 90% by weight of the balance, preferably at least 95% by weight, particularly preferably at least 99% by weight or more).

The amount of elements other than iron in the balance should be chosen such that the finished steel alloy according to the invention is ferritic. The initial basis for this is provided by the Schaeffler diagram mentioned at the outset, and the additional elements are calculated by Briggs and Parker by means of the equivalents of nickel and chromium. In individual cases, according to the measurement method mentioned at the outset, it can be determined by experimental verification whether the alloy obtained is actually ferrite according to the invention or not.

The alloys of the invention can be prepared by standard methods. By way of example, reference is made to "Ullmann's Encyklop  die der Technischen Chemie [Ullmann's Encyclopedia of Technical Chemistry]" 4th Edition, Chapter 2 in the "Steel" section in Verlag Chemie and the literature mentioned therein.

In the steel production process according to the invention, refining operations are preferably carried out using the AOD and VOD methods in succession; thus VOD refining can also be used simultaneously for nitriding.

For high-alloy steels, inhomogeneities in the microstructure lead to point accumulations of individual structural components. This can lead to unwanted changes in microstructure formation and physical and mechanical properties. Therefore, it is preferred that during the production of the steel alloy according to the invention, as is conventional in the art, in order to avoid point accumulation of individual structural constituents and the accompanying formation of inhomogeneities, during forging, at about 800 to 900° C., More preferably, the annealing is performed at a temperature of about 850°C. For this reason, so-called "soaking" of hot-rolled slabs or prolonging the preheating time before hot rolling is recommended.

Preferably the alloy according to the invention is annealed at a temperature of 750 to 850° C., preferably about 800° C., for about 0.5 to 2 hours after forging or cold forming, followed by water cooling. Thus, due to the diffusion process, the chromium concentration equilibrates in the matrix in the region of the finely dispersed, precipitated chromium nitride particles. However, the precipitation of chromium nitride can be greatly suppressed by optimizing the nitrogen content.

The steel alloy according to the invention can be reproducibly polished by conventional methods in the watch industry and is therefore acceptable as a raw material for use in the watch industry. Nitrogen added to the alloy in amounts up to 0.1% is present at the annealing temperature, which is preferably used in the steel alloys of the invention, either dissolved or in the form of finely precipitated chromium nitrides, typically about 1 μm in size, Therefore there is no negative impact on polishability.

The steel alloys of the invention, in particular those of claims 3 to 7, typically have the following machinability (metal plate, thickness 6 mm, hot rolled, annealed at 800°C for 30 minutes, quenched in water).

Yield strength R _p0.2 420MPa

Tensile strength R _m 603MPa

Elongation at break A ₀ 28%

Hardness HB30 188

Therefore, the alloy according to the invention can be compared to the quality of standard steel No. 1.4521.

According to the present invention, by adding nitrogen to the alloy instead of niobium or titanium, the precipitation of relatively large niobium or titanium carbides, which impairs polishability, is eliminated. In addition, precipitation of chromium carbides on grain boundaries is suppressed. This occurs through a change in the precipitation kinetics, resulting in the precipitation of chromium nitrides instead of chromium carbides, which is positively preferred. In the case of excess nitrogen solubility in steel alloys, very finely dispersed chromium nitride particles with a diameter of approximately 1 μm and smaller precipitate out, but do not have a negative effect on the polishing properties due to their fineness.

Due to the low content of titanium and aluminium, the alloys according to the invention have a low content of relevant oxides, which can be defined by test method M (spherical oxides, DIN 50602). Due to the almost complete absence of titanium and niobium, corresponding carbides are also almost completely absent. On the other hand, by coordinating the simultaneous addition of nitrogen and the remaining alloying elements except chromium, although the content of nitrogen (austenite forming elements) is increased, there is basically no precipitation of chromium carbides, and the alloy of the present invention is still iron sdsee. Therefore, the purity grades of the non-metallic oxide or carbide inclusions of the steel alloys according to the invention are adjusted together to such a high level that remelting according to the ESU method mentioned at the outset is no longer necessary; however, if If desired, remelting can be performed with the steel alloys of the present invention.

The steel alloys of the invention are soft magnetic in the sense of the definition mentioned at the outset.

The steel alloys preferred according to claims 3 to 7 of the invention exceed their effective total as defined at the outset, a minimum value of 26 for the injection steel required in medical technology.

Due to the good polishability and soft magnetic properties in the alloys of the invention, these can be used in the watch industry for the preparation of magnetically shielded case parts, for example for watches or other timepieces where the magnetic shielding of the watch mechanism is important. The steel alloys according to the invention, in particular those claimed in claim 7, may also be suitable for the production of parts for connecting watch straps.

The term "case parts" encompasses within the scope of the present application components generally used in the manufacture of watch cases, in particular the casings of watches, thus eg case bottoms and casings. However, within the scope of the present application, the term "housing part" also includes surfaces. The term "housing parts" includes the parts appearing in the tableware, as well as any blanks and semi-finished products thereof, which are further processed, optionally using other materials or semi-finished products made of alloys and other materials according to the invention, to prepare the final part.

The magnetically shielded watch case of the invention may consist of a bottom, a shell and a face, all of which are prepared according to the steel alloy of the invention. Accordingly, the steel alloy according to the invention is used both as material for components and as a shield against magnetic fields. Thus, it is possible to eliminate the complicated preparation of an additional soft iron cover, which has to be provided inside the normal casing in non-magnetic CrNi steel and which would lead to an increase in the thickness of the watch.

The steel variant 1.4521 according to the invention is uncommonly suitable for powder metallurgical processing using the MIM (Metal Injection Moulding) method, in particular because it can be supplied without problems during the pressing process (sintering) in a nitrogen atmosphere. Invention required nitrogen content. In the field of watch production, the MIM method is known per se. To prepare watch parts according to the invention, a steel alloy containing the final amounts of required elements (these will be specified in any one of claims 1 to 7) but not containing sufficient nitrogen is ground, formed into a powder and glued using a liquid Mixture suspension. This suspension is forced, for example by means of an extruder, into a mold whose cavity has the shape of the housing part to be produced. Then, the binder is evaporated, preferably in a vacuum, and the powder residue remaining in the mold is sintered. If the nitrogen content in the alloy powder is initially insufficient, a nitrogen atmosphere of suitable pressure is supplied during the sintering step so that the alloy also absorbs nitrogen during sintering. The choice of nitrogen at the appropriate pressure to achieve the nitrogen concentration according to the invention in the finished housing part can be determined by a series of experiments.

Preparation example

An example for the preparation of steel alloys according to the invention is given below:

a) Melting of about 5t in an induction furnace

b) Secondary metallurgy in VOD converter

c) In the form of slab 1250×250×1270mm, continuous casting

d) chemical analysis

e) Preheating in a chamber furnace to a rolling temperature of about 1080°C

f) Start rolling to a thickness of 120mm

g) Grinding on all sides of the slab

h) Preheating in a continuous furnace at 1080°C

i) Rolled to the final required thickness of 3-12mm on a four-roll rolling stand

j) Annealing at 750-850°C

k) Quenching in water

l) Descaling

m) Test mechanical properties R _p0.2 , R _m , A, Z

n) Metallographic determination of grain size

o) Determination of purity grade

p) Test polishability

q) Straightening

r) cut to final size

s) release

Claims (13)

1. high alloy Alfer, its comprise based on described alloy at the most molybdenum, 0.01 to 0.10 weight percent of chromium, 1.80 to 2.50 weight percents of silicon, 18.0 to 22.0 weight percents of 1.00 weight percents nitrogen, at the most 0.01 weight percent titanium, at the most 0.01 weight percent niobium, the aluminium and the surplus of 0.01 weight percent are iron basically at the most.

2. according to the Steel Alloy of claim 1, it comprises based on described alloy titanium, aluminium, niobium, manganese, the phosphorus and the carbon of 0.025 weight percent at the most of 0.04 weight percent at the most of 1.00 weight percents at the most of 0.005 weight percent at the most of 0.005 weight percent at the most of 0.005 weight percent at the most.

3. according to the Steel Alloy of claim 1 or 2, it comprises based on the molybdenum of the chromium of described alloy 19.5 to 20.5 weight percents, 1.90 to 2.10 weight percents and the nitrogen of 0.05 to 0.10 weight percent.

4. according to any one Steel Alloy of claim 1 to 3, it comprises based on the nitrogen of the molybdenum of the chromium of the silicon of about 0.8 weight percent of described alloy, about 20 weight percents, about 2 weight percents, about 0.05 weight percent and the titanium of 0.002 weight percent at the most.

5. according to any one Steel Alloy of top described claim, it comprises based on the described alloy nickel of 0.10 weight percent at the most.

6. according to any one Steel Alloy of top described claim, it comprises based on the described alloy sulphur of 0.03 weight percent at the most.

7. according to the Steel Alloy of claim 6, it comprises the sulphur based on described alloy 0.015 to 0.03 weight percent.

8. by the Housing for a meter parts of forming according to any one Steel Alloy of claim 1 to 7.

9. case member according to Claim 8, its form are at the bottom of the shell or the form of housing.

10. by the surface of forming according to any one Steel Alloy of claim 1 to 7.

11. by the connection watchband parts of forming according to any one Steel Alloy of claim 1 to 7.

12. according to claim 1 to 7 any one Steel Alloy the table magnetic shielding in application.

13. the preparation method of Housing for a meter parts, it is characterized in that, suspend according to the Steel Alloy of any one powder type of claim 1 to 7 with liquid adhesive, and described Steel Alloy can be chosen wantonly and comprises low-level nitrogen, in suspension introducing and the corresponding mould of case member, the evaporation tackiness agent, and in mould the sintered powder residuum; Precondition is if the alloy of powder type comprises low-level nitrogen, then carries out sintering in nitrogen containing atmosphere.