EP4588592A1

EP4588592A1 - Solid solution held chromium carbides for thermal spraying and method of making the same

Info

Publication number: EP4588592A1
Application number: EP24152105.3A
Authority: EP
Inventors: Barbara MAROLI; Arashk Memarpour; Oliver Lanz; Florian Baumgartner; Sedigheh Bigdeli
Original assignee: Hoganas Germany GmbH; Hoganas AB
Current assignee: Hoganas Germany GmbH; Hoganas AB
Priority date: 2024-01-16
Filing date: 2024-01-16
Publication date: 2025-07-23
Also published as: TW202544264A; WO2025153591A1

Abstract

In the present disclosure there is detailed a chromium-based powder consisting by total weight of powder of:
Iron (Fe) :
15 - 18 wt%,
Carbon (C) :
4.7 - 5.5 wt%,
Tungsten (W) :
2.2 - 3.4 wt%,
Molybdenum (Mo):
1.4 - 2.3 wt%,
Boron (B) :
0.3 - 1.0 wt%,
Silicon (Si) :
0.1 - 1.0 wt%,
Niobium (Nb) :
0.35 - 0.60 wt%,
the balance being chromium (Cr) and unavoidable impurities not exceeding 0.3 wt%, wherein nickel (Ni) if present is only present as an unavoidable impurity in amounts not exceeding 0.10 wt%, which when used in a HVOF and/or a HVAF process provides primarily chromium carbides in solid solution in a BCC-phase iron-chrome stainless-steel alloy. As the binder is free of nickel and cobalt it provides a sustainable yet cost beneficial replacement for conventional binders for carbide products in particular for uses where nickel and/or cobalt contamination is undesired.

It is recommended that Figure 2 is published with the abstract.

Description

TECHNICAL FIELD

In the field of powder technology for HVOF and HVAF applications there is suggested a range of solid solution held chromium carbides for thermal spraying together with method of making the same and uses thereof.

BACKGROUND

Tungsten/chromium Carbide powders are hard materials (hardness ≈1000 HV), used for dense coatings. They can be sprayed using High-Velocity Oxygen-Fuel (HVOF) and High-Velocity Air-Fuel (HVAF) spray methods onto various metallic parts and structures to improve the surface resistance of these parts and structures to severe wear and corrosion. Conventional carbide powders consist of hard WC or Cr₃C₂ particles in a binder matrix, for which the CoCr powders are used. Different alloying elements, e.g., Ni, Fe, Ti, etc., may be added to the matrix to improve mechanical, corrosion, and spray-ability properties, c.f. e.g., J. Garcia et al. (J. Garcia, V. Collado Ciprés, A. Blomqvist and B. Kaplan, "Cemented carbide microstructures: a review," International Journal of Refractory Metals and Hard Materials, vol. 80, pp. 40-68, 2019.)
In the recent years, use of some elements, such as Co and Ni in particular, has become of concern due to their harmful characteristics to the environment and health and there have been attempts to replace these elements by less harmful elements in the binder, c.f., e.g., M. Walbrühl et al. (M Walbrühl, D. Linder, K. Ågren and A. Borgenstam, "Diffusion modeling in cemented carbides: Solubility assessment for Co, Fe and Ni binder systems," International Journal of Refractory Metals and Hard Materials, vol. 68, pp. 41-48, 2017) .
It is known that conventional binders can be replaced by high-alloyed steels, or atomized powders, c.f., e.g., J. Garcia et al. Herein, the present inventors introduce new alloys that suitable for use as hard face coatings prepared by thermal spraying from an atomized powder. In the type of material introduced, instead of conventional carbide/binder concept, hard carbides precipitate in solid solution as a coherent phase during cooling after melting in the herein detailed matrix BCC-phase iron-chromium alloy, as the solid solution.
Since the detailed alloys are essentially free of hazardous species, i.e., Ni and Co, they are excellent candidates for all industries wherein sustainability and trace mineral contamination is a concern. Food industries for example are promoting a new class of "new food" where coating made from the present alloys can be used for packaging materials. Also, they are strong candidates for coating different components in aerospace or power plants, e.g., sliding tubes, sliding pistons, axles, bolts, bushings, flanges, etc., as well as having potential uses for coating grinding rolls, crushers, and calender rolls in the relevant industries.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1:: Phase diagram for the molten alloy in the temperature as a function of carbon-content calculated using Thermo-Calc.
Figure 2:: EM-cross section of pre-alloyed, gas atomized powder according to the invention. A) powder particle, B) enlarged section of particle.
Figure 3:: Material consumption versus coverage rate for different spray techniques and parameters, with comparative.
Figure 4:: Cross section of the coating achieved by JP spraying, in different magnifications. A) scalebar 100 pm, B) scalebar 50 µm.
Figure 5:: Cross section of the coating achieved by DJ spraying, in different magnifications. A) scalebar 100 pm, B) scalebar 50 µm.
Figure 6:: NSS tested coupons after A) 168 hours for JP-sprayed and B) after 504 hours for DJ-sprayed samples.
Figure 7:: Gas permeability test results for coated samples.
Figure 8:: Cavitation test results versus material consumption for coated samples.
Figure 9:: Hardness measurements for sprayed samples using different techniques and parameters.
Figure 10:: Roughness measurements for sprayed samples using different techniques and parameters.
Figure 11:: Young modulus measurements for sprayed samples using different techniques and parameters.
Figure 12:: Material consumption for spraying versus wear resistance for sprayed samples.
Figure 13:: SEM image and EDX map of elements showing different types of carbides in a BCC-matrix.

It is to be understood, that the embodiments shown in the figures are for illustration of the present invention and cannot be construed as being limiting on the present invention. Unless otherwise indicated, the drawings are intended to be read (e.g., cross-hatching, arrangement of parts, proportion, degree, etc.) together with the specification, and are to be considered a portion of the entire written description of this disclosure.

DETAILED DESCRIPTION

In a first aspect of the present invention and embodiment thereof, a BCC-phase iron-chrome stainless-steel alloy consisting by total weight of alloy of:

Iron (Fe) :	44.0 - 47.0 wt%,
Silicon (Si) :	5.0 - 7.0 wt%,
Molybdenum (Mo):	0.60 - 0.80 wt%,
Tungsten (W) :	0.40 - 0.60 wt%,
Carbon (C) :	0.01 - 0.10 wt%,
Boron (B) :	0.001 - 0.010 wt%,
Niobium (Nb) :	0.005 - 0.010 wt%,

the balance being chromium (Cr) and unavoidable impurities not exceeding 0.1 wt%, wherein nickel (Ni) if present is only present as an unavoidable impurity in amounts not exceeding 0.05 wt%.

In a preferred aspect thereof, the BCC-phase iron-chrome stainless-steel alloy of is present as a powder. In particularly preferred embodiments thereof, wherein the comprises at least 80% by weight of the stainless-steel powder contained within a sieved fraction of the stainless-steel powder having a size distribution from 1 µm to 100 pm, preferably from 2.5 µm to 75 µm, or even more preferably from 5 µm to 50 pm, as measured by sieving in accordance with ISO-14232-1-2017-E, Particle distribution by sieving, and/or preferably comprises at least 85% by weight, at least 90% by weight, or more preferably at least 95% by weight of the stainless-steel powder having a size distribution from 2.5 µm to 100 µm as measured by sieving in accordance with ISO-14232-1-2017-E, Particle distribution by sieving.
In embodiments of the BCC-phase iron-chrome stainless-steel alloy according to any embodiment herein, iron (Fe) is present in the alloy from 44.5 wt% to 46.5 wt%, preferably from 45.0 wt% to 46.0 wt%, more preferably from 45.4 wt% to 45.9 wt%.
In embodiments of the BCC-phase iron-chrome stainless-steel alloy according to any embodiment herein, silicon (Si) is present in the alloy from 5.3 wt% to 6.7 wt%, preferably from 5.5 wt% to 6.3 wt%, more preferably from 5.7 wt% to 6.1 wt%.
In embodiments of the BCC-phase iron-chrome stainless-steel alloy according to any embodiment herein, molybdenum (Mo) is present in the alloy from 0.62 wt% to 0.78 wt%, preferably from 0.65 wt% to 0.75 wt%, more preferably from 0.63 wt% to 0.73 wt%.
In embodiments of the BCC-phase iron-chrome stainless-steel alloy according to any embodiment herein, tungsten (W) is present in the alloy from 0.42 wt% to 0.58 wt%, preferably from 0.45 wt% to 0.55 wt%, more preferably from 0.47 wt% to 0.53 wt%.
As detailed in the below experimental section, the stainless-steel alloys of the present invention are useful as solid solution matrix alloys for various carbides, in particular for chromium and tungsten carbides.
The alloys of the invention can be manufactured as powders for HVOF and/or HVAF spray coating by pre-alloying the elements of the alloy, atomizing, e.g., water-atomizing, the pre-alloyed elements, whereby a pre-alloyed stainless-steel powder containing the alloys of the invention is obtained.
An advantage of the alloys of the present invention is that they can be mixed with carbides of a suitable powder size for HVOF and/or HVAF spray coating and spray coated together directly onto a suitable surface.
However, it is more preferable to allow the alloys of the invention to form jointly with the carbides from melt during thermal spray coating as will be detailed herein below.

To this purpose, it is preferable to prepare a chromium-based powder consisting by total weight of powder of:

Iron (Fe) :	15 - 18 wt%,
Carbon (C) :	4.7 - 5.5 wt%,
Tungsten (W) :	2.2 - 3.4 wt%,
Molybdenum (Mo):	1.4 - 2.3 wt%,
Boron (B) :	0.3 - 1.0 wt%,
Silicon (Si) :	0.1 - 1.0 wt%,
Niobium (Nb) :	0.35 - 0.60 wt%,

the balance being chromium (Cr) and unavoidable impurities not exceeding 0.3 wt%, wherein nickel (Ni) if present is only present as an unavoidable impurity in amounts not exceeding 0.10 wt%.

In the most preferred embodiments of the present invention, the chromium-based powder is a pre-alloyed powder, preferably pre-alloyed from a melt. When the powder is pre-alloyed before powder formation, such as pre-alloyed from melt, e.g., done by gas or water atomization, the abovementioned BCC-phase iron-chrome stainless-steel alloy will form as a solid solution matrix for co-precipitated carbide phases in solid solution. As discussed below, such pre-alloyed powders are directly useable in thermal spray processes with high transfer ratios of the elemental constituents to the surfaces coated by thermal spray coating processes.
Preferred embodiments of the chromium-based powder are detailed herein below.
In embodiments of the chromium-based powder according to invention, the amount of iron (Fe) is from 15.5 wt% to 17.5 wt%, preferably from 16.0 wt% to 17.0 wt%.
In embodiments of the chromium-based powder according to invention, the amount of carbon (C) is from 4.9 to 5.3 wt%, preferably from 5.0 to 5.2 wt%.
In embodiments of the chromium-based powder according to invention, the amount of tungsten (W) is from 2.5 wt% to 3.1 wt%, preferably from 2.7 wt% to 2.9 wt%.
In embodiments of the chromium-based powder according to invention, the amount of molybdenum (Mo) is from 1.6 wt% to 2.1 wt%, preferably from 1.7 wt% to 2.0 wt%.
In embodiments of the chromium-based powder according to invention, the amount of boron (B) is from 0.4 to 0.9 wt%, preferably from 0.5 wt% to 0.8 wt%.
In embodiments of the chromium-based powder according to invention, the amount of silicon (Si) is from 0.3 wt% to 0.9 wt%, preferably from 0.5 wt% to 0.8 wt%. In general, enough silicon must be present in the chromium-based powders for the subsequent forming of the abovementioned alloys of the invention.
In embodiments of the chromium-based powder according to invention, the amount of niobium (Nb) is from 0.40 wt% to 0.55 wt%, preferably from 0.45 wt% to 0.50 wt%.
When the chromium-based powder detailed herein is a pre-alloyed powder, carbides, primarily chromium and tungsten carbides, will be in solid solution in a BCC-phase iron-chrome stainless-steel alloy according to any of the herein detailed embodiments.
In preferred embodiments of the chromium-based powder whether pre-alloyed or mixed, the chromium-based powder preferably comprises at least 80% by weight of the chromium-based powder contained within a sieved fraction of the chromium-based powder having a size distribution from 1 µm to 100 pm, preferably from 2.5 µm to 75 pm, or even more preferably from 5 µm to 50 µm, as measured by sieving in accordance with ISO-14232-1-2017-E, Particle distribution by sieving, and/or preferably comprises at least 85% by weight, at least 90% by weight, or more preferably at least 95% by weight of the chromium-based powder having a size distribution from 2.5 µm to 100 µm as measured by sieving in accordance with ISO-14232-1-2017-E, Particle distribution by sieving. Thereby the powders of the present invention will have optimal sizes for the intended use in thermal spray processing methods.
Accordingly, there is herein detailed the use of a chromium-based powder according to any embodiment of the present invention for the coating of a surface by means of a thermal spray method.
Further, there is herein detailed a shaped object having a coating comprising a BCC-phase iron-chrome stainless-steel alloy according to any embodiment of the herein detailed invention.
Further, there is herein detailed a method for the production of a shaped object having the steps:

provision of a chromium-based powder according to any embodiment herein detailed in a form or formulation that is suitable for thermal spraying;
carrying-out of a thermal spraying process using the chromium-based powder;
obtaining of the shaped object.

EXPERIMENTAL

Preparation of pre-alloyed and gas atomized powders

In preparation to the herein detailed experiments, powder mixtures as detailed herein above and having the below given specific compositions were pre-alloyed, and either stored as a pre-alloyed ingot for subsequent gas atomization, or directly gas atomized from the pre-alloy melt. In this way, each powder particle was cooled fast enough for the atomized powder to be considered as a separate bulk material, in which carbides can nucleate and grow upon cooling as intermetallics. These intermetallics form a coherent part of the material and no fusion was needed to create or bind them.
Powder sizes were determined in accordance with ISO-14232 - 1-2017-E Particle distribution by sieving and are stated as 95% of the powder mass falling inside the given size exclusion interval. The measured size exclusion range for the particular atomized powders of the present experiments was: 3 wt% > 53µm ≥ 45µm; 30 wt% > 45µm ≥ 38µm; 55 wt% > 38 µm ≥ 15pm; 2 wt% > 15pm.

HVOF-coating experiments

Coating properties were tested for different HVOF spray parameters. In the present work, two different jet guns were used for thermal spraying of the samples: Diamond jet gun (DJ), and high-pressure jet gun (JP) . The fuel for the DJ consisted of O₂+H₂+air and for the JP it was a mixture of oxygen and argon.
The high-pressure jet gun (JP-5000) is designed for liquid-fuel (kerosene) and oxygen operation. Fuel and oxygen are fed into the gun, atomized by the coaxial stabilizer, and ignited in the combustion chamber, resulting in a supersonic flame. Spray powder from the powder feeder is fed radially into the supersonic flame through two powder ports positioned directly after the combustion chamber. The spray stream is accelerated through a converging/diverging nozzle several times the speed of sound. The spray particles are heated to a molten or semi-molten state and propelled at high velocity, impacting the coating surface in a plastic state. Table 1 provides an overview of the spray parameters used in the present experiments. Table 1: Spray parameters for high-pressure jet gun (JP-5000)

Chemistry X-CrNiC X-CrNiC X-CrNiC X-CrNiC CrC-FeCr CrC-FeCr

Grain size [µm] 45/10 45/10 45/15 45/15 45/15 45/15

Parameter

O2 scfh 336 489 336 489 336 489

nlpm 148 215 148 215 148 215

H2 scfh 1637 1450 1637 1450 1637 1450

nlpm 720 638 720 638 720 638

Shroud (Air) scfh 1000 786 1000 786 1000 786

nlpm 440 346 440 346 440 346

Powder feeder

Feed rate g/min 50.0 50.0 50.0 50.0 50.0 50.0

Coating procedure

Surface speed m/min 75 75 75 75 75 75

Offset mm 5 5 5 5 5 5

Spray distance mm 240 240 240 240 240 240

The DiamondJet, DJ-process, uses oxygen, fuel gas and air to produce a high-pressure annular flame, which provides uniform heating of the axially introduced powder spray material. The gas stream is accelerated through a converging/diverging nozzle to supersonic speeds. The gas stream propels the powder particles towards the substrate. Individual particles deform plastically upon impact, tenaciously bonding the coating to the substrate. Table 2 details the spray parameters used for the present experiments.

Table 2: Spray parameters for Diamond jet gun

Chemistry		CrC-FeCr	CrC-FeCr	CrC-FeCr	CrC-FeCr	CrC-FeCr	CrC-FeCr	CrC-FeCr	CrC-FeCr
Grain size [µm]		45/15	45/15	45/15	45/15	45/15	45/15	45/15	45/15

Parameter
	inch	4	4	4	4	4	4	6	6
	mm	101,6	101,6	101,6	101,6	101,6	101,6	152.4	152.4
Oxygen	nlpm	860	800	835,5	900	900	835,5	835,5	810
	scfh	1956	1820	1900	2047	2047	1900	1900
Fuel	lph	25	23,5	20,79	24	24	20,79	22	23

Powder feeder
	g/min	80	80	80	80	80	80	80	80
Coating procedure
Surface speed	m/min	50	50	50	50	50	50	50	50
Offset	mm/U	5	5	5	5	5	5	5	5
Spray distance	mm	320	300	380	300	300	380	380	320

Different spray parameters were tested, e.g., power feeder, nozzle size, combustion pressure, etc., c.f., Tables 1 and 2. Parameters were adjusted in a way that a dense coating with optimal deposition efficiency is achieved. Separate coupons were sprayed with the same parameters for different tests.
Hardness, roughness, gas permeability, Young's modulus, and wear resistance were measured for each spray parameter.
After spraying, coated samples were analyzed with optical microscope to measure the coating thickness and porosity and additionally examined using electron microscopy.
Another set of coupons were placed in the natural salt spray chamber and evaluated after specific periods of time to study the corrosion properties. Corrosion resistance of the material was also evaluated based on gas permeability and cavitation tests, c.f. Figure 8.
Finally, coated samples were analyzed using SEM/EDX analysis to find a better understanding of the final product.

Calphad-based calculation

Figure 1 shows the phase diagram for the presently developed alloys as calculated using Thermo-Calc software, steel database TCFE12.
Composition range marked with vertical stippled lines in Figure 1 shows composition ranges of for the carbon (C) content for this powder, which results in carbides as hard phase, precipitated in a BCC matrix. Small amounts of Cr-boride precipitates also form which can have a positive effect on hardness.
The starting pre-alloyed powders' compositions were selected such that the formed BCC-phase, which is predominately an iron-chromium-silicon alloy, forms a soft solid solution matrix having optimized elastic properties for the resulting coatings from thermal spraying while being able to contain the formed carbide phases strongly in solid solution.
In the shown calculations, the BCC-phase forms as an eutectic composition having the composition given below in Table 3. Table 3: Composition of BCC-phase from Thermo-Calc

Fe Nb B Mo C W Si Cr

45.7 0.07 0.008 0.7 0.066 0.5 5.9 Bal.
As can be seen from the resulting equilibrium composition, essentially all niobium, boron, and carbon has been consumed in the formation of the various carbide phases distributed in the matrix alloy, although at least the amount of carbon remains sufficient for interaction with the main alloy elements of iron (Fe), silicon (Si), molybdenum (Mo), tungsten (W), and chromium (Cr) as the balance, whereas niobium (Nb) and boron (B) appear to be present only in amounts commensurate with both of these elements being present in the matrix alloy as unavoidable impurities based on the starting materials used.

Microstructure analysis

Examination of pre-alloyed powder

Figure 2 A) and B) show (EM) the same cross section of the atomized powder at two resolutions (B enlarged). Dark gray carbides (M₂₃C₆ and M₇C₃ according to the phase diagram in Figure 1) can be seen in a light-color matrix of solid solution BCC. Small amounts of Cr-boride precipitates also form which improve hardness.

Sprayed coupons

Sprayed coupons were cut and analyzed by a LEICA DM6 M light optical microscope, to measure the coating thickness and porosity.
Figure 3 shows indexes correlated to deposition efficiency and coating's thickness for different spraying methods and parameters in accordance with Tables 1 and 2. The results are also compared with an existing product, Amperit^® 588.
Most of the trails fall in the high-productivity/high-efficiency area of the plot (compatible with, and in some cases better than the existing products) which shows that this product is cost-beneficial through which a dense coating can be achieved. The JP-technique seems to have higher productivity than Amperit^® 588, while the DJ-technique has a higher efficiency.
Figures 4 and 5 show cross sections of the coating using JP and DJ techniques respectively. JP method seems to be able to create denser coatings (at about 0.2 - 0.9 area% porosity), while the porosity level of DJ sprayed sample appears higher (at about 3 area%). However, since the porosity content is measured by image analysis, which is based on the contrast of dark spots versus light bulk in the micrographs, the certainty of these values is not very high, as it is possible that the dark spots are small oxide particles. Nevertheless, it should be noted that even 3% porosity is completely acceptable for this type of coatings.

Corrosion Properties

Salt Spray Testing:

Corrosion properties of the coating was studied using natural salt spray (NSS) test by natural salt spray (NSS) test using a SC1000 Weiss GmbH machines according to standard ASTM B117. Samples were placed in the chamber and inspected after specific times, i.e., 168, 336, 504, 672, 840 and 1008 hours.
Figure 6 shows the tested coupons after A) 168 hours for JP-sprayed samples, at which time severe corrosion became observable, and after B) 504 hours for DJ sprayed samples, when signs of corrosion were only then becoming observable. Accordingly, the corrosion resistance of the present coatings is compatible or better than currently marketed products, such as e.g., Amperit^® 588, which complies with a minimum of 168 hours exposure to the test conditions before severe corrosion becomes observable.

Gas Permeability:

Gas permeability test results were used as further tool for providing an index useful in evaluating corrosion resistance of the coated samples. Figure 7 shows these results for the two different spray techniques measured using a GPT-03 machine in accordance with standard ISO 4022.
The coating seems rather dense but at higher experimental pressures the gas penetration accelerates.

Cavitation Tests:

Cavitation test was run on the coated samples using a KLN Type 587 machine in accordance with standard ASTM G32-85. Results are shown in Figure 8.
It is interesting that although DJ sprayed coatings are less dense (also confirmed by gas permeability and EM), they show a better corrosion resistance in the NSS test.
Overall, the present experiments confirm the corrosion resistance of the present coatings, ranking at on par with or better than commercialized products, but in general being intermediate corrosion resistance coatings.

Mechanical Properties

Mechanical properties of the coatings were measured. Results for hardness, roughness, Young's modulus and wear resistance are shown in Figures 9 to 12.
Hardness Vickers was measured using a Struers Dura Scan machine according to standard ISO 6507,1-4:2018. The present product shows a general hardness of 900-1000 HV, c.f. Figure 9, which makes it a good candidate for the intended applications.
Roughness of coated samples were measured based on standards DIN EN ISO 4287 and ASME B46.1, using a MarSurf PS10 machine. The results presented in Figure 10 show an average value of 5-7 Ra for these compositions, which is slightly higher than expected for this property among different carbides (c.f., J. Garcia et al.).
Young's modulus represents elastic properties of material and is correlated to hardness. The measurements were done using a LA-wave V2-1 Fraunhofer IWS apparatus. The average value of 100-130 GPa (Figure 11) is expected for a hard material and makes it a good candidate for applications where heavy loading is applied.
Wear resistance of the coated samples was measured according to ASTM G65 (Figure 12) using a built-in machine. Volume loss is shown versus material consumption for spraying in this figure.
It shows that all coatings have excellent wear resistance, i.e., very low volume loss for medium powder consumption in comparison with Amperit^® 588. This makes the present product significantly beneficial from cost point of view and a strong candidate for application where wear properties play an important role.

SEM Analysis

A Hitachi SU6600 Scanning Electron Microscope was used to analyze coated samples. Figure 13 shows the cross section together with EDX map for high-content elements, using voltage of 15kV. The results are aligned with the thermodynamic calculation, showing different types of carbides in a BCC matrix.

CLOSING COMMENTS

Although the present invention has been described in detail for purpose of illustration, it is understood that such detail is solely for that purpose, and variations can be made therein by those skilled in the art in practicing the claimed subject matter, from a study of the drawings, the disclosure, and the appended claims.
The term "comprising" as used in the claims does not exclude other elements or steps. The indefinite article "a" or "an" as used in the claims does not exclude a plurality. A unit may fulfill the functions of several means recited in the claims. A reference sign used in a claim shall not be construed as limiting the scope.

Claims

A BCC-phase iron-chrome stainless-steel alloy consisting by total weight of alloy of: Iron (Fe) : 44.0 - 47.0 wt%, Silicon (Si) : 5.0 - 7.0 wt%, Molybdenum (Mo): 0.60 - 0.80 wt%, Tungsten (W) : 0.40 - 0.60 wt%, Carbon (C) : 0.01 - 0.10 wt%, Boron (B) : 0.001 - 0.010 wt%, Niobium (Nb) : 0.005 - 0.010 wt%,

the balance being chromium (Cr) and unavoidable impurities not exceeding 0.1 wt%, wherein nickel (Ni) if present is only present as an unavoidable impurity in amounts not exceeding 0.05 wt%.
A BCC-phase iron-chrome stainless-steel alloy of claim 1 as a powder.
A BCC-phase iron-chrome stainless-steel alloy according to claim 2, wherein the stainless-steel powder comprises at least 80% by weight of the stainless-steel powder contained within a sieved fraction of the stainless-steel powder having a size distribution from 1 µm to 100 pm, preferably from 2.5 µm to 75 pm, or even more preferably from 5 µm to 50 pm, as measured by sieving in accordance with ISO-14232-1-2017-E, Particle distribution by sieving, and/or preferably comprises at least 85% by weight, at least 90% by weight, or more preferably at least 95% by weight of the stainless-steel powder having a size distribution from 2.5 µm to 100 µm as measured by sieving in accordance with ISO-14232-1-2017-E, Particle distribution by sieving.
A BCC-phase iron-chrome stainless-steel alloy according to any of the claims 1 to 3, wherein iron (Fe) is present in the alloy from 44.5 wt% to 46.5 wt%, preferably from 45.0 wt% to 46.0 wt%, more preferably from 45.4 wt% to 45.9 wt%.
A BCC-phase iron-chrome stainless-steel alloy according to any of the claims 1 to 4, wherein silicon (Si) is present in the alloy from 5.3 wt% to 6.7 wt%, preferably from 5.5 wt% to 6.3 wt%, more preferably from 5.7 wt% to 6.1 wt%.
A BCC-phase iron-chrome stainless-steel alloy according to any of the claims 1 to 5, wherein molybdenum (Mo) is present in the alloy from 0.62 wt% to 0.78 wt%, preferably from 0.65 wt% to 0.75 wt%, more preferably from 0.63 wt% to 0.73 wt%.
A BCC-phase iron-chrome stainless-steel alloy according to any of the claims 1 to 6, wherein tungsten (W) is present in the alloy from 0.42 wt% to 0.58 wt%, preferably from 0.45 wt% to 0.55 wt%, more preferably from 0.47 wt% to 0.53 wt%.
A chromium-based powder consisting by total weight of powder of: Iron (Fe) : 15 - 18 wt%, Carbon (C) : 4.7 - 5.5 wt%, Tungsten (W) : 2.2 - 3.4 wt%, Molybdenum (Mo): 1.4 - 2.3 wt%, Boron (B) : 0.3 - 1.0 wt%, Silicon (Si) : 0.1 - 1.0 wt%, Niobium (Nb) : 0.35 - 0.60 wt%,

the balance being chromium (Cr) and unavoidable impurities not exceeding 0.3 wt%, wherein nickel (Ni) if present is only present as an unavoidable impurity in amounts not exceeding 0.10 wt%.
A chromium-based powder according to claim 8, wherein the amount of iron (Fe) is from 15.5 wt% to 17.5 wt%, preferably from 16.0 wt% to 17.0 wt%.
A chromium-based powder according to claim 8 or claim 9, wherein the amount of carbon (C) is from 4.9 to 5.3 wt%, preferably from 5.0 to 5.2 wt%.
A chromium-based powder according to any of the claims 8 to 10, wherein the amount of tungsten (W) is from 2.5 wt% to 3.1 wt%, preferably from 2.7 wt% to 2.9 wt%.
A chromium-based powder according to any of the claims 8 to 11, wherein the amount of molybdenum (Mo) is from 1.6 wt% to 2.1 wt%, preferably from 1.7 wt% to 2.0 wt%.
A chromium-based powder according to any of the claims 8 to 12, wherein the amount of boron (B) is from 0.4 to 0.9 wt%, preferably from 0.5 wt% to 0.8 wt%.
A chromium-based powder according to any of the claims 8 to 13, wherein the amount of silicon (Si) is from 0.3 wt% to 0.9 wt%, preferably from 0.5 wt% to 0.8 wt%.
A chromium-based powder according to any of the claims 8 to 14, wherein the amount of niobium (Nb) is from 0.40 wt% to 0.55 wt%, preferably from 0.45 wt% to 0.50 wt%.
A chromium-based powder according to any of the claims 8 to 15 as a pre-alloyed powder.
A chromium-based powder according to claim 16, wherein carbides are in solid solution in a BCC-phase iron-chrome stainless-steel alloy according to any of the claims 1 to 7.
A chromium-based powder according to either of the claims 16 or 17, wherein the chromium-based powder comprises at least 80% by weight of the chromium-based powder contained within a sieved fraction of the chromium-based powder having a size distribution from 1 µm to 100 pm, preferably from 2.5 µm to 75 pm, or even more preferably from 5 µm to 50 pm, as measured by sieving in accordance with ISO-14232-1-2017-E, Particle distribution by sieving, and/or preferably comprises at least 85% by weight, at least 90% by weight, or more preferably at least 95% by weight of the chromium-based powder having a size distribution from 2.5 µm to 100 µm as measured by sieving in accordance with ISO-14232-1-2017-E, Particle distribution by sieving.
Use of a chromium-based powder according to any one of claims 8 to 18 for the coating of a surface by means of a thermal spray method.
A shaped object having a coating comprising a BCC-phase iron-chrome stainless-steel alloy according to any of the claims 1 to 7.
A method for the production of a shaped object according to claim 20, having the steps:
- provision of a chromium-based powder according to one or more of claims 8 to 18 in a form or formulation that is suitable for thermal spraying;

- carrying-out of a thermal spraying process using said chromium-based powder;

- obtaining of said shaped object.