STEEL POWDER AND A METHOD OF PRODUCING SUCH A POWDER

Abstract

A steel powder is provided. The steel powder has a composition of, in wt. %, C 0.05-2.0, Mn 14.0-30.0, Al 5.0-10.0, Cr 3.0-10.0, Si 0.1-2.0, Ti 0.05-0.5, and, as optionals, Ni 0.0-0.2, N 0.0-1.0, O 0.0-0.50, with a balance of Fe and unavoidable impurities. A method of producing the powder is also provided.

Claims

1. A steel powder, comprising, in wt. %: C 0.05-2.0; Mn 14.0-30.0; Al 5.0-10.0; Cr 3.0-10.0; Si 0.1-2.0; Ti 0.05-1.0; and, as optionals, Ni 0-1.0; O 0-0.50; and a balance of Fe and unavoidable impurities.

2. The steel powder according to claim 1, comprising, in wt. %, C 0.80-1.2, Mn 15.0-26.0, Al 5.0-8.5, Cr 3.0-7.0, Si 0.3-1.1, Ti 0.05-0.5, and, as optionals, Ni 0-0.2, N 0-1.0, O 0-0.50, and the balance of Fe and unavoidable impurities.

3. The steel powder according to claim 1, comprising in wt. % C 0.80-1.20, Mn 15.0-23.0, Al 5.5-8.5, Cr 5.0-7.0, Si 0.3-1.1, Ti 0.05-0.3, and, as optionals, Ni 0-0.2, N 0-0.50, O 0-0.50, and the balance of Fe and unavoidable impurities.

4. steel powder according to claim 1, the wherein a composition of the steel powder is such that, for a fraction of the powder having a median particle diameter of m=10 an explosion factor
Ef<3.0 (MJ/kg*?m.sup.?0.5), wherein
Ef=Hf?(1/?{square root over (m)}), wherein Hf is the sum of a heat of combustion contributions Hc(element) of each of the elements of Fe, Cr, Ti, Mn, C, Al and Si, wherein the heat of combustion contribution Hc for each element is expressed by:
Hc(element)=Hci(element)?wt. % (element)/100, wherein Hci(element) is a heat of combustion value of each respective element as measured in MJ/kg, wherein Hci(Fe)=7.4; Hci(Cr)=6.0; Hci(Ti)=19.7; Hci(Al)=31.0; Hci(Mn)=7.0; Hci(C)=7.0; and Hci(Si)=16.0.

5. The steel powder according to claim 4, wherein Ef<2.95 (MJ/kg*?m.sup.?0.5).

6. The steel powder according to claim 1, wherein a density D of the steel forming the steel powder, defined as a density of a particle being fully dense and without any closed porosity therein, is less than 7.20 g/cm.sup.3.

7. The steel powder according to claim 5, wherein D<6.97 g/cm.sup.3.

8. The steel powder according to claim 1, wherein the powder is a gas-atomised powder having a median particle diameter m, wherein m<100 ?m.

9. The steel powder according to claim 1, wherein the powder is a gas-atomised powder having a median particle diameter m, wherein m<20 ?m.

10. The steel powder according to claim 1, wherein Mn?16.5 wt. %.

11. The steel powder according to claim 1, wherein Mn?19 wt. %.

12. The steel powder according to claim 1, wherein Al>6.0 wt. %.

13. The steel powder according to claim 1, wherein Al>6.5 wt. %.

14. A method of producing a powder comprising the steps of providing a steel melt having a composition such that, when subjected to an atomization process, will form a powder according to claim 1; providing a powder by atomising the steel melt; and extracting, from the atomised powder, a powder fraction, which has a median particle diameter m<100 ?m.

Description

DETAILED DESCRIPTION

[0079] In the following, essential elements of the steel of the invention and their contribution to the functionality and characteristics of the steel and the steel powder will be discussed.

[0080] Carbon, C, is used as a carbide-former, thereby adding mechanical strength to the steel, and preventing to some extent the formation of unwanted intermetallic phases. C increases the stability of the austenite and has a strong solid solution hardening effect.

[0081] Manganese, Mn, is used as main austenite stabilizer, as Ni should be avoided.

[0082] Aluminium, Al, is used for lowering the density of the steel and for contributing to the strength of the steel by forming carbides, or by forming nitrides if nitrogen is present in the steel. Al is a ferrite stabilizer. It also has a high heat of combustion value, thereby adding to the explosion tendency of a powder. At least for the latter reason, the amount of aluminium should not be too high.

[0083] Chromium, Cr, contributes to the corrosion resistance of the steel. Cr is a ferrite stabilizer, and should, at least for that reason, not be too high in content. It has a lower heat of combustion value than other essential elements in the steel, and could therefore be used to compensate for the more negative impact of Al in that respect.

[0084] Titanium, Ti, contributes to the strength of the steel by forming carbides and/or nitrides. Ti stabilizes ferrite and has a high heat of combustion value. It is therefore only present from 0.05% up to 1.0 wt. % in the steel.

[0085] Silicon, Si, makes the melt more fluid and thereby facilitates the atomization process. Si also has a low density. However, Si stabilizes ferrite and has a high heat of combustion value. It is therefore only present from 0.1% up to 2.0 wt. % in the steel.

[0086] Nitrogen, N, may be present up to 1.0 wt. % in the steel powder. However, too much N may result in large amount of precipitates with a risk of reducing ductility of the steel.

[0087] Nickel, Ni, may be present up to 0.2 wt. %. Above that level, Ni may cause allergic reactions for people being allergic to nickel. Absence of Ni from the powder will remedy the problem completely.

EXAMPLES

[0088] Examples of different compositions, some of which are within the claimed scope of protection of the present invention, are presented hereinafter with the aim of showing how the steel composition affects the explosion risk, as defined by the explosion factor.

[0089] In all examples, and for the purpose of defining the particle sizes as defined in the present invention, measurements of particle size have been performed by Malvern Mastersizer 2000 with Wet Dispersion Unit and using Mie theory to calculate the best fit size distribution according to the ISO standard 13320:2020.

[0090] When calculating and comparing the explosion factor (E f), a reference value of median particle diameter (d.sub.50) of 10 ?m defined in volume % is used as Ef is also dependent on the particle size. This means that of a certain volume of particles analysed, d.sub.50 is the median diameter within that volume.

Example 1

[0091] A powder according to the present invention was manufactured by providing a steel melt with composition according to Table 1. The steel melt preferably comprises raw materials in the form of virgin feedstocks and commercially available ferroalloys. The steel melt was transformed into powder by using a gas atomization technique where the steel melt was disintegrated into droplets through a nozzle by a high-pressure gas stream in a nitrogen atmosphere. The pressure of the disintegrating gas stream was preferably kept above 30 bar. The droplets cooled down in an atomisation tower containing nitrogen flow gas to form solid particles. Particles in the fraction referred to in example 1 were subsequently extracted using an air classification equipment, such as the ATP Turboflex Air Classifier from Hosokawa Micron Ltd.

[0092] The composition of example 1 (Table 1) is within the claimed scope, and the explosion factor is as low as 2.82 MJ/kg*?m.sup.?0.5.

TABLE-US-00001 TABLE 1 1. Fe16Mn6.5Al6Cr Hc.sub.i Composition Hc (MJ/kg) = Elements (MJ/kg) (wt. %) Hc.sub.i*wt. %(element)/100 Fe 7.4 68.54 5.07196 Cr 6.0 5.9 0.354 Ti 19.7 0.28 0.05516 Al 31.0 6.6 2.046 Mn 7.0 16.8 1.17768 C 7.0 1.08 0.0756 Si 16.0 0.8 0.128 Hf (MJ/kg) = 8.9084 ? Hc Median (d.sub.50) ?m 10 Ef (MJ/kg*?m.sup.?0.5) 2.82 Hc.sub.i: heat of combustion value of each respective element expressed in MJ/kg

[0093] Hc: heat of combustion contribution for each element in the alloy calculated expression in MJ/kg and calculated according to

Hc(element)=Hci(element)*wt. % (element)/100 [0094] Hf: Heat of formation (expressed in MJ/kg) of the alloy calculated as the sum of the Hc (element) of the elements comprising the alloy. [0095] Ef: explosion factor calculated as Ef=Hf*(1/?{square root over (m)}), where m is the median (d.sub.50) equal to 10 ?m in the calculation. Ef is expressed in MJ/kg*?m.sup.?0.5

Example 2

[0096] A powder according to the present invention was manufactured by providing a steel melt with composition according to Table 2 and using the same technique as described in Example 1. The composition of example 2 is within the claimed scope, and the explosion factor is as low as 2.91 MJ/kg*?m.sup.?0.5.

TABLE-US-00002 TABLE 2 2. Fe22Mn7.5Al6Cr Hc.sub.i Composition Hc (MJ/kg) = Elements (MJ/kg) (wt. %) Hc.sub.i*wt. %(element)/100 Fe 7.4 61.07 4.51918 Cr 6.0 6.2 0.372 Ti 19.7 0.25 0.04925 Al 31.0 7.8 2.418 Mn 7.0 22.5 1.57725 C 7.0 1.08 0.0756 Si 16.0 1.1 0.176 Hf (MJ/kg) = 9.18728 ? Hc Median (d.sub.50) ?m 10 Ef (MJ/kg*?m.sup.?0.5) 2.91

Example 3

[0097] The composition shown in Table 3 (calculated composition) is outside the claimed scope, due to the lack of Cr, and has therefore a reduced corrosion resistance.

TABLE-US-00003 TABLE 3 3. Fe16Mn6.5Al0Cr Hc.sub.i Composition Hc (MJ/kg) = Elements (MJ/kg) (wt. %) Hc.sub.i*wt. %(element)/100 Fe 7.4 74.44 5.50856 Cr 6.0 Ti 19.7 0.28 0.05516 Al 31.0 6.6 2.046 Mn 7.0 16.8 1.17768 C 7.0 1.08 0.0756 Si 16.0 0.8 0.128 Hf (MJ/kg) = 8.991 ? Hc Median (d.sub.50) ?m 10 Ef (MJ/kg*?m.sup.?0.5) 2.84

Example 4

[0098] The composition shown in Table 4 (calculated composition) is outside the claimed scope, due to the lack of Cr and the relatively high Al content. The high Al content results in a remarkably higher explosion risk, which can not be mitigated by Cr, due to its absence.

TABLE-US-00004 TABLE 4 4. Fe25Mn9Al0Cr Hc.sub.i Composition Hc (MJ/kg) = Elements (MJ/kg) (wt. %) Hc.sub.i*wt. %(element)/100 Fe 7.4 63.84 4.72416 Cr 6.0 Ti 19.7 0.28 0.05516 Al 31.0 9.0 2.79 Mn 7.0 25.0 1.7525 C 7.0 1.08 0.0756 Si 16.0 0.8 0.128 Hf (MJ/kg) = 9.52542 ? Hc Median (d.sub.50) ?m 10 Ef (MJ/kg*?m.sup.?0.5) 3.01

Example 5

[0099] The composition shown in Table 5 (calculated composition) has an even higher content of Al, a high Mn content and low Cr content. The explosion factor is remarkably higher than for examples 1 and 2.

TABLE-US-00005 TABLE 5 5. Fe25Mn12Al3Cr Hc.sub.i Composition Hc (MJ/kg) = Elements (MJ/kg) (wt. %) Hc.sub.i*wt. %(element)/100 Fe 7.4 57.84 4.28016 Cr 6.0 3.0 0.18 Ti 19.7 0.28 0.05516 Al 31.0 12.0 3.72 Mn 7.0 25.0 1.7525 C 7.0 1.08 0.0756 Si 16.0 0.8 0.128 Hf (MJ/kg) = 10.19142 ? Hc Median (d.sub.50) ?m 10 Ef (MJ/kg*?m.sup.?0.5) 3.22

Example 6

[0100] The composition shown in Table 6 (calculated composition) is within the claimed scope. It has a low explosion factor.

TABLE-US-00006 TABLE 6 6. Fe23Mn8.5Al5Cr Hc.sub.i Composition Hc (MJ/kg) = Elements (MJ/kg) (wt. %) Hc.sub.i*wt. %(element)/100 Fe 7.4 62.35 4.6139 Cr 6.0 5.0 0.3 Ti 19.7 0.05 0.00985 Al 31.0 8.5 2.635 Mn 7.0 23.0 1.6123 C 7.0 0.8 0.056 Si 16.0 0.3 0.048 Hf (MJ/kg) = 9.27505 ? Hc Median (d.sub.50) ?m 10 Ef (MJ/kg*?m.sup.?0.5) 2.93

Example 7

[0101] The composition shown in Table 7 (calculated composition) has a lower content of Al combined with a relatively low content of Mn and Cr. As will be shown in Table 9, the resulting density is slightly higher than earlier examples, but still below 7.20 g/cm.sup.3. The explosion factor is however, low.

TABLE-US-00007 TABLE 7 7. Fe15Mn5.5Al5Cr Hc.sub.i Composition Hc (MJ/kg) = Elements (MJ/kg) (wt. %) Hc.sub.i*wt. %(element)/100 Fe 7.4 73.35 5.4279 Cr 6.0 5.0 0.3 Ti 19.7 0.05 0.00985 Al 31.0 5.5 1.705 Mn 7.0 15.0 1.0515 C 7.0 0.8 0.056 Si 16.0 0.3 0.048 Hf (MJ/kg) = 8.59825 ? Hc Median (d.sub.50) ?m 10 Ef (MJ/kg*?m.sup.?0.5) 2.72

Example 8

[0102] The composition shown in Table 8 (calculated) has a high content of Al combined with a high content of Mn and a relatively low content of Cr. The explosion factor is still below 2.95 (MJ/kg*?m.sup.?0.5). As will be shown in Table 9, the resulting density is below 7.00 g/cm.sup.3.

TABLE-US-00008 TABLE 8 8. Fe30Mn8.5Al3Cr Hc.sub.i Composition Hc (MJ/kg) = Elements (MJ/kg) (wt. %) Hc.sub.i*wt. %(element)/100 Fe 7.4 56.7 4.1958 Cr 6 3 0.18 Ti 19.7 0.2 0.0394 Al 31 8.5 2.635 Mn 7.0 30 2.103 C 7 1.1 0.077 Si 16 0.5 0.08 Hf (MJ/kg) = 9.3102 ? Hc Median (d.sub.50) ?m 10 Ef (MJ/kg*?m.sup.?0.5) 2.94

[0103] Table 9 shows the theoretical full density (calculated density) of the compositions of examples 1-8 disclosed hereinabove. Measured densities of samples of examples 1 and 2 are also indicated.

TABLE-US-00009 TABLE 9 Explosion risk (compositions outside present invention) Examples Elements % 1 2 3 4 5 6 7 8 Fe 68.44 61.07 74.44 63.84 57.08 62.35 73.35 57.15 Cr 5.9 6.2 0.0 0.0 3.0 5.0 5.0 3.0 Ti 0.28 0.25 0.28 0.28 0.28 0.05 0.05 0.25 Al 6.6 7.8 6.6 9.0 12.0 8.5 5.5 8.5 Mn 16.8 22.5 16.8 25.0 25.0 23.0 15.0 30.0 C 1.08 1.08 1.08 1.08 1.08 0.8 0.8 1.1 Si 0.8 1.1 0.8 0.8 0.8 0.3 0.3 0.5 Measured Density 6.95 6.82 (g/cm.sup.3) Calculated Density 6.95 6.79 6.85 6.54 6.29 6.81 7.18 6.59 (g/cm.sup.3)