GB2634031A

GB2634031A - Alloy

Info

Publication number: GB2634031A
Application number: GB2314757.2A
Authority: GB
Inventors: Eduardo Jose Rivera Diaz Del Castillo Pedro; Eskandari Sabzi Hossein; Hao Xinjiang
Original assignee: Globus Metal Powders Ltd
Current assignee: Globus Metal Powders Ltd
Priority date: 2023-09-26
Filing date: 2023-09-26
Publication date: 2025-04-02
Also published as: GB202314757D0; WO2025068681A1

Abstract

An alloy comprising (by weight): 13.0-16.0 % chromium, 3.0-6.0 % nickel, 5.0-7.8 % copper, not more than 0.1 % carbon, not more than 1.5 % manganese, not more than 1.0 % niobium, not more than 0.1 % nitrogen and not more than 1.0 % silicon, with the balance being iron and impurities. The alloy preferably has a higher copper content than nickel content, e.g. a ratio of copper to nickel in the range 10:9 to 7.8:3. The alloy preferably has a higher niobium content than manganese content. It can comprise at least 50 % martensite and have a microstructure with an average grain size of up to 40 microns. It can be formed as a powder and used to make articles by additive manufacturing using a post build heat treatment.

Description

ALLOY

The present disclosure relates to an alloy, more particularly a steel, e.g. a stainless steel such as a precipitation-hardened (PH) stainless steel.

The present disclosure also relates to an article comprising such an alloy and to a method of manufacture of such an article. The method of manufacture may comprise an additive manufacturing process.

An additive manufacturing (AM) process fabricates an article, e.g. a component, in a layer-by-layer method, typically under the control of computer-aided design (CAD) information, as opposed to the traditional use of casting moulds and forming dies. Typically, additive manufacturing may be termed three-dimensional (3D) printing. An example of an additive manufacturing process is Laser Powder Bed Fusion (LPBF), IS which may also be known as Selective Laser Melting (SLM).

An additive manufacturing (AM) process may allow for net-shape or near-net-shape fabrication of complex geometries. Other potential benefits of additive manufacturing processes may include: lower manufacturing costs; higher material utilisation rates; reduced energy consumption; reduced fabrication time; reduced component costs; the ability to produce one-off or difficult-to-source articles; and/or no or a reduced need for any post-build treatments such as heat treatments.

However, for many alloys, articles fabricated using an additive manufacturing (AM) process may tend to be of lower quality, particularly in an as-built condition, than their wrought counterparts.

US2022/0081745A I discloses examples of stainless steel powders for additive manufacturing.

Metals 2020, 10, 255;Lf1) provides a review of laser powder bed fusion of precipitation-hardened martensitic stainless steels.

A first aspect provides an alloy comprising or consisting essentially of 13.0 wt % to 16.0 wt % chromium; 3.0 wt% to 6.0 wt% nickel; 5.0 wt% to 7.8 wt% copper; no more than 0.1 wt% carbon; no more than 1.5 wt% manganese; no more than 1.0 wt% niobium; no more than 0.1 wt% nitrogen: no more than 1.0 wt% silicon; and the balance of weight percent comprising, or consisting essentially of, iron and incidental elements and impurities.

The alloy may comprise up to or at least 13.5 wt% chromium, up to or at least 14.0 wt% chromium, up to or at least 14.5 wt% chromium, up to or at least 15.0 wt% chromium or up to or at least 15.5 wt% chromium.

The alloy may comprise up to or at least 3.5 wt% nickel, up to or at least 4.0 wt% nickel, up to or at least 4.5 wt% nickel, up to or at least 5.0 wt% nickel or up to or at least 5.5 wt% The alloy may comprise up to or at least 5.5 wt% copper, up to or at least 6 wt% copper, up to or at least 6.5 wt% copper, up to or at least 7 wt% copper or up to or at least 7.5 wt% copper.

The alloy may comprise up to or at least 0.2 wt% silicon, up to or at least 0.3 wt% silicon, up to or at least 0.4 wt% silicon, up to or at least 0.5 wt% silicon, up to or at least 0.6 wt% silicon or up to or at least 0.7 wt% silicon.

The alloy may comprise up to or at least 0. t wt% manganese, up to or at least 0.2 wt% manganese, up to or at least 0.3 wt% manganese, up to or at least 0.5 wt% manganese, up to or at least 1.0 wt% manganese or up to or at least 1.5 wt% manganese.

The alloy may comprise up to or at least 0.2 wt% niobium, up to or at least 0.3 wt% niobium, up to or at least 0.4 wt% niobium, up to or at least 0.5 wt% niobium, up to or at least 0.6 wt% niobium, up to or at least 0.7 wt% niobium, up to or at least 0.8 wt% niobium or up to or at least 0.9 wt% niobium.

The alloy may comprise up to or at least 0.01 wt% nitrogen or up to or at least 0.05 wt% nitrogen. The nitrogen content of the alloy may be carefully controlled, since nitrogen can be a very strong austenitic stabiliser. If the nitrogen content is more than 0.1 wt%, then presence of retained austenite may significantly decrease mechanical properties such as yield strength and ultimate tensile strength.

The alloy may have a higher copper content than nickel content.

A ratio of copper to nickel may be from 10:9 to 7.8:3. The ratio of copper to nickel may be up to or at least 5:3, up to or at least 10:7 or up to or at least 5:4.

The alloy may have a higher niobium content than manganese content.

The alloy may be a stainless steel.

The alloy may be a precipitation hardened (PH) stainless steel.

The alloy may be a maraging steel.

The alloy may be martensitic at least in part.

The alloy may be suitable for use in powder metallurgy and/or additive manufacturing.

The alloy may have a microstructure that is at least 50% martensite, at least 75% martensite or at least 85% martensite. The alloy may have a microstructure that is substantially fully martensitic.

The alloy may have a microstructure having an average grain size of up to 40 pm, up to 30 pm, up to 20 pm, up to 10 1,tm, up to 6µm. For example, the alloy may have a microstructure having an average grain size of 4 ± 2 pm. I5

The alloy may have a hardness of at least 350 HV, at least 400 HV or at least 420 HV.

The alloy may have a yield stress of at least 1000 MPa or at least 1050 MPa.

The alloy may have an ult mate tens le stress of at least 1200 MPa or at least 1250 MPa.

In a heat treated condition, the alloy may have a microstructure that is at least 50% martensite, at least 75% martensite, at least 85% martensite or is substantially fully martensitic.

In the heat treated condition, the alloy may have a microstructure having an average grain size of up to 40 inn, up to 30 p.m, up to 20 pm, up to 10 pm, up to 6 Rm. For example, in the heat treated condition the alloy may have a microstructure having an average grain size of 4 ± 2 pan.

in the heat treated condition, the alloy may have a hardness of at least 400 HV, at least 410 HV, at least 420 HV or at least 450 HV. In the heat treated condition, the alloy may have a hardness of up to 500 HV or up to 550 HV.

In the heat treated condition, the alloy may have a yield stress of at least 1200 MPa or at least 1250 MPa.

in the heat treated condition, the alloy may have an ultimate tensile stress of at least 1300 MPa or at least 1350 MPa.

A second aspect provides an alloy powder, e.g. an atomized alloy powder, comprising alloy particles comprising or consisting essentially of: 13.0 wt% to 16.0 wt% chromium; 3.0 wt% to 6.0 wt% nickel; 5.0 wt% to 7.8 wt% copper; no more than 0.1 wt% carbon; no more than 1.5 wt% manganese; no more than 1.0 wt% niobium; no more than 0.1 wt% nitrogen; no more than 1.0 wt% silicon; and the balance of weight percent comprising, or consisting essentially of, iron and incidental elements and impurities.

The alloy powder may be usable in additive manufacturing.

The alloy particles may comprise up to or at least 13.5 wt% chromium, up to or at least 14.0 wt% chromium, up to or at least 14.5 wt% chromium, up to or at least 15.0 wt% chromium or up to or at least 15.5 wt% chromium.

The alloy particles may comprise up to or at least 3.5 wt% nickel, up to or at least 4.0 wt% nickel, up to or at least 4.5 wt% nickel, up to or at least 5.0 wt% nickel or up to or at least 5.5 wt% nickel.

The alloy particles may comprise up to or at least 5.5 wt% copper, up to or at least 6 wt% copper, up to or at least 6.5 wt% copper, up to or at least 7 wt% copper or up to or at least 7.5 wt% copper.

The alloy particles may comprise up to or at least 0.2 wt% silicon, up to or at least 0.3 wt% silicon, up to or at least 0.4 wt% silicon, up to or at least 0.5 wt% silicon, up to or at least 0.6 wt% silicon or up to or at least 0.7 wt% silicon.

The alloy particles may comprise up to or at least 0.1 wt% manganese, up to or at least 0.2 wt% manganese, up to or at least 0.3 wt% manganese, up to or at least 0.5 wt% manganese, up to or at least 1.0 wt% manganese or up to or at least 1.5 wt% manganese.

The alloy particles may comprise up to or at least 0.2 wt% niobium, up to or at least 0.3 wt% niobium, up to or at least 0.4 wt% niobium, up to or at least 0.5 wt% niobium, up to or at least 0.6 wt% niobium, up to or at least 0.7 wt% niobium, up to or at least 0.8 wt% niobium or up to or at least 0.9 wt% niobium.

The alloy particles may comprise up to or at least 0.01 wt% nitrogen or up to or at least 0.05 wt% nitrogen.

The alloy particles may have a higher copper content than nickel content.

The alloy particles may have a higher niobium content than manganese content.

The alloy particles may have a mean particle diameter of at least 0.25 pm, up to or at least 10 p.m, up to or at least 50 pm, up to or at least 100 itm or up to at least 250 itrn.

A third aspect provides a method of manufacture of an article comprising: providing an alloy according to the first aspect in a first form; and employing one or more forming techniques to produce the article from the first form I5 The first form may comprise a powder. The first form may comprise a sheet, a plate, a coil, a rod or a bar.

One or more of the forming techniques may be an additive manufacturing process. The additive manufacturing process may comprise sintering or melting the or a powder. The additive manufacturing process may comprise laser powder bed fusion (LPBF) The additive manufacturing process may comprise cold spraying the or a powder.

Laser powder bed fusion may be carried out using a laser power of at least 60 W and/or up to 1000 W. The laser power may be up to or at least 200 W, up to or at least 500 W or up to or at least 750 W. Laser powder bed fusion may be carried out using a scan speed of at least 0.05 m/s and/or up to 2 m/s. The scan speed may be up to or at least 0.1 m/s, up to or at least 0.5 m/s or 1 m/s.

Laser powder bed fusion may be carried out using a hatch distance of at least 10 p.m and/or up to 300 pm. The hatch distance may be up to or at least 50 pm, up to or at least 100 p.m or up to or at least 200 p.m.

Laser powder bed fusion may be carried out using a layer thickness of at least 5 pm and/or up to 200 pm. The layer thickness may be up to or at least 20 pm, up to or at least 50 Rm or up to or at least 100 Rm.

One or more of the forming techniques may be a subtractive manufacturing process.

in an as-built condition, the alloy may have a microstructure that is at least 50% martensite, at least 75% rnartensite, at least 85% martensite or is substantially fully martensitic.

In the as-built condition, the alloy may have a microstructure having an average grain size of up to 40 pm, up to 30 Rim up to 20 pm, up to 10 pm, up to 6 pm. For example, in the as-built condition the alloy may have a microstructure having an average grain size of 4 ± 2 Rm.

In the as-built condition, the alloy may have a hardness of at least 350 HV, at least 400 HV or at least 420 HV.

In the as-built condition, the alloy may have a yield stress of at least 1000 MPa or at least 1050 MPa.

in the as-built condition, the alloy may have an ultimate tensile stress of at least 1200 MPa or at least 1250 MPa.

The method may include a post-build treatment of the article. The post-build treatment of the article may include an ageing process. The post-build treatment of the article may include a heat treatment.

The ageing process and/or the heat treatment may include heat treating the article at a temperature of up to or at least 400°C, up to or at least 450°C, up to or at least 500°C, up to or at least 550°C, up to or at least 600°C, up to or at least 650°C, up to or at least 700°C, up to or at least 750°C. up to or at least 800°C, up to or at least 850°C, up to or at least 900°C, up to or at least 950°C, up to or at least 1000°C, up to or at least 1050°C or up to or at least 1100°C. I5

The ageing process and/or the heat treatment may be carried out for at least 15 minutes, up to or at least two hours, up to or at least three hours, up to or at least four hours, up to or at least five hours, up to or at least 10 hours or up to or at least 50 hours.

The ageing process and/or the heat treatment may include heat treating the article at a substantially constant temperature for a duration of the ageing process and/or the heat treatment.

In the heat treated condition, the alloy may have a microstructure having an average grain size of up to 40 Rm, up to 30 Rm, up to 20 pm, up to 10 pm, up to 6 pm. For example, in the heat treated condition the alloy may have a microstructure having an average grain size of 4 ± 2 Rm.

A fourth aspect provides a method of manufacture of an article comprising: providing a powder according to the second aspect; employing an additive manufacturing process to produce the article from the powder The additive manufacturing process may comprise sintering or melting the powder. The additive manufacturing process may comprise laser powder bed fusion (LPBF). The additive manufacturing process may comprise cold spraying the powder.

Laser powder bed fusion may be carried out using a laser power of at least 60 W and/or up to 1000 W. The laser power may be up to or at least 200 W. up to or at least 500 W or up to or at least 750 W. Laser powder bed fusion may be carried out using a scan speed of at least 0.05 m/s and/or up to 2 m/s. The scan speed may be up to or at least 0.1 m/s, up to or at least 0.5 m/s or 1 m/s.

Laser powder bed fusion may be carried out using a hatch distance of at least 10 pm and/or up to 300 pm. The hatch distance may be up to or at least 50 pm, up to or at least 100 vim or up to or at least 200 pm.

Laser powder bed fusion may be carried out using a layer thickness of at least 5 pm and/or up to 200 pm. The layer thickness may be up to or at least 20 pm. up to or at least 50 p.m or up to or at least 100 pm.

In an as-built condition, the alloy may have a microstructure that is at least 50% martensite, at least 75% martensite, at least 85% martensite or is substantially fully martensitic.

In the as-built condition, the alloy may have a microstructure having an average grain size of up to 40 pm, up to 30 p.m, up to 20 pm, up to 10 pm, up to 6 pm. For example, in the as-built condition the alloy may have a microstructure having an average grain size of 4 f 2 pm.

In the as-built condition, the alloy may have a hardness of at least 350 HV, at least 400 ITV or at least 420 HV.

The ageing process and/or the heat treatment may include heat treating the article at a temperature of up to or at least 400°C, up to or at least 450°C, up to or at least 500°C, up to or at least 550°C, up to or at least 600°C, up to or at least 650°C, up to or at least 700°C, up to or at least 750°C. up to or at least 800°C, up to or at least 850°C, up to or at least 900°C, up to or at least 950°C, up to or at least 1000°C, up to or at least 1050°C or up to or at least 1100°C.

In a heat treated condition, the alloy may have a microstructure that is at least 50% martensite, at least 75% martensite, at least 85% martensite or is substantially fully martensitic in the heat treated condition, the alloy may have a microstructure having an average grain size of up to 40 itm, up to 30 pm, up to 20 pm, up to 10 pm, up to 6 pm. For example, in the heat treated condition the alloy may have a microstructure having an average grain size of 4 ± 2 pm.

A fifth aspect provides an article comprising, or consisting essentially of, an alloy according to the first aspect.

A sixth aspect provides a computer-readable medium carrying instructions for the manufacture of an article according to the fifth aspect, e.g. according to a method of manufacture of the third aspect or a method of manufacture of the fourth aspect.

The instructions may be executable in an additive manufacturing process. The additive manufacturing process may be laser powder bed fusion (LPBF).

The skilled person will appreciate that except where mutually exclusive, a feature or parameter described in relation to any one of the above aspects may be applied to any other aspect. Furthermore, except where mutually exclusive, any feature or parameter described herein may be applied to any aspect and/or combined with any other feature or parameter described herein.

Embodiments will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure I shows four images: an optical micrograph of a stainless steel according to the present disclosure in an as-built condition; an electron backscatter diffraction (EBSD) inverse pole figure map of a stainless steel according to the present disclosure in an as-built condition; an optical micrograph of a commercially-available martcnsitic 17-4 PH stainless steel in an as-built condition; and an electron backscatter diffraction (EBSD) inverse pole figure map of a commercially-available martensitic 17-4 PH stainless steel in an as-built condition; Figure 2 is a graph showing the results of hardness measurements carried out on a stainless steel according to the present disclosure and, for comparison, a commercially-available 17-4 PH stainless steel; Figure 3 is a graph showing monotonic stress-strain curves for five samples of a stainless steel according to the present disclosure in an as-built condition; and Figure 4 shows an example of a method of manufacture of an article.

The ability to print an alloy during manufacture of an article without the alloy cracking or having too much porosity is known as printability of the alloy. The alloys 10 according to the present disclosure may have good printability, typically in combination with high hardness.

Ideally, the alloy may be suitable for use in printing on one or more commercial printing machines, I5 As used herein, the term "as-built condition" refers to the state that printed articles or parts thereof were in when they were taken out of a manufacturing machine, i.e. without any post-build heat treatment.

As used herein. the term "heat treated condition" refers to the state of printed articles or parts thereof that have undergone a post-build heat treatment.

Typically, an alloy according to the present disclosure may be suitable for printing in three dimensions using a process known as metal additive manufacturing. An example of a metal additive manufacturing process may be laser powder bed fusion (LPBF).

Known martensitic 17-4 precipitation-hardened (PH) stainless steels can be particularly useful, due to their having a high yield strength and superior corrosion resistance. Martensitic 17-4 PH stainless steels consequently have a range of industrial applications, including, for example, in the aerospace, nuclear, medical equipment and/or automotive sectors.

Table 1 shows the composition of a typical martensitic 17-4 PH stainless steel, with the amounts expressed in terms of weight percentage (wt%).

C Cr Ni Cu Si Mn Nb Fe c 0.07 15.5-17.5 3-5 3-5 < 1 < 1 0.15-0.4 Balance

Table 1

LPBF, which may also be known as Selective Laser Melting (SLM), is the primary additive manufacturing technique for printing 17-4 PH stainless steels. However, articles made by printing 17-4 PH stainless steels tend to exhibit in the as-built condition low strength, low hardness and low elongation compared with their wrought counterparts. In addition, articles made by printing 17-4 PH stainless steels may include, e.g. in the as-built condition, undesirable phases such as austenite and ferrite compared with their wrought counterparts.

Without wishing to be bound by any theory, the inventors consider that these problems may be related to the very non-equilibrium nature of LPBF, which typically includes ultrafast heating and cooling cycles, which may prevent formation of a fully martensitic microstructure upon building.

Consequently, 17-4 PH stainless steel articles made using LPBF may require post-build heat treatment such as solution treatment followed by quenching (to generate the desirable martensitic matrix for precipitation hardening) and subsequent ageing (to induce Cu-based nano-precipitates), which can significantly increase the cost of manufacture. As a result, when it comes to manufacturing articles comprising 17-4 PH stainless steels one or more of the advantages of three-dimensional printing techniques such as LPBF over conventional manufacturing techniques may not be realised. These advantages may include: lower manufacturing costs; near net shape manufacturing; high(er) dimensional accuracy; high(er) material utilisation rates; and/or no or a reduced need for post-build heat treatment, in order to achieve the desirable mechanical properties associated, for example, with martensitic 17-4 PH stainless steels.

Table 2 shows the composition of an example of a martensitic PH stainless steel according to the present disclosure, with the amounts expressed in terms of weight percentage (wt%).

C Cr Ni Cu Si Mn Nb Fe 0.02 13-14.5 3-5.5 5.5-6 0.2-0.7 0.1-0.3 0.2-0.5 Balance

Table 2

In an implementation, an article made of a martcnsitic PH stainless steel having a composition according to Table 2 was manufactured using an LPBF process. The LPBF process was carried out using the following parameters: a laser power of 180 W; a scan speed of 0.3 m/s; a hatch distance of 75 gm; and a layer thickness of 30 111-11. The martensitic PH stainless steel having a composition according to Table 2 was found to have very good printability when these parameters were applied to the LPBF process.

Properties of the article made of the martensitic PH stainless steel having a composition according to Table 2 in the as-built condition are shown in Table 3 below.

Yield strength Ultimate tensile Elongation Hardness Density (MPa) strength (MPa) (%) (HV) (%) 1229+23 1433+6 10.3+1 426+16 99.9

Table 3

in the as-built condition, the article has high density, high yield strength, high tensile strength, high elongation and high hardness. Accordingly, the article's properties in the as-built condition may be sufficient such that the article may not require a post- build heat treatment and/or ageing. Nevertheless, in some implementations, a post-build heat treatment and/or ageing may be carried out.

Figure 1 shows four images. The upper left image is an optical micrograph of a martcnsitic PH stainless steel having a composition according to Table 2 in the as-built condition.

By way of a comparative example to the upper left image, the upper right image in Figure 1 is an optical micrograph of a commercially-available martcnsitic 17-4 PH stainless steel having a composition according to Table 1 in the as-built condition.

The lower left image is an electron backscatter diffraction (EBSD) inverse pole figure map of a martensitic PH stainless steel having a composition according to Table 2 in the as-built condition.

By way of a comparative example to the lower left image, the lower right image in Figure 1 is an electron backscatter diffraction (EBSD) inverse pole figure map of a commercially-available martensitic 17-4 PH stainless steel having a composition according to Table 1 in the as-built condition.

Referring to Figure 1, it can be seen that the martensitic PH stainless steel having a composition according to Table 2 in the as-built condition has a significant grain refinement compared with the commercially-available martensitic 17-4 PH stainless steel having a composition according to Table 1 in the as-built condition. The average grain size for the martensitic PH stainless steel having a composition according to Table 2 in the as-built condition is 4+2 pan. The average grain size for the commercially-available martensitic 17-4 PH stainless steel having a composition according to Table 1 is 44+5 um. Without wishing to be bound by any particular theory, it is thought that the significant grain refinement may be related to in situ precipitation of nanoscale Cu particles and niobium carbonitrides.

As a consequence of the in situ precipitation of nanoscale Cu particles and niobium carbonitrides, the martensitic PH stainless steel having a composition according to Table 2 in the as-built condition has a higher hardness value than the commercially-available martensitic 17-4 PH stainless steel having a composition according to Table 1 in the as-built condition. This is shown in Figure 2.

Figure 2 is a graph showing the results of hardness measurements carried out on a martensitic PH stainless steel having a composition according to Table 2 and, for comparison, a commercially-available martensitic 17-4 PH stainless steel having a composition according to Table 1. Hardness (Hv 1) is plotted on the y-axis and time, measured in hours, is plotted on the x-axis.

Hardness measurements were carried out on the two samples in the as-built condition and at one, two and four hours through a subsequent direct ageing process. A first line 22 is plotted on the graph connecting the four data points for the martensitic PH stainless steel having a composition according to Table 2. A second line 21 is plotted on the graph connecting the four data points for the commercially-available martensitic 17-4 PH stainless steel having a composition according to Table 1.

The direct ageing process included heat treating the alloys at 482°C (900°F) for four hours. After four hours, it was found that an optimum amount of precipitation of nanoscale Cu particles had occurred. As the first line 22 in Figure 2 shows, this direct ageing process resulted in a significant increase in hardness of the martensitic PH stainless steel having a composition according to Table 2.

The direct ageing process described above is different from what is typically done in industry for similar alloys, namely a solution treatment (typically at from 1000°C to 1100°C for 1 hour) followed by quenching to achieve a fully martensitic structure, subsequently followed by ageing typically at 482°C to promote Cu precipitation.

Referring to Figure 2, it can be seen that the martensitic PH stainless steel having a composition according to Table 2 has a hardness of around 426 HV in the as-built condition and a hardness of around 500 HV after four hours of the direct ageing process. in contrast, the martensitic 17-4 PH stainless steel having a composition according to Table 1 has a hardness of around 315 HV in the as-built condition and a hardness of around 400 HV after four hours of the direct ageing process.

Figure 3 is a graph showing monotonic stress-strain curves for five samples of the martensitic PH stainless steel having a composition according to Table 2 in the as-built condition. Stress, measured in MPa, is plotted on the y-axis. Strain, measured in %, is plotted on the x-axis. A first monotonic stress-strain curve 31 for a first sample is plotted on the graph. A second monotonic stress-strain curve 32 for a second sample is plotted on the graph. A third monotonic stress-strain curve 33 for a third sample is plotted on the graph. A fourth monotonic stress-strain curve 34 for a fourth sample is plotted on the graph. A fifth monotonic stress-strain curve 35 for a fifth sample is plotted on the graph.

Also shown on Figure 3 are the literature-reported yield stress ranges for commercially-available 17-4 PH stainless steel and commercially-available 15-5 PH stainless steel in an as-built condition and the literature-reported ultimate tensile stress ranges for commercially-available 17-4 PH stainless steel and commercially-available 15-5 PH stainless steel in an as-built condition.

A lower bound of the literature-reported yield stress range for commercially-available 17-4 PH stainless steel in the as-built condition is indicated by a first dashed line 36a extending horizontally across the graph. An upper bound of the literature-reported yield stress range for commercially-available 17-4 PH stainless steel in the as-built condition is indicated by a second dashed line 36b extending horizontally across the graph.

A lower bound of the literature-reported yield stress range for commercially-available 15-5 PH stainless steel in the as-built condition is indicated by a third dashed line 37a extending horizontally across the graph. An upper bound of the literature-reported yield stress range for commercially-available 15-5 PH stainless steel in the as-built condition is indicated by a fourth dashed line 37b extending horizontally across the graph.

A lower bound of the literature-reported ultimate tensile stress range for commercially-available 17-4 PH stainless steel in the as-built condition is indicated by a fifth dashed line 38a extending horizontally across the graph. An upper bound of the literature-reported ultimate tensile stress range for commercially-available 17-4 PH stainless steel in the as-built condition is indicated by a sixth dashed line 38b extending horizontally across the graph.

A lower bound of the literature-reported ultimate tensile stress range for commercially-available 15-5 PH stainless steel in the as-built condition is indicated by a seventh dashed line 39a extending horizontally across the graph. An upper bound of the literature-reported ultimate tensile stress range for commercially-available 15-5 PH stainless steel in the as-built condition is indicated by an eighth dashed line 39b extending horizontally across the graph.

Figure 3 shows that the PH stainless steel having a composition according to Table 2 has a superior yield strength and a superior ultimate tensile strength in an as-built condition compared with as-built commercially-available 17-4 and 15-5 PH stainless steels. The ranges of strength for the commercially-available 17-4 and 15-5 PH stainless steels come from open literature (references [1-16[ listed below).

Figure 4 shows an example of a method 400 of manufacture of an article.

In a first step 401, the method 400 includes providing a powder comprising particles having an alloy composition according to the present disclosure, e.g. a martensitic PH stainless steel having a composition according to Table 2.

In a second step 402, the method 400 includes carrying out an additive manufacturing process such as LPBF to produce an article in an as-built condition.

In a third step 403, the method 400 may optionally include carrying out one or more post-build treatments on the article. For example, one of the post-build treatments IS may include a direct ageing process, which may include a heat treatment.

While the alloy according to the present disclosure may be well-suited for use in additive manufacturing, it will be appreciated that the alloy may be suitable for use in non-additive manufacturing applications.

It will be understood that the invention is not limited to the embodiments described above. Various modifications and improvements can be made without departing from the concepts disclosed herein. Except where mutually exclusive, any of the features may be employed separately or in combination with any other features and the disclosure extends to all combinations and sub-combinations of one or more features disclosed herein.

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Claims

CLAIMS1. An alloy comprising or consisting essentially of: 13.0 wt% to 16.0 wt% chromium; 3.0 wt% to 6.0 wt% nickel; 5.0 wt% to 7.8 wt% copper; no more than 0.1 wt% carbon; no more than 1.5 wt% manganese; no more than 1.0 wt% niobium; no more than 0.1 wt% nitrogen; no more than 1.0 wt% silicon; and the balance of weight percent comprising, or consisting essentially of, iron and incidental elements and impurities.
2. The alloy of claim 1 comprising up to or at least 3.5 wt% nickel, up to or at least 4.0 wt% nickel, up to or at least 4.5 wt% nickel, up to or at least 5.0 wt% nickel or up to or at least 5.5 wt% nickel.
3. The alloy of claim 1 or claim 2 comprising up to or at least 5.5 wt% copper, up to or at least 6 wt% copper, up to or at least 6.5 wt% copper, up to or at least 7 wt% copper or up to or at least 7.5 wt% copper.
4. The alloy of claim I, claim 2 or claim 3, wherein the alloy has a higher copper content than nickel content.
5. The alloy of any one of the preceding claims comprising a ratio of copper to nickel from 10:9 to 7.8:3.
6. The alloy of any one of the preceding claims, wherein the alloy has a higher niobium content than manganese content.
7. The alloy of any one of the preceding claims, wherein the alloy has a microstructure that is at least 50% martensite, at least 75% martensite or at least 85% martensite.
8. The alloy of any one of the preceding claims, wherein the alloy has a microstructure having an average grain size of up to 40 pm, up to 30 pm, up to 20 pm, up to 10 pm or up to 6 pm.
9. The alloy of any one of the preceding claims, wherein the alloy has a hardness of at least 350 HV and/or a yield stress of at least 1000 MPa and/or an ultimate tensile stress of at least 1200 MPa.
10. An alloy powder comprising alloy particles comprising or consisting essentially of: 13.0 wt% to 16.0 wt% chromium; 3.0 wt% to 6.0 wt% nickel: 5.0 wt% to 7.8 wt% copper; no more than 0.1 wt% carbon; I5 no more than 1.5 wt% manganese; no more than 1.0 wt% niobium; no more than 0.1 wt% nitrogen; no more than 1.0 wt% silicon; and the balance of weight percent comprising, or consisting essentially of, iron and incidental elements and impurities.
11. The alloy powder of claim 10, wherein the alloy particles comprise up to or at least 3.5 wt% nickel, up to or at least 4.0 wt% nickel, up to or at least 4.5 wt% nickel, up to or at least 5.0 wt% nickel or up to or at least 5.5 wt% nickel.
12. The alloy powder of claim 10 or claim 11, wherein the alloy particles comprise up to or at least 5.5 wt% copper, up to or at least 6 wt% copper, up to or at least 6.5 wt% copper, up to or at least 7 wt% copper or up to or at least 7.5 wt% copper.
13. The alloy powder of claim 10, claim 11 or claim 12, wherein the alloy particles have a higher copper content than nickel content.
14. The alloy powder of any one of claims 10 to 13, wherein the alloy particles have a higher niobium content than manganese content.
15. A method of manufacture of an article comprising: providing an alloy according to any one of claims 1 to 9 in a first form; and employing one or more forming techniques to produce the article from the first form
16. The method of manufacture of claim 15, wherein the first form comprises a powder, a sheet, a plate, a coil, a rod or a bar.
17. A method of manufacture of an article comprising: providing a powder according to any one of claims 10 to 14; and employing an additive manufacturing process to produce the article from the powder
18. The method of manufacture of claim 17, wherein the additive manufacturing process comprises sintering or melting the powder.
19. The method of manufacture of any one of claims 15 to 18 including a post-build treatment of the article.
20. The method of manufacture of claim 19, wherein the post-build treatment of the article includes a heat treatment.
21. The method of manufacture of claim 20, wherein the heat treatment includes heat treating the article at a temperature of up to or at least 400°C, up to or at least 450°C, up to or at least 500°C, up to or at least 550°C, up to or at least 600°C, up to or at least 650°C, up to or at least 700°C, up to or at least 750°C, up to or at least 800°C. up to or at least 850°C, up to or at least 900°C, up to or at least 950°C, up to or at least 1000°C, up to or at least 1050°C or up to or at least I100°C.
22. The method of manufacture of claim 20 or claim 21, wherein the heat treatment is carried out for at least 15 minutes, up to or at least two hours, up to or at least three hours, up to or at least four hours, up to or at least five hours, up to or at least 10 hours or up to or at least 50 hours.
23. The method of manufacture of claim 20, claim 21 or claim 22, wherein the heat treatment includes heat treating the article at a substantially constant temperature for a duration the heat treatment.
24. An article comprising, or consisting essentially of, an alloy according to any one of claims 1 to 9.
25. A computer-readable medium carrying instructions for the manufacture of an article according to claim 24, e.g. according to a method of manufacture of any one of claims 15 to 23.