CN110088323B

CN110088323B - Article comprising a duplex stainless steel and use thereof

Info

Publication number: CN110088323B
Application number: CN201780079046.9A
Authority: CN
Inventors: 托马斯·福斯曼
Original assignee: Sandvik Intellectual Property AB
Current assignee: Alleima AB
Priority date: 2016-12-21
Filing date: 2017-12-18
Publication date: 2022-03-22
Anticipated expiration: 2037-12-18
Also published as: EP3559295B1; WO2018114865A1; CN110088323A; ES2870648T3; US20190323110A1; EP3559295A1

Abstract

The present disclosure relates to an article comprising a duplex stainless steel, in particular the article is suitable for use in elastic applications. The duplex stainless steel has the following composition in weight%: c is less than or equal to 0.040; si is less than or equal to 0.60; 0.80-10.0 Mn; 21.0-28.0 Cr; 4.0 to 9.0 Ni; 0.9 to 4.5 Mo; n is 0.10 to 0.45; cu is less than or equal to 0.50; v is less than or equal to 0.10; p is less than or equal to 0.010; s is less than or equal to 0.006; the balance being Fe and unavoidable impurities. The present disclosure also relates to a method of manufacturing an article comprising the duplex stainless steel.

Description

Article comprising a duplex stainless steel and use thereof

Technical Field

The present disclosure relates to an article comprising a duplex stainless steel, in particular the article is suitable for use in elastic applications or as a spring per se. The present disclosure also relates to a method of making the article.

Background

Elastic applications in the form of wires or strips can be statically or dynamically loaded. The most important properties of steel grades for static elastic applications are high spring or yield strength, well-defined modulus of elasticity, high corrosion resistance and high stress relaxation resistance. The most important properties of steel grades for dynamic elastic applications are high proof strength or yield strength, well-defined modulus of elasticity, high corrosion resistance, high stress relaxation resistance and high fatigue fracture resistance.

JP 2010059541 discloses a method wherein the final step is an annealing process aimed at obtaining the maximum elongation of stainless steel, which is a low alloy duplex steel. This grade of austenite phase is unstable and partially transforms into martensite upon plastic deformation.

Stainless spring steel grades of austenitic or martensitic origin generally have an excellent combination of most of the above properties. However, one major drawback of austenitic steel grades is that the modulus of elasticity increases with load to the spring limit stress (Rp)_0.2) But decreases almost linearly and, as mentioned above, the steel grade for elastic applications should have a modulus of elasticity which remains at a high level even when the load is increased and does not decrease in a linear manner. Martensitic steel grades may exhibit an elastic modulus that does not decrease linearly with increasing load. However, one major drawback of martensitic steel grades is that the corrosion resistance of these steels is problematic.

Accordingly, it is an aspect of the present disclosure to provide an article suitable for elastic applications and which will solve or at least reduce the above mentioned disadvantages.

Disclosure of Invention

Accordingly, it is an aspect of the present disclosure to provide an article made from a duplex stainless steel, wherein the duplex stainless steel comprises the following composition in weight%:

c is less than or equal to 0.040;

si is less than or equal to 0.60;

Mn 0.80～10.0；

Cr 21.0～28.0；

Ni 4.0～9.0；

Mo 0.9～4.5；

N 0.10～0.45；

cu is less than or equal to 0.50;

v is less than or equal to 0.10;

p is less than or equal to 0.010;

s is less than or equal to 0.006;

the balance of Fe and inevitable impurities;

and wherein the duplex stainless steel consists of 55 to 75 volume% of an austenite phase and 25 to 45 volume% of a ferrite phase;

and wherein the article has alternating layers of ferrite and austenite phases that are substantially parallel to a plane of the article and have an average layer thickness of less than or equal to about 4.5 μm. As used herein, the term "about" refers to the numerical value of the number to which it is applied plus or minus 5%. Further, in the present disclosure, the abbreviation "FCC" refers to the austenite phase, and the abbreviation "BCC" refers to the ferrite phase. Further, the expression "substantially parallel" as used herein is intended to mean a deviation from plane of less than 10%.

In addition, the article comprising the duplex stainless steel as defined above or below will have a low content or no content of sigma phases and/or precipitated chromium nitrides. In addition, the article will have an elastic modulus that will remain relatively high under increased loads compared to the behavior of pure austenitic stainless steel. A low content of sigma phase and/or precipitated chromium nitride or no sigma phase and/or precipitated chromium nitride means that the amount present should not seriously deteriorate the corrosion resistance or toughness of the duplex stainless steel.

Another aspect of the present disclosure provides a method for manufacturing an article as defined above or below, the method comprising the steps of:

-providing a body of a duplex stainless steel as defined above or below;

-one or more thermal processes to transform the body into a workpiece, and the thermal processes are performed at a temperature of about 1050 ℃ to about 1300 ℃;

-one or more cold working processes to transform the workpiece into the article.

Wherein the final step of the process must be a cold working process.

The final step of the method must be a cold working process, as this process will affect the microstructure of the duplex stainless steel to the maximum extent, having a significant effect on the elastic modulus. In addition, the method of the present invention will provide the article with greater strength after cold working, and cold working will also ensure that strain hardening will occur in the article.

Detailed Description

The present disclosure relates to an article made from a duplex stainless steel, wherein the duplex stainless steel comprises the following composition in weight%:

c is less than or equal to 0.040;

si is less than or equal to 0.60;

Mn 0.80～10.0；

Cr 21.0～28.0；

Ni 4.0～9.0；

Mo 0.9～4.5；

N 0.10～0.45；

cu is less than or equal to 0.50;

v is less than or equal to 0.10;

p is less than or equal to 0.010;

s is less than or equal to 0.006;

the balance of Fe and inevitable impurities;

and wherein the article has alternating layers of ferrite and austenite phases that are substantially parallel to a plane of the article and have an average thickness of less than or equal to about 4.5 μm.

The duplex stainless steel as defined above or below will be referred to as an articleHigh corrosion resistance. Furthermore, the alternating layers of ferrite and austenite phases will provide the article with a well-defined modulus of elasticity that will remain relatively high upon increasing load. By well-defined elastic modulus is meant that the elastic modulus will remain at a high level as the load on the material increases, and as the load increases to the elastic limit stress (Rp)_0.2) And hardly linearly decreases. Thus, the article will be suitable for elastic applications.

According to one embodiment, the duplex stainless steel has a PRE greater than 28. PRE is defined herein as PRE ═ Cr +3.3 × Mo +16 × N (coefficient multiplied by the respective weight percentages of the respective alloying elements). Thus, a duplex stainless steel as defined above or below will provide an article with a high corrosion resistance, in particular a high pitting corrosion resistance, due to its high PRE-value in both the ferrite and austenite phases, i.e. the PRE-value of the ferrite and austenite phases is greater than about 28. Thus, the respective amounts of Cr, Mo, and N are selected such that PRE in the austenite and ferrite phases is greater than about 28, respectively.

According to an embodiment, the duplex stainless steel as defined above or below consists of 55-70 vol-% austenite phase and 30-45 vol-% ferrite phase, such as 65-70 vol-% austenite phase and 30-35 vol-% ferrite phase. This means that there is no deformation-induced martensite in the duplex stainless steels of the present disclosure, and thus in articles composed of the duplex stainless steels. This is possible because the duplex stainless steel as defined above or below is highly alloyed, so the article will have the ability to produce cold deformation by cold working without transforming its austenitic structure into a martensitic structure.

According to one embodiment, the article as defined above or below is in the form of a sheet or a tape or a wire. The sheet or strip or wire may be used to make a spring, and the disclosure therefore also relates to a spring.

According to one embodiment, the at least one hot working process is hot rolling. The thermal processing process is performed at a temperature of 1050 ℃ to 1300 ℃. Further, according to an embodiment, the at least one hot working process is performed one or more times, e.g. in an embodiment, hot working, such as hot rolling, may be performed on the body several times, such as 6 times or until a desired hot working compression of the workpiece is obtained. Hot working also forms layers of austenite and ferrite phases, but the thickness of these layers is greater than in the final article. According to yet another embodiment, the workpiece may be heated between thermal processing steps.

According to one embodiment, the at least one cold working process is cold rolling. According to another embodiment, the at least one cold working is cold drawing. According to an embodiment, the cold working process is performed one or more times. In one embodiment, the cold working process may be performed on the workpiece several times, for example 4 times or until the desired cold deformation of the final article is obtained. According to an embodiment, the cold deformation of the final article, thus referring to the deformation of the article, is at least 10%, such as at least 25%, such as at least 50%, such as at least 75%, such as 75% to 95%. According to one embodiment, the final product obtained has a thickness in its cold rolled condition comprised between 20 μm and 5 mm.

According to one embodiment, the method comprises one hot working process, one cold working process, one hot working process and one cold working process. According to another embodiment, the method comprises one hot working process, one cold working process, one hot working process, one cold working process and one cold working process.

According to one embodiment, the method as defined above or below comprises a heat treatment step, wherein said heat treatment is an annealing of the obtained article after the cold working step. Annealing may be performed to reduce any intermetallic phases formed, such as sigma phases and chromium nitride, or to reduce the strength of the article or to alter the content of austenite or ferrite phases in the article. The annealing temperature will depend on the composition and thickness of the article. Typically, the annealing temperature is above 1000 ℃. According to another embodiment, the article is subjected to an annealing step at least between the penultimate cold working step and the last cold working step. Further, according to another embodiment, several annealing steps (such as more than one annealing step) may be applied between each cold working step (such as more than one cold working step). According to one embodiment, the article is annealed at a temperature in the range of 1050 ℃ to 1250 ℃ for a time in the range of about 1 second to 600 seconds. During heating of the article to this temperature range, it is important to avoid exposing the product to a temperature of 750 ℃ to 1000 ℃ for too long, since this is the temperature range in which the sigma phase and/or chromium nitride forms most rapidly. Thus, the temperature rise may be such that the time to pass through the range is less than about 2 minutes. Additionally, the final step of the process is a cold working step.

According to one embodiment, the method of the invention further comprises a step of ageing the obtained article after the cold working step or after the annealing step. Such a step will provide an additional increase in the elastic limit stress of the article and a further improvement in the elastic modulus behaviour. Prior to being subjected to the aging treatment, the article may be subjected to a forming operation in which it is formed into a spring. The aging may be performed at a temperature of 400 to 450 ℃ for 0.25 to 4 hours. Since the aging step is performed at a low temperature, it may be performed after the final cold working step.

In the following, alloying elements of the duplex stainless steel as defined above or below are discussed. These amounts are given in weight% (wt%):

carbon, C, is a representative element that stabilizes the austenite phase, and is an important element to maintain mechanical strength. However, if a large amount of carbon is present, carbides are precipitated, which lowers the corrosion resistance. Therefore, the carbon content is limited to less than 0.040 wt%.

Manganese, Mn has a deformation hardening effect and counteracts the transformation from an austenitic structure to a martensitic structure when deformed. In order to produce these effects, Mn must be present in an amount of at least or equal to 0.80 wt%. In addition, Mn has an austenite stabilizing effect at a content of up to about 10 wt.%. Above this level, the stability of ferrite will increase, and it is therefore difficult to add other ferrite stabilizing elements such as Cr and Mo without obtaining too much ferrite. Therefore, the maximum content of Mn should not be higher than 10 wt%. According to one embodiment, the content of Mn is equal to or less than 6.0 wt.%. According to another embodiment, it is equal to or less than 5.0% by weight. According to one embodiment, the content of Mn is in the range of 2.0 wt.% to 5.0 wt.%. When Mn is present in the amount as suggested above, it will increase the deformation hardening ability of the duplex stainless steel and also prevent the austenite phase from becoming so unstable that it will prevent transformation from the austenite structure to the martensite structure upon deformation.

Nitrogen, N has a positive effect on the corrosion resistance of the duplex stainless steel as defined above or below and also has a strong influence on the pitting corrosion resistance equivalent PRE, PRE defined as Cr +3.3Mo + 16N. In addition, N has a strong contribution to the solid solution strengthening and deformation hardening of duplex stainless steel. N also has a strong austenite stabilizing effect and counteracts the transformation from the austenite structure to the martensite structure upon plastic deformation. To contribute to all these positive effects, N is added in an amount of 0.10 wt% or more. At too high a level, however, N tends to form chromium nitrides, which should be avoided due to negative effects on ductility and corrosion resistance. Therefore, the content of N should be equal to or lower than 0.45 wt%. According to one embodiment, the content of N is 0.30 to 0.42 wt%.

Molybdenum, Mo has a strong influence on the corrosion resistance of the duplex stainless steel as defined above or below, and it heavily affects PRE and has a strong contribution to both solid solution strengthening and deformation hardening. Therefore, the addition amount of Mo is 0.90% by weight or more. However, Mo also increases the temperature at which the undesirable σ phase is stabilized and promotes the generation rate thereof, and thus the content of Mo should be equal to or less than 4.5 wt%. According to one embodiment, the content of Mo is 2.0 wt% to 4.0 wt%.

Chromium, Cr, has a strong influence on the corrosion resistance, especially pitting corrosion resistance, of the duplex stainless steel as defined above or below. In addition, Cr improves yield strength and counteracts the transformation of the austenitic structure into the martensitic structure when the duplex stainless steel is deformed. Cr also has a ferrite stabilizing effect on duplex stainless steels. Therefore, the content of Cr should be equal to or greater than 21.0 wt%. At high levels, an increase in the Cr content will lead to higher temperatures and faster sigma phase formation for the undesired stable sigma phase and chromium nitride. Therefore, the content of Cr is equal to or less than 28.0 wt%. According to an embodiment, the content of Cr is 24.0 to 28.0 wt. -%, such as 26.0 to 28.0 wt. -%.

Copper, Cu, has a positive effect on corrosion resistance. However, Cu is optionally added to the duplex stainless steel as defined above or below. Generally, Cu is present in scrap used for producing steel and is allowed to remain in steel at a moderate level. Therefore, the content of Cu may be equal to or lower than 0.50 wt%. According to one embodiment, the content of Cu is equal to or less than 0.02 wt%.

Nickel, Ni has a positive effect on resisting general corrosion. Ni also has a strong austenite stabilizing effect and counteracts the transformation from the austenite structure to the martensite structure when the duplex stainless steel is deformed. Therefore, the content of Ni is equal to or greater than 4.0 wt%. At levels above 9.0 wt.%, Ni will result in austenite levels above 70%. Therefore, the content of Ni should be not more than 9.0 wt%. According to one embodiment, the Ni content is 7.0 wt% to 9.0 wt%.

Silicon, Si, is almost always present in duplex stainless steels because it may have been used for deoxidation, or in scrap for duplex stainless steels, although the aim is to have as small an amount as possible. It has a ferrite stabilizing effect and, at least partly for this reason, the content of Si should be less than 0.60 wt%, such as between 0.40 wt% and 0.60 wt%.

Vanadium, V may be present as an impurity element in duplex stainless steel, and since it generally follows scrap, it is difficult to control the content thereof. The duplex stainless steel should preferably contain as little amount as possible due to precipitation of carbides, and the content of V should be equal to or less than 0.10 wt%, such as equal to or less than 0.01 wt%, for the duplex stainless steel of the present invention.

Phosphorus (P) may be an impurity and is contained in the duplex stainless steel as defined above or below; the content is less than 0.010 wt%.

Sulphur (S) may be an impurity contained in the duplex stainless steel as defined above or below. S may deteriorate hot workability at low temperatures. Therefore, the allowable content of S is less than 0.006 wt%.

Optionally, small amounts of other alloying elements may be added to the duplex stainless steel as defined above or below in order to improve e.g. machinability or hot workability properties such as hot ductility. Examples, but not limiting, of these elements are As, Ca, Co, Ti, Nb, W, Sn, Ta, Mg, B, Pb and Ce. The amount of one or more of these elements is at most 0.5 wt%, such as at most 0.1 wt%.

According to one embodiment, the article of the invention comprises a duplex stainless steel consisting of all the elements mentioned above or below.

When the term "up to" or "less than or equal to" is used, one skilled in the art will appreciate that the lower limit of the range is 0 wt% unless another number is specifically stated.

The balance of the elements of the duplex stainless steel as defined above or below are iron (Fe) and impurities usually present.

Examples of impurities are elements and compounds which are not deliberately added but cannot be completely avoided, since they are usually present as impurities in, for example, the raw materials or further alloying elements used for the manufacture of the duplex stainless steel.

According to one embodiment, the duplex stainless steel consists of alloying elements and the ranges described above.

The step of providing a body of a duplex stainless steel as defined above or below may comprise providing a melt of said duplex stainless steel and casting said melt to obtain a body of a duplex stainless steel as defined above or below. The casting may comprise continuous casting of the melt.

As a result of the method steps used, alternating layers of ferrite and austenite can be seen in the article, as previously described, which layers are substantially parallel to the plane of the article. The thickness of the layer will affect the elastic limit stress of the product. To obtain sufficient elastic limit stress, the average FCC thickness and BCC thickness of each layer should be less than or equal to about 4.5 μm. According to other embodiments, each layer has a thickness of 0.01 μm to about 4.5 μm, such as about 0.5 μm to about 4.5 μm, such as about 1.0 μm to about 4.2 μm, such as 2.0 μm to 4.2 μm. The thickness of the product in the final cold worked condition (after the final cold working step) may be 20 μm to 5 mm. Prior to cold working, the body comprising the duplex stainless steel as defined above or below is hot worked, wherein according to an embodiment the thickness of the body is reduced from about 100 to 200mm to 2 to 15 mm.

The thickness of the BCC phase and the FCC phase is measured separately by taking a vertical cross-section of the article (strip, sheet or wire) and then in an acid (such as HNO)₃) Middle polishing and etching to obtain a contrast between the two phases. Measurements were then performed under an optical microscope using appropriate magnification (100-1000 times) so that each phase was visible, so that enough phase boundaries could be counted to obtain reasonable statistical certainty (over 30 phase boundaries). A suitable cross-sectional location for measurement in the wire is at 25% of its diameter. The strip or sheet should be measured at the center of the thickness at 25% width from the edge. The thickness of each BCC and FCC phase in the diameter direction of the wire or in the thickness direction of the strip or sheet is measured and from this the average BCC and FCC thickness, respectively, is calculated.

The disclosure is further illustrated by the following non-limiting examples.

Examples

Alloys having the chemical composition shown in table 1 were melted and cast into 1kg ingots. After melting and casting, the ingot obtained was hot-rolled into strip at a temperature of about 1250 ℃ using 9 rolling passes. The samples were reheated 3 times during hot rolling to maintain the temperature above 1050 ℃. The final thickness of the strip is 3.7mm to 4.0 mm.

The hot rolled strip was then cold rolled until about 75% cold compression was obtained. 5 passes were used in the cold rolling mill.

The ferrite content was determined by using magnetic scale measurements. The magnetic scale measurements were performed according to IEC 60404-1. The magnetic phase content is assumed to be equal to the ferrite content and the remainder is assumed to be austenite. The values are listed in table 2.

For measuring the thickness of the BCC phase and the FCC phaseMeasurement, sampling at a vertical cross section of the strip at 25% width from the edge, then polishing and etching the sample (1M HNO)₃). Measurements were performed under an optical microscope (Nikon) using a suitable magnification (1000 x), i.e. each phase was visible and more than 30 phase boundaries were seen. The thickness of each of the BCC phase and the FCC phase is measured in the thickness direction, and the average BCC thickness and the average FCC thickness are calculated, respectively. The values obtained are shown in table 2.

The strength of the cold-rolled strip was determined by tensile testing in the rolling direction according to SS EN ISO 6891-1. Two tensile specimens were water jet cut from each cold rolled strip specimen. The results are collected in table 3. As can be seen from the table, all samples had good tensile strength.

Table 1 chemical composition of the samples-all values are given in weight% (wt%).

Sample (I)	Mn	N	Cr	Ni	Mo	C	Si	V	P	S	Cu
												1	0.86	0.15	22.1	5.28	3.28	0.030	0.51	0.006	0.006	0.004	0.013
2	1.94	0.16	22.6	6.45	3.02	0.032	0.51	0.006	0.006	0.004	0.013
												3	1.85	0.32	23.0	4.04	3.14	0.031	0.53	0.005	0.006	0.005	0.015
4	1.87	0.34	27.0	6.50	1.15	0.032	0.51	0.006	0.006	0.005	0.012
												5	9.14	0.26	22.9	6.13	2.96	0.031	0.52	0.006	0.010	0.005	0.014
6	1.85	0.18	22.9	4.03	0.98	0.033	0.51	0.005	0.006	0.004	0.011
												7	1.67	0.21	21.7	4.05	3.14	0.031	0.50	0.005	0.006	0.003	0.013
8	1.85	0.20	24.7	6.25	2.94	0.033	0.52	0.006	0.006	0.003	0.012
												9	0.83	0.27	25.8	7.22	4.07	0.035	0.53	0.007	0.006	0.005	0.013
10	1.12	0.24	26.6	7.52	3.10	0.030	0.52	0.005	0.007	0.005	0.014
												11	2.68	0.41	26.0	6.51	3.30	0.032	0.51	0.005	0.008	0.003	0.015
12	2.69	0.31	27.8	8.03	2.95	0.035	0.52	0.007	0.009	0.006	0.010
												13	5.86	0.32	25.7	7.69	3.36	0.035	0.53	0.006	0.009	0.004	0.013
14	2.76	0.34	27.9	7.42	2.08	0.035	0.50	0.006	0.008	0.005	0.013
												15	2.65	0.34	23.4	5.51	3.34	0.036	0.49	0.005	0.008	0.005	0.014

TABLE 2 phase thickness of the samples and phase content of the samples

TABLE 3 tensile test results

It can be seen that the obtained articles will have an elastic limit stress Rp higher than 1200MPa after cold rolling_0.2。

The experimental grade pitting resistance was evaluated using the PRE formula (defined as PRE ═ Cr +3.3Mo +16N) as previously described. By inputting

The equilibrium composition in each phase at a specific BCC content (from table 2) can be derived from the total composition in (table 1), so that the PRE for each phase can be calculated from table 4.

TABLE 4 composition and pitting corrosion resistance of each of the two phases

Thus, from the above experiments, it can be seen that the articles of the present disclosure will have high yield strength with good ductility as well as good corrosion resistance and high tensile strength due to solid solution strengthening and deformation hardening, variations in phase thickness and content.

From the above results it can be seen that the very fine microstructure obtained in the cold worked duplex stainless steel of the invention (as shown in table 5) will have an impact on the mechanical properties when the average phase thickness is below 4.5 μm.

Claims

1. An article of manufacture made from a duplex stainless steel, wherein the duplex stainless steel consists of, in weight%:

c is less than or equal to 0.040;

si is less than or equal to 0.60;

Mn 0.80～10.0；

Cr 21.0～28.0；

Ni 4.0～9.0；

Mo 0.9～4.5；

N 0.10～0.45；

cu is less than or equal to 0.50;

v is less than or equal to 0.10;

p is less than or equal to 0.010;

s is less than or equal to 0.006;

the balance of Fe and inevitable impurities;

and wherein the duplex stainless steel consists of 55-70 vol% of an austenite phase and 30-45 vol% of a ferrite phase;

wherein the duplex stainless steel has a PRE of greater than 28, and wherein PRE is defined as PRE ═ Cr +3.3Mo + 16N;

and wherein the article has alternating layers of ferrite and austenite phases that are substantially parallel to a plane of the article and have an average layer thickness of less than or equal to 4.5 μm.

2. The article of claim 1, wherein the duplex stainless steel consists of 65 to 70 volume percent of an austenite phase and 30 to 35 volume percent of a ferrite phase.

3. The article of any one of claims 1 to 2, wherein the average ferritic or austenitic thickness is 0.01 μ ι η to 4.5 μ ι η.

4. The article of any one of claims 1 to 2, wherein the average ferritic or austenitic thickness is 0.5 μ ι η to 4.5 μ ι η.

5. The article of any one of claims 1 to 2, wherein the average ferritic or austenitic thickness is 1.0 μ ι η to 4.5 μ ι η.

6. The article of any one of claims 1 to 2, wherein the average ferritic or austenitic thickness is 1.0 μ ι η to 4.2 μ ι η.

7. The article of claim 1 or 2, wherein the content of Mn in the duplex stainless steel is in the range of 2 to 5 wt.%.

8. The article of claim 1 or 2, wherein the content of N in the duplex stainless steel is in the range of 0.3 to 0.42 wt.%.

9. The article of claim 1 or 2, wherein the content of Mo in the duplex stainless steel is in the range of 2 to 4 wt.%.

10. The article of claim 1 or 2, wherein the content of Cr in the duplex stainless steel is in the range of 24 to 28 wt.%.

11. The article of claim 1 or 2, wherein the content of Cr in the duplex stainless steel is in the range of 26 to 28 wt.%.

12. The article of claim 1 or 2, wherein the Ni content in the duplex stainless steel is in the range of 7.0 wt% to 9.0 wt%.

13. The article of claim 1 or 2, wherein the article is a sheet or tape or wire.

14. A spring comprising the article of any one of claims 1-13.

15. A method of manufacturing the article of any one of claims 1 to 14, comprising the steps of:

-providing a body of a duplex stainless steel as defined in any one of claims 1 to 13;

-one or more thermal processes to transform the body into a workpiece, and the thermal processes are performed at a temperature of 1050 ℃ to 1300 ℃;

-one or more cold working processes to transform the workpiece into the article,

wherein the final step of the process must be a cold working process.

16. The method of claim 15, wherein the hot working process is hot rolling.

17. The method of claim 15 or claim 16, wherein the cold working process is cold rolling.

18. The method of claim 15 or 16, wherein the method further comprises one or more heat treatment steps, wherein the one or more heat treatment steps is annealing, the annealing being performed at a temperature of above 1000 ℃ to 1250 ℃.

19. The method of claim 15 or 16, comprising the further step of aging the article at a temperature of 400 ℃ to 450 ℃ for 0.25 hours to 4 hours, wherein the aging is performed after the final cold working step.