WO2005031018A1

WO2005031018A1 - Austenitic fe-cr-ni alloy for high temperature use.

Info

Publication number: WO2005031018A1
Application number: PCT/SE2004/001288
Authority: WO
Inventors: Bo JÖNSSON; Thomas Helander
Original assignee: Sandvik Intellectual Property Ab
Priority date: 2003-10-02
Filing date: 2004-09-08
Publication date: 2005-04-07
Also published as: EP2426226A2; DE04775393T1; CN100540702C; US20180371592A1; US10683569B2; US20070081917A1; EP1680523B1; US20110147368A1; DE202004021125U1; SE0302611L; KR100803684B1; CN1860245A; EP1680523A1; SE0302611D0; JP2007507611A; KR20060094533A; EP2426226B1; EP2426226A3; SE527319C2; US20160083822A1

Abstract

Alloy for high temperature use. The invention is characterized in, that the alloy mainly comprises Fe, Ni and Cr and in that the alloy has the following main composition, given in weigth%, Ni 38 - 48 Cr 18 - 24 Si 1.0 - 1.9 C < 0.1 Fe balance.

Description

Austenitic Fe-Cr-Ni alloys for high temperature use

The present invention refers to an alloy for use at high temperatures .

Austenitic Ni-base alloys containing Cr up to 30wt%, Si up to 3wt%, varying amounts of Fe and sometimes additions of R.E.- ^' elements (Rare Earth) are since long used for a variety of high temperature parts up to 1100°C service temperature. Regarding electric resistance alloys used for heating in industrial furnaces and in appliances, several alloys with varying amount of Ni are standardised in ASTM B 344-83 and in DIN 17470. These standards are not fully compatible as seen from table 1. There are several commercial resistance alloys using variations on the theme, such as the 37-21 alloy, comprising 37Ni, 20 to 21% Cr, 2% Si and bal. Fe and minor additions of rare eath elements including Yttrium (designated R.E. ) . It is the aim for the present invention to find alloy compositions that would combine the lower cost of a Ni content in the range, if possible, close to NiCr 30/20, i.e. 30 wt% Ni and 20wt% Cr, with i) a good hot form stability and ii) an oxidation resistance and iii) a relatively high electrical resistance and low change of resistance (Ct) of a higher Ni content alloy such as NiCr 60/15.

Table 1. Summary of ASTM and DIN Standards for resistance eCr(Fe) alloys

* Maximum 1% Co State of the art

In general, the maximum operating temperature and lifetime increases with increased Ni-content, but several other ele- ments have great impact on these properties as well. All of these alloys form a protective oxide layer composed of mainly Cr₂0₃ and in case of Si additions also Si0₂ to some extent. Smaller additions like rare earth elements have been used to further enhance the properties of the oxide layer, and sev- eral patents advice additions to provide a material with good oxidation life, see e.g. EP 0 531 775 and EP 0 386 730.

In addition to good oxidation there is also a demand for good hot strength. In case of electric elements, the cost for hangers and support systems can be reduced if the material is strong enough to support its own weight and therefore to maintain its shape at operating temperature.

For use as electric elements, the relatively high resistivity and low C_t

ratio of resistance change from room temperature to working temperature is an important parameter. In general the higher the Ni, the higher the resistivity and the lower the C_t factor.

Addition of elements such as Mo and up to levels of several wt % are known to enhance the mechanical properties at high temperatures but they are expensive and are therefore not desirable additions in applications where cost is important.

In a wide range of open coil electric resistance heating elements, NiCr 60/15 and NiCr 30/20 type (DIN) or 60 Ni, 16 Cr and 35 Ni, 20 Cr (ASTM) alloys are used. From a cost point of view, the NiCr 30/20 or 35Ni, 20Cr type is preferred due to their lower content of expensive Ni . In applications where the watt density and therefore the element temperature are high, the oxidation life of alloys with this level of Ni is up to now insufficient. At the same time, the mechanical properties at working temperatures have to be within acceptable limits.

Description of the invention

The present invention refers to alloy for high temperature use, and is characterized in, that the alloy mainly comprises

Fe, Ni and Cr and in that the alloy has the following main composition, given in weigth%,

Ni 38 - 48 Cr 18 - 24

Si 1.0 - 1.9

C < 0.1 and in that Fe is the balance.

It is important that the content of C is below 0.1 wt%

Eight test melts were cast, hot rolled, and cold drawn to wire according to standard practice with chemical composition according to Table 2.

Table 2. Chemical composition of test melts

The wires were coiled into helixes and mounted on sample holders. These were exposed to a high temperature, 950°C, by means of a laboratory furnace for 168 hours. Deformation of the helixes was measured by means of a micrometer screw according to the set up in Fig. 1.

Since these products are working at a high temperature, the oxidation life and in particular the cyclic oxidation life is an important design factor. In order to evaluate this property a cyclic oxidation test was performed. The sample wires were heated by passing electric current through them and the saple wires were exposed to a 2 minutes on/2 minutes off cycle. The time to burn off was recorded and the results were grouped according to performance.

A combination of the deformation performance that occurs from relatively small applied forces such as gravity acting on e.g. suspended heater coils and oxidation performance at high temperature is therefore the aim of the present invention.

The results indicate that not only the level of each element but in addition the relative contents of the base elements Nickel, Chromium and Silicon and have a surprisingly large impact on performance.

Table 3. Results from deformation and oxidation tests. "+ designates a better than average result.

We have now found that the relation between these elements has to be within a narrow range that is given on the one hand of sufficient deformation performance and on the other hand by adequate oxidation performance. Only in this narrow band of compositions, the optimum compromise was achieved that gave the working solution.

An alloy according to the invention, has the main composition (in wt%) of Ni ranging from 38 to 48, a Cr level is larger than

Cr = -O.lNi + 24

and lower than

Cr = -0.1667Ni + 30

At the same time, the Si level is larger than

Si = 1.0

and smaller than Si = -O . O lNi + 1 . 9 .

In Figure 3 the above mentioned Si content and Cr content are shown by means of diagrams, where alloys according to the invention are compared with alloys according to the invention.

The alloy may also contain up to 5 % Co as substitute of Ni and Mn up to 2%. Further it contains Al up to 0.6% and pref- erably above 0.03 %, and R.E., Y and Ca up to a level of 0.2% in total. C should be <0.1 and N in a range up to 0.15 %, preferably above 0.03 %. Nitride and carbide formers such as Ti, Zr, Hf Ta, Nb and V may be added up to a total level of 0.4% but are not necessary to benefit from the advantage of the invention. The remainder consists of iron and various elements originating from the raw materials and the production process up to a total level of <2%.

A specific example of an alloy according to the invention contains (in wt%)

Ni 39-41 Cr 20-22 Si 1-1.5 N 0.15

Ce 0.01-0.04 C < 0.1

Impurities up to 2% Fe balance.

Another example of an alloy according to the invention with further improved oxidation performance due to the higher Ni content but with otherwise comparable properties is Ni 44-46

Cr 20-22

Si 1-1.5

N < 0.15

Ce 0.01-0.04

C < 0.1

Impurities up to 2'-

Fe balance.

Preferred embodiments are as follows, with the composition in weight%.

An alloy comprising

Ni 38 - 48

Cr between -O.lNi + 23 and -0.2667Ni + 36 Si between 0.8 and -0.0133 Ni + 2.2 Fe Balance.

An alloy comprising

Ni 40

Cr 21

Si 1.2

N < 0.15

Ce 0.03 C < 0.1 impurities up to 2% and

Fe balance. An alloy comprising

Ni 45

Cr 21

Si 1.2

N < 0.15

Ce 0.03 C < 0.1 impurities up to 2% and

Fe balance.

Another alloy that is preferred comprises

Ni 38 - 48

Cr larger than

Cr = -O.lNi + 24

and lower than

Cr = -0.1667Ni + 30

Si larger than Si = 1.0 and smaller than Si = -O.OINi + 1.9

and C < 0.1 and Al up to 0.6 Fe balance .

The alloy may also contain up to 5 % Co as substitute of Ni

Mn up to 2 Al up to 0.3

R.E., Y and Ca up to a level of 0.2% in total

C <0.1

N < 0.15

Ti, Zr, Hf Ta, Nb and V up to a total level of 0.4 <50 wt ppm S various elements originating from the raw materials and the production process up to a total level of <2 and

Fe balance.

An alternative is :

38 - 48 Ni

18 - 22 Cr

1.0 -1.5 Si Al < 0.6

<0.1 c

N < 0.15

<1 Mn

<50 wt ppm S <0.5 in total sum of elements belonging to the group

Ti, Zr, Hf, Y, Rare Earth Elements (Lantanoid group) , Ca, Mg,

Ta

<5 totally of elements belonging to the group Mo, Co, Ta, W

<0,4 totally of elements belonging to the group Ti, Zr, Hf Ta, Nb and V

<1 of other elements arising from impurities in the melting process and

Fe balance. Further preferred embodiments are an alloy comprising,

Ni 39-41 Cr 20-22 Si 1-1.5 Mn 0.5 C 0.02

N < 0.15

Ce 0.01-0.04 impurities up to 2% and in that Fe is balance.

And an alloy comprising,

Ni 44-46

Cr 20-22 Si 1-1.5

Mn 0.5

C 0.02

N < 0.15

Ce 0.01-0.04 impurities up to 2% and in that Fe is balance.

Table 2 below is a comparison of commercially available al- loys with alloys according to the invention.

Alloys Ni Cr Si Other 353MA 35 25 1,5 N 0, 17 Incolloy 37 18 2,3 DS Incolloy 32 21 0,5 800 Incolloy 52 22 0,5 Al 1,2 617 Haynes 37 25 0,6 Nb 0,7 HR-120 Nikrothal 80 20 1,35 80 Nikrothal 57,5 16 1,5 60 Nikrothal 37 20 2 40 Nikrothal 30 21 2 •o 30 Nikrothal 21 25 2,3 20 Invention 40 21 1,3 ex 1 Invention 45 21 1,2 ex 2

The alloy 353MA is produced by Outokompo Stasinless, Finland.

The alloy Incolloy is produced by Special Metals Corp., USA. Haynes is produced by Haynes international Inc., USA.

Nikrothal is produced by Applicant.

As is apparent from the above said, the present invention fullfills the aim mentioned in the opening part of the pre- sent description.

Claims

Claims.

1. Alloy for high temperature use, c h a r a c t e r i z e d i n, that the alloy mainly comprises Fe, Ni and Cr and in that the alloy has the following main composition, given in weigth%, Ni 38 - 48 Cr 18 - 24

Si 1.0 - 1.9

C < 0.1 and in that Fe is the balance.

2. Alloy according to claim 1, c h a r a c t e r i z e d i n, that the alloy mainly comprises Fe, Ni and Cr and in that the alloy has the following main composition, given in weigth%, Ni 38 - 48

Cr 18 - 24

Si 1.0 - 1.9

C < 0.1

Mn less than 2 Al,C,Ca,N,Ti,Zr,Hf, Ta, Nb, V,Mg, Ta, , Ce and REE together less than approximately 7

Fe balance.

3. Alloy according to claim 1 or 2, c h a r a c t e - r i z e d i , that the alloy comprises,

Ni 38 - 48

Cr between -O.lNi + 23 and -0.2667Ni + 36 Si between 0.8 and -0,0133 Ni + 2.2 C < 0.1.

4. Alloy according to claim 1, 2 or 3, c h a r a c t e - r i z e d i n, that the alloy comprises,

Ni 39-41

Cr 20-22

Si 1-1.5 N < 0.15

Ce 0.01-0.04

C < 0.1 impurities up to 2% and

Fe balance.

5. Alloy according to claim 1, 2 or 3, c h a r a c t e r i z e d i n, that the alloy comprises,

Ni 44-46 Cr 20-22

Si 1-1.5

N < 0.15

Ce 0.01-0.04

C < 0.1 impurities up to 2% and

Fe balance.

6. Alloy according to claim 1 or 2, c h a r a c t e r i z e d i n, that the alloy comprises, Ni 38 - 48

Cr between -O.lNi + 24 and -0.1667N1 + 30 Si between 1.0 and -O.OINi + 1.9, and in that he alloy contains up to 5 wt% Co as substitute of Ni in that the alloy further contains Mn up to 2 Al up to 0.6 R.E., Y and Ca up to 0.2% in total C < 0.1 N < 0.15

Ti, Zr, Hf Ta, Nb and V up to 0.4 in total S <50 wt ppm other elements <2 in total and in that Fe is balance

7. Alloy according to claim 1, 2 or 6, c h a r a c t e r ^¬ i z e d i n, that the alloy comprises, Ni 38 - 48

Cr 18 - 22

Si 1.0 -1.5

Al < 0.6

C <0.1 N < 0.15

Mn <1

S <50 wt ppm , in that the alloy further contains elements belonging to the group Ti, Zr, Hf, Y, Rare Earth Elements (Lantanoid group) , Ca, Mg and Ta with less than 0.5 in total, and elements belonging to the group Mo, Co, Ta, W with less than 5, and elements belonging to the group Ti, Zr, Hf Ta, Nb and V with less than 0.4, in that other elements < 2 in total and in that Fe is balance.

8. Alloy according to claims 1, 2, 6 and 7, c h a r a c t e r i z e d i n, that the alloy comprises, Ni 39-41 Cr 20-22 Si 1-1.5 C 0.02 N < 0.15

Ce 0.01-0.04 impurities up to 2% and in that Fe is balance.

9. Alloy according to claims 1, 2 and 6, c h a r a c t e r i z e d i n, that the alloy comprises, Ni 44-46 Cr 20-22 Si 1-1.5 C 0.02

N < 0.15

Ce 0.01-0.04 impurities up to 2% and in that Fe is balance.