Bimetallic tube and method for manufacturing a bimetallic tube

Abstract

The present disclosure relates to a bimetallic tube comprising a first metallic tube having an inner diameter and an outer diameter, and a second metallic tube having an inner diameter and an outer diameter, wherein the first metallic tube is arranged within and force-fitted to the second metallic tube and wherein the first metallic tube comprises a zirconium (Zr) based alloy and wherein the second metallic tube comprises an austenitic stainless steel. The present disclosure also relates to a method for manufacturing a bimetallic tube comprising the steps of providing a first metallic tube having an inner diameter and an outer diameter, providing a second metallic tube having an inner diameter and an outer diameter, wherein the outer diameter of the first metallic tube is smaller than the inner diameter of the second tube, insetting the first metallic tube into the second metallic tube, cold-drawing the first and second metallic tubes together, such that the first and second metallic tubes are force-fitted together.

Claims

1. A bimetallic tube comprising a first metallic tube having an inner diameter (ID.sub.1st) and an outer diameter (OD.sub.1st), and a second metallic tube having an inner diameter (ID.sub.2nd) and an outer diameter (OD.sub.2nd), wherein the first metallic tube is arranged within and force-fitted to the second metallic tube, wherein the first metallic tube comprises, in weight %, Fe+Cr≤1.0; C≤0.1; O≤0.2; Hf≤5.0; balance Zr and normally occurring impurities, wherein the second metallic tube is an austenitic stainless steel comprising, in weight, C≤0.04; Mn≤3.0; P≤0.05; S≤0.04; Si≤1.0; Cr 15.0-30.0; Ni 7.0-25.0; Mo≤1.0; N≤0.10; balance Fe and normally occurring impurities, and wherein the force-fitting of the first metallic tube to the second metallic tube is at least 20 μm determined by the following procedure: measuring the inner diameter (ID.sub.BM) of the bimetallic tube; removing the second metallic tube from the first metallic tube; measuring the inner diameter (ID.sub.1st) of the first metallic tube after the second metallic tube has been removed; and calculating the absolute value of the difference (ID.sub.BM−ID.sub.1st) between the inner diameter (ID.sub.BM) of the bimetallic tube and the inner diameter (ID.sub.1st) of the first metallic tube after the second metallic tube has been removed.

2. The bimetallic tube according to claim 1, wherein the content of Cr present in the second metallic tube is in a range of from 17 to 21 weight %.

3. The bimetallic tube according to claim 1, wherein the content of Cr present in the second metallic tube is in a range of from 23 to 27 weight %.

4. A method for manufacturing a bimetallic tube comprising the steps of: providing a first metallic tube having an inner diameter (ID.sub.1st) and an outer diameter (OD.sub.1st), and providing a second metallic tube having an inner diameter (ID.sub.2nd) and an outer diameter (OD.sub.2nd), wherein the outer diameter (OD.sub.1st) of the first metallic tube is smaller than the inner diameter (ID.sub.2nd) of the second tube; inserting the first metallic tube into the second metallic tube; and cold-drawing the first and second metallic tubes together, such that the first and second metallic tubes are force-fitted together, wherein in the step of providing the first metallic tube, the first metallic tube comprises, in weight %; Fe+Cr≤1.0; C≤0.1; O≤0.2; Hf≤5.0; balance Zr and normally occurring impurities, wherein in the step of providing the second metallic tube, the second metallic tube is an austenitic stainless steel comprising, in weight %; C≤0.04; Mn≤3.0; P≤0.05; S≤0.04; Si≤1.0; Cr 15.0-30.0; Ni 7.0-25.0; Mo≤1.0; N≤0.10; balance Fe and normally occurring impurities, and wherein after the step of cold-drawing the first metallic tube is force-fitted to the second metallic tube so that the spring back is least 20 μm determined by the following procedure: measuring the inner diameter (ID.sub.BM) of the bimetallic tube; removing the second metallic tube from the first metallic tube; measuring the inner diameter (ID.sub.1st) of the first metallic tube after the second metallic tube has been removed; and calculating the absolute value of the difference (ID.sub.BM−ID.sub.1st) between the inner diameter (ID.sub.BM) of the bimetallic tube and the inner diameter (ID.sub.1st) of the first metallic tube after the second metallic tube has been removed.

5. The bimetallic tube according to claim 4, wherein the content of Cr present in the second metallic tube is in a range of from 17 to 21 weight %.

6. The bimetallic tube according to claim 4, wherein the content of Cr present in the second metallic tube is in a range of from 23 to 27 weight %.

7. The method according to claim 4, wherein in the step of cold-drawing, the outer diameter (OD.sub.2nd) of the second tube is reduced 10% or less compared to outer diameter (OD.sub.2nd) of the second metallic tube before cold-drawing.

8. The method according to claim 4, wherein in the step of cold-drawing, the outer diameter (OD.sub.2nd) of the second tube is reduced 4% or less compared to outer diameter (OD.sub.2nd) of the second metallic tube before cold-drawing.

9. The method according to claim 4, wherein after the step of cold-drawing the second metallic tube has an elongation of at least or equal to 35% and a hardness not more than or equal to 90 HRB.

10. The method according to claim 4, wherein in the step of providing the first metallic tube and/or the second metallic tube is heat-treated before the step of inserting the first metallic tube into the second metallic tube.

11. The method according to claim 4, wherein in the steps of providing first and second metallic tubes, the first metallic tube and/or the second metallic tube are cold worked tubes.

12. The method according to claim 4, wherein in the step of providing the first metallic tube, the first metallic tube is a seamless tube.

13. The method according to claim 4, wherein in the step of providing the first metallic tube, the average wall thickness of the first metallic tube is 0.3 mm to 2 mm.

14. The method according to claim 4, wherein in the step of providing the second metallic tube, the second metallic tube is a seamless tube.

15. The method according to claim 4, wherein in the step of providing the second metallic tube, the average wall thickness of the second metallic tube is 0.5 mm to 4 mm.

16. The bimetallic tube according to claim 2, wherein the content of Cr present in the second metallic tube is in a range of from 18 to 20 weight %.

17. The bimetallic tube according to claim 3, wherein the content of Cr present in the second metallic tube is in a range of from 24 to 26 weight %.

18. The bimetallic tube according to claim 5, wherein the content of Cr present in the second metallic tube is in a range of from 18 to 20 weight %.

19. The bimetallic tube according to claim 6, wherein the content of Cr present in the second metallic tube is in a range of from 24 to 26 weight %.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) FIG. 1a is schematic cross-section of a bimetallic tube according to an embodiment of the present disclosure.

(2) FIG. 1b is a schematic cross-section of a bimetallic tube according to an embodiment of the present disclosure indicating the removal of the second metallic tube.

(3) FIG. 1c is a schematic cross-section of the bimetallic tube according to FIG. 1b with the first metallic tube left after removal of the second metallic tube.

DETAILED DESCRIPTION

(4) The bimetallic tube 1 according to an embodiment of the present disclosure as depicted in FIG. 1a comprises a first metallic tube 2 and a second metallic tube 3. The first metallic tube 2 comprises, in weight % (wt-%), Fe+Cr≤1.0; C≤0.1; O≤0.2; Hf≤5.0; balance Zr and normally occurring impurities. The second metallic tube is an austenitic stainless steel comprising, in weight % (wt-%), C≤0.04; Mn≤3.0; P≤0.05; S≤0.04; Si≤1.0; Cr 15.0-30.0; Ni 7.0-25.0; Mo≤1.0; N≤0.10; balance Fe, and normally occurring impurities.

(5) Each of the first metallic tube 2 and the second metallic tube 3 comprises an inner diameter ID.sub.1st or ID.sub.2nd, respectively, and an outer diameter OD.sub.1st or OD.sub.2nd, respectively. Before cold-drawn together, the outer diameter OD.sub.1st of the first metallic tube 2 is slightly smaller than the inner diameter ID.sub.2nd of the second metallic tube 3, such that the first metallic tube 2 can be easily inserted into the second metallic tube 3.

(6) Afterwards, i.e. after the first metallic tube 2 has been inserted into the second metallic tube 3, the first metallic tube 2 and the second metallic tube 3 are cold-drawn together through a drawing die. During the cold-drawing step, a force is applied to both the second metallic tube 3 and the first metallic tube 2 inserted therein yielding a plastic deformation and a reduction of the inner diameter ID.sub.2nd of the second metallic tube 3 and of the outer diameter OD.sub.1st of the first metallic tube 2. In a state after cold-drawing, as it is depicted in FIG. 1a, the outer diameter OD.sub.1st of the first metallic tube 2 equals the inner diameter ID.sub.2nd of the second metallic tube 3. Further, in a state after cold-drawing, as it is depicted in FIG. 1a, the inner diameter ID.sub.BM of the bimetallic tube equals the inner diameter ID.sub.1sd of the first metallic tube 2.

(7) The deformation of the first and second metallic tubes 2, 3 obtained during cold-drawing depends on size of the outer diameter OD.sub.1st of the first metallic tube, the inner diameter ID.sub.2nd and the outer diameter OD.sub.2nd of the second metallic tube and the inner dimension of the drawing die. The parameters applied in the cold-drawing step are chosen, such that the force-fitting of the first metallic tube 2 to the second metallic tube 3 is at least 20 μm.

(8) The force-fitting is determined by the following procedure: The inner diameter (ID.sub.BM) of the bimetallic tube (1) is measured; the second metallic tube (3) is removed from the first metallic tube (2); the inner diameter (ID.sub.1st) of the first metallic tube (2) is measured after removing the second metallic tube (3); the absolute value of the difference ID.sub.BM−ID.sub.1st between the inner diameter ID.sub.BM of the bimetallic tube 1 and the inner diameter ID.sub.1st of the first metallic tube 2 after the second metallic tube 3 has been removed is calculated.

(9) The removal of the second metallic tube 3 from the first metallic tube 2 is indicated in FIG. 1b. FIG. 1b is a cross-section of the bimetallic tube 1 according to the embodiment of FIG. 1a. Although in the present embodiment the second metallic tube 3 is removed by milling off the second metallic tube 3, the second metallic tube 3 could also be removed by pressing the first metallic tube 2 out of the second metallic tube 3. It is to be understood that a whole tube does not have to be used in the procedure, a sample of the bimetallic tube 1 is sufficient for obtaining the values of force-fitting.

(10) After the second metallic tube 3 has been completely removed from the first metallic tube 2, as it is depicted in FIG. 1c, the first metallic tube 2 expands again and the inner diameter ID.sub.1st of the first metallic tube 2 is measured. The outer diameter OD.sub.1st and the inner diameter ID.sub.1st of the first metallic tube 2 is larger than in the cold-drawn state shown in FIG. 1a.

(11) The absolute value of the difference ID.sub.BM−ID.sub.1st between the inner diameter ID.sub.BM of the bimetallic tube 1 and the inner diameter ID.sub.1st of the first metallic tube 2 after the second metallic tube 3 has been removed is calculated. By means of the present disclosure, the deformation applied in the cold-drawing step is sufficiently high when the value is at least 20 μm.

(12) For purposes of original disclosure, it is pointed out that all features which are apparent for a person skilled in the art from the present description, the figures and the claims, even if they have only been described with further features, could be combined on their own or together with all the combinations of the features disclosed herein, if not excluded explicitly or technically impossible. A comprehensive explicit description of all possible combinations of features is only omitted in order to provide readability of the description.

(13) While the disclosure has been described with respect to a limited number of embodiments, it will be understood that the disclosure of which is not limited to those embodiments. Other embodiments comprising various changes do not depart from the scope of the disclosure. In particular, the description of preferred embodiments shall not be understood to be limited to what is explicitly shown and described in the specification and drawings but shall encompasses the disclosure of the specification and drawings as a whole.