Bimetallic tube and method for manufacturing a bimetallic tube

A method for manufacturing a bimetallic tube comprising the steps of:

• providing a first metallic tube having an inner diameter (ID1st) and an outer diameter (OD1st), and providing a second metallic tube having an inner diameter (ID2nd) and an outer diameter (OD2nd), wherein the outer diameter (OD1st) of the first metallic tube is smaller than the inner diameter (ID2nd) 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 (IDBM) of the bimetallic tube;
• removing the second metallic tube from the first metallic tube;
• measuring the inner diameter (ID1st) of the first metallic tube after the second metallic tube has been removed;
• and
• calculating the absolute value of the difference (IDBM−ID1st) between the inner diameter (IDBM) of the bimetallic tube and the inner diameter (ID1st) of the first metallic tube after the second metallic tube has been removed.