Method for producing a strand from stainless steel and strand made of stainless steel

Abstract

A method for manufacturing a strand from a stainless steel by cold forming a billet into the cold-hardened strand and subsequently annealing the strand is provided. The method allows stainless steel strands to be produced, which have both a high tensile strength, as well as a high degree of elongation. The strand is heated to a temperature ranging from 400 C. to 460 C. while the strand is being annealed, and the cold-hardened strand is surrounded by a protective gas atmosphere during the heating process.

Claims

1. A method for manufacturing a strand of stainless steel comprising: cold forming a billet into a strain-hardened strand; and subsequently annealing the strand, wherein during annealing of the strand the strand is heated to a temperature in a range from 400 C. to 460 C., and wherein the strain-hardened strand is surrounded by a protective gas atmosphere during heating, and wherein the material of the billet is an austenitic stainless steel having a composition consisting of not more than 0.06 weight % carbon, not more than 2 weight % manganese, not more than 0.7 weight % silicon, 16 to 20 weight % chromium, 2.0 to 2.6 weight % molybdenum, with a balance of iron and unavoidable impurities.

2. The method according to claim 1, wherein the strand is heated to a temperature in the range from 410 C. to 450 C.

3. The method according to claim 1, further comprising the step of cooling the strand after heating, wherein the strand during cooling is surrounded by the protective gas atmosphere.

4. The method according to claim 1, wherein the protective gas atmosphere includes argon, having a fraction of argon of more than 95% by volume.

5. The method according to claim 1, wherein the protective gas atmosphere has an oxygen content of less than 50 ppm.

6. The method according to claim 1, wherein a dew point of the protective gas atmosphere at atmospheric pressure is at a temperature of 40 C. or less.

7. The method according to claim 1, wherein the strand is a tube.

8. The method according to claim 1, wherein the billet and the strand are in the form of a tube with an inner diameter and an outer diameter, and wherein by the cold forming a tube is formed, the inner diameter of which is half of the outer diameter or less.

9. The method according to claim 1, wherein the cold forming is carried out by cold pilger milling.

10. A strand of stainless steel made according to the method of claim 1.

11. The strand of stainless steel according to claim 10, wherein the strand is a tube with an inner diameter and an outer diameter, the inner diameter being one half of the outer diameter or less.

12. The method according to claim 1, wherein the strand is heated to a temperature in the range from 435 C. to 445 C.

13. The method according to claim 1, wherein the strand is heated to a temperature of 440 C.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows a flow chart of a method for manufacturing a stainless steel tube according to an embodiment of the present disclosure.

DETAILED DESCRIPTION

(2) In a test, a tube was formed from an austenitic stainless steel according to DIN1.44/41 containing carbon in a fraction of not more than 0.06% by weight, manganese in a fraction of not more than 1.8% by weight, silicon in a fraction of not more than 0.7% by weight, nickel in a fraction of 1% by weight, chromium in a fraction of 17% by weight and molybdenum in a fraction of 2.3% by weight with a balance of iron and unavoidable impurities.

(3) The billet was first cold-reduced by means of cold pilger milling into a ready-made stainless steel tube.

(4) The tube milled like this has an elongation A(H) of 25.0% and a tensile strength Rp 0.2 of 762 N/mm.sup.2.

(5) Subsequently, this cold-drawn tube was annealed under a protective gas atmosphere with a fraction of argon of more than 95% by volume at a temperature of 440 C. The oxygen content in the protective gas atmosphere was less than 10 ppm.

(6) The annealed tube has an elongation A(H) of 15.1% after annealing. The tensile strength Rp 0.2 is 812 N/mm.sup.2.

(7) For purposes of explanation, the method for manufacturing a stainless steel tube according to the present disclosure is briefly summarized again with reference to the flow chart of FIG. 1.

(8) First, in step 1, a tube of austenitic stainless steel is provided as the starting material as a billet. In addition to iron and unavoidable impurities, the stainless steel contains carbon in a fraction of not more than 0.06% by weight, manganese in a fraction of not more than 1.8% by weight, silicon in a fraction of not more than 0, 7% by weight, nickel in a fraction of 11% by weight, chromium in a fraction of 17% by weight and molybdenum in a fraction of 2.3% by weight. This billet is then cold-formed by cold pilger milling in step 2 into the completely dimensioned tube.

(9) The finished tube is then annealed in step 3 under a protective gas atmosphere with an argon content of more than 95% by volume and an oxygen content in the protective gas atmosphere of less than 10 ppm at a temperature of 440 C.

(10) For the purposes of the original disclosure, it is to be understood that all features as will become apparent to those skilled in the art from the present description, drawings and claims, although described specifically only in combination with certain further features, can be combined both individually and in arbitrary combinations with other features or groups of features disclosed herein, as far as such combination has not been expressly excluded or technical circumstances make such combinations impossible or meaningless. A comprehensive, explicit description of all conceivable combinations of features is omitted here only for the sake of brevity and the legibility of the description.

(11) While the disclosure has been illustrated and described in the drawings and the foregoing description, this description is given by way of example only and is not intended to form a limitation of the scope of the disclosure as defined by the claims. The disclosure is not restricted to the examples disclosed.

(12) Modifications of the disclosed examples will be apparent to those skilled in the art from the drawings, the specification, and the appended claims. In the claims, the word comprise does not exclude other elements or steps and the undefined article a or an does not exclude a plurality. The mere fact that certain features are claimed in different claims does not exclude their combination. Reference signs in the claims are not intended to be limiting the scope of protection.