CS263613B1 - Corrosion-resistant austenitic steel - Google Patents

Abstract

Steel contains in % by weight 0.03 to 0.06% carbon, 0.8 to 1.2 i manganese, 0.2 to 0.7% silicon, traces up to 0.035 » phosphorus, traces up to 0.015% sulfur, 17.3 to 18.3% chromium, 9.3 to 9.8% nickel, traces up to 0.05% molybdenum, 0.010 to 0.025% nitrogen, 0.01 to 0.06% aluminum and 0.001 to 0.002 5% calcium. The essence is that the content of ferrite-forming elements expressed by the chromium equivalent Ecr = * Cr + ϊ Mo + 1.5 Ϊ Si is in the range of 17.8 to 19.0 and the content of austenite-forming elements expressed by the nickel equivalent Ejjí — % Ni + 30%N + 30%C + + 0.5 I Mu is in the range of 11.0 to 12.6.

Description

The invention relates to austenitic stainless steel comprising 0.03 to 0.06% carbon, 0.8 to 1.2% manganese, 0.2 to 0.7% silicon, traces up to 0.035% phosphorus, traces up to 0.015% sulfur 17.3 to 18.3% of chromium, 9.3 to 9.8% of nickel and traces of up to 0.05% of molybdenum and are intended for the manufacture of disposable needles. The structure of this steel is austenitic, with a low delta-ferrite content, due to the combination and amount of alloys.

Disposable injection needles have so far been manufactured with a high degree of mechanization from a 9x0.25 mm tape. The manufacturing process is characterized in that a cannula is rolled from the tape, which is automatically fusion-welded without an additional electrode. After welding, the cannula is cold drawn, gradually to the final dimension of the needles. In doing so, a precise degree of reinforcement must be obtained, which guarantees sufficient flexibility of the needle so that it does not bend during application.

The core of the problem of disposable needles lies in steel, since all previous attempts to produce the tape from the austenitic grade steel to date have encountered either difficulty in welding cannulae, especially as slags formed periodically on the weld surface during welding. cold drawing depreciated the quality of the drawn tube. The second reason for the unsuitability of austenitic stainless steel, which was commonly produced, was the lack of cold hardening, which resulted in low elasticity of the needles prescribed by the acceptance conditions and their bending during possible application. All common and less common ways to overcome the above shortcomings were ineffective. For example, titanium-stabilized steel, steel remelted under slag, steel produced by vacuum technology with conventional chemical composition scattering and refining were tested. In any case, the required properties to be introduced into production have not been achieved.

The above-mentioned disadvantages are overcome by austenitic stainless steel with guaranteed weldability and mechanical properties after cold forming according to the invention, which consists in that it contains 0.03 to 0.06% carbon, 0.8 to 1.2% manganese by weight, 0.2 to 0.7% silicon, traces up to 0.035% phosphorus, traces up to 0.015% sulfur, 17.3 to 18.3% chromium, 9.3 to 9.8% nickel, traces up to 0.05% molybdenum, 0.010 to 0.025% nitrogen, 0.01 to 0.06% aluminum and 0.001 0 to 0.002 5% calcium, while at the same time maintaining the content of ferrite forming elements expressed in chromium equivalent E _Cr =% Cr +% Mo + 1.5 í Si v and a content of austenite-forming elements expressed as nickel equivalent =% Ni + 30% N + 30% C + + 0.5% Mn in the range of 11.0 to 12.6.

As a consequence of keeping the chromium and nickel equivalents within the given limits, a balanced structure is located close to the austenite-martensite phase interface. This structure has the ability to transform austenite into g ¹ -martensite when cold deformed in the required volume, which gives steels the necessary strength properties necessary for the application of needles in practice - prevents their bending. The content of 1 to 4% delta-ferrite in the structure prevents cracks in the welds during fusion welding of the cannulae. A second requirement is the high micro-purity of the steel, which prevents the formation of slag nests on the weld surface, preventing subsequent cold drawing. The high purity is the result of a special metallurgical process which, at a content of 0.010 to 0.060 wt. % aluminum and 0.001 0 to 0.002 5 wt. Calcium produces liquid inclusions of steel that easily flow out of the bath. This steel is preferably vacuum decarburized, depth deoxidation is applied by calcium alloys and cast in an inert gas atmosphere. ^IN

In an exemplary embodiment, austenitic stainless steel disposable injection needle was prepared in a 25 wt% electric arc furnace and in a VOD furnace vacuum oxidation apparatus. 0.04% carbon, 0.89% manganese, 0.56% silicon, 0.018% phosphorus, 0.007% sulfur, 17.64% chromium, 9.46% nickel, 0.03% molybdenum, 0.016% aluminum, 02% nitrogen and 0.002 5% calcium, with a chromium equivalent of E _{Cr of} 18.51 and a nickel equivalent of E 2 of 11.705. The steel produced was cast from below into rolling ingots weighing 1,290 kg under argon protection. It was further processed after hot rolling and cold rolling into the final product, ie disposable injection needles - without problems both in terms of weldability and mechanical properties after cold drawing.

Claims (1)

Austenitic stainless steel for single use injection needles, guaranteed weldability on automatic welding unit and guaranteed cold forming after vacuum oxidation, containing by weight 0,03 to 0,06% carbon, 0,8 to 1 , 2% manganese, 0.2 to 0.7% silicon, traces up to 0.035% phosphorus, traces up to 0.015% sulfur, 17.3 to 18.3% chromium, 9.3 to 9.8% nickel, traces up to 0 0.05% molybdenum, 0.010 to 0.025% nitrogen, 0.01 to 0.06% aluminum and 0.001 0 to 0.002 5% calcium, characterized in that the content of ferrite forming elements expressed as chromium equivalent E _Cr =% Cr +% Mo + 1, 5% Si is in the range of 17.8 to 19.0 and the content of austenite-forming elements expressed as nickel equivalent =% Ni + 30% N + 30% C + + 0.5% Mn is in the range 11.0 to 12.6.