RU2385948C2 - Method of receiving of stainless austenitic steel - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: method includes melting of semi-product in one furnace and ligature alloy in the other with its following blending and refinement in casting ladle. In the capacity of semi-product it is molten alloy on the basis of iron and elements introduced into steel composition and reducing solubility of nitrogen in iron and ligation alloy is molten with content of elements introduced into composition of steel and increasing solubility of nitrogen in iron. Into ligation alloy it is introduced nitrogen up to content which is calculated by formula.

EFFECT: invention increases steel strength at an increasing of nitrogen concentration in steel.

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Description

The invention relates to the field of metallurgy and can be used in the production of stainless austenitic steels alloyed with nitrogen.

A known method of producing stainless steel by obtaining a high-nitrogen alloy containing chromium, manganese and nitrogen, and an alloy containing elements such as nickel, followed by the manufacture of a combined electrode from both alloys and mixing them during electroslag remelting. (German Patent No. 2528588 IPC С21С 5/52).

The disadvantage of this method is that the alloys are previously crystallized, and their mixing proceeds during electroslag remelting. Each of these stages is accompanied by nitrogen losses, which does not allow to obtain a nitrogen content that is significantly higher than the standard solubility in the production of steel at atmospheric pressure.

A known method of producing alloy steel with nitrogen using nitrided ferroalloys. Nitrided ferroalloys are seated in a furnace or in a ladle during the release of metal from the furnace. (Svyazhin A.G. “Alloying steel with nitrogen”, Bulletin of scientific and technical information “Ferrous metallurgy”, issue 6 (1094), 1990. P.23).

The disadvantages of the method when it is used in plants for secondary processing are unstable and low absorption of nitrogen. In the case of subsequent vacuum treatment, almost complete loss of nitrogen introduced with ferroalloys occurs. The supply of nitrided ferroalloys to a ladle with metal leads to the melting and dissolution of ferroalloys in the surface layer of steel and the removal of most of the nitrogen into the atmosphere.

The closest in technical essence is a method for producing alloy steel by smelting an intermediate in one furnace and a master alloy in another, followed by their mixing and refining in a steel pouring ladle. (USSR author's certificate No. 351901, IPC С21С 5/52, 11.01.71. Prototype).

The specified method allows to increase the strength of steel due to refining in the bucket.

The disadvantage of this method is the impossibility of obtaining steels with a nitrogen content exceeding its standard solubility, since the ligature alloy contains elements not only increasing the solubility of nitrogen (such as chromium, vanadium, niobium, manganese), but also lowering it (nickel, carbon, silicon) .

The objective of the invention is to increase the strength of stainless austenitic steel due to alloying with nitrogen to a concentration exceeding its standard solubility.

This problem is solved by the fact that in the method of producing stainless austenitic steel, including the smelting of a semi-product in one furnace and a ligature alloy in another, followed by their mixing and refining in a steel pouring ladle, an alloy based on iron and elements that make up steel is smelted as a intermediate reducing the solubility of nitrogen in iron, and the ligature alloy is smelted with the composition of the elements that make up the steel and increasing the solubility of nitrogen in iron, and nitrogen is introduced into the ligature alloy, which is calculated by the formula:

where Q is the nitrogen content in the ligature alloy, wt.%;

M _l - the mass of the ligature alloy, t;

M _p - the mass of the intermediate product, t;

[N] _p - standard solubility of nitrogen in the melted steel, wt.%

The exclusion from the composition of the ligature alloy of elements that reduce the solubility of nitrogen, leads to an increase in the concentration of elements that increase its solubility in iron. When alloying such a ligature alloy with nitrogen, the solubility of nitrogen increases exponentially with an increase in the concentration of these elements to maximum values that significantly exceed the standard solubility of nitrogen in steel after mixing the ligature alloy with the intermediate. When a semi-product and a ligature alloy with a nitrogen content with standard solubility are mixed in a ladle, its solubility in steel decreases, but in a linear relationship. Therefore, the concentration of nitrogen in steel increases. With an increase in the concentration of nitrogen in steel, the strength of steel is proportionally increased. The calculation formula allows you to determine the amount of nitrogen in the ligature, necessary for the smelting of steel with high strength properties. The relationship between the chemical composition of steel and the standard solubility of nitrogen in it, the possibility of dissolving nitrogen of the ligature and the quality of steel has been experimentally established. The chemical composition of steel affects the solubility of nitrogen in steel, therefore, for each chemical composition, the standard solubility of [N] _{p is} calculated. The mass of iron in the ligature alloy is selected based on the capacity of the furnaces used and the solubility of nitrogen in the ligature.

By increasing the concentration of nitrogen in steel, the strength increases, which is the technical result of the method.

When the nitrogen content in the ligature alloy is less than calculated by the formula, the strength properties of steel decrease. When the nitrogen content in the ligature is more calculated by the formula, the nitrogen activity in the steel becomes sufficient for nucleation of nitrogen bubbles at the crystallization front and the ingots are porous.

The introduction of nitrogen into the ligature alloy is carried out by the addition of nitrided ferroalloys and (or) by blowing the melt with gaseous nitrogen.

An example of the method

Steel 55Kh20G9AN10 and Kh25N16G7AR were smelted in two DSP12 furnaces. The standard solubility of nitrogen in these steels, calculated using the parameters of the interaction of nitrogen with the elements that make up the steel, is 0.29 wt.% And 0.35 wt.%, Respectively.

The intermediate product according to the prototype method was smelted by melting steel scrap, followed by purging the melt with oxygen. According to the proposed method, nickel was introduced into the melt before oxygen purging. The chemical composition of the intermediate is presented in table 1.

Ligature alloy was obtained by melting in a furnace ferrochrome, manganese metal and nitrided, and by the prototype method additionally nickel and ferrosilicon. When smelting ligatures for Kh25N16G7AR steel, spar and lime were introduced into the filling to prevent carburization for early slag formation. The standard solubility of nitrogen in the ligature alloy, calculated using the parameters of the interaction of nitrogen with the elements of the ligature alloy, is 2.2 wt.% For 55Kh20G9AN10 steel, and 2.8 wt.% For Kh25N16G7AR steel, the nitrogen content in the ligature alloy was varied by the amount of nitrated manganese and determined on the instrument of the company "Balzers". The compositions of ligature alloys are presented in table 2.

Melts were mixed in a 30-ton bucket. Refining was carried out using synthetic slag and bottom purging through an argon lance. The mass of melts was controlled using a crane scale. The refining duration was 10-15 minutes. The results are presented in table 3.

The tensile strength (σ _in ) was determined on cast metal. As can be seen from table 3, the proposed method will increase the strength of steels by increasing the nitrogen content by 1.2-1.4 times.

Table 1 The chemical composition of the intermediate №№ Way Chemical composition, wt.% Mass, t steel grade FROM Ni Si Fe inevitable impurities one Prototype 0.3 - - Ost. 12.1 55X20G9AN10 2 Proposed 1,02 16.9 0.8 Ost. 14.8 55X20G9AN10 3 Proposed 1,03 16.85 0.82 Ost. 14.7 55X20G9AN10 four Proposed 1.01 17.0 0.8 Ost. 14.8 55X20G9AN10 5 Proposed 1.05 16.9 0.84 Ost. 14.8 55X20G9AN10 6 Proposed 1,04 16.9 0.83 Ost. 14.8 55X20G9AN10 7 Prototype 0,03 - - Ost. 9.5 X25N16G7AR 8 Proposed 0,03 29.1 0.8 Ost. 13.75 X25N16G7AR 9 Proposed 0.04 29.3 0.82 Ost. 13.7 X25N16G7AR 10 Proposed 0,03 29.2 0.81 Ost. 13.8 X25N16G7AR eleven Proposed 0.04 29.1 0.80 Ost. 13.75 X25N16G7AR

table 2 The chemical composition of the ligature alloy №№ Way Chemical composition, wt.% Mass, t The nitrogen content, wt.% steel grade FROM Mn Cr Si Ni Fe one Prototype 0.8 18,4 38.8 1,0 19,4 Ost 12.9 0.58 55X20G9AN10 2 Proposed 0.1 23.3 49.1 - - Ost. 10,2 0.73 55X20G9AN10 3 Proposed 0.09 23,2 49.5 - - Ost. 10,2 1,1 55X20G9AN10 four Proposed 0.1 23.5 49.0 - - Ost. 10.2 1.46 55X20G9AN10 5 Proposed 0.08 23.6 49.2 - - Ost. 10,2 0.65 55X20G9AN10 6 Proposed 0.10 23,4 49.3 - - Ost. 10,2 1,5 55X20G9AN10 7 Prototype 0.1 11,4 40.7 1,0 25.8 Ost. 15,5 0.55 X25N16G7AR 8 Proposed 0.1 15.6 56.0 - - Ost. 11.25 0.77 X25N16G7AR 9 Proposed 0.08 15.4 56.4 - - Ost. 11,2 1,54 X25N16G7AR 10 Proposed 0.08 15.4 56.4 - - Ost. 11,2 1,6 X25N16G7AR eleven Proposed 0.09 15.8 56.3 - - Ost. 11.25 0.7 X25N16G7AR

Table 3. Experiment Results №№ Production method The nitrogen content,%, mass. steel grade Calc. according to the formula soder. nitrogen (Q), wt.% σ _in , MPa Note Ligature alloy Finished steel one. Prototype 0.58 0.28 55X20G9AN10 - 611 - 2. Proposed 0.73 0.29 55X20G9AN10 0.73-1.46 640 - 3. Proposed U 0.43 55X20G9AN10 5555 710 - four. Proposed 1.46 0.58 55X20G9AN10 55? 9 820 - 5. Proposed 0.65 0.26 55X20G9AN10 5555 610 - 6. Proposed 1,50 0.59 55X20G9AN10 5553 - Porous ingots 7. Prototype 0.55 0.34 X25N16G7AR - 516 - 8. Proposed 0.77 0.35 X25N16G7AR 0.77-1.54 530 - 9. Proposed 1,54 0.68 X25N16G7AR 5555 750 - 10. Proposed 1,60 0.69 X25N16G7AR E555 - Porous ingots eleven. Proposed 0.70 0.32 X25N16G7AR 5559 520

Claims (1)

A method of producing stainless austenitic steel, including the smelting of an intermediate in one furnace and a ligature alloy in another, followed by their mixing and refining in a steel pouring ladle, characterized in that an alloy based on iron and elements that make up the steel and reduce the solubility of nitrogen is smelted as an intermediate in iron, and the ligature alloy is smelted with the composition of the elements that make up the steel and increase the solubility of nitrogen in iron, and nitrogen is introduced into the ligature alloy to a content that is calculated They are according to the formula:

where Q is the nitrogen content in the ligature alloy, wt.%;
M _l - the mass of the ligature alloy, t;
M _p - the mass of the intermediate product, t;
[N] _p is the standard solubility of nitrogen in the melted steel, wt.%.