RU2413029C2 - Martensite nitrogen containing corrosion resistant steel - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: steel contains carbon, silicon, manganese, chromium, nickel, molybdenum, vanadium, nitrogen, niobium, iron and impurities at following ratio of components, wt %: carbon 0.07 - 0.12, nitrogen 0.10 - 0.30, silicon 0.20 - 0.50, manganese 0.70 - 1.00, chromium 12 - 14, nickel 0.9 -2.5, molybdenum 0.4 - 0.8, niobium 0.04-0.08, vanadium 0.05-0.10, iron and impurities - the rest. As impurities steel contains in wt %: sulphur not over 0.010, phosphorus not over 0.010, copper not over 0.200, tin not over 0.015, lead not over 0.002 and after tempering at 950±20° C and annealing at 200 - 650° C it has fine grain structure with actual grain of 8-10 number. Ratio of total contents of niobium and vanadium to carbon (Nb+V)/C is not less, than 1.2, while ratio of chromium contents to total contents of nickel and manganese is 4.8÷7.5.

EFFECT: increased corrosion and brittle fracture resistance of item at simultaneous high hardness and ductility.

4 cl, 1 dwg, 2 tbl, 2 ex

Description

The invention relates to the metallurgy of alloyed corrosion-resistant steels of the martensitic class used for the manufacture of medical instruments.

Martensitic nitrogen-containing corrosion-resistant steel (JP 11-229093 A, C22C 38/52, 08.24.1999, abstract) containing carbon, nitrogen, silicon, manganese, chromium, nickel, molybdenum, niobium, vanadium, iron is known as a foreign analogue and impurities in the following ratio of components, wt.%:

Carbon ≤0.30 Nitrogen 0.07 ÷ 0.20 Silicon ≤1.0 Manganese + Nickel 0.50 ÷ 5.00 Chromium 6 ÷ 18 Molybdenum ≤2.0 Niobium + vanadium 0,02 ÷ 1,0 Iron and impurities rest.

The grades of corrosion-resistant steel used in the manufacture of medical instruments are currently described in GOST 5632. The main disadvantage of these steels is their insufficient corrosion resistance and high brittleness.

The closest in composition of the ingredients and the purpose of the proposed steel is steel grades 30X13 GOST5632, p.7, 36, GOST5582, p.5, content, wt.%:

Carbon 0.26 ÷ 0.35 Silicon no more than 0.8 Manganese no more than 0.8 Chromium 12.0 ÷ 14.0

In this case, the steel contains the following impurities:

Nickel no more than 0.6 Molybdenum no more than 0.3 Copper no more than 0.3 Tungsten no more than 0.2 Vanadium no more than 0.2 Sulfur no more than 0,025 Phosphorus no more than 0,025

The content of lead and tin is not standardized. Moreover, the above steel grades are not alloyed with nickel, copper, tungsten, vanadium, in this case the permissible residual content of these elements is given.

Known steel has high hardness, provides the required level of mechanical properties, however, it has insufficient corrosion resistance and resistance to brittle fracture at an operating temperature of + 20 ° C.

Due to the high carbon content in steel (up to 0.35 wt.%), The formation of chromium carbides takes place and, as a result, its content in the surface layers decreases and subsequent corrosion in organic media occurs.

At a low content of carbide-forming elements, which are the centers of nucleation of new grains in the process of γ → α transformation, the grain sizes in semi-finished products increase. With increasing grain sizes, the tendency of the metal to brittle fracture increases. In addition, the sulfur content in steel is at the level of 0.015 ÷ 0.025%, the content of tin and lead is not standardized, which also negatively affects the resistance of steel to brittle fracture.

The technical result of the invention is to provide higher corrosion resistance and resistance to brittle fracture of steel at a temperature of + 20 ° C while maintaining a given level of mechanical properties and hardness, providing high cutting properties.

The technical result is achieved due to the fact that in the steel containing carbon, silicon, manganese, chromium and iron, nitrogen, molybdenum, nickel, niobium and vanadium are additionally introduced in the following ratio of components, wt.%:

Carbon 0.07 ÷ 0.12 Nitrogen 0.10 ÷ 0.30 Silicon 0.20 ÷ 0.50 Manganese 0.70 ÷ 1.00 Chromium 12 ÷ 14 Nickel 0.9 ÷ 2.5 Molybdenum 0.4 ÷ 0.8 Niobium 0.04 ÷ 0.08 Vanadium 0.05 ÷ 0.10 iron and impurities rest,

steel contains the following impurities:

Copper no more than 0.20 Sulfur no more than 0,010 Phosphorus no more than 0,010 Tin no more than 0.015 Lead no more than 0,004

the ratio (Nb + V) / C≥1.2, the ratio of chromium to total nickel and manganese should be in the range of 4.8 ÷ 7.5.

The introduction of nitrogen into steel with a wt% of 0.10 ÷ 0.30 leads to the replacement of carbon in the solid solution with nitrogen and the precipitation of nitrides and carbonitrides, which ensures the required level of strength and hardness of steel, while reducing the carbon content in steel to 0, 07 ÷ 0.12 wt.%. This allows, in comparison with analogues, to increase the corrosion resistance of steel and its viscosity. A carbon content of less than 0.07 wt.% Does not allow to obtain, after a heat treatment consisting of hardening and low tempering, the specified level of strength and hardness of steel, and an increase in carbon content of more than 0.12% negatively affects the corrosion resistance and brittleness at operating temperature + 20 ° C. A nitrogen content of more than 0.30 wt.% Can not be obtained in the steel of this alloy composition due to the limited solubility of nitrogen in iron, a decrease in nitrogen content of less than 0.10% does not allow to provide the required level of hardness, strength and corrosion resistance of steel.

The silicon content of 0.20 ÷ 0.50% in steel is associated with the need to perform the process of deoxidation of steel. The increased silicon content (more than 0.50%) will lead to the formation of a large number of non-metallic inclusions in steel, an increase in the content during hardening of polygonal ferrite, which reduces the hardenability of steel to a martensite-bainitic mixture.

The introduction of manganese in an amount of 0.7 ÷ 1.0 wt.% Promotes the passage of steel deoxidation processes, increases its hardenability, and increases the solubility of nitrogen in steel.

Limiting the content of harmful impurities of sulfur and phosphorus to less than 0.010 and 0.010%, respectively, reduces their content at the grain boundaries and thereby increase the viscosity of steel.

The chromium content of 12.0 ÷ 14.0 wt.% Allows you to provide a given level of mechanical properties, hardness and corrosion resistance, as well as to increase the solubility of nitrogen in steel and its hardenability in air. With a decrease in chromium content of less than 12.0 wt.% In the steel corrosion processes occur in organic environments. An increase in chromium content of more than 14.0 wt.% Increases the resistance of steel.

Nickel in an amount of 0.90 ÷ 2.5 wt.% Increases the ability of steel to resist brittle fracture, increases the mechanical properties and hardness of steel, increases the solubility of nitrogen in steel. An increase in nickel content of more than 2.0% increases the resistance of steel, a decrease in nickel content of less than 0.90 wt.% Increases the brittleness of steel and does not allow to obtain the required level of strength and hardness.

The ratio Cr / (Ni + Mn) in the range from 4.8 to 7.5 provides high solubility of nitrogen, hardenability of steel and the required level of mechanical properties.

The introduction of molybdenum into steel in an amount of 0.4 ÷ 0.8 wt.% Allows you to lower the temperature and the rate of γ → α conversion, which allows you to harden the semi-finished products in air, increasing hardenability, tempering resistance of steel. An increase in the molybdenum content of more than 0.80 wt.% Increases the resistance of steel, a decrease in its content of less than 0.40 wt.% Reduces the hardenability of steel.

Introduction to steel of niobium and vanadium 0.04 ÷ 0.08 and 0.05 ÷ 0.10 wt.%, Respectively, provide an increase in carbide-nitride hardening, obtaining fine real grains of 8-10 numbers according to GOST5639, which favorably affects the mechanical properties and hardness of steel. A decrease in the content of these elements will lead to a larger real grain, which in turn will adversely affect the mechanical properties and hardness of the steel. The content of vanadium and niobium above 0.10 wt.% Does not allow for a further reduction in the size of the actual grain and will lead to an increase in the resistance of steel.

The introduction of niobium and vanadium in the ratio (Nb + V) / C≥1,2 contributes to the preparation of semi-finished products with a fine-grained structure due to the precipitation of stable niobium and vanadium carbides, which inhibit grain growth during austenitization. The fine-grained structure of steel significantly increases technological plasticity and reduces the brittleness of steel during the operation of a medical instrument. At higher contents of niobium and vanadium in steel, precipitation of intermetallic compounds is possible, which reduce the ductility of the metal. At lower contents of niobium and vanadium, an insufficient amount of stable carbides is formed, the number of crystallization centers decreases, and semi-finished products are obtained with a coarse-grained structure. With a coarse-grained structure along the grain boundaries, thick layers of intermetallic compounds, sulfides and other impurities are formed, which increases the brittleness of steel and reduces its manufacturability.

At a ratio of (Nb + V) / C≤1,2, a decrease in corrosion resistance is observed due to the formation of a large number of chromium carbides and a decrease in the chromium content in the solid solution to values at which corrosion resistance is lost.

Content:

Tin - "- 0.015 Lead - "- 0.004,

since their higher content decreases ductility during hot deformation due to the formation of fusible interlayers along grain boundaries. A decrease in the content of fusible impurities virtually eliminates the appearance of fusible interlayers at the grain boundaries, which contributes to an increase in technological plasticity and plastic properties of semi-finished products.

An example of a specific implementation.

4 smelts of 100 kg each of the inventive steel were made in an electric induction furnace, ingots were forged on dies and rolled into sheets 5 mm thick with a heating temperature of 1200 ° C for rolling. After rolling, the sheets underwent slow cooling between asbestos sheets. Further, the rolling was subjected to heat treatment, consisting of hardening and low tempering. The temperature of heating for quenching was 950 ± 20 ° С; the exposure at this temperature was 4 min / mm. To assess the change in mechanical properties (primarily hardness) and corrosion resistance, tempering of workpieces was performed at temperatures from 200 to 650 ° C.

After heat treatment, a visual inspection of the sheets and sampling for mechanical, corrosion tests, metallographic studies were performed. The chemical composition determined by ladle chemical analysis of the declared steel of two melts and known steels is given in table 1, the requirements for the mechanical properties and hardness of the known steel, and the results of determining the mechanical properties and hardness of the declared steel are presented in table 2. Samples of the declared steel, selected from sheet metal subjected to tempering at temperatures from 200 to 650 ° C, were subjected to corrosion tests at the Military Medical Academy (VMA) of St. Petersburg. in chlorine-containing solutions, a solution of formic acid with the addition of 5% hydrogen peroxide. The antiseptic treatment cycle included: washing in a soap solution, rinsing, being in a chlorine-containing solution for 60 minutes, heat treatment at a temperature of up to 250 ° C for 8 hours. Tests have confirmed the possibility of quick processing in aggressive environments, which is especially important in the field. The presented samples went through the VMA for 10 cycles of antiseptic treatment. No traces of visible corrosion, color changes were observed (see drawing).

The mechanical properties, hardness of the known and claimed steel are presented in table 2.

The expected technical and economic effect of the use of the inventive steel will be expressed in an increase in the service life of tools (a decrease in the service life of tools is associated with their corrosion) and an improvement in their consumer properties. The use of the inventive steel in the medical industry will make it possible to master the manufacture of domestically produced medical instruments that are competitive on the world market and refuse to purchase medical instruments abroad.

Surgical instruments were manufactured from the developed steel at the Russian medical equipment factories: surgical scissors, scalpels, pulmonary shoulder blades, etc. In the process of using these instruments for 3-4 years in the surgical practice of VMA, high service characteristics, no corrosion, high wear resistance and cutting properties, etc.

Claims (4)

1. Martensitic nitrogen-containing corrosion-resistant steel containing carbon, silicon, manganese, chromium, nickel, molybdenum, vanadium, nitrogen, niobium, iron and impurities, characterized in that it contains components in the following ratio, wt.%:
carbon 0.07-0.12 nitrogen 0.10-0.30 silicon 0.20-0.50 manganese 0.70-1.00 chromium 12-14 nickel 0.9-2.5 molybdenum 0.4-0.8 niobium 0.04-0.08 vanadium 0.05-0.10 iron and impurities rest
however, after quenching at 950 ± 20 ° C and tempering at 200-650 ° C, it has a fine-grained structure with a real grain of 8-10 numbers. 2. Martensitic nitrogen-containing corrosion-resistant steel according to claim 1, characterized in that it contains phosphorus, sulfur, copper, tin, lead as impurities at the following content, wt.%:
sulfur no more than 0,010 phosphorus no more than 0,010 copper no more than 0,200 tin no more than 0.015 lead no more than 0.002 3. Martensitic nitrogen-containing corrosion-resistant steel according to claim 1, characterized in that the ratio of the total content of niobium and vanadium to carbon (Nb + V) / C is at least 1.2. 4. Martensitic nitrogen-containing corrosion-resistant steel according to claim 1, characterized in that the ratio of the chromium content to the total content of nickel and manganese is 4.8 ÷ 7.5.

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