RU2369657C1 - Corrosion-resistant steel of martensite class and item made out of this steel - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention refers to iron and steel metallurgy, particularly to compositions of corrosion-resistant high-carbon steel of martensite class, and also to items produced out of this steel. Steel contains carbon, silicon, manganese, chromium, molybdenum, vanadium, sulphur, phosphorus, nickel, copper, nitrogen, titanium, iron and unavoidable impurities at the following ratio of components, wt %: carbon 0.70-0.75, silicon 0.20-1.20, manganese 0.20-1.0, chromium 15.0-17.0, molybdenum 0.50-0.80, vanadium 0.10-0.20, nickel 0.15-0.30, copper 0.10-0.30, nitrogen 0.01-0.07, titanium 0.01-0.10, sulphur 0.001-0.010, phosphorus 0.015-0.030, iron and unavoidable impurities - the rest. The following ratios are maintained: Cr/C=22-24 and Cr_equiv/Ni_equiv=0.75-0.90, where Cr_equiv=%Cr+1.5·%Si+4·%Ti+Mo+2·%V, and Ni_equiv=%Ni+0.5·%Mn+Cu+30·%C+N.

EFFECT: increased hardness, wear resistance, and processability at maintaining corrosion resistance in mediums of average corrosion activity.

5 cl, 2 tbl

Description

The invention relates to ferrous metallurgy, and in particular to compositions of corrosion-resistant high-carbon steels of the martensitic class, as well as to products made from them.

Products - a sheet, grade of the proposed steel, can be used for the manufacture of various products, including cutting tools (high-quality knives for various purposes, scalpels, scissors, etc.) in many industries (food, meat, medical, domestic and other).

In areas where the material requires a combination of high hardness and wear resistance, corrosion resistance in aggressive environments (diluted with acetic and phosphoric acids, hot tap water at temperatures up to 60 ° C with a high content of sodium chloride, etc.), martensitic steels are used for the manufacture of cutting tools with a high content of chromium (ranging from 10 to 19%) and carbon (up to 1.2%). The content of chromium and carbon is balanced so that after quenching and tempering, a martensitic structure with the required level of hardness, strength and corrosion resistance is provided.

Corrosion resistance in a significant number of corrosive media is mainly determined by the chromium content in the solid solution of martensite (austenite) steel and increases with increasing concentration, especially sharply at a transition from 12 to 13%. The value of 13% is threshold and provides corrosion resistance of steel due to its transition to a passive state.

The carbon content of steel is responsible for its hardness. Molybdenum, vanadium, tungsten, niobium, and titanium are used as additional alloying elements.

Known high carbon martensitic steel for the manufacture of tools for cold working.

Steel contains the following components, wt.%:

Carbon - 0.60-0.85

(Silicon + aluminum) from trace amounts - up to 0.3

Manganese - 0.10-2.0

Chrome - 4.5-5.5

Molybdenum - 1.5-2.6

Tungsten - maximum 1.0

Vanadium - 0.42-0.65

Niobium - maximum 0.1

Titanium - maximum 0.1

Zirconium - maximum 0.1

Cobalt - maximum 0.1

Iron and unavoidable impurities are the rest.

Steel after quenching and high temperature tempering (at 500-600 ° C) has a high level of hardness (from 57 to 63HRC). Steel has high mechanical properties. However, it is not corrosion resistant, since it contains a low chromium content (4.5-5.5%).

(RF patent 2322531, IPC С22С 38/24, published on July 27, 2005)

Known steel of the Japanese company Aichi Steel Works brand AUS-8 for the manufacture of a variety of knives with high wear resistance and hardness of the cutting edge

(60-61HRC), containing, wt.%:

Carbon - 0.70-0.75

Silicon - maximum 1.0

Manganese - maximum 0.5

Chrome - 13-14.5

Molybdenum - 0.10-0.30

Vanadium - 0.10-0.26

Nickel - maximum 0.5

Iron and unavoidable impurities are the rest.

Steel, however, is not sufficiently corrosion resistant in medium-aggressive environments due to the fact that carbon, binding chromium to carbides (type M ₂₃ C ₆ ), impoverishes it with a solid solution below a threshold level (13%).

(Maryanko A.A. Reference manual “To help a person who chooses a knife”, Moscow: Universal Publishing House, 2005, p.196.)

Known corrosion-resistant steel for cutting tools, containing, wt.%:

Carbon - 0.65-1.15

Silicon - 0.46-1.59

Manganese - 0.15-0.55

Chrome - 13-18.6

Molybdenum - 0.05-0.35

Titanium - 0.04-0.52

Vanadium - 0.05-0.57

Aluminum - 0.001-0.05

Calcium - 0.001-0.05

REM - 0.01-0.12

Iron is the rest.

(USSR AS No. 1081234, IPC S22C 38/50, 1982)

A disadvantage of the known steel is the low technological ductility during hot deformation. In addition, due to the declared wide limits of the content of chromium (13-18.6%) and carbon (0.65-1.15%), a number of specific compositions do not provide the required corrosion resistance (for example, 13% Cr and 1.15% C) .

The prototype of the invention is steel and a product made from it, 50X14MF martensitic steel is selected, from which the cutting tool is made in the medical (all-metal scalpels, removable blades, etc.), food (knives) industry. Metal products from this steel (sheet, tape, bar) are supplied in annealed condition. After complete annealing, the steel has the structure of granular perlite, and its hardness is 197–207НВ.

Steel contains the following components, wt.%:

Carbon - 0.48-0.55

Silicon - ≤0.6

Manganese - ≤0.6

Chrome - 14.0-15.0

Molybdenum - 0.45-0.80

Vanadium - 0.10-0.15

Sulfur - ≤0.030

Phosphorus - ≤0.030

Iron is the rest.

Normalized values of hardness of metal products after quenching and tempering should not be lower than 50HRC. Its actual values range from 50-57HRC, which is not always enough to ensure the required abrasion of the tool. The disadvantages of this steel can also include reduced manufacturability in the production of metal products.

(Shlyamnev A.P., Svistunova T.V., Sorokina N.A. et al. Handbook “Corrosion-Resistant, Heat-Resistant and High Strength Steels and Alloys”. M: PROMMET-ALLOY, 2008, p. 32-34) .

The problem to which the invention is directed, is to increase the manufacturability of steel in the manufacture of metal products, as well as the operational stability of products from it, including cutting tools with a higher level of hardness and wear resistance while maintaining corrosion resistance.

The technical result of the present invention is the creation of a new martensitic steel with a balanced chemical composition, improved structure (including reduction and grinding of non-metallic inclusions, increased dispersion of the structure with a uniform distribution of carbides), increased hardness, wear resistance, processability compared to the known analogue while maintaining corrosion resistance in medium corrosive environments, including resistance to pitting corrosion in chloride-containing environments.

The specified technical result is achieved in that the corrosion-resistant martensitic steel containing carbon, silicon, manganese, chromium, molybdenum, vanadium, sulfur, phosphorus and iron, according to the invention additionally contains nickel, copper, nitrogen and titanium, and also has a high content carbon and chromium and a decrease in sulfur content in the following ratio of components, wt.%:

Carbon - 0.70-0.75

Silicon - 0.20-1.20

Manganese - 0.20-1.0

Chrome - 15.0-17.0

Molybdenum - 0.50-0.80

Vanadium - 0.10-0.20

Nickel - 0.15-0.30

Copper - 0.10-0.30

Nitrogen - 0.01-0.07

Titanium - 0.01-0.10

Sulfur - 0.001-0.010

Phosphorus - 0.015-0.030

Iron is the rest

when the following ratios are fulfilled: Cr / C = 22-24, Cr _equiv / Ni _equiv = 0.75-0.90, where Cr _equiv =% Cr + 1.5 ·% Si + 4 ·% Ti + Mo + 2 · % V and Ni _equiv =% Ni + 0.5 ·% Mn + Cu + 30 ·% C + N.

The specified technical result is also achieved by the fact that the products are made of stainless steel of the above composition.

Products can be made in the form of a sheet or in the form of rods that are used for the manufacture of various products, including cutting tools with the required set of properties.

The main alloying elements in steel are carbon and chromium.

A carbon content of less than 0.70% does not provide the necessary hardness, and therefore, cutting properties. A carbon content of more than 0.75% leads to the formation of large excess carbides and their possible chipping during sharpening of the cutting tool. The carbon content determines the hardness of martensite after quenching.

Chromium in the amount of 15.0-17.0% (with the ratio Cr / C = 22-24) provides the corrosion resistance of the cutting tool in the hardened and tempered condition under operating conditions in medium aggressive environments.

Molybdenum in the declared range (0.50-0.80%) increases the resistance of steel against pitting corrosion in chloride-containing environments, strengthens the solid solution, and also helps to reduce the diffusion mobility of atoms. A molybdenum content of less than 0.50% does not fully ensure the preservation of a fine-grained structure during high-temperature heating. When the content is more than 0.80%, the ductility of the steel in the hardened state decreases.

Vanadium improves the uniform distribution of chemical elements in solid solution, promotes the formation of thermally stable finely dispersed carbides and, in combination with chromium and molybdenum, forms carbides of the type (Cr, Mo, V) ₂₃ C ₆ within the stated limits. A vanadium content of less than 0.10% does not significantly affect grain refinement. A vanadium content of more than 0.20% enhances carbide segregation, which cannot be eliminated in the range of quenching temperatures (1045-1100 ° C).

Manganese and nickel increase the hardenability and toughness of steel, which is especially good when they are present in solid solution. Their most positive effect is manifested with a joint presence within Mn = 0.2-1.0% and Ni = 0.15-0.30%. In combination with molybdenum, manganese forms a finely divided structure during quenching and increases hardness. Manganese also has the ability to bind the extremely low amounts of sulfur present in steel to form manganese sulfides. The manganese content should be 0.2-1.0%, preferably 0.30-0.70%.

Silicon is introduced as a deoxidizer. The lower limit of 0.2% is determined by the fact that at a lower content it does not provide deoxidation of steel. An increase in silicon content of more than 1.2% affects the technological properties of steel.

The preferred silicon content is 0.4-0.7%. In the proposed range, silicon contributes to the preservation of fine grain during heating, increases hardenability. In addition, silicon increases the activity of carbon in steel, thus contributing to giving the steel increased hardness and wear resistance.

Copper increases the corrosion resistance and strength of steel. However, with contents of more than 0.30% copper, there is a high probability of the development of red brittleness due to the possible appearance of a copper-rich two-phase structure along grain boundaries.

Nitrogen, combining with nitride-forming elements (Ti, V), grinds grain and provides hardening of steel.

The titanium content in an amount of up to 0.10% is sufficient for nitrogen binding to dispersed nitrides and carbonitrides, which favorably affects the increase in the resistance of steel to grain growth upon heating under quenching. When the titanium content is less than 0.01%, nitrides as an independent phase are not formed and their positive effect is absent.

The lower and upper limits of the sulfur content (0.01-0.10%) and phosphorus (0.15-0.30%) are determined by the technical capabilities for steelmaking in open steelmaking units using subsequent electroslag remelting. The decrease in sulfur content increases the technological ductility of steel in the temperature range of hot plastic deformation. In addition, a decrease in sulfur content reduces the number of non-metallic inclusions of the MnS type, which has a positive effect on the resistance of steel against pitting corrosion.

The claimed ratio of CR _eq / Ni _eq = 0.75-0.90 provides after quenching and tempering obtaining in the steel structure of tempered martensite with the required set of properties: hardness, wear resistance and corrosion resistance.

The following are embodiments of the invention, not excluding others in the scope of the claims.

The steel of the claimed composition was smelted by a duplex process, including smelting in a 30-ton electric arc furnace followed by electroslag remelting of the consumable electrode into an ESR ingot. The composition of the heats corresponds to the proposed and known steel (table 1). The obtained metal was subjected to pressure treatment on industrial forging and rolling equipment with the production of either sheet metal (0.8–4.0 mm thick) or rods (⌀ 4–20 mm). The steel of the claimed composition has a higher level of ductility in the temperature range of hot plastic deformation (1000-1200 ° C) compared with the prototype (table 2).

The metal products were annealed at a temperature of 750 ° C, providing granular perlite with a hardness of 235НВ.

After quenching from 1045-1050 ° C, the size of the austenitic grain in the proposed steel corresponds to No. 10-11 GOST 5639-65 and the size of the carbides M ₂₃ C ₆ 1.2-5 microns, while the known steel size of austenitic grain No. 9 and the size of carbides is 1.5-8 μm (table 2).

The optimal heat treatment mode used in the manufacture of cutting tools from the proposed steel includes quenching from 1045 ° C to oil + tempering in the temperature range 200-400 ° C. After this heat treatment, the proposed steel has a higher level of hardness.

(57-62HRC) and impact strength (0.4-0.6 mJ / m ² ), as well as cutting resistance (87-90 conventional units) in comparison with known steel (HRC - 52-49, KCU - 0, 4-0.5 mJ / m ² , cutting resistance - 82 conventional units) (table 2).

The steel of the claimed composition 70X16MFS-Sh has satisfactory corrosion resistance in a 3% solution of sodium chloride in water after quenching and tempering up to 400 ° C. In addition, it has increased resistance to pitting corrosion due to the reduced content of non-metallic inclusions in steel, primarily MnS.

The proposed steel ensures the manufacturability of semi-finished products in the cycle of metallurgical production and manufacturing of cutting tools with the required range of operational properties: hardness - 57-62HRC, high wear resistance and cutting ability, corrosion resistance in medium aggressive environments, resistance to pitting corrosion in chloride-containing environments.

Table 1 The chemical composition of the experimental swimming trunks Steel Conventional heat number The content of components, wt.% FROM Si Mn Cr Mo V Ni Cu Ti N S R Fe Cr / C Cr _eq / Ni _eq Proposed one 0.71 0.40 0.32 15.65 0.55 0.18 0.17 0.16 0.02 0,03 0.005 0,025 main 22 0.79 2 0.75 0.31 0.55 16.67 0.62 0.14 0.28 0.18 0.05 0.06 0.008 0,030 main 22.5 0.78 3 0.70 0.8 1,0 16.8 0.60 0.15 0.15 0.22 0.01 0.05 0.006 0,023 main 24 0.86 four 0.73 0.49 0.24 16.10 0.70 0.11 0.25 0.12 0.08 0,07 0.005 0,030 main 22 0.80 Famous 5 0.48 0.28 0.25 14.5 0.50 0.10 - - - - 0,025 0,030 main - -

table 2 Properties and structure of hot-rolled sheet (4 mm thick) of experimental melts after various types of processing Steel Conditional but
melt measures Cross contraction (ψ) at temperature, ° C Properties at 20 ° C after quenching and tempering * Resistance to pitting corrosion ** Quenching from 1045-1050 ° C 1000 1100 1200 Hardness HRC Impact strength, mJ / m ² Cutting stand
bone, conv. units The area occupied by pitting, cm ² / m ² Austenite grain size according to GOST 5639-65 The size of carbides, microns Proposed one 85 75 73 58/57 0.4 / 0.5 - 0-10 10 1.0-4.0 2 74 73 74 62/59 0.5 / 0.6 90 0-15 eleven 1.2-5.0 3 78 76 75 58/57 0.4 / 0.5 87 0-12 10 - four 75 74 74 59/58 0.45 / 0.6 - 0-15 10 - Famous 5 72 70 70 52/49 0.4 / 0.5 82 0-60 8-9 1,5-8,0 Note: * - heat treatment mode: quenching from 1045 ° C to oil + tempering at 200 ° C (numerator) and 400 ° C (denominator) ** - test in solution l% NaCl + 3% (NH ₄ ) ₂ SO ₂ for 1000 hours (after quenching and tempering)

Claims (5)

1. Corrosion-resistant steel of the martensitic class containing carbon, silicon, manganese, chromium, molybdenum, vanadium, sulfur, phosphorus and iron, characterized in that it additionally contains nickel, copper, nitrogen and titanium in the following ratio of components, wt.% :
carbon 0.70-0.75 silicon 0.20-1.20 manganese 0.20-1.0 chromium 15.0-17.0 molybdenum 0.50-0.80 vanadium 0.10-0.20 nickel 0.15-0.30 copper 0.10-0.30 nitrogen 0.01-0.07 titanium 0.01-0.10 sulfur 0.001-0.010 phosphorus 0.015-0.030 iron and inevitable impurities rest
when the following ratios are fulfilled: Cr / C = 22-24 and Cr _eq / Ni _eq = 0.75-0.90,
where Cr _equiv =% Cr + 1.5 ·% Si + 4 ·% Ti + Mo + 2 ·% V,
Ni _equiv =% Ni + 0.5% Mn + Cu + 30% C + N. 2. The product is made of corrosion-resistant steel of the martensitic class, characterized in that it is made of steel according to claim 1. 3. The product according to claim 2, characterized in that it is made in the form of a hot-rolled or cold-rolled sheet. 4. The product according to claim 2, characterized in that it is made in the form of a bar. 5. The product according to claim 3 or 4, characterized in that it is made in the form of a cutting tool, including knife products with a high level of operational properties: hardness, wear resistance, corrosion resistance.