RU2269587C1 - Cold-resistant steel with enhanced strength - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: cold-resistant steel of enhanced strength comprises components taken in the following ratio, wt.-%: carbon, 0.04-0.10; manganese, 1.00-1.40; silicon, 0.15-0.35; nickel, 0.1-0.8; niobium, 0.02-0.06; vanadium, 0.02-0.10; aluminum, 0.02-0.06; sulfur, 0.001-0.005; copper, 0.05-0.20, and iron, the balance. Invention provides enhancing cold-resistance and corrosion stability, improved welding capacity and resistance against lamellar destructions in retaining high strength of steel. Invention can be used in manufacturing sheet roll of improved welding capacity used in ship building, fuel-energy complex, transport and heavy machine building, bridge building and others branches.

EFFECT: improved and valuable properties of steel.

3 tbl, 1 ex

Description

The invention relates to metallurgy, and more particularly to the production of plate products from cold-resistant steel with increased strength and improved weldability for shipbuilding, the fuel and energy complex, transport and heavy engineering, bridge building and other industries.

The steel of grade 10HSND delivered in accordance with GOST 6713 and GOST 19281 is widely used, with the following chemical composition, wt.%: Carbon - not more than 0.12, silicon - 0.80-1.10, manganese - 0.50-0.80, chrome - 0.60-0.90, nickel - 0.50-0.80, copper - 0.40-0.60, sulfur - not more than 0.035. Rolled steel delivered in a state after quenching and tempering or normalization provides a yield strength of at least 390 MPa.

The main disadvantages of the analogue are low cold resistance (guaranteed impact strength on specimens with a sharp notch KCV at -40 ° C - 30 J / cm ² ) and the lack of guarantee resistance to layered fractures (sulfur content up to 0.035%).

Known steel, adopted for the prototype, containing (wt.%): Carbon - 0.06-0.15, silicon - 0.1-0.5, manganese - 1.5-2.2, chromium - 0.3- 0.8, nickel - 0.3-0.7, vanadium - 0.02-0.10, niobium - 0.01-0.05, titanium - 0.01-0.05, aluminum, calcium - 0.001- 0.01, nitrogen - 0.006-0.014, iron - the rest, and the following ratios should be fulfilled (RF patent 2016127):

600≥830-270C-90 Mn-37Ni-70Cr≥550

0.13≥C-12 / 93Nb-12 / 51V-12/48 (Ti-3.4N) ≥0.03.

уже при содержании углерода 0,09% и более превышают нормируемое Морским Регистром для хорошо свариваемой стали значение Р_см 0,22%. Кроме того, отсутствие ограничений по содержанию серы в известной стали не позволяет гарантировать такую важную для крупногабаритных сварных конструкций характеристику, как сопротивляемость слоистым разрушениям. Данные по прочности и хладостойкости листового проката толщиной больше 10 мм, не указываются.A disadvantage of the known steel is that, as a result of accelerated cooling from the temperature of the end of hot rolling, the known steel retains high strength and improved cold resistance, but only in thicknesses up to 10 mm, however, the chemical composition of the known steel does not guarantee good weldability, because values of the coefficient of crack resistance during welding

already at a carbon content of 0.09% or more, exceed the value of P _cm 0.22% normalized by the Maritime Register for well-welded steel. In addition, the absence of restrictions on the sulfur content in the known steel does not allow us to guarantee such an important characteristic for large welded structures as resistance to layered fractures. Data on the strength and cold resistance of sheet metal with a thickness of more than 10 mm are not indicated.

The technical result of the invention is to increase the cold resistance and corrosion resistance, providing improved weldability and guaranteed resistance to layered fracture of steel while maintaining high strength.

The technical result is achieved due to the fact that cold-resistant steel of increased strength, containing carbon, manganese, silicon, nickel, vanadium, niobium, iron, additionally contains sulfur and copper in the following ratio of components, wt.%: Carbon - 0.04-0, 10, manganese - 1.00-1.40, silicon - 0.15-0.35, nickel - 0.1-0.8, niobium - 0.02-0.06, vanadium - 0.02-0, 10, aluminum - 0.02-0.06, sulfur - 0.001-0.005, copper - 0.05-0.20, iron - the rest.

Strengthening the strength of low alloy steel can be achieved due to the following factors: hardening of solid solution (25-40%), dispersion hardening (20-25%) and grinding grain (30-40%).

The most effective mechanism, which, simultaneously with an increase in the yield strength, causes an increase in cold resistance, is grain grinding (grain boundary hardening).

The use of thermomechanical treatment provides an increase in the number of ferrite nuclei and contributes to the formation of a developed substructure upon completion of deformation at a temperature close to the Ar ₃ point and uniform release of a superfine carbide phase over the entire area of ferrite grains.

The carbon content in the selected range in combination with a fine-grained structure provides high strength combined with improved weldability and cold resistance at - 60 ° C. A carbon content of less than 0.04% does not allow to achieve the required level of strength and significantly complicates the process of steel smelting, more than 0.10% C degrades weldability and reduces the viscosity of steel.

Additives of manganese, copper, nickel within the claimed limits contribute to the solid solution hardening of the metal and contribute to an increase in cold resistance. A lower content of these elements does not allow to provide the required cold resistance, a larger one reduces weldability and is not economically feasible.

Additives of vanadium and niobium within the specified limits serve the purpose of dispersion hardening, and also inhibit the growth of austenitic grain and contribute to the appearance of a subgrain structure, which is fixed and stabilized by dispersed carbide particles, upon cooling.

The combined alloying of Nb and V within the accepted limits is especially effective for mild steel, since the dissolution temperature of NbC is 50-70 ° C higher than VC, and as a result, dispersed VC carbides precipitate upon cooling, and NbC inhibits the growth of austenite grain upon heating.

In addition, the combined alloying of Nb and V increases the hot ductility of cast billets.

Reducing the content of niobium and vanadium below the specified limits does not provide sufficient dispersion and grain boundary hardening, exceeding the specified level impairs weldability and reduces cold resistance.

Copper additions within the specified limits significantly increase (up to 3 times) the corrosion resistance of steel, including in the marine environment due to the formation of a spinel-type oxide layer on the surface. In addition, copper additives, especially in combination with a low sulfur content, increase the resistance to hydrogen cracking. A lower copper content does not allow to achieve the desired effect, a larger one is impractical.

The sulfur content in the claimed range guarantees resistance to layered fractures. A lower content is technically difficult to achieve, while a larger content decreases the resistance to layered fractures.

Tests of sheet metal showed that the developed chemical composition of steel and the technology for its production provide, along with the required strength, high values of impact work at - 60 ° С (not less than 50 J), improved weldability, resistance to layered fractures and corrosion in thicknesses up to 50 mm.

Example. Steel was smelted in a shaft furnace, after refining and evacuation, it was poured into cast billets.

The chemical composition is given in table 1.

The billets were subjected to austenitization at a temperature of 1130–1140 ° С, preliminary deformation at a temperature of 930–880 ° С with a total deformation of 45%, final deformation of a rolled sheet 50 mm thick at a temperature of 830–780 ° С with a total deformation of 64%, and subsequent accelerated cooling in installation of controlled cooling (UCO) to a temperature of 420 ° C with delayed cooling to 150 ° C.

The mechanical properties of rolled products were determined on transverse samples: explosive type III No. 4 according to GOST 1497, impact type 11 according to GOST 9454. Resistance to layered fractures was determined according to GOST 28870 on samples cut in the direction of sheet thickness. The results are presented in table.2. The cold resistance threshold T ₅₀ (50% fiber component) was determined according to GOST 4543 on type 11 samples according to GOST 9454.

Resistance to hydrogen cracking was determined by the British Petroleum method by immersing samples in synthetic seawater saturated with H ₂ S for 96 hours and then metallographically examining the surface of the sample to determine the fraction of the affected surface and measure the corrosion removal Δh g / m ² (mass of metal dissolved during the dive). The test results are shown in table.2.

Weldability assessment was performed for steel with the highest alloying level (composition 2) on K-shaped welded joints welded by automatic submerged arc welding with linear energy of 3.5 kJ / mm without after welding.

From welded joints are made and tested:

,- tensile flat specimens with an estimated length

,

- on impact bending - samples with a V-shaped notch made perpendicular to the surface of the rolled products along the fusion line and at a distance of 2.5 and 20 mm from the fusion line of the welded joint.

Vickers hardness was determined in the heat-affected zone and in the base metal, bend tests were performed for bending in the direction along and across the weld. The results are shown in table 3.

Table 1 The chemical composition of steel No. The chemical composition of steel, wt.% composition Carbon Silicon Manganese Nickel Copper Vanadium Niobium Sulfur Aluminum Chromium Iron Steel offered one 0.04 0.15 1.00 0.10 0.05 0.02 0.02 0.001 0.02 - rest 2 0.10 0.35 1.40 0.80 0.20 0.10 0.06 0.005 0.05 - rest 3 0.08 0.28 1.26 0.63 0.12 0.04 0,03 0.003 0.04 - rest Prototype four 0.015 0.1 2.2 0.4 - 0.08 0.01 there is no data 0.01 0.3 rest 5 0.010 0.3 1,5 0.7 - 0.02 0.05 0,03 0.6 rest

table 2 Mechanical and operational properties Structure Thickness mm Yield Strength, MPa Temporary resistance, MPa Relative extension, % Relative narrowing in the direction of rolled thickness,% Impact strength KCV, J at temperature Cold resistance threshold, T ₅₀ , ° C (GOST 4543) Corrosion Test Results -40 -60 -80 The mass of metal dissolved in 96 hours Δh, g / m ² Hydrogen cracking,% of the affected surface Steel offered one fifty 450 530 thirty 62 269 227 180 <-80 12 21 2 fifty 470 530 27 48 248 236 203 <-80 fourteen 24 3 fifty 470 560 26 fourteen 253 224 193 <-80 13 22 Prototype four 10 695 850 17 - 95 - - -75 - - 5 10 610 730 twenty - 116 - - -one hundred - -

Table 3 - Weldability Test Results Composition number Temporary resistance, MPa Work impact KV ^-60 , J at a distance from the drug, mm Hardness HV ₅ 120 ° bend 0 2 5 twenty HAZ Base metal Along Across 2 540 60 90 one hundred 190 230-250 180-190 No cracks No cracks

Claims (1)

High-strength cold-resistant steel containing carbon, manganese, silicon, nickel, vanadium, niobium, iron, characterized in that it additionally contains sulfur and copper in the following ratio, wt.%: Carbon 0.04-0.10 Manganese 1.00-1.40 Silicon 0.15-0.35 Nickel 0.1-0.8 Niobium 0.02-0.06 Vanadium 0.02-0.10 Aluminum 0.02-0.06 Sulfur 0.001-0.005 Copper 0.05-0.20 Iron Rest