RU2562734C1 - High-strength cold-resistant steel - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: proposed steel contains components in the following ratio in wt %: carbon - 0.07-0.11, silicon - 0.15-0.40, manganese - 0.30-0.60, chromium - 0.30-0.70, nickel - 1.80-2.20, copper - 0.40-0.70, molybdenum - 0.25-0.35, vanadium - 0.03-0.06, aluminium - 0.01-0.05, calcium - 0.001-0.005, sulphur - 0.001-0.005, phosphorus - 0.001-0.010, arsenic - 0.001-0.006, tin - 0.001-0.010, lead - 0.001-0.004, zinc - 0.001-0.012, iron making the rest. Total content of arsenic, tin, lead and zinc does not exceed 0.020 wt % while crack growth resistance factor at welding P_tot does not exceed 0.27%.

EFFECT: guaranteed yield point, high cold resistance.

2 tbl, 1 ex

Description

The invention relates to metallurgy and can be used in the production of plates of high strength steel with improved weldability for use in shipbuilding, fuel and energy complex, transport and heavy engineering, bridge building and other industries.

For the manufacture of critical welded structures, the following chemical composition is widely used, wt.% [1]:

Carbon 0.08-0.12 Silicon 0.2-0.4 Manganese 0.45-0.75 Chromium 1.05-1.30 Copper 0.35-0.65 Nickel 1.05-2.20 Molybdenum 0.10-0.18 Aluminum 0.01-0.06 Vanadium 0.04-0.06 Niobium 0.02-0.05 Calcium 0.005-0.050 Cepa 0.001-0.005 Iron rest

moreover, the value of the coefficient of crack resistance during welding P _cm , calculated by the formula

should not be higher than 0.28%.

Known steel provides high requirements for cold resistance up to minus 80 ° C, improved weldability (by the value of the coefficient of crack resistance), high crack resistance according to the CTOD criterion in the heat affected zone of the weld. The main disadvantage of this steel is an insufficient level of strength - the guaranteed value of the yield strength is 500 MPa, which limits the use of steel for the manufacture of heavily loaded structures.

For the manufacture of ship hulls and marine technical structures, low-carbon chromium-nickel-molybdenum steel is used, adopted as a prototype, containing components in the following ratio, wt.% [2]:

Carbon 0.07-0.11 Silicon 0.17-0.37 Manganese 0.30-0.60 Chromium 0.30-0.70 Nickel 1.80-2.30 Copper 0.40-0.70 Molybdenum 0.25-0.35 Vanadium 0.02-0.05 Aluminum 0.005-0.04 An element from the group containing calcium, barium 0.005-0.05 Sulfur 0.003-0.015 Phosphorus 0.003-0.015 Iron rest

provided that the amount (nickel + copper) is not less than 2.4 wt.%; the amount (sulfur + phosphorus) of not more than 0.025 wt.%.

In sheet metal with a thickness of up to 30 mm, steel provides high strength while maintaining high ductility, resistance to brittle and corrosion-mechanical fractures, good weldability, isotropic properties and resistance to layering, however, high impact strengths are guaranteed at temperatures not lower than minus 40 ° C.

The technical result of the invention is the development of structural steel of high strength with a guaranteed yield strength of at least 590 MPa, with high cold resistance at temperatures up to minus 80 ° C.

The technical result is achieved in that the steel containing carbon, silicon, manganese, chromium, nickel, copper, molybdenum, vanadium, aluminum, calcium, sulfur, phosphorus and iron, additionally contains arsenic, tin, lead and zinc in the following ratio of components, wt .%:

Carbon 0.07-0.11 Silicon 0.15-0.40 Manganese 0.30-0.60 Chromium 0.30-0.70 Nickel 1.80-2.20 Copper 0.40-0.70 Molybdenum 0.25-0.35 Vanadium 0.03-0.06 Aluminum 0.01-0.05 Calcium 0.001-0.005 Sulfur 0.001-0.005 Phosphorus 0.001-0.010 Arsenic 0.001-0.006 Tin 0.001-0.010 Lead 0.001-0.004 Zinc 0.001-0.012 Iron rest

provided that the sum (arsenic + tin + lead + zinc) is not more than 0.020 wt.%, and the value of the coefficient of crack resistance during welding P _cm , calculated by the formula

(Clause 4.2.2 of Part XII of the “Rules for Classification, Construction and Equipment of RAS and SMEs”) shall not exceed 0.27%.

The carbon content in these limits helps to ensure high strength steel. Exceeding the specified limits is impractical due to a significant decrease in ductility, viscosity, cold resistance, as well as an increase in hardenability and an increase in the tendency of steel to form hot and cold cracks during welding.

The content limits of manganese, chromium, copper, nickel and molybdenum provide the necessary strength of steel and low temperature toughness of steel by means of solid solution hardening, as well as hardenability by increasing the stability of austenite in the ferrite region during γ-α transformation and the formation of predominantly bainitic martensitic structures during quenching thicknesses up to 30 mm.

Vanadium contributes to the achievement of the required level of strength and viscosity due to grinding of the microstructure due to the release of dispersed particles of carbides and carbonitrides during the rolling process. Aluminum is introduced into steel as a deoxidizer, as well as for the purpose of grinding grain. Calcium is introduced into steel within the specified limits in order to modify non-metallic inclusions, which favorably affects the isotropy of the mechanical properties and toughness of steel, including at low temperatures.

Sulfur and phosphorus are elements that adversely affect the isotropy of the mechanical properties of steel, ductility and toughness at low temperatures. Phosphorus causes an increased tendency to brittle fractures with lower test temperatures and temper brittleness due to enrichment of grain boundaries. The limitation of the phosphorus content in the specified limits helps to ensure high cold resistance of steel at temperatures up to minus 80 ° C, and in combination with the introduction of molybdenum in the specified limits eliminates temper brittleness.

The effect of arsenic on the properties of steel is similar to that of phosphorus, and when the mass fraction in steel is not more than 0.008, arsenic does not adversely affect the properties of steel [3]. Tin, lead and zinc have a negative effect on the hot and cold ductility of steel during rolling and bending of sheet metal. When the total content of arsenic, tin, lead and zinc in the metal is more than 0.020%, the impact strength decreases and the temperature of the viscous-brittle transition shifts to higher temperatures. Such an effect is known and is associated with the tendency of non-ferrous metal impurities to form fusible eutectics during crystallization in the interaxial sections of dendrites [4].

Example

Steel was smelted in an electric furnace and, after out-of-furnace refining and evacuation, was cast into continuously cast slabs. The chemical composition is shown in table 1.

The slabs were rolled onto sheets with a thickness of 8-30 mm, which were subjected to thermal improvement (quenching in water from a temperature of 920 ± 20 ° C with tempering in a temperature range of 610 ÷ 680 ° C).

Mechanical properties were determined on samples cut across the rolling direction. Tensile testing was performed according to GOST 1497 on flat samples of type I No. 18 (for sheets with a thickness of 8 mm), cylindrical samples of type III No. 6 (for sheets with a thickness of 20 mm), cylindrical samples of type III No. 3 (for sheets with a thickness of 30 mm). Impact bending tests were performed according to GOST 9454 on samples with a V-notch type 11 at temperatures plus 20, minus 40, minus 60 ° C and minus 80 ° C.

The results of mechanical tests (average values for the results of two tensile tests and three for impact bending) are shown in table 2.

Information sources

1. Patent of the Russian Federation No. 2269588, IPC C22C 38/48, 2004

2. Patent of the Russian Federation No. 1676276, IPC C22C 38/46, 1994

3. Yavoysky V.I., Kryakovsky Yu.V., Grigoriev V.P. and others. Metallurgy of steel. - M.: Metallurgy, 1983 .-- 584 p.

4. Bernstein M.L., Dobatkin S. B., Kaputkina L. M., Prokoshkin S. D. Hot deformation diagrams, structure and properties of steels. - M.: Metallurgy, 1989 .-- 544 p.

Claims (1)

Cold-resistant high-strength steel containing carbon, silicon, manganese, chromium, nickel, copper, molybdenum, vanadium, aluminum, calcium, sulfur, phosphorus and iron, characterized in that it additionally contains arsenic, tin, lead and zinc in the following ratio of components, wt.%:
carbon 0.07-0.11 silicon 0.15-0.40 manganese 0.30-0.60 chromium 0.30-0.70 nickel 1.80-2.20 copper 0.40-0.70 molybdenum 0.25-0.35 vanadium 0.03-0.06 aluminum 0.01-0.05 calcium 0.001-0.005 sulfur 0.001-0.005 phosphorus 0.001-0.010 arsenic 0.001-0.006 tin 0.001-0.010 lead 0.001-0.004 zinc 0.001-0.012 iron rest
the total content (arsenic + tin + lead + zinc) is not more than 0.020 wt.%, and the value of the coefficient of crack resistance during welding P _cm does not exceed 0.27%.