RU2397269C2 - High strength weld steel - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention refers to metallurgy, particularly to production of plate iron out of high strength cold resistant steel for ship-building, fuel-energy complex, and transport and heavy-duty machine building. Steel contains carbon, silicon, manganese, chromium, nickel, molybdenum, copper, niobium, sulphur, phosphorus, and iron at the following ratio of elements, wt %: carbon 0.08 - 0.10, silicon 0.20 - 0.40, manganese 0.20 - 0.40, chromium 0.60 - 1.00, nickel 3.00 - 3.90, copper 0.8 - 1.30, molybdenum 0.40 - 0.60, niobium 0.02 - 0.05, sulphur 0.001 - 0.005, phosphorus 0.005 - 0.012, iron - the rest. Summary contents of nickel and copper is not less 4.2 wt %, while value of fracture strength ratio at welding P_cm does not exceed 0.33 %.

EFFECT: raised yield point, cold resistance, fracture strength at welding and resistance to laminar destructions.

2 tbl, 1 ex

Description

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

Known are high-strength steels containing manganese, chromium, nickel, molybdenum, copper and vanadium, grades NU100, NU130 (USA), NS80 (Japan), WELDOX900 (Sweden), etc.

However, these grades have become not well welded, especially in open air conditions, and also do not provide the level of resistance to brittle fracture required in the Far North.

Known steel 70 mm thick, adopted as a prototype, with the following chemical composition, wt.%: Carbon - 0.07-0.11, silicon - 0.17-0.37, manganese - 0.30-0.60, chrome - 0.30-0.70, copper - 0.40-0.70, nickel - 2.40-3.00, molybdenum - 0.35-0.45, aluminum - 0.005-0.06, vanadium - 0 , 01-0.03, calcium, barium - 0.005-0.020, sulfur - 0.001-0.015, phosphorus - 0.005-0.015, iron - the rest, provided that the sum (nickel + copper) ≥3.0, (sulfur + phosphorus ) ≤0.025 (RF patent No. 1676277).

Known steel with a yield strength of ≥620 MPa has a satisfactory impact work at temperatures up to -50 ° C, but for steel intended for the most critical welded structures in the northern version in order to ensure sufficient reliability and performance, impact work should be provided at -60 ° C for at least 80 J, and the normalized fracture toughness coefficient in welding P _cm.

The technical result of the invention is the development of steel with a yield strength of at least 780 MPa, high cold resistance, crack resistance during welding and resistance to layered fractures in thicknesses up to 70 mm.

The technical result is achieved in that the steel containing carbon, manganese, silicon, chromium, nickel, molybdenum, copper, sulfur, phosphorus and iron, additionally contains niobium, in the following ratio of components, wt.%: Carbon - 0.08-0, 10, silicon - 0.20-0.40, manganese - 0.20-0.40, chromium 0.60-1.00, copper - 0.8-1.3, nickel - 3.00-3.90 , molybdenum - 0.40-0.60, niobium - 0.02-0.05, sulfur - 0.001-0.005, phosphorus - 0.005-0.012, iron - the rest, and the value of the coefficient of crack resistance during welding

(Clause 3.2.2 of Part XIII of the "Rules for the Construction and Classification of Sea Ships") should not be higher than 0.33% and the total nickel and copper content should not be lower than 4.2% for sheets up to and including 40 mm thick and 4.6 % for sheets with a thickness of over 40 to 70 mm inclusive.

The carbon content in the selected range is sufficient to provide the required level of strength, while achieving an increase in weldability, cold resistance and crack resistance of steel.

The nickel and copper content limits are selected to ensure cold and crack resistance during operation of welded structures in extreme climatic conditions for sheets up to 70 mm thick.

The indicated total nickel and copper content is optimal for ensuring high cold resistance and the required level of strength, achieved due to the formation of a predominantly martensitic structure during the γ → α transformation during quenching and hardening due to the release of ε-copper during tempering.

Chrome and manganese are accepted within the limits necessary to ensure hardenability of steel in sections up to 70 mm, and do not impair the weldability and cold resistance characteristics.

Joint alloying with molybdenum and niobium within the claimed limits most effectively contributes to the hardening of steel. Molybdenum, not bonded to carbides and in solid solution, reduces the rate of carbon diffusion and thereby determines the required strength characteristics.

The dissolution temperature of niobium carbides in austenite is 50-70 ° C higher than vanadium carbides, as a result of which niobium carbides limit the growth of austenitic grain during heating under quenching, and contribute to the hardening of steel. Thus, solid solution, grain boundary and dispersion hardening is simultaneously ensured. Grinding grain due to the introduction of niobium improves the cold resistance and crack resistance. Thus, the introduction of niobium allows for a specified level of strength with a carbon, nickel and molybdenum content within the specified limits, and helps to ensure the necessary weldability.

Regulation of sulfur within the specified limits provides an increase in the isotropy of steel (especially in the direction of thickness) and an increase in resistance to layered fractures.

Limiting the value of the coefficient of crack resistance during welding eliminates the formation of cold cracks and increases the weldability of steel.

Tests of sheet metal showed that the selected chemical composition of steel manufactured using modern technology ensures high strength, crack resistance and weldability in thicknesses up to 70 mm.

Example. Steel was smelted in a laboratory induction furnace with casting of 25 kg of ingot.

The chemical composition is shown in table 1.

The ingots were forged onto billets with a section of 40 × 120 mm, which were rolled onto plates with a thickness of 13 mm. Samples for impact bending tests, type 11 according to GOST 9454, were cut from the plates, on which a hardening of a plate 70 mm thick was simulated. The samples were tested at temperatures of +20 -80 ° С, after which tensile samples with a diameter of 3 mm were made from the tested samples, on which strength and plastic characteristics were determined. The test results are shown in table 2.

Samples were quenched from a temperature of 880-900 ° C and tempered at a temperature of 620-630 ° C.

The test results show that the proposed steel provides a higher level of strength than the known, while ensuring satisfactory weldability and high resistance to brittle fracture at low temperatures.

These advantages allow you to significantly expand the range of steel applications, to increase the reliability and performance of structures made from it. The manufacturability and the complexity of the manufacture of semi-finished products at the same time practically does not change.

Claims (1)

High strength weldable steel containing carbon, silicon, manganese, chromium, nickel, molybdenum, copper, sulfur, phosphorus and iron, characterized in that it additionally contains niobium in the following ratio of components, wt.%:
carbon 0.08-0.10 silicon 0.20-0.40 manganese 0.20-0.40 chromium 0.60-1.00 nickel 3.00-3.90 copper 0.8-1.30 molybdenum 0.40-0.60 niobium 0.02-0.05 sulfur 0.001-0.005 phosphorus 0.005-0.012 iron rest,
the total content of nickel and copper is not lower than 4.2 wt.%, and the value of the coefficient of crack resistance during welding P _cm does not exceed 0.33%.