RU2627079C1 - Method of manufacture of high-strengthen corrosive-resistant hot-rolled steel with low specific weight - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: blank is prepared from steel containing mass. %: Carbon 0.03-0.07, Silicon 0.5-0.8, Manganese 0.4-0.7, Sulfur no more than 0.01, Phosphorus 0.005-0.015, Aluminium 8.0-11.0, Chromium 6.0-10.0, Nickel 0.005-0.03, Molybdenum 1.01-2.0, Titanium 0.01-0.03, Vanadium 0.05-0.07, Niobium not more than 0.06, Nitrogen 0.005-0.05, Iron and unavoidable impurities are the rest, the sum of [Cr+Al] wt % = 14.1-18, the blank is heated in the range from 1100°C to 1300°C, milling is conducted in at least five stages with a reduction ratio in each step from 10% to 25%, the time between two subsequent milling stages not exceeding 9 s, and the milling end temperature of 810-890°C, then the resulting strip is cooled to ambient temperature.

EFFECT: increasing the strength and corrosion resistance of the strip while maintaining low specific gravity.

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Description

The invention relates to the field of metallurgy, in particular to the development of hot rolled steel with a low specific gravity, high strength and corrosion properties, intended for use in structures and structures for various purposes in the Arctic and Antarctic.

A known method of manufacturing a high-strength steel sheet with an austenitic structure, including hot rolling with heating to 1000-1200 ° C and the end of rolling at 850 ° C or higher, tempering at temperatures above 600 ° C. In this case, the steel contains the following components, wt. %: C 0.6-1.0, Si 0.1-2.5, Mn 10-15, Al 5-8, Ti 0.01-0.20, S≤0.015, P≤0.02, N ≤0.02, iron and unavoidable impurities - the rest, the ratio of the content of manganese and aluminum is related by the dependence Mn / Al = 2-3, and the specific gravity of steel is 7.4 g / cm ² . In special cases, the steel may additionally contain one or more elements from the groups: Cr 0.1-3.0, Mo 0.05-0.5, Ni 0.05-2.0 and Cu 0.1-2.0, and / or Nb 0.005-0.2, V 0.005-0.5, Zr 0.005-0.2 and B 0.0005-0.0030, also Sb 0.005-0.2 and Ca 0.001-0.02. Properties of hot rolled steel: tensile strength 800-1200 MPa, elongation of more than 30%, and the ratio of yield strength 60% or more (European application EP 2653581, IPC C21D 8/02, C22C 38/06, published October 23, 2013).

The disadvantage of this method is the high content of an expensive alloying element - manganese.

The closest analogue of the present invention is a method of manufacturing a hot rolled ferritic sheet of steel with low density, comprising casting a semi-finished product, heating it for hot rolling to a temperature greater than or equal to 1150 ° C, hot rolling at a temperature greater than or equal to 1050 ° C, at least in two stages, while the compression ratio at each stage of rolling is greater than or equal to 30%, the time between each stage is greater than or equal to 10 s. Rolling is completed at a temperature exceeding or equal to 900 ° C, the sheet is cooled so that the time interval between 850 and 700 ° C exceeds 3 s, then the sheet is wound at a temperature in the range from 500 to 700 ° C. Moreover, the steel contains, by weight. %:

0.001 С C 0 0.15, Mn 1 1, Si l l, 5, 6 A Al 10 10, 0.02 T Ti 0 0.5, S 0 0.050, P 0 0.1, and optionally one or more of the following elements: Cr≤1, Mo≤1, Ni≤1, Nb≤0.1, V≤0.2, B≤0.01, iron and unavoidable impurities - the rest. The tensile strength is at least 400 MPa. Density less than 7.3 g / cm ³ (Patent RU 2436849, IPC C22C 38/06, C22C 38/14, published on December 20, 2011 - prototype).

The disadvantage of the method of manufacturing known steel is the inability to control the strength and corrosion properties of steel, increasing the content of chromium, molybdenum above the specified concentration intervals, as well as the high temperature of the end of rolling, leading to increased energy consumption and deterioration of the strength properties of steel.

The technical problem to which the invention is directed is the optimization of the production method, the chemical composition of the steel and the parameters of its hot rolling, providing a technical result in the form of an increase in strength and corrosion resistance while maintaining a low specific gravity.

The technical result is achieved by the fact that in the method for the production of high-strength corrosion-resistant hot-rolled steel with a low specific gravity, including the preparation of a billet from steel, hot rolling of a billet, according to the invention, the billet is obtained from steel containing components in the following ratio, wt. %:

Carbon 0.03-0.07 Silicon 0.5-0.8 Manganese 0.4-0.7 Sulfur no more than 0,01 Phosphorus 0.005-0.015 Aluminum 8.0-11.0 Chromium 6.0-10.0 Nickel 0.005-0.03 Molybdenum 1.01-2.0 Titanium 0.01-0.03 Vanadium 0.05-0.07 Niobium no more than 0,06 Nitrogen 0.005-0.05 Iron and inevitable impurities rest,

the content of chromium and aluminum is due to the dependence [Cr +% Al] = 14.1-18,

while heating the billet before hot rolling is carried out in the range from 1100 ° C to 1300 ° C, rolling is carried out in at least five stages, the degree of compression at each stage is from 10% to 25%, and the time between two subsequent rolling stages does not exceed 9 s, and the end of the rolling is carried out at a temperature of 810-890 ° C, then cooled to ambient temperature.

The invention is aimed at increasing the strength due to the formation of a pronounced cellular substructure with a high density of dislocations, solid-solution hardening by aluminum and the inhibition of recrystallization processes caused by a high content of aluminum nitride precipitates, which leads to grinding of ferrite grains, and also to increase corrosion resistance due to the formation of steel on the surface sheet of protective oxide films that impede the development of corrosion processes, and, in addition, to preserve low specific gravity of steel due to its high aluminum content.

To increase the strength characteristics, the composition of the steel contains 0.005-0.05% nitrogen, which leads to the formation of nitride and carbonitride precipitates. The formation of a large number of precipitates of aluminum nitride during the hot rolling process can lead to inhibition of recrystallization processes and to corresponding grinding of ferrite grains. A nitrogen content of less than 0.005 does not lead to a significant strengthening effect, and a content of more than 0.05% leads to a noticeable embrittlement of steel.

The aluminum content in the steel at the level of 8-11% provides a sufficient reduction in the specific gravity of the steel and the necessary solid-solution hardening of the steel sheet, and also provides high corrosion resistance due to the formation of protective oxide films on the surface. An aluminum content of less than 8% does not allow a sufficient reduction in the specific gravity of steel, and an aluminum content of more than 11% can lead to embrittlement.

6.0-10% chromium contained in the metal, like aluminum, is involved in the formation of protective oxide films on the surface of the steel. Moreover, to ensure the best corrosion and strength properties, the total content of chromium and aluminum (% Cr +% Al) is advisable to provide at the level of 14.1-18%. Exceeding the specified value does not lead to a significant increase in corrosion properties, and lower values do not provide sufficient resistance to corrosion in sea water.

Doping with molybdenum in an amount of 1.01% to 2% increases the resistance to pitting corrosion. Alloying steel with molybdenum in an amount of less than 1.01% slightly affects the resistance to pitting corrosion, and more than 2% is impractical, since the contribution of an expensive alloying element, molybdenum, to the resistance to pitting corrosion above the indicated concentrations is insignificant.

Heating for rolling in the temperature range 1200–1300 ° C is necessary for sufficient dissolution of carbonitride precipitates with a view to their subsequent isolation during rolling, leading to grain refinement and increased strength.

The degree of compression during hot rolling of steel should be in the range of 10-25% between the two subsequent stages of rolling, since exceeding these values can lead to brittle destruction of the steel billet during rolling due to the formation of intermetallic phases in steel containing nitrogen at the declared level. Lower values of the degree of reduction are impractical due to an increase in the number of rolling stages and, consequently, an increase in rolling time, which in turn can lead to an unacceptable drop in the temperature of the rolled billet.

Since the declared degree of compression is relatively small, in order to ensure the necessary degree of development of the metal structure, an increased number of rolling steps is required of at least five, and therefore, the time between two successive rolling steps must be selected so as to ensure the required temperature of the steel at the end of rolling. The recommended time between two consecutive rolling stages does not exceed 9 seconds. Exceeding this time will lead to an unacceptable drop in the temperature of the rolled metal and may lead to the need for re-heating.

The temperature of the metal at the end of the hot rolling should be in the range of 810-890 ° C to ensure the necessary strength of the rental. At a temperature of the end of rolling above 890 ° C, the strength of the rolled products is not high enough, and at a temperature below 810 ° C, increased wear of the rolling equipment is possible.

Examples of specific performance of the method

In an induction furnace, a semi-product is smelted from pure materials, the chemical composition of which is shown in table 1. The parameters of hot rolling and the properties of the resulting rolled products are presented in table 2.

The intermediate product is poured into ingots and after complete cooling is subjected to hot rolling in several stages with a degree of deformation of 10-25% per stage, pre-heating the ingot of the intermediate product to a temperature of 1100-1300 ° C. Rolling is completed at a temperature of 810-890 ° C and a thickness of the resulting hot-rolled strip of about 4 mm. Hot rolled strips are placed in a resistance furnace heated to 750-850 ° C and cooled together with the furnace to room temperature. The steel obtained has a ferritic structure with a well-developed dislocation cellular substructure, a tensile strength of 700–950 MPa, and a corrosion rate in sea water of not more than 0.1 mm / year with a specific gravity of 7.0–7.2 g / cm ³ .

Claims (3)

A method of manufacturing a high-strength hot-rolled strip of corrosion-resistant steel with a low specific gravity, including obtaining a steel billet, heating, hot rolling of a billet, characterized in that the billet is obtained from steel containing in wt. %: carbon 0.03-0.07 silicon 0.5-0.8 manganese 0.4-0.7 sulfur no more than 0,01 phosphorus 0.005-0.015 aluminum 8.0-11.0 chromium 6.0-10.0 nickel 0.005-0.03 molybdenum 1.01-2.0 titanium 0.01-0.03 vanadium 0.05-0.07 niobium no more than 0,06 nitrogen 0.005-0.05 iron and inevitable impurities rest, the total content of chromium and aluminum is [Cr + Al] wt.% = 14.1-18, the workpiece is heated before hot rolling in the range from 1100 ° C to 1300 ° C, hot rolling is carried out in at least five stages with the degree of compression at each stage from 10% to 25% and the time between two subsequent rolling stages, not exceeding 9 s, and the end of the rolling is carried out at a temperature of 810-890 ° C, then the resulting strip is cooled to ambient temperature.