RU2695719C1 - Method of producing reinforcement steel - Google Patents

Abstract

FIELD: metallurgy.SUBSTANCE: to obtain strength of not less than 1700 N/mm, conditional yield point of not less than 1550 N/mmand relative elongation at break of not less than 7.5 % method involves melting of steel of specified chemical composition with total content of Cr + Ni + Cu + Mn ≤ 1.4 and ratio Al/V within range of less than 0.09, rolling into rolled stock, thermal treatment of rolled wire by heating in furnace to temperature of 900–940 °C followed by isothermal quenching for 85–110 seconds in molten lead at temperature of 530–560 °C and final cooling by water, etching, cold drawing of rod with total reduction degree of 60–65 %.EFFECT: invention relates to metallurgy, namely, to production of steel high-strength wire fittings produced by cold drawing and thermomechanical treatment.1 cl

Description

The invention relates to metallurgy, namely, to the production of high-strength steel wire reinforcement produced by cold drawing and with the preliminary obtaining of the necessary microstructure by thermomechanical processing.

A known method for the production of high-strength steel nanostructured reinforcement, including steelmaking, rolling into wire rod, heat treatment of wire rod, etching, cold drawing, applying a periodic profile, thermomechanical processing and cutting the reinforcement to a measured length. Steel is melted with the following chemical composition, (mass%): carbon from 0.77 to 0.85; manganese from 0.50 to 0.80; silicon from 0.20 to 0.37; sulfur from 0.016 to 0.020; phosphorus from 0.016 to 0.025; chrome no more than 0.10; nickel no more than 0.10; copper no more than 0.10; aluminum from 0.01 to 0.03; boron from 0.001 to 0.003; iron - the rest, in which the total content of Chrome plus nickel plus copper is kept below 0.14 (Cr + Ni + Cu <0.14), and the ratio of aluminum to boron (Al / B) is in the range of 10-20, the wire rod is heat treated by heating in a furnace to a temperature of 900-940 ° C (degrees Celsius) followed by isothermal quenching for 85-110 seconds in a lead melt at a temperature of 530-560 ° C (degrees Celsius) and final cooling with water, and the wire rod is drawn with a total the degree of compression of 57-62%.

The selected limits of carbon content (0.77-0.85%) in combination with manganese (0.50-0.80%), chromium, nickel and copper (up to 0.10 each, but with a ratio of chromium plus nickel plus copper less 0.14 (Cr + Ni + Cu <0.14) with the introduction of aluminum and boron into the steel will allow grinding the microstructure of the steel during its heat treatment.The ratio of aluminum to boron (Al / B) in the range of 10-20 provides in the final product - cold deformed high-strength reinforcement - strength not less than 1570 N / mm ² , conditional yield strength not less than 1400 N / mm and elongation at break of not less than 6% (RU, invention patent No. 2471004 dated December 16, 2011, IPC class: C2D 8/08, C21D 9/52, C22C 38/54, B82Y 40/00, B82B 3/00 published: December 27, 2012, Bulletin No. 36 )

Steel of the following chemical composition is also known (mass%): carbon 0.75-0.81; Manganese 0.60-0.80; silicon 0.20-0.37; sulfur 0.016-0.020; phosphorus 0.016-0.025; chrome 0.20-0.30; nickel no more than 0.10; copper no more than 0.10; aluminum no more than 0.005; boron 0.001-0.003; iron - the rest, in which the total content of chromium plus nickel plus copper is less than 0.50 (Cr + Ni + Cu <0.50), the ratio of aluminum to boron (Al / B) is in the range of 5.00-1.65, and the ratio of chromium to boron (Cr / B) 100-200. The introduction of chromium in a ratio of 100-200 to boron allows to increase the strength of reinforcing steel up to 1700 N / mm ² , and the conditional yield strength of at least 1450 N / mm ² (RU, patent for invention No. 2543045 dated 11/27/2013, IPC class: C21D 8 / 08 (2006.01); C21D 9/52 (2006.01); C22C 38/54 (2006.01) published: 02.27.2015, Bulletin No. 6).

With the further use of reinforcing steel in reinforced concrete structures with heavy concrete, it became necessary not only to increase strength, but also the ductility of reinforcing steel against the above grades of steel, the strength and ductility of which was insufficient.

When using eutectoid carbon steels containing finely divided perlite (sorbitol), insignificant regions of bainitic inclusions cannot be avoided. The size of carbides in a bainitic structure is an important factor determining its strength. For this purpose, microalloying with vanadium is proposed, through the introduction of which vanadium carbides are formed, which in turn become nuclei for the formation of granular perlite (sorbitol) in the subsequent patenting process of hot-rolled round steel. At the same time, the introduction of vanadium as an alloying additive increases the ductility of steel.

To obtain the necessary properties, the following chemical composition of steel (wt.%) Is proposed:

carbon 0.77-0.79 manganese 0.70-0.80 silicon 0.20-0.30 sulfur no more 0.010 phosphorus no more 0,020 chromium 0.15-0.30 nickel no more than 0.10 copper no more than 0.20 aluminum no more than 0,005 vanadium 0.06-0.08 nitrogen no more 0.008 iron rest

The total content of chromium plus nickel plus copper is less than 0.50 (Cr + Ni + Cu <0.50), the ratio of aluminum to vanadium (Al / V) is in the range of 0.063-0.083, and the ratio of chromium to vanadium (Cr / V) 2, 50-3.75. The introduction of vanadium as a carbide-forming element contributes to the rapid growth of "nuclei" in the form of vanadium carbides (VC). Carbides are evenly located in the alloy, which contributes to the creation of a fine-grained steel structure and increases the strength parameters of steel, as well as its viscosity, wear resistance, preventing the structural growth of steel grains during heating. In this case, the addition of vanadium additionally serves as a deoxidizing agent.

Heat treatment of wire rod is carried out by heating in a furnace to a temperature of 900-940 ° C (degrees Celsius), followed by isothermal hardening for 85-110 seconds in a lead melt at a temperature of 530-560 ° C (degrees Celsius) and final cooling with water, and drawing wire rods are produced with a total degree of compression of 60-65%.

The selected limits of carbon content (0.77-0.79%) in combination with manganese (0.50-0.80%), chromium, nickel up to 0.10 and copper up to 0.20 each, but with a ratio of chromium plus nickel plus copper less than 0.14 (Cr + Ni + Cu <0.14) when vanadium is introduced into the steel, it is possible to grind the microstructure of the steel during its heat treatment. The ratio of aluminum to vanadium (Al / V) in the range of less than 0.09 provides cold-deformed high-strength reinforcement in the final product — strength not less than 1700 N / mm ² , conditional yield strength not less than 1550 N / mm ² and elongation at break not less than 7.5%

The technical result to which the invention is directed is to obtain in a cold-deformed high-strength reinforcement with a strength of at least 1700 N / mm ² , a conditional yield strength of at least 1550 N / mm ² and a relative elongation at break of at least 7.5%.

The specified technical result is achieved by the fact that in the method of manufacturing reinforcing steel, including steel smelting, rolling into wire rod, heat treatment of wire rod, etching, cold drawing, applying a periodic profile, thermomechanical processing and cutting reinforcement to a measured length, steel of the following chemical composition is melted, ( mass%):

carbon 0.77-0.79 manganese 0.70-0.80 silicon 0.20-0.30 sulfur no more than 0,010 phosphorus no more than 0,020 chromium 0.15-0.30 nickel no more than 0.10 copper no more than 0.20 aluminum no more than 0,005 vanadium 0.06-0.08 nitrogen no more than 0,008 iron rest,

the mass fraction of titanium should be no more than 0.005% with a total content of chromium plus nickel plus copper plus manganese less than or equal to 1.4 (Cr + Ni + Cu + Mn <1.4) and the ratio of aluminum to vanadium (Al / V) in limits less than 0.09. An important condition for eliminating the formation of cementite (Fe ₃ C) during steelmaking is that the carbon content should not exceed 0.79%.

Heat treatment of wire rod is carried out by heating in a furnace to a temperature of 900-940 ° C (degrees Celsius), followed by isothermal quenching for 85-110 seconds in a lead melt at a temperature of 530-560 ° C (degrees Celsius) and final cooling with water, and drawing wire rods are produced with a total degree of compression of 60-65%. EFFECT: invention enables to obtain strength of not less than 1700 N / mm ² , conditional yield strength of not less than 1550 N / mm ² and relative elongation at break of not less than 7.5% in cold-deformed high-strength reinforcement.

An example of the method of manufacturing reinforcing steel.

According to the chemical composition developed by BET, steel was smelted in a 180-ton electric furnace at OJSC MMK, processed in a ladle furnace, cast into a continuous casting machine into a billet with a section of 150 × 150 mm and rolled into a round wire rod with a diameter of 15.5 mm on the high-quality mill "170", having the following chemical composition (wt.%):

Carbon 0.790 Manganese 0.720 Silicon 0.247 Sulfur 0.001 Phosphorus 0.005 Chromium 0.220 Nickel 0,033 Copper 0,041 Aluminum 0.003 Vanadium 0,062 Nitrogen 0.008 Iron rest

The ratio of chromium plus nickel plus copper plus manganese (Cr + Ni + Cu + Mn) was 1.014, and the Al / V ratio was 0.048.

The changes in the chemical composition, namely microalloying with chromium, manganese, vanadium and the exclusion of aluminum during the deoxidation of the proposed steel, made it possible to obtain a conditional yield strength above 1550 N / mm ² ; tensile strength above 1700 N / mm ² and elongation at break of not less than 7.5%.

The heat-treated wire rod was rolled into a wire with a diameter of 11-0.1 mm, after which a trilateral periodic profile was drawn on its surface with a tightening, subjected to tempering on a stabilization line under tension at a temperature of 400 ° C (degrees Celsius), cooled with running water and cut to length . Mechanical tests of the obtained steel high-strength reinforcement with a nominal diameter of 9.6-0.1 mm showed the following properties:

temporary tensile strength 1700-1740 N / mm;

conditional yield strength 1570-1590 N / mm ² ;

elongation at break 7.5-8.0%;

hardness 41.5-43.0 HRC,

which fully complies with the technical requirements for high-strength cold-rolled rod reinforcement of a periodic profile with a diameter of 5 mm; 7.5 mm; 9.6 mm for reinforcing concrete sleepers.

Claims (3)

A method of manufacturing a steel high-strength reinforcement, including steelmaking of the following chemical composition, wt. %: carbon 0.77-0.79 manganese 0.70-0.80 silicon 0.20-0.30 sulfur no more than 0,010 phosphorus no more than 0,020 chromium 0.15-0.30 nickel no more than 0.10 copper no more than 0.20 aluminum no more than 0,005 vanadium 0,060-0,080 nitrogen no more than 0,008 titanium no more than 0,005 iron rest, with a total content of chromium, nickel, copper and manganese Cr + Ni + Cu + Mn ≤ 1.4, the ratio of aluminum to vanadium Al / V is less than 0.09, rolling into wire rod, heat treatment of wire rod by heating in a furnace to a temperature of 900-940 ° С followed by isothermal quenching for 85-110s in a lead melt at a temperature of 530-560 ° С and final cooling with water, etching, cold drawing with a total degree of reduction of 60-65%, applying a periodic profile, thermomechanical processing and cutting of reinforcement to dimensional length.