RU2303646C2 - Thermally and mechanically reinforced steel for ferroconcrete constructions - Google Patents

Abstract

FIELD: metallurgy, in particular, working out of thermally and mechanically reinforced steels for ferroconcrete constructions of various strength classes.

SUBSTANCE: reinforced steel for ferroconcrete constructions of At400 to At1200 strength classes contains, wt%: carbon 0.08-0.32; silicon 0.4-2.4; manganese 0.5-2.3; aluminum 0.02-0.07; titanium 0.01-0.1; nitrogen 0.006-0.03; vanadium 0.01-0.12; niobium 0.005-0.02; copper no more than 0.3; nickel no more than 0.3; chromium no more than 0.30; phosphor no more than 0.03; sulfur no more than 0.03; iron the balance. Carbon equivalent is defined from formula: C_eq=C+Si/6+Mn/7+(Ti+V+Nb)/5+(Cu+Ni+Cr)/15 and is equal to 0.35-0.56 for At400, At500 class steel, or 0.44-0.70 for At600, At800 class steel, or at least 0.67 for At1000, At1200 class steel. Steel of such composition may be used for manufacture of thermally and mechanically reinforced bars of 12-32 mm diameter.

EFFECT: improved welding capability, high mechanical properties and increased resistance from corrosion cracking.

2 tbl, 1 ex

Description

The invention relates to metallurgy, in particular to the development of reinforcing thermomechanically hardened steels for reinforced concrete structures of strength classes from At400 to At1200.

Closest to the proposed technical essence and the achieved result is steel according to GOST 10884-94 (reinforcing steel thermomechanically hardened for reinforced concrete structures), containing, wt.%:

Carbon 0.08-0.32 Silicon 0.6-2.4 Manganese 0.5-2.3 Copper no more than 0.3 Nickel no more than 0.3 Chromium no more than 0.3 Phosphorus no more than 0,03 Sulfur no more than 0,03 Iron rest

This steel has a relatively high mechanical properties due to the rational ratio of the content of its constituent elements.

However, the increasing requirements for weldability with increasing levels of mechanical properties limits its application.

The objective of the invention is the development of high-quality reinforcing steel. The technical result is the development of steel for the manufacture of rods of heat-strengthened reinforcement with a diameter of 12-32 mm with increased weldability, increased mechanical properties and resistance to corrosion cracking without aging.

The technical result is achieved by the fact that the known steel containing carbon, silicon, manganese, copper, nickel, chromium, phosphorus, sulfur and iron, additionally contains aluminum, titanium, nitrogen, vanadium, niobium in the following ratio of components, wt.%:

Carbon 0.08-0.32 Silicon 0.4-2.4 Manganese 0.5-2.3 Aluminum 0.02-0.07 Titanium 0.01-0.1 Nitrogen 0.006-0.03 Vanadium 0.01-0.12 Niobium 0.005-0.02 Copper no more than 0.3 Nickel no more than 0.3 Chromium no more than 0.30 Phosphorus no more than 0,03 Sulfur no more than 0,03 Iron rest

In this case, the carbon equivalent is determined by the formula:

С _equiv = C + Si / 6 + Mn / 7 + (Ti + V + Nb) / 5 + (Cu + Ni + Cr) / 15

and equal for steel of class At400, At500 - 0.35-0.56; class At600, At800 - 0.44-0.70, and for class At1000, At1200 - at least 0.67.

The content of carbon, silicon, manganese, chromium, nickel and copper in the proposed steel coincides with the limits of their content in the known steel.

An additional input of nitrogen, vanadium, titanium, niobium and aluminum into the inventive steel within the proposed limits due to the formation of nitrides and carbonitrides forming a stable finely divided structure, regardless of the hot machining technology, provides the necessary weldability and increased mechanical properties of the metal without aging.

The proposed formula for calculating the carbon equivalent and the procedure for normalizing it force the manufacturer to precisely set the chemical composition of steel according to the lower limit of carbon, and silicon according to the upper limit, which makes it possible to more accurately determine the necessary composition of alloying chemical elements in steel depending on the level of mechanical properties obtained and the requirements for weldability, resistance to corrosion cracking for a given strength class of reinforcing steel.

The content in nitrogen steel is most effective in the range of 0.006-0.03 wt.%. A decrease in nitrogen content below 0.006 wt.% Does not provide the required level of properties. An increase in nitrogen content above 0.03 wt.% Leads to a decrease in ductility as a result of metal hardening and an increase in its tendency to aging.

The optimum content of vanadium in steel is 0.01-0.12. The decrease in its content below 0.01 wt.% Does not affect the level of mechanical properties of the inventive steel. The vanadium content above 0.12 wt.%, In this case, leads to a further increase in mechanical properties, but also significantly increases the cost of production of the proposed steel, which is impractical.

The titanium content in the steel of less than 0.01 wt.% Does not contribute to a noticeable grinding of grain and an increase in mechanical properties, and more than 0.1 wt.% Does not reduce the tendency to intergranular corrosion.

The niobium content of less than 0.005 wt.% Does not lead to a significant grinding of grain, increasing strength and hardness. And the content of more than 0.05 wt.% Does not lead to a significant increase in the mechanical properties of the inventive steel.

An aluminum content of less than 0.02 wt.% Leads to incomplete binding of nitrogen during crystallization, and above 0.07 wt.% Leads to the possibility of formation of line-wise non-metallic inclusions and an increase in the cost of the proposed steel.

Metal smelting was carried out in a 250-ton open-hearth furnace. Order - reinforcing steel grade At800. Preliminary deoxidation was carried out in a furnace. Deep and cost-effective deoxidation is achieved through the use of carbon dissolved in the metal while introducing the aluminum in the immersion container and the calculated amount of lump ferrosilicon manganese. The metal was produced 6 minutes after the introduction of the submersible deoxidizing container, preventing the boiling of the bath again. The steel composition was adjusted for silicon and manganese, as well as alloying with nitrogen, vanadium, titanium, and niobium was carried out by adding ferrosilicon manganese, ferrotitanium, ferroniobium, and nitrided ferrovanadium with nitrated ferromanganese into the ladle, which were introduced last. The final deoxidation was carried out by an additive in pig aluminum.

To get into the order, we calculated the carbon equivalent according to the proposed formula: _Сequal = С + Si / 6 + Mn / 7 + (Ti + V + Nb) / 5 + (Cu + Ni + Cr) / 15 taking into account the obtained steel composition on production, the chemical composition of the ferroalloys used, and their introduction into the ladle was carried out at a rate based on C _eq falling into the interval recommended for At800 steel.

As a result, steel of the following composition was obtained, wt.%: Carbon — 0.2, silicon — 1.0, manganese — 1.4, aluminum — 0.03, titanium — 0.06, nitrogen — 0.006, vanadium — 0.03 , niobium - 0.005, copper - 0.25, nickel - 0.25, chromium - 0.20, phosphorus - 0.027, sulfur - 0.023, iron - the rest.

Determined by the formula C _{eq of the} finished metal. Got C _equiv = 0.632, that is, C _equiv is in the range recommended for At800 steel.

After casting, the metal was rolled onto reinforcing bars with a diameter of 25 mm using thermomechanical treatment in the following modes: compression from rolling heating followed by electric heating and cooling in air.

Similar steels are smelted for all strength classes of reinforcing steel specified in the formula from At400 to At1200.

Then, mechanical tests were carried out in accordance with the requirements of GOST (the results are shown in table 1), and compared with the characteristics of known steel.

Table 1.
Characteristics of smelted steel of strength class At800 No pp Mechanical properties Prototype Steel Proposed steel one Tensile strength, N / mm ² 1000 1160 2 Conditional yield strength, N / mm ² 800 890 3 Relative extension, % 8 7.6 four Cold bending test D _spec . = 5d = 125 mm, bend angle 45 °, bend -20 ° Cracks and tears were not visually observed. Cracks and tears were not visually observed.

Table 2 shows the mechanical properties of the proposed steel steels with normalized carbon equivalent for various strength classes.

table 2 Strength grade of reinforcing steel Carbon equivalent% Nominal diameter mm Mechanical properties Test on
bend in
cold
condition
degree Temporary tensile strength, σ _in , N / mm ² Conditional or physical yield strength σ _0.2 (σ _t ), N / mm ² Relative extension, % σ ₅ σ _p no less At400 0.351 25 750 640 16 - 90 At500 0.560 25 800 750 fourteen - 90 At600 0.443 25 998 760 12 1.21 45 At800 0.632 25 1160 890 7.6 1.99 45 At1000 0.670 25 1310 1230 6 2.0 45 At1200 0.812 25 1560 1300 4.8 2.0 45

From the tables it follows that the proposed steel in comparison with the known one has higher mechanical properties while maintaining a sufficiently high level of weldability for this steel grade and allows its use for the production of reinforcing bars of strength class from At400 to At1200.

Claims (1)

Reinforcing steel thermomechanically hardened for reinforced concrete structures containing carbon, silicon, manganese, copper, nickel, chromium, phosphorus, sulfur and iron, characterized in that it additionally contains aluminum, titanium, nitrogen, vanadium and niobium in the following ratio of components, wt. %: Carbon 0.08-0.32 Silicon 0.4-2.4 Manganese 0.5-2.3 Aluminum 0.02-0.07 Titanium 0.01-0.1 Nitrogen 0.006-0.03 Vanadium 0.01-0.12 Niobium 0.005-0.02 Copper No more than 0.3 Nickel No more than 0.3 Chromium No more than 0.30 Phosphorus No more than 0,03 Sulfur No more than 0,03 Iron Rest, the carbon equivalent of steel, determined by the formula C _equiv = C + Si / 6 + Mn / 7 + (Ti + V + Nb) / 5 + (Cu + Ni + Cr) / 15 It is equal to 0.35-0.56 for steel of the class At400, At500, or 0.44-0.70 for the class of steel At600, At800, or at least 0.67 for the class of steel At1000, At1200.