RU2381283C1 - Manufacturing method of high-strength weld rebars - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to metallurgy field, particularly to rolling manufacture, and is provided for receiving on section mills of steel weld rebars from uninterruptedly-casted blanks. For improving and yield method includes continuous casting at temperature 1520-1570°C at a rate 0.6-0.9 m/min, heating of blanks up to temperature 1150-1250°C, multipass rolling in rolls with gages with cumulative elongation ratio not less than 15 and finishing temperature 900-1100°C, accelerated cooling of moved strips by water up to temperature 200-570°C at a rate 50-150°C/s and following spontaneous cooling on air, herewith steel contains, wt %: 0.04-0.17 C, 0.15-0.35 Si, 1.30-1.95 Mn, not more than 0.08 Nb, not more than 0.07 Ti, not more than 0.08 V, the rest - iron and admixtures.

EFFECT: improving.

3 cl, 3 tbl

Description

The invention relates to the field of metallurgy, specifically to rolling production, and is intended to produce high-strength steel welded reinforcing profiles from continuously cast billets on high-quality mills.

High-strength welded reinforcing profiles of low alloy steel in a heat-strengthened state must meet the following set of mechanical and operational properties (table 1):

Table 1
Properties of high strength reinforcing profiles σ _in
MPa σ _t
MPa δ ₅ ,
% KCU ^-60 ,
MJ / m ² Bending angle α,
hail. Weldability not less than 840 not less than 600 not less than 14 not less than 0.6 not less than 90 sat.

A known method for the production of steel reinforcing profiles, including heating billets made of carbon steel grade St3, multi-pass rolling in rolls with calibers, cooling the moving strips with water at first by 35-40 ° C directly at the exit from the rolls of the finishing stand, then their accelerated cooling with water to a temperature of 600 -650 ° C and final cooling in air [1].

The disadvantages of this method are that the reinforcing profiles have low strength and viscosity properties. This reduces their quality and yield.

There is also known a method of producing a steel reinforcing profile from carbon steel of the St3sp brand, including heating the workpiece, multi-pass rolling with a draw ratio in the last pass µ = 1.20, accelerated cooling of moving strips with water and subsequent cooling in air [2].

The specified method also does not provide high strength and viscous properties of reinforcing profiles, which reduces their quality and yield.

The closest analogue to the invention is a method for the production of round high-strength long products from low alloy steel of the following chemical composition, wt.%:

Carbon 0.6-1.0 Silicon No more than 1,0 Manganese No more than 1,5 Iron Rest

The method includes heating billets, multi-pass rolling at a 10-stand mill 300-3 in rolls with calibers, accelerated cooling of water of the moving strips directly at the exit of the rolls of the finishing stand, first to a temperature of 770-850 ° C, then to a temperature of 750 ° C and subsequent cooling in air in two stages, and the cooling time is regulated depending on the content of alloying elements in steel [3].

The disadvantages of this method are that the high-strength reinforcing profiles obtained during its use are of poor quality and yield due to insufficient plastic, viscous properties and weldability.

The technical problem solved by the invention is to improve the quality and yield of reinforcing profiles.

To solve the technical problem in the known method for the production of high-strength welded reinforcing profiles of low alloy steel, including continuous casting and heating of workpieces, multi-pass rolling in rolls with calibers, accelerated cooling of moving strips with water and subsequent spontaneous cooling in air, according to the invention, the workpieces are heated to a temperature 1150-1250 ° C, rolling is carried out with a total drawing ratio of at least 15 and is completed at a temperature of 900-1100 ° C, and accelerated cooling in Doi produce a temperature 200-570 ° C at 50-150 ° C / sec. Low alloy steel has the following chemical composition: 0.04-0.17% carbon; 0.15-0.35% silicon; 1.30-1.95% manganese; no more than 0.08% niobium; not more than 0.07% titanium; not more than 0.08% vanadium; iron and impurities - the rest; which is subjected to continuous casting into billets at a temperature of 1520-1570 ° C at a speed of 0.6-0.9 m / min.

The essence of the proposed technical solution is as follows. The required combination of the mechanical properties of the welded reinforcing profiles (table 1) is carried out by simultaneously optimizing the chemical composition of the steel, the modes of its continuous casting and deformation-heat treatment in the combined rolling process and subsequent heat hardening. Due to the fact that additional hardening is achieved by dispersing the microstructure of the steel during multi-pass rolling and hardening of freshly deformed austenite, it is possible to reduce the degree of alloying. This allows, while ensuring high strength of finished reinforcing profiles, to increase their weldability, toughness and ductility.

It was experimentally established that heating continuously cast steel billets of the proposed chemical composition to a temperature below T _a = 1150 ° C does not ensure complete dissolution of carbides in austenite. This reduces the strength of heat-strengthened reinforcing profiles. With an increase in T _and more than 1250 ° C, burnout and oxidation of the grain boundaries of continuously cast billets are not excluded, which increases scale formation and reduces yield.

The degree of mechanical study of the cast structure of the workpiece is determined by the coefficient of total drawing λ _Σ , defined as the ratio of the cross-sectional area of the workpiece and the finished reinforcing profile. With a total drawing coefficient λ _{Σ of} less than 15, the degree of “study” of the microstructure of the continuously cast billet is reduced. As a result, the microstructure of reinforcing profiles contains intact coarse fragments of crystallites formed during the crystallization of liquid steel. This leads to a sharp decrease in the viscosity and plastic properties of steel, reducing yield.

In the case of completion of rolling at a temperature of T _cp below 900 ° C, the processes of recrystallization of deformed austenite are slowed down. Subsequent quenching from rolling heating does not provide the necessary degree of thermal hardening of reinforcing profiles. An increase in T _cp more than 1100 ° C leads to coarsening of the microstructure, uneven growth of austenitic grains, and a decrease in the viscosity, strength and plastic properties of reinforcing profiles.

The accelerated cooling of moving strips with water to a temperature above T _s = 570 ° C (interrupted quenching) leads to their softening during self-tempering. This reduces the quality of reinforcing profiles and yield. With a decrease in T _c below 200 ° C, the reinforcing profiles have low viscosity and plastic properties (especially in small sections), which impairs their quality.

When the cooling rate V _s exceeds 150 ° C / s, the finished reinforcing profiles have an uneven microstructure and low ductility. In cases where V _{s is} lower than 50 ° C / s, heat strengthening of varietal profiles is insufficient, which degrades their quality and reduces the yield. Continuous casting of steel billets of the proposed composition at a temperature T _r above = 1570 ° C and a casting speed V _r above 0.9 m / min worsens their macrostructure, increases the score of non-metallic inclusions, the amount of segregation, the unevenness of the chemical composition and the yield of reinforcing profiles. At the same time, a decrease in T _p below 1520 ° C or the casting speed V _p less than 0.6 m / min leads to the formation of discontinuities, coarsening of the macrostructure. This adversely affects the quality of high-strength reinforcing profiles and yield.

Carbon in the proposed low alloy steel is the main reinforcing element, therefore, when its concentration is less than 0.04%, the strength properties decrease, which affects the quality of reinforcing profiles. At the same time, an increase in carbon concentration of more than 0.17% leads to a loss of viscous and plastic properties, impairs the weldability of high-strength reinforcing profiles.

Silicon is introduced as a deoxidizing agent and a strengthening element.

However, an increase in the silicon content of more than 0.35% leads to an increase in the number of nonmetallic inclusions in the microstructure, and a decrease in the plastic and viscous properties of thermally hardened reinforcing profiles. A decrease in the silicon content of less than 0.15% leads to a loss of strength properties. All this reduces the quality and yield of reinforcing profiles.

Manganese simultaneously increases the strength and hardenability of steel by reducing the rate of transformation of austenite during cooling. With its content of 1.30-1.95%, it strengthens the steel without reducing the viscosity and plastic properties. An increase in the manganese content in excess of 1.95% leads to a loss in the ductility of steel in a heat-strengthened state. A decrease in the manganese content of less than 1.30% causes a decrease in the strength and plastic properties of steel. And in fact, and in another case, there is a decrease in the quality and yield of reinforcing profiles.

Niobium, titanium and vanadium are elements that have a positive effect on the properties of reinforcing profiles. With a niobium content of not more than 0.08%, titanium of not more than 0.07% and vanadium of not more than 0.08%, they contribute to the grinding of the microstructure grain, increase the strength and ductility of steel, but lead to an increase in the cost of production of high-strength reinforcing profiles. At the same time, an increase in the concentration of niobium over 0.08%, titanium over 0.07% and vanadium over 0.08% increases the cost of production of high-strength reinforcing profiles, worsens their weldability. This leads to a decrease in yield.

Method implementation examples

Smelting of steels of various chemical composition was carried out in an electric furnace. To deoxidize and alloy steel, ferrosilicon, ferromanganese, ferrotitanium, ferrovanadium, and niobium were introduced into the melt. The chemical composition of the smelted steels is given in table 2.

table 2
The composition of low alloy steels Composition number The content of chemical elements, wt.% FROM Si Mn Nb Ti V Fe + impurities one. 0,03 0.14 1.20 0,03 0.02 0,03 Rest 2. 0.04 0.15 1.30 0.04 0.04 0.05 -: - 3. 0,07 0.22 1,60 0.05 0.06 0.06 -: - four. 0.17 0.35 1.95 0.08 0,07 0.08 -: - 5. 0.18 0.36 2.00 0.09 0.08 0.09 -: - 6. (prototype) 0.80 1.15 1.40 - - - -: -

Smelted steel is subjected to continuous casting at a temperature of T _p = 1545 ° C in the workpiece square section 100 × 100 mm The casting speed is maintained equal to V _p = 0.7 m / min.

Continuously cast billets of low alloy steel with composition No. 3 are heated in a methodical furnace of a section rolling mill 350 to an austenitizing temperature of T _a = 1200 ° C and multi-pass hot rolling of reinforcing profiles with a diameter of 28 mm is carried out. Rolling is carried out with a total drawing coefficient λ _Σ = 16.25. The last pass is carried out at a temperature T _kn = 1000 ° C in a round gauge with helical grooves to form a periodic reinforcing profile.

The rolled reinforcing profile is passed through tubular refrigerators, in which it is accelerated by cooling water (quenching) from temperature

T _kp = 1000 ° C to a temperature T _h = 340 ° C at a rate _of V = 100 ° C / s. The cooling rate is controlled by the flow rate and pressure of the water supplied to the tube coolers.

The final cooling of the hardened reinforcing profile from T _s = 340 ° C to ambient temperature is carried out in air. During cooling in air, tempered steel self-releases. The microstructure of the heat-strengthened reinforcing profile over the entire cross section consists of martensite, lower and partially upper bainite. Such a microstructure is characterized by a combination of high strength, ductility, impact strength. Due to this, an increase in the quality and yield of high-strength welded reinforcing profiles is achieved.

Variants of the method and indicators of their effectiveness are shown in table 3.

The data presented in table 3 indicate that the implementation of the proposed method (options No. 2-4) achieves the highest quality of high-strength weldable reinforcing profiles while increasing yield. In cases of transcendental values of the declared parameters (options No. 1 and 5), as well as the prototype method (option No. 6), the quality and yield of high-strength profiles are reduced, their weldability becomes unsatisfactory due to the high degree of alloying.

The technical and economic advantages of the proposed method consist in the fact that the simultaneous optimization of the chemical composition of steel and the parameters of the deformation-heat treatment provide an increase in the complex of mechanical properties, accurate fulfillment of the cross-sectional shape of the reinforcing profile. As a result, the quality (mechanical properties, weldability) and the yield of suitable Q reinforcing profiles are improved.

Using the proposed method will increase the level of profitability of the production of high-strength welded reinforcing profiles by 10-15%.

Table 3
Modes of production of high-strength reinforcing profiles and their effectiveness Option No. Composition number Technological Modes Quality indicators Q% T _r , ° C V _p , m / min T _a
° C λ _Σ T _CP , ° C V _s
° C / s T _s
° C σ _in , MPa σ _t , MPa δ ₅ ,% KCU ^-60 , MJ / m ² α, city Weldability one. one. 1580 1,0 1260 14.80 1110 49 580 820 560 22 0.4 one hundred sat. 84.1 2. four. 1570 0.9 1250 15.00 1100 fifty 570 840 610 eighteen 0.7 one hundred sat. 99,2 3. 3. 1545 0.7 1200 16.25 1000 one hundred 340 860 630 eighteen 0.7 110 sat. 99.3 four. 2. 1520 0.6 1150 24.54 900 150 200 865 640 17 0.7 90 sat. 99,2 5. 5. 1510 0.5 1149 23.12 890 160 190 870 640 13 0.4 83 unsatisfied. 85.3 6. 6. 1580 0.8 1200 14.12 890 70 800 700 600 10 0.2 45 unsatisfied. 87.7

Information sources

1. RF patent No. 2197340, IPC B21B 1/16, 2003

2. RF patent No. 2254179, IPC B21B 1/16, 2005

3. RF patent No. 2212458, IPC C21D 8/06, C21D 1/02, 2003 - prototype.

Claims (3)

1. A method of manufacturing high-strength weldable reinforcing profiles of low alloy steel, including continuous casting, heating of billets, multi-pass rolling in rolls with calibers, accelerated cooling of moving strips with water and subsequent spontaneous cooling in air, characterized in that the billets are heated to a temperature of 1150-1250 ° C, rolling is carried out with a total drawing ratio of at least 15 and is completed at a temperature of 900-1100 ° C, and accelerated cooling with water is carried out to a temperature of 200-570 ° C at a speed of 50-150 ° C / s. 2. The method according to claim 1, characterized in that the steel has the following chemical composition, wt.%:
carbon 0.04-0.17 silicon 0.15-0.35 manganese 1.30-1.95 niobium no more than 0.08 titanium no more than 0,07 vanadium no more than 0.08 iron and impurities rest 3. The method according to any one of claim 1 or 2, characterized in that the continuous casting of the preforms is carried out at a temperature of 1520-1570 ° C at a speed of 0.6-0.9 m / min.