RU2558786C1 - Reinforcing steel - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to metallurgy, namely to steel of a construction grade intended for the manufacture of hot-rolled reinforcement of the strength class A400 (A-III). The steel contains carbon, manganese, silicon, nitrogen, vanadium and iron, at the following component ratio, wt %: carbon 0.30-0.37, manganese 0.80-1.10, silicon 0.17-0.37, nitrogen 0.016-0.020, vanadium 0.008-0.022, iron and hydrogen - the rest. The ratio of vanadium/nitrogen amounts to 0.25-2.4, and the ratio of nitrogen/hydrogen amounts to no more than 30.

EFFECT: improvement of steel mechanical properties with providing of good conditions of steel pouring by continuous casting machines.

2 tbl, 1 ex

Description

The present invention relates to metallurgy, in particular to reinforcing steel, intended primarily for the production of hot-rolled reinforcement of strength class A400 (A-III).

Known steel for the production of reinforcement grade 25G2S according to GOST 5781-82, containing, wt.%: 0.20 ÷ 0.29 C; 1.20 ÷ 1.60 Mn, 0.60 ÷ 0.90 Si, the rest is iron.

A disadvantage of the known steel when used for the production of hot-rolled reinforcement is the low level of mechanical properties, namely, low ductility, insufficient elongation, as well as poor test results for bending and low weldability of the metal with a manganese content in the range of 1.20-1.60.

The closest to the proposed technical solution according to the technical essence and the achieved result (prototype), according to the authors, is steel used for the production of hot-rolled fittings of grade 35GS according to GOST 5781-82, containing, wt.%: 0.30 ÷ 0.37 C ; 0.80 ÷ 1.20 Mn, 0.60 ÷ 0.90 Si, the rest is iron.

A disadvantage of the known technical solution is the high cost of steel production due to the increased content of manganese and silicon in it when obtaining standard mechanical properties.

The task to which the technical solution is aimed is to reduce the cost of production of steel in the construction sector by reducing the content of manganese and silicon in it while ensuring the conditions for casting on continuous casting machines (CCM). At the same time, obtaining such a technical result as increasing the mechanical properties of steel, namely increasing the yield strength and elongation, is achieved.

The above disadvantages are eliminated by the fact that reinforcing steel contains carbon, manganese, silicon, nitrogen, vanadium and iron in the following ratio of components, wt.%:

carbon 0.30 ÷ 0.37 manganese 0.80 ÷ 1.10 silicon 0.17 ÷ 0.37 nitrogen 0.016 ÷ 0.020 vanadium 0.008 ÷ 0.022 iron and hydrogen rest

the ratio of vanadium / nitrogen is 0.25 ÷ 2.4, and the ratio of nitrogen / hydrogen is not more than 30.

A comparative analysis of the proposed technical solution with the prototype shows that the claimed technical solution differs from the known one in that it additionally contains nitrogen and vanadium in the following ratio of components, wt.%:

carbon 0.30 ÷ 0.37 manganese 0.80 ÷ 1.10 silicon 0.17 ÷ 0.37 nitrogen 0.016 ÷ 0.020 vanadium 0.008 ÷ 0.022 iron and hydrogen  rest

the ratio of vanadium / nitrogen is 0.25 ÷ 2.4 and the ratio of nitrogen / hydrogen is not more than 30; The claimed technical solution meets the criteria of the invention of "Novelty."

Since the present invention can be used in the metallurgical industry, and tests of the proposed solution showed higher mechanical properties (increased yield strength and elongation), therefore, this technical solution meets the criteria of the invention "Industrial applicability".

A comparative analysis of the proposed technical solution not only with the prototype, but also with other technical solutions, did not allow us to identify the essential features inherent in the claimed solution. It follows that the claimed combination of significant differences allows to obtain the above technical result, which, according to the authors, meets the criteria of the invention "Inventive step".

The elements that make up the proposed steel form its structure and, being in a complex relationship, provide a high level of mechanical properties.

When the carbon content is less than 0.30 wt.%, The steel is not sufficiently deoxidized, as a result of which unfavorable conditions are created for nitriding (penetration of nitrogen into the steel), which leads to a decrease in the yield strength.

When the carbon content is more than 0.37 wt.%, The ductility of the steel deteriorates, the elongation decreases, and it does not pass the bending test.

When the manganese content is less than 0.80 wt.%, The yield strength of steel is reduced by reducing the alloying of the latter.

With a manganese content of more than 1.10 wt.%, A noticeable improvement in the mechanical properties of steel is not observed, with an over-expenditure of manganese, which leads to an increase in the cost of steel production.

When the silicon content is less than 0.17 wt.%, The steel is not sufficiently deoxidized, which worsens the conditions for the penetration of nitrogen into the melt (nitriding) and leads to a decrease in the yield strength.

When the silicon content is more than 0.37 wt.%, Silicon is overused without a noticeable improvement in the mechanical properties of steel. Overspending of silicon also leads to an increase in the cost of steel production.

When the nitrogen content is less than 0.016 wt.%, The yield strength is reduced due to the fact that an insufficient amount of the nitride phase is formed in the steel.

When the nitrogen content is more than 0.020 wt.%, The elongation decreases, since the excess nitrogen is in an unbound state, the likelihood of a steel defect, the subcortical bladder, also increases.

The introduction of a nitride-forming element, for example, vanadium together with nitrogen, provides a change in the grain structure of the metal, thereby increasing strength characteristics and saving manganese while maintaining stable castability on continuous casting machines, in particular in high-quality billets, for example, with a cross section of not more than 150 × 150 mm .

When the vanadium content is less than 0.008 wt.%, An insufficient amount of the nitride phase is formed, which leads to a decrease in the yield strength.

When the vanadium content is more than 0.022 wt.%, The consumption of vanadium increases significantly, which increases the cost of steel production.

When the ratio of vanadium to nitrogen is less than 0.25, the yield strength is reduced due to the fact that an insufficient amount of the nitride phase is formed in the steel.

When the ratio of vanadium to nitrogen is more than 2.4, the consumption of vanadium increases significantly, which contributes to an increase in the cost of steel production.

Atomic nitrogen is introduced into the steel due to the addition of urea (NH ₂ ) ₂ × CO, which contains hydrogen, which interacts with nitrogen in the ratio defined by the claims.

When the ratio of nitrogen to hydrogen is more than 30, the cast metal will have increased fragility, damage by a bubble, which will cause gusting of the strip during rolling and rejection of rolled metal through captures and flaws, which is unacceptable.

Other methods of introducing nitrogen into the metal (nitrided ferroalloys, purging a liquid metal with nitrogen) do not imply the interaction of nitrogen with hydrogen, which are part of the nitride-forming substance. In addition, in these cases, nitrogen is not atomic, but is molecular in nature.

Below are the options for the implementation and use of the invention, not excluding other options in scope, claims (tables. 1 and 2). Example.

Metal melting 1 (table. 1) is obtained as follows. In the DSP-120 arc steel-smelting furnace, the intermediate product (iron-carbon melt) is melted, which is released into the steel ladle. At the beginning of production, they give coke breeze to 0.028-0.35% carbon, ferrosilicon manganese to 0.90% manganese, and ferrosilicon to 0.23% silicon in finished steel. After the specified ferroalloys are melted, the steel is refined by 0.36% carbon in finished steel with coke breeze additive, a flux-cored filler wire 80 is filled with vanadium content of 0.008-0.012%, and a carbamide flux-cored wire is introduced to obtain a nitrogen content of 0.016- 0.020%. Upon reaching the specified composition of the melt (table. 1, heat 1), the ratio V / N = 0.5, the ratio N / H = 35 and its temperature, the steel ladle with liquid metal is transferred to a continuous steel casting machine. The control of the hydrogen content in liquid steel is carried out, for example, using the express analyzer of the Hydris Elektro-Nait system.

The resulting billet is rolled in a mill 250 onto reinforcing steel profiles No. 8-40 of strength class A400. Samples are taken for mechanical testing.

The data of mechanical tests are presented in table. 2. As can be seen from the table. 1 and 2, steel that satisfies the claimed composition (smelting 2-6) with respect to both the well-known solution - the prototype, and steel, with the content of components that go beyond the stated limits (smelting 1.7), while saving manganese and silicon has higher rates by mechanical properties (yield strength and elongation).

Thus, the use of the proposed technical solution allows to reduce the cost of its production by reducing the content of manganese and silicon in steel, while ensuring the casting conditions at the continuous casting machine. This achieves an increase in the mechanical properties of steel, namely, the yield strength and elongation.

From this we can conclude that the task to which the technical solution is directed is fulfilled, while achieving the above technical result is achieved.

Claims (1)

Reinforcing steel containing carbon, manganese, silicon, nitrogen, vanadium and iron, characterized in that it contains components in the following ratio, wt.%:
carbon 0.30-0.37 manganese 0.80-1.10 silicon 0.17-0.37 nitrogen 0.016-0.020 vanadium 0.008-0.022 iron and hydrogen rest
while the ratio of vanadium / nitrogen is 0.25-2.4, and the ratio of nitrogen / hydrogen is not more than 30.