RU2558790C1 - Low alloy structural steel - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to metallurgy, namely to low alloy structural steel intended for the manufacture of metal structures. The steel contains, wt %: carbon 0.14-0.16, manganese 0.25-0.29, silicon 0.17-0.22, nitrogen 0.009-0.014, aluminium 0.029-0.043, iron and hydrogen- the rest. The ratio of aluminium/nitrogen amounts to 2.5-3.5, and the ratio of nitrogen/hydrogen amounts to no more than 30.

EFFECT: improvement of mechanical properties of steel.

2 tbl, 1 ex

Description

The present invention relates to metallurgy, in particular to economically alloyed structural steel, intended primarily for the manufacture of metal structures.

The closest to the proposed technical solution in terms of technical nature and the achieved result (prototype), according to the authors, is steel intended for the manufacture of steel structures of 3sp grade according to GOST 380-2005, containing, wt.%: 0.14 ÷ 0.20 C ; 0.40 ÷ 0.55 Mn, 0.15 ÷ 0.30 Si, 0.025 ÷ 0.05 Al; not more than 0.008 N; the rest is iron.

A disadvantage of the known technical solution is the high cost of steel production due to its increased content of manganese and silicon while maintaining high mechanical properties.

The task to which the technical solution is directed is to reduce the cost of steel production by reducing the content of manganese in it. This achieves the achievement of such a technical result as an increase in the mechanical properties of steel, namely impact strength and elongation.

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

carbon 0.14 ÷ 0.16 manganese 0.25 ÷ 0.29 silicon 0.17 ÷ 0.22 nitrogen 0.009 ÷ 0.014 aluminum 0,029 ÷ 0,043 iron and hydrogen rest

while the ratio of aluminum / nitrogen in the range of 2.5 ÷ 3.5 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 economically alloyed structural steel contains carbon, manganese, silicon, nitrogen, aluminum and iron, in the following ratio of components, wt.%:

carbon 0.14 ÷ 0.16 manganese 0.25 ÷ 0.29 silicon 0.17 ÷ 0.22 nitrogen 0.009 ÷ 0.014 aluminum 0,029 ÷ 0,043 iron and hydrogen rest

the ratio of aluminum / nitrogen in the range of 2.5 ÷ 3.5 and the ratio of nitrogen / hydrogen is not more than 30. Thus, 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 have shown higher rates in mechanical properties (impact 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 structural steel form its structure and, being in a complex relationship, provide a high level of mechanical properties.

When the carbon content is less than 0.14 wt.%, The steel is not sufficiently deoxidized, it contains an increased amount of oxygen and oxide inclusions.

When the carbon content is more than 0.16 wt.%, The ductility of the steel deteriorates and the damage to the cast product by hot cracks increases.

When the manganese content is less than 0.25 wt.%, The steel will have reduced strength characteristics due to the presence of an increased amount of sulfur inclusions.

When the manganese content is more than 0.29 wt.%, It is overused, which leads to an increase in the cost of steel production, while there is no noticeable improvement in the mechanical properties of steel.

When the silicon content is less than 0.17 wt.%, The steel will have a high content of oxide non-metallic inclusions.

When the silicon content is more than 0.22 wt.%, Silicon ferroalloys are overused without a noticeable improvement in the mechanical properties of steel.

When the nitrogen content is less than 0.009 wt.% The amount of the metal hardening nitride phase will be insufficient and, accordingly, the strength properties of the metal will be reduced.

If the nitrogen content is more than 0.014 wt.%, Gas bubbles will form in the cast metal, which during rolling and / or forging can lead to marriage through cracks and flaws.

When the aluminum content is less than 0.029 wt.%, The amount of aluminum nitrides that increase the strength of the metal will be insufficient to achieve the required strength properties.

When the aluminum content is more than 0.043 wt.% During metal casting, steel-conducting refractory wires and castings will be contaminated with refractory inclusions based on aluminum oxide, which is unacceptable.

The introduction of a nitride-forming element, for example aluminum together with nitrogen, provides the formation of nitrides, grinding the metal structure, and increase its strength characteristics.

When the ratio of aluminum to nitrogen is less than 2.5, the amount of aluminum nitrides hardening the metal will not be enough to achieve the required strength.

If the ratio of aluminum to nitrogen is more than 3.5, the metal will be contaminated with an excessive amount of inclusions based on aluminum oxide, which is unacceptable.

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 brittleness, will be hit 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.

The following are embodiments and uses of the invention that do not exclude other options within the scope of the claims (Tables 1 and 2).

Example

Metal swimming trunks (table. 1) receive as follows. An intermediate product (iron-carbon melt) is smelted in a steel-smelting unit (converter, electric furnace), which is released into a steel ladle. Before releasing the melt, a part of the ferroalloys containing silicon and manganese, slag-forming and granular aluminum are seated at the bottom of the steel ladle. The melt in the steel ladle is mixed with argon, a sample is taken for chemical analysis, and, if necessary, additives are added that correct the chemical composition of the metal and a flux-cored wire with urea filler. After that, the metal in the ladle is again mixed with argon, a sample is taken, the steel temperature, hydrogen content are measured and cast.

As can be seen from the table. 1, steel that satisfies the claimed composition (smelting 2-6) with respect to both the well-known solution of the prototype, and steel with the content of components beyond the stated limits (smelting 1, 7), while saving manganese has higher mechanical properties (impact viscosity and elongation).

Thus, the use of the proposed technical solution allows by reducing the content of manganese in steel (manganese-containing ferroalloys) to reduce the cost of its production. This achieves an increase in the mechanical properties of steel, namely impact 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)

Economically alloyed structural steel containing carbon, manganese, silicon, nitrogen, aluminum and iron, characterized in that it contains components in the following ratio, wt.%:
carbon 0.14 ÷ 0.16 manganese 0.25 ÷ 0.29 silicon 0.17 ÷ 0.22 nitrogen 0.009 ÷ 0.014 aluminum 0,029 ÷ 0,043 iron and hydrogen rest
the ratio of aluminum / nitrogen is 2.5 ÷ 3.5, and the ratio of nitrogen / hydrogen is not more than 30.