Steel

 

(57) Abstract:

The invention relates to metallurgy, and in particular to compositions of steels for pipelines and gas pipelines. The proposed steel that contains components in the following ratio, wt. %: carbon 0.05 to 0.15, silicon 0,30-0,90, manganese 0.40 to-0,90, vanadium 0,05-0,20, niobium 0,01-0,08, aluminum 0,01-0,08, sulfur 0,001-0,020, phosphorus 0,005-0,02, Titan of 0.001 to 0.04, iron - rest. The technical result of the invention is to improve the corrosion resistance and toughness of steel. 3 table.

The invention relates to metallurgy, and in particular to compositions of steels for pipelines and gas pipelines.

The steel used in the manufacture of pipes for main pipelines, must combine high mechanical and corrosion properties. Technical agreement TC-105-21-98 regulates the following set of properties (table. 1).

Known steel [1] , having the following chemical composition, wt. %:

Carbon - 0,06-0,10

Silicon - 0,17-0,37

Manganese - 1,0-1,6

Molybdenum - 0,3-0,5

Vanadium - 0,05-0,1

Aluminum - 0,02-0,05

Cerium - 0,0005-0,005

Calcium - 0,0005-0,005

Iron - Rest

The disadvantage of steel is the known structural steel of the following chemical composition, wt. % [2] :

Carbon - 0,15-0,35

Silicon - 0,15-1,0

Manganese - 0,4-1,5

Vanadium - 0,04-0,18

Niobium - 0,008-0,1

Aluminum - 0,02-0,15

REM - 0,002-0,2

Iron - Rest

Known structural steel for corrosion resistance and toughness does not meet the requirements of steels for pipelines and gas pipelines.

Most similar in their chemical composition and properties to the proposed steel is steel [3] containing, by weight. %:

Carbon - 0,08-0,16

Silicon - 0,17-0,37

Manganese - 1,40-1,70

Vanadium - 0,06-0,12

Niobium - 0,06-0,12

Aluminum - 0,015-0.04

Sulfur - 0,015-0,035

Phosphorus - 0,010-0,030

Bor - 0,0008-0,004

Cerium - 0,005-0,01

Iron - Rest (prototype)

Known steel has a low corrosion resistance and toughness.

The technical problem solved by the invention is to improve the corrosion resistance and toughness of steel.

To solve this technical problem, the steel containing carbon, silicon, manganese, vanadium, niobium, aluminum, sulfur, phosphorus and iron, additionally contains titanium in the following ratio, wt. %:

Carbon - 0,05-0,15

Silicon ->/BR>Phosphorus - 0,005-0,02

Titanium is 0.001-0.04

Iron - Rest

Mapping of known composition became adopted as a prototype [3] , and proposed shows that the content of carbon, silicon, vanadium, niobium, aluminum, sulfur and phosphorus fully or partially overlapping. The proposed steel further comprises 0.001 to 0.04% of titanium and a smaller amount of manganese. Due to this enhanced corrosion resistance and impact toughness of the steel.

The carbon steel of the proposed structure determines its strength. The lower carbon content of less than 0.05% causes a reduction in strength below acceptable levels. The increase of carbon content in excess of 0.15% deteriorates the ductility and toughness of steel.

Silicon rascism and strengthens steel, improves its elastic properties. The deoxidation of steel silicon flows through the reaction:

2FeO + Si ---> 2Fe + SiO2.

When the silicon content less than 0.3% strength become insufficient. The increase in silicon content higher than 0.9% leads to an increase in the number of silicate inclusions, abruptive steel, impairs its plasticity.

Manganese entered for deoxidation and increase the strength of steel. Rascislau action is no place decrease of the strength and viscosity properties. The increase in the content of this element more than 0.90% deteriorates the ductility of the steel to5< 24% , which is unacceptable.

Vanadium is carbidopa element in the steel. Crushing the grain, it improves weldability, strength and toughness of steel. When the vanadium content less than 0.05% of its positive effect is not manifested. The increase in the content of vanadium is more than 0.20% were found to be inappropriate, because it does not lead to the improvement of the properties of steel.

Niobium is an effective caridovascular, grinding grain microstructure. When the content of niobium, less than 0.01% of the toughness of steel is below acceptable. The increase in the content of niobium more than 0.08% leads to its selection on the grain boundaries in the form of intermetallic compounds. This impairs the properties of the steel.

Aluminum is rescission and the modifying element. In addition, it binds to nitrogen in the nitride. When the aluminum content less than 0.01% of its influence slowly, the steel has a low mechanical properties. Increasing the aluminum content more than 0.08% causes graphitization of steel, the loss of strength and deterioration of weldability.

Sulfur present in the steel, forming sulfides of manganese. When the content of the series is riodic to increase the threshold jednoralski. The increase in the sulphur content of more than 0.02% affects viscosity, strength and plastic properties of steel below an acceptable level, especially in the direction across the direction of rolling of the strip.

Phosphorus in the amount of 0.005-0.02% of the whole dissolves into-the gland that leads to hardening of the metal matrix, the improvement of corrosion resistance of steel. However, the increase in the content of phosphorus more than 0.02% causes embrittlement of steel and the decrease in toughness, which is unacceptable. Reducing the phosphorus content of less than 0,005%, first, impairs corrosion resistance of steel and, secondly, it is not economically feasible.

Introduction in this steel titanium increased its corrosion resistance and toughness. When the titanium content less than 0.001% deteriorates corrosion resistance: the rate of General corrosion of steel Q > 0.8 mm/year, CLR > 4, CTP > 6. The increase in the titanium content in excess of 0.10% deteriorates the complex mechanical properties of steel leads to the formation of sub-cortical porosity at the surface of the ingot and the decline in the quality of hot-rolled strips.

In table. 2 shows the chemical composition of steels with different alloying elements, and table. 3 - the results of the tests with the higher corrosion resistance and toughness steel suitable for the manufacture of pipes, pipelines and gas pipelines. In cases beyond the contents of the alloying elements (compositions No. 1 and No. 5) corrosion resistance and toughness are reduced. Lower corrosion resistance and toughness has steel-prototype (composition No. 6).

Technical appraisal and economic benefits the proposed steel lies in the fact that the additional introduction in its composition of 0.001 to 0.04% titanium regulated when the content of the remaining elements ensures the formation of a favorable microstructure having high corrosion resistance and frictional properties at a regulated combination of strength and ductility. The proposed steel is also characterised by a good weldability. Therefore, it is suitable for the manufacture of oil and gas pipelines, term trouble-free operation of which will be increased.

As the base object is selected steel prototype. The use of the proposed steel will increase the profitability of production of electric-welded pipes by 10-15%.

Literature

1. The patent of Russian Federation N 2100470, IPC With 22 38/12, 1997

2. Auth. St. USSR N 753924, IPC With 22 38/12, 1980

vanadium, niobium, aluminum, sulfur, phosphorus and iron, characterized in that it additionally contains titanium in the following ratio, wt. %:

Carbon - 0,05 - 0,15

Silicon - 0,30 - 0,90

Manganese - 0,40 - 0,90

Vanadium - 0,05 - 0,20

Niobium - 0,01 - 0,08

Aluminum - 0,01 - 0,08

Sulfur is 0.001 - 0.020

Phosphorus - 0,005 - 0,02

Titanium is 0.001 - 0.04

Iron - Rest

 

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2 tbl, 1 ex

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