RU2243287C1 - Steel - Google Patents

Abstract

FIELD: metallurgy, in particular steel composition.

SUBSTANCE: invention relates to steel for cold-rolled strips, bands and sheets to produce products by deep drawing. Claimed steel contains (mass %): carbon 0.001-0.012; silicium 0.01-0.04; manganese 0.08-0.15; chromium 0.01-0.03; nickel 0.01-0.03; copper approximately 0.01; aluminium 0.01-0.06; nitrogen 0.002-0.007; titanium 0.01-0.04; niobium 0.025-0.055; sulfur <=0.015; phosphorus <=0.015; vanadium <=0.008; boron <=0.0007; molybdenum <=0.005; and balance: iron.

EFFECT: increased recovery of strips, bands and sheets.

3 tbl

Description

The invention relates to metallurgy, and in particular to compositions of steels used for the production of cold rolled strips, tapes and sheets intended for the manufacture of products by deep drawing.

Cold-rolled steel strips, tapes and sheets used for manufacturing products by deep drawing should have the following set of mechanical properties (Table 1):

In addition to the indicated mechanical properties, cold-rolled steel should not have defects of metallurgical origin in the form of captives and large non-metallic inclusions, the presence of which increases the rejection of cold-rolled strips, tapes and sheets.

Known steel for the manufacture of cold rolled sheets of the following chemical composition, wt.%:

Carbon 0.020

Silicon 0.1-2.2

Manganese less than 2.5

Titanium 0.1-0.5

Aluminum 0.01-0.1

Nitrogen less than 0.010

Iron Else

while the content in the steel of silicon, manganese and titanium should satisfy the ratios:

1.9 (Si) + 0.9 (Mn) ≥1; (Mn)> 0.5 (Si); (Ti) / {(C) + (N)} ≥1 [1].

A disadvantage of the known steel is low ductility and poor stampability of cold-rolled strips and sheets. In the manufacture of sheets, a large amount of metal is sorted by defects of “captivity” and “non-metallic inclusions”.

Steel is also known for the manufacture of cold rolled sheets for deep drawing, containing, wt.%:

Carbon 0.001-0.05

Silicon 0.11-0.40

Manganese 0.51-1.20

Chrome 2.0-5.0

Nickel 0.1-0.3

Copper 0.20-0.50

Titanium 0.03-0.15

Aluminum 0.08-0.20

Nitrogen 0.006-0.015

Boron 0.0003-0.003

Iron Else [2].

Cold rolled sheets made of steel of known composition have low exhaust properties and are affected by defects of metallurgical origin. In addition, the known steel does not contain impurities of sulfur and phosphorus inevitably present in industrially produced steels. Deep removal of these impurities significantly increases the cost of steel.

The closest in its chemical composition and properties to the proposed one is the following steel for the manufacture of cold-rolled strips, tapes and sheets, containing, wt.%:

Carbon Less than 0.05

Silicon Less than 0.10

Manganese Less than 1.0

Chrome 1.8-3.0

Nickel 0.10-0.50

Copper 0.10-0.50

Aluminum 0.06-0.15

Sulfur Less than 0.05

Phosphorus Less than 0.05

Nitrogen Less than 0.02

Titanium, zirconium,

niobium, vanadium More (C) + (N)

Iron The rest [3] is a prototype.

The disadvantages of the known steel are that cold-rolled strips, tapes and sheets made on its basis have a low ability to deep draw and are affected by defects in the form of captives and large non-metallic inclusions. In addition, the presence of boron and molybdenum in the form of impurity elements in steel is unacceptable. All this leads to a decrease in the yield of strips, tapes and sheets.

The technical problem solved by the invention is to increase the yield of strips, tapes and sheets.

The stated technical problem is solved in that the steel containing carbon, silicon, manganese, chromium, nickel, copper, aluminum, nitrogen, titanium, niobium, sulfur, phosphorus, vanadium and iron, additionally contains boron and molybdenum in the following ratio of components, wt. %:

Carbon 0.001-0.012

Silicon 0.01-0.04

Manganese 0.08-0.15

Chrome 0.01-0.03

Nickel 0.01-0.03

Copper 0.01-0.03

Aluminum 0.01-0.06

Nitrogen 0.003-0.007

Titanium 0.01-0.04

Niobium 0.025-0.055

Sulfur Not more than 0.015

Phosphorus Not more than 0.015

Vanadium Not more than 0.008

Bor Not more than 0,0007

Molybdenum Not more than 0.005

Iron Else

Carbon in steel is a reinforcing element. With a decrease in carbon concentration of less than 0.001%, the strength properties of cold-rolled steel are insufficient. An increase in carbon concentration in excess of 0.012% reduces its exhaust properties.

Silicon is introduced into steel for deoxidation and hardening of steel. When the silicon concentration is less than 0.01%, the steel remains oxidized, the mechanical properties of cold-rolled sheets deteriorate. An increase in its concentration of more than 0.04% reduces the plastic properties.

Manganese deoxidizes steel, provides the required combination of strength and ductility. With a manganese content of less than 0.08%, the steel is not sufficiently deoxidized and strong. An increase in its content in excess of 0.15% overly strengthens the steel, reduces its ductility.

Chrome, nickel and copper increase the strength of steel. A decrease in the content of chromium, nickel or copper less than 0.01% is unprofitable, because limits the use in the smelting of scrap metal. An increase in the content of chromium, nickel and copper in excess of 0.03% impairs the ability of cold-rolled sheets to deep drawing.

Aluminum stabilizes steel and prevents its aging. A decrease in the aluminum content of less than 0.01% intensifies the degradation of the properties of cold-rolled steel, and an increase in its content of more than 0.06% leads to a decrease in the coefficient of normal plastic anisotropy and a decrease in the yield.

Nitrogen, forming nitrides of aluminum and titanium, strengthens steel. An increase in nitrogen content in excess of 0.007% affects the properties of steel and reduces the yield of cold-rolled sheets. A decrease in nitrogen content of less than 0.003% is impractical because significantly increases its production without a noticeable improvement in properties.

Titanium strengthens steel, provides an increase in the strain hardening index, and improves the drawing properties. A decrease in titanium content of less than 0.01% reduces the punchability indices of R ₉₀ and n ₉₀ , the strength properties of steel, and cause their instability. With an increase in the titanium content of more than 0.04%, although the exhaust properties improve, the number of captives and nonmetallic inclusions in steel increases, due to which the yield of cold-rolled sheets decreases sharply.

Niobium in this steel replaces the lack of titanium and reduces the possibility of the formation of captives and non-metallic inclusions. When the niobium content is less than 0.025%, the ability of the steel to deep drawing is deteriorating. An increase in the niobium content of more than 0.055% leads to an increase in the strength and ductility of cold-rolled steel, and a decrease in the yield.

Sulfur and phosphorus in this steel are impurity elements, the concentration of which should be limited so as not to impair the properties. Deep cleaning of steel from these impurities leads to a significant increase in its cost. When the content of sulfur or phosphorus is more than 0.015%, the quality of cold-rolled strips, tapes and sheets deteriorates, which leads to a decrease in yield. At lower sulfur and phosphorus contents, the steel of the proposed composition neutralizes their harmful effect due to the optimal concentration of the remaining elements. This eliminates the need for a deep degree of desulfurization and dephosphorization, reduces the cost of steel production.

Boron modifies steel, improving the complex of its properties. But at a boron concentration in excess of 0.0007%, the number of non-metallic inclusions increases, and the yield decreases.

Molybdenum favorably affects the exhaust properties of cold rolled steel. An increase in its concentration in excess of 0.005% leads to hardening of steel and increases the cost of alloying materials.

Steel is smelted in an electric arc furnace from pig iron. Ferrosilicon, ferromanganese, ferrotitanium, ferroboron, ferrovanadium, metallic aluminum, molybdenum, and niobium are introduced into the steel in the tundish. The amount of chromium, nickel and copper is regulated by their content in the scrap mixture. The concentration of sulfur and phosphorus is reduced to acceptable values in the process of desulfurization and dephosphorization of the melt. The nitrogen concentration to predetermined limits is reduced during the evacuation of the melt.

The finished steel is poured into slabs with a thickness of 250 mm, heated and rolled on a semi-continuous broadband mill 1700 into strips of 3 × 1400 mm section. Then the strip is subjected to etching and cold rolling on a 5-stand mill 1700 to a thickness of 0.7 mm Cold-rolled strips are annealed and trained with a compression of 0.8%, after which the mechanical properties are tested and the substandard metal is screened for captivity and non-metallic inclusions.

Table 2 shows the chemical compositions of the steels used for the production of cold-rolled strips, tapes and sheets intended for the manufacture of products by deep drawing, and in table 3 - mechanical properties and yield.

From table 3 it follows that the steel of the proposed chemical composition (compositions No. 2-4) provides the best quality cold-rolled sheet steel according to all regulated indicators and the highest yield. With prohibitive values of the declared parameters (options No. 1 and No. 5), the mechanical properties of cold-rolled sheet steel deteriorate, and the yield decreases. Also, unsatisfactory properties and yield have cold rolled steel sheets of the prototype (option No. 6).

The technical and economic advantages of the steel of the proposed composition are that due to the optimization of the concentration of alloying elements in it, the required combination of mechanical properties is achieved even with fluctuations in the technological modes of production of cold-rolled sheet steel inevitable in real production processes. Due to this, the yield is increased. In addition, the proposed steel allows the presence of impurities in it of sulfur, phosphorus, non-ferrous metals, vanadium, boron and molybdenum in amounts achieved in normal melting conditions in an oxygen converter using scrap metal. The elimination of the need for deep desulfurization and dephosphorization, as well as the use of high-purity charge materials significantly reduces the cost of steel production.

The prototype steel was adopted as the base object. The use of steel of the proposed composition will increase the profitability of the production of cold-rolled strips, tapes and sheets for the manufacture of parts by deep drawing by 25-30%.

Sources of information

1. US patent No. 4571367, NKI 428/653, 1986

2. Auth. testimonial. USSR No. 1749308, IPC C 22 C3 8/54, 1992

3. Japanese application No. 63-18043, IPC C 22 C3 8/00, 1988 - prototype.

Claims (1)

Steel containing carbon, silicon, manganese, chromium, nickel, copper, aluminum, nitrogen, titanium, niobium, sulfur, phosphorus, vanadium and iron, characterized in that it additionally contains boron and molybdenum with the following components, wt.%: Carbon 0.001-0.012 Silicon 0.01-0.04 Manganese 0.08-0.15 Chrome 0.01-0.03 Nickel 0.01-0.03 Copper 0.01-0.03 Aluminum 0.01-0.06 Nitrogen 0.003-0.007 Titanium 0.01-0.04 Niobium 0.025-0.055 Sulfur Not more than 0.015 Phosphorus Not more than 0.015 Vanadium Not more than 0.008 Bor Not more than 0,0007 Molybdenum Not more than 0.005 Iron Else