RU2362815C2 - Low-alloy steel and product implemented from it - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to ferrous metallurgy, particularly to manufacturing of steels, used for manufacturing of hot-rolled and cold-rolled sheets of high strength for manufacturing by method of cold deformation of high-loaded parts of automobiles, field engines, agricultural machinery, building structure. Steel contains carbon, manganese, silicon, copper, aluminium, phosphorus, calcium, boron, nitrogen, sulphur, chrome, nickel, titanium and iron, at following ratio of components, wt %; carbon 0.06 - 0.10, manganese 0.20 - 0.50, silicon 0.01 - 0.30, copper 0.01 - 0.30, aluminium 0.02 - 0.07, phosphorus 0.07 - 0.12, nitrogen 0.003 - 0.009, sulphur 0.005 - 0.025, calcium 0.0005 - 0.001, boron 0.0008 - 0.005, chrome 0.01 - 0.30, nickel 0.01 - 0.30, titanium 0.002 - 0.02, iron and unavoidable admixtures are the rest. Content of phosphorus, chrome, nickel, nitrogen and carbon is linked by correlation 5.0 ≥ (P + Cr + Ni) / (N + C) ≥ 1.0, content of silicon, chrome, nickel and copper by relation (Si + Cr) / (Ni + Cu) ≥ 0.5, and content of boron, titanium and sulphur by relation (B + Ti) / S ≥ 0.2.

EFFECT: it is increased static and fatigue strength after rolling and after welding, there are prevented superficial and inner defects, it is provided cold deformability.

2 cl, 2 tbl

Description

The invention relates to ferrous metallurgy, in particular to compositions of steels and to products made from them, and can be used in the manufacture of high strength sheet for the manufacture of cold deformation of highly loaded parts of automobiles, tractors, agricultural machinery, building structures.

The development of mechanical engineering places high demands on the technological and mechanical properties of a thin sheet of structural steels to reduce metal consumption and ensure the operational reliability of the finished product. It is especially important to increase the static and fatigue strength of critical products.

Known steel for the production of hot-rolled and cold-rolled sheet, containing, wt.%:

carbon 0.002-0.015;

manganese 0.10-0.35;

chrome 0.05-0.40;

titanium 0.02-0.15;

aluminum 0.01-0.06;

nitrogen <0.006;

sulfur <0.02;

oxygen <0.01;

iron and inevitable impurities - the rest, when the relation

Ti / (C + N) <0.8.

Steel may additionally contain silicon up to 0.1%, boron up to 0.0035%, rare-earth metals up to 0.05%.

(US patent No. 4331488, NKI 148/36, publ. 06/26/1982.)

The disadvantages of this steel.

Low aluminum content at the lower limit (0.01 wt.%), Not providing deoxidation and binding of nitrogen. The high titanium content at the upper limit (0.15 wt.%), Causing the formation of non-metallic inclusions and grinding of ferritic grains, which impairs ductility. Low strength at specified limits of carbon content (0.002-0.015 wt.%), Chromium (0.05-0.40 wt.%) And manganese (0.10-0.35 wt.%).

Known hot rolled strips with a thickness of 2.0 mm or more, cold rolled strips with a thickness of 0.5 mm or more, made of steel containing, wt.%:

carbon 0.02-0.07;

manganese 0.15-0.30;

copper 0.02-0.30;

aluminum 0.03-0.07;

boron 0.0005-0.005;

phosphorus 0.04-0.10;

nitrogen 0.001-0.007;

iron is the rest.

(RF patent No. 1741459, IPC C22C 38/16, published on November 10, 1995)

The disadvantages of this steel and products made from it.

The possibility of intense oxidation of aluminum and boron with insufficient protection at the lower limit of carbon (0.02 wt.%) And manganese (0.15 wt.%), And therefore - increased pollution by inclusions and reduced stampability.

The formation of a mixed-grained ferrite base when the content near the lower limit of carbon (0.02 wt.%), Manganese (0.15 wt.%) And phosphorus (0.04 wt.%) And the deterioration of the hood.

Low tensile strength with a phosphorus content of about 0.04 wt.%, Carbon 0.02 wt.% And nitrogen about 0.001 wt.%.

Weakened crack resistance and reduced hot ductility due to increased segregation heterogeneity when the content near the upper limit of phosphorus - 0.10 wt.%, Copper and manganese - up to 0.30 wt.% Each.

Known steel containing, wt.%:

carbon 0.02-0.08;

manganese 0.20-0.60;

silicon 0.005-0.10;

copper 0.01-0.10;

aluminum 0.02-0.07;

boron 0.001-0.005;

calcium 0.0005-0.01;

nitrogen 0.001-0.006;

vanadium 0.0005-0.0030;

niobium 0.0005-0.0030;

iron - the rest, while the total content of vanadium and niobium is ≤0.0055%.

(RF patent No. 2154123, IPC C22C 38/16, publ. 08/10/2000)

The disadvantages of this steel.

Reduced static and fatigue strength with compositions near the lower limit of carbon and nitrogen (respectively, 0.02 and 0.003 wt.% C and N).

The tendency to uneven grain growth and the formation of large ferrite grains at the lower limits of carbon, nitrogen, silicon and copper (respectively 0.02 wt.% C; 0.001 wt.% N; 0.005 wt.% Si; 0.01 wt.% Cu) causing a defect in rough roughness of the metal surface during stamping (“orange peel”).

Reduced crack resistance during deformation and welding in the case of boron content near the upper limit (0.005 wt.%) Due to deterioration of ductility during the formation of inclusions of oxides and boron carbonitrides.

The closest analogue of the present invention are products made of low alloy steel containing the following components, wt.%:

carbon 0.05-0.09;

manganese 0.25-0.40;

silicon 0.01-0.10;

copper 0.01-0.50;

aluminum 0.02-0.07;

phosphorus 0.07-0.12;

calcium 0.0005-0.001;

boron 0.0008-0.005;

nitrogen 0.003-0.007;

sulfur 0.005-0.025;

iron and inevitable impurities - the rest, while the contents of phosphorus, carbon and manganese, as well as sulfur and manganese are related by mathematical dependencies.

Hot-rolled strips 2-15 mm thick and a cold-rolled sheet or strip 0.5-3.0 mm thick are made of steel.

(RF patent No. 2212469, IPC С22С 38/16, publ. September 20, 2003 - prototype.)

The disadvantages of this steel and products made from it.

The possibility of the formation of hot cracks and defects such as “captivity”, “delamination” due to segregation heterogeneity with copper content at the upper limit (0.50 wt.%).

The inconsistent content at the upper limit of carbon is 0.09 wt.%, Nitrogen is 0.07 wt.% And phosphorus is 0.12 wt.%, Which can cause embrittlement during deformation and welding.

The possibility of intensive oxidation of boron and its reduction by inclusions of fatigue resistance, with boron content up to 0.005 wt.%, Without special protection with an additional deoxidizer.

The problem solved by the present invention is to obtain a thin hot-rolled and cold-rolled sheet of structural low alloy steel with high strength, weldability and stampability, designed for critical products, in particular bearing parts of the body, wheels, car lining.

The technical result of the invention is to increase the static and fatigue strength of the metal after rolling and after welding, to prevent surface and internal defects, to ensure cold deformation by stamping with complex drawing, cutting, bending.

This is achieved by the fact that the low-alloy steel product according to the invention is made in the form of a cold-rolled sheet or strip 0.15-3.0 mm thick from steel containing carbon, manganese, silicon, copper, aluminum, phosphorus, calcium, boron, nitrogen, sulfur , chromium, nickel, titanium and iron in the following ratio of components, wt.%:

carbon 0.06-0.10;

manganese 0.20-0.50;

silicon 0.01-0.30;

copper 0.01-0.30;

aluminum 0.02-0.07;

phosphorus 0.07-0.12;

nitrogen 0.003-0.009;

sulfur 0.005-0.025;

calcium 0.0005-0.001;

boron 0.0008-0.005;

chromium 0.01-0.30;

nickel 0.01-0.30;

titanium 0.002-0.02;

iron and unavoidable impurities - the rest, while the content of phosphorus, chromium, nickel, nitrogen and carbon is connected by the dependence 5.0≥ (P + Cr + Ni) / (N + C) ≥1.0; the content of silicon, chromium, nickel and copper is expressed by the dependence (Si + Cr) / (Ni + Cu) ≥0.5, and the content of boron, titanium and sulfur is determined by the ratio (B + Ti) / S≥0.2, and also that the product of low alloy steel according to the invention is made in the form of a hot rolled strip from 2.0 to 15.0 mm thick from steel containing carbon, manganese, silicon, copper, aluminum, phosphorus, calcium, boron, nitrogen, sulfur, chromium, nickel , titanium and iron in the following ratio of components, wt.%:

carbon 0.06-0.10;

manganese 0.20-0.50;

silicon 0.01-0.30;

copper 0.01-0.30;

aluminum 0.02-0.07;

phosphorus 0.07-0.12;

nitrogen 0.003-0.009;

sulfur 0.005-0.025;

calcium 0.0005-0.001;

boron 0.0008-0.005;

chromium 0.01-0.30;

nickel 0.01-0.30;

titanium 0.002-0.02;

iron and unavoidable impurities - the rest, while the content of phosphorus, chromium, nickel, nitrogen and carbon is connected by the dependence 5.0≥ (P + Cr + Ni) / (N + C) ≥1.0; the content of silicon, chromium, nickel and copper is expressed by the dependence (Si + Cr) / (Ni + Cu) ≥0.5, and the content of boron, titanium and sulfur is determined by the ratio (B + Ti) / S≥0.2

To harden steel, alloying is used with components that increase the hardness and strength of ferrite and grind its grain - phosphorus, manganese, silicon, chromium, together with its microalloying with components that create hardening of ferrite by the formation of dispersed precipitates of additional phases (carbides, carbonitrides, sulfocarbonitrides, etc. ), - carbon, nitrogen, aluminum, chromium, boron, sulfur. The lower limits of the content of phosphorus, manganese, silicon for hardening alloying are, respectively, wt.%: Phosphorus 0.07, manganese 0.20, silicon 0.01, the upper limits of the content of phosphorus, manganese, silicon to limit segregation heterogeneity and preserve stampability are wt.%: 0.12 phosphorus, 0.50 manganese, 0.30 silicon. The lower limits of the content of carbon, nitrogen, aluminum, chromium, boron, sulfur for microalloying and hardening became dispersed precipitates, respectively, wt.%: Carbon 0.06, nitrogen 0.003, aluminum 0.02, chromium 0.01, boron 0.0008 , sulfur 0.005, the upper limits of the content of the same elements to prevent an increase in the number and size of precipitated inclusions (carbides, carbonitrides, sulfocarboborides), causing a decrease in ductility and a deterioration in surface quality due to defects of “scale”, “captivity”, microcracks oxidized, large rough st equal, wt.%: carbon 0.10, N 0.009, aluminum 0.07, chromium 0.30 boron 0.005, 0.025 sulfur. Plasticity for deformation is also ensured by the complex use for the deoxidation of components - calcium, aluminum, silicon, and for desulfurization - components - titanium, manganese. For grinding of inclusions of oxides and their spheroidization, the lower limits of the content of calcium, aluminum, silicon are, wt.%: Calcium 0.0005, aluminum 0.02, silicon 0.01, to prevent the formation of complex multiphase inclusions (type FeО · Аl ₂ О ₃ ; Si ₂ O · Al ₂ O ₃ ; CaO · Al ₂ O ₃ ) the upper limits of the content of calcium, aluminum, silicon are, wt.%: Calcium 0.001, aluminum 0.07, silicon 0.30.

In addition, the improvement of strength and stampability, including after welding, is facilitated by an improvement in surface quality as a result of easier descaling when the content of phosphorus and boron in the steel is within the selected limits: P = 0.07-0.12 wt.%, B = 0.0008-0.005 wt.%, As well as an increase in oxidation resistance with copper additives. To protect against oxidation, the lower limit of these components is, wt.%: Copper 0.01, chromium 0.01, nickel 0.01, titanium 0.002. To maintain ductility, the upper limit for copper is 0.30 wt.%, For chromium 0.30 wt.%, For nickel 0.30 wt.%, For titanium 0.02 wt.%. Within the specified limits, copper, boron and titanium also prevent the segregation of carbon, phosphorus and sulfur along the boundaries of ferritic grains, which is harmful to strength and ductility.

To ensure the required properties, steel contains effective elements in quantities that allow their separate and joint influence. In this case, it is necessary that these elements, taken together, be within controlled quantitative limits. So, for solid solution, granular and dispersion hardening of ferrite, alloying substitution elements (phosphorus, chromium, nickel) and interstitial elements (carbon, nitrogen) are used. But to maintain ductility and stampability, it is necessary to limit the content of carbon and nitrogen, which contribute to the formation of carbide and carbonitride precipitates. This is expressed by the relation 5.0≥ (P + Cr + Ni) / (N + C) ≥1.0.

Scale resistance is enhanced by elements - silicon, chromium, nickel, copper. But with an increase in their content, contamination with non-metallic inclusions can increase, stiffness, embrittlement, and manufacturability worsen. Therefore, the dependence (Si + Cr) / (Ni + Cu) ≥0.5 is proposed. To increase weldability, fracture toughness, and viscosity, intensive desulfurization and refining (without deterioration of alloying) with a content of (B + Ti) / S≥0.2 are proposed.

An example of a specific implementation.

The steels of the proposed composition (table 1) were poured onto continuously cast billets, the resulting slabs were rolled into hot rolled strips (3.2 mm thick), butt welded, etched, rolled into cold rolled strips (1.0 mm thick), annealed and trained. The tensile mechanical properties (yield strength σ _t , tensile strength σ _B , relative yield strength σ _t / σ _B , elongation δ ₄ , plastic anisotropy coefficient R, hardening index n), and fatigue strength (endurance σ _R ) were determined. The obtained values for the finished metal were compared (the middle of the strip and the butt welding zone). The properties of the hot rolled strip and cold rolled sheet of low alloy steel of the proposed composition in the delivery state are shown in table 2.

On the surface and inside the strips there are no defects of metallurgical origin. From hot-rolled and cold-rolled steel, parts of the car body were cut and stamped. All products have passed field tests. There are no technological defects. The above data show that the products of new steel of the proposed composition in the hot-rolled and cold-rolled state have a high set of characteristics of static and fatigue strength in the state after rolling and after welding. This confirms the receipt of the claimed technical result of the invention.

Claims (2)

1. The product of low alloy steel, made in the form of a cold-rolled sheet or tape, characterized in that it is made of a thickness of 0.15-3.0 mm from steel containing carbon, manganese, silicon, copper, aluminum, phosphorus, calcium, boron, nitrogen, sulfur, chromium, nickel, titanium and iron in the following ratio of components, wt.%:
carbon 0.06-0.10 manganese 0.20-0.50 silicon 0.01-0.30 copper 0.01-0.30 aluminum 0.02-0.07 phosphorus 0.07-0.12 nitrogen 0.003-0.009 sulfur 0.005-0.025 calcium 0.0005-0.001 boron 0.0008-0.005 chromium 0.01-0.30 nickel 0.01-0.30 titanium 0.002-0.02 iron and inevitable impurities rest,
the content of phosphorus, chromium, nickel, nitrogen and carbon is related by the dependence 5.0≥ (P + Cr + Ni) / (N + C) ≥1.0, the content of silicon, chromium, nickel and copper by the dependence (Si + Cr ) / (Ni + Cu) ≥0.5, and the content of boron, titanium and sulfur - by the dependence (B + Ti) / S≥0.2. 2. A low-alloy steel product made in the form of a hot-rolled strip, characterized in that it is made of a thickness of more than 2.0 to 15.0 mm from steel containing carbon, manganese, silicon, copper, aluminum, phosphorus, calcium, boron, nitrogen, sulfur, chromium, nickel, titanium and iron, in the following ratio of components, wt.%:
carbon 0.06-0.10 manganese 0.20-0.50 silicon 0.01-0.30 copper 0.01-0.30 aluminum 0.02-0.07 phosphorus 0.07-0.12 nitrogen 0.003-0.009 sulfur 0.005-0.025 calcium 0.0005-0.001 boron 0.0008-0.005 chromium 0.01-0.30 nickel 0.01-0.30 titanium 0.002-0.02 iron and inevitable impurities rest,
the content of phosphorus, chromium, nickel, nitrogen and carbon is related by the dependence 5.0≥ (P + Cr + Ni) / (N + C) ≥1.0, the content of silicon, chromium, nickel and copper by the dependence (Si + Cr ) / (Ni + Cu) ≥0.5, and the content of boron, titanium and sulfur - by the dependence (B + Ti) / S≥0.2.