RU2330890C2 - Section iron hot-rolled made of microalloyed spring steel - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention concerns the metallurgy field. Particularly it concerns manufacturing of bundled rolled or bar metal of gage from 12 to 34 mm for producing gross heavy-loaded springs for various purposes. Rolled metal is obtained from steel, which consists in mass % of: C-(0.56-0.64), Mn-(0.40-0.70), Si-(1.40-1.80), Cr-(0.70-1.20), Ni-(0.005-0.25), V-(0.005-0.20), S-(0.005-0.025), N-(0.005-0.010), As-(0.0001-0.03, Sn-(0.0001-0.02), Pb-(0.0001-0.01), Zn-(0.0001-0.005), iron and inevitable admixtures, provided the implementation of ratio: (As+Sn+Pb+5×Zn)≤0.07; 1.12≤ [C+Si/4+Mn/6+(Cr+V)/5]≤1.50, performed as hot-rolled, hot-calibrated, tempered and drawn. Also it has ferrite-pearlite composition without graphite, martensite, bainite and widmanstatten pattern areas, where effective grain size is 6-12 points, decarbonisated layer depth is not more than 1.5% to the side, macrostructure is: center porosity, spot inhomogeneity, liquating square is not more than 3 points for every kind, undershrinked sweat is not more than 3 points, liquating strip is not more than 1 point, nonmetallic - spot sulphides, spot oxide, stitch oxide, fragile silicate, plastic silicate, unstrained silicate - not more than 2.5 points, average for every kind of impurities, tensile strength is not less than 1470 N/mm², yield strength is not less than 1425 N/mm², δ not less than 6%, ψ not less than 25%.

EFFECT: support of heightened level of consumer behavior.

4 cl, 3 ex

Description

The invention relates to the field of metallurgy, in particular to the production of hot-rolled, hot-rolled steel in coils or rods with a diameter of 12 to 34 mm for the production of large heavily loaded springs for various purposes.

Known hot-rolled bars of spring steel, having predetermined parameters of structure, non-metallic inclusions, macrostructure, mechanical properties, hardenability and elasticity (RU 2092257 C1, B21B 1/46, 10/10/1997).

The closest analogue to the claimed invention is the well-known long products, round, hot rolled, hot-calibrated from spring steel, hardened and tempered, having predetermined parameters of structure, macrostructure, non-metallic inclusions, mechanical properties (Reference. Modern materials in the automotive industry. M .: Mechanical Engineering, 1977, p. 101-107).

The most important requirement for hot-calibrated spring steel rolling is, on the one hand, ensuring the uniformity of the micro- and macrostructure, low content of non-metallic inclusions, on the other hand, ensuring an increased complex of consumer properties and a given morphology of non-metallic inclusions.

The objective of the invention is to provide a high level of consumer properties while ensuring a favorable ratio of strength, ductility, elasticity and viscosity, a minimum level of anisotropy of mechanical properties, low content of non-metallic inclusions, a homogeneous macro- and microstructure of rolled products.

The problem is solved in that the known long products from microalloy spring steel, hot-rolled, hot-calibrated, hardened and tempered, having predetermined structural parameters, non-metallic inclusions, mechanical properties, according to the invention is made of steel containing the following ratio of components in wt.%:

Carbon [C] 0.56-0.64 Manganese [Mn] 0.40-0.70 Silicon [Si] 1.40-1.80 Chrome [Cr] 0.70-1.20 Nickel [Ni] 0.005-0.25 Vanadium [V] 0.005-0.20 Sulfur [S] 0.005-0.025 Nitrogen [N] 0.005-0.010 Arsenic [As] 0.0001-0.03 Tin [Sn] 0.0001-0.02 Lead [Pb] 0.0001-0.01 Zinc [Zn] 0.0001-0.005 Iron and inevitable impurities  rest,

when the relations are satisfied: (As + Sn + Pb + 5 × Zn) ≤0.07; 1.12≤ [C + Si / 4 + Mn / 6 + (Cr + V) / 5] ≤ 1.50, has a ferrite-pearlite structure without graphite, martensite, bainite and vidmanstätt sites, the actual grain size is 6-12 points , the depth of the decarburized layer is not more than 1.5% per side, the macrostructure is the central porosity, point heterogeneity, segregation square - not more than 3 points for each species, shrinkable segregation - not more than 3 points; segregation strips - not more than 1 point, non-metallic inclusions - point sulfides, point oxides, stitch oxides, brittle silicates, plastic silicates, undeformed silicates - not more than 2.5 points, average for each type of inclusions, mechanical properties after quenching and tempering: temporary tensile strength not less than 1470 N / mm ² , yield strength not less than 1425 N / mm ² , elongation not less than 6%, relative narrowing not less than 25%.

As impurities, the steel additionally contains in wt.%: Phosphorus not more than 0.025; copper no more than 0.15.

When the content in steel in wt.%: Chromium 0.90-1.20, vanadium 0.10-0.20, rolling has mechanical properties: temporary tensile strength not less than 1670 N / mm ² , yield strength not less than 1470 N / mm ² , elongation of at least 6%, relative narrowing of at least 25%.

When the content in steel in wt.%: Chromium is 0.70-1.00, vanadium 0.005-0.10, the rolling has mechanical properties: temporary tensile strength not less than 1570 N / mm ² , yield strength not less than 1460 N / mm ² , elongation of at least 6%, relative narrowing of at least 25%.

The given combinations of alloying elements (item 1) make it possible to obtain a finely dispersed ferrite-pearlite structure, the optimal content and morphology of nonmetallic inclusions, a homogeneous macrostructure, and a favorable combination of strength, elasticity, and ductility characteristics.

Carbon is introduced into the composition of this steel in order to ensure a given level of its strength, elasticity and hardenability. The upper limit of the carbon content (0.64%) is due to the need to ensure the required level of toughness and elasticity of steel, and the lower limit, respectively 0.56%, to ensure the required level of strength and hardenability of this steel.

Manganese and chromium are used on the one hand as solid solution hardeners, and on the other hand as elements that increase the stability of supercooled steel austenite. At the same time, the upper level of manganese is 0.70%, chromium is 1.20% is determined by the need to ensure the required level of steel viscosity, and the lower is 0.40% and 0.70%, respectively, by the need to provide the required level of strength and hardenability and heat resistance of this steel .

Silicon refers to ferrite-forming elements. The lower limit for silicon - 1.40% due to the need to provide a given level of elasticity of steel. A silicon content above 1.80% will adversely affect the elasticity characteristics of the steel.

Nitrogen promotes the formation of nitrides in steel. The upper limit of nitrogen content is 0.010% due to the need to obtain a given level of ductility and toughness of steel, and the lower limit is 0.005% by issues of manufacturability.

Vanadium is introduced into the composition of this steel in order to provide a finely dispersed, uniform grain structure. Moreover, it controls the processes in the lower part of the austenitic region (determines the tendency of steel to grow austenite grains, stabilizes the structure during thermomechanical processing, increases the recrystallization temperature and, as a result, affects the nature of the γ-α transformation. The upper limit of the vanadium content is 0.20 %, due to the need to ensure the required level of ductility of steel, and the lower - respectively 0.005% - to ensure the required level of strength of this steel.

Nickel within the specified limits affects the characteristics of hardenability and toughness of steel. In this case, the lower level of nickel content - 0.005% is determined by the need to ensure a given level of steel viscosity, and the upper - 0.25% by the need to obtain a martensitic structure during hardening of steel (since nickel is an austenitizer).

Sulfur determines the level of ductility and machinability by cutting steel. The upper limit (0.025%) is due to the need to obtain a given level of ductility and toughness of steel, and the lower limit (0.005%) is due to issues of manufacturability.

Arsenic, tin, lead and zinc determine the overall level of ductility of steel and its tendency to manifest reversible temper brittleness during subsequent heat treatment of finished products. The lower limit for arsenic, tin, lead and zinc (0.0001% for each element, respectively) is determined by the technology of steel production, and the upper limit (0.03%, 0.02%, 0.01% and 0.005%, respectively) determines the increased the tendency of steel to reversible temper brittleness.

The ratio (As + Sn + Pb + 5 × Zn) ≤0.05 determines the reduced tendency of steel to manifest reversible temper embrittlement, and 1.12≤ [C + Si / 4 + Mn / 6 + (Cr + V) / 5] ≤ 1.50 ... determines the required hardenability of steel.

The analysis of patent and scientific and technical information did not reveal solutions having a similar set of features that would achieve a similar effect - providing an increased level of consumer properties while ensuring a favorable ratio of strength, ductility and viscosity, a minimum level of anisotropy of mechanical properties, low content of non-metallic inclusions, homogeneous macro - and microstructure rolled.

Examples of carrying out the invention, not excluding others in the scope of the claims. Smelting of the investigated steel, chemical composition in wt.%:

Example 1: carbon — 0.59, manganese — 0.65, silicon — 1.61, chromium — 0.99, nickel — 0.03; vanadium - 0.14; sulfur — 0.008, nitrogen — 0.007, arsenic — 0.007, tin — 0.009, lead — 0.006, zinc — 0.002;

Example 2: carbon — 0.58, manganese — 0.69, silicon — 1.55, chromium — 0.81, nickel — 0.05; vanadium - 0.01; sulfur — 0.009, nitrogen — 0.008, arsenic — 0.008, tin — 0.009, lead — 0.004, zinc — 0.001;

Example 3: carbon — 0.61, manganese — 0.59, silicon — 1.62, chromium — 0.85, nickel — 0.09; vanadium - 0.04; sulfur — 0.008, nitrogen — 0.008, arsenic — 0.007, tin — 0.007, lead — 0.004, zinc — 0.001; They are produced in 150-ton steel-arc furnaces using 100% metallized pellets in the charge, which ensures a low content of color impurities. The preliminary alloying of the metal with manganese and silicon is carried out in the ladle upon discharge from the particleboard. After the release, the metal was purged with argon through the bottom purge unit, during which the steel was deoxidized by aluminum. After that, the metal enters the integrated steel processing unit (AKOS), where it is possible to heat the metal to the required temperature, purge it with argon through the bottom blowing unit, dosed the necessary ferroalloys and treat the steel with flux-cored wire with various fillers. At AKOS, refining slag is induced with an additive of lime and fluorspar, heating to a temperature that ensures further processing. After processing at AKOS, the metal is subjected to vacuum treatment at a batch vacuum. During evacuation, a final adjustment of the chemical composition is made. The casting is carried out on radial four-strand UNRS in an ingot 300 × 360 mm in size with a drawing speed of 0.6 ÷ 0.7 m / min, with metal protection from oxidation by using cover slag mixtures in the intermediate ladle and mold, protective tubes, immersion glasses and argon feed. It also provides a low nitrogen and oxygen content and metal purity from non-metallic inclusions. After casting and cutting to a measured length, the continuously cast billets obtained were cooled in controlled cooling furnaces. Hot rolling of long products starts at a temperature of 900-950 ° C and ends at a temperature of 740-850 ° C with a deformation in the last passes of at least 20%. The final rolling operation is a hot calibration on the calibration block. To determine the level of mechanical properties of the billets, the heat treatment was carried out according to the following regime: hardening 870 ° С, oil, tempering 470 ° С, air.

As a result of hot rolling we get long products ⌀16 mm, length - 4800 mm, respectively, from steel according to:

Example 1: Ferrite-pearlite structure, lamellar perlite, real grain score - 7. Macrostructure: central porosity - 2 points, point heterogeneity - 1 point, segregation square - 1 point, shrink segregation - 2 points, segregation strips - 1 point. Non-metallic inclusions: point sulfides - 1 point, point oxides - 0.5 points, line oxides - 1 point, brittle silicates - 0.5 points, plastic silicates - 0.5 points, non-deforming silicates - 1 point. Tensile strength 1692 N / mm ² , yield strength 1498 N / mm ² , elongation of 7%, relative narrowing of 27%.

(As + Sn + Pb + 5 × Zn) = 0.032 [C + Si / 4 + Mn / 6 + (Cr + V) / 5] = 1.33

Example 2: Ferrite-pearlite structure, lamellar perlite, real grain score - 8. Macrostructure: central porosity - 1.5 points, point heterogeneity - 1.5 points, segregation square - 1 point, shrink segregation - 1.5 points, segregation strips - 0.5 points. Non-metallic inclusions: point sulfides - 0.5 points, point oxides - 0.5 points, line oxides - 0.5 points, brittle silicates - 1.0 points, plastic silicates - 0.5 points, non-deforming silicates - 1.0 point . Tensile strength 1501 N / mm ² , yield strength 1452 N / mm ² , elongation of 6.5%, relative narrowing of 27%.

As + Sn + Pb + 5 × Zn = 0.026 [C + Si / 4 + Mn / 6 + (Cr + V) / 5] = 1.25

Example 3: Ferrite-pearlite structure, lamellar perlite, real grain score - 7. Macrostructure: central porosity - 1.0 point, point heterogeneity - 1.0 point, segregation square - 1.5 points, shrink liquation - 1.0 point , liquidation strips - 1.0 point. Non-metallic inclusions: point sulfides - 1.5 points, point oxides - 0.5 points, line oxides - 0.5 points, brittle silicates - 1.5 points, plastic silicates - 0.5 points, non-deforming silicates - 1.5 points . Tensile strength not less than 1586 N / mm ² , yield strength not less than 1488 N / mm ² , elongation of 7%, relative narrowing of 26%.

(As + Sn + Pb + 5 × Zn) = 0.025 [C + Si / 4 + Mn / 6 + (Cr + V) / 5] = 1.29

The introduction of hot-rolled, hot-calibrated long products made of spring steel provides an increased level of consumer properties of the product with a favorable ratio of strength, ductility and toughness, a minimum level of anisotropy of mechanical properties, a low content of non-metallic inclusions, a homogeneous macro- and microstructure, and improved characteristics of machining by cutting.

Claims (4)

1. Long products made of micro-alloyed spring steel, hot-rolled, hot-calibrated, hardened and tempered, having the specified parameters of the structure, non-metallic inclusions, mechanical properties, characterized in that it is made of steel containing, wt.%: Carbon [C] 0.56-0.64 Manganese [Mn] 0.40-0.70 Silicon [Si] 1.40-1.80 Chrome [Cr] 0.70-1.20 Nickel [Ni] 0.005-0.25 Vanadium [V] 0.005-0.20 Sulfur [S] 0.005-0.025 Nitrogen [N] 0.005-0.010 Arsenic [As] 0.0001-0.03 Tin [Sn] 0.0001-0.02 Lead [Pb] 0.0001-0.01 Zinc [Zn] 0.0001-0.005 Iron and Inevitable impurities Rest, when fulfilling the relations: (As + Sn + Pb + 5 Zn) ≤0.07; 1.12 ≤ [C + Si / 4 + Mn / 6 + (Cr + V) / 5] ≤ 1.50, at the same time, it has a ferritoperlite structure without graphite, martensite, bainite, and Widmanstätt sites with a real grain size of 6-12 points, the depth of the decarburized layer is not more than 1.5% per side, macrostructure: central porosity, point heterogeneity, segregation square with a size of not more than 3 points for each species and shrink segregation - not more than 3 points, segregation strips - not more than 1 point, non-metallic inclusions: point sulfides, point oxides, line oxides, brittle silicates, plastic silicates, silica you are undeformed with the average size for each type of inclusions not more than 2.5 points, temporary tensile strength not less than 1470 N / mm ² , yield strength not less than 1425 N / mm ² , relative elongation not less than 6%, relative narrowing not less than 25% . 2. Long products according to claim 1, characterized in that, as inevitable impurities, the steel contains phosphorus not more than 0.025 wt.%, Copper not more than 0.15 wt.%. 3. Long products according to any one of claims 1 and 2, characterized in that when the content of chromium in the steel is 0.90-1.20 wt.% And vanadium 0.10-0.20 wt.%, The steel has a temporary tensile strength not less than 1670 N / mm ² , yield strength not less than 1470 N / mm ² , elongation not less than 6%, relative narrowing not less than 25%. 4. Long products according to any one of claims 1 and 2, characterized in that when the content of chromium in the steel is 0.70-1.00 wt.% And vanadium 0.005-0.10 wt. % rolling has a temporary tensile strength of at least 1570 N / mm ² , yield strength of at least 1460 N / mm ² , elongation of at least 6%, relative narrowing of at least 25%.