RU2310690C1 - Round rolled bars of alloy spring steel - Google Patents

Abstract

FIELD: metallurgy, namely production of rolled round bars of spring steel for making springs for important designation.

SUBSTANCE: rolled bars are produced from steel containing next relation of ingredients, mass.%: carbon, 0.53 - 0.58; manganese, 0.60 - 0.80; silicon, 1.40 - 1.60; chrome, 0.60 - 0.80; aluminum, 0.005 - 0.025; nitrogen, 0.005 - 0.008; arsenic, 0.0001 - 0.03; tin, 0.0001 - 0.002; lead, 0.0001 - 0.001; zinc, 0.0001 - 0.005; iron and inevitable impurities, the balance at relation As + Sn + Pb + 5 x Zn < 0.07. Content of impurities, mass.%: copper, no more than 0.08; vanadium, no more than 0.005; nickel, no more than 0.10; titanium, no more than 0.03; molybdenum, no more than 0.10; sulfur, no more than o.015; phosphorus, no more than 0.015; oxygen, no more than 0.002. Hot rolled piece has ferrite-pearlite microstructure without martensite, total depth of decarburized layer no more than 0.2 mm for side, temporary rupture resistance 900 - 1150 N/mm², percentage necking no less than 35%. As for non-metallic inclusions, rolled piece includes point sulfides, point oxides, line oxides, brittle silicates, plastic silicates, non - deformed silicates, no more than 2.5 marks for each type of inclusions.

EFFECT: high level of consumer's properties, desired relation of strength, ductility and viscosity values, minimum degree of properties anisotropy, rational winding condition.

2 cl, 1 ex

Description

The invention relates to the field of metallurgy, in particular to the production of hot-rolled long products in coils of spring steel grade for the production of springs for critical purposes.

Known long products of round alloy steel, made of hot rolled steel containing carbon and alloying elements, and having predetermined metallurgical quality parameters for non-metallic inclusions, structure, mechanical properties, hardenability (RU 2180277 C1, 03/10/2002).

Known long products of round steel made of spring steel, made of hot rolled steel containing carbon and alloying elements, and having predetermined metallurgical quality parameters for non-metallic inclusions, structure, mechanical properties, hardenability (RU 2092257 C1, C21D 8/06, 10.10.1997).

The objective of the invention is to provide rational conditions for winding the springs while providing improved characteristics of consumer properties, low content of non-metallic inclusions, homogeneous macro- and microstructure.

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

carbon 0.53-0.58 manganese 0.60-0.80 silicon 1.40-1.60 chromium 0.60-0.80 aluminum 0.005-0.025 nitrogen 0.005-0.008 arsenic 0.0001-0.03 tin 0.0001-0.02 lead 0.0001-0.01 zinc 0.0001-0.005 iron and inevitable impurities rest,

when the following ratio is fulfilled, the sum (arsenic + tin + lead + 5 × zinc) ≤0.07; long products have a ferrite-pearlite microstructure, martensite is not allowed, the total depth of the decarburized layer is not more than 0.2 mm per side, macrostructure: central porosity, point heterogeneity, segregation square, shrink segregation - not more than 3 points for each type, segregation strips - not more than 1 point, mechanical properties after hardening with low tempering, tensile strength 900-1150 N / mm ^2, yield stress of 680-1300 N / mm ^2, an elongation of at least 10%, contraction ratio is not less than 35%, non-metallic Inclusions: point sulfides, point oxides, line oxides, brittle silicates, plastic silicates, undeformed silicates - not more than 2.5 points for each type of inclusion. As impurities, steel additionally contains in wt%: copper no more than 0.08, vanadium no more than 0.005, nickel no more than 0.10, titanium no more than 0.03, molybdenum no more than 0.10, sulfur no more than 0.015, no phosphorus more than 0.015, oxygen not more than 0.002.

The given combinations of alloying elements (p. 1) make it possible to obtain a homogeneous finely dispersed structure in a finished product with a favorable combination of strength and ductility characteristics.

Carbon is introduced into the composition of this steel in order to ensure a given level of its strength and hardenability. The upper limit of the carbon content (0.58) is due to the need to ensure the required level of ductility of steel, and the lower - respectively 0.53 - to ensure the required level of strength and hardenability of this steel.

Silicon refers to ferrite-forming elements and helps to ensure the necessary level of elasticity of the material. The lower limit for silicon - 1.40% due to the need to provide the required parameters of elasticity of steel. A silicon content above 1.60% will adversely affect the ductility characteristics of 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 austenite of steel. At the same time, the upper level of manganese — 0.80% and chromium — 0.80% is determined by the need to ensure the required level of ductility of steel, and the lower manganese — 0.60% and 0.60% of chromium, respectively, by the need to provide the required level of strength and hardenability of this become.

Aluminum is used as a deoxidizer of steel and an element that provides the formation of a finely dispersed, grain structure. The upper limit (0.025%) is due to the need to obtain a given level of ductility and toughness of steel, and the lower (0.005%) due to technological issues of production, as well as ensuring a uniform grain structure of steel.

Nitrogen promotes the formation of nitrides in steel. The upper limit of nitrogen content - 0.008 due to the need to obtain a given level of ductility and toughness of steel, and the lower limit - 0.005% - issues of manufacturability.

Arsenic, tin, lead and zinc are colored impurities that determine the overall level of ductility of steel and its tendency to manifest reversible temper brittleness during subsequent heat treatment of finished products from the pipe billet under consideration. The lower limit for arsenic, tin, lead and zinc (0.0001% for each element, respectively) is due to steel production technology, and the upper limit (0.03%, 0.02%, 0.01% and 0.005%, respectively) determines an increased tendency steel to reversible temper brittleness.

The ratio As + Sn + Pb + 5 × Zn≤0.07 determines the reduced tendency of steel to manifest reversible temper brittleness.

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 rational conditions for winding the springs while ensuring enhanced characteristics of consumer properties, metallurgical quality: low content of non-metallic inclusions, homogeneous macro- and microstructure.

An example embodiment of the invention. Smelting of the test steel, chemical composition in wt.%: Carbon - 0.56%, manganese - 0.65%, silicon - 1.44%, chromium - 0.62%, aluminum - 0.021%, nitrogen - 0.007%, arsenic - 0.007%, tin - 0.008%, lead - 0.006%, zinc - 0.001%) is produced in 150-ton arc steel-smelting furnaces (DSP) using 100% metallized pellets in the charge, which ensures the mass fraction of nitrogen before being released from the DSP no more than 0.003%, as well as 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 release, the metal was purged with argon through the bottom purge unit, during which the steel was deoxidized with 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 imposed with an additive of lime and fluorspar, slag is deoxidized with granulated aluminum, the metal is alloyed with aluminum to a content of 0.050%, the metal is refined according to the manganese content, and it is heated 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 a four-strand radial type ONRS with an ingot of 300 × 360 mm in size with a drawing speed of 0.6 ÷ 0.7 m / min with protection of the metal from oxidation by using cover slag mixtures in the intermediate ladle and mold, protective tubes, immersion glasses and feeding argon. 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% and is subjected to heat treatment: quenching in oil and low tempering.

As a result of hot rolling, rolled products with a diameter of Ø13 mm with a structure of ferrite and plate perlite were obtained, the actual grain score was 7. The total depth of the decarburized layer was 0.05 mm per side. Macrostructure: central porosity - 1 point, point heterogeneity - 1 point, segregation square - 1 point, shrink segregation - 1 point, segregation strips - 1 point. Non-metallic inclusions: point sulfides - 1 point, point oxides - 1 point, line oxides - 0.5 points, brittle silicates - 0.5 points, plastic silicates - 0.5 points, undeformed silicates - 0.5 points. Mechanical properties after quenching with low tempering: temporary tensile strength 1050 N / mm ² , yield strength 830 N / mm ² , elongation 12%, relative narrowing 45% (As + Sn + Pb + 5 × Zn) = 0.026.

The introduction of the proposed rolled steel from alloy spring steel provides an increased level of consumer properties of rolled products with a favorable ratio of strength, ductility and toughness, a minimum level of anisotropy of mechanical properties, low content of non-metallic inclusions, homogeneous macro- and microstructure of rolled products.

Claims (2)

1. High-quality round steel spring steel, made hot-rolled and having the specified parameters of the structure, non-metallic inclusions, mechanical properties and hardenability, characterized in that it is made of steel containing components, wt.%: carbon 0.53-0.58 manganese 0.60-0.80 silicon 1.40-1.60 chromium 0.60-0.80 aluminum 0.005-0.025 nitrogen 0.005-0.008 arsenic 0.0001-0.03 tin 0.0001-0.02 lead 0.0001-0.01 zinc 0.0001-0.005 iron and inevitable impurities rest, when the ratio is fulfilled, the sum (arsenic + tin + lead + 5 · zinc) ≤0.07, while long products have a ferrite-pearlite structure without martensite, the total depth of the decarburized layer is not more than 0.2 mm per side, the mechanical properties of hardened steel: tensile strength 900–1150 N / mm ² , yield strength 680–1300 N / mm ² , elongation at least 10%, relative narrowing at least 35%, macrostructure: central porosity, point heterogeneity, segregation square, shrink segregation - no more than 3 points for each type , segregation strips - not more than 1 point, non-metallic inclusions: point sulfides, point oxides, line oxides, brittle silicates, plastic silicates, undeformed silicates - not more than 2.5 points for each type of inclusion. 2. Long products according to claim 1, characterized in that the steel further comprises, as impurities, wt.%: Copper not more than 0.08, vanadium not more than 0.005, nickel not more than 0.10, titanium not more than 0.03, molybdenum is not more than 0.10, sulfur is not more than 0.015, phosphorus is not more than 0.015, oxygen is not more than 0.002.