RU2337148C2 - Band out of medium carbon boron containing steel of upgraded hardenability and cutability - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: band of 32×90 mm is produced out of steel containing wt %: C 0.34-0.38, Mn 1.00-1.30, Si 0.15-0.35, Cr 0.05-0.20, Nb 0.005-0.020, S 0.020-0.040, Al 0.020-0.050, Ti 0.020-0.04, Ca 0.001-0.010, N 0.005-0.010, B 0.001-0.005, As 0.0001-0.03, Sn 0.0001-0.02, Pb 0.0001-0.01, Zn 0.0001-0.005, iron and impurities at ratio (As+Sn+Pb+5×Zn)≤0.07, Ca/S≥0.065, (Ti/48+Al/27)-N/14≥0.6×10^-3. Band is produced hot rolled, it has ferrite-pearlite structure, dimension of actual grain is 5-9 points, depth of decarbonized layer is not more than 0.7 mm, non-metallic inclusions of pointed sulphides, pointed oxides, stripped oxides, fragile silicates, plastic silicates, non-deforming silicates are with average point of not more than 3.0 in each kind, macrostructure on central porosity, pointed non-uniformity, liquation square, sub-shrinking liquation is not more than 1 point, σt is not more than 640 MPa, δ is not less than 16%, ψ is not less than 50%, hardenability on hardness of sample at end tempering at distance from end of 1.5 mm is not more than 51-58 HRC, at distance from end of 9 mm is not more than 46 HRC, at distance from end of 15 mm is not more than 42 HRC. Cutability on cutter back facet wear value h₃ is not more than 0.35 mm at cut path L=1320m.

EFFECT: upgraded hardenability, wear resistance and cutability at optimal viscosity and plasticity.

2 cl, 1 ex

Description

The invention relates to the field of metallurgy, in particular the production of a hot-rolled strip 32 × 90 mm in size, made from medium-carbon boron-containing steel of increased hardenability and wear resistance, used in various engineering industries.

A known strip of medium-carbon boron-containing steel containing carbon, manganese, silicon, chromium, nickel, copper, boron, aluminum, titanium, calcium, iron and impurities, hot-rolled, having predetermined structure parameters, non-metallic inclusions, mechanical properties, hardenability and machinability by cutting ( RU 2238332 C1, C21D 8/02, 20.10.2004).

The technical result of the invention is to provide improved characteristics of hardenability and wear resistance, machinability by cutting with a favorable ratio of viscosity and ductility of steel.

To achieve a technical result, a strip of medium-carbon boron-containing steel, hot rolled, having predetermined parameters of the structure, non-metallic inclusions, mechanical properties, hardenability and machinability by cutting, is made of steel containing the following ratio of components in wt.%:

carbon 0.34-0.38 manganese 1.00-1.30 silicon 0.15-0.35 chromium 0.05-0.20 niobium 0.005-0.020 sulfur 0,020-0,040 aluminum 0,020-0,050 titanium 0.02-0.04 calcium 0.001-0.010 nitrogen 0.005-0.010 boron 0.001-0.005 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 performing the following ratios:

(As + Sn + Pb + 5 × Zn) ≤0.07;

Ca / S> 0.065;

has a ferrite-pearlite structure, the actual grain size is 5–9 points, the decarburized layer depth is not more than 0.7 mm, non-metallic inclusions are the average score for point sulfides, point oxides, building oxides, brittle silicates, plastic silicates, non-deformable silicates - not more than 3.0 for each type of inclusions, macrostructure - central porosity, point heterogeneity, segregation square - not more than 3 points for each type, shrinkable segregation - not more than 3 points; segregation strips - not more than 1 point, temporary tensile strength not more than 640 MPa, elongation not less than 16%, relative narrowing not less than 50%, hardenability: hardness of the specimen at end hardening at a distance of 1.5 mm from the end 51-58 HRC, at a distance of 9 mm from the end face at least 46 HRC, at a distance from the end face 15 mm - no more than 42 HRC, machinability - the amount of wear along the rear edge of the cutter (h ₃ ) with an equal cutting path (L) - at L = 1320 m, h ₃ not more than 0.35 mm. As an impurity, steel additionally contains in wt.%: Nickel not more than 0.30, copper not more than 0.15, phosphorus not more than 0.030.

The given combinations of alloying elements (item 1) make it possible to obtain a favorable ferrite-pearlite structure with globular sandwich inclusions in the hot-rolled strip, which provides, on the one hand, improved cutting characteristics even with wide cutters during transverse feeding of the cutting tool, on the other hand, a favorable combination 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 (0.38%) is due to the need to ensure the required level of ductility of steel, and the lower - respectively 0.34% - 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 significantly increase the stability of supercooled austenite of steel. At the same time, the upper level of manganese — 1.30% and chromium — 0.20% is determined by the need to ensure the required level of ductility of steel, and the lower - 1.00 and 0.05%, respectively, by the need to provide the required level of strength and hardenability of this steel.

Silicon refers to ferrite-forming elements. The lower limit on silicon - 0.15% is due to the technology of deoxidation of steel. A silicon content above 0.35% will adversely affect the ductility characteristics of steel.

Sulfur determines the level of ductility of steel. The upper limit (0.040%) is due to the need to obtain a given level of ductility and toughness of steel, and the lower limit (0.020%) is due to issues of manufacturability, as well as providing a given level of machinability by cutting this steel.

Aluminum and titanium are used as deoxidizing agents for steel and elements providing the formation of a finely dispersed, uniform grain structure, as well as elements that effectively protect boron from binding to nitrides. The upper limit of the content of aluminum is 0.050% and titanium - 0.040% due to the need to obtain a given level of ductility and toughness and hardenability of steel, and the lower limit to 0.020 and 0.020%, respectively, by issues of manufacturability and ensuring a uniform grain structure of 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.

Calcium is an element that modifies non-metallic inclusions. The upper limit (0.010%), as in the case of sulfur, is due to the need to obtain a given level of ductility and toughness of steel, and the lower (0.001%) limit is due to technological issues of production.

Boron contributes to a sharp increase in the hardenability of steel. The upper limit of boron content - 0.005% is determined by considerations of ductility of steel, and the lower - 0.001%, the need to ensure the required level of hardenability.

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 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 calcium / sulfur ratio of ≥0.065% determines the conditions for the formation of globular nonmetallic inclusions (sulfides). If this ratio is fulfilled, the sulfides are globular, otherwise elongated sulfides are present in the steel, which increases the anisotropy of the properties of the steel and worsens the strength-toughness ratio, especially strongly in the transverse direction of the rolled product.

The ratio (As + Sn + Pb + 5 × Zn) ≤0.05 determines the reduced tendency of steel to manifest reversible temper brittleness.

определяет эффективность защиты бора от связывания в нитриды и, как следствие, обеспечивает требуемый уровень прокаливаемости стали.Ratio

determines the effectiveness of boron protection from binding to nitrides and, as a result, provides the required level of hardenability of steel.

An example embodiment of the invention

Smelting of the studied steel with a chemical composition in wt.%: Carbon 0.36, manganese 1.22, silicon 0.32, chromium 0.13, niobium 0.01, sulfur 0.034, aluminum 0.037, titanium 0.031, calcium 0.0028, nitrogen, 0.008, oxygen, 0.010, boron, 0.0034, arsenic, 0.009, tin, 0.005, lead, 0.003, zinc, 0.001, were carried out in 150-ton steel-arc furnaces (DSP-150, transformer power 80 mVA) using 60% metallized pellets in a charge and 40% scrap metal, which ensures that the mass fraction of nitrogen before release from the particleboard is not more than 0.003%, as well as a low content of non-ferrous impurities. Preliminary alloying of metal with manganese and silicon was carried out in a ladle when discharged from particleboard (Release of peroxidized metal into a ladle. Metal deoxidation — when released by aluminum, ferrosilicon — deoxidation, alloying — FeMn (SiMn), FeCr). After release, the metal was purged with argon through the bottom purge unit for 5-7 minutes. Then evacuation on a portion vacuum, while doping (fine) - carbon, manganese and silicon. After evacuation - processing on a ladle furnace. 15-30 minutes before the end of the treatment, an oxidizing agent is introduced, in this case, oxidized pellets. Then again introduced aluminum (wire). For 10-15 minutes treatment with flux-cored wires with silicocalcium and pure sulfur. Steel casting was carried out on a high-quality radial type continuous casting machine in NLZ 300 × 360 mm with a draw speed of 0.6-0.7 m / min. During casting, the jet was protected from secondary oxidation as follows: steel-ladle-blast-bucket - immersion pipe with argon supply, bucket-slag-forming mixture, bucket-crystallizer - immersion glass (corundum-graphite), in the mold - slag-forming mixture.

After casting and cutting to a measured length, continuously cast billets were cooled in controlled cooling furnaces. Next, the ingots were rolled in a mill 700 into a billet (170 mm square). The entire initial billet was subjected to dressing, descaling, and surface control. The billets were heated before rolling in two walking-hearth furnace furnaces. The heating temperature of the billet is 900 ° C, which ensures a 15% reduction in energy consumption and significantly reduces the decarburization of rolled products. Dross from the surface of the workpiece was removed with high-pressure water at a descaling unit. Rolling was carried out in continuous lines - small-grade and medium-grade. The test to determine the characteristics of hardenability was carried out on samples by end hardening from 845 ° C.

As a result of hot rolling, a hot-rolled strip 32 × 90 mm in size is obtained. The structure of lamellar ferrite-perlite, decarburized layer of 0.1 mm, the actual grain score is 7. Sulfide inclusions globular with an oxide shell. Macrostructure: central porosity - 1 point, point heterogeneity - 1 point, segregation square - 0.5 points, shrink segregation - 0.5 points, segregation strips - 0.5 points. Non-metallic inclusions: point sulfides - 2 points, point oxides - 1 point, line oxides - 2 points, brittle silicates - 1 point, plastic silicates - 1 point, non-deformable silicates - 1 point.

Mechanical properties: temporary tensile strength 621 MPa, elongation of 18%, relative narrowing of 58%. Hardenability: the hardness of the sample during end hardening at a distance of 1.5 mm from the end - 56 HRC, at a distance of 9 mm from the end - 49 HRC, at a distance of 15 mm from the end - 41 HRC. Machinability - the amount of wear along the rear edge of the cutter (h ₃ ) with an equal cutting path (L) - at L = 1320 m, h ₃ not more than 0.29 mm.

As + Sn + Pb + 5 × Zn = 0.022, calcium / sulfur = 0.082;

The introduction of medium carbon steel strips into production provides improved cutting performance and a favorable ratio of strength and toughness of steel.

Claims (2)

1. A strip of medium-carbon boron-containing steel, hot rolled, having predetermined parameters of the structure, non-metallic inclusions, mechanical properties, hardenability and machinability by cutting, characterized in that it is made of steel containing the following ratio of components, wt.%: carbon 0.34-0.38 manganese 1.00-1.30 silicon 0.15-0.35 chromium 0.05-0.20 niobium 0.005-0.020 sulfur 0,020-0,040 aluminum 0,020-0,050 titanium 0.02-0.04 calcium 0.001-0.010 nitrogen 0.005-0.010 boron 0.001-0.005 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 performing the following ratios: (As + Sn + Pb + 5 Zn) ≤0.07; Ca / S≥0.065;

Moreover, it has a ferrite-pearlite structure, the actual grain size is 5–9 points, the decarburized layer depth is not more than 0.7 mm, non-metallic inclusions for point sulfides, point oxides, building oxides, brittle silicates, plastic silicates, non-deformable silicates with an average score no more than 3.0 for each species, macrostructure by central porosity, point heterogeneity, segregation square, shrink segregation no more than 3 points for each species, segregation strips no more than 1 point, temporary resistance a tensile strength of not more than 640 MPa, elongation of not less than 16%, relative narrowing of not less than 50%, hardenability in hardness of a specimen at end hardening at a distance of 1.5 mm from the end of 51-58HRC, at a distance of 9 mm from the end of at least 46 HRC , at a distance from the end face of 15 mm no more than 42 HRC, machinability by cutting according to the amount of wear of the rear edge of the cutter h ₃ not more than 0.35 mm with a cutting path L = 1320 m. 2. The strip according to claim 1, characterized in that as inevitable impurities the steel contains, wt.%: Nickel not more than 0.30; copper no more than 0.15; phosphorus no more than 0,030.