RU2329309C1 - Rolled section out of medium carbon boron containing steel of upgraded hardenability - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention refers to production of rolled section of a diameter from 40 to 170 mm for fabricating spline shafts, piston rods, traverses and other products. To achieve rational conditions of cutting at simultaneous upgrading of hardenability, plasticity and viscosity rolled section is fabricated out of steel containing elements, mas.%: C-0.38-0.43, Mn - 0.50-0.80, Si - 0.17-0.37, Cr - 0.70-1.00, S - 0.005-0.040, Mo - 0.03-0.06, V - 0.04-0.08, Al - 0.020-0.045, Ti - 0.020-0.045, B - 0.001-0.003, N - 0.005-0.012, As - 0.0001-0.03, Sn - 0.0001-0.02, Pb - 0.0001-0.01, Zn - 0.0001-0.005, iron and unavoidable impurities - the rest, at a following ratio of elements: (As+Sn+Pb+5×Zn)≤0.07: Ti/48+Al/27-N/14≥0.6×10^-3. Rolled section has a following macrostructure - central porosity, pointed nonuniformity, a liquation square - not more, than 3 points for each type, subshrinking liquation not more, than 2 points, liquation strips not more, than 1 point, steel dirtyness with nonmetallic inclusions: a medium point for pointed sulphides, pointed oxides, lined oxides, fragile silicates, plastic silicates, nondeformed silicates not more, than 3.5 for each type of inclusion. Rolled section has a laminar ferrite pearlite structure; the dimension of an actual grain is 5-9 points; mechanical properties are as follows: after hardening and low tempering σ_t not less, than 1300 MPa, σ_0.2 not less, than 1210 MPa, δ not less, than 10%, ψ not less, than 55%. Hardenability is as follows: hardenability of a sample at end tempering at a distance of 10 mm from the end is not less, than 47 HRC. Cutting machinability is as follows: wear value on the back edge of a cutting tool (h₃) at an equal cutting path (L) is at L=1320m h₃ is not more, than 0.30 mm.

EFFECT: provision of rational conditions for cutting machinability at simultaneous upgrading of hardenability, plasticity and viscosity.

3 cl, 2 ex

Description

The invention relates to the field of metallurgy, in particular to the production of long products of hot-rolled round diameter from 40 to 170 mm, made from medium-carbon boron-containing steel of high hardenability, used for the manufacture of splined shafts, rods, set screws, traverses, shafts of excavators and other parts requiring increased wear resistance.

Known long products from high-hardenability boron-containing steel containing carbon, manganese, silicon, boron, vanadium, aluminum, titanium, sulfur, nitrogen, calcium, iron and impurities, the rolling has the specified parameters of macro- and microstructure and mechanical properties, made of hot-rolled, hardened released (RU 2249627 C1, C21D 8/06, 04/10/2005).

Known long products are round, from high-hardenability boron-containing steel containing carbon, manganese, silicon, sulfur, chromium, vanadium, molybdenum, nickel, niobium, titanium, boron, aluminum, nitrogen, iron and inevitable impurities, hot-rolled and heat-treated, the steel has the specified pollution parameters became non-metallic inclusions on sulfides, oxides, silicates and nitrides, a homogeneous spheroidized structure of perlite, real grain size of 5-10 points and specified mechanical properties (RU 2249626 C1, C21D 8/06, 04/10/2005).

The technical result of the invention is the provision of rational conditions for processing by cutting while providing enhanced characteristics of hardenability, ductility and viscosity.

To achieve a technical result, long products made of medium-carbon boron steel, having predetermined parameters of steel contamination with non-metallic inclusions, structure, mechanical properties, hardenability and machinability by cutting, according to the invention are made of steel containing the following ratio of components in wt.%:

carbon 0.38-0.43 manganese 0.50-0.80 silicon 0.17-0.37 chromium 0.70-1.00 sulfur 0.005-0.040 molybdenum 0.03-0.06 vanadium 0.04-0.08 aluminum 0,020-0,045 titanium 0,020-0,045 boron 0.001-0.003 nitrogen 0.005-0.012 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,

, прокат имеет неметаллические включения по сульфидам точечным, оксидам точечным, оксидам строчечным, силикатам хрупким, силикатам пластичным, силикатам недеформируемым со средним баллом не более 3,5 по каждому виду включений, пластинчатую феррито-перлитную структуру, размер действительного зерна 5-9 баллов, макроструктуру - центральная пористость, точечная неоднородность, ликвационный квадрат не более 3 баллов по каждому виду, подусадочная ликвация - не более 2 баллов; ликвационные полоски - не более 1 балла, механические свойства после закалки и низкого отпуска: временное сопротивление разрыву не менее 1300 МПа, предел текучести не менее 1210 МПа, относительное удлинение не менее 10%, относительное сужение не менее 55%, обрабатываемость резанием - величина износа по задней грани резца (h₃) при равном пути резания (L) - при L=1320 м, h₃ не более 0,30 мм, твердость в состоянии поставки 187-255 НВ, прокаливаемости: твердость образца при торцевой закалке на расстоянии 10 мм от торца - не менее 47 HRC, на расстоянии 20 мм от торца - не менее 40 HRC.when the relations are satisfied: (As + Sn + Pb + 5 × Zn) ≤0.07;

, the rolling stock has non-metallic inclusions for point sulfides, point oxides, line oxides, brittle silicates, plastic silicates, non-deformable silicates with an average score of not more than 3.5 for each type of inclusions, lamellar ferrite-pearlite structure, actual grain size 5-9 points, macrostructure - central porosity, point heterogeneity, liquation square not more than 3 points for each species, shrink liquation - not more than 2 points; segregation strips - not more than 1 point, mechanical properties after hardening and low tempering: temporary tensile strength not less than 1300 MPa, yield strength not less than 1210 MPa, elongation not less than 10%, relative narrowing not less than 55%, machinability - 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 0.30 mm, hardness on delivery 187-255 HB, hardenability: sample hardness at end hardening at a distance of 10 mm from the end - not less than 47 HRC, at a distance of 20 mm from the end - not less ie 40 HRC.

As impurities, steel additionally contains in wt.%: Copper no more than 0.30, nickel no more than 0.30, phosphorus no more than 0.030, tungsten no more than 0.02.

When the sulfur content of 0.020-0.040% machinability by cutting - the amount of wear is - h ₃ not more than 0.20 mm

The given combinations of alloying elements (p. 1) make it possible to obtain a favorable lamellar structure with globular sandwich inclusions at the box office, which provides, on the one hand, improved cutting characteristics even with wide cutters during transverse feeding of the cutting tool, and, on the other hand, a favorable combination of strength characteristics ductility, viscosity and hardenability.

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 (0.43%) is due to the need to ensure the required level of ductility of steel, and the lower - respectively 0.38% - to ensure the required level of strength and hardenability of this steel.

Manganese, molybdenum 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 steel austenite. The upper level of manganese is 0.80%, molybdenum is 0.06% and chromium is 1.00% is determined by the need to ensure the required level of ductility of steel, and the lower is 0.50%, 0.03% and 0.70% accordingly, the need to provide the required level of strength and hardenability of this steel.

Silicon refers to ferrite-forming elements. The lower limit for silicon - 0.17% due to the technology of deoxidation of steel. A silicon content above 0.37% will adversely affect the ductility characteristics of steel.

A carbonitride-forming element, vanadium, is introduced into the composition of this steel in order to provide a finely dispersed, uniform grain structure, which will increase both its strength level and provide a given level of ductility. In this case, vanadium controls the processes in the lower part of the austenitic region and in the intercritical temperature range (determines the tendency to growth of austenite grain, stabilizes the structure during thermomechanical processing, increases the recrystallization temperature, and, as a result, affects the nature of the γ-α transformation). Vanadium also contributes to the hardening of steel during thermal improvement. The upper limit of the vanadium content is 0.04% due to the need to ensure the required level of ductility of steel, and the lower - respectively 0.02% - to ensure the required level of strength of this 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 (0.005%) is due to issues of manufacturability, as well as providing a given level of machinability by cutting this steel.

Boron contributes to a sharp increase in the hardenability of steel. The upper limit of boron content - 0.003% is determined by considerations of ductility of steel, and the lower - 0.001% - the need to ensure the required level of hardenability.

Aluminum and titanium are used as deoxidizers of steel, elements that provide the formation of a finely dispersed, uniform grain structure, and also effectively protect boron from binding to nitrides. The upper limit of the aluminum content of 0.045% and titanium of 0.045% is due to the need to obtain a given level of ductility and toughness of steel, and the lower limit of 0.020% and 0.020%, respectively, due to issues of manufacturability, as well as ensuring a uniform grain structure of steel.

Nitrogen promotes the formation of nitrides in steel. The upper limit of the nitrogen content is 0.012% due to the need to obtain a given level of ductility and toughness of steel, and the lower limit of 0.005% due to 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 the technology of steel production, 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≤0.05 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.

Comparative analysis with the prototype allows us to conclude that the claimed composition differs from the known one by the introduction of new components and the ratios: As + Sn + Pb + 5 × Zn≤0.07;

Examples of carrying out the invention, not excluding others in the scope of the claims.

Smelting of the studied steels with chemical compositions in wt.%:

Example 1: carbon — 0.39, manganese — 0.73, silicon — 0.27, chromium — 0.92, molybdenum — 0.04, sulfur — 0.011, vanadium — 0.05, aluminum — 0.037, titanium — 0.024 boron - 0.0023, nitrogen - 0.007, arsenic - 0.007, tin - 0.011, lead - 0.009, zinc - 0.002;

Example 2: carbon — 0.41, manganese — 0.78, silicon — 0.21, chromium — 0.94, molybdenum — 0.05, sulfur — 0.032, vanadium — 0.06, aluminum — 0.039, titanium — 0.029 , boron - 0.0028, nitrogen - 0.008, arsenic - 0.008, tin - 0.010, lead - 0.008, zinc - 0.002 was carried out in 150-ton steel arc furnaces (DSP-150, transformer power 80 mW) using 60% of the charge metallized pellets 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 furnace - immersion pipe with argon supply; promkovsh - slag-forming mixture; bucket mold - immersion cup (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. The entire initial billet was subjected to dressing, descaling, and surface control. To test the billets of the test steel, they were heat treated in the following mode: normalization 930 ° C, air, quenching 880 ° C, oil, tempering 200 ° C, air.

We get long products ⌀40 mm, length - 5900 mm, having:

according to example 1: the structure of lamellar perlite, decarburized layer is absent, the real grain score is 7. 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-deforming silicates - 1 point. Hardness on delivery is 217 HB. Tensile strength 1310 MPa, yield strength 1275 MPa, elongation 11%, relative narrowing 56%. Hardenability characteristics: sample hardness at end hardening at a distance of 10 mm from the end - 49 HRC, at a distance of 20 mm from the end - 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 = 0.24 mm.

,As + Sn + Pb + 5 × Zn = 0.037,

,

according to example 2: the structure of lamellar perlite, decarburized layer is absent, the actual grain score is 8. Sulfide inclusions globular with an oxide shell. Macrostructure: central porosity - 1.0 point, point heterogeneity - 1.0 point, segregation square - 1.0 point, shrink segregation - 0.5 points, segregation strips - 0.5 points. Non-metallic inclusions: point sulfides - 2.5 points, point oxides - 2.0 points, line oxides - 2.0 points, brittle silicates - 1.5 points, plastic silicates - 1 point, non-deforming silicates - 1 point. Hardness on delivery is 225 HB. Tensile strength 1310 MPa, yield strength 1275 MPa, elongation 11%, relative narrowing 56%. Hardenability characteristics: sample hardness at end hardening at a distance of 10 mm from the end - 51 HRC, at a distance of 20 mm from the end - 43 HRC. Machinability by cutting is 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 = 0.17 mm.

As + Sn + Pb + 5 × Zn = 0.036,

Sections made of boron-containing steel have increased machinability by cutting and a favorable ratio of strength, ductility and toughness of steel.

Claims (3)

1. Rolled steel, round from medium-carbon boron steel, having predetermined parameters of steel contamination by non-metallic inclusions, structure, mechanical properties, hardenability and machinability by cutting, characterized in that the steel contains the following ratio of components, wt.%: carbon 0.38-0.43 manganese 0.50-0.80 silicon 0.17-0.37 chromium 0.70-1.00 sulfur 0.005-0.040 molybdenum 0.03-0.06 vanadium 0.04-0.08 aluminum 0,020-0,045 titanium 0,020-0,045 boron 0.001-0.003 nitrogen 0.005-0.012 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 - the rest, when the relations (As + Sn + Pb + 5 × Zn) ≤0.07;

moreover, it has non-metallic inclusions for point sulfides, point oxides, row oxides, brittle silicates, plastic silicates, non-deformable silicates with an average score of not more than 3.5 for each type of inclusions, lamellar ferritic-pearlite structure with a real grain size of 5-9 points , macrostructure - central porosity, point heterogeneity, liquation square no more than 3 points for each species, shrink liquation - no more than 2 points; segregation strips - not more than 1 point, mechanical properties after hardening and low tempering: temporary tensile strength not less than 1300 MPa, yield strength not less than 1210 MPa, elongation not less than 10%, relative narrowing not less than 55%, machinability - wear along the rear edge of the cutter (h ₃ ) with an equal cutting path L = 1320 m h ₃ not more than 0.30 mm, hardness on delivery 187-255 HB, hardenability: sample hardness at end hardening at a distance of 10 mm from the end not less than 47 HRC, at a distance of 20 mm from the end of at least 40 HRC. 2. Long products according to claim 1, characterized in that the steel further comprises, as impurities, wt.%: Copper, not more than 0.30, nickel, not more than 0.30, phosphorus, not more than 0.030, tungsten, not more than 0.02. 3. Long products according to claim 1 or 2, characterized in that when the sulfur content is 0.020-0.040% machinability by cutting, the amount of wear is h ₃ not more than 0.20 mm.