RU2262547C1 - Mean-carbon steel with enhanced workability by cutting - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to steel used in making rods for shock-absorbers for cars. Steel with enhanced workability by cutting comprises components taken in the following ratio, wt.-%: carbon, 0.42-0.50; manganese, 0.50-0.80; silicon, 0.17-0.37; sulfur, 0.020-0.040; phosphorus, 0.001-0.030; aluminum, 0.03-0.05; calcium, 0.001-0.010; oxygen, 0.001-0.015; iron and imminent impurities, the balance. The following dependences are necessary: ratio oxygen/calcium = 1-4,5, and ratio calcium/sulfur ≥ 0.065. Steel can comprise the following impurities additionally, wt.-%: chrome, 0.25, not above; nickel, 0.25, not above; copper, 0.25, not above; molybdenum, 0.10, not above; arsenic, 0.08, not above; phosphorus, 0.035, not above; nitrogen, 0.015, not above being nonmetallic inclusions show bilayer structure as sulfide with oxide envelope. Invention provides enhancing workability of steel by cutting, provides complete penetration hardenability of bar rolled products of diameter up to 20 mm.

EFFECT: improved and valuable properties of steel.

3 cl, 2 tbl, 1 ex

Description

The invention relates to the field of metallurgy, in particular to the development of medium carbon steel with high machinability, used for the manufacture of automobile shock absorber rods.

Known structural steel containing (wt.%): Carbon 0.38-0.47%, manganese 0.8-1.2%, silicon 0.17-0.37%, vanadium 0.08-0.18%, boron 0.001-0.005%, nitrogen 0.005-0.025%, sulfur 0.036-0.080%, calcium 0.001-0.010%, the rest, provided that the ratio of manganese to calcium is 100-1100 (USSR author's certificate SU 1689426 A1, C 22 C 38/60 of 11/07/1989. Bull. No. 41). The disadvantage of this steel is the relatively high nitrogen content and the absence of elements in the composition that protect boron from binding to nitrides, which in some cases will not allow the authors claimed effect to increase the hardenability characteristics.

The closest in technical essence and the achieved effect to the proposed steel is steel containing (wt.%): Carbon 0.42-0.50%, silicon 0.17-0.37%, manganese 0.50-0.80%, sulfur - not more than 0.040%, phosphorus - not more than 0.035%, the rest is iron. Impurities: chromium - not more than 0.25%, nickel - not more than 0.30%, arsenic - not more than 0.08%, nitrogen - not more than 0.008%, copper - not more than 0.30% (Marochnik steels and alloys. / Edited by A.S. Zubchenko , M., Engineering, 2003, p. 102).

The disadvantage of this steel is an unregulated sulfur content, which will lead to a significant deterioration in the cutting characteristics, a decrease in the resistance of the cutting tool, an increase in tool loads at a lower sulfur content in the proposed interval, i.e. less than 0.012%. The disadvantages include the absence of modifying elements, such as calcium, in its composition, which will contribute to the presence of elongated sulfide inclusions in the steel, and, as a result, increased anisotropy of the mechanical properties of hot-rolled products.

The objective of the invention is to increase the characteristics of machinability by cutting while increasing the characteristics of hardenability while ensuring through hardenability of long products with a diameter of up to 20 mm.

The task is achieved by the fact that

1. Proposed steel containing: carbon, manganese, silicon, sulfur, phosphorus, iron and inevitable impurities, characterized in that it additionally contains aluminum, calcium and oxygen, in the following ratio of components in wt.%:

carbon 0.42-0.50 manganese 0.50-0.80 silicon 0.17-0.37 sulfur 0,020-0,040 phosphorus 0.001-0.030 aluminum 0.03-0.05 calcium 0.001-0.010 oxygen 0.001-0.015

iron and inevitable impurities - the rest, while the ratio of oxygen and calcium, as well as the ratio of calcium and sulfur are determined by the following relationships: oxygen / calcium = 1 ÷ 4.5 and calcium / sulfur ≥0.065.

2. The steel according to claim 1, characterized in that it further comprises chromium, nickel, copper, molybdenum, arsenic and nitrogen as impurities in the following ratio, in wt.%:

chromium no more than 0.25% nickel no more than 0.25% copper no more than 0.25% molybdenum no more than 0.10% arsenic no more than 0.08%, nitrogen no more than 0.015%

3. Steel according to claim 1, characterized in that it contains non-metallic inclusions having a two-layer structure - sulfide with an oxide shell.

The given combinations of alloying elements (item 1) make it possible to obtain a favorable lamellar structure with globular sandwich inclusions in the proposed steel (hot-rolled section bar of round diameter up to 20 mm), which provides, on the one hand, increased cutting characteristics even with wide cutters with transverse supply of the cutting tool, on the other hand, is favorable by a 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 (0.50%) is due to the need to ensure the required level of ductility of steel, and the lower - 0.42%, respectively - to ensure the required level of strength and hardenability of this steel.

Manganese is used, on the one hand, as a hardener of solid solution, on the other hand, as elements that significantly increase the stability of supercooled austenite of steel. The upper level of manganese content - 0.80% is determined by the need to ensure the required level of ductility of steel, and the lower - 0.50%, 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 - 0.17% is due to steel deoxidation technology. A silicon content above 0.37% 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%) due to issues of manufacturability, as well as providing a given level of machinability by cutting this steel.

Phosphorus is an element that contributes to the increase in steel cutting performance. At the same time, the upper level of phosphorus content - 0.030% is due to the need to prevent the development of processes of reversible temper brittleness of steel, as well as to provide the required level of ductility of steel, and the lower - 0.0010%, respectively, by the need to provide the required level of strength and machinability by steel cutting.

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 due to issues of manufacturability.

Oxygen, forming an oxide film on sulfides, helps to increase the machinability of steel by cutting while maintaining a high complex of consumer properties of steel. In this case, the upper level of oxygen content - 0.015% is due to the need to ensure the required level of ductility of steel, and the lower - 0.001%, respectively, the need to provide the required level of strength and machinability by cutting steel.

Ratios:

The ratio of oxygen / calcium = 1 ÷ 4.5 is responsible for the possibility of the formation of a sandwich-non-metallic inclusion. Moreover, the upper limit of the ratio of 4.5 is due to the need to ensure the required level of ductility of steel, and the lower one is 1, respectively, the possibility of the formation of a two-layer sandwich-non-metallic inclusion.

The ratio of calcium / sulfur ≥0.065% determines the conditions for the formation of globular non-metallic inclusions (sulfides). If this ratio is fulfilled, then 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.

Comparative analysis with the prototype allows us to conclude that the claimed composition is different from the known introduction of new components - aluminum, calcium and oxygen, as well as the ratios: oxygen / calcium = 1 ÷ 4.5 and calcium / sulfur≥0.065%.

Thus, the claimed technical solution meets the criterion of "novelty."

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 - improving the machinability of cutting while maintaining a favorable ratio of strength-ductility and toughness of steel.

Therefore, the claimed combination of characteristics meets the criterion of "significant differences".

The following are examples of the implementation of the invention, not excluding others in the scope of the claims.

The experimental batch of the studied steel (the chemical composition is presented in Table 1) was smelted in 150-ton arc steel-smelting furnaces (DSP-150, transformer capacity 80 mVA) using 60% metallized pellets and 40% metal scrap in the charge, which ensures mass the proportion of nitrogen before release from the particleboard is not more than 0.003%, as well as a low content of colored 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-tundish - dip tube with argon feed

- industrial ladle - slag-forming mixture

- tundish-crystallizer - 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 (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 costs 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. High rigidity of the stands, automatic adjustment of the speed of the stands, and a loop control system in the finishing group of the small-grade line made it possible to obtain high-precision rolled products. Finishing of the rolling was carried out off-stream. Finishing included the operations of dressing, control of surface defects and ultrasonic control of internal defects, selective abrasive cleaning, continuous abrasive grinding, turning of round bars. The accuracy of rolling after turning corresponds to the h11 quality. At the BUNT-PRUTOK installation, turned coils of bar up to 6 meters long with a cutting accuracy of ± 5 mm are obtained from coils of hot-rolled steel.

The mechanical properties are presented in table 2.

As can be seen from table 2, the proposed steel in comparison with the known has higher machinability by cutting with a favorable ratio of strength and ductility.

The introduction of the proposed steel with increased machinability provides two-sandwich non-metallic inclusions that guarantee, on the one hand, the provision of improved cutting characteristics, on the other hand, a favorable ratio of strength, ductility and toughness of steel.

Table 1.
CHEMICAL COMPOSITION OF OFFERED AND KNOWN STEEL Swimming trunks number The content of elements, wt.% Ratio FROM Mn Si S R Al Sa O Cr Ni Cu Mo As N Fe 1* 2 * Steel offered 1 0.42 0.50 0.37 0.020 0.022 0.03 0.003 0.003 0.02 0.01 0.12 0.02 0.01 0.007 rest 1 0.150 2 0.44 0.70 0.25 0.025 0.005 0.05 0.002 0.002 0.11 0.11 0.05 0.01 0.01 0.008 rest 1 0.080 3 0.46 0.80 0.27 0.029 0.020 0.03 0.002 0.007 0.21 0.14 0.08 0.09 0.02 0.010 rest 3.5 0.069 4 0.48 0.60 0.20 0.040 0.015 0.04 0.004 0.015 0.15 0.19 0.06 0.03 0.03 0.010 ost 3.35 0.100 5 0.50 0.60 0.17 0.035 0.030 0.04 0.003 0.012 0.14 0.22 0.09 0.04 0.04 0.011 ost 4 0.086 Outside of the claimed 6 0.40 0.45 0.17 0.045 0.005 0.02 0.002 0.001 0.28 0.15 0.14 0.01 0.05 0.012 ost 0.5 0.022 7 0.45 0.85 0.38 0.021 0.020 0.02 0.001 0.005 0.21 0.27 0.22 0.03 0.01 0.014 ost 5 0.048 8 0.51 0.81 0.16 0.031 0.040 0.06 0.001 0.003 0.19 0.17 0.26 0.02 0.01 0.016 ost 3 0.032 nine 0.53 0.44 0.25 0.01 0.008 0.05 0.001 0.015 0.18 0.18 0.27 0.02 0.10 0.009 ost fifteen 0.100 Famous steel 10 0.45 0.66 0.25 0.011 0.012 - - - ost The ratio of 1 * is oxygen / calcium, The ratio of 2 * - calcium / sulfur

Table 2.
MECHANICAL PROPERTIES OF OFFERED AND KNOWN STEEL Melting Temporary resistance, σ _in , MPa Elongation, δ,% Relative narrowing, Ψ,% Hardness HB The size of the actual grain score Processing results in the conditions of the existing production of OJSC "SAAZ" Steel offered 1 650 12 44 229-241 6-8 Without remarks 2 670 10 40 229-241 6-8 Without remarks 3 670 10 35 229-241 7-8 Without remarks 4 690 8 35 241-255 7-8 Without remarks 5 680 nine 39 229-241 5-7 Without remarks Outside of the claimed b 630 fifteen 45 217-229 6-8 Rod breakage 7 630 14 42 217-229 7-9 Increased tool consumption 8 680 nine 33 255-269 6-8 Increased tool consumption nine 670 nine 31 255-269 5-6 Rod breakage Famous steel 10 680 10 38 229-241 4-8 Increased tool consumption

Claims (3)

1. Medium carbon steel with high machinability, containing carbon, manganese, silicon, sulfur, phosphorus, iron and inevitable impurities, characterized in that it additionally contains aluminum, calcium and oxygen in the following ratio, wt.%: Carbon 0.42-0.50 Manganese 0.50-0.80 Silicon 0.17-0.37 Sulfur 0,020-0,040 Phosphorus 0.001-0.030 Aluminum 0.03-0.05 Calcium 0.001-0.010 Oxygen 0.001-0.015 Iron and inevitable impurities - The rest the ratio of oxygen and calcium, as well as the ratio of calcium and sulfur are determined by the following dependencies: oxygen / calcium = 1 ÷ 4.5 and calcium / sulfur ≥0.065. 2. Steel according to claim 1, characterized in that it further comprises chromium, nickel, copper, molybdenum, arsenic and nitrogen in the following ratio, wt.%: Chromium No more than 0.25 Nickel No more than 0.25 Copper No more than 0.25 Molybdenum No more than 0.10 Arsenic No more than 0,08 Nitrogen No more than 0.015 3. Steel according to claim 1, characterized in that it contains non-metallic inclusions having a two-layer structure - sulfide with an oxide shell.