RU2262549C1 - Medium-carbon steel with elevated cutting ability - Google Patents

Abstract

FIELD: metal-working.

SUBSTANCE: invention relates to steel, used, for example, in manufacture of ball wrists, pull shaft tips, and spherical joints of car suspension by cold die forging methods. Medium-carbon steel according to invention contains following components, wt %: carbon 0.35-0.42, manganese 0.50-0.80, silicon 0.17-0.37, chromium 0.80-1.10, sulfur 0.020-0.040, vanadium 0.005-0.020, calcium 0.001-0.010, oxygen 0.001-0.015, iron and inevitable impurities - the rest. Oxygen-to-calcium ratio is 1÷4.5 and calcium-to-sulfur ratio ≥0.065. Above-mentioned impurities, in particular, are: Ni up to 0.25, Co up to 0.25, Mb up to 0.10, As up to 0.08, P up to 0.035, and N up to 0.015. Nonmetallic inclusions have two-layer structure: sulfide with oxide shell.

EFFECT: enhanced cutting ability and enabled cross hardenability of profiled iron up to 25 mm in diameter at the same process plasticity.

3 cl, 2 tbl

Description

The invention relates to the field of metallurgy, in particular to the development of medium-carbon chrome-containing steel of high machinability, used for the manufacture of ball fingers, tie rods and ball bearings of a car suspension obtained by cold forming.

Known structural steel containing (wt.%): Carbon 0.36-0.44%, manganese 0.50-0.80%, silicon 0.25-0.45%, chromium 0.85-1.50%, titanium 0.02-0.04%, aluminum 0.005-0.015% , boron 0.003-0.005%, calcium 0.001-0.004%, copper 0.2-0.6%, nickel 0.2-0.5, barium 0.01-0.04%, iron - the rest, with the ratio Cu / Mn + Ni = 0.15-0.75. (RU Patent of the Russian Federation 2023048 C1, C 22 C 38/54, published November 15, 1994).

The closest in technical essence and the achieved effect to the proposed steel is steel containing (wt.%): Carbon 0.35-0.45%, manganese 0.50-0.80%, silicon 0.17-0.37%, chromium 0.8-1.10%, vanadium 0.04-0.09%, aluminum 0.005-0.015%, calcium 0.001-0.004%, nitrogen 0.005-0.009, copper 0.25-0.40%, magnesium 0.0005-0.0009%, iron and unavoidable impurities - the rest. The sulfur content is 0.01-0.02 wt.%; the phosphorus content is 0.015-0.020 wt.% (SU USSR Copyright Certificate SU 1216241 A, C 22 C 38/24, published on 03/07/1986).

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 high phosphorus content in steel, which will contribute (given the presence of manganese and chromium in the steel and the absence of molybdenum) to the intensive development of reversible temper brittle processes during heat treatment.

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 25 mm, as well as maintaining a high level of technological ductility of steel.

The task is achieved by the fact that proposed

1) medium-carbon chromium-containing steel with increased machinability, containing carbon, manganese, silicon, chromium, sulfur, vanadium, calcium, iron and inevitable impurities, characterized in that it additionally contains oxygen in the following ratio, wt.%:

carbon 0.35-0.42 manganese 0.50-0.80 silicon 0.17-0.37 chromium 0.80-1.10 sulfur 0,020-0,040 vanadium 0.005-0.020 calcium 0.001-0.010 oxygen 0.001-0.015 iron and inevitable impurities             rest

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 also contains nickel, copper, molybdenum, arsenic and nitrogen as impurities in the following ratio, wt.%:

nickel no more than 0.25% copper no more than 0.25% molybdenum no more than 0.10% arsenic no more than 0.08%, phosphorus no more than 0.035% 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 (a bar of hot-rolled long products of round diameter up to 25 mm), which provides, on the one hand, increased cutting characteristics even with wide cutters during transverse feeding a cutting tool, on the other hand, is 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 (0.42%) is due to the need to ensure the required level of ductility of steel, and the lower - 0.35%, respectively - to ensure the required level of strength and hardenability of this 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 hardening the upper limit of the vanadium content of 0.02% is due to the need to ensure the required level of ductility of steel, and the lower - respectively 0.005% - to ensure buoy strength level of the 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. Moreover, the upper level of manganese 0.80% and chromium 1.10% is determined by the need to ensure the required level of ductility of steel, and the lower 0.50% manganese and 0.80% chromium, respectively, by the need to provide the required level of strength and hardenability of this steel.

Silicon refers to ferrite-forming elements. The lower silicon limit of 6.17% 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.

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 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. The upper level of oxygen content of 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.

The ratio

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

A calcium / sulfur ratio of ≥ 0.065% determines the conditions of globular non-metallic 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.

Comparative analysis with the prototype allows us to conclude that the claimed composition differs from the known one by the 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 features 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-industrial ladle - immersion pipe with argon feed,

- tundish - slag-forming mixture,

- tundish - 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 workpiece 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. 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 medium-carbon chrome-containing steel with increased machinability provides two-layer sandwich-nonmetallic inclusions that guarantee, on the one hand, the provision of improved cutting characteristics, on the other hand, a favorable ratio of 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 Cr V Al Cu Sa Mg N O Ni Mo As Fe 1* 2 * Steel offered 1 0.35 0.80 0.37 0.020 0.011 1.10 0.02 0.02 0.003 - 0.003 0.003 0.01 0.02 0.01 rest 0.150 1 2 0.39 0.70 0.25 0.025 0.016 1.0 0.01 0.03 0.002 - 0.002 0.002 0.11 0.01 0.01 rest 0.080 1 3 0.40 0.80 0.27 0.029 0.012 0.92 0.01 0.0) 0.002 - 0.007 0.007 0.14 0.09 0.02 rest 0.069 3.5 4 0.38 0.60 0.20 0.040 0.011 0.85 0.02 0.01 0.004 - 0.015 0.015 0.19 0.03 0.03 rest 0.100 3.75 5 0.42 0.50 0.17 0.035 0.014 0.80 0.005 0.02 0.003 - 0.012 0.012 0.22 0.04 0.04 rest 0.086 4 Outside of the claimed 6 0.39 0.85 0:17 0.045 0.015 1.15 0.022 0.01 0.002 - 0.001 0.001 0.15 0.01 0.05 rest 0.022 0.5 7 0.45 0.90 0.38 0.021 0.017 0.82 0.015 0.02 0.001 - 0.005 0.005 0.27 0.03 0.01 rest 0.048 5 8 0.33 0.48 0.16 0.031 0.015 0.77 0.03 0.03 0.001 - 0.003 0.003 0.17 0.02 0.01 rest 0.032 3 nine 0.40 0.54 0.25 0.010 0.016 0.98 0.02 0.01 0.001 - 0.015 0.015 0.18 0.02 0.10 rest 0.100 fifteen Famous steel 10 0.40 0.66 0.25 0.011 0.018 0.92 0.05 0.01 0.32 0.001 0.0007 0.007 The ratio 1 * - oxygen / calcium, The ratio 2 * - calcium / sulfur

Table 2. MECHANICAL PROPERTIES OF OFFERED AND KNOWN STEEL Melting Temporary resistance, σ _in , MPa Elongation, δ,% Relative narrowing, ψ,% Hardenability, critical diameter Processing Results Steel offered 1 520 24 64 29th Without remarks 2 530 25 62 thirty Without remarks 3 535 23 64 35 Without remarks 4 545 22 65 37 Without remarks 5 540 21 61 32 Without remarks Outside of the claimed 6 570 eighteen 65 25 Increased tool consumption 7 560 19 62 22 Increased tool consumption 8 580 eighteen 63 26 Increased tool consumption nine 570 19 61 twenty Increased tool consumption Famous steel 10 580 19 58 21 Increased tool consumption

Claims (3)

1. Mid-carbon chromium-containing steel with increased machinability, containing carbon, manganese, silicon, chromium, sulfur, vanadium, calcium, iron and inevitable impurities, characterized in that it additionally contains oxygen in the following ratio, wt.%: Carbon 0.35-0.42 Manganese 0.50-0.80 Silicon 0.17-0.37 Chromium 0.80-1.10 Sulfur 0,020-0,040 Vanadium 0.005-0.020 Calcium 0.001-0.010 Oxygen 0.001-0.015 Iron and inevitable impurities Rest 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. Steel according to claim 1, characterized in that it also contains nickel, copper, molybdenum, arsenic and nitrogen as impurities in the following ratio, wt.%: Nickel No more than 0.25 Copper No more than 0.25 Molybdenum No more than 0.10 Arsenic No more than 0,08 Phosphorus No more than 0,035 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.