RU2507293C1 - Low-carbon alloyed steel of high cutting processibility - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: steel has the following chemical composition, wt %: carbon 0.13-0.21, silicon 0.17-0.37, manganese 0.70-1.10, chrome 0.80-1.10, nickel 0.80-1.10, stannum 0.05-0.30, and iron and impurities are the rest. Steel contains the following components as impurities, wt %: sulphur - not more than 0.025, phosphorus - not more than 0.025, molybdenum - not more than 0.10, copper - not more than 0.20. Ratio of stannum content to copper content is within 0.3 to 6, and total content of sulphur and stannum does not exceed 0.31 wt %.

EFFECT: enhanced steel processibility by cutting and increased productivity of its hot pressure treatment process at maintaining the required mechanical properties of metal; improved environmental situation of a production process.

4 cl, 2 tbl, 15 ex

Description

The invention relates to ferrous metallurgy, and in particular to the production of steels with special technological properties that are used to produce critical machine parts.

The prior art steel with high machinability (patent JP 1047839, publ. 02.22.1989, IPC C22C 38/60) containing carbon, silicon, manganese, copper, tin and iron in the following ratio, wt.%:

- carbon - 0.06-0.60;

- silicon - 0.01-0.50;

- manganese - 0.30-2.00;

- copper - 0.05-0.30;

- tin - 0-0.015;

- iron is the basis.

In addition, the composition of the steel may include, wt.%:

- chrome - not more than 2.00;

- nickel - not more than 5.00;

- sulfur - not more than 0.035;

- phosphorus - not more than 0.035;

- molybdenum - not more than 1.00.

The phase composition of this steel is characterized by the presence of tin in the form of a solid solution in iron, which increases the brittleness of ferrite and facilitates the destruction of the surface layer during the machining of metal. At the same time, it includes manganese sulfide, the presence of which helps to prevent the particles of the processed material from sticking to the cutting edge of the blade tool due to the formation of a lubricating layer in their contact zone.

Known steel has the following disadvantages:

- there is no information about the maximum permissible total content of components that improve machinability, which determines the mechanical properties of steel, and therefore its suitability for further use in accordance with the intended purpose;

- while tin and copper are present in the composition for the last element, the most favorable content is not indicated from the point of view of the possibility of preventing the appearance of defects during the hot processing operation that occur when the concentration of this impurity is increased due to a decrease in the melting temperature of the excess metal phase in the surface a layer of steel;

- there is no data on the content of sulfur and phosphorus, at which the best combination of high machinability of steel by cutting and its increased hot deformability is achieved, provided that the specified values of the mechanical properties of metal products are maintained;

- the chemical composition does not provide the necessary machinability required for the implementation of high-speed machining of steel on modern metal-cutting equipment.

In addition, it is known low alloy steel with high machinability (TU 14-136-344-98. Calibrated steel, carbon and alloy bismuth containing high machinability by cutting (with Change No. 1). - Introduction. 1998-08-01), containing carbon, silicon, manganese, chromium, nickel, bismuth and iron in the following ratio of components, wt.%:

- carbon - 0.13-0.21;

- silicon - 0.17-0.37;

- manganese - 0.70-1.10;

- chrome - 0.80-1.10;

- nickel - 0.80-1.10;

- bismuth - 0.12-0.20;

- iron is the basis.

In addition, the steel as impurities may additionally contain, wt.%:

- sulfur - not more than 0.035;

- phosphorus - not more than 0.035;

- molybdenum - not more than 0.10;

- copper - not more than 0.30.

The disadvantages of this steel include the following:

- bismuth is extremely toxic and, according to established hygienic standards, refers to “highly hazardous” substances, which limits its use in the steel industry due to a sharp deterioration in the working conditions of workers in the production of automatic steels;

- the fundamental impossibility of further improving machinability by cutting, which is required under current conditions to increase the share of high-speed machining in the total volume of all surface shaping methods, by sequentially increasing the content of bismuth steel more than the known values, since exceeding its ultimate solubility in the iron matrix leads to a significant deterioration in mechanical properties metal;

- there is no data on the maximum permissible total content of elements that facilitate the process of blade processing, which, while present, can impair the complex of mechanical properties of steel, thereby directly affecting the operational reliability of the finished product, in particular, and the entire metal structure as a whole;

- the optimum residual copper content is not indicated, which avoids the deterioration in the hot deformability of steel due to the release of structurally free copper, which penetrates to the grain boundaries of the surface layer, reducing its strength, or as a result of strong oxidation of the grain boundaries without significant enrichment with this impurity;

- due to the low degree of assimilation by steel, due to the high elasticity of bismuth vapor and its sufficiently low boiling point, to achieve the required mechanical and technological properties of the structural material in the metallurgical industry, it is necessary to implement complex technical and design solutions;

- the high cost of bismuth, which, together with its extremely small assimilation, requiring a deliberate large cost overrun, leads to a significant increase in the cost of automatic steels, a decrease in profits and a decrease in the competitiveness of the metallurgical enterprise;

- the uneven distribution of bismuth in the body of the ingot due to its high physical density makes it difficult to guarantee the required properties of steel from melting to melting and causes a decrease in the yield of metal, and, consequently, the productivity of the hot pressure treatment due to the formation of defects in the places of the greatest accumulation of this element.

This steel, as the most similar in chemical composition and mechanical properties, is taken as the closest analogue.

The problem to which this invention is directed is to increase the machinability of steel by cutting and to increase the productivity of the process of its hot pressure treatment while maintaining the required mechanical characteristics of the metal, as well as improving the environmental situation of production by reducing the aggressiveness of harmful emissions into the atmosphere due to the complete exclusion from the composition of the material highly toxic components.

The technical solution of the problem is achieved due to the fact that the proposed steel in its composition as an element that improves machinability by cutting, contains tin in the following ratio of components, wt.%:

- carbon - 0.13-0.21;

- silicon - 0.17-0.37;

- manganese - 0.70-1.10;

- chrome - 0.80-1.10;

- nickel - 0.80-1.10;

- tin - 0.05-0.30;

- iron is the basis.

In addition, as impurities, the steel may additionally contain, wt.%:

- sulfur - not more than 0.025;

- phosphorus - not more than 0.025;

- molybdenum - not more than 0.10;

- copper - not more than 0.20.

The ratio of tin to copper content is in the range from 0.3 to 6, and the total sulfur and tin content does not exceed 0.31 wt.%.

Tin, as an alloying element that improves the machinability of steel by cutting, has certain advantages over traditionally used bismuth for this purpose.

Firstly, tin has a high degree of absorption of the molten metal bath, which is explained by the low vapor pressure of this element and the boiling point, which is much higher than the operating temperatures of steelmaking processes, which impede its free evaporation from the surface of the melt. This avoids unnecessary complication of steel production technology.

Secondly, the price of tin on the world metals market is on average 30% lower than that of bismuth. In combination with high assimilation, this allows for more rational use of material resources and in some cases to reduce the cost of steel by reducing the consumption of alloying components, since when determining the required amount of additional materials, they are preliminarily based on their increased versus the required mass, taking into account the expected losses of oxidation and evaporation.

Thirdly, tin is evenly distributed in the body of the ingot, which is due to its density comparable to the density of liquid steel. In combination with the optimal copper content and in regulating the concentration ratios of these elements, this helps to prevent the appearance of defects in the surface layer of the metal during the pressure treatment operation and thereby increase the yield rate, increasing the productivity of the third redistribution.

Fourth, bismuth is a “highly hazardous” substance, and its content in the workshop’s atmosphere is limited by the average shift maximum permissible concentration (MPC) of 0.5 mg / m ³ , and the MPC and an approximately safe level of exposure (SEC) in the air a working area for pure tin is not currently established.

In addition, unlike bismuth tin, under no circumstances does steel smelting produce harmful gas and dust emissions. On the one hand, this is due to a lower chemical affinity for oxygen compared with iron, and on the other hand, a high boiling point and low vapor pressure, as a result of which tin, without oxidation, remains almost completely in the dissolved metal in the metal.

Thus, the use of tin contributes to a significant improvement in the environmental situation of production and the sanitary and hygienic working conditions of workers by reducing the aggressiveness of harmful emissions into the atmosphere due to the complete exclusion of highly toxic components from steel.

The essence of the invention is the identification of the optimal content of tin, copper, sulfur and phosphorus, which achieves the best combination of high machinability of steel by cutting and increase the productivity of the process of its processing by pressure, provided that the required values of mechanical properties are maintained.

As a result of the studies established the following:

- when the tin content is less than the lower limit, it is not possible to achieve the required high level of machinability of steel by cutting;

- subject to the lower limit of tin, the workability of the proposed steel is comparable to the workability of a metal of a similar bismuth-containing grade;

- an increase in the content of tin, sulfur and phosphorus above the stated limits leads to a deterioration in the mechanical properties of the metal, as a result of which steel cannot be used for its intended purpose;

- when the total content of sulfur and tin is greater than the regulated limit, the toughness of steel does not meet the requirements of technical conditions;

- excess of the declared copper content, as well as non-compliance with the ratio of tin and copper concentrations in steel leads to a deterioration of the technological properties of the metal;

- when the content of tin, sulfur, phosphorus and copper is within the declared limits, the machinability level of the proposed steel is 12% higher than the machinability of the bismuth-containing analogue, and the productivity of the hot pressure treatment process increases by 8%; at the same time, steel retains its high mechanical characteristics, and its production is characterized by reduced air pollution of the working area and safer working conditions for production personnel.

Tests to determine the mechanical machinability of steel and the productivity of the operation of hot metal forming were carried out on the technical basis of the South Ural State University.

The effectiveness of turning was evaluated by changing the resistance of the tool material at a given cutting speed of the workpieces. As a criterion for assessing the machinability of steel, the value of reduced resistance was established, expressed by the amount of wear of the cutting tool on the rear surface when machining one part.

The productivity of the pressure processing process was estimated by the value of the yield of metal, determined by the ratio of the number of defect-free billets to the total number of deformed ingots.

The workability by cutting and the productivity of pressure treatment of the known low-carbon alloy steel adopted as the closest analogue, which is produced in accordance with the requirements established by TU 14-136-344-98, are set as the base level.

The chemical composition of the analyzed steels is given in table 1.

Table 1 The chemical composition of steels Steel No. pr. The content of the component, wt.% C Si Mn S R Cr Ni Mo Cu Sn Famous one 0.16 0.21 0.17 0.37 0.70 1.10 n.b. 0,035 n.b. 0,035 0.80 1.10 0.80 1.10 n.b. 0.10 n.b. 0.30 - 2 0.13 0.18 0.17 0.37 0.70 1.00 n.b. 0,035 n.b. 0,035 0.80 1.10 0.80 1.10 n.b. 0.10 n.b. 0.30 - Proposed 3 0.20 0.32 0.86 0,034 0,032 0.94 0.91 0.01 0.19 0.29 four 0.19 0.21 0.76 0,021 0,023 0.86 0.89 0.02 0.21 0.28 5 0.19 0.24 0.81 0.019 0.016 0.88 0.95 0.02 0.11 0,03 6 0.20 0.31 0.87 0.014 0.018 0.90 0.92 0.04 0.08 0.05 7 0.18 0.26 0.79 0,025 0,025 0.94 0.83 0,03 0.20 0.30 8 0.18 0.28 0.81 0.012 0,020 0.96 0.87 0.01 0.16 0.32 9 0.19 0.35 0.86 0.011 0.017 1.05 0.94 0,03 0.17 0.05 10 0.17 0.24 0.88 0.018 0.015 0.91 0.85 0,03 0.20 0.06 eleven 0.19 0.32 0.80 0.019 0,021 0.98 0.88 0.02 0.04 0.24 12 0.18 0.33 0.74 0,023 0,022 0.96 0.90 0.02 0.04 0.27

Continuation of table 1 Steel No. pr. The content of the component, wt.% C Si Mn S R Cr Ni Mo Cu Sn Proposed 13 0.17 0.27 0.94 0,020 0.014 0.82 0.86 0.05 0.05 0.29 fourteen 0.19 0.29 0.76 0.024 0,020 0.90 0.88 0.01 0.10 0.29 fifteen 0.18 0.25 0.79 0.008 0.016 0.89 0.85 0,07 0.06 0.25

The strength and plastic characteristics of the compared steels in the deformed and heat-treated state (after quenching and tempering), as well as the measured level of mechanical workability and approximated productivity of the technological operation of hot plastic deformation are presented in table 2.

table 2 Mechanical and technological properties of steels Steel No. pr. Temporary resistance σ _in , MPa Yield strength σ _0.2 , MPa Elongation δ,% Impact strength KCU, J / cm ² Pressure processing performance Machinability Famous one N.M. 1180 N.M. 930 N.M. 7.0 N.M. 69 1.00 1.00 2 N.M. 1080 N.M. 835 N.M. 8.0 N.M. 78 3 1374 1293 6.2 61 No evaluation four 1372 1294 8.0 80 0.93 1.13 5 1318 1262 10.0 97 1.17 0.94 6 1329 1273 9.8 96 1.16 1.00 7 1377 1296 8.0 78 1,02 1.14 8 1371 1290 7.0 67 No evaluation Proposed 9 1333 1276 9,4 94 1.14 0.98 10 1336 1274 9.2 94 1.14 1.00 eleven 1366 1284 8.4 85 1.00 1,11 12 1368 1291 8.0 82 0.99 1.12 13 1373 1294 8.4 69 1,03 1.14 fourteen 1376 1290 8.2 68 No evaluation fifteen 1370 1287 8.8 86 1,08 1.12

Examples 1, 2. Known low-carbon alloy steel with high machinability by cutting according to TU 14-136-344-98. The level of mechanical workability and the productivity of hot processing are taken as reference values for comparison. During the processes of steel production, the release of highly toxic bismuth vapors into the surrounding atmosphere.

Example 3. The content of sulfur and phosphorus is greater than the declared values. The mechanical characteristics of the metal do not meet the requirements of TU. Evaluation of the effectiveness of machining steel and the performance of the hot forming process was not carried out.

Example 4. The copper content is greater than the upper limit. There is a decrease in the productivity of the process of hot plastic deformation of the metal.

Example 5. The tin content is less than the lower limit. The machinability level of the proposed steel is lower than that of the known analogue.

Example 6. The tin content in the steel is at the lower limit of the claimed range. The machinability by cutting of the proposed steel is comparable to the machinability of its analogue.

Example 7. The content of sulfur, phosphorus, copper and tin is at the upper limit of the claimed ranges. The indicators of the mechanical properties of the metal correspond to the minimum maximum permissible values adopted for the bismuth-containing analog.

Example 8. The tin content is greater than the upper limit. The values of the mechanical properties of the metal are beyond the scope established by TU. The study of the technological properties of the proposed steel was not conducted.

Example 9. The ratio between the content of tin and copper goes beyond the lower regulated border. The efficiency of the turning process is reduced.

Example 10. The ratio between the content of tin and copper is at the lower limit of the claimed range. The level of machinability of the proposed steel is comparable to the machinability of the known analogue.

Example 11. The ratio between the content of tin and copper has a value corresponding to the upper declared limit. There is no increase in the efficiency of the process of hot plastic deformation of steel.

Example 12. The ratio between the content of tin and copper goes beyond the upper set limit. The productivity of metal forming decreases.

Example 13. The total content of sulfur and tin is at the level of the established limit. The value of impact strength of steel corresponds to the minimum allowable value from the technical conditions developed for the analogue.

Example 14. The total sulfur and tin content exceeds the regulated value. The toughness of steel does not meet the requirements of TU, and steel cannot be used in accordance with the intended purpose. The study of technological characteristics was not conducted.

Example 15. The content of all elements is within the stated limits. The complex of technological properties of low-carbon alloy steel is optimal. The machinability index while maintaining the mechanical characteristics of the metal is 12% higher than that of the known analogue, and the productivity of hot pressure processing increases by 8%. At the same time, air pollution of the working area is significantly reduced.

Thus, a higher level of machinability by cutting the proposed steel and an increase in the productivity of the hot forming process together with maintaining the complex of the required mechanical properties of the metal and improving the ecology of metallurgical production allows us to recommend it for industrial applications.

Claims (4)

1. Low-carbon alloy steel with high machinability, containing carbon, silicon, manganese, chromium, nickel and iron, characterized in that it additionally contains tin in the following ratio, wt.%:
carbon 0.13-0.21 silicon 0.17-0.37 manganese 0.70-1.10 chromium 0.80-1.10 nickel 0.80-1.10 tin 0.05-0.30 iron the basis 2. Steel according to claim 1, characterized in that it additionally limits the content of harmful impurities, wt.%: Sulfur - not more than 0.025, phosphorus - not more than 0.025, copper - not more than 0.20. 3. Steel according to claim 2, characterized in that the ratio of tin to copper content is in the range from 0.3 to 6. 4. Steel according to claim 2, characterized in that the total sulfur and tin content does not exceed 0.31 wt.%.