RU2511008C1 - Intermediate-carbon structural steel of high cutting processibility - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: steel contains the following component ratio, wt %: carbon 0.37-0.43, silicon 0.17-0.37, manganese 0.50-0.80, chrome 0.60-0.90, nickel 0.70-1.10, molybdenum 0.15-0.25, 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, copper not more than 0.20. Ratio of molybdenum content to stannum content does not exceed 0.8.

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

3 cl, 2 tbl, 10 ex

Description

The invention relates to ferrous metallurgy, and in particular to the production of steels with special technological properties used for the manufacture of 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;

- molybdenum - not more than 1.00;

- sulfur - not more than 0.035;

- phosphorus - not more than 0.035.

The tin present in the form of a solid solution with iron increases the brittleness of the ferritic component of the structure of this steel and reduces the cutting force necessary to break its surface layer. The excess phase, which includes manganese sulfide inclusions, forms a lubricant layer in the contact zone of the processed material with the cutting tool and helps to prevent their setting during metal turning.

Known steel has the following disadvantages:

- at a high residual content of molybdenum, its optimum value is not indicated despite the fact that it helps to clean the grain boundaries from colored impurities, and with an increase in the mass fraction of this component, the likelihood of a decrease in the productivity of the machining operation increases due to a decrease in the concentration of structurally free tin in the indicated region of the structure become;

- 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 required level of mechanical properties is maintained;

- the chemical composition as a whole and the tin content in particular do not provide the required level of machinability necessary for the implementation of high-performance blade cutting under conditions of increasing the share of high-speed machining of steel in the total volume of all surface shaping methods.

In addition, medium-carbon structural steel of high machinability by cutting AV40KHGNM (TU 14-136-344-98. Steel is calibrated, carbon and alloyed bismuth-containing high machinability by cutting (with Change No. 1). - Introduction. 1998-08-01) containing carbon , silicon, manganese, chromium, nickel, molybdenum, bismuth and iron in the following ratio of components, wt.%:

- carbon - 0.37-0.43;

- silicon - 0.17-0.37;

- manganese - 0.50-0.80;

- chrome - 0.60-0.90;

- nickel - 0.70-1.10;

- molybdenum - 0.15-0.25;

- bismuth - 0.12-0.20;

- iron is the basis.

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

- sulfur - not more than 0,030;

- phosphorus - not more than 0.035;

- copper - not more than 0.30.

The disadvantages of this steel include the following:

- a low degree of assimilation of bismuth, due to the high vapor pressure and low boiling point, and, as a result, a significant increase in the cost of steel due to its deliberate cost overruns, because when calculating the required amount of alloying additives in advance, they are assumed to be higher than the required mass taking into account the expected oxidation losses and evaporation reaching 80%;

- 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 engaged in the production of this metal product;

- uneven distribution of bismuth in the body of the ingot due to its high physical density, which makes it difficult to guarantee the desired properties of steel and causes a decrease in the yield of metal, and, consequently, the productivity of the hot pressure treatment due to the accumulation of this component in certain parts of the volume and enhancing the anisotropy of properties over the cross section of the conversion workpiece;

- bismuth has a pronounced toxicological effect on the human body and, according to established hygienic standards, refers to “highly hazardous” substances, therefore, ferrous metallurgy enterprises are gradually abandoning its use due to a sharp deterioration in the working conditions of workers in the production of automatic steels;

- the impossibility of further improving the mechanical workability of steel, which is required in modern conditions of a constant desire to increase labor productivity, by the method of successively increasing the bismuth content is more than the known values, since exceeding its solubility limit in iron leads to a deterioration in the mechanical properties of steel, as a result of which it cannot be used in accordance with the intended purpose.

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 - 0.37-0.43;

- silicon - 0.17-0.37;

- manganese - 0.50-0.80;

- chrome - 0.60-0.90;

- nickel - 0.70-1.10;

- molybdenum - 0.15-0.25;

- 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;

- copper - not more than 0.20.

Moreover, the ratio of molybdenum to tin does not exceed 0.8.

Tin in comparison with bismuth, traditionally used earlier to increase the machinability of steel by cutting, has several advantages.

First, tin has a much higher solubility limit in iron compared with bismuth: 9.20 at.% And 0.17 at.%, Respectively. In combination with the optimal content of sulfur and phosphorus in steel, this will further expand the permissible limits of its content in steel and opens up broad prospects for the development of progressive high-performance methods of surface shaping.

Secondly, this element has a high degree of assimilation 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.

Thirdly, 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.

Fourth, tin is evenly distributed in the body of the ingot, which is due to its density comparable to the density of liquid steel. This allows you to prevent the appearance of defects in the surface layer of the workpiece during the operation of its hot pressure treatment and to increase the percentage of yield of metal, increasing the productivity of the third redistribution.

Fifthly, 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.

This is due to the fact that 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 the approximately safe exposure level (SEC) in the air of the working area for pure metal tin is not installed today. In addition, tin, due to the lower chemical affinity for oxygen compared with iron, a high boiling point, and low vapor pressure, under no circumstances does steel smelting produce harmful gas and dust emissions, due to which this element remains almost completely oxidized without oxidation in metal in a dissolved state.

The essence of the invention is the identification of the optimal content of tin, sulfur, phosphorus, copper and molybdenum, 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 mechanical machinability of steel;

- 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;

- non-compliance with the ratio of concentrations of molybdenum and tin in steel leads to a deterioration in its technological properties;

- when the content of tin, sulfur, phosphorus and molybdenum is within the stated 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 increases by 9%; 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 machinability by cutting and the productivity of pressure processing of medium-carbon structural steel of high machinability by cutting AV40KHGNM, which is produced in accordance with the requirements of TU 14-136-344-98, are taken as the basic level.

The chemical composition of the known steel grade AB40HGNM, which is taken as the closest analogue, and the proposed steel are shown in table 1.

Table 1 The chemical composition of steels Steel No. pr. The content of the component, wt.% FROM Si Mn S P Cr Ni Mo Cu Sn AB40HGNM one 0.37 0.43 0.17 0.37 0.50 0.80 n.b. 0,030 n.b. 0,035 0.60 0.90 0.70 1.10 0.15 0.25 n.b. 0.30 - Proposed 2 0.38 0.30 0.66 0,031 0,030 0.74 0.76 0.17 0.19 0.27 3 0.39 0.23 0.63 0,023 0.024 0.76 0.82 0.16 0.22 0.25 four 0.39 0.27 0.71 0.012 0.015 0.68 0.73 0.20 0.12 0,03 5 0.38 0.33 0.57 0,020 0.017 0.80 0.78 0.17 0.15 0.05 6 0.41 0.25 0.69 0,025 0,025 0.84 0.81 0.19 0.20 0.30 7 0.40 0.29 0.72 0.024 0,020 0.79 0.77 0.16 0.19 0.31 8 0.38 0.28 0.76 0.017 0.013 0.66 0.79 0.16 0.18 0.20 9 0.41 0.35 0.78 0.015 0.016 0.81 0.85 0.17 0.11 0.20 10 0.40 0.26 0.69 0.013 0.014 0.69 0.75 0.18 0,07 0.26

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 _B , MPa Yield strength σ _0.2 , MPa Elongation δ,% Impact strength KCU, J / cm ² Pressure processing performance Machinability AB40HGNM one N.M. 980 N.M. 835 N.M. 12.0 N.M. 88 1.00 1.00 2 1276 1225 10,4 75 No evaluation 3 1273 1221 12.0 90 0.94 1.13 four 1232 1197 13.8 106 1.17 0.99 5 1234 1203 13.6 104 1.16 1.00 Proposed 6 1277 1245 12.0 88 1.01 1.14 7 1269 1242 11.8 85 No evaluation 8 1253 1218 12.8 96 1.10 1.09 9 1251 1215 12.6 95 1D1 1,07 10 1270 1239 12,4 91 1.09 1.12

Example 1. Known medium-carbon structural steel with high machinability by cutting AB40HGNM. The level of mechanical workability and the productivity of hot processing are taken as reference values for comparison. During steelmaking processes, extremely toxic bismuth vapors are released into the surrounding atmosphere.

Example 2. 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 3. 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 4. 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 5. The tin content in 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 6. The content of sulfur, phosphorus, copper and tin is at the upper limit of the declared ranges. The indicators of the mechanical properties of the metal correspond to the minimum maximum permissible values adopted for the bismuth-containing analog.

Example 7. The tin content is greater than the upper limit. The values of the mechanical properties of the metal are beyond the scope established by the technical conditions. The study of the technological properties of the proposed steel was not conducted.

Example 8. The ratio between the content of molybdenum and tin has a value corresponding to the declared limit. The machinability of steel by cutting is optimal for a given tin content.

Example 9. The ratio between the content of molybdenum and tin goes beyond the upper regulated border. There is a weakening of the effect of tin on improving the machinability of steel.

Example 10. The content of all elements is within the stated limits. The complex of technological properties of medium-carbon structural steel has an optimal character. The machinability index while maintaining the mechanical characteristics of the metal is 12% higher than that of the well-known analogue, and the productivity of hot pressure processing increases by 9%. 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 (3)

1. Medium carbon structural steel with high machinability, containing carbon, silicon, manganese, chromium, nickel, molybdenum, iron and impurities, characterized in that it additionally contains tin in the following ratio, wt.%:
carbon 0.37-0.43 silicon 0.17-0.37 manganese 0.50-0.80 chromium 0.60-0.90 nickel 0.70-1.10 molybdenum 0.15-0.25 tin 0.05-0.30 iron and impurities rest 2. Steel according to claim 1, characterized in that the harmful impurities are additionally limited in content, 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 the molybdenum content to the tin content does not exceed 0.8.