RU2467088C1 - Low-alloy chromium steel of higher machinability - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to ferrous metallurgy, namely, to production of special steels for making critical parts of machinery. Proposed steel comprises the following components in wt %: carbon 0.36 - 0.44, silicon 0.17 - 0.37, manganese 0.60 - 0.90, chromium 0.80 - 1.10, tin 0.05 - 0.30, iron and impurities making the rest. Said impurities contain the following components in wt %: sulfur - not over 0.025, phosphorus - not over 0.025, copper - not over 0.20. Tin-to-copper ratio may vary from 0.3 to 6.

EFFECT: better machinability, efficiency and better ecology.

3 cl, 2 tbl, 12 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.

In the prior art, steel with high workability (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;

- sulfur - not more than 0.035;

- phosphorus - not more than 0.035;

- nickel - not more than 5.00;

- molybdenum - not more than 1.00.

The structure of this steel due to the sufficiently high solubility of tin in the iron matrix is characterized by its existence in the form of a solid solution, which leads to an increase in the brittleness of ferrite in the process of metal machining. Along with this, it includes a sulfide phase based on manganese compounds, which increases the wear resistance of turning tools due to the formation of a lubricant layer and to prevent sticking of particles of the processed material on the cutting edge of the blade tool.

Known steel has the following disadvantages:

- with the simultaneous presence of tin and copper in the last element, the optimum content is not indicated, which avoids the formation of defects during the pressure treatment process and the manifestation of red brittleness, which, with an increase in the concentration of this impurity, is a consequence of a decrease in the melting temperature of the excess metal phase in the surface layer enriched with it become;

- there is no information 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 the products are maintained;

- the chemical composition does not provide the necessary machinability by cutting required for the performance of high-quality machining of steel on modern high-tech equipment.

In addition, low-alloy chrome steel of high machinability AC40X is known (GOST 1414-75. Rolled steel of high machinability by cutting. Technical conditions (Reprint, as amended No. 1, 2, 3, as amended). - Introduction. 1977-01-01 . - M .: Publishing house of standards) containing carbon, silicon, manganese, chromium, lead and iron in the following ratio of components, wt.%:

- carbon - 0.36-0.44;

- silicon - 0.17-0.37;

- manganese - 0.60-0.90;

- chrome - 0.80-1.10;

- lead - 0.15-0.30;

- 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;

- nickel - not more than 0.30;

- copper - not more than 0.30.

The disadvantages of this steel include the following:

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

- traditional components that facilitate the blade cutting process - sulfur and phosphorus - in the presence of lead do not give a tangible effect, and the excess of their content, which provides high-quality steel, is impractical due to the additive negative effect of these elements on the complex of mechanical characteristics of the metal;

- the impossibility of realizing a further increase in machinability by cutting by the method of successively increasing the concentration in lead steel of more than the known values, since exceeding the limit of its solubility in the iron matrix leads not only to a deterioration in the mechanical properties of the metal, but also to an increase in their anisotropy as a whole;

- low absorption by steel due to the high vapor pressure and a sufficiently low boiling point, as well as the large specific gravity of lead, which determines its uneven distribution in the body of the ingot, in order to obtain a given level of mechanical and technological properties of the structural material, complex technical and design decisions are required in the metallurgical industry;

- in the process of high-temperature deformation of steel containing lead, it diffuses to the surface of the workpiece, which leads to a decrease in the yield of metal, and, consequently, the productivity of the pressure treatment due to the formation of surface defects in places of the greatest accumulation of this element;

- Lead has a pronounced toxicological effect on the human body and, according to the standards established to date, refers to “extremely dangerous” 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.

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, contains tin in the following ratio of components, wt.%:

- carbon - 0.36-0.44;

- silicon - 0.17-0.37;

- manganese - 0.60-0.90;

- chrome - 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;

- nickel - not more than 0.30;

- copper - not more than 0.20.

Moreover, the ratio of tin to copper content is in the range from 0.3 to 6.

The first advantage of using tin as an alloying element that improves machinability is that it is autonomously released at grain boundaries and, without weakening the positive effect of phosphorus and manganese sulfides on the results of mechanical cutting, initiates intergranular destruction of the surface layer of the metal. In combination with the optimum content of sulfur and phosphorus in steel, this allows you to get the effect of increasing its machinability by 14% while maintaining the necessary values of the mechanical characteristics established by GOST.

The second advantage is a sufficiently large degree of assimilation of tin by the melt, which is due to the low vapor pressure and high boiling point. This will allow more rational use of material resources and in some cases reduce the cost of steel by reducing the consumption of alloying elements, 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.

The third advantage is the uniform distribution of tin over the cross section of the ingot, which is determined by its density, comparable with the density of liquid steel. In combination with the optimal copper content and when regulating the concentration ratio of these elements, this avoids metal loss during high-temperature deformation and thereby increase its yield, increasing the productivity of the third redistribution.

The fourth advantage of using tin is the lack of mass transfer to the interface between the rolls and the steel strip, which improves their adhesion and reduces the downtime of equipment associated with the readjustment of the rolling mill, thereby increasing the productivity of the metal forming process.

The fifth advantage is associated with the improvement of the ecology of metallurgical production and needs more detailed consideration. Lead is an “extremely hazardous” substance, and its content in the workshop’s atmosphere is limited by the average shift maximum permissible concentration (MPC) of 0.05 mg / m ³ , and the MPC and the approximately safe level of exposure (SEC) in the air of the working area for Tin is not currently installed.

Tin in steel does not form any toxic compounds, as compared with iron it has a lower chemical affinity for oxygen and, as a result, it remains almost completely in the metal in a dissolved state, without being oxidized during smelting. Also, in the production of steel, the possibility of the existence of tin in the gaseous state, which is most dangerous for most metals, is excluded, since this element has a high boiling point, significantly higher than the operating temperatures of steelmaking processes, and has a low vapor pressure, which prevents its free evaporation from the melt surface.

Thus, unlike lead, tin does not form harmful substances under any circumstances, and therefore the environmental aspect of producing automatic grades is no longer relevant.

The listed advantages of tin are evidence of the advisability of its use as an alternative to lead as an alloying component that improves the machinability of steel by cutting.

The essence of the invention is the identification of the optimal content of tin, sulfur, phosphorus and copper, 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 lead-containing grade;

- an increase in the content of tin, sulfur and phosphorus above the stated limits leads to the output of the values of the mechanical properties of steel beyond the limits established by GOST;

- excess of the declared copper content, as well as non-compliance with the ratio of the concentrations of tin and copper 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 stated limits, the machinability level of the proposed steel is 14% higher than the machinability of the lead-containing analogue, and the productivity of the hot pressure treatment increases by 10%; 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 machinability of steel and the efficiency 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 treatment of low-alloy chrome-plated steel AS40X, produced in accordance with the requirements of GOST 1414-75, are taken as the basic level.

The chemical composition of the known steel grade AC40X, taken as the closest analogue, and the proposed steel are given in table 1.

Table 1 The chemical composition of steels Steel No. The content of the component, wt.% etc. FROM Si Mn S P Cr Ni Cu Sn AC40X, GOST 1414-75 one 0.36 0.17 0.60 n.b. n.b. 0.80 n.b. n.b. - 0.44 0.37 0.90 0,035 0,035 1.10 0.30 0.30 2 0.41 0.25 0.72 0,033 0,034 0.90 0.15 0.18 0.28 3 0.41 0.29 0.66 0,023 0,023 0.96 0.17 0.25 0.29 four 0.42 0.28 0.68 0.016 0.017 0.99 0.22 0.09 0.04 5 0.39 0.30 0.74 0.015 0.019 0.94 0.18 0.14 0.05 6 0.38 0.26 0.81 0,025 0,025 0.89 0.26 0.20 0.30 Proposed 7 0.41 0.27 0.73 0,021 0.024 0.91 0.16 0.21 0.34 8 0.42 0.35 0.69 0.014 0.015 1,04 0.23 0.17 0.05 9 0.40 0.31 0.76 0.012 0.014 0.90 0.19 0.20 0.06 10 0.39 0.26 0.70 0,020 0,020 0.92 0.08 0.04 0.24 eleven 0.41 0.33 0.65 0.024 0,022 0.95 0.12 0.04 0.27 12 0.38 0.25 0.69 0.010 0.016 0.88 0.25 0.08 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 hot plastic deformation process are presented in table 2.

Example 1. Known low-alloy chrome steel high machinability AC40X. The level of mechanical workability and the productivity of hot processing are taken as reference values for comparison. During steelmaking processes, extremely toxic lead 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 GOST. 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 of the proposed steel by cutting 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 established by GOST for a lead-containing analogue.

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 GOST. The study of the technological properties of the proposed steel was not conducted.

Example 8. The ratio between the content of tin and copper goes beyond the lower regulated border. The efficiency of the turning process is reduced.

Example 9. 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 10. 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 11. The ratio between the content of tin and copper goes beyond the upper set limit. The productivity of metal forming decreases.

Example 12. The content of all elements is within the stated limits. The complex of technological properties of low-alloy chromium steel is optimal. The machinability index while maintaining the mechanical characteristics of the metal is 14% higher than that of the known analogue, and the productivity of hot pressure processing increases by 10%. 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. Low-alloy chromium steel of high workability, containing carbon, silicon, manganese, chromium and iron, characterized in that it additionally contains tin in the following ratio of components, wt.%:
carbon 0.36-0.44 silicon 0.17-0.37 manganese 0.60-0.90 chromium 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.