RU2696798C1 - Medium carbon chrome-molybdenum easily processed bn-containing steel - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to ferrous metallurgy, particularly, to production of steels with special technological properties used in serial and mass production of critical parts of machines. Steel has the following chemical composition, wt. %: carbon 0.27–0.33, silicon 0.17–0.37, manganese 0.40–0.70, chrome 0.80–1.10, molybdenum 0.15–0.25, boron 0.005–0.009, nitrogen 0.007–0.012, aluminium 0.02–0.04, iron and impurities are the rest. As impurities steel contains, wt. %: sulphur not more, than 0.035, phosphorus not more, than 0.035, nickel not more, than 0.25, copper not more, than 0.30.

EFFECT: increasing machinability of steel by cutting at maintaining required mechanical properties of metal, as well as improving environmental situation of production due to reduction of aggressiveness of hazardous emissions to ambient atmosphere due to exclusion of introduced high-toxic components.

1 cl, 2 tbl, 9 ex

Description

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

Steel 30XM is known from the prior art (GOST 4543-2016. Metal products from structural alloyed steel. Specifications. - Introduction. 2017-10-01. - M.: Standardinform, 2017), containing carbon, silicon, manganese, chromium, molybdenum and iron in the following ratio of components, mass. %:

- carbon - 0.26 - 0.33;

- silicon - 0.17 - 0.37;

- manganese - 0.40 - 0.70;

- molybdenum - 0.15-0.25;

- chrome - 0.80-1.10;

- iron is the basis.

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

- nickel - not more than 0.30;

- copper - not more than 0.30;

- sulfur - not more than 0.035;

- phosphorus - not more than 0.035.

The disadvantages of this steel include the following:

- sulfur and phosphorus, contributing to the improvement of steel cutting, do not significantly affect the mechanical cutting process.

- there are no elements improving the machinability of steel by cutting.

In addition, medium-carbon chrome-molybdenum steel with improved machinability by AC30XM cutting is known (GOST 1414-75. Rolled from structural steel with 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, molybdenum, lead and iron in the following ratio of components, mass%:

- carbon - 0.27-0.33;

- silicon - 0.17-0.37;

- manganese - 0.40-0.70;

- chrome - 0.80-1.10;

- molybdenum - 0.15-0.25;

- lead - 0.15-0.30

- iron is the basis.

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

- sulfur - not more than 0.035;

- phosphorus - not more than 0.035;

- copper - not more than 0.30;

- Nickel - not more than 0.30.

The disadvantages of this steel include the following:

- the obvious futility of further improving the workability of steel by increasing the lead content is greater than the regulated values, since exceeding its maximum solubility in iron leads to a deterioration in mechanical characteristics and an increase in their anisotropy, as well as enhancing the redness of the surface layer during hot metal pressure treatment;

- uneven distribution of lead in the body of the ingot due to its high physical density and high vapor pressure, which makes it difficult to guarantee the required properties of steel from smelting to smelting and causes a decrease in metal yield and, consequently, the productivity of the pressure process due to the formation of defects in places the largest accumulation of this element;

- during hot plastic deformation of steel containing lead, it diffuses to the surface of the workpiece, which leads to the formation of a capillary layer in the indicated area, which worsens the conditions for the rolls to capture a metal strip due to a decrease in the friction coefficient and a decrease in the productivity of rolling equipment;

- Lead is extremely toxic and, according to established hygienic standards, belongs to the highest hazard class 1, therefore, in the steel industry there is a more distinct tendency to abandon its use due to a serious environmental degradation.

Also, medium carbon chromium-molybdenum steel is known with improved machinability by cutting AV30XM (RF Patent 2132401 publ. 06/27/1999, IPC C22C 38/22) containing carbon, silicon, manganese, chromium, molybdenum, bismuth, and iron in the following ratio of components, wt. %:

- carbon - 0.27-0.33;

- silicon - 0.17-0.37;

- manganese - 0.40-0.70;

- chrome - 0.80 - 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, mass. %:

- sulfur - 0.008-0.035;

- phosphorus - 0.008-0.035.

The disadvantages of this steel include the following: - the futility of further improving the workability of steel by increasing the bismuth content is more than real values, since it exceeds its maximum solubility in iron and the cost of smelting increases.

- Bismuth, according to the hygiene standard established today, belongs to hazard class 2 and forms bismuth oxides upon evaporation, which are removed into the atmosphere during its introduction into steel and worsen the environment.

- to reduce the level of environmental pollution, it is necessary to design and install additional gas cleaning equipment and increase the material costs of its maintenance.

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

The problem to which this invention is directed is to increase the machinability of steel by cutting while maintaining the required mechanical characteristics of the metal and reduce the aggressiveness of harmful emissions of toxic components (lead and bismuth) into the atmosphere.

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 boron, nitrogen and aluminum in the following ratio of components, wt. %:

- carbon - 0.27-0.33;

- silicon - 0.17-0.37;

- manganese - 0.40-0.70;

- chrome - 0.80-1.10;

- molybdenum - 0.15-0.25;

- boron - 0.005-0.009;

- nitrogen - 0.007-0.012;

- aluminum - 0.02-0.04.

- iron is the basis.

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

- sulfur - not more than 0.035;

- phosphorus - not more than 0.035;

- copper - not more than 0.30;

- nickel - not more than 0.25;

The use of boron and nitrogen for additional alloying of steel in order to improve its machinability by cutting has a number of advantages.

In the production of steel containing inclusions of boron nitride, toxic compounds are not formed, since boron has a lower chemical affinity for oxygen than bismuth and lead and therefore does not oxidize during the smelting process. The possibility of evaporation of boron is also excluded, since it has a high boiling point, significantly exceeding the operating temperatures of steelmaking processes, and low vapor pressure. For alloying steel with nitrogen, nitrogen containing ferroalloys are used, which allows high nitrogen uptake by steel during alloying. Thus, unlike lead and bismuth, boron and nitrogen under no existing conditions of smelting, casting and metal pressure treatment of steel do not form harmful gas and dust emissions.

Boron nitride is called white graphite. It has the same crystalline structure and has a lubricating effect when cutting steel.

The listed advantages of boron nitride are evidence of the advisability of its use as an alternative to bismuth and 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 boron, nitrogen and aluminum, which achieves the best combination of high machinability of steel by cutting, while maintaining the required values of mechanical properties.

As a result of the studies established the following:

- when the content of boron and nitrogen 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 boron and nitrogen, the workability of the proposed steel is comparable to the workability of a metal of a similar bismuth-containing grade;

- when the boron content is above the specified values, boron is released along the grain boundaries, which leads to a deterioration in the mechanical properties of steel;

- when the aluminum content in the declared limits in the steel will allow you to get the size of the austenitic grain in the finished product more than 7 points and positively affect the mechanical properties of steel;

- when the content of boron, nitrogen and aluminum is within the stated limits, the processability level of the proposed steel is 11% higher than the processability of the bismuth-containing analogue; Along with this, 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 mechanical properties were carried out on the technical basis of the South Ural State University (NRU).

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 a part.

As a basic level, machinability by cutting and mechanical properties of medium-carbon chromium-molybdenum steel AV30XM are adopted (RF Patent No. 2132401).

The chemical composition of the known steel grade AB30XM, taken as the closest analogue, and the proposed steel are shown in table 1.

Strength and plastic characteristics of the compared steels in a deformed and heat-treated state, as well as the measured level of mechanical workability are presented in table 2.

Example 1. Known medium-carbon chromium-molybdenum steel with improved machinability by cutting AB30XM. The level of machinability and mechanical properties are taken as reference values for comparison. During steelmaking processes, toxic bismuth vapors are released into the 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 technical conditions. Evaluation of the effectiveness of turning steel has not been carried out.

Example 3. The nickel content is greater than the upper limit. The mechanical properties of steel are lower than that of the AV30XM. Machinability is comparable to analog steel.

Example 4. The content of boron and nitrogen is less than the lower limit. The machinability level of the proposed steel is lower than that of the known analogue.

Example 5. The nitrogen and boron content in the steel are 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 aluminum content is less than 0.01%, the indicators of the mechanical properties of the metal correspond to the minimum maximum permissible values established by the technical conditions for the bismuth-containing analog. The study of the technological properties of the proposed steel was not conducted.

Example 7. The aluminum 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 nitrogen and boron content goes beyond the upper regulated border, which leads to a deterioration in the mechanical workability of steel.

Example 9. The content of all elements is within the stated limits. The complex of technological properties of medium carbon chromium-molybdenum steel has an optimal character. The machinability by cutting while maintaining the mechanical characteristics of the metal is 11% higher than that of the known analogue. At the same time, air pollution of the working area is significantly reduced.

Thus, a higher level of machinability by cutting the proposed steel in combination with preserving the complex of the required mechanical properties of the metal and improving the ecology of metallurgical production allows us to recommend it for industrial use.

Claims (4)

1. Mid-carbon chromium-molybdenum steel with improved machinability, containing carbon, silicon, manganese, chromium, molybdenum, iron and impurities, characterized in that it additionally contains boron, nitrogen and aluminum in the following ratio, wt.%: carbon 0.27-0.33 silicon 0.17-0.37 manganese 0.40-0.70 chromium 0.80-1.10 molybdenum 0.15-0.25 boron 0.005-0.009 nitrogen 0.007-0.012 aluminum 0.02-0.04 iron and impurities rest 2. Steel under item 1, characterized in that it further limits the content of harmful impurities, wt.%: sulfur no more than 0,035 phosphorus no more than 0,035 nickel no more than 0.25 copper no more than 0.30