RU2556189C1 - Easy treated structural medium carbon chrome-manganese-nickel-molybdenum steel - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: steel has the following chemical composition, 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 0.08-0.13, calcium 0.002-0.003, aluminium 0.005-0.015, iron is basis. Steel contains following substances as impurities, in wt %: copper - max. 0.25, sulphur - max. 0.025, phosphorus - max. 0.025. Ratio of calcium and aluminium is from 0.20 to 0.40.

EFFECT: increased steel machinability by cutting upon keeping of the required metal mechanical properties, and improved ecological situation during production die to reduced aggression of harmful discharges to atmosphere of high toxic components.

3 cl, 2 tbl, 11 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.

The prior art steel with improved machinability by cutting (GOST 1414-75). Rolled from structural steel with high machinability. Specifications (Reprint, as Amended No. 1, 2, 3, as Amended) containing carbon, silicon, manganese, chromium, molybdenum, lead, nickel 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;

- molybdenum - 0.15-0.25;

- lead - 0.15-0.30;

- nickel - 0.70-1.10;

- iron is the basis.

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

- copper - not more than 0.30;

- sulfur - not more than 0,030;

- phosphorus - not more than 0.035.

The disadvantages of this steel include the following:

- sulfur and phosphorus, which improve the machinability of steel, in the case of alloying it with lead, do not significantly affect the mechanical cutting process, and an increase in their content above the values that provide high-quality steel is inappropriate due to the accumulative negative effect of these elements on the mechanical properties of metal products ;

- 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 the yield of metal, and, consequently, the productivity of the pressure processing 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.

In addition, steel is known with high machinability (patent RU 2128726) containing carbon, silicon, manganese, chromium, molybdenum, bismuth, nickel, sulfur, phosphorus and iron in the following ratio of components, mass. %:

- carbon - 0.37-0.43;

- silicon - 0.17-0.37;

- manganese - 0.50-0.80;

- chrome - 0.60-0.90;

- molybdenum - 0.15-0.25;

- sulfur - 0.008-0.030;

- phosphorus - 0.008-0.035;

- bismuth - 0.12-0.20;

- nickel - 0.70-1.10;

- iron is the basis.

Known steel has the following disadvantages:

- the futility of further improving the workability of steel by increasing the bismuth content is greater than the real values, since it exceeds its maximum solubility in iron and increases the cost of smelting.

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, by reducing the aggressiveness of harmful emissions of toxic components into the atmosphere.

The technical solution of the problem is achieved due to the fact that the proposed steel in its composition contains carbon, silicon, manganese, chromium, nickel, molybdenum, bismuth, calcium, aluminum 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;

- molybdenum - 0.15-0.25;

- bismuth - 0.08-0.13;

- calcium - 0.002-0.003;

- aluminum - 0.005-0.015;

- nickel - 0.70-1.10;

- iron is the basis.

The ratio of calcium to aluminum is in the range from 0.20 to 0.40.

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 0.25.

The use of bismuth, calcium and aluminum for additional alloying and deoxidation of steel in order to improve its machinability by cutting has a number of advantages.

Firstly, a reduction in the amount of aluminum used for the deoxidation of steel will contribute to a decrease in non-metallic inclusions Al ₂ O ₃ in steel.

Secondly, calcium is a kind of substitute for aluminum, as a deoxidizer, and provides the formation of calcium aluminates in the sulfide shell - complex oxysulfide inclusions, promotes the globization of sulfide inclusions and prevents the formation of microcracks in acute-angled inclusions of alumina, which have a positive effect on the workability of steel.

Thirdly, the optimal Ca / Al ratio promotes the formation of globular, slightly deformable nonmetallic inclusions.

Fourth, a decrease in bismuth content, without a decrease in machinability, provides the formation of brittle chips and expands the range of steel application (when drilling, drilling holes, cutting and milling) and does not weaken the positive effect on the process results from phosphorus and manganese sulfide inclusions. It is less toxic than lead and provides a high level of workability when its content is 1.5..2 times less than lead.

Fifth, bismuth is evenly distributed over the cross section of the ingot, which is due to its density comparable to that of liquid steel, and the use of bismuth contributes to the solution of environmental problems that occur in the production of automatic steels. This is due to the fact that, unlike lead belonging to hazard class 1, the bismuth content in the workshop atmosphere is limited by the average shift maximum permissible concentration (MPC) of 0.50 mg / m ³ .

The essence of the invention is the identification of the optimal content of bismuth, aluminum and calcium, in which the best combination of high machinability of steel by cutting is achieved, provided that the required values of mechanical properties are maintained.

As a result of the studies established the following:

- when the content of bismuth 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 upper limit of bismuth, the workability of the proposed steel is comparable to the workability of a metal of a similar bismuth-containing grade;

- when the content of bismuth, calcium and aluminum is within the declared limits, the workability level of the proposed steel is 11% higher than the workability of the bismuth-containing analogue, while the 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 .

The effectiveness of turning was evaluated on the technical basis of the Federal State Budgetary Educational Establishment of Higher Professional Education “South Ural State University” (NRU) by changing the resistance of tool material at a given cutting speed of 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 processing one part.

As a base level, machinability by cutting medium-carbon chromium-manganese-nickel-molybdenum steel AB40KHGNM is taken.

The chemical composition of the known steel grade марки40ΧΓΉΜ, adopted for the closest analogue, and the proposed steel are given in table 1.

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

Example 1. Known structural medium-carbon chromium-manganese-nickel-molybdenum steel with improved machinability by cutting AB40HGNM (RU 2128726). The level of machinability is taken as reference values for comparison.

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 turning steel has not been carried out.

Example 3. The nickel content is greater than the upper limit. The productivity of hot metal forming decreases. A workability assessment was not performed.

Example 4. The bismuth 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 bismuth content in the steel is greater than the upper limit. The machinability of the proposed steel by cutting is comparable to the machinability of its analogue.

Example 6. The content of sulfur, phosphorus, copper 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 established by the requirements for the bismuth-containing analog.

Example 7. The ratio between the content of calcium and aluminum goes beyond the lower regulated border. Grain size below regulated. Cups are overgrown with continuous casting machine (CCM). The level of machinability of the proposed steel is comparable to the machinability of the known analogue.

Example 8. The ratio between the content of calcium and aluminum is at the lower limit of the specified range. Grain size meets specifications. The caster cups do not overgrow. The level of workability is higher than the known counterpart.

Example 9. The ratio between the content of calcium and aluminum has a value corresponding to the upper declared limit. Steel meets specifications.

Example 10. The ratio between the content of calcium and aluminum goes beyond the upper set limit. Steel does not meet specifications.

Example 11. The content of all elements is within the stated limits. The complex of technological properties of chromium-manganese-nickel-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 while maintaining the set of required mechanical properties of the metal and improving the ecology of metallurgical production allows us to recommend it for industrial use.

Claims (3)

1. Easily machined structural chromium-manganese-nickel-molybdenum steel containing carbon, silicon, manganese, chromium, nickel, molybdenum, bismuth and iron, characterized in that it additionally contains calcium and aluminum 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 molybdenum 0.15-0.25 bismuth 0.08-0.13 calcium 0.002-0.003 aluminum 0.005-0.015 nickel 0.70-1.10 iron rest 2. Steel according to claim 1, characterized in that the content of harmful impurities is limited in it, wt.%: Sulfur not more than 0.025, phosphorus not more than 0.025, copper not more than 0.25. 3. Steel under item 2, characterized in that the ratio of calcium to aluminum content is in the range from 0.20 to 0.40.