RU2744600C1 - Wear-resistant steel - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to metallurgy and namely to wear-resistant steel used for the production of high-quality parts operating under conditions of contact-dynamic loading with the effect of an abrasive. Steel contains components in the following ratio, wt%: carbon - 0.2-0.6, silicon - 0.8-1.2, manganese - from more than 7.0 to 10.0, titanium - 0.5-1.2, nitrogen - 0.1-0.2, boron - 0.5-1.0, molybdenum - 2.0-4.0, vanadium - 0.5-1.0, aluminum - 0.2-0.8, sulfur - 0.006-0.019, phosphorus - 0.011-0.017, oxygen -0.0024-0.0044, hydrogen - 0.0002-0.0006, iron - the rest.

EFFECT: invention provides increased resistance to shock loads and high resistance to abrasive wear and cracking.

1 cl, 2 tbl

Description

The invention relates to metallurgy, in particular to materials of high wear resistance, used for the manufacture of parts operating under conditions of contact dynamic loading with the influence of an abrasive, for example, undercarriage of tracked vehicles.

Known steel for the manufacture of parts operating under conditions of intense abrasive wear with minor shock loads (USSR author's certificate SU No. 1070203, C22c 38/50, publ. BI No. 4, 1984), containing components in the following ratio, wt. %:

carbon - 2.0 h 3.5 manganese - 15.0 h 24.0 titanium - 2.5 h 6.0 iron - the rest.

The steel of known composition has an unstable austenite structure with carbide strengthening. The disadvantage of the alloy is its low initial hardness (290–350 HB), which does not provide its high wear resistance in the initial period of operation.

Known steel for the manufacture of parts of cryogenic technology (British patent GB No. 1159098 C22c 39/30, publ. 1969), containing components in the following ratio,%:

manganese - 3.0 h 11.0 silicon - 1.5 h 2.0 titanium - 0.6 h 1.2 molybdenum - 0.4 h 3.4.

The structure of the steel is carbon-free martensite. The specificity of alloying this steel consists in using only a slight precipitation hardening effect. After hardening, such steel has a hardness of about 25 HRC, and after aging only 39 HRC, which does not allow it to be used as a wear-resistant material.

The closest in chemical composition and purpose is manganese steel for the manufacture of rolling rolls, parts of sand and mud pumps (RF patent RU No. 2327806, C22c 38/60, publ. BI No. 18, 2008), containing, by weight. %:

carbon - 0.8 h 1.2 silicon - 0.8 h 1.2 manganese - 10.0 h 12.0 titanium - 0.1 h 0.2 nitrogen - 0.1 h 0.2 boron - 0.5 h 1.0 antimony - 0.03 h 0.05 calcium - 0.005 h 0.01 iron - the rest.

Steel of known composition has an unstable austenite structure with carbide-boride-nitride hardening. The disadvantage of the alloy is its low wear resistance when operating under contact-shock loading with intense abrasive action. In addition, the known steel is prone to cracking. Therefore, it is difficult to obtain cracks-free castings from steel of a similar composition.

The technical objective of the present invention is to create high quality steel in terms of the content of harmful impurities, and to increase resistance to shock loads with high resistance to abrasive wear and cracking.

The technical result is achieved due to the fact that steel including carbon, silicon, manganese, titanium, nitrogen, boron and iron additionally contains molybdenum, vanadium, aluminum, sulfur, phosphorus, oxygen and hydrogen in the following ratio of elements, wt. %:

carbon - 0.2 h 0.6 silicon - 0.8 h 1.2 manganese - from more than 7.0 to 10.0 titanium - 0.5 h 1.2 nitrogen - 0.1 h 0.2 boron - 0.5 h 1.0 molybdenum - 2.0 h 4.0 vanadium - 0.5 h 1.0 aluminum - 0.2 h 0.8 sulfur - 0.006 h 0.019 phosphorus - 0.011 h 0.017 oxygen - 0.0024 h 0.0044 hydrogen - 0.0002 h 0.0006 iron - the rest.

In the proposed steel, the carbon concentration is set in the range of 0.2–0.6%. Reducing it by more than two times in comparison with the prototype increases the resistance of steel to shock loads and reduces the tendency to cracking, and in combination with the proposed percentage of other components, it makes it possible to obtain steel with a sufficiently high hardness and wear resistance.

The introduction of 2.0–4.0% molybdenum ensures the formation of a boride eutectic and uniform precipitation of carbides, an increase in their dispersion during aging, and also allows the use of a higher aging temperature to increase ductility and toughness while maintaining equal hardness with the composition of steel without molybdenum. Boride eutectic, located in the form of a framework along the grain boundaries during crystallization, absorbs part of the impact energy and disperses it over a large surface area, which increases the metal's resistance to both shock loads and cracking. The content of molybdenum in the proposed steel is less than the lower limit leads to the formation of an insufficient amount of boride eutectic and carbides, which does not provide a sufficiently high plasticity and crack resistance of such steel. At a content of more than 4% molybdenum, binding a significant amount of carbon into special carbides, depletes the solid solution in this component, worsens the plastic properties and reduces the resistance to cracking.

The introduction of 0.5-1.0% vanadium, which is a strong carbide and nitride former, increases the hardness and wear resistance, which is important for products operating under high contact loads. Vanadium is a good modifier that allows a significant refinement of the grain, prevents the growth of large columnar crystals, as a result of which the possibility of cracking is eliminated. At the same time, when vanadium is introduced into steel, complex titanium – vanadium carbides (TiV) C hardness, which exceeds the hardness of titanium and vanadium monocarbides, are formed. An increase in the hardness of the carbide phase contributes to an increase in the wear resistance of steel during abrasive wear. When the vanadium content in steel is up to 0.5%, the required level of crack resistance is not achieved due to insufficient refinement of the steel structure. With an increase in the vanadium content of more than 1.0% in steel, instead of special titanium-vanadium carbides, less wear-resistant carbides of the cementite type appear, which embrittle the steel.

The introduction of aluminum in the range of 0.2-0.8% promotes deoxidation of the proposed steel, provides modification and enhances the efficiency of precipitation hardening. Aluminum leads to the formation of a fine-grained structure due to the formation of nitrides, which serve as additional crystallization centers. In turn, the fine-grained structure increases wear resistance, since under abrasive action, the resistance of particles to separation is much higher than with a coarse-grained metal structure. The formation of additional crystallization centers also leads to the elimination of the columnar structure, and therefore to the equalization of the properties of the casting in all sections, and, in addition, reduces the tendency of the metal to form cracks. At an aluminum concentration of less than 0.2%, no noticeable effect is observed. With an increase in the aluminum concentration over 0.8%, a ferrite component appears in the structure, which reduces the strength characteristics and wear resistance.

The combined introduction of molybdenum, vanadium and aluminum provides a more effective precipitation hardening of steel during tempering (aging) at temperatures above 500 ° C, the maximum degree of which reaches 11 HRC.

The proposed composition of elements provides complex dispersed hardening of steel due to the formation of carbide, boride, nitride and intermetallic phases during secondary hardening.

The presence of dissolved oxygen, hydrogen, sulfur and phosphorus in high-alloyed alloys negatively affects the mechanical properties of the metal and resistance to cracks. This is explained by the fact that in the alloy contaminated with these elements, the deformation energy is concentrated mainly at structural defects (mainly in non-metallic inclusions), therefore, the energy is distributed unevenly over the section of the part. The oxygen content in the alloy is in the range of 0.0024-0.0044%; hydrogen in the range of 0.0002-0.0006%; sulfur 0.006-0.019%; phosphorus 0.011-0.017% ensures the absence of large inclusions, which makes it possible to distribute the energy of deformations more evenly and significantly increase the endurance of the metal in conditions of shock loads.

An example of a specific implementation. Three compositions of the proposed steel were smelted at the lower, middle and upper limits of the content of components, as well as two compositions of steel with the content of elements below the lower and above the upper limits. For a comparative assessment, a steel of known composition (prototype) was obtained at the average limit of the content of components (Table 1).

Table 1

The chemical composition of the heats for the main alloying elements was monitored using a DFS-500 optical emission spectrometer. The carbon content in the trunks was determined by infrared spectroscopy by burning a sample at a temperature of 1350 ° C in an oxygen atmosphere using a METAVAK-CS30 analyzer. The nitrogen content in the trunks was determined by melting a sample at a temperature of 2500 ° C in a helium atmosphere using a METAVAK-AK analyzer.

The study of the properties of the cast metal was carried out on samples cut from the obtained blanks in the cast state and after aging (500 ° C - 2 hours). Rockwell hardness was measured on a TK-2 device (the average hardness value was taken as the value of hardness - 5 measurements).

Wear tests were carried out on a laboratory setup under conditions of wet abrasive friction of metal on metal (disk-cam) at a specific pressure on the wearing surfaces of 1 MPa. The results obtained were expressed as a coefficient of relative wear resistance e, numerically equal to the ratio of the weight losses of the standard (steel 30X13) and the test metal for the same time.

Tests for the resistance of aged cast metal to brittle fracture were carried out on a MA4129 hammer at an impact energy
0.1 kJ. In this case, the number of impacts before the appearance of the first crack was a criterion for determining the resistance of the metal to brittle fracture.

The test results are shown in Table 2.

table 2

Test results

Cast metal properties Steel composition options one 2 3 four five 6-prototype Mechanical characteristics As-cast hardness, HRC 36 40 42 45 48 54 Cast cracks not not not not 1-2 on
10 cm ² 1-2 on
10 cm ² Hardness after aging at 500 ° C -
2 hours, HRC 42 48 51 54 56 57 Coefficient e 2.1 2.4 2.8 3.1 3.2 2.2 Number of strokes 43 34 28 23 12 8

The test results shown in Table 2 show that the compositions of steels NN 2-4 are optimal and provide an aged metal of increased hardness and high wear resistance, not prone to brittle fracture and cracking.

The analysis of the test results showed that, in comparison with the prototype steel, the proposed compositions of the new steel make it possible to increase the coefficient of relative wear resistance of the cast metal e from 2.2 to 2.4-3.1, while the brittle fracture resistance increases by 2.8- 4.2 times.

Such properties of the metal of the claimed compositions can be explained by the fact that, due to the introduction of molybdenum, vanadium and aluminum, it is possible to obtain a new composite precipitation-hardening metal with a boride eutectic and a large number of high-strength dispersed phases, which is additionally hardened as a result of aging, and thereby acquires increased resistance under shock conditions. -abrasive wear.

The metal of castings, depending on the concentration of alloying elements, has a hardness of 40h45 HRC, after aging at 500 ° C for 2 hours 48h54 HRC.

The use of the proposed steel for the manufacture of parts of the undercarriage of tracked vehicles can significantly increase their wear resistance and service life.

This technical solution was created within the framework of the RSF grant, Agreement No. 17-19-01224.

Claims (2)

Wear-resistant steel for the manufacture of parts operating under contact-dynamic loading with an abrasive effect, containing carbon, silicon, manganese, titanium, nitrogen, boron, molybdenum, vanadium, aluminum, sulfur, phosphorus, oxygen, hydrogen and iron, characterized in that it contains components in the following ratio, wt%: carbon 0.2-0.6 silicon 0.8-1.2 manganese from more than 7.0 to 10.0 titanium 0.5-1.2 nitrogen 0.1-0.2 boron 0.5-1.0 molybdenum 2.0-4.0 vanadium 0.5-1.0 aluminum 0.2-0.8 sulfur 0.006-0.019 phosphorus 0.011-0.017 oxygen 0.0024-0.0044 hydrogen 0.0002-0.0006 iron rest