RU2750257C2 - Method of producing high-speed steel for manufacture of composite rolls - Google Patents

Abstract

FIELD: metallurgy.SUBSTANCE: invention relates to the area of metallurgy, namely to production of high-speed steel used for manufacture of composite roll shells and rolls of small diameter for multi-roll mills. A steel melt is obtained containing components in the following ratio, wt.%: carbon 1.70 to 1.80, silicon 0.10 to 0.50, manganese 0.40 to 0.80, sulfur ≤ 0.03, phosphorus ≤ 0.03, chromium 3.80 to 4.50, nickel 0.80 to 1.50, tungsten 4.30 to 4.80, molybdenum 3.40 to 3.60, vanadium 6.00 to 6.20, cerium 0.005 to 0.02, zirconium 0.02 to 0.04, calcium 0.005 to 0.02, aluminium 0.008 to 0.05, iron the rest. The melt is modified by introducing a modifier thereto in an amount of 0.03 to 0.25% of the melt weight. A mixture in equal proportions of titanium carbonitride and zirconium carbonitride nanopowders with a particle size of 60 to 70 nm placed in an amount of 5 to 10 wt.% in an iron matrix with an iron particle size of 10 to 50 mcm is used as a modifier. The modifier is preliminarily compacted before introduction into the melt, and is introduced into the melt prior to completion of melting or into the melt stream during discharge thereof.EFFECT: ensured production of high-speed steel with high wear resistance.3 cl, 2 tbl

Description

The invention relates to the field of metallurgy, and in particular to a method for producing parts from high-speed steel with high mechanical properties, which can be used for the manufacture of composite rolls and small diameter rolls for multi-roll mills.

Known high-speed steel for the manufacture of composite two-layer rolls obtained by the method of electroslag surfacing with liquid metal on a steel axis containing carbon, silicon, manganese, sulfur, phosphorus, chromium, nickel, molybdenum, vanadium, tungsten and iron, with the following ratio of components, wt. %: carbon 1.6-1.8; silicon 0.4-0.8; manganese 0.4-1.0; sulfur ≤ 0.03; phosphorus ≤ 0.04; chrome 4.0-5.0; nickel 0.5-1.0; molybdenum 4.0-5.0; vanadium 1.5-2.5; tungsten 4.0-5.00; the rest of the iron.

(Prospectus of Novokramatorsk Machine-Building Plant, nkmz.com> fileadmin / data / prospekts / valki_nkmz.pdf).

There is a known method of producing castings, including steel smelting, casting, cleaning, cutting and heat treatment: double normalization, which consists in their initial heating to 920-930 ° C and holding at it for 3-3.5 hours, followed by cooling in air to 200 ° С, and then in repeated heating to (870-880 ° С and holding at it for 2.5-3.0 h, followed by cooling in air to 20 ° С, while using steel of the following chemical composition, wt: carbon 0, 20-0.40, manganese 0.90-1.50, silicon 0.17-0.40, chromium 1.20-1.80, nickel 0.30-0.60, copper 0.20-0.40 , vanadium 0.15-0.30, boron 0.001-0.01, aluminum 0.02-0.06, iron - the rest.

(RU 2105821, C21D 1/28, C21D 1/78, published 27.02.1998)

The disadvantages of this method are the low strength and hardness of steel due to the absence of alloying elements and low carbon content in it, which excludes its use for parts operating under conditions of abrasive wear at high loads.

Known high-speed steel for the manufacture of composite rolls containing carbon, silicon, manganese, chromium, nickel, cobalt, tungsten, molybdenum, vanadium, cerium, niobium, aluminum, titanium, zirconium, sulfur, phosphorus and iron in the following ratio of components, wt. %: carbon 0.8-1.2; silicon ≤ 0.8; manganese ≤ 1.5; chrome 8.0-10.0; nickel 2.2-2.6; cobalt 6.5-7.5; tungsten 1.2-1.6; molybdenum 5.0-7.0; vanadium 2.0-3.0; cerium 0.4-0.6; niobium 0.2-0.4; aluminum 0.1-0.4; titanium 0.2-0.4; zirconium 0.05-0.2; sulfur ≤ 0.03; phosphorus ≤ 0.04; the rest of the iron.

(CN 102758148, C22C 38/56, published 10/31/2012)

The closest in technical essence and the achieved result is a method for manufacturing high-speed steel rolls containing carbon, silicon, manganese, sulfur, phosphorus, chromium, nickel, cobalt, tungsten, molybdenum, vanadium, zirconium, cerium and iron, with the following ratio of components, wt. %: carbon 3.2-3.6; silicon ≤ 0.8; manganese ≤ 1.5; chrome 8.0-10.0; nickel 2.2-2.6; cobalt 6.5-7.5; tungsten 1.2-1.6; molybdenum 5.0-7.0; vanadium 2.0-3.0; cerium 0.4-0.6; niobium 0.2-0.4; aluminum 0.1-0.4; titanium 0.2-0.4; zirconium 0.05-0.2; sulfur ≤ 0.03; phosphorus ≤ 0.04; the rest of the iron.

After the high speed steel is cast to form a workpiece and the workpiece is roughly processed, the workpiece is quenched, the quenching process is carried out when the furnace is heated to 1260-1280 ° C, the temperature is maintained for 3-5 hours, then the workpiece is quenched in oil and tempered after quenching. the tempering process is carried out when the furnace is heated to 620 ° C to 650 ° C, the temperature is maintained for 5-7 hours, the furnace is cooled and then heated, up to 610 ° C to 630 ° C, the temperature is again maintained for 5-7 hours, and after air cooling, finishing is carried out, so that a roll is obtained, the dimensional accuracy and surface roughness of which meet the requirements.

(CN 102766745, C22C 38/56, published on 07.11.2012)

The disadvantage of this method is the increased fragility of the high speed steel roll due to the high carbon content. In addition, the proposed heat treatment mode does not provide high wear resistance of the rolls.

The disadvantage of all known steels is the insufficient level of strength, ductility, hardness and wear resistance.

The task and the technical result of the invention is to develop a method for producing high-speed steel that provides high wear resistance at high loads.

The technical result is achieved in that the method of obtaining high-speed steel for the manufacture of composite rolls, including the production of steel melt, its subsequent modification and casting, characterized in that a steel melt is obtained containing components in the following ratio, wt. %: carbon 1.70-1.80, silicon 0.10-0.50, manganese 0.40-0.80, sulfur ≤ 0.03, phosphorus ≤ 0.03, chromium 3.80-4.50, nickel 0.80-1.50, tungsten 4.30-4.80, molybdenum 3.40-3.60, vanadium 6.00-6.20, cerium 0.005-0.02, zirconium 0.02-0.04, calcium 0.005-0.02, aluminum 0.008-0.05 and iron - the rest, and modification is carried out by introducing a modifier in an amount of 0.03-0.25% of the melt mass, while using a modifier containing a mixture in equal proportions of titanium carbonitride nanopowders and zirconium carbonitride with a particle size of 60-70 nm, placed in an amount of 5-10 wt. % in an iron matrix with an iron particle size of 10-50 microns.

The technical result is also achieved in that the method for producing high-speed steel for the manufacture of composite rolls includes preliminary compaction of the modifier and its introduction into the melt before the end of melting or into the stream of the melt during its release.

The technical result is also achieved by the fact that high-speed steel for the manufacture of composite rolls is obtained by the above methods.

The method of obtaining high-speed steel for the manufacture of composite rolls according to the invention differs from the known methods in that a modifier in the form of nanopowders of titanium carbonitride and zirconium carbonitride (obtained by plasma-chemical synthesis) with particle sizes of 60-70 nm is additionally introduced into the steel melt containing the components in the specified ratio in an iron matrix (in the form of a powder with a particle size of 10-50 microns) in equal proportions in the range of 5-10 wt. %. The iron powder is selected to prevent adhesion, oxidation, spontaneous combustion and explosion of nanopowder particles. The modifier is compacted and introduced into the melt before the end of the melt or into the stream of the melt when it is released in an amount of 0.03-0.25% of the melt mass. The use of compacted modifiers is due to the fact that nanopowder particles with a particle size of 60-70 nm easily stick together, their oxidation begins at relatively low temperatures, and they are also poorly wetted by liquid metal. When modifiers are introduced into melts in the form of nanopowders, they easily form a dusty suspension in the air, which, under certain conditions, can spontaneously ignite and explode.

The use of titanium and zirconium carbonitride in a mixture with an iron matrix provides a high modifying effect at a low cost. The introduction of a modifier into the melt in an amount of 0.03-0.25% of the melt mass leads to a significant change in both the resulting structure and the morphology and topography of the carbide phase. At the same time, there is a sharp grinding of the grain, the columnarity of the grains and the uneven graininess are eliminated. The dendritic structure of the cast metal is thin and uniform over the section of the casting. Carbides acquire a compact equiaxed shape and are evenly distributed over the grain volume. The use of a modifier improves the strength and wear resistance of steel.

With an increase in the amount of modifier above the specified upper limit, the boundary concentration of the elements of grain boundary hardeners decreases, as a result of which the strength of the casting decreases, which negatively affects the wear resistance of the steel, and also a decrease in the characteristics of plasticity and toughness is possible.

When the amount of the modifier is reduced to less than 0.03%, the modifying effect is sharply reduced. In an unmodified casting, carbide inclusions in the form of frameworks are located mainly along the grain boundaries and have a large extent. Carbides of this type have a negative effect on the wear resistance of steel.

The steel according to the invention differs from the known steel by a lower carbon content of 1.70-1.80 wt. %, against 3.2-3.6 wt. %. The carbon content is 1.70-1.80 wt. % is optimal for providing high strength, hardness and high ductility due to the higher hardenability of the steel, and the steel of the prototype is prone to embrittlement.

If the carbon content exceeds 1.80 wt. %, then there is a noticeable embrittlement of high-speed steel, which can lead to the unsuitability of the rolls due to spalling. The content is less than 1.70 wt. % reduces the proportion of carbides and decisively reduces the wear resistance of the material.

Silicon with a content of 0.10-0.50 wt. % in steel has a hardening effect on mixed crystals, as well as a deoxidizing effect, it is a stronger deoxidizer than manganese. For hardenability of the material, its content should not exceed 0.50 wt. %.

Manganese in the range of 0.40-0.80 wt. % can affect the hardness characteristics of the material, but it should be considered mainly in conjunction with the sulfur content, and sulfur and manganese, due to the formation of sulfide inclusions, should be considered as elements improving the processing of steel. It facilitates hot working of steel by forming refractory compounds with sulfur and oxygen. This manganese content has a positive effect on the mechanical properties of the steel. Within these limits, manganese improves the hardenability of the steel and increases the yield strength of the steel, which has a positive effect on the wear resistance.

The steel according to the invention differs from the known one by a lower chromium content of 3.80-4.50 wt. %, against 8.0-10.00 wt. %, this chromium content is optimal. Chromium at this content increases the strength and hardness of the steel without reducing the ductility. The chromium content in the prototype steel is excessive, since the declared content is sufficient to ensure the heat resistance of the steel.

Chromium content with a maximum value of 4.5 wt. % is justified by the fact that a higher content leads to an increase in the proportion of retained austenite in the matrix after quenching.

The steel according to the invention differs from the known one by a lower nickel content of 0.80-1.50 wt. %, versus 2.20-2.60 wt. %, which is optimal for increasing strength and especially impact strength and reducing cost. In addition, nickel at a given value reduces the tendency of the steel to crack.

The steel according to the invention differs from the known one by a lower molybdenum content of 3.40-3.60 wt. %, versus 5.00-7.00 wt. %, which ensures the same properties along the entire length of the workpiece. Molybdenum also improves the fracture toughness of the steel and prevents grain boundary precipitation of austenite during aging. Molybdenum is of great importance in the kinetics of the reaction or the formation of mixed carbides, and a content of 3.40 to 3.60 is considered effective according to the invention. Studies have shown that the required amount does not exceed 3.60 wt. %, a higher content of molybdenum is not economically justified.

The steel according to the invention differs from the known high tungsten content of 4.30-4.80 wt. %, versus 1.20-1.60 wt. %, which provides high strength, hardness and wear resistance. Tungsten and molybdenum have a high affinity for carbon and form nearly identical carbides and can be used interchangeably.

The steel according to the invention differs from the known higher vanadium content of 6.00-6.20 wt. %, which provides an increase in wear resistance and strength of steel due to the formation of a larger amount of wear-resistant vanadium carbides. Vanadium is one of the strongest monocarbide-forming elements, the carbides of which are characterized by high hardness and determine the special wear resistance of the material.

Wear resistance is facilitated by a fine structure and a generally uniform distribution of monocarbides. In particular, vanadium, as well as tungsten and molybdenum, should be partially transformed into a solid solution at high temperatures, so that after rapid cooling the product has a significant potential of secondary hardness due to the release of finely dispersed, vanadium-rich secondary carbides after tempering.

Higher than 6.20 wt. %, the vanadium content determines either a higher carbon content in the alloy, which makes it embrittle, or depletion and a decrease in strength occurs, in particular, a decrease in the thermal resistance of the matrix. The vanadium content is less than 6.00 wt. %) leads to a noticeable deterioration in the wear characteristics.

Microalloying of steel with zirconium (0.02-0.04 wt%) in combination with an increased vanadium content increases the strength and toughness of heat-treated steel due to the refinement of the actual grain, a decrease in the carbon content in austenite and an increase in the forces of interatomic bonds and the magnitude of the separation resistance, since vanadium and zirconium carbides have similar crystal lattice parameters and have unlimited mutual solubility. Complex alloying of steel with zirconium in combination with vanadium, tungsten and other elements affects the properties of steel more than alloying with zirconium alone.

When the content of zirconium is more than 0.04 wt. % formation of zirconium carbides occurs at higher temperatures than similar vanadium compounds, which does not allow optimizing the heat treatment modes and reduces the yield strength of steel, hardness and, as a consequence, wear resistance of steel.

Cerium content 0.005-0.02 wt. %. against 0.4-0.6 wt. % is sufficient to ensure high processability and contributes to obtaining high strength and higher values of impact strength. The introduction of cerium in an amount of 0.4-0.6 wt. % leads to the formation of the so-called cerium heterogeneity, which greatly reduces the toughness of the steel.

The steel according to the invention differs from the known additional calcium content in the amount of 0.005-0.02 wt. %, which, in combination with cerium, favorably changes the shape of non-metallic inclusions, reduces the oxygen and sulfur content in steel, reduces the amount of sulfide inclusions, cleans and strengthens grain boundaries and refines the steel structure, which leads to an increase in strength, ductility, impact strength and wear resistance.

The introduction of aluminum into the composition of steel in 0.008-0.05 wt. % versus 0.10-0.40 wt. % in combination with reactive elements calcium and cerium favorably changes the shape of non-metallic inclusions, reduces the oxygen and sulfur content in steel, reduces the amount of sulfide inclusions, cleans and strengthens grain boundaries and refines the steel structure, which leads to an increase in strength, ductility and toughness. Calcium and cerium favorably affect the nature of carbide and carbonitride inclusions, promote the transition of film inclusions of aluminum nitrides into globular complexes of oxysulfonitride formations.

The introduction of aluminum in the amount of 0.10-0.40 wt. %, as in the prototype, in steel reduces its fluidity and complicates pouring, since a hard film and even a crust forms on the jet due to secondary oxidation. If it gets into the body of the casting, it leads to defects in inclusions and leaks. Therefore, it is important to ensure the stability of the deoxidation process, a high degree of assimilation of aluminum and its optimal content in steel.

Table 1 shows the chemical composition of the proposed steel of 3 heats (1, 2, 3), as well as the composition of the prototype steel (4).

Smelting was carried out in a 150 kg induction furnace with metal casting onto centrifugally cast tires. During casting, a total mixture of titanium and zirconium carbonitrides in the form of compressed tablets was introduced into the metal stream. The bands were cut into blanks with a cross section of 20 × 20 mm and 12 × 12 mm to make the required samples. After annealing at a temperature of 860-880 ° C with isothermal holding at 700-720 ° C, quenching from a temperature of 1190-1210 ° C and 3-time tempering for 1 hour at 560-580 ° C, static bending strength tests were carried out, wear resistance and hardness.

Bending tests were carried out on cylindrical specimens with a diameter of 10 mm, a length of 80 mm, and a distance between the supports of 60 mm. The wear resistance was determined by the weight loss of the sample for 1 h (diameter 2 mm) during friction against hardened and tempered steel at HRC = 48-50. The specific load on the sample is 10 kgf / mm ² . Hardness HRC was determined on a Rockwell apparatus.

Table 2 shows the mechanical properties obtained after optimal heat treatment.

As can be seen from table 2, the proposed method and composition of high-speed steel has a significant advantage in terms of strength, hardness and wear resistance in comparison with the known steel.

The proposed method for obtaining high-speed steel for the manufacture of composite rolls can be used for the manufacture of tires of combined rolls and rolls of small diameter for multi-roll mills.

Literature

1 Prospectus of Novokramatorsk Machine-Building Plant, nkmz.com> fileadmin / data / prospekts / valki_nkmz.pdf.

2 Patent CN102758148, С22С 38/56, published on October 31, 2012.

3 Patent CN102766745, С22С 38/56, published on 07.11.2012.

4 RU 2105821, C21D 1/28, C21D 1/78, published 27.02.1998.

Claims (3)

1. A method of obtaining high-speed steel for the manufacture of composite rolls, including obtaining a steel melt, its subsequent modification and casting, characterized in that a steel melt is obtained containing components in the following ratio, wt%: carbon 1.70-1.80, silicon 0.10-0.50, manganese 0.40-0.80, sulfur ≤ 0.03, phosphorus ≤ 0.03, chromium 3.80-4.50, nickel 0.80-1.50, tungsten 4, 30-4.80, molybdenum 3.40-3.60, vanadium 6.00-6.20, cerium 0.005-0.02, zirconium 0.02-0.04, calcium 0.005-0.02, aluminum 0.008- 0.05, iron - the rest, and modification is carried out by introducing a modifier in an amount of 0.03-0.25% on the mass of the melt, while using a modifier containing a mixture in equal proportions of nanopowders of titanium carbonitride and zirconium carbonitride with a particle size of 60-70 nm, placed in an amount of 5-10 wt.% in an iron matrix with an iron particle size of 10-50 microns. 2. The method according to claim 1, characterized in that the modifier is pre-compacted and introduced into the melt before the end of the melt or into the stream of the melt when it is tapped. 3. High speed steel for the manufacture of composite rolls, characterized in that it is obtained by the method according to claim 1 or 2.