RU2625861C1 - Production of steel sheets of higher wear resistance - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: producing the slabs of steel containing, wt %: 0.17-0.28 C, 0.10-0.30 Si, 0.75-1.50 Mn, 0.60-1.20 Cr, 0.60 -1.20 Ni, 0.20 -0.40 Mo, 0.04-0.10 V, 0.02-0.08 Al, 0.001-0.010 N, 0.01 -0.10 Cu, 0.001-0.020 Nb, 0.002-0.040 Ti, 0.001-0.005 B, no more than 0.010 S, no more 0.015 P, the rest is Fe. Slabs are heated in the temperature range 1180-1250°C, the finish temperature of the finishing rolling is set no higher than 960°C, hardening, including rolling heat, is carried out at a temperature of 920-970°C. To relieve internal stresses after tempering with a temperature vacation 150-250°C.

EFFECT: providing high hardness and strength while maintaining sufficient ductility and toughness.

2 cl, 4 tbl

Description

The invention relates to ferrous metallurgy, in particular to the production of high-hard wear-resistant sheet metal for heavy lifting and handling equipment.

Hot rolled sheets used in the manufacture of welded metal structures of transport and mining machines must have high strength and hardness to withstand intense wear during prolonged impact and abrasion, and sufficient viscosity to undergo bending without cracking. The required set of properties of hot rolled sheets in the delivery state is given in table. one.

Known wear-resistant steel containing carbon, silicon, manganese, chromium, nickel, copper, molybdenum, vanadium, calcium, aluminum, niobium, titanium, rare earth metals (REM), iron and inevitable impurities in the following ratio of components, wt. %: carbon 0.25-0.60; silicon 0.10-1.50; manganese 0.20-1.30; chromium 0.30-1.90; nickel 0.70-2.0; copper no more than 0.45; molybdenum 0.10-0.90; vanadium 0.001-0.40; calcium 0.0001-0.01; aluminum 0.005-0.10; niobium 0.001-0.20; titanium 0.001-0.20; REM 0.0001-0.005; iron and other unavoidable impurities (RF Patent No. 2546262, C22C 38/50, publ. 04/10/2015, Bull. No. 10).

Products made from this steel have a tensile strength σ of _at least 1300 N / mm ² , an elongation of δ _{5 of} at least 12%, impact strength KCU of at least 105 J / cm ² and Brinell hardness in the range of 380-422 HB.

Known low-carbon alloy steel with high machinability, containing carbon, silicon, manganese, chromium, nickel, tin and iron in the following ratio, wt. %: carbon 0.13-0.21; silicon 0.17-0.37; manganese 0.70-1.10; chrome 0.80-1.10; nickel 0.80-1.10; tin 0.05-0.30; iron base. Additionally, the content of harmful impurities, wt. %: sulfur - not more than 0.025, phosphorus - not more than 0.025, copper - not more than 0.20. The ratio of tin to copper content is in the range from 0.3 to 6, and the total sulfur and tin content does not exceed 0.31 wt. % (RF Patent No. 2507293, C22C 38/40, publ. 02.20.2014, Bull. No. 5).

Products made from this steel have a yield strength σ _{t of} at least 1290 N / mm ² , tensile strength σ of _at least 1318 N / mm ² , elongation δ _{5 of} at least 6.2%, impact strength KCU of at least 61 J / cm ² , the productivity of processing by pressure of not less than 0.93 and machinability by cutting of not less than 0.94.

A disadvantage of the known inventions is that the casting of steel with a content of both rare-earth metals and tin leads to overgrowing and rapid wear of the CCM submersible glasses, and products made from these steels have low viscosity properties and insufficient hardness.

The closest in technical essence and the achieved result is a method of producing sheet steel with high wear resistance, including continuous casting of steel into slabs, their heating, multi-pass hot rolling of sheets in a regulated temperature range, water quenching and tempering. Steel contains wt.%: Carbon 0.14-0.19; silicon 0.17-0.37; manganese 1.1-1.6; vanadium 0.06-0.12; chrome 0.7-1.1; nickel 0.5-1.0; molybdenum 0.20-0.35; aluminum 0.02-0.06; titanium 0.02-0.05; boron 0.001-0.005; calcium 0.002-0.030; sulfur not more than 0.008; phosphorus no more than 0.015; iron the rest. The slabs are heated to a temperature of 1280 ° C, the temperature of the end of the finish rolling is set no higher than 800 ° C, water quenching is carried out in two stages, first from a temperature of 940-970 ° C, after which the sheets are reheated and quenched from a temperature of 840-870 ° C, and tempering is carried out at a temperature of 500-560 ° C (RF Patent No. 2533469, IPC C21D 8/02, C22C 38/54, C22C 38/58, publ.: 20.11.2014, Bull. No. 32).

The disadvantage of the prototype is that double hardening leads to increased energy consumption and high costs of heat treatment, which increases the cost of steel production.

The technical result of the invention is to achieve the necessary strength properties and hardness of low alloy steel plate while maintaining sufficient ductility and toughness with a single hardening and tempering.

The specified technical result is achieved in that in the known method for the production of sheet steel with high wear resistance, including continuous casting of steel into slabs, their heating, multi-pass hot rolling of sheets and their quenching with water, unlike the closest analogue, steel of the following chemical composition is subjected to continuous casting, wt. %:

carbon 0.17-0.28 silicon 0.10-0.30 manganese 0.75-1.50 chromium 0.60-1.20 nickel 0.60-1.20 molybdenum 0.20-0.40 vanadium 0.04-0.10 aluminum 0.02-0.08 nitrogen 0.001-0.010 copper 0.01-0.10 niobium 0.001-0.020 titanium 0.002-0.040 boron 0.001-0.005 sulfur no more than 0,010 phosphorus no more than 0.015 iron rest

In this case, the slabs are heated in the temperature range 1180-1250 ° C, the temperature of the end of the finish rolling is set no higher than 960 ° C, quenching, including from rolling heating, is carried out at a temperature of 920-970 ° C. To relieve internal stresses after quenching, tempering is carried out at a temperature of 150-250 ° C.

The essence of the invention lies in the fact that the final mechanical and functional properties of sheet steel are determined by its chemical composition, temperature conditions of rolling, as well as temperature conditions of hardening and tempering. In the process of conducting experimental studies, all significant factors were varied, achieving stable production of a given level of hardness of plate steel while maintaining a sufficiently high ductility and toughness.

The carbon content in the steel of the proposed composition determines its strength. At a carbon concentration of less than 0.17%, the required strength and hardness of the steel are not achieved. An increase in carbon content of more than 0.28% impairs the plastic and viscous properties of sheet steel.

When the silicon content is less than 0.10%, the deoxidation of steel deteriorates, and the strength of sheet metal decreases. An increase in the silicon content of more than 0.30% leads to an increase in the number of silicate inclusions, which reduces the toughness of the metal.

Manganese deoxidizes and strengthens steel, binds sulfur. When the manganese content is less than 0.75%, the strength and hardness of the steel are insufficient. An increase in manganese content of more than 1.50% leads to a decrease in the toughness of the proposed steel.

Chrome increases the strength of steel. When its concentration is less than 0.60%, the strength properties do not reach the required values. An increase in chromium content of more than 1.20% leads to a loss of ductility.

Nickel helps to increase the plastic and viscous properties of sheet steel at low operating temperatures. When the nickel content is less than 0.60%, the ductility and toughness indicators are reduced, and the yield is reduced. When the nickel content is more than 1.20%, carbides are intensively coalesced and grow to sizes that reduce the positive effect of nickel on ductility. In addition, the residual austenite content in the microstructure of rack martensite increases, which further reduces ductility and increases the tendency of steel to brittle fracture.

The addition of molybdenum in the specified range helps to obtain the required strength characteristics of steel, and also improves its hardenability. When the molybdenum content is less than 0.20%, the strength properties of steel do not reach the required level, and an increase in its content of more than 0.40% affects the weldability and ductility of hardened steel.

A vanadium content of more than 0.10% leads to a deterioration in the weldability of steel and is not economically feasible in view of the increase in alloying costs. When the content of vanadium is less than 0.04%, the strength properties of steel are lower than the required level.

Aluminum deoxidizes and modifies steel, binding nitrogen to nitrides, inhibits its negative effect on the properties of sheets. When the aluminum content is less than 0.02%, the complex of mechanical properties of sheet metal is reduced. An increase in its concentration of more than 0.08% leads to a deterioration in the viscosity properties of hot-rolled sheets.

Nitrogen promotes the formation of nitrides in steel. The upper limit of nitrogen content - 0.010% is due to the need to obtain a given level of ductility and toughness of steel, and the lower limit - 0.001% - to questions of manufacturability.

The addition of copper in the range of 0.01-0.10% increases the strength and corrosion resistance of steel. A higher copper content is not economically feasible.

The niobium additives within the specified limits serve the purpose of dispersion hardening, and also inhibit the growth of austenitic grain and contribute to the appearance of a subgrain structure during cooling, which is fixed and stabilized by dispersed carbide particles. When the niobium content is less than 0.001%, sufficient hardening is not provided. An increase in the niobium content of more than 0.020% is not economically feasible due to the increase in doping costs.

Titanium is a strong carbide forming element that strengthens steel. When the titanium content is less than 0.002%, sufficient hardening is not provided. An increase in titanium content in excess of 0.040% leads to a decrease in the viscosity properties of the metal.

Alloying with boron increases the strength properties after hardening and low tempering, without changing or slightly reducing viscosity and ductility. Boron, added in the range of 0.001-0.005%, significantly increases the hardenability of steel, contributing to the formation of potentially hardening components - bainite or martensite, and at the same time slowing down the formation of softer ferrite and pearlite components during cooling of steel from high temperatures to ambient temperatures. Boron in an amount of more than 0.005% can contribute to the formation of embrittling particles - iron carbides. To obtain the maximum effect on hardenability, a boron concentration of at least 0.001% is desirable.

Sulfur and phosphorus for steels are harmful impurities, an increase in their content leads to a deterioration in the plastic and viscosity properties. However, at a sulfur concentration of not more than 0.010% and phosphorus not more than 0.015%, their negative effect on the properties of steel is negligible. At the same time, deeper desulfurization and dephosphorization of steel significantly increase its production cost.

Heating steel slabs of the proposed chemical composition in the temperature range 1180-1250 ° C provides homogeneous austenitization and complete dissolution of sulfides, phosphides, alloying and impurity compounds, carbide hardening particles. At a heating temperature below 1180 ° C, complete dissolution is not observed, the microstructure of the slab is not homogeneous. At a heating temperature above 1250 ° C, overheating of steel occurs, accompanied by an exponential growth of austenitic grain, which adversely affects the mechanical and operational properties.

The temperature of the end of rolling (TKP) should be no more than 960 ° C. At a temperature of over 960 ° C, no nanosized particles of vanadium and titanium carbonitrides are released in the required amount, and the required level of yield strength and strength are not provided. The hardening of hot-rolled sheets is regulated by a temperature range of 920-970 ° C. Quenching temperatures above 970 ° C lead to an unacceptable decrease in the toughness of sheet steel. Lowering this temperature to less than 920 ° C does not provide stable mechanical properties, which reduces yield.

After stress hardening, tempering can be carried out at a temperature of 150-250 ° C to relieve internal stresses. The tempering of tempered sheets at temperatures above 250 ° C reduces their strength properties below the permissible level. The decrease in tempering temperature below 150 ° C leads to the loss of plastic and viscous properties of high-strength sheets.

Thus, the full use of the resource of properties corresponding to the low alloy steel of the proposed chemical composition is ensured by temperature conditions of rolling, as well as temperature conditions of hardening and tempering.

An example of the method

Using the induction melting furnace IST 0.03 / 0.05 I1, steel of various chemical composition was smelted (Table 2).

The obtained ingots were heated in a chamber furnace PKM 3.6.2 / 12.5 to a temperature of 1210 ° C. Next, the ingots were squeezed using a P6334 hydraulic press (simulation of the rough rolling stage) and on a single-strand reversible hot rolling mill 500 “DUO” (modeling the final rolling stage). The compression end temperature was 800 ° C to 970 ° C. The ingots were rolled to a thickness of 6, 8 and 10 mm. The resulting peals were cooled in air. Quenching and tempering of rolled samples was carried out according to various modes (table. 3).

Further, the resulting peals were “cut out” for testing.

Mechanical properties were determined on transverse samples in accordance with generally accepted conditions:

- tensile tests were carried out on flat samples according to GOST 1497;

- Brinell hardness tests were carried out in accordance with GOST 9012;

- impact bending tests were carried out in accordance with GOST 9454 on samples with a V-shaped notch at a temperature of -40 ° C;

- the bending test was carried out in accordance with GOST 14019. The test results showed that in the sheet steel obtained by the proposed method (options No. 2-5, table. 4), a combination of the necessary strength, plastic and viscosity properties is achieved. In cases of deviations from the declared parameters (options No. 1 and No. 6), as well as when using the prototype method, the claimed complex of mechanical properties is not provided.

Thus, the use of the claimed method achieves the desired technical result - receiving sheet steel with high wear resistance and a complex set of mechanical properties: yield strength σ _0.2 is not less than 1100 N / mm ^2, tensile strength σ _at least 1400 N / mm ² ; hardness 420-480 HBW, elongation δ ₅ not less than 9%, impact strength KCV ^-40 not less than 40 J / cm ² .

Claims (4)

 1. A method of manufacturing sheet steel with high wear resistance, including continuous casting of steel into slabs, heating them, multi-pass hot rolling into sheets, hardening and tempering of sheets, characterized in that they carry out continuous casting of steel containing, by weight. %: carbon 0.17-0.28 silicon 0.10-0.30 manganese 0.75-1.50 chromium 0.60-1.20 nickel 0.60-1.20 molybdenum 0.20-0.40 vanadium 0.04-0.10 aluminum 0.02-0.08 nitrogen 0.001-0.010 copper 0.01-0.10 niobium 0.001-0.020 titanium 0.002-0.040 boron 0.001-0.005 sulfur no more than 0,010 phosphorus no more than 0.015 iron rest, while heating the slab is carried out in the temperature range 1180-1250 ° C, the temperature of the end of the finish rolling is set no higher than 960 ° C, and hardening is carried out at a temperature of sheets 920-970 ° C with cooling in water. 2. The method according to p. 1, characterized in that the vacation is carried out at a temperature of 150-250 ° C.