RU2603404C1 - Method for production of high-hardness wear-resistant sheet products - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to ferrous metallurgy, particularly to production of a new highly efficient type of metal products - thick-sheet wear-resistant low-alloy steel for heavy handling equipment. Method involves production of slabs from steel containing, wt%: 0.20-0.28 C, 0.15-0.30 Si, 0.75-1.30 Mn, 0.30-0.65 Cr, 0.85-1.55 Ni, 0.25-0.40 Mo, 0.02-0.06 V, 0.02-0.05 Al, 0.001-0.010 N, 0.10-0.20 Cu, 0.002-0.060 Nb, 0.002-0.010 Ti, 0.001-0.005 B, not more than 0.005 S, not more than 0.010 P, Fe - balance, heating, multipass hot rolling of sheets, tempering with water at temperature of 930-980 °C, tempering at temperature 150-250 °C.

EFFECT: high hardness and strength while maintaining sufficient ductility and impact strength.

1 cl, 4 tbl, 1 ex

Description

The invention relates to ferrous metallurgy, in particular to the production of a new highly efficient type of metal products - plate wear-resistant sheet products of low alloy steel 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.

A known method for the production of high-strength plate steel, including continuous casting of steel into slabs, heating, multi-pass hot rolling of sheets in a regulated temperature range, water quenching and tempering, according to which steel of the following chemical composition is subjected to continuous casting, wt. %: carbon 0.13-0.18, silicon 0.40-0.60, manganese 0.70-0.90, chromium 1.3-1.6, aluminum 0.02-0.07, niobium 0, 03-0.06, titanium 0.01-0.06, calcium 0.002-0.030, nickel not more than 0.30, copper not more than 0.30, nitrogen not more than 0.010, iron and impurities - the rest, while cast slabs before by heating, annealing at a temperature of 640-660 ° C, the slabs are heated to a temperature of 1200-1260 ° C and subjected to hot rolling in the temperature range up to 870-950 ° C (RF Patent No. 2533244, IPC C21D 8/02, C22C 38/50 , 2013).

Products made from this steel have a tensile strength σ of _at least 690 N / mm ² , yield strength σ _{t of} at least 590 N / mm ² , elongation δ _{5 of} at least 14%, impact strength KCV ^{-40 of} at least 30 J / cm ² and Brinell hardness in the range of 340-400 HB.

The disadvantage of this method is that the hot-rolled sheets after thermal improvement (tempering with tempering) have low viscosity properties and insufficient hardness.

The closest in technical essence and the achieved result is a method for the production of sheet steel with high wear resistance, including the manufacture of slabs from steel containing, by weight. %: 0.14-0.19 C; 0.17-0.37 Si; 1.10-1.60 Μn; 0.70-1.10 Cr; 0.50-1.00 Ni; 0.10-0.35 Mo; 0.06-0.12 V; 0.02-0.06 Al; 0.02-0.05 Ti; 0.001-0.005 V; 0.002-0.030 Ca; no more than 0.015 Ρ; not more than 0.008 S; iron - the rest, their heating, multi-pass hot rolling of sheets in a regulated temperature range, water quenching and tempering. Hot rolling is carried out in a temperature range from 1280 ° C to 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, tempering is carried out at a temperature 500-560 ° C (RF Patent No. 2533469, IPC C21D 8/02, C22C 38/54, C22C 38/58, 2013).

Products made from this steel have a tensile strength σ of _at least 1050 N / mm ² , yield strength σ _{t of} at least 950 N / mm ² , elongation of at least 11%, impact strength KCV ^{-40 of} at least 30 J / cm ² , Brinell hardness in the range of 340-400 HB.

The disadvantage of the prototype is that it does not provide the required level of mechanical properties, namely sheet steel does not have sufficient hardness and toughness.

The technical result of the invention is to increase the strength properties and hardness of economically alloyed steel plate while maintaining sufficient ductility and toughness.

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

carbon 0.20-0.28 silicon 0.15-0.30 manganese 0.75-1.30 chromium 0.30-0.65 nickel 0.85-1.55 molybdenum 0.25-0.40 vanadium 0.02-0.06 aluminum 0.02-0.05 nitrogen 0.001-0.010 copper 0.10-0.20 niobium  0.002-0.060 titanium 0.002-0.010 boron 0.001-0.005 sulfur no more than 0,005 phosphorus no more than 0,010 iron rest,

while hardening is carried out at a temperature of 930-980 ° C, 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 both by its chemical composition and the temperature conditions of quenching 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 0.20%, 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 hardened and tempered sheet steel.

When the silicon content is less than 0.15%, 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, and 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 1.30% leads to a decrease in the toughness of hardened steel.

Chrome increases the strength of steel. When its concentration is less than 0.30%, the strength properties do not reach optimal values. An increase in chromium content of more than 0.65% leads to a loss of ductility.

Nickel helps to increase the plastic and viscous properties of sheet steel at low operating temperatures. With a nickel content of less than 0.85%, ductility and toughness are reduced, and yield is reduced. When the nickel content is more than 1.55%, 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 0.25%, 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 0.06% 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 0.02%, the strength properties of steel are lower than the required level.

Aluminum deoxidizes and modifies steel. By binding nitrogen to nitrides, it inhibits its negative effect on the properties of the 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 0.05% leads to a deterioration in the viscosity properties of hot-rolled sheets.

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

The addition of copper in the range of 0.10-0.20% 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 0.002%, sufficient hardening is not provided. An increase in the niobium content of more than 0.060% leads to a deterioration in the weldability of steel and is not economically feasible due to the increase in alloying 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 0.010% 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 embrittlement particles Fe ₂₃ (C, B) ₆ (a form of iron borocarbide). To obtain the maximum effect on hardenability, a boron concentration of at least 0.001% is desirable.

Sulfur and phosphorus in this steel 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 0.005% and phosphorus not more than 0.010%, their negative effect on the properties of steel is negligible. At the same time, deeper desulfurization and dephosphorization of steel will significantly increase the cost of its production, which is impractical.

Heating of hot-rolled sheets for hardening to temperatures above 980 ° C leads to an unacceptable decrease in the toughness of sheet steel. Lowering this temperature to less than 930 ° C does not provide a stable obtaining of the specified strength properties, which reduces the yield.

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 low alloy steel of a given chemical composition is ensured by the heat treatment modes of plate products.

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 1200 ° C. Then, ingots were crimped using a P6334 hydraulic press (rough rolling simulation) and 500 “DUO” single-strand reversible hot rolling mill (finishing rolling). The temperature of the end of the compression ranged from 850 to 950 ° C. The ingots were rolled to a thickness of 6, 10, 20, 30 mm. The resulting peals were cooled in air.

The heat treatment of the rolled samples consisted of quenching at a temperature of 900-1000 ° C and subsequent tempering at a temperature of 150-300 ° C (Table 3), after which the resulting peals were cut 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;

- bending tests were 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 highest strength, plastic and viscosity properties is achieved.

In cases of transcendental values of the declared parameters (options No. 1 and No. 6), as well as when using the prototype method, the specified set of mechanical properties is not provided.

Thus, the use of the claimed method achieves the desired result - obtaining high hard wear-resistant rolled sheet with 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 45 J / cm ² .

Claims (1)

A method of manufacturing a high-hardness wear-resistant sheet metal, including continuous casting of steel into slabs, heating them, multi-pass hot rolling of sheets, heating the sheet, quenching with water and tempering, characterized in that they carry out continuous casting of steel containing, by weight. %:
carbon 0.20-0.28 silicon 0.15-0.30 manganese 0.75-1.30 chromium 0.30-0.65 nickel 0.85-1.55 molybdenum 0.25-0.40 vanadium 0.02-0.06 aluminum 0.02-0.05 nitrogen 0.001-0.010 copper 0.10-0.20 niobium 0.002-0.060 titanium 0.002-0.010 boron 0.001-0.005 sulfur no more than 0,005 phosphorus no more than 0,010 iron rest,
while heating the sheet for hardening is carried out to a temperature of 930-980 ° C, and tempering is carried out at a temperature of 150-250 ° C.