RU2442830C1 - Method for production of high-strength steel products - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: The invention relates to metallurgy. The result is achieved by producing the rough piece, deforming it in the temperature range from 1050-1150°C to 850-900°C, its normalization or hardening at the temperature of 850-950°C, relieving at 400-600°C. The rough piece is produces from a steel with the following chemical composition, %: 0,3-0,6 C; 0,6-1,4 Mn; 0,1-0,3 Si; 1,0-1,4 Cr; 0,6-2,8 Ni; 0,03-0,85 Cu; 0,3-0,6 Mo; 0,10-0,16 V; 0,05-0,10 Nb; 0,01-0,08 Ti; 0,02-0,08 Al; 0,002-0,010 B; less than 0,010 S; less than 0,015 P; rest - Fe. To ensure the temporal resistance to breakage of 1450-1500 N/mm² and impact resilience KCV⁺²⁰ of at least 20 J/cm² the rough piece is relieved at the temperature below 500°C, and to ensure the temporal resistance to breakage of 1350-1500 N/mm² and impact resilience KCV⁺²⁰ of at least 30 J/cm² the rough piece is relieved at the temperature of at least 500°C.

EFFECT: improvement of numerous mechanical properties of steel products and increase of production yield.

2 cl, 1 ex, 2 tbl

Description

The invention relates to the field of metallurgy and mechanical engineering and can be used for the manufacture of highly hardened sheet and long products, as well as products for various purposes, obtained by stamping.

A known method for the production of high-strength steel products, including the manufacture of a workpiece from chromium-nickel steel grade 24X2NAch, containing (wt.%):

Carbon 0.23 Manganese 0.32 Silicon 0.24 Chromium 1.55 Nickel 1.14 Sulfur 0.005 Phosphorus 0.015 REM 0,03 Aluminum 0.02 Iron The basis

The workpiece is subjected to hot plastic deformation by rolling into a strip with a thickness of 7.5 mm Samples made from the strip are quenched from a temperature of 900 ° C, and then released at a temperature of 600 ° C [1].

The disadvantages of this method are that the samples after quenching and tempering have low strength and viscosity properties.

The closest analogue to the present invention is a method for the production of high-strength steel products (sheets). The method includes the manufacture of a workpiece from steel grade 17GS of the following chemical composition, wt.%:

Carbon 0.14-0.20 Silicon 0.4-0.6 Manganese 1.0-1.4 Chromium no more than 0,3 Nickel no more than 0,3 Copper no more than 0,3 Phosphorus no more than 0,035 Sulfur no more than 0,04 Iron and impurities Rest

The billet is heated and subjected to hot plastic deformation by rolling into a sheet on a reversible plate mill. The rolled sheet is subjected to normalization or hardening, followed by tempering (thermal improvement) [2].

The disadvantages of this method are that the finished steel products (sheets) have a low complex of mechanical properties, namely: low strength and toughness. This, in turn, leads to a decrease in yield.

The technical problem solved by the invention is to increase the complex of mechanical properties and increase the yield.

To solve the technical problem in the known method for the production of high-strength steel products, including the manufacture of a workpiece, its hot plastic deformation, normalization or hardening and subsequent tempering, according to the invention, plastic deformation is carried out in the temperature range from 1050-1150 ° C to 850-900 ° C, normalization or hardening is carried out from a temperature of 850-950 ° C, and tempering is carried out at a temperature of 400-600 ° C, and the billet is made of steel of the following chemical composition, wt.%:

Carbon 0.3-0.6 Manganese 0.6-1.4 Silicon 0.1-0.3 Chromium 1.0-1.4 Nickel 0.6-2.8 Copper 0.03-0.85 Molybdenum 0.3-0.6 Vanadium 0.10-0.16 Niobium 0.05-0.10 Titanium 0.01-0.08 Aluminum 0.02-0.08 Boron 0.002-0.010 Sulfur no more than 0,010 Phosphorus no more than 0.015 Iron Rest

In addition, to provide a temporary tensile strength of 1450-1500 N / mm ² and impact strength KCV ^{+20 of} at least 20 J / cm ^2, tempering is carried out at a temperature below 500 ° C, and to provide a temporary tensile strength of 1350-1500 N / mm ² and impact strength KCV ⁺²⁰ not less than 30 J / cm ² vacation is carried out at a temperature of not lower than 500 ° C. That is, the choice of tempering temperature is carried out taking into account the specific requirements for the steel factory.

The essence of the proposed technical solution is as follows. The complex of mechanical properties of high-strength steel products is determined by the microstructural-phase state of the steel after the final heat treatment, which, in turn, depends on the chemical composition of the steel, the temperature range of plastic deformation, the temperature of normalization or hardening, and also tempering.

Heating the preform before plastic deformation leads to complete dissolution of large carbide inclusions in austenite. Complex alloying of steel with carbonitride-forming elements (vanadium, niobium, titanium, boron), as shown by studies, prevents the polygonization processes from occurring at all stages of the heat-treatment. These elements are released at dislocations and slow down the formation of ferrite grains.

Plastic deformation of the workpiece in the temperature range from 1050-1150 ° C to 850-900 ° C provides grinding of austenitic grains, stimulates the precipitation of hardening finely dispersed carbide and carbonitride particles from the solid solution. Hardening (or normalization) after heating to a temperature of 850-950 ° C ensures the complete occurrence of the polymorphic transformation of austenite into dislocation martensite, due to which the steel product acquires extremely high strength properties.

The microstructural-phase state of the hardened (or normalized) steel of the proposed chemical composition is characterized by increased thermal stability. As a result, high tempering at temperatures of 400-600 ° C does not lead to a significant softening, while at the same time it removes residual internal thermal and phase stresses. Due to this, steel products, while maintaining extremely high strength properties, acquire increased viscosity properties. The consequence of this increase in the complex of mechanical properties is an increase in the yield of suitable steel products.

It was experimentally established that at the onset temperature of plastic deformation above 1150 ° C, the formation of internal cracks is not excluded due to the weakening and oxidation of grain boundaries of crystallites. A decrease in this temperature below 1050 ° C leads to incomplete dissolution of carbide inclusions in austenite, which reduces the strength properties of the products.

At the temperature of completion of plastic deformation above 950 ° C, uncontrolled post-deformation growth of austenitic grains occurs, which reduces the complex of mechanical properties. A decrease in this temperature below 850 ° C reduces the toughness and ductility of steel products.

In cases of normalization or hardening of steel products from temperatures above 950 ° C, the proportion of residual austenite in the phase composition of steel increases, which reduces its strength properties. When normalizing or hardening from a temperature below 850 ° C, stable obtaining of the set strength properties is not ensured, which reduces the yield.

The release of normalized or hardened sheets at temperatures above 600 ° C dramatically reduces their strength properties. A decrease in tempering temperature below 400 ° C leads to a loss of the viscous and plastic properties of high-strength sheets, which reduces the yield.

At tempering temperatures of 500 ° C and above, there is a slight decrease in strength properties, but higher viscosity properties are achieved. At the same time, when the tempering temperature is not more than 500 ° C, the maximum possible strength is achieved, but the viscosity and plastic properties of steel are reduced.

Carbon reinforces steel. When the carbon content is less than 0.3%, the required strength of the products is not achieved, and when its content is more than 0.6%, the toughness and ductility deteriorate.

Manganese deoxidizes and strengthens steel, binds sulfur. When the manganese content is less than 0.6%, the strength and toughness of the steel is insufficient. An increase in manganese content of more than 1.4% leads to a decrease in toughness and a deterioration in the plastic properties of the products.

Silicon deoxidizes steel, increases its strength. At a silicon concentration of less than 0.1%, the strength of the steel is lower than acceptable, and at a concentration of more than 0.3%, the viscosity and ductility of thermally improved steel are reduced.

Chrome increases the strength and toughness of steel. When its concentration is less than 1.0%, the strength and viscosity are below acceptable values. An increase in chromium content of more than 1.4% leads to a loss of ductility and a decrease in viscosity due to the growth of carbides.

Nickel and copper increase the strength and ductility of steel. In addition, nickel and copper increase the stability of austenite, which is especially important during the final heat treatment of steel products. When the nickel concentration is less than 0.6% or copper less than 0.03%, the steel products have insufficient plastic properties, which reduces the yield. An increase in the concentration of nickel over 2.8% or copper over 0.85% leads to a decrease in impact strength KCV ⁺²⁰ .

Molybdenum increases strength and improves the viscosity properties of steel products. When the molybdenum content is less than 0.3%, the strength and toughness of the steel are insufficient, and an increase in its concentration in excess of 0.6% leads to a decrease in the ductility of steel products.

Vanadium, niobium, titanium, aluminum and boron inhibit the occurrence of an undesirable polygonization process, which prevents the loss of strength and hardness of hardened (normalized) steel after high-temperature tempering, and also contribute to the grinding of microstructure components. However, if the content of vanadium is more than 0.16%, niobium more than 0.10%, titanium more than 0.08%, aluminum more than 0.08% or boron more than 0.010%, then there is a decrease in plastic properties and yield. When the content of vanadium is less than 0.10%, niobium is less than 0.05%, titanium is less than 0.01%, aluminum is less than 0.02% and boron is less than 0.002%, high-temperature tempering will lead to a sharp decrease in strength properties and lower yield.

Sulfur and phosphorus in this steel are harmful impurities, their concentration should be as low as possible. 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 will significantly increase the cost of its production, which is impractical.

Method implementation examples

Example 1

For the production of high-strength steel products, steel billets were used, the chemical composition of which is given in Table 1.

Steel billets with composition No. 3 were heated to the temperature of the onset of plastic deformation T _nd = 1100 ° C and they were forged into 14 × 14 mm square bars. Forging was completed at a temperature T _cd = 870 ° C.

The products were heated to a quenching temperature T _s = 900 ° C, after which they were quenched in water. The hardened products were subjected to high temperature tempering at a temperature T _OT = 480 ° C (i.e., below 500 ° C).

After tempering, the products acquired the following set of mechanical properties: σ _in = 1500 N / mm ² ; σ _t = 1200 N / mm ² ; δ ₅ = 24%; KCV ⁺²⁰ = 29 J / cm ² .

The yield (in terms of mechanical properties) of high-strength steel products was: Q = 99.9%.

Example 2

Billets made of steel with composition No. 3 were heated to the temperature of the onset of deformation T _nd = 1140 ° C and subjected to hot rolling on a high-grade mill 250 in round rods with a diameter of d = 16 mm. Rolling was completed at a temperature T _cd = 900 ° C. The resulting products were heated to a temperature of T _s = 905 ° C and cooled in air (subjected to normalization). Then the products were released by heating to a temperature T _OT = 560 ° C (i.e., not lower than 500 ° C).

After tempering, high-strength steel products acquired the following set of mechanical properties:

σ _in = 1400 N / mm ² ; σ _t = 1100 N / mm ² ; δ ₅ = 28%; KCV ⁺²⁰ J / cm ² .

The yield (in terms of mechanical properties) of high-strength steel products was: Q = 99.8%.

Implementation options of the proposed method and indicators of their effectiveness are presented in table.2.

Table 1 Compositions of steel for the production of high-strength products Composition number The content of chemical elements, wt.% C Mn Si Cr Ni Cu Mo V Nb Ti Al B S P Fe one. 0.2 0.5 0.09 0.9 0.5 0.02 0.2 0.09 0.04 0.009 0.01 0.001 0.005 0.007 Rest 2. 0.3 0.6 0.1 1,0 0.6 0,03 0.3 0.10 0.05 0.01 0.02 0.002 0.005 0.006 -: - 3. 0.5 1,0 0.2 1,2 1,6 0.44 0.5 0.14 0,07 0.04 0.05 0.006 0.007 0.009 -: - four. 0.6 1.4 0.3 1.4 2,8 0.85 0.6 0.16 0.10 0.08 0.08 0.010 0.010 0.015 -: - 5. 0.7 1,5 0.4 1,5 2.9 0.86 0.7 0.17 0.11 0.09 0.09 0.011 0.011 0.016 -: - 6. 0.2 0.7 0.5 0.3 0.3 0.2 - - - - - - 0,030 0,028 -: -

table 2 Modes of production of high-strength steel products and their effectiveness No. p / p Composition number T _nd , ° C T _cd , ° C T _s , ° C T _otp , ° С σ _in , N / mm ² σ _t , N / mm ² δ ₅ ,% KCV ⁺²⁰ , J / cm ² Q% one. one 1040 840 840 390 800 670 fourteen 16 70,2 2. 2 1050 850 850 400 1450 1230 21 22 99.5 3. 3 1100 870 900 480 1480 1200 24 29th 99.9 four. four 1150 900 950 490 1500 1190 25 28 99.7 5. four 1060 860 860 500 1500 1180 27 thirty 99.8 6. 3 1140 900 905 560 1390 1100 28 35 99.8 7. 2 1145 890 945 600 1350 1150 29th 36 99.7 8. 5 1160 910 960 620 990 820 19 eighteen 65.0 9. 6 1200 840 845 390 750 620 19 twenty 86.7

From the data presented in table 2, it follows that when implementing the proposed method (options No. 2-7, compositions of steels No. 2-4), an increase in the complex of mechanical properties of high-strength steel products and an increase in yield are achieved. In cases of transcendental values of the declared parameters (options No. 1 and No. 8, the compositions of steel No. 1 and No. 5), as well as the prototype method (option No. 9, the composition of steel No. 6), there is a decrease in the set of mechanical properties and yield.

As a base object for determining the effectiveness of the proposed method, the prototype method is selected. Implementation of the proposed method will increase the profitability of the production of high-strength steel products by 25-30%.

Information sources

1. RF patent No. 2131932, IPC C21D 1/25, C21D 1/02, C21D 8/00, 1999

2. Matrosov Yu.I. and others. Steel for gas pipelines. M .: Metallurgy, 1989, p. 242-243, 268.

Claims (2)

1. The method of production of steel products, including the manufacture of the workpiece, its hot plastic deformation, normalization or hardening and subsequent tempering, characterized in that plastic deformation is carried out in the temperature range from 1050-1150 ° C to 850-900 ° C, normalization or hardening from a temperature of 850-950 ° C, and tempering is carried out at a temperature of 400-600 ° C, and the billet is made of steel of the following chemical composition, wt.%:
carbon 0.3-0.6 manganese 0.6-1.4 silicon 0.1-0.3 chromium 1.0-1.4 nickel 0.6-2.8 copper 0.03-0.85 molybdenum 0.3-0.6 vanadium 0.10-0.16 niobium 0.05-0.10 titanium 0.01-0.08 aluminum 0.02-0.08 boron 0.002-0.010 sulfur no more than 0,010 phosphorus no more than 0.015 iron rest 2. The method according to claim 1, characterized in that to provide a temporary tensile strength of 1450-1500 N / mm ² and impact strength KCV ^{+20 of} at least 20 J / cm ^2, tempering is carried out at a temperature below 500 ° C, and to provide temporary tensile strength 1350-1500 N / mm ² and impact strength KCV ⁺²⁰ not less than 30 J / cm ² vacation is carried out at a temperature of not lower than 500 ° C.