CN112342474B

CN112342474B - Ultrahigh-strength nanocrystalline 40Cr3Ni4 structural steel and preparation method thereof

Info

Publication number: CN112342474B
Application number: CN202011051830.9A
Authority: CN
Inventors: 王海; 任玲; 张书源; 杨柯
Original assignee: Institute of Metal Research of CAS
Current assignee: Institute of Metal Research of CAS
Priority date: 2020-09-29
Filing date: 2020-09-29
Publication date: 2022-02-15
Anticipated expiration: 2040-09-29
Also published as: CN112342474A

Abstract

The invention relates to the technical field of materials, in particular to ultrahigh-strength nanocrystalline 40Cr3Ni4 structural steel and a preparation method thereof. The chemical composition of the structural steel is as follows (weight percent): c is 0.32-0.48; 2.2-3.8 parts of Cr; 3.2 to 4.8 of Ni; v is 0.1 to 0.2; 0.01 to 0.03 percent of Ce; 0.01 to 0.2 Mn; 0.01 to 0.2 of Si; the balance being Fe. The preparation method of the structural steel comprises the following steps: (1) after preserving the heat for a period of time at 850-930 ℃, rapidly cooling to room temperature to obtain a nano-batten precursor; (2) for the nano-lath precursor, the temperature is 680-760 ℃, and the strain rate is 0.5-2 s^‑1The total strain amount is more than or equal to 70 percent, so that the precursor of the nano-lath is converted into a nano-crystal structure; (3) tempering the nanocrystalline material at 200-250 ℃ for 1-2 h. The nanocrystalline structural steel prepared by the invention has ultrahigh strength and good plasticity and toughness, and can be widely used for preparing large-scale important parts such as various gears, connecting rods, aircraft engine shafts, aircraft landing gears and the like.

Description

Ultrahigh-strength nanocrystalline 40Cr3Ni4 structural steel and preparation method thereof

Technical Field

The invention relates to the technical field of materials, in particular to ultrahigh-strength nanocrystalline 40Cr3Ni4 structural steel and a preparation method thereof.

Background

Structural steel is the most widely used and most used metal material in economic construction, and occupies an extremely important position in modern industrial production. With the rapid development of science and technology, people put more and more demands on the properties of the conventional structural steel materials, which have properties in many aspects that are difficult to satisfy the demands in practical production even through various strengthening means such as cold working, hot working, heat treatment and the like. Under such circumstances, there is a high necessity for developing a structural steel material having higher performance.

Compared with the traditional coarse-grain steel material, the nanocrystalline metal material has higher strength and plasticity under the room temperature condition; under the condition of high temperature, the material also has superplasticity, which brings a plurality of convenient conditions for plastic processing and forming of the material. The above-mentioned advantages of nanocrystalline metal materials make them very attractive for practical applications. Therefore, the development and preparation of the nanocrystalline structural steel open up a new way for the performance optimization of the traditional steel materials.

At present, the preparation of bulk nanocrystalline metal materials is mainly achieved by a large plastic deformation (SPD) method. Common large plastic deformation methods comprise Equal Channel Angular Pressing (ECAP), accumulative composite rolling (ARB), Multidirectional Forging (MF), High Pressure Torsion (HPT) and the like, all of which need high-power equipment and expensive dies, and the prepared material has smaller size and cannot meet the requirement of large-scale industrial production. Therefore, the invention provides the nanocrystalline structural steel and the preparation method thereof, the preparation of the nanocrystalline structural steel can be realized through conventional hot rolling deformation, and new foundation and opportunity are brought for the development of the traditional structural steel material.

Disclosure of Invention

The invention aims to provide nanocrystalline structural steel, and in order to achieve the aim, the technical scheme of the invention is as follows:

a nanocrystalline 40Cr3Ni4 structural steel comprises the following chemical components in percentage by weight: c is 0.32-0.48; 2.2-3.8 parts of Cr; 3.2 to 4.8 of Ni; v is 0.1 to 0.2; 0.01 to 0.03 percent of Ce; 0.01 to 0.2 Mn; 0.01 to 0.2 of Si; the balance being Fe. More preferably: c is 0.38-0.44; 2.6-3.2 parts of Cr; 3.8 to 4.4 of Ni; v is 0.14 to 0.17; 0.01 to 0.03 percent of Ce; 0.01 to 0.2 Mn; 0.01 to 0.2 of Si; the balance being Fe.

The preparation method of the nanocrystalline structural steel comprises the following steps: a vacuum induction furnace is adopted to obtain a raw material ingot, and the ingot is polished and then is subjected to cogging forging and finish forging at the temperature of more than 950 ℃ to form a blank.

Preserving the temperature of the blank obtained by the finish forging processing at the temperature of 850-930 ℃ for a period of time, and quickly cooling to room temperature to obtain a nano lath precursor; thermally deforming the obtained nano-lath precursor to obtain a nano-crystal structure; and tempering the nanocrystalline structure to finally obtain the nanocrystalline structural steel.

As a preferred technical scheme:

and (3) keeping the temperature of the blank at 850-930 ℃ for a period of time, wherein the heat preservation time t is (2.5-3.5) Dmin, wherein D is the effective thickness of the sample, and the unit is millimeter mm.

The cooling rate of the rapid cooling is 20-80 ℃/s.

The nano-batten precursor has the temperature of 680-760 ℃ and the strain rate of 0.5-2.0 s^-1Is thermally deformed within the range of (1), and the total strain amount is 70% or more. Preferably: the thermal deformation temperature is 700-730 ℃, and the strain rate is 0.8-1.4 s^-1The total strain amount is 90% or more.

The microstructure of the material prepared by the method is a nanocrystalline structure, and the grain size is 30-95 nm.

The invention has the beneficial effects that:

(1) different from the situation of the prior art, the nanocrystalline steel material provided by the invention can realize the preparation of nanocrystalline structural steel through conventional thermal deformation without depending on high-power equipment and expensive dies.

(2) The bulk nanocrystalline metal material prepared by the method is not limited by size, and compared with the prior art, the bulk nanocrystalline metal material with larger size can be prepared, so that the requirement of large-scale industrial production is met.

(3) The method can obviously improve the comprehensive mechanical property of the structural steel, and the obtained nanocrystalline structural steel has ultrahigh strength and good plasticity and toughness, and can be widely used for preparing various gears, connecting rods, shafts of aircraft engines, aircraft landing gears and other large-scale important parts. The preferable alloy composition (C content is 0.38-0.44; Cr content is 2)6-3.2; the Ni content is 3.8-4.4; v content of 0.14-0.17) and thermal deformation condition (thermal deformation temperature of 700-730 deg.C, strain rate of 0.8-1.4 s)^-1And the total strain is more than or equal to 90 percent), the tensile strength of the prepared nanocrystalline structural steel is as high as 1600-1750 MPa, the elongation is 15-20 percent, and the Vickers hardness is 460-510.

Drawings

FIG. 1 TEM photograph of a nanostring precursor.

FIG. 2 is a TEM photograph of the structure of the nanocrystal formed by thermally deforming the precursor of the nano-lath.

Detailed Description

In order to make the purpose, technical solution and effect of the present application clearer and clearer, the present application is further described in detail below with reference to the accompanying drawings and examples.

The invention provides nanocrystalline structural steel, which comprises the chemical components of 0.32-0.48 of C; 2.2-3.8 parts of Cr; 3.2 to 4.8 of Ni; v is 0.1 to 0.2; 0.01 to 0.03 percent of Ce; 0.01 to 0.2 Mn; 0.01 to 0.2 of Si; the balance being Fe.

Please refer to fig. 1-2. FIG. 1 shows the nano-lath precursor formed by rapidly cooling the material of example 7 of the present invention, and it can be seen from the TEM tissue photograph that the width of the lath is between 16 nm and 40 nm. FIG. 2 shows the structure of the nano-scale crystals formed by thermal deformation of the nano-slab precursor of example 7 of the present invention, and it can be seen from the TEM photograph that the crystal grain size is between 30 nm and 70 nm.

The present application will now be illustrated and explained by means of several groups of specific examples and comparative examples, which should not be taken to limit the scope of the present application.

Example (b): examples 1 to 9 are structural steels smelted in the chemical composition range provided by the present invention, in which the contents of Cr and V elements are gradually reduced, and the contents of C and Ni elements are gradually increased, and the corresponding preparation processes are also appropriately adjusted within the technical parameter ranges specified by the present invention. The size of the prepared bulk nanocrystalline metal material is 140 multiplied by 1200 multiplied by 10 mm.

Comparative example: the chemical compositions of C, Cr, Ni and V in comparative example 1 are all lower than the lower limit of the chemical composition range provided by the invention, and the chemical compositions of C, Cr, Ni and V in comparative example 9 are all higher than the upper limit of the chemical composition range provided by the invention, and the effect of the change of the chemical compositions of C, Cr, Ni and V on the preparation of the nanocrystalline structural steel is illustrated by comparing with example 1 and example 9 respectively. Comparative example 2, in which the amount of strain is less than the lower limit of the amount of strain provided by the present invention, illustrates the effect of the amount of strain on the production of nanocrystalline structural steel by comparison with example 2. The strain rate of comparative example 3 is higher than the upper limit of the strain rate provided by the present invention and the strain rate of comparative example 4 is lower than the lower limit of the strain rate provided by the present invention, and the effect of the strain rate on the preparation of the nanocrystalline structural steel is illustrated by comparing with example 3 and example 4, respectively. Comparative example 5 slowly cooled to room temperature after heat treatment, and the effect of the cooling rate after heat treatment on the preparation of nanocrystalline structural steel is illustrated by comparison with example 5. Comparative example 6, in which the heat treatment temperature is lower than the lower limit of the heat treatment temperature provided by the present invention, illustrates the effect of the heat treatment temperature on the preparation of the nanocrystalline structural steel by comparison with example 6. The effect of the heat distortion temperature on the preparation of the nanocrystalline structural steel is illustrated by comparing the heat distortion temperature of comparative example 7 with the upper limit of the heat distortion temperature provided by the present invention and the heat distortion temperature of comparative example 8 with the lower limit of the heat distortion temperature provided by the present invention, respectively. In addition, the invention also shows that the nanocrystalline structural steel provided by the invention has good comprehensive mechanical properties by comparing with the 40CrNiMoA structural steel which is widely used commercially.

TABLE 1 chemical composition, Heat treatment Process and Hot Rolling Process of example and comparative materials

1. Hardness test

The hardness of the materials of the examples and comparative examples were tested. The Vickers hardness of the material after tempering for 2h at 200 ℃ was measured using an HTV-1000 type durometer. Before testing, the sample surface was polished. The sample was a thin sheet with dimensions of 10mm diameter and 2mm thickness. The test loading force is 9.8N, the pressurizing duration is 15s, and the hardness value is automatically calculated by measuring the diagonal length of the indentation through computer hardness analysis software. The final hardness values were averaged over 5 points and three replicates were selected for each set of samples.

2. Tensile Property test

The room temperature tensile mechanical properties of the comparative and example materials after tempering were tested using an Instron 8872 model tensile tester at a tensile rate of 0.5 mm/min. Before testing, a lathe is adopted to process the material into standard tensile samples with the thread diameter of 10mm, the gauge length of 5mm and the gauge length of 30mm, three parallel samples are taken from each group of heat treatment samples, and the mechanical properties obtained by the experiment comprise tensile strength, yield strength and elongation, and the results are shown in table 2.

3. Grain size statistics

The material was characterized using a Transmission Electron Microscope (TEM) and the grain size of the material was counted using a line cut. The preparation method of the TEM sample comprises the following steps: firstly, manually grinding and thinning a sample to be less than 40 mu m by using No. 2000 abrasive paper, and preparing the sample by using a punching machine

A sheet of (a); and then, thinning the sample by adopting a Tenupol-5 chemical double-spraying thinning instrument, wherein the double-spraying liquid is 6% perchloric acid, 30% butanol and 64% methanol, and the double-spraying thinning temperature is-25 ℃. And (3) observing the double-sprayed thinned sample by using a TECNAI20 transmission electron microscope, wherein the working voltage during TEM observation is 200kV, and the alpha and beta angle rotation ranges are +/-30 degrees by using a double-inclined magnetic sample table. Drawing parallel fixed-length straight lines on the TEM picture, and calculating the grain size of the material according to the number of the fixed-length straight lines passing through the grains.

TABLE 2 texture characteristics and mechanical properties after tempering of the materials of the examples and comparative examples

As can be seen from the results in Table 2, examples 1 to 9 are all nanocrystalline structures, which make them have high strength, good plasticity and large hardness. Within the chemical composition range specified by the invention, as the chemical composition content of Cr and V is reduced and the chemical composition content of C, Ni is increased, the grain size of the material is gradually reduced, the strength and the hardness of the material are improved, and the elongation and the reduction of area are gradually reduced.

In comparative example 1, the contents of C, Cr, Ni and V elements are all lower than the lower limit of the chemical composition range specified in the present invention, a bainite structure is obtained after rapid cooling, and a nanocrystalline structure cannot be obtained by performing thermal deformation with the precursor as an original structure. The comparative example 9, in which the contents of C, Cr, Ni, and V elements are higher than the chemical composition range defined in the present invention, obtained austenite + nano lath structure after rapid cooling and also failed to obtain nanocrystalline structure after hot deformation.

The strain of comparative example 2 is small, and the structure of the nano-lath is still formed after deformation, so that the preparation of the nano-crystalline structure cannot be realized.

Comparative example 3 has a large strain rate and fails to realize the preparation of a nanocrystalline structure. Comparative example 4 has a small strain rate, and the grains are coarsened during thermal deformation, so that the preparation of the nanocrystalline structure cannot be achieved.

Comparative example 5 was slowly cooled to room temperature after heat treatment, and comparative example 6 was at a lower heat treatment temperature, which made their precursors non-lath structures of the nano-scale provided by the present invention, and thus none of them could achieve the preparation of nanocrystalline structure.

The temperature ranges for hot deformation of the nano-lath precursors of comparative examples 7 and 8 are outside the range provided by the present invention, and the preparation of the nanocrystalline structure cannot be achieved.

Compared with the 40CrNiMoA structural steel widely used in commerce at present, the nanocrystalline 40Cr3Ni4 structural steel provided by the invention not only has higher strength and hardness, but also has better plasticity and toughness than the traditional structural steel material.

The above description is only for the purpose of illustrating embodiments of the present application and is not intended to limit the scope of the present application, and all modifications of equivalent structures and equivalent processes, which are made by the contents of the specification and the drawings of the present application or are directly or indirectly applied to other related technical fields, are also included in the scope of the present application.

Claims

1. An ultrahigh-strength nanocrystalline 40Cr3Ni4 structural steel is characterized in that: the structural steel comprises the following chemical components in percentage by weight: c is 0.32-0.48; 2.2-3.8 parts of Cr; 3.2 to 4.8 of Ni; v is 0.1 to 0.2; 0.01 to 0.03 percent of Ce; 0.01 to 0.2 Mn; 0.01 to 0.2 of Si; the balance being Fe;

the preparation method of the structural steel comprises the following steps:

smelting by adopting a vacuum induction furnace to obtain a raw material ingot; grinding the cast ingot, cogging and forging the cast ingot at a temperature of more than 950 ℃, and finish forging the cast ingot to obtain a blank, keeping the temperature of the obtained blank at 850-930 ℃ for a period of time, and rapidly cooling the blank to room temperature to obtain a nano-lath precursor; thermally deforming the obtained nano-lath precursor to obtain a nano-crystal structure; tempering the nanocrystalline structure to finally obtain the ultrahigh-strength nanocrystalline 40Cr3Ni4 structural steel;

keeping the blank at 850-930 ℃ for a heat preservation time t = (2.5-3.5) D min, wherein D is the effective thickness of the sample, and the unit is mm;

the cooling rate of the rapid cooling is 20-80 ℃/s;

the nano-lath precursor has a temperature of 680-760 ℃ and a strain rate of 0.5-2.0 s^-1Is thermally deformed within the range of (1), the total strain amount is more than or equal to 70 percent;

the tempering temperature is 200-250 ℃, and the tempering time is 1-2 h.

2. The ultra-high strength nanocrystalline 40Cr3Ni4 structural steel according to claim 1, characterized in that: according to weight percentage, C is 0.38-0.44; 2.6-3.2 parts of Cr; 3.8 to 4.4 of Ni; v is 0.14 to 0.17; 0.01 to 0.03 percent of Ce; 0.01 to 0.2 Mn; 0.01 to 0.2 of Si; the balance being Fe.

3. The ultra-high strength nanocrystalline 40Cr3Ni4 structural steel according to claim 1, characterized in that: thermal changeThe forming temperature is 700-730 ℃, and the strain rate is 0.8-1.4 s^-1The total strain amount is 90% or more.

4. The ultra-high strength nanocrystalline 40Cr3Ni4 structural steel according to claim 1 or 3, characterized in that: the microstructure of the prepared material is nanocrystalline, and the grain size is 30-95 nm; the tensile strength of the material is as high as 1600-1750 MPa, the elongation is 15-20%, and the reduction of area is more than 50%.