CN112251681B

CN112251681B - Ultrahigh-strength nanocrystalline 40Cr16Co4W2Mo stainless steel and preparation method thereof

Info

Publication number: CN112251681B
Application number: CN202011051342.8A
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: 2022-03-18
Anticipated expiration: 2040-09-29
Also published as: CN112251681A

Abstract

The invention relates to the technical field of materials, in particular to an ultra-high-strength nanocrystalline 40Cr16Co4W2Mo stainless steel and a preparation method thereof. The chemical composition of the stainless steel is as follows (wt%): C: 0.3-0.5; Cr: 15.0-18.0; Co: 3.0-5.0; Mo: 0.5-1.5; W: 1.5-2.5; Nb: 0.03-0.05; Ce: 0.01 ~ 0.03; Mn < 0.15 and the remainder is Fe. The preparation method of the stainless steel is as follows: (1) after holding at 1150-1250°C for a period of time, rapidly cooled to room temperature to obtain a nano-slab precursor; (2) the nano-slat precursor is strained at a temperature of 880-960°C. The thermal deformation is carried out in the range of the rate of 0.5～2s ^‑1 , and the total strain is greater than or equal to 70%, so that the nano-slab precursor is transformed into a nanocrystalline structure; (3) The nanocrystals are cryogenically treated with liquid nitrogen, and cryogenically treated at 460～ Aging at 500℃ for 4h. The nanocrystalline stainless steel prepared by the invention has ultra-high strength, good plastic toughness and excellent corrosion resistance, and can be widely used for preparing various cutting tools, molds, steam turbine blades, rolling bearings and wear-resistant medical instruments and other devices.

Description

Ultrahigh-strength nanocrystalline 40Cr16Co4W2Mo stainless steel and preparation method thereof

Technical Field

The invention relates to the technical field of materials, in particular to high-strength nanocrystalline 40Cr16Co4W2Mo stainless steel and a preparation method thereof.

Background

With the rapid development of economy and society, the performance of the traditional stainless steel material is gradually difficult to meet the requirements of various industries, and the development of a novel stainless steel material with higher performance is urgently needed. Attempts have been made to increase the hardness and wear resistance of stainless steel materials by increasing the carbon and chromium content. However, as the strength of the material is increased, the plasticity and corrosion resistance of the material are remarkably reduced, and the bottleneck problem can not be solved properly all the time, so that the development of the traditional stainless steel material is in a stagnation state for a long time.

Compared with the coarse-grain steel material, the nanocrystalline steel material has excellent comprehensive mechanical properties such as higher strength and plasticity, larger fatigue strength, high-temperature superplasticity and the like, and also has good corrosion resistance and a plurality of unique physical and chemical properties, so that the nanocrystalline steel material is very attractive in practical application, and a new way for developing the nanocrystalline stainless steel to optimize the performance of the traditional stainless steel is opened up.

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 novel nanocrystalline stainless steel and a preparation method thereof, the nanocrystalline stainless steel can be prepared by conventional hot rolling deformation, and new foundation and opportunity are brought to the development of the traditional stainless steel material.

Disclosure of Invention

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

a nanocrystalline 40Cr16Co4W2Mo stainless steel comprises the following chemical components in percentage by weight: c is 0.3-0.5; 15.0-18.0 parts of Cr; 3.0-5.0% of Co; 0.5 to 1.5 parts of Mo; w is 1.5-2.5; 0.03 to 0.05 Nb; 0.01 to 0.03 percent of Ce; mn is less than 0.15, and the balance is Fe. Preferred ranges for some of the elements are: c: 0.35 to 0.43; cr: 15.8-17.0; co: 3.5 to 4.2; mo: 0.8 to 1.1; w: 1.8 to 2.1.

The preparation method of the nanocrystalline stainless 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 1200 ℃ to form a blank.

Preserving the temperature of the blank obtained by the finish forging processing at 1150-1250 ℃ for a period of time, and then rapidly cooling to room temperature to obtain a nano lath precursor; thermally deforming the obtained nano-lath precursor to obtain a nano-crystal structure; and carrying out liquid nitrogen deep cooling on the nanocrystalline structure, and then carrying out aging treatment to finally obtain the nanocrystalline stainless steel.

As a preferred technical scheme:

and (3) keeping the blank at 1150-1250 ℃ for a period of time, wherein the heat preservation time t is (3.5-4.5) D min, wherein D is the effective thickness of the sample, and the unit is millimeter mm.

The cooling rate of the rapid cooling is 10-20 ℃/s.

The nano-batten precursor has the strain rate of 0.5-2.0 s at the temperature of 880-960 DEG C^-1Is thermally deformed within the range of (1), and the total strain amount is 70% or more. Preferably: the thermal deformation temperature is 910-940 ℃, and the strain rate is 1.0-1.6 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 35-90 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 the nanocrystalline stainless 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 stainless steel, and the obtained nanocrystalline stainless steel has ultrahigh strength, good plasticity and toughness and excellent corrosion resistance, and can be widely used for preparing various cutting tools, dies, turbine blades, rolling bearings, wear-resistant medical instruments and other devices. In the preferred alloy compositionThe alloy is characterized by comprising (C content is 0.35-0.43; Cr content is 15.8-17.0; Co content is 3.5-4.2; Mo content is 0.8-1.1; W content is 1.8-2.1) and under the condition of thermal deformation (thermal deformation temperature is 910-940 ℃, strain rate is 1.0-1.6 s)^-1And the total strain is more than or equal to 90 percent), the tensile strength of the prepared nanocrystalline stainless steel is up to 1900-2300 MPa, the elongation is 10-16 percent, and the Vickers hardness is 530-650.

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 novel nanocrystalline stainless steel, which comprises the chemical components of 0.3-0.5 of C; 15.0-18.0 parts of Cr; 3.0-5.0% of Co; 0.5 to 1.5 parts of Mo; w is 1.5-2.5; 0.03 to 0.05 Nb; 0.01 to 0.03 percent of Ce; mn is less than 0.15, and the balance is Fe.

Please refer to fig. 1-2. FIG. 1 shows the nano-slab precursor formed by rapidly cooling the material of example 5 of the present invention, and it can be seen from the TEM tissue photograph that the width of the slab is between 20 nm and 50 nm. FIG. 2 shows the structure of the nano-scale crystals formed by thermal deformation of the nano-slab precursor of example 5 of the present invention, and it can be seen from the TEM photograph that the crystal grain size is between 40 nm and 85 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 stainless steels smelted in the chemical composition range provided by the present invention, the contents of C, Cr, Co, Mo, and W elements are gradually increased, and the corresponding preparation processes are also appropriately adjusted within the technical parameter range specified by the present invention. The size of the prepared bulk nanocrystalline metal material is 150 multiplied by 800 multiplied by 10 mm.

Comparative example: the chemical compositions of C, Cr, Co, Mo and W 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, Co, Mo and W 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, Co, Mo and W on the preparation of the nanocrystalline stainless steel is illustrated by comparing with example 1 and example 9 respectively. Comparative example 2, in which the amount of strain is below 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 stainless steel by comparison with example 2. The effect of strain rate on nanocrystalline stainless steel production is illustrated by comparing the strain rate of comparative example 3, which is above the upper limit of the strain rate provided by the present invention, and the strain rate of comparative example 4, which is below the lower limit of the strain rate provided by the present invention, with example 3 and example 4, respectively. Comparative example 5 slow cooling to room temperature after heat treatment illustrates the effect of cooling rate after heat treatment on nanocrystalline stainless steel preparation 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 nanocrystalline stainless steel by comparison with example 6. Comparative example 7, in which the heat distortion temperature is higher than the upper limit of the heat distortion temperature provided by the present invention and comparative example 8, in which the heat distortion temperature is lower than the lower limit of the heat distortion temperature provided by the present invention, illustrates the influence of the heat distortion temperature on the preparation of nanocrystalline stainless steel by comparing with example 7 and example 8, respectively. In addition, the invention also shows that the nanocrystalline stainless steel provided by the invention has good comprehensive mechanical properties by comparing with the 40Cr13 stainless 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 4h aging at 480 ℃ 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 15 points and three replicates were selected for each set of samples.

2. Tensile Property test

The room temperature tensile mechanical properties of the aged comparative and example materials were tested using an Instron model 8872 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.

4. Corrosion performance test

Processing the material to be measured into the size of

The cylindrical sample is connected with a copper wire, and the rest parts outside the working surface are sealed by epoxy resin, so that the wire is ensured not to be contacted with corrosive liquid. Grinding and polishing a sample to be tested, adopting a 3.5% NaCl aqueous solution, and testing a dynamic polarization curve of the material by using a Gamry electrochemical workstation, thereby giving the self-corrosion potential E of the material_corrV and self-corrosion current I_corr/(A/cm²)。

TABLE 2 structural characteristics of the materials of the examples and comparative examples and mechanical properties after cryogenic ageing

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. In the chemical composition range specified by the invention, as the chemical composition contents of C, Cr, Co, Mo and W are 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, Co, Mo and W elements are all lower than the lower limit of the chemical composition range specified in the present invention, ferrite structure is obtained after rapid cooling, and nanocrystalline structure is not obtained after thermal deformation with the precursor as the original structure. The comparative example 9, in which the contents of C, Cr, Co, Mo, and W elements are higher than the chemical composition range defined in the present invention, obtained martensite + austenite 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, and their precursors were not the nano-lath structure 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 40Cr13 stainless steel which is widely and commercially applied at present, the novel nanocrystalline 40Cr16Co4W2Mo stainless steel provided by the invention not only has higher strength and hardness, but also has better plasticity and toughness than the traditional stainless steel material.

As can be seen from the results in Table 3, the self-corrosion currents of examples 1 to 9 are lower than those of comparative examples 1 to 9 and commercial 40Cr13 stainless steel; the self-corrosion potential is higher than that of the stainless steels of comparative examples 1-9 and commercial 40Cr13, which shows that the nanocrystalline 40Cr16Co4W2Mo stainless steel provided by the invention has good corrosion resistance.

TABLE 3 self-corrosion potential and self-corrosion current for the materials of the examples and comparative examples

Material	Self-etching potential E_corr/V	Self-corrosion current I_corr/(A/cm²)
			Example 1	-0.38	8.3×10^-6
Example 2	-0.32	4.2×10^-6
			Example 3	-0.28	2.4×10^-6
Example 4	-0.26	1.1×10^-6
			Example 5	-0.22	7.4×10^-7
Example 6	-0.18	4.5×10^-7
			Example 7	-0.15	2.3×10^-7
Example 8	-0.13	1.6×10^-7
			Example 9	-0.11	1.1×10^-7
Comparative example 1	-0.49	1.3×10^-5
			Comparative example 2	-0.47	7.5×10^-6
Comparative example 3	-0.42	4.3×10^-6
			Comparative example 4	-0.38	3.2×10^-6
Comparative example 5	-0.34	1.4×10^-6
			Comparative example 6	-0.30	6.8×10^-7
Comparative example 7	-0.27	4.5×10^-7
			Comparative example 8	-0.23	2.9×10^-7
Comparative example 9	-0.20	2.1×10^-7
			40Cr13	-0.51	1.4×10^-5

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 ultra-high strength nanocrystalline 40Cr16Co4W2Mo stainless steel, is characterized in that: by weight percentage, the chemical composition of this stainless steel is as follows: C: 0.3～0.5; Cr: 15.0～18.0; Co: 3.0～5.0; Mo: 0.5～0.5～ 1.5; W: 1.5~2.5; Nb: 0.03~0.05; Ce: 0.01~0.03; Mn<0.15, the balance is Fe;

The preparation method of the stainless steel is:

The raw material ingot is obtained by smelting in a vacuum induction furnace; after the ingot is repaired and ground, it is processed into a billet through billet forging and precision forging at a temperature above 1200 °C. At room temperature, a nano-slab precursor is obtained; the nano-slab precursor is thermally deformed at a temperature of 880-960° C. and a strain rate of 0.5-2.0 s ^-1 , and the total strain is greater than or equal to 70% to obtain Nanocrystalline structure; liquid nitrogen deep cooling is performed on the nanocrystalline structure, followed by aging treatment, and finally nanocrystalline 40Cr2NiMnW structural steel is obtained.

2. The ultra-high strength nanocrystalline 40Cr16Co4W2Mo stainless steel according to claim 1, characterized in that: by weight percentage, C: 0.35-0.43; Cr: 15.8-17.0; Co: 3.5-4.2; Mo: 0.8-1.1; W : 1.8~2.1.

3. according to the described ultra-high strength nanocrystalline 40Cr16Co4W2Mo stainless steel of claim 1, it is characterized in that: at 1150～1250 ℃ of insulation, holding time t =(3.5～4.5) D min, wherein, D is the effective thickness of the sample, The unit is mm, and it is rapidly cooled to room temperature after the heat preservation to obtain the nano-slab precursor.

4. according to the described ultra-high strength nanocrystalline 40Cr16Co4W2Mo stainless steel of claim 1 or 3, it is characterized in that: the cooling rate of described rapid cooling is between 10～20 ℃/s.

5. The ultra-high strength nanocrystalline 40Cr16Co4W2Mo stainless steel according to claim 1, wherein the liquid nitrogen cryogenic time is 0.5~2h, the aging temperature is 460~500°C, and the aging time is 3.0~5.0h.

6. according to the described ultra-high strength nanocrystalline 40Cr16Co4W2Mo stainless steel of claim 1, it is characterized in that: thermal deformation temperature is 910～940 ℃, strain rate is 1.0～1.6s ⁻¹ , and total strain amount is greater than or equal to 90%.

7. The ultra-high strength nanocrystalline 40Cr16Co4W2Mo stainless steel according to claim 5 or 6 is characterized in that: the microstructure of the obtained material is nanocrystalline, and the grain size is between 35 and 90 nm; the tensile strength of the material is as high as 1900~2300MPa, the elongation is between 10~16%, and the section shrinkage rate is more than 30%.