WO2021012322A1

WO2021012322A1 - High-strength-plasticity nano/submicron grain cold-rolled 304 stainless steel strip and preparation method therefor

Info

Publication number: WO2021012322A1
Application number: PCT/CN2019/099886
Authority: WO
Inventors: 孙国胜; 杜林秀; 杜预; 张梅; 张彬; 吴红艳; 高秀华
Original assignee: 东北大学
Priority date: 2019-07-19
Filing date: 2019-08-09
Publication date: 2021-01-28
Also published as: CN110241364B; CN110241364A

Abstract

Disclosed are a high-strength-plasticity nano/submicron grain cold-rolled 304 stainless steel strip and a preparation method therefor, belonging to the field of manufacturing cold-rolled austenitic stainless steel strips. The stainless steel strip has the following chemical ingredients in weight percentages: C < 0.08%, Si < 0.80%, Mn < 2.0%, Cr 17%-20%, Ni 8%-10%, and the balance being Fe, trace microalloy elements Mo, Nb and V, and other inevitable impurities. In the present invention, by means of the integrated control of hot-rolling- and cold-rolling-annealing, a high-strength-plasticity nano/submicron grain cold-rolled 304 stainless steel strip finished product is obtained, wherein the microstructure of the finished product steel is a multiscale nano/submicron grain austenite structure composed of ultra-fine grains with a grain size of 150-500 nm and coarse recrystallized austenite grains, a part of which has a grain size of larger than 1 μm. The high-strength-plasticity nano/submicron grain cold-rolled 304 stainless steel strip has excellent strong plasticity matching, a yield strength of ≥ 800 MPa, a tensile strength of ≥ 900 MPa, a total elongation of ≥ 40 %, and a thickness specification covering 0.3-1 mm.

Description

High-strength plastic nano/submicron crystal cold rolled 304 stainless steel strip and preparation method thereof

Technical field

The invention belongs to the manufacturing field of cold-rolled austenitic stainless steel strip, and specifically relates to a high-strength plastic nano/submicron crystal cold-rolled 304 stainless steel strip and a preparation method thereof.

Background technique

Austenitic stainless steel is widely used in civil, transportation, petrochemical, nuclear power defense, aerospace and other fields for its non-magnetic, excellent corrosion resistance, high temperature oxidation resistance, easy welding, easy forming and good comprehensive mechanical properties. . Among them, 300 series austenitic stainless steels such as 304 and 301 are the most widely used austenitic stainless steels. As a typical metastable austenitic stainless steel, 304 and 301 stainless steel have good corrosion resistance, plasticity and toughness, and excellent high and low temperature mechanical properties; making this stainless steel the preferred structural material for the vehicle manufacturing industry, developed countries in the world 304 and 301 stainless steel are commonly used in the body materials of railway passenger cars such as railways and subways. At present, the body materials of rail passenger cars mainly include ordinary steel (carbon steel and weathering steel), stainless steel, and aluminum alloy. The stainless steel car body can save the painting process, and because of its excellent corrosion resistance, it can realize the maintenance-free structure of the car body, which greatly reduces the maintenance cost during operation. In addition, the manufacturing cost of the stainless steel body is much lower than that of the aluminum alloy body, and the weight reduction effect of the stainless steel body is obvious. Considering factors such as manufacturing cost, maintenance cost and lightweight level, the stainless steel car body is currently the most economical car body and has a very broad application prospect.

With the development of the transportation industry in the direction of high quality and light weight, how to reduce the weight of vehicles while ensuring strength has become an important research direction for rail passenger car body materials. The development of lightweight stainless steel car bodies can achieve energy saving and emission reduction, reduce environmental pollution, comply with the strategy of sustainable development, and bring huge economic benefits. At the same time, the reduction of body weight is conducive to the improvement of the speed of rail passenger cars, which is important Social Significance. The lightweight of the vehicle is mainly the lightweight of the car body, and the main method to reduce the weight of the car body is to use high-strength lightweight materials. However, the yield strength of austenitic stainless steel is generally low. Since it has an austenitic structure at room temperature, it cannot be strengthened by heat treatment, and cold working is usually used to increase the strength. In the process of cold deformation, certain deformation induced martensite and residual stress will be generated in the structure, which will cause a significant decrease in plasticity, which will affect the further forming of complex parts, increase the risk of delayed material cracking, and also affect zero Corrosion resistance of components during service. Therefore, the development of austenitic stainless steel with both high yield strength and excellent plasticity has become a current research hotspot, which not only has very important scientific research significance, but also provides certain theoretical guidance for the industrial production of high-strength plastic austenitic stainless steel.

Summary of the invention

technical problem

The solution to the problem

Technical solutions

Aiming at the deficiencies of the prior art, the present invention provides a high-strength plastic nano/submicron crystal cold rolled 304 stainless steel strip and a preparation method thereof.

The high-strength plastic nano/submicron crystal cold-rolled 304 stainless steel strip prepared by the present invention has chemical composition in weight percentage: C: <0.08%, Si: <0.80%, Mn: <2.0%, Cr: 17-20%, Ni: 8-10%, the balance is Fe, trace microalloying elements Mo, Nb, V and other inevitable impurities, the total weight percentage of each component is 100%; the high-strength plastic nano/submicron crystal cold rolled 304 The microstructure of the stainless steel strip is multi-scale nano/sub-micron crystalline austenite, the austenite grains are equiaxed, and the ultrafine austenite matrix with a grain size of 150～500nm exists in some parts with a size greater than 1μm The recrystallized austenite coarse grains; its thickness is 0.3～1mm; its yield strength is ≥800MPa, its tensile strength is ≥900MPa, and its total elongation is ≥40%.

A method for preparing high-strength plastic nano/submicron crystal cold rolled 304 stainless steel strip includes the following steps:

Step 1, forging and hot rolling:

(1) Forging a 304 stainless steel ingot into a billet with a thickness of 50-60mm, and then placing the forging billet in a heating furnace to heat to 1150-1250°C and keep it for 2 to 3 hours;

(2) The forged billet is rolled into a hot-rolled plate with a thickness of 3-6mm through a hot rolling mill through 5 to 7 passes, and then water-cooled to room temperature, the opening temperature is 1100-1200℃, and the final rolling temperature is 950-1050 ℃, the total hot rolling reduction ratio is 90-94%;

Step 2, solution treatment and cold rolling:

The above hot-rolled sheet is kept at 1000-1100°C for 10-60 minutes, and solution treatment is carried out to fully dissolve the carbides produced during the hot rolling; after pickling to remove the surface oxide scale, it is carried out on the cold rolling mill for multiple passes Sub-room temperature cold rolling, the total cold rolling reduction is 78-92%;

Step 3. Isothermal annealing:

The cold-rolled sheet is subjected to isothermal annealing treatment at 700-800°C for a holding time of 1-10min, and then quenched to room temperature to obtain a finished product of high-strength plastic nano/submicron crystal cold-rolled 304 stainless steel strip.

In the step 1, the water cooling rate is 20-40°C/s.

In the step 2, the reduction of the cold rolling pass is controlled to be 0.1 to 0.5 mm, and the final plate thickness is 0.3 to 1 mm.

In the step 3, the heating furnace used for annealing is a box-type resistance furnace.

The chemical composition of the high-strength plastic nano/sub-micron crystal cold rolled 304 stainless steel strip by weight percentage is: C: <0.08%, Si: <0.80%, Mn: <2.0%, Cr: 17-20%, Ni: 8～ 10%, the balance is Fe, trace microalloying elements Mo, Nb, V and other unavoidable impurities, the total weight percentage of each component is 100%.

The microstructure of the high-strength plastic nano/sub-micron crystal cold rolled 304 stainless steel strip is multi-scale nano/sub-micron crystal austenite, the austenite grains are equiaxed, and the grain size is 150-500nm. The bulk ultra-fine crystals originate from the reverse phase transformation of deformation-induced martensite to austenite, and the coarse recrystallized austenite crystals with a size greater than 1 μm originate from the recrystallization of retained austenite.

The high-strength plastic nano/sub-micron crystal cold-rolled 304 stainless steel strip developed by the invention has a yield strength of ≥800MPa, a tensile strength of ≥900MPa, and a total elongation of ≥40%, which can satisfy the use of high-strength components such as side beams and columns for rail passenger cars. Claim. The preparation process is simple, and industrial production can be realized under the conditions of existing process equipment.

The beneficial effects of the invention

Beneficial effect

Compared with the prior art, the present invention has the following innovations:

(1) The finished product prepared by the present invention has a multi-scale nano/submicron crystalline austenite structure, which does not contain martensite and has low residual stress, which can effectively reduce the risk of delayed material cracking.

(2) The finished product prepared by the present invention has both high strength and high plasticity, and the thickness specification covers 0.3-1.0mm, which satisfies the mechanical properties of high-strength structural parts and frame steel of rail passenger cars, and can achieve effective weight reduction of the car body , Can meet the needs of different locations.

(3) In the preparation process of the present invention, the annealing temperature used is 700-800°C, which is lower than the annealing temperature (above 1000°C) used in the existing cold-rolled austenitic stainless steel sheet, which can effectively save energy consumption and reduce Cost of production.

(4) In the preparation process of the present invention, the holding time of reverse phase change annealing is relatively short, 1-10min, which effectively avoids the intergranular corrosion caused by the long-term holding of the finished steel in the sensitization temperature range (450-850℃) Inclination.

The preparation process of the present invention is simple and convenient, has no special requirements for equipment and technology, and can realize industrialized production under the conditions of existing process equipment.

Brief description of the drawings

Description of the drawings

Figure 1 is an EBSD quality diagram of the microstructure of the finished high-strength plastic nano/submicron crystal cold-rolled 304 stainless steel strip prepared in Example 1;

Figure 2 is an EBSD quality diagram of the microstructure of the finished high-strength plastic nano/submicron crystal cold rolled 304 stainless steel strip prepared in Example 2;

Fig. 3 is the engineering stress-engineering strain curve of the high-strength plastic nano/submicron crystal cold-rolled 304 stainless steel strip products in Examples 1 to 3.

Invention embodiment

Embodiments of the invention

Example 1

The composition of the 304 stainless steel blank in this embodiment is C: 0.055%, Si: 0.40%, Mn: 1.63%, Cr: 17.30%, Ni: 8.45%, Mo: 0.12%, Nb: 0.04%, V: 0.08%, The balance is Fe and other unavoidable impurities, and the total weight percentage of each component is 100%.

The method for preparing high-strength plastic nano/submicron crystal cold rolled 304 stainless steel strip of the present invention includes the following steps:

Step 1, forging and hot rolling:

The forging billet with a thickness of 50mm is placed in a heating furnace and heated to 1250°C with the furnace and kept for 2h, and then rolled on a hot rolling mill for 5 passes to form a hot-rolled plate with a thickness of 4.5mm, followed by a temperature of 30°C/s Cool speed water to room temperature. The start rolling temperature is 1200℃, the final rolling temperature is 1050℃, and the total hot rolling reduction ratio is 91%;

Step 2, solution treatment and cold rolling:

The above-mentioned hot-rolled sheet is held at 1050°C for 30 minutes for solution treatment to fully dissolve the carbides generated during the hot rolling process, and then after pickling to remove the surface oxide scale, it is subjected to multiple passes of room temperature cold rolling on the cold rolling mill , The final thickness of the cold-rolled sheet is 1mm, and the total cold-rolled reduction is 78%;

Step 3. Isothermal annealing:

The cold-rolled plate is kept at 750°C for 3 minutes in a heating furnace, and then quenched to room temperature to obtain a high-strength plastic nano/submicron crystal cold-rolled 304 stainless steel strip product.

The microstructure of the finished steel is shown in Fig. 1, which is equiaxed austenite grains, composed of reverse phase transformation austenite with a size of about 200nm and some coarse recrystallized austenite with a size larger than 1μm.

The mechanical properties of the finished steel are tested, and the corresponding engineering stress-engineering strain curve is shown in Figure 3. The yield strength and tensile strength are 863MPa and 945MPa, respectively, and the total elongation is 45%.

Example 2

The composition of the 304 stainless steel blank in this embodiment is C: 0.075%, Si: 0.28%, Mn: 1.58%, Cr: 17.4%, Ni: 8.2%, Mo: 0.10%, Nb: 0.04%, V: 0.07%, The balance is Fe and other unavoidable impurities, and the total weight percentage of each component is 100%.

Step 1, forging and hot rolling:

The forging billet with a thickness of 60mm is placed in a heating furnace and heated to 1200°C with the furnace and kept for 3h, and then rolled into a hot-rolled plate with a thickness of 6mm on a hot rolling mill for 7 passes, and then cooled at 40°C/s. Cool quickly to room temperature. The start rolling temperature is 1160℃, the final rolling temperature is 1000℃, and the total hot rolling reduction rate is about 90%;

Step 2, solution treatment and cold rolling:

The above-mentioned hot-rolled sheet is held at 1000°C for 60 minutes for solution treatment to fully dissolve the carbides produced during the hot rolling process, and then after pickling to remove the surface oxide scale, it is subjected to multiple passes of room temperature cold rolling on the cold rolling mill , The final thickness of the cold-rolled sheet is 0.5mm, and the total cold-rolled reduction is 92%;

Step 3. Isothermal annealing:

The cold-rolled plate is kept at 700° C. for 5 minutes in a heating furnace, and then quenched to room temperature to obtain a high-strength plastic nano/submicron crystal cold-rolled 304 stainless steel strip product.

The microstructure of the finished steel is shown in Fig. 2. It is equiaxed austenite grains composed of austenite with a size of about 230nm and some coarse recrystallized austenite with a size greater than 1μm.

The mechanical properties of the finished steel are tested, and the corresponding engineering stress-engineering strain curve is shown in Figure 3. The yield strength and tensile strength are 846MPa and 1007MPa, respectively, and the total elongation is 41.5%.

Example 3

The composition of the 304 stainless steel blank in this embodiment is C: 0.062%, Si: 0.38%, Mn: 1.57%, Cr: 17.2%, Ni: 8.5%, Mo: 0.09%, Nb: 0.01%, V: 0.02%, The balance is Fe and other unavoidable impurities, and the total weight percentage of each component is 100%.

Step 1, forging and hot rolling:

The forging billet with a thickness of 60mm is placed in a heating furnace and heated to 1180℃ with the furnace and kept for 2h, and then rolled into a hot-rolled plate with a thickness of 5mm by 7 passes on a hot rolling mill, and then cooled at 35℃/s. Cool quickly to room temperature. The start rolling temperature is 1150℃, the final rolling temperature is 1010℃, and the total hot rolling reduction rate is about 92%;

Step 2, solution treatment and cold rolling:

The above-mentioned hot-rolled sheet is held at 1050°C for 30 minutes for solution treatment to fully dissolve the carbides generated during the hot rolling process, and then after pickling to remove the surface oxide scale, it is subjected to multiple passes of room temperature cold rolling on the cold rolling mill , The final thickness of the cold-rolled sheet is 0.3mm, and the total cold-rolled reduction is 93%;

Step 3. Isothermal annealing:

The cold-rolled plate is kept at 800° C. for 1 min in a heating furnace, and then quenched to room temperature to obtain a finished product of high-strength plastic nano/submicron crystal cold-rolled 304 stainless steel strip.

The microstructure of the finished steel is equiaxed austenite grains, which are composed of reverse transformation austenite with a size of about 150nm and some coarse recrystallized austenite with a size greater than 1μm.

The mechanical properties of the finished steel are tested, and the corresponding engineering stress-engineering strain curve is shown in Figure 3. The yield strength and tensile strength are 909MPa and 994MPa, respectively, and the total elongation is 44.5%.

Example 4

The composition of the 304 stainless steel blank in this embodiment is C: 0.045%, Si: 0.48%, Mn: 0.79%, Cr: 18.2%, Ni: 8.1%, Mo: 0.03%, Nb: 0.04%, V: 0.12%, The balance is Fe and other unavoidable impurities, and the total weight percentage of each component is 100%.

Step 1, forging and hot rolling:

The forging billet with a thickness of 55mm is placed in a heating furnace and heated to 1220℃ with the furnace and kept for 2.5h, and then rolled on a hot rolling mill for 6 passes to form a hot-rolled plate with a thickness of 5mm, followed by a temperature of 25℃/s Cool speed water to room temperature. The start rolling temperature is 1180℃, the final rolling temperature is 950℃, and the total hot rolling reduction ratio is 91%;

Step 2, solution treatment and cold rolling:

The above-mentioned hot-rolled sheet is held at 1060°C for 30 minutes for solution treatment to fully dissolve the carbides produced during the hot rolling process, and then after pickling to remove the surface oxide scale, it is subjected to multi-pass room temperature cold rolling on the cold rolling mill , The final thickness of the cold-rolled sheet is 0.7mm, and the total cold-rolled reduction is 86%;

Step 3. Annealing and heat preservation:

The cold-rolled plate is kept at 750°C for 2 minutes in a heating furnace, and then quenched to room temperature to obtain a finished product of high-strength plastic nano/submicron crystal cold-rolled 304 stainless steel strip.

The microstructure of the finished steel is equiaxed austenite grains, which are composed of reverse transformation austenite with a size of about 500nm and coarse recrystallized austenite with a size of more than 1μm.

The mechanical properties of the finished steel were tested, and its yield strength and tensile strength were 810MPa and 920MPa, respectively, and the total elongation was 49%.

Example 5

The composition of the 304 stainless steel blank in this embodiment is C: 0.042%, Si: 0.46%, Mn: 1.2%, Cr: 18.5%, Ni: 8.0%, Mo: 0.01%, Nb: 0.01%, V: 0.13%, The balance is Fe and other unavoidable impurities, and the total weight percentage of each component is 100%.

Step 1, forging and hot rolling:

The forging billet with a thickness of 50mm is placed in a heating furnace and heated to 1150°C with the furnace and kept for 2h, and then rolled on a hot rolling mill for 7 passes to form a hot-rolled plate with a thickness of 3mm, and then cooled at 20°C/s Cool quickly to room temperature. The start rolling temperature is 1130℃, the final rolling temperature is 1020℃, and the total hot rolling reduction ratio is 94%;

Step 2, solution treatment and cold rolling:

The above-mentioned hot-rolled sheet is held at 1100°C for 10 minutes for solution treatment to fully dissolve the carbides produced during the hot rolling process, and then after pickling to remove the surface oxide scale, it is subjected to multiple passes of room temperature cold rolling on the cold rolling mill , The final thickness of the cold-rolled sheet is 0.6mm, and the total cold-rolled reduction is 80%;

Step 3. Annealing and heat preservation:

The cold-rolled plate is kept at 700°C for 10 minutes in a heating furnace, and then quenched to room temperature to obtain a high-strength plastic nano/submicron crystal cold-rolled 304 stainless steel strip product.

The microstructure of the finished steel is equiaxed austenite grains, which are composed of a reverse phase transformation austenite with a size of about 350nm and some coarse recrystallized austenite with a size of more than 1μm.

The mechanical properties of the finished steel were tested, and the yield strength and tensile strength were 835MPa and 960MPa, respectively, and the total elongation was 42%.

Claims

A high-strength plastic nano/submicron crystal cold-rolled 304 stainless steel strip, characterized in that its chemical composition is as follows by weight percentage: C: <0.08%, Si: <0.80%, Mn: <2.0%, Cr: 17-20 %, Ni: 8-10%, the balance is Fe, trace microalloying elements Mo, Nb, V and other unavoidable impurities, the total weight percentage of each component is 100%.
The high-strength plastic nano/submicron crystal cold rolled 304 stainless steel strip according to claim 1, wherein the microstructure is multi-scale nano/submicron crystal austenite, and the austenite grains are equiaxed It is composed of ultra-fine austenite with a grain size of 150～500nm and a small amount of coarse recrystallized austenite with a size greater than 1μm; its yield strength is ≥800MPa, tensile strength is ≥900MPa, and total elongation is ≥40% .
A method for preparing high-strength plastic nano/submicron crystal cold rolled 304 stainless steel strip according to claim 1, characterized in that it comprises the following steps:

Step 1, forging and hot rolling:

(1) Forging a 304 stainless steel ingot into a billet with a thickness of 50-60mm, and then placing the forging billet in a heating furnace to heat to 1150-1250°C and keep it for 2 to 3 hours;

(2) The forged billet is rolled into a hot-rolled plate with a thickness of 3-6mm through a hot rolling mill through 5 to 7 passes, and then water-cooled to room temperature, the opening temperature is 1100-1200℃, and the final rolling temperature is 950-1050 ℃, the total hot rolling reduction ratio is 90-94%;

Step 2, solution treatment and cold rolling:

The above-mentioned hot-rolled sheet is held at 1000-1100°C for 10-60 minutes for solution treatment to fully dissolve the carbides generated during the hot rolling process; after pickling to remove the surface oxide scale, it is subjected to multiple passes on the cold rolling mill at room temperature Cold rolling, the total cold rolling reduction is 78-92%;

Step 3. Isothermal annealing:

The cold-rolled sheet is subjected to isothermal annealing treatment at 700-800°C for a holding time of 1-10min, and then quenched to room temperature to obtain a finished product of high-strength plastic nano/submicron crystal cold-rolled 304 stainless steel strip.
The method for preparing high-strength plastic nano/submicron crystal cold rolled 304 stainless steel strip according to claim 3, characterized in that, in the step 1, the water cooling rate is 20-40°C/s.
The method for preparing high-strength plastic nano/sub-micron crystal cold rolled 304 stainless steel strip according to claim 3, characterized in that, in the step 2, the reduction of the cold rolling pass is controlled at 0.1-0.5 mm, and the final The plate thickness is 0.3 to 1mm.
The method for preparing high-strength plastic nano/submicron crystal cold rolled 304 stainless steel strip according to claim 3, wherein, in the step 3, the heating furnace used for annealing is a box-type resistance furnace.