CN110241364B

CN110241364B - A kind of high-strength plastic nano/submicron crystal cold-rolled 304 stainless steel strip and preparation method thereof

Info

Publication number: CN110241364B
Application number: CN201910653258.4A
Authority: CN
Inventors: 孙国胜; 杜林秀; 杜预; 张梅; 张彬; 吴红艳; 高秀华
Original assignee: Northeastern University China
Current assignee: Northeastern University China
Priority date: 2019-07-19
Filing date: 2019-07-19
Publication date: 2021-03-26
Anticipated expiration: 2039-07-19
Also published as: CN110241364A; WO2021012322A1

Abstract

A high-strength plastic nano/submicron crystal cold-rolled 304 stainless steel strip and a preparation method thereof belong to the field of manufacturing cold-rolled austenitic stainless steel strips; the chemical components by weight percentage are as follows: c: < 0.08%, Si: < 0.80%, Mn: < 2.0%, Cr: 17-20%, Ni: 8-10% of Fe, trace microalloy elements Mo, Nb, V and other inevitable impurities; the invention prepares a finished product of the high-strength plastic nano/submicron crystal cold-rolled 304 stainless steel strip by integrated control of hot rolling, cold rolling and annealing, wherein the microstructure of the finished product steel is a multi-scale nano/submicron crystal austenite structure consisting of ultrafine crystals with the grain size of 150-500 nm and recrystallized austenite coarse crystals with the grain size of more than 1 mu m; the high-strength plastic nano/submicron crystal cold-rolled 304 stainless steel strip has excellent strength-plasticity matching, the yield strength is more than or equal to 800MPa, the tensile strength is more than or equal to 900MPa, and the total elongation is more than or equal to 40%; the thickness specification covers 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 field of manufacturing of cold-rolled austenitic stainless steel strips, and particularly relates to a high-strength plastic nano/submicron crystal cold-rolled 304 stainless steel strip and a preparation method thereof.

Background

The austenitic stainless steel is widely applied to the fields of civil use, traffic, petrochemical industry, nuclear power national defense, aerospace and the like due to the non-magnetism, 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 ones. As 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; the stainless steel becomes a preferred structural material in the vehicle manufacturing industry, and 304 and 301 stainless steel is commonly adopted as the vehicle body material of rail passenger cars such as railways, subways and the like in developed countries in the world. At present, the body materials of the railway passenger car mainly comprise three types of common steel (carbon steel and weathering steel), stainless steel and aluminum alloy. The stainless steel car body can save the coating process, and the maintenance-free structure of the car body can be realized due to the excellent corrosion resistance, so that the maintenance cost in the running process is greatly reduced. In addition, the manufacturing cost of the stainless steel vehicle body is greatly lower than that of an aluminum alloy vehicle body, and the weight reduction effect of the stainless steel vehicle body is obvious. The stainless steel car body is the most economic car body at present and has very wide application prospect by comprehensively considering factors such as manufacturing cost, maintenance cost, light weight level and the like.

With the development of the transportation industry towards high quality and light weight, how to realize the weight reduction of vehicles under the condition of ensuring the strength has become an important research direction of the current rail passenger car body material. The development of the lightweight stainless steel car body can realize energy conservation and emission reduction and reduce environmental pollution, and the sustainable development strategy is met, so that great economic benefits are brought; meanwhile, the weight of the car body is reduced, the running speed of the railway passenger car is improved, and the car body has important social significance. The weight reduction of the vehicle is mainly the weight reduction of the vehicle body, and the main method for reducing the self weight of the vehicle body is to adopt high-strength lightweight materials. However, austenitic stainless steel generally has a low yield strength, and has an austenitic structure at room temperature, and therefore cannot be strengthened by heat treatment, and strength is generally increased by cold working. During cold deformation, certain deformation-induced martensite and residual stress are generated in the structure, so that the plasticity is obviously reduced, further forming of the complex parts is influenced, the risk of delayed cracking of the materials is increased, and the corrosion resistance of the parts in the service process is also influenced. Therefore, the development of the austenitic stainless steel with high yield strength and excellent plasticity becomes a current research hotspot, not only has very important scientific research significance, but also can provide certain theoretical guidance for the industrial production of the high-strength plastic austenitic stainless steel.

Disclosure of Invention

Aiming at the defects of the prior art, the 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 invention comprises the following chemical components in percentage by weight: c: < 0.08%, Si: < 0.80%, Mn: < 2.0%, Cr: 17-20%, Ni: 8-10% of Fe, trace microalloy elements Mo, Nb, V and other inevitable impurities, wherein the total weight percentage of all the components is 100%; the microstructure of the high-strength plastic nano/submicron grain cold-rolled 304 stainless steel strip is multi-scale nano/submicron grain austenite, austenite grains are in an equiaxial shape, and a part of recrystallized coarse austenite grains with the size larger than 1 mu m exist in an ultrafine grain austenite matrix structure with the grain size of 150-500 nm; the thickness of the film is 0.3-1 mm; the yield strength is more than or equal to 800MPa, the tensile strength is more than or equal to 900MPa, and the total elongation is more than or equal to 40%.

A preparation method of a high-strength plastic nano/submicron crystal cold-rolled 304 stainless steel strip comprises the following steps:

step 1, forging and hot rolling:

(1) forging a 304 stainless steel ingot into a blank with the thickness of 50-60 mm, then placing the forged blank in a heating furnace, heating to 1150-1250 ℃, and preserving heat for 2-3 hours;

(2) rolling the forged blank into a hot rolled plate with the thickness of 3-6 mm by a hot rolling mill for 5-7 times, and then cooling to room temperature by water, wherein the initial rolling temperature is 1100-1200 ℃, the final rolling temperature is 950-1050 ℃, and the total hot rolling reduction rate is 90-94%;

step 2, solution treatment and cold rolling:

preserving the heat of the hot rolled plate at 1000-1100 ℃ for 10-60 min, and carrying out solid solution treatment to fully dissolve carbide generated in the hot rolling process; removing surface iron oxide scales through acid pickling, and then performing multi-pass room-temperature cold rolling on a cold rolling unit, wherein the total cold rolling reduction is 78-92%;

step 3, isothermal annealing:

and (3) carrying out isothermal annealing treatment on the cold-rolled sheet at 700-800 ℃, keeping the temperature for 1-10 min, and then quenching to room temperature to obtain a high-strength plastic nano/submicron crystal cold-rolled 304 stainless steel strip finished product.

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

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

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

The high-strength plastic nano/submicron crystal cold-rolled 304 stainless steel strip comprises the following chemical components in percentage by weight: c: < 0.08%, Si: < 0.80%, Mn: < 2.0%, Cr: 17-20%, Ni: 8-10 percent of Fe, trace microalloy elements Mo, Nb, V and other inevitable impurities, wherein the total weight percentage of all the components is 100 percent.

The microstructure of the high-strength plastic nano/submicron grain cold-rolled 304 stainless steel strip is multi-scale nano/submicron grain austenite, austenite grains are in an equiaxial shape, the grain size is 150-500 nm, austenite superfine grains are derived from reverse phase transformation from deformation induced martensite to austenite, and recrystallized austenite coarse grains with the size larger than 1 mu m are derived from recrystallization of retained austenite.

The high-strength plastic nano/submicron crystal cold-rolled 304 stainless steel strip developed by the invention has the yield strength of more than or equal to 800MPa, the tensile strength of more than or equal to 900MPa and the total elongation of more than or equal to 40 percent, and meets the use requirements of high-strength components such as side beams, stand columns and the like for railway vehicles. The preparation process is simple, and industrial production can be realized under the condition of the existing process equipment.

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

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

(2) The finished product prepared by the invention has high strength and high plasticity, the thickness specification covers 0.3-1.0 mm, the mechanical property indexes of high-strength structural parts of the railway passenger car and the steel for the frame are met, the effective weight reduction of the car body can be realized, and the requirements of different positions can be met.

(3) In the preparation process, the annealing temperature is 700-800 ℃, which is lower than the annealing temperature (more than 1000 ℃) adopted by the prior austenitic stainless steel cold-rolled sheet, so that the energy consumption can be effectively saved, and the production cost can be reduced.

(4) In the preparation process, the heat preservation time of the reverse phase transition annealing is shorter and is 1-10 min, so that the increase of intercrystalline corrosion tendency of the finished steel caused by long-time heat preservation in a sensitization temperature range (450-850 ℃) is effectively avoided.

(5) The preparation process is simple and convenient, has no special requirements on equipment and technology, and can realize industrial production under the condition of the existing process equipment.

Drawings

FIG. 1 is an EBSD quality chart of the microstructure of the finished high-strength plastic nano/submicron crystal cold-rolled 304 stainless steel strip prepared in example 1;

FIG. 2 is an EBSD quality chart 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 a graph of engineering stress-engineering strain of the high-strength plastic nano/submicron crystal cold-rolled 304 stainless steel strip finished product in examples 1 to 3;

detailed description of the preferred embodiments

Example 1

The 304 stainless steel blank in this example comprises the following components: 0.055%, Si: 0.40%, Mn: 1.63%, Cr: 17.30%, Ni: 8.45%, Mo: 0.12%, Nb: 0.04%, V: 0.08 percent of the total weight of the components, and the balance of Fe and other inevitable impurities, wherein the total weight percent of the components is 100 percent.

The invention relates to a preparation method of a high-strength plastic nano/submicron crystal cold-rolled 304 stainless steel strip, which comprises the following steps:

step 1, forging and hot rolling:

the forging blank with the thickness of 50mm is placed in a heating furnace to be heated to 1250 ℃ along with the furnace and is kept warm for 2h, then the forging blank is rolled into a hot-rolled plate with the thickness of 4.5mm on a hot rolling mill for 5 times, and then the hot-rolled plate is cooled to room temperature by water at the cooling speed of 30 ℃/s. The initial rolling temperature is 1200 ℃, the final rolling temperature is 1050 ℃, and the total hot rolling reduction rate is 91%;

step 2, solution treatment and cold rolling:

carrying out solid solution treatment on the hot rolled plate at 1050 ℃ for 30min to fully dissolve carbides and the like generated in the hot rolling process, then carrying out acid pickling to remove surface iron scales, and carrying out multi-pass room temperature cold rolling on a cold rolling unit, wherein the final plate thickness of the cold rolled plate is 1mm, and the total cold rolling reduction is 78%;

step 3, isothermal annealing:

and (3) preserving the heat of the cold-rolled sheet in a heating furnace at 750 ℃ for 3min, and then quenching the cold-rolled sheet to room temperature to obtain a high-strength plastic nano/submicron crystal cold-rolled 304 stainless steel strip finished product.

The microstructure of the finished steel is shown in fig. 1 as equiaxed austenite grains consisting of reverse transformed austenite of about 200nm in size and coarse recrystallized austenite grains of greater than 1 μm in size.

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

Example 2

The 304 stainless steel blank in this example comprises the following components: 0.075%, Si: 0.28%, Mn: 1.58%, Cr: 17.4%, Ni: 8.2%, Mo: 0.10%, Nb: 0.04%, V: 0.07 percent, and the balance of Fe and other inevitable impurities, wherein the total weight percent of all the components is 100 percent.

step 1, forging and hot rolling:

the forging blank with the thickness of 60mm is placed in a heating furnace to be heated to 1200 ℃ along with the furnace and is kept warm for 3h, then the forging blank is rolled on a hot rolling mill for 7 times to form a hot rolled plate with the thickness of 6mm, and then the hot rolled plate is cooled to room temperature by water at the cooling speed of 40 ℃/s. The initial 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:

carrying out solution treatment on the hot rolled plate at 1000 ℃ for 60min to fully dissolve carbides and the like generated in the hot rolling process, then carrying out acid pickling to remove surface iron scales, and carrying out multi-pass room-temperature cold rolling on a cold rolling unit, wherein the final plate thickness of the cold rolled plate is 0.5mm, and the total cold rolling reduction is 92%;

step 3, isothermal annealing:

and (3) preserving the heat of the cold-rolled sheet in a heating furnace at 700 ℃ for 5min, and then quenching the cold-rolled sheet to room temperature to obtain a high-strength plastic nano/submicron crystal cold-rolled 304 stainless steel strip finished product.

The microstructure of the finished steel is shown in fig. 2 as equiaxed austenite grains consisting of reverse transformed austenite of about 230nm in size and coarse recrystallized austenite grains of greater than 1 μm in size.

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

Example 3

The 304 stainless steel blank in this example comprises the following components: 0.062%, Si: 0.38%, Mn: 1.57%, Cr: 17.2%, Ni: 8.5%, Mo: 0.09%, Nb: 0.01%, V: 0.02 percent, and the balance of Fe and other inevitable impurities, wherein the total weight percent of all the components is 100 percent.

step 1, forging and hot rolling:

the forging blank with the thickness of 60mm is placed in a heating furnace to be heated to 1180 ℃ along with the furnace, the temperature is kept for 2 hours, then the forging blank is rolled on a hot rolling mill for 7 times to form a hot rolled plate with the thickness of 5mm, and then the hot rolled plate is cooled to room temperature at the cooling speed of 35 ℃/s. The initial 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:

carrying out solution treatment on the hot rolled plate at 1050 ℃ for 30min to fully dissolve carbides and the like generated in the hot rolling process, then carrying out acid pickling to remove surface iron scales, and carrying out multi-pass room-temperature cold rolling on a cold rolling unit, wherein the final plate thickness of the cold rolled plate is 0.3mm, and the total cold rolling reduction is 93%;

step 3, isothermal annealing:

and (3) preserving the heat of the cold-rolled sheet in a heating furnace at 800 ℃ for 1min, and then quenching the cold-rolled sheet to room temperature to obtain a high-strength plastic nano/submicron crystal cold-rolled 304 stainless steel strip finished product.

The microstructure of the finished steel is equiaxed austenite grains, which consist of reverse transformation austenite with the size of about 150nm and coarse recrystallized austenite grains with the partial size of more than 1 μm.

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

Example 4

The 304 stainless steel blank in this example comprises the following components: 0.045%, Si: 0.48%, Mn: 0.79%, Cr: 18.2%, Ni: 8.1%, Mo: 0.03%, Nb: 0.04%, V: 0.12 percent, and the balance of Fe and other inevitable impurities, wherein the total weight percent of all the components is 100 percent.

step 1, forging and hot rolling:

the forging blank with the thickness of 55mm is placed in a heating furnace to be heated to 1220 ℃ along with the furnace and is kept warm for 2.5h, then the forging blank is rolled into a hot-rolled plate with the thickness of 5mm on a hot rolling mill for 6 times, and then the hot-rolled plate is cooled to room temperature at the cooling speed of 25 ℃/s. The initial rolling temperature is 1180 ℃, the final rolling temperature is 950 ℃, and the total hot rolling reduction rate is 91%;

step 2, solution treatment and cold rolling:

carrying out solution treatment on the hot rolled plate at 1060 ℃ for 30min to fully dissolve carbides and the like generated in the hot rolling process, then carrying out acid pickling to remove surface iron scales, and carrying out multi-pass room-temperature cold rolling on a cold rolling unit, wherein the final plate thickness of the cold rolled plate is 0.7mm, and the total cold rolling reduction is 86%;

step 3, annealing and heat preservation:

and (3) preserving the heat of the cold-rolled sheet in a heating furnace at 750 ℃ for 2min, and then quenching the cold-rolled sheet to room temperature to obtain a high-strength plastic nano/submicron crystal cold-rolled 304 stainless steel strip finished product.

The microstructure of the finished steel is equiaxed austenite grains, which consist of reverse transformation austenite with the size of about 500nm and coarse recrystallized austenite grains with the partial size of more than 1 mu m.

The mechanical property of the finished steel is detected, the yield strength and the tensile strength are 810MPa and 920MPa respectively, and the total elongation is 49%.

Example 5

The 304 stainless steel blank in this example comprises the following components: 0.042%, Si: 0.46%, Mn: 1.2%, Cr: 18.5%, Ni: 8.0%, Mo: 0.01%, Nb: 0.01%, V: 0.13 percent, and the balance of Fe and other inevitable impurities, wherein the total weight percent of all the components is 100 percent.

step 1, forging and hot rolling:

the forging blank with the thickness of 50mm is placed in a heating furnace to be heated to 1150 ℃ along with the furnace and is kept warm for 2h, then the forging blank is rolled on a hot rolling mill for 7 times to form a hot rolled plate with the thickness of 3mm, and then the hot rolled plate is cooled to room temperature at the cooling speed of 20 ℃/s. The initial rolling temperature is 1130 ℃, the final rolling temperature is 1020 ℃, and the total hot rolling reduction rate is 94%;

step 2, solution treatment and cold rolling:

carrying out solution treatment on the hot rolled plate at 1100 ℃ for 10min to fully dissolve carbides and the like generated in the hot rolling process, then carrying out acid pickling to remove surface iron scales, and carrying out multi-pass room-temperature cold rolling on a cold rolling unit, wherein the final plate thickness of the cold rolled plate is 0.6mm, and the total cold rolling reduction is 80%;

step 3, annealing and heat preservation:

and (3) preserving the heat of the cold-rolled sheet in a heating furnace at 700 ℃ for 10min, and then quenching the cold-rolled sheet to room temperature to obtain a high-strength plastic nano/submicron crystal cold-rolled 304 stainless steel strip finished product.

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

The mechanical property of the finished steel is detected, the yield strength and the tensile strength are 835MPa and 960MPa respectively, and the total elongation is 42%.

Claims

1. A high-strength plastic nano/submicron crystal cold-rolled 304 stainless steel strip, characterized in that its chemical composition by weight is: C: greater than or equal to 0.042% and less than 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 sum of the weight percentages of each component is 100%; its microstructure It is multi-scale nano/submicron austenite, the austenite grains are equiaxed, composed of ultrafine austenite with a grain size of 150-500nm and a small amount of recrystallized austenite with a size larger than 1μm. composition; its yield strength ≥ 800 MPa, tensile strength ≥ 900 MPa, total elongation ≥ 40%;

The preparation method of the 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 50-60 mm, then placing the forged billet in a heating furnace and heating it to 1150-1250 °C and keeping the temperature for 2-3 hours;

(2) The forging billet is rolled into a hot-rolled sheet with a thickness of 3-6 mm through 5-7 passes through a hot rolling mill, and then water-cooled to room temperature, the rolling temperature is 1100-1200 °C, and the final rolling temperature is 950-1020 °C ℃, the total hot rolling reduction rate is 90-94%;

Step 2, Solution Treatment and Cold Rolling:

The above-mentioned hot-rolled sheet is kept at 1000-1100°C for 10-60 minutes for solution treatment, so that the carbides produced during the hot-rolling process are fully dissolved; 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 1-10 minutes, and then quenched to room temperature to obtain a finished product of high-strength plastic nano/submicron crystal cold-rolled 304 stainless steel strip.

2. the preparation method of a kind of high-strength plastic nano/submicron crystal cold-rolled 304 stainless steel strip according to claim 1, is characterized in that, comprises the steps:

Step 1, Forging and Hot Rolling:

Step 2, Solution Treatment and Cold Rolling:

Step 3, isothermal annealing:

3 . The method for preparing a high-strength plastic nano/submicron crystal cold-rolled 304 stainless steel strip according to claim 2 , wherein, in the step 1, the rate of water cooling is 20-40° C./s. 4 .

4. The method for preparing a high-strength plastic nano/submicron crystal cold-rolled 304 stainless steel strip according to claim 2, wherein in the step 2, the cold rolling pass reduction is controlled at 0.1-0.5 mm , and the final plate thickness is 0.3 to 1 mm.

5 . The method for preparing a high-strength plastic nano/submicron crystal cold-rolled 304 stainless steel strip according to claim 2 , wherein in the step 3, the heating furnace used for annealing is a box-type resistance furnace. 6 .