US20220355355A1

US20220355355A1 - Ultra-thin precision stainless steel foil with high strength and high plasticity and production method thereof

Info

Publication number: US20220355355A1
Application number: US17/604,548
Authority: US
Inventors: Tianxiang Wang; Xi LIAO; Haojie DUAN; Xianbing WU; Xiaoquan Han; Yongshun ZHAO; Huiwen WANG; Xiangyu WANG; Xiaodong Liu; Xing Yang; Xu Fang
Original assignee: Shanxi Taigang Stainless Steel Precision Strip Co Ltd
Current assignee: Shanxi Taigang Stainless Steel Precision Strip Co Ltd
Priority date: 2021-03-23
Filing date: 2021-07-09
Publication date: 2022-11-10
Also published as: CN113042527A; WO2022198837A1

Abstract

A method for producing a stainless steel foil comprises the following steps: rolling a raw material steel coil in an intermediate rolling process comprising three rolling processes; rolling the finished product in the rolling process; annealing and straightening the finished product. The application also provides a stainless steel foil prepared by the method. The method can solve the defect that the high strength and high plasticity of the ultra-thin stainless steel foil are difficult to meet at the same time.

Description

TECHNICAL FIELD

The application relates to the technical field of production and manufacture of ultra-thin precision stainless steel strips, in particular to an ultra-thin precision stainless steel foil with high strength and high plasticity and a production method thereof.

BACKGROUND

At present, the ultra-thin precision stainless steel strip has been applied in the fields of aerospace, petrochemical industry, medical electronics, communication semiconductors, auto parts, computer products, etc., and has a very high added value, which puts forward higher requirements for the metal characteristics, corrosion resistance and surface quality of stainless steel. Especially, for the precision stainless steel foil products with ac high strength with a width of more than 600 mm, a thickness of less than 0.05 mm and an elongation of at least 50%, there is no technology to produce such products at present. At present, only a few enterprises in Japan and the United States can produce stainless steel foil products with a thickness of 0.05 mm, but the width is limited, and only products with a width of less than 450 mm can be produced, and the elongation of the foil is less than 50%.
On the one hand, there is a great demand for high-performance stainless steel foil in the market, but on the other hand, there is currently a lack of rolling technology for precision stainless steel foils with a width exceeding 600 mm. Therefore, developing a high-strength and high-plasticity precision stainless steel foil with a width of more than 600 mm and a thickness of less than 0.05 mm to fill the technical gap and meet the market demand has become an urgent technical problem for those skilled in the art.

SUMMARY

In order to solve all or part of the above problems, the purpose of the present application is to provide a production method of an ultra-thin precision stainless steel foil with high strength and high plasticity and the ultra-thin precision stainless steel foil with high strength and high plasticity prepared by the production method.
Specifically, the application is realized by the following technical solution:
A method for producing a stainless steel foil which includes the following steps of:
S1, rolling a raw material steel coil in an intermediate rolling process comprising three rolling processes;
S2, rolling a finished product in a rolling process;
S3, carrying out annealing treatment and straightening treatment on the finished product.
Optionally, the raw material steel coil is 301 L steel coil.
Optionally, the intermediate rolling process includes a first rolling process with a deformation of 45%˜55%, a second rolling process with a deformation of 50%˜60%, and a third rolling process with a deformation of 50%˜60%, wherein high-temperature intermediate flexible bright annealing is respectively carried out immediately after the first rolling process, the second rolling process and the third rolling process are completed, with an annealing temperature being 950˜1150° C., and an annealing TV value being 2.5˜15, and TV values of the three annealing processes are gradually reduced.
Optionally, each rolling process of the intermediate rolling process adopts five rolling passes, wherein, a high-roughness wire drawing roller is adopted in the first pass, the material of the roller is M2, the roughness Ra of the roller is 1.5˜3.0 μm, and a single pass deformation is 23%˜28%; rollers with a roughness Ra of 0.1˜0.5 μm are adopted for the remaining passes.
Optionally, the finished product rolling process sequentially comprises: a first rolling pass with a deformation of 25%˜30%; a second rolling pass with deformation of 20%˜28%; a third rolling pass with deformation of 15%˜20%; a fourth rolling pass with a deformation of 5%˜10%; wherein, after finishing the third rolling pass, a TA stress relieving heat treatment is carried out at 600˜800° C. and a TV value is not less than 1, and then the fourth rolling pass is carried out.
Optionally, the rolling tension is 230˜300 N/mm²and the rolling force is ≤500 KN in the finished product rolling process.
Optionally, for a work roller used in the finished product rolling process, the diameter is Φ20˜30 mm, the material is M2, the roughness Ra is 0.1˜0.25 μm, and the surface hardness is HRC 63˜68.
Optionally, an annealing temperature of the finished product is 900˜1100° C.
Optionally, the straightening treatment adopts 23-rollers stretch-bend straightening, with an opening degree of −1.5˜−2.0 mm and an elongation of 0.3%˜0.45%, and a diameter of a straightening roller is 12˜16 mm.
A stainless steel foil obtained by the above-mentioned method for producing a stainless steel foil, wherein the stainless steel foil has a thickness of ≤0.05 mm, a width of ≥600 mm, a tensile strength of ≥650 Mpa, and an elongation of ≥50%.
Compared with the prior art, the ultra-thin precision stainless steel foil with high strength and high plasticity and the production method thereof have at least the following beneficial effects:
In the step of selecting a raw material, raw materials are selected through the comparative analysis of strength and elongation after heat treatment. In the production process and the intermediate annealing grain structure design step, the flexible annealing process design in the intermediate rolling process is carried out, and the grains are refined to 9˜10 grades through process innovation, thus laying a foundation for the ultra-fine grain finished products; in the intermediate rolling process and finished product rolling process, a new design of TA stress relieving process is provided so that the deformation of the finished product rolling process is more sufficient and the internal organization structure is more uniform. At the same time, process parameter optimization, pass design and rolling force and tension control for the work roller of the finished product rolling process are carried out. In the annealing process of the finished product, the heat treatment process of rapid annealing at a low temperature is designed to inhibit grain growth and realize the control of a 3˜5 m ultra-fine grain structure. In the straightening and leveling process, a 23-rollers stretch-bend straightening process is designed, with an opening degree of −1.5˜−2.0 mm and an elongation of 0.3%˜0.45%. Therefore, the production process of the ultra-thin precision stainless steel foil with high strength and high plasticity with a thickness of less than 0.05 mm is realized, and the surface quality of the steel strip is good, and the performance is uniform and stable, thus meeting the demand of high quality.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a process flow chart of the production method of the ultra-thin precision stainless steel foil with high strength and high plasticity according to the present application.

FIG. 2 is a schematic diagram of a work roller used in finished product rolling process according to one embodiment of the present application.

FIG. 3 is a diagram of the roller system of the SUNDWIG 4-column 20-high reversible rolling mill.

DESCRIPTION OF EMBODIMENTS

In order to fully understand the purpose, characteristics and efficacy of the present application, the present application will be described in detail through the following specific embodiments. Except for the following contents, the process method of the application adopts conventional methods or devices in the field. Unless otherwise stated, the following terms have the meanings commonly understood by those skilled in the art.
As far as stainless steel strip is concerned, the strength of the material will increase while the plasticity of the material will decrease under the conventional process, and there is a big contradiction between plasticity and strength. Taking austenitic stainless steel as an example, its strength exceeds 700 MPa, and its plasticity (usually measured by elongation) is lower than 50%. Conventionally, the method of obtaining a high strength is mainly through a certain proportion of work hardening, which will directly lead to a sharp decline in plasticity. At present, the conventional process cannot achieve high strength and high plasticity at the same time.
Aiming at the problem that the wide and ultra-thin precision stainless steel foil cannot have high strength and high plasticity at the same time at present, the inventor of the present application creatively improves the process through research, thus proposing a production method of the ultra-thin precision stainless steel foil with high strength and high plasticity. The method can realize that refinement of the internal organizational structure, thereby improve the strength of the material on the basis of ensure the plasticity of the strip.
The production method of the ultra-thin precision stainless steel foil with high strength and high plasticity includes the following steps of: rolling a raw material steel coil in an intermediate rolling process comprising three rolling processes; finished product rolling process; and, carrying out annealing treatment and straightening treatment on the finished product.
According to the application, the process flow of three rolling processes−intermediate flexible annealing−large deformation rolling in a finished product rolling processes+process TA heat treatment−finished product rapid annealing at a low temperature, is adopted, and the production of a stainless steel foil with a thickness ≤0.05 mm, a width ≥600 mm, a tensile strength ≥650 MPa and an elongation ≥50% is realized.
FIG. 1 shows the process flow chart of the production method of ultra-thin precision stainless steel foil with high strength and high plasticity. With reference to FIG. 1, the production method of the ultra-thin precision stainless steel foil with high strength and high plasticity of the present application will be described in detail below.
The production method of the ultra-thin precision stainless steel foil with high strength and high plasticity can be applied to raw steel coils of any brand. In the implementation process, in order to achieve the best effect, a preparation step, i.e., step S0 of selecting a raw material steel coil, is performed before the method of the present application is executed.
In the step S0, the rolling raw materials most suitable for the production method of the present application are selected by analyzing the rolling properties and representative compositions of raw materials of different materials after heat treatment.
According to the research of the inventor, the production method of the application preferably adopts 301 L (Chinese National standard brand) steel coil as the raw material.
Taking 301 L as an example, through the analysis of rolling and heat treatment of different materials, it can be seen that with the reduction of C content, the strength of 301 L decreases slightly, but the elongation is relatively high when the deformation is 50%. Under the condition of the same deformation, the rolling deformation resistance of the 301 L steel is small, and its plastic toughness is strong, which is beneficial to the production of rolling and heat treatment processes. Therefore, 301 L is selected as the raw material of the production method of the present application.
Preferably, in order to ensure various performance indexes and plate shape of the stainless steel foil obtained by the production method of the present application, the thickness of the raw steel coil is ≥0.5 mm (preferably 0.5˜1.0 mm), the width is 500˜650 mm, and the surface finish is 2B (matte surface, GB/T 3280).
Subsequently, the production method of the stainless steel foil of the present application is started, including:
S1, rolling the raw material steel coil in an intermediate rolling process.
The intermediate rolling process includes three rolling processes: a first rolling process with a deformation of 45%˜55%; a second rolling process with a deformation of 50%˜60%; a third rolling process with a deformation of 50%˜60%. After the completion of the first rolling process, the second rolling process and the third rolling process, high-temperature intermediate flexible bright annealing is carried out at 950˜1150° C., and the annealing TV value (that is, the product of the thickness of the steel coil and the running speed of the steel coil) is 2.5˜15. Moreover, the TV value of the third annealing is gradually reduced, thus ensuring the grain structure refinement after intermediate annealing.
Five rolling passes are adopted for each rolling process. Among them, the first pass adopts high-roughness wire drawing roller, the material of the roller is M2 (namely molybdenum high speed steel), the roughness Ra of the roller is 1.5˜3.0 m, the single pass deformation is 23%˜28%, the remaining passes adopt conventional rollers with the roughness Ra of 0.1˜0.5 m, and the single pass deformation of the remaining four passes is gradually reduced to ensure the overall deformation.
Through the process of “rolling-annealing-rolling-annealing-rolling-annealing”, the total deformation of the intermediate rolling process can reach 87.5%˜93%, which ensures sufficient deformation of the original structure of the strip. Through three times of rapid annealing at a high temperature, the internal grain coarseness is suppressed, and the size and uniformity of the internal structure grain are adjusted. After the internal grains are refined to 9˜10 grades, it will provide good machinability for the rolling of the finished product with a deformation above 60% grade. If the grain structure is below grade 9, especially below grade 7, the machinability of the material will not meet the requirements of large deformations in the rolling of the finished product, and problems such as strip breakage may occur. After three times of “rolling-annealing” design, the internal uniformity of the strip can be guaranteed, and at the same time, the possibility of a uniform deformation of the strip is provided. In the first pass of each rolling process, the roughness Ra is 1.5˜3.0 μm, and the single pass deformation is 23%˜28%, so as to ensure the rapid microstructure transformation in the rolling process.
S2, finished product rolling process.
In step S2, the diameter of the work roller used for rolling is Φ20˜30 mm, the material of the work roller is M2 (namely molybdenum high-speed steel), the roughness Ra of the work roller is 0.1˜0.25 μm, and the surface hardness of the work roller reaches HRC 63˜68. As a specific example, as shown in FIG. 2, the work roller used in step S2 has a length of, for example, 780 mm, and the supporting sections at both ends are, for example, 110 mm each.
The finished product rolling process of step S2 is divided into four rolling passes, and the deformation of each pass is gradually reduced. Specifically, in the first rolling pass, the deformation is 25%˜30%; in the second rolling pass, the deformation is 20%˜28%; in the third rolling pass, the deformation is 15%˜20%; in the fourth rolling pass, the deformation is 5%˜10%. Preferably, after finishing the third rolling pass, TA stress relieving heat treatment (i.e., tension low-temperature stress-relieving heat treatment) is carried out at a temperature of 600˜800° C. and a TV value of not more than 1, and then the fourth rolling pass is carried out.
In step S2, the rolling tension of the finished product is controlled at 230˜300 N/mm², and the rolling force is controlled below 500 KN.
In step S2, a TA stress relieving process is added to ensure that the internal stress of the strip is eliminated under the condition of large deformation in the first three passes, reduce the deformation resistance in the last pass, and improve the rolling dimensional accuracy and rolling plate shape of the finished product, thereby achieving more than 60% of the rolling deformation of the finished product, making the organizational structure more fragmented, ensuring more nucleation points in the solid solution process during the heat treatment of the finished product, and thus refining the grains, which is the basis of the finished product 3˜4 m grain structure. After TA stress relieving treatment, the internal deformation resistance of the strip is reduced, which greatly promotes the stable control of rolling force and tension in the last pass and ensures the refinement of the internal structure of the strip.
S3, carrying out annealing treatment and straightening treatment on the finished product.
After the finished product rolling process, the steel foil is annealed at a low temperature of 900˜1100° C. with a TV value of not less than 2. By rapid annealing at low temperature, the grain growth is restrained and the microstructure of 3˜5 m ultrafine grains is controlled.
After annealing, straightening and leveling are carried out. 23-rollers stretch-bend straightening process is adopted, the opening degree is −1.5˜−2.0 mm, the elongation is 0.3%˜0.45%, and the roller diameter of straightening roller is 12˜16 mm.
The production method of the application can be carried out by adopting a SUNDWIG 4-column 20-high reversible rolling mill. FIG. 3 shows the roller system diagram of SUNDWIG 4-column 20-high reversible rolling mill, which is mainly composed of a pair of work rollers 1, two pairs of first intermediate rollers 2, three pairs of second intermediate rollers 3 and four sets of backing bearings 4. The unique 4-column frame structure of the rolling mill makes it possible to adopt inclined rolling according to the actual situation of the coil in the rolling process, thus ensuring good coil shape and reducing the fluctuation of the coil shape in the rolling process. Of course, this is only an example, and the method of the present application can also be implemented by other rolling mills.
The above-mentioned production method can solve the contradiction between high strength and high plasticity, realize the bidirectional regulation of high strength and high plasticity, and make the foil material have good surface quality and uniform and stable performance. Particularly, the thickness of the stainless steel foil is ≤0.05 mm, the width is ≥600 mm, the tensile strength is ≥650 MPa, and the elongation is ≥50%.

EXAMPLES

The following examples further illustrate the present application, but do not limit the present application to the scope of the examples. The experimental methods for which specific conditions are not indicated in the following examples shall be selected according to the conventional methods and conditions, or according to the commodity specifications.
The following examples and comparative examples refer to GB/T228.1 (Standard for Tensile Test of Metallic Materials) for testing the parameters.
The following examples and comparative examples are all carried out by SUNDWIG 4-column 20-high reversible mill of SUNDWIG, Germany.

Example 1

The method of this embodiment includes the following steps:
S0, selecting raw material steel coil: 301 L stainless steel coil with a thickness of 0.5 mm×a width of 615 mm and a surface finish of 2B (matte) was selected as a rolling raw material.
S1, intermediate rolling process: the design parameters and related technical requirements of the intermediate rolling process are shown in table 1.

TABLE 1

	Incoming	Thick-		Require-	Other
	material	ness		ment for	technical
	thick-	after		annealing	require-
Pass	ness	rolling	Deformation	temperature	ments

First	0.5 mm	0.22 mm	56.0%	1080° C.,	Trimming
rolling				TV value 8.8	before
process					rolling.
Second	0.22 mm	0.1 mm	54.5%	1050° C.,
rolling				TV value 4.5
process
Third	0.1 mm	0.05 mm	50.0%	1000° C.,	Trimming
rolling				TV value 2.6	before
process					rolling.

Five rolling passes are adopted for each rolling process, wherein, the first pass adopts high-roughness wire drawing roller, the roller material is M2 (namely molybdenum high speed steel), the roughness Ra of the roller is 1.65 μm, and the single pass deformation is 25%; the remaining passes adopt conventional rollers with the roughness Ra of 0.28 μm, and the single pass deformation of the remaining four passes is gradually reduced to ensure the overall deformation.
S2, finished product rolling process:
The diameter of the work roller was Φ25 mm, the material of the work roller was M2, and the roughness Ra of the work roller was 0.15 μm. The finished product rolling process included: a first pass, rolling from 0.05 mm to 0.036 mm; a second pass, rolling from 0.036 mm to 0.027 mm; a third rolling pass, rolling from 0.027 mm to 0.022 mm; TA stress relieving heat treatment at 720° C.; a fourth pass, rolling from 0.022 mm to 0.02 mm. The design parameters and related technical requirements of finished product rolling process are shown in Table 2:

TABLE 2

	Incoming	Thick-
	material	ness
	thick-	after
Pass	ness	rolling.	Deformation	Remarks

First pass	0.05 mm	0.036 mm	28%
Second pass	0.036 mm	0.027 mm	25%
Third pass	0.027 mm	0.022 mm	18.5%
TA treatment	0.022 mm			Heat treatment
				temperature 720° C.
Fourth pass	0.022 mm	0.02 mm	9.1%

The rolling tension of the finished product process was controlled at 280 N/mm², and the rolling force was controlled at 450 KN.
S3, carrying out low-temperature rapid heat treatment, wherein the heat treatment temperature was 950° C., the grain size was controlled to be 3˜5 μm, and the grain size of the finished product must be strictly controlled and detected; then 23-rollers stretch-bend straightening treatment was adopted, and the opening degree was −1.6 mm, the elongation was 0.45%, and the roller diameter was 12 mm.
The foil obtained in this example was tested, and the thickness of the working side was measured to be 0.019 mm, the thickness of the transmission side was measured to be 0.02 mm (the overall size was 0.02 mm), the width was 600 mm, the tensile strength was 700 MPa, and the elongation was 50%.

Comparative Example

S0, selecting raw material steel coil: 301 L stainless steel coil with a thickness of 0.35 mm×a width of 615 mm and a surface finish of 2B (matte) was selected as a rolling raw material.
S1, intermediate rolling process: the intermediate rolling process was designed to include three passes, wherein the first pass was from 0.35 mm to 0.15 mm, the second pass was from 0.15 mm to 0.07 mm, the third pass was from 0.07 mm to 0.035 mm, and the annealing temperature was 1050° C.
S2, finished product rolling process: the diameter of the work roller was (1) 25 mm, the material of the work roller was M2, and the roughness Ra of the work roller was 0.15 m.
The finished product rolling process specifically included: rolling from 0.035 mm to 0.029 mm in the first pass, rolling from 0.029 mm to 0.025 mm in the second pass, rolling from 0.025 mm to 0.022 mm in the third pass, and rolling from 0.022 mm to 0.02 mm in the fourth pass at an annealing temperature of 1050° C. The tension was controlled at 300 N/mm², and rolling force was controlled at 450 KN.
The measured thickness of the foil was 0.019 mm on the working side, 0.02 mm on the transmission side, 580 mm in width, 590 MPa in tensile strength and 40% in elongation.
The above-mentioned embodiments are preferred embodiments of the present application, but the implementation of the present application is not limited by the above-mentioned embodiments. Any other substitutions, modifications, combinations, changes, simplifications, etc. made without departing from the spirit and principles of the present application shall be equivalent substitutions and shall be included in the scope of protection of the present application.

Claims

1. A method for producing a stainless steel foil, comprising the following steps of:

rolling a raw material steel coil in an intermediate rolling process comprising three rolling processes;

finished product rolling process;

carrying out annealing treatment and straightening treatment on the finished product.

2. The method for producing a stainless steel foil according to claim 1, wherein the raw material steel coil is 301 L steel coil.

3. The method for producing a stainless steel foil according to claim 1, wherein the intermediate rolling process comprises a first rolling process with a deformation of 45%˜55%, a second rolling process with a deformation of 50%˜60%, and a third rolling process with a deformation of 50%˜60%, wherein high-temperature intermediate flexible bright annealing is respectively carried out immediately after the first rolling process, the second rolling process and the third rolling process are completed, with an annealing temperature being 950˜1150° C., and an annealing TV value being 2.5˜15, and TV values of the three annealing processes are gradually reduced.

4. The method for producing a stainless steel foil according to claim 3, wherein each rolling process of the intermediate rolling process adopts five rolling passes, wherein, a high-roughness wire drawing roller is adopted in a first pass, the material of the roller is M2, the roughness Ra of the roller is 1.5˜3.0 μm, and a single pass deformation is 23%˜28%; rollers with a roughness Ra of 0.1˜0.5 μm are adopted for the remaining passes.

5. The method for producing a stainless steel foil according to claim 1, wherein the finished product rolling process sequentially comprises: a first rolling pass with a deformation of 25%˜30%; a second rolling pass with deformation of 20%˜28%; a third rolling pass with deformation of 15%˜20%; a fourth rolling pass with a deformation of 5%˜10%; wherein, after finishing the third rolling pass, a TA stress relieving heat treatment is carried out at 600˜800° C. and a TV value is not less than 1, and then the fourth rolling pass is carried out.

6. The method for producing a stainless steel foil according to claim 1, wherein the rolling tension is 230˜300 N/mm²and the rolling force is ≤500 KN in the finished product rolling process.

7. The method for producing a stainless steel foil according to claim 1, wherein for a work roller used in the finished product rolling process, the diameter is φ20˜30 mm, the material is a molybdenum high speed steel, the roughness Ra is 0.1˜0.25 μm, and the surface hardness is HRC 63˜68.

8. The method for producing a stainless steel foil according to claim 1, wherein the annealing temperature of the finished product is 900˜1100° C.

9. The method for producing a stainless steel foil according to claim 1, wherein the straightening treatment adopts 23-rollers stretch-bend straightening, with an opening degree of −1.5˜−2.0 mm and an elongation of 0.3%˜0.45%, and the diameter of the straightening roller is 12˜16 mm.

10. A stainless steel foil obtained by the method for producing a stainless steel foil according to claim 1, wherein the stainless steel foil has a thickness of ≤0.05 mm, a width of ≥600 mm, a tensile strength of ≥650 Mpa, and an elongation of ≥50%.