Preparation Method of High-Temperature Molten Salt-Based Heat-Resistant Steel Sheet for Energy Storage

This application claims priority to Chinese Patent Application No. 202410418883.1, filed Apr. 9, 2024, the entire disclosure of which is hereby incorporated by reference in its entirety.

The present disclosure relates to the technical field of materials, and in particular to a method for preparing a high-temperature molten salt-based heat-resistant steel sheet for energy storage.

Concentrated solar power (CSP) is a power generation system of a concentrated solar power plant. Currently, several molten eutectic salt mixtures are the most popular candidate materials for heat transfer fluids (HTFs) and thermal energy storage (TES) in CSP systems. In order to compete with other energy storage technologies to reduce the cost of CSP and improve thermal utilization efficiency, an operating temperature of a power generation unit is increased from 560° C. to not less than 650° C., which puts higher requirements on heat transfer as well as heat storage equipment that carries a molten salt. Molten chlorides decompose at higher temperatures than molten nitrates and are extremely corrosive to alloys. In comparison, lithium-containing carbonates are much less corrosive, can operate at temperatures up to 800° C. without decomposing, and do not require delicate preparation in an inert atmosphere. Therefore, novel alloys that could be used in high-temperature carbonate corrosion environments have attracted increasing attention.

310S heat-resistant steel is widely used in various high-temperature structural materials due to excellent mechanical properties, desirable creep resistance, fatigue resistance, and corrosion resistance, as well as relatively low cost. The 310S heat-resistant steel is expected to become a structural candidate material for the next-generation CSP system. Studies of the present disclosure show that cold rolling could significantly refine a grain structure of the material, increase both strength and hardness of a alloy, and improve a processing performance of the alloy, while avoiding stress concentration and reducing internal defects of the alloy. Moreover, the cold rolling could improve surface quality and smoothness of the alloy, thereby enhancing the corrosion resistance. Therefore, the present disclosure prepares a high-temperature molten salt-based heat-resistant steel sheet for energy storage.

In view of the deficiencies in the prior art, the present disclosure provides a method for preparing a high-temperature molten salt-based heat-resistant steel sheet for energy storage.

To achieve the above object, the present disclosure is implemented by the following technical solutions.

The present disclosure provides a method for preparing a high-temperature molten salt-based heat-resistant steel sheet for energy storage, including: cutting an aluminum-containing 310S heat-resistant steel sheet into a block, and subjecting the block to cold rolling at room temperature with a rolling reduction of 0.2 mm per pass to obtain a cold-rolled sheet with a rolling deformation of 90%; and subjecting the cold-rolled sheet to annealing.

In some embodiments, the aluminum-containing 310S heat-resistant steel sheet consists of the following compositions: 15 wt. % to 25 wt. % of Ni, 8 wt. % to 15 wt. % of Cr, 1 wt. % to 5 wt. % of Al, 1 wt. % to 5 wt. % of Mn, 0.7 wt. % to 3 wt. % of Si, 0.025 wt. % to 0.5 wt. % of C, and Fe as a balance.

In some embodiments, the annealing is conducted at a temperature of 800° C.±20° C. for 60 min±20 min.

In some embodiments, the temperature for the annealing is raised to 800° C.±20° C. at a heating rate of 10° C./min±2° C./min.

In some embodiments, the cold rolling is conducted at a rolling speed of 0.4 m/min and a roller speed of 15 r/min.

The present disclosure has the following beneficial effects.

1. In the present disclosure, an aluminum-containing 310S heat-resistant steel sheet after hot-rolled solid solution is subjected to cold rolling with a rolling deformation of 90% to obtain a cold-rolled aluminum-containing 310S heat-resistant steel sheet, and the cold-rolled aluminum-containing 310S heat-resistant steel sheet is subjected to annealing to obtain a high-temperature molten salt-based heat-resistant steel sheet. The high-temperature molten salt-based heat-resistant steel sheet shows desirable corrosion resistance and oxidation resistance at high temperatures, and has been regarded as a structural candidate for the next-generation CSP system. high-temperature molten salt-based heat-resistant steel sheet could be used in heat storage tanks, heat exchangers, heat transfer pipes and other components of the CSP system.

2. In the present disclosure, the cold rolling and the annealing each have a low cost and a simple process, and the prepared high-temperature molten salt-based heat-resistant steel sheet shows desirable mechanical properties. After the annealing at 800° C. for 60 min, the heat-resistant steel sheet has a tensile strength of 865.37 MPa, a yield strength of 675.09 MPa, and an elongation of 38.1%. Moreover, the heat-resistant steel sheet also has excellent corrosion resistance in a carbonate at 650° C., exhibiting a corrosion rate of 127.1 μm/year after 480 h of corrosion.

The technical solutions of the embodiments of the present disclosure are clearly and completely described below with reference to the drawings. Apparently, the described embodiments are merely a part rather than all of the embodiments of the present disclosure. All other embodiments obtained by a person of ordinary skill in the art based on the embodiments of the present disclosure without creative efforts shall fall within the scope of the present disclosure.

Unless otherwise specified, the technical means used in the embodiments are conventional means well known to those skilled in the art.

The present disclosure provides a method for preparing a high-temperature molten salt-based heat-resistant steel sheet for energy storage, in which an aluminum-containing 310S heat-resistant steel sheet is adopted, the aluminum-containing 310S heat-resistant steel sheet consisting of the following compositions: 15 wt. % to 25 wt. % of Ni, 8 wt. % to 15 wt. % of Cr, 1 wt. % to 5 wt. % of Al, 1 wt. % to 5 wt. % of Mn, 0.7 wt. % to 3 wt. % of Si, 0.025 wt. % to 0.5 wt. % of C, and Fe as a balance. The aluminum-containing 310S heat-resistant steel sheet is in a hot-rolled solid solution state, has an initial thickness of 6.8 mm, and is subjected to cold rolling with a rolling deformation of 90% to obtain a sheet.

In some embodiments, the aluminum-containing 310S heat-resistant steel sheet is a high-aluminum 310S heat-resistant steel alloy sheet.

The above high-temperature molten salt-based heat-resistant steel sheet is prepared by the following steps:

Step (1), the aluminum-containing 310S heat-resistant steel sheet is cut into a rectangular block of 60 mm×30 mm×6.8 mm by electric spark wire cutting.

Step (2), a surface of the rectangular block is polished using sandpaper, and the surface is cleaned with anhydrous ethanol.

Step (3), a cleaned rectangular block is subjected to cold rolling at room temperature using a two-roller hot and cold rolling mill; in order to prevent cracking and warping of the sheet due to a large single rolling reduction, the rolling reduction in each pass is controlled to about 0.2 mm; the cold rolling is conducted until a sheet thickness is 0.68 mm to obtain a cold-rolled sheet with a rolling deformation of 90%; where the cold rolling is performed under a rolling speed of the rolling mill of 0.4 m/min and a roller speed of 15 r/min.

Step (4), the cold-rolled sheet is subjected to annealing at a temperature of 800° C.±20° C. for 60 min±20 min, in which a cooling is performed by air cooling, and the sheet is introduced into a furnace when the furnace reaches the annealing temperature. In the annealing, the furnace for heat treatment is heated to a temperature of 800° C.±20° C. at 10° C./min±2° C./min, the cold-rolled sheet is placed in the furnace, and subjected to heat preservation for 60 min±20 min, and then taken out and cooled in the air. The cold-rolled sheet has a large internal stress due to a large cold rolling deformation, and dislocations are entangled, resulting in high material strength and low elongation. The annealing could effectively eliminate the stress inside the cold-rolled sheet, thereby improving the comprehensive performance of the alloy.

Step (5), a resulting annealed cold-rolled sheet is cut into a block of 12 mm×12 mm×0.68 mm by wire cutting; the block is polished with 600 #, 1000 #, 1500 #, and 2000 #sandpapers in sequence, and a polished block is ultrasonically cleaned in anhydrous ethanol for 30 min, taken out and blown dry for later use.

Step (6), the resulting annealed cold-rolled sheet is immersed in carbonate and subjected to a molten salt corrosion test at 650° C. for 480 h, and then a batch of samples is taken out at 72 h, 144 h, 216 h, 288 h, 384 h, and 480 h separately to observe the corrosion morphology and quality changes. The carbonate used in the corrosion test is LiCO+NaCO+KCO, with a ratio of 32.1:33.4:34.5 (wt. %). The samples each are placed in a crucible containing the carbonate. The crucible is placed in a box-type resistance furnace. The box-type resistance furnace is heated to 650° C. at a heating rate of 10° C./min, and then the timing is started.

In the present disclosure, the aluminum-containing 310S heat-resistant steel sheet has an increased Al content and a reduced Cr content, and is subjected to cold rolling and annealing to obtain a heat-resistant steel sheet with excellent mechanical properties and high corrosion resistance. The preparation method has the advantages of simple process, low cost, and no pollution, and is suitable for large-scale production.

The present disclosure is further described below with reference to a specific example.

1. Compositions of a high-aluminum 310S heat-resistant steel alloy used are shown in Table 1.

(1) Cutting: the high-aluminum 310S heat-resistant steel alloy was cut into a block of 60 mm×30 mm×6.8 mm by wire cutting.

(3) Cold rolling deformation: the resulting block after solution treatment was subjected to cold rolling using a two-roller hot and cold rolling mill at a rolling speed of 0.4 m/min, a roller speed of 15 r/min, and a rolling reduction of 0.2 mm per pass, to obtain a cold-rolled sheet with a rolling deformation of 90%. A comparison diagram of macroscopic morphology between the high-aluminum 310S heat-resistant steel alloy and the cold-rolled sheet after cold rolling with a cold rolling deformation of 90% is shown in.

(4) Annealing: a box-type resistance furnace was heated from room temperature to 800° C. at a heating rate of 10° C./min, the cold-rolled sheet after 90% cold rolling was placed in the furnace, subjected to heat preservation for 60 min, taken out and cooled naturally in the air.

(5) Corrosion test: a resulting annealed sheet was cut into a block of 12 mm×12 mm×0.68 mm, polished and cleaned, and then placed in an alumina crucible filled with a ternary carbonate (32.1 wt. % LiCO+33.4 wt. % NaCO+34.5 wt. % KCO). After the alumina crucible was placed in a muffle furnace, the muffle furnace was heated to 650° C. at a heating rate of 10° C./min, and a batch of samples was taken out at 72 h, 144 h, 216 h, 288 h, 384 h, and 480 h separately to observe their corrosion morphology and quality changes.

3.1 XRD patterns of the high-aluminum 310S heat-resistant steel alloy under different treatment processes are shown in. Basic structures of the high-aluminum 310S heat-resistant steel alloy and the cold-rolled sheet after 90% cold rolling are both an austenite single phase. After the cold-rolled sheet after 90% cold rolling was subjected to annealing at 800° C. for 60 min, the resulting annealed sheet has NiAl precipitation phase in addition to austenite in structure.

3.2shows stress-strain diagrams of the high-aluminum 310S heat-resistant steel alloy under different treatment processes. It can be seen from the figure that after 90% cold rolling, the tensile strength of the alloy increases, while the elongation decreases significantly; after 90% cold rolling and annealing, the tensile strength of the material decreases, but the elongation increases.

3.3 The mechanical properties of the high-aluminum 310S heat-resistant steel alloy under different treatment processes are shown in Table 2. After 90% cold rolling deformation, the sheet has a tensile strength increased to 1,208.11 MPa and an elongation of only 0.9; after annealing at 800° C. for 60 min, the tensile strength is 865.37 MPa and the elongation is 38.1%.

3.4shows a diagram of the alloy in a corrosion test device, and a corrosion method is hanging corrosion. The corrosion test was performed as follows: A weighed salt was put into a drying oven and dried at 120° C. for 24 h. The block of 12 mm×12 mm×0.68 mm was polished to 2,000 mesh with sandpaper and then ultrasonically cleaned in anhydrous ethanol for 30 min. A mass of the sample was recorded on an analytical balance with an accuracy of 0.0001. The length, width, and height of the sample were measured with an electronic vernier caliper. The alumina crucible was ultrasonically cleaned, and dried and preheated in the muffle furnace at 120° C. The salt was loaded into the crucible, the mixed carbonate was loaded thereto, the crucible was covered with an alumina crucible lid, and then placed in the muffle furnace. The muffle furnace was heated to 650° C. at a heating rate of 10° C./min, and the time was recorded. Samples were taken at 72 h, 144 h, 216 h, 288 h, 384 h, and 480 h, respectively, where the crucible was taken out at each time point and then cooled to room temperature.

The sample was taken out of the crucible and the salt-coated sample was placed in deionized water, and ultrasonically cleaned to remove the salt on the sample surface. Corroded samples were ultrasonically pickled with an acid solution having nitric acid:hydrofluoric acid:water=10:2:88 to remove the corrosion layer of the corroded samples. Weighing was conducted 1 time once every 1 min of pickling and the data was recorded.

A mass loss of the sample was calculated according to the following formula (1):

A corrosion rate was calculated according to formula (2), in μm/year.

shows a comparison diagram of the corroded samples before and after pickling. A corrosion rate curve calculated according to the formula is shown in. The corrosion rate reaches a maximum of 365.993 μm/year at 144 h and the corrosion rate is 127.112 μm/year at 480 h.

The above are only intended to describe the preferred embodiments of the present disclosure, but not to limit the scope of the present disclosure. Various alterations and improvements made by those of ordinary skill in the art based on the technical solution of the present disclosure without departing from the design spirit of the present disclosure shall fall within the scope of the appended claims of the present disclosure.