Method for improving corrosion performance of 316L stainless steel in PEMFC cathode environment

Abstract

According to the method for improving the corrosion performance of the 316L stainless steel in the PEMFC cathode environment, the purpose of improving the corrosion performance of the 316L stainless steel in the PEMFC cathode environment is achieved by increasing the proportion of low sigma CSL grain boundaries of the 316L stainless steel. The method comprises the following steps of: homogenizing a 316L stainless steel plate at 1120-1180 DEG C for 1-3 hours, preserving heat at 1100-1150 DEG C for 1-2 hours, and performing water quenching or oil quenching to obtain a single-phase austenite structure; the stainless steel plate is subjected to multi-pass one-way cold rolling through a two-roller mill, the single-pass cold rolling deformation is 3%-5%, and a cold-rolled plate with the total cold rolling deformation being 40%-50% is obtained; the proportion of the low sigma CSL grain boundary of the stainless steel is 68.81%-71.57%, and the corrosion current density of the stainless steel in the PEMFC cathode environment is in the range of 4.336 * 10 <-7 >-1.782 * 10 <-7 > A / cm < 2 >.

Description

Technical Field

[0001] The present invention belongs to the field of hydrogen energy batteries, and relates to improving the corrosion resistance of highly corrosion-resistant bipolar plate materials and components required for hydrogen energy batteries, and can also be widely used in the fields of energy, electricity, chemical industry and daily life. Technical Background

[0002] Proton exchange membrane fuel cells (PEMFCs) can convert chemical energy in fuel into electrical energy and are considered to be the most promising energy device. Bipolar plates are one of the core components of PEMFCs. The interior of PEMFC is an acidic (pH = 3-5), high humidity and high temperature (70-80°C) corrosive environment, so the bipolar plate material is required to have strong corrosion resistance. Metal materials such as stainless steel and titanium are candidate materials for bipolar plates. Among them, austenitic stainless steel has attracted much attention in the field of bipolar plates due to its excellent ductility, toughness, corrosion resistance and easy cutting properties.

[0003] The preparation methods of metal bipolar plates include stamping, hydraulic forming, casting and machining. Among them, stamping is widely used due to its advantages of low cost, high speed and high productivity. In the process of manufacturing bipolar plates, cold deformation may not only change the microstructure and grain orientation of the organization, but also increase the dislocation density of stainless steel. In addition, the degree of cold deformation varies greatly due to the complexity of the flow channel.

[0004] The effects of deformation such as rolling, stretching, compression, torsion and sandblasting on the corrosion performance of metals have always attracted much attention. Among them, the effect of cold rolling deformation on the corrosion performance of stainless steel has received more attention. Studies have found that when the deformation of SLM316L stainless steel alloy is 20%, the corrosion performance in 0.9wt% NaCl solution reaches the best, and then the corrosion current density increases with the continued increase in cold deformation. Cold rolling deformation changes the composition of the passivation film, especially affects its chromium oxide content, thereby affecting the corrosion resistance of the bipolar plate in the PEMFC working environment.

[0005] Cold rolling deformation can cause changes in the microstructure, including deformation bands, deformation twins (DTs), dislocations, etc. When stainless steel is plastically deformed, it will also promote the transformation of part of the austenite structure into the martensite structure, that is, the martensitic phase transformation occurs. For many years, whether there is a correlation between the corrosion performance of metastable austenitic stainless steel and the martensitic phase transformation has also been a research hotspot. With the increase in deformation, the residual stress, dislocation density, and volume fraction of martensite of austenitic stainless steel also increase, making it prone to local stress corrosion in chloride ion-containing media. Based on the theory of preferential dissolution of martensite in the activated state, the potential of martensite is lower than that of austenite, making martensite an anode relative to austenite, resulting in preferential dissolution. However, some studies have shown that the preferential dissolution of martensite is attributed to the high dislocation density.

[0006] Therefore, the microstructure of 316L stainless steel and its influence on corrosion performance restrict the flow channel structure design and cold stamping process optimization of hydrogen energy battery bipolar plates. Summary of the invention

[0007] The purpose of the present invention is to provide a method for improving the corrosion performance of 316L stainless steel in a PEMFC cathode environment, which increases the proportion of low ∑CSL grain boundaries of 316L stainless steel, thereby achieving the purpose of improving the corrosion performance of 316L stainless steel in a PEMFC cathode environment. The specific steps are:

[0008] After homogenizing the 316L stainless steel plate at 1120-1180°C for 1-3 hours, the plate is kept at 1100-1150°C for 1-2 hours and then water quenched or oil quenched to obtain a single-phase austenite structure;

[0009] A two-roller rolling mill is used to perform multiple passes of unidirectional cold rolling on the stainless steel plate, wherein the deformation of each pass is 3-5%, and a cold-rolled plate with a total cold rolling deformation of 40-50% is obtained;

[0010] By controlling the above process parameters, the proportion of low ∑CSL grain boundaries of stainless steel is 68.81%-71.57%, making its corrosion current density in the PEMFC cathode environment at 4.336×10 -7 -1.782×10 -7 A / cm 2 within the range.

[0011] The corrosion current density was tested using an electrochemical workstation, using a traditional three-electrode device, with a saturated calomel electrode (SCE, +0.242V vs. hydrogen electrode (NHE)) as the reference electrode, a platinum sheet as the auxiliary electrode, and the above-mentioned 316L stainless steel cold-rolled plate as the working electrode. The non-working surface of the working electrode was welded with a copper wire, and the non-working surface was encapsulated in a PVC plastic tube using epoxy resin. The working surface was polished step by step using SiC sandpaper to 2000#, and then polished with a diamond polishing paste with a particle size of 1.5μm, and finally cleaned with acetone and distilled water, and dried for use.

[0012] In order to simulate the cathode environment of PEMFC, the electrochemical test used 0.5M H2SO4+2ppm HF electrolytic solution, the test temperature was kept constant at 70±2℃, and air bubbling was used.

[0013] The proportion of low ∑CSL grain boundaries of 316L stainless steel that is not treated by the process of the present invention or the process parameters are not within the scope of the present invention is lower than 68.81%, and the corrosion current density is higher than 4.336×10 -7 A / cm 2For example, the proportion of low ∑CSL grain boundaries of 316L stainless steel without cold rolling is 60.39%, and its corrosion current density is higher than 1.588×10 -5 A / cm 2 When the cold rolling deformation exceeds 50%, martensite appears and the corrosion resistance decreases. When the cold rolling deformation is 60%, the proportion of low ∑CSL grain boundaries reaches 60.39% and the corrosion current density is 2.348×10 -6 A / cm 2 .

[0014] It can be seen that within the control range of the organization and process parameters of the present invention, the corrosion resistance of 316L stainless steel in the PEMFC cathode environment is significantly improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 Polarization curve diagram of Example 1 of the present invention;

[0016] Figure 2 Grain boundary feature distribution diagram of Example 1 of the present invention;

[0017] Figure 3 Polarization curve diagram of Example 2 of the present invention;

[0018] Figure 4 Grain boundary feature distribution diagram of Example 2 of the present invention;

[0019] Figure 5 Polarization curve diagram of comparative example 1 of the present invention;

[0020] Figure 6 Grain boundary characteristic distribution diagram of comparative example 1 of the present invention;

[0021] Figure 7 Polarization curve diagram of comparative example 2 of the present invention;

[0022] Figure 8 Grain boundary characteristic distribution diagram of comparative example 2 of the present invention;

[0023] Fig. 9 Transmission electron microscope image and corresponding electron diffraction spots of Comparative Example 2 of the present invention. DETAILED DESCRIPTION

[0024] The method of improving corrosion resistance by controlling low ∑CSL grain boundaries described in the present invention is not limited to two-roll cold rolling, and is suitable for other cold deformation or methods of obtaining a considerable amount of deformation. Any improvements and changes within the scope of protection required by the claims of the present invention are within the protection scope of the present invention.

[0025] In order to meet the requirements of shape, size specifications and surface quality, the prepared stainless steel and its parts can be subsequently subjected to mechanical processing, polishing and corresponding chemical cleaning and polishing treatments, which are not specifically limited in the present invention.

[0026] Example 1

[0027] The 316L stainless steel plate was homogenized at 1120℃ for 3h, kept at 1100℃ for 2h and then oil quenched to obtain a single-phase austenite structure.

[0028] The stainless steel plate is subjected to multiple passes of unidirectional cold rolling by a two-roll rolling mill, wherein the deformation of each pass is 3%, and a cold-rolled plate with a total cold rolling deformation of 40% is obtained.

[0029] Figure 1 This is the polarization curve of the cold-rolled plate measured in the PEMFC cathode environment, indicating that the corrosion current density is 4.336×10 -7 A / cm 2 .

[0030] Figure 2 This is the grain boundary characteristic distribution diagram of this example, indicating that the proportion of its low ∑CSL grain boundaries reaches 68.81%.

[0031] Example 2

[0032] The 316L stainless steel plate was homogenized at 1180℃ for 1h, kept at 1150℃ for 1h and then water quenched to obtain a single-phase austenite structure.

[0033] A two-roll rolling mill is used to perform multiple passes of unidirectional cold rolling on the stainless steel plate, wherein the cold rolling deformation of each pass is 5%, and a cold-rolled plate with a total cold rolling deformation of 50% is obtained;

[0034] Figure 3 This is the polarization curve of the cold-rolled plate measured in the PEMFC cathode environment, indicating that the corrosion current density is 1.782×10 -7 A / cm 2 .

[0035] Figure 4 This is the grain boundary characteristic distribution diagram of this example, indicating that the proportion of its low ∑CSL grain boundaries reaches 71.57%.

[0036] Example 3

[0037] The 316L stainless steel plate was homogenized at 1150 for 2 h, kept at 1120 °C for 1 h and then water quenched to obtain a single-phase austenite structure.

[0038] The stainless steel plate was subjected to multiple passes of unidirectional cold rolling using a two-roll mill, where the deformation of each pass was 4%, and the cold-rolled plate with a total cold rolling deformation of 45% was obtained; the proportion of low ∑CSL grain boundaries of the obtained stainless steel reached 70.23%, and the corrosion current density was 3.218×10 -7 A / cm 2 .

[0039] Comparative Example 1

[0040] This comparative example is a situation where the cold rolling deformation is out of the control range, resulting in the proportion of low ∑CSL grain boundaries not meeting the requirements of the invention patent.

[0041] The 316L stainless steel plate was homogenized at 1150℃ for 2h, kept at 1120℃ for 1h and then quenched with water to obtain a single-phase austenite structure.

[0042] A two-roller mill is used to perform multiple passes of unidirectional cold rolling on the stainless steel plate, wherein the cold rolling deformation of each pass is 3%, and a cold-rolled plate with a total cold rolling deformation of 30% is obtained;

[0043] Figure 5 This is the polarization curve of the cold-rolled plate measured in the PEMFC cathode environment, indicating that the corrosion current density is 2.348×10 -6 A / cm 2 .

[0044] Figure 6 This is the grain boundary characteristic distribution diagram of this example, indicating that the proportion of its low ∑CSL grain boundaries reaches 60.39%.

[0045] Comparative Example 2

[0046] This comparative example is a case where martensite appeared.

[0047] The 316L stainless steel plate was homogenized at 1180℃ for 3h, kept at 1150℃ for 1h and then water quenched to obtain a single-phase austenite structure.

[0048] A two-roller mill is used to perform multiple passes of unidirectional cold rolling on the stainless steel plate, wherein the cold rolling deformation of each pass is 5%, and a cold-rolled plate with a total cold rolling deformation of 60% is obtained;

[0049] Figure 7 This is the polarization curve of the cold-rolled plate measured in the PEMFC cathode environment, indicating that the corrosion current density is 5.338×10 -6 A / cm 2 .

[0050] Figure 8 This is the grain boundary characteristic distribution diagram of this example, indicating that the proportion of its low ∑CSL grain boundaries reaches 50.75%.

[0051] Fig. 9 The transmission electron microscope image and the corresponding electron diffraction spots of this embodiment show the presence of martensite.

Claims

1. A method for improving the corrosion performance of 316L stainless steel in a PEMFC cathode environment, characterized by: The 316L stainless steel plate was homogenized and water quenched to obtain a single-phase austenite structure. Then, multiple passes of unidirectional cold rolling were used to achieve a low ∑CSL grain boundary ratio of 68.81%-71.57% in the stainless steel cold-rolled plate, making its corrosion current density in the PEMFC cathode environment 4.336×10 -7 -1.782×10 -7 A / cm 2 .

2. A method for improving the corrosion performance of 316L stainless steel in a PEMFC cathode environment as claimed in claim 1, characterized in that: The homogenization and water quenching treatment is to homogenize the 316L stainless steel plate at 1120-1180° C. for 1-3 hours, keep it at 1100-1150° C. for 1-2 hours, and then water quench or oil quench it.

3. A method for improving the corrosion performance of 316L stainless steel in a PEMFC cathode environment as claimed in claim 1, characterized in that: The multi-pass unidirectional cold rolling is to cold roll the stainless steel plate with a two-roll rolling mill, wherein the deformation of a single pass is 3-5%, and the cold rolled plate with a total cold rolling deformation of 40-50% is obtained.

Images