TW201631179A - Germanium-bearing ferritic stainless steels - Google Patents

Abstract

A kind of germanium-bearing ferritic stainless steels that are made from a raw material of a ferritic stainless steel with small amounts of germanium; while the ferritic stainless steels are principally with main constituents of iron and chromium; iron and chromium and small amounts of germanium all together they make a ferritic stainless steels. The said germanium-containing ferritic stainless steels made above, after made and analyzed, show that the addition of small amounts of germanium improves the inert film formation and meanwhile stabilizes the film, which improves the ability of film repairing, and thus increases the corrosion resistance, and most importantly it changes the pitting corrosion behavior into the general corrosion mode in chloride solution. The said germanium-containing ferritic stainless steels have a breakthrough in applications.

Description

Iron-containing stainless steel

The invention relates to a stainless steel containing strontium ferrite, in particular to a strontium-rich ferro-iron stainless steel prepared by using ferrite-grained stainless steel as a base material and adding a small amount of strontium.

In the development of industrial technology, metal has become an indispensable and important material, including daily necessities, tools and facilities. However, as long as it is a metal material, it will face the problem of aging and deterioration caused by corrosion in the use environment, resulting in deterioration of properties, which not only causes inconvenience in use, but also causes serious environmental pollution and accidents, which threatens the safety of the public.

In order to reduce the loss of metal corrosion and increase the corrosion resistance of the alloy, it becomes an important issue. Industrially common methods include stainless steel using resist, surface coating, anode protection, and cathodic corrosion protection. The fundamental way is to use stainless steel to face the corrosive environment. Stainless steel has developed many different branches due to the different requirements of use and the use of stainless steel with different properties in different environments.

If it is classified by the difference of the added elements, it is a change of the content of different nickel-chromium alloy elements. The classification list can be divided into four types: chromium, chrome-nickel, chrome-nickel-manganese and low-chromium. The characteristics are as follows: (1) Chromium: 400 series, nickel-free or nickel-containing less than 2.5 wt%, including Ma Tian loose iron stainless steel and fat iron stainless steel. (2) Chromium-nickel system: 300-series Worstian iron stainless steel and 600-series precipitation-hardened stainless steel. The Worstian iron structure, which is stabilized by the addition of nickel, is the most common stainless steel on the market. (3) Chromium-nickel-manganese system: The 200-series is mainly used to replace nickel in the 300 series with cheap manganese, which is another cheaper Worthite iron stainless steel. (4) Low-chromium system: 500 series is the main one, and the chromium content is only 4 to 6 wt%. In fact, it cannot be called stainless steel, and its price is low, which is mainly used in the petrochemical industry.

However, there are many different ways to classify stainless steel. If classified by organizational structure, they can be divided into five categories: Worth Iron, Fertilizer Iron, Matian Iron, Precipitation Hardening and Duplex Stainless Steel. The alloy content of stainless steel has different ratios depending on the type, which makes the corrosion resistance and mechanical properties different. Therefore, it is very important to clarify the influence of the addition of alloying elements on the properties of stainless steel, such as chromium and nickel. Increased corrosion resistance; the addition of niobium and titanium can reduce intergranular corrosion, and the addition of aluminum enhances mechanical properties.

Common stainless steel is mainly based on Worthfield iron-based stainless steel containing a large amount of nickel. Nickel is an FCC phase stabilizer. By adding nickel, stainless steel can be converted into a FCC structure with better mechanical properties. Increased use. For example, 304 stainless steel can be used in almost any environment due to its high corrosion resistance, high ductility and good weldability. However, due to the high price of nickel, coupled with the increasing output of stainless steel, the demand for nickel in the world has risen sharply. It is easy to cause the price of nickel to influence the trend of stainless steel cost and sales. Therefore, in recent years, research on stainless steel has gradually changed to other trace elements, replacing nickel, and it is expected to have high corrosion resistance and better welding and processing without adding nickel, at a lower cost. Formability.

Therefore, the selected trace elements must have a lower cost and can obtain better characteristics than the addition of nickel, such as having high corrosion resistance, and better welding and formability, which should be the best. solution.

The invention relates to a stainless steel containing strontium ferrite, which is made of ferrite iron stainless steel as a base material, and is added with a trace amount of strontium to prepare a stainless steel containing strontium ferrite.

The invention relates to a strontium-containing granulated iron stainless steel, which is characterized in that it can promote the formation of a passivation film, improve the stability of the passivation film, improve the reliability of the passivation film, and improve the alloy. Corrosion resistance, and the ability to convert the corrosion mechanism in the chloride ion-containing solution into uniform corrosion.

The invention relates to a strontium-containing granulated iron stainless steel, and the prepared bismuth-containing granulated iron stainless steel material is immersed in sodium chloride to convert the corrosion phenomenon into uniform corrosion.

The above-mentioned bismuth-containing granulated iron stainless steel can be obtained by forming a raw material into a slag-containing granulated iron stainless steel, and the composition of the raw material comprises: 15 - 25 wt% chromium, 0.1 wt% manganese, 0.12 wt. Between % and 0.1% to 1.2 wt% (where the trace amount of lanthanum may be 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%, 0.6 wt%, 0.7 wt%, 0.8 wt%) %, 0.9 wt%, 1 wt%, 1.1 wt% or 1.2 wt%) and the remaining weight percent of iron.

More specifically, the raw material has a cerium content of 0.1 to 0.3 wt%.

More specifically, the raw material has a cerium content of 0.3 to 0.8 wt%.

More specifically, the raw material has a cerium content of 0.8 to 1.2 wt%.

More specifically, the bismuth-containing iron-iron stainless steel is uniformly corroded after being immersed in a sodium chloride solution.

Other details, features, and advantages of the present invention will be apparent from the following description of the preferred embodiments.

As shown in Fig. 1, since the gluten-free granulated iron of the present invention is based on 430 stainless steel, iron (Fe), chromium (Cr), manganese (Mn), bismuth (Si) are the main constituent elements, and After the addition of bismuth (Ge) (the main component is as shown in Fig. 2), the above-mentioned raw materials are melt-formed into the slag-containing granulated iron stainless steel material, and the raw material must be placed in a vacuum arc melting furnace before the melting method. After the copper mold is 101 and covered with the cover of the vacuum arc melting furnace, the cavity of the evacuated vacuum arc melting furnace is evacuated to 2.4 x 10 ^-2 torr, then pure nitrogen is introduced to 8 torr, and finally the pumping is repeated. After three times of vacuum and nitrogen flow, the vacuum arc melting furnace can be used to start smelting 102;

In a vacuum arc melting furnace, the pure raw material is melted uniformly by a vacuum arc, and then cooled and solidified by a water-cooled copper mold to form a bowl-shaped test piece, and then the test piece is turned over and then smelted four times until the alloy composition is confirmed. It has been completely melted and uniformly mixed 103. Finally, the cavity is vacuumed, and the ingot is taken out, that is, the cast state of the CS alloy, and then the cutting and grinding treatment is performed to form the test piece 104 containing the slag-fertilized iron stainless steel material.

Thereafter, in order to reduce the influence of voids and trace segregation in the alloy, the test piece containing the slag-fertilized iron stainless steel material was heat-treated at 1100 °C. Before the heat treatment, the smelted cast test piece is sealed in a quartz tube, and heated continuously to 1100 ° C at a heating rate of 4.5 ° C per minute, and then held for 6 hours. After the time is up, the quartz sealed tube is taken out for water quenching treatment. After the temperature of the test piece in the sealed tube is lowered to room temperature, the test piece is taken out by breaking the tube, which is the homogenized test piece of the CS alloy.

The test piece of the ruthenium-containing granulated iron stainless steel material of the present invention is added with Cu-Sn by linear polarization scanning, impedance spectrum method, cyclic voltammetry, electrochemical experiment of open circuit potential method and different corrosion solution tests. The corrosion characteristics of the CS alloy with Ge were investigated. Then, the composition analysis of the alloy immersion test solution was carried out by optical microscopy OM inspection microstructure and inductively coupled plasma ICP, and X-ray photoelectron spectrum XPS and Auger electron spectrometer AES were used. The structure and composition analysis of the alloy passivation film were carried out. In addition, in addition to the test piece containing the ruthenium-rich granulated iron stainless steel material of the present invention, the present invention further relates to the data of the conventional addition of Cu and Sn, as shown in FIG. 3, for simultaneous analysis to compare the trace addition of Ge and The difference between Cu and Sn was added in a small amount.

First, the corrosion test was carried out with a sulfuric acid solution, and the following results were obtained: (1) Linear polarization method: (a) It can be seen from Fig. 4A and Fig. 4B that after homogenization, with the addition of Cu-Sn, the corrosion current density There is no obvious trend. Similarly, there is no obvious trend in the critical current density after homogenization, which shows that the degree of corrosion cannot be effectively reduced after homogenization in terms of the current density of the active region. However, the passivation current density can be effectively reduced after homogenization, which means that the homogenization has a significant effect on the density of the passivation film for the addition of Cu-Sn CS alloy. (b) It can be seen from Fig. 5A and Fig. 5B that after homogenization, the corrosion current density decreases remarkably with the addition of Ge. Similarly, the critical current density also shows a significant downward trend after homogenization. The passivation current density can also be effectively reduced after homogenization. The above results show that the addition of Ge to the CS alloy can increase the corrosion resistance by reducing the corrosion current density before the alloy is passivated. (c) It can be seen that after homogenization, the addition of Cu-Sn CS alloy has no obvious trend in the parameters of the active region, and the passivation current density is significantly improved. For the addition of Ge CS alloy, the corrosion resistance of the active region or the passivation region can be significantly improved, and the CS212Ge reduction effect is most remarkable. (2) Impedance spectrum method EIS: (a) Impedance spectrum method is an electrochemical tool commonly used for corrosion detection in recent years. The surface of the passivation layer can be evaluated by simulation software, and the change of corrosion characteristics can be understood. (b) After analysis by the impedance spectrum method, the CS alloy passivation film belongs to a single layer film, and the Fe ions are strongly dissolved. As the addition of Cu-Sn increases, the thickness of the passivation film decreases and the impedance value decreases. As the addition of Ge increases, the thickness of the passivation film decreases but the impedance value becomes larger, and the structure of the alloy passivation film is affected. The CS alloy passivation film after the addition of Ge is relatively slow to form. (3) Cyclic voltammetry: (a) The ability of CS alloy to inhibit and repair pores in 0.1 M sulfuric acid was investigated by cyclic voltammetry. First, from the area of the hysteresis loop, the negative hysteresis loop area and the amount of trace addition are compared as a graph. As shown in Fig. 6, it is a schematic diagram of the negative hysteresis loop area of the CS alloy with the micro-addition variable, which shows whether Cu-Sn is added or not. Or the more the amount of Ge added, the negative hysteresis ring area will increase first and then decrease. (b) It can be seen that the CS alloy added with Cu-Sn or Ge belongs to the negative hysteresis loop, which indicates that it is less affected by pitting corrosion in the sulfuric acid solution, and the passivation film has good repairing ability. (4) Open circuit potential method: (a) Add Cu-Sn homogenized CS alloy. As shown in Fig. 7, the CS200 can remain in the passivation interval after 18,000 seconds of immersion test, showing at low concentration (0.1 M) The passivation film is not easily broken under sulfuric acid corrosion environment and has good stability. However, after the addition of Cu-Sn CS alloy, the potentials entered the active region at a nearly vertical angle with a soaking time of less than 5000 seconds, indicating that the stability of the passivation film decreased. With the increase of Cu-Sn content, the time of passivation film collapse is not more than 1500 seconds, and there is no obvious trend with the increase of the addition amount. The above results show that the addition of Cu-Sn has a detrimental effect on the passivation film of the CS alloy in a low concentration (0.1 M) sulfuric acid corrosion environment. (b) Adding a homogenized CS alloy of Ge, as shown in Fig. 8, in a (0.1 M) low-concentration sulfuric acid corrosive environment, the CS alloy potential can be maintained above the passivation zone after 18000 seconds, showing (0.1 M) The corrosion strength of low concentration sulfuric acid is still insufficient to destroy the passivation film of CS alloy added with Ge. Therefore, as the content of added Ge increases, no tendency is observed for the stability of the passivation film. (c) It can be seen that the addition of Cu-Sn has an adverse effect on the stability of the passivation film in a low-concentration sulfuric acid environment. In the high-concentration sulfuric acid, the CS200 itself is not resistant to the corrosion of a high-concentration sulfuric acid environment. Adding Cu-Sn does not reveal a clear trend. The addition of Ge in the low concentration of sulfuric acid is because the passivation film does not collapse, so there is no obvious trend. For the high concentration sulfuric acid environment, the effect of adding Ge on the stability of the alloy passivation film can be clearly seen. (5) Metallographic behavior after corrosion: (a) When Cu-Sn is added to the CS alloy, the corrosion phenomenon occurs rapidly and is quite obvious. As more Cu-Sn is added, the local corrosion is more serious. (b) When the addition of Ge to the CS alloy, there is no obvious corrosion phenomenon, and only the pores have a slight change trend. Among them, the surface of the CS203Ge alloy is the most complete, but no significant difference is observed from the 120-minute immersion test. (6) Comparison of ICP components before and after immersion: (a) Figures 9 and 10 show a comparison of the solution concentration of the CS alloy after immersion in a 0.1 M sulfuric acid solution with the concentration of the original alloy component. The ratio of the components in the cross-reference table shows that the CS alloy is a mechanism of uniform corrosion, but the corrosion resistance of the chromium oxide in the passivation film is better than that of the iron oxide. With the increase of trace addition, most of them show a phenomenon of uniform corrosion, and there is no obvious phenomenon of selective corrosion, so it is impossible to provide a comparison of the effects of corrosion after micro-addition. (b) By comparison of the relative amounts of dissolved, it can be found that the CS alloy after adding Ge has better corrosion resistance than the addition of Cu-Sn, and can protect the dense chromium oxide film from corrosion damage. (7) ESCA and AES passivation film analysis: (a) The results of full-spectral scanning by chemical analysis electron spectroscopy (ESCA) show that the CS alloy has enhanced the signal intensity of Fe and Cr after a slight addition. The trend, other elements have no obvious trend. After chemical shift analysis, the main oxides of the alloy passivation film are Fe ₃ O ₄ , FeO/Fe ₂ O ₃ , Cr ₂ O ₃ , CuO, SnO ₂ , GeO ₂ . The thickness variation of CS alloy passivation film decreases with the increase of Cu-Sn content. With the increase of Ge content, the decreasing trend is more obvious. It shows that the micro-addition will reduce the thickness of the passivation film and the structure of the passivation film of the alloy. Change (tight or loose). (b) The nanometer-level Auger electron spectrometer (AES) can scan the distribution of elemental distribution in the passivation film with thickness. It can be found that the passivation film thickness curve of CS203Ge decreases sharply at the beginning, and with the addition The more the Ge content, the more the thickness of the passivation film drops, indicating that the passivation film changes structure due to the addition of Ge. From this, it is understood that when Ge is added, the thickness of the CS alloy passivation film is lowered.

Corrosion test with sodium chloride solution can obtain the following results: (1) According to the linear polarization method, the addition of Cu-Sn to the CS alloy has no significant effect on the corrosion resistance; while the addition of Ge to the CS alloy causes cross-pressure. The increase, the pitting potential increases, the corrosion current density decreases, and the passivation current density decreases. It shows that the addition of Ge can improve the corrosion resistance of the CS alloy. (2) According to the impedance spectrum method, there is no obvious tendency for the CS alloy to increase with the addition of Cu-Sn; the addition of Ge to the CS alloy can increase the impedance of the passivation film, and when more than a certain amount of Ge is added, ions will diffuse. (3) According to the cyclic voltammetry method, the CS alloy exhibits a phenomenon of positive hysteresis, which shows pitting corrosion and poor repair ability of the passivation film. With the increase of Cu-Sn addition, the repair ability of CS alloy passivation film is deteriorated; with the increase of Ge addition, the repair ability of CS alloy passivation film is better. (4) According to the ICP component analysis of inductively coupled plasma method before and after immersion, CS alloy is a type of selective corrosion, which begins with corrosion of iron oxide. It can be seen from Fig. 11 and Fig. 12 that the concentration of the solution after the CS alloy is immersed in a 0.1 M sodium chloride solution is compared with the concentration of the original alloy component. The ratio of the components in the cross-reference table can be found that when Cu-Sn is added, Cu becomes one of the main targets of corrosion attack in CS alloy, and there is obvious corrosion and dissolution phenomenon, and Sn is not obviously corroded, which means adding Cu to chlorine. Corrosion in sodium has an adverse effect. When Ge is added, the corrosion phenomenon of CS alloy is transformed into uniform corrosion phenomenon. The selective corrosion mainly based on iron oxide is not obvious, which means that the addition of Ge will change the corrosion mechanism of alloy passivation film in sodium chloride solution. .

Corrosion test with sodium hydroxide solution can obtain the following results: (1) According to the linear polarization method, after adding Cu-Sn to CS alloy, corrosion resistance can be increased by reducing critical current density and corrosion current density. . For the addition of Ge, in addition to reducing the current density of the active region, the trend of decreasing the passivation current density and increasing the actual passivation interval is more obvious, indicating that the addition of Ge slightly improves the corrosion resistance of the CS alloy in sodium hydroxide solution. Effect. (2) According to the impedance spectrum method, the corrosion resistance of CS alloy itself is good in sodium hydroxide environment. With the increase of Cu-Sn addition, the impedance of passivation film slightly increases. With the increase of Ge addition, the impedance of passivation film is improved. There is a clear upward trend.

After the corrosion test of the above three solutions, it can be known that in sulfuric acid, both Cu-Sn and Ge can inhibit the corrosion of the active region, but the addition of Cu-Sn has an adverse effect on the passivation film, and the addition of Ge can change the passivation film. Structure, promote the formation of passivation film and improve the stability of passivation film; in the pitting corrosion environment of sodium chloride, the trend of adding Cu-Sn is not obvious, adding Ge can change the corrosion mechanism, and the passivation film repair ability is better; In sodium, both Cu-Sn or Ge can slightly improve the corrosion resistance of the alloy.

The advantages of the present invention are as follows: 1. The invention is based on a fermented granular iron stainless steel material, mainly based on iron, chromium, manganese,矽 is the main constituent element, and after adding a small amount of lanthanum, the raw materials are mixed to prepare the strontium-containing granulated iron stainless steel material. 2. After analyzing the cerium-containing granulated iron stainless steel material of the present invention, it can be known that after the micro-addition of strontium The system has the characteristics of promoting the formation of a passivation film, improving the stability of the passivation film, improving the repairing ability of the passivation film, improving the corrosion resistance of the alloy, and converting the corrosion phenomenon into uniform corrosion. 3. The cerium-containing granulated iron stainless steel material of the present invention can be transformed into uniform corrosion after being immersed in sodium chloride. This phenomenon is a breakthrough for the treatment of corrosion in the industry.

The present invention has been disclosed in the above embodiments, and is not intended to limit the present invention. Any of those skilled in the art can understand the foregoing technical features and embodiments of the present invention without departing from the invention. In the spirit and scope, the scope of patent protection of the present invention is subject to the definition of the claims attached to the present specification.

no

[Fig. 1] Fig. 1 is a schematic view showing the preparation process of the bismuth-containing granulated iron stainless steel of the present invention. [Fig. 2] is a schematic view showing the alloy composition of the bismuth-containing granule iron stainless steel of the present invention. [Fig. 3] Schematic diagram of alloy composition of a ferrite-grained stainless steel containing copper and tin and a preparation method thereof. [Fig. 4A] is a schematic diagram showing the polarization curves of homogenized CS200 + Cu-Sn in 0.1 M sulfuric acid using a ferrite-rich stainless steel containing copper and tin and a preparation method thereof. [Fig. 4B] is a schematic diagram showing the polarization curve parameters of homogenized CS200 + Cu-Sn in 0.1 M sulfuric acid using a ferrite-rich stainless steel containing copper and tin and a preparation method thereof. [Fig. 5A] is a schematic diagram showing the polarization curve of homogenized CS200 + Ge of ruthenium-containing granulated iron stainless steel in 0.1 M sulfuric acid. [Fig. 5B] is a schematic diagram showing the polarization curve parameters of homogenized CS200 + Ge of ruthenium-containing granulated iron stainless steel in 0.1 M sulfuric acid. [Fig. 6] is a schematic diagram showing the change of the hysteresis area of the homogenized CS alloy containing the bismuth-fermented iron-iron stainless steel according to the present invention. [Fig. 7] is a schematic diagram showing the results of an open circuit potential method of homogenizing CS200 + Cu-Sn in 0.1 MH ₂ SO ₄ using a ferrite-rich stainless steel containing copper and tin and a preparation method thereof. [Fig. 8] Fig. 8 is a schematic diagram showing the results of an open circuit potential method of homogenizing CS200 + Ge of the present invention containing 0.1 MH ₂ SO ₄ . [Fig. 9] is a schematic diagram showing the comparison of ion concentrations in a sulfuric acid solution of a copper-added stainless steel containing copper and tin and a preparation method thereof. [Fig. 10] Fig. 10 is a schematic view showing the comparison of ion concentrations in a sulfuric acid solution of a CS alloy containing Ge in a ruthenium-containing granular iron stainless steel. [Fig. 11] is a schematic diagram comparing the ion concentration of a Cu-Sn-added CS alloy in a sodium chloride solution using a ferrite-rich stainless steel containing copper and tin and a preparation method thereof. [Fig. 12] Fig. 12 is a schematic view showing the comparison of ion concentrations in a sodium chloride solution of a Ge alloy containing Ge of the ruthenium-containing granular iron stainless steel of the present invention.

Claims (5)

An iron-containing stainless steel containing strontium fertilizer, which is made of a raw material of iron-containing stainless steel containing bismuth, the composition of the raw material comprises: 15 - 25 wt% chromium, 0.1 wt% manganese, 0.12 wt % of 矽, between 0.1 and 1.2 wt% and the remaining weight percentage of iron. The bismuth-containing granulated iron stainless steel according to claim 1, wherein the raw material has a cerium content of 0.1 to 0.3 wt%. The bismuth-containing granulated iron stainless steel according to claim 1, wherein the raw material has a cerium content of 0.3 to 0.8 wt%. The bismuth-containing granulated iron stainless steel according to claim 1, wherein the raw material has a cerium content of 0.8 to 1.2 wt%. The glutinous-containing granulated iron stainless steel according to claim 1, wherein the bismuth-containing granulated iron stainless steel material is uniformly immersed in a sodium chloride solution to cause uniform corrosion.