CN112665954B - Multiphase austenitic stainless steel weld metal metallographic corrosion method - Google Patents
Multiphase austenitic stainless steel weld metal metallographic corrosion method Download PDFInfo
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- CN112665954B CN112665954B CN202011400896.4A CN202011400896A CN112665954B CN 112665954 B CN112665954 B CN 112665954B CN 202011400896 A CN202011400896 A CN 202011400896A CN 112665954 B CN112665954 B CN 112665954B
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Abstract
The invention discloses a metallographic corrosion method for multiphase austenitic stainless steel weld metal, and belongs to the technical field of metallographic corrosion. The method comprises the following operation processes: firstly, preparing a mixed aqueous solution of ferric trichloride, hydrochloric acid and nitric acid, then soaking a sample in the solution for 25-60 s, taking out the sample, washing the sample with water and alcohol in sequence, and drying the sample with hot air. The metallographic corrosion method can clearly display the delta ferrite in the austenitic stainless steel welding seam in a welding state and the decomposition products of the delta ferrite after long-term high-temperature aging, avoid a large amount of the delta ferrite and the decomposition products thereof from falling off in corrosion, provide support for subsequent analysis of the types of the decomposition products of the delta ferrite, have simple corrosion conditions and operation, are easy to quantitatively control and have good reproducibility, and are suitable for metallographic structure corrosion of multiphase austenitic stainless steel welding seam metal containing a small amount of the delta ferrite and the decomposition products thereof.
Description
Technical Field
The invention relates to the technical field of metallographic corrosion, in particular to a metallographic corrosion method for multiphase austenitic stainless steel weld metal.
Background
In the process of melting and welding austenitic stainless steel, when the structural restraint degree is larger, the hot cracking tendency is easy to generate. To prevent cracking during welding, it is generally desirable to form a certain amount of delta ferrite in the weld structure. Because the delta/gamma phase interface energy is lower, and the gamma/gamma interface energy is higher, the formation of a low-melting eutectic liquid film on the interface can be effectively reduced due to the delta ferrite, and the hot cracking tendency in the welding solidification process is reduced. However, the delta ferrite of the austenitic stainless steel welding seam containing the delta ferrite can be decomposed to form M in the high-temperature long-term service process 23 C 6 Carbide and intermetallic compounds with the same sigma phase deteriorate the mechanical property and the corrosion property of weld metal, in order to research the precipitation mechanism of different phases and the influence rule of the precipitation mechanism on the weld metal property, the appearance of the different phases needs to be observed on the metallographic phase, but the existing metallographic corrosive agent is difficult to simultaneously display and distinguish all existing phases due to the existence of multiple phases, so that the metallographic structure observation is disturbed, and a metallographic structure corrosion method suitable for the multiphase austenitic stainless steel weld metal containing a small amount of delta ferrite and decomposition products thereof needs to be developed.
Disclosure of Invention
The invention aims to provide a metallographic corrosion method for multiphase austenitic stainless steel weld metal, which is provided for multiphase austenitic stainless steel weld metal containing a small amount of delta ferrite and decomposition products thereof and can enable the delta ferrite and M in the austenitic stainless steel weld to be in a state of being corroded 23 C 6 Carbides and sigma-phase intermetallic compounds are clearly shown, so that the austenitic stainless steel welding seam containing a small amount of delta ferrite in a welding state is convenient, and the delta ferrite is decomposed to form a stainless steel welding seam containing a small amount of delta ferrite and M after long-term high-temperature aging 23 C 6 And observing the metallographic structure of the stainless steel weld joint of the multi-phase austenitic structure with the same sigma.
In order to realize the purpose, the technical scheme adopted by the invention is as follows:
a metallographic corrosion method for a multiphase austenitic stainless steel weld metal comprises the following steps:
(1) Preparing an etching solution: the etching solution is prepared by mixing ferric trichloride, hydrochloric acid with the concentration of 37wt.%, nitric acid with the concentration of 65wt.% and water according to the weight ratio of (35-45) g: (25-35) ml:20ml: (75-85) ml of the mixture;
(2) Soaking a sample to be corroded in the corrosion solution prepared in the step (1) for 25-60 s; and taking out the sample, washing with water and alcohol in sequence, and drying with hot air.
The invention has the advantages that:
1. by adopting the metallographic corrosion method, the delta ferrite in the austenitic stainless steel weld joint in the welding state and the delta ferrite decomposition product after long-term high-temperature aging can be clearly displayed, the delta ferrite and the decomposition product thereof are prevented from largely falling off in corrosion, and support is provided for the subsequent analysis of the type of the delta ferrite decomposition product.
2. The invention has simple corrosion condition and operation, easy quantitative control and better reproducibility, and can lead the delta ferrite and M in the austenitic stainless steel welding seam 23 C 6 Carbides and sigma-phase intermetallic compounds are clearly shown, and the metallographic structure observation of the multiphase austenitic stainless steel weld metal containing a small amount of delta ferrite and decomposition products of the delta ferrite is facilitated.
Drawings
FIG. 1 is a photograph of metallographic structure of a 316H weld metal in an electroerosive state of welding with a 10% oxalic acid aqueous solution.
FIG. 2 is a photograph of the metallographic structure of the weld metal in the 316H state of electroerosive welding by 10% aqueous solution of potassium hydroxide.
FIG. 3 is a photograph of the metallographic structure of 316H weld metal in a state of corrosion in a solution of 10g of copper chloride, 50ml of hydrochloric acid and 50ml of ethanol at 750 ℃ for 0.5H.
FIG. 4 is a photograph of the metallographic structure of 316H weld metal in an aged state at 750 ℃ for 20H after being corroded by 10g of copper sulfate, 50ml of hydrochloric acid, 5ml of sulfuric acid and 100ml of aqueous solution.
FIG. 5 is a photograph of the metallographic structure of 316H weld metal in a state of Murakami reagent (10 g of potassium ferricyanide +10g of sodium hydroxide +100mL of water) hot-etched in a water bath at 90 ℃ for 20H at 750 ℃.
FIG. 6 is a photograph of the metallographic structure of a 316H weld metal in a corrosion state by the corrosion method of the present invention.
FIG. 7 is a photograph of the metallographic structure of 316H weld metal in an aged state at 750 ℃ for 0.5H, which is corroded by the corrosion method of the invention.
FIG. 8 is a photograph of the metallographic structure of 316H weld metal in an aged state at 750 ℃ for 20H after being corroded by the corrosion method of the invention.
Detailed Description
The invention is described in detail below with reference to the figures and examples.
Comparative example 1:
electrolytic etching was carried out for 20s (electrolytic voltage 5V, current density 0.3A/cm) using a 10% oxalic acid aqueous solution 2 ) And obtaining a metallographic structure photograph of the weld 316H weld metal, as shown in FIG. 1, wherein the delta ferrite falls off in the corrosion process.
Comparative example 2:
electrolytic etching was carried out for 8s (electrolytic voltage 5V, current density 0.3A/cm) using 10% aqueous potassium hydroxide solution 2 ) And obtaining a metallographic structure photo of the weld 316H weld metal in a welded state, as shown in FIG. 2, wherein delta ferrite is stripped off in the corrosion process similarly to FIG. 1.
Comparative example 3:
corroding for 10s by using 10g of copper chloride, 50ml of hydrochloric acid and 50ml of ethanol solution to obtain a 316H weld metal metallographic structure photo in an aging state at 750 ℃ for 0.5H, as shown in figure 3, under the aging conditionPartial decomposition of delta ferrite to M 23 C 6 Wherein M is 23 C 6 And part of delta ferrite falls off in the corrosion process, and the rest delta ferrite remains.
Comparative example 4:
corroding with 10g of copper sulfate, 50ml of hydrochloric acid, 5ml of sulfuric acid and 100ml of aqueous solution for 10s to obtain a 316H weld metal metallographic structure photo of an aged state at 750 ℃ for 20H, wherein all delta ferrite is decomposed into M under the aged condition as shown in figure 4 23 C 6 And sigma phase, where M 23 C 6 And sigma phase are both shed during corrosion.
Comparative example 5:
heat-etching with Murakami reagent (10 g potassium ferricyanide +10g sodium hydroxide + water 100 mL) in water bath at 90 deg.C for 15s to obtain 316H weld metal metallographic structure photograph in aging state at 750 deg.C for 20H, as shown in FIG. 5, when delta ferrite is totally decomposed into M under the aging condition 23 C 6 And sigma phase, where M 23 C 6 During the etching process, the sigma phase is removed and retained.
Example 1:
preparing a mixed aqueous solution (metallographic corrosive solution) of ferric trichloride, hydrochloric acid and nitric acid, which comprises the following specific steps: 40g of ferric trichloride, 30ml of hydrochloric acid with the concentration of 37wt%, 20ml of nitric acid with the concentration of 65wt% and 80ml of water are uniformly mixed to prepare the alloy, then a welded 316H welding seam metal sample is soaked in a metallographic corrosive solution for 50s, and (3) taking out the sample, washing the sample with water and alcohol in sequence, drying the sample with hot air, and taking a metallographic photograph as shown in figure 6, wherein the delta ferrite does not fall off in the corrosion process, so that the delta ferrite in the austenite matrix can be clearly distinguished.
Example 2:
preparing ferric trichloride, hydrochloric acid and nitric acid aqueous solution, wherein the specific proportion is as follows: 40g of ferric trichloride, 30ml of 37wt% hydrochloric acid with the concentration of 30ml, 20ml of 65wt% nitric acid with the concentration of 80ml of water, then soaking a 316H welding seam metal sample in an aging state at 750 ℃/0.5H into the solution for 40s, taking out the sample, then sequentially washing the sample with water and alcohol, drying the sample by hot air, and taking out a metallographic photograph as shown in figure 7, wherein the delta ferrite part is decomposed into M under the aging condition 23 C 6 ，M 23 C 6 And delta ferrite does not fall off in the corrosion process and can be clearly dividedIdentification of M in an Austenitic matrix 23 C 6 And delta ferrite.
Example 3:
preparing ferric trichloride, hydrochloric acid and nitric acid aqueous solution, wherein the specific proportion is as follows: 40g of ferric trichloride, 30ml of 37wt% hydrochloric acid with concentration, 20ml of 65wt% nitric acid with concentration and 80ml of water, then soaking a 316H welding seam metal sample in an aging state at 750 ℃/20H into the solution for 30s, taking out the sample, sequentially washing the sample with water and alcohol, drying the sample by hot air, and taking a metallograph as shown in figure 8, wherein all delta ferrite is decomposed into M ferrite under the aging condition 23 C 6 And sigma phase, M 23 C 6 And the sigma phase does not fall off in the corrosion process, and delta ferrite transformation products in an austenite matrix can be clearly distinguished.
Claims (1)
1. A metallographic corrosion method for multiphase austenitic stainless steel weld metal is characterized by comprising the following steps: the method comprises the following steps:
(1) Preparing an etching solution: the etching solution was prepared by mixing ferric trichloride, hydrochloric acid at a concentration of 37wt.%, nitric acid at a concentration of 65wt.% and water in the following (35-45) g: (25-35) ml:20ml: (75-85) ml of the mixture;
(2) Soaking a sample to be corroded in a corrosive solution for 25 to 60s, taking out the sample, sequentially washing the sample with water and alcohol, and drying the sample by hot air;
the method is suitable for multi-phase austenitic stainless steel weld metal containing a small amount of delta ferrite and decomposition products thereof.
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| CN114594098A (en) * | 2022-03-07 | 2022-06-07 | 国家电投集团河南电力有限公司 | Corrosive agent for detecting sigma phase of austenitic stainless steel and application thereof |
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