Metallographic etchant suitable for nickel-molybdenum alloy and etching method

Abstract

The invention discloses a metallographic etchant suitable for nickel-molybdenum alloy and an erosion method. The metallographic etchant comprises the following components in parts by mass: 10-25 parts of 36-38% hydrochloric acid, 10-20 parts of phosphoric acid, 15-25 parts of methanol, 10-15 parts of p-toluenesulfonic acid, 10-20 parts of diphenyl glycolic acid and 20-30 parts of water. The metallographic etchant provided by the invention can be used for carrying out electrolytic corrosion on nickel-molybdenum alloy and achieves the technical effect of clear grain boundary and carbide in a metallographic structure.

Description

technical field [0001] The invention relates to a metallographic etchant and a method, in particular to a metallographic etchant and an etching method suitable for nickel-molybdenum alloys. Background technique [0002] Nickel-based corrosion-resistant alloys, the main alloying elements are copper, chromium, molybdenum, etc., have good comprehensive properties, can resist various acid corrosion and stress corrosion, and are used to manufacture various corrosion-resistant parts. Among them, the corrosion resistance of nickel-molybdenum alloy is stronger than that of conventional nickel-copper alloy (such as Monel alloy) and nickel-chromium alloy, and can withstand the corrosion of most non-oxidizing organic acids and organic compounds. For example, it can solve 70 HCl solution in all concentration ranges at -100°C, HCl wet gas has corrosion problems on the pipe wall, and it still exhibits ideal corrosion resistance under the condition of boiling point sulfuric acid below 60%,...

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Problems solved by technology

This step is especially important, the metallographic structure cannot be observed in the microscope, or the structure is blurred if the composition or ratio of the corrosive solution is wrong

[0005]Based on the corrosion resistance of the above-mentioned nickel-molybdenum alloys to non-oxidizing strong acids and intolerance to oxidizing strong acids, nickel-molybdenum alloys were treated with conventional etchants or electrolytic methods. When the alloy is subjected to corrosion treatment, the ideal corrosion effect is often not obtained, or excessive corrosion affects the observation of grain boundaries or carbides

[0006]Patent CN104451851A provides an electrolytic corrosion agent that exhibits the metallographic structure of nickel-based corrosion-resistant alloys, mainly using oxalic acid and glycerin as the main corrosion agents, but in its actual operation, the main Applied to nickel-chromium alloys, the corrosion effect on nickel-molybdenum alloys is not good, and it is easy to cause difficult observation of grain boundaries

[0007]CN110174296A provides a method for displaying carbides in the metallographic structure of nickel-based alloys, using hydrochloric acid aqueous solution, pure bromine / methanol mixed solution, sodium lauryl sulfate Aqueous solution, three-step treatment to display carbides, but more steps are required, and pure bromine is volatile and corrosive, and is not easy to operate, and nickel-molybdenum alloy has good durability to hydrochloric acid, and the treatment effect on nickel-molybdenum alloy is not good. good

[0008]At present, there are mainly methods for treating nickel-molybdenum alloys, which use acidic solutions such as aqua regia, sulfuric acid, nitric acid, hydrogen peroxide, perchloric acid or hydrogen fluoride to etch, but strong Oxidizing acids are too corrosive to metals, which can easily lead to excessive corrosion, poor metallographic clarity, and difficult to distinguish structures; at the same time, corrosive agents containing perchloric acid and hydrogen fluoride are too dangerous, which is harmful to the personal safety and health of operators. will cause harm

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