Original austenite grain boundary corrosion method of martensitic stainless steel for steam turbine bolt

Abstract

The invention discloses an original austenite grain boundary corrosion method of martensitic stainless steel for a steam turbine bolt. The method comprises the following steps of preserving heat of the martensitic stainless steel for 2Cr11Mo1NiWVNbN steam turbine bolt at 970-1120 DEG C for 30 minutes, performing oil quenching, performing coarse grinding, fine grinding, polishing and ultrasonic cleaning, and blow-drying by using a blower to obtain a metallographic sample with a bright and scratch-free detection surface; the container containing the metallographic corrosive agent being placed in a constant-temperature water bath kettle at the room temperature, the test sample being placed in the metallographic corrosive agent with the detection face facing upwards, and the test sample being heated to 70-80 DEG C along with the water bath kettle and then kept at the constant temperature for 30-35 min; removing surface corrosion dirt by using an oxalic acid aqueous solution; and washing and blow-drying. By means of the method, the original austenite grain boundary of the martensitic stainless steel for the 2Cr11Mo1NiWVNbN steam turbine bolt can be clearly displayed, the defect that original austenite grains are difficult to clearly display due to the fact that other corrosive agents corrode a martensitic stainless steel matrix and the original austenite grains at the same time can be overcome, the corrosion time is shortened to about 35 min, operation is easy, and the time is saved.

Description

technical field [0001] The invention relates to the technical field of new materials, and more specifically relates to a prior austenite grain boundary corrosion method of martensitic stainless steel used for steam turbine bolts. Background technique [0002] With the continuous improvement of the steam parameters of the steam turbine thermal power generation unit, the performance requirements of the steam turbine high temperature bolts used to connect the cylinder flange and valve flange are getting higher and higher. 2Cr11Mo1NiWVNbN is a new type of martensitic heat-resistant steel developed on the basis of 12% Cr steel. Due to the addition of Nb, V, N and other elements in the steel, the precipitation strengthening effect of the steel is enhanced, and it has higher strength and With good high temperature performance, it is widely used in the flange connection of high parameter steam turbine units. [0003] 2Cr11Mo1NiWVNbN is a new type of martensitic stainless steel used...

AI Technical Summary

Problems solved by technology

In particular, it is worth noting that the etchant composition of this patent includes picric acid, which is now a controlled drug and is no longer suitable for promotion as a generally applicable metallographic etchant composition

Patent CN103983502A discloses a metallographic corrosion method for clearly displaying the original austenite grain boundary of 9-12% Cr heat-resistant steel. The purpose of the original austenite grain boundary in this material

Patent CN107014661A discloses a corrosion method for displaying the original austenite grain boundary of high-nitrogen martensitic stainless steel, but it requires the content of N in the steel to be between 0.25-0.5%, while the content of N element in this material is 0.035-0.065% %, which is far from the patent requirements and therefore does not apply

[0005] It can be seen that there is a lack of etchant and corrosion methods for the prior austenite grain boundary of martensitic stainless steel used for steam turbine bolts in the prior art, and it is urgent to develop a metallographic etchant suitable for this material in order to study the structure and properties of this material. Provide reference for the formulation of heat treatment process

Images