WO2021135226A1

WO2021135226A1 - Method for displaying austenite grains of spring steel

Info

Publication number: WO2021135226A1
Application number: PCT/CN2020/107419
Authority: WO
Inventors: 刘青; 王晨; 王兴宇; 韩延申; 袁桥军; 陈军
Original assignee: 北京科技大学
Priority date: 2019-12-31
Filing date: 2020-08-06
Publication date: 2021-07-08
Also published as: CN110926913A; CN110926913B

Abstract

A method for displaying austenite grains of spring steel. The method comprises the steps of: (1) heating a sample to 850℃ to 900℃ for 10-40 min, then quenching at a cooling rate of complete hardening, after cooling, tempering the sample at 400℃ to 600℃ for 8 h or more, and after cooling with a furnace to 350℃, air-cooling to room temperature; (2) selecting the cross section of a hardened sample in a rolling direction for cutting and inlaying; then grinding with sandpaper, and finally polishing; (3) adding 50 ml of deionized water, 2-2.5g of picric acid, 1.5-2 g of shampoo, 1 g of iron oxide scale produced by a high-speed wire steel rolling mill to a 70℃ water bath beaker, and stirring evenly to prepare an etching solution; and (4) keeping a metallographic sample still in the etching solution for 30-60 s, then taking out the metallographic sample, rinsing with alcohol, drying, and then observing a grain size using a metallographic microscope. The method has a good display effect, it is simple and easy to obtain etching raw materials, and the etching time is short.

Description

Method for displaying austenite grains of spring steel

Technical field

The invention relates to a method for displaying austenite grains, in particular to a method for displaying austenite grains of spring steel.

Background technique

The original austenite grains of the steel directly affect the change of the structure during the subsequent processing. The original austenite grains not only affect the strength of steel, but also have a greater impact on the mechanical properties of materials such as cold brittle transformation and fracture. Therefore, it is very important to accurately display the austenite grains of steel.

Patent application CN201811095252.1 discloses a method for displaying the grain size of spring steel austenite. The method steps are as follows: (1) Put the sample at 850℃～900℃ for 0.5～1h, and then use the fully hardened Quenching at the cooling rate; after cooling, the sample is tempered at 400℃～600C for 1～3h, and cooled to obtain a hardened sample; (2) The hardened sample is selected from the cross section of the rolling direction. Cut and inlay; then grind with metallographic water sandpaper, and finally polish; you can get the metallographic sample; (3) Add 2～3g sodium dodecylbenzene sulfonate to 100ml saturated picric acid solution in the beaker, and stir until After completely dissolving, add 1 to 3 drops of 2 to 5% CuCl ₂ solution to prepare an etching solution; (4) At room temperature, put the metallographic sample in the etching solution for 1 to 3 minutes and then take it out, wash and dry After that, the grain size can be observed with a metallurgical microscope. The tempering holding time is too short, the effect of P, S and other elements in the grain boundary segregation is not obvious, resulting in the insignificant display of the grain boundary, and CuCl ₂ is added to the etchant, and it can react with picric acid in the solution to produce hydrochloric acid and hydrochloric acid. The presence of it is easy to corrode the structure, which is not conducive to the display of original austenite grains.

Patent application CN 201610176121.0 discloses a method for displaying the original austenite grain boundaries of 85Cr2MnMo liner steel, including the following steps: (1) sample preparation; (2) determination of phase transition temperature: the Accm( of 85Cr2MnMo steel is measured by thermal expansion method Cementite and carbides are completely dissolved into austenite) The temperature is 835℃; (3) Quenching treatment: heat the sample to 860℃～920℃, and then quench it into No. 10 engine oil after holding for 60 minutes; (4) Corrosion : Mix 100ml of deionized water, 4g of picric acid, 2g of Seagull brand shampoo and 0.1g of CuCl2.2H2O to make a corrosive, and put it in a 55℃～60℃ water bath for heat preservation; after quenching, it will be ground and polished. Put the sample in the corrosive agent, take it out after eroding for 50-60 seconds, wipe off the reactant on the surface with absorbent cotton dipped in alcohol, rinse it and blow dry. Observation under an optical microscope can clearly show the original austenite grain boundaries of the 85Cr2MnMo liner steel. However, the sample is not tempered after quenching, and the austenite grain boundary of spring steel cannot be corroded.

Patent application CN201010276594.0 discloses an etchant for quickly displaying ultra-fine austenite grains and a thermal etching method. The etchant is composed of saturated picric acid aqueous solution, CuCl2 saturated aqueous solution, HF acid and xylene, and each component corresponds to The volume ratio is 100～200:1～1.5:0.5～1.5:1～2. The thermal etching method is as follows: After the sample is ground and polished, the section is immersed in an etching solution at 60-70°C for thermal etching for 5-15 seconds, and then wiped and dried with absolute ethanol. However, HF acid is added to the etching solution of this method. If it is used to etch spring steel, its microstructure is likely to appear, and the austenite grain boundaries cannot be seen clearly.

Patent application CN 201410255299.5 discloses a metallographic corrosion method that clearly displays the original austenite grain boundaries of 9-12% Cr heat-resistant steel. The method steps are: (1) Cut the sample and use 200#, 600# and 1000# sandpaper is ground sequentially; (2) Use diamond polishing paste to polish the pattern; (3) Put the pattern into a nitric acid aqueous solution with a temperature of 90～110℃ and a volume ratio of 55-65% for erosion; (4) Polish the corroded sample again and then dry it after cleaning with ethanol solution. In this method, the nitric acid in the etching solution has an obvious chemical reaction with the steel matrix, and the spring steel structure is easily eroded, causing serious corrosion of the intragranular structure and inconspicuous display of grain boundaries. Therefore, although this method can make the etching solution contain Fe ³⁺ and play a role in inhibiting the corrosion of the intragranular structure in the steel to a certain extent, it is not suitable for the display of austenite grain boundaries in spring steel.

Summary of the invention

The technical problem to be solved by the present invention is to provide a quick and clear method for detecting and displaying austenite grains of spring steel.

In order to solve the problem of unclear display of grain boundaries and easy erosion of the intragranular structure during the characterization of spring steel austenite grains, the present invention increases the segregation of solute elements on the grain boundaries by controlling the tempering holding time to more than 8h. Improved the display clarity of the spring steel austenite grain boundary; and adding iron oxide scale to the etching agent, which reacts with picric acid to form Fe ³⁺ , Fe ³⁺ will inhibit the corrosion of the intragranular structure, thereby making the spring steel austenite The bulk grain boundaries can be displayed quickly and clearly. The specific technical solutions are:

A method for displaying austenite grains of spring steel includes the following steps:

(1) Heat the sample to 850℃～900℃, and then quench it at a cooling rate of complete hardening; after cooling, temper the sample at 400℃～600℃, cool it to 350℃ with the furnace, and then air-cool to room temperature;

(2) The quenched sample is cut and inlaid with the cross-section in the rolling direction; then it is ground with sandpaper, and finally it is polished;

(3) Add deionized water, picric acid, shampoo, and iron oxide scale to the water bath container, stir evenly, and configure it as an erosion solution, where the weight ratio of picric acid and iron oxide scale is 2:1-2.5:1, The ratio of the added amount of shampoo to the added weight of picric acid is 0.6:1 to 1:1;

(4) The metallographic sample is left standing in the etching solution and then taken out after being etched, washed and dried, and then the grain size can be observed with a metallographic microscope.

Further, in the step (1), the heat preservation time at 850-900°C is 10-40 min, and the tempering time is more than 8 hours.

Further, in the step (3), the temperature of the water bath is 60-80°C.

Further, in the step (4), the erosion time is 30-60s.

Further, in the step (3), the shampoo is Seagull brand shampoo, and the iron oxide scale is iron oxide scale produced by a high-speed wire rolling mill.

Further, in the step (2), the metallographic water sandpaper of 80#, 200#, 400#, 800#, 1000#, 1500# is used in order to grind from coarse to fine.

Further, in the step (2), 2.5um diamond polishing agent is used for polishing.

Further, in the step (4), the metallographic sample is left standing in the etching solution with the side to be tested facing up.

In the experimental scheme of the present invention, excessive addition of iron oxide scale in the etching solution or too small addition of picric acid will cause most of the acid in the etching solution to react with the iron oxide scale, resulting in prolonged erosion time of the austenite grain boundary of the spring steel. Ineffective. Too little addition of iron oxide scale in the etching solution or too much addition of picric acid will result in ^{low Fe 3+} content in the etching solution and strong acidity, which will easily erode the intragranular structure of spring steel, which is not conducive to observing austenite crystals. World. At the same time, the tempering time is not easy to be too short, and the tempering holding time is too short, which causes the effect of P, S and other elements to segregate in the grain boundary to be insignificant, resulting in the unobvious display of the grain boundary. During the erosion process, the polar groups in the shampoo as a wetting agent are adsorbed by the metal surface, and the non-polar groups form a directional arrangement to separate the sample from the picric acid and avoid direct contact between the sample and the picric acid. The erosion process of the matrix plays a role in inhibiting. Therefore, when configuring the corrosive agent, it is necessary to control the amount of shampoo added. Excessive addition of shampoo will cause the erosion process to be extremely slow. Too little shampoo will cause serious erosion of the steel matrix, and no austenite can be seen. Bulk grain boundaries. The adding weight ratio of picric acid and iron oxide scale in the reaction system of the present invention is 2:1-2.5:1, and the adding weight ratio of the shampoo cream to the adding weight of picric acid is 0.6:1 to 1:1. The invention has the characteristics of good display effect, simple and easily available erosion raw materials, short erosion time and the like.

Description of the drawings

The present invention will be further described in detail below in conjunction with the drawings and specific embodiments.

Figure 1 is a metallographic diagram of Example 1 of the present invention after etching;

Figure 2 is a metallographic diagram of Example 2 of the present invention after etching;

Fig. 3 is a metallographic diagram after etching in Comparative Example 1 of the present invention;

Fig. 4 is a metallographic diagram after etching in Comparative Example 2 of the present invention.

Detailed ways

(1) Heat treatment of the sample: Put the sample at 850℃～900℃ for 10～40min, put it into fast-flowing water, after cooling, then temper the sample at 400℃～600℃ for more than 8h , After cooling to 350℃ with the furnace, air cooling to room temperature;

(2) Preparation of the metallographic sample: the quenched sample is cut and inlaid with the cross-section in the rolling direction; then 80#, 200#, 400#, 800#, 1000#, 1500# metallographic water sandpaper are used in sequence Grind from coarse to fine, then polish with 2.5um diamond polishing agent;

(3) The configuration of the corrosive solution: add 50ml deionized water, 2～2.5g picric acid, 1.5～2g Seagull brand shampoo, 1g high-wire steel mill scale iron oxide scale into the 70℃ water bath beaker, mix well, and configure into Erosion fluid

(4) Metallographic corrosion: The metallographic sample is placed in the etching solution for 30-60 seconds and then taken out, washed and dried, and then the grain size can be observed with a metallographic microscope.

Example 1

The detection and display method of the austenite grains of this spring steel is specifically as follows:

The chemical composition of the 55SiCrA sample is (wt): C 0.56%, Si 1.45%, Mn 0.65%, Cr 0.65%, P 0.011%, S 0.007%, and the rest are Fe and unavoidable impurity elements.

(1) Heat the sample to 860°C for 30 minutes and put it into fast-flowing water; after cooling, temper the sample at 550°C for 17 hours, then cool it to 350°C with the furnace and air-cool to room temperature;

(2) Select the cross-section of the hardened sample in the rolling direction to cut and inlay; then use 80#, 200#, 400#, 800#, 1000#, 1500# metallographic water sandpaper to grind from coarse to fine. Finally, use 2.5um diamond polishing agent for polishing;

(3) Add 50ml deionized water, 2.2g picric acid, 1.8g Seagull brand shampoo, 1g high-wire steel mill scale iron oxide scale into the 70℃ water bath beaker, mix it evenly, and configure it into an etching solution;

(4) The metallographic sample is placed in the etching solution for 40 seconds and then taken out, rinsed with alcohol, and then blown dry. As shown in Figure 1, the pattern clearly shows the austenite grain boundaries.

Example 2

The detection and display method of the austenite grains of the spring steel is specifically as follows.

The chemical composition of the 55SiCrA sample is (wt): C 0.55%, Si 1.47%, Mn 0.67%, Cr 0.64%, P 0.012%, S 0.008%, and the rest are Fe and unavoidable impurity elements.

(1) Heat the sample to 860°C for 30 minutes and put it into fast-flowing water; after cooling, temper the sample at 550°C for 13 hours, then cool it to 350°C with the furnace and air-cool it to room temperature;

(3) Add 50ml deionized water, 2.1g picric acid, 2g Seagull brand shampoo, 1g high-wire steel mill scale iron oxide scale into the 70℃ water bath beaker, mix it evenly, and configure it as an etching solution;

(4) The metallographic sample is placed in the etching solution for 45 seconds and then taken out, rinsed with alcohol, and then blown dry. As shown in Figure 2, the pattern clearly shows the austenite grain boundaries.

Comparative example 1

The chemical composition of the 55SiCrA sample is (wt): C 0.55%, Si 1.46%, Mn 0.65%, Cr 0.65%, P 0.011%, S 0.008%, and the rest are Fe and inevitable impurity elements.

(1) Heat the sample to 860°C for 30 minutes and put it into fast-flowing water; after cooling, temper the sample at 550°C for 17h, then cool it to 350°C with the furnace and air-cool to room temperature;

(3) Add 50ml deionized water, 2.2g picric acid, 1.8g Seagull brand shampoo, no iron oxide scale, and stir evenly into a 70℃ water bath beaker to prepare an erosion solution;

(4) The metallographic sample is placed in the etching solution for 40 seconds and then taken out, rinsed with alcohol, and then blown dry. As shown in Figure 3, since no iron oxide scale is added to the etchant, the eroded structure and part of the severely eroded steel matrix seriously affect the observation of austenite grain boundaries, and the austenite grain boundaries cannot be clearly seen.

Comparative example 2

The chemical composition of the 55SiCrA sample is (wt): C 0.55%, Si 1.48%, Mn 0.65%, Cr 0.64%, P 0.012%, S 0.007%, and the rest are Fe and inevitable impurity elements.

(1) Heat the sample to 860°C for 30 minutes and put it into fast-flowing water; after cooling, temper the sample at 550°C for 3 hours, then cool it to 350°C with the furnace and air-cool to room temperature;

(4) The metallographic sample is placed in the etching solution for 45 seconds and then taken out, rinsed with alcohol, and then blown dry. As shown in Figure 4, due to the short holding time of tempering, the segregation of solute elements in the grain boundary is not obvious, and the pattern can only slightly show the austenite grain boundary, which makes it impossible to clearly see the austenite grain boundary.

Claims

A method for displaying austenite grains of spring steel, which is characterized in that it comprises the following steps:

(1) Heat the sample to 850℃～900℃, and then quench it at a cooling rate of complete hardening; after cooling, temper the sample at 400℃～600℃, cool it to 350℃ with the furnace, and then air-cool to room temperature;

(2) The quenched sample is cut and inlaid with the cross-section in the rolling direction; then it is ground with sandpaper, and finally it is polished;

(3) Add deionized water, picric acid, shampoo, and iron oxide scale to the water bath container, stir evenly, and configure it as an erosion solution, where the weight ratio of picric acid and iron oxide scale is 2:1-2.5:1, The ratio of the added amount of shampoo to the added weight of picric acid is 0.6:1 to 1:1;

(4) The metallographic sample is left standing in the etching solution and then taken out after being etched, washed and dried, and then the grain size can be observed with a metallographic microscope.
The method according to claim 1, characterized in that: in the step (1), the holding time at 850-900°C is 10-40 min, and the tempering time is more than 8 hours.
The method according to claim 1, wherein in the step (3), the temperature of the water bath is 60-80°C.
The method according to claim 1, wherein in the step (4), the erosion time is 30-60s.
The method according to any one of claims 1-4, characterized in that: in the step (2), 80#, 200#, 400#, 800#, 1000#, 1500# metallographic water sandpaper is made of coarse Grind until fine.
The method according to any one of claims 1 to 4, characterized in that: in the step (2), 2.5um diamond polishing agent is used for polishing.
The method according to any one of claims 1 to 4, wherein in the step (3), the shampoo is Seagull brand shampoo, and the iron oxide scale is iron oxide scale produced by a high-speed wire rolling mill. .
The method according to any one of claims 1 to 4, wherein in the step (4), the metallographic sample is left standing in the etching solution with the side to be tested facing up.