CN111426534A - Preparation method of sample for detecting austenite grain size of steel by oxidation method - Google Patents
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Abstract
The invention discloses a preparation method of a sample for detecting the austenite grain size of steel by an oxidation method, which comprises the following steps: (1) taking a sample; (2) polishing the detection surface of the sample; (3) placing the polished test sample in a furnace with the detection surface facing upwards for heat treatment, heating the test sample with the carbon content (mass fraction) not more than 0.35% at 890 +/-10 ℃, heating the test sample with the carbon content (mass fraction) more than 0.35% at 860 +/-10 ℃, preserving heat for 1h, and then quenching in cold water or brine; (4) dropwise adding a hydrochloric acid solution on the detection surface of the heat-treated sample, and after bubbles appear on the surface of the sample, washing and drying the sample by using clear water; (5) polishing the detection surface; (6) and (4) after the etching is carried out by using 15% hydrochloric acid alcohol solution, washing and drying the alcohol solution to be detected. The sample obtained by the method has larger detection area and higher sample preparation success rate.
Description
Technical Field
The invention relates to a preparation method of a sample for detecting the austenite grain size of steel, in particular to a preparation method of a sample for detecting the austenite grain size of steel by an oxidation method.
Background
The direct hardening method has the best detection effect of the austenite grain size of the steel and the simplest and simplest operation, and is the most accurate austenite grain size detection method recognized at home and abroad. The direct hardening method uses supersaturated picric acid solution to erode and display austenite grain size, but picric acid belongs to one type of explosive, and the picric acid cannot be purchased along with the more and more strict national control on toxic explosive products; this results in a limitation in the use of the method in which the hardening method shows austenite grain size. The detection of the austenite grain size of the steel material urgently needs other methods.
The oxidation method specified in GB/T6394-2017 "method for measuring average grain size of metals" is also a widely used method for detecting austenite grains of steel materials, and may become a trend of future methods for detecting austenite grain size. However, when a sample for detecting the austenite grain size by an oxidation method is prepared, the requirements on a grinding angle and a grinding method are high, excessive grinding is easy to cause sample preparation failure, and re-sampling, heat treatment and grinding are needed, so that the detection period is prolonged; in other words, if the sample preparation is successful, the area of the sample capable of displaying the austenite grain size is very limited, and the representativeness of the batch material corresponding to the austenite grain size on the detection surface is greatly reduced.
The prior operation steps for detecting the austenite grain size according to an oxidation method comprise:
i, taking a sample;
II, polishing the detection surface;
III, placing the sample in a furnace with the detection surface facing upwards, heating the sample with the carbon content (mass fraction) of not more than 0.35% at 890 +/-10 ℃ unless otherwise specified, heating the sample with the carbon content (mass fraction) of more than 0.35% at 860 +/-10 ℃, keeping the temperature for 1h, and then quenching in cold water or saline water;
IV, properly inclining the heat-treated sample by 10-15 degrees according to the oxidation condition, lightly grinding the sample by using sand paper, and polishing to remove the iron scale on the detection surface;
and V, after the etching is carried out by using a 15% hydrochloric acid alcohol solution, washing and drying the alcohol solution to be detected.
The current operating procedures have the following problems:
the principle of detecting the austenite grain size by an oxidation method is that the surface of a sample is oxidized when the sample is heated and insulated at high temperature; because the oxidation resistance of the grain boundary is poorer than that of the grain boundary, the austenite grain boundary is preferentially oxidized to form an oxide network at high temperature; along with the prolonging of the heating and heat preservation time, fine austenite grains grow gradually, and an oxide layer on the surface of the sample is thickened continuously to reflect that an oxide network of the austenite grains forms iron scales at the previous moment; the oxide network reflecting the austenite grains at the present moment is a brand new grain boundary which is equivalent to the size of the grown austenite grains in the sample.
The sample for detecting the austenite grain size by an oxidation method only has a layer of oxidized austenite grain boundary surface which is close to the surface iron scale and is thin below the surface iron scale, and the surface can be used as a detection surface of the austenite grain, and in order to ensure that the austenite grain boundary oxidation network can be observed on the detection surface of the sample after grinding and polishing, the following work is required:
before a sample is subjected to oxidation treatment, a detection surface is ground to be flat as much as possible so as to ensure that a surface oxidation layer is on the same plane as much as possible when the detection surface is heated and oxidized;
when the sample is subjected to oxidation treatment, the detection surface faces upwards, and the detection surface of the sample is ensured to be oxidized fully and uniformly;
and III, after the sample is oxidized, removing the iron scale on the surface of the detection surface of the sample, exposing the oxidized part of the austenite grain boundary below the iron scale, and detecting the austenite grain size by observing an oxidation network of the austenite grain boundary. The standard recommended method is that a test sample detection surface is properly inclined by 10-15 degrees according to the oxidation condition, sand paper is lightly ground and polished to remove the iron scale of the detection surface, in the method, the proper inclination of 10-15 degrees is difficult to grasp in manual sample preparation, either the removal degree of the iron scale of the detection surface is not enough, the removal of the iron scale of the detection surface is excessively carried out, a grain boundary oxidation network layer is also removed, or only a small area of the grain boundary oxidation layer is reserved, so that sample preparation failure is caused, once the surface oxidation layer of the oxidation method austenite grain size test sample is ground, the test sample can be re-sampled, heat treated again and ground again, the test period is greatly increased, and a large amount of manpower and material resources are consumed.
A simple and feasible method is needed to be found, and the detection area and the one-time sample preparation success rate of the austenite grain size sample detected by the oxidation method are increased.
Disclosure of Invention
The invention aims to solve the technical problem of providing a preparation method of a sample for detecting the austenite grain size of steel by an oxidation method, wherein the sample obtained by the method has larger detection area and higher sample preparation success rate.
In order to solve the technical problems, the technical scheme adopted by the invention is as follows:
a preparation method of a sample for detecting the austenite grain size of steel by an oxidation method comprises the following steps:
(1) taking a sample;
(2) polishing the detection surface of the sample;
(3) placing the polished test sample in a furnace with the detection surface facing upwards for heat treatment, heating the test sample with the carbon content of not more than 0.35% at 890 +/-10 ℃, heating the test sample with the carbon content of more than 0.35% at 860 +/-10 ℃, preserving heat for 1h, and then quenching in cold water or saline water;
(4) dropwise adding a hydrochloric acid solution on the detection surface of the sample subjected to heat treatment in the step (3), and after the iron oxide scale on the surface of the sample is completely reacted, washing with clear water and drying;
(5) polishing the detection surface of the sample;
(6) and (4) after the etching is carried out by using 15% hydrochloric acid alcohol solution, washing and drying the alcohol solution to be detected.
In the step (2) of the present invention, the test surface of the sample is polished with an abrasive of 3 μm.
The carbon content in step (3) of the present invention means the mass fraction of carbon.
The hydrochloric acid solution in the step (4) of the invention is an undiluted hydrochloric acid solution, and the mass fraction of the hydrochloric acid is 36-38%.
In the step (4) of the invention, when bubbles appear on the surface of the sample, the scale reaction on the surface of the sample is complete.
In the step (5), a polishing agent with the grain size of 3 mu m is adopted to polish the detection surface of the sample.
In the step (4), the iron scale on the detection surface is removed by adopting a hydrochloric acid decomposition method, the process of lightly grinding sand paper inclined by 10-15 degrees is omitted, and then the sample is directly polished, so that the detection area and the one-time sample preparation success rate of the austenite grain size sample detected by an oxidation method are increased.
Reacting hydrochloric acid with iron scale, and controlling the reaction degree of the hydrochloric acid and the surface oxide layer of the sample by emphasis:
Fe2O3+6HCl=2FeCl3+3H2O
Fe3O4+8HCl=FeCl2+2FeCl3+4H2O
Fe+2HCl=FeCl2+H2↑
during the implementation of the test, hydrochloric acid is controlled to completely dissolve the iron oxide layer on the surface of the sample, the austenite grain boundary oxide layer is reserved, bubbles appear on the surface of the dissolution reaction, which indicates that the hydrochloric acid starts to react with the matrix iron, and then the sample is washed by clear water.
The method is suitable for carbon steel and alloy steel with the carbon content of 0.25-0.60%, wherein the carbon content refers to the mass fraction of carbon.
Adopt the produced beneficial effect of above-mentioned technical scheme to lie in:
the hydrochloric acid is adopted to dissolve the iron scale on the detection surface of the sample, so that the iron scale of the whole sample can be accurately stripped, and the detection area of the sample is increased; meanwhile, the sample is directly polished, so that a very thin austenite grain boundary oxide layer is prevented from being worn off in the sample preparation process, and the one-time success rate of sample preparation is improved. On the premise of improving the detection accuracy, the detection period is greatly shortened.
Drawings
FIG. 1 is a gold phase diagram of a sample prepared in example 1
FIG. 2 is a gold phase diagram of the sample prepared in comparative example 1
FIG. 3 is a phase diagram of the gold phase of the sample prepared in example 2
FIG. 4 is a gold phase diagram of the sample prepared in comparative example 2
Detailed Description
The preparation method of the sample for detecting the austenite grain size of the steel by the oxidation method adopts the following process steps.
And (3) process design test: the method comprises the steps of cutting a sample, grinding and polishing the sample, carrying out heat treatment on the sample, removing iron oxide from the sample, polishing the sample, carrying out corrosion on the sample and grading the austenite grain size to execute GB/T6394-2017, wherein a direct hardening method is internationally recognized as the most accurate austenite grain size detection method, and in order to verify the accuracy of the austenite grain size detection of the austenite grain size sample prepared by the method, each case is compared by a direct hardening method.
Example 1: the preparation method of the sample for testing the austenite grain size of the steel by the oxidation method comprises the following specific steps:
(1) sampling from steel with 20 grades, wherein the carbon content in the steel is less than or equal to 0.35 wt%;
(2) polishing the detection surface of the sample by using a 3-micron grinding agent;
(3) placing the polished test sample in a furnace with the detection surface facing upwards for heat treatment, heating at 890 +/-10 ℃, keeping the temperature for 1h, and then quenching in cold water;
(4) the detection surface of the sample subjected to heat treatment in the step (3) is upward, a hydrochloric acid solution is dripped on the detection surface, and after bubbles appear on the surface of the sample, the sample is washed by clear water and dried;
(5) polishing the detection surface of the sample by using a polishing agent with the granularity of 3 mu m;
(6) and (4) after the etching is carried out by using 15% hydrochloric acid alcohol solution, washing and drying the alcohol solution to be detected.
(7) The metallographic microscope detects the austenite grain size to be 8.0 grade, the effective detection area of the sample is about 85 percent, and the sample preparation is successful at one time.
After the oxide layer of the oxidized sample is fully removed, the quenching method adopts supersaturated picric acid solution to corrode and detect the austenite grain size of 8.0 grade, and a gold phase diagram is shown in figure 1.
Comparative example 1: the preparation method of the sample for detecting the austenite grain size of the steel by the oxidation method comprises the following specific steps:
(1) sampling from steel with 20 grades, wherein the carbon content in the steel is less than or equal to 0.35 wt%;
(2) polishing the detection surface of the sample by using a 3-micron grinding agent;
(3) placing the test sample in a furnace with the test surface facing upwards, heating at 890 +/-10 ℃, keeping the temperature for 1h, and then quenching in cold water;
(4) the heat-treated sample is properly inclined by 10-15 degrees according to the oxidation condition, and then is lightly ground by sand paper and polished to remove the iron scale on the detection surface;
(5) and (4) after the etching is carried out by using 15% hydrochloric acid alcohol solution, washing and drying by using alcohol, and waiting to be detected.
(6) And (4) detecting the austenite grain size by a metallographic microscope to be 8.0 grade. The inclination angle of a sample prepared for one time is slightly larger, and the effective detection area of the sample is less than 10%; the effective area of the secondary sample preparation is about 30 percent.
After the oxide layer of the oxidized sample is fully removed, the quenching method adopts supersaturated picric acid solution to corrode and detect the austenite grain size of 8.0 grade, and a gold phase diagram is shown in figure 2.
Example 2: the preparation method of the sample for detecting the austenite grain size of the steel by the oxidation method comprises the following specific steps:
(1) sampling from a steel material with the steel grade of 38MnVS6, wherein the carbon content in the steel is more than 0.35 wt%;
(2) polishing the detection surface of the sample by using a 3-micron grinding agent;
(3) placing the polished test sample in a furnace with the detection surface facing upwards for heat treatment, heating at 860 +/-10 ℃, preserving heat for 1h, and then quenching in saline water;
(4) the detection surface of the sample subjected to heat treatment in the step (3) is upward, a hydrochloric acid solution is dripped on the detection surface, and after bubbles appear on the surface of the sample, the sample is washed by clear water and dried;
(5) polishing the detection surface of the sample by using a polishing agent with the granularity of 3 mu m;
(6) and (4) after the etching is carried out by using 15% hydrochloric acid alcohol solution, washing and drying the alcohol solution to be detected.
(7) The metallographic microscope detects the austenite grain size of 7.5 grades, the effective detection area of the sample is about 90 percent, and the sample preparation is successful at one time.
After the oxide layer of the oxidized sample is sufficiently removed, the quenching method adopts supersaturated picric acid solution to corrode and detect the austenite grain size of 7.5 grade, and a gold phase diagram is shown in figure 3.
Comparative example 2: the preparation method of the sample for detecting the austenite grain size of the steel by the oxidation method comprises the following specific steps:
(1) sampling from a steel material with the steel grade of 38MnVS6, wherein the carbon content in the steel is more than 0.35 wt%;
(2) polishing the detection surface of the sample by using a 3-micron abrasive;
(3) placing the sample in a furnace with the detection surface facing upwards, heating at 860 +/-10 ℃, preserving heat for 1h, and then quenching in saline water;
(4) the heat-treated sample is properly inclined by 10-15 degrees according to the oxidation condition, and then is lightly ground by sand paper and polished to remove the iron scale on the detection surface;
(5) and (4) after the etching is carried out by using 15% hydrochloric acid alcohol solution, washing and drying by using alcohol, and waiting to be detected.
(6) The metallographic microscope detects the austenite grain size of 7.5 grades, the effective detection area of the sample is about 40 percent, and the sample preparation at one time is successful.
After the oxide layer of the oxidized sample is sufficiently removed, the quenching method adopts supersaturated picric acid solution to corrode and detect the austenite grain size of 7.5 grade, and a gold phase diagram is shown in figure 4.
Case counting: randomly extracting 50 batches of steel plates, and comparing the steel plates by adopting the method with a standard recommendation method: the method is adopted to prepare the sample successfully in one time, and the available test areas of the test are all larger than 80% of the test area of the whole sample; by adopting a standard recommendation method, the samples of 23 batches are successfully prepared for one time, the samples of 16 batches are successfully prepared for the second time, the samples of 11 batches are cut again after one time of invalidation, and the effective detection areas of the samples are all less than 50%. The quenching method is used for detection, and the austenite grain size grades detected by the two methods are basically the same.
Claims (5)
1. The preparation method of the sample for detecting the austenite grain size of the steel by the oxidation method is characterized by comprising the following steps of:
(1) taking a sample;
(2) polishing the detection surface of the sample;
(3) placing the polished test sample in a furnace with the detection surface facing upwards for heat treatment, heating the test sample with the carbon content of not more than 0.35% at 890 +/-10 ℃, heating the test sample with the carbon content of more than 0.35% at 860 +/-10 ℃, preserving heat for 1h, and then quenching in cold water or saline water;
(4) dropwise adding a hydrochloric acid solution on the detection surface of the sample subjected to heat treatment in the step (3), and after the iron oxide scale on the surface of the sample is completely reacted, washing with clear water and drying;
(5) polishing the detection surface of the sample;
(6) and (4) after the etching is carried out by using 15% hydrochloric acid alcohol solution, washing and drying the alcohol solution to be detected.
2. The method for preparing the sample for detecting the austenite grain size of the steel by the oxidation method according to claim 1, which is characterized in that: in the step (2), the detection surface of the sample is polished by using an abrasive of 3 μm.
3. The method for preparing the sample for detecting the austenite grain size of the steel by the oxidation method according to claim 1, which is characterized in that: the hydrochloric acid solution in the step (4) is undiluted hydrochloric acid solution, and the mass fraction of the hydrochloric acid is 36-38%.
4. The method for preparing the sample for detecting the austenite grain size of the steel by the oxidation method according to claim 1, which is characterized in that: and (4) indicating that the scale reaction on the surface of the sample is complete when bubbles appear on the surface of the sample.
5. The method for preparing the sample for detecting the austenite grain size of the steel by the oxidation method according to claim 1, which is characterized in that: and (5) polishing the detection surface of the sample by adopting a polishing agent with the granularity of 3 mu m.
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN112525903A (en) * | 2020-11-13 | 2021-03-19 | 东风汽车集团有限公司 | Corrosion display method for austenite grain size of high-strength steel |
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| CN101063189A (en) * | 2006-04-29 | 2007-10-31 | 宝山钢铁股份有限公司 | Hot-rolled fine-grained steel for electrostatic enamel and manufacturing method thereof |
| CN109943765A (en) * | 2019-04-30 | 2019-06-28 | 马鞍山钢铁股份有限公司 | A kind of 800MPa grades of high-yield-ratio cold-rolled biphase steel and preparation method thereof |
| CN110441201A (en) * | 2019-07-30 | 2019-11-12 | 石家庄钢铁有限责任公司 | A kind of method that oxidizing process examines steel autstenitic grain size |
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- 2020-04-14 CN CN202010291483.0A patent/CN111426534A/en active Pending
Patent Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN101063189A (en) * | 2006-04-29 | 2007-10-31 | 宝山钢铁股份有限公司 | Hot-rolled fine-grained steel for electrostatic enamel and manufacturing method thereof |
| CN109943765A (en) * | 2019-04-30 | 2019-06-28 | 马鞍山钢铁股份有限公司 | A kind of 800MPa grades of high-yield-ratio cold-rolled biphase steel and preparation method thereof |
| CN110441201A (en) * | 2019-07-30 | 2019-11-12 | 石家庄钢铁有限责任公司 | A kind of method that oxidizing process examines steel autstenitic grain size |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN112525903A (en) * | 2020-11-13 | 2021-03-19 | 东风汽车集团有限公司 | Corrosion display method for austenite grain size of high-strength steel |
| CN112525903B (en) * | 2020-11-13 | 2022-06-24 | 东风汽车集团有限公司 | Corrosion display method for austenite grain size of high-strength steel |
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