CN115356456A

CN115356456A - Experimental method for determining high-temperature brittleness cause of steel

Info

Publication number: CN115356456A
Application number: CN202210488780.3A
Authority: CN
Inventors: 李智丽; 刘莉; 史文义; 靳燕
Original assignee: Baotou Iron and Steel Group Co Ltd
Current assignee: Baotou Iron and Steel Group Co Ltd
Priority date: 2022-05-06
Filing date: 2022-05-06
Publication date: 2022-11-18

Abstract

The invention discloses an experimental method for determining a high-temperature brittleness cause of steel, which is characterized by comprising the following steps of: the method comprises the following steps: designing the size of a sample of a thermal simulation experiment; 2) Welding thermocouples at the positions of the sample in the length direction L/2 and the width direction W/2; 3) Carrying out a high-temperature thermal simulation test; 4) After the experiment, a V-shaped groove is formed in the L/2 position of the thermocouple welded on the sample in the direction vertical to the length direction, and the depth of the groove is 1.5-2.5mm; 5) Placing the slotted thermal simulation sample in a container containing liquid nitrogen for cooling for more than 15 minutes; 6) Quickly taking out the cooled sample, breaking the sample on a testing machine, and putting the sample into a beaker filled with pure alcohol for standing for 8 to 12 minutes until the temperature of the sample returns to the room temperature; 7) And taking out the dried fracture sample for observing and analyzing the fracture of the scanning electron microscope. The method can obtain perfect fracture morphology, and is convenient for experimenters to carry out fracture scanning electron microscope analysis, thereby judging the reason of high-temperature brittleness of steel products.

Description

Experimental method for determining high-temperature brittleness cause of steel

Technical Field

The invention relates to an experimental method for determining the cause of high-temperature brittleness of steel, which can be used for researching the cause of the high-temperature brittleness of the steel, thereby helping scientific research and production technicians to purposefully take control measures and reducing the quality problem caused by the high-temperature brittleness of the steel, and belongs to the technical field of metal material detection.

Background

Thermal simulation testing machines are used, and experimental and research personnel develop various experimental methods to meet the requirements of material research and field quality improvement. The invention designs a thermal simulation experiment method for detecting the high-temperature brittleness cause of the steel aiming at the high-temperature performance research of the steel, can help scientific research and production technicians to effectively research the high-temperature fracture of the steel, analyze the cause of the brittleness and reduce the quality problem caused by the high-temperature brittleness of the steel.

The high-temperature brittleness of steel is generally researched by performing a series of high-temperature tensile tests on a thermal simulation testing machine and obtaining a high-temperature brittleness temperature interval of the material by measuring the surface shrinkage values of samples at different temperatures. Generally, high-temperature brittleness is caused by weakening of a material grain boundary, such as second phase precipitation, impurity element enrichment and the like on the grain boundary, so that the observation of a sample fracture in a brittleness temperature range is particularly necessary, however, in the actual thermal simulation experiment process, because the sample is easy to ignite and melt at the moment of fracture or is influenced by factors such as high-temperature oxidation caused by the reduction of the vacuum degree of a thermal simulation testing machine, the fracture morphology of a high-temperature tensile sample is easy to damage and cannot be directly observed (see figure 1).

Disclosure of Invention

In order to solve the technical problems, the invention aims to provide an experimental method for determining the high-temperature brittleness cause of steel.

In order to solve the technical problems, the invention adopts the following technical scheme:

the invention relates to an experimental method for determining a high-temperature brittleness cause of steel, which comprises the following steps:

1) The sample sizes for the thermal simulation experiments were designed as follows: h multiplied by w multiplied by L, the units are all mm, wherein h is the thickness of the sample, w is the width of the sample, and L is the length of the sample;

2) Before the thermal simulation test, thermocouples are welded at the positions of the sample in the length direction L/2 and the width direction W/2;

3) Carrying out a high-temperature thermal simulation test, sequentially heating and insulating the sample at each experiment temperature, and then rapidly cooling to room temperature;

4) After the experiment, a V-shaped groove is formed in the L/2 position of the thermocouple welded on the sample in the direction vertical to the length direction, and the depth of the groove is 1.5-2.5mm;

5) Placing the slotted thermal simulation sample in a container containing liquid nitrogen for cooling for more than 15 minutes;

6) Quickly taking out the cooled sample, breaking the sample on a testing machine, and putting the sample into a beaker filled with pure alcohol for standing for 8 to 12 minutes until the temperature of the sample returns to the room temperature;

7) And taking out the dried fracture sample to perform observation and analysis on the fracture of the scanning electron microscope.

Furthermore, the thickness h of the size selection is 5mm-10mm, the width w is 8-12mm, and L is more than or equal to 55mm.

Further, the depth of the groove is 2mm.

Further, the mixture is placed into a beaker filled with pure alcohol and stands for 10 minutes until the temperature of the mixture is returned to the room temperature.

Furthermore, if the height of the fracture sample exceeds the height requirement of the scanning electron microscope on the sample, the fracture is wrapped and protected by clean filter paper, the side edge of the fracture sample is fixed by adhesive tape, then the fracture sample is cut to the height of the sample required by the scanning electron microscope, and the fracture sample is cleaned by alcohol again.

Further, L is more than or equal to 55 and less than or equal to 100mm.

Compared with the prior art, the invention has the beneficial technical effects that:

the method can obtain perfect fracture morphology, and is convenient for experimenters to carry out fracture scanning electron microscope analysis, thereby judging the reason of high-temperature brittleness of steel products; the principle of the method is suitable for various thermal simulation experiment machines, and a novel experimental method is provided for the research of high-temperature brittleness of steel by personnel engaged in experiments and research and development.

Drawings

The invention is further illustrated in the following description with reference to the drawings.

FIG. 1 is a typical high-temperature tensile fracture, and it can be seen that the fracture is locally melted due to ignition (FIG. 1 a), and the fracture is covered with a high-temperature oxide layer (FIG. 1 b), so that the scanning electron microscope analysis of the fracture cannot be performed;

FIG. 2 is a thermal simulation sample of the present invention;

FIG. 3 is a schematic view showing that a V-shaped groove is formed in a portion (L/2 portion) of a sample where a thermocouple is welded in a vertical longitudinal direction after an experiment.

Detailed Description

An experimental method for determining the cause of high-temperature brittleness of steel comprises the following steps:

1) Making a design

Referring to an impact sample in a Charpy impact test method of GB/T229-2007 metal materials, the bayonet shape of a sample fixture of a thermal simulation testing machine used in the experiment and the distance required by clamping are combined, and the sample size of the thermal simulation experiment is designed as follows: h is multiplied by w is multiplied by L (mm), wherein h is the thickness of the sample, w is the width of the sample, the actual bayonet size of the clamp and the heating and especially cooling effects of the sample in the experiment are referenced, the size can be selected to be 5-10 mm in thickness h, 10mm in width w and 55-100 mm in length L of the sample, the size can be determined according to the stroke among various thermal simulation testing machine clamps, and the minimum length is more than or equal to 55mm in order to meet the requirement that the sample is safely placed on and broken by the impact testing machine.

2) Before the thermal simulation test, thermocouples were welded to the portions of the test piece in the length direction L/2 and the width direction W/2, as shown in FIG. 2.

3) And (4) carrying out a high-temperature thermal simulation test, heating and preserving the temperature of the sample at each experiment temperature in sequence, and then rapidly cooling to room temperature.

4) After the experiment, a V-shaped groove is formed in the position (L/2 position) where the thermocouple is welded on the sample in the direction vertical to the length direction, the depth of the groove is 2mm, and specifically, reference can be made to a Charpy impact test method for GB/T229-2007 metal materials, and the method is shown in an attached figure 3.

5) And (3) cooling the slotted thermal simulation sample in a container filled with liquid nitrogen for more than 15 minutes.

6) The cooled sample is quickly taken out, broken on a testing machine, and placed into a beaker filled with pure alcohol to stand for about 10 minutes until the temperature returns to the room temperature.

7) And taking out the blow-dried fracture sample to perform observation and analysis on the fracture of the scanning electron microscope.

If the height of the fracture sample exceeds the height requirement of the scanning electron microscope on the sample, the fracture can be wrapped and protected by clean filter paper, the side edge of the fracture sample is fixed by tape pasting, the fracture sample is cut to the height of the sample required by the scanning electron microscope, and the fracture sample is cleaned by alcohol again.

Example 1

The invention is described below with reference to specific implementation steps and the accompanying drawings.

FIG. 1 shows a typical high-temperature tensile fracture, and it can be seen that the fracture is locally melted due to ignition (FIG. 1 a), and the fracture covers a high-temperature oxidation layer (FIG. 1 b), so that the scanning electron microscope analysis of the fracture cannot be performed.

Fig. 2 is a thermal simulation sample of the present invention, and the thermocouple welding portion is a high-temperature simulation portion of the sample, which can represent the actual state of the sample at the thermal simulation test temperature.

In the thermal simulation test, the sample is heated and kept at each experimental temperature, and then needs to be rapidly cooled to room temperature, generally the cooling rate is more than 15 ℃/S, and water cooling, air cooling (argon and helium) and the like can be adopted in a laboratory according to the instrument condition. The purpose is to retain the changes of grain growth, second phase precipitation and the like of the sample at various experimental temperatures.

As shown in the attached figure 3, after the experiment, a V-shaped groove is formed in the vertical length direction of the part (L/2 part) of the sample where the thermocouple is welded, and the fracture obtained by cutting the sample through the groove can fully represent the high-temperature fracture at the test temperature.

And (3) placing the slotted thermal simulation sample in a container filled with liquid nitrogen for cooling for more than 15 minutes, so as to embrittle the thermal simulation sample, so that more ductile fractures are obtained on the fracture of the sample, and the observation of a grain boundary precipitated phase is facilitated.

And quickly taking out the cooled sample, breaking the sample on a testing machine, putting the sample into a beaker filled with pure alcohol, standing for about 10 minutes until the temperature of the sample returns to room temperature, and aiming at preventing the fracture from rusting after frosting.

And finally, taking out the dried fracture sample to perform observation and analysis on the fracture of the scanning electron microscope. If the height of the fracture sample exceeds the height requirement of the scanning electron microscope on the sample, the fracture can be wrapped and protected by clean filter paper, then the fracture sample is cut to the height of the sample required by the scanning electron microscope, and the fracture sample is cleaned by alcohol again.

The above-described embodiments are merely illustrative of the preferred embodiments of the present invention, and do not limit the scope of the present invention, and various modifications and improvements of the technical solutions of the present invention can be made by those skilled in the art without departing from the spirit of the present invention, and the technical solutions of the present invention are within the scope of the present invention defined by the claims.

Claims

1. An experimental method for determining the cause of high-temperature brittleness of steel is characterized in that: the method comprises the following steps:

2) Before the thermal simulation test, welding thermocouples at the positions of the sample in the length direction L/2 and the width direction W/2;

3) Carrying out a high-temperature thermal simulation test, heating and preserving the temperature of the sample at each experimental temperature in sequence, and then rapidly cooling to room temperature;

5) Placing the slotted thermal simulation sample in a container filled with liquid nitrogen for cooling for more than 15 minutes;

2. An experimental method for determining the cause of high temperature brittleness of a steel product according to claim 1, comprising: the size selection thickness h is 5mm-10mm, the width w is 8-12mm, and L is more than or equal to 55mm.

3. An experimental method for determining a cause of high temperature brittleness of a steel material according to claim 1, comprising: the depth of the groove is 2mm.

4. An experimental method for determining the cause of high temperature brittleness of a steel product according to claim 1, comprising: placing the mixture into a beaker filled with pure alcohol and standing for 10 minutes until the temperature of the mixture is returned to the room temperature.

5. An experimental method for determining the cause of high temperature brittleness of a steel product according to claim 1, comprising: if the height of the fracture sample exceeds the height requirement of the scanning electron microscope on the sample, wrapping and protecting the fracture by using clean filter paper, adhering and fixing the side edge by using an adhesive tape, cutting the fracture sample to the sample height required by the scanning electron microscope, and cleaning the fracture sample by using alcohol again.

6. The experimental method for determining the cause of high-temperature brittleness of a steel material according to claim 2, wherein: l is more than or equal to 55 and less than or equal to 100mm.