DL/T 2054-2019 English Translation: Metallographic Inspection and Assessment of Welded Joints in Electric Power Construction

Document: DL/T 2054-2019, Metallography inspection and assessment guideline of welding joints in electric power construction.

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Page 01

ICS 27.100
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FP TE OO. Be Ee A Be] Fa 99 49 Ib as HE
DL/T 2054—2019
Electric power construction welding joints
Technical Guidelines for Metallographic Inspection and Assessment
Metallography inspection and assessment guideline of welding joints in
electric power construction
Published on 2019-11-04 2020-05-01 Sciiti
Released by the National Energy Administration

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DL/T 2054-2019
Table of contents
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Appendix A (Informative Appendix) Pictures of common macroscopic defects in welded joints and 1
Appendix (Informative Appendix) Metallographic microstructural characteristics of various areas of welded joints and 12
Attached is the “informative appendix”) Common welded joint metallographic structure pictures PN
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DL/T 2054—2019
Foreword

This standard is drafted in accordance with the rules given in GB/T 1.1-2009 “Standardization Work Guidelines Part 1: Structure and Numbering of Standards”.

This standard is proposed by China Electricity Council.

This standard is under the jurisdiction of the Technical Committee on Standardization of Metallic Materials for Power Stations in the Electric Power Industry (DL/TC 23).

The main drafting units of this standard are: China Electric Power Research Institute Co., Ltd., Beijing Guodian Futong Technology Development Co., Ltd.,
An Thermal Engineering Research Institute Co., Ltd., Suzhou Thermal Engineering Research Institute Co., Ltd., China Energy Construction Anhui Electric Power Construction First Engineering Co., Ltd., Jiangsu
Fangtian Electric Power Technology Co., Ltd., Energy China Zhejiang Thermal Power Construction Co., Ltd., Liaoning Electric Power Co., Ltd. Electric Power Research Institute, Shan

Dongfang Electric Power Construction Third Engineering Co., Ltd.

The main drafters of this standard: AACK. ER. MEL ERK. BER. MR. MAA. HB. KAA,
Zeon. RE. RR. ER. BAL ESL. FL. BAI. I.

This standard is published for the first time.

Feedback your opinions or suggestions during the implementation of this standard to the Standardization Management Center of China Electricity Council (No. 2, Baiguang Road, Beijing)
Article No. 1, 100761).

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DL/T 2054-2019
Technical Guidelines for Metallographic Inspection and Assessment of Welded Joints in Electric Power Construction
1 range
This standard specifies the personnel, equipment, sample management and preparation, inspection, image collection and analysis, and results for metallographic inspection of welded joints.
Technical requirements for assessment and inspection reports.
This standard is applicable to the technical assessment of welders in electric power construction, the evaluation of welding procedures, and the evaluation of welded joints during the manufacturing and installation of electric power equipment.
Metallographic inspection and evaluation. The metallographic inspection and evaluation of welded joints involved in the replacement of power station components can be implemented as a reference.
2 Normative reference documents
The following documents are essential for the application of this document. For dated references, only the dated version applies to this article.
pieces. For undated referenced documents, the latest version (including all amendments) applies to this document.
GB/T 13298 “Metal Microstructure Examination Method
GB/T 13299 Microstructure evaluation method of steel
DL/T 438 “Technical Supervision Regulations for Metals in Thermal Power Plants”
DL/T 679 Welder Technical Assessment Regulations
DL/T 868 Welding procedure qualification procedures
DL/T 869 “Technical Specifications for Welding of Thermal Power Plants
DL/T 884 “Technical Guidelines for Metallographic Inspection and Assessment of Thermal Power Plants”
DL/T 931 Assessment procedures for physical and chemical inspection personnel in the power industry
3 General provisions
3.1 Inspection personnel
311 Metallographic inspection personnel should obtain a junior (1M). PR IM) MAR MM) metallographic inspection personnel training certificate,
Engage in corresponding metallographic inspection work and assume corresponding technical responsibilities.
3.1.2 “Junior metallographic inspection personnel should have the following technical capabilities:
a) Understand the main chemical composition, metallographic structure, welding process, heat treatment process and
Common defects;
b) Be familiar with national standards, industry standards and enterprise standards related to metallographic inspection, and understand relevant foreign standards;
c) Able to operate inspection equipment independently and perform routine maintenance;

d) Under the guidance of intermediate or senior metallographic inspection personnel, be able to implement sample preparation in accordance with relevant standards, inspection plans and work instructions.
Prepare the entire process of inspection to organization and defect identification, and record and analyze the inspection results.
3.1.3 “Intermediate metallographic inspection personnel should have the following technical capabilities:
a) Be familiar with the main chemical composition, metallographic structure, welding process, heat treatment process and
Common defects;
b) Be familiar with national standards, industry standards and enterprise standards related to metallographic inspection, and be familiar with relevant foreign standards;
c) Be able to formulate inspection plans and operations based on the chemical composition, welding process, heat treatment process and related standards of metal materials and welding materials.
Business Instructions;
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DL/T 2054—2019

d) Be familiar with the working principles of inspection equipment and be able to operate it correctly, perform daily maintenance and troubleshoot general faults;

e) Able to independently implement the entire process of inspection from sample preparation to tissue and defect identification, record and analyze inspection results, and write inspection

reporting;

“Completely” review and issue individual inspection and analysis reports, and be responsible for the inspection and analysis results;

g) Prepare a comprehensive inspection and analysis report and be responsible for the inspection and analysis results;

h) Guide the work of junior metallographic inspectors.
3.1.4 In addition to the technical abilities of intermediate metallographic inspectors, senior metallographic inspectors should also have the following technical abilities: |

a) Develop and review inspection plans and work instructions;

b) Develop special inspection methods, technologies and process procedures for non-standard inspection;

c) Review and issue comprehensive inspection and analysis reports, and be responsible for the inspection and analysis results;

d) Guide the work of junior and intermediate metallographic inspection personnel.
3.1.5 “For other requirements for metallographic examination personnel, see DL/T 931.
3.2 “Inspection equipment and use
3.2.1 Metallographic inspection equipment, including metallographic sample cutting machines, mounting machines, grinding and polishing machines, electrolytic etching equipment, metallographic microscopes, etc., should all meet the requirements.
Meet relevant usage and safety requirements.
3.2.2 “Configuration of metallographic microscope, including magnification, objective numerical aperture, camera, dark field, human and polarization, differential interference and other parameters and
Accessories should meet the technical requirements for metallographic examination.
3.2.3 “Laboratory metallographic microscopes should be installed in a dry and ventilated room without exposure to sunlight, vibration, and corrosive atmosphere, and placed in a
On a stable table or pedestal. The indoor temperature should be maintained at 20 C ± SC, and the relative temperature should be less than 70%.
3.2.4 A clear metallographic microstructure should be observed with a portable metallographic microscope on site. Portable metallographic microscope with acquisition function

Clear metallographic microstructure images should be collected.
3.25 “The metallographic microscope lens should be handled with care, without collision, and fingers should not touch the lens surface. Dust on the lens surface affects the metallographic display.
When observing micro-tissues and collecting images, you can use an ear cleaning ball to blow it out, or use a soft degreasing brush to wipe and clean it. It can be used when there is oil on the lens surface.
Wipe the paper core of the lens, take a little detergent (optical lens anti-mildew and decontamination cleaner), dimethyl or ether and wipe it clean. Lenses should be kept in a dedicated
in a desiccator and check frequently to ensure there are no spots.
3.2.6 “When observing metallographic microstructure, select the objective lens and eyepiece of the metallographic microscope, adjust the light source, select the color filter, and aperture diaphragm
and the adjustment of the field diaphragm, etc. shall be carried out in accordance with the provisions of GBMT 13298.
3.2.7_” The scale in the eyepiece of the metallographic microscope should be calibrated using a micrometer scale. The micrometer scale should be qualified and used within the validity period.
Use. For metallographic microscopes equipped with image analysis software, the system ruler of the image analysis software should be verified and calibrated regularly.
The calibration of the ruler was carried out according to the instructions of the image analysis software.
3.2.8 “Metallographic inspection equipment should be used and maintained in accordance with the instruction manual or operating procedures.
3.3 “Sample and replica sample management
3.3.1 Metallographic specimens should have unique identification, and the identification should remain clear and identifiable throughout the metallographic inspection process.
3.3.2 “The prepared metallographic specimens should be kept clean and dry, and the etched surface should not be touched with hands or collided with other objects. After observation and
Store it properly in a desiccator to prevent rust, contamination, and oxidation.
3.3.3 “The prepared metallographic replica sample should be kept clean, dry and flat, and the replica surface should not be touched with hands. After observation, place it flatly into the test
Put it in a sample bag, or stick it on a glass slide and place it in a sample box to prevent the currency from deformation and contamination. Sample bags or slide sample boxes should be numbered and placed in a dry
Store properly in a dryer.
3.3.4 The desiccant in the dryer should be dried or replaced regularly to keep it dry.
3.3.5 “The storage period of metallographic samples and replica samples shall be determined according to relevant regulations or mutual agreement. When not required, the sample should be kept for at least 3
months. Particularly important samples should be stored for a long time.
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DL/T 2054—2019
34 “Safety Protection and Environmental Protection
341 Metallographic inspection personnel should master relevant safety protection knowledge and have safety protection awareness to prevent sample preparation equipment, hazardous chemicals, etc.
Personal injury.
3.4.2″ Metallographic inspection personnel should master relevant environmental protection knowledge, abide by relevant national laws and regulations, and avoid hazardous chemicals causing environmental damage.
pollution.
4 Sample preparation

4.1 Laboratory sample preparation
4.1.1 Sample interception, mounting and marking
4.1.1.1 The interception position, direction and quantity of metallographic specimens shall be determined according to the inspection purpose, relevant standards and agreement between the two parties.
41.1.2 “Metalographic specimens of welded joints should be taken perpendicular to the axis of the weld and include full thickness specimens of the weld end, fusion zone, heat affected zone and base metal.
Like. The test specimens of welded joints of the same type of steel should at least include the weld and the fusion zone, heat affected zone and base metal on either side. The test specimens of the welded joints of dissimilar steels should include
The sample should include the weld and the fusion zone, heat affected zone and base metal on both sides. When the locations of the welding peak and heat-affected zone cannot be determined, the interception test can be
Before sampling, show the weld end and heat affected zone through appropriate etching.
4.1.1.3 “During the sample interception process, measures should be taken to avoid changes in the metallographic microstructure of the sample due to heat or force.
4.1.1.4. When the sample size is too small, the shape is irregular, or the edge of the sample needs to be inspected, the sample should be mounted. See the method of setting and tearing the sample.
GB/T 13298, there are specific instructions on the equipment that can be operated according to the equipment instructions.
41.1.5 The intercepted and moxibustion samples should be marked with a unique identification, and the information represented by the identification should be recorded. Marking method and identification location
The principle is to ensure that it will not be worn or obscured during the sample preparation process, and will not affect the display of the metallographic microstructure.
4.1.2” Sample grinding, polishing and etching
414.21 The specimen may be ground by manual or mechanical grinding and polished by mechanical, electrolytic or chemical polishing. For details on related methods, see
GB/T 13298 and DLAT 884.
4.1.2.2 “Shall be based on the sample base material grade according to DL/T 884 “SAR MEER IEA EULA] DL RE
It is appropriate to show the details of the metallographic structure, and the distortion of the structure caused by excessive erosion should be avoided.
4.1.2.3 “After the macroscopic metallographic sample is etched, if the etching is too shallow, the etching should continue until the requirements are met. If the etching is too deep, it should be reground and
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41.24 WOULSHIRENS UR, FARR, MSR BR. HSH RA
indicates that it should be re-polished, etched, and re-grinded if necessary.
4.1.2.5 “For microscopic metallographic specimens of dissimilar steel welded joints, the etching agents should be selected according to the grades of the base materials on both sides of the weld. The etching agents on both sides are different.
“The sample should be etched and inspected step by step; in order to avoid excessive etching, the side that is prone to corrosion should be etched and inspected first.
4.2 “On-site sample preparation
4.2.1 Inspection area selection and recording
4.2.1.1 The location and number of inspection areas should be determined based on the purpose of the inspection, relevant standards and agreement between the two parties.

4.2.1.2 “The inspection area of welded joints should be selected perpendicular to the axis of the weld and include the weld warp, fusion zone, heat affected zone and base metal. The same type of steel
The inspection area of welded joints should at least include the welding ridge and the fusion zone, heat affected zone and base material on either side. The inspection area of dissimilar steel welded joints should include
“It will weld the fusion zone, heat affected zone and base metal on both sides of the welding ridge. When the locations of the welding peak and heat-affected zone cannot be determined, they can be revealed through appropriate diffusion etching.
Shows the weld end and heat affected zone.
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DL/T 2054—2019
4213 After the inspection area is selected, the location and related information of the inspection area should be recorded in diagrams or text.
42.2 “Grinding, polishing and etching in inspection area
4221 The final weld in the inspection area should be polished to the same height as the base metal, and the oxide scale and decarburization layer should be removed; if the polishing is difficult, the weld can be polished to the
The smooth transition of the base material does not affect the observation of metallographic microstructure.
4.2.2.2 Please refer to 4.1.2 for the grinding, polishing and etching methods in the inspection area.
423 See.
42.31 In general on-site metallographic inspection, a portable metallographic microscope can be used to directly complete metallographic microstructure observation and images on site.
collection. When the inspection area is in a location that is difficult to observe or there are doubts about the observation results, a metallographic replica will be made on site.
4.2.3.2” Metallographic replicas shall be made in accordance with the requirements of DL/T 884. When the span of each area of the welded joint is large, making a copy cannot meet the requirements.
At this time, multiple copies can be made to cover each area of the welded joint.
423.3 “When making a metallographic replica, the etching of the inspection area can be slightly deeper than that of the general sample, or an appropriate amount of colorant can be added to the organic solvent.
5 Macroscopic metallographic inspection and evaluation
51 Macroscopic metallographic examination
5.1.1 Macroscopic metallographic inspection of welded joints refers to using the naked eye or low-power optical instruments (generally the magnification is less than 50 times) to inspect the welded joints.
Macroscopic defects such as pores, wine inclusions, lack of fusion, incomplete welding, and welding cracks. If the client requires to check the size and quantity of weld beads, it can be
5.1.2 “Sampling should be carried out for macro-metallographic inspection of welded joints in accordance with the requirements of DLT 679. DL/T 868 and other standards.
5.1.3 “When macro defects are discovered, the nature, size and location of the defects should be recorded, and if necessary, drawing a simplified diagram or taking photos can be used
record. When taking photos of macroscopic defects, a ruler should be added to determine the image magnification. See Appendix A for pictures of common macroscopic defects in welded joints.
5.2 “Result Evaluation

5.2.1 “The macroscopic metallographic inspection results of welded joints shall meet the following requirements,
a) No cracks;
b) No unfusion;
c) There must be no incomplete penetration of the welding ridges required for penetration.
5.2.2 “The macro-metallographic examination results of welded joints in the welder technical assessment shall be evaluated in accordance with the provisions of DL/T 679.
523 “The macro-metallographic examination results of welded joints in welding procedure qualification shall be evaluated in accordance with the provisions of DL/T 868.
5.24 When there is an agreement between the two parties, the macro-metallographic inspection results of the welded joints shall be evaluated in accordance with the provisions of the agreement.
6”Micrometallographic inspection and evaluation
6.1 Microscopic metallographic examination
6.1.1 The micrometallographic inspection of welded joints refers to the observation of various aspects of welded joints through an optical or electron microscope (generally the magnification is greater than 50 times).
The constituent phases of the area’s metallographic microstructure and their shape, size, distribution and quantity, and the grain size, non-metallic inclusions,
Decarburization layer, Widmanstatten structure, micro cracks, welding defects, etc. are evaluated.
6.1.2 “Before conducting micrometallographic examination of welded joints, the chemical composition of the base metal and welding materials, the original structure of the base metal, and the welding
Process and heat treatment process, etc., clarify the purpose of inspection.
6.1.3 “Micrometallographic inspection of welded joints can be carried out according to the welding end, fusion zone, overheating zone, recrystallization zone, incomplete recrystallization zone, and base metal zone inspection.
Inspection is required, among which the welding edge, fusion zone, overheated zone and base metal are required inspection areas. Welded joints of the same type of steel should at least be inspected on the weld seam and all areas on either side.
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DL/T 2054—2019
Inspection; dissimilar steel welded joints should be inspected on the weld and the areas on both sides. Austenitic stainless steel welded joints should be welded and fused according to the
Area, heat affected zone and base metal zoning inspection. For the metallographic microstructural characteristics of each area of the welded joint, please refer to Appendix Bo
6.1.4 For welded joints that have undergone post-weld heat treatment, the impact of the welding heat treatment process on the metallographic microstructure of each zone should be considered during inspection.
6.15 During microscopic metallographic examination, welding can be analyzed by observing the crack source area, shape and expansion characteristics before and after etching of the sample.
Crack types and causes. Please refer to Appendix C for welding crack types and microscopic characteristics.
6.1.6 “When observing the metallographic microstructure, the welded joints should be observed at low magnification first, and then divided into high magnification observations. Common
See Appendix D for pictures of the metallographic structure of welded joints.
6.1.7” The metallographic microstructure shape can be collected and recorded using optical photography or digital imaging.
6.1.8 When collecting images, the magnification should be selected according to the characteristics of the metallographic microstructure, so that the characteristics of the metallographic microstructure can be clearly displayed.

Image magnification should be recorded by adding a scale to the image or other methods.
6.1.9 For welded joints of the same type of steel, images should be collected at least in three areas: the welding edge, the heat-affected zone on either side and the base metal, and the image collection should be recorded.
Information; dissimilar steel welded joints should collect images from at least five areas of the weld, the heat affected zone on both sides and the base metal, and record the image collection
information.
6.1.10 “When a defect is discovered, images should be collected separately, and the nature, size and location of the defect should be recorded through diagrams or text.
6.1.11 “When quantitative metallographic analysis is required, it shall be carried out in accordance with the requirements of standards such as DLAT 884.
6.2 “Result evaluation
6.2.1 The micrometallographic inspection results of welded joints should meet the following requirements:
a) No cracks;
b) There is no overheated tissue in the non-overheated area;
c) No hard martensite structure.
6.2.2 “The micrometallographic examination results of welded joints in the welder technical assessment shall be evaluated in accordance with the provisions of DL/T 679.
6.2.3 “The micrometallographic examination results of welded joints in welding procedure qualification shall be evaluated in accordance with the provisions of DL/T 868.
6.2.4 The micrometallographic examination results of welded joints during the manufacturing and installation of power equipment shall be evaluated in accordance with the provisions of DL/T 869. DL/T 438.
6.2.5 “Widmanstatten shall be graded in accordance with the provisions of GB/T 13299.
6.2.6 “When both parties have an agreement, the micrometallographic examination results of the welded joints shall be evaluated according to the provisions of the agreement; if there is no provision, refer to the attached
Metallographic microstructure evaluation of corresponding base metal grades, etching agents, welding and heat treatment conditions in SD.
7 Inspection records and reports
Inspection records and reports should include but not be limited to the following:
a) Commissioning unit, project name and execution standards.
b) Workpiece name, specifications, base metal and welding material grades, welding process and heat treatment process, etc.
c) Sample (inspection area) location, quantity, and number.
d) Etching methods and etching agents.
e) Verify equipment name and number.
f) Inspection results and images. The image should indicate the magnification and describe the macroscopic shape or metallographic microstructure characteristics; if there are abnormal groups
If there is any weaving or defect, its nature, size and location should be described, and a schematic diagram should be attached if necessary.
g) Inspection record or inspection report date and number.
h) Signature of inspection and audit personnel.

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DL/T 2054-2019
B
“Informative Appendix”)
Metallographic microstructural characteristics of various areas of welded joints
Bl welded joint consists of weld seam, fusion zone, heat affected zone and base metal, as shown in Figure B.1.
a) Weld: The joint part formed by welding the weldment.
b) BGK: In a welded joint, the area where the weld metal transitions to the heat affected zone.
c) Heat-affected zone: Under the action of the welding heat cycle, the base metal in the solid state on both sides of the welding edge is affected by heat (but not melted).
Area showing changes in microstructure and mechanical properties. According to different organizational characteristics, the heat-affected zone can be divided into overheated zone, heavy junction zone and
volume zone and incomplete recrystallization zone.
6 5 43 2 1
N Y
FIN
Description:
1-Welding metal;
2-One fusion zone;
4 Recrystallization zone;
5—Incomplete recrystallization zone;
6-1 base material.
Figure B.1 Schematic diagram of welded joint composition
B.2 “The metallographic microstructural characteristics of each zone in the welded state of the welded joint depend on the peak temperature of the welding thermal cycle, the heating rate, and the high temperature residence time.
and subsequent cooling rate.
a) Welding ridge: The structure in this area has the characteristics of joint formation and growth, and its metallographic microstructure is columnar crystals, dendrites, equiaxed crystals, etc.;
During multi-layer welding, the front weld layer is reheated by the subsequent weld layer and undergoes phase change and recrystallization, resulting in the metallographic structure of various parts of the weld area.
Differences in microstructure morphology.
b) Overheated zone: This zone is severely overheated during the welding thermal cycle. The metallographic microstructure is characterized by coarse grains, also known as the rough zone.
The overheated area is a sensitive area for reheat cracking. For low carbon steel, it is also an area prone to Widmanstatten structure.
c) Recrystallization zone: The peak temperature of the welding thermal cycle in this zone is greater than 43°C. At high temperatures, the original structure is all austenitized and during the cooling process
Phase transformation and recrystallization occur in the process, and the metallographic microstructure is characterized by fine and uniform grains, also known as the fine singing area, normalizing area and “not easy to fire”.
Steel) or Bay Fire District “〈Easy Bay Fire Steel”.
d) Incomplete recrystallization zone: The peak temperature of the welding thermal cycle in this zone is between 4 and 43°C, and part of the original structure is austenitized at high temperatures.
During the cooling process, phase transformation and recrystallization occur, forming a structure with fine and uniform grains, while the original structure that has not been austenitized remains.

Eventually, a metallographic microstructure with uneven thickness is formed, which is also called incomplete normalizing zone (hard-to-fire steel) or incomplete normalizing zone.
(SEK) 0
e) For the base material, the metallographic microstructure in this area has not changed significantly and the characteristics of the original metallographic microstructure are retained.
B.3 “Since austenitic stainless steel has the special characteristic of not undergoing phase transformation with temperature changes, there is no recrystallization zone and imperfection in its heat-affected zone.
Division of total recrystallization zone.
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Appendix C
“Informative Appendix”)
Welding crack types and microscopic characteristics
C.{Due to the joint action of metallurgical and mechanical factors during the welding process, various parts of the welded joint may produce cracks under different temperature and time conditions.
Various types of welding cracks occur.
C.2 Welding cracks can be divided into hot cracks, cold cracks and reheat cracks according to the temperature or time conditions in which they occur.
a) Hot cracks: During the welding process, the welding edge and the heat-affected zone metal cool to the high-temperature zone near the solidus line.
The occurrence is related to the weakening of grain boundaries caused by boundary behavior at high temperatures. Common welding hot cracks include crystal cracks, liquefaction cracks, high
b) ARMA: Welding cracks occur when the welded joint is cooled below the AM4 temperature. Its occurrence is related to the stress state, material plasticity and
Oxygen activity and other factors are related. Common welding cold cracks include delayed cracks, deep hard embrittlement cracks, lamellar tears, etc.
c) Reheat cracks; cracks produced when the welded joint is heated again after welding (post-weld heat treatment or working at a certain temperature).
It is related to the precipitation hardening effect of metal.
C.3 “Welding cracks can be divided into crystal cracks, liquefaction cracks, high temperature and low plasticity cracks, delayed cracks, and deep hard embrittlement according to their formation mechanism.
Cracks, lamellar cracks, reheat cracks, etc. During microscopic metallographic inspection, the type and cause of welding cracks can be analyzed through microscopic features.
The microscopic characteristics of various types of cracks are as follows:
a) SAMA: When the welding pool solidifies and crystallizes, in the temperature range where the liquid phase and the solid phase coexist in the late crystallization period, due to crystal segregation and shrinkage
Due to the action of shrinkage stress and strain, cracks formed along the primary crystallization boundary of the welding edge or fusion zone metal are hot cracks. Commonly found in carbon steel,
Welding edges or fusion zones of low alloy steels, medium alloy steels, austenitic stainless steels and nickel-based alloys.
b) Liquefaction cracks; the metal in the fusion zone and overheated zone of the welded joint or the interlayer metal of the multi-layer welding ridge is produced at the peak temperature of the welding thermal cycle.
When the temperature is slightly lower than the solidus line, the intergranular metal remelts when heated and sings along the austenite under a certain shrinkage stress.

Cracks formed at the boundary are also called thermal cracks and are thermal cracks. Commonly found in nickel-chromium high-strength steel and austenitic stainless steel with high C, S, and P content
The fusion zone, superheated zone or interlayer metal of multi-layer welding of stainless steel and nickel-based alloys.
c) High temperature and low plasticity cracks; when the liquid phase is cooled to a certain temperature range after completion, due to the strain rate and certain metallurgical factors,
Intergranular cracking caused by the decrease in metal plasticity of the welded joint caused by interaction is a hot crack. Generally occurs in heat-affected zones.
d) Delayed cracks; for welded joints cooled below the M4 point after welding, the joint will crack due to the combined action of the hard structure, oxygen accumulation and welding residual stress.
When used, cracks generated after a delay ranging from a few seconds to several months have the characteristics of transgranularity or a mixture of transgranularity and intergranularity, and are cold cracks.
Pattern. Commonly found in the heat-affected zones or welds of medium and high carbon steels and low and medium alloy steels.
e) Hard embrittlement cracks: intergranular or transgranular cracks produced by the hard structure formed during the welding process under the action of welding residual stress.
Generally formed near the MA point, it is a cold crack. Commonly found in the heat-affected zone or weld ridge of carbon-containing NiCrMo steel and martensitic stainless steel.
“Potential” lamellar tearing, when there are non-metallic inclusions distributed in layers along the rolling direction in the steel plate, the welding generated perpendicular to the rolling direction
Under the action of axial stress, transgranular or intergranular “step” layered cracks occur along the interface between the inclusion and the matrix, which are generally formed in
Below 400, it is a cold crack. Commonly found near the heat-affected zone of low-alloy high-strength steel thick plate structures.
g) Reheat cracks; during post-weld heat treatment to eliminate residual stress, or when the weldment without any heat treatment is at a certain temperature.
Intergranular cracks occur due to the additional deformation caused by stress relaxation being greater than its creep plasticity. They are generally formed between 600 C and 700 *C.
Commonly found in the superheated zone of high-strength steel, pearlitic steel, austenitic stainless steel and nickel-based alloys containing precipitation strengthening elements.

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Technical Guidelines for Metallographic Inspection and Assessment
DL/T 2054-2019
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