阅读说明：本技术 测试金属材料液化裂纹敏感性的方法 (Method for testing liquefaction crack sensitivity of metal material ) 是由 曾凡伟 张玮 杨华春 赖仙红 于 2021-02-19 设计创作，主要内容包括：本发明公开了一种测试金属材料液化裂纹敏感性的方法,包括：A)取样：取全厚度试样；B)堆焊：采取熔化焊进行全厚度堆焊；C)切割；D)分析：如能借助光学显微镜观察裂纹形貌特征和分布特点,确认裂纹性质则直接判断；如裂纹细小不能判别时则：(1)利用金相显微镜核实细小裂纹的位置；(2)在细小裂纹四周标记出预取长条试样轮廓、并切割；(3)将长条形试样放置在-50℃至-100℃的环境中并保温,再沿着细小裂纹一次性掰断长条形试样；(4)利用扫描电镜对打开的裂纹缺陷面进行微观观察,确认其是否为液化裂纹；本发明解决了取样试验不具代表性的问题,降低了测试难度,具有简单有效的优点,并对细小裂纹缺陷也可准确判别。(The invention discloses a method for testing the susceptibility of a metal material to a liquefaction crack, which comprises the following steps: A) sampling: taking a full-thickness sample; B) surfacing: adopting fusion welding to carry out full-thickness surfacing welding; C) cutting; D) and (3) analysis: if the appearance characteristics and the distribution characteristics of the cracks can be observed by means of an optical microscope, and the properties of the cracks are directly judged if the properties of the cracks are confirmed; if the crack is small and can not be distinguished: (1) verifying the position of the fine cracks by using a metallographic microscope; (2) marking the outline of a pre-taken strip sample around the fine crack and cutting the pre-taken strip sample; (3) placing the strip-shaped sample in an environment of-50 ℃ to-100 ℃, preserving heat, and breaking the strip-shaped sample along the fine cracks at one time; (4) microscopic observation is carried out on the opened crack defect surface by using a scanning electron microscope to determine whether the crack defect surface is a liquefied crack or not; the invention solves the problem that the sampling test is not representative, reduces the testing difficulty, has the advantages of simplicity and effectiveness, and can accurately judge the fine crack defect.)

1. A method for testing the susceptibility of a metallic material to liquefaction cracking, comprising the steps of: A) sampling: taking a full-thickness sample of the workpiece in the thickness direction; B) surfacing: adopting fusion welding to carry out full-thickness surfacing on the cross section of the sample; C) cutting: carrying out full-thickness dissection on the well-surfaced sample according to the direction vertical to the surfacing layer to prepare a full-thickness metallographic sample; d) And (3) analysis: observing whether crack defects exist in a weld heat affected zone of the metallographic specimen, and if the appearance characteristics and the distribution characteristics of cracks can be observed by means of an optical microscope, directly judging the crack properties if the crack properties are confirmed; if the crack is small and can not be distinguished: (1) verifying the position of the fine cracks by using a metallographic microscope; (2) marking the contour of a pre-taken strip sample around the fine crack, and cutting the strip sample according to the contour; (3) placing the strip-shaped test sample containing the fine cracks in an environment with the temperature of-50 ℃ to-100 ℃ and preserving the heat for more than 10 minutes, and breaking the strip-shaped test sample along the fine cracks at one time; (4) and microcosmically observing the opened crack defect surface by using a scanning electron microscope, judging the property of the crack defect according to the morphological characteristics and the distribution characteristics of the crack defect, and determining whether the crack defect is a liquefied crack.

2. The method for testing the susceptibility of a metallic material to liquefaction cracking of claim 1, wherein: the fusion welding in the step B) is submerged arc welding, laser welding or arc welding.

3. The method of testing the susceptibility of a metallic material to liquefaction cracking according to claim 1 or 2, wherein: and in the step (2) of the step B), four positioning indentations are made around the fine cracks by using a micro Vickers hardness tester, and the outline of the pre-fetched elongated sample is outlined along the indentations by using a pen.

4. The method for testing the susceptibility of a metallic material to liquefaction cracking according to claim 3, wherein the pre-fetched elongated specimen profile has a length direction perpendicular to a length direction of the fine crack.

5. The method of testing the susceptibility of a metallic material to liquefaction cracking according to claim 1 or 2, wherein: and in the step (2) of the step B), the cut strip-shaped sample is cleaned by alcohol.

Technical Field

The invention relates to a method for testing the susceptibility of a metal material to a liquefaction crack.

Background

The research and development and application process of new materials need to research the welding manufacturability of the materials, particularly high-grade materials. When the welding process is evaluated, in addition to detecting the mechanical properties of the welding seam and the heat affected zone, whether the welding seam and the heat affected zone have defects, particularly welding crack defects, needs to be observed. The welding cracks are divided into: cold cracks, reheat cracks, and thermal cracks, wherein thermal cracks include liquefaction cracks, crystallization cracks, and multilateral cracks. In the case of the base material liquid crack, the heat affected zone of the metal material is melted by the heat cycle of welding to form a low melting point eutectic (or a low melting point eutectic exists at the original grain boundary), and the crack occurring at the melted grain boundary position during the subsequent cooling shrinkage process is called a liquid crack. Liquefaction cracks are often found in the heat affected zones of high alloy steels, stainless steels, and heat resistant alloy steels. Currently, the commonly used methods for testing the susceptibility to liquefaction cracking include: a Y-shaped groove test method, a T-shaped joint test, an annular groove crack resistance test, a fishbone test and the like; for the test methods, the precondition is that the sample is required to be representative, the sample is required to be provided with a groove, the test is required to adopt a tool fixture and the like, the opened crack defect surface is microscopically observed, and the property of the crack defect is judged according to the appearance characteristic and the distribution characteristic of the crack defect surface; the test methods have the defects of complex working procedures and more tool fixtures, have inconvenience and limitation on the test of the liquefaction crack sensitivity of the metal material, and increase the test difficulty, and particularly when the high-grade material (G115, iron-nickel-based alloy, nickel-based alloy and the like) is used as a thick-wall pipe or a forge piece and the like and has obvious chemical component (such as W, Nb and other elements) segregation in the thickness direction, the test sample is taken to be in a non-full-size thickness according to the method, and the test result may not be representative; and for fine cracks, the real appearance of the defect surface of the crack is difficult to obtain due to the metal toughness, and the accurate judgment cannot be carried out.

Disclosure of Invention

The invention aims to provide a method for testing the susceptibility of the liquefaction cracks of the metal material, which solves the problem that a sampling test has no representativeness, reduces the testing difficulty, has the advantages of simplicity and effectiveness, and can accurately judge the tiny crack defects.

In order to achieve the above object, the method for testing the susceptibility of a metallic material to liquefaction cracking of the present invention is characterized by comprising the steps of: A) sampling: taking a full-thickness sample of the workpiece in the thickness direction; B) surfacing: adopting fusion welding to carry out full-thickness surfacing on the cross section of the sample; C) cutting: carrying out full-thickness dissection on the well-surfaced sample according to the direction vertical to the surfacing layer to prepare a full-thickness metallographic sample; d) And (3) analysis: observing whether crack defects exist in a weld heat affected zone of the metallographic specimen, and if the appearance characteristics and the distribution characteristics of cracks can be observed by means of an optical microscope, directly judging the crack properties if the crack properties are confirmed; if the crack is small and can not be distinguished: (1) verifying the position of the fine cracks by using a metallographic microscope; (2) marking the contour of a pre-taken strip sample around the fine crack, and cutting the strip sample according to the contour; (3) placing the strip-shaped test sample containing the fine cracks in an environment with the temperature of-50 ℃ to-100 ℃ and preserving the heat for more than 10 minutes, and breaking the strip-shaped test sample along the fine cracks at one time; (4) microscopic observation is carried out on the opened crack defect surface by utilizing a scanning electron microscope, the property of the crack defect is judged according to the morphological characteristics and the distribution characteristics of the crack defect, and whether the crack defect is a liquefied crack or not is confirmed;

the fusion welding in the step B) can be one of submerged arc welding, laser welding or arc welding;

the invention adopts the surfacing method in the range of full-thickness samples, the samples do not require to be processed with grooves, and the constraining devices such as tooling clamps and the like are also not needed, the liquefaction crack sensitivity test of the full-thickness metal material can be realized, the invention is particularly suitable for the liquefaction crack sensitivity test of the metal material with the microcosmic component segregation, the problem that the taken samples cannot be representative when the conventional test method is used for sampling is well solved, and the test method is simple, reduces the test difficulty and has the advantages of simplicity and effectiveness; for fine cracks, accurately positioning, taking down a strip-shaped sample, performing cold-brittle treatment, breaking the strip-shaped sample, opening a crack defect surface without damage, and determining whether the sample is a liquefied crack or not by means of amplification of a scanning electron microscope, wherein the fine crack defect can also be accurately judged;

as a further improvement of the invention, in the step (2) of the step B), four positioning indentations are made around the fine crack by using a micro Vickers hardness tester, and the pre-fetched elongated sample profile is sketched out along the indentations by using a pen; four positioning indentations are pressed by a micro Vickers hardness tester, so that the four positioning indentations are not easy to be eliminated by subsequent procedures, and accurate delineation of a pre-fetching elongated sample and breaking operation are facilitated;

as a further improvement of the invention, the length direction of the pre-fetching elongated sample profile is perpendicular to the length direction of the fine crack; the strip-shaped sample is broken off easily;

as a further improvement of the present invention, in the step (2) of the step B), the cut strip-shaped sample is washed with alcohol; impurities generated in each procedure can be removed;

in conclusion, the invention solves the problem that the sampling test is not representative, reduces the testing difficulty, has the advantages of simplicity and effectiveness, and can accurately judge the fine crack defect.

Drawings

FIG. 1 is a perspective view of a tile-like full thickness specimen cut out of a steel pipe in accordance with an embodiment of the present invention.

Fig. 2 is a perspective view of fig. 1 after build-up welding.

Fig. 3 is a perspective view of a full thickness metallographic specimen obtained by cutting.

FIG. 4 is a gold phase diagram of a fine crack observed by an optical microscope.

FIG. 5 is a gold phase diagram after positioning and indentation around a fine crack defect by using a micro Vickers hardness tester.

Fig. 6 is a perspective view of a strip sample.

FIG. 7 is a metallographic image of a fine crack defect surface magnified by 200 times by a scanning electron microscope.

FIG. 8 is a metallographic image of a fine crack defect surface magnified 1000 times by a scanning electron microscope.

FIG. 9 is a metallographic image of a fine crack defect surface magnified 3000 times by a scanning electron microscope.

FIG. 10 is a metallographic image of a fine crack defect surface magnified 5000 times by a scanning electron microscope.

Detailed Description

The present invention will be described in further detail below with reference to the drawings, taking a steel pipe as an example of a workpiece.

The method of testing the susceptibility of a metallic material to liquefaction cracking of this embodiment comprises the steps of: A) sampling: as shown in fig. 1, a tile-shaped full thickness sample 1 of the steel pipe in the thickness direction is taken; B) surfacing: as shown in fig. 2, submerged arc welding is adopted for full-thickness overlaying on the cross section of the tile-shaped full-thickness sample 1 to obtain an overlaying layer 2; C) cutting: as shown in fig. 3, performing full-thickness dissection on the overlaid sample in a direction perpendicular to the overlaying layer to prepare a full-thickness metallographic sample 3; d) And (3) analysis: observing whether crack defects exist in a weld heat affected zone of the metallographic specimen, if the appearance characteristics and the distribution characteristics of cracks can be observed by means of an optical microscope, and if the crack properties are confirmed, directly judging whether the cracks are liquefied cracks; if the crack is small and can not be distinguished: (1) as shown in fig. 4, the position of the fine crack 4 was verified using a metallographic microscope; (2) as shown in fig. 5, a micro vickers hardness tester is used for making four positioning indentations 5 around the fine crack 4, then a marking pen or a sign pen is used for outlining the pre-fetched elongated sample along the indentations, the length directions of two pre-fetched elongated sample outline lines 6 are vertical to the length direction of the fine crack 4, the fine crack 4 is located at the middle position of the elongated sample in the length direction as much as possible, the elongated sample is cut according to the outline, and the elongated sample is cleaned by alcohol; (3) as shown in fig. 6, the strip-shaped sample 7 containing the fine cracks 4 is placed in an alcohol bath at-80 ℃ and kept warm for 20 minutes, and then the strip-shaped sample is broken off along the fine cracks at one time; (4) microscopic observation is carried out on the opened crack defect surface by using a scanning electron microscope, as shown in fig. 7 to 10, the scanning electron microscope can be amplified to a higher multiple, the metallographic picture is clear and identifiable, the property of the crack defect is judged according to the morphological characteristics and the distribution characteristics of the crack defect, and whether the crack defect is a liquefied crack or not is confirmed;

the invention adopts the surfacing method in the range of full-thickness samples, the samples do not require to be processed with grooves, and the constraining devices such as tooling clamps and the like are also not needed, the liquefaction crack sensitivity test of the full-thickness metal material can be realized, the invention is particularly suitable for the liquefaction crack sensitivity test of the metal material with the microcosmic component segregation, the problem that the taken samples cannot be representative when the conventional test method is used for sampling is well solved, and the test method is simple, reduces the test difficulty and has the advantages of simplicity and effectiveness; for fine cracks, accurately positioning through positioning indentation, taking down a strip-shaped sample, performing cold-brittle treatment at low temperature, breaking the strip-shaped sample off to realize nondestructive opening of a crack defect surface, keeping the real appearance of the crack defect surface, and determining whether the crack defect surface is a liquefied crack or not after being amplified by a scanning electron microscope, wherein the fine crack defect can also be accurately judged whether the crack defect is a liquefied crack or not; the four positioning indentations are pressed by a micro Vickers hardness tester, so that the four positioning indentations are not easy to be eliminated by subsequent alcohol cleaning and low-temperature cold-brittle processes, and the contour of a pre-fetched strip sample is accurately outlined and breaking operation is facilitated;

the present invention is not limited to the above embodiment, and the fusion welding in step B) may be one of laser welding and arc welding, and the temperature at the time of cold embrittlement may be adjusted, all of which belong to the protection scope of the present patent.