CN111965030B - Method for predicting tensile strength and yield strength of metal material base metal and weld joint - Google Patents
Method for predicting tensile strength and yield strength of metal material base metal and weld joint Download PDFInfo
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Abstract
The invention discloses a method for predicting tensile strength and yield strength of a metal material parent metal and a welding line, which is characterized in that the parent metal and the welding line are subjected to hardness test and micro-tensile test to obtain the linear relation between the tensile strength and the hardness of different materials of the parent metal and the welding line, when the tensile strength of the welding line welded by the same parent metal and welding line is required to be tested, the tensile strength and the yield strength of the welding line are predicted according to the hardness test result, and the hardness test is simple, convenient and feasible, has lower requirements on sample processing and small destructiveness on workpieces.
Description
[ field of technology ]
The invention relates to a method for predicting mechanical properties of a welding seam and a base metal, in particular to a method for predicting tensile strength and yield strength of a metal material base metal and the welding seam.
[ background Art ]
At present, the accident frequently occurs when the welding line of the oil and gas pipeline fails, and larger casualties, environmental pollution and property loss are often caused, so that the problem of circumferential weld safety is more and more important to pipeline operators. In actual engineering, the applicability evaluation result is an important basis for repairing the girth weld, and the accuracy of the applicability evaluation result is a key factor for determining whether the pipeline can be safely serviced. And the accuracy of the applicability evaluation result depends on the value of the evaluation parameter.
In the existing weld suitability evaluation, the mechanical property of a base material is generally used for replacing the mechanical property of a weld. The method is characterized in that in the welding process of the welding seam, the mechanical properties of the finally formed welding seam in different areas are greatly different due to the influences of welding rod materials, welding processes, welding currents and other parameters of different welding layers, and the sample processing is difficult because of smaller areas, so that the welding seam is difficult to sample and test the tensile properties, and the technology for testing the tensile mechanical properties of the welding seam is also a great difficulty in practical engineering research. In the welding of low-steel-grade pipelines, the welding seam and the base metal are in strong matching, the performance of the base metal is brought into a welding seam safety evaluation model, and the calculated result is slightly conservative. However, with the application of the X70 and higher steel grade pipelines, the problem of strong and weak matching between the welding seam and the parent metal still needs experimental verification. To answer this question, it is necessary to grasp the different mechanical properties of the weld, in particular the tensile strength and the yield strength. However, the related standards at present are that the welding seam is used as an integral structure to be researched, a welding seam tensile property test sample spans the whole welding seam area, and the macroscopic mechanical properties of the welding seam are obtained by the method, so that the mechanical property differences of different characteristic areas of the welding seam cannot be distinguished. For defects in the weld joint, the tensile property of materials nearby the defects plays a role in determining the formation and expansion of the defects, so that the mechanical property of the weld joint materials is a key for researching the formation and expansion mechanisms of the defects in the weld joint and improving the applicability evaluation accuracy and reliability of the defects in the weld joint. At present, all methods for determining the tensile mechanical properties of the welding seam adopt an indoor test, a sample needs to be processed, the sample processing and the test for the tensile properties of the welding seam are complicated, the method is not suitable for practical engineering, and for pipelines which cannot be subjected to destructive sampling on site, an effective prediction method for the tensile strength and the yield strength of a characteristic region of the welding seam is not available.
[ invention ]
The invention aims to overcome the defects of the prior art and provides a method for predicting the tensile strength and the yield strength of a metal material base metal and a welding line so as to overcome the defect of the prior art that the tensile strength and the yield strength of an actual welding line characteristic area are not predicted
In order to achieve the purpose, the invention is realized by adopting the following technical scheme:
a method for predicting tensile strength and yield strength of a metal material base material and a welding line comprises the following steps:
step 1, polishing and corroding one end face of a sample processing section, so that a welding line appears on the end face, and dividing the sample processing section into a first parent material area and a second parent material area by the welding line; the welding seam comprises a root welding layer, a filling layer and a cover layer which are sequentially stacked from bottom to top, and the two sides of the welding seam and the junction area of the two base metal areas are two heat affected areas;
step 2, determining the size of the tensile sample according to the size of each area;
the tensile sample is divided into two clamping sections, and a testing section is arranged between the two clamping sections; the widths of the test section and the clamping section are smaller than the width of the root welding layer, the width of the clamping section is larger than the width of the test section, the width of the test section is larger than the thickness of the test section, and the thicknesses of the test section and the clamping section are equal to the width of the heat affected zone;
step 3, arranging and drawing processing positions in each area on the end face according to the width and the thickness of the tensile sample, wherein the processing positions are rectangular frames, the length of the processing positions is the width of the clamping section, and the height of the processing positions is the thickness of the clamping section;
step 4, measuring the hardness value of each processing position;
step 5, cutting and processing all the tensile samples, and carrying out tensile mechanical property test on each tensile sample to obtain tensile strength and yield strength values of the tensile samples in each region in the base metal and the welding line;
step 6, according to the hardness value of each processing position, the tensile strength value and the yield strength value of all the tensile samples, establishing a prediction model of the relation between the tensile strength and the hardness of each region and a prediction model of the relation between the yield strength and the hardness of each region;
and 7, for the welding seam of the pipeline base material with the same material, obtaining the tensile strength and the yield strength of each region according to the hardness values of each region in the base material and the welding seam and the two prediction models.
The invention further improves that:
preferably, in step 2, the roughness of the end surface is less than 0.8.
Preferably, in step 2, the tensile test specimen satisfies the test section width x the test section thickness x σs, wherein σs is the yield strength of the weld characteristic region material, and is less than 80% of the measuring range of the tensile equipment.
Preferably, in step 3, the processing positions are drawn in each region by a grid drawing method.
Preferably, in step 4, the hardness of M positions is measured at each processing position, M is greater than or equal to 3, and the average value of the hardness of all the positions is the hardness value at the processing position.
Preferably, in the step 5, a wire cutting mode is adopted to cut and obtain a tensile sample; firstly, cutting two heat affected zones, then cutting each other zone according to layers, dividing each layer into a plurality of processing positions, and then cutting individual tensile samples from the heat affected zones and each layer.
Preferably, in the step 5, in the tensile test, deformation data of the tensile sample is recorded by an optical extensometer, load data is recorded by a tensile testing machine, and stress-strain curves of the tensile samples are determined by the deformation data and the data, so that tensile strength and yield strength values of the base material and each region of the weld joint are finally obtained.
Preferably, in step 6, the prediction model of the relationship between the tensile strength and the hardness of the base material and the weld characteristic region is:
σ l ＝A 1 ×H+B 1 (1)
the prediction model of the relation between the yield strength and the hardness of the base metal and the weld characteristic area is as follows:
σ s ＝A 2 ×H+B 2 (2)
in sigma 1 For tensile strength, σs is yield strength, H is characteristic zone hardness, A 1 、A 2 、B 1 And B 2 Is a fitting parameter.
Preferably, A 1 、A 2 、B 1 And B 2 Obtained by a least square method.
Preferably, in step 7, there are two methods for obtaining the hardness values of the base material and each region in the weld bead: the first method is that a hardness sample is processed indoors, hardness test is carried out, and hardness values of each area of a base metal and a welding line are obtained; the second is to obtain the hardness value for nondestructive testing in situ.
Compared with the prior art, the invention has the following beneficial effects:
the invention discloses a method for predicting tensile strength and yield strength of a metal material parent metal and a welding line, which is characterized in that the parent metal and the welding line are subjected to hardness test and micro-tensile test to obtain the linear relation between the tensile strength and the hardness of different materials of the parent metal and the welding line, when the tensile strength of the welding line welded by the same parent metal and welding line is required to be tested, the tensile strength and the yield strength of the welding line are predicted according to the hardness test result, and the hardness test is simple, convenient and feasible, has lower requirements on sample processing and small destructiveness on workpieces.
[ description of the drawings ]
FIG. 1 is an experimental flow for predicting the tensile strength of a base material and a weld characteristic region based on the relation between the strength and the hardness of a metal material;
FIG. 2 is a schematic diagram of a weld feature area structure distribution;
FIG. 3 illustrates a method for dividing a sample of a characteristic region of a base material and a weld;
wherein fig. 3 (a) is a schematic view of a base material and a weld cross section, and fig. 3 (b) is a cross section taken from A-A of fig. 3 (a);
the tensile strength and hardness relationship of the weld characteristic region material obtained in the first embodiment of fig. 4, wherein the abscissa represents the vickers hardness of the base material and the weld characteristic region, and the ordinate represents the tensile strength of the weld characteristic region material in MPa;
the relationship between the yield strength and the hardness of the weld characteristic region material obtained in the first embodiment of fig. 5, wherein the abscissa represents the vickers hardness of the base material and the weld characteristic region material, and the ordinate represents the tensile strength of the weld characteristic region material in MPa;
in the figure:
1. a first parent material region; 2. a second parent material region; 3. a cover layer; 4. a filling layer; 5. root welding layer; 6. a first heat affected zone; 7. a second heat affected zone; 8. stretching the sample in the characteristic area; 9. a hardness test point; 10-weld joint.
[ detailed description ] of the invention
The invention is described in further detail below with reference to the attached drawing figures:
in the description of the present invention, it should be noted that, directions or positional relationships indicated by terms such as "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., are based on directions or positional relationships shown in the drawings, are merely for convenience of description and simplification of description, and do not indicate or imply that the apparatus or element to be referred to must have a specific direction, be constructed and operated in the specific direction, and thus should not be construed as limiting the present invention; the terms "first," "second," and "third" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance; furthermore, unless explicitly specified and limited otherwise, the terms "mounted," "connected," and "connected" are to be construed broadly, and may be either fixed or removable, for example; can be directly connected or indirectly connected through an intermediate medium, and can be communication between two elements. The specific meaning of the above terms in the present invention will be understood in specific cases by those of ordinary skill in the art.
Referring to fig. 1, the experimental method for predicting the tensile strength of a base metal and a weld characteristic region based on the relation between the strength and the hardness of a metal material provided by the invention specifically comprises the following steps: sample processing section selection, characteristic region division, tensile sample design and arrangement, hardness test, tensile sample processing and testing, prediction model and prediction method.
Step one: and selecting a sample processing section.
Observing the weld joint material, and marking out the parts containing geometric defects such as staggered edges, undercut, weld flash and the like; and carrying out nondestructive detection on the welding line, and marking out welding defect positions such as surface cracks, incomplete penetration, incomplete fusion and the like. And selecting a defect-free part as a sample processing section. The length of the sample processing section along the weld joint is greater than the length of the tensile sample in a characteristic area, wherein the characteristic area is a generic name of a weld joint cover layer, a filling layer, a weld heel and a heat affected zone.
Step two: and (5) dividing characteristic areas.
Cutting the selected sample processing section into blanks with the length longer than the design length of the tensile sample in the characteristic area along the direction of a vertical welding line, and polishing two cutting surfaces of the blanks to ensure that the surface roughness of the two cutting surfaces is lower than Ra0.8 and the two cutting surfaces are parallel to each other; etching one surface by using a welding seam etching solution until a heat affected zone, a root welding layer 5, a filling layer 4 and a cover layer 3 of the welding seam are displayed; as shown in fig. 2, the whole sample processing section is divided into a first parent material zone 1 and a second parent material zone 2 by a welding line 10, the welding line 10 is arranged between the first parent material zone 1 and the second parent material zone 2, the junction of the welding line 10 and the first parent material zone 1 is a first heat affected zone 6, and the junction of the welding line 10 and the second parent material zone 2 is a second heat affected zone 7; the welding seam 10 sequentially comprises a root welding layer 5, a filling layer 4 and a cover layer 3 from bottom to top, wherein the width of the root welding layer 5 is smaller than that of the filling layer 4, and the width of the filling layer 4 is smaller than that of the cover layer 3.
Step three: and (5) designing and arranging tensile samples.
The test section and the clamping section of the test sample are transited through an arc, so that the size of the welding seam tensile test sample is maximized on the premise that the welding seam tensile test sample does not exceed the range of the characteristic area; taking the width of a heat affected zone as the thickness H of a tensile sample, wherein two ends of the tensile sample are clamping sections, the middle part of the tensile sample is a test section, the width W of the test section is larger than the thickness H of the tensile sample and smaller than the width of a root welding layer 5 part, and meanwhile, the condition that sigma s is smaller than 80% of the measuring range of test equipment is satisfied, wherein sigma s is the yield strength of a welding seam characteristic region material; the width of the tensile sample clamping section is smaller than the width of the root welding layer part and larger than the width of the test section.
The sample sizing results are shown in the following table
Because the characteristic area material property of the weld joint is tested, and the characteristic area size is smaller, the whole sample needs to be processed in the characteristic area, and the sample size should be increased as much as possible in order to reduce the processing difficulty and the size effect of the test. In addition, the heat affected zone is the most elongated zone among all the characteristic zones, so the sample thickness direction is distributed along the width direction of the heat affected zone in the heat affected zone, in order to ensure that the sample size processed in each zone is the same, the sample thickness is based on the width of the heat affected zone, and other zones can necessarily contain the sample thickness as long as the sample thickness can be contained in the width of the heat affected zone.
The arrangement of the tensile test samples in each characteristic area is marked on the corroded end face of the blank by a marker pen, the length direction of the tensile test samples is along the longitudinal direction of the welding line, and one end face of the tensile test samples is positioned in the corroded face of the blank. The number and positions of the machinable tensile samples in each region are designed according to the sizes of the weld heat affected zone, the cover layer, the filling layer and the root weld layer. Designing the processing positions and the number of the tensile samples in each layer by utilizing the geometric shape characteristics of each region and a grid drawing method on the cover layer, the filling layer and the root welding layer, wherein one grid is one processing position; in the heat affected zone of the welding seam, the width direction of the tensile sample is distributed along the outline of the heat affected zone, the thickness direction of the tensile sample is distributed along the stacking direction of the welding seam at the cover layer, the filling layer and the root welding layer part of the welding seam, and the processing position and the number of the tensile sample in each layer are designed by utilizing the geometric shape characteristics of each area and through a grid drawing method. Each tensile specimen processing location is numbered. And (3) carrying out stretching sample arrangement on the parent material area in the same mode as the weld filling layer.
Step four: hardness testing.
And testing the hardness of the material at each sample processing position by using a hardness tester, wherein the test surface is the corroded end surface of the blank, the hardness test point of each sample is positioned in the divided tensile sample end surface grids, at least 3 hardness tests at different positions are carried out in the same grid, and the hardness values obtained by multiple tests are averaged to obtain the hardness value of the position (grid).
Step five: and (5) processing and testing a tensile sample.
The sample processing adopts a linear cutting mode, firstly, two heat affected zones of a blank are integrally cut along the outline by using a slow wire method, and then, the cut heat affected zone slices are cut into a tensile sample along the designed position by using a slow wire. And (3) cutting the rest blank by adopting a slow wire, firstly cutting each layer of the grid shape designed in each region integrally, and then cutting each sample by utilizing the slow wire. The sample position is marked in the drawing.
During tensile mechanical property test, a tensile sample is clamped on a tensile testing machine, the deformation of a gauge length section of the tensile sample is monitored and recorded by an optical extensometer in the test process, and the loads at two ends of the tensile sample are monitored and recorded by the tensile testing machine. After the test is finished, the stress-strain curve of each tensile sample is calculated by using the sample deformation data recorded by the optical extensometer and the load data recorded by the tensile experiment machine, so that the tensile strength and the yield strength values of the base material and the materials in each characteristic area of the welding seam are obtained.
Step six: and (5) a prediction model.
The tensile strength and hardness relation prediction model of the base metal and the weld characteristic area is as follows:
σ l ＝A 1 ×H+B 1 (1)
the prediction model of the relation between the yield strength and the hardness of the base metal and the weld characteristic area is as follows:
σ s ＝A 2 ×H+B 2 (2)
in sigma 1 For tensile strength, σs is yield strength, H is characteristic zone hardness, A 1 、A 2 、B 1 And B 2 Is a fitting parameter.
And (3) performing linear fitting on the tensile strength of the base material and the weld characteristic region and the hardness of the corresponding position by using a least square method to obtain parameters A1 and B1 in the formula (1), namely determining a prediction model of the relationship between the tensile strength and the hardness of the base material and the weld characteristic region.
And (3) performing linear fitting on the yield strengths of the base metal and the weld characteristic region and the hardness of the corresponding position by using a least square method to obtain parameters A2 and B2 in the formula (2), namely determining a prediction model of the relation between the yield strengths and the hardness of the base metal and the weld characteristic region.
Step seven: a prediction method.
After a predicting model of the relation between the tensile strength and the hardness of the characteristic areas of the welding line and the base material is obtained through the first six steps of an experiment, the hardness values of the base material and the characteristic areas of the welding line are obtained through a hardness test for the base material and the welding line of the pipeline with the same material, and after the hardness units are converted into the same units as those when the parameters of the formula (1) are fitted, the tensile strength of the base material and the characteristic areas of the welding line can be predicted according to the formula (1), and similarly, the yield strength of the base material and the characteristic areas of the welding line can be predicted according to the formula (2). The specific method comprises the following steps:
(1) And for indoor detection, processing a hardness sample, performing hardness test to obtain hardness values of different characteristic areas of the base metal and the welding line, and converting the hardness units into the hardness units consistent with those in the prediction model. Substituting the hardness values of different positions into the formula (1), and calculating to obtain the tensile strength values of the base metal and the weld characteristic region; substituting the hardness values of different positions into formula (2), and calculating to obtain yield strength values of the base metal and the weld characteristic region.
(2) And for on-site nondestructive detection, performing hardness test on the surfaces of the base metal and the weld joint cover layer to obtain the surface hardness of the base metal and the weld joint cover layer, and converting the hardness unit into the hardness unit consistent with that in the prediction model. Substituting hardness values of different positions of the surfaces of the base metal and the weld joint cover layer into the formula (1), and calculating to obtain tensile strength values of the positions; substituting the hardness values of different positions of the surfaces of the base metal and the weld joint cover layer into the (2), and calculating to obtain the yield strength value of the position.
Example 1
The embodiment is a test method for predicting the tensile strength of a base metal and girth weld characteristic area of a pipeline of a natural gas station based on the relation between the strength and the hardness of a metal material. The girth weld is a butt-joint girth weld of pipelines with different wall thicknesses and different materials. The butt joint steel pipe parent metal a1 is X60 steel, and the thickness is 28mm; the base material b2 was X80 steel and had a thickness of 43mm. The outer diameters of the butt joint steel pipes are 914mm.
The experimental method for predicting the tensile strength of the base metal of the natural gas station and the characteristic region of the girth weld based on the relation between the strength and the hardness of the metal material provided by the embodiment specifically comprises the following steps: sample processing section selection, characteristic region division, tensile sample design and arrangement, hardness test, tensile sample processing and testing, prediction model and prediction method.
Step one: and selecting a sample processing section.
Observing the weld joint material, and marking out the parts containing geometric defects such as staggered edges, undercut, weld flash and the like; and carrying out nondestructive detection on the welding line, and marking out welding defect positions such as surface cracks, incomplete penetration, incomplete fusion and the like. And selecting a part which accords with the research characteristics as a sample processing section, wherein the circumferential length of the sample processing section along the girth weld is 300mm, and the length of the vertical weld is 120mm.
Step two: and (5) dividing characteristic areas.
Cutting the selected sample processing section into blanks with the length longer than the design length of the tensile sample in the characteristic area along the direction of a vertical welding line, and polishing two cutting surfaces of the blanks to ensure that the surface roughness of the two cutting surfaces is lower than Ra0.8 and the two cutting surfaces are parallel to each other; and (3) corroding one surface by using the welding seam corrosive liquid until the welding seam corrosive liquid shows a heat affected zone, a root welding layer, a filling layer and a cover layer of the welding seam.
Cutting the selected sample processing section perpendicular to the girth weld into blanks with the length of 35mm, and polishing two cutting surfaces of the blanks, wherein the surface roughness is lower than Ra0.8 and the two cutting surfaces are parallel to each other. One end face is corroded by the welding seam corrosive liquid, and a first heat affected zone 6, a second heat affected zone 7, a root welding layer 5, a filling layer 4 and a cover layer 3 of the girth weld are displayed.
Step three: and (5) designing and arranging tensile samples.
The widths of the first heat affected zone 6 and the second heat affected zone 7 of the weld were measured to be 2mm, the lengths were measured to be 32mm, and the heights of the root welds 5 were measured to be 4mm, and the widths were measured to be 10mm. The geometry of the tensile sample in the design characteristic area is in a flat dog-bone shape, the thickness is 1mm, the width of the test section is 2mm, the width of the clamping section is 5mm, and the test section and the clamping section of the sample are transited through an arc with the radius of 3mm.
The arrangement of the tensile test pieces 8 in the characteristic areas is marked by a marker on the corroded end face of the blank. According to the sizes of the first heat affected zone 6, the second heat affected zone 7, the cover layer 3, the filling layer 4 and the root welding layer 5 of the welding seam, the number of machinable samples in each area is designed as follows: the first heat affected zone 6 and the second heat affected zone 7 each processed 6 samples along the contour, 3 layers in the cover layer 3, 4 samples per layer, 6 layers in the filler layer 4, 4 samples per layer, 3 layers in the root weld layer 5, 2 samples per layer. Sample arrangement is carried out on the parent material area in the same mode as the weld filling layer.
Step four: hardness testing.
And testing the hardness of the material at the processing position of each welding seam characteristic region sample by using a hardness tester, wherein the testing surface is the corroded end surface of the blank, the hardness test point 9 of each sample is positioned in the drawn grid, the hardness test at different positions is carried out 3 times in the same grid, and the average value of the hardness values tested for multiple times is taken as the hardness value of the position. The hardness adopts a Vickers hardness tester, and the probe is HV1.
Step five: and (5) processing and testing a tensile sample.
The sample processing adopts a linear cutting mode, a first heat affected zone 6 and a second heat affected zone 7 of the blank are firstly cut off along the whole outline by using a slow wire method, then cut off heat affected zone slices into a characteristic area tensile sample 8 along the designed position by using a slow wire, and each sample is numbered and position marked. And (3) cutting the rest blank by adopting a slow wire, firstly cutting each layer of the grid shape designed in each region integrally during cutting, and then cutting each sample by utilizing the slow wire. And numbering each processed sample, and marking the sample position in the drawing.
When the tensile mechanical property of the characteristic region of the welding line is tested, firstly, designing and processing a clamp of the tensile sample of the characteristic region according to the size of the tensile sample 8 of the characteristic region; before testing, marking a white small point at each end of a test section of the sample by using a marking pen as an identification point of an optical extensometer, and measuring the width and thickness of a gauge length section of the sample by using a vernier caliper or a micrometer; during the experiment, the characteristic region tensile sample 8 is clamped on a tensile testing machine, the deformation of the sample gauge length section is monitored and recorded by utilizing an optical extensometer in the experimental process, and the tensile force at two ends of the characteristic region tensile sample 8 is detected and recorded by utilizing the tensile testing machine. After the test is finished, the stress-strain curve of the tensile sample in the characteristic region is calculated by using the deformation data of the sample recorded by the optical extensometer and the load data recorded by the tensile experiment machine, and then the tensile strength and the yield strength value of the material in each region of the welding line are obtained.
Step six: and (5) a prediction model.
And (3) performing linear fitting on the tensile strength of the base material and the weld characteristic region and the hardness of the corresponding position by using a least square method to obtain parameters A1 and B1 in the formula (1), namely determining a prediction model of the relationship between the tensile strength and the hardness of the base material and the weld characteristic region.
And (3) performing linear fitting on the yield strengths of the base metal and the weld characteristic region and the hardness of the corresponding position by using a least square method to obtain parameters A2 and B2 in the formula (2), namely determining a prediction model of the relation between the yield strengths and the hardness of the base metal and the weld characteristic region.
Step seven: a prediction method.
After a predicting model of the relation between the tensile strength and the hardness of the characteristic areas of the welding line and the base material is obtained through the first six steps of an experiment, the hardness values of the base material and the characteristic areas of the welding line are obtained through a hardness test for the base material and the welding line of the pipeline with the same material, and after the hardness units are converted into the same units as those when the parameters of the formula (1) are fitted, the tensile strength of the base material and the characteristic areas of the welding line can be predicted according to the formula (1), and similarly, the yield strength of the base material and the characteristic areas of the welding line can be predicted according to the formula (2). The specific method comprises the following steps:
(1) For indoor detection, a hardness sample is processed, hardness test is carried out, a probe is HV1, hardness values of different characteristic areas of a base material and a welding line are obtained, and hardness units are converted into the same hardness units in a prediction model. Substituting the hardness values of different positions into the formula (1), and calculating to obtain the tensile strength values of the base metal and the weld characteristic region; substituting the hardness values of different positions into formula (2), and calculating to obtain yield strength values of the base metal and the weld characteristic region.
(2) For on-site nondestructive detection, a portable D-type impact device with the Brinell hardness is adopted to perform characteristic region hardness test on the surfaces of the base metal and the weld joint cover layer, so that the surface hardness of the base metal and the weld joint cover layer is obtained, and the hardness unit is converted into the hardness unit consistent with that in a prediction model. Substituting hardness values of different positions of the surfaces of the base metal and the weld joint cover layer into the formula (1), and calculating to obtain tensile strength values of the positions; substituting the hardness values of different positions of the surfaces of the base metal and the weld joint cover layer into the (2), and calculating to obtain the yield strength value of the position.
The foregoing description of the preferred embodiments of the invention is not intended to be limiting, but rather is intended to cover all modifications, equivalents, alternatives, and improvements that fall within the spirit and scope of the invention.
Claims (7)
1. A method for predicting tensile strength and yield strength of a metal material base material and a weld joint is characterized by comprising the following steps:
step 1, polishing and corroding one end face of a sample processing section, so that a welding line (10) appears on the end face, and dividing the sample processing section into a first parent material area (1) and a second parent material area (2) by the welding line (10); the welding seam (10) comprises a root welding layer (5), a filling layer (4) and a cover layer (3) which are sequentially stacked from bottom to top, and two heat affected zones are arranged at two sides of the welding seam (10) and in a junction area of two base metal zones;
step 2, determining the size of the tensile sample according to the size of each area;
the tensile sample is divided into two clamping sections, and a testing section is arranged between the two clamping sections; the widths of the test section and the clamping section are smaller than the width of the root welding layer (5), the width of the clamping section is larger than the width of the test section, the width of the test section is larger than the thickness of the test section, and the thicknesses of the test section and the clamping section are equal to the width of the heat affected zone;
in the step 2, the tensile sample meets the requirements that the width of a test section is multiplied by the thickness of the test section, and multiplied by sigma s is smaller than 80% of the measuring range of a tensile device, wherein sigma s is the yield strength of a welding seam characteristic area material;
taking the width of the heat affected zone as the thickness H of the tensile sample;
step 3, arranging and drawing processing positions in each area on the end face according to the width and the thickness of the tensile sample, wherein the processing positions are rectangular frames, the length of the processing positions is the width of the clamping section, and the height of the processing positions is the thickness of the clamping section;
in the heat affected zone of the weld joint, the width direction of the tensile sample is distributed along the contour line of the heat affected zone, and in the cover layer, the filling layer and the root welding layer part of the weld joint, the thickness direction of the tensile sample is distributed along the stacking direction of the weld joint;
step 4, measuring the hardness value of each processing position;
in the step 4, the hardness of M positions is measured at each processing position, M is more than or equal to 3, and the average value of the hardness of all the positions is the hardness value at the processing position;
step 5, cutting and processing all the tensile samples, and carrying out tensile mechanical property test on each tensile sample to obtain tensile strength and yield strength values of the tensile samples in each region in the base metal and the welding line;
step 5, cutting in a linear cutting mode to obtain a tensile sample; firstly cutting two heat affected zones, then cutting each other zone according to layers, dividing each layer into a plurality of processing positions, and then cutting independent tensile samples from the heat affected zones and each layer;
step 6, according to the hardness value of each processing position, the tensile strength value and the yield strength value of all the tensile samples, establishing a prediction model of the relation between the tensile strength and the hardness of each region and a prediction model of the relation between the yield strength and the hardness of each region;
and 7, for the welding seam of the pipeline base material with the same material, obtaining the tensile strength and the yield strength of each region according to the hardness values of each region in the base material and the welding seam and the two prediction models.
2. The method for predicting tensile strength and yield strength of a metal material base material and weld joint according to claim 1, wherein in step 2, the roughness of the end face is less than 0.8.
3. The method for predicting the tensile strength and yield strength of a metal material base material and weld joint according to claim 1, wherein in step 3, the machining positions are drawn in each region by a grid drawing method.
4. The method for predicting the tensile strength and the yield strength of a metal material base material and a weld joint according to claim 1, wherein in the step 5, deformation data of the tensile test specimen is recorded by an optical extensometer, load data is recorded by a tensile testing machine, and stress-strain curves of the tensile test specimen are determined by the deformation data and the data, so that the tensile strength and the yield strength values of each region of the base material and the weld joint are finally obtained.
5. The method for predicting tensile strength and yield strength of a metal material base material and weld joint according to claim 1, wherein in step 6, a model for predicting the relationship between tensile strength and hardness of the base material and the weld joint characteristic region is:
σ l ＝A 1 ×H+B 1 (1)
the prediction model of the relation between the yield strength and the hardness of the base metal and the weld characteristic area is as follows:
σ s ＝A 2 ×H+B 2 (2)
in sigma l For tensile strength, σs is yield strength, H is characteristic zone hardness, A 1 、A 2 、B 1 And B 2 Is a fitting parameter.
6. The method for predicting the tensile strength and yield strength of a weld joint and a base metal material as set forth in claim 5, wherein A 1 、A 2 、B 1 And B 2 Obtained by a least square method.
7. The method for predicting the tensile strength and yield strength of a metal material base material and a weld joint according to any one of claims 1 to 5, wherein in step 7, there are two methods for obtaining the hardness values of each region in the base material and the weld joint: the first method is that a hardness sample is processed indoors, hardness test is carried out, and hardness values of each area of a base metal and a welding line are obtained; the second is to obtain the hardness value for nondestructive testing in situ.
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| CN112950633B (en) * | 2021-04-19 | 2023-06-23 | 上海电机学院 | Aluminum alloy weld joint surface defect detection method based on line structured light |
| CN114216772A (en) * | 2021-12-09 | 2022-03-22 | 中国石油大学(北京) | Welding seam constitutive relation determining method and device and electronic equipment |
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