CN108676975B - Heat treatment method for removing segregation defects in metal welding seam - Google Patents
Heat treatment method for removing segregation defects in metal welding seam Download PDFInfo
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- CN108676975B CN108676975B CN201810558393.6A CN201810558393A CN108676975B CN 108676975 B CN108676975 B CN 108676975B CN 201810558393 A CN201810558393 A CN 201810558393A CN 108676975 B CN108676975 B CN 108676975B
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/34—Methods of heating
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D6/00—Heat treatment of ferrous alloys
- C21D6/005—Heat treatment of ferrous alloys containing Mn
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D6/00—Heat treatment of ferrous alloys
- C21D6/008—Heat treatment of ferrous alloys containing Si
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
- C21D9/50—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for welded joints
- C21D9/505—Cooling thereof
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/001—Austenite
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Abstract
The invention providesThe heat treatment method for removing the segregation defect in the metal welding seam comprises the steps of firstly carrying out spectral measurement on welding seam metal and determining the contents of C element and each alloy element; recalculating Ar for austenite to ferrite transformation3(ii) temperature; then, the weld metal is heated to complete austenitization Ar3Keeping the temperature above 30 ℃ to ensure that the welded part is completely austenitized; and then air-cooled. Compared with the prior art, the heat treatment process provided by the invention adopts a mode of homogenizing the chemical components of the weld joint area of the welding part, eliminating the use defect caused by segregation and improving the use performance of the welding part. The method is mainly characterized in that a welding seam of a welding part is heated to the highest temperature on the premise of not melting, heat preservation is carried out for a long time, and after various alloy elements in the welding part are diffused and tend to be uniformly distributed, slow cooling is carried out.
Description
Technical Field
The invention belongs to the field of metal heat treatment, and particularly relates to a heat treatment method for removing segregation defects in a metal welding seam.
Background
The phenomenon of uneven distribution of chemical components contained in steel is called segregation, and weld segregation is formed in the process that when liquid metal is crystallized once during metal welding, the metal is transformed from a liquid state to a solid state. Due to the difference in welding process, different micro-segregation and zone segregation may occur.
Microsegregation is also called intragranular segregation, and the main factor affecting microsegregation is the chemical composition of the metal. Since metals have different chemical compositions, the temperature range from the start of crystallization to the end of crystallization is different, and microscopic segregation tends to occur as the temperature range is larger. Generally, for low-carbon steel, the microsegregation is not serious, and the damage to a welding seam is not great; and the welding of high carbon steel and alloy steel can cause defects such as heat cracks and the like due to serious microsegregation. The region segregation is formed by accumulating a large amount of impurities and a low-melting-point alloy in a cooling portion (weld center) of the weld. The occurrence of segregation can cause potential cracks to appear in the welding seam under the condition of working stress, particularly hot cracks appear in the environment with higher temperature, the mechanical property of the welding seam is invalid, and unnecessary accidents occur.
The method can not be carried out in a welding place under ideal working environment and technical parameters all the time, and the metal segregation of the welding seam caused by too high welding cooling speed and welding process errors is difficult to avoid. In some welding processes, in order to avoid welding defects caused by segregation, the number, width and depth of welding layers of welding beads are directly increased in the welding process, and a mode of welding multiple welding channels at increased cost is rather adopted, so that the welding safety index is increased, and the welding cost is increased.
Disclosure of Invention
The invention aims to provide a heat treatment method for removing segregation defects in metal welding seams, which adopts a proper heat treatment process to homogenize chemical components in the welding seam areas of welding parts, eliminates use defects caused by segregation, improves the use performance of the welding parts, avoids potential cracks of the welding seams in a working stress state caused by the occurrence of segregation, particularly avoids mechanical property failure and unnecessary accidents of the welding seams caused by the occurrence of hot cracks in a high-temperature environment, and reduces the loss of the economic value of the welding process.
The specific technical scheme of the invention is as follows:
a heat treatment method for removing segregation defects in a metal welding seam comprises the following steps:
1) performing spectral measurement on weld metal, and determining the contents of C element and each alloy element;
2) calculating Ar for converting austenite to ferrite according to the content of each element3(ii) temperature;
3) heating the weld metal to full austenization Ar3Keeping the temperature above 30 ℃ to ensure that the welded part is completely austenitized;
4) and (5) after heat preservation, air cooling is carried out, and the product is obtained.
Further, the incubation time in step 3) is at least 20 minutes.
Further, air cooling is carried out in the step 4), and the average cooling speed is 120 +/-10 ℃/h.
In the invention, weld metal austenitizing Ar is firstly carried out3And (3) temperature measurement:
① measuring the content of weld metal element, namely performing spectral measurement by using weld metal as a sample to determine the content of C element and various alloy elements;
② calculating the weld metal carbon equivalent according to the empirical formula:
CE＝C+A(C){Si/24+Mn/16+Cu/15+Ni/20+(Cr+Mo+V+Nb)/5+5B}
③ selection of suitable Ar for austenite to ferrite transformation based on calculated carbon equivalent and content of alloying elements3Temperature ofCalculation formulas, such as the following scientific empirical formulas:
Ar3＝868-396C-68.1Mn+24.6Si-36.1Ni-24.8Cr-20.7Cu；
or, Ar3＝910-273C-74Mn-56Ni-16Cr-9Mo-5Cu；
Then, a heat treatment process is established, and the heating and heat preservation time and the cooling rate of the welding workpiece in the cooling stage are determined:
① heating and heat-preserving stage, wherein the welding workpiece needs to be heated with the furnace, and needs to be heated to be higher than the welding seam metal steel grade to be completely austenitized (Ar)3) The temperature is 30 ℃ above. To fully austenitize the material, the weld metal is heated to fully austenitize (Ar) the weld metal3) After the temperature is 30 ℃ above, the temperature is kept for at least 20 minutes to ensure that the welded part is completely austenitized.
② cooling stage, taking out the welded part after heat preservation, and performing tests by using cooling means with different cooling rates such as air cooling, sand cooling, air cooling, water cooling and the like.
The two stages respectively need to be tested to determine the process parameters of the heating holding time and the cooling rate of the cooling stage, and the optimal and effective combination of the two process parameters also needs to be determined by cross tests. After the process theory is determined, a large number of test samples prove that the effect is excellent.
The invention adopts proper heat treatment process to carry out heat treatment on the welded workpiece, which can eliminate weld segregation, and moreover, the heat treatment mode can further refine crystal grains, improve the strength of steel grade and avoid accidents caused by defects in the use process of the welded workpiece.
Firstly, performing spectral measurement on weld metal, and determining the contents of C element and each alloy element; then calculating the Ar3 temperature for the transformation from austenite to ferrite; then, heating the welding metal to a temperature of more than 30 ℃ of the complete austenitizing Ar3 temperature, and preserving heat to enable the welding part to be completely austenitized; and then air-cooled. The process of the invention not only eliminates the segregation defect (see a metallographic diagram) in the material structure of the welding seam of the welding part, avoids the potential cracks of the welding seam due to the segregation of the metal of the welding seam in the working stress state or the high temperature state, avoids the possible safety accidents, and reduces the welding layer number, the width and the depth of the welding seam during the welding process for increasing the safety index of the welding seam during the welding work, thereby reducing the welding cost. Through the air cooling heat treatment process, the segregation defect in the metallographic structure of the welding seam is obviously improved, the structure crystal grains are refined, the mechanical property of the workpiece is improved, and in the aspect of mechanical strength, the yield strength and the tensile strength of the welded workpiece after the heat treatment process are different from those of the workpiece before the heat treatment.
Compared with the prior art, the heat treatment process provided by the invention adopts a mode of homogenizing the chemical components of the weld joint area of the welding part, eliminating the use defect caused by segregation and improving the use performance of the welding part. The method is mainly characterized in that a welding seam of a welding part is heated to the highest temperature on the premise of not melting, heat preservation is carried out for a long time, and after various alloy elements in the welding part are diffused and tend to be uniformly distributed, slow cooling is carried out.
Drawings
FIG. 1 shows the metallographic structure of a weld before heat treatment according to the invention;
FIG. 2 shows the metallographic structure of the air-cooled weld after the heat treatment of the present invention.
Detailed Description
Example 1
A heat treatment method for removing segregation defects in a metal welding seam comprises the following steps:
1) performing spectral measurement on weld metal, and determining the contents of C element and each alloy element; specifically, see table 1 below:
table 1 basic chemical composition of the test steel material, the balance being iron and unavoidable impurities,
| C | Si | Mn | P | S | Als |
| 0.12 | 0.25 | 1.40 | ≤0.015 | ≤0.005 | 0.030 |
the most common hot rolled structural steel used in this test.
2) Calculating the Ar3 temperature for the transformation from austenite to ferrite according to the content of each element;
② calculating the weld metal carbon equivalent according to the empirical formula:
CE＝C+A(C){Si/24+Mn/16+Cu/15+Ni/20+(Cr+Mo+V+Nb)/5+5B}
③ selecting proper Ar3 temperature calculation formula for transformation from austenite to ferrite according to the calculated carbon equivalent and the content of alloy elements, such as the following scientific empirical formula:
Ar3＝868-396C-68.1Mn+24.6Si-36.1Ni-24.8Cr-20.7Cu；
or, Ar3＝910-273C-74Mn-56Ni-16Cr-9Mo-5Cu；
Then, a heat treatment process is established, and the heating and heat preservation time and the cooling rate of the welding workpiece in the cooling stage are determined:
① heating and heat-preserving stage, wherein the welding workpiece needs to be heated along with the furnace, and needs to be heated to a temperature higher than the temperature of the welding seam metal steel type Ar3 by 30 ℃ (760 ℃), and the temperature is preserved for at least 30min to ensure the complete austenitization of the welding part.
② cooling stage, taking out the welded part after heat preservation, and performing tests by using cooling means with different cooling rates such as air cooling, sand cooling, air cooling, water cooling and the like.
The two stages respectively need to be tested to determine the process parameters of the heating holding time and the cooling rate of the cooling stage, and the optimal and effective combination of the two process parameters also needs to be determined by cross tests. After the process theory is determined, a large number of test samples prove that the effect is excellent.
3) After the welding metal is heated to the temperature of over 30 ℃ of the Ar3 complete austenitizing temperature (760 ℃), the temperature is kept for 30min, and the heating to the complete austenitizing temperature is to make the temperature reach the austenite transformation temperature so as to transform the ferrite and the cementite in the structure back to the austenite. The heat preservation time is ensured to be favorable for ensuring that the structure in the material has sufficient time to transform after reaching the complete austenitizing temperature, so that the structure can be fully and completely transformed into austenite.
4) And after heat preservation, cooling at an average cooling speed of 120 ℃/h.
Comparative example
The sample and the heat treatment method used were the same as in example 1, except that the weld was taken out after the heat preservation, and the test was carried out by cooling means having different cooling rates such as air cooling, sand cooling, air cooling, and water cooling.
And manufacturing metallographic samples from weld metals of the welding parts of the heat treatment processes with different cooling modes.
The metallographic structures after the heat treatment processes of different cooling modes are compared with each other and the original metallographic structures, and the air cooling mode can be determined to be the best cooling mode by observing segregation.
FIG. 1 shows the metallographic structure of a weld before heat treatment according to the invention; FIG. 2 shows the metallographic structure of the air-cooled weld after the heat treatment of the present invention. As can be seen from FIG. 1 and FIG. 2, the grains in the metallographic structure of the weld before the air cooling heat treatment test are coarse and are accompanied by some lamellar segregation aggregates, the grains in the metallographic structure of the weld after the air cooling heat treatment test are obviously reduced and thinned, and the lamellar segregation aggregates are also obviously improved.
The mechanical properties of the 3 samples after treatment of example 1 were compared with those before treatment, and the results are shown in table 2 below.
TABLE 2
| Numbering | Yield strength (Mpa) | Tensile strength (Mpa) |
| Original sample before heat treatment | 385 | 520 |
| Sample 1 after air-cooled heat treatment | 380 | 525 |
| Sample 2 after air-cooled heat treatment | 390 | 530 |
| Sample 3 after air-cooled heat treatment | 400 | 550 |
As can be seen from Table 2, the strength values of the weld of the welded parts after heat treatment were not affected by the heat treatment process, and the strength values were substantially different from those of the original samples before the heat treatment process.
The heat treatment method for removing the segregation defect in the metal welding seam can microscopically effectively remove the segregation defect generated in the welding seam of a welding part, and simultaneously refine the grain structure and improve the comprehensive mechanical property of the welding part. Macroscopically, potential cracks of the welding line are avoided under the working stress state or the high-temperature state due to the metal segregation of the welding line, possible safety accidents are avoided, and the welding cost is reduced. The segregation defect generated in the welding seam of the welding part is effectively removed, the grain structure is refined, the strength of the metal of the welding seam of the welding part is ensured to be unchanged, and the normal use of the metal is ensured.
Claims (1)
1. A heat treatment method for removing segregation defects in a metal welding seam is characterized by comprising the following steps:
1) performing spectral measurement on weld metal, and determining the contents of C element and each alloy element;
2) calculating the Ar3 temperature for the transformation from austenite to ferrite according to the content of each element;
3) heating the welding metal to a temperature of more than 30 ℃ of the complete austenitizing Ar3 temperature, and then preserving heat to enable the welding part to be completely austenitizing;
4) after heat preservation, air cooling is carried out;
the heat preservation time in the step 3) is at least 20 minutes;
step 4), air cooling is carried out, and the average cooling speed is 120 +/-10 ℃/h;
the weld metal consists of the following elements in percentage by weight: 0.12% of C, 0.25% of Si, 1.40% of Mn, less than or equal to 0.015% of P, less than or equal to 0.005% of S, 0.030% of Als, and the balance of iron and inevitable impurities.
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Citations (1)
| Publication number | Priority date | Publication date | Assignee | Title |
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| JPS6479320A (en) * | 1987-09-19 | 1989-03-24 | Nippon Steel Corp | Improvement of material quality of metal for welding austenitic stainless steel |
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| CN101503757A (en) * | 2009-03-11 | 2009-08-12 | 中国科学院金属研究所 | Heat treatment technique for improving niobium-containing low-carbon steel weld metal structure and comprehensive property |
| US9879334B2 (en) * | 2011-03-29 | 2018-01-30 | Jfe Steel Corporation | Abrasion resistant steel plate or steel sheet excellent in resistance to stress corrosion cracking and method for manufacturing the same |
| CN102912108A (en) * | 2012-10-23 | 2013-02-06 | 鞍钢股份有限公司 | Heat treatment process for improving microstructure and properties of micro-alloy steel weld joint |
| JP6128276B2 (en) * | 2014-03-17 | 2017-05-17 | Ｊｆｅスチール株式会社 | Steel for welding |
| CN106755868B (en) * | 2016-12-13 | 2019-01-18 | 钢铁研究总院 | A kind of low cost can Large Heat Input Welding high-strength and high ductility steel plate manufacturing method |
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| JPS6479320A (en) * | 1987-09-19 | 1989-03-24 | Nippon Steel Corp | Improvement of material quality of metal for welding austenitic stainless steel |
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