阅读说明：本技术 一种316l工艺管线焊接热影响区抗点蚀和晶间腐蚀协同提升的焊接方法 (Welding method for cooperatively improving pitting corrosion resistance and intergranular corrosion resistance of welding heat affected zone of 316L process pipeline ) 是由 韩永典 李武成 徐连勇 赵雷 郝康达 荆洪阳 于 2021-08-23 设计创作，主要内容包括：本发明提供了316L工艺管线焊接热影响区抗点蚀和晶间腐蚀协同提升的焊接方法,涉及焊接技术领域。本发明提供的316L工艺管线惰性气体钨极氩弧焊焊接方法,即一种针对316L工艺管线合理控制惰性气体钨极氩弧焊热输入的焊接工艺。本发明所述焊接方法可以快速选取合适的焊接线热量,并且通过热模拟技术得到尺寸较大的焊接热影响区,方便开展组织和性能试验；实现各阶段参数严格合理控制,流程规范,减少时间成本与经济成本,从而综合提高316L工艺管线在海洋环境服役下焊接工艺的开发；在保证焊接质量的情况下,简化了焊接操作步骤,提高了焊接工作效率。(The invention provides a welding method for synergistically improving pitting corrosion resistance and intergranular corrosion resistance of a welding heat affected zone of a 316L process pipeline, and relates to the technical field of welding. The invention provides an inert gas argon tungsten-arc welding method for a 316L process pipeline, namely a welding process for reasonably controlling the heat input of inert gas argon tungsten-arc welding aiming at the 316L process pipeline. The welding method can quickly select proper welding line heat, and obtains a welding heat affected zone with a larger size through a thermal simulation technology, so that organization and performance tests are conveniently carried out; the strict and reasonable control of parameters of each stage and the normative flow are realized, and the time cost and the economic cost are reduced, so that the development of the welding process of the 316L process pipeline under the service of the marine environment is comprehensively improved; under the condition of ensuring the welding quality, the welding operation steps are simplified, and the welding work efficiency is improved.)

1. A welding method for synergistically improving pitting corrosion resistance and intergranular corrosion resistance of a welding heat affected zone of a 316L process pipeline is characterized by comprising the following steps of: simulating the welding process of inert gas argon tungsten-arc welding of a 316L process pipeline by adopting a thermal simulation technology to obtain welding heat affected zone tissues at different cooling speeds; and then, the structure and the corrosion resistance of the heat affected zone with different parameters are characterized, and a proper welding process is determined.

2. The welding method of claim 1, wherein said simulation is performed using a Gleeble 3500 thermal simulation tester.

3. Welding method according to claim 1 or 2, wherein said simulating comprises: and (3) performing experiments on the machined parent metal with the diameter of phi 6mm by using different thermal simulation parameters, and simulating the welding process to obtain the tissues of the welding heat affected zone at different cooling speeds.

4. Welding method according to claim 3, characterized in that the base material used is a 316L process line and that a rod-shaped test specimen with a diameter of phi 6 x 80mm is machined parallel to the rolling direction of the base material.

5. Welding method according to claim 3, characterised in that the thermal simulation uses experimental parameters of heating to 1300 ℃ at 200 ℃/s, holding for 1s, and controlling the difference to t_12/5Cooling for 20s, 30s, 40s, 50s, 65s, 80s, 100s and 150s, finally air cooling to room temperature to obtain welding heat affected zones under different heat input parameters, and then exploring the structure and corrosion performance of different samples.

6. Welding method according to claim 5, characterized in that the difference t is evaluated by the magnitude of the pitting potential and the intergranular corrosion index of the potentiodynamic polarization test and the double potentiodynamic polarization test_12/5Corrosion resistance under the conditions.

Technical Field

The invention belongs to the technical field of welding, and particularly relates to a welding method for synergistically improving pitting corrosion resistance and intergranular corrosion resistance of a welding heat affected zone of a 316L process pipeline.

Background

The AISI 316L stainless steel not only contains a proper amount of chromium and nickel, but also contains about 2 percent of molybdenum element, is favorable for obtaining a single-phase austenite structure, and has higher electrode potential than AISI 304, so the stainless steel has good ductility, corrosion resistance, weldability and processability. The comprehensive use cost is low in a corrosive environment, 316L is widely applied in the fields of chemical industry, coastal, food, biomedicine, petrochemical industry and the like, and the global speed is increased by 3-5% every year. The good sealing and economic performance of welded structures has become one of the most common forms of use for stainless steel, and welded structures produced in major industrial countries of the world account for 50% -60% of the steel production. The heat affected zone in a welded joint is the weakest, complex part of the overall structure and is more susceptible to corrosion than the base, especially after experiencing an improper heat input. Failure modes such as pitting, intergranular corrosion, etc. may occur in stainless steel in environments containing halogen ions, particularly chloride ions, for 316L weld joints. Therefore, the welding process of 316L stainless steel is especially critical to control the welding heat input.

At present, TIG, MIG and other gas shielded welding are mostly adopted for welding 316L process pipelines, and the welding joint with attractive appearance and good performance is obtained conveniently under the action of shielding gas. However, the welding process inevitably causes deterioration of the performance of the weldment due to heat input, and particularly, the performance of the heat affected zone of the welded joint is seriously deteriorated, which directly affects the service life of the weldment. And the service environment of many process pipelines contains certain chloride ions and sulfur ions, such as the offshore environment and oil transportation, which are easy to cause pitting corrosion and intergranular corrosion of the heat affected zone of the joint. Pitting is a corrosion behavior concentrated in a pinpoint-shaped and punctiform micro-area on the surface of metal and rapidly and continuously develops to the deep or even penetrates through the metal. Local corrosion often occurs in an aggressive medium at weak points where the surface oxide film is damaged, etc. Intergranular corrosion refers to corrosion occurring in a region, including grain boundaries, which is relatively small in size compared to the grains, and is generally invisible to the naked eye when corrosion failure occurs, but fractures along the grain boundaries when stress is applied, almost loses strength, and brings great potential safety hazards to a welded structure. In the face of such problems, the welding heat simulation technology developed in recent years can be used for researching various performances of a welding heat affected zone, selecting the optimal welding process for welding engineering, and providing reliable basis and test means for ensuring the performances of the welding heat affected zone.

Disclosure of Invention

In view of this, the present invention aims to overcome the defects of the prior art, and provides a welding method of inert gas argon tungsten-arc welding for a 316L process pipeline, that is, a welding process for reasonably controlling heat input of inert gas argon tungsten-arc welding for a 316L process pipeline, and particularly, the present invention can improve the local corrosion resistance of a joint weak area under the condition that stainless steel fails to work in a heat affected zone of a welded joint, and can complete the development of the welding process with high efficiency and low cost.

The technical purpose of the invention is realized by the following technical scheme:

based on a thermal simulation technology, a Gleeble 3500 testing machine and a 316L process pipeline inert gas argon tungsten-arc welding process are utilized, and the following steps are carried out:

the Gleeble 3500 thermal simulation testing machine is a resistance heating type full simulation device, consists of a force application system, a heating system and a computer control system, has extremely fast cooling and heating speeds, and simultaneously records the change curves of parameters such as temperature, stress, strain and the like in the thermal simulation process of a sample. The method can accurately simulate the relation between the process and the material performance change of each stage of metal material welding, and can accurately simulate the welding structure with different heat inputs in different areas. By using the equipment, the parent metal with the diameter of phi 6mm after being machined is tested by different thermal simulation parameters, and the welding process is simulated to obtain the welding heat affected zone tissues at different cooling speeds. And then, the structure and the corrosion resistance of the heat affected zone with different parameters are characterized, and a proper welding process is determined.

In the technical scheme, the adopted parent metal is a 316L process pipeline, and a rod-shaped test sample with the diameter of phi 6 x 80mm is processed along the rolling direction parallel to the parent metal.

In the technical scheme, the experimental parameters adopted by the thermal simulation are that the temperature is heated to 1300 ℃ at 200 ℃/s, the temperature is kept for 1s (namely, the heat affected zone of the joint is simulated), and then the difference is controlled to t_12/5Cooling for 20s, 30s, 40s, 50s, 65s, 80s, 100s and 150s (the time for cooling from 1200 ℃ to 500 ℃) and finally air cooling to room temperature to obtain the weld heat affected zone under different heat input parameters, and then exploring the structure and corrosion performance of different samples.

In the technical scheme, the simulated welding heat affected zone weldment is processed into various samples according to the test scheme. The method comprises the following steps of cutting a small rod along the middle of thermal simulation, taking a leaked cross section as a surface to be tested of subsequent tissues and electrochemical corrosion, wherein the electrochemical test mainly comprises a potentiodynamic polarization test for reflecting pitting corrosion sensitivity and a double potentiodynamic test for reflecting intercrystalline corrosion sensitivity.

In the technical scheme, different t is evaluated through the sizes of pitting potentials and intergranular corrosion indexes of a potentiodynamic polarization test and a double potentiodynamic test_12/5Corrosion resistance under the conditions.

In the above technical solution, an optimal set of t is selected_12/5Then, according to the standard Lei Kaolin heat transfer formula, t can be obtained_12/5Corresponding weld heat inputs, namely:

where Q is the input line energy in kJ; t is₁、T₂Temperature in units for determining cooling time; d is the actual plate thickness in cm; rho is the density of the material in g/cm³(ii) a c is specific heat capacity, unit J/(g ℃.); Δ T is from T₁To T₂Cooling time of (d), in units of s; λ is the thermal conductivity, unit W/(cm. cndot.).

In the technical scheme, inert gas argon tungsten-arc welding is adopted, 316L base metal welding is carried out according to the obtained heat input, and a corrosion tendency test is carried out on a weld joint weld line area according to an intercrystalline corrosion bending test, so that the corrosion resistance of an actual weld part is further verified.

Has the advantages that: (1) in the welding method, the proper welding line heat can be quickly selected, and a welding heat affected zone with a large size is obtained through a thermal simulation technology, so that organization and performance tests are conveniently carried out; the method realizes strict and reasonable control of parameters of each stage and normative flow, reduces time cost and economic cost, and thus comprehensively improves the development of the welding process of the 316L process pipeline under the service of marine environment. (2) In the welding method of the invention, the pre-welding preheating treatment to the welding base metal and the post-welding heat treatment to the welding seam in the welding process are saved. Therefore, the welding operation steps are simplified and the welding work efficiency is improved under the condition of ensuring the welding quality.

Drawings

FIG. 1 is a thermal simulation curve according to the present invention;

FIG. 2 is a schematic diagram of an electrochemical sample according to an embodiment of the present invention;

FIG. 3 is an electrochemical test performance index in the technical scheme of the invention.

Detailed Description

The invention provides a method for producing a composite material.

The present invention will be described in detail with reference to examples, but they should not be construed as limiting the scope of the present invention.

Example 1

Step one, selecting a base material: domestic 316L parent metal is selected.

Step two, sample processing: and processing a round bar-shaped sample with phi 6 x 80mm along the rolling direction of the base metal of 316L, cutting the sample along the middle of a thermal simulation area to leak out of a surface to be tested after the thermal simulation is used for thermal simulation, then processing the sample into a metallographic sample with phi 6 x 7mm for electrochemical test, and analyzing a microstructure, wherein the metallographic sample comprises a microscopic metallographic sample and an EBSD experiment, and a small disc with phi 6mm and 0.5mm in thickness is processed along a thermal simulation center and is used for a TEM experiment.

Step three, thermal simulation experiment (fig. 1): a round bar with the diameter of 6 x 80mm is taken, a thermocouple wire is welded at the central point and used for recording the real-time change of temperature and time, and the heating and cooling processes are monitored. Heating to 1300 deg.C at 200 deg.C/s, holding for 1s (i.e. simulating heat affected zone), air cooling to 1200 deg.C, and controlling to t_12/5Cooling for 20s, 30s, 40s, 50s, 65s, 80s, 100s and 150s (the time taken for cooling from 1200 ℃ to 500 ℃) and finally cooling to room temperature in air.

Step four, microstructure experiment: and processing the sample subjected to thermal simulation into a metallographic sample and a transmission sample for SEM, EBSD and TEM experiments. Wherein, the SEM sample is ground by 2000# abrasive paper, and is observed and qualitatively analyzed by aqua regia after being polished; grinding an EBSD sample by using 7000# abrasive paper, and then performing surface treatment by using perchloric acid alcohol solution with volume fraction of 5% at 20V for 30s through electrolytic polishing; the TEM samples were hand ground to a thickness of 70 μm and then ion thinned for post-processing. And respectively recording the microstructure appearance, residual ferrite content and form, boundary characteristics and secondary phase generation of different thermal simulation samples for determination.

Step five, electrochemical test (fig. 2): and welding a lead on the electrochemical sample, carrying out epoxy resin cold-embedding, exposing the surface to be detected, then grinding to 2000# abrasive paper, and carrying out action potential polarization and double-loop action potential reactivation tests after polishing. Electrochemical tests are carried out in a Gamry Interface 1000 workstation, the experimental temperature is 25 ℃, and a three-electrode system with saturated calomel as a reference electrode, a platinum sheet electrode as an auxiliary electrode and a sample as a working electrode is adopted. Wherein the potentiodynamic reactivation test adopts 3.5% sodium chloride solution by mass fraction, the test is soaked for a period of time before the start of the test, and after the open circuit potential is stabilized, the test is polarized from the positive direction of-0.5V relative to the open circuit potentialTo 1.2V, according to ASTM G61-86, at a scan rate of 0.167 mV/s; pitting potential (E) of comparative sample after obtaining polarization curve_pit) Size, by Tafel fitting, the self-corrosion current density (I) of the sample is obtained_corr) And a comparison is made. Potentiodynamic reactivation experiments were performed at 0.5mol/L H according to the relevant standard₂SO₄+0.01mol/L KSCN in the mixed solution, and the scanning speed is 1.67 mV/s; after obtaining the double loop curve, the reactivation scan peak current (Ir) and the corresponding activation scan peak current (I) are measured_p) The ratio of the two is obtained, namely the sensitization degree index (DOS), and the larger the value is, the larger the sensitization degree is, and the more serious the intergranular corrosion is. According to the index E of corrosion resistance_pitAnd optimal t selected by DOS_12/5。

Step five, calculating welding heat input: calculating the relation between the selected t12/5 and the welding heat input according to a Lecanin heat transfer formula:

where Q is the input line energy in kJ; t is₁、T₂Temperature in units for determining cooling time; d is the actual plate thickness in cm; rho is the density of the material in g/cm³(ii) a c is specific heat capacity, unit J/(g ℃.); Δ T is from T₁To T₂Cooling time of (d), in units of s; λ is the thermal conductivity, unit W/(cm. cndot.).

Step six, welding heat input: the relationship between welding current (I), arc voltage (U) and welding speed (V) is obtained by substituting the obtained welding heat input into the following equation according to the above steps, thereby obtaining 316L process line welding parameters.

E＝IUη/V

Wherein I is welding current; u is the arc voltage; v is the welding speed; eta is the thermal efficiency coefficient of inert gas argon tungsten-arc welding.

Seventhly, detecting the corrosion resistance of the weldment (shown in figure 3): according to the optimized welding parameters, inert gas argon tungsten-arc welding is adopted for 316L base metal welding, the obtained welding joint is sampled, the corrosion tendency of an actual heat affected zone after welding is researched according to potentiodynamic polarization and double potentiodynamic reactivation tests, then a macroscopic intergranular corrosion bending test is carried out on the joint heat affected zone, and the stress surface of a bent sample is observed to have macroscopic cracking or microcracking defects after the test. And the cracking specification shows that the corresponding welding parameters are unqualified, otherwise, the welding parameters are proper, so that the welding process for resisting pitting corrosion and intergranular corrosion in the heat affected zone of the 316L process pipeline welding joint is obtained.

The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.