Nj it. When welding pressure vessels, when a sharp temperature gradient with a temperature difference of more than 100 degrees is generated in the adjacent areas of the parent material, uneven plastic strain is caused in ferritic steel or other equivalent materials, and in the subsequent cooling process, a residual stress field with a peak stress reaching the yield point will be generated. In addition, the uneven plastic strain in the manufacture of pressure vessels leads to residual strain in elastic-plastic materials, and the residual strain can be mechanical (mainly cold rolling, cold straightening and other cold working) thermal (mainly generated by welding process), or both, that is, thermomechanical reasons. Therefore, a residual elastic strain field will be left in the final product after the pressure vessel is processed, and it will be subjected to Ustrezni elastični preostali stres . Obstoj preostalega napetosti bo vplival na delovanje tlačne posode ., da bi odpravili najvišji sev na območju varjenja in dosegli cilj enakomerne porazdelitve notranjega seva, ki se lahko sprejmejo različni metodi, kot so metode, kot so številne potenciale, itd. Iz metalurške poškodbe na območju zvara uporaba mehanskih metod za zmanjšanje notranjega seva ne zadostuje za preprečevanje številnih težav, ki se lahko pojavijo v prihodnjem procesu delovanja . Poleg tega je pojav vodika, ki je v embritlu, pritegnil več pozornosti. po tem, da se je jeklo, ki jih je treba povečati, ki jih je treba povečati. in plastičnost se znatno zmanjša, vodik, raztopljen v kovinski rešetki, pa povzroči krhko okvaro jekla med počasno deformacijo . vodik v kovinskem materialu se lahko med proizvodnim postopkom kovinskega materiala absorbira, kot je vodik, ki jo vodijo v hidro. environment. For the hydrogen absorbed in the weld, the more effective elimination method is to perform post-weld heat treatment, which can not only relax and alleviate the welding residual stress, improve the weld heat affected zone that is hardened and embrittled due to welding, and improve the ductility and fracture toughness of the weld metal, but also diffuse and escape harmful gases such as hydrogen in and near območje varjenja . Obstajata dve vrsti metod toplotne obdelave v tlačnih posodah: ena je toplotna obdelava za izboljšanje mehanskih lastnosti, drugo pa je po vabitvi toplotne obdelave (PWHT) . v širšem smislu je toplotna obdelava po varišču ali varjene komponente. annealing, complete annealing, solution, normalizing, normalizing and tempering, tempering, low-temperature stress relief, precipitation heat treatment, etc. In a narrow sense, post-weld heat treatment only refers to stress relief annealing, that is, in order to improve the performance of the welding area and eliminate harmful effects such as welding residual stress, the welding area and related parts are uniformly and fully heated below the metal phase Temperaturna točka transformacije in nato enakomerno ohlajena . V mnogih primerih je obravnavana toplotna obdelava po vališču v bistvu po varovanju toplotne obdelave s stresom .
Nj b. Reduce the hardness of the heat-affected zone. c. Improve fracture toughness. d. Improve fatigue strength. e. Restore or increase the yield strength reduced during cold forming. 4. Improve the ability to resist stress Korozija . 5. Nadalje sprostite škodljive pline v kovini zvara, zlasti vodik
3. Judgment of the necessity of PWHT: Whether the pressure vessel needs post-weld heat treatment should be clearly specified in the design, and the current pressure vessel design specifications have requirements for this. For welded pressure vessels, there is a large residual stress in the welding area, and the adverse effects of residual stress are only manifested under certain conditions. When the residual stress combines with the hydrogen in the weld, it will promote the hardening of the heat-affected zone, leading to the generation of cold cracks and delayed cracks. When the static stress remaining in the weld or the dynamic load stress in the load operation is combined with the corrosive effect of the medium, it may cause crack-like corrosion, which is the so-called stress corrosion. Welding residual stress and the hardening of the parent material caused by welding are important factors in the generation of stress corrosion cracks. The research results show that the main effect of deformation and residual stress on metal materials is to transform the metal from uniform corrosion to local corrosion, that is, to intergranular or transgranular corrosion. Of course, metal corrosion cracking and intergranular corrosion both occur in media with certain characteristics for this metal. In the presence of residual stress, the nature of corrosion damage may change depending on the composition, concentration and temperature of the corrosive medium, as well as the composition, structure, surface state, stress state, etc. of the parent material and the weld zone. Whether the welded pressure vessel needs post-weld heat treatment should be determined based on the purpose, size (especially the wall thickness), performance of the materials used, and working conditions of the vessel. Post-weld heat treatment should be considered in any of the following situations: 1. Harsh conditions of use, such as thick-walled vessels with a risk of brittle fracture pri nizkih temperaturah in posodah, ki nosijo velike obremenitve in izmenične obremenitve . 2. varjene tlačne posode z debelino, ki presega določeno mejo ., vključno z kotli, petrokemičnimi tlačnimi posodami itd. Izdelano iz jekla z veliko nagnjenostjo k trjenju . 5. tlačnih posod s tveganjem za stres korozije . 6. Druge tlačne posode s posebnimi predpisi, specifikacijami in risbami . v jeklenih varjenih tlačnih posoda Struktura, pomešana z Austenitom . Številni raziskovalci so poudarili, da lahko za odpravo preostalega napetosti po varjenju lahko kaljenje na 650 stopinj dobro vpliva na jeklene varjene tlačne posode . hkrati pa ne moremo doseči, če se ustrezna toplotna obdelava ne bo izvedla po valilnici, po valinju, ki se varing ne bo izvedla po valižu, korozijsko-rasistent Na splošno velja, da je toplotna obdelava stresa, v katerem je varjeni obdelovanec segret na 500-650 stopinj in nato počasi ohlajen . Zmanjšanje stresa povzroča lezenje pri visoki temperaturi, kar se začne od 450 stopinj v ogljikovem jeklom in 550 stopinj v molibi, ki se nahajajo v molibih in 550 stopinjah v molibih, ki se nahajajo v molibih, kar je višje, in 550 stopinj v molibih, ki se nahajajo v molibih in 550 stopinjah v molibih, ki se v molibih in 550 stopinja is to eliminate stress. However, once the original tempering temperature of the steel is exceeded, the strength of the steel will be reduced. Therefore, the heat treatment for stress relief must master the two elements of temperature and time, and neither is indispensable. However, in the stress of the weldment, tensile stress and compressive stress are always accompanied, and stress and elastic deformation exist at the same time. When the temperature of steel rises, the yield strength decreases, and the original elastic deformation will become plastic deformation, thus causing stress relaxation. The higher the heating temperature, the more fully the internal stress is eliminated. However, when the temperature is too high, the steel surface will be severely oxidized. In Poleg tega pri načelu za temperaturo PWHT kaljenega in kaljenega jekla ne sme presegati prvotne temperature kaljenja jekla, ki je na splošno približno 30 stopinj nižja od prvotne temperature kaljenja jekla, sicer bo material izgubil dušilno in kaljenje, trdnost in lom žilast pa se bo znižala .. treatment temperature for eliminating internal stress, the greater the softening℃of the steel. Usually, the internal stress can be eliminated by heating to the recrystallization temperature of the steel. The recrystallization temperature is closely related to the melting temperature. Generally, the recrystallization temperature K=0.4X melting temperature (K) . Čim bližje je temperatura toplotne obdelave temperature rekristalizacije, bolj učinkovit je pri odpravljanju preostalega napetosti .
4. Upoštevanje celovitega učinka PWHT po toplotni obdelavi po valu ni popolnoma koristno . Na splošno je popravljeno toplotno zdravljenje pripomoreno k lajšanju preostalega stresa in se izvaja le, kadar obstajajo stroge zahteve za stresne korozije . test, ki ni v vplivu, da se test udarcev s pohodom ne zdi, da je udarna test o vplivu hudega testa na to, da je udarna test, ki ni v vplivu, ki se ne pojavlja, test vpliva na to, da je test, ki je post-Weld, ki se ukvarja s pohodom, ki ne pride do udarcev, da je test vpliva na test, ki ni v vplivu, da se post-Welding test neže the deposited metal and the weld heat affected zone, and sometimes intergranular cracking may occur within the grain coarsening range of the weld heat affected zone. In addition, PWHT relies on the reduction of material strength at high temperatures to achieve stress relief. Therefore, during PWHT, the structure may lose rigidity. For structures that adopt overall or partial PWHT, the support capacity of the weldment at high temperatures must be considered before heat treatment. Therefore, when considering whether to perform post-weld heat treatment, the advantages and disadvantages of heat treatment should be comprehensively compared. From the perspective of structural performance, there is a side that improves performance and a side that reduces performance. A reasonable judgment should be made based on the basic work of comprehensively considering oba vidika .
