Sut Mae'r Lleihad mewn Lluniad Oer Canran Tiwbiau Gwain Gwresogydd 316L yn Rheoli'r Straen-Ffurfiad Martensite Cymhelledig a'i Effaith Dilynol ar Athreiddedd Magnetig ac Ymwrthedd Brithiad Hydrogen

Trawsnewid Cyfnod a Achosir gan Anffurfiad: Cleddyf Dwbl -ymyl

Y dull mwyaf cyffredin o gael dimensiynau diamedr allanol cywir a gorffeniad arwyneb ar gyfer tiwbiau gwresogi trydan wedi'u gorchuddio â dur di-staen 316L a gynhyrchir trwy luniad oer yw gostyngiad yn y canran, sy'n rheoli'n uniongyrchol ffracsiwn cyfaint y straen -martensite a achosir (-martensite) a gynhyrchir yn ystod anffurfiad. 316Mae gan L gynnwys carbon is (<0.03%) than ordinary 316 making it more austenitically stable at room temperature and needing greater cold work levels to generate martensite. The martensite volume fraction that can be determined by magnetic permeability (μr) affects two important but conflicting service properties: magnetic permeability (important for applications that require non-magnetic sheaths such as MRI rooms or sensitive electronic equipment) and hydrogen embrittlement resistance (critical for cathodically protected systems or sour service). When the reduction percentage is below 20% the 316L stays practically entirely austenitic (μr <1.01, martensite <2%), giving excellent non-magnetic properties but with a lower yield strength. Martensite is formed gradually (μr =1.01-1.10, martensite 2-15%) with a 20-40% reduction, with an increase in yield strength but a decrease in resistance to hydrogen embrittlement. For reductions more than 40%, the martensite content is higher than 15-20% (μr >1.10) sy'n achosi ymateb magnetig uchel a sensitifrwydd sylweddol i embrittlement hydrogen. Mae'r papur hwn yn asesu'r gydberthynas rhwng gostyngiad lluniadu oer, ffracsiwn martensite, athreiddedd magnetig a gwrthiant embrittlement hydrogen ar gyfer gwainiau gwresogydd 316L.

Mae mecanwaith ffurfio martensite a achosir gan straen yn 316L

Mae austenitig 316L yn feta-sefydlog o ran cynhyrchu martensite yn ystod dadffurfiad plastig. $\\gama$ (FCC, paramagnetig) $\\i$$\\epsilon$ (HCP, gwan magnetig) $\\to$$\\alpha^\\prime$ (BCC, ferromagnetic). Mae ffracsiwn cyfaint alffa'{4}}martensite yn dilyn cyfraith Olson-cyfraith Cohen: Valpha'=1 - exp(-betaxepsilon_plastic^n) (10) lle epsilon_plastic yw'r straen plastig gwirioneddol (epsilon_plastic=ln(1/(1{{{1)){2} yn ffactor tymheredd sy'n dibynnu ar beta' a'r ffactor duct yw'r ffactor ductiant a'r (1{{1)x}). tua 2 ar gyfer 316L. Mae'r tymheredd lle mae 50 % martensite yn cael ei ffurfio ar 30 % o straen gwirioneddol (Md30) ar gyfer 316L tua -30 gradd i -50 gradd sy'n golygu ar dymheredd arferol mae ffurfiant martensite wedi'i gyfyngu hyd at ostyngiad o 20-30% ar gyfer 2-30% o fartensite. ε) ac yn meddu ar rinweddau canolraddol rhwng y rhai o ddur di-staen cwbl austenitig a llawn martensitig.

Perthnasoedd meintiol rhwng lleihau oerfel, ffracsiwn o martensite ac eiddo ar 25 gradd

Defnyddir lluniad oer rheoledig o diwbiau 316L (yn cychwyn OD 12 mm, wal 1.5 mm, wedi'i anelio'n llawn ar 1050 gradd) i ddangos cysylltiadau rhwng ffracsiwn martensite (difreithiant pelydr X-), athreiddedd magnetig (ferritescope) a pharamedrau mecanyddol.

Gostyngiad Lluniadu Oer (%) Straen Gwir (ε=ln(1/(1-R))) '-Ffrisiwn Cyfaint Martensite (%) Athreiddedd magnetig (μr, 25 gradd ) Cryfder cnwd (MPa, gwrthbwyso 0.2%) Elongation (%) Ar gyfer Cymwysiadau Anfagnetig<1.05 μr Recommended for Sour/Hydrogen Service
0 (annealed) 0.00 0 1.00-1.01 205 50 Ydy Ydy 5 0.05 0 1.00-1.01 240 45 Ydy Ydy 10 0.11 0 1.01-1.02 280 40 Ydy Ydy 15 0.16 0-1 1.02-1.03 320 35 Ydy Ydy 20 0.22 1-2 1.03-1.05 360 30 Ymylol Derbyniol 25 0.29 2-4 1.05-1.07 400 25 Nac ydy Ymylol 30 0.36 4-7 1.07-1.10 440 20 Nac ydy Nac ydy Nac ydy Nac ydy Nac ydy 40 0.51 12-18 1.15-1.25 520 15 Nac ydy Nac ydy 45 0.60 18-25 1.25-1.40 560 12 Na Na Na 45 0.60 18-25 1.25-1.40 560 12 Na Na Na Na Na {{10}
Effaith Cynnwys Martensite ar Ymwrthedd i Brithiad Hydrogen

The susceptibility to hydrogen embrittlement (HE) of 316L heater sheaths in cathodically protected systems or sour service (H2S-containing) rises with martensite content because the BCC structure of martensite shows substantially higher hydrogen diffusivity and solubility than FCC austenite. The HE thresholds are given in the table below. α'-martensite fraction (%)Hydrogen Diffusivity at 25 oC (cm2/s, relative to austenite =1) Time to HE Cracking in NACE TM0177 Solution A at 25 oC 75% yield (hours)Maximum Permissible Cold Reduction for Sour Service (Recommended) 0 1X >720 (pasio)Unrhyw (wedi toddi)
1-3 5-10 × 500-720 (ffiniol)<20% reduction
3-5 20-30× 200-500 (fail)Not permitted 5-10 50-80× 50-200 (fail)Not allowed >10 >100× <50 (severe) Not allowed
Athreiddedd Magnetig Yn Angenrheidiol ar gyfer Cymhwysiad AnMagnetig

Uchafswm athreiddedd magnetig (ee μr<1.01 or <1.05) is specified for 316L sheaths for MRI rooms, or sensitive electronic equipment, or degaussing systems. Limits on cold decrease are as follows.

Cais Uchafswm μr Lleihad Oerni Uchaf a Ganiateir (% )Llwybr Gweithgynhyrchu a Argymhellir Ffracsiwn Martensite Cyfatebol
Ystafell MRI (hanfodol) 1.01<10% 0% Fully annealed, + no cold work
Offer pelydr electron 1.02<15% 0-1%Light cold working + finish anneal
Cyffredinol an-magnetig 1.05<22% <2% Cold drawn + tension reliefing
Commercial (no specification) >1.05 (unrhyw) Unrhyw Unrhyw Fanylebau Ymarferol ar gyfer Cynhyrchu Gwain Gwresogydd 316L

Ar gyfer prynwyr sy'n nodi tiwbiau 316L ar gyfer amgylchiadau gwasanaeth amrywiol, argymhellir y cyfyngiadau canlynol o leihau lluniad oer:

Cyflwr Gwasanaeth Uchafswm Lleihad Tynnu Oer(%) Triniaeth Wres Terfynol Angenrheidiol Uchafswm μr Isafswm Ymwrthedd AU
An-magnetig (MRI, electroneg) 10 Aneliad llawn ar ôl lluniadu 1.02 Da
Diwydiannol cyffredinol (dim clorid, dim H2S) 30 Dim (gan-dynnu'n dderbyniol) 1.10 (unrhyw un) Ddim yn angenrheidiol
Gwasanaeth clorid (<500 ppm, <80°C) 20 Stress relief 400°C, 1h 1.05 OK
Sour service (H2S >10 ppm) 15 Anelio datrysiad llawn 1.03 Angenrheidiol (pasio NACE)
Gwarchodaeth cathodig (morol) 15 Lleddfu straen 450 gradd , 2 awr 1.03 Derbyniol
High strength (pressure vessels) 40 None >1.15 Gwael (ddim ar gyfer H2S)
Dilysu Cynnwys a Phriodweddau Martensite

Buyers who require specified restrictions have three verification options available. The first is a non-destructive measurement with a ferritescope, which gives μr values with a precision of ±0.005-0.01. The second is X-ray diffraction (XRD) coupled with Rietveld refinement for accurate measurement of α'. The final test is a simple magnetic attraction test: if a permanent magnet clings strongly to the sheath, then μr >1.10 (ddim yn addas ar gyfer cymwysiadau anfagnetig). Ar gyfer ymwrthedd AU, y gofyniad cymeradwyo yw dim cracio ym mhrawf NACE TM0177 (720 h, 25 gradd , Ateb A gyda H₂S).

Casgliadau: Sefydlu Terfynau Lleihau Oer ar gyfer 316L yn Seiliedig ar Ofynion Gwasanaeth

Ar gyfer tiwb gwain gwresogydd dur di-staen 316L, y gostyngiad % o luniad oer yw'r ffactor rheoli uniongyrchol mewn ffurfio martensite a achosir gan straen, sy'n pennu'r athreiddedd magnetig a'r ymwrthedd embrittlement hydrogen. Ar gyfer cymwysiadau anfagnetig (μr<1.01-1.05) cold reduction must be minimised to <10-15% with a final anneal. For HE resistant sour or cathodically protected service, cold decrease must be limited to < 15-20% with stress relief or full anneal. For general industrial service where neither attribute is critical reductions of 30-40% are tolerable. Engineers designing 316L sheaths have to define maximum magnetic permeability or minimum HE resistance criteria dependent on the environment of operation. The framework presented here correlates the cold reduction percentage to the martensite volume fraction and its two critical consequences-magnetic response and hydrogen embrittlement susceptibility, and enables buyers to choose the best drawing reduction and post-drawing heat treatment for their particular application.