Basic Metallurgy
Tag nrho cov hlau tsis muaj steel muaj ntau dua lossis sib npaug li 10.5% Cr, uas ua rau tus kheej - kho cov yeeb yaj kiab tsis zoo. Lawv muab faib ua:
Austenitic (300-series): Lub ntsej muag-centred cubic, non-magnetic, zoo heev corrosion kuj tab sis nquag ua hauj lwm-hardening.
Martensitic (400-series): Lub cev-centred cubic, magnetic, tuaj yeem kho cua sov kom siab dua lossis sib npaug li 55 HRC, qis dua corrosion.
Ferritic (400-series): Sib nqus, nruab nrab corrosion, qis ua haujlwm- tawv, zoo rau nyias-phab ntsa.
Cov dej nag-hardening (15-5 PH, 17-4 PH): Martensitic + Cu/Nb ntxiv; tov-soft ces muaj hnub nyoog rau 40-50 HRC.
Lub cev tseem ceeb rau Machining
Thermal conductivity: 16 W m⁻¹ K⁻¹ (≈ ¼ ntawm carbon steel) → tshav kub nyob ntawm lub cuab yeej.
Cov cua kub tshwj xeeb: 500 J kg⁻¹ K⁻¹ → kub nce sai.
Elastic modulus: 200 GPa → siab txiav quab yuam, lub caij nplooj ntoos hlav muaj zog- rov qab rau ntawm phab ntsa nyias.
Ua haujlwm- hardening exponent (n) 0.3–0.5 → deg hardness tuaj yeem dhia 30–50% hauv 0.1 s ntawm kev txiav.
Nrov Qib & Machining Behavior
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| Qib (AISI) | Qhov xwm txheej | Tensile [MPa] | Hardness [HB] | Machinability Index * | Kev siv yam | Cov lus qhia rau Machining |
|---|---|---|---|---|---|---|
| 303 | Annealed | 415–450 | 190–240 | 160 % | Screws, shafts | S- ntxiv rau cov chips tawg; zoo tshaj plaws ntawm austenitic. |
| 304 | Annealed | 520–720 | 170–220 | 100% (lub hauv paus) | Khoom noj khoom haus, kho mob | Cov khoom sib npaug; muaj zog ua hauj lwm- hardening, xav tau cov cuab yeej ntse . |
| 316L | Annealed | 490–690 | 160–210 | 95 % | Marine, Pharma | Mo tsa txiav quab yuam 5–8 % vs 304 . |
| 416 | Annealed | 550–750 | 200–240 | 180 % | Valves, iav | Dawb-machining sulfur; tuaj yeem hardened rau 40 HRC. |
| 17-4 PHN | Kev daws | 800–950 | 290–350 | 70 % | Aero, pwm | Hnub nyoog rau 40–48 HRC; siv CBN lossis ceramic rau kev txiav tiav. |
| 440C | Annealed | 750–950 | 250–270 | 60 % | Cov hniav, bearings | Harden rau 58-60 HRC; grind es mills yog tias tag nrho nyuaj. |
*Index txheeb ze rau 304=100 % (siab dua=yooj yim dua).
Xaiv Daim Ntawv Teev Npe
Kauj Ruam 1: Ib puag ncig
Cov av noo hauv tsev tsuas yog → 303, 416, 430F OK.
Chloride / marine → 316L, 2205 duplex, los yog 630 (17-4 PH) tom qab passivation.
Kauj Ruam 2: Mechanical Load
Kev qaug zog lossis siab> 300 MPa → 17-4 PH, 15-5 PH, martensitic 431.
Kev cuam tshuam ntawm -40℃→ 304L, 321, 347 (austenitic toughness).
Kauj Ruam 3: Tshaj tawm -Machining Heat Treatment
Xav tau 40–50 HRC → Xaiv hardenable martensitic lossis PH qib.
Yuav tsum nyob tsis tau -magnetic → Nyob nrog austenitic (303, 304, 316).
Kauj Ruam 4: Machining Economy
Kev tsim khoom siab tshaj plaws / lub neej ntev tshaj plaws → 303, 416, 430F.
Tus nqi sib npaug & corrosion → 304, 3CR12.
Hwm corrosion + zog → 316L, 904L, 17-4 PH; txais kev ua haujlwm qis dua.
Tsob Ntoo Txiav Txim Siab
Siab - ntim cov ntsia hlau / fittings → 303 lossis 416
Khoom noj khoom haus/pharma, vuam yuav tsum tau → 304L los yog 316L
Marine sab nrauv, chloride raug → 316L lossis 2205
Aerospace, siab zog, 200℃kev pab cuam → 17-4 PH (H1150)
Txiav hniav, 55 HRC tom qab hardening → 440C los yog 1.4112
