{"id":6215,"date":"2026-09-25T19:52:50","date_gmt":"2026-09-25T16:52:50","guid":{"rendered":"https:\/\/www.defencemetal.com\/index.php\/2026\/09\/25\/aisi-8740-aisi-4340-farki\/"},"modified":"2026-09-30T10:44:24","modified_gmt":"2026-09-30T07:44:24","slug":"aisi-8740-aisi-4340-farki","status":"publish","type":"post","link":"https:\/\/www.defencemetal.com\/index.php\/2026\/09\/25\/aisi-8740-aisi-4340-farki\/","title":{"rendered":"AISI 8740 ile AISI 4340 Aras\u0131ndaki Fark Nedir?"},"content":{"rendered":"

AISI 8740<\/strong> ve AISI 4340<\/strong> ikisi de \u0131slah edilerek kullan\u0131lan d\u00fc\u015f\u00fck ala\u015f\u0131ml\u0131 \u00e7eliklerdir — paslanmaz de\u011fildirler. Karbon oranlar\u0131 ayn\u0131d\u0131r (%0,38 – 0,43). Fark, ala\u015f\u0131m elementlerinin miktar\u0131ndad\u0131r: 4340 \u00e7ok daha fazla nikel ve krom i\u00e7erir.<\/strong><\/p>\n

Bile\u015fimdeki fark<\/h3>\n

8740 bir 87xx serisi \u00e7eliktir: az miktarda krom, nikel ve molibden i\u00e7erir. 4340 ise nikeli \u00fc\u00e7 kattan fazlaya<\/strong>, kromu ise yakla\u015f\u0131k bir bu\u00e7uk kat\u0131na \u00e7\u0131kar\u0131r. Molibden ikisinde de ayn\u0131 seviyededir.<\/p>\n

Bunun pratik kar\u015f\u0131l\u0131\u011f\u0131 sertle\u015febilirliktir. Earle M. Jorgensen 4340’\u0131n “4100 serisinden \u00e7ok daha derin sertle\u015febilirli\u011fe” sahip oldu\u011funu, voestalpine B\u00d6HLER “sertle\u015febilirli\u011finin iyi, \u00e7ekme ve akma dayan\u0131m\u0131n\u0131n 4140’tan y\u00fcksek” oldu\u011funu belirtiyor. Service Steel Aerospace ise 4340 i\u00e7in yakla\u015f\u0131k 89 mm (3,5 in\u00e7) \u00e7apa kadar boydan boya sertle\u015fme<\/strong> bildiriyor.<\/p>\n

Rakamlarla kar\u015f\u0131la\u015ft\u0131rma<\/h3>\n

De\u011ferler d\u00f6k\u00fcm analizi s\u0131n\u0131rlar\u0131d\u0131r.<\/p>\n

\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n
\u00d6ZELL\u0130K<\/th>\nAISI 8740<\/th>\nAISI 4340<\/th>\n<\/tr>\n<\/thead>\n
Karbon (C)<\/td>\n%0,38 – 0,43<\/td>\n%0,38 – 0,43<\/td>\n<\/tr>\n
Mangan (Mn)<\/td>\n%0,75 – 1,00<\/td>\n%0,60 – 0,80<\/td>\n<\/tr>\n
Krom (Cr)<\/strong><\/td>\n%0,40 – 0,60<\/strong><\/td>\n%0,70 – 0,90<\/strong><\/td>\n<\/tr>\n
Nikel (Ni)<\/strong><\/td>\n%0,40 – 0,70<\/strong><\/td>\n%1,65 – 2,00<\/strong><\/td>\n<\/tr>\n
Molibden (Mo)<\/td>\n%0,20 – 0,30<\/td>\n%0,20 – 0,30<\/td>\n<\/tr>\n
Silisyum (Si)<\/td>\n%0,15 – 0,35<\/td>\n%0,15 – 0,35<\/td>\n<\/tr>\n
Fosfor (P)<\/td>\nmax %0,035<\/td>\n—<\/td>\n<\/tr>\n
K\u00fck\u00fcrt (S)<\/td>\nmax %0,040<\/td>\n—<\/td>\n<\/tr>\n
Havac\u0131l\u0131k \u015fartnamesi<\/td>\nAMS 6322<\/strong><\/td>\nAMS 6414<\/strong> (VAR) \/ AMS 6415<\/strong> (hava ergitme)<\/td>\n<\/tr>\n
Paslanmaz m\u0131?<\/td>\nhay\u0131r<\/td>\nhay\u0131r<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n

Molibden notu:<\/em> TimkenSteel\/Metallus 8740 i\u00e7in %0,15 – 0,25 yay\u0131ml\u0131yor; Aircraft Materials, AMS Resources, MW Components ve Titanium Industries %0,20 – 0,30 veriyor. \u00c7o\u011funluk ikinci de\u011ferde birle\u015fiyor, ama fark\u0131 belirtiyoruz.<\/p>\n

AISI 8740’\u0131n mekanik de\u011ferleri<\/h3>\n

8740 i\u00e7in tek bir “mekanik \u00f6zellikler tablosu” yay\u0131mlamak do\u011fru olmaz: de\u011ferler teslim durumuna g\u00f6re de\u011fi\u015fir ve kaynaklar normalize edilmi\u015f durumda bile birbirini tutmuyor. Bulunabilenler, kaynak ad\u0131yla:<\/p>\n

\n\n\n\n\n\n\n\n\n\n\n\n\n\n
NORMAL\u0130ZE DURUM<\/th>\nDE\u011eER<\/th>\nKAYNAK<\/th>\n<\/tr>\n<\/thead>\n
Sertlik<\/td>\n269 HB \/ 27 HRC<\/td>\nMW Components, Alloys International, Titanium Industries<\/td>\n<\/tr>\n
Kopma uzamas\u0131<\/td>\n%16<\/td>\nMW Components, Alloys International, Titanium Industries<\/td>\n<\/tr>\n
Elastisite mod\u00fcl\u00fc<\/td>\n205 GPa (29.700 ksi)<\/td>\nMW Components, Alloys International, Titanium Industries<\/td>\n<\/tr>\n
\u00c7ekme (Rm)<\/td>\n930 MPa (135.000 psi)<\/td>\nMW Components (870 °C’de normalize, 13 mm yuvarlak)<\/td>\n<\/tr>\n
\u00c7ekme (Rm)<\/td>\n938 MPa<\/td>\nAlloys International<\/td>\n<\/tr>\n
\u00c7ekme (Rm)<\/td>\n855 MPa (120 ksi)<\/td>\nASTM A519 (boru, “tipik”)<\/td>\n<\/tr>\n
Akma (Rp0,2)<\/td>\n550 MPa (79.800 psi)<\/td>\nMW Components<\/td>\n<\/tr>\n
Akma (Rp0,2)<\/td>\n620 MPa<\/td>\nAlloys International<\/td>\n<\/tr>\n
Akma (Rp0,2)<\/td>\n621 MPa (90 ksi)<\/td>\nASTM A519 (boru, “tipik”)<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n

Akma dayan\u0131m\u0131ndaki 70 MPa’l\u0131k fark ger\u00e7ektir ve ortalamas\u0131 al\u0131namaz.<\/strong> Tasar\u0131m yap\u0131yorsan\u0131z hangi kayna\u011fa g\u00f6re \u00e7al\u0131\u015ft\u0131\u011f\u0131n\u0131z\u0131 belirtin, ya da d\u00f6k\u00fcm\u00fcn kendi sertifikas\u0131n\u0131 isteyin.<\/p>\n

Su verilmi\u015f ve temperlenmi\u015f durum<\/h3>\n

Bulabildi\u011fimiz tek ba\u011f\u0131ms\u0131z ve tam \u00f6l\u00e7\u00fcm seti NASA’n\u0131n 1973 tarihli TM X-64791 raporudur<\/strong> (J. W. Montano). Yakla\u015f\u0131k 25 mm \u00e7ap\u0131nda \u00e7ubuk, 899 °C’den ya\u011fda su verilmi\u015f:<\/p>\n

\n\n\n\n\n\n\n
TEMPERLEME<\/th>\nSertlik<\/th>\nRm<\/th>\nRp0,2<\/th>\nA (50 mm)<\/th>\nKesit daralmas\u0131<\/th>\n<\/tr>\n<\/thead>\n
635 °C (1175 °F)<\/td>\n28 – 29 HRC<\/td>\n906 MPa (131,4 ksi)<\/td>\n822 MPa (119,2 ksi)<\/td>\n%23,0<\/td>\n%65,1<\/td>\n<\/tr>\n
454 °C (850 °F)<\/td>\n40 HRC<\/td>\n1271 MPa (184,3 ksi)<\/td>\n1205 MPa (174,8 ksi)<\/td>\n%16,7<\/td>\n%57,5<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n

Kaynak: NASA TM X-64791. Bu iki nokta d\u0131\u015f\u0131nda \u00e7ok s\u0131cakl\u0131kl\u0131 bir temperleme e\u011frisi do\u011frulanamad\u0131; internette dola\u015fan e\u011friler tek bir veri toplay\u0131c\u0131ya dayan\u0131yor.<\/em><\/p>\n

Is\u0131l i\u015flem<\/h3>\n

Su verme ortam\u0131 ya\u011fd\u0131r<\/strong>. \u00c7evrim i\u00e7in bulunan tek tam set SECO\/WARWICK’in Is\u0131l \u0130\u015flem Veri Kitab\u0131’ndan gelir: normalize 816 – 871 °C<\/strong>, tavlama 816 – 871 °C<\/strong>, sertle\u015ftirme 829 – 857 °C<\/strong>, temperleme “istenen sertli\u011fe g\u00f6re”. Dikkat:<\/strong> NASA ayn\u0131 \u00e7elikte 899 °C’den ostenitlemi\u015ftir; iki de\u011fer de kayna\u011f\u0131yla birlikte verilmelidir, ortalamas\u0131 al\u0131nmamal\u0131d\u0131r.<\/p>\n

8740H: sertle\u015febilirlik garantili s\u00fcr\u00fcm<\/h3>\n

8740’\u0131n bir de H<\/strong> s\u00fcr\u00fcm\u00fc vard\u0131r (UNS H87400): sertle\u015febilirlik band\u0131 garanti edilir ve ASTM A304 ile SAE J1268<\/strong> kapsam\u0131ndad\u0131r. Bile\u015fim s\u0131n\u0131rlar\u0131 standart 8740’tan biraz farkl\u0131d\u0131r:<\/p>\n

\n\n\n\n\n\n\n\n\n\n\n
ELEMENT<\/th>\n8740H (ASTM A304 \/ SAE J1268)<\/th>\n<\/tr>\n<\/thead>\n
Karbon (C)<\/td>\n%0,37 – 0,44<\/td>\n<\/tr>\n
Mangan (Mn)<\/td>\n%0,70 – 1,05<\/td>\n<\/tr>\n
Silisyum (Si)<\/td>\n%0,15 – 0,35<\/td>\n<\/tr>\n
Nikel (Ni)<\/td>\n%0,35 – 0,75<\/td>\n<\/tr>\n
Krom (Cr)<\/td>\n%0,35 – 0,65<\/td>\n<\/tr>\n
Molibden (Mo)<\/td>\n%0,20 – 0,30<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n

Sertle\u015febilirlik band\u0131n\u0131n say\u0131sal Jominy de\u011ferleri her iki standartta da yaln\u0131zca grafik olarak verilir; say\u0131sal tablo yay\u0131mlanmam\u0131\u015ft\u0131r. \u0130nternette bulaca\u011f\u0131n\u0131z 8740H Jominy tablolar\u0131na g\u00fcvenmeyin.<\/em><\/p>\n

Havac\u0131l\u0131k c\u0131vatalar\u0131nda mukavemet s\u0131n\u0131flar\u0131<\/h3>\n

8740’\u0131 as\u0131l \u00f6nemli k\u0131lan budur. \u00dc\u00e7 standart mukavemet s\u0131n\u0131f\u0131nda kullan\u0131l\u0131r:<\/p>\n

\n\n\n\n\n\n\n\n
SINIF<\/th>\nMinimum \u00e7ekme dayan\u0131m\u0131<\/th>\nStandart<\/th>\nSertlik<\/th>\n<\/tr>\n<\/thead>\n
125 ksi<\/td>\n862 MPa (125.000 psi)<\/td>\nAN c\u0131vatalar\u0131 (Jet-Tek, Aircraft Spruce)<\/em><\/td>\n—<\/td>\n<\/tr>\n
160 ksi<\/strong><\/td>\n1103 MPa (160.000 psi)<\/td>\nNAS6203 – NAS6220<\/td>\n36 – 40 HRC (Military Fasteners)<\/em><\/td>\n<\/tr>\n
180 ksi<\/strong><\/td>\n1241 MPa (180.000 psi)<\/td>\nNAS624 – NAS644 (12 k\u00f6\u015fe)<\/td>\n39 – 43 HRC (FastenerDimensions)<\/em><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n

NAS6203–6220 standard\u0131n\u0131n kendi metni, izin verilen malzemeleri 4140 (AMS 6349), 4340 (AMS 6415 \/ 6484) ve 8740 (AMS 6322 veya AMS 6325\/6327)<\/strong> olarak sayar; \u0131s\u0131l i\u015flem AMS 2759’a g\u00f6re yap\u0131l\u0131r. SPS Technologies kendi katalo\u011funda 180 ksi s\u0131n\u0131f\u0131n\u0131 AISI 8740 ile, maksimum servis s\u0131cakl\u0131\u011f\u0131 232 °C (450 °F) olarak veriyor.<\/p>\n

\n

AMS 6322’nin say\u0131sal mekanik \u015fartlar\u0131n\u0131 yay\u0131mlam\u0131yoruz.<\/p>\n

SAE’nin tam metni \u00fccretlidir ve internette dola\u015fan \u00fc\u00e7 ayr\u0131 “AMS 6322 de\u011ferleri” birbiriyle \u00e7eli\u015fiyor; birinde sertlik ile \u00e7ekme dayan\u0131m\u0131 metalurjik olarak ba\u011fda\u015fm\u0131yor. \u015eartname de\u011feri gerekiyorsa SAE AMS 6322’nin g\u00fcncel bask\u0131s\u0131<\/strong> sat\u0131n al\u0131nmal\u0131d\u0131r.<\/p>\n<\/div>\n

Bu tablonun okunu\u015fu.<\/strong> Kaynak ad\u0131 yaz\u0131lmayan sat\u0131rlar en az d\u00f6rt ba\u011f\u0131ms\u0131z kurulu\u015fta do\u011frulanm\u0131\u015ft\u0131r. Parantez i\u00e7inde kurulu\u015f ad\u0131 ge\u00e7en sat\u0131rlar daha az say\u0131da kaynakta bulunabildi\u011fi i\u00e7in kayna\u011f\u0131yla birlikte veriliyor. Do\u011frulayamad\u0131\u011f\u0131m\u0131z hi\u00e7bir de\u011fer yaz\u0131lmam\u0131\u015ft\u0131r.<\/p>\n

Sipari\u015f verirken dikkat — en s\u0131k yap\u0131lan hata<\/h3>\n
\n

AMS 6349, 8740 veya 4340 de\u011fildir — 4140’t\u0131r.<\/p>\n

AMS 6349’un ba\u015fl\u0131\u011f\u0131 “Steel Bars, 0.95Cr – 0.20Mo (0.38 to 0.43C) (SAE 4140), Normalized”<\/em>dir. Bu \u015fartnamenin bu \u00e7iftteki hi\u00e7bir malzemeyle ilgisi yoktur. 8740’\u0131n havac\u0131l\u0131k \u015fartnamesi AMS 6322<\/strong>‘dir (“0.50Cr – 0.55Ni – 0.25Mo (0.38–0.43C) (SAE 8740)”).<\/p>\n<\/div>\n

\n

AMS 6414 ile AMS 6415 aras\u0131ndaki fark kimya de\u011fil, ergitme y\u00f6ntemidir.<\/p>\n

\u0130kisi de SAE 4340’t\u0131r. AMS 6414 vakum ark ref\u00fczyonlu (VAR\/CEVM)<\/strong>, AMS 6415 hava ergitmelidir.<\/strong> 6414 istenen bir yere 6415 vermek uygunsuzluktur — ve sertifikada ay\u0131rt edilmesi gereken tek sat\u0131r budur.<\/p>\n<\/div>\n

Is\u0131l i\u015flem ve iki metalurjik uyar\u0131<\/h3>\n

4340 tipik olarak yakla\u015f\u0131k 800 – 860 °C’den ya\u011fda su verilir<\/strong> ve istenen mukavemet seviyesine g\u00f6re 204 – 649 °C aras\u0131nda temperlenir. voestalpine B\u00d6HLER, m\u00fchendislik uygulamalar\u0131 i\u00e7in 540 – 680 °C band\u0131n\u0131 \u00f6neriyor.<\/p>\n

Hidrojen gevrekli\u011fi.<\/strong> Y\u00fcksek mukavemetli bu \u00e7elikler kapland\u0131\u011f\u0131nda (kadmiyum, \u00e7inko-nikel) hidrojen al\u0131r ve gevrekle\u015febilir. Gevreklik giderme f\u0131r\u0131nlama \u015fartlar\u0131 SAE AMS 2759\/9<\/strong> ile y\u00f6netilir. \u0130nternette dola\u015fan s\u0131cakl\u0131k ve s\u00fcre de\u011ferlerini kullanmay\u0131n; standard\u0131n kendisine bak\u0131n.<\/p>\n

Temper k\u0131r\u0131lganl\u0131\u011f\u0131.<\/strong> voestalpine, molibden katk\u0131s\u0131n\u0131n 4340’\u0131 klasik temper k\u0131r\u0131lganl\u0131\u011f\u0131na kar\u015f\u0131 kordu\u011funu belirtiyor. Bundan ayr\u0131 olarak literat\u00fcrde 4340’a \u00f6zg\u00fc bir temperlenmi\u015f martenzit k\u0131r\u0131lganl\u0131\u011f\u0131<\/em> (yakla\u015f\u0131k 250 – 400 °C temperleme b\u00f6lgesi) tan\u0131mlanm\u0131\u015ft\u0131r. Bu iki olgu farkl\u0131d\u0131r, birbirine kar\u0131\u015ft\u0131r\u0131lmamal\u0131d\u0131r.<\/p>\n

\u0130kisi de paslanmaz de\u011fildir<\/h3>\n

Krom oranlar\u0131 %0,40 – 0,90 aral\u0131\u011f\u0131ndad\u0131r. Bir \u00e7eli\u011fin paslanmaz say\u0131lmas\u0131 i\u00e7in EN 10088-1 en az %10,5 krom ister. Dolay\u0131s\u0131yla her iki malzeme de koruyucu kaplama olmadan kullan\u0131lamaz.<\/strong><\/p>\n

Nerede kullan\u0131l\u0131r?<\/h3>\n

4340:<\/strong> a\u011f\u0131r hizmet ve u\u00e7ak milleri, krank milleri, aks milleri, di\u015fliler, ini\u015f tak\u0131m\u0131 par\u00e7alar\u0131, y\u00fcksek mukavemetli c\u0131vata ve saplamalar, kuyu i\u00e7i tak\u0131mlar, kal\u0131plar.<\/p>\n

8740:<\/strong> akslar, tij ba\u011flant\u0131lar\u0131, sondaj a\u011f\u0131rl\u0131klar\u0131, piston kollar\u0131, u\u00e7ak motoru c\u0131vatalar\u0131.<\/p>\n

G\u00f6sterimler, standartlar ve AMS kar\u015f\u0131l\u0131klar\u0131<\/h3>\n

Ayn\u0131 \u00e7elik, hangi sistemde konu\u015ftu\u011funuza g\u00f6re farkl\u0131 isimle an\u0131l\u0131r. Sipari\u015f ve sertifika kar\u0131\u015f\u0131kl\u0131klar\u0131n\u0131n \u00e7o\u011fu buradan \u00e7\u0131kar, o y\u00fczden k\u0131saca \u00f6zetleyelim:<\/p>\n