Tham khảo tài liệu 'volume 06 - welding, brazing and soldering part 8', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Fusion zone 2 3 4 Base metal Four HAZ regions 2 3 4 1 Ỵ ferrite ma do ns He lerrfte 2 Coarse-grained martensite 3 Fine-grained 1 martensite 4 Overlempered base metal FIG. 3 FOUR HAZ REGIONS OBSERVED IN HT9 WELDMENTS. Ỵ REPRESENTS AUSTENITE. SOURCE REF 3 FIG. 4 AS-WELDED GAS-TUNGSTEN ARC FUSION ZONE MICROSTRUCTURE IN HT9 WELDMENTS. AR ROWS INDICATE METASTABLE 0FERRITE WHICH CONSTITUTES APPROXIMATELY 2 TO 3 VOL OF THE STRUCTURE. 1ŨOOÔSOURCE REF 2 Four distinct regions were identified within the HAZ. These regions can be related to the phase fields on the i chromium-carbon equilibrium diagram shown in Fig. 5. The microstructures associated with these four regions are . REGION 1 WHICH IS A TWO-PHASE REGION ADJACENT TO THE FUSION LINffHAT CONSISTS OF UNTEMPERED MARTENSITE AND FERRITE. THE FERRITBRMS ALONG PRIOR AUSTENITE GRAIN BOUNDARIES AS THIS REGIONS HEATED INTO THE AUSTENITE-PLUS-FERRITE PHASE FIELD DESIGNATED 1 IN FIG. 3 AND 5 . . REGION 2 WHICH CONSISTS ENTIRELY OF UNTEMPERED J RTENSITE. AS THIS PORTION OF THE HAZ IS HEATED INTO THE HIGH-TEMPERATURE REGIMEFOTHE AUSTENITE PHASE FIELD ALLOY CARBIDES FROM THE ORIGINAL BASE4ETAL MICROSTRUCTURE COMPLETELY DISSOLVE RESULTING IN A CARBIDEREE UNTEMPERED MARTENSITE THAT EXHIBITS A LARGE PRIOR AUSTENITE GRAIN. . REGION 3 WHICH CONTAINS UNTEMPERED MARTENSITE INTERSPERSED WITT UNDISSOLVED ALLOY CARBIDES. BECAUSE THIS REGION EXPERIENCES fl TEMPERATURE EXCURSION INTO THE LOWER REGIME OF THE AUSTENITEHASE FIELD CARBIDE DISSOLUTION IS INCOMPLETE AND THE PRIOR AUSTBTE GRAIN SIZE IS SMALLER RELATIVE TO REGION 2. . REGION 4 WHICH CONSISTS OF TEMPERED MARTENSITE AND OVERAGED CARES. IT APPEARS TO BE VIRTUALLY IDENTICAL TO THE BASE-METAL MICROSTRUCTURE. Representative microstructures of these four regions are shown in Fig. 6. FIG. 5 IRON-CHROMIUM-CARBON PSEUDO-BINARY PHASE DIAGRAM FOR 12 WT CR STEE L. CIRCLED NUMBERS REPRESENT THE FOUR HAZ REGIONS SHOWN IN FIG. 3 AND 6. SOURCE ADAPTED FROM REF 5 FIG. 6 GAS-TUNGSTEN ARC WELDED HAZ .
