PENGARUH TEMPERATUR ANNEALING SAMBUNGAN LAS SMAW (SHIELDED METAL ARC WELDING)TERHADAP SIFAT MEKANIS DAN FISIS BAJA K-945 EMS-45

Abstract

Tujuan dari penelitian ini adalah untuk mengetahui adakah pengaruh dari suhu Post Weld Heat Treatment Annealing pada pengelasan baja Bohler Grade K-945 EMS 45 terhadap sifat mekanis (uji kekerasan dan uji tarik) dan sifat fisis (foto mikro). Penelitian menggunakan jenis baja K-945 EMS 45 yang mengadung kadar karbon 0,52%. Pembuatan spesimen dengan cara memotong plat baja tersebut dan dibuat kampuh X untuk pengelasan, spesimen bentuk uji tarik sesuai dengan standar ASTM E8. Pengelasan menggunakan jenis las SMAW. Kemudian dilakukan proses PWHT annealing dengan variasi suhu 6500 C, 6950 C dan 7400 C yang dipanaskan dalam furnace selama 1 jam dan didinginkan di dalam furnace. Hasil penelitian menunjukan bahwa nilai rata-rata tegangan maksimal spesimen non PWHT sebesar 702,95 MPa, spesimen PWHT 6500 C sebesar 614,51 MPa. Tegangan maksimal untuk spesimen PWHT 6950 C sebesar 567,96 MPa, sementara untuk nilai tegangan maksimal spesimen PWHT 7400 C sebesar 531,65 MPa. Nilai rata-rata tegangan luluh pada spesimen non PWHT sebesar 384,5 MPa, spesimen PWHT 6500 C sebesar 340,46 MPa. Tegangan luluh untuk spesimen PWHT 6950 C sebesar 309,77 MPa, sementara untuk nilai rata-rata tegangan luluh spesimen PWHT 7400 C sebesar 283,69 MPa. Selanjutnya untuk nilai rata-rata presentase regangan dari spesimen non PWHT sebesar 30,44 %, spesimen PWHT 6500 C sebesar 22,22 %. Nilai rata-rata presentase regangan spesimen PWHT 6950 C sebesar 22,31 % sementara untuk nilai rata-rata presentase regangan spesimen PWHT 7400 C sebesar 24,81 %. Hasil foto struktur mikro untuk spesimen non PWHT nampak berupa struktur ferit, perlit, dan grafit. Sedangkan spesimen yang mengalami perlakuan PWHT mengalami perubahan bentuk struktur yang berubah ukuran butirnya dan lebih halus. Penampang patah yang terjadi pada spesimen non PWHT berbentuk granullar, sedangkan penampang patah yang terjadi pada spesimen yang mengalami perlakuan berbentuk cup-cone. Hasil dari penelitian menunjukan bahwa dengan PWHT annealing dapat menurunkan tegangan tarik dan meningkatkan keuletan.

The objectives of this study is to find out the influence of Post Weld Heat Treatment Annealing temperature of the Bohler Grade K-945 EMS 45 steel welding towards the mechanical characteristics (hardness and stretching test) and the physical character (micro photograph). The research used the K-945 EMS 45 steel which contains 0.52% carbons. Specimen making was done by cutting the metal steel and made it into X joint for the welding. The specimen of stretching test was based on ASTM E8 standard. The welding was using the SMAW weld. After that, PWHT annealing process was done by furnace heating for about 1 hour with the temperature variations of 6500 C, 6950 C and 7400 C, and then it remained inside the furnace for cooling. The result of the research showed that the average rate of maximum tension of the specimen non PWHT was 702.95 MPa, the specimen PWHT 6500 C was 614.51 MPa. The maximum tension of the specimen PWHT 6950 C was 567.96 Mpa, while the maximum tension of specimen PWHT 7400 C was 531.65 MPa. The average of melting tension of the specimen non PWHT was 385.5 MPa, specimen PWHT 6500 C was 340,46 MPa. The melting tension of specimen PWHT 6950 C was 309.77 MPa, while the average rate of melting tension of the specimen PWHT 7400 C was 283.69 MPa. Then, for the average percentage of the elasticity of specimen non PWHT was 30.44%, specimen PWHT 6500 C was 22.22%. The average percentage of the elasticity of specimen PWHT 6950 C was 22.31%. Then, for the average percentage of the elasticity of specimen PWHT 7400 C was 24.81%. The photographic result of micro structure of specimen non PWHT was in a form of ferite, perlite and graphic structure. While the specimen from the PWHT treatment had the structure changes of its granule size and was softer. The fracture of the specimen non PWHT was of granular shape, while the fracture of the specimen that underwent a treatment was in a shape of cup-cone. The result of the research showed that doing the PWHT annealing was able to reduce the stretching tension and increase the tenacity.