Pengaruh Variasi Arus Listrik Terhadap Struktur Kristal, Kekerasan, dan Kuat Tarik pada Baja Karbon Sedang dengan Las Laser untuk Perbaikan Mold

Nainggolan, Cherie Yolanda (2022) Pengaruh Variasi Arus Listrik Terhadap Struktur Kristal, Kekerasan, dan Kuat Tarik pada Baja Karbon Sedang dengan Las Laser untuk Perbaikan Mold. S1 thesis, Universitas Kristen Indonesia.

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Abstract

Pengaruh pengujian variasi arus listrik pengelasan laser pada baja karbon sedang terhadap kekerasan, kuat tarik, dan struktur kristal telah dilakukan. Baja M300 merupakan baja bahan dasar pembuatan mold. Las laser sering digunakan sebagai upaya perbaikan kerusakan pada mold. Baja M300 dilas menggunakan las laser dengan variasi arus listik 60,70, dan 80 A, lalu spesimen uji kekerasan dan uji tarik diterapkan proses PWHT-Tempering untuk membandingkan nilai kekerasan dan kuat tarik antara spesimen yang mendapat perlakuan PWHT-Tempering dan yang tidak mendapat perlakuan PWHT. Uji struktur kristal menggunakan metode XRD meliputi ukuran kristal, regangan kisi, dan kerapatan dislokasi. Ukuran kristal terbesar terdapat pada spesimen dengan kuat arus pengelasan 80 A, yaitu sebesar 12.8428 MPa, sedangkan ukuran kristal terkecil terdapat pada matriks, yaitu sebesar 8.7155 nm. Regangan kisi tertinggi terdapat pada spesimen dengan kuat arus pengelasan 60 A, yaitu sebesar 2.6841 %, sedangkan regangan kisi terendah terdapat pada spesimen dengan kuat arus pengelasan 80 A, yaitu sebesar 0.0210 %. Kerapatan dislokasi terbesar terdapat pada matriks, yaitu sebesar 0.0675 garis/mm2, sedangkan kerapatan dislokasi terkecil terdapat pada spesimen dengan kuat arus pengelasan 70 A, yaitu sebesar 0.0173 garis/mm2. Uji kekerasan skala Brinell menunjukkan kekerasan tertinggi terdapat pada spesimen dengan kuat arus pengelasan 80 A, tanpa perlakuan PWHT, di daerah pusat las dengan nilai kekerasan sebesar 388 HB, sedangkan nilai kekerasan terendah terdapat pada spesimen dengan kuat arus pengelasan 60 A, dengan perlakuan PWHT-Tempering, di daerah induk metal dengan nilai kekerasan sebesar 275.95 HB. Uji kuat tarik menunjukkan nilai kuat tarik tertinggi terdapat pada spesimen dengan kuat arus pengelasan 80 A, tanpa perlakuan PWHT, di daerah pusat las dengan nilai kuat tarik sebesar 1340.187 MPa, sedangkan nilai kuat tarik terendah terdapat pada spesimen dengan kuat arus pengelasan 60 A, dengan perlakuan PWHT-Tempering, di daerah induk metal dengan nilai kuat tarik sebesar 952.028 MPa./ The variation of laser welding electric current effect on medium carbon steel on hardness, tensile strength, and the crystal structure has been tested. M300 is the primary material for making molds. Laser welding is often used as an effort to repair damage to the mold. M300 steel is welded using laser welding with variations in electric current of 60, 70, and 80 A. Then, the hardness and tensile specimens were applied to the PWHT-Tempering to compare the values of hardness and tensile strength between the specimens that were applied to PWHT-Tempering and those that did not. The Brinell scale hardness test showed that the highest hardness was found in specimens with a welding current of 80 A, without PWHT, in the weld zone with a hardness value of 388 HB, while the lowest hardness values were found in specimens with a welding current of 60 A, that applied to PWHT-Tempering, in the base metal zone with a hardness value of 275.95 HB. The tensile strength test showed that the highest tensile strength value was found in the specimen with a welding current of 80 A, without PWHT, in the weld zone with a tensile strength value of 1340.187 MPa, while the lowest tensile strength value was found in a specimen with a welding current of 60 A, that applied to PWHT-Tempering, in the base metal zone with a tensile strength value of 952,028 MPa. Crystal structure test using the XRD method includes crystal size, lattice strain, and dislocation density. The largest crystal size was found in the specimen with a welding current of 80 A, 12.8428 MPa, while the smallest crystal size was found in the matrix, which is 8.7155 nm. The highest lattice strain was found in specimens with a welding current of 60 A, which is 2.6841 %, while the lowest lattice strain was found in specimens with a welding current of 80 A, which is 0.021 %. The largest dislocation density was found in the matrix, which is 0.0675 lines/mm2, while the smallest dislocation density was found in specimens with a welding current of 70 A, which is 0.0173 lines/mm2.

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