PENGARUH VARIASI MEDIA PENDINGIN PADA PROSES PENGELASAN SMAW MATERIAL BAJA 

ST37 TERHADAP KEKUATAN IMPACT, KEKERASAN, DAN STRUKTUR MIKRO

THE EFFECT OF VARIATIONS IN COOLING MEDIA IN THE SMAW WELDING PROCESS OF ST37 STEEL 

MATERIAL ON IMPACT STRENGTH, HARDNESS AND MICRO STRUCTURE

Baja ST 37 merupakan baja karbon rendah dengan kandungan karbon dibawah 0,3%. Baja St 37 adalah baja karbon rendah, dengan komposisi kimia karbon : 0.20% C%, Mangan : 0.8 %, Silikon : 0.3 % ditambah unsur lainnya. Baja karbon rendah ST 37 adalah salah satu jenis logam yang sering digunakan dalam bidang otomotif, Salah satunya untuk chasis sepeda motor. Dalam produksi chasis sepeda motor diperlukan pengelasan. Pada proses pengelasan chasis sepeda motor menyebabkan tegangan sisa dan perubahan sifat mekanik yang menyebabkan chasis retak,bengkok sampai juga patah. Untuk memperbaiki perubahan sifat mekanik setelah pengelasan maka dapat digunakan proses pendinginan Penelitian ini menggunakan metode eksperimen dengan memvariasikan media pendingin setelah proses pengelasan SMAW pada material baja ST 37, selanjutnya masing-masing variabel diuji impact, kekerasan, dan struktur mikro. Spesimen yang sudah diuji impact, kekerasan, dan uji foto mikro kemudian dianalisa pengaruh dari varibel bebas terhadap variabel terikat. Variabel bebas meliputi media pendingin gel lidah buaya dan nira tebu.Berdasarkan hasil penelitian diperoleh pengaruh variasi media pendingin pengelasan baja SMAW ST 37 terhadap uji impact, kekerasan dan struktur mikro. Pada pengujian kekerasan didapatkan nilai kekerasan mengalami penurunan pada weld metal, HAZ, dan base metal. Nilai kekerasan tertinggi terdapat pada media pendingin gel lidah buaya pada area weld metal 92,2 HRB, HAZ 86,5, dan base metal 79,2 HRB dan nilai terendah terdapat pada spesimen tanpa media pendingin weld metal 83,6 HRB, HAZ 81,4 , dan base metal 79,2 HRB. Pada pengujian impact pengelasan SMAW dengan berbagai macam media pendingin. Nilai uji impact tertinggi terdapat pada spesimen tanpa media pendingin sebesar 0,303 J/mm² dan nilai terendah terdapat pada spesimen media pendingin gel lidah buaya sebesar 0,066 J/mm². Pada penelitian ini diperoleh hasil terbaik tanpa media pendingin, dengan hasil uji impact tertinggi dan kekerasan terendah. Sedangkan struktur mikro tanpa media pendingin menghasilkan struktur ferit dan perlit yang menandakan material ulet, berbeda dengan struktur mikro pada media pendingin gel lidah buaya dan nira tebu menghasilkan struktur perlit, ferit dan martensit yang menandakan material bersifat keras dan getas

Kata Kunci : Baja ST 37, Chasis, Las SMAW, Media Pendingin, Uji Kekuatan Impact, Kekerasan dan Struktur Mikro

ST 37 low carbon steel is low carbon steel with a carbon content below 0.3%. St 37 steel is low carbon steel, with a chemical composition of carbon: 0.20% C%, Manganese: 0.8%, Silicon: 0.3% plus other elements. ST 37 low carbon steel is a type of metal that is often used in the automotive sector, one of which is for motorbike chassis. In the production of motorbike chassis welding is required. The welding process of a motorbike chassis causes residual stress and changes in mechanical properties which cause the chassis to crack, bend and even break. To improve changes in mechanical properties after welding, a cooling process can be used. This research uses an experimental method by varying the cooling media after the SMAW welding process on ST 37 steel material, then each variable is tested for impact, hardness and microstructure. Specimens that have been tested for impact, hardness, and micro photo tests are then analyzed for the influence of the independent variable on the dependent variable. The independent variables include cooling media, aloe vera gel and sugar cane juice. Based on the research results, it was found that the influence of variations in the cooling medium for welding SMAW ST 37 steel on impact, hardness and microstructure tests was obtained. In the hardness test, it was found that the hardness value decreased for the weld metal, HAZ, and base metal. The highest hardness value was found in the aloe vera gel cooling media in the weld metal area 92.2 HRB, HAZ 86.5, and base metal 79,2 HRB and the lowest value was found in the weld metal area without cooling media 83.6 HRB, HAZ 81.4, and base metal 79,2 HRB. In SMAW welding impact testing with a variety of cooling media. The highest value for the impact test was found in the specimen without cooling media, 0.303 J/mm² and the lowest value was in the aloe vera gel cooling media specimen, 0.066 J/mm². In this research, the best results were obtained without cooling media, with the highest impact test results and lowest hardness. Meanwhile, the microstructure without a cooling medium produces a ferrite and pearlite structure which makes the material not hard and ductile different from the microstructure in the cooling media of aloe vera gel and sugarcane juice, it produces pearlite, ferrite and martensite structures which cause the material to be hard and brittle. Keywords: ST 37 Steel, Chassis Motorcycle, SMAW Welding, Cooling Media, Impact Strength Test, Hardness and Microstructure