ABSTRACT
The effect of pre-strain and voltage on the weldability and the strength of
dissimilar materials resistance spot welded joints between low carbon steel SS400
and austenitic stainless steel J4 has been investigated. The 3 mm thick of low
carbon steel SS400 and 1 mm of austenitic stainless steel J4 were welded using
Resistance Spot Welding (RSW) process with same electrode pressure and weld
time. In the joining process, three different level pre-strain (1%; 1,5%; 2%) and
four different voltage (2,02V; 2,30V; 2,67V; 3,20V) were chosen. Micro and
macrostructure, microhardness, tensile-shear strength, and failure mode were
conducted to evaluate spot welding result.
The results showed that the increasing of voltage lead to bigger nugget size
and increased tensile load bearing capacity on the same level pre-strain. It also
changed the failure mode from interfacial to pullout failure mode on the specimen.
The different results shown when the increasing level pre-strain on the same
voltage, which the nugget size became smaller and lead to decrease tensile load
bearing capacity on RSW joint. It caused by increased hardness due to martensite
formation during pre-strain process and led to the welds brittle.
Keywords : resistance spot welding, pre-strain, weldability, dissimilar materials,
low carbon steel, austenitic stainless steel.
ABSTRAK
Pengaruh pre-strain dan tegangan listrik terhadap sifat mampu las dan
kekuatan sambungan las titik beda material antara baja karbon rendah SS400 dan
baja tahan karat austenitik J4 telah diteliti. Baja karbon rendah SS400 dengan
tebal 3 mm dan baja tahan karat austenitik J4 tebal 1 mm dilas menggunakan
proses Resistance Spot Welding (RSW) dengan tekanan elektroda dan waktu
pengelasan sama. Proses penyambungan menggunakan tiga level pre-strain yang
berbeda (1%; 1,5%; 2%) dan empat tegangan listrik yang berbeda (2,02V; 2,30V;
2,67V; 3,20V. Struktur mikro dan makro, kekerasan mikro, kekuatan tarik-geser,
dan jenis kegagalan digunakan untuk mengevaluasi hasil pengelasan titik.
Hasil penelitian menunjukkan bahwa peningkatan tegangan listrik
menyebabkan ukuran nugget menjadi semakin besar dan tensile load bearing
capacity meningkat pada level pre-strain yang sama. Hal tersebut mengakibatkan
perubahan jenis kegagalan dari interfacial menjadi jenis kegagalan pullout pada
spesimen. Hasil yang berbeda ditunjukkan pada saat peningkatan level pre-strain
pada tegangan listrik yang sama, dimana ukuran nugget menjadi semakin kecil
dan menyebabkan tensile load bearing capacity semakin menurun. Hal tersebut
disebabkan meningkatnya kekerasan karena pembentukan martensit selama proses
pre-strain yang mengakibatkan lasan menjadi getas.
Kata kunci : resistance spot welding, pre-strain, sifat mampu las, beda material,
baja karbon rendah, baja tahan karat austenitik.