Abstrak Telah dilakukan sintesis pelapisan lapisan NiCo dan CrAl pada baja ST-37 dengan menerapkan metode elektroplating NiCo 5% pada temperatur ± 50 °C, kemudian dilanjutkan dengan metode pack cementation pada temperatur ± 800 °C guna mendifusikan chromium (Cr) dan aluminium (Al) pada baja ST-37 sehingga diperoleh lapisan FeNiCoCrAl dengan sifat mekanik yaitu flexural strength dan modulus flexural yang lebih baik. Untuk keperluan tersebut maka uji tekuk (bending test) dilakukan terhadap 4 sampel yang berbeda, yaitu Fe­-base, FeNiCo, FeNiCoCr, dan FeNiCoCrAl. Diperoleh hasil flexural strength dan modulus flexural terbesar berturut-turut sebesar 681,96 MPa dan 12.855,0 MPa yang dimiliki lapisan FeNiCo, sedangkan flexural strength terkecil sebesar 483,48 MPa yang dimiliki lapisan FeNiCoCrAl, serta modulus flexural terkecil sebesar 4.434,8 MPa yang dimiliki lapisan FeNiCoCr. Simpulan dari penelitian ini ialah dengan dilakukannya proses pelapisan NiCoCrAl pada baja ST-37 yang meliputi proses elektroplating NiCo 5% dan pack cementation Cr dan Al, maka diperoleh sifat mekanik (flexural strength dan modulus flexural) yang justru menurun bukan meningkat seperti yang diharapkan. Hal diakibatkan karena pengaruh pemanasan yang cukup tinggi pada pack cementation sehingga dapat mempengaruhi mikrostruktur dari logam dasarnya (Fe-base) menjadi semakin lunak dan tidak stabil fasenya. Kata Kunci : Elektroplating, Pack Cementation, NiCoCrAl, Flexural Strength, Modulus Flexural, Baja ST-37, Uji Tekuk (bending test). Abstract Synthesis on coating of NiCo and CrAl layer to ST-37 steel type was carried out by using electroplating and pack cementation methods. The first coating method was aimed to add NiCo layer to the surface of steel at 50 °C, while the second was addressed to diffuse CrAl layer into the FeNiCo substrate and this was carried out at 800 °C. The aim of coating is to improve mechanical properties (flexural strength and modulus flexural) of the steel. To do that, bending test was carried out to 4 different samples, namely Fe-base, FeNiCo, FeNiCoCr, and FeNiCoCrAl. The result are flexural strength and modulus flexural, respectively for the largest are 681.96 MPa and 12855.0 MPa is owned by FeNiCo layer, while the smallest flexural strength is 483.48 MPa owned by FeNiCoCrAl layer, and the smallest modulus flexural is 4434.8 MPa owned by FeNiCoCr layer. It was obtained that the thicker the NiCo coated onto the surface of the steel, then the higher the flexural strength and modulus flexural. On the other hand, the thicker the CrAl layer diffused into the FeNiCo, then the thinner the flexural strength and modulus flexural. So, by doing NiCoCrAl coating process on ST-37 steel that include electroplating NiCo 5% process and pack cementation Cr and Al can decrease the mechanical properties (flexural strength and modulus flexural) which is instead of increasing as expected. It is caused by the effect of heating is high enough so that the pack cementation can affect the microstructure of basic metals (Fe-base) become soft and unstable phase. Keywords : Electroplating, Pack Cementation, NiCoCrAl, Flexural Strength, Modulus Flexural, ST-37 Steel, Bending Test.