UMKM bengkel manufaktur membuat <em>Shank Holder Dovetail Cutter </em>berbahan AISI 4340 secara mandiri. Nilai kekerasan pada<em> Shank Holder Dovetail Cutter </em>wajib dimiliki agar alat memiliki umur pakai panjang. Proses <em>hardening </em>menimbulkan dilema berupa resiko kerusakan pada area kritis <em>shank holder</em>, yaitu material pecah bila kekerasan terlalu tinggi namun ketangguhan rendah, atau material mengalami deformasi bila kekerasan rendah. Diperlukan analisis parameter proses <em>hardening </em>untuk menghasilkan kombinasi nilai kekerasan dan ketangguhan yang optimal, serta biaya proses minimal guna mendukung UMKM bengkel manufaktur. Desain eksperimen menggunakan metode <em>Response Surface Method</em> untuk optimalisasi respon dan analisis statistik ANOVA untuk mengidentifikasi kontribusi setiap parameter bagi variabel respon. Parameter suhu austenite, media <em>quench, </em>dan suhu temper menjadi variabel prediktor. Hasil pengujian kekerasan Rockwell-C ASTM E18 dan uji ketangguhan <em>Impact Charpy V-notch</em> E23 diterapkan sebagai variabel respon. Suhu temper merupakan parameter proses <em>hardening </em>yang secara signifikan mempengaruhi nilai kekerasan dan ketangguhan. Suhu temper memberikan kontribusi sebesar 87,44% terhadap respon nilai kekerasan, serta kontribusi 24,77% dan 43,44% terhadap respon nilai ketangguhan. Kombinasi parameter suhu austenite 871,76°C, media <em>quench</em> air, suhu temper 200°C memberikan respon optimal terbaik dengan nilai <em>desirability</em> 0,790; biaya proses Rp.42.586,58; nilai kekerasan 51,211 HRC; dan nilai ketangguhan 1,131 J/mm²

ASSAB 705 steel is a machinery steel that used in several industries due to its mechanical properties, for components manufacturing. Hardening process is applied to ASSAB 705 to increase mechanical strength thereby increasing hardness. Conversely, an increase in the hardness value will decrease toughness value so that components are easily damaged due to heavy workloads. The optimal combination of hardness and toughness enhances abrasion resistance and maintains component strength against working loads. It is necessary to investigate parameters of hardening process and its effect on the hardness and toughness of ASSAB 705 steel. This study used Design of Experiment with Taguchi method and ANOVA statistical analysis. Hardening parameter with austenite temperature factor, quench media, and tempering temperature, is used to optimize the combination of hardness-toughness value of ASSAB 705 steel. Results of this research show that tempering temperature is the most influential factor on hardness and toughness values. Optimal combination of mechanical strength is obtained at a hardness value of 50.78 HRC (increase of 44.85%) and a toughness value of 1.15 J/mm2 (increase of 109.09%). These values ​​were obtained from the hardening method: austenite temperature of 825°C, oil quench medium, and tempering temperature of 180°C. The desirability value for combination of hardening process parameters is 0,682802.