D6AC鋼經旋形加工與電子束銲接之製程研究

Abstract

本研究之主要目的為「探究D6AC超高強度鋼結合65%減縮率之旋形加工、電子束銲接兩項高精度加工法之管件製程研究」，將本身極具優質機械性質的D6AC鋼材，結合了無縫、無屑、加工快速且高精度的旋形加工技術，以及於真空環境中施銲、且銲後所產生之銲道極窄之電子束銲接，期能研發出高品質的管件。 本研究在流程上首先為母材、旋形胚盂之製備，隨後進行試旋加工，確立最佳參數後，再正式旋形加工，隨後進入試銲階段，待銲接參數確立後，即正式銲接並研究銲後施予不同溫度回火所帶來的影響與改變，整個實驗過程，每個階段前後均會加以量測試片之機械性質包含強度、硬度、金相、破裂面或拉伸破斷面的顯微觀察其延性與脆性，隨不同加工參數所呈現的趨勢，透過XRD量測其晶體結構等資訊，最後綜合各實驗階段之各項結果，比較與分析後歸納出各個環節所需注意的重點。 結果顯示：首先母材經900℃持溫105分鐘隨後空冷至室溫，並將其車製加工為旋形胚盂，此時之旋胚雖經正常化熱處理，其硬度與強度數值仍然過高，無法順利旋形出高旋形量，因此需再進行620℃持溫120分鐘隨後空冷至室溫之退火熱處理使其晶粒成長並更為軟化，硬度下降後即可順利達成65%減縮率之旋形加工。 旋形管件完成後，即對管件與管件之間進行不同射束電流大小之電子束試銲，經分析後確立銲接參數，並正式銲接，隨後量測銲後未回火之管件機械性質，發現銲後未回火，其銲道熔融區呈現硬脆、強度較低之特性，拉伸試驗之試片斷裂處均在熔融區，且破斷面呈現脆性且具有些許微裂痕，因此銲後回火成為銲後提升其機械性質之關鍵，銲後回火350℃可獲得最高抗拉強度，回火550℃則可獲得最佳延伸率。

The mechanical properties of D6AC tube have been flow-formed by 65 % reduction and welded by electron-beam. Their microstructural state, hardness, subsequently yield strength, ultimate tensile strength, and elongation were investigated. We tried different parameters in flow-forming and EBW to find the D6AC tube with best mechanical properties. After flow-forming and EBW, we tempered the welded D6AC tubes from 250°C to 550°C, then we tried to find the effect of the mechanical properties with different tempering temperatures. We found that increasing tempering temperatures from 250°C to 550°C resulted in decrease in the yield strength and ultimate tensile strength, and increase in percentage elongation remarkably. We also found that hardness average of fusion zone (FZ) decreased from 65.74HRC to 44.55HRC and heat-affected zone (HAZ) decreased from 55.47 HRC to 41.91HRC. EBW with a high energy input resulted in a seriously inadequate percentage elongation of the weldment. In order to investigate microstructures under each set of experimental conditions; optical microscopy and scanning electron microscopy was employed to observe the HAZs and FZs view of weldment.