熱作工具鋼的淬火條件與韌性分析

Abstract

本研究使用JIS SKD61熱作工具鋼及其改良種為實驗材料，在固定的升 溫速率(11℃/min)及冷卻速率及冷卻速率(8.27-10℃/min)下，使用淬火溫度1050℃、1020℃、990℃、960℃及淬火持溫時間及淬火持溫時間 30min、90min、120min互相搭配進行淬火。試片經過淬火後，測量試片中心的維克氏硬度並觀察淬火顯微組織。後的試片進行兩次或以上的回火至目標硬度HRC 46-47.5內，並觀察其回火顯微組織及量測衝擊值。最後比較不同鋼材間，淬火條件對其硬度、顯微組織回顯微組織、衝擊韌性之影響。 研究結果顯示，隨著淬火溫度上升與持時間的增 加，Cr、Mo、V合金碳化 物固溶量增多，各鋼種的淬火硬度也會隨之上升。但淬火溫度過高或持時間長則會使晶粒粗大，導致淬火硬度降低，衝擊韌性也會下。淬火溫度過低或持溫時間過短，碳化物固溶量較少，材料硬能不足容易出現大的變韌鐵及 殘留碳化物，導致淬火硬度及衝擊韌性皆會降低。規範鋼的Si、V含量較高，其MC合金碳化物溶解溫度較高。因此，在同樣的淬火條件下，合金碳化物固溶量較少，且含有較多的變韌鐵與殘留碳化物，嚴重降低淬火硬度及衝擊韌性。Cr、Mo、V含量多的鋼材，硬化能較高，淬火後變韌鐵含量較少，韌性較高。

This research used JIS SKD61 hot work tool steel and its modified steel as experimental materials. Under the fixed heating rate (11℃/min) and cooling rate (8.27-10℃/min), the specimens were quenched at the quenching temperature of 1050℃, 1020℃, 990℃ and 960℃ and holding time of 30min, 90min and 120min. After quenching, measure the Vickers hardness in the center of specimen and observe the microstructure. The specimen went through twice (or above) tempering after quenching until the tempering hardness is within HRC 〖47〗_(-1)^(+0.5), and then observe its tempering microstructure and measure the impact toughness. Lastly, the effects of quenching conditions on its hardness, microstructure of quenching, microstructure of tempering and impact toughness after quenching was analyzed among different steel materials. The research results show that with the increase in quenching temperature and holding time, the amount of Cr, Mo, V carbide dissolved in matrix will increase and the quenching hardness will also increase. However, higher quenching temperature or longer holding time will make grains grow quickly, causing the quenching hardness and impact toughness to decrease. When quenching temperature is too low or holding time is too short, carbide dissolved in matrix will decrease and the hardenability of materials is insufficient. Thus, bainites and residual carbides are more likely to appear, causing quenching hardness and impact toughness to decrease. Standard SKD61 steel contains higher MC carbides, and its dissolving temperature of carbides is higher than MODs. Under the same quenching condition, MC carbides dissolved into austenite is less than MODs and contains more bainites and residual carbides, which significantly decreases the quenching hardness and impact toughness. The steel material which contains higher Cr, Mo and V has higher hardenability. After quenching, the amount of bainites is lower and impact toughness is higher.