奈米級析出物強化熱軋汽車用鋼開發
Other Title
The Development of Nano-Precipitation Strengthened Hot-Rolled Automobile Steels
Journal
鑛冶：中國鑛冶工程學會會刊
Journal Volume
53
Journal Issue
4
Start Page
45
End Page
60
ISSN
0451-0011
Date Issued
2009-12
Abstract
為了節省能源消耗與兼顧乘車安全性，汽車用鋼材使用的強度等級愈來愈高。過去高強度鋼通常採用麻田散鐵或變韌鐵為主要顯微組織的相變態強化設計，然而此類鋼材加工成形性不夠好。為了得到優良強度與加工性組合，本研究採用高鈦（＞0.08wt%）複合添加釩之合金設計配合熱軋軋延參數之精緻控制，利用肥粒鐵晶粒細化及奈米析出複合強化機構來產製高強度熱軋汽車用鋼。其冶金機制是利用高溫時非常穩定之TiN來抑制熱軋製程再加熱時沃斯田鐵晶粒成長，並於熱軋製程上控制完軋溫度盡可能接近Ar3來大幅增加肥粒鐵成核位置，配合採用快速冷卻模式來防止於高溫產生肥粒鐵相變化，以避免肥粒鐵晶粒粗化。另外再藉由熱軋盤捲溫度的適當控制，使奈米尺寸的（Ti,V）C界面析出物（＜10nm）持續於肥粒鐵相變化過程中析出，而得到大量均勻散布於肥粒鐵晶粒中之析出物，充分發揮良好的析出強化效果。本研究藉由微米級（＜3μm）細晶肥粒鐵中奈米級析出物之大量產生，使得熱軋後之鋼材不需再經過任何熱處理，其抗拉強度可以穩定達到＞780MPa的超高強度，而且伸長率還可達到18%的水準。此鋼材超高強度與良好加工成形性，已經被廣泛應用於卡車大樑及汽車之防撞鋼樑、安全汽囊零件等汽車部件上。
To save the energy and increase the passenger safety, the required strength level of automobile steels has become higher and higher. Traditionally, the microstructure of the high strength steels is mainly composed of martensite or bainite for getting the transformation strengthening effect, but these steels usually exhibit poor formability. To reach the demand of high strength and formability balance, the steels with composition of high Ti content (＞0.08wt%) and minor V addition undergoing careful control of hot rolling parameters are used to get the grain refinement and nano-precipitation coupled strengthening mechanisms for the production of high strength automobile steel. The stable TiN precipitates inhibit the grain growth during reheating treatment. In addition, the proper control of the finish rolling temperature nearby the Ar3 temperature promotes a lot of ferrite nucleation sites on the prior austenite grain boundaries. During the subsequent cooling stage, fast cooling is applied to further prevent the occurrence of ferrite transformation and corresponding coarsening of ferrite grain size. Additionally, by controlling the coiling temperature of the strip, lots of nano-sized (＜10 nm) (Ti,V)C interface precipitates are consecutively appeared during the slow cooling period. The ultra fine grained refinement and nano-precipitation technologies ensure the strength of steel higher than 780 MPa, and the elongation of the steel better than 18%, sparing the common strengthening by heat treatment. This steel has been applied in several parts of automobile, such as truck frame, door impact beam, and container of safety steam capsule etc.
Type
journal article