高溫Q&P製程之中錳低碳鋼的碳化物析出行為

Precipitation of microalloyed carbides in medium-manganese low-carbon steels subjected to high-temperature Q&P process

江孟軒(Meng-Hsuan Chiang)

指導教授 ： 顏鴻威

國立臺灣大學/工學院/材料科學與工程學研究所/碩士(2017年)

https://doi.org/10.6342/NTU201703329

摘要

傳統焠火散佈鋼通常在300-500°C溫區退火進而散佈碳元素以達穩定殘留沃斯田鐵之效果。此研究目標在於開發焠火高溫散佈鋼提高錳元素穩定沃斯田鐵之使用效率。為滿足此目的，此研究將發展有別於傳統的新型熱製程及合金成分。新型熱製程在兩相區進行散佈熱製程，錳元素的擴散將伴隨著沃斯田鐵逆相變共同發生而導入均勻分散之細小沃斯田鐵相於回火麻田散鐵基地相中。然而，由於高溫退火的影響，麻田散鐵片層的兼併及差排的消弭將使合金強度大幅下降。為此，新合金鋼種中導入鈮釩碳化析出物可透過晶粒細化及析出強化補足鋼種機械強度。本實驗同時檢視鋁元素添加對於焠火高溫散佈鋼之影響，研究結果顯示含鋁及不含鋁焠火高溫散佈鋼在5分鐘熱製程中，其最佳熱處理溫度各為690 °C及710 °C，然而兩種合金成分的機械性能與顯微結構皆與退火溫度有很高的相關性，而析出強化效果在含鋁添加焠火高溫散佈鋼較高，約30-40MPa。

關鍵字

焠火散佈鋼 ； 沃斯田鐵逆相變 ； 析出強化

並列摘要

In conventional quenching and partitioning (Q&P) processing, carbon partitions into retained austenite and stabilizes it during partitioning heat treatment at 300-500°C. The current research aimed at developing quenching and high temperature partitioning (Q&HTP) processing, in which manganese and carbon both partitioned into and stabilized retained austenite during high temperature partitioning heat treatment. To achieve this goal, new heat treatment processing and newly-designed alloys were developed. High temperature partitioning accompanied with austenite reversion was carried out at intercritical annealing temperature, producing fine austenite phase uniformly distributed in tempered martensite matrix. However, during intercritical annealing, martensite lath coalescence and dislocation annihilation would reduce the strength of Q&HTP steels. To compensate the softening effect, niobium and vanadium carbides were introduced into newly-designed alloy to enhance strength by grain refinement and precipitation strengthening. In present work, the increments of yield strength due to precipitation strengthening were about 100-200 MPa. Also, the effect of aluminum containing was investigated in this research. The optimum temperature of Al-free and Al-containing Q&HTP steels was 690 °C and 710 °C for 5 min heat treatment. However, the mechanical properties and microstructures of two steels were strongly related to the annealing temperature. The effect of precipitation strengthening in Al-containing steels were about 30-40 MPa higher than in Al-free steels.

並列關鍵字

Q&P ； austenite reversion ； precipitation strengthening

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