Metals and Materials International ( IF 3.3 ) Pub Date : 2021-08-05 , DOI: 10.1007/s12540-021-01009-3 Ramadan N. Elshaer 1 , Mohamed K. El-Fawakhry 2 , Ahmed I. Z. Farahat 3
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Abstract
The effect of quenching after martensitic finish (QAMf) or quenching & partitioning (Q&P) on microstructure evolution, mechanical properties, and strain hardening instability of low and medium carbon hot rolled steels were investigated. Two heats of low and medium carbon steels were cast in an induction open furnace. The chemical composition of low carbon steel is 0.16C–0.27Si–1.47Mn–0.02Al while medium carbon steel is 0.49C–0.30Si–0.91Mn–0.03Al. They were hot-rolled at 1200 °C for 30 min followed by air cooling. The microstructure after hot-rolled gives bands of ferrite and pearlite for 0.16 wt% low carbon steel. On the other hand, 0.49 wt% medium carbon steel produces coarse pearlite islands surrounded by ferrite phase. To enhance mechanical properties, it was necessary to modify the microstructure of low and medium carbon steels using QAMf or Q&P processes. The resultant matrix of microstructure after QAMf and Q&P processes contained ferrite, bainite, lath martensite, and retained austenite for 0.16 wt% low carbon steel, and polygonal ferrite, lath martensite, and retained austenite for 0.49 wt% medium carbon steel, respectively. In low carbon steel, QAMf process increased uniform elongation from 6.6 to 13.5% (105% increase) while ultimate tensile strength (UTS) improved slightly from 645 to 692 MPa (7% increase). However, in medium carbon steel, Q&P reduced uniform elongation from 12.4 to 4.8% (61% decrease) while increased UTS from 769 to 1242 MPa (61.5% increase). It is worthy to mention that QAMf process exhibited strain hardening instability zone (7.8% strain before necking) compared to hot-rolled process (0% strain before necking). On the other hand, Q&P process highly decreased strain hardening instability zone (0.77% strain before necking) compared to hot-rolled process (3.4% strain before necking).
Graphic Abstract
中文翻译：
中低碳淬火分割钢的组织演变、力学性能及应变硬化不稳定性
摘要
马氏体精加工后的淬火效果（QAM f) 或淬火和分配 (Q&P) 对低碳和中碳热轧钢的组织演变、机械性能和应变硬化不稳定性进行了研究。在感应敞开式炉中浇铸两炉低碳和中碳钢。低碳钢的化学成分为0.16C-0.27Si-1.47Mn-0.02Al，中碳钢的化学成分为0.49C-0.30Si-0.91Mn-0.03Al。它们在 1200°C 下热轧 30 分钟，然后空冷。热轧后的显微组织为 0.16 wt% 的低碳钢提供铁素体和珠光体带。另一方面，0.49 wt% 的中碳钢会产生被铁素体相包围的粗珠光体岛。为了提高机械性能，有必要使用 QAM f对低碳和中碳钢的微观结构进行改性。或 Q&P 流程。QAM f和 Q&P 工艺后得到的显微组织基体分别含有铁素体、贝氏体、板条马氏体和 0.16 wt% 低碳钢的残余奥氏体，以及 0.49 wt% 中碳钢的多边形铁素体、板条马氏体和残余奥氏体。在低碳钢中，QAM f工艺将均匀伸长率从 6.6% 提高到 13.5%（增加 105%），而极限抗拉强度 (UTS) 从 645 MPa 略微提高到 692 MPa（增加 7%）。然而，在中碳钢中，Q&P 将均匀伸长率从 12.4% 降低至 4.8%（降低 61%），同时将 UTS 从 769 MPa 提高至 1242 MPa（提高 61.5%）。值得一提的是，QAM f与热轧工艺（颈缩前应变为 0%）相比，该工艺表现出应变硬化不稳定区（颈缩前应变为 7.8%）。另一方面，与热轧工艺（颈缩前应变为 3.4%）相比，Q&P 工艺大大降低了应变硬化不稳定区（颈缩前应变为 0.77%）。
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