Tempering behavior of a 0.53%C-1.6%Si-0.9%Mn-0.76%Cr-0.14%V-0.05%Nb steel was examined. Water quenching produced lath martensite structure with a 10.5% volume fraction of retained austenite (RA) with film-like shape. Low temperature tempering (LTT) leads to precipitation of transition carbides and carbon partitioning between martensite and RA. The following precipitation sequence was found: martensite →non-stoichiometric η-carbide→stoichiometric η-carbide→FeC. Highest density of non-stoichiometric FeC η−carbides was found after isochronal tempering at 280 °C that provided attractive combination of high yield stress (YS) (1890 MPa) with a ductility of ∼6% and a Charpy V-notch (CVN) impact energy of ∼10 J/cm. At 400 °C, the replacement of non-stoichiometric η-carbide by the stoichiometric one decreases strength and increases ductility due to 30% decrease in its volume fraction. No tempered martensite embrittlement was found due to the fact that Si effectively suppresses the precipitation of cementite at T ≤ 400 °C. The replacement of transition η-carbide by boundary cementite after isochronal tempering at 500 °C leads to considerably decrease in YS down to 1360 MPa, while elongation to failure increases up to 9.3%. Effect of decomposition of RA on strength, ductility and fracture toughness is insignificant.

中文翻译：

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含 1.6 wt% Si 的超高强度钢在中低温下的回火行为

研究了0.53%C-1.6%Si-0.9%Mn-0.76%Cr-0.14%V-0.05%Nb钢的回火行为。水淬产生板条马氏体组织，残余奥氏体（RA）体积分数为10.5%，呈膜状。低温回火 (LTT) 导致过渡碳化物析出以及碳在马氏体和 RA 之间分配。发现以下沉淀顺序：马氏体→非化学计量的η-碳化物→化学计量的η-碳化物→FeC。在 280 °C 等时回火后发现了非化学计量 FeC η−碳化物的最高密度，它提供了高屈服应力 (YS) (1890 MPa)、延展性 ~6% 和夏比 V 型缺口 (CVN) 的有吸引力的组合冲击能量~10 J/cm。在 400 °C 时，化学计量碳化物取代非化学计量碳化物会降低强度并提高延展性，因为其体积分数减少了 30%。由于Si在T≤400℃时有效抑制渗碳体析出，因此未发现回火马氏体脆化。在 500 °C 等时回火后，过渡态 η-碳化物被边界渗碳体取代，导致 YS 显着降低至 1360 MPa，而断裂伸长率增加至 9.3%。RA 分解对强度、延展性和断裂韧性的影响微不足道。