含N量對Mn18Cr18N奧氏體不銹鋼的析出行為及力學(xué)性能的影響

含N量對Mn18Cr18N奧氏體不銹鋼的析出行為及力學(xué)性能的影響THE EFFECT OF NITROGEN CONTENT ON PRECIPITATION BEHAVIOR AND MECHANICAL PROPERTIES OF Mn18Cr18N AUSTENITIC STAINLESS STEEL

采用JmatPro軟件和OM、SEM和TEM等方法研究了不同含N量的Mn18Cr18N奧氏體不銹鋼的沉淀析出行為及其對力學(xué)性能的影響。結(jié)果表明：析出物主要為六方結(jié)構(gòu)的Cr2N和少量 M23C6，其中氮化物Cr2N優(yōu)先沿著晶界析出，隨后以不連續(xù)胞狀方式向奧氏體晶粒內(nèi)部生長。隨著N含量的增加，Cr2N氮化物的析出變得更加敏感，當(dāng)N含量為0.7%時，Cr2N氮化物的最敏感析出溫度為750 ℃，而孕育期僅為10 min；而碳化物M23C6主要以顆粒狀形式形成在奧氏體晶界上，與相鄰的奧氏體晶粒保持相同的位向關(guān)系。力學(xué)性能測試結(jié)果表明，Cr2N氮化物的析出對Mn18Cr18N奧氏體不銹鋼的強度有較小的影響，但對于塑性卻有強烈的惡化作用。時效后Cr2N的析出導(dǎo)致伸長率和斷面收縮率明顯降低，伸長率從52.9%降低到27.7%，斷裂模式也隨著Cr2N氮化物數(shù)量的增加從韌性斷裂轉(zhuǎn)變?yōu)榇嘈缘难鼐嗔押痛┚嗔?。TEM分析表明，固溶態(tài)試樣在拉伸變形過程中通過滑移和孿生方式協(xié)調(diào)變形，呈現(xiàn)了良好的塑性變形能力。而時效后，位錯通過滑移和繁殖最終堆積在Cr2N片層之間和顆粒狀M23C6周圍，降低Mn18Cr18N奧氏體不銹鋼的塑性變形能力。Mn18Cr18N austenitic stainless steel with excellent mechanical properties and corrosion resistance is widely used in nuclear industries, power plants and medicine field. However, precipitation of the second phases during hot deformation deteriorates the mechanical properties and hot formability. In order to clarify the precipitation behavior of this steel, the precipitation behavior and its influence on mechanical properties of Mn18Cr18N austenitic stainless steel with different nitrogen content were investigated by JmatPro software and OM, SEM and TEM analytical methods. The results indicate that precipitation phases consist of Cr2N and a few M23C6, in which Cr2N preferentially precipitates along grain boundaries and then grows up to the interior of austenite grain by discontinuous cellular. With increasing of ageing temperature, the precipitation of Cr2N became more sensitive. When the nitrogen content increases to 0.7%, the most sensitive precipitation temperature of Cr2N is 750℃ with an incubation period of 10min. However, M23C6 mainly precipitates by granular at austenitic grain boundaries and maintains cube-on-cube orientation relationship with adjacent austenite grain. The results of mechanical property test indicate that the precipitation of Cr2N have a negligible effect on strength and obvious deterioration on plasticity of Mn18Cr18N austenitic stainless steel. The precipitation of Cr2N after ageing treatment leads to remarkable decrease in elongation and reduction of area, and the elongation reduced from 52.9% to 27.7%. Meanwhile, fracture mode also transformed from ductile fracture to intergranular fracture and transgranular fracture with the increasing of Cr2N. TEM analysis shows that solution treatment sample reveals good plastic deformation ability and coordinates deformation by slip and twinning, simultaneously. Nevertheless, dislocations slipped, propagated and eventually piled up between lamellas of Cr2N and around granular M23C6, which induce the degeneration of the plastic deformation capacity of Mn18Cr18N austenitic stainless steel.

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