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为了研究近平衡凝固对液相线和包晶反应温度的影响,分别采用差热分析仪和自制的高温相转变凝固试验装置对Q345D低碳钢进行凝固相转变试验及高温凝固组织研究。试验表明,试样在近平衡冷却条件下20和30℃/min冷却时,与平衡凝固相转变相比初生铁素体析出温度分别降低了56和88℃,包晶反应转变温度分别降低了29和68℃。另外,在液相线以上发生近平衡凝固后得到的组织为液相直接形成奥氏体;在包晶转变温度发生近平衡凝固时,形成奥氏体晶粒形核较小,晶内组织为针状马氏体,晶界处有少量δ-铁素体,包晶反应未发生;而在奥氏体转变区发生近平衡凝固时,奥氏体晶粒充分长大,即包晶反应转变完全发生,同时δ-铁素体消失。
In order to study the influence of near-equilibrium solidification on liquidus and peritectic reaction temperature, the phase transition experiment and high-temperature solidification microstructure of Q345D mild steel were studied by differential thermal analyzer and self-made high temperature transformation solidification test equipment respectively. The experimental results show that when the sample is cooled at 20 and 30 ° C / min under near-equilibrium cooling conditions, the precipitation temperature of primary ferrite decreases by 56 and 88 ° C, respectively, and the peritectic reaction transition temperature decreases by 29% And 68 ° C. In addition, the microstructure obtained by near-equilibrium solidification above the liquidus is in the liquid phase and forms austenite directly. When the peritectic transition temperature is near equilibrium, the austenite grain nucleus is formed to be small, the microstructure is Acicular martensite, a small amount of δ-ferrite grain boundaries, peritectic reaction did not occur; in the austenite transformation zone near equilibrium solidification, the austenite grains fully grown, that peritectic reaction transformation Totally occurs, while δ-ferrite disappears.