【作者】 裴剑；

【导师】 傅万堂； 王春旭；

【作者基本信息】 燕山大学 ， 材料学， 2011， 硕士

【摘要】 300M钢作为低合金超高强度钢的典型代表,因其成本低（合金元素含量低）、生产工艺简单而广泛用于航空、航天领域,如制造飞机大梁、起落架、发动机轴、高强度螺栓、固体火箭发动机壳体和化工高压容器等。为了提高300M钢的韧性,本文通过调整韧化元素Ni的含量,研究Ni含量对300M钢的连续冷却转变、显微组织演变以及力学性能变化的影响规律,并且研究了回火工艺对高Ni含量300M钢的组织与性能的影响,取得如下主要研究结果:300M钢的Ms点随着Ni含量的增加而逐渐降低,Ni含量由2%提高至5%时,Ms点由270℃降到220℃;元素Ni促进300M钢的马氏体相变,推迟其贝氏体相变,并使其连续冷却转变过程中贝氏体相变区逐渐右移,当Ni含量分别为2%和4%时,发生贝氏体转变的临界冷速约为0.28℃/s和0.05℃/s,而Ni含量提高到5%时,冷却速度为0.03℃/s时仍未发生贝氏体相变;随着Ni含量的提高,300M钢淬火后残余奥氏体的体积分数逐渐增加,强度降低而冲击韧性提高。3%Ni含量的300M钢在150℃⁶00℃回火时,随着回火温度的升高,抗拉强度单调降低,屈服强度和硬度先升高后降低,且在250℃³00℃回火时达到峰值,当回火温度高于400℃,抗拉强度和屈服强度降低速度加快;随着回火温度的升高,冲击韧性在250℃³00℃时达到极大值,在450℃时达到极小值,该钢在450℃附近存在第二类回火脆性,。在回火过程中,试验钢的马氏体及残余奥氏体均发生分解。当回火温度较低时（150℃³50℃）,在马氏体基体中主要析出细小的ε-碳化物,此时试验钢具有最佳的强韧性配合。随着回火温度的进一步提高,马氏体和残余奥氏体的分解速度加快,而ε-碳化物也逐渐转变为M₃C型碳化物,当回火温度提高到600℃时,残余奥氏体量最小,ε-碳化物完全转变为M₃C型碳化物。更多还原

【Abstract】 In the aviation and aerospace fields, 300M steel, as a typical representative of low-alloy high strength steel, due to its low content of alloying elements, low cost, simple production technology, are widely used, such as the manufacture of aircraft beams, landing gear, engine shaft, high strength bolts, solid rocket motor case and chemical high-pressure containers. Based on the 300M steel, in order to improve its toughness, we adjust Ni content of 300M steel, study the effect of Ni content to continuous cooling transformation and microstructure evolution of microstructure, the impact of changes of mechanical properties. The results obtained are as follows:With the Ni content increases from 2% to 5%, Ms temperature of 300M steel reduces from the 270℃to 220℃; Ni element promotes martensitic transformation, delays bainite transformation, with the Ni content increases, during continuous cooling transformation, bainitic transformation zone of 300M steel shifts to the right gradually; when the increase of Ni content is 2%, the critical cooling rate of bainitic transformation is about 0.28℃/s, when the Ni content increases to 4%, the critical cooling rate of bainitic transformation is about 0.05℃/s, while the Ni content increases to 5%, the bainite transformation has not occurred even the cooling rate is 0.03℃/s. With Ni content increases, the volume fraction of retained austenite of 300M steel after quenching gradually increases, which reduces the strength while increases the impact toughness of test steel.After tempered at the range from 150℃to 600℃, the tensile strength of 3% Ni test steel decreases, the yield strength and hardness increases firstly and then decreases, at 250℃³00℃reaches a peak, and when the tempering temperature is higher than 400℃, the decreased rate of tensile strength and yield strength increase; there is a second class of temper brittleness of 3% Ni steel, with the tempering temperature increase the impact toughness reaches the maximum value at 250℃ 300℃,and reaches the minimum value at 450℃.During the process of tempering ,martensite and retained austenite of test steel are decomposed, when the tempering temperature below （150℃ 350℃）, a large number of tinyε-carbide are precipitated in the martensitic body , then strength and toughness of test steel achieves the best match. With further increase of the tempering temperature, the decomposition of martensite and retained austenite gets faster,ε-carbide gradually transforms into M₃C, when the tempering temperature increases to 600℃, the retained austenite volume fraction reaches the minimum value,ε-carbide transforms into M₃C completely. Keywords 300M steel; Ni content; microstructure; continuous cooling更多还原