【作者】 李勇；

【导师】 左秀荣；

【作者基本信息】 郑州大学 ， 材料物理与化学， 2010， 硕士

【摘要】 我国模具工业发展迅速,但与工业发达国家相比仍存在较大差距,模具寿命普遍较低。热处理对模具钢的性能有着重要的影响,通过热处理可以使模具钢具有必要的强韧性,大幅度提高模具的寿命。因此为了提高我国模具工业的技术水平,充分发挥现有材料的潜力,本研究对模具钢的热处理工艺及技术进行全面深入的研究。本论文利用扫描电镜、金相显微镜、硬度计、拉伸试验机等分析测试手段分析了淬火以及回火温度对P20和H13模具钢的淬火组织和回火组织及性能的影响,以及两相区淬火工艺对P20模具钢组织及力学性能的影响,研究结果如下：P20钢高于830℃淬火得到板条马氏体组织,随淬火温度升高模具钢的硬度升高,组织有粗化趋势,但直到890℃后,组织才‘会有明显粗化,分析认为淬火温度选取为860℃是适宜的；随回火温度升高,碳化物析出增多并聚集长大,材料的硬度降低,830～890℃淬火620℃回火时,回火硬度几乎不受淬火温度的影响,并且回火硬度满足预硬化要求,据此对P20钢的预硬化工艺进行优化,得出最佳工艺是：860℃×30min淬火+620℃×60min回火。对H13钢进行了正交试验,结果表明除第一次回火温度对屈服强度的影响不显著外,淬火、回火温度对材料的强度指标的影响均显著,除第二次回火温度对断面收缩率的影响显著外,淬火、回火温度对其他塑性指标影响不显著；通过对其淬火组织及性能的分析,确定其最佳淬火温度为1040℃,通过对回火性能的分析,发现最高回火温度为600℃时材料性能最好,因此,最终确定其最佳热处理工艺是：1040℃×15min淬火+600℃×2h回火+580℃×2h回火。对P20钢在两相区淬火后的组织及性能进行研究,发现原始组织不同,淬火后铁素体形态及未溶碳化物数量不同,保温时间延长,铁素体形态不变,未溶碳化物减少,淬火后的力学性能趋同；原始组织不同的钢在785～800℃的两相区淬火,原始组织为板条马氏体的比原始组织为珠光体加铁素体的钢淬火后的性能好,当淬火温度提高到815～830℃,淬火组织主要为马氏体,此时淬火的力学性能以原始组织为珠光体加铁素体的较好。更多还原

【Abstract】 Development of China’s mold industry is rapid, but compared with the industrialized countries there is still a wide gap, and the die life is generally low. Heat treatment has a significant impact on the performance of the die steel. By heat treatment, die steel can be given the necessary strength and toughness, and the life can be substantially increased. So in order to improve the technological level of China’s mold industry and give full play to the potentiality of existing materials, conducting a comprehensive in-depth study is very necessary on the heat treatment process and technology of die steel. Using scanning electron microscopy, optical microscopy, hardness tester and tensile testing machine analyses the influence of quenching and tempering temperature on microstructure and mechanical properties of the P20 and H13 die steel, and microstructure and mechanical properties of P20 steel with ferrite and martensite obtained by intercritical quenching were studied.It is found that for the P20 steel, when the quenching temperature is above 830℃, almost all quenching microstructure is lath martensite, and their microstructures generally coarsen and the hardness increases with the quenching temperature increasing, but the microstructure will not be significantly coarsening until it reaches 890℃.860℃is considered as more appropriate quenching temperature. Precipitating carbides increase and grow up together, and the strength of the materials reduces with the tempering temperature increasing. When 620℃for 30min is selected as tempering temperature, the tempering hardness is from 32.8HRC to 35.8HRC, it can satisfy pre-hardening hardness requirement. In addtion, tempering hardness remains almost constant when the steel is quenched at 830-890℃and tempered at 620℃, which will be benefit for actual production in factory. Based on those, the best pre-hardened process is 860℃×30min quenching+620℃×60min tempering.For H13 steel, the result of orthogonal experiment show that the yield strength is not significantly affected by the first tempering temperature, but other strength indexes of the materials are all significantly affected by quenching and tempering temperature; the plasticity indexes are not significantly affected by quenching and tempering temperature except that reduction of area is significantly affected by second tempering temperature, so quenching temperature is designated as 1040℃by the analysis of microstructure and hardness. Through the analysis of tempering tensile properties, it has been found that when the higher tempering temperature is 600℃in two annealing, better mechanical properties can be got. So the optimum heat treatment process is 1040℃×15min quenching+600℃×2h tempering+580℃×2h tempering.After the intercritical quenching, the stucture and performance of P20 plastic die steel have been researched, and found that when the original organization is different, the ferrite morphology and the number of the undissolved carbide are also different. With the extension of holding time, the ferrite morphology remains unchanged, undissolved carbide reduces, the difference of mechanical properties is decreased. When the steel is quenched at 785～800℃, in general, the mechanical properties of the steel whose original organization is lath martensite is better than the steel whose original organization is pearlite. When the quenching temperature come to 815～830℃, quenching microstructure is mainly martensite, mechanical properties of the steel whose original organization is lath martensite is better.更多还原