提高热作模具用H13钢性能的研究

【作者】 周健；

【导师】 樊刚； 马党参；

【作者基本信息】 昆明理工大学 ， 材料物理与化学， 2009， 硕士

【摘要】 H13钢以其高的淬透性、强韧性和热疲劳性能在国内外得到广泛的应用,用于制作热挤压模、铝合金压铸模、热锻模等,是当前世界范围内使用最广泛的热作模具钢之一。H13钢在服役过程中必须承受很大的冲击力和较大的摩擦、磨损、塑性变形、热疲劳、机械性破坏,因此,要求H13钢具有抵抗这些现象的特性。与进口H13钢相比,国产H13钢仍然存在很多不足,带状偏析较为严重,模具在使用过程中过早的出现龟裂,使用寿命不高,横向冲击韧性较低等。由此提高H13钢的等向性研究具有重要意义。在钢的化学成分不变的情况下,热处理过程是改变它们的组织和结构的最有效方法。对于H13钢,从原始的铸态组织枝晶偏析到可以供货的均匀球化珠光体组织,其组织演变是个复杂的过程。通过高温扩散可以改善H13钢组织中合金元素偏析情况,同时H13钢铸锭中存在孔洞型缺陷会减弱高温扩散效果,采用高温扩散前锻造技术对H13钢进行预处理,可以消除这些孔洞缺陷,从而加强高温扩散效果。高温扩散后配合超细化工艺,细化晶粒,同时为随后的等温球化过程提供良好的组织准备,良好的球化组织可以提高淬、回火后H13钢的韧性。本文通过光学金相显微镜、SEM、TEM、能谱分析、相分析等试验方法,研究了高温扩散对H13钢中元素偏析、球化组织的影响,并由此比较高温扩散对H13钢最终淬、回火态冲击韧性的影响,借助Thermo-calc热力学计算软件探索了淬、回火态试样碳化物析出长大规律,优化H13钢的强韧化热处理工艺,以指导实际生产。本研究以非真空感应炉冶炼+电渣重熔(ESR)生产的H13钢锭为实验原材料,通过分析,主要得出以下结论：1.铸态H13钢组织为粒状珠光体,心部枝晶偏析较严重,共晶碳化物较多,元素偏析严重,且存在部分孔洞型缺陷。通过1260℃×8h的高温扩散处理基本消除元素偏析,减轻了带状偏析,为等温退火做了良好的组织准备。2.H13钢高温扩散前进行锻造,能加强高温扩散效果,消除高温扩散前铸锭的孔洞型缺陷,从而显著降低H13钢退火态硬度,提高H13钢的退火态和淬、回火态冲击韧性。3.H13钢的超细化温度为1000℃时,随后相同的热处理能够表现出较好的性能。更多还原

【Abstract】 H13 steel with high hardenability,strength and toughness, thermal fatigue behavior is widely used in and abroad,which can be used in the manufacture of hot extrusion die,aluminium alloy die-casting die, hot forging die,etc.In nowadays,H13 steel is one of the most widely used hot die steel in worldwide.H13 steel will suffer from strong impact force, friction, abrasion, plastic distortion, thermal fatigue, mechanical deterioration while being used,therefore,the properties that resist the above phenomena of H13 steel is required.Compared with import H13 steel, Domestic H13 steel still have some deficiencies,especially with serious banding microsegregation,and also the heat checking appears early, with short service life,and the transverse orientation impact toughness is much lower while being used,there fore,the research on the isotropy of H13 steel is significative.The heat treatment process is the most effective method to change the microstructure of steels while the chemical composition is invariable.The microstructure development of H13 steel from original cast-microstructure dendritic segregation to uniform nodularization pearlitic structure is a complicated process.The chemical composition segregation in the microstructure of H13 steels can be improved through high temperature diffusion,and also the pore-cave defect existing in H13 ingot can relieve high temperature deffusion effect.Some pretreatments are done on H13 steel by high temperature diffusion pre-forging technology,which can elimate pore-cave defect,furthermore,the high temperture diffusion effect can be reinforced. Refine grain through ultrafining process after high temperature diffusion and also prepare well microstructure for the isothermal nodularization process,well nodularization microstructure can improve toughness of quenched-tempered of H13 steel.In this paper,the effect of high temperature diffusion on chemical composition segregation, nodularization microstructure of H13 steel was researched by the method of optical Metallurgical Microscopy,SEM,TEM, energy spectrum analysis and phase analysis,etc,so to investigate the effect of high diffusion on the impact toughness of the final quenched-tempered of H13 steel.With the help of Thermo-calc computation software,the precipitated and growth law of quenched and tempered carbide was probed in order to optimize the annealing heat treatment process for H13 steel,then the practical production can be realized.H13 steel ingot produced by non-vacuum induction furnace and ESR is used as experimantal material in this paper,through analyzing, the following results are concluded:1. The microstructure of as-cast H13 steel is granular pearlite, so the core dendritic segregation is much serious,also with more eutectic carbide and high element segregation,at the same time, some pore-cave defects exist.Through high temperature treatment at 1260℃for 8h,the element segregation is removed basically and the banding segregation is relieved,well prepared for the isothermal annealing.2. H13 steel forged before high temperature diffusion can reinforce high temperature diffusion effect and elimate the pore-cave defect of ingot before high temperature diffusion,so to reduce the annealed hardness of H13 steel dramaticlly and enhance the impact toughness of annealed,quenched-tempered of H13 steel.3. When the ultrafining temperature of H13 steel is at 1000℃, the same heat treatment followed shows well properties.更多还原