【作者】 张赫；

【导师】 邱丰； 许长林；

【作者基本信息】 吉林大学 ， 材料工程（专业学位）， 2022， 硕士

【摘要】 工模具钢的应用是制造业和基础建设的重要基础材料,是国家实现产品工业化生产和经济建设不可缺少的工具。我国工模具的生产总值已经位于世界第三,对工模具钢的需求量还在日益增长。随着制造业的不断升级,对模具钢的质量和新产品的开发迫在眉睫。现代工业对工模具钢的性能,包括硬度和红硬性、室温及高温强韧性和耐磨性等,提出了更高的要求。然而,运用传统方法提高钢的性能,例如:微合金化、超纯净化、大锻造比和热处理工艺优化对钢性能的提升似乎进入瓶颈,很难通过这些方法来大幅提高钢的力学性能。将纳米陶瓷颗粒加入钢中,可使钢在细化显微组织的基础上保持原有特性,同时因晶粒细化和碳化物分布均匀而提高钢的强度和延伸率,可能成为一种新的研究高性能钢的方法。但是,高含量的纳米陶瓷颗粒会显着降低钢的延展性,从而降低了韧性,纳米陶瓷颗粒的加入方式存在许多问题。在本文中,采用Al-Ti-C/B₄C体系,通过自蔓延高温合成（SHS）反应制备纳米TiC/Al与TiC+TiB₂/Al中间合金,然后将预粉碎的微量中间合金随钢水的流动逐渐加入到钢水中。解决了纳米陶瓷颗粒润湿性差、易污染、难分散的问题。研究了纳米颗粒调控锻态高Cr工模具钢的微观组织,力学性能和耐磨性演变规律,深入分析了纳米颗粒调控锻态高Cr工模具钢的组织机制,强韧化机制和耐磨性机制。主要创新点如下:1.揭示了不同含量纳米TiC颗粒调控铸态和热处理后40Cr钢的微观组织演变规律和作用机制:发现添加不同含量TiC陶瓷颗粒后40Cr钢生成更细小的珠光体,粗大长条状铁素体细化且复杂化,出现许多颗粒状铁素体,铁素体含量明显增加。发现添加微量纳米TiC颗粒后40Cr钢残余铁素体含量减少,马氏体内位错密度降低,原奥氏体晶粒显著减小,马氏体板条显著细化,珠光体中铁素体和渗碳体之间的层片状间距细化。揭示纳米TiC陶瓷颗粒在凝固过程中充当初生奥氏体形核点位,减小了初生奥氏体晶粒尺寸;随后充当了铁素体形核点位,使长条状铁素体变得更为细小。并细化了原奥氏体晶粒和板条马氏体。由于铁素体形态改变,减少了热处理后残余铁素体含量,原奥氏体中碳元素变得更加均匀且含碳量降低,降低了马氏体中位错密度。2.揭示了微量纳米TiC+TiB₂陶瓷颗粒调控对高Cr模具钢（含碳量=0.32 wt.%）组织演变、力学性能以及抗高温摩擦磨损性能的影响规律及其作用机制:发现添加微量纳米TiC+TiB₂陶瓷颗粒后显著细化了铁素体和粒状珠光体晶粒,明显改善锻态高Cr钢中碳化物偏析,铁素体晶粒的平均尺寸分别降低至7.81μm和4.92μm,分别降低了26.5%和53.6%。显著改善热处理后高Cr模具钢的晶界碳化物偏析,细化了马氏体板条,使板条内的位错分布更均匀,析出的碳化物变得更加细小均匀。发现添加微量纳米TiC+TiB₂陶瓷颗粒后,高Cr模具钢室温力学性能和冲击韧性显著提高。添加0.02 wt.%纳米TiC+TiB₂陶瓷颗粒后,钢的室温屈服强度、抗拉强度、延伸率和冲击韧性分别为1694 MPa、2087 MPa、6.64%和568.79 J/cm²,分别提高了4.0%、5.4%、26.7%和86.3%。高温力学性能也显著提高,添加0.02 wt.%纳米颗粒后钢在600℃下高温屈服强度和抗拉强度分别为656.5 MPa和751.4 MPa,分别提高了36.5%和26.5%。力学性能强化机制:细晶强化,高位错密度强化和弥散强化,弥散强化是微量纳米TiC+TiB₂陶瓷颗粒调控钢的主要强化手段。发现添加纳米颗粒后高Cr热作模具钢抗高温摩擦耐磨性均显著提高。添加0.02 wt.%纳米陶瓷颗粒后高Cr热作模具钢的体积磨损率为5.6×10^-13m³/m,比普通高Cr热作模具钢体积磨损率降低了34.9%。揭示高温力学性能强化机制:高温作用下纳米颗粒附近产生了大量缺陷,促进位错攀移,有利于塑性提高。位于晶界处纳米颗粒在高温下钉扎晶界,显著提高钢高温下抗塑性变形能力,提高钢高温强度。纳米陶瓷颗粒强化钢的高温屈服强度显著提高,抵抗塑性变形能力提高,耐磨性显著提高。3.揭示了微量纳米TiC+TiB₂陶瓷颗粒调控对高Cr工具钢（含碳量=0.41 wt.%）组织演变、力学性能以及耐磨粒磨损性能的影响规律及其作用机制:发现随着回火温度逐渐升高,首先在晶界处析出少量碳化物,随后在内部形成许多C原子偏聚区,温度进一步升高,C原子偏聚区开始析出粒状碳化物,形成回火屈氏体。室温下,硬度为58.4 HRC钢的屈服强度,抗拉强度,延伸率分别为1923.6MPa,2415.5 MPa,2.88%。在相同硬度下,高Cr工具钢和H13钢的室温冲击韧性分别为39.54 J/cm²和12.85 J/cm²。发现在相同硬度下纳米调控高Cr工具钢磨粒磨损耐磨性显著高于H13钢。58.4HRC硬度下的高Cr工具钢在25N和35N条件下的体积磨损率分别为1.82×10^-11m³/m和3.21×10^-11m³/m,分别降低了32.8%和29.0%。揭示出在相同硬度下,钢的韧性是影响磨粒磨损性能的最关键的因素,而微量纳米TiC+TiB₂颗粒调控高Cr工具钢的韧性明显高于H13刀盘钢,在被剥离时越不容易产生微裂纹,减轻了高Cr工具钢的微裂纹磨损特征,从而提高钢的耐磨性。更多还原

【Abstract】 The application of tool and die steel is an important basic material for manufacturing and infrastructure construction,and it is an indispensable tool for the country to realize industrialized production of products and economic construction.The gross production value of Chinese tool and die has already ranked third in the world,and the demand for tool and die steel is still increasing.With the continuous upgrading of the manufacturing industry,higher requirements have been placed on the quality of die steel and the development of new products.Modern industry has put forward higher requirements for the properties of tool and die steel,including hardness and red-hardness,room-temperature and high-temperature strength,toughness,and wear resistance.However,the use of traditional methods to improve the properties of steel,such as micro-alloying,ultra-purification,large forging ratio,and heat treatment process optimization,seems to have entered a bottleneck,and it is difficult to greatly improve the mechanical properties of steel by these methods.Adding nano-ceramic particles to steel can keep the original characteristics of steel based on refined microstructure,and improve the strength and elongation of steel due to grain refinement and uniform distribution of carbides,simultaneously,which may become a new method for the study of high-performance steels.However,the high content of nano-ceramic particles will significantly reduce the ductility of steel,thereby reducing the toughness,and there are many problems in the way of adding nano-ceramic particles.In this paper,the Al-Ti-C/B₄C system was used to prepare nano-TiC/Al and TiC+TiB₂/Al master alloys in situ by SHS reaction.It solves the problems of poor wettability,easy pollution,and difficult dispersion of nano-ceramic particles.The evolution law of microstructure,mechanical properties and wear resistance of forged high Cr tool steel controlled by nanoparticles was studied,and the microstructure,toughening mechanism and wear resistance of nanoparticle controlled high Cr tool steel were deeply analyzed.mechanism.The main innovations are as follows:1.Revealed the microstructure evolution law and action mechanism of 40Cr steel regulated by different contents of nano-TiC particles after as-cast and after heat treatment:It was found that 40Cr steel with different contents of TiC ceramic particles formed finer pearlite,thicker and larger elongated ferrite refined and more complex,a lot of granular ferrite appears,and the ferrite content increases significantly.It was found that the residual ferrite content of 40Cr steel after quenching and tempering treatment decreased,the dislocation density in the martensite decreased,the prior-austenite grains decreased significantly,the martensite laths were significantly refined,and the lamellar spacing between the medium ferrite and cementite is refined.It is revealed that the nano-TiC ceramic particles act as primary austenite nucleation sites during the solidification process,reducing the primary austenite grain size;then act as ferrite nucleation sites,making the elongated ferrite more for small.And refine the prior austenite grains and lath martensite.Due to the change of ferrite morphology,the residual ferrite content after heat treatment is reduced,the carbon element in the prior austenite becomes more uniform and the carbon content decreases,which reduces the dislocation density in the martensite.2.Revealed the effect of trace nano-TiC+TiB₂ ceramic particle regulation on the microstructure evolution,mechanical properties and high temperature friction and wear resistance of high Cr die steel（carbon content=0.32 wt.%）and its mechanism of action:found that,the ferrite and granular pearlite grains are significantly refined,the carbide segregation in the forged high Cr steel is significantly improved,and the average size of the ferrite grains is reduced to 7.81μm and 4.92μm,respectively,after adding trace nano-TiC+TiB₂ ceramic particles.decreased by 26.5%and 53.6%.The grain boundary carbide segregation of the high Cr die steel after heat treatment is significantly improved,the martensitic lath is refined,the dislocation distribution in the lath is more uniform,and the precipitated carbides become finer and uniform.It was found that the room temperature mechanical properties and impact toughness of the high Cr die steel were significantly improved after adding a small amount of nano-TiC+TiB₂ ceramic particles.After adding 0.02 wt.%nano-TiC+TiB₂ ceramic particles,the room temperature yield strength,tensile strength,elongation,and impact toughness of the steel were 1694 MPa,2087 MPa,6.64%and 568.79 J/cm²,which were increased by4.0%and 568.79 J/cm²,respectively.5.4%,26.7%and 86.3%.The high-temperature mechanical properties are also significantly improved.After adding 0.02 wt.%nanoparticles,the high-temperature yield strength and tensile strength of the steel at600°C are 656.5 MPa and 751.4 MPa,which are increased by 36.5%and 26.5%,respectively.Mechanical properties strengthening mechanism:fine-grain strengthening,high dislocation density strengthening and dispersion strengthening.Dispersion strengthening is the main strengthening method for trace nano-TiC+TiB₂ ceramic particles to control steel.It is found that the high Cr hot work die steels have significantly improved high temperature friction and wear resistance after adding nanoparticles.The volume wear rate of high Cr hot work die steel after adding 0.02 wt.%nano-ceramic particles is 5.6×10^-13m³/m,which is 34.9%lower than that of ordinary high Cr hot work die steel.Revealing the mechanism of high temperature mechanical properties enhancement:Under the action of high temperature,many defects are generated near the nanoparticles,which promotes dislocation climbing and is beneficial to the improvement of plasticity.The nanoparticles located at the grain boundary pin the grain boundary at high temperature,which significantly improves the plastic deformation resistance of the steel at high temperature and improves the high temperature strength of the steel.The high temperature yield strength of nano-ceramic particle reinforced steel is significantly improved,the resistance to plastic deformation is improved,and the wear resistance is significantly improved.3.The effect of trace nano-TiC+TiB₂ ceramic particle regulation on the microstructure evolution,mechanical properties,and wear resistance of high Cr tool steel（carbon content=0.41 wt.%）and its mechanism of action were revealed.As the fire temperature gradually increased,a small number of carbides were first precipitated at the grain boundaries,and then many C atom segregation areas were formed inside.The temperature further increased,and the C atom segregation areas began to precipitate granular carbides to form tempered troostite.At room temperature,the yield strength,tensile strength,and elongation of HRC steel with a hardness of 58.4 are1923.6 MPa,2415.5 MPa,and 2.88%,respectively.Under the same hardness,the room temperature impact toughness of high Cr tool steel and H13 steel are 39.54 J/cm² and12.85 J/cm²,respectively,which are increased by 207.7%.It is found that the abrasive wear resistance of nano-controlled high Cr tool steel is significantly higher than that of H13 steel under the same hardness.The volume wear rates of the high Cr tool steel with58.4 HRC hardness under the conditions of 25N and 35N are 1.82×10^-11m³/m and3.21×10^-11m³/m,which are reduced by 32.8%and 29.0%,respectively.It is revealed that under the same hardness,the toughness of the steel is the most critical factor affecting the abrasive wear performance,and the toughness of the high Cr tool steel controlled by the trace nano-TiC+TiB₂ particles is significantly higher than that of the H13 cutter head steel,and the less likely it is to be peeled off.It is easy to produce micro-cracks,which reduces the micro-crack wear characteristics of high Cr tool steel,thereby improving the wear resistance of the steel.更多还原