热作模具钢中纳米级析出物及钢的综合强化机理研究

发布时间：2018-12-08 17:26

【摘要】：4Cr5MoSiV1钢,即美国钢号H13(AISI)是一种空冷硬化型热作模具钢,H13钢具有较高的热强度和硬度,在中温条件下具有很好的韧性、热疲劳性能和一定的耐磨性。在较低的奥氏体化温度下空淬,热处理变形小,空淬时产生氧化皮倾向小,可以抵抗熔融铝的冲蚀作用。该钢广泛用于制造热挤压模具,芯棒、模锻锤的锤模,锻造压力机模具,精锻机用模具以及铝、铜及其合金的压铸模。本文根据国家自然科学基金项目“热作模具钢中纳米析出物与钢的综合强化机理研究”(No.51274031)所要求的内容,研究了不同热处理状态下析出物的情况,特别是纳米级析出物的种类和分布规律以及它们对钢力学性能的影响,得出如下主要结论： 1)电渣锭态H13主要析出V8C7和M23C6,形态为方形和球形,尺寸在200nm左右。通过计算发现：电渣凝固过程中析出物种类及析出相对量为V8C7:VC:V2C:Cr7C3:Cr23C6:MoC:Mo2C=1.19:1.22:0.28:4.33:5.36:1.65:1.56。 2)利用热力学计算+电解化学相分析+碳复型+透射电镜的方法,研究了H13电渣锭退火态下析出物的分布规律及其对屈服强度的影响。发现,从H13钢锭的横向看,由中心到表面析出物尺寸有减小的趋势,体积分数增大；从H13钢锭的纵向看,由上部到下部,析出数量不断增多,尺寸不断减小,由中部到下部析出物尺寸略有增大。退火态析出物主要以VC、M6C和M7C3为主,总平均尺寸为243.5nm,单位面积析出量为1.44个。研究发现,纳米级析出物对屈服强度的贡献为311.32MPa。 3)利用相同方法分析了H13淬火及回火态析出物的情况。淬火态析出物种类主要是VC、M6C及少量的M23C6,总平均尺寸为150.5nm,单位面积析出量0.67个。析出强化量对屈服强度的贡献为19%。通过研究2小时和20小时的回火态析出物情况发现,析出物的种类主要是：VC、M6C、M3C以及M23C6；回火2小时的总平均尺寸减小为82.6nm,但单位面积析出量增加到5.37个。析出强化量对屈服强度的贡献也相应增加到28%。回火20小时后析出物总平均尺寸有少量增加,为88.3nm,单位面积析出量也相应增加为6.5个,但析出强化量对屈服强度的贡献却增加到39%。 4)从纳米级析出物对H13的强化角度出发,对不同的淬火、回火温度以及保温时间研究析出物对钢性能的影响。研究表明：H13的淬回火的最佳工艺路线为：1373K淬火30min,油冷至室温：在863K下回火4小时,空冷。在这样的工艺条件下,H13中的析出物细小,数量适中。力学性能最好。 5)研究了两种不同回火时间下细晶强化、析出强化、固溶强化和位错强化对H13的综合强化机理。结果表明,回火态下,H13各强化机制对屈服强度的贡献强弱依次为：细晶强化、析出强化、固溶强化和位错强化。
[Abstract]:4Cr5MoSiV1 steel, American steel H13 (AISI), is a kind of air-cooled hardening hot work die steel. H13 steel has high thermal strength and hardness, and has good toughness, thermal fatigue property and certain wear resistance at medium temperature. When austenitizing temperature is low, the deformation of heat treatment is small, and the tendency of oxidation is small, which can resist the erosion of molten aluminum. The steel is widely used in manufacturing hot extrusion die, mandrel, hammer die of die forging hammer, die of forging press, die of precision forging machine and die casting die of aluminum, copper and its alloy. According to the requirement of the National Natural Science Foundation of China, "Comprehensive strengthening Mechanism of Nano-precipitates and Steel in Hot work Die Steel" (No.51274031), the situation of precipitates in different heat treatment states has been studied in this paper. The main conclusions are as follows: 1) the electroslag ingot H13 precipitates V8C7 and M23C6, the shape is square and spherical, and the size is about 200nm. It is found by calculation that the type and relative amount of precipitates during electroslag solidification is V8C7: VC7: V2C7C3: Cr23C6: Mo2C1.191.22: 0.284.33: 5.36: 1.56: 1.56. 2) the distribution of precipitates in H13 electroslag ingot annealed and its influence on yield strength were studied by means of thermodynamics calculation of electrolysis chemical phase analysis of carbon complex transmission electron microscope (TEM). It is found that the size of the precipitates from the center to the surface decreases and the volume fraction increases from the transverse side of the H13 ingot. From the longitudinal point of view of H13 ingot, the amount of precipitate increases and the size decreases from the upper part to the lower part, and the size of the precipitate increases slightly from the middle to the lower part. The main precipitates in annealed state are VC,M6C and M7C3, the total average size is 243.5 nm and the amount of precipitation per unit area is 1.44. It is found that the contribution of nanometer precipitates to yield strength is 311.32 MPa. 3) the precipitation of H 13 quenching and tempering was analyzed by the same method. The main precipitates in quenched state are VC,M6C and a small amount of M23C6, the total average size is 150.5 nm, and the precipitation amount per unit area is 0.67. The contribution of precipitation strengthening amount to yield strength is 19. By studying the tempering state precipitates for 2 hours and 20 hours, it is found that the types of precipitates are mainly VC,M6C,M3C and M23C6, and the total average size of tempering for 2 hours decreases to 82.6 nm, but the amount of precipitation per unit area increases to 5.37. The contribution of precipitation strengthening amount to yield strength is also increased to 28%. After tempering for 20 hours, the total average size of precipitates increased slightly to 88.3 nm, and the amount of precipitation per unit area increased to 6.5, but the contribution of precipitation strengthening to yield strength increased to 39. 4) from the point of view of strengthening H13 by nanometer precipitates, the effect of precipitates on the properties of steel was studied at different quenching, tempering temperature and holding time. The results showed that the optimum quenching and tempering process of H13 was 1373K for 30 min, oil cooled to room temperature, tempering at 863K for 4 hours and air cooling. Under such technological conditions, the precipitates in H 13 are fine and moderate in quantity. The mechanical properties are the best. 5) the mechanism of strengthening H13 by fine grain strengthening, precipitation strengthening, solution strengthening and dislocation strengthening at two different tempering times was studied. The results show that the contribution of H13 strengthening mechanism to yield strength is as follows: fine grain strengthening, precipitation strengthening, solid solution strengthening and dislocation strengthening.
【学位授予单位】：北京科技大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TG142.1

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