Development of Flow Stress of AISI H13 Die Steel in Hard Machining

An approach was presented to characterize the stress response of workpiece in hard machining, accounting for the effect of the initial workpiece hardness in addition to temperature, strain and strain rate on flow stress in this paper. AISI H13 die steel was chosen to verify this methodology. The proposed flow stress model demonstrates a good agreement with experimental data. Therefore, the proposed model can be used to predict the corresponding flow stress-strain response ofAISl H13 die steel with variation of the initial workpiece hardness in hard machining.

Effect of rare earth on primary carbides in H13 die steel and their addition method:a review

Larger-sized primary carbides lead to stress concentration during the application of H13 hot-work die steel,resulting in microcracks and fatigue failure.Rare earth was usually added to modify the carbides and inclusions.The existing literature is reviewed on the effect of rare earth on primary carbides in H13 steel.A comprehensive review on the effect of rare earth on the characteristics of primary carbides,i.e.,number,size,morphology,and thermal stability in H13 steel,was done.The precipitation mechanism and nucleation of primary carbides with rare earth were summarized.The position and form of rare earth in steel and their effects on alloying elements segregation were reviewed.The addition techniques of rare earth in H13 steel were compared,and the prospects for other uncommon rare earth and emerging technology were present.Based on the current references,it can be known that adding rare earth facilitated refined and dispersed primary carbides.The size of primary carbides would be reduced,and their morphology would be improved because the rare earth inclusions formed in H13 steel can act as nucleation cores forγ-Fe orδ-Fe,refining the dendritic structure.Besides,the number of primary carbides at grain boundaries would be significantly reduced.However,rare earth had little impact on thermal stability.The nucleation of primary carbides tended to be inhibited due to the modification of inclusions by rare earth which were likely to be nucleation cores for primary carbides.Rare earth had been reported to affect the mechanism and process of primary carbide precipitation.Additionally,the addition of rare earth can inhibit the segregation of alloying elements and carbon diffusion by calculation.Thus,laboratory experiments and theoretical calcu-lations need to be conducted to study the states and evolution of rare earth steels.

H13钢模具型腔表面堆焊工艺参数研究

在基于小电流短弧焊的前提下,采用手工电弧焊在H13钢模具型腔表面堆焊4到6 mm厚度的高硬度耐磨层,研究了堆焊速度对H13钢模具型腔表面堆焊层性能的影响。发现,随着堆焊速度的增加,热影响区产生相变;试验获得了合理的堆焊工艺参数。工艺研究的结果投入生产后证明:模具的寿命提高了30%。

H-13热作加厚模淬火开裂成因分析

通过对H-13热作加厚模在淬火过程中产生裂纹的原因进行分析，指出了合适的热处理工艺是确保获得最佳的强韧性及热疲劳抗力的关键，也是确保淬火质量的关键，结果表明，在H—13钢淬火过程中操作不当是热作加厚模产生裂纹的主要因素。

H13模具钢的热处理实践

H13模具钢经过热处理可以获得优良的性能,诸如高强度、红硬性及高的冲击韧性值。从解析H13的化学成分入手,对选用高温球化退火、淬火及二次回火做了说明,提供了工艺数据,并在结论中给出了生产实践中获得的五条经验。

H13钢的真空热处理

介绍了北美压铸模协会(NADCA)推荐的H13钢的真空热处理工艺,详细讨论了对热处理设备的要求,工件的装炉,热电偶的放置,奥氏体化,淬火速率与工件组织和性能的关系,回火工艺和硬度控制,模具的去应力处理H,13钢模具的热处理质量和检测,以及热处理合格证书的内容,并附有H13钢淬火组织级别图。

Evaluating oxygen level of Si-deoxidized H13 die steel using ferrous oxide-containing slags at 1873 K

Laboratory-scale experiments were conducted to investigate the oxygen content of Si-deoxidized H13 die steel by ferrous oxide-containing slags at 1873 K.The calculation of thermodynamics and kinetics was performed to evaluate the oxygen level of molten steel through[Si]-[O]equilibrium and[Fe]-[O]equilibrium.The results show that as the FeO content in slag increases,the oxygen content with[Si]-[O]equilibrium(w([O])Si)has almost no change.When both the oxygen content with[Fe]-[O]equilibrium(w([O])Fe)and w([O])Si are less than the initial oxygen content in steel(w(TO)i),the oxygen content in steel(w([O]))depends on the higher value between w([O])Si and w([O])Fe.In the case of w([O])Fe>w(TO)i,the value of w([O])is the difference between the sum of w(TO)i and w([O])Si and the value of w([O])Fe.The reaction rates of[Si]-[O]and[Fe]-[O]are equal,which are controlled by the mass transfer of oxygen in molten steel.The evaluation method is suitable to the whole smelting process of Si-deoxidized H13 die steel.

The Study on Plasma Boriding of H13 Steel at Low Temperature Assisted by Surface Nanocrystallization Technology

Plasma boriding treatment was carried out at low temperature for the hot work die steel H13 assisted by surface nanocrystallization technology in this paper.At the same time,the thermal fatigue property of it was investigated through thermal fatigue testing with 3000 continuous cycles from room temperature to 700℃.The changes of structure and grain size in surface layer were characterized by high-resolution transmission electron microscopy(HRTEM).After plasma boriding at 580℃ for 4 h,the phase composition,morphology and in-situ nanomechanical property of boride layer were investigated by X-ray diffraction spectroscopy(XRD),scanning electron microscope(SEM),nanoindentation test,respectively.The results show that the boride layer with about thickness of 5μm is composed with two phases of Fe2B and FeB.The nanohardness of boride layer is as high as 21 GPa.Furthermore,thermal fatigue testing shows that the boride layer with excellent oxidation resistance and mechanical strength at elevated temperatures could effectively delay the crack initiation and impede the crack propagation.Therefore,the thermal fatigue property of H13 can be remarkably improved.

H13钢热锻模具早期失效分析

通过对失效的H13热锻模具钢化学成分、宏观形貌及显微组织的检测,分析其失效原因。结果表明,该模具的失效形式属脆性断裂;失效模具钢中V含量偏低,而Si含量偏高,组织中存在大量块状组织,模具坯料(退火态)组织存在较为严重的偏析区,属于不合格组织。成分超限和组织偏析是造成模具早期失效的主要原因。

H13钢制分流模低周疲劳寿命的预测方法及其应用

为优化挤压工艺和模具结构,降低H13钢制分流模的疲劳失效率,通过热压缩试验及力学性能测试,建立了H13钢的本构方程和应变-低周疲劳寿命关系,结合FEM提出了一种预测H13钢制分流模低周疲劳寿命的方法;应用此法分析了工艺和结构参数对模具疲劳寿命的影响,结果表明:疲劳寿命随着挤压速度的增加而减小,随着模桥根部圆角半径的增大而增大,而结构参数为影响疲劳寿命的关键。最后通过实际生产验证了该方法的可靠性。

温镦挤模具磨损失效分析

对失效的H13温锻模具钢进行了分析,发现模具钢硬度、晶粒大小、合金元素含量基本符合标准。高温摩擦磨损实验及磨损形貌观测表明,模具磨损的主要形式为黏着磨损,氧化磨损和磨粒磨损。运用DEFORM-3D软件模拟分析了模具硬度和毛坯温度等工艺参数对模具磨损的影响,结果与实际磨损状况基本吻合。这可为延长模具寿命提供帮助。

等离子喷涂纳米Al_2O_3/TiO_2陶瓷复合涂层高温氧化和热震性能研究

采用等离子喷涂设备在H13热作模具钢表面制备含有不同质量分数TiO2的Al2O3纳米陶瓷复合涂层。采用X射线衍射仪(XRD)、高温氧化试验、热震试验等手段研究等离子喷涂纳米涂层的相组成及其性能。结果表明,等离子喷涂使α-Al2O3转变为亚稳态的γ-Al2O3相,喷涂后涂层中Al2O3由α-Al2O3相和γ-Al2O3相组成,TiO2仍以金红石相存在。纳米AT20涂层比其他涂层具有更好的抗氧化性能;与其他涂层相比,纳米AT13涂层具有最佳的抗热震性能。

工艺参数对模具复合粉末冷喷涂涂层性能的影响

采用不同的工艺参数进行了H13钢模具的Cr-25%Sr-0.5%RE复合粉末冷喷涂实验,并进行了涂层厚度、降低涂层孔隙率、提高涂层的结合强度和耐磨损性能的测试与对比分析。结果表明,随载气温度从350℃升高至550℃、喷涂距离从15mm增加至30mm,模具涂层的初始摩擦系数保持0.1左右、平稳时摩擦系数先减小后增大、摩擦寿命先延长后缩短、涂层厚度先增大后减小,涂层孔隙率先减小后增大;其优选的载气温度为450℃、喷涂距离为25mm。