Isothermal Fatigue of Tool Steel AISI H11

Lifetime of hot‐work tools is often limited by the development of crack nets as a consequence of thermal and/or mechanical fatigue loading. In this paper, the isothermal fatigue behaviour of the tool steel AISI H11 (German grade X38CrMoV 5‐1) under stress controlled uniaxial tension‐compression loading with zero mean stress is investigated in the temperature range between room temperature and 500 °C. Different surface conditions (polished, shot peened, hard turned) were taken into account and a small influence of the near‐surface states on the measured plastic strain amplitudes could be detected. In all cases, for the most part, strain softening occurred with increasing numbers of cycles, which is also influenced by the stress amplitude applied. Due to manufacturing induced near‐surface compressive residual stresses and strain hardening, shot peened specimens exhibit higher fatigue lifetimes than hard turned or polished ones.     

IF钢铸坯表层显微夹杂分析

针对IF钢铸坯表层显微夹杂的变化,采用氧氮分析仪、金相显微镜、扫描电镜、能谱分析等方法,对钢中表层夹杂物的尺寸、数量、形态、分布和来源进行分析。结果表明,铸坯表层显微夹杂在距内弧表面3~4 mm处存在明显的聚集现象,其含量分别达到9.2个/mm~2、8.8个/mm~2,而其它位置上夹杂物数量为5.1~6.8个/mm~2;宽度方向上夹杂物分布具有随机性;表层显微夹杂以Al_2O_3-TiO_x、Al_2O_3类夹杂为主,尺寸多在20μm以内,两者合计占夹杂物总量的84%。     

超低氧弹簧钢60Si2MnA疲劳断口夹杂物来源研究

为了探究疲劳断口处夹杂物的来源，针对60Si2MnA弹簧钢生产工艺流程不同工位和疲劳断口处夹杂物，通过金相、SEM-EDX等手段，分别对夹杂物的数量、尺寸、形貌及组成进行了系统研究，并在夹杂物生成热力学计算形成条件的基础上，结合工艺实际状况得出，疲劳断口处大尺寸夹杂物来源主要是精炼过程脱氧反应产物没有排除掉所致。     

H13钢制分流模低周疲劳寿命的预测方法及应用

 利用Gleeble1500热模拟试验机对H13模具钢在650-800℃温度范围,0.1-20s-1应变速率下的热压缩变形行为进行了研究,并得到了该材料在20-650℃范围内的弹性模量,建立了H13钢的有限元模型;通过高温拉伸实验和通用斜率法建立了H13钢的应变-低周疲劳寿命关系;结合有限元方法提出了一种预测H13钢制铝型材挤压模具低周疲劳寿命的方法,并在此基础上得到了工艺和结构参数对模具疲劳行为的影响规律。结果表明：疲劳应变损伤值随着挤压速度的增加以及模桥根部圆角半径的减小而增大,其中结构参数为关键影响因素。最后通过生产实际验证了该方法的可靠性。     

Thermal Fatigue Behavior of AISI H13 Hot Work Tool Steel Produced by Direct Laser Metal Deposition

Direct laser metal deposition (DLMD) is an additive manufacturing technique getting growing attention thanks to the possibility of producing very complex parts in a short time and in a cost-effective manner. The possible applications of this technology are tools with conformal cooling channels and claddings for dies and molds reparation. One of the damaging mechanisms of tools is thermal fatigue (TF) cracking, leading to surface deterioration and, consequently, the processed parts. Herein, the TF behavior of DLMD-H13 submitted to two different heat treatments, namely direct tempering (T) and quenching and tempering (QT), is investigated. T does not significantly change the solidification microstructure after DLMD, whereas QT produces a more homogenous tempered martensite microstructure. A customary laboratory test is developed to induce TF damage under a cyclic temperature variation between 630 and 60 °C. The results evidence that the T-H13 has a slightly better TF resistance with respect to QT-H13 due to the higher tempering resistance of T-H13 with respect to QT-H13. Thus, according to TF test results, direct tempering can be preferred to quench and tempering since the elimination of quenching can decrease the costs of production as well as distortions-related issues, increasing the competitiveness of DLMD.     

Tribological Properties of CrN Coated H13 Grade Tool Steel简

The characteristics of CrN coated martensitic H13 grade tool steels were studied. CrN coatings were depos- ited by the arc physical vapor deposition （PVD） before and after the pulse plasma nitriding of the samples. The PVD and plasma nitriding techniques were applied in relevant workshops by following the commercial practice parameters. Experimental results showed that CrN coating deposited on the nitrided surfaces exhibited superior scratch and wear resistances as compared to that deposited on the original martensitic surface.     

热处理状态对H13模具钢渗氮层的影响

 采用X射线衍射、扫描电镜及显微硬度等技术,综合比较和分析了H13模具钢在不同热处理状态下经相同气体渗氮处理后表层的组织结构和硬度。结果表明,经淬火＋二次回火和淬火+三次回火的试样渗氮后,渗氮层厚度均达到约0.24 mm,致密化合物层厚度达到10 μm以上,表面硬度HV达到950 (约为HRC 67)。这两种热处理状态下渗层中化合物层均由ε相（Fe2N）、γ′相和Fe3O4构成,扩散层均由α Fe相、ε相（Fe3N）、CrN相和γ′相构成,但各相含量有差别。而淬火态和淬火+一次回火态的渗氮试样未能获得具有足够好综合性能的渗层组织。     

20Cr13不锈钢热轧棒材夹杂物研究

针对以EAF-VOD-LF-模铸工艺流程生产的20Cr13不锈钢热轧棒材,利用扫描电镜和能谱仪分别对棒材横纵截面的边缘部位、1/2半径处和中心部位的夹杂物进行了检测,分析了夹杂物的尺寸、数量、分布、形貌和成分。结果表明：20Cr13不锈钢热轧棒材中的夹杂物主要有锰铝酸盐类夹杂物、硫化锰夹杂物和以硅酸盐为核心、外围为MnS或锰铝酸盐的复合夹杂物3种。从边缘到中心,夹杂物总数呈递增趋势,复合夹杂物的数量和比例也相应呈递增趋势。棒材横截面上的夹杂物大部分小于3μm,长宽比小于3;棒材纵截面上的夹杂物明显变长,中心部位夹杂物平均长为9.53μm,平均长宽比为8.22。     

Effect of Niobium on Microstructure of Cast AISI H13 Hot Work Tool Steel

The effect of niobium addition on the microstructure of cast AISI H13 hot work tool steel was evaluated by using EDX analyzer attached to the scanning electron microscope. The volume percent of eutectic area and eutectic cell size and also volume percent of different carbides of new steel, which is heat treated under different conditions, are also determined. The results show that the a niobium addition modifies the cast structure of Nb-alloyed hot work tool steel, and reduces the size and volume of eutectic cells, and increases the maximum hardness of the steel.     

非金属夹杂物对钙系与钙硫系易切削钢切削性能的影响

研究了在18t钢包中采用喷粉方法生产的钙系与钙硫系易切削钢中非金属夹杂物对切削性能的影响。试验结果表明：以200m/min的速度切削Y40CrCa钢时，刀具寿命比切削40Cr钢时高6－10倍；以160m/min的速度切削Y40CrCaS钢时，刀具寿命比切削40Cr钢时高20倍。经能谱仪查明在刀具后面形成保护薄膜，它是延长刀具寿命的主要原因。     

轴承钢中TiN夹杂的形成机理及控制措施

针对鞍钢股份有限公司炼钢总厂轴承钢中存在大颗粒TiN夹杂物的问题,分析了TiN夹杂析出的热力学条件。通过优化转炉及精炼操作、加强连铸保护浇铸、控制钢铁料及合金料中的钛含量、优化钢中酸溶铝及精炼渣中氧化钛的含量,最终将轴承钢中的氮含量由0.0050%降至0.0038%,钛含量由0.0045%降至0.0013%。     

The Effect of Ladle Treatment on Inclusion Composition in Tool Steel Production

An in‐depth SEM‐investigation of the inclusion composition change in the ladle refining process during tool steel production was done. Plant trials were carried out at Uddeholm Tooling AB in Hagfors, Sweden. A series of samples was taken during ladle refining, from deslagging through vacuum treatment. The goal was evaluating the effects of the top slag and other process parameters on the inclusion composition during ladle refining. The main conclusion was that normal variations in the process have a large influence on inclusion composition. Furthermore, it was concluded that the MgO content in the top slag had a large influence on the inclusion composition throughout the whole ladle refining process. Also, the SiO₂ content in the ladle slag originating from the EAF‐slag, had a noticeable effect on the inclusions. The inclusions belonging to the system Al₂O₃‐CaO‐MgO‐SiO₂ showed a continuous composition change throughout the ladle refining process, from high Al₂O₃, via MgO‐spinel to finally complex types rich in CaO and Al₂O₃.     

超低氧钢中复合夹杂物形成的实验室研究简

 通过实验室真空感应炉试验,研究了超低氧条件下钢中复合非金属夹杂物的形成。研究发现：在含有一定硫的超低氧钢中高熔点氧化物夹杂很少,大部分为MnS。钢中Al2O3的尺寸较MgO-Al2O3系夹杂要大。以高熔点夹杂物为异质形核核心析出的MnS能显著提高钢材的疲劳寿命,此种复合夹杂物的形成与钢液成分、高熔点夹杂物的尺寸有关。     

疲劳性能不合格的38Si7弹簧钢夹杂物分析

  针对工业生产38Si7弹簧钢疲劳强度不合格的问题,借助光学显微镜和扫描电镜,并结合数学理论模型,从夹杂物的角度分析38Si7弹簧钢疲劳强度不合格的原因。研究结果表明：工业生产38Si7弹簧钢中的夹杂物主要组成为CaO(MgO) Al2O3 SiO2三元复合夹杂物,而且圆截面上中心区域复合夹杂物中Al2O3的含量明显低于外层复合夹杂物中Al2O3的含量;根据夹杂物等效投影面积模型得出,当疲劳失效为内部起裂时,临界夹杂物尺寸大约为6.5μm,当疲劳失效为表面起裂时,临界夹杂物尺寸大约为5.5μm。当弹簧钢中的夹杂物尺寸大于临界夹杂物尺寸时,容易造成疲劳强度失效。     

结构钢表面疲劳损伤演化过程的显微硬度研究方法

通过对疲劳过程中结构钢表面显微硬度测试结果的检验，证明了不同疲劳阶段的显微硬度测试值服从正态概率分布。依据损伤力学的基本理论建立了用显微硬度定义疲劳损伤变量的概率表达式，并应用于材料表面的损伤行为研究。分析表明，材料微观性能劣化是导致材料表面萌生显微裂纹的主要原因，而在微细观尺度上材料的损伤演化将呈现出显的不均匀性和概率统计特征。并从疲劳裂纹萌生的无损检测角度指出了显微硬度方法是一种较方便和灵敏     

High Temperature Tribological Studies on Surface Engineered Tool Steel and High Strength Boron Steel

The popularity of hot sheet metal forming processes in the recent years has necessitated research efforts to improve tool life and control the friction level during hot forming operations. In this work, the tribological properties of tool steel and ultra high strength boron steel (UHSS) pairs at elevated temperatures have been studied by using a special hot sheet metal forming test rig that closely simulates the conditions prevalent in the real process. This test involves linear unidirectional sliding of a preheated UHSS sheet between two tool steel specimens where new workpiece material is continuously in contact with the tool surface. The study is aimed at investigating different surface treatments/coatings applied on either the tool or sheet surface or on both. The results have shown that it is possible to control the coefficients of friction through surface treatments and coatings of the tool and workpiece materials. The application of a coating onto the sheet material has a greater influence on the friction compared to changing the tool steel surface. After running‐in, the investigated tool steel variants show almost similar frictional behaviour when sliding against the same sheet material. Although coating the UHSS sheet reduces friction, it abrades the tool surface and also results in transfer of the sheet coating material to the tool surface.     

Influences of Manufacturing-Related Microstructural Variations on Fatigue in Carbide-Rich Tool Steels

In cold-work applications, tool steels with high carbide contents are used as cutting and stamping tools. The tool service life is limited by wear resistance and fatigue strength. The relationship between manufacturing-related microstructural influences and fatigue strengths of tool steels has not yet been adequately investigated. To investigate these influences on high-cycle fatigue (HCF) strength (N_G = 10⁷), rotating bending tests are performed on AISI D2 and AISI M2/M3. Raw materials are produced by conventional ingot casting and subsequent hot working (HW) as well as in a powder metallurgy (PM) process with hot isostatic pressing (HIP) and forging. Herein, a statistically validated correlation of process-related defect size and the resulting fatigue strength is presented. Both PM steels show significantly higher HCF strength than the HW steels. Critical defects in PM appear to be exclusively small oxide inclusions. In contrast, fatigue cracks in HW are typically initiated by the fracture of large, blocky eutectic carbides. The main factor influencing HCF strength is defect size. Other critical features of the microstructure include matrix hardness, circularity, and defect type. Improvements in fatigue strength can be obtained by reducing the size of fracture mechanical defects, inclusions for PM, and eutectic carbides for HW microstructures.     

LF精炼炉渣成分对H13钢中夹杂物的影响

对早期失效的H13钢材进行了金相分析。结果表明:H13钢中大尺寸夹杂物数量多,夹杂物评级达不到要求,影响了H13钢材的使用性能。采用优化精炼炉渣成分的方法来控制钢中夹杂物数量和尺寸。使用优化的精炼炉渣后,在真空处理结束时测得钢液中T[S]、T[O]含量分别为5×10-4%和1.29×10-3%;夹杂物级别明显降低,钢中大尺寸夹杂物的数量和尺寸都有显著下降,大大提高了钢材的冶金性能。