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1.
可淬火硼钢板热冲压成形实验研究   总被引:10,自引:2,他引:8  
为研究淬火加热温度、保温时间及冷却水流速等热冲压工艺参数对热冲压零件力学性能及微观组织的影响规律,通过在不同工艺参数条件下进行弯曲件热冲压工艺试验,测量弯曲件的力学性能并观察其金相组织.结果表明,在所设计的模具上可实现高强硼钢热成形零件的有效淬火,热冲压弯曲件的抗拉强度可达到1500MPa以上,主要形成均匀细小的马氏体组织.确定了热冲压工艺参数的选择范围.  相似文献   

2.
现代汽车制造中越来越多地应用硼钢板热冲压技术来减轻车身重量并提高碰撞安全性,淬火时间对该过程中板料热力学行为和组织转变有重要作用。以汽车热冲压件的典型特征结构——U形梁为对象,将马氏体相变动力学模型嵌入硼钢板热冲压全过程热力耦合三维有限元模型中,实现了对该过程中板料热力学行为和马氏体相变的有效预测,预测结果与实验结果吻合良好。揭示了淬火时间对硼钢板热冲压的影响,结果表明,随淬火时间的延长,板料温度和温降速率均降低,温度分布越均匀;马氏体转化率增加,分布趋于均匀,但淬火时间超过22s后,马氏体转化率的大小和分布不再发生变化;最大回弹值减小。  相似文献   

3.
提高调质高强度钢韧性及其机理的研究   总被引:2,自引:0,他引:2  
本文以28Cr_2MoV 钢为对象,研究了通过改善显微组织形态提高调质高强度钢强韧性的效果和强韧化机理。实验表明:合理设计新的热处理工艺,可使这种钢从低温到高温整个回火温区的韧性(a_K、K_(1c))普遍提高。分析指出,改善调质态韧性是由于未溶尽的碳化物颗粒在快速奥氏体化淬火中对改善组织形态所起特殊作用的结果。这种颗粒在加热时提供形核位置以细化奥氏体晶粒,在冷却时切变型转变过程中充当位错增殖源,使淬火组织具有高密度位错,这又为回火提供大量形核位置,使碳化物呈细小、均匀分布并大量析出。相应地韧化基体,提高分散强化效果,改善调质钢的韧性。  相似文献   

4.
本文以28Cr_2MoV 钢为对象,研究了通过改善显微组织形态提高调质高强度钢强韧性的效果和强韧化机理。实验表明:合理设计新的热处理工艺,可使这种钢从低温到高温整个回火温区的韧性(a_K、K_(1c))普遍提高。分析指出,改善调质态韧性是由于未溶尽的碳化物颗粒在快速奥氏体化淬火中对改善组织形态所起特殊作用的结果。这种颗粒在加热时提供形核位置以细化奥氏体晶粒,在冷却时切变型转变过程中充当位错增殖源,使淬火组织具有高密度位错,这又为回火提供大量形核位置,使碳化物呈细小、均匀分布并大量析出。相应地韧化基体,提高分散强化效果,改善调质钢的韧性。  相似文献   

5.
新型超强耐热齿轮轴承钢具有优越的强韧性。通过改变钢的淬火加热温度,结合拉伸、冲击、断裂韧度等力学性能测试以及TEM,SEM,EDS等微观分析技术,研究不同奥氏体化温度下钢的显微组织与力学性能。结果表明:1060℃奥氏体化后,钢中存在未溶碳化物M_(6)C,冲击功和断裂韧度较低;1080~1100℃奥氏体化后,M_(6)C碳化物固溶,冲击功和断裂韧度显著增加。在1060~1100℃奥氏体化后,抗拉强度和塑性变化不大,规定塑性延伸强度随奥氏体化温度的增加略有降低。M_(6)C碳化物加速裂纹的萌生与扩展,导致韧性下降。在1080~1100℃奥氏体化后,超强耐热齿轮轴承钢可获得超高强度和高韧性,抗拉强度不小于2000 MPa,规定塑性延伸强度不小于1800 MPa,断裂韧度不小于100 MPa·m^(1/2)。  相似文献   

6.
目的 研究热处理温度对Q235堆焊复合板的冲击性能影响。方法 采用THD212铬钼钢焊条堆焊的方法制备高强度和高耐磨的复合板,对Q235复合板分别进行850, 900, 950℃、保温15 min的淬火处理,探讨堆焊后的热处理温度对复合板微观组织和冲击性能的影响。结果 随着淬火温度的升高,复合板冲击韧性先升高后降低,在900 ℃淬火处理时冲击功最大,为75.0 J;在950 ℃淬火时冲击功最小,为19.4 J。微观组织分析发现,当淬火温度在850和900 ℃时,堆焊层出现塑性和韧性较好的针状位错马氏体,在一定程度上提高焊接接头的韧性,断口形貌也表现出显著的韧性断裂特征;当淬火温度为950 ℃时,随着奥氏体化温度升高,淬火后获得脆性粗大条状马氏体组织,显著降低韧性,焊缝区和高强堆焊区均为脆性断裂。结论 在焊后进行一定温度范围内的热处理方法可以提高Q235堆焊复合板的冲击韧性。  相似文献   

7.
以Pamstamp有限元软件中22MnB5高强钢板的力学及热物理性能数据库为基础,建立了U形件的热冲压成形有限元分析模型,进行了热冲压成形及淬火全部过程的数值模拟分析,根据模拟结果,采用相同的工艺参数对该U形件热冲压成形过程进行了物理实验验证,结果表明:板料在900℃加热炉内加热保温5 min可达到理想的奥氏体状态,在板料加热过程中通氮气将氧气含量控制在10%以内的防氧化措施可明显降低氧化程度,提高工件表面质量,满足该工件的技术要求.  相似文献   

8.
零件的阶梯式变强度分区设计是实现汽车轻量化结构设计中零件兼具高强度和高塑性的前提,然而不同分区交界处存在的力学性能突变成了难以突破的技术瓶颈。为寻求超高强度钢板的梯度控温相变强化的理想模式,借助数值模拟技术研究了梯度控温相变强化模式实现热成形零件不同区域组织性能平稳过渡的热冲压方法。基于开发的自动控温梯度相变强化试验平台,进行了系列梯度控温相变热冲压试验,建立了在热成形过程中超高强硼钢板不同梯度冷却条件与最终板料力学性能(硬度、强度、延伸率)的映射关系模型。结果表明,梯度控温相变强化模式可使热成形零件兼具高强度和高塑性,且能够实现组织性能平稳过渡。随着模具加热温度升高、初始成形温度降低、保压时间延长,则贝氏体含量增加、板料抗拉强度和维氏硬度降低,而断裂延伸率则增加。  相似文献   

9.
使用OM、SEM、TEM和XRD等手段观察并表征在不同温度淬火的7Ni钢的组织形貌和逆转奥氏体含量的变化,研究了淬火温度对7Ni钢的低温强度和低温韧性的影响。结果表明:当淬火温度从830℃提高到930℃时钢的低温韧性急剧下降,低温抗拉强度和屈服强度明显降低。同时,随着淬火温度的提高延伸率下降,与低温强度的变化趋势基本一致。在830℃淬火的试验钢,原奥氏体晶粒和马氏体板条束最为细小。而当淬火温度超过830℃时钢中的原奥氏体晶粒和马氏体板条束都显著长大,钢的低温强度和低温韧性随着晶粒尺寸与板条束宽度的增大而下降,粗化的组织对钢的低温强度与低温韧性都有不利的影响。随着淬火温度的提高钢中的逆转奥氏体含量基本上呈下降趋势,在830℃淬火的试验钢中逆转奥氏体含量最高,其低温冲击功也最高。  相似文献   

10.
为比较拟合韧脆转变温度曲线各方法的优劣,确定船用低温钢韧脆转变温度,研究其冲击断裂行为,在20℃至–196℃系列温度下对试验钢进行Charpy冲击试验,并对其金相组织和断口进行分析。结果表明:使用Boltzmann函数拟合韧脆转变温度曲线的物理意义明确;船用低温钢韧脆转变温度为(–97±5)℃;试验温度高于韧脆转变温度时,裂纹形核功及延性裂纹扩展阻力变化不明显,但裂纹脆性扩展的阻力和裂纹失稳后的止裂能力随温度下降有较明显的降低;试验温度低于韧脆转变温度后,裂纹形核功及延性裂纹扩展阻力随温度降低迅速减小;试验钢的有效晶粒为(3.1±0.4)μm,细小的有效晶粒尺寸,是保证其低温韧性良好,韧脆转变温度低的主要原因。  相似文献   

11.
It has been shown recently that a strength function, expressed by a tensorial polynomial for an anisotropic material, can be only of the form
F4(σ) + F2(σ) + F1(σ) ≤ 1
where Fi(σ) are the respective polynomials of order i of the σ tensor components. Some further work in this field is now presented. It will be seen that a notable simplification has been achieved, bringing down the initial number of components of an 8th rank tensor from 38 = 6561 to a more managable number of 42 for orthotropic materials and 11 for the planar case. It is also shown that the three Fi(σ) polynomials cannot exist simulataneously, leading either to the known Tsai and Wu proposal or a new tensorial form. Some considerations to strength theory for isotropic materials are given as well. Finally, applicability of strength theories for composite laminates is discussed, with some suggestions for practical use.  相似文献   

12.
Long corrugated boxes were supported at both ends and bent by a concentrated force applied at the middle. Boxes with different lengths, cross‐sectional shapes, flute directions and board strengths were tested, using a standard compression tester with a fixed platen in accordance with ASTM D‐642. An equation was developed to relate compression strength to the various properties of the box. The correlation coefficient R2 for the fit to actual data was about 0.4. Boxes having the flutes run around the box had a 20% higher compression strength than with horizontal flutes. The most significant factor was found to be the board edge crush strength. The results suggest that failure of boxes in bending is due to localized crushing at the point of application of the load, rather than whole‐box collapse. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

13.
The specificity of the transition from elastic to elastoplastic deformation in defect-free single crystals during the localization of the deformation in a submicron region has been studied by nanoindentation. A sharp transition from elastic to elastoplastic deformation has been observed in tested single crystals at depths of about 20–50 nm. To define the yield strength using the nanoindentation data, the stressed-strained state in the contact region has been analyzed. It has been shown that the yield strength in submicrovolumes of single crystals is tens-hundreds times higher than that at the macroscopic level and approaches the value of the theoretical shear strength. A mechanism of the transition from elastic to elastoplastic deformation has been discussed in the framework of the phenomenological model of the nucleation of dislocations. The transition has been induced by the homogeneous nucleation of dislocations in a contact.  相似文献   

14.
The relationships between fatigue strength and ultimate tensile strength as well as hardness have been studied in high-strength NZK alloys (Mg–yNd–zZn–xZr) and other magnesium alloys. In the absence of casting defects, clear linear relationships have been found between the fatigue strength and the ultimate tensile strength and the hardness values in these magnesium alloys in both T4 (solutionized) and T6 (solutionized and aged) conditions. The fatigue strength models developed in this work alloys can be directly applied to other defect-free magnesium alloys.  相似文献   

15.
Dynamic crushing strength of hexagonal honeycombs   总被引:3,自引:0,他引:3  
Based on the repeatable collapsing mechanism of cells’ structure under dynamic crushing, an analytical formula of the dynamic crushing strength of regular hexagonal honeycombs is derived in terms of impact velocity and cell walls’ thickness ratio. It is consistent with the equation obtained from the shock wave theory that regards cellular material as continuum, in which the key parameter is approximately measured from the “stress–strain” curve of the cellular material. The effect of unequal thickness of cell walls on the honeycomb's dynamic crushing strength is discussed, and the result shows that the dynamic crushing strength of the hexagonal honeycomb with some double-thickness walls is about 1.3 times of that of the hexagonal honeycomb without double-thickness wall. All of the analytical predictions are compared with the numerical simulation results, showing good agreements.  相似文献   

16.
The paper is focused on shear bond strength–masonry compressive strength relationships and the influence of bond strength on stress–strain characteristics of masonry using soil–cement blocks and cement–lime mortar. Methods of enhancing shear bond strength of masonry couplets without altering the strength and modulus of masonry unit and the mortar are discussed in detail. Application of surface coatings and manipulation of surface texture of the masonry unit resulted in 3–4 times increase in shear bond strength. After adopting various bond enhancing techniques masonry prism strength and stress–strain relations were obtained for the three cases of masonry unit modulus to mortar modulus ratio of one, less than one and greater than one. Major conclusions of this extensive experimental study are: (1) when the masonry unit modulus is less than that of the mortar, masonry compressive strength increases as the bond strength increases and the relationship between masonry compressive strength and the bond strength is linear and (2) shear bond strength influences modulus of masonry depending upon relative stiffness of the masonry unit and mortar.  相似文献   

17.
The resistance to shear deformation developed by a granular material layer in contact with a topographically rough natural or manufactured solid material surface is critical to the stability of a variety of composite systems. By using discrete-element method numerical simulations, we show that evolution of fabric and contact force anisotropy at the boundary between the surface and the granular media controls shear behavior. Full mobilization of granular material strength occurs when the contact force anisotropy developed at the interface is equal to the maximum contact force anisotropy of the granular media.  相似文献   

18.
Fatigue tests have been carried out on lean-alloyed dual-phase steels with tensile strengths ranging from 300–800 MPa. Smooth specimens and specimens with punched holes were tested. The fatigue strength of dual-phase steel was found to be similar to that of other types of steel (eg solution hardened or microalloyed steels) of equal tensile strength. The fatigue strength increases with increasing yield strength. For notched specimens it is also related to the yield ratio. Work and bake hardening increase the fatigue strength of smooth specimens in proportion to the increase in yield strength. For notched specimens this effect is less and is dependent on the yield ratio. Bake hardening of material which was not work hardened also increased the fatigue strength. The notch sensitivity of low yield ratio dual-phase steel is found to be low. The notch sensitivity seems to increase with increasing yield ratio.  相似文献   

19.
Controlled low strength material (CLSM) is a flowable mixture that can be used as a backfill material in place of compacted soils. Flowable fill requires no tamping or compaction to achieve its strength and typically has a load carrying capacity much higher than compacted soils, but it can still be excavated easily. The selection of CLSM type should be based on technical and economical considerations for specific applications. In this study, a mixture of high volume fly ash (FA), crushed limestone powder (filler) and a low percentage of pozzolana cement have been tried in different compositions. The amount of pozzolana cement was kept constant for all mixes as, 5% of fly ash weight. The amount of mixing water was chosen in order to provide optimum pumpability by determining the spreading ratio of CLSM mixtures using flow table method. The shear strength of the material is a measure of the materials ability to support imposed stresses on the material. The shear strength properties of CLSM mixtures have been investigated by a series of laboratory tests. The direct shear test procedure was applied for determining the strength parameters Phi (angle of shearing resistance) and C(h) (cohesion intercept) of the material. The test results indicated that CLSM mixtures have superior shear strength properties compared to compacted soils. Shear strength, cohesion intercept and angle of shearing resistance values of CLSM mixtures exceeded conventional soil materials' similar properties at 7 days. These parameters proved that CLSM mixtures are suitable materials for backfill applications.  相似文献   

20.
In this study, Al2O3 particles were employed to improve the microstructure of LM24 and therefore, to increase the yield strength and tensile strength of this kind of alloy. In situ Al2O3 particles were obtained by direct reaction between oxygen and Al melt at 750–800 °C. Microstructure examination shows that the size of in situ formed Al2O3 particles was about 1–2 μm, and interestingly, with addition of in situ Al2O3 particles, the coarse primary Si phase was disappeared completely. More important, the yield strength and the tensile strength of Al2O3/LM24 are increased by 52 MPa, 16 MPa than that of LM24 alloy with 0.1% Sb addition. The value of 181 MPa and 315 MPa is for yield strength and tensile strength of Al2O3/LM24 respectively. Besides, the yield strength and tensile strength are 180 MPa and 314 MPa respectively for Al2O3/LM24 alloy after remelting and casting. This verifies that the improvement of mechanical properties of such kind of material possesses stability and reliability.  相似文献   

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