316L及420不锈钢粉末温压工艺研究

【作者】 李春香；

【导师】 曹顺华；

【作者基本信息】 中南大学 ， 材料学， 2008， 硕士

【摘要】 粉末不锈钢密度低，耐腐蚀性能与力学性能比传统致密不锈钢材料低，从而限制了其广泛应用。本研究采用温压技术提高粉末不锈钢件的密度。研究中，采用Archimede法测量样品密度，利用金相显微镜观察样品显微组织，扫描电镜（SEM）观察粉末形貌及断口形貌，能谱技术（EDS）分析断口微区成分。系统地研究了润滑剂含量、压制压力、粉末温度、模具温度，以及细粉添加种类与含量对压坯密度的影响。同时，比较了温压工艺与冷压工艺所制备样品的密度及弹性后效差异。本研究所有样品于分解氨气氛下经1130℃烧结。对烧结后部分样品的硬度与抗拉强度进行了分析。研究结果显示，对420粉末不锈钢而言，适宜的温压工艺为：润滑剂含量0．7％，粉末温度90℃、模具温度120℃。在压制压力为784MPa时，压坯密度为6．86g／cm³，与冷压工艺相比提高了0．18g/cm³。烧结后样品硬度为33HRC，而密度为6．83g/cm³，较压坯密度降低了0．03g/cm³。对于316L粉末不锈钢，适宜的温压工艺为：润滑剂含量0．8％，粉末温度90℃，模具温度120℃。在压制压力为784MPa时，压坯密度为6．92g/cm³。比冷压的压坯密度提高了0．26g／cm³。烧结后样品硬度为76HRB，密度为7．02g／cm³，较压坯密度提高了0．10g/cm³。316L不锈钢压坯密度与细粉添加量的关系曲线呈双峰分布，峰值对应细粉添加量为2％和30％。添加粒度小于20μm的球形细粉后，当压制压力为784MPa时，峰值处的压坯密度为7．00g／cm³和7．09g/cm³。添加粒度小于43μm的水雾化细粉后，当压制压力为784MPa时，峰值处的压坯密度为6．972／cm³和7．03g／cm³。添加细粉后的316L粉末不锈钢压坯经烧结后，密度有所提高。密度增幅随细粉添加量的提高而增大，且添加球形细粉样的密度增幅高于添加水雾化细粉样的密度增幅。密度的增幅与压制压力无明显关系。当样品的烧结密度为7．21g/cm³时，对应硬度为95HRB，与同条件下没有添加细粉的316L粉末不锈钢样品的硬度（76HRB）相比，提高25％。同时，对于密度相近的样品，添加细粉后的样品硬度更高。样品抗拉强度随密度增大而增大，且当密度大于7．00g／cm³时，增大趋势明显。当样品的烧结密度为7．14g／cm³时，对应抗拉强度为486MPa。本研究中，公式σ_b=σ₀exp（-bθ）中的b值为6-7，与文献中b为4-7的结论相符。更多还原

【Abstract】 The resistance to chemical corrosion and the mechanical property of powder stainless steels is poor compared to the conventional wrought stainless steels because of their lower densities, which limits their wide applications. In order to increase the density, warm-pressing was used for powder stainless steel in this research. During the present experiment, density was examined by Archimedes’ method, optical microscope was used to observe the micro-structure,SEM was used to observe the particle morphology and fracture morphology, EDS was used to analyse the component in microregions. Effects of the contents of lubricant, compacting pressure, temperature of powder and die, contents and types of fine powders on green density were studied systematically. And the comparison of green density and spring back between warm-pressing and conventional pressing were also carried out in the experiment. Samples were sintered in cracked ammonia at 1130℃.Results show that, the optimum condition to product stainless steel is that, the maximum green density are obtained at 784MPa as they are, lubricant contents is 0.7% for 420 powder stainless steel and 0.8% for 316L powder stainless steel, temperatures of powder and die are 90℃and 120℃respectively. The green density of 420 powder stainless steel obtained by this process is 6.86g/cm³, which is 0.18g/cm³ higher than conventional pressing. The hardness is 33HRC and the density is 6.83g/cm³ which is 0.03g/cm³ lower than the green density after sintering. The green density of 316L stainless steel obtained by the optimum process is 6.92 g/cm³, which is 0.26g/cm³ higher than conventional pressing. The hardness is 76HRB and the density is 7.02g/cm³ which is 0.10g/cm³ higher than the green density after sintering.The green density exhibits bimodal distribution, when the fine powder contents is 2% and 30% , on the curve which is about the relation between the green density and the fine powder contents. When adding spherical fine powders（ < 20μm） , the peak values of green density are 7.00 g/cm³ and 7.09g/cm³ respectively at 784MPa. When adding water atomized fine powders（ < 43μm） ,the peak values of green density are 6.97 g/cm³ and 7.03g/cm³ respectively at 784MPa.For Samples which were added with fine powders, the density are improved after sintering. The extent of density improvement, which is greater when adding spherical fine powders than water atomized fine powders and is almost irrelated with the pressing pressure, increases with the contents of fine powders. The hardness is 95HRB when the sample’s density is 7.21 g/cm³. Comparing with samples with no fine powders, the hardness is improved even when the density is almost the same. The tensile strength, which increases with the density, especially when the density is bigger than 7.0g/cm³, is 486MPa while the density is 7.14 g/cm³. The b in formulaσ_b=σ₀exp（-bθ）is 6-7 which matches with the conclusion of that b is 4-7.更多还原