Effect of low-pressure carburizing and plasma nitriding on mechanical properties and fatigue endurance limits of low alloy sintered steels

ABSTRACT

Thermochemical treatments like plasma nitriding or surface carburizing are commonly used to enhance surface hardness of steel components. An important difference between these treatments is the temperature at which they are carried out. In the present paper, the surface carburizing was carried out following a recently reported non-isothermal low pressure carburizing (LPC) treatment. In order to gain a comparative view of the effect of different treatments on the microstructure, microhardness, fatigue and impact properties, materials with distinct hardenability and widely used in the industrial production were evaluated. Tests were also carried out using industrially processed components aimed to an application demanding high wear resistance. The microstructural evolution during case hardening was studied by optical and electron microscopy.     

Evaluation of particle recovery from microalgae

Coccoliths are micro-structured biomineral particles found in cell protective covering layers of coccolithophore species. They are mainly composed of CaCO₃ and their individual crystal entities are arranged in such a way that they construct complex and unique structures. This complexity is found down to the individual particle level and appears to have promising properties to offer. This study focuses on the essential step prior to any kind of implementation, which is the recovery of the material. It summarizes cleaning protocols found in literature, compares them for the first time for the same freshly cultivated material and addresses challenges that still need to be overcome. Further, it highlight the advantages and disadvantages of the best cleaning protocols, suggests optimizations with promising results and uses size distribution measurements to analyse the recovery efficiency. To that end, further characterization techniques, new for coccoliths, are introduced and used to improve our current knowledge of the particles behaviour.     

The analysis for morphological evolution and crystallography of degenerate pearlite in 100Mn13 steel

During approximate 773 K aging treatment of 100Mn13 steel, degenerate pearlite will occur and evolve into lamellar pearlite during growth process. The microstructures of degenerate pearlite and its evolutionary lamellar pearlite are observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results show that after 748 K, 773 K and 798 K aging, degenerate pearlites occur at grain boundary. At growth front of degenerate pearlite forming at 773 K and 798 K, pearlite presents a morphology of short lamellae of carbide and ferrite, indicating a trend of developing into lamellar pearlite. The higher the temperature is, the more obvious the trend is, and even a conventional lamellar pearlite has developed. However, there is no morphological evolution for degenerate pearlite forming at 748 K aging. Besides, the constituents of degenerate pearlite is identified as M₂₃C₆ and ferrite, and Kurdjumov-Sachs orientation relationship exists between them, (01 )_α//( 1 )_M23C6, [111]_α//[110]_M23C6. This orientation relationship maintains in morphological evolution from degenerate pearlite to lamellar pearlite.     

The influence of cryogenic rolling on a transformation-induced plasticity steel

ABSTRACT

Here, a novel cryogenic rolling plus intercritical annealing process was applied to a transformation-induced plasticity (TRIP) steel with a low chemical composition of carbon and manganese. Compared with traditional cold rolling, obvious grain refinement was observed, due to a high amount of dislocations retained. In addition, austenite volume fraction was increased, because of a unique nucleation mechanism. Subjected to cryogenic rolling, strength and ductility were increased, due to the enhanced austenite stability, which provided continuous and active TRIP effect. Consequently, tensile strength was increased to 1030?MPa, and elongation was increased to 38.2%. Thus, a great mechanical combination was obtained in a steel with a relatively low chemical composition with carbon and manganese, only by cryogenic rolling process.     

冷轧螺纹钢筋的力学性能研究

介绍了冷轧螺纹钢筋的轧制原理,从屈服强度、抗拉强度、延伸率、冷弯条件等方面说明了冷轧螺纹钢筋力学性能标准(新技术的生产工艺),研究了冷轧螺纹钢筋的力学性能及其影响因素。     

新建风井留设小保护煤柱与抗变形技术的研究

以平煤集团公司四矿新建千米进风井为例,系统研究了新建风井留设小保护煤柱的可能性,提出了井筒抗变形技术措施,为深部矿井风井建设提供了可资借鉴的技术途径。     

氰化工艺过程中金属存量计算方法探讨

为搞好金属平衡，减少理论与实际差值，依据某黄金矿山氰化工艺流程特点，对脱药用单层浓密切、漫出槽、三层洗涤浓密机三个作业中的金属存量的计算方法进行了探讨。     

宜昌三峡机场灯光带滑坡特征及治理

三峡机场灯光带滑坡，属典型的人工加载“后推式”碎石土滑坡类型。该滑坡治理前，稳定系数仅１．０７，处于极限平衡状态，不仅严重阻碍机场灯光带导航系统的建设，且危及相距仅２００ｍ的汉宜高等级公路。该滑坡通过工程治理，达到了预期目的，收到了良好的社会和经济效益。     

矿用对旋轴流风机小流量工况下内部流动数值模拟

由于轴流式通风机小流量工况出现的非稳定工作特性,由此带来的缩小了风机的安全可靠运行区域,严重时可能带来颤振毁坏设备等安全性问题。通过数值模拟手段,对一矿用对旋式轴流式通风机小流量工况内部流动进行了深入研究。     

蓬莱田横栈道维修加固技术

结合蓬莱田横栈道维修加固工程实例,介绍了针对滨海环境下不同的工程构件采取的不同的处理措施以及施工效果。