Energy-Based Prediction of Low Cycle Fatigue Life of High-Strength Structural Steel

 Energy-based models for predicting the low-cycle fatigue life of high-strength structural steels are presented. The models are based on energy dissipation during average of cycles, cycles to crack propagation and total cycles to failure. Plastic strain energy per cycle was determined and found as an important characteristic for initiation and propagation of fatigue cracks for high-strength structural steels. Fatigue strain-life curves were generated using plastic energy dissipation per cycle (loop area) and compared with the Coffin-Manson relation. Low cycle fatigue life was found similar from both methods. The material showed Masing-type behavior. The cyclic hysterisis energy per cycle was calculated from cyclic stress-strain parameters. The fracture surfaces of the fatigue samples were characterized by scanning electron microscope and the fracture mechanisms were discussed.     

我国汽车用超纯铁素体不锈钢的应用和发展

以排气系统为中心,介绍了国内外超纯铁素体不锈钢的开发和应用现状,并对我国超纯铁素体不锈钢的生产和发展进行了展望。     

电化学方法在不锈钢腐蚀研究中的应用现状及发展趋势

电化学手段可以实现对不锈钢材料的快速评价和腐蚀机理研究,因而受到广泛应用。在不锈钢耐蚀性评价方面,最常采用的电化学手段主要有腐蚀电位测试、交流阻抗测试、恒电位极化测试以及循环动电位极化测试。本文分别针对上述四种电化学方法在不锈钢耐蚀性评价上的应用情况进行了介绍,明确了各种检测方法的特点。腐蚀电位及交流阻抗测试是无损检测手段,可以满足长周期腐蚀监测需求;恒电位极化和循环动电位极化测试可以获得材料的极化特征参数,有利于对材料的腐蚀机理及耐蚀性进行评价。结合当前的不锈钢腐蚀研究现状,展望了电化学方法在腐蚀研究领域的发展趋势:未来电化学方法将更多作为腐蚀调控手段,需要结合其他检测技术实现对不锈钢腐蚀过程的精细分析。      

Antibacterial Properties of Cerium-Bearing Stainless Steel Bearing Cerium

Antibacterial Properties of Cerium-Bearing Stainless Steel Bearing Cerium     

Recent developments in stainless steels:austenitic,ferritic,duplex

A review is given concerning some of the recent industrial developments of stainless steels. In austenitic stainless steels,two different directions of alloy development are noticeable:low nickel austenitic stainless steels and high nitrogen stainless steels.In these two cases the aims are different,particularly in terms of strength,but the philosophy of alloy development and the scientific approaches are very similar and they all revolve about the role of nitrogen as an alloying element and how this affects strength,ductility and corrosion resistance. There is now a broad and useful basis of information as to how nitrogen affects solid solution hardening,grain boundary hardening and work hardening and how to make use of these effects in developing materials required by the world market. In the field of corrosion resistance,ferritic,duplex and austenitic stainless steels compete with each other and now there is a growing body of information concerning the relative corrosion resistance based on laboratory data. However,for practical applications and for alloy selection,more than just laboratory data are needed,and thus,the first results are presented here of a many years comparison of the corrosion resistance of 24 commercial stainless steels exposed to corrosion in outdoors marine atmosphere.Hope is expressed to involve in the near future even more steels from a wider range of manufacturers in such corrosion studies.This might help consumers in appropriate alloy selection.It might also help steel makers in developing appropriate stainless steel grades.     

Wedge type creep damage in low cycle fatigue

A model is proposed to quantify the accumulation of wedge type creep damage in low cycle fatigue. It is proposed that such damage is produced primarily during the ramp periods of the cycle. Equations are developed for estimating incremental accumulation of damage per cycle in fully reversed, multiaxial loading. The rate of accumulation of damage depends on the strain-rate, the temperature, and the microstructure. The analysis is kept simple by making physically reasonable assumptions. Cycles to failure are predicted by invoking a fracture criterion. The model is applied to two sets of data; one set is a well characterized life test data on an aluminum alloy, and the other is phenomenological data on austenitic stainless steels. In both cases the predictions are good enough to prompt further experimental evaluation of the model. This paper deals with only one mechanism of creep-fatigue interaction. Other mechanisms of failure,e.g., ‘r’ type cavitation, or fatigue crack initiation and propagation, are also viable. The model described here may be expected to apply only under those conditions when wedge damage is the dominant failure mechanism.     

Introducing a multi-criteria indicator to better evaluate impacts of rare earth materials production and consumption in life cycle assessment

Life cycle assessment （LCA） is based on the basic principles of sustainable development. LCA method demonstrated its efficiency in providing a systematic environmental assessment approach of a product or a process. The effectiveness and efficiency of these methods lies in the fact that they take into account all life cycle stages of a product, from the extraction of raw materials to end of life treatment （recycling, ...） through an assessment covering different impact categories such as climate change, human health, ecosystems and resources. Existing LCA indicators reflect different issues surrounding resource depletion, creating inconsistency and moreover confusion among LCA practitioners. The evaluation of different life cycle impacts assessment （LCIA） methods done by EC JRC showed that available models did not address the same parameters： short- vs long-term, stock vs backup technology, etc. It also showed that if the correlation between the methods was sufficient for some resources, others such as rare earth elements showed a high level of inconsistency between methods. It was therefore necessary to develop a relevant indicator and harmonized assessment of impacts on resources in LCA. Furthermore, a resource strategy indicator based on the three pillars of sustainable development （eco- nomic, environmental and social） would better address wider challenges and making it a more powerful decision making tool. This study aimed to introduce an indicator for evaluating the strategy implications of metal resources for products and to compare different ways of production resulting from extraction of raw materials or recycling, with a special focus on rare earth materials. The indicator would assess the impacts based on a reserve-resource vision [BGS NERC] and the evolution over time and founded over three pa- rameters： technical feasibility, economic viability and political stability （including social and environmental aspects） in representing countries.     

Overview on Basic Types of Hot Rolling Textures of Steels

The present study gives a review on basic types of crystallographic textures developing during hot rolling of polycrystalline steels. The results are grouped into three fundamental classes of textures. The first group comprises pure Fe, some weakly bonded B2 and DO₃ structured intermetallics, as well as closely related alloys such as ferritic low carbon and microalloyed interstitial free steels. The second group includes highly alloyed corrosion‐resistant ferritic stainless and Fe‐Si transformer steels. Typical examples are steels with about 10 wt.%‐17 wt.% Cr, with about 3 wt.% Si, as well as body centered cubic transition metals such as Ta, Mo, and Nb which do not undergo any phase transformation during hot rolling. The third group comprises stable and instable austenitic stainless steels for instance on the basis of larger amounts of Cr and Ni or on Mn as well as duplex steels. Most L1₂ structured intermetallic alloys can also be assigned to this group. The suggested classification scheme is discussed in terms of different processing parameters, thermodynamics, microstructure, and crystallographic aspects.     

Study of Fracture Mechanisms at Cyclic Fatigue of Steels Used in Nuclear Reactors I

This study deals with the possible reasons of nucleation and propagation of macrocracks, mesocracks, and microcracks in stainless austenitic steels after low‐cycle fatigue tests at room temperature. It is shown that macrocracks in these steels are formed only after completion of 20–30% of cycles of total deformation. Statistical analysis showed that the average length of slip bands and that of microcomponents of a macrocrack are equal, and they are always parallel to each other, that indicates their crystallographic character. Macrocracks preferably propagate through the grains with no apparent signs of plastic deformation and through isolated mesocracks, but not through mesocracks and grain boundaries.     

选择性激光熔化成形17–4PH不锈钢研究

选择性激光熔化技术具有一次成形、节省原材料、可成形任意复杂结构工件及性能优良等特点，是17–4PH不锈钢成形研究的新方向。本文综述了近几年选择性激光熔化制备17–4PH不锈钢研究现状，包括工艺参数对17–4PH不锈钢性能的影响，热处理和热等静压对17–4PH不锈钢力学性能的改善，不同成形方式和不同后处理17–4PH不锈钢的显微组织变化，以及在选择性激光熔化成形17–4PH不锈钢过程中出现的问题和发展趋势。     

Research Progress and Development Tendency of Nitrogen-alloyed Austenitic Stainless Steels

Research progress on nitrogen-alloyed austenitic stainless steels was expounded through the development of steel grades.In addition,hot topics in the research of nitrogen-alloyed austenitic stainless steels were discussed,including the solubility of nitrogen,brittle-ductile transition,and welding.On this basis,it was proposed that the future development tendency of nitrogen-alloyed austenitic stainless steels lied in the three fields of high-performance steels,resource-saving steels,and biologically friendly steels.The problems encountered during the research of nitrogen-alloyed austenitic stainless steels were discussed.     

高氮不锈钢粉末冶金制备技术的研究进展

高氮不锈钢作为一种重要新型工程材料,具有优异的力学性能和耐腐蚀性能,受到国内外广泛重视。介绍了粉末冶金制备高氮不锈钢的原理和特点;论述了高氮不锈钢粉末的制备与成形技术;指出了利用粉末冶金制备高氮不锈钢所具有的技术优势,其中注射成形——氮化烧结工艺更具发展潜力。     

Development of heat-resistant ferritic stainless steels for exhaust lines at Nisshin Steel

Exhaust emission regulations of the automotive are enforced in each country to prevent air pollution and global warming,and the restriction standard tends to become severer.Various techniques such as the combustion improvement of gasoline,upgrades of the catalyst,and the thermal capacity decreases in the exhaust lines are adopted to suit the regulations,and these lead to an increase of the maximum temperature of the exhaust gas. Recently,ferritic stainless steels are mainly used to parts of exhaust lines,as their thermal expansion coefficient is small,and the cyclic oxidation resistance and the thermal fatigue property are better than austenitic stainless steels. This paper presents newly developed heat-resistant stainless steels from Nisshin Steel for exhaust lines usage,and describes the currents of the steel development that could be envisaged in the future.With regard to improving the high-temperature strength of ferritic stainless steels,the addition of Nb,Mo and Cu is effective in solution hardening and precipitation hardening at 700℃,while the addition of Nb,Mo and W is effective in mainly solution hardening at 900℃.The addition of Cr,Si and Mn suppress the breakaway oxidation in air at 950℃up to 200 h of ferritic stainless steels containing 14%Cr.Especially,the addition of 0.8%or higher Mn would effectively improve the adherence of oxide scale.It is confirmed that ferritic stainless steels,NSSHR-1(14Cr-lMn-0.9Si-Nb) and NSSHR-2(10Cr-0.9Si-Nb-Ti ),is having a superior heat resistance,formability and cost performance compared to conventional Type441 and Type439 respectively.     

高氮不锈钢粉末冶金制备技术的研究进展

高氮不锈钢作为一种重要新型工程材料,具有优异的力学性能和耐腐蚀性能,受到国内外广泛重视。介绍了粉末冶金制备高氮不锈钢的原理和特点;论述了高氮不锈钢粉末的制备与成形技术;指出了利用粉末冶金制备高氮不锈钢所具有的技术优势,其中注射成形——氮化烧结工艺更具发展潜力。     

不锈钢研发的最新进展——奥氏体、铁素体和双相不锈钢

评价了近期不锈钢的部分工业发展状况。对于奥氏体不锈钢而言,有两大引人注目的合金开发方向:低镍奥氏体不锈钢和高氮奥氏体不锈钢。这两类合金的设计目的不同,尤其是强度方面,但其合金开发原理和科研方法很相似,都围绕着氮这一合金元素对强度、塑性和耐蚀性的积极作用展开。现在人们已经相当了解氮对固溶强化、晶界强化和加工硬化的影响以及如何充分利用这些影响来开发全球市场所需的材料。在耐蚀性方面,铁素体、奥氏体和双相不锈钢彼此竞争,有关其耐蚀性比较的实验室数据也越来越多。但是,对于实际应用和合金选择而言,仅仅是实验室的数据是不够的,因此文章给出了多年来对24种工业生产的不锈钢暴露在室外海洋大气环境下的最新耐蚀性研究结果。希望在不久的将来能将更多制造商提供的钢种纳入到此项耐蚀性研究中来。这既能帮助消费者合理地选择合金,也可以帮助钢铁生产企业开发合适的钢种。     

σ相析出对不锈钢力学性能的影响概述

σ相是不锈钢中常见的一种硬而脆的金属间相,它可在铸造、轧制、热处理以及焊接等过程中析出,显著影响不锈钢的力学性能.从冲击韧性、塑性、拉伸强度、高温蠕变以及耐磨性等方面综述了国内外关于σ相对不锈钢力学性能影响研究的状况,分析了σ相的影响机制,并提出了目前研究中存在的一些问题以及将来可能的研究方向.     

稀土元素在铁素体不锈钢中的作用和应用前景

铁素体不锈钢(11%～30%Cr)的抗点蚀、抗应力腐蚀和抗高温氧化性能均优于奥氏体不锈钢。但普通铁素体不锈钢晶间腐蚀敏感性较高,塑性和韧性较低,焊接裂纹倾向较大。经分析得出,铁素体不锈钢加稀土元素可改善钢的凝固组织,影响碳、氮化物析出形态,细化晶粒,改变钢中硫化物形态和夹杂物成分,从而改善钢的横向韧性、焊接性能和疲劳性能。因此,稀土元素在铁素体不锈钢中的应用研究工作有广阔的前景。     

Stress corrosion cracking of stainless steels in NaCl solutions

The metallurgical influences on the stress corrosion resistance of many commercial stainless steels have been studied using the fracture mechanics approach. The straight-chromium ferritic stainless steels, two-phase ferritic-austenitic stainless steels and high-nickel solid solutions (like alloys 800 and 600) investigated are all fully resistant to stress corrosion cracking at stress intensity (K₁) levels ≤ MN • m-^3/2 in 22 pct NaCl solutions at 105 °C. Martensitic stainless steels, austenitic stainless steels and precipitation hardened superalloys, all with about 18 pct chromium, may be highly susceptible to stress corrosion cracking, depending on heat treatment and other alloying elements. Molybdenum additions improve the stress corrosion cracking resistance of austenitic stainless steels significantly. The fracture mechanics approach to stress corrosion testing of stainless steels yields results which are consistent with both the service experience and the results from testing with smooth specimens. In particular, the well known “Copson curve” is reproduced by plotting the stress corrosion threshold stress intensity (AT_ISCC) vs the nickel content of stainless steels with about 18 pct chromium. Formerly with the BBC Brown Boveri Company, Baden, Switzerland     

不锈钢腐蚀试验方法标准现状与发展

介绍了不锈钢的腐蚀类型与产生原因,结合国内外不锈钢腐蚀试验方法标准的现状与发展,提出了制修订我国不锈钢腐蚀试验方法标准的工作方向。     

Transformation Induced Martensite Evolution in Metal Forming Processes of Stainless Steels

Because of their high corrosion resistance and deformation characteristics, the industrial application of stainless steels is of high importance. During deep drawing processes, phase transformation of austenite to martensite occurs, which leads to an increased strain hardening of the material. The phase transformation depends on alloying constituents, transformation temperatures, stresses and strains. Consequently, in the design of deep drawing processes of stainless steels the phase transformation has to be considered. This paper presents a mathematical model for the calculation of the martensite evolution depending on temperatures, stresses and strains. The precise simulation of deep drawing processes of stainless steels can be enabled by the implementation of this model into commercial FE‐programs.