Plasma Surface Cu Alloyed Layer as a Lubricant on Stainless Steel Sheet:Wear Characteristics and On-job Performance in Incremental Forming

To solve the problems of poor forming and easy adhesion of the stainless steel,Cu alloyed layer on the stainless steels was prepared by the double glow plasma surface alloying technique.The experimentalresults indicated that the supersaturated copper dispersedly precipitated in grain interior and crystalboundaries and formed the vermicular structure.The tribologicaltests indicated that the friction coefficient of the Cu alloyed layer was lower than that of the stainless steels.The wear rate of stainless steelin the presence of Cu alloyed layer was approximately 2-fold lower than that in the absence of the alloyed layer.The results of the incrementalforming indicated that the ploughing phenomenon was not observed on the stainless steelin the presence of Cu alloyed layer during the incrementalforming,while the stainless steelpresented the deep ploughing.Therefore,Cu alloyed layer on stainless steelexhibited excellent self-lubrication and forming properties.

Effect of Colouring Process on Pitting Susceptibility of Austenitic Stainless Steel

Colouring of the austenitic stainless steel alloy （20.45% Cr, 8.57% Ni） was carried out in NaNO3-KNO3 eutectic melt without and with additions of Na2O2, NaCl and their mixtures at different temperatures ranging from 400-600℃, under open-circuit and galvanostatic anodic polarization conditions. The produced colours greatly depend on the thickness of oxide films, which in turn depends on the composition of the molten bath and its temperature. The more attractive, bright, adherent and uniform coloured oxide films can be obtained at 400, 450 and 500℃ in molten nitrate bath containing NaCl and Na2O2 mixtures. The pitting corrosion susceptibility of the coloured oxide films was tested in FeCl3 and NaCl as corrosive media. The obtained results indicate that the pitting corrosion susceptibility of the coloured oxide films greatly depends on the previous operating conditions of the colouring process of the stainless steel specimens such as the composition of molten bath, temperature and technique of colouring process.

Interfacial Features of Stainless Steel/Titanium Alloy Multi-metal Fabricated by Laser Additive Manufacturing

Laser additive manufacturing(LAM)is promising for fabricating multi-metallic component,but the mechanism of microstructural evolution at the interface of two metals is still needed to research further.In this study,a 316L stainless steel/Ti6Al4V alloy multi-metal was fabricated by LAM,and the mechanism of intermetallic phase transformation was deeply investigated.Results show that a strong reaction zone(SRZ)can be induced at the interface of the multi-metal.The phase constituents at the SRZ vary fromχ(Ti_(5)Fe_(17)Cr_(5))+Fe_(2)Ti+α′-Ti+β-Ti or FeTi to Fe_(2)Ti+χwhen the laser power is increased.When the scanning speed is further decreased,the thickness of the SRZ is significantly increased,andα′-Ti phase is also formed at this region besides Fe_(2)Ti andχphases.Moreover,the micro-hardness at the SRZ is increased,caused by the intermetallic phase transformation and elemental interdiffusion at the interface.

Micro-alloying Effects of Yttrium on Recrystallization Behavior of an Alumina-forming Austenitic Stainless Steel

Micro-alloying effects of yttrium on the recrystallization behavior of an alumina-forming austenitic（AFA）stainless steel were investigated.It was found that the grain growth kinetics of the steels doped with different amounts of yttrium（i.e.,0,0.05 and 0.10mass% Y）could be described by an Arrhenius type empirical equation.Added Y could interact with carbon and influence the morphology of carbides both inside grains and on the grain boundaries,thus altering the grain boundary mobility and grain growth.The steel doped with 0.05mass% yttrium showed the highest activation energy of grain growth and the most retarded recrystallization behavior,which mainly resulted from the high density of fine carbides both inside grains and on the grain boundaries.However,excess addition of0.10mass% Y induced coarsening and then lowered density of carbides,which alleviated the yttrium effects.The results also manifest that micro-alloying of rare-earth elements such as yttrium is an effective way for controlling grain growth behavior during recrystallization of AFA steels,which may have great implications on engineering applications.

Direct smelting process for stainless steel crude alloy recovery from mixed low-grade chromite, nickel laterite and manganese ores

Stainless steel crude alloy recovery from direct smelting of low-grade chromite, nickel laterite and manganese ores was investigated. The mixed low-grade ores were directly smelted in an elevator furnace at smelting temperatures ranging from 1550 to 1600 ℃. Smelting experiments were conducted in a laboratory elevator furnace equipped with 8 U-shaped high- quality molybdenum disilicide heating elements. A low-grade coal was used as the reductant. Experimental results showed that the recovery of Fe, Cr, Ni, Mn and Si within the alloy increased from 34.22, 60.27, 57.14, 25.42 and 13.02% to 69.91, 99.26, 86.02, 60.8 and 34.21%, respectively, when the temperature was increased from 1550 to 1600 ℃. There was a general increase in the total recoveries of Fe, Cr, and Ni in the alloy with CaO addition increasing from 0.4 g up to 1.2 g. However, the recoveries of Mn and Si vividly decreased as the CaO contents were increased. In general, the recoveries of the metal contents of the crude alloy increase with the increase in the amount of manganese ore. Compared to the recoveries of Fe, Cr, and Ni when CaO was added, the recoveries of Fe, Cr and Ni were lower when manganese ore was used as an additive.

Effect of Ni and Mn on the Mechanical Properties of 22Cr Microduplex Stainless Steel

The tensile properties of 22Cr–2Ni–4Mn–0.2N micro-duplex stainless steels with different Ni and Mn contents were investigated. Duplex stainless steels were vacuum induction melted and hot rolled, then annealed at 1,000–1,100 °C, at which temperature both the austenite and ferrite phases were stable. The volume fraction of the ferrite phase was markedly affected by the alloying elements of Mn and Ni; 1 wt% of Mn was equivalent to 0.4 wt% of Ni. All of the steels tested at room temperature showed the common strain-hardening behavior, while the steels tested at lower temperatures（-30 or-50 °C）showed a distinct inflection point in their stress–strain curves, which resulted from the transformation of the austenite to straininduced martensite. The onset strain（e0） of the inflection point in the stress–strain curve depended on the Md30 value of the steel. Testing at lower temperatures resulted in smaller e0 and consequently higher strengths and fracture strains（ef）. The tensile behavior was examined from the perspective of austenite stability of the micro-duplex stainless steels with the different Ni and Mn contents.

A review of friction stir welding of steels： Tool, material flow, microstructure, and properties

Considerable progress has been achieved in friction stir welding （FSW） of steels in every aspect of tool fab- rication, microstructure control and properties evaluation in the past two decades. With the development of reliable welding tools and precise control systems, FSW of steels has reached a new level of technical maturity. High-quality, long welds can be produced in many engineering steels. Compared to traditional fusion welding, FSW exhibits unique advantages producing joints with better properties. As a result of active control of the welding temperature and/or cooling rate, FSW has the capability of fabricating steel joints with excellent toughness and strength. For example, unfavorable phase transformations that usu- ally occur during traditional welding can be avoided and favorable phase fractions in advanced steels can be maintained in the weld zone thus avoiding the typical property degradations associated with fusion welding. If phase transformations do occur during FSW of thick steels, optimization of microstructure and properties can be attained by controlling the heat input and post-weld cooling rate.