Spray Forming of Homogeneous 20MnCr5 Steel of Low Distortion Potential

Spray forming is an advanced technology for the manufacture of homogeneous material from the melt. In this study, 20MnCr5 steel, a typical case hardening steel for gear and shaft production, has been spray formed and hot worked to semi‐finished bars. Shaft‐like specimens have been made from the spray‐formed material for distortion investigation. Material characteristics of the spray‐formed 20MnCr5 steel have been studied. In cooperation with other projects of the Collaborative Research Center SFB570 ‘’Distortion Engineering’’, evaluation of distortion behavior of the shaft specimens after machining and heat treatment has been made in comparison with continuous cast material. Spray‐formed 20MnCr5 steel shows lower distortion potential due to improved material homogeneity.     

Nitrogen Containing Austenitic Stainless Steels

Nickel and nitrogen are the two most widely used alloying elements which can impart the face‐centered‐cubic crystal lattice to stainless steels. With the recent price increases and the price volatility of nickel, nitrogen is ever more important as an alloying element for a number of reasons. First, nitrogen is easily available everywhere and thus is not subject to speculation at the Metal Exchange. Second, in addition to making stainless steels austenitic, nitrogen can also make them stronger and more corrosion resistant. It is also a well and clearly established fact since many years, that nitrogen in solid solution makes austenitic stainless steels more wear resistant and more fatigue resistant. Austenitic stainless steel alloy design with nitrogen has for many years now taken account of the role of carbon. This is not only because carbon is just a useful austenite former, but also because nitrogen reduces the temperature where carbides begin to form. Thus there is always an optimum carbon to nitrogen ratio. Finally it is now well established that carbon in solid solution helps to increase the strength, the corrosion resistance and the wear resistance of austenitic stainless steels. A number of quantitative correlations between alloy composition and materials properties are presented and their useful role in alloy design is pointed out. This will further help to lower the nickel content in austenitic stainless steels or even replace nickel altogether.     

Effect of pre‐processing annealing and ram speed on mechanical properties for low carbon steel processed by constrained groove pressing

Constrained groove pressing (CGP) has emerged for producing ultra‐fine‐grained materials with distinguished properties. Low carbon steel sheets were subjected to severe plastic deformation by constrained groove pressing process. The effect of pre‐processing annealing temperature, ram speed and number of passes on microstructure, mechanical properties and wear behaviour of the sheets were investigated. The 3 mm thick sheets were deformed by a constrained groove pressing die at ram speeds: 5 mm/min, 10 mm min^?1 and 20 mm min^?1. Furthermore, the as received sheets were annealed at 600 °C and 900 °C, then deformed at ram speed 20 mm min^?1. The annealing temperature 900 °C led to slightly coarser grains, lower strength and larger ductility compared to those obtained after annealing at 600 °C. With lowering the ram speed to 5 mm min^?1, the number of passes could be increased to 10 passes while increasing ram speed from 5 mm min^?1 to 20 mm min^?1 improved the mechanical properties; after 3 constrained groove pressing passes, the ultimate tensile strength increased from 420 MPa to 490 MPa, the hardness from 174 HV 1 to 190 HV 1 and the elongation from 7.6 % to 9.5 %. Finer grains were also obtained by increasing ram speed. Wear resistance was greatly enhanced by constrained groove pressing and by the increase in ram speed.     

Optimization of mixed silanes agent solution and curing process for composite γ-glycidoxypropyl trimethoxysilane (γ-GPS)/bis-1.2-(triethoxysilyl)ethane (BTSE) silane film on Q235 steel surface

In this investigation, the mixed γ-GPS/BTSE silane solution for preparing well adhered composite γ-GPS/BTSE silane film on Q235 carbon steel surface has been successfully optimized by orthogonal test, and the curing process parameters of temperature and time have also been optimized. The results indicate that the optimized hydrolysis parameters for mixed silanes agent solution are as follows: V_ethanol/V_water 3 : 1, V_γ-GPS/V_BTSE 2 : 3, V_silanes 6 vol.%, pH 4.0 and hydrolysis time 72 h. In addition, the optimized curing condition for composite γ-GPS/BTSE silane film is 120 °C and 30 min. After immersion in the optimized mixed γ-GPS/BTSE silanes agent solution and curing under the optimized condition, the prepared composite γ-GPS/BTSE silane film on Q235 steel surface can have an adhesion strength of 24.52 MPa to underlying steel substrate.     

Diffusionslöten von Aluminium mittels PVD applizierter Lotzusatzwerkstoffe

Diffusion brazing of aluminium by PVD applied filler metals Diffusion brazing of aluminium and aluminium alloys precoated with filler metal components enables fluxless wetting and obtains braze joints of high strength at moderate brazing temperatures. Previously deposited components of filler metals on the base materials as thin film, using Arc‐PVD‐process lead during a subsequently diffusion brazing process to the formation of a local liquid phase (transient liquid phase). The liquid phase is formed from the deposited thin film material and the base material and is solidified isotherm due to diffusion procedures. In doing so braze joints of higher melting point than brazing temperature can be realised. In this work, vacuum brazing of the two systems, Al‐Cu and Al‐Cu‐Si have been investigated. Cu and Al‐Cu‐Si were deposited on the base material using Arc‐PVD‐process. The base materials were pure aluminum and EN‐AW6060. Metallographic and scanning electron microscope analyses proved that the braze seam area after the completed diffusion brazing process shows similar structure and composition as the base material.     

Mikrobiologisch beeinflusste Korrosion nichtrostender Stähle und ihre Vermeidung

Microbiologically Influenced Corrosion (MIC) is not a new type of corrosion, but refers instead to the influence of microbiological activity on known forms of corrosion. Typically MIC promotes pitting corrosion and — to a lesser degree — crevice corrosion. The extent of this promoting effect can vary widely. Raw water with a high content of organic and inorganic matter requires special attention. Typically MIC starts on stainless steels at sites where the corrosion resistance has been lowered by manufacturing methods, e.g. at or around welded joints. The remedial measures are the same as those taken to avoid pitting and crevice corrosion. However, they have to be applied much more rigorously to prevent bacterial action. The most effective remedial action is clearly biocidal water treatment wherever permissible and possible.