Effect of microstructure and low cycle fatigue deformation on tensile properties of P91 steel

Isothermal furnace heat treatments were carried out to simulate the microstructures of inter-critical, fine grain and coarse grain heat-affected zones of P91 steel weld joint at different soaking temperatures ranging from just above AC₁ (837 °C) to well above AC₃ (903 °C). Interrupted low cycle fatigue tests were performed on the specimens of P91 steel up to 5 %, 10 %, 30 %, and 50 % of the total fatigue life at the strain amplitude of ±0.6 %, strain rate of 0.003 s⁻¹ and temperatures of 550 °C and 600 °C. Subsequently, tensile tests were conducted on the interrupt tested specimens at the same strain rate and temperatures. Soaking at the inter-critical temperature region reduces / deteriorates the tensile and yield strengths of base metal compared to fine grain and coarse grain regions. The inter-critical heat-affected zone accounted higher damage contribution towards the overall tensile behavior of the actual P91 steel weld joint. Substructural coarsening during strain cycling at elevated temperatures attributes to the rapid reduction in the initial yield strength up to 10 % of fatigue life of P91 steel. A higher amount of plastic strain accumulation during low cycle fatigue deformation resulted in a decrease in fatigue life of the inter-critical heat-affected zone of P91 steel.     

Einfluss der Schweißparameter auf das Ermüdungsverhalten hochfester Baustähle

High strength low alloy steels are used in many different engineering areas. A commonly used joining technique for those steels is fusion welding. Generally, these components have to withstand fatigue due to dynamic loading. Using thermal joining techniques affect the mechanical properties of the steel. This study focuses on the influence of the heat input on the microstructure of high strength low alloy steels (S690). Furthermore, the fatigue behaviour with special regard to crack initiation and crack propagation is characterized.     

Evaluation of fatigue life of steel using steel grain size

The insightful discussion of the relationship between the construction of metallographic and fatigue life and proposition of mathematical relationships describing this relationship was conducted in the paper. This paper presents a method for estimating the fatigue life, based on the construction of the microstructural material taking into account the grain size and the participation of ferrite and pearlite phase.     

Features of austenitic steels' microstructure following plastic deformation

The carried out transmission electron microscopic (TEM) analysis of steels 316L and TWIP, has shown that important mechanisms of plastic deformation are mechanical twinning, shear band formation and deformation martensitic transformations. Mechanical twinning is a characteristic feature of a plastic deformation at ε ≈ (20–50) % deformation degrees. At ε = (20–70) % the basic contribution in plastic deformation of a material brings shear band formation. The contribution deformation martensitic transformations into plastic deformation is defined by level of phase instability of steels.     

Verbundschmieden hybrider Stahl‐Aluminium Bauteile

Compound forging of hybrid steel aluminium components Due to a major increase of energy prices the importance of lightweight construction has increased. The production of hybrid compounds by forging is a promising method to successfully manufacture functional parts by few process steps. The heating of hybrid material work pieces made of steel and aluminum is a great challenge. Steel is forged at a temperature of at least 900 °C, while aluminum should not exceed a temperature of 500 °C. For this inhomogenous temperature distribution warming up possibilities are presented.     

Prediction of the remaining lifetime of stainless steels under conditions of stress corrosion cracking

The prediction of the lifetime of metal structures and equipment under conditions of stress corrosion is very complicated because of the complexity of this process of degradation. Recently a new method, based on the so‐called corrosion elongation curves, has been found, which can be used to predict the time to failure under these conditions. By upgrading of these curves (and thus obtaining Upgraded Corrosion Elongation Curves – UCEC's) it has been possible to obtain a precise definition of the time needed for the initiation of the corrosion crack, and for its stable growth. It is upon this basis that diagrams for the prediction of remaining lifetime (DPRL's) have been developed. DPRL's can also be used to predict the values of various critical parameters which have to be achieved if a stress corrosion crack is to occur.     

Acoustic emissions during tensile test of DC06 and HCT600X

In this paper the acoustic emission behaviour during tensile tests of the materials DC06 and HCT600X is studied. Two steels with different characteristics (mild deep‐drawing steel DC06 and high‐strength steel HCT600X) are consciously chosen to show the influence of the material properties on the generated acoustic emissions. The acoustic emission behaviour and the corresponding signals differ clearly from each other. In addition, the effect of the strain rate as well as the rolling direction (0°, 90°) on the acoustic emission behaviour is investigated. Both parameters have a significant influence on the resulting acoustic emissions during tensile deformation. Furthermore, a new criterion based on the acoustic emission parameter FCOG (centroid frequency) for detection of damage beginning in dual‐phase steels is developed. The criterion supports the assumption that during tensile deformation of dual‐phase steels two failure mechanisms, ferrite/martensite interface decohesion and martensite phase fracture, exist.     

Langzeitverhalten feuerverzinkter Bewehrungsbänder für Bewehrte Erde Bauwerke

Long‐term behaviour of hot‐dip galvanized reinforcing strips for reinforced earth constructions For reinforced earth constructions the following parameters are found as a solution to ensure the corrosion prevention of strips for a longtime period: ? use of specific nonbinding grounds, ? preventing the penetration of salt from outside, ? choosing a zinc‐galvanized coverage with a minimum‐thickness of 100 μm. Now a corrosion induced failure of strips is almost impossible considering a building‐relevant period.