Minimum design metal temperature of Q345R determined by exemption curve in ASME VIII-2 and its derived methods

In order to prevent the brittle fracture accident, minimum design metal temperature of ferrite steel should be limited. After the minimum design metal temperature curve in American Society of Mechanical Engineers VIII-2 (2007) was proposed, much related research has been done in recent years. In this paper, firstly the theoretical basis of four methods used to determine the minimum design metal temperature was introduced. Secondly, the mechanical properties of Q345R was measured by tensile test, Charpy v-notch impact test and fracture toughness test Thirdly, minimum design metal temperature curve of Q345R that determined by four methods were obtained. There are obvious difference between the curves of Q345R that determined by four methods. It can be concluded that low temperature fracture toughness of Q345R is underestimated when classifying Q345R into exemption curve A in American Society of Mechanical Engineers VIII-2 (2007).

A study on mechanical properties of ferritic alloy by physical testing for nuclear power fusion reactors

The ferrite plays an important role in key component materials for nuclear power plant. The study was performed on ferritic alloys with various Cr content ranging from 10 to 38wt%. The Vickers-hardness and mechanical test results indicate that the high Cr content will cause a hardening and strengthening effect on the ferrite steel. Meanwhile, it can be concluded that the ferritic alloy suffers a reduction of toughness and a failure mode transition from ductile to brittle fracture with the increasing Cr content from the SEM fractography analysis.

Effect of Carbon Content and Intercritical Annealing on Microstructure and Mechanical Tensile Properties in FeCMnSiCr TRIP-Assisted Steels

Four TRIP (Transformation Induced Plasticity) assisted steels, three TBF (TRIP Bainitic Ferrite) steels and one TPF (TRIP Polygonal Ferrite) steel, were manufactured from three different carbon contents (0.2, 0.3 and 0.4 wt.% C), to study the evolution of their microstructure and tensile mechanical properties in 15 mm thick plates. TBF steels were subjected to the same austenitization heat treatment and subsequent bainitization isothermal treatment. The TPF steel was subjected to an intercritical annealing and subsequent isothermal bainitization treatment. All were microstructurally characterized by optical, scanning electron and atomic force microscopy, as well as X-ray diffraction. Mechanically, they were characterized by the ASTM E8 tensile test and fractographies. For the TBF steels, the results showed that when the carbon content increased, there were an increase in volume fraction of retained austenite, of the microconstituent “martensite/retained austenite” and in the tensile strength; and a decrease in the volume fraction of bainitic ferrite matrix and elongation; with an improvement in TRIP behavior due to the increase in retained austenite. The TPF steel presented around 50% ductile polygonal ferrite developing better TRIP behavior than the TBF steels. The evolution of the fractographies was ductile to brittle for TBF steels with an increase in carbon content, and for TPF, the appearance of the fracture surface was ductile.

Experimentally validated atomistic simulation of the effect of relevant grinding parameters on work piece topography, internal stresses, and microstructure

In this work, we present a fully atomistic approach to modeling a finishing process with the goal to shed light on aspects of work piece development on the microscopic scale, which are difficult or even impossible to observe in experiments, but highly relevant for the resulting material behavior. In a large-scale simulative parametric study, we varied four of the most relevant grinding parameters: The work piece material, the abrasive shape, the temperature, and the infeed depth. In order to validate our model, we compared the normalized surface roughness, the power spectral densities, the steady-state contact stresses, and the microstructure with proportionally scaled macroscopic experimental results. Although the grain sizes vary by a factor of more than 1,000 between experiment and simulation, the characteristic process parameters were reasonably reproduced, to some extent even allowing predictions of surface quality degradation due to tool wear. Using the experimentally validated model, we studied time-resolved stress profiles within the ferrite/steel work piece as well as maps of the microstructural changes occurring in the near-surface regions. We found that blunt abrasives combined with elevated temperatures have the greatest and most complex impact on near-surface microstructure and stresses, as multiple processes are in mutual competition here.

Improving the mechanical performance of a resistance spot welded 1200 MPa TBF steel

In the present work different approaches to improve the mechanical properties of a resistance spot welded 1200 MPa transformation induced plasticity-aided bainitic ferrite steel are evaluated. An extension of the welding time results in coarsening of the microstructure of the outer fusion zone and the maximum force derived by the cross tension strength test did not improve significantly. A temper pulse after a long cooling time leads to pronounced softening of the fusion zone, as determined by hardness mapping, which resulted in enhanced weld properties. A recrystallization pulse modifies the shape of the prior austenite grains at the outer fusion zone, which was visualized with electron backscatter diffraction. This also resulted in a significant improvement of maximum force. For all approaches the failure mode improved, which can be attributed to an increased fraction of high angle grain boundaries at the edge of the fusion zone.