One trend in today’s structural design for automobiles is towards application of stainless Steel in addition to traditional carbon Steel. This is mainly due to the advantages offered by stainless steel to the designer, i.e. its high corrosion resistance, heat resistance, strength and formability. Welding of austenitic stainless steel involves a high risk of solidification cracking due to low melting eutectics containing different kinds of impurities and to accumulated strain behind the weld pooi in the mushy zone. As a result, the quality of stainless steel welded joints will greatly be affected which may give cause for safety concerns. The intention of this study was to investigate the hot cracking sensitivity of laser welded fully austenitic stainless steels and to determine the critical local strain and strain rate from the formation of solidification cracks. C02-laser welding experiments were conducted using the steel X8CrMnNi19-6-3 (Nirosta H400). Solidification cracking susceptibility was examined with the help of the Controlled Tensile Weldability (CTW) Test developed by BAM Federal Institute for Materials Research and Testing in Berlin. The critical strain and strain rate of solidification cracking was measured at the surface of the workpiece directed to the laser beam in the close vicinity of the weld pool by using the Digital Image Correlation (DIC) technique and diode laser as the illuminating source.
In-situ analysis of solid state phase transformation in TRIP-aided steels by synchrotron diffraction
(2011)
Energy dispersive synchrotron diffraction (EDXRD) analysis and 3 dimensional digital image correlations were conducted to investigate the stress and strain effected transformation behavior during tensile loading of low alloyed TRansformation Induced Plasticity (TRIP) steel. This technique allowed for phase specific stress measurement during certain tensile load steps in the elastic and also plastic regime. Additionally the simultaneous determination of the load dependent phase content was realized. The results show that the martensite transformation starts only after exceeding the overall yield point and is finished before reaching the uniform elongation, whereas a large portion of the austenite remains unchanged in the structure. Furthermore, the martensite transformation related to the stress in the γ-phase and α-phase was analyzed and quantified.
Direct measurement and quantification of phase transformation in a low-alloyed transformation induced plasticity steels depending on the tensile load as well as determination of the real true stress and true strain values were carried out in-situ using high energy synchrotron radiation. Digital image correlation technique was used to quantify more precisely the true strain values. The aim of the work was to obtain a better understanding of the phase transformation of commercial low-alloyed transformation induced plasticity steel depending on the true strain and true stress values.