Materials Science Forum Vol. 762

Abstract: The effect of hot deformation temperature on the deformed microstructures and evolution of microstructure and texture of a 21Cr Ti-Nb dual-stabilized ferritic stainless steel was studied using plane strain hot compression tests on a Gleeble 1500 thermomechanical simulator. The deformation was carried out at 550 - 950 °C with a strain of 0.5 at 1 s^-1. The compression was followed by fast cooling to room temperature in order to study the deformed microstructures. Some specimens were heated from the deformation stage to either 750 or 950 °C and held for 0 or 30 s in order to study the nucleation process of recrystallization. The electron backscatter diffraction technique was used to analyze the resultant microstructures and textures. Lowering of the deformation temperature increased the rate of static recrystallization (SRX) and decreased the recrystallized grain size. After deformation at 550 and 600 °C and complete SRX, beneficial γ-fibre texture formed presumably as a result of nucleation at in-grain shear bands. SRX after deformation at 750 °C or above led to the formation of harmful α-fibre textures with weak γ-fibre.

Abstract: Physical simulation of the most critical sub-zones of the heat-affected zone is a useful tool for the evaluation of the toughness of welded joints in high-strength and ultra-high-strength steels. In two high-strength offshore steels with the yield strength of 500 MPa, the coarse grained, intercritical and intercritically reheated coarse grained zones were simulated using the cooling times from 800 to 500 °C (t_8/5) 5 s and 30 s. Impact and CTOD tests as well as microstructural investigations were carried out in order to evaluate the weldability of the steels without the need for expensive welding tests. The test results showed that the intercritically reheated coarse grained zone with the longer cooling time t_8/5=30 s was the most critical sub-zone in the HAZ due to the M-A constituents and coarse ferritic-bainitic microstructure. In 6 mm thick ultra-high-strength steel Optim 960 QC, the coarse grained and intercritically reheated coarse grained zones were simulated using the cooling times t_8/5 of 5, 10, 15 and 20s and the intercritical zone using the cooling times t_8/5 of 5 and 10 s in order to select the suitable heat input for welding. The impact test results from the simulated zones fulfilled the impact energy requirement of 14 J (5x10 mm specimen) at -40 °C for the cooling times, t_8/5, from 5 to 15 s, which correspond to the heat input range 0.4-0.7 kJ/mm (for a 6 mm thickness).

Abstract: Controlling the processes, which take place during consumable-electrode shield-gas welding, is one of the main problems of the welding industry. The paper shows that under the certain conditions the electrode-metal drop and heat distribution in the weld area are influenced by the active shielding gas jet. The paper provides the results of modeling heat distribution in the weld area and active shielding gas outflow from the traditional and double-jet welding torch nozzles.

Abstract: This paper reports the effects of chemical composition on the hardness of the heat affected zone of re-austenitized and water quenched steels. Heat affected zone peak temperatures in the range 300–1350 °C were simulated using a Gleeble 3800 simulator using thermal cycles appropriate to welds with cooling times between 800 and 500 °C of 12s. The maximum softening relative to the base material occurred in the intercritical and subcritical heat affected zones at the peak temperatures of 700 or 800 °C. Usually softening was greatest when the peak temperature was 700 °C. Linear regression analysis showed that carbon, and to some extent manganese and nickel, are detrimental at the peak temperature of 700 °C, but beneficial at the peak temperature of 800 °C in respect to softening relative to the base material, whereas niobium and especially molybdenum are beneficial at both temperatures. The beneficial effects of molybdenum alloying are seen down to peak temperatures of 400 °C whereas the effect of niobium microalloying is not statistically significant at peak temperatures lower than 700 °C. The softening in the intercritical, fine-grained and coarse grained heat affected zones are discussed and the effects of the alloying elements on the hardness of the subcritical heat affected zone are compared with their known effects on martensite hardness during conventional tempering.

Abstract: Surface and interface properties of Fe-Cr, Fe-Al, and Fe-Cr-Al are studied using Exact Muffin-Tin Orbitals and Monte Carlo methods and with x-ray photoelectron and Auger electron techniques. Surface composition is investigated as a function of oxidation (heating) time. Hard x ray photoelectron spectroscopy (HAXPES) is used to scan non destructively the compositions below the surface. It is found that Cr boosts the Al segregation to the surface.

Abstract: Corrosion resistance of gas-tungsten arc welds in two 21% chromium ferritic stainless steels was benchmarked against ferritic type 441 and austenitic type 304L stainless steels. Salt spray, pitting corrosion and ferric chloride tests were carried out for autogenous welds. Also, electron microscopy and glow discharge optical emission spectroscopy examinations were made.The corrosion resistance in 21% chromium ferritic steel welds in chloride environments was seen comparable to those in type 304L, and an improvement was observed when compared to type 441 steel. However, the Mn-Cr-Ti-S sulfide domain may have an undesirable influence on end-grain pitting in ferric chloride test. Weld oxidation results in poor corrosion protection, and artificial mechanical cleaning alone is inadequate for restoring this, and hence pickling is advised.

Abstract: The grain structure and intensities of the relevant magnetic texture of the hot band affect remarkable the resulting microstructure and texture in the cold rolled and annealed nonoriented electrical steel grades based on ferritic Fe-Si alloys. The coiling or annealing after finishing the hot rolling process is an important factor, which gives rise to different grain structure across the thickness. We describe in this paper the effect of annealing in the temperature range of 750 °C up to 850°C by a confocal laser scanning microscopy technology.

Abstract: FeSi steels with and without addition of Al are widely used as electrical steels. To improve the knowledge of the effects by the addition of Si and Al on the hardening and softening under hot rolling conditions, the behaviour of the flow curves in a wide range of temperatures and deformation velocities have been studied.

Abstract: A study on the hot deformation behavior and microstructural changes of nickel based superalloy are presented. Constitutive equation allowing the calculation of peak stress was derived. A study of the effect of the temperature-deformation parameters on the kinetic of austenitic heat-resistant superalloy dynamic recrystallization and on the microstructure evolution was performed as well.

Abstract: The Stress-Strain Relationship of Materials can only be Obtained by Experimental Testing, and it is an Important Relationship Needed to Calculate the Plastic Deformation of the Materials. in this Paper, the Stress-Strain Relationships of Sintered Tungsten Powders and Swaged Tungsten Bars were Measured by Upsetting Tests on Gleeble1500, and the Relationships were Described in Four Dimensions by MatlabÔ which Displays the Relationships more Comprehensively and Clearly and Makes them Easy to be Understood and Compared with each other.