Papers by Keyword: Cold Work

Abstract: The effects of silicon (Si) addition and continuous annealing (CA) parameters on the microstructure and mechanical properties of low carbon Nb-Ti steels were investigated. Steels with and without Si were subjected to CA simulations, varying annealing temperature, line speed (LS), and cold work (CW) levels. Low-temperature thermomechanical controlled processing (TMCP) during hot rolling produced a fine polygonal ferrite matrix with uniformly distributed, spherical cementite - finer and more homogeneously dispersed in the Si-containing steel. Surface oxides in the as-rolled Si steel consisted mainly of wüstite and magnetite, with no deleterious hematite or fayalite observed due to high temperature descaling. Recrystallization during CA began near 650°C and completed above 780°C but was delayed by Si addition, higher line speeds, and moderate cold work. The final ferrite grain size remained fine, averaging 4–5 μm, across a broad annealing temperature range, aided by effective grain boundary pinning from carbonitrides. In the 690–760°C annealing range, the Si-containing steel exhibited increased strength due to solid solution strengthening, carbonitride precipitation hardening and restricted recrystallisation. Despite this, elongation was preserved through the formation of fine, soft, ductile, uniformly dispersed spherical cementite (Fe₃C) in the Si steel. Higher levels of cold work reduced strength slightly after annealing above 780°C but improved elongation due to full recrystallisation and coarsening of NbTi (C,N) particles.

Abstract: The purpose of this research is to investigate cold work effect on corrosion behavior of stainless steels of type AISI 304, AISI 316L and AISI 2101. The specimen were processed through cold work simulated by the tensile test at various percentages elongation and then tempered at 600°C for different time intervals. Two electrochemical techniques and hardness test were utilized in this investigation. The first technique was the double loop electrochemical potentiokinetic reactivation (DL-EPR) that yields the values of degrees of sensitization (DOS). The second one was the cyclic potentiodynamic polarization (CPP) to study the ability of the metals to build or repair the damaged films under localized corrosion. The DOS values from the DL-EPR tests of the samples under the same heating conditions suggested that specimens drawn at higher percentage elongation tend to have more chromium depleted areas. Also, the test specimens with more exposure time to heat were more prone to chromium deficiencies. As for the ability of the metal to create or repair damaged film after corrosion has occurred, it was found that AISI 316L had hihger corrosion resistance than AISI 304. However, AISI 2101 stainless steel had highest corrosion resistance. In this study, it was also found that AISI 2101 did not exhibit pitting corrosion, but the crevice corrosion. This could be due the fact that AISI 2101 which is a duplex stainless steel has high corrosion resistance and could trigger the crevice corrosion take place before the pitting initiation.

Abstract: This paper presents the results of a study of changes in mechanical properties, namely tensile strength, yield strength and elongation when drawing a wire from NP2 nickel (Ni 99.6). The wire samples taken along the drawing route were tested for tension. Based on the test results obtained, graphs of changes in tensile strength, yield strength and elongation were plotted depending on cold work. The approximation of the graphs made it possible to obtain equations for the change in tensile strength (UTS), yield strength (0.2 US) and elongation (δ) depending on cold work (ɛ∑). The obtained dependences are recommended to be used to predict the mechanical properties of nickel wire during drawing and when developing software for designing resource-saving drawing routes.

Abstract: Tantalum has characteristics such as excellent ductility, high corrosion resistance, high mechanical strength at high temperatures and high resistance to etching of acids and bases. Its high ductility allows the realization of large reductions without the need for intermediate heat treatment. A process for the production of tantalum wire is drawing. However, when using this process, the high ductility of the tantalum (Ta) metal causes a retention/accumulation of the Ta in the spinneret. Therefore, to be drawn is necessary that the tantalum is encapsulated in a copper tube. In this work was produced a Ta wire by means of rotary forging and drawing process. In the drawing process of the tantalum encapsulated in copper tube, was the appearance of striation on the surface of tantalum, when applied to an area reduction (AR) of approximately 22%. This fact is possibly related to the different sliding systems with consequent formation of non-hydrostatic stress fields at the interface Cu / Ta. After an area reduction (AR) of 94% the Cu was removed from the surface of the wire, through chemical etching, and this wire was drawn up to 0.43mm without retention/accumulation of the Ta in the spinneret.

Abstract: Very high cycle fatigue degradation of type 316L austenitic stainless steel, which is used as the structural material of neutron spallation sources under intensive neutron irradiation environment, is investigated by using an ultrasonic fatigue testing machine. The strain rate imposed on the structure of neutron spallation source is almost equivalent to that produced in the testing machine. The temperature on the surface was controlled by the air-cooling. The effect of strain rate on the fatigue strength is recognized to increase the fatigue limit.

Abstract: The sensitization of stainless steel type AISI304 (304SS) is evaluated as a function of pre-welding cold work and welding heat input. 304SS is cold rolled to various percentages of thickness reduction of up to 50% at ambient temperature before being TIG welded. The susceptibility of 304SS to sensitization (weld decay) is evaluated using ASTM A262, practice A and electrochemical potentiokinetic reactivation tests. The results indicate that the influence of pre-welding cold work on the degree of sensitization (DOS) is distinct and appreciable within the range of 10% to 35% CR. In addition, within this range the optimum level of cold work after which the DOS starts to decrease is found to be inversely related to the amount of welding heat input. At higher levels of cold work of ≥ 35% CR, it is found that neither the cold work nor the heat input significantly influences the amount of DOS. Microstructural investigation showed that the predominant intergranular corrosion (IGC) occurs at austenite grain boundaries and less likely at ferrite / austenite interfaces of the weld metal. Meanwhile, transgranular attack at austenite bulk matrix along the defects is rarely observed.

Abstract: Metal spinning can be used to produce hollow, axially symmetric sheet metal parts with low tooling and production costs, high flexibility, and low waste. Spinning parameters determine the quality of the spinned parts and are of interest for enabling the spinning of thick sheet metals. In this study, conventional metal spinning was conducted on a 6 mm thick low carbon steel with process below its recrystallization temperature to fabricate tube head, requiring maximum deflection of about 90º at its edge. Spinning parameters varied were temperature (at room temperature and 300°C), feed (2 mm and 5 mm), and spinning speed (200 rpm and 250 rpm). Evaluation was made on the resulted surface morphology, thickness variation, and further analysis on hardness and microstructure of the spinned tube head. The resulted tube heads were of acceptable quality in terms of surface morphology and thickness variation, while hardness and microstructure analysis showed that inner parts of the workpiece were not affected by the spinning process.

Abstract: In this study, cold rolling and annealing are used to refine the austenite grains of 301 austenitic stainless steel. The 301 austenitic stainless steel was cold rolled for 70 and 90% strain and then annealed. Effects of cold rolling factors and temperatures and annealing times on microstructure, hardness and tensile properties have been studied.

Abstract: The behaviors of precipitation and recrystallization aging at 900 after cold work in a Fe-18Cr-12Mn-0.48N high-nitrogen austenitic stainless steel were investigated by means of optical microscopy (OM) and transmission electron microscopy (TEM). The results show that precipitation and recrystallization occur simultaneously after aging at 900 for 10min. The precipitates firstly appear at dislocation, sub-boundary and inside the subgrain. Precipitation at these positions hinders the formation of recrystallization nucleus. With aging time increasing, precipitates appear in the recrystallized grain boundary and inside the grain. Precipitation at these positions hinders the growth of the recrystalized grains.

Abstract: The SSRT behavior in hydrogen dissolved hot water was investigated for cold worked SUS316L at a strain rate of 5 x 10-7/sec. The cold work to 75% thickness reduction of the as-annealed steel resulted in the hardness increase from 150 HV to 420 HV. The tensile yield stress of the cold worked specimens (CW=75%) was about 1000 MPa and the total tensile elongation was significantly reduced from 0.8% of annealed specimen to 0.14% of the 75%CW specimen. The results of EPR tests on SUS316L steel indicated that the EPR-DOS increased with increasing sensitization period at 700°C and decreased with increasing degree of cold work or reduction in thickness. In the water with hydrogen dissolution of 0.4 ppm, many IGSCC type cracks were nucleated on the specimen side surfaces, while the fractured surface was almost TGSCC. No such a SCC as observed in hydrogen dissolved water was observed after the test in oxygen dissolved water. The susceptibility to SCC increased with increasing hydrogen content in hot water. Cold work caused the reduction of the number of surface cracks and disappearance of IGSCC.