Papers by Keyword: Low Alloyed Steel

Abstract: The application of “masteralloys” as alloying carriers in Powder Metallurgy (PM) steels enables the introduction of highly oxygen‑sensitive alloying elements for advanced PM‑steels, by using a tailored liquid phase. The characteristics of the liquid and its interaction with the iron base powder are determining factors for final microstructure and dimensional behaviour. In this study, theoretical calculations and experimental findings are presented for the masteralloy systems Fe_Mn_Si_C, Fe_Cr_Si_C and Fe_Mn_Cr_Si_C. Lowered melting temperatures and narrow melting temperature intervals could be achieved. The interaction between Fe base material and the masteralloys was studied by infiltration and DTA experiments. It was found that by adjusting the C and Si content in the masteralloy, liquids with widely varying properties could be obtained. This might be a key for tailoring microstructures, properties and dimensional stability of advanced PM‑steels.

Abstract: The research followed the development of deep joint brazing joints with economic efficient materials between the reinforcement, made from sintered wolfram carbide, and the support, drill bit made from low alloy steel with chromium, from the earthmoving equipment. The brazing procedure selected is heating until the semi-products of the addition materials reach melting temperature, with oxyacetylene flame slightly carburized. The pressure of reducing manufacturing costs for drill bits highlighted the need to replace brazing alloys Ag156 according to SR EN ISO 17672 with coated rods type VIAg140R, which are less expensive and successively deposit two layers in one melt, one buffer layer and a filler layer. The buffer layer has a high moistening capacity of sintered wolfram carbides; it contains Ag156 that comes from the coat of the covered rods, in which it participates with up to 10%. The filler layer of the brazed joint is made out of Ag140. The global chemical composition of the deposited metal with VIAg140R complies with prescriptions SR EN ISO 17672 for Ag140. Metallographic analysis and sclerometric tries of specific area of the brazed joints did not highlight any embrittlement imperfections, which lead to the possibility of suggesting the new technology for brazing and extending it to a large number of similar joints

Abstract: Abstract. Paper presents the results of the studies of the service properties of the 235JR and S355J2 low alloy steels subjected to the surface modification by friction-mechanical treatment, as tested in sea water simulated solution. The resistance of steels used in the marine vessels to the wear, cavitation erosion, general corrosion, corrosion cracking and hydrogen absorption has been examined. To evaluate the effect of the surface treatment, the comparative studies of the service properties of steels before and after treatment have been considered.

Abstract: In the paper low (LCF) and high cycle fatigue (HCF) behavior of the S355J2 low alloyed steel after surface frictional-mechanical treatment in a corrosive environment (3.5 % NaCl ) has been presented. The treatment was used in order to improve mechanical and fatigue properties of the steel. Obtained experimental results indicate an insignificant improvement of mechanical and fatigue properties of the strengthened steel under the conditions of corrosion at constant amplitude cyclic loading. It is particularly noticeable in the range of low-cycle fatigue.

Abstract: In the paper low (LCF) and high cycle fatigue (HCF) behavior of the S235JR low alloyed steel after surface frictional-mechanical treatment in a corrosive environment (3.5 % NaCl ) has been presented. The treatment was used in order to improve mechanical and fatigue properties of the steel Obtained research results indicate an insignificant improvement of mechanical and service properties of the strengthened steel under the conditions of corrosion at constant load. Under variable loads and operating corrosion, fatigue strength results of the steel do not unequivocally confirm a favourable effect of the applied treatment. It is particularly noticeable in the range of low-cycle fatigue.

Abstract: Low alloy steels are an attractive option for high performance structural applications due to cost and availability factors. A low carbon low alloyed steel, DMR 249A, was developed for strategic applications by Indian Navy at Steel Melting Shop II, Bokaro Steel Plant (SMS II, BSL). This paper enumerates the detail process variables modified for this development. DMR 249A grade was having the specified gas contents of hydrogen <2 ppm in final product for the avoidance of detrimental phenomenon like “Hair Line Cracks”. So the Hydrogen content of liquid steel was to be less than 3 ppm and this demand vacuum treatment of the steel. In absence of any Degassing unit at SMS II, BSL, making of DMR 249A steel was a challenging task. The hydrogen content of steel was controlled through restriction of hydrogen in input raw materials, control in degree of deoxidation during tapping, slag basicity at ladle furnace, argon rinsing regime and cooling of slabs i.e. control over diffusion of H₂. The steel was produced with the existing infrastructure at Bokaro Steel Plant with various alloying elements and processed suitably to obtain the desired yield strength, toughness and gaseous content. The control was exercised at various stages of steel making and hot strip rolling to enable achievement of a higher degree of consistency in mechanical properties and microstructure. Quality fulfillment was a great challenge without vacuum degasser unit but Bokaro successfully made the steel with 100% customer satisfaction.

Abstract: Since low alloyed sintered steels were introduced in the market of the structural parts, we have followed the evolution of a material with poor mechanical properties and any uniformity (in the sense of reproducibility) to materials that today are produced with high reliability and performance. The working efficiency could be equivalent in many cases with the best wrought steel, and maintaining a good margin in terms of cost and competitively. In this paper a complete review of the topic is accomplished, from the early times when the first parts were made by plain iron or iron-carbon, going through the different alloying systems: Fe-Cu, Fe-P, Fe-Cu-Ni-Mo, and more recently Fe-Cr-Mo and Fe-Mn. The development in processing routes has been considered too. The main milestones in the field of new alloying systems have been: 1) the introduction of Cu in 60-70’s, 2) the new complex systems with Cu-Ni-Mo in the 80’s and 3) the introduction of alloying elements with high oxygen affinity (in the late 90’s). Regarding the milestones in processing could be considered: 1) the development of new mixing procedures, 2) the warm compaction and high velocity compaction, 3) the improvements in sintering control and high temperature sintering. Several decades of research and innovation, acting on the processing system (mixing, pressing, sintering, post-sintering operations,…) and on the alloying system (from the earliest times with plain iron to complex systems used today), has allowed us to have a highly competitive materials, in terms of performance, and processes in terms of cost. The future is still open to new developments.

Abstract: Many components can reach or exceed 109 cycles in their service time. When fatigue life is beyond 106, the Wöhler S-N curve was always considered to be asymptotic in horizontal axis, but the fatigue behaviour over 106 cycles can not be neglected. It is not usual to carry out a fatigue test beyond 109 cycles due to the conventional fatigue test’s constraints, time consuming and expensive. High strength steel is widely applied in automobile, railway industry after surface treatment in order to improve performance of material in practice. Carburizing process hardens surface to increase wear and fatigue resistance and shot peening has a beneficial effect on the material fatigue strength from the surface residual compressive stresses. A piezoelectric gigacycle fatigue machine is used to do the tests in gigacycle regime on specimens with different surface treatments. The effect of different surface treatments is investigated in gigacycle regime at a frequency of 20KHz with a fixed stress ratio R=0.1 at room temperature. Moreover, Scanning Electron Microscopy (SEM) observations of fracture surfaces are analyzed to evaluate the mechanism of damage related to surface treatments, microstructure scored inclusion size. The role of inclusions and microstructure is emphasized at 109 cycles.

Abstract: In this paper we try to summarize the research activities of the PM group in the University Carlos III of Madrid. This research group is highly devoted to PM activities covering different fields (both under the point of view of the materials and the processes). In the PM lab powders can be produced by spray pyrolysis, mechanical alloying and water/gas atomization. These powders can be processed by pressing and sintering, powder injection moulding, isostatic pressing,… Sintering facilities cover vacuum and gas controlled sintering. Regarding the materials, in the group we have different research lines covering low alloyed steels, stainless steels, HSS, ferrites, metal matrix composite (Al and Fe base), Ti, intermetallics, ceramics with functional and structural propierties, … In this paper we describe slightly some of the recent developments produced in the group which is not exhaustive (are there a few more) but representative about we are doing at present.