A. Natarajan

Metallographic investigations of the heat-affected zone II/parent metal interface cracking in 18Ni maraging steel welded structures

During the fabrication of a large diameter pressure vessel out of 18 Ni maraging steel by manual TIG welding, microcracks were noticed at the heat-affected zone (HAZ)/parent metal interface. The location of these cracks was very different from those reported at the fusion zone/HAZ I interface due to “constitutional liquation”. Extensive optical metallography, scanning electron microscopy and energy dispersive X-ray analyses were carried out to identify the cause for the occurrence of these cracks. It is inferred from the experimental results that the microsegregation of titanium and nickel due to repeated thermal cycling during multipass welding led to the formation of TiC/Ti(CN) and stable austenite film on the grain boundaries. Under severe thermal stresses developed during welding, microvoids generated at the interface of TiC/Ti(CN) inclusions and austenite and further propagated intergranularly due to the premature failure of the austenite films.

Development of heat treatment parameters to improve fracture toughness and grain size of an embrittled maraging steel

An embrittled 18 Ni maraging steel rolled ring was examined and samples cut from the ring were subjected to a wide range of heat treatments including high temperature solutioning and thermal cycling. The effects of these treatments on toughness were evaluated by measuring impact energy and plain strain fracture toughness. The microstructural analyses were carried out using extensive optical and scanning electron microscopy, and scanning electron fractography. It has been established that the ring was embrittled due to the combined effects of deformed structure and grain boundary precipitation of TiC or Ti (CN). Heat treatment parameters have been devised to improve the fracture toughness and grain size of the materials affected by these two types of embrittlement. It has been suggested that toughness and grain size can be improved by (a) annealing at 1223 K followed by water quenching in the case where deterioration in toughness is marginal and is caused by nonrecrystallized grains or deformation texture, and (b) solutioning at 1473 K followed by water quenching, and thermal cycling twice between room temperature and 1198 K with a holding time of 30 min at peak temperature in the case where the loss in toughness is considerably large due to excessive grain boundary precipitation of second phase particles.

Grain growth in 18Ni 1800 MPa maraging steel

The grain-growth behaviour in 18Ni8Co5MoO.4Ti maraging steel was investigated in the temperature range 1123–1323 K. Grain sizes were estimated by measuring the diameter of the equivalent area of the individual grains directly on the optical microscope using a calibrated digital eyepiece. Grain-boundary migrations and substructure analyses were done using an electron microscope. These studies indicate that the overall grain growth in the steel follows the relationship ΔD=ktn where ΔD is the increase in the grain size. However, during the initial stage, a “time lag” for the grain growth to start is observed which is attributed to the presence of highly dislocated austenitic matrix on annealing. Evidence of abnormal grain growth is also seen after annealing at 1173 K for 480 min and at 1123 K for 300 min. The growth exponents for the normal and abnormal grain growth were found to be 0.40–0.44 and 0.90–2.0, respectively. One significant deviation observed in the study wasn decreasing from 0.44-0.40 at higher temperatures during the normal growth. This has been critically discussed in the light of the unique transformation characteristics of the steel. The activation energy for growth was calculated to be 60.0–62.5 kcal mol−1, indicating the overall growth is controlled by self diffusion in γ-iron.

Assessment of Land Degradation and Its Impacts on Land Resources of Sivagangai Block, Tamil Nadu, India

A detailed cadastral level survey of land resources occurring in Sivagangai block of Tamil Nadu state, India, covering an area of about 44,600 ha, was carried out during the period 2006−2007. Based on this, 18 soil series were identified and 103 phases mapped at 1:12,500 scale. The study revealed severe sheet erosion on the uplands, heavy siltation of tanks and development of salinity/sodicity at the lowlands as major causes for the drastic decline in productivity. The study warrants systematic and timely efforts to arrest soil erosion on the uplands, proper maintenance of tanks to increase the storage capacity and recharge of the aquifers and providing drainage facilities to reclaim the lowlands and prevent the development of salinity/sodicity in the study area.

Microstructural aspects of weld repair in 18 nickel 1800 MPA maraging steel

The study of the microstructural aspects of the maraging steel weld repair has become important as this material finds extensive applications in aerospace and other strategic areas. The details available on these at present are very limited. During one of the fabrication trials of a large pressure vessel made of 18 Ni 1800 MPa maraging steel plates, 7.8 mm thick, defects were observed in the welds which were to be repaired. This called for simulated experiments. The microstructural variations observed in the repaired areas were the result of the repeated thermal cycles they had undergone. Based on this microstructural evidence, a new diagram depicting the newly formed weld zones is constructed from which the mechanical properties of the repair welds can be predicted.

Inventory and Mapping of Land Resources for Land Use Planning Through Detail Soil Survey Coupled With Remote Sensing and Gis Techniques: A Case Study in Nagenahalli Watershed, Doddaballapur Taluk, Bangalore Rural District, India

The land resources are under severe strain due to the pressure of the growing population and competing demands of the various land uses. The key to meet the present day challenges lies in the integrated management of the natural resources. Therefore the knowledge of soil and land resources with respect to their spatial distribution, characteristics, potentials, limitations and their suitability for alternate land uses helps in formulating strategies to obtain higher productivity on sustained basis. The data required for farm planning can be obtained by carrying out detailed characterization and mapping of all the existing land resources like soils, climate, minerals and rocks, ground water, vegetation, crops, land use pattern etc. From the data collected, the problems and potentials of the area for agriculture development, suitable land use options and soils management International Journal of Current Microbiology and Applied Sciences ISSN: 2319-7706 Volume 6 Number 8 (2017) pp. 314-331 Journal homepage: http://www.ijcmas.com