Showing papers by "Steel Authority of India published in 1998"

Weldability and toughness evaluation of pressure vessel quality steel using the shielded metal arc welding (SMAW) process

Abstract: The present study was carried out to assess the weldability properties of ASTM A 537 Cl. 1 pressure-vessel quality steel using the shielded metal arc welding (SMAW) process. Implant and elastic restraint cracking (ERC) tests were conducted under different welding conditions to determine the cold cracking susceptibility of the steel. The static fatigue limit values determined for the implant test indicate adequate resistance to cold cracking even with unbaked electrodes. The ERC test, however, established the necessity to rebake the electrodes before use. Lamellar tearing tests carried out using full-thickness plates under three welding conditions showed no incidence of lamellar tearing upon visual examination, ultrasonic inspection, and four-section macroexamination. Lamellar tearing tests were repeated using machined plates, such that the central segregated band located at the midthickness of the plate corresponded to the heat-affected zone (HAZ) of the weld. Only in one (no rebake, heat input: 14.2 kj cm-1, weld restraint load: 42 kg mm-2) of the eight samples tested was lamellar tearing observed. This was probably accentuated due to the combined effects of the presence of localized pockets of a hard phase (bainite) and a high hydrogen level (unbaked electrodes) in the weld joint. Optimal welding conditions were formulated based on the above tests. The weld joint was subjected to extensive tests and found to exhibit excellent strength (tensile strength: 56.8 kg mm-2, or 557 MPa), and low temperature impact toughness (7.4 and 4.5 kg-m at-20 °C for weld metal, WM, and HAZ) properties. Crack tip opening displacement tests carried out for the WM and HAZ resulted in δm values 0.36 and 0.27 mm, respectively, which indicates adequate resistance to brittle fracture.

SCADA control systems in integrated steel plants

Abstract: Supervisory control and data acquisition (SCADA) systems have been in existence for a number of years now, They are employed in various applications which involve the simultaneous acquisition of large amounts of data, real-time processing, display and supervisory control. SCADA based controllers have been incorporated in integrated iron and steel plants in two packages-one to meet the requirements of SCADA control for electricity supply systems and a second for gas/heat, water supply and metallurgical facilities. Computer-based systems for SCADA help control system operators to achieve real-time data acquisition, processing, display and control of data pertaining to large process environments. Systems engineering techniques provide solutions by optimally configuring state-of-the-art hardware and appropriate software. Aspects of expansion and maintenance are given due regard to enhance the useful life of such control systems.

Microstructure and Properties of Quenched-and-Aged Plates Produced from a Copper-Bearing HSLA Steel

Abstract: For the first time in India, quenched-and-tempered (Q and T) plates of copper-bearing high-strength low-alloy (HSLA) steel have been commercially developed for naval structural applications. A 50 ton production heat was made through electric arc furnace (EAF)-vacuum are degassing (VAD) route and continuously cast into 170 mm thick slabs. These slabs were conditioned, reheated in walking-beam furnace and hot rolled in plate mill into plates of 10 to 16 mm thickness. The as-rolled plates were hardened through oil quenching and subsequently tempered (aged) at 630 C to achieve the combination of high-strength and good low-temperature impact toughness. The microstructures of heat treated plates showed fine acicular ferrite with grain sizes ranging between ASTM No. 9 and 10. From the standpoint of tensile properties, Q and T plates of all thicknesses exhibited significantly higher yield strengths than the minimum stipulated value of 552 MPa for HY-80/HSLA-80 steels. The elongation (22.20 to 26.00%) and reduction in area (62.12 to 67.62%) values achieved also exceeded the respective minimum requirements of 20 and 50% stipulated for such steels. The trend in variation of Charpy V-notch (CVN) impact energies at room temperature, {minus}18, and {minus}62 C not only showed significantly higher values than that stipulatedmore » for HY-80 and HSLA-100 steels at {minus}18 C, but also indicated that the CVN impact energies achieved (105.15 to 144.25 J) at {minus}62 C were higher than the estimated value of 90 J for HSLA-80/HSLA-100 steels at this temperature.« less

Estimation of early fatigue damage in heat treated En-8 grade steel

Abstract: Generally, the failure of major machinery parts is due to fatigue damage Because of the structural inhomogeneity of metals, fatigue damage may sometimes occur significantly below the yield strength of the material due to microplastic deformation at low stress levels Commercial En-8 grade steel (widely used for making secondary metalworking products) was used to estimate the fatigue damage response during cyclic loading nearer to the fatigue endurance limit Estimation of fatigue damage was carried out with the aid of a nondestructive testing (NDT) method, that is, Elastosonic measurement of fatigue damping coefficient and slope of fatigue damping curves Results indicate that fatigue damage increases in annealed En-8 steel with an increase in peak stress and with an increase in the number of cycles However, for hardened and tempered En-8 steel, experimental results may not provide a true indication of fatigue damage during fatigue loading nearer to the endurance limit, most likely due to the more homogeneous structure Generally, fatigue failure occurs in this grade of steel due to microcrack generation in the cementite of the pearlite phase of annealed steel

Microstrength Characteristics of High Ash Coke

Abstract: Experiments were carried out to determine the microstrength of different high ash coke samples obtained from 2 and 250 kg ovens. Microstrength of coke is determined using small quantity of sample (50 m/) with small sample size (3-6 mm) and is an indicator of the inherent strength of the coke matter. The microstrength values obtained were then correlated with the ash, VM/reflectance and fluidity of the parent coal and also conventional strength indices of coke like M10 and CSR. The correlations obtained indicate that except in the case of very strong coke, correlation exists between microstrength, M10 and CSR values of coke.

Post-traumatic epilepsy: its complications and impact on occupational rehabilitation--an epidemiological study from India.

Abstract: The objective of this study was to assess the prevalence of seizure disorder, neuropsychiatric disorders and reproductive outcome of employees with post-traumatic epilepsy (PTE) and their effect on occupational rehabilitation. A case-comparison group study design was used to compare 30 subjects with PTE with (1) 129 non-PTE and (2) 55 non-PTE matched control employees. The 55 non-PTE matched controls were selected from the 129 non-PTE employees on the basis of age, age at onset of seizure, age at marriage and length of employment. The PTE group had a lower fertility rate than the controls and more neuropsychiatric disorders and seizure disability. PTE employees were more occupationally rehabilitated than non-PTE employees (p = 0.033). Of the 30 PTE subjects, thirteen who were rehabilitated by placement had more seizure disability (p = 0.007) and a higher fertility rate (p = 0.018). High prevalence of seizure disability and increased fertility rate among the placed PTE employees suggested that there might be some association between severity of seizures and increased production of live offspring and work placement. Work suitability or placement should not be judged on clinical assessment only but psychosocial seizure assessment, disability evaluation and other psychometric tests which are of equal importance.

Process for the removal of carbon, silicon, manganese and sulphur from molten high carbon ferrous metal

Abstract: An improved process for the removal of silicon, carbon, manganese and sulphur together in a single reaction vessel (ladle) comprises the steps of: a) adding a mixture of iron oxide containing material and a flux into a ladle; b) adding high carbon molten ferrous metal (hot metal) into the said mixture for the oxidation of silicon, carbon, and manganese present in the hot metal, the reaction resulting in the formation of a slag which floats on the surface of the hot metal; c) introducing magnesium below the surface of the hot metal in a perforated plunger, which is gradually lowered into the molten hot metal till it touches the bottom of the ladle and, immediately after the plunger touches the bottom of the ladle, lifting the plunger to a position such that a gap between the bottom of the ladle and the head of the plunger, ranging between 5 to 50 mm is created; whereby magnesium vapour escapes through the holes of the plunger head into the hot metal resulting in the desulphurisation of the molten hot metal; d ) intimate mixing of the molten hot metal and the unreacted iron oxide present in the slag by the turbulence produced during the release of the magnesium vapour, resulting in further oxidation of silicon and manganese and reduction of iron oxide into iron; and e) removing the slag at the completion of the reaction. A corresponding apparatus is also provided.