Sanak Mishra

Analysis of the temperature dependence of strain-hardening behavior in high- strength steel

The stress-strain data of a high-strength low-alloy (HSLA) steel were measured at different temperatures and analyzed in terms of strain-hardening laws proposed by Hollomon,[1] Ludwik,[2] Swift,[3] and Voce.[4] Four methods of analysis, as suggested by Kleemola and Nieminen (K-N),[7] Crussard and Jaoul (C-J),[16] Ramani and Rodriguez (R-R),[11] and Guimarães (G),[15] have been employed. The C-J analysis has been extended to the Voce equation for the first time. The results have been discussed in terms of the linear correlation coefficient and error in the estimation of uniform strain. The Voce equation has been found to describe the flow be-havior most accurately. The observed increase in flow stress in the dynamic strain aging (DSA) range has been explained in terms of temperature-dependent strain-hardening parameters. It has been established that with increase in the value of the Voce strain component, nv, the magnitude of the saturation stress approaches that of the ultimate tensile stress. A linear relationship has been established between ultimate tensile stress and saturation stress.

New information on texture development in regular and high-permeability grain-oriented silicon steels

The formation of the Goss texture in Fe-3 Pct Si has been studied using crystallite orientation distribution function (ODF) analysis. Textural and microstructural changes through various stages of processing have been investigated for silicon steel with MnS (regular) as well as for steel with a combination of MnS and A1N (high permeability) as grain-growth inhibitor. In both cases the genesis of the final sharp cube-on-edge texture seems to lie in the grains already present in the Goss position in the surface layers of the hot-rolled strip. The major difference in the mechanism of Goss texture formation in the two types of steels is with respect to the relationship between the strengths of the {011}〈100〉 and {111}〈112〉 components through successive processing operations.

Co-precipitation of copper-manganese sulphide in Fe-3%Si steel

Abstract In Fe-3%Si grain-oriented steel, there are two prerequisites for development of the sharp {110}〈001〉 Goss texture during secondary recrystallization: the presence, in the primary recrystallized matrix, of (i) a {110}〈001〉 texture component, and (ii) a dispersion of second-phase particles of appropriate number and size to inhibit normal grain growth. The nature of the dispersion is dependent on the prior processing history, particularly slab reheating and hot rolling practice. The present paper gives, in the first part, a breif review of the role of manganese sulphide as an inhibitor of normal grain growth in Fe-3%Si. The second part of the paper deals with novel information obtained on the precipitation of manganese sulphide, and the co-precipitation of copper-manganese sulphide, in hot-rolled strips of commercially produced grain-oriented silicon steel. It was observed, using transmission electron microscope energydispersive analysis of X-rays (TEM-EDAX), that an increase in copper concentration in the sulphide particles was associated with (i) a change in shape from spherical to parallelopipedal to cuboidal, and (ii) a simultaneous decrease in size.

Influence of microstructure on the premature failure of a second-intermediate sendzimir mill drive roll

Although a precise understanding of roll failure genesis is complex, the microstructure of a broken roll can often unravel intrinsic deficiencies in material quality responsible for its failure. This is especially relevant in circumstances when, even under a similar mill-operating environment, the failure involves a particular roll or a specific batch of rolls. This paper provides a microstructural insight into the cause of premature breakage of a second-intermediate Sendzimir mill drive roll used at a stainless steel sheet rolling plant under the Steel Authority of India Limited. Microstructural issues influencing roll quality, such as characteristics of carbides, tempered martensite, retained austenite, etc., have been extensively studied through optical and scanning electron microscopy, electron-probe microanalysis, image analysis, and x-ray diffractometry. These are discussed to elucidate specific microstructural inadequacies that accentuated the failure. The study reveals that even though retained austenite content is low (6.29 vol%) and martensite is non-acicular, the roll breakage is a consequence of intergranular cracking caused by improper carbide morphology and distribution.

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

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.

Defects in rails

The performance of rails in service is greatly influenced by the presence of metallurgical defects. Hydrogen-induced shatter crack is the most prominent among these and has been discussed in detail. Principal causes of rail failure have been outlined and different types of defects leading to failure of rails during service have been documented. Wear of rails which accounts for reduced life has been considered. Influence of microstructure on wear rate has been described.

Orientation distribution function analysis of the recrystallization texture in a boron-treated deep-drawing steel

The textural components present in a boron-treated deep-drawing quality nonaging steel, processed and annealed in the mill, have been determined using the orientation distribution function (ODF) analysis technique. The main components are a 〈111〉 fiber parallel to sheet plane normal or normal direction, ND, and an incomplete 〈337〉∥ND fiber. Minor {110}〈001〉, {310}〈001〉, {001}〈110〉, and {110} 〈110〉 orientations were also found. The texture on the whole is somewhat similar to that in A1-killed steels, but not as strongly developed. It is expected that this boron-treated steel would be suitable for moderate forming applications.

On the formability of sheet steels

AbstractFormability of sheet steel in stamping operation primarily depends on strain hardening exponent (n), average plastic strain ratio (

Effects of tempering in a ferrite-martensite steel

\bar r