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Three different compositions of C–Mn–Si–Al type Q&P steels, A, B and C, were subjected to thermo-mechanically controlled processing (TMCP) at two different rolling temperatures viz. 1075 °C and 1150 °C, using two different levels of strain 0.51 and 1.1, given in single pass, followed by direct quench and partitioning (DQP) to produce a martensite – austenite structure. It was observed that Si and Al significantly influenced the formation of prior austenite grains (PAGs) during TMCP and thereby the evolution of microstructure after the subsequent Q&P treatment. With the help of constitutive models, it was found that mainly dynamic recrystallization (DRX) along with/without meta-dynamic recrystallization (MRX) were likely to occur during TMCP and their effects would be retained by immediate quench from the high temperature of processing. Electron back-scattered diffraction (EBSD) results confirmed that the PAGs were essentially DRX grains. Rolling at the lower temperature produced finer PAGs, thereby favouring the formation of larger amount of retained austenite. Effect of strain, which enhanced the enrichment of carbon in the austenite, was more pronounced at the lower rolling temperature and at higher applied strain. More than the grain refinement, dislocation density was found to be the dominant strengthening mechanism in the martensite. A maximum dislocation density of 2.18 × 1015 m−2 was observed for the steel rolled with 1.1 strain at 1150 °C. Higher rolling temperature favoured higher dislocation density in the steels, owing to the attainment of higher martensite carbon content. Consequently, TMCP with a higher rolling temperature favoured higher strength properties. In fact, the maximum strength of 1593 MPa, with yield strength of 1042 MPa and total elongation of 13% were achieved in Steel-A rolled at 1150 °C with 1.1 strain (1.1-DQP-1150 °C Steel A). After evaluating the different strengthening mechanisms operating in these steels, it was concluded that the maximum strength achieved in Steel A was primarily due to its alloy composition.

Deep drawable steels are widely used in the automobile industry for their ability to be formed into intricate shapes. These steels are essentially low carbon steels that are characterized by excellent rm (average Lankford Parameters) value. These steels can be broadly classified into three different categories, such as Al-killed (AK), Interstitial Free (IF), and Bake Hardenable (BH) grades. IF steels possess higher rm value and lower strength than AK steels. IF steels are generally processed through continuous annealing whereas AK- steels are produced preferably through the batch annealing route. Substitutional alloying elements (such as Mn, P, etc.) are often added to IF steels to produce the interstitial free high strength grade, the higher strength version of IF steels. In the BH grade of low carbon steels, yield strength can be further increased by high temperature strain aging of the steel, caused by the presence of low amounts of free carbon. In these grades, a very small amount of carbon (10–20 ppm) is deliberately kept free in the Fe matrix after the final annealing treatment. The final properties of deep drawing steels are essentially dependent upon the cleanliness, grain size, texture, and precipitation behavior of these steels. Very often these parameters have a synergistic effect on each other. Thus close control over every step in the production process is of utmost importance in order to achieve the desired properties in these grades of steel.

An evaluation of the ‘back‐annealing’ approach for the production of high strength steel sheet is presented. This approach is different from those used in conventional current practice, e.g. for rephosphorised, microalloyed, dual phase, multiphase and transformation induced plasticity steels. The principle is to retain as much as possible of the hardening due to cold rolling while gaining ductility by controlled low temperature heat treatment (back‐annealing) through recovery and/or partial recrystallisation. Unlike other processes to achieve high strength, this approach offers the possibility of cost effective high speed production in continuous annealing lines. The important role of ‘back‐annealing’ or recovery annealing in the production of ultrafine grains in steels and in the development of higher strength ultra‐thin strip cast products has also been widely recognised. In the present review, the fundamentals of the back‐annealing process are discussed in terms of the constituent phenomena of ...

Thin-layer chromatography of a variety of inert cobalt(III) complexes of different charges ( + 3, + 2, + 1, 0, −1, −3) shows that silica gel is charged negatively in contact with water. Cationic complexes do not move on an anionic silica gel bed; strong adsorption is observed between the complex cation and the negatively charged silanol group of the silica gel. Such strong binding can be reduced considerably by using electrolytes such as KI, KCl, K2SO4, etc. In the case of neutral and anionic complexes no such binding is observed. A close connection between RF values and charges of complexes was observed.

Heating trans -[Co(NH 3 ) 2 (AAUH) 2 ] 3+ salts (AAUH = 1-amidino- O -alkylurea) with amino acids (ABH = glycine, alanine, valine, or histidine) causes the evolution of ammonia and separation of [Co(AB)(AAUH) 2 ] 2+ salts, which were characterized by chemical methods; paper chromatography; and measurement of conductance, equivalent weight, and electronic and infrared spectra. Trans to cis isomerization occurs in the presence of amino acid, especially at elevated temperatures. Orange-red [Co(histŌ) (AMUH/AEUH) 2 ] 2+ (histOH = histidine; AMUH = 1-amidino- O -methylurea; AEUH = 1-amidino- O -ethylurea) shows only one band at higher energy (21052 cm −1 ) than the transition (20410 cm −1 ) of the red-violet [Co(AB)(AAUH) 2 ] 2+ . Histidinate ion behaves as an NN didentate donor rather than an NO donor. Infrared spectra indicate that the AAUH secondary amine nitrogens are the donor atoms. A strong band (1100 cm −1 ), characterized as an ether (COR) group, is observed in both AAUH and their metal complexes. A new prominent band (1230–1270 cm −1 ), assigned as a chelate ring, is observed in all metal chelates.

Acetylacetone(acacH), 8-hydroxy quinoline (OxinH), picolinic acid (PicH), dipicolinic acid (dipicH2), iminodiacetic acid (IDAH2) and dimethylglyoxime (DMGH2) react readily with [Co(NH3)2(EBG)]3+ to form the mixed chelates [Co(acac)(EBG)]2+], [Co(Oxin)(EBG)]2+, [Co(pic)(EBG)]2+ and [Co(dipic)(EBG)]+ (EBG  N1, Nu1  ethylene-dibiguanide). A number of salts of each cation have been prepared and characterized by elemental analysis, conductance and equivalent weights measurements, paper chromatography, IR spectra and electronic absorption spectra. The dipicolinate anion and iminodiacetate anion behave as bidentates in these mixed chelates.

Substituted biguanides and ethylenediamine (C2H8N2) react readily with diammine(ethylenedibiguanide)cobalt(III) hydroxide sulfate, [Co(NH3)2(EBG)](OH)SO4.(EBG = N1, N1-ethylenedibiguanide, C6H16N10), to form mixed chelates of the types [Co(AA)(EBG)]X3-nH2O (AA = methylbiguanide (C3H9N5), ethylbiguanide (C4 H11.N5), n-propylbiguanide (C5H13N5), isopropylbiguanide (C5H13N5), phenylbiguanide (C8H11N5)) and [Co(en)(EBG)]X3-nH2O (X = Cl, I, l/2SO4; n = 1, 2, 3, etc.). The complexes formed have been characterized by elemental analysis, conductance measurements, eguivalent weight determination, electronic and infrared spectra, and magnetic susceptibility measurements. They are red in color, highly crystalline, and very soluble in water. The movement of the cationic complexes on cellulose in different electrolytes was also studied. Conductance values indicate that the salts are tri-univalent electrolytes in water. Vibrational spectra provide useful information regarding the bonding sites of the title lig...

EPR and optical absorption spectra of some bis- (substituted biguanide)copper(II) bases and their corresponding chloride salts have been measured both in the solid state and in aqueous media in order to obtain information concerning the structure and nature of the bonding between the central metal atom and the ligands. Powder spectra of all copper(II) complexes provided approximate g values. In aqueous media and in nickel(II) complex matrix all the copper(II) complexes exhibited nine nitrogen superfine lines on the high field 3 2 ↔ 3 2 copper hyperfine splitting components, indicating the presence of four equivalent or nearly equivalent nitrogen atoms surrounding the copper(II) ion. The evaluation of covalency parameters indicated that the unpaired electron of the copper(II) ion spends about 35–37% of its time in the nitrogen donor sites of the biguanides. The hyperfine structure of the compounds further revealed the interaction between the unpaired electron of the copper(II) ion with four equivalent nitrogen nuclei of the title ligands. The degree of covalence of the σ-bond calculated by the hyperfine splitting is consistent with that obtained by the hyperfine structure of the copper(II) ion. α′2 values indicated that, like other strong field ligands (biguanides, β-phthalocyanine and tetraphenylporphine), substituted biguanides and their protonated forms are equally strong field in character and suggest the formation of an [CuN4] chromophore.

The EPR and optical spectra of bis(diethylbiguanide)copper(II) base and its salts and mono(diethylbiguanide)copper(II) salts have been measured both in the solid state and in N,N-dimethylformamide (DMF) in order to elucidate the structure and nature of the bonding between the central metal atom and the ligand. From the spectral data the degree of covalency of σ- and π-bonds of the copper(II) ion with the nitrogen atoms of the ligands have been calculated. The σ-bonds present a moderate degree of covalence while the in-plane π-bonds possess a strong covalent character. The covalency of the biguanide complexes is attributed to the strong σ-interaction of the copper(II) ion with deprotonated imino ligand bonding sites and electron delocalization over the chelate ring. The superfine structure of some compounds may be ascribed to the interaction of the unpaired electron of the copper(II) ion with four equivalent or nearly equivalent nitrogen atoms of the ligands. The general properties of the complexes studied, which contain the equivalent CuN42− chromophore, are summarized.

EPR and optical absorption studies have been made on some square planar pink CuN 4 2− chromophore complexes, viz. bis(amidinourea/ O -isopropyl-1- amidinourea/ O -ethoxyethyl-1-amidinourea/ O -methoxyethyl- 1-amidinourea)copper(II) complexes, in the solid state and in different solvents (water, DMF and DMSO) to investigate solute-solvent interaction, if any; spin-Hamiltonian constants of the copper(II) ion; metal-ligand bond parameters; and the environment around the copper(II) ion. In an aqueous medium nine nitrogen superfine lines on the high field 3/2 ↔ 3/2 copper hyperfine splitting component is indicative of four equivalent or nearly equivalent nitrogen atoms surrounding the copper(II) ion. The spectra obtained from different media permitted calculation of the degree of covalence of σ- and π-bonds of the copper(II) ion with the four nitrogen atoms of the ligands. The metal-ligand covalency in these compounds is comparable to that found in copper(II) phthalocyanine and porphine complexes. The covalency of the bis(ligand)copper(II) complexes is attributed to the strong σ-interaction of the copper(II) ion with a deprotonated imino ligand bonding site, and electron delocalization occurs throughout the entire chelate ring.

A series of new cobalt(III) complexes of the formulation [Co(meth-O − )(EBG)] 2+ (where meth-OH = DL -methionine, L -methionine; EBG = ethylenedibiguanide) has been prepared, and characterized using elemental analyses, conductivity measurements, visible and IR spectral data. The electronic absorption spectra reveal two ligand-field bands representing the transitions 1 A 1 g → 1 T 1 g and 1 A 1 g → 1 T 2 g . The ligands obey their expected position in the spectrochemical series. The visible spectra of all the [Co(meth-O − )(EBG)] 2+ salts are very similar, which reveals that coordination of methionine is through the amino and carboxylated groups. The mercaptide group of methionine remains uncoordinated in the mixed chelate [Co(meth-O − )(EBG)] 2+ .

The syntheses of 1-amidino-O-alkylurea sulphates and their corresponding copper(II) and nickel(II) complexes are described. These compounds exhibit bi-univalent electrolyte conductances in aqueous solution. The electronic spectra and magnetic moments of the copper(II) and nickel(II) complexes are characteristic of square planar stereochemistry. Vibrational spectra provide useful information regarding ligand bonding sites.

With acidic mixed solvents (40:60:0.2 formamide:methanol:acetic acid or 40:60:0.25 N,N-dimethylformamide:methanol:perchloric acid) cationic cis and trans isomers of cobalt(III) mixed chelates were successfully separated by thin layer chromatography (TLC) using silica gel H adsorbent. The mechanism of separation is based on an ion-exchange process. RF values of cis complexes were found to be greater than those of the trans complexes. In addition to other factors, solubilities of the complexes have a profound effect on the RF values of these cationic complexes.

(Amino acidato)dibiguanidecobalt(III) salts of the type [Co(AB)en(bigH) 2 ] 2+ have been prepared and characterized (ABH = DL -α-alanine, β-alanine, L -leucine, DL -valine and L -histidine; en(bigH) 2 = N 1 ,N 1 -ethylenedibiguanide). A number of salts of each cation have been prepared, and their ionic nature has been confirmed by conductance measurements. IR spectra have furnished positive information regarding the bonding sites of the title ligands. Electronic spectra revealed expected trends. In the case of the [Co(hist)en(bigH) 2 ] 2+ cation, the histidinate (hist) anion behaves as a bidentate NN donor not as an NO donor.

Copper(II) complexes of substituted biguanides have been studied by ESR spectroscopy in water, in their polycrystalline form and in the corresponding nickel(II) complex matrix. In aqueous solution, nine nitrogen superfine lines on the higher field 3/2 a3 3/2 copper hyperfine splitting component is indicative of four equivalent or nearly equivalent nitrogen atoms surrounding the copper(II) ion. α′ 2 values indicate that like biguanide, 1-amidino-O-alkylureas, β-phthalocyanine and tetraphenylporphine, substituted biguanides and their protonated forms are equally strong-field ligands. The evaluation of the covalency parameters indicate that the unpaired electron of copper(II) spends about 36% of its time in the nitrogen donor sites of the ligands.

A phosphodiesterase (orthophosphoric diester phosphohydrolase, EC 3.1.4.1) which has been partially purified from the lysate of P22(C1)-infected spheroplasts of Salmonella typhimurium is dependent on either K+ or Mg2+ for its activity and displays maximal activity in the presence of both. The enzyme is practically free from interfering activities and specifically hydrolyses single-stranded polyribonucleotides leading to the production of 5′-nucleotides. The homopolymers are hydrolysed in the following sequence: poly A > poly U > poly C . Poly C and tRNA are poorly hydrolysed, and poly I is not hydrolysed at all. The enzyme is most active at neutral or slightly alkaline pH. It is thermolabile but could be protected against heat denaturation by native and denatured DNA's as well as by poly A. During the hydrolysis of homopolymers no oligonucleotides could be detected as intermediate products, which indicates the exonucleolytic nature of the enzyme. Though there are some differences in properties, the behaviour of this phosphodiesterase is similar to that of ribonuclease II of Escherichia coli.

FIG. 2. Upper part: zero strain resistivity pa as a function of l/T. From the slope of the curve below 3°K one obtains F~ = 1.5 x 10-s eV (for a definition of cs see reference 2). Lower part: The ratio px/pO measured at x = 3 x 10s dyn/cm2 as a function of l/T for the longitudinal case A and the two transverse cases B and C. The slope of the curves below 5°K yields l = 1.6 x 10-4 eV (see text). TRANSPORT 259