Boriding kinetics of H13 steel

It is known that boriding has been employed to increase the service life of parts such as orifices; ingot molds, and dies for hot forming made of AISI H13 steel. In this study, case properties and kinetics of borided AISI H13 steel have been investigated by conducting a series of experiments in Ekabor-I powders at the process temperature of 1073, 1173 and 1273 K for periods of 1-5 h. The presence of borides FeB and Fe₂B of steel substrate was confirmed by optical microscopy and scanning electron microscopy (SEM). The results of this study indicated that the morphology of the boride layer has a smooth and compact morphology, and its hardness was found to be in the range of 1650-2000 HV. Transition zone observed between the hard boride coating and the matrix was relatively softer than the substrate. The kinetics of boriding shows a parabolic relationship between layer thickness and process time, and the calculated activation energy for the process is 186.2 kJ/mol. Moreover, boriding parameter BOP, which is only a function of boride layer thickness and activation energy, has been suggested for the prediction of layer thickness in boriding of AISI H13. There is a reasonable correlation between the progress of boride layer thickness and proposed time-temperature-compensated parameter. Similar findings have been found when it is applied to another steels including tool and low alloy steels, as well as Armco iron.     

Transformation kinetics of the ferromagnetic alloy Mn-Al-C

Mn1-x-yAlxCyforms a ferromagnetic metastable tetragonal τ-phase in the composition range0.42 leq x leq 0.47and0 leq y leq 0.021. Its high unaxial magnetocrystalline anisotropy makes it an interesting candidate for a permanent magnet. In order to investigate the kinetics of the transformations which occur in this system, we established the time-temperature-transformation diagram of a ternary alloy with the composition Mn0.538Al0.446C0.016. It was homogenized for 2 h at 1375 K, quenched, and subsequently isothermally annealed at temperatures between 625 K and 1025 K for various times ranging from one minute up to seven days. The quantitative phase analyses were performed by means of x-ray diffraction and stereological analysis of the microstructures. The addition of carbon increases the stability of the τ-phase, thereby allowing longer annealing times for the formation of single-phase samples.     

Transformation texture of allotriomorphic ferrite in steel

Abstract

Many aspects of the crystallographic texture which develops when austenite transforms into martensite or bainite are well established because the process by which the parent lattice is transformed into that of the product is mathematically defined. This is not the case when the ferrite forms by a reconstructive mechanism. The allotriomorphic ferrite nucleates heterogeneously at austenite grain boundaries, and although a reproducible, low energy orientation relationship is expected to exist between the ferrite and one of the austenite grains with which it is in contact, there are reports that the ferrite can simultaneously adopt this orientation with more than one austenite grain. The authors examine this possibility using crystallographic theory in order to assess the probability of such events as a function of the strength of the texture within the austenite before its transformation.     

Microstructure and mechanical properties of a hot pressing-dynamic partition treated steel

The microstructure and mechanical property of improved press-hardened steel with hot pressing combined dynamic partitioning (HP-DP) treatment are presented. Microstructure of the steel subjected to HP-DP treatment is featured by multi-martensite phases and the retained austenite (RA) phase with carbon content gradient. Compared with conventional hot-pressed samples, the HP-DP samples show better tensile property especially ductility. The effect of HP-DP parameters on the evolution of RA and mechanical property is then discussed. Finally, hot pressing of a double U-shaped part using both 22MnB5 steel sheet and the developed HP-DP steel sheet was carried out with exact control of part temperature at the end of hot pressing followed by air cooling.     

Two types of kinetics of corrosion cracking of a high-strength steel with a martensitic structure

The authors are grateful to S. L. Namm, V. G. Khanzhin, and A. A. Petrunenkov for useful discussion, and also to V. I. Chizhikov and V. V. Savele'va for help in electron microscopic examination.     

The kinetics of steel corrosion in sea water

The kinetics of corrosion damage accumulation in stainless steels of various systems was studied using samples exposed in a model aqueous NaCl solution and in sea water. The time variation of the degree of corrosion damage corresponds to a reaction of the first order. The values of the corrosion activation energy and a parameter characterizing protective properties of a protective film on the metal surface are determined.     

Spreading kinetics of liquid metals on mild steel

Abstract

The kinetics of the spread of molten copper, Cu–Mn alloy, and aluminium on solid mild steel were investigated at temperatures from 800 to 1100°C under an anhydrous borate flux. The molten copper and Cu–Mn alloy seem to spread largely by surface diffusion and the spread of molten aluminium follows linear kinetics. The spread coefficient, interfacial tension, and work of adhesion are evaluated from the relationship between an observed rate constant and Yin's theoretical formulism. The spread of molten copper on mild steel indicates complete wetting, while the spread of molten aluminium shows the least wetting. In the aluminium–mild steel spread system, the spread tends to increase with temperature: with increasing temperature, the spread coefficient increases and the interfacial tension decreases, while the work of adhesion remains much the same.

MST/743     

Corrosion kinetics and patina evolution of galvanized steel in a simulated coastal-industrial atmosphere

The corrosion kinetics and patina (corrosion products) layer evolution of galvanized steel submitted to wet/dry cyclic corrosion test in a simulated coastal-industrial atmosphere was investigated. The results show that zinc coating has a greater corrosion rate during the initial period and a lower corrosion rate during the subsequent period, and the patina composition and structure can greatly affect the corrosion kinetics evolution of zinc coating. Moreover, Zn₅(OH)₆(CO₃)₂ and Zn₄(OH)₆SO₄ are identified as the main stable composition and exhibit an increasing relative amount; while Zn₁₂(OH)₁₅Cl₃(SO₄)₃ cannot stably exist and diminish in the patina layer as the corrosion develops.     

Final-stage steel failure kinetics examined by acoustic emission

Acoustic emission has been applied to the failure of steels in various classes in the final stages of strain as affected by the state of strain and the rigidity of the loading system. In the final stages, the informative parameters of acoustic emission characterizing the failure are the amplitude of the discrete emission, the level of continuous emission, the number of oscillations, and the duration of the discrete emission.Translated from Problemy Prochnosti, No. 1, pp. 82–90, January 1996.     

The kinetics of structure transformations in martensitic structural steel

The behavior of the acoustic properties and acoustic-emission activity of 08Kh14AN4MDB (chrome-nitrogen-nickel-molybdenum-copper-niobium) structural steel is investigated in the process of annealing and after quenching. The significant information content of acoustic methods is demonstrated, especially that of the acoustic emission method, from the standpoint of investigating the kinetics of the processes occurring in materials of nonequilibrium structure.     

Anomalous kinetics of lath martensite formation in stainless steel

The kinetics of lath martensite formation in Fe–17·3 wt-%Cr–7·1 wt-%Ni–1·1 wt-%Al–0·08 wt-%C stainless steel was investigated with magnetometry and microscopy. Lath martensite forms during cooling, heating and isothermally. For the first time, it is shown by magnetometry during extremely slow isochronal cooling that transformation rate maxima occur, which are interrupted by virtually transformation free temperature regions. Microscopy confirms martensite formation after athermal nucleation of clusters followed by their time dependent growth. The observations are interpreted in terms of time dependent autocatalytic lath martensite formation followed by mechanical stabilisation of austenite during the transformation process.     

In situ synchrotron X-ray study of bainite transformation kinetics in a low-carbon Si-containing steel

The bainite transformation in a low-carbon Si-containing steel has been studied in situ by synchrotron X-rays. While the austenite is homogeneous prior to transformation, the carbon distribution becomes nonuniform as bainite plates form. This is because of the different degrees of physical isolation of films and blocks of residual austenite. The method for converting dilatational strain into bainite volume fraction, using lattice strain as a reference, during isothermal transformation was found to overestimate it. The bainitic and martensitic ferrite did not exhibit a tetragonal unit cell due to the low-carbon content of the steel and the high transformation temperature.     

Microstructure of cryogenic treated M2 tool steel

Cryogenic treatment has been claimed to improve wear resistance of certain steels and has been implemented in cutting tools, autos, barrels etc. Although it has been confirmed that cryogenic treatment can improve the service life of tools, the underling mechanism remains unclear. In this paper, we studied the microstructure changes of M2 tool steel before and after cryogenic treatment. We found that cryogenic treatment can facilitate the formation of carbon clustering and increase the carbide density in the subsequent heat treatment, thus improving the wear resistance of steels.     

Transformation kinetics of unalloyed and high Mn austempered ductile iron

Abstract

The kinetics of bainitic transformation was studied in unalloyed and 1%Mn alloyed ductile irons. The samples were subjected to different austempering heat treatment cycles in dilatometry equipment. The results showed the effect of Mn on delaying the start and end of bainitic transformation, supposedly because of Mn segregation to the primary austenite grain boundaries. Decreasing austempering temperature led to precipitation of carbides inside the lower bainitic ferrite plates and therefore, more dilatation during the bainitic reaction. The dilatometric results were also used to calculate n and k in the Johnson-Mehl-Avrami equation and to derive the time-temperature-transformation diagrams. X-ray results were used to calculate the quantitative amount of precipitated carbides within lower bainitic ferrite and the dilatation during austempering.     

Effect of nitrogen and vanadium on austenite grain growth kinetics of a low alloy steel

Austenite grain growth kinetics in a steel containing 0.4% C, 1.8% Cr with different nitrogen contents (in the range 0.0038–0.0412%) and a micralloying addition of 0.078% V were investigated. The investigations were carried out in an austenitising temperature range of 840–1200 °C for 30 min. The results of investigations showed that N promotes the grain growth of austenite. The microalloying addition of vanadium protects the austenite grain growth because of carbonitride V(C,N) precipitation and the grain boundary pinning effect of undissolved particles of V(C,N). Using a thermodynamic model, the carbonitride V(C,N) content, undissolved at the austenitising temperature was calculated. At temperatures when a coarsening and dissolution of carbonitride occurs, the austenite grains start to growth. The effect of nitrogen on the type of chord length distribution of austenite grains was analysed.     

Calculation of the kinetics of steel austenization in laser heating

We examine both the kinetic features and the present the formulation of the problem dealing with the distribution of carbon concentrations in an austenite, as well as the motion of the phase separation boundaries in the case of laser heating of pre-, post-, and eutectoid steels. We also obtain results from calculations carried out on a number of laser treatment regimes on eutectoid steel.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 57, No. 6, pp. 959–964, December, 1989.     

Modified dilatometric technique for determining the austenitizing kinetics of a low alloy Mn-Mo-Ni pressure-vessel steel

While dilatometry is a powerful technique to study the kinetics of phase transformations, the fact that both the thermal expansion (or contraction) and dimensional changes due to phase transformations are measured simultaneously limits the sensitivity of this method. As the thermal expansion is largely linear, it is possible to compensate for this contribution to the dimensional change of the specimen. A technique based on this approach was developed and used to study the austenitizing kinetics of a low alloy Mn-Mo-Ni pressure-vessel steel. Owing to the increased sensitivity it was possible to establish that austenitizing started at a temperature much lower than the temperature normally assumed to be theA _c1. This has implications for the maximum tempering temperature. Possible metallographic evidence for austenitization at a temperature lower than the temperature normally assumed to be theA _c1 is presented.     

Phase transition kinetics in iron and steel during heating

Similarity theory is used to analyze phase transformations in iron and steel during heating. A kinetic equation is obtained by assumption of self-similarity of the phase transition. Experimental data are processed and effective kinetic parameters determined. It is concluded from the results obtained that the elementary act of phase transition consists of a cooperate transition into the new phase of regions containing (1–2)·10² atoms.Translated from Inzhenerno-fizicheskii Zhurnal, Vol. 61, No. 4, pp. 669–672, October, 1991.