Deformation and fracture characteristics of ferrite/bainite dual-phase steels

The deformation and fracture characteristics of a low carbon Si–Mn steel with ferrite/bainite dual–phase structure were investigated by thermo–mechanical controlled process (TMCP). The results showed that the curves of the instantaneous work–hardening factor n* value versus true strain ε are made up with three stages during uniform plastic deformation: n* value is relatively higher at stage I, decreases slowly with ε in stage II, and then decreases quickly with ε in stage III. Compared tothe equiaxed ferrite/bainite dual–phase steel, the quasi–polygonal ferrite/bainite dual–phase steel shows higher tensile strength and n*value in the low strain region. The voids or micro–cracks formed not only at ferrite–bainite interfaces but also within ferrite grains in the necked region, which can improve the property of resistance to crack propagation by reducing local stress concentration of the crack tips.

Microstructures and properties of ferrite/bainite dual-phase steels with high hole-expanding ratio

The effects of Si and Mn contents on microstructure, mechanical properties and formability of low carbon Si-Mn steels were studied, and the crack propagation of ferrite/bainite dual-phase steel was also investigated. The results showed that the increase in Si content increases the volume fraction of equiaxed ferrite. However, the increase in Mn content increases both strength and ductility, but decreases elongation and hole-expanding ratio. The crack of ferrite/bainite dual-phase steel is formed by the mode of microvoid coalescence. When a microcrack meets the bainite, it mostly propagates along the phase interface between ferrite and bainite and by cutting off ferrite grains. The hot-rolled ferrite/bainite dual-phase steel, which has a hole-expanding ratio of 95% and good property combination, could be produced by designing proper contents of Si and Mn as well as parameters of TMCP.

Continuous cooling transformation of deformed austenite in highly hole-expandable steels

The effects of Si and Mn contents on transformation temperature _r3, transformed microstructure and mechanical properties of three kinds of low-carbon steels during continuous cooling were investigated. A _r3 rises by 15-25°C when increasing Si content from 0.50% to 1.35%, and it drops by 30-50°C when increasing Mn content from 0.97% to 1.43%. The effect of Mn on A _r3 is more significant than Si. Si stimulates the precipitation of the high-temperature equiaxed ferrite to suppress the bainite transformation, but Mn not only provides the grain refining of transformed microstructure but also stimulates the forming of bainite. The homogeneous and grain refining diphase ferrite/bainite steel (w(Si)=0.56, w(Mn)=1.43) can be obtained after deformed at 850°C and cooled at the rate 30°C/s, of which the tensile strength is up to 654 MPa.

Comparative study of ni effect on the corrosion behavior of low alloy steels in FGD and acid rain environments

The alloying effect of a small amount of nickel on low alloy steel for application to flue gas desulfurization(FGD) systems was studied. The structural characteristics of the rust layer were investigated by scanning electron microscopy(SEM). The electrochemical properties were examined by means of potentiostatic polarization test, potentiodynamic polarization test, and electrochemical impedance spectroscopy(EIS) in a modified green death solution of 16.9 vol.% H2SO4+0.35 vol.% HC1 at 60°C and an acid rain solution of 6.25 X 10-5 M H2S04+5.5 X 10-3 M NaCl at room temperature. It was found that as the amount of nickel increased, the corrosion rate increased in the modified green death solution, which seemed to result from micro-galvanic corrosion between NiS and alloy matrix. In acid rain solution, the corrosion rate decreased as the amount of nickel increased due to the repulsive force of NiFe204 rust against Cl-ions by electronegativity.

Carbon dioxide emission mitigation and disclosures : the size effect

The analysis provided in this research ainis to improve the understanding of the structure and nature of organisations in the transport industry so that policy-makers and researchers can be informed about the impact of size of an organisation on its preparation for the transition to a low carboneconomy. Descriptive and infetential are calculated to aid in understanding how organisations manage their C02mitigation action and carbon emission disclosure. It is noted that small and medium sized companies appear to be less financially capable of responding to the challenges of transiting to a low carbon environment that large companies.

A corrosion inhibition study of steel grinding balls in an oxygen and alkaline environment

The corrosion of steel grinding balls is a major recurrent cost for mill operators concerned with the production gold. Subsequently, the use of corrosion inhibitors in production fluids, which is typically at pH >9, is an attractive and economical option. This study reports on the corrosion wear of steel grinding balls under alkaline/oxygen conditions and in presence of cyanide. A fundamental study on the influence of several inorganic-based inhibitors (i.e., nitrite, chromate, silicate, hexametaphosphate) on the corrosion rate of carbon steel was undertaken. Subsequently, the corrosion performances of various inhibitors were evaluated in stirred vessels. Corrosion rates were determined via mass loss and electrochemical methods (i.e., linear polarisation, Tafel). It was observed that inhibitors based upon chromate provide superior protection under the conditions investigated in this study. In lime treated, high chloride waters, chromate gave over 80% protection at levels of 10 100 ppm with no evidence of pitting.

Uniform elongation and the stress-strain flow curve of steels calculated from hardness using empirical correlations

An empirical relationship between the hardness and uniform elongation of non-Austenitic hypoeutectoid steels has been developed. This new hardness-elongation relationship was combined with previously developed correlations of hardness and strength (yield and ultimate tensile strength) to predict the stressstrain flow curve from a single hardness test. The current study considers both power law hardening behavior and exponential hardening behavior. Reasonable agreement was observed between the experimental and predicted flow curves of a high strength, low alloy steel. Additionally, an empirical correlation of the flow strength at instability with hardness is provided. © ASM International.

Characterization of microstructures and tensile properties of TRIP-aided steels with different matrix microstructure

Three different heat treatment processes have been proposed as a fundamental method to produce three kinds of TRIP-aided steels with polygonal ferritic matrix (F-TRIP), bainitic matrix (B-TRIP) and martensitic matrix (M-TRIP) in a newly designed low alloy carbon steel. By means of dilatometry study and detailed characterization, the relationships among transformation, microstructure and the resulting mechanical behavior were compared and analyzed for the three cases. The work hardening of the samples was evaluated by calculating the instantaneous n value as a function of strain. The M-TRIP sample exhibits the highest strength with the highest work hardening rate at low strains and subsequent rapid descending at high strains. In contrast, the B-TRIP sample has relatively high continuously constant work hardening behavior over strain levels greater than 0.067. The difference in work hardening behavior corresponds directly to the rate of the retained austenite-martensitic transformation during straining, which can be attributed to the carbon content, the morphology of the retained austenite and the matrix microstructure in the respective TRIP-aided samples. © 2014 Elsevier B.V.

Heat affected zone microstructures and their influence on toughness in two microalloyed HSLA steels

Microstructures and Charpy impact properties have been examined in two microalloyed steels following heat treatments to simulate weld heat affected zone (HAZ) structures over a range of heat input conditions, characterised by the cooling time from 800 to 500°C (Δt8/5). The base materials were low carbon structural steel plates microalloyed with vanadium and nitrogen (V-N) and niobium (Nb), respectively. The toughnesses of the HAZs displayed remarkably different behaviours as shown by their impact transition temperatures. For the V-N steel, the toughness improved with increasingly rapid cooling (low heat input conditions) whereas the Nb steel showed an opposite trend. Some of this behaviour could be explained by the presence of coarse ferrite grains in the slowly cooled V-N steel. However, other conditions where all the structures were bainitic and rather similar in optical micrographs gave widely different toughness values. The recently developed method of five dimensional boundary analysis based on electron backscattering diffraction has been applied to these cases for the first time. This showed that the lath boundaries in the bainite were predominantly on {1 1 0} planes of the ferrite and that the average spacing of these boundaries varied depending on steel composition and cooling rate. Since {1 1 0} is also the slip plane in ferrite, it is considered that close spacing between the lath boundaries inhibits general plasticity at stress concentrations and favours initiation of fracture. The differences between the two steels are believed to be due to their transformation behaviours on cooling where precipitation of vanadium nitride in austenite accelerates ferrite formation and raises the temperature of the phase transformation in V-N steels.

Synergistic corrosion inhibition of mild steel in aqueous chloride solutions by an imidazolinium carboxylate salt

Mild steel infrastructure is constantly under corrosive attack in most environmental and industrial conditions. There is an ongoing search for environmentally friendly, highly effective inhibitor compounds that can provide a protective action in situations ranging from the marine environment to oil and gas pipelines. In this work an organic salt comprising a protic imidazolinium cation and a 4-hydroxycinnamate anion has been shown to produce a synergistic corrosion inhibition effect for mild steel in 0.01 M NaCl aqueous solutions under acidic, neutral, and basic conditions; an important and unusual phenomenon for one compound to support inhibition across a range of pH conditions. Significantly, the individual components of this compound do not inhibit as effectively at equivalent concentrations, particularly at pH 2. Immersion studies show the efficacy of these inhibitors in stifling corrosion as observed from optical, SEM, and profilometry experiments. The mechanism of inhibition appears to be dominated by anodic behavior where dissolution of the steel, and in particular the pitting process, is stifled. FTIR spectroscopy provides confirmation of a protective interfacial layer, with the observation of interactions between the steel surface and 4-hydroxycinnamate.

An inverse routine to predict residual stress in sheet material

A method is presented to determine residual stress distribution in sheet material from data collected in a free bending test. It may be used where the residual stress distribution is symmetrical about the mid-surface as it is usually the case for frequently-used sheet metal post-processing techniques such as skin-pass or temper rolling, tension- and roller leveling. An existing inverse technique is used to obtain a residual stress profile and material constants that provide the best fit in a finite element analysis of bending with the experimentally derived moment-curvature relation. The method is verified for bending of a low-carbon stainless steel using measurement of residual stress by X-ray diffraction. The residual stresses were induced in the sheet by cold rolling. The technique described here can be used industrially as a rapid method of investigating residual stresses in incoming sheet. In processes where the deformation is principally one of bending, such as cold roll forming, it is known that residual stresses have an influence on shape defects and springback and the method presented here can be used to determine whether incoming sheet is suitable for further processing and also as a means of obtaining improved material data input for numerical simulation.

The role of thermomechanical routes on the distribution of grain boundary and interface plane orientations in transformed microstructures

In the current study, a series of thermomechanical routes were used to produce different microstructures (i.e., ferrite and martensite) in low-carbon low alloy steels. The five-parameter grain boundary character distribution was measured for all microstructures. The thermomechanical processing route altered the texture of the fully ferritic microstructure and significantly influenced the anisotropy of the grain boundary character distribution. Generally, the population of (111) planes increased with an increase in the γ-fiber texture for the ferritic microstructure, but it did not change the shape of the grain boundary plane distribution at specific misorientations. The most commonly observed boundaries in the fully ferritic structures produced through different routes were {112} symmetric tilt boundaries with the Σ3 = 60 deg/[111] misorientation; this boundary also had a low energy. However, the grain boundary plane distribution was significantly changed by the phase transformation path (i.e., ferrite vs martensite) for a given misorientation. In the martensitic steel, the most populous Σ3 boundary was the {110} symmetric tilt boundary. This results from the crystallographic constraints associated with the shear transformation (i.e., martensite) rather than the low-energy interface that dominates in the diffusional phase transformation (i.e., ferrite).

Inferring dynamic recrystallization in ferrite using the kinetics of static recrystallization

A general relationship between the kinetics of dynamic and static recrystallization is developed. It is predicted that conventional dynamic recrystallization will occur whenever the deformation time exceeds the adjusted start time for static recrystallization. This approach is verified using data for austenite and lead. It is then applied to current and previous work on ferrite. The model provides support for the contention that conventional dynamic recrystallization occurs in low carbon ferrite if deformation is carried out at high temperatures and low strain rates. In the present work, which was carried out at 700 °C, evidence for dynamic recrystallization was observed for strain rates less than around 0.01 s−1. At higher strain rates, the model predicts a critical strain for the onset of dynamic recrystallization that exceeds the critical strain for the beginning of the recovery steady-state region. While the model allows dynamic recrystallization to begin in this region, the critical strain for its onset is expected to increase rapidly with increasing strain rate and decreasing temperature once steady state has been reached.

Hot working microstructure map for magnesium AZ31

A thermomechanical processing (TMP) structure map is proposed that plots the critical strains required for dynamic recrystallization along with the grain sizes that result. These maps are useful in identifying the limits to grain refinement and designing hot working processes. They are readily constructed for well studied alloys such as plain carbon steel. In light of the recent interest in the hot working of magnesium, initial steps are taken here to construct a TMP structure map for the most common wrought magnesium alloy, AZ31. The completion of dynamic recrystallization is estimated using a geometrical approach and a twinning region is identified.

Climate change and social inclusion: opportunities for justice and empowerment

...the greatest untapped resource at our disposal lies in the disadvantaged Australians living in our most excluded communities. (Nicholson 2007 p. 4)

The commons are where justice and sustainability converge, where ecology and equity meet. (Shiva 2005 p. 50)

Since 1990, the Intergovernmental Panel on Climate Change (IPCC) has recognised human induced climate change to be primarily a result of burning fossil fuels and land clearing (Lee 2007). Changes to the world's climate patterns have been occurring for decades, but only in recent times has climate change arrived in our collective conscious. An onslaught of extreme weather events, destruction and failure of crops, increasing levels of water restrictions, government announcement of desalination plants. proposed increase in prices for utilities such as power and water - have ushered climate change into the Australian lexicon.

The challenges for all of us are many and varied and perhaps even unimaginable. as many propose a global reduction in annual C02 emissions of between 60-80% (compared to 1990 levels) by 2050.

We are not talking just about the re-construction of our world, but about its re-invention. Ryan (2007)

How will climate change affect us? Who is most vulnerable? What will be the features of policies and strategies to combat climate change that ensure an equitable and just response across our entire society? Are our present social-cultural justice paradigms of social exclusion and inclusion adequate in addressing the impending health consequences that are likely to result from climate change, and in supporting an equitable. harmonious and fruitful life for all population groups in the future?

This paper, written in the spirit of solution-oriented research. focusing on the causes of positive health rather than the causes of disease and other problems (Robinson & Sirard 2005). explores the possibility of a paradigm shift which imagines the social inclusion of specific population groups, not as an appended extra, but integral to the design of an equitable, sustainable low carbon society of the future.