Kinetics of low temperature precipitation in a ULC-bake hardening steel

De, A. K.; Vandeputte, S.; Cooman, Bruno C. De

doi:10.1016/s1359-6462(00)00638-2

Cited by 63 publications

(43 citation statements)

References 14 publications

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“…The effect is due to tempering of martensite. Tempering of martensite occurs at temperatures below the lower critical Ac 1 and was also reported as the main reason for softening in martensitic steels [24][25][26].…”

Section: Introductionmentioning

confidence: 78%

Use of the Aging Effect to Change the Local Properties of Structure Components

Asadi

Schulze

Palkowski

2010

AMR

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Abstract. This research deals with processes leading to local strengthening effects in Advanced High Strength Steels (AHSS). Dual phase (DP), retained austenite (RA) -both hot and cold rolledand complex phase (CP) steels have been investigated to examine the effect of thermal and mechanical processing parameters on local properties. For this purpose, a method has been investigated to achieve local strengthening, namely local deformation and local heat treatment. Samples were locally deformed by bending and embossing processes. A local deformation with defined pre-strains leads to enhanced hardness and strengthening. A subsequent aging treatment leads to a further increase in mechanical properties. Local heat treatment was applied using a laser and an electron beam. Following local heat treatment with selected parameters, the microstructure of the surface and the cross section as well as the mechanical properties were evaluated by light optical, scanning as well as transmission electron microscopy, hardness measurement, tensile testing and thermal modelling. It can be stated that with partial heat treatment, local high strengthening can be produced. At lower heat treating temperatures, this effect could be attributed to bake hardening. With increased heat treating temperature, the initial microstructure near the surface is affected. A model can be improved, which defines the correlation between the influencing parameters and the local properties. The influence of over-aging in locally strengthen regions has been studied. For this investigation, parameters are stable to locally adjust the strengthening effect. Partial strengthening of AHSS by local deformation or local heat treatment can open up new fields of applications for locally using the strengthening effect to only influence relevant areas of interest, thus providing the potential for saving energy and designing the component's behaviour. Introduction:

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Section: Introductionmentioning

confidence: 78%

Use of the Aging Effect to Change the Local Properties of Structure Components

Asadi

Schulze

Palkowski

2010

AMR

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“…The bake hardening response was measured as the strength difference between the upper yield strength after PS/BH treatment and the strength value after 4 pct prestraining. [36] X-ray diffraction analysis was performed using a Rigaku D/max 2400 diffractometer (Rigaku Corp., Tokyo, Japan) (40 kV, 25 mA) equipped with a monochromator using Cu K a radiation to confirm the amount of RA in the microstructure. Spectra were taken in the range from 30 to 120 deg with a 0.02-deg step size.…”

Section: Methodsmentioning

confidence: 99%

“…[32] Extensive investigations have established the mechanisms and stages of the bake hardening behavior of low carbon steels, which are controlled by the amount of interstitial carbon atoms and the formation of Cottrell atmosphere and precipitations. [35,36] Compared with the low carbon steels, the bake hardening behavior in TRIP steels is expected to be more complex in nature due to their complex multiphase microstructure. Limited data showed that the bake hardening behavior of the TRIP steels depend on the processing methods and on the phase morphologies/ fractions resulting from their chemical compositions.…”

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confidence: 99%

Understanding the Behavior of Advanced High-Strength Steels Using Atom Probe Tomography

Pereloma

Beladi

Zhang

et al. 2011

Metall Mater Trans A

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The key evidence for understanding the mechanical behavior of advanced high strength steels was provided by atom probe tomography (APT). Chemical overstabilization of retained austenite (RA) leading to the limited transformation-induced plasticity (TRIP) effect was deemed to be the main factor responsible for the low ductility of nanostructured bainitic steel. Appearance of the yield point on the stress-strain curve of prestrained and bake-hardened transformationinduced plasticity steel is due to the unlocking from weak carbon atmospheres of newly formed during prestraining dislocations.

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“…It is established that within a temperature range of 100-250°C, the carbide that precipitates from a supersaturated solid solution of carbon in bcc iron is hexagonal ecarbide. 4) Recently, advanced high strength steels with multiphase microstructures, consisting of ferrite, bainite, martensite and retained austenite have been developed which also show bake hardening properties. 5,6) These materials are characterized by an interesting combination of high strength, good ductility, continuous yielding, high initial work hardening rates (n values) and a low yield stress to tensile strength ratio (YS/TS).…”

Section: Introductionmentioning

confidence: 99%