Austenite Stability and Strain Hardening in C-Mn-Si Quenching and Partitioning Steels

Finfrock, Christopher B.; Clarke, Amy J.; Thomas, G.; Clarke, Kester D.

doi:10.1007/s11661-020-05666-8

Cited by 31 publications

(19 citation statements)

References 66 publications

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“…In a previous study performed by the authors, which referred to the steel of interest as ''QP980-B'', quantitative optical and electron microscopy and image analysis revealed the microstructure contained approximately 20 vol pct intercritical ferrite and 10 vol pct retained austenite, with the remainder being martensite. [22] The retained austenite existed in both blocky and film type morphologies. The martensitic fraction of the microstructure was slightly tempered from the partitioning step of the Q&P thermal cycle.…”

Section: Methodsmentioning

confidence: 99%

“…This was primarily attributed to crystallographic texture in the ferrite, martensite, and austenite inherited from thermomechanical processing. [22,55] Standard sheet-type tensile specimens conforming to ASTM E8 [56] were removed from the rolling direction of the QP980 sheet. Interrupted and continuous tensile testing was performed using an MTS Alliance RT/100 load frame equipped with a two inch extensometer.…”

Section: Methodsmentioning

confidence: 99%

“…The enhanced work hardening capacity due to DIMT is usually attributed to (a) increased dislocation density in the austenite and (b) increased content of hard freshly formed martensite, [20,21] which induces a composite-like strengthening effect due to the plastic incompatibility of martensite with the surrounding softer matrix phases. Because the stability of retained austenite substantially influences mechanical performance, [6,[20][21][22][23] many studies intending to optimize alloying, heat treatment, and resulting microstructure have been performed for Q&P steels. [24][25][26][27][28][29] Deformation factors such as strain state, strain rate, strain path, and temperature also affect the apparent stability of austenite, which affect formability.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Strain Rate Dependent Ductility and Strain Hardening in Q&P Steels

Finfrock

Thrun

Bhattacharya

et al. 2021

Metall Mater Trans A

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Due to their high strength, formability and affordable cost, quenched and partitioned (Q&P) steels have shown the potential to reduce the mass of vehicles, thereby decreasing fuel consumption during service. Furthermore, because a lower mass of steel is used in each vehicle, energy consumption associated with the steelmaking process is also reduced. Q&P steels utilize the deformation-induced martensitic transformation (DIMT) of metastable retained austenite to enhance ductility and strain hardening. Accordingly, improvement of mechanical performance is contingent on the ability to precisely control the chemical and mechanical stability of austenite. Considering the multitude of factors that influence austenite stability, optimizing microstructures to delay necking or fracture is challenging, particularly as temperature and strain rate increase. Tensile tests of an intercritically annealed C-Mn-Si Q&P steel were performed over a range of strain rates (10 À4 to 10 À1 s À1 ) to evaluate effects on the DIMT and sheet tensile properties. As strain rates increased from 10 À4 to 10 À1 s À1 , the uniform elongation decreased from approximately 19 to 14 pct. This reduction in uniform elongation is associated with a decrease in the strain hardening exponent near the onset of strain localization. Based on experimental data from this study and review of previous research, it is postulated that the strengthening contribution of DIMT is controlled by competing effects of: (i) a decreasing chemical driving force for DIMT caused by deformation-induced heat accumulation at higher strain rates and (ii) an increasing number of martensite nucleation sites. This suggests that tailoring austenite stability for specific deformation conditions could enable further optimization of formability and vehicle crash behavior.

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Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Strain Rate Dependent Ductility and Strain Hardening in Q&P Steels

Finfrock

Thrun

Bhattacharya

et al. 2021

Metall Mater Trans A

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“…In a study done by Streicher et al, a TRIP780 steel exhibited differing amounts of retained austenite transformation during straining in different strain states relative to the rolling direction, showing an increase in amount of martensite formed as a function of strain (Streicher et al, 2002). In a recent study by Finfrock et al, the amount of retained austenite transformation was dependent on the strain state relative to the rolling direction (Finfrock et al, 2020). The amount of transformation from austenite to martensite has also been shown to be dependent on strain state in 304 stainless-steel, with biaxial tension transforming more austenite than uniaxial tension (Hecker et al, 1982).…”

Section: Introductionmentioning

confidence: 97%

Effects of Unloading on Subsequent Yielding Behavior in 304 Stainless Steel

et al. 2021

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Forming operations are known to be complex, involving many strain states, strain rates, temperatures, strain paths, and friction conditions. Material properties, such as strength and ductility, are large drivers in determining if a material can be formed into a specific part, and for selecting the equipment required for the forming operation. Predicting yielding behavior in situations such as these has been done using yield surfaces to describe material yielding in specific stress states. These models typically use initial mechanical properties, and will require correction if the material has experienced previous straining. Here, we performed interrupted uniaxial tensile testing of a 304 stainless steel to observe the effects of unloading and subsequent reloading on yielding and tensile properties. An increase in yield point developed, in which a higher yield was observed prior to returning to the bulk work hardening behavior, and the magnitude of the yield point varied with unloading conditions and strain imposed. The appearance of a yield point is attributed to strain aging or dislocation trapping at obstacles within the matrix. These results suggest that both strain aging and dislocation trapping mechanisms may be active in the matrix, which may present challenges when forming austenitic stainless and new advanced high strength steels that likely show a similar behavior. These results provide a potential area for refinement in the calculation of yielding criteria that are currently used to predict forming behavior.

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“…The role of Niobium (Nb) was highlighted in previous work [11] [12], and the focus was mainly on the grain refinement effect. Other concepts were highlighted, such as Partitioning kinetics [13], stability of Retained Austenite [14], effect of multiphase-microstructure and attained properties relationship [15], the effect of Partitioning temperature and time [16] [17].…”

Section: Introductionmentioning

confidence: 99%

Feasibility of 0.02% Nb-Based Microalloyed Steel for the Application of One-Step Quenching and Partitioning Heat Treatment

Tarek¹,

El-Shenawy²,

Elsabbagh³

et al. 2021

MSA

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To attain an enhanced combination of mechanical properties for low alloyed steel, the current study has been made to fulfill that growing need in the industry. Its results are introduced within this paper. One step Quenching and Partitioning (Q&P) heat treatment has been applied on Niobium-based microalloyed steel alloy with 0.2 %C, in the form of 2 mm thickness sheets. The target of this study is to investigate the viability of applying that significantly recommended, results-wise, heat treatment on the highly well-suited alloy steel samples, to achieve the main target of enhanced properties. A single temperature of 275˚C was used as quenching and Partitioning temperature. Four Partitioning periods (30, 200, 500, and 1000 Seconds) were used for soaking at the same temperature. The results were analyzed in the light of microstructural investigation and mechanical testing. All applied cycles did not enhance the strength but moderately improved the ductility and toughness, mainly caused by the slightly high soaking temperature used. Niobium impact of grain refining was apparent through all cycles. The cycle of 500 Seconds Partitioning time obtained optimum values at that particular temperature. The 1000 Seconds Cycle obtained the worst combination of properties. A set of recommendations are set. More research is required at this point, where a lower Partitioning temperature is advised. In the light of the applied combination of parameters, the Partitioning period at such temperature is advised to be between 500 and 1000 Seconds. A high probability that periods closer to 500 than 1000 Seconds will produce better results. More research is needed between those two values of Partitioning time to precisely determine the optimum time at that temperature on that specific alloy.

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Austenite Stability and Strain Hardening in C-Mn-Si Quenching and Partitioning Steels

Cited by 31 publications

References 66 publications

Strain Rate Dependent Ductility and Strain Hardening in Q&P Steels

Strain Rate Dependent Ductility and Strain Hardening in Q&P Steels

Effects of Unloading on Subsequent Yielding Behavior in 304 Stainless Steel

Feasibility of 0.02% Nb-Based Microalloyed Steel for the Application of One-Step Quenching and Partitioning Heat Treatment

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