Improvement of AISI 4340 steel properties by intermediate quenching – microstructure, mechanical properties, and fractography (original) (raw)
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Journal of Engineering Science and Technology Review, 2018
The influence of Martensite Volume Fraction (MVF) on fracture mechanisms in a Dual Phase steel with two different grain sizes was studied in this work. Ferrite-Martensite microstructure was obtained by an intercritical heat treatment for both groups of grain sizes. The results show a direct relationship between a higher temperature during the intercritical heat treatment and the increase of the MVF. The fine microstructure with higher MVF presents a high tensile strength and a good ductility. Furthermore, in relation to the material behavior under impact conditions, grain refinement and higher values of MVF promote ductile fracture by typical microvoid coalescence. High values of impact energy refer to the presence of low-carbon martensite formed at higher temperatures, which is more ductile than high carbon martensite formed at lower temperatures. Additionally, fine-grained materials have a better ability to dissipate impact energy. It was shown that an increase of 10.0% in MVF allows fine grain microstructures to improve their capacity to dissipate impact energy by 11.4%. This behavior may be explained because of the low carbon content of the as-received material, and the mechanical properties of the martensite obtained by the intercritical heat treatment.
Impact and tensile properties of ferrite-martensite dual-phase steels
Fatigue & Fracture of Engineering Materials & Structures, 2009
The effect of martensite morphology on the impact and tensile properties of dual phase steels with a 0.25 volume fraction of martensite (V m) under different heat treatments was investigated. These treatments are direct quenching (DQ) and step quenching (SQ) that result in different microstructures and mechanical properties. To process dual phase steels, a low carbon manganese steel was used. At first the banding present in the initial steel was eliminated, then the two different heat treatments were applied. To reach a 0.25 volume fraction of martensite a variation of intercritical annealing temperatures was adopted for both treatments that allowed the evolution of different volume fraction of martensite. Phase analysis showed that an intercritical temperature of 725 • C (between A 3 , A 1) gives the desired 0.25 V m of martensite. A comparison of impact, tensile and ductile-brittle transition temperature (DBTT) indicates that the microstructure of the direct treatment has a better toughness. The DBTT for the DQ and SQ treatment is −49 and −6 • C, respectively. Keywords dual phase steels; fixed volume fraction of martensite; impact properties; toughness.
Materials & Design, 2012
This investigation is concerned to evaluate the effect of double quenching and tempering (DQT) with conventional quenching and tempering (CQT) heat treatment processes on microstructure and mechanical behavior of a commercially developed hot rolled AISI 4140 type steel. Comparison of microstructure and mechanical properties of DQT and CQT heat treated specimens have been established in details. Optical and scanning electron microscopies have been used to follow impurity concentration and microstructural changes, and their relation to the associated mechanical properties. The results indicate that the improvement of mechanical properties particularly impact toughness of DQT heat treated specimens is much higher than that of the CQT condition, and this observation is rationalized in terms of finer austenite grain size developed in the DQT condition providing much finer martensitic packets within the grains and a lower level of impurity concentration of sulfur (S) and phosphorus (P) near the prior austenite grain boundaries as well.
Tecnologia em Metalurgia, Materiais e Mineração, 2020
In this work the quenching and partitioning (Q&P) treatment is applied to AISI 9260 steel combining different quenching temperatures (QT), and partitioning times and temperatures in order to evaluate mechanical properties (e.g. ultimate tensile strength, elongatin, toughness, and their combination). AISI 9260 steel, besides having the advantage of a lower cost than most of the low alloy steels, can achieve high retained austenite (RA) fraction levels through the application of the Q&P treatment thanks to its few alloying elements, mainly silicon. The importance of RA lies in its ability to improve ductility and toughness; in this work, RA is determined via X-ray diffraction analysis (XRD) and the mechanical properties are assessed through conventional tensile test and, fracture toughness test (FT)-FT being seldom reported in several Q&P studies. The results of the present work suggest that the Q&P treatment applied to AISI 9260 steel could increase its industrial use by virtue of a good combination of strength, ductility and toughness.
Microstructure and Mechanical Properties Analysis of Quenched and Tempered AISI 4340
2019
This research was conducted to determine the optimum parameters in quenching and tempering processes of AISI 4340 steel. Quenching and tempering processes were carried out to modify the microstructure and mechanical properties, especially to achieve the high strength and toughness resilience for steel armor application. Steel is widely use as armor material due to its ease processing, lower production costs, high strength, good toughness, and heat treatment capabilities. This material has also a reasonable price and good availability. Metallurgical structure becomes a crucial factor, especially for ballistic-resistant vehicle applications. The samples of AISI 4340 commercial steel with dimension of 55x10x10 mm3 were austenized at temperature of 800 ∘C for 1 and 2 h in a muffle furnace and followed by quenching process with oil as the media. Furthermore, the quenched samples were then tempered at 300 ∘ C for 2, 3, and 4 h at the muffle furnace as well. Microstructure analysis was con...
Effect of microstructure on the impact toughness transition temperature of direct-quenched steels
Materials Science and Engineering: A, 2018
A sufficient level of toughness at low temperatures is paramount for the use of structural steels intended for arctic applications. Therefore, it is important for the steel industry to identify the factors that control brittle fracture toughness. In this study, the quantitative effect of microstructure on the impact toughness transition temperature has been investigated with 18 different thermomechanically rolled and direct-quenched low-carbon ultra-high-strength steels with varying martensite and bainite contents. The steels were produced by altering their chemical composition, the finish rolling temperature and the total reduction of the prior austenite grains in the non-recrystallisation temperature regime, i.e. austenite pancaking, and characterised in terms of microstructural constituents, grain size distributions and texture as well as by using Charpy-V impact and tensile testing. It is shown for the first time that the impact toughness transition temperatures T 28J and T 50 closely follow a dynamic reference toughness, defined by yield strength and the size of the coarsest grains in the effective grain size distribution at 80th percentile. Decreasing the area fraction of {100} cleavage planes oriented within 15°of the macroscopic fracture plane by increasing austenite pancaking is also shown to improve T 28J. The best toughness is achieved with the lowest finish rolling temperatures that are nevertheless high enough to avoid the subsequent formation of granular bainite, which weakens both the toughness and strength. The results show that it is perfectly possible to produce untempered ultra-high-strength martensitic and martensitic-bainitic structural steels with adequate low-temperature toughness when the grain size is properly controlled.
Quenching and Partitioning of Aisi 4340 Steel
JOURNAL OF FACULTY OF ENGINEERING & TECHNOLOGY, 2017
Quenching and Partitioning (Q & P), an innovative heat treatment process was developed by J. G. Speer in 2003 to produce third generation high strength steels with improved toughness for making chassis of high speed cars. The Q & P process was applied to the low alloy AISI-4340 steel for different partitioning time periods. The characterization process encompassed m icroscopic study through optical microscope and hardness testing by micro Vickers hardness tester. Also, corrosion behaviour of different samples, partitioned at various time periods was studied by Gamry Potentiostat. Light optical microscopy revealed that microstructure consists of lath martensite and inter lath blocky retained austenite. The volume fraction of the retained austenite showed an initial progressive increase in proportion with the partitioning time but later pursued a decrease at partitioning time of 60 and 120 sec, steadily. The hardness values were increased from 236 HV for a non-heat treated sample to 4...
ISIJ International, 2015
The relationships between microstructure, mechanical properties and damage mechanisms in asquenched and in quenched-and-tempered high martensite fraction (> 60%) dual phase (DP) steels were investigated. The mechanical behaviour was determined by tensile and hole expansion (HE) tests. In the as-quenched condition, the HE ratio decreased with increasing ferrite content and showed a non-linear inverse relation to the uniform elongation. Tempering significantly improved the HE ratio for all studied martensite fractions; the increase in HE was found to be monotonic for tempering temperatures between 230°C and 460°C, even though the yield stress dependence was complex in this range. Tempering studies showed that, at constant martensite fractions, there was a linear dependence between the HE ratio and the ductile fracture strain, ε f. However, the parameters of the linear relation changed significantly when the martensite fraction was varied. The dominant damage mechanism in simple tensile tests evolved from ferrite/martensite or martensite/martensite interface decohesion in the as-quenched state to martensite/ carbide interface decohesion after tempering. The damage mechanisms were qualitatively described using the Beremin local criteria.
Metallurgical and Materials Transactions A
The influence of Cu-rich precipitates (CRPs) and reverted austenite (RA) on the strength and impact toughness of a Cu-containing 3.5 wt pct Ni high-strength low-alloy (HSLA) steel after various heat treatments involving quenching (Q), lamellarization (L), and tempering (T) is studied using electron back-scatter diffraction, transmission electron microscopy, and atom probe tomography. The QT sample exhibits high strength but low impact toughness, whereas the QL samples mostly possess improved impact toughness but moderate strength, but the QLT samples again have degraded impact toughness due to additional tempering. The dispersion of nanoscale CRPs, which are formed during tempering, is responsible for the enhanced strength but simultaneously leads to the degraded impact toughness. The RA formed during lamellarization contributes to the improved impact toughness. Based on the present study, new heat treatment schedules are proposed to balance strength and impact toughness by optimizing the precipitation of CRPs and RA.
Three ferrite/martensite dual-phase steels varying in the ferrite grain size (12.4, 2.4 and 1.2 lm) but with the same martensite content ($30 vol.%) were produced by large-strain warm deformation at different deformation temperatures, followed by intercritical annealing. Their mechanical properties were compared, and the response of the ultrafine-grained steel (1.2 lm) to aging at 170°C was investigated. The deformation and fracture mechanisms were studied based on microstructure observations using scanning electron microscopy and electron backscatter diffraction. Grain refinement leads to an increase in both yield strength and tensile strength, whereas uniform elongation and total elongation are less affected. This can be partly explained by the increase in the initial strain-hardening rate. Moreover, the stress/strain partitioning characteristics between ferrite and martensite change due to grain refinement, leading to enhanced martensite plasticity and better interface cohesion. Grain refinement further promotes ductile fracture mechanisms, which is a result of the improved fracture toughness of martensite. The aging treatment leads to a strong increase in yield strength and improves the uniform and total elongation. These effects are attributed to dislocation locking due to the formation of Cottrell atmospheres and relaxation of internal stresses, as well as to the reduction in the interstitial carbon content in ferrite and tempering effects in martensite.