Effect of V Addition on Microstructure and Mechanical Properties in C–Mn–Si Steels after Quenching and Partitioning Processes

Three C-Si-Mn Q&P steels with different V addition after one-step and two-step quenching and partitioning (Q&P) processes were investigated by means of optical microstructure observation, X-ray diffraction (XRD) measurement, transmission electron microscopy (TEM) characterization and particle size distribution (PSD) analysis. The effect of V addition on strength and ductility of the steels was elucidated by comparative analysis on the microstructure and mechanical properties as functions of partitioning time and temperature. For one-step Q&P treatment, the mechanical properties were mainly controlled by the tempering behavior of martensite during partitioning. V addition was helpful to mitigate the deterioration of mechanical properties by precipitation strengthening and grain refinement strengthening. For two-step Q&P treatment, the satisfying plasticity was attributed to the transformation-induced plasticity (TRIP) effect of retained austenite maintaining the high work hardening rate at high strain regime. The higher volume fraction of retained austenite with high stability resulted from the refined microstructure and the promoted carbon partitioning for the steel with 0.16 wt% V addition. However, the carbon consumption due to the formation of VC carbides led to the strength reduction of tempered martensite.

Effects of Partitioning Time and Temperature on the Microstructure and Mechanical Properties of a High Strength Microalloyed Steel

In the present study, in a quenching-partitioning (Q-P) process, the effects of partitioning time (Pt) and partitioning temperature (PT) on the mechanical and microstructural properties of a microalloyed Fe-0.21C-1.5Si-2.2Mn-0.054Al-0.08Ti steel were studied. The XRD and SEM results confirmed increases in retained austenite (γR) volume fraction (VγR) and (γR)carbon concentration by increasing Pt and PT. XRD patterns confirmed reduction in (VγR)by further increasing the Pt and PT over 500 sec and 390°C, respectively, due to super-saturation of austenite (γ) with carbon. PT of 390°C and Pt of 500 sec were recorded as the optimum values for PTs and Pts, which allowed the present steel to obtain higher formability and higher fracture strain characteristics, while retaining higher hardness and strength. The highest yield and tensile strength, hardness and fracture elongation were obtained for the sample partitioned at 390°C for about 500 sec, which were about 741MPa, 1366 MPa, 424 HV and 25.2 %, respectively.

Effects of quenching and partitioning (Q&P) technology on microstructure and mechanical properties of VC particulate reinforced wear-resistant alloy

To improve the wear resistance, toughness, and hardness of alloy, the quenching and partitioning (Q&P) technology was applied in the VC particulate (VCp) reinforced wear-resistant alloys, which were prepared by adding different Mn contents (2–5 wt%). The effects of partitioning time on the distribution of alloying elements shown by EDX mapping, retained austenite fraction, microstructure, macro-hardness, and impact toughness were investigated. The results showed that the effect of carbon partitioning time on the hard phase of the wear-resistant alloy was not significant. However, the carbon partitioning time greatly affected the microstructure and the mechanical properties of alloys, such as retained austenite, hardness, and impact toughness, and there was also a strong correlation with the Mn content. When the Mn content was lower (2.51 wt%), the retained austenite content increased with the carbon partitioning time, which resulted in decreased hardness and increased impact toughness. However, when the Mn content was higher (4.52 wt%), the opposite results occurred. This study provided an application of the Q&P technology in a VCp-reinforced wear-resistant alloy.

VOLUMETRIC CHANGES AT HEATING IN STEEL 60Si2CrV SUBJECTED TO Q&P TREATMENT

The paper presents results of the investigation of phasestructural transformations and volumetric changes that occur during heating in high-silicon spring steel 60Si2CrV subjected to Q&P(quenching and partition) treatment. Chemical composition of the steel was: 0.53 % C; 1.46 % Si; 0.44 % Mn; 0.95 % Cr; 0.10 % V; 0.016 % S; 0.013 % P. Steel samples were subjected to Q-n-P treatment as follows: a) austenitization at 880 °C; b) quenching with the cooling stop at 120, 160, 200 and 240 °C; c) subsequent holding at 220, 250 and 300 °С with duration from 10 to 3600 s; d) final cooling in water. The volumetric changes during heating were studied using an optical differential dilatometer at a heating rate of 1 K/s. As a reference, a sample of the same steel stabilized by high tempering was used. The amount of retained austenite was determined by X-ray diffraction using a diffractometer DRON-3 with Fe-radiation. It is found that on the heating curves of Q&P samples, the sections corresponding to different transformations during tempering are clearly identified. On dilatograms of the Q&P samples, dilatometric effect corresponding to the second transformation during tempering (270 – 430 °C) was found to be increased dramatically, indicating an increase in retained austenite amount compared to the quenched state as a result of Q&P treatment (as confirmed by Xray study). At the same time, value of the effect corresponding to the third transformation during tempering was found to be decreased. To obtain the maximum amount of retained austenite in 60Si2CrV steel, the partitioning temperature should be of 260 – 300 °С, while the quenching completion temperature should be of 160 – 240 °С. The amount of retained austenite rises substantially as the quenching temperature increases. Duration of the partitioning stage should be selected taking into account the extreme character of austenite dependence on the partitioning time. As a result of the work, an effective applicability of the dilatometric method for analyzing the steel structural state and choosing the optimal mode of Q&P treatment was demonstrated.

Effect of manganese pre-partitioning process on the microstructure and mechanical properties of low carbon dual phase steel

A low carbon (0.11 wt.%) steel with 1.78% Mn was subjected to pre-partitioning quenching and partitioning (PQ&P), quenching and tempering (Q&T), quenching and partitioning (Q&P) to develop ferrite-martensite dual phase (DP) steel. The study suggested that all the treatments resulted into ferrite, martensite (or tempered martensite) and retained austenite microstructure. The amount of retained austenite was ∼ 5%, when the steel was treated by PQ&P process with partitioning time of 100 s, because of Mn pre-partitioning stage increased in the stability of retained austenite. But only ∼ 1% for Q&T and Q&P processes. With the increase of partitioning time from 10 to 100 s in the PQ&P process, the amount of retained austenite was increased, the tensile strength decreased, and yield strength and elongation were both increased. Among the different heat treatment processes, PQ&P sample clearly yields most attractive combination of strength and ductility compared to Q&T and Q&P samples. The experimental steel after pre-partitioning quenching and partitioning (PQ&P) process had higher uniform elongation of 16.3% and strength-ductility balance (UTS × TEL) of 17013 MPa.%. In contrast to conventional Q&T process, 27.3% higher uniform elongation and 7.4% greater strength-ductility balance were obtained.

Microstructure Characterization of Quenching and Partitioning Steels

A steel containing Fe-0.2C-2Mn-Si-Al was annealed using intercritical Q&P cycles. Quenching temperature and partitioning time at 440°C was varied. Analysis of microstructure evolution during such Q&P treatments was performed using different characterization tools: FEG-SEM, EBSD, dilatometer and saturation magnetization measurements. Especially, phenomena taking place during partitioning were investigated. The microstructure was analyzed at the end of soaking, before and after partitioning and at the end of the annealing cycle. It was found that bainite transformation happens during partitioning and has a significant effect on the final retained austenite fraction. Quenching temperature has an important effect on both martensitic transformation during cooling and subsequent bainite transformation during partitioning.

Evolution of Microstructure and Mechanical Properties with Different Partitioning Conditions of Q&P Steels

Q&P annealing cycles with different partitioning conditions were performed on cold rolled 0.2C-2.22Mn-1.44Si-0.21Cr steel. An important influence of partitioning temperature and time on the evolution of retained austenite fraction was shown through the saturation magnetization measurements. Such effect of partitioning conditions was also observed on the evolution of mechanical behavior. The evolution of microstructure and mechanical properties with the partitioning conditions was analyzed. Mechanical stability of retained austenite as a function of partitioning time was also assessed. Finally, modeling of the obtained stress-strain curves was performed and some explanations of the observed tendencies between partitioning conditions and tensile properties were proposed.

A New Hot Stamping Process with Quenching and Partitioning Treatment

A new hot stamping process with quenching and partitioning treatment is proposed in the paper. Compared to direct hot stamping process, the microstructures with some retained austenite not only including martensite are formed according to the constrained carbon equilibrium (CCE) model. During the new hot stamping process, tools with high temperature are used to control the quenching temperature (QT) between Ms and Mf, and the partitioning treatment of the part is also implemented in the tools by prolonging holding times. In this paper, different holding times (partitioning times) controlled by servo press, are used to research the influence of partitioning time on mechanical properties.

Microstructure and Mechanical Properties of a Low-Carbon Steel Treated by One-Step Quenching and Partitioning Process

A low carbon steel was treated by quenching and partitioning (Q&P) process, and a detailed characterization of the microstructural evolution and testing of mechanical properties were carried out. The resulted mechanical properties indicate that with the partitioning time increasing, the tensile strength decreases rapidly first and then remains stable, and the total elongation increases first then decreases. The investigated steel subjected to Q&P process exhibits excellent products of strength and elongation (17.8-20.6 GPa•%). The microstructural evolution of martensite matrix during the partitioning step was observed, and the morphology and content of retained austenite were characterized. The working hardening behavior of the samples was analyzed, and the retained austenite with higher carbon content contributes to the uniform elongation more effectively.