The transformation-induced plasticity (TRIP) in advanced high-strength steels (AHSS) is reviewed, where the main concepts and the recent progress in the processing and properties of AHSS are introduced. The metastable austenitic stainless and multiphase TRIP-assisted steels, as well as the more recent third generation AHSS grades, namely the medium-Mn and quenching and partitioning (Q&P) steels, are critically discussed. These steels utilize the TRIP effect and the enhanced work-hardening rate through the transformation of (retained) austenite in their microstructures to martensite during plastic deformation for the improvement of strength-ductility balance, which make them especially suitable for the automotive industry to be used in the lightweight car body for addressing the safety, fuel consumption, and air pollution issues. The kinetics of strain-induced martensitic transformation (SIMT) as well as the effects of chemical composition, grain size, deformation temperature, strain rate, and deformation mode on the austenite stability are reviewed. The effects of holding temperature and time during the isothermal bainitic transformation (IBT) in TRIP-aided steels, during the austenite-reverted-transformation (ART) annealing in medium-Mn steels, and during the quenching and partitioning steps in the Q&P steels are critically discussed towards enhancement of the amount of retained austenite and optimization of strength-ductility trade off. The alternative thermomechanical processing routes as well as the modified grades such as δ-TRIP and quenching-partitioning-tempering steels are also introduced.

Transformation-induced plasticity (TRIP) in advanced steels: A review

Thermomechanical processing of advanced high strength steels

The effects of prior austenite grain boundaries and microstructural morphology on the impact toughness of intercritically annealed medium Mn steel

Multistage work hardening assisted by multi-type twinning in ultrafine-grained heterostructural eutectic high-entropy alloys

This study is concerned with a correlation between the microstructure and the local brittle zone (LBZ) phenomena in high-strength low-alloy (HSLA) steel welds. The influence of the LBZ on toughness was investigated by means of simulated heat-affected zone (HAZ) tests as well as welded joint tests. Micromechanical processes involved in microvoid and cleavage microcrack formation were also identified using notched round tensile tests and subsequent scanning electron microscopy (SEM) analyses. The LBZ in the HAZ of a mUltipass welded joint is the intercritically reheated coarse-grained HAZ whose properties are strongly influenced by metallurgical factors such as an effective grain size and high-carbon martensitic islands: The experimental results indicated that Charpy energy was found to decrease monotonically with increasing the amount of martensitic islands, confirming that the martensitic island is the major microstructural factor controlling the HAZ toughness. In addition, microvoids and microcracks were found to initiate at the interface between the martensitic island and the ferrite matrix, thereby causing the reduction in toughness. These findings suggest that the LBZ phenomena in the coarse-grained HAZ can be explained by the morphology and the amount of martensitic islands.

Microstructure and Local Brittle Zone Phenomena in High-Strength Low-Alloy Steel Welds

Optimization of chemical compositions in low-carbon Al-killed enamel steel produced by ultra-fast continuous annealing

Isothermal Growth Kinetics of Ultra-fine Austenite Grains in a Nb-V-Ti Microalloyed Steel

Immersion experiment was used to elucidate the corrosion mechanism of low-alloy pipeline steel exposed to vapor-saturated H2S/CO2 and H2S/CO2-saturated brine conditions in terms of microstructure, corrosion kinetics, corrosion products, surface/cross-sectional morphology, and elemental distribution. The experimental results demonstrate that the microstructure of designed steel is tempered martensite, and the corrosion rate in H2S/CO2-saturated brine condition is larger than that in vapor-saturated H2S/CO2 condition. The main corrosion product in two corrosion conditions is FeS, which shows various crystal structures. The size of corrosion products formed in vapor-saturated H2S/CO2 condition is smaller than that of corrosion products formed in H2S/CO2-saturated brine condition, which contributes to the difference of water chemistry in two corrosion conditions. Cr-rich compounds are primarily formed on the coupons surface of two corrosion conditions. The schematic models of corrosion mechanism in vapor-saturated H2S/CO2 condition and H2S/CO2-saturated brine condition are proposed based on experimental results.

Corrosion mechanism of low-alloy steel used for flexible pipe in vapor-saturated H2S/CO2 and H2S/CO2-saturated brine conditions

The invention aims at providing a V-N microalloyed Q550 grade medium plate and a preparation method thereof which are specific to the condition that in the prior art, the Q550 grade medium plate expensive alloy is in large consumption and the preparation process is complex. The chemical constitutions of the steel are as follows by weight percentage: 0.06 to 0.12 percent of C, 1.20 to 2.00 percent of Mn, 0.10 to 0.50 percent of Si, 0.002 to 0.01 percent of S, 0.003 to 0.01 percent of P, 0.01 to 0.05 percent of Al, 0.06 to 0.15 percent of V, 0.01 to 0.02 percent of N and the balance of Fe and other unavoidable impurities; the preparation method comprises the steps of heating a steel billet to 1000 to 1200 DEG C along with a furnace and performing heat preservation for 3 to 4 hours, and further carrying out hot rolling on the steel billet to form a hot rolled plate being 20 to 50mm in thickness, wherein the beginning temperature and the finishing temperature in a rough rolling stage are respectively 1030 to 1150 DEG C and 980 to 1020 DEG C, and the beginning temperature and the finishing temperature in a finish rolling stage are respectively 908 to 925 DEG C and 820 to 845 DEG C; cooling the plate by water to 545 to 650 DEG C after the hot rolling, and then cooling by air to room temperature. The plate is a high-toughness ultra-low-carbon medium-manganese medium plate, and the metallographic structure of the plate is a fine crystalline ferrite, a pearlite and an acicular ferrite; the method is simple in operation process, has no need of quenching and tempering treatment, and is easy to realize industrial production.

V-N microalloyed Q550 grade medium plate and preparation method thereof

There exist strong interests of developing nano-grained steels because of the outstanding properties including high strength/weight ratio, wear resistance, excellent toughness, and favorable cellular activity. This article reviews the main fabrication process and microstructural control of nano-structured steels over the last decades. Severe plastic deformation is considered as an effective route of obtaining the nano-grained microstructures. The process of cold-rolling and annealing of martensitic steel is a viable method to obtain bulk nano-structured low carbon steel, while the final thickness of the cold-rolling plate is limited. According to the theoretical results of the thermal simulation studies, a novel alloy design combined with the rapid transformation and rolling process is proposed to successfully fabricate nano-grained high strength bulk steel. The refinement mechanisms are expected to be taking advantage of increase in the transformation nucleation sites and inhibiting the grain coarsening. Moreover, corresponding mechanical properties are summarized.

Linxiu Du

Papers

Optimization of chemical compositions in low-carbon Al-killed enamel steel produced by ultra-fast continuous annealing

Isothermal Growth Kinetics of Ultra-fine Austenite Grains in a Nb-V-Ti Microalloyed Steel

Corrosion mechanism of low-alloy steel used for flexible pipe in vapor-saturated H2S/CO2 and H2S/CO2-saturated brine conditions

V-N microalloyed Q550 grade medium plate and preparation method thereof

Fabrication and Microstructural Control of Nano-structured Bulk Steels: A Review