Effect of Welding Heat Input on Microstructure and Impact Toughness in the Simulated CGHAZ of Low Carbon Mo-V-Ti-N-B Steel

Welding thermal cycles with heat inputs ranging from 25 to 75 kJ/cm were performed on a Gleeble 3500. The impact energy improved significantly (from 10 to 112 J), whereas the simulated coarse-grain heat-affected zone (CGHAZ) microstructure changed from lath bainite ferrite (LBF) and granular bainite ferrite (GBF) + martensite/austenite (M/A) to acicular ferrite (AF) + polygonal ferrite (PF) + M/A as the heat input increased. Simultaneously, the mean coarse precipitate sizes and the degree of V(C,N) enrichment on the precipitate surface increased, which provided favorable conditions for intragranular ferrite nucleation. The Ar3 of CGHAZ increased from 593 °C to 793 °C with increasing heat inputs; the longer high-temperature residence time inhibited the bainite transformation and promoted the ferrite transformation. As a result, acicular ferrite increased and bainite decreased in the CGHAZ. The CGHAZ microstructure was refined for the acicular ferrite segmentation of the prior austenite, and the microstructure mean equivalent diameter (MED) in the CGHAZ decreased from 7.6 µm to 4.2 µm; the densities of grain boundaries higher than 15° increased from 20.3% to 45.5% and significantly increased the impact toughness. The correlation of heat input, microstructure, and impact toughness was investigated in detail. These results may provide new ideas for the development of high welding heat input multiphase steels.

Fracture Mechanical Analysis of Gleeble Simulated Heat Affected Zones in High Strength Steels

During the research work the fracture mechanical investigation of heat affected zones of thermomechanical rolled high strength steels (Voestalpine Alform 960M) were carried out. For production of appropriate heat affected zones Gleeble 3500 physical simulator was applied, with different heating cycles and specific cooling times. Following the simulation, fracture mechanical investigations were performed, in favor of determination crack tip opening displacement (CTOD or δ) values.

Creep Strain Behaviors of Ti-6Al-4V Using Gleeble 3500

During forging operations, strain can occur through three primary mechanisms: strain due to load applied through dies, strain due to thermal contraction, and strain due to creep. In materials behavior models, strain due to applied load and thermal contraction are directly considered and predictions are based on thermophysical properties and flow stress behaviors as inputs to the models. Strain due to creep after forging (during cooling) is often more difficult to predict and capture due to lack of materials data. In particular, data that capture the changing flow stress behavior during cooling (rather than from isothermal testing) are not commonly available. In this project, creep strain behavior during cooling was investigated by physical simulations using a Gleeble 3500. Standard cylinder-shaped Ti-6Al-4V samples with 10 mm diameter were heated to below β-transus temperature (1775°F) or above β-transus (1925°F), followed by constant cooling rates of 250°F/min and 1000°F/min with and without applied load during cooling to 1000°F. Total strain for the tests ranged from 2 – 6%. Characterization of prior microstructure and texture was carried out using XRD, optical microscopy, and SEM. The results provide insights on the relationship of flow stress behavior and microstructure as a function of temperature and cooling rate and are applicable to forging practices. These materials data can be used as input for future process modeling, potentially giving better prediction accuracy in industry applications.

Microstructure Evolution of near α Titanium Alloy during Multi-Step Thermomechanical Deformation Process

A new type of near α high temperature titanium alloy of Ti-Al-Sn-Zr-Mo-Si-Er was studied. The samples with different primary α phase content were prepared by solid solution at 950 °C/1 h—1010 °C/1 h. The multi-step hot compression experiments were carried out by Gleeble-3500 in a sequence of upper region of α + β phase, then followed by lower region of α + β phase. The effects of primary α phase content and deformation temperature on the microstructure of the alloy were studied by means of true stress-strain curve and optical microscope. The results show that the content of primary α phase gradually decreases from 45.4% at 950°C to 0% at 1010°C. As the deformation temperature decreases from 940°C to 900°C, the content of α phase increases gradually from 65% to 94%, which is changed from dynamic recrystallization to deformed structure elongated along RD direction. It is found that the arrangement of α phase along RD direction is the longest at 920°C. With the increase of the deformation temperature in the multi-step high temperature region from 970°C to 990°C, the width of deformed α phase decreases from 3.64 μm at 970°C to 2.71 μm at 990°C. The optimized microstructure is composed of 20% primary α phase arranged along RD direction. This process has a certain potential in the process of hot deformation of the alloy. Key words: high temperature titanium alloy, primary α phase, multi-step hot deformation

Influence of Multi-Step Heating Methods on Properties of Al–Si Coating Boron Steel Sheet

In this study, the influence of the multi-step heating methods, such as two-step heating methods and three-step heating methods, on the properties of Al–Si coating boron steel sheet were evaluated by using the Gleeble-3500 thermal simulator. The evolution of microstructure and 3D surface topography of the Al–Si coating were also investigated. The results showed that the heating rates of 50 °C/s, named rapid heating, at the stage of 20–500 °C did not significantly influence the microstructure and 3D surface topography of the Al–Si coating in the two-step heating methods. The results also indicated that the volume fractions of Fe3Al2Si3 intermetallic compound, FeAl intermetallic compound and a-Fe phase in the Al–Si coating reduced by rapid heating at the stage of 700–930 °C in the three-step heating methods. The roughness of 3D surface topography of the Al–Si coating increased by rapid heating at the stage of 700–930 °C. Rapid heating at the stage of 700–930 °C had little influence on the porosity of the Al–Si coating. The results provided a theoretical basis for the popularization and application of rapid heating in the Al–Si coating boron steel sheet.

Comparative HAZ softening analysis of three different automotive aluminium alloys by physical simulation

The development of high strength aluminium alloy has revolutionized the automotive industry with innovative manufacturing and technological process to provide high-performance components, weight reduction and also diversified the application field and design consideration for the automotive parts that work under severe conditions, but the selection of proper production parameters is most challenging task to get excellent results. Growing industrial demand of aluminium alloys led to the development of new welding technologies, processes and studies of various parameters effects for its intended purposes. The microstructural changes lead to loss of hardening and thereby mechanical strength in the HAZ welded joint even though the base materials are heat treatable and precipitation hardened. So, our goal is to analyse HAZ softening and analyse the sub-zones as a function of the parameter. In this paper, the influence of weld heat cycle on the heat-affected zone (HAZ) is physically simulated for Tungsten Inert Gas Welding (TIG) using Gleeble 3500 thermomechanical simulator for three different automotive aluminium alloy (AA5754-H22, AA6082-T6 & AA7075-T6) plate of 1 mm thickness. In order to simulate the sub-zones of the heat-affected zone, samples were heated to four different HAZ peak temperatures (550 °C, 440 °C, 380 °C and 280 °C), two linear heat input (100 J/mm and 200 J/mm) by the application of Rykalin 2D model. A series of experiments were performed to understand the behaviour, which make it possible to measure the objective data on the basis of the obtained image of the aluminium alloys tested with heat-affected zone tests in a Gleeble 3500 physical simulator. The main objective is to achieve the weldability of three different automotive aluminium alloys and their comparison based on the welding parameters like heat input. Further, the investigation of HAZ softening and microstructure of the specimens were tested and analysed using Vicker's hardness test and optical microscope respectively. The paper focuses on HAZ softening analysis of different grades of aluminium alloys for automotive application.

Ausztenites korrózióálló acél szemcsehatármenti korrózióra való hajlamának elemzése fizikai szimulációval

Mint ismeretes, az ausztenites korrózióálló acélok, ha azok karbontartalma meghaladja a 0,03-0,04%-ot, nagyobb hőmérsékletről lassan hűtve, vagy 500 - 900 ˚C hőmérséklet közben hőn tartva, nem lesznek homogén szövetszerkezetűek. Az ausztenit mellet számos intermetallikus vegyület válik ki, amelyek közül a szemcsehatármenti korrózió kialakulása szempontjából a M23C6 karbid kiválása a meghatározó. A kiváló nagy krómtartalmú (kb. 65%) fázis környezetében az ausztenit Cr tartalma 10,5% alá csökkenhet, így az acél kristályközi korrózióra hajlamossá válhat. A szemcsehatármenti korrózióra hajlamos ausztenites korrózióálló acélok esetén a hegesztési hőfolyamat hatására is kialakulhat a nem kívánt kiválás. Az egyes ausztenites korrózióálló acélok érzékenységének jellemzése érdekében ún. szenzibilizációs diagramokat célszerű meghatározni, amelyeknél a hőntartás hőmérséklete és ideje függvényében a karbidok elhelyezkedési, előfordulási területeit jelenítik meg. Tekintettel arra, hogy a hegesztés hőciklusa jelentősen különbözik az állandó hőmérsékletű kezelésnél alkalmazottól, a szemcsehatármenti korróziós hajlamot a hegesztési hőfolyamat paramétereinek függvényében célszerű elemezni. Jelen kutatómunkában fizikai szimulációval előállított hegesztési hőciklus(ok)nak kitett próbatesteken (X5CrNi18-10, 1.4301) végeztünk kísérleteket egy Gleeble 3500 típusú berendezésen, amelynek során különböző maximális hőmérsékleteket létrehozva, változó lehűlési profilokat vizsgáltunk. A vizsgálati eredmények felhasználásával különválasztottunk néhány olyan hegesztési hőciklust, amelyek alkalmazása esetén bekövetkezhet szemcsehatármenti korrózió, illetve az elkerülhető a vizsgált ausztenites alapanyagon.

Hot deformation behavior and processing maps of 9Cr3W3Co oxide dispersion-strengthened steel

The hot deformation behavior of as-cast 9Cr3W3Co oxide dispersion-strengthened (ODS) steel was investigated by Gleeble 3500 facility in the temperature range of 900–1,150℃ and at strain rates range of 0.01–10 s−1. The constitutive equation and processing maps were established to describe this complex hot deformation process. The true stress–strain curves showed that the softening effects of dynamic recovery and dynamic recrystallization are stronger than the effect of work hardening with further increasing the temperature and strain. The optimal hot working parameters of 9Cr3W3Co-ODS steel are suggested to be T = 1,050–1,100°C and ε ̇ \dot{\varepsilon } = 0.03–0.3 s−1.

Effects of Sn and Sb on the Hot Ductility of Nb+Ti Microalloyed Steels

Referencing the composition of a typical Nb+Ti microalloyed steel (Q345B), two kinds of steels, one microalloyed with Sn and Sb, and the other one only microalloyed with Sb were designed to study the effects of Sn and Sb on the hot ductility of Nb+Ti microalloyed steels. The Gleeble-3500 tester was adopted to determine the high-temperature mechanical properties of the two test steels. Fracture morphologies, microstructures and interior precipitation status were analyzed by SEM, CLSM (Confocal laser scanning microscope) and EDS, respectively. Results revealed that within the range of 950–650 °C, there existed the ductility trough for the two steels, which were mainly attributed to the precipitation of TiN and Nb (C, N). Additionally, precipitation of Sn and Sb were not observed in this research and the hot ductility was not affected by the addition of Sn and Sb, as compared with the Nb+Ti microalloyed steel. Therefore, addition of a small amount of Sn and Sb (≤0.05 wt.%) to the Nb+Ti microalloyed steel is favorable due to the improvement on corrosion resistance.

Effect of Cooling Rate and Austenite Deformation on Hardness and Microstructure of 960MPa High Strength Steel

In order to develop 960MPa grade high strength steel, the effects of cooling rate and austenite deformation on the hardness and the microstructure of high strength steel has been studied by Scanning Electron microscope (SEM), Transmission Electron Microscope (TEM), Gleeble-3500 thermal simulation testing machine and T2500 Vickers hardness tester. The results show that only when the cooling rate was higher than 10∘C/s and the final cooling temperature was lower than 250∘C, the microstructure mainly consists of martensite, and the strength of high strength steel could be above 960MPa; and austenite deformation could effectively refine the width of martensite lath, thus improving the strength and toughness.