Pre-bainitic Transformation in Fe-Ni Alloy

Ｔｈｅｐｒｅ－ｂａｉｎｉｔｉｃｐｈｅｎｏｍｅｎｏｎｉｓｏｎｅｏｆｔｈｅｉｍ－ｐｏｒｔａｎｔｓｕｂｊｅｃｔｓｏｆｂａｉｎｉｔｉｃｔｒａｎｓｆｏｒｍａｔｉｏｎｗｈｉｃｈｉｓｓｔｉｌｃｏｎｔｒｏｖｅｒｓｉａｌ．Ｏｎｅｖｉｅｗｉｓｔｈａｔｔｈｅｓｏｌｕｔｅａ...     

Dilatometric Investigation on Isothermal Transformation after Hot Deformation

Itiswellknownthattheferritetransformationisacceleratedandenhancedbyaustenitedeforma tion ,especiallyinnon recrystallizationregion ,andbysubsequentcoolingwithrelativehighrate[1] .Suchprocessobviouslyrefinestheferritegrainandotherphasetransformationproductsandbecomesaneffectivewaytoimprovethepropertiesofsteel ,basedonwhichthecontrolledrollingandcontrolledcoolingtechniquegoesforwardfurther .　　However ,someyearsago ,itwasfoundthatthedeformationofunder cooledaustenitecaninducefer ritetransformati…     

Effects of Sm on Phase Transformation in Ni-Mn-Ga Alloys

The effects of small amount additions of Sm on the martensitic transition and magnetic phase transition of polycrystalline Ni-Mn-Ga alloys were investigated. The experimental results show that the Sm doped alloys also undergo a thermal-elastic martensitic transformation and reverse transformation during cooling and heating process and the addition of Sm decreases the martensitic transformation temperature and Curie temperature in different degree respectively. Ni-Mn-Ga alloys of adding Sm still possess Heusler structure, but their crystal lattice parameters are modified slightly. The addition of a proper amount of Sm does not basically decrease Tc of the alloy when avoiding the appearance of second phase. In addition, the doped alloys have favorable toughness because of grain refinement of Sm.     

In-Situ Synchrotron Diffraction Studies on Transformation Strain Development in a High-Strength Quenched and Tempered Structural Steel—Part II. Martensitic Transformation

In-situ synchrotron diffraction studies on the kinetics of phase transformation and transformation strain development during bainitic transformation were presented in part I of the current article. In the current article, in-situ phase transformation behavior of a high-strength (830 MPa yield stress) quenched and tempered S690QL1 [Fe-0.16C-0.2Si-0.87Mn-0.33Cr-0.21Mo (wt. pct)] structural steel, during continuous cooling and under different mechanical loading conditions to promote martensitic transformation, has been studied. Time–temperature–load resolved 2D synchrotron diffraction patterns were recorded and used to calculate the phase fractions and lattice parameters of the phases during heating and cooling cycles under different loading conditions. In addition to the thermal expansion behavior, the effects of the applied stress on the elastic strains during the martensitic transformation were calculated. The results show that small tensile stresses applied at the transformation temperature do not change the kinetics of the phase transformation. The start temperature for the martensitic transformation increases with the increasing applied tensile stress. The elastic strains are not affected significantly with the increasing tensile stress. The variant selection during martensitic transformation under small applied loads (in the elastic region) is weak.     

Frictional HeatInduced Phase Transformation on Train Wheel Surface

By combining thermomechanical coupling finite element analysis with the characteristics of phase transformation [continuous cooling transformation (CCT) curve], the thermal fatigue behavior of train wheel steel under high speed and heavy load conditions was analyzed. The influence of different materials on the formation of the phase transformation zone of the wheel tread was discussed. The result showed that the peak temperature of wheel/track friction zone could be higher than the austenitizing temperature for braking. The depth of the austenitized region could reach a point of 09 mm beneath the wheel tread surface. The supercooled austenite is transformed to a hard and brittle martensite layer during the following rapid cooling process, which may lead to cracking and then spalling on the wheel tread surface. The decrease in carbon contents of the train wheel steel helps inhibit the formation of martensite by increasing the austenitizing temperature of the train wheel steel. When the carbon contents decrease from 07% to 04%, the Ac3 of the wheel steel is increased by 45 ℃, and the thickness of the martensite layer is decreased by 30%, which is helpful in reducing the thermal cycling fatigue of the train wheel tread such as spalling.     

Bainite Transformation Under Continuous Cooling of Nb-Microalloyed Low Carbon Steel

Utilizing Gleeble-1500 thermomechanical simulator, the influences of hot deformation parameters on continuous cooling bainite transformation in Nb-microalloyed low carbon steel were investigated. The results indicate that bainite starting temperature decreases with raising cooling rate and increases with increasing deformation temperature. Deformation has an accelerative effect on the bainite transformation when the specimens are deformed at 950 ℃. When the deformation temperature increases, the effect of deformation on bainite starting temperature is weakened. The amount of bainite is influenced by strain, cooling rate, and deformation temperature. When the specimens are deformed below 900 ℃, equiaxed ferrites are promoted and the bainite transformation is suppressed.     

Bainite Transformation of Low-carbon and Boron-containing Steel under Continuous Cooling

The effects of deformation temperature and strain on bainite transformation of low carbon steel and boroncontaining steel were investigated under continuous cooling conditions by means of dilatometric measurement and microstructure observation.The results show that with decreasing the deformation temperature from 1 000to 800 ℃and increasing strains,bainite start temperature for boron-containing low carbon steel increases,whereas it decreases for low carbon steel under the same condition.The bainite microstructures are easily obtained for boron-containing steel deformed at different temperatures and different strains compared with plain low carbon steel.With increasing the continuous cooling rate,the bainite start temperature under deformed condition is about 20 ℃ higher than that under undeformed condition for boron-containing steel,but it changes slightly when the cooling rate is 20℃/s or more.     

Effect of WarmRolled Pearlite Microstructural Features on Austenitic Transformation

The austenite transformation characteristics for various warmrolled pearlite during rapid heating were investigated. The results indicate that the start temperature (Ts) is sensitive to the microstructural feature of pearlite, whereas the dislocation plays an important role in the transformation rate; at the same time, the uniformity of austenite grains is more or less affected by the amount of spheroidized pearlite. A critical effect on the state of austenite grain is created through the influence of initial microstructures on the start temperature of transformation.     

Prediction of Deformation-Induced γ→α Transformation of 16MnNb Steel

Inpastdecades ,manyresearchershavebeendevelopingatechniquethatcan producelowalloysteelwithferritegrainsizesmallerthan 5 μmsincerefiningthegrainsizeofsteelisthebestwaytoim provebothstrengthandtoughnesssimultaneously .Amongthemsomeresearchershaveproduced 1μmfinegrainedferritesteelthroughthedeformation in ducedtransformation ,i e duringtransformationratherthanafterdeformation[1-3 ] ,andtheirexperi mentshaveshownthatthecombinationofappropri ateaustenitecondition ,deformationconditionandtemperatur…     

Effect of Rare Earths on Fractionation and Transformation of Soil Available Nitrogen

Chinahasthelargestreservesandproductionofrareearths (RE )intheworld ,andadvancedre searchesonapplicationofREinagriculturehavebeencarriedoutthroughoutthecountry[1] .Moreandmoreattentionhasbeenpaidtotheenvironmentaleffectofthelong termREapplicationsinagriculture ,andtheaccumulationofREintheplant soilsystemhasbe comeoneofthehotresearchtopics[2 ] .Previousstud iesshowthatlessthan 10 %ofthetotalREexistintheexchangeableformwhentheextraneousREareaddedtosoils ,asmostofthemarequicklyabsorbedandfixe…     

Grain Size Prediction after Continuous Cooling Transformation from Deformed Austenite to Ferrite

Ｐｒｅｃｉｓｅｐｒｅｄｉｃｔｉｏｎｏｆｆｅｒｒｉｔｅｇｒａｉｎｓｉｚｅ，ｄα，ｉｓｏｆｇｒｅａｔｉｍｐｏｒｔａｎｃｅｉｎｉｍｐｒｏｖｉｎｇｐｒｏｃｅｓｓｉｎｇｓｃｈｅｄｕｌｅａｎｄｍｅｃｈａｎｉｃａｌｐｒｏｐｅｒｔｉｅｓｏｆα＋Ｐｏｒα＋Ｂｓｔｅｅｌ...     

Martensitic Transformation Characteristics of Bonded Ni52Mn24.4Ga23.6 Magnets

Polycrystalline alloy Ni52 Mn24.4 Ga23.6 was prepared by repeated induction melting and bonded Ni52 Mn24.4 Ga23.6 magnets were prepared by powder compression method. The morphology, grain size,martensite transformation temperature and thermal hysteresis were investigated by means of DSC, XRD and SEM. The effects of external stress and magnetic fieldon martensitic transformation of bonded Ni52 Mn24.4Ga23.6 magnets were discussed.     

Effect of Laminar Cooling on Phase Transformation Evolution in Hot Rolling Process

 In the hot rolling processes, it always uses the laminar cooling system to control the cooling of plate and get the microstructure of different constitution. To investigate the effect of temperature variation due to the cooling pattern, rolling speed and thickness of plate on the microstructure evolution, a thermal-mechanical coupled FE model has been established. A set of constitutive equations of phase transformation is implemented into the commercial FE solver MARC through the user defined subroutine CRPLAW, and the temperature field is calculated by another user defined subroutine FILM. The effect of cooling pattern, rolling speed and thickness of plate on the temperature variation is numerically studied. Furthermore, the effect of temperature variation on the evolution of each phase transformation is investigated for various cooling pattern.     

Influence of Holding Time After Deformation on Bainite Transformation in Niobium Microalloyed Steel

  Using Gleeble 1500 system, the influence of holding time on bainite transformation in deformed niobium microalloyed steel during continuous cooling was analyzed, and the carbides in upper bainite were also systematically researched. The results show that the occurrence of the static recrystallization decreases the amount of bainite with an increase in the holding time and the emergence of retained austenite (RA) with the longer holding time. Two types of carbides were observed in upper bainite with regard to their precipitation sites. They either existed between the bainite ferrite laths or co existed with RA. The formation mechanism of two kinds of carbides was analyzed by combining TEM micrographs with the model.     

Effects of Rare Earths on the Tempering Transformation Kinetics of High Carbon Steel

ＥｆｆｅｃｔｓｏｆＲａｒｅＥａｒｔｈｓｏｎｔｈｅＴｅｍｐｅｒｉｎｇＴｒａｎｓｆｏｒｍａｔｉｏｎＫｉｎｅｔｉｃｓｏｆＨｉｇｈＣａｒｂｏｎＳｔｅｅｌＬｉｎＱｉｎ（林勤）；ＦｕＴｉｎｇ－Ｌｉｎｇ（付廷灵）；ＤｕＹｕａｎ－Ｓｈｅｎｇ（杜垣胜）ＹｕＺｏｎｇ－Ｓ...     

Laser Ultrasonic Measurements of Phase Transformation Kinetics in Lean Ti–Mo Alloys

Metallurgical and Materials Transactions A - Molybdenum (Mo) is one of the most common $$\beta $$ -stabilizing elements used in commercial titanium alloys. In comparison with other traditional...     

In-Situ High Temperature X-Ray Diffraction Study of Structure and Phase Transformation of Nd-FePt Alloys

The structure and disorder-order transformation of NdxFe60.5-x Pt39.5（x = 0, 0.5, 1.0, 1.5） alloys were investigated in situ by high temperature X-ray diffraction. The results show that the lattice parameter a of disordered γ phase （FCC, Al structure type） and the lattice parameter ratio c/a of ordered γ1 phase （FCT, L10 structure type） increase linearly with increasing Nd concentration, whereas the c/a ratio decreases with increasing temperature. The transition temperature from ordered FCT to disordered FCC decreases with increasing Nd concentration, but for alloys quenched rapidly from γ phase region into ice-water it increases with increasing Nd.     

Effect of Lanthanum on Nitrification, Phosphorus Transformation and Phenol Decomposition in Red Soil

The effect of La on nitrification, P transformation and phenol decomposition in red soil was studied by incubation and pot culture experiments. La at low concentration has stimulative effect on soil nitrification and P transformation while its high concentration has inhibitory effects, and the inhibition is strengthened with increasing concentration of La. La has strongly inhibitory effect on soil phenol decomposition and the inhibition is strengthened with increasing concentration of La. When the incubation time is prolonged, the inhibitory effect of La on soil nitrification and phenol decomposition tends to decrease.     

Computer Model of Phase Transformation From HotDeformed Austenite in Niobium Microalloyed Steels

Based on thermodynamics and kinetics, a new mathematical model was developed to calculate the CCT diagrams and the transformation kinetics in low carbon niobium steels, in which the effect of deformation on the degree of supercooling was taken into account. The undercooling caused by deformation is the major reason for the increase of the starting transition temperature during continuous cooling. The critical cooling rate of bainite formation is within 2-5 ℃/s for the studied niobium steels and deformation is suitable for the occurrence of pearlite. The ferrite volume fraction increases with the increase of the austenite boundary area, and decreases with the increase of the cooling rate. The calculated CCT diagrams and the volume fraction of each phase are in good agreement with the measurements.     

Austenite Grain Refinement by Reverse α′→γ Transformation in Metastable Austenitic Manganese Steel

Microstructure of metastable austenitic manganese steel after reverse transformation treatment was investigated using optical microscopy,X-ray diffraction(XRD),electrical resistivity and hardness testing.Austenite grain refinement was successfully achieved by a two-step heat treatment.First,martensite was produced by cooling the solution-treated samples to-196 ℃.Then,the deep cryogenic treated samples were heated to 850 ℃ upon slow or rapid heating.The mean size of original austenite grain was about 400μm.But the mean size of equiaxed reversion austenite was refined to 50μm.Microstructure evolution and electrical resistivity change showed that martensite plates underwent tempering action upon slow heating,and the residual austenite was decomposed,resulting in the formation of pearlite nodules at the austenite grains boundaries.The refinement mechanism upon slow heating is the diffusion-controlled nucleation and growth of austenite.However,the reverse transformation upon rapid heating was predominated by displacive manner.The residual austenite was not decomposed.The plateα-phase was carbon-supersaturated until the starting of reverse transformation.The reverse transformation was accompanied by surface effect,resulting in the formation of plate austenite with high density dislocations.The refinement mechanism upon rapid heating is the recrystallization of displacive reversed austenite.