Mechanical Properties and Microstructure Evolution of Cold-deformed High-nitrogen Nickel-free Austenitic Stainless Steel during Annealing

The mechanical properties and microstructure evolution of cold-deformed CrMnN austenitic stainless steel annealed in a temperature ranging from 50 ℃ to 650 ℃ for 90 min and at 550 ℃ for different time were investigated by tensile test, micro hardness test, and Transmission Electron Microscope （TEM）. The steel was strengthened when it got annealed at temperatures ranging from 100 ℃ to 550 ℃, while it was softened when it got annealed at temperatures ranging from 550 ℃ to 650 ℃. Annealing temperature had stronger effect on mechanical properties than annealing time. TEM observations showed that nano-sized precipitates formed when the steel was annealed at 150 ℃ for 90 min, but the size and density of precipitates had no noticeable change with annealing temperature and time. Recrystallization occurred when the steel was annealed at temperatures above 550 ℃ for 90 min, and its scale increased with annealing temperature. Nano-sized annealing twins were observed. The mechanisms that controlled the mechanical behaviors of the steel were discussed.

Microstructural evolution during ultra-rapid annealing of severely deformed low-carbon steel: strain, temperature, and heating rate effects

An interaction between ferrite recrystallization and austenite transformation in low-carbon steel occurs when recrystallization is delayed until the intercritical temperature range by employing high heating rate. The kinetics of recrystallization and transformation is affected by high heating rate and such an interaction. In this study, different levels of strain are applied to low-carbon steel using a severe plastic deformation method. Then, ultra-rapid annealing is performed at different heating rates of 200–1100°C/s and peak temperatures of near critical temperature. Five regimes are proposed to investigate the effects of heating rate, strain, and temperature on the interaction between recrystallization and transformation. The microstructural evolution of severely deformed low-carbon steel after ultra-rapid annealing is investigated based on the proposed regimes. Regarding the intensity and start temperature of the interaction, different microstructures consisting of ferrite and pearlite/martensite are formed. It is found that when the interaction is strong, the microstructure is refined because of the high kinetics of transformation and recrystallization. Moreover, strain shifts an interaction zone to a relatively higher heating rate. Therefore, severely deformed steel should be heated at relatively higher heating rates for it to undergo a strong interaction.

Study on Microstructure and Thermal Stability Behavior of Rapidly Solidified Al-Fe-Ce Alloy

Rapidly solidified Al 8Fe 4Ce alloy was prepared by melt spinning.As quenched and as annealed microstructures were studied by TEM and energy dispersive spectrum analysis.The microhardness of the alloy at different annealing temperature was measured.The results obtained indicated that as quenched microstructure varied with different cooling rates.The microstructure annealed at 300℃ was much the same as that of the as quenched.The dispersed phases at grain boundary of the microstructure annealed at 400℃ became coarsening.After annealing at 450℃ for 2 hours,the primary phase and the intercellular dispersed phases,metastable phase Al 6Fe and Al 20 Fe 5Ce respectively,coarsened further.The soften temperature was deduced at over 300℃ by measuring microhardness.

Microstructure of Differently Annealed NanocrystallineFe_(72.7)Cu_1Nb_(1.8)Mo_2Si_(13)B_(9.5) Alloy

The microstructure of differently annealed nanocrystalline Fe72.7Cu1Nb1.8Mo2Si13B9.5 alloy was investigated by using Mssbauer spectroscopy and transmission electron microscope. The specimens were isochronally annealed at temperatures between 480℃ and 600℃ for 0.5 h. The experimental results show that the microstructure mainly consists of the nanoscale bcc α-Fe(Si) grains and the residual amorphous matrix phase. A trace paramagnetic phase was found for annealing about above 500℃. The volume fraction of cr-Fe(Si) grain increases with increasing annealing temperature, whereas the average size of grain is almost unchanged above 480℃ up to 580℃. The calculated thickness of the intergranular layer of the residual amorphous matrix clearly decreases with increasing annealing temperature.

Evolution of microstructure and texture in copper during repetitive extrusion-upsetting and subsequent annealing

The evolution of the microstructure and texture in copper has been studied during repetitive extrusionupsetting（REU） to a total von Mises strain of 4.7 and during subsequent annealing at different temperatures. It is found that the texture is significantly altered by each deformation pass. A duplex 001 ＋ 111 fiber texture with an increased 111 component is observed after each extrusion pass,whereas the 110 fiber component dominates the texture after each upsetting pass. During REU, the microstructure is refined by deformation-induced boundaries. The average cell size after a total strain of 4.7 is measured to be ~0.3 μm. This refined microstructure is unstable at room temperature as is evident from the presence of a small number of recrystallized grains in the deformed matrix. Pronounced recrystallization took place during annealing at 200？C for 1 h with recrystallized grains developing predominantly in high misorientation regions. At 350？C the microstructure is fully recrystallized with an average grain size of only 2.3 μm and a very weak crystallographic texture. This REU-processed and subsequently annealed material is considered to be potentially suitable for using as a material for sputtering targets.

Characterizing microstructure and texture after recrystallization annealing of Hi-B steel with simutaneous decarburization and nitriding

How to manufacture the high magnetic induction grain-oriented silicon steel（Hi-B steel）by the process featured with the primary recrystallization annealing was demonstrated,during which nitriding and decarburizing were simultaneously realized in laboratory.By the techniques of optical microscope,scanning electronic microscope and electron backscattered diffraction,both the microstructure and the texture in the samples were characterized.The samples had been subjected to nitriding to different nitrogen contents at two specified temperatures using the two defined microstructural parameters：the grain size inhomogeneity factorσ＊and the texture factor AR.The former is the ratio of the mean value to standard deviation of grain sizes;the latter is the ratio of the total volume fraction of the harmful textures to that of beneficial textures including {110}〈001〉.When the N content increased from 0.0055%to 0.0330%after the annealing at both 835 and 875°C,the resultant recrystallized grain size decreased butσ＊changed little;whilst the rise of annealing temperature from 835 to 875°C resulted in the increase in both grain size andσ＊.Moreover,either the injected N content or temperature had insignificant influence on the components of primary recrystallization texture developed during annealing.However,the increase of temperature led to the decreases in both intensity and volume fraction of{001}〈120〉and{110}〈001〉textures but increases in the{114}〈481〉andγfiber textures and the resultant decrease of AR.

Effect of Subcritical Annealing Temperature on Microstructure and Mechanical Properties of SCM435 Steel

The effect of subcritical annealing temperature on microstructure and mechanical properties of SCM435 steel was investigated through changing the heating and soaking temperature as 660 °C, 680 °C, 700 °C, 720 °C and 745 °C. The microstructure and mechanical properties of intercritically annealed specimens were analyzed. With increasing the subcritical annealing temperature from 660 °C to 720 °C, the spheroidization ratio gradually increased, and the mechanical properties, formability and Vickers hardness were improved. According to the comprehensive comparison of mechanical properties and formability, the subcritical process at soaking temperature of 680-720 °C could achieve similar annealing effect as that of intercritical process. Therefore, the subcritical annealing temperature could be set as 700 °C in practice, with the Ac1 temperature fluctuation within ±20 °C, and the applicability and stability of subcritical annealing were guaranteed in industrial application. The plant results of the cold heading showed that the subcritical annealing could replace original intercritical annealing successfully with significantly saving time and energy.

Effects of Cr Content and Annealing Temperature on Microstructure and Wear Characteristics of Cast Ausferrite Nodular Iron

The effects of Cr content and annealing temperature on abrasive wear characteristics of cast ausferrite nodular iron were investigated with Suga type abrasive wear tester. The surface morphology and Vickers hardness of the tested samples were analyzed by scanning electron microscopy（SEM）, digital microscope and Vickers hardness tester. The results show that the cast ausferrite nodular iron could be obtained by alloying with Cr in the as-cast ductile cast iron and permanent mold casting, and the bainite content in the matrix increased with increasing Cr content. However, the decomposition of bainite took place during annealing at 500 °C to 800 °C; especially, at 800 °C, the bainite transformed into a mixture of fine lamellar pearlite and ferrite matrix structure. The wear loss of specimens was reduced with increasing Cr content in the cast ausferrite nodular iron. The wear loss of the sample cast ausferrite nodular iron with 0.4mass% Cr is the least. The wear loss began to increase while the Cr content is 0.6mass%. The wear loss of annealed ductile irons at different annealing temperatures was higher than that of as-cast samples. During the abrasive wear, the shear stress transformed austenite to martensite, and the hardness of specimens increased and the wear resistance of as-cast ductile cast iron was improved.

Microstructures in a Nb-Cr-V-W-Ta high entropy alloy during annealing

A Nb-Cr-V-W-Ta high entropy alloy has been subjected to annealing treatment at 600,700 and 800℃in air for 6 h.Five different phases have been identified based on their composition in the as received condition.The annealing treatment does not alter the phase analysis and compositions except for the W-rich phase where minor changes in the composition have been observed.This is considered as an experimental evidence of sluggish diffusivity associated with HEAs.Absence of phase transformation during the heating and the minimal changes in observed compositions of the phases is an indication of the resistance to diffusion offered by the elements of the high entropy alloy.Scanning electron microscopy(SEM),energy dispersive spectroscopy(EDS)and color X-ray elemental mapping have been used to conduct this research.