Austenite Grain Size Of Steel Research Articles

Prediction of austenite grain growth during austenitization of a 0.7%C pearlitic rail steel

The prior austenite grain size of steels greatly influences the phase transformation kinetics during austenitization and the microstructure which determines the mechanical properties. The effect of temperature and time on austenite grain growth of 0.7% carbon rail steel during reheating was studied. The grain growth behaviour of this steel was investigated under different heating temperatures and holding times at a constant heating rate of 4°C/min. Samples were heated in a tube furnace at temperatures of 1150, 1200 and 1250oC and held for 0, 1800, 3600, 5400, 7200 and 9000 seconds before quenching into water. The prior austenite grains were observed using an optical microscope and austenite grain sizes were measured by the linear intercept method. The measured austenite grain sizes were used in determining the grain growth constants Q, A and n which were used in developing the constitutive equation for grain growth prediction. A good agreement was found between the actual and the predicted austenite grain size within the typical industrial soaking temperature range of 1150 and 1200oC.

The important role of titanium microalloying in refining austenite grain of heavy‐duty H‐beam steel during rough rolling produced by a new technology

AbstractA new technology of austenite grain refinement, fine austenite enhanced ferrite transformation, is proposed for heavy‐duty hot‐rolled H‐beam steels in this work. Titanium microalloying is very important and necessary for the new technology. The effect of titanium on the prior austenite grain size of steels during simulated rough rolling was investigated. The results show that the prior austenite grain sizes of specimens with titanium and niobium elements are much finer than those of specimens with niobium but without titanium deformed at the same parameters. For the alloying composition of studied steels, titanium nitride particle maybe precipitated in specimens with titanium at above 1,200 °C, however, niobium carbide particles can't form in specimens without titanium at above 1,150 °C. The thermodynamically stable titanium nitride particles can impede the grain growth at high temperature for example furnace heating before rough rolling and bring the epitaxial growth of niobium carbide on pre‐existing themselves which induces a large number of titanium nitride‐niobium carbide composite precipitates. These fine precipitates can pin austenite grain boundaries effectively and ensure austenite grain refinement.

Metal additive manufacturing of carbon steel with direct laser deposition: computer simulation

Metal 3D printing technology is commercially available, but the quality of the printed product is still a challenging issue that needs to be improved. More research is needed to address the essential technical details of metal 3D printing. Important technical details are the alloy microstructure, imperfections like pores, distortion, surface roughness, and residual stress, which affect the mechanical properties of the printed sample like fatigue performance. This research has computationally studied metal 3D printing for carbon steel to address the parameters that affect the quality of the final product printed by direct laser deposition. Multiscale multiphysics computational algorithms were coding in Microsoft Visual Basics 2015 to simulate the thermal stress, deformation, and austenite grain topology. Energy and force equilibrium equations were numerically solved to simulate the thermal and mechanical history versus print’s adjustable parameters like scan speed, laser power, and rate of metal powders injection through the nozzle. The austenite grain size of steel is an important parameter that is directly related to the local thermal history. A stochastic computational code was developed to simulate grain morphology based on calculated thermal history. The simulation showed the dependence of von Mises stress and thermal history on the rate of metal powders injection, laser power, and scan speed. The simulation showed a rise in von Mises stress by increasing the scan speed and laser power. Print speed and laser power also change the local maximum temperature and the local alloy microstructure. The local austenite grain size increases by reducing scan speed in the heat-affected zone. The simulation showed that the microstructure of the printed part is not uniform, and different layers are distinctive.

Prediction model of austenite growth and the role of MnS inclusions in non-quenched and tempered steel

The austenite growth behavior of non-quenched and tempered steels (casted by continuous casting and molding casting processes) was studied. The austenite grain size of steel B casted by continuous casting process is smaller than that of steel A casted by molding casting process at the same heating parameters. The abnormal austenite growth temperature of the steels A and B are 950 °C and 1000 °C, respectively. Based on the results, the models for the austenite grain growth below and above the abnormal austenite growth temperature of the investigated steels were established. The dispersedly distributed fine particles MnS in steel B is the key factor refining the austenite grain by pinning the migration of austenite grain boundary. The elongated inclusions MnS are ineffective in preventing the austenite grain growth at high heating temperature. For the non-quenched and tempered steel, the continuous casting process should be adopted and the inclusion MnS should be elliptical, smaller in size and distributed uniformly in order to refine the final microstructure and also improve the mechanical properties.

Abnormal relationship between Ms temperature and prior austenite grain size in Al-alloyed steels

It has been generally accepted in the literature that the decrease in prior austenite grain size leads to a decrease in Ms temperature in steels. However, in the present study, it is found that Ms temperature increases with the decrease of prior austenite grain size in steels with an addition of Al content higher than 1wt%. It is revealed that the Al segregation at prior austenite grain boundaries may be the origin of this abnormal phenomenon.

The Effect of B and Microalloying Elements (V, Ti, Nb) Additions on the Austenite Grain Growth of Low Alloy Steel

The effect of B and microalloying additions of V, V+Ti, V+Nb on austenite grain growth of low alloy steel containing 0.3% C, 1 % Cr and 0.2 % Mo was investigated. As a measure of austenite grain size the mean chord length of austenite grains was assumed. The boron content in investigated steel was in the range of 0 to 0.008 %. The investigations were carried out in austenitising temperature range of 850 to 1100oC. Using the thermodynamic model the contents of undissolved compounds of carbonitride V(C,N) and boron nitride BN were calculated and the effect of undissolved compounds content on austenite grain size was investigated. Obtained results showed, that vanadium content below 0.1 % was ineffective as austenite grain growth inhibitor of boron containing steel and austenite grain size of steel was higher compare to non-alloyed steel. The most effective for decreasing of austenite grains size of boron containing steel was addition of 0.18 % V + 0.03 % Nb

Influence of TiN particles distribution on static recrystallisation in structural steels at reheating temperature

Results of investigations concerning the influence of Ti and N contents on static recrystallisation kinetics are presented. By means of torsion tests, and applying the back extrapolation method, the statically recrystallised fraction has been determined for four structural steels with different Ti and N contents, at different temperatures, equivalent strain of 0.35 and strain rate of 3.63 s−1. Two reheating temperatures have been used to obtain different austenite grain sizes and different precipitate mean size in steels containing Ti. The results show that a low precipitated volume and a relatively large size of precipitates, at reheating temperature, did not impede grain boundary self‐diffusion during the static recrystallisation, the main mechanism governing static recrystallisation. Nevertheless, the smaller size of the precipitates acted as an obstacle to grain boundary self‐diffusion. These effects were measured by calculation of the activation energy for static recrystallisation. On the other hand, the influence of austenite grain size in steels containing Ti can not be correctly determined, as at each reheating temperature, in addition to a different austenite grain, the distribution of precipitates is also different, affecting the activation energy and making it impossible to clearly appreciate the influence of austenite grain size.

Fe-Mn合金のεマルテンサイト変態および機械的性質に及ぼす結晶粒径の影響

The effects of austenite (γ) grain size on the transformation to ε martensite (ε) and mechanical properties have been investigated in high manganese steels by means of calorimetric analysis, optical microscopy, scanning electron microscopy and X-ray diffraction analysis. Austenite grain size of steels was controlled to be 100 μm or 10 μm in the mean grain size by the recrystallization method. With grain refining, the starting temperature of γ→ε transformation tends to be lowered and the formation of ε is suppressed in all of high manganese steels which undergo γ→ε transformation. For 15∼31 mass%Mn steels, both of elongation and tensile strength are markedly enlarged by grain refining. Fracture modes of these high manganese steels are largely dependent on microstructures and deformation behavior. Effect of γ grain size on the fracture modes was discussed in detail for 22 mass%Mn and 27 mass%Mn steels. When the size of γ grains is as large as 100 μm, a significant stress concentration takes place at the intersections of ε plates in a 22 mass%Mn steel, while does at grain boundaries on which deformation induced ε plates impinge in a 27 mass%Mn steel. Such a stress concentration at ε plates or grain boundaries causes the formation of microcracks and this leads to the onset of quasi-cleavage fractures. When the size of γ grains is refined to 10 μm, however, quasi-cleavage fractures are suppressed in the both steels. Refining of γ grains produces favorable effects; 1) change in the morphology of athermal ε, 2) decrease in the stress concentration at grain boundaries, 3) uniform dispersion of strain. For the suppression of quasi-cleavage fractures by γ grain refining, the effect 1) is most contributive in a 22 mass%Mn steel, while in a 27 mass%Mn steel, only the effects of 2) and 3) are workable.

Effect of the amount and dispersity of hard-to-dissolve particles on austenite grain size in steel with 0.6% C

We propose steels with additions of vanadium or niobium to ensure a fine austenite grain size (grade 13–14) heated at moderate rates (20–60 deg/sec) to 1050° with isothermal holding (at 950°) for 5–6 min.

鋼のオーステナイト結晶粒度に及ぼす鍛造, 前熱処理の影響およびオーステナイトとフェライト結晶粒度の関係

鋼のオーステナイト結晶粒度に及ぼす鍛造, 前熱処理の影響およびオーステナイトとフェライト結晶粒度の関係

鋼のオーステナイト結晶粒度におよぼすほう素, 酸素, いおう, ニッケル, 銅およびジルコニウムの影響

鋼のオーステナイト結晶粒度におよぼすほう素, 酸素, いおう, ニッケル, 銅およびジルコニウムの影響

鋼のオーステナイト結晶粒度におよぼすアルミニウム, 窒素, 炭素, けい素, およびマンガンの影響

鋼のオーステナイト結晶粒度におよぼすアルミニウム, 窒素, 炭素, けい素, およびマンガンの影響

オーステナイト結晶粒度現出方法に関する考察

オーステナイト結晶粒度現出方法に関する考察

High Temperature Microscope Observation of the Austenite Grain Size of Steels

In order to determine continuously the austenite grain size of steels with a high temperature microscope, observations of the austenite grain growth of 0.2% C steels (Si–Mn killed, or Al killed) in various atmospheres were carried out. The results obtained were as follows:(1) When 0.2% C steels were heated in 3×10−5 mmHg vacuum, the austenite grains on the surface were coarsened remarkably to ASTM No.2 at 950°C, and their grain size was markedly different from that in the inner zone.(2) When these steels were heated in extremely pure argon atmosphere in the pressure range of 0.6∼1.0 atm, the austenite grains on the surface maintained a grain size of ASTM No. 8 up to about 1150°C, and then coarsened. The value of their grain size was nearly equal to that of the inner grains.(3) According to an electron microscopic study, the degree of oxidation on the specimen surface in high vacuum was less than that in argon. Therefore a high vacuum was replaced with the argon atmosphere at 950°C or 1000°C, but no changes in grain size were observed.(4) As regards the surface grain growth of 0.2% C steels in various atmospheres, it was observed that the lower the degree of vacuum or the higher the argon pressure, the higher the grain coarsening temperature.(5) Remarkable grain growth which occurred at about 950°C in high vacuum was also observed at the specimen surface several microns in depth even after removing the mechanically polished layer by electrolytic polishing.

鋼のオーステナイト粒度の高温顕微鏡観察

鋼のオーステナイト粒度の高温顕微鏡観察

正誤表

正誤表

鋼のオーステナイト結晶粒度におよぼす前処理の影響

鋼のオーステナイト結晶粒度におよぼす前処理の影響

オーステナイト結晶粒度現出法に関する研究

As the revealing method of austenite grain size of steel, usually, various technique such as carburizing method has been used, although these are not sufficient because of unquickness for determination, complex procedure, and difficulties caused by the influence of alloying elements.Authors studied on methods of carburizing-, graphite-, double quenching-, quenching-and oxidizing and found the metal diffusion method being easy for determination of grain size, and determined its application range.On the metal diffusion method, the new technique using lead as diffused metal was devised. The authors were convinced that the grain size could be determined by this method without the influence of alloying elements on any steels.

Mr-Cr肌焼鋼の低温焼戻脆性に及ぼすAl, Ti及びBの影響

The cause of the hard tempered martepsite brittleness which has come to be known as "500°F embrittlement" has not been explained until today. The phenomenon was much relatd to the deoxidation, nitrogen-fixation, and austenite grain size of steel. The tempering characteristics of the steel plays a major role in the development of embrittlement. This investigation consists of a stuay of the effect of Al, Ti and B addition on the impact-resistance and an electron micrgscopic study of the manganese-chromium case hardening steel when tempered between 120° and 420°C. The results obtained are as follows:(1) The Al-Ti (0.05-0.10%) addition markedly improves the impact values during tempering at these temperatures, especially with Ti addition the benefibal effect in the ternperature range of embrittlement is distinct.(2) The tempering embrittlement temperqture is not changed with the Al or Al-Ti addition and it occures at 300°C to 360°C; however in the case of Al-Ti-B addition it is the temperature range at 300°C to 420°C(3) The impact minimum occurs in 20 to 30 minutes at the tempering embrittlement temperatures and the value is decreased with keeping time at 300°C, it is almost constant up to 10h at 360°C.(4) The transition temperature is lowered by the Al, Ti and Al-Ti-B additiop; with the Al (0.04%), Ti(0.10%) and Al-Ti (0.06%)-B addition it falls down to 0°C-10°C.(5) It is obeerved that the embrittlement arises from a precipitation of elongated thin cementite network along ferrite grain boundaries, with the B addition the formation is obserVed at the higher tempering temperature.

Metallographic Techniques for Austenite Grain Size of Steels in the As-Cast State

Metallographic Techniques for Austenite Grain Size of Steels in the As-Cast State