Time-dependent synchrotron X-ray diffraction on the austenite decomposition kinetics in SAE 52100 bearing steel at elevated temperatures under tensile stress

We have studied the decomposition kinetics of the metastable austenite phase present in quenched-and-tempered SAE 52100 steel by in situ high-energy synchrotron X-ray diffraction experiments at elevated temperatures of 200–235 °C under a constant tensile stress. We have observed a continuous decomposition of austenite into ferrite and cementite. The decomposition kinetics is controlled by the long-range diffusion of carbon atoms into the austenite ahead of the moving austenite/ferrite interface. The presence of a tensile stress of 295 MPa favours the carbon diffusion in the remaining austenite, so that the activation energy for the overall process decreases from 138–148 to 82–104 kJ mol^?1. Before the austenite starts to decompose, a significant amount of carbon atoms partition from the surrounding martensite phase into the metastable austenite grains. This carbon partitioning takes place simultaneously with the carbide precipitation due to the over-tempering of the martensite phase. As the austenite decomposition proceeds gradually at a constant temperature and stress, the elastic strain in the remaining austenite grains continuously decreases. Consequently, the remaining austenite grains act as a reinforcement of the ferritic matrix at longer isothermal holding times. The texture evolution in the constituent phases reflects both significant grain rotations and crystal orientation relationships between the parent austenite phase and the newly formed ferritic grains.     

Isothermal transformation of supercooled austenite in steel 75KhSMF

Conclusion A T-T-T diagram for steel 75KhSMF was plotted. It was found that the transformation ceases in the pearlitic and intermediate temperature ranges.Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 1, pp. 66–67, January, 1972.     

Iterative taguchi analysis: Optimizing the austenite content and hardness in 52100 steel

Three iterations of Taguchi designed experiments and analyses were used to determine optimal thermal treatments for minimizing retained austenite content while maximizing Rockwell hardness (HRC) in AISI 52100 bearing steel. Experimental variables chosen for this study included austenitizing and tempering temperatures, tempering time and cold treatment. After one iteration, tempering temperature and cold treatment were seen to have the greatest effect on austenite content while austenitizing and tempering temperatures had the greatest influence on hardness. After the second and third experimental iterations, two thermal treatments were noted each producing hardness of 58–59 HRC in combination with zero retained austenite as measured by x-ray diffraction.     

Transformation of supercooled austenite in now-alloy steel 16GFR during continuous cooling

Conclusions A C–C–T diagram was plotted for steel 16GFR, which makes it possible to predict with adequate reliability the character of the structure formed during cooling of pipe at given rates under plant conditions and thus to correct the heat-treatment process for pipe made of steel 16GFR with strength _b=720 MPa and guarantee the mechanical properties and cold resistance required.Institute of Ferrous Metallurgy, Dnepropetrovsk. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 7, pp. 54–56, July, 1981.     

热处理工艺对SAE4320钢奥氏体晶粒度的影响

对出现严重混晶的SAE4320钢在640~1000℃保温2 h后空冷,再采用模拟渗碳法进行奥氏体晶粒度检测及分析。结果表明,渗碳轴承钢SAE4320奥氏体晶粒度出现混晶与终轧温度过低有关;当SAE4320钢出现混晶时,经740~760℃保温2 h空冷后奥氏体晶粒度可达8.0~7.0级。     

1.25Cr0.5MoSiNb钢过冷奥氏体连续冷却转变

在Formastor-FⅡ相变仪上,用膨胀法测定了 1.25Cr0.5MoSiNb钢在不同冷速下过冷奥氏体连续冷却时的膨胀曲线;采用切线法获得了相转变点,结合硬度和金相测试,用Origin 软件绘制了实验钢过冷奥氏体连续冷却相转变曲线(CCT 曲线),并用实验验证了 CCT曲线的准确性.结果表明:实验钢的临界点Acl和...     

Influence of refrigeration/lubrication condition on SAE 52100 hardened steel turning at several cutting speeds

Nowadays, the use of cutting fluids on machining operations has been questioned, due to problems they may cause to the environment, due to damage to human health and also more due to the severe laws regarding industrial waste that have been passed. Therefore, industries are being forced to review the production processes aiming either, at elimination or, when it is not possible, a sharp reduction in the use of these fluids. The technique of minimum volume of oil (MVO) has been studied in machining processes as one alternative to the use of abundant cutting fluid. Research has shown that this technique, which is the pulverisation of a minimum volume of oil in a flow of compressed air, in several cases, reduces tool wear when compared to complete dry cutting, causing the improvement of the workpiece surface quality and an increase in tool life. In this work, the influence of MVO (oil flow of 10 ml/h) in the wear of a cubic boron nitride (CBN) tool, when turning 52100 hardened steel, was studied. Aiming at a comparison of the results, the experiments were also carried out under two other conditions: dry cutting and cutting with abundant soluble oil (wet cutting). During the experiments, the influence of cutting speed on CBN tool wear for the three refrigeration conditions was also checked. Besides this, tool wear and workpiece surface roughness was also measured as cutting time elapsed.     

Influence of kinetics of supercooled austenite decomposition on structure formation in sparingly-alloyed tool steel

The decomposition of supercooled austenite in 70Kh3G2VTB steel under isothermal conditions and continuous cooling have been studied. The isothermal and continuous cooling tranformation curves of the decomposition of austenite in the experimental steel have been constructed. The effect of alloying elements on phase transformations in the steel under heating and cooling have been established. The features of the formation of a microstructure in the 70Kh3G2VTB steel after different regimes of heat treatment have been described. The optimal parameters of hardening heat treatment have been developed.     

Metallurgical influence on quench distortion of SAE 52100 long cylinders

Abstract

Quenching of steel components results in complex and hard-to-predict dimensional and shape changes (distortion). Even the components manufactured from different parts of the same semifinished product may show significantly different distortion behaviours during quenching. The reason is thought to be non-uniform distribution of distortion potential carriers in the final component (i.e. alloying elements, segregations, residual stresses and phases) which are accumulated throughout the whole manufacturing chain. This study focuses on the effects of alloying element distribution and segregation on quench distortion. For this aim, long cylinders of various diameters were machined from 45 mm diameter SAE 52100 steel bars, and marked to define their exact positions in the initial bar. Then the cylinders were austenitised in a vertical furnace under nitrogen atmosphere and quenched in a gas nozzle field. The coordinate measurement results show that dimensional changes deviate significantly with machining position; however, the bending magnitudes and directions do not exhibit a distinct correlation with machining position and the cylinder diameter.     

冶金因素对SAE52100长圆柱体淬火畸变的影响

钢件淬火会导致其产生复杂且难以预测的尺寸和形状改变(畸变)。甚至用同一块坯料不同部位的材料制作的零件,其淬火过程中发生的畸变行为也大不相同。这是由于若干引起畸变的潜在因素(如合金元素、偏析、残余应力和相组成等)不均匀分布所造成的,而这些潜在因素作用的累积贯穿于零件制造的全过程。本文研究了合金元素的分布和偏析对淬火畸变的影响。研究用试棒为用直径45 mm的SAE 52100钢棒料加工成的不同直径圆柱体,并将其编号,以便分辨其在原棒料上的确切位置。然后将试棒装入通氮气保护的井式炉加热奥氏体化,随后进行喷气淬火。测量结果表明,试棒在淬火过程中的尺寸变化与其在坯料中的取样位置密切相关,而试棒的弯曲程度和方向与取样位置和直径之间没有显著的关联。