Molybdenum alloying in cast iron and steel

Metal casting is an important manufacturing technology for efficiently producing massive components with complex shape. A large share of industrial castings is made from iron and steel alloys, combining attractive properties and low production cost. Upgrading of properties in cast iron and steel is mainly achieved by alloying and in fewer cases by heat treatment. Molybdenum is an important alloying element in that respect, increasing strength, hardness and toughness. It also facilitates particular heat treatments such as austempering. The paper describes the metallurgical functionality of molybdenum alloying in iron-based castings and demonstrates its effectiveness for applications in the automotive and mining industry.The full text can be downloaded at https://link.springer.com/content/pdf/10.1007/s40436-019-00282-1.pdf     

Phase transformation and microstructure evolution of pearlite heat-resistant steel during heating

ABSTRACT

The phase transformation and microstructure evolution of pearlite heat-resistant steel during heating were observed with an ultra-high temperature confocal scanning laser microscope. The α-ferrite completely disappeared earlier than Fe₃C during the formation of γ-austenite, which is inconsistent with the fact that the Fe₃C should disappear completely earlier under equilibrium conditions. After the Fe₃C?+?α→γ transformation, static recrystallisation of γ-austenite occurred, accompanied by the dissolution of cementite. During the γ→δ transformation, the δ-cell first precipitated at the triple point of the γ-austenite grain boundaries, and then the δ-cell platelet with one tip appeared in the γ-austenite grain. The law of δ/γ inter-phase boundaries was analysed based on inter-phase boundary types and element diffusion.     

加热炉炉管的安全评定及剩余寿命预测

某炼油厂加热炉炉管仅运行18个月,就发生失效,造成巨大经济损失,因此有必要对剩余炉管进行全面的安全评定和剩余寿命预测,以保证炉管在一个检修周期内能安全平稳运行.通过对炉管的化学成分及金相组织进行了分析,发现材料的珠光体显微组织已经球化,通过现场对管线硬度及壁厚的检测,以及对壁厚进行的强度校核,得出在目前的工况条件下,仍...     

珠光砂进入低温系统的故障排除

由于6000 m3/h空分设备的低温管道焊缝开裂,珠光砂进入低温系统,导致上塔精馏工况不正常,产品氧气纯度和产品氮气量不达标。简介故障发生时空分设备运行参数的异常情况,介绍清除珠光砂的方案及调整后的吹扫方法,最后总结了从中得到的教训。     

Effect of dissolved niobium on eutectoid transformation behavior

The effect of dissolved niobium on the eutectoid transformation behavior in near-eutectoid high-carbon steels has been studied.Dissolved niobium is important in the eutectoid transformation behavior.It increases the eutectoid carbon content significantly(by~0.0477% per 0.00001% dissolved niobium),increases the hardenability of steel markedly,yields finer,more uniform,polygonal proeutectoid ferrite,induces a transition in morphology of eutectoid cementite from lamellar to somewhat spheroidal,and increases the misorientation angle of pearlite colonies from being focused near 0°to near 60°.     

Simplification of heat treatment process in a tool steel by aluminium addition

A novel concept for simplification of heat treatment process in a tool steel by the addition of aluminium has been proposed in this research. The addition of 1.08?wt-% aluminium leads to an approximately fully pearlitic state, of which the cementite lamellae are largely spheroidised. Excessive addition of 1.58?wt-% aluminium would result in the formation of a large amount of δ-ferrite. These results are mainly attributed to the synthetic effect of aluminium on the driving force of pearlite transformation and the inter-spacing distance between the proeutectoid carbides. The mechanical properties’ analyses show that aluminium has promising potential to substantially simplify the processing method for developing a relative low-cost mould steel without the concomitant mechanical properties’ reductions.     

Theoretical and numerical study of lamellar eutectoid growth influenced by volume diffusion

We investigate the lamellar growth of pearlite at the expense of austenite during the eutectoid transformation in steel. To begin with, we extend the Jackson–Hunt-type calculation (previously used to analyze eutectic transformation) to eutectoid transformation by accounting for diffusion in all the phases. Our principal finding is that the growth rates in the presence of diffusion in all the phases are different compared to the case when diffusion in growing phases is absent. The difference in the dynamics is described by a factor ’ρ’ which comprises the ratio of the diffusivities of the bulk and the growing phases, along with the ratios of the slopes of the phase coexistence lines. Thereafter, we perform phase-field simulations, the results of which are in agreement with analytical predictions. The phase-field simulations also reveal that diffusion in austenite as well as ferrite leads to the formation of tapered cementite along with an overall increase in the transformation kinetics as compared to diffusion in austenite (only). Finally, it is worth noting that the aim of present work is not to consider the pearlitic transformation in totality; rather it is to isolate and thereby investigate the influence of diffusivity in the growing phases on the front velocity.     

0.75C共析钢压缩变形时的组织演变

通过Gleeble 2000和1500热模拟试验机,研究了0.75C共析钢珠光体和过冷奥氏体在压缩变形过程 中的组织演变。试验结果表明,试样以10℃/s加热至700 ℃ 3 min进行60%压缩变形,钢中珠光体片层发生断裂、 破碎;试样加热至1150℃1 min奥氏体化后以20℃/s冷却至700 ℃,压缩变形60%,在变形作用下,钢中部分过冷奥氏体转变成细片层珠光体。     

Pearlite determination in plain carbon steel by eddy current method

Eddy current method has been used for the evaluation of pearlitic microstructure in low to high plain carbon steels. Plain carbon steel samples were heat treated in a furnace. Half of these were slowly cooled in the furnace and half in the air. This resulted in different pearlitic microstructures in the samples. Eddy current readings for all the samples were recorded and studied. It was found that eddy current measurement can be used for obtaining reliable and quick detection of pearlitic percentage in plain carbon steels.