Influence of alloying elements Cu,Ni and Mo on mechanical properties and austemperability of austempered ductile iron

Abstract

Austempered ductile iron (ADI) is the most recent development in the nodular iron family. The austempering treatment produces a unique microstructure, ausferrite, which provides high mechanical strength combined with ductility, toughness, and good fatigue and wear resistance. The effect of alloying elements Cu, Ni and Mo on the mechanical properties and austemperability of ADI is reported. The mechanical strength and toughness decreased with the addition of Mo, but both wear resistance and austemperability increased with Mo content.     

等温淬火球墨铸铁的等淬工艺及其壁厚敏感性

本文研究了奥氏体－贝氏体等温淬火球墨铸铁（以下简称ＡＤＩ）等淬工艺对组织、性能的影响,得到了各项力学性能指标所对应的工艺参数;对２０ｍｍ－５０ｍｍ范围试样壁厚敏感性进行了试验,认为通过控制合金成分、球化、孕育、等淬工艺可使断面组织均匀、齐一性好,并作了理论分析。     

Austempered Ductile Iron—Processing and Properties

Recent research on austempered ductile irons (ADI) has been reviewed. The physical metallurgy of the austempering reaction and the important effects of alloying elements are discussed, along with an analysis of research results from the perspectives of ADI foundry and heat treatment process control and quality assurance. Both the existing database of ADI mechanical properties and progress made toward the specification of various ADI grades worldwide have been summarised. Although many fundamental questions remain regarding microstructure/property/processing relationships for the new and metallurgically complex family of ADI materials, foundry processing and heat treatment guidelines have been established for the successful production of ADI. Casting quality requirements are high due to the demanding combination of strength and toughness desired for ADI and to ensure consistent heat-treatment response during austempering.     

奥-贝球铁焊接研究进展

介绍了近１０年来奥－贝球铁焊接研究进展,重要介绍了奥－贝球铁焊接冶金,获得奥－贝球铁焊缝金属的等温热处理工艺和焊接工艺特点,焊态直接获得奥－贝球铁焊缝的途径及奥－贝球铁焊接新材料。奥－贝球铁焊缝金属可以通过等温热处理获得,也可以在焊态下直接获得。对于前者,研究工作主要集中在合金元素对球铁焊缝白口倾向的影响,球铁焊缝金属等温转变及组织结构特点,等温热处理工艺对奥－贝球铁焊缝组织与力学性能的影响。而对于后者的研究则更多地集中于焊缝化学成分和冷却速度对焊态奥－贝球铁焊缝组织与力学性能的影响。研制成功的奥－贝球铁焊接新材料,其焊缝的组织与力学性能满足奥－贝球铁的要求。     

Effects of Cu， Ni， Mn and Mo on the austemperability， microstructures and mechanical properties of ADI weld metal

ＥｆｆｅｃｔｓｏｆＣｕ，Ｎｉ，ＭｎａｎｄＭｏｏｎｔｈｅａｕｓｔｅｍｐｅｒａｂｉｌｉｔｙ，ｍｉｃｒｏｓｔｒｕｃｔｕｒｅｓａｎｄｍｅｃｈａｎｉｃａｌｐｒｏｐｅｒｔｉｅｓｏｆＡＤＩｗｅｌｄｍｅｔａｌＳＵＮＤａｑｉａｎ；ＺＨＯＵＺｈｅｎｆｅｎｇａｎｄＲＥＮＺ...     

等温处理工艺对等温淬火球铁显微组织和硬度的影响

上世纪70年代,通过奥氏体等温淬火开发出抗拉强度大于1000MPa、伸长率大于15％的高强度、高韧性等温淬火球铁。利用正交试验法,研究了等温淬火工艺参数对等温淬火球铁显微组织及硬度的影响。结果发现,在设计的试验工艺内全部可以得到以针状铁素体和富碳奥氏体为基体的等温淬火球铁组织;在等温淬火工艺中,等温淬火温度对试样硬度影响最为显著,其次是奥氏体化温度与奥氏体化时间,而等温淬火时间对于试样硬度的影响最小。     

镍、铜低合金奥贝球铁特性研究

阐明了含Ni、Cu质量分数分别为1.5%和0.8%的奥贝球铁的凝固/相变和性能特点。测定了凝固过程的微分热分析曲线、膨胀仪曲线、绘制了奥氏体连续冷却较变曲线和等温转变动力学曲线，对比分析了该成分铸铁的淬透性。测定了Ni、Cu合金化奥贝球铁的常温力学性能。     

The influence of nickel and copper on the austempering of ductile iron

In the present investigation, the effect of alloying elements on the austempering process, austempered microstructure, and structural parameters of two austempered ductile irons (ADI) containing 0.6% Cu and 0.6% Cu/1.0% Ni as the main alloying elements was investigated. The optical metallography and x-ray diffraction were used to study the changes in the austempered structure. The effect of alloying additions on the austempering kinetics was studied using the Avrami equation. Significantly more upper bainite was observed in the austempered Cu-Ni alloyed ADI than in Cu alloyed ADI. The volume fraction of retained austenite (X _γ), the carbon level in the retained austenite (C _γ), and the product X _γ C _γ in an austempered structure of Cu-alloyed ADI are higher than in Cu-Ni-alloyed ADI. The austempering Kinetics is slowed down by the addition of Ni.     

等温淬火球墨铸铁表面热处理工艺的研究

等温淬火球墨铸铁(ADI)具有多方面优越的性能特点,然而,单纯的等温淬火难以同时具有高强度、高硬度及高的韧性与塑性。为了进一步扩大ADI的应用范围,采用不同的表面高频淬火工艺考察了ADI表面热处理的可行性,并着重探讨了不同表面处理工艺对ADI表层组织及硬度的影响规律。研究表明,对ADI采用二步法表面热处理可以得到理想的效果。     

Assessment of the microstructure evolution of an austempered ductile iron during austempering process through strain hardening analysis

The aim of this investigation was to determine a procedure based on tensile testing to assess the critical range of austempering times for having the best ausferrite produced through austempering. The austempered ductile iron (ADI) 1050 was quenched at different times during austempering and the quenched samples were tested in tension. The dislocation-density-related constitutive equation proposed by Estrin for materials having high density of geometrical obstacles to dislocation motion, was used to model the flow curves of the tensile tested samples. On the basis of strain hardening theory, the equation parameters were related to the microstructure of the quenched samples and were used to assess the ADI microstructure evolution during austempering. The microstructure evolution was also analysed through conventional optical microscopy, electron back-scattered diffraction technique and transmission electron microscopy. The microstructure observations resulted to be consistent with the assessment based on tensile testing, so the dislocation-density-related constitutive equation was found to be a powerful tool to characterise the evolution of the solid state transformations of austempering.     

等淬工艺参数对等淬球铁组织与性能的影响

研究了等淬工艺参数淬工艺参数对的显微组织与力学性能的影响。结果表明，丰等温温度的升高，贝氏体的形态由针着下贝氏体一羽毛状上贝氏体→片状；温度升高，等淬球铁的组织和性能对等温时间的敏感性增大，“过程窗口”变小，不易得到理想的奥贝组织。     

等温淬火温度对奥贝球铁水脆化行为的影响

研究了等温淬火温度对奥贝球铁(ADI)水脆化行为的影响，水附着条件下不同等温淬火温度处理的ADI均发生水脆化行为，抗拉强度和伸长率显著降低；但随着等温淬火温度升高，ADI的水脆化程度降低。高强度的ADI、淬火回火球铁和珠光体球铁均发生水脆化行为，而铁素体含量高的铸态球铁和铁素体球铁无明显的水脆化行为。     

Unique microstructure and excellent mechanical properties of ADI

I t has been a mission for cast iron metallurgists to improve the properties of cast irons. For many years the strength of cast iron was very low, with a tensile strength of only 60-100 MPa in 1860. During World War I, the tensile strength was increased to 120-140 MPa, by adding scrap steel during melting. In 1922, inoculated iron was invented and the tensile strength of cast iron increased further to 300 MPa. Later, alloyed, inoculated grey iron reached strength of 400 MPa. Although Whi…     

Fundamental Wear Mechanisms when Machining Austempered Ductile Iron (ADI)

Austempered Ductile Iron (ADI) is characterised by improved mechanical properties but low machinability compared to conventional ductile iron materials and steels of similar strengths. The mechanical properties of ADI are achieved by a very fine austenitic-ferritic microstructure. However this unusual microstructure significantly affects mechanical and thermal machining properties. A keen understanding for the interactions of microstructure, chip formation, machining properties, cutting material and wear mechanisms is essential for the optimisation of the cutting process. This paper describes material and machining investigations as well as cutting simulations to reveal the wear mechanisms being responsible for the low machinability of ADI.     

The influence of cobalt on the austempering reaction in ductile cast iron

Austempering kinetic measurements and mechanical property measurements are reported for two Mn ductile irons with and without Co and three austempering treatments. It is shown that Co accelerates the stage I reaction in each of the irons and for each of the austempering treatments but has little affect on the stage II reaction. Consequently, the processing window is widened and moves to earlier austempering times. This can be useful in the austempering of thicker section components to obtain the higher ductility grades of the ADI standard and to increase process productivity.     

奥氏体—贝氏体合金球铁磨球的研制与应用

研究了一种新型磨球材质———奥贝合金球铁，采用合金化和等温淬火处理，可以获得下贝氏体、残余奥氏体、少量马氏体基体组织的球铁。该材质的磨球在不同工况下装机考核。结果表明，其耐磨性明显优于低合金球铁和锻钢。它的推广应用具有显著的综合效益。     

Microstructure and properties of austempered ductile cast iron with refined graphite nodules

Abstract

The present study examined the influence of refinement of graphite nodules on microstructure and tensile properties of austempered ductile cast iron (ADI). A casting technique using deoxidation treatment enabled manufacture of thin walled castings made of ductile cast iron without ledebulite. The thin walled casting (t=2 mm) was subjected to extreme refinement of graphite nodules, where the number of graphite nodules was 1750 mm^?2. Decrease in graphite nodule diameter resulted in refinement of ausferrite and γ-pool structures in ADI and rapid reaction of austempering. The significant increase in the number of graphite nodules resulted in a remarkable drop in the tensile strength and elongation of ADI. These results can be explained by the graphite nodule distance.     

Effect of austempering time on mechanical properties of a low manganese austempered ductile iron

An investigation was carried out to examine the influence of austempering time on the resultant microstructure and the room-temperature mechanical properties of an unalloyed and low manganese ductile cast iron with initially ferritic as-cast structure. The effect of austempering time on the plane strain fracture toughness of this material was also studied. Compact tension and round cylindrical tensile specimens were prepared from unalloyed ductile cast iron with low manganese content and with a ferritic as-cast (solidified) structure. These specimens were then austempered in the upper (371 °C) and lower (260 °C) bainitic temperature ranges for different time periods, ranging from 30 min. to 4 h. Microstructural features such as type of bainite and the volume fraction of ferrite and austenite and its carbon content were evaluated by X-ray diffraction to examine the influence of microstructure on the mechanical properties and fracture toughness of this material. The results of the present investigation indicate that for this low manganese austempered ductile iron (ADI), upper ausferritic microstructures exhibit higher fracture toughness than lower ausferritic microstructures. Yield and tensile strength of the material was found to increase with an increase in austempering time in a lower bainitic temperature range, whereas in the upper bainitic temperature range, time has no significant effect on the mechanical properties. A retained austenite content between 30 to 35% was found to provide optimum fracture toughness. Fracture toughness was found to increase with the parameter (XγCγ/d)^1/2, where Xγ is the volume fraction of austenite, Cγ is the carbon content of the austenite, and d is the mean free path of dislocation motion in ferrite.     

等温淬火球铁热处理

本文简要地介绍了等温淬火球铁的机械性能,详细地分析了球铁等温淬火的工艺过程,并展望了这种材料广阔的生产应用前景.     

Effect of Cu content on microstructures and mechanical properties of ADI treated by twostep austempering process

The effect of Cu content on the microstructures and mechanical properties(yield strength,ultimate tensile strength,impact energy,fracture toughness) of austempering ductile iron(ADI) treated by two-step austempering process were investigated. High Cu content in nodular cast irons leads to a significant volume fraction of retained austenite in the iron after austempering treatment,but the carbon content of austenite decreases with the increasing of Cu content. Moreover,austenitic stability reaches its maximum when the Cu content is 1.4% and then drops rapidly with further increase of Cu. The ultimate tensile strength and yield strength of the ADI firstly increases and then decreases with increasing the Cu content. The elongation keeps constant at 6.5% as the Cu content increases from 0.2% to 1.4%,and then increases rapidly to 10.0% with further increase Cu content to 2.0%. Impact toughness is enhanced with Cu increasing at first,and reaches a maximum 122.9 J at 1.4% Cu,then decreases with the further increase of Cu. The fracture toughness of ADI shows a constant increase with the increase of Cu content. The influencing mechanism of Cu on austempered ductile iron(ADI) can be classified into two aspects. On the one hand,Cu dissolves into the matrix and functions as solid solution strengthening. On the other hand,Cu reduces solubility of C in austenite and contributes more stable retained austenite.