用"三项平衡法"确定灰铸铁薄壁小件化学成分

薄小灰铸铁件生产中,为同时兼顾铸造性能、力学性能和加工性能,以有关理论为基础,通过生产实践。总结出采用“三项：平衡法”确定灰铸铁成分的方法：即根据碳当量、碳硅比值、共晶平衡三要素,结合铸件壁厚确定碳硅成分搭配。生产实践证明,这种方法能较好地解决铸造性能和加卫生能要求与力学性能要求的矛盾,得到了组织均匀、综合性能优良的铸件。     

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…     

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.     

Effect of Retained Austenite on Properties of Austempered Ductile Iron

Austempered ductile iron (ADI) exhibits a favourable combination of strength and toughness, and has been used as a substitute for quench-tempered or carburise-quenched steel. A characteristic feature of bainite transformation of cast iron, as opposed to carbon steel, is that precipitation of carbide is suppressed by the high concentration of silicon. Thus, a favourable structure, consisting of bainitic ferrite and retained austenite without carbide, can be provided by the optimum austempering treatment. Such microstructure and the mechanical properties of the iron are significantly affected by the conditions of the austempering treatment and the chemical composition. In this study, several grades of ductile iron were austempered under various conditions. The relationship between the impact strength, the quantity of retained austenite and the isothermal transformation curve was investigated. The stability of the retained austenite is considered important, because ADI contains a large amount of retained austenite which contributes to the improvement of ductility and toughness and which may transform to martensite when held at low temperature or subjected to stress. In this study, the stability of the retained austenite at low temperatures was examined by holding or stressing to establish the relations between transformation and temperature, stress and strain.

When the austempering time is short, the untransformed austenite partially transforms to martensite during air cooling, due to the lower carbon content, resulting in lower impact strength. As the austempering time increases, the untransformed austenite is stabilised by carbon-enrichment and there is little transformation to martensite, resulting in a large amount of retained austenite and higher impact strength. When the austempering time becomes much longer, the carbon-enriched austenite decomposes, presumably to bainitic ferrite and carbide, decreasing impact strength. In increasing the silicon content, precipitation of carbide in bainite is suppressed and both the maximum impact value and the content of retained austenite increase. The decreasing rates after the maxima through an additional isothermal holding becomes smaller.

By holding at temperatures down to –40°C, the decrease in retained austenite and the increase in hardness are both small. The retained austenite is stable under stress lower than that required to cause plastic deformation. Compressive stress hinders the martensitic transformation, because the transformation is accompanied by volume expansion.     

两相区退火对不同硅含量TRIP钢残留奥氏体和力学性能的影响

研究了硅含量分别为1．5wt％和1．0wt％的冷轧低碳硅锰TRIP钢两相区退火温度对残留奥氏体量和力学性能的影响。结果表明，随两相区退火温度的升高，两种钢的残留奥氏体量和残留奥氏体中的含碳量以及其屈服强度和抗拉强度都上升。当硅含量降至1．0％时，对钢的残留奥氏体量没有影响，但是降低了残留奥氏体中的碳含量，同时降低了钢的抗拉强度。两种钢的最大强塑积值相近，约为22000MPa%。     

Effect of silicon on the spheroidization of cementite in hypereutectoid high carbon chromium bearing steels

The effect of silicon on the spheroidization of cementite in hypereutectoid high carbon chromium bearing steels has been investigated on the basis of microstructural analysis and thermodynamic calculations. The results showed that an increase of silicon content in high carbon chromium bearing steels retards the spheoridization of cementite. The thermodynamic calculations revealed that the shrinkage of the austenite phase field in bearing steels with increasing silicon content gave rise to an increase of volume fraction of cementite at an annealing temperature, possibly resulting in incomplete spheroidization. Furthermore, due to the low solubility of silicon in cementite, an increase of silicon content can raise the activity or chemical potential of carbon atoms in austenite at the austenite/cementite interfaces. Consequently, the difference in chemical potential of carbon atoms at the interfaces would be reduced with increasing silicon content, causing a decrease of the driving force for their diffusion from cementite to austenite.     

Effect of silicon content and annealing temperature on formation of retained austenite and mechanical properties in multi-phase steels

Cold-rolled and annealed ultra-high strength sheet steels with good ductility accompanied by TRIP of retained austenite have received considerable attention in recent years. This paper discusses the effect of silicon content and annealing temperature on the formation of retained austenite and the mechanical properties in Fe-0.34%C-1.7% Mn steels whose structure consists of ferrite, bainite and retained austenite. Silicon inhibited the cementite formation in bainite during isothermal holding and partitioned carbon from bainite to austenite, resulting in an increase in retained austenite content. When the silicon content was increased to 1.0 wt.% or higher, the amount of retained austenite markedly increased leading to good mechanical properties. 0.34%C-1.03%Si-1.7%Mn steel showed a high tensile strength of 1,030 MPa and a total elongation of 34.5% when annealed at 780°C for 5 min followed by isothermal holding at 400°C for 5 min. In this case, the amount of retained austenite was about 25%. The variation in tensile strength-elongation combination had good correlation with that in the amount of retained austenite with both annealing temperature and silicon content. The most retained austenite was obtained in the steel annealed at just above A_C1 temperature. The annealing temperature which gives the most retained austenite was decreased with decreasing the silicon content.     

Wear Performance of Cu-Alloyed Austempered Ductile Iron

An investigation was carried out to examine the influence of structural and mechanical properties on wear behavior of austempered ductile iron (ADI). Ductile iron (DI) samples were austenitized at 900 °C for 60 min and subsequently austempered for 60 min at three temperatures: 270, 330, and 380 °C. Microstructures of the as-cast DI and ADIs were characterized using optical and scanning microscopy, respectively. The structural parameters, volume fraction of austenite, carbon content of austenite, and ferrite particle size were determined using x-ray diffraction technique. Mechanical properties including Vicker’s hardness, 0.2% proof strength, ultimate tensile strength, ductility, and strain hardening coefficient were determined. Wear tests were carried out under dry sliding conditions using pin-on-disk machine with a linear speed of 2.4 m/s. Normal load and sliding distance were 45 N and 1.7 × 10⁴ m, respectively. ADI developed at higher austempering temperature has large amounts of austenite, which contribute toward improvement in the wear resistance through stress-induced martensitic transformation, and strain hardening of austenite. Wear rate was found to depend on 0.2% proof strength, ductility, austenite content, and its carbon content. Study of worn surfaces and nature of wear debris revealed that the fine ausferrite structure in ADIs undergoes oxidational wear, but the coarse ausferrite structure undergoes adhesion, delamination, and mild abrasion too.     

EFFECTS OF RETAINED AUSTENITE ON DUPLEX MICROSTRUCTURE OF MARTENSITE AND LOWER BAINITE

ＥＦＦＥＣＴＳＯＦＲＥＴＡＩＮＥＤＡＵＳＴＥＮＩＴＥＯＮＤＵＰＬＥＸＭＩＣＲＯＳＴＲＵＣＴＵＲＥＯＦＭＡＲＴＥＮＳＩＴＥＡＮＤＬＯＷＥＲＢＡＩＮＩＴＥＷＥＮＣｕｉ’ｅ;ＬＩＮＪｉａｎｇｕｏ;ＺＨＯＵＹａｊｉａｎ（ＤｅｐａｒｔｍｅｎｔｏｆＭａｔｅｒｉａ...     

厚大断面ADI材料的试验研究

介绍了厚大断面ADI的技术要求,详细阐述了附铸试块的生产工艺:设计合理的化学成分,采用树脂砂造型,500 kg中频电炉熔炼铁液,出炉温度为1500℃,包底冲入法进行球化及孕育处理,奥氏体化温度选择为890℃,保温时间为4 h,为得到不同的力学性能,等温淬火温度选择2个温度,分别为360℃与320℃,等温时间为2.5 h。生产结果显示:320℃等温淬火处理后由针状铁素体和富C奥氏体组成的奥铁体更加细小;360℃与320℃等温淬火温度处理得到不同的力学性能,伸长率比牌号要求提高很多。     

高韧性等温淬火球铁力学性能的研究

根据欧洲等淬球铁标准EN1564的数据，建立各力学性能之间的数学模型。对高韧性等淬球铁铸件的生产检测结果进行了分析，发现合金化的高韧性等淬球铁铸件的力学性能之间的关系与一般非合金化等淬球铁铸件不同，其伸长率、冲击韧度、屈服强度、硬度在一定范围内随抗拉强度的提高改变不大。生产实践证明：设计合理的化学成分，经过适当的合金化，铸造优质的球铁毛坯，采用有效的热处理工艺，可大幅度提高等淬球铁的综合力学性能，稳定生产高韧性等淬球铁铸件。     

Effect of C and Si on mechanical properties of austempered ductile iron

It is well known that ductile cast iron can be strengthened and toughened by austempering. The tensile strength and the fatigue strength of austempered ductile iron (ADI) are equal to those of forged steel. Previous studies have been aimed at establishing a suitable process to obtain both strength and toughness in ADI.^1,2 These studies focused on the effect of alloying such as Mo, Ni, Mn, Cu, etc. and the austempering conditions such as temperature and holding time. In this study, a new type of ADI with higher toughness and higher elongation was developed as compared with conventional ADI. A new type of ADI with a low carbon content was achieved by reducing the initial carbon content, long annealing and ordinary austempering. The suitable silicon content was found to be 2.5% and effective alloying was 0.25% Mo and 0.7% Cu to obtain maximum impact energy and elongation.     

Thermomechanical treatment of austempered ductile iron

The production of lightweight ferrous castings with increased strength properties became unavoidable hter aluminum and magnesium castings. The relatively new ferrous casting alloy ADI offers promising strength prospects, and the thermo-mechanical treatment of ductile iron may suggest a new fluence of thermomechanical treatment,either by ausforming just after quenching and before the onset of austempering reaction or by cold rolling after of this work, ausforming of ADI up to 25％ reduction in height during a rolling operation was found to add a mechanical processing component compared to the conventional ADI heat treatment, thus increasing the rate ics of ausferrite formation was studied using both metallographic as well as XRD-techniques. The effect of ausforming on strength was quite dramatic (up to 70％ and 50％ increase in the yield and ultimate strength respectively). A mechanism involving both a refined microstructural scale and an elevated dislocation density was suggested. Nickel eformation is necessary to alleviate the deleterious effect of alloy segregation on ductility.luence of cold rolling (CR) on the mechanical properties and structural characteristics ofADI wasinvestigated. The variation in properties was related to the amount of retained austenite nsformation. In the course of tensile deformation of ADI, transformation induced plasticity (TRIP) takes place, indicated by the increase of the instantaneous value of strain-hardening exponent with o partial transformation of γr to martensite under the CR strain. Such strain-induced transformation resulted in higher amounts of mechanically generated therefore increased, while ductility and impact toughness decreased with increasing CR reduction.     

含硅量及等温时间对奥贝球墨铸铁机械性能的影响

探讨了含硅量及等温时间对奥贝球铁冰冷处理前后机械性能及低温冲击韧性的影响。试验表明,随着含硅量的增加,不但冷处理前常温机械性能提高,而且冰冷处理后的机械性能及低温冲击韧性也提高。而含硅3.39％和3.68％的机械性能已趋一致,等温时间为120分钟的试样,冰冷处理前后的机械性能和低温冲击韧性均最高。     

等温淬火球铁组织与性能间的关系

本文研究了等温淬火球(ADI)的组织与性能之间的关系,热处理工艺对组织形态的影响。用贝氏体束间的残余奥氏体(A_(r-f))与大块的残余奥氏体(A_(r-b)的比值作为组织指标,发现当比值y=10左右时,等淬球铁有较佳的综合机械性能。降低等温温度可大大提高y值,使强度提高,但是由于残余奥氏体量也减少,从而对塑韧性不利,特别是残余奥氏体量小于25%,并出现下贝氏体后。块状残余奥氏体是非碳饱和的奥氏体,在一定条件下(温度、应力与应变),将发生非回火马氏体转变,导致脆性增加。等温淬火球铁在较佳的组织条件下,也有好的低温性能,残余奥氏体非常稳定。     

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.     

Mn含量对0.15C-0.6Si-Mn TRIP钢组织和力学性能的影响

经过在两相区退火和贝氏体区等温处理，研究了两种不同锰含量的低硅TRIP钢的组织和力学性能，试验结果表明，低硅和低锰钢的残留奥氏体量少，力学性能差；增加锰含量，能提高残留奥氏体量及拉伸强度和伸长率，其力学性能与常规低碳Si-MnTRIP钢的水平相关，用电子探针测试了两相区退火钢中锰和硅的分布情况，发现锰在临界区退火时不发生再分配。     

30CrMo钢Q-P-T及深冷处理后的组织与性能

利用光学显微镜(OM),扫描电镜(SEM),X射线衍射仪(XRD)和力学性能测试等研究了不同深冷处理工艺对经Q-P-T工艺处理后30CrMo钢组织和力学性能的影响。结果表明,30CrMo钢最佳的Q-P-T+深冷工艺为:260℃淬火温度,400℃碳配分温度、60 s碳配分时间、-100℃深冷温度、1 h深冷保温时间和一次深冷。经最优的Q-P-T+深冷工艺处理后,30CrMo钢的碳化物的平均尺寸较小,残留奥氏体含量明显增加,残留奥氏体的体积分数约为7.9%,显微硬度约为482 HV,抗拉强度约为1629 MPa,强塑积约为20525 MPa·%,伸长率约为12.6%,其综合力学性能得到了较大幅度提高。     

Calculation of carbon content of austenite during heat treatment of cast irons

The austenitizing temperature controls the carbon content of the austenite which,in turn,influences the structure and properties of cast irons after subsequent cooling to room temperature.In this paper,for a cast iron with known silicon content,a formula of calculating austenite carbon content at a certain austenitizing temperature was developed.This relationship can be used to more accurately select carbon content of austenite or austenitizing temperature to produce desired properties after subsequent cool...     

EFFECT OF CARBON CONTENT ON MICROSTRUCTURE AND PROPERTIES OF HIGH STRENGTH AND HIGH ELONGATION STEELS

The micro structure and mechanical properties of new kind of hot-rolled high strength and high elongation steels with retained austenite were studied by discussing the influence of different carbon content. The research results indicate that carbon content has a significant effect on retaining austenite and consequently resulting in high elongation. Besides, new findings about relationship between carbon content and retained austenite as well as properties were discussed in the paper.