THE EFFECT OF MINOR ADDITIONS OF SULPHUR ON PORE CLOSURE AND CASE-HARDENABILITY OF SINTERED IRON

Abstract

Interconnected porosity in sintered iron structural parts can have a detrimental effect on case-hardening by permitting penetration of the carburizing gases to the interior of the compact. Experiments have shown that small additions of sulphur to the iron powder may provide a means of effecting the desired pore closure, though this method has still to be proved applicable on an industrial scale.     

EFFECT OF POROSITY AND PARTICLE SIZE ON THE MECHANICAL STRENGTH OF SINTERED IRON

Abstract

The flexural and tensile strengths and the fatigue limits of sintered iron materials have been measured as a function of porosity and pore size. The resulting experimental values were lower than the theoretical. This discrepancy is attributed to a pore-size effect, analogous to the results of earlier work in which the influence of pore size on elastic modulus was studied (G. Artusio, V. Gallina, G. Mannone, and E. Sgambetterra, Powder Met., 1966, 9, (17), 89).     

THE EFFECT OF DEFORMATION ON TENSILE AND IMPACT PROPERTIES OF HOT PM-FORMED NICKEL-MOLYBDENUM STEELS

Abstract

Hardenability, tensile, and impact properties have been determined for two nickel-molybdenum powder-formed steels. The compositions of the two steels were Fe-1·8% Ni?0·5% Mo and Fe ?0·5% Ni ?0·6% Mo; carbon contents studied for both materials were 0·2, 0·3, and 0·4%. Preforms (50 × 50 × 127 mm) were pressed and then sintered for 1 h in a dissociated ammonia atmosphere at 1120°C, to provide a density of 6·5 g/cm³. Preforms were hot formed to full density by upsetting (plane strain) at 980°C or by re-pressing (uniaxial strain) at 1040°C.

Standard 25 mm-dia. × 100 mm-long Jominy end-quenched tests were made to determine hardenability. Room-temperature tensile properties were determined using 6·4 mm-dia. specimens with a 25 mm gauge-length. Standard Charpy V-notch specimens were used to determine the impact properties at ?40, 0, 22, and 100°C. Triplicate tests were made in the as formed as well as the quenched-and-tempered conditions.

The additional flow that was realized by upsetting provided higher tensile and impact strengths than re-pressing. Tensile ductility was the same for both processing conditions. Tensile yield strength (heat-treated to ～26 HV) increased with increasing carbon content for the slack quenched material and levelled off for fully martensitic structures. Room-temperature impact strength also increased with increasing carbon content owing to a decrease in the amount of ferrite in the slack quenched structure. Increasing carbon content caused a decrease in impact strength once fully martensitic structures were achieved.

Impact strength at ?40°C ranged from ～20 to 40 J. Room-temperature impact strength ranged from ～20 to 50 J. These properties were obtained for materials heat-treated to a UTS level of ～850 N/mm². At the lower carbon contents the hardenability curve was found to fall within the AISI ‘H’ band for 4620 wrought steel. At the higher carbon level (0.4% C) the Jominy curves were close to the lower limit of the ‘H’ band for the 4640 wrought steels.     

EFFECT OF POROSITY ON THE FATIGUE BEHAVIOUR OF SINTERED PRECIPITATED NICKEL POWDER

Abstract

Groups of specimens with nominally 4% and 12% porosity have been prepared from fine (?240 + 300), medium (?200 + 240), and coarse (?150 ? 200) mesh sieve fractions of Sherritt-Gordon nickel powder by die compaction, preliminary sintering, re-pressing, and finally sintering at 1573K (1300°C). Irrespective of porosity content and the powder fraction from which they were prepared, all specimens exhibited a mixture of rounded and film-like porosity. The film-like porosity was more extensive in the more porous specimens, but in all specimens markedly influenced the fatigue behaviour. The development of persistent film-like porosity is attributed to the botryoidal form of the powder particles. The endurance limits of the less-porous specimens were almost identical, irrespective of the powder fractions from which they were prepared. However, the endurance limits of the more-porous specimens made from the coarse powder fraction were significantly lower than those made from the fine and medium powder fractions. The endurance limits of the less-porous specimens were much higher than those of the more-porous specimens and the endurance ratios were significantly higher. In all specimens, fatigue fractures were intergranular. The influence of film-like porosity on the fatigue behaviour is discussed.     

添加铁矿粉对焦炭机械强度及反应性的影响

炼焦煤中添加不同粒度、比例及成分的铁矿粉制备高反应性焦炭,测定焦炭的转鼓强度、等温与非等温气化反应参数,综合评定添加催化剂对高反应性焦炭机械强度和气化反应的影响。配入铁矿粉后焦炭的机械强度有不同程度的下降,当添加比例小于10%时,焦炭的机械强度变化幅度较小;大于10%时,焦炭的机械强度大幅度下降;添加铁矿粉的成分和粒度均对焦炭机械强度有较大影响。添加铁矿粉的比例处于容惰范围内时,增加添加铁矿粉的比例、添加高品位铁矿粉或适当地减小添加铁矿粉的粒度均有利于降低焦炭的起始反应温度、提高低温反应指数。     

添加高速钢粉对烧结钢组织与性能的影响

研究了添加高速钢粉对烧结钢组织与性能的影响。实验结果表明，含２０％高速钢的烧结钢综合力学性能最好；添加高速钢粉能导致烧结钢密度减小的冲击韧性降低，当高速钢含量增中时，硬度随之增加，烧结钢中残余奥氏体和马氏体的含量与高速钢的含量呈线性关系。烧结钢中的马氏体显微硬度很高，它主要原高速钢粒子和原铁粒子的连接区域形成。     

INFLUENCE OF IRON POWDER TYPE ON THE PROPERTIES OF SINTERED IRON AT VARIOUS DENSITY LEVELS

Abstract

The properties of various commercial and experimental iron powder types and of compacts made from them in the density range 6·8–7·87 kg/dm³ by single-pressing, double-pressing, and hot-forging techniques have been determined. It was shown that the ductility in all cases was more adversely affected than the tensile strength by the presence of porosity. However, it was also shown that at any particular density level or with a given processing schedule the mechanical properties varied widely, depending on the iron powder used. On the basis of the mechanical-property results, the powder types to be preferred at different density levels are indicated.     

钼粉对烧结制品表面性能的影响

本文结合国内外发展现状对钼烧结制品表面加工性能与钼粉之间的关系进行系统探讨。根据不同粒度、分散性钼粉对烧结坯、表面粗糙度、激光反射率的影响分析得出细粒、均匀、分散的钼粉是提高钼烧结晶表面性能的重要保证。     

EFFECT OF POROSITY AND PORE SIZE ON THE ELASTIC MODULI OF SINTERED IRON AND COPPER-TIN

Abstract

The Young’s modulus and shear modulus of iron and copper-tin sintered materials have been measured by the resonance method, with a view to determining the effects of porosity and pore size upon the values of the elastic moduli. The experimental values obtained were lower than those calculated on the basis of the Mackenzie theory. The discrepancy is attributed to a pore-size effect, since in the case of pores of sufficiently small dimensions the two results tend to coincide     

EFFECT OF ADDITIONAL ALLOYING ELEMENTS ON THE PROPERTIES OF SINTERED MANGANESE STEELS

Abstract

Sintered alloys based on the Fe-Mn system have been investigated by using single-pressing and double-pressing techniques. Fe-Mn (Mn up to 8 wt.-%) and Fe-Mn-C (C up to 1·4 wt.-%) alloys were prepared both with manganese as an electrolytic powder and with a Fe-Mn master alloy. The influence of sintering temperature and sintering time on mechanical properties and homogenization is discussed. The effect of the additional alloying elements Cr, Mo, eu, and of their combinations on mechanical properties has been determined. Further investigations were carried out with a Fe-Mn-Cr-Mo-C master alloy. The optimum single-pressed and double-pressed alloy (Fe with Mn 0·8, Cr 0·8, Mo 0·8, and total C 0·6%) has a tensile strength (σ_B) of >700 N/mm². Optimum alloys of all investigated systems were hot-forged and their mechanical properties are compared with those of single- and double-pressing techniques. The alloys were heat-treated and their tempering behaviour determined. Jominy standard tests were carried out to determine hardenability of the porous sintered materials.     

EFFECT OF POROSITY CONTENT ON THE TENSILE STRENGTH OF POROUS MATERIALS

Abstract

A theory that takes into account the stress-concentrating effect of the pores in porous materials is proposed. Upper and lower limits between which the strengths of porous materials must lie are predicted. A pore-sensitivity factor is defined and, assuming that this is proportional to the fractional porosity, an equation is derived which describes the variation in relative strength with porosity content and which empirically can take account of the matrix ductility. The equation is shown to agree well with published experimental data.     

高强度铁基粉末冶金换档摆杆的研制

我国轿车工业的快速发展,给铁基粉末冶金制品带来了前所未有的发展机遇.扩大粉末冶金汽车零件应用的有效途径是开发研制高强度的铁基粉末冶金结构件.本文分析了汽车变速箱换档摆杆的结构尺寸、力学性能等特点,制定合理的开发方案,确定了使用材料、生产工艺流程及模具.成功研制出了符合要求的高强度粉末冶金换档摆杆.     

添加铜合金的方法对烧结Fe-Cu-C钢的尺寸敏感性的影响

在用压制-烧结工艺制造粉末冶金零件中,Fe-Cu-C是最常用的合金系统.这个合金系统有许多优势;优异的力学性能,烧结性及可竞争的生产成本.可是,当最终客户要求成品零件的尺寸进行更精密控制时,由于这种合金内在的尺寸易变性,其是不易达到的.改变添加铜或钢合金的方法时,会影响这个合金系统的尺寸稳定性.这个工作研究了使用添加雾化铜粉,扩散合金化的Fe-Cu粉及化学粘结铜粉的方式添加铜时,烧结Fe-Cu-C钢的力学性能,尺寸及显微组织的差异.     

水雾化铁粉的粒径对工艺性能的影响

通过筛分分级得到0.147 mm(100目)以下的4种不同粒度的水雾纯铁粉粉末,研究了颗粒粒径对铁粉流动性、松装密度、压缩性和压坯孔隙结构的影响。结果表明,随着颗粒粒径的减小,铁粉的流动性降低、松装密度增大。应用方程F=(16πr2Pφm)/(Nmφ)对不同粒径的颗粒进行了受力分析,表明大颗粒压制时平均受到的压力比小颗粒的大。使用艾西压制方程对铁粉压制密度进行拟合分析,表明不同粒度的铁粉都能很好的符合艾西方程,其压缩系数β在0.002 178~0.002 323之间,颗粒粒径大的粉末其压缩系数大,压缩性好。在总孔隙度相当的情况下,粉末粒径小的压坯其孔隙尺寸较小、孔隙数量较多、孔隙的分布较均匀。     

高强度弹簧钢的发展现状和趋势

随着现代交通运输业的不断发展,对弹簧钢的性能要求越来越高,迫切要求提高弹簧钢的强度和延长使用寿命。对此,国内外近年来开展了大量的研究工作。评述了弹簧钢高强度化的途径和发展趋势、弹簧钢中碳和各种合金元素的作用及其合金化特点。     

基于烧结杯实验验证烧结矿铁料消耗的实践

2017年6月~7月份,安钢技术人员利用烧结杯实验,分别对3个烧结系统铁料消耗偏高的问题进行了实验验证分析。由于3个烧结系统铁采用了3种不同的供料方式,所以在烧结杯实验计算铁料消耗时采用了几种不同的计算方式,实验结果可以帮助技术人员研判铁料消耗偏高的原因。     

THE INFLUENCE OF POROSITY AND CARBON CONTENT ON THE FRACTURE TOUGHNESS OF SOME SINTERED STEELS

Abstract

Fracture toughness (K_IC) and mechanical properties at room temperature (RT) and at 200 K were evaluated for a range of sintered steels. In a series of quenched and tempered samples prepared from a lowalloy, atomized powder (Höganäs ATST-A) with 0·45 wt.-%C and density varying between 6·7 and 7·8 g/cm³ (powder forged), the K_IC varied between 28 and 80 MN/m^3/2 at RT and between 34 and 58 MN/m^3/2 at 200 K. There was a correlation between the K_IC and the yield strength of the porous materials, due to the fact that fracture of the specimen is effected by plastic instability on a micro scale. Adding carbon (0–0·84%C) and copper (2%) to a sponge-iron powder and sintering to a final density of 6·8 g/cm³ gave a material with a fracture toughness of ～34 MN/m^3/2 when the C content was >0·6%. At lower C contents the toughness was considerably increased, but it was not possible to obtain a valid. K_IC determination. In this investigation a new type of fracture-toughness specimen was used, the RCT specimen, diameter 75 mm and thickness 29 mm; by using this type as opposed to the ordinary CT variant, specimens ～50% larger could be used.     

THE EFFECT OF INTERPARTICLE CONTACT AREA ON THE STRENGTH OF COLD-PRESSED ALUMINIUM POWDER COMPACTS

Abstract

Measurements of the tensile strength of spherical cold-pressed aluminium powder, pressed to various densities up to the theoretical maximum, have shown that compaction is a two-stage process. At some high, intermediate pressure, interparticle sliding occurs in a way that does not itself increase densification but makes it easier for further deformation to occur. It is likely that the pressure at which this sliding takes place is dependent on the work-hardening rate of the powder as well as the powder size and morphology. In any case, it is shown to be important to the densification and strength reached by the compact.

It is concluded that the strength of a green compact is dependent upon the interparticle metallic contacts made during compaction. However,the green strength is well below that of wrought aluminium, probably due to the presence of broken-up oxides,which act as stress-concentrators at the interparticle boundaries.     

镍铜总量对液相烧结钼基合金性能的影响

研究了镍铜总量对液相烧结Mo-W-Ni-Cu合金性能的影响,结果发现,在镍铜比一定时,随镍铜总量的增加,烧结温度下降;抗拉强度σ_b先是急剧地上升,上升到最大值1100 MPa后缓慢地下降;烧结硬度在镍铜总量不超过6％时保持最高值HB 370左右,超过6％后硬度下降;晶粒则随镍铜总量增加而细化。     

Ti、石墨含量对铁基粉末冶金烧结材料的组织与性能影响

本文以雾化铁粉、羰基镍粉、钼粉、电解铜粉、钛粉及石墨粉为实验原料,在Fe-2%Ni-0.5%Mo-2%Cu-0.3%C基础上,按Ti和C原子比1∶1同时添加Ti和石墨(Ti的添加量为质量分数0～4%),利用粉末冶金与原位烧结合成技术制备了TiC颗粒增强铁基粉末冶金烧结材料,并用光学显微镜(OM)和扫描电子显微镜(SEM)等手段研究了实验材料的显微组织及性能。研究结果表明:实验粉末冶金烧结材料的组织主要为珠光体、铁素体及贝氏体。随着Ti加入量的增加,珠光体含量增多,且珠光体片间距更细小,而铁素体及贝氏体组织逐渐减少。原位合成的TiC颗粒尺寸约在0.3μm,主要分布在珠光体晶粒边界处。随Ti加入量的增大,材料的表观硬度提高,而抗弯强度和密度下降。断口形貌没有表现出明显的塑性变形,属于脆性断裂。