EVALUATION OF THE MECHANICAL PROPERTIES OF SINTERED LOW-ALLOY STEEL COMPONENTS

Abstract

When adopting low-alloy sintered steel components instead of traditional machined steel parts, it is misleading to attempt a direct comparison of the mechanical properties of the two products. Instead it is preferable to consider in each case the service conditions to which the parts are to be subjected and then to devise suitable mechanical tests under simplified loading conditions. The paper describes certain case histories illustrating this point and discusses briefly the definition of low-alloy “sintered steel”.     

THE MECHANICAL PROPERTIES OF SOME SINTERED MARAGING STEELS

Abstract

Maraging steels based on 18 and 12% nickel, and containing cobalt, molybdenum, silicon, copper, chromium, titanium, and aluminium in various proportions, were prepared in sintered form under varied processing conditions. The mechanical properties of the steels have been examined with particular reference to the effects of: (1) composition; (2) degree of shrinkage; (3) atmosphere, time, and temperature of sintering; and (4) compacting pressure. The influence of the type of iron-powder base was also studied.

The results demonstrate the possibility of producing, in the sintered and maraged condition and with only slight shrinkage on sintering, tensile strengths of the order of 95–110 kgf mm^?2 (60–70 tonf in^?2). Two compositions appear promising for further development as high-strength materials, and another to provide enhanced ductility. In all cases impact properties are similar to those characteristic of conventional sintered steels.     

MECHANICAL PROPERTIES OF SINTER/FORGED LOW-ALLOY STEELS

Abstract

The paper describes preliminary work on sinter/forged low-alloy steels. The mechanical properties and structures of both atomized and blended alloys were investigated. By using a good-quality atomized powder of the SAE 4600 type, tensile and fatigue properties equivalent to those of wrought steels could be obtained. Atomized alloy powders with higher oxygen contents had poor ductility and impact values because of surface oxides on the powder particles.

Blended iron alloys gave tensile strengths up to 72 tonf/in² (1112 MN/m²) with much higher ductility and impact-resistance than would be obtained with conventionally pressed and sintered alloys.     

SOME NEW APPLICATIONS OF SINTERED LOW-ALLOY STEELS

Abstract

Practical details are given of the application of powder metallurgy to the production of a number of machine parts in low-alloy steels.     

A THEORETICAL EVALUATION OF THE STRENGTHS OF SINTERED PLAIN CARBON AND LOW-ALLOY STEELS

Abstract

The strengths of porous bodies depend on the strength of the matrix and are a function of porosity content. In practice, such bodies are required to possess a limited amount of ductility if they are to be useful as engineering materials. A criterion for minimum acceptable ductility is proposed. This and a theory of strength of porous bodies are used to evaluate a maximum strength/porosity relationship for heat-treated steels. Experimental data are found to be in fair agreement with this relationship.     

THE MECHANICAL PROPERTIES OF HOT-RECOMPACTED IRON-NICKEL SINTERED ALLOYS

Abstract

Powder-metallurgy components which are to withstand high dynamic stress are frequently required to possess both high strength and great toughness. This combination of properties can best be achieved by increasing the density of the sintered component and one method of doing so is bot pressing.

This paper deals with the mechanical properties of sintered iron–nickel alloys produced by hot compacting in six stages, as follows:

(1) Preparation of the powder mix.

(2) Production of compacts under a pressure of 8 Mp/cm²

(3) Heating the compacts to 1000°C (1275 K).

(4) Re-pressing the hot compacts in a die heated to 300°C (575 K).

(5) Cooling in air.

(6) Sintering at optimum temperature and time under optimum furnace conditions.

The investigation covered the dependence of tensile strength, elongation at fracture, and Brinell hardness of alloys with Ni contents of 1–10% on the sintering temperature and time, on the furnace conditions, and on raw-material variables.

It was found that Fe–Ni powder-metallurgy parts with a maximum tensile strength of ～60 kp/cm² could be produced. The Brinell hardness reached 190 kp/mm² with 10% Ni content. Elongation at fracture was in the region of 45% with 1% Ni and remained comparatively satisfactory even with high Ni contents if very pure raw materials were used. Powder-metallurgy materials with a tensile strength of 60 kp/cm² and an elongation at fracture of 17% can be obtained by the process.     

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.     

低合金角钢力学性能探讨

应用数理统计方法，分析了唐钢低合金钢的力学性能，并对执行新标准ＧＢ／Ｔ１５９１－９４应采取的措施进行了探讨。     

CONTROLLING THE HARDENABILITY OF SINTERED STEELS

Abstract

The factors influencing the hardenability of sintered steels are discussed. Special problems are encountered in establishing hardenability tests suitable for porous materials. A dilatometric method is described by which the transformation characteristics of sintered steel may be determined. Such data can be used directly as a hardenability criterion. Data are given in the form of continuous cooling diagrams on some typical sintered steels.     

残余奥氏体对TRIP钢机械性能的影响

简要介绍了TRIP(transformation induced plasticity, 相变诱导塑性)钢中残余奥氏体的形成及其微观组织形貌,综合阐述了残余奥氏体对TRIP钢性能的影响,并由此提出对TRIP钢进一步改善的途径.     

A COMPARISON OF THE MECHANICAL PROPERTIES OF SOME POWDER-FORGED AND WROUGHT STEELS

Abstract

The tensile, impact, and fatigue properties of a range of powder-forged steels have been examined. A relationship has been found between the content of non-metallic inclusions and the fatigue performance. The properties of powder-forged steels at 900 N/mm² strength were compared with those of En16 wrought steel at the same level. The properties of wrought steel are demonstrably extremely variable, depending on the degree of hot work imparted during processing and on the relationship of the test-piece axis to the principal direction of working. The properties of powder-forged steel lie between the highest and lowest that can be expected in wrought steel; comparisons between the two types of material can be made only after careful consideration of their specific characteristics. Powder-forged steels were shown to be capable of developing useful properties over wide ranges of composition.     

THE FRACTURE-RESISTANCE OF A RANGE OF SINTERED STEELS

Abstract

The fracture-resistance of a range of sintered steels containing additions of copper and carbon has been measured in terms of their critical stress-intensity factor, K_c. All the fractures were apparently of the flat plane-strain type, the micro cracking being a process of microvoid coalescence rather than of cleavage. Toughness, in terms of K_c, is shown to depend on the percentage porosity, the level of the copper addition, and the carbon content. Higher toughness is achieved with copper + carbon additions than with either independently. A major feature of the results is that toughness increases with the yield stress, a trend that is contrary to the general behaviour of wrought materials.     

加速冷却对热轧C－Mn钢力学性能的影响

三种试验用Ｃ－Ｍｎ钢热轧及轧后的加速冷却实验表明，典型组织为多边形铁素体＋粒状贝氏体；这种组织不会恶化钢材的塑性指标；贝氏体相变强化效果远高于各种组织因加速冷却而产生的自身强化效果。     

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。     

METHODS OF EXTENDING THE APPLICABILITY OF SINTERED STEELS

Abstract

It is a common opinion among users of structural parts that applications for sintered steels are limited to those where requirements for strength are low to moderate. Furthermore, sintered steels of moderate strength are thought to be very brittle. It is the object of this paper to draw attention to significant improvements which have been achieved in the last few years. These are basically a result of powder developments which are based partly on traditional alloying additions, such as Cu, Ni, Mo, and C, and partly on unique combinations of iron powders and phosphorus or on combinations of iron powders, phosphorus, carbon, and/or copper. Unusually favourable combinations of strength and ductility can be achieved with diffusion-alloys based on iron and phosphorus. Components of high-duty sintered steels capable of replacing components of conventional wrought steels can be produced from partially prealloyed combinations of iron, copper, nickel, molybdenum, and carbon. For many applications these materials can also be an alternative to powder-forged steels. All the above powder combinations show consistent and low dimensional changes during sintering so that close tolerances of intricately shaped components can be maintained. Material and processing costs are such that the improved properties can be achieved economically.     

INFLUENCE OF THIN OXIDE FILMS ON THE MECHANICAL PROPERTIES OF SINTERED METAL-POWDER COMPACTS

Abstract

The influence of thin oxide films, in the range 200–1200Å thick, on the mechanical properties of sintered iron, copper, and nickel powder compacts has been investigated. As the thickness of the oxide film on the metal powders increased, the properties studied, namely, densification parameter, hardness, and tensile strength improved and attained a maximum at a critical oxide-film thickness, the value of which was ～ 625 Å for iron and nickel and ～ 500 Å for copper. Further increase in thickness to ～ 1200 Å led to a gradual decline in the properties. The improvement in the properties obtained with powders having the optimum oxide thickness was independent of the sintering atmosphere. A probable explanation in terms of activated sintering is given.     

烧结钕铁硼的力学性能研究现状

分析了烧结钕铁硼呈脆性的原因，介绍了烧结钕铁硼的力学性能研究现状以及研究烧结钕铁硼力学性能的重要性。     

STRUCTURAL AND MECHANICAL PROPERTIES OF SINTERED MAGNESIUM PRODUCTS AT ELEVATED TEMPERATURES

Abstract

The use of products sintered from pure magnesium or a magnesium alloy is envisaged for certain structural components in the field of nuclear technology. The mechanical properties at elevated temperatures (up to 525°C) of sintered compacts of oxidized Mg-Zr or Mg-MgO of various particle-size ranges (～20–800 μm) are discussed. Comparison of the tensile properties and of the values of the creep parameters in tension and compression emphasizes the direct dependence of the increase in mechanical strength at elevated temperatures on the content and distribution of the oxide and on the particle-size distribution of the oxidized powders. Metallographic examination of the various materials confirms these observations. The ductility varies with the size of the original particles.

Finally, data are presented for comparison on a material obtained by sintering magnesium-zirconium and magnesium-aluminium cuttings. In this case hardening occurs as a result of the formation of intermetallic compounds between the zirconium and the aluminium.     

THE EFFECTS OF IRON-POWDER CONTAMINATION ON THE PROPERTIES OF POWDER-FORGED LOW-ALLOY STEEL

Abstract

Contamination of low-alloy steel powder intended for powder-forging purposes occasionally occurs by virtue of processing through plant normally producing plain iron sintering powders. This paper shows that the effects of moderate amounts of plain iron-powder contamination on the tensile properties of a through-hardened low-alloy steel powder are not significant, provided that the carbon content is maintained at the design level. The results also show that the fatigue endurance limit is lowered although the ratio of fatigue endurance to elastic limit remains constant. In carburizing-grade material, however, there is a significant reduction in the tensile and fatigue strength attainable; and the presence of ‘soft spots’ may have a deleterious effect upon the performance of case-hardened components     

复合添加剂对Fe-Cu-C烧结钢力学性能和切削加工性的影响

研究了新型复合添加剂（MnS＋S）、（MnS＋P）和（MnS＋Ca）对Fe－Cu－C烧结钢力学性能及切削加工性能的影响，通过添加（MnS＋S）、（MnS＋P）和（MnS＋Ca）复合添力口剂，可以明显地改善Fe－Cu-C烧结钢的切削加工性，同时保持或提高其力学性能，其中以（MnS＋Ca）效果最佳。