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The introduction of direct injection turbocharged engines has increased the need for higher performance connecting rods, able to withstand higher compressive loads in operation. In this respect, new materials with high compressive yield strength and fatigue performance for powder-forged connecting rods, such as HS150, HS160, and HS170M, were developed and successfully introduced in production. Among them, HS170M, currently used to manufacture connecting rods for several high performance engines, not only has exceptional strength, but less variation in mechanical properties as a function of its chemical composition variation within the specified limits compared to other powder-forged materials.

The advent of more efficient direct injection turbocharged engines has increased the need for higher performance connecting rods, able to withstand in particular higher compressive loads in operation. In this respect, new high strength materials for powder forged connecting rods were developed and introduced in production with excellent results. Among them, HS170M is currently used to manufacture connecting rods for several high performance engines, which not only have higher strength, but have less variation in their mechanical properties. The results of numerous benchmark studies have shown that powder forged connecting rods manufactured with HS170M are stronger than their steel forged counterparts manufactured with microalloyed steels, are easier to machine and fracture split, and represent a cost effective way to manufacture this important high reliability automotive component.

Over the last two decades, powder forging (PF) has been proven as a very reliable way to successfully manufacture connecting rods for both gasoline and diesel applications. The inherent value in the near net formed product (NVH performance, material utilization efficiency, total cost economics) coupled with the attractive strength levels achieved with the introduction of HS150, HS160, and HS170 materials [1, 2, 3], have made it possible for PF connecting rods to meet and exceed the increasing performance specifications required by the next generation of diesel and gasoline engines. The goal of this work was to continue the research performed so far in developing new higher strength materials for PF connecting rods [1, 2, 3, 4, 5, 6] in order to further optimize the chemical composition of Fe-Cu-C systems for maximum performance.

The powder forging (PF) process is used to produce fully dense powder metallurgy (PM) parts for high performance automotive applications. PF connecting rods have been widely accepted in the US, Japan, and other countries due to higher performance and lower manufacturing costs when compared to conventionally forged steel connecting rods [1, 2]. In order to meet and exceed requirements for higher fatigue strength and better machinability of PF connecting rods, a newly developed machinability enhancer, consisting of complex calcium oxide, named KSX, was introduced [3]. Minimal additions of KSX were found to be very effective in protecting the surface of the cutting tool during machining, with virtually no effect on mechanical properties obtained after the forging process. A comparison study between materials prepared with 0.3% MnS and with 0.1% KSX additions showed higher fatigue strength and better machinability in the case of the mix with KSX.

The main requirement for the satisfactory function and service life of a connecting rod is the fatigue strength, which is dependent on design, material, microstructure, and surface condition. Much work has been accomplished to study and optimize these factors in the case of powder forged connecting rods [1, 2, 3, 4, 5, 6, 7 and 8]. To meet the current and increasing performance specifications required by the next generation of diesel and gasoline engines, new high strength powder forged materials have been introduced into production to successfully compete with wrought steels [9, 10, 11 and 12]. Currently, there are two main processing technologies available to manufacture connecting rods: fracture-split drop forging and fracture-split powder forging. The cost effectiveness of each one of these technologies is another main consideration, other than performance, in high volume production.

The automotive industry is being challenged to continuously improve the performance of components used in vehicles and to reduce manufacturing costs. As a result, automotive components manufacturers are looking for lower cost materials which can perform better in service. The most widely used material for a powder metal forged connecting rod is P/F-10C50 (FC-0205) admixed with manganese sulfide (MnS) to enhance the machinability. A main requirement for a satisfactory function and service life of a powder metal forged connecting rod is the fatigue strength. Fatigue strength mainly depends on design, material, microstructure, and surface condition. Much work has been accomplished to study and optimize these factors [1, 2, 3, 4, 5, 6, 7 and 8], but the industry is still under pressure to further optimize them. The goal of this research work was to engineer powder metal mixtures with higher strength, good machinability and at reasonable cost.

A main requirement for a satisfactory function and service life of a forged powder metal connecting rod is the fatigue strength. Fatigue strength mainly depends on design, material, microstructure, and surface condition. Much work has been accomplished to optimize these factors, but still a variety of surface defects such as localized porosity, roughness, oxide penetration, decarburization, etc., can be developed during manufacturing. These surface defects impact the fatigue strength in various ways. The impact of the decarburized layer depth on the fatigue life of a forged powder metal connecting rod is the focus of this work. Several connecting rods were submitted to a Weibull test at the same loading pattern. After the fatigue tests, the connecting rods were divided into groups with different decarburized layer depths. Both Maximum Likelihood Estimates (MLE) and Rank Regression (RR) techniques were used to analyze test results from all the groups obtained.

Transfer case sprockets usually require quenching to improve hardness and mechanical properties. This additional process step can be avoided with sinter hardening. Indeed, sinter hardening allows the production of P/M parts with high strength and apparent hardness directly from sintering because the martensitic transformation takes place during the cooling portion of the sintering operation. Therefore, this process eliminates the need for a post-sintering heat treatment with all the inherent related problems such as part distortion, oil contamination and added processing costs. Many low alloy steel powders have been developed for sinter hardening applications. These materials, combined with the availability of sintering furnaces equipped with enhanced cooling capacity, make sinter hardening particularly attractive for parts that are difficult to quench because of their size and shape.

The influence of sintering parameters on mechanical properties of three different sinterhardenable grades of powder has been studied. Dimensional change, hardness, strength, and microstructure of specimens were evaluated in different sintering conditions, such as temperature, belt speed, and cooling rate. Conclusions were used to convert a major line of sprockets from a traditional mold, sinter, size, and quench process to a cost effective mold and sinterhard one. Mechanical tests, such as crush tests and engine tests were performed on real parts manufactured using both processes, confirming the validity and the benefits of this conversion.