Forging processes include various steps to attain favorable material properties such as heat treatment, rapid quench, cold work stress relieving, and artificial aging. These steps, however, also contribute to bulk residual stress. Excessive bulk residual stresses cause a wide of problems, including part distortion during machining and in use, reduced crack initiation life, increased crack growth rates, and an overall reduction in part life. This paper summarizes recent work aimed at measurement-based assessment of bulk residual stresses in cold-compressed aluminum die forgings. The results show that forging process induced residual stress is a repeatable phenomenon with RMS repeatability less than 5% of yield.

An attempt was made to characterize microstructure, mechanical properties and cleanliness of continuous cast as rolled billets versus microstructure, mechanical properties and cleanliness of the forging in normalized condition, upset forged from AISI 41B30 modified chemistry billets. Two forgings were compared, one in as forged condition and one in normalized or heat treated condition. Upsets were produced by upsetting only one end of the billet by hydraulic press. Samples from cold portion of the forgings, near the flange location and from flanges were taken and examined. Results of microstructure, mechanical properties and hardness are presented. Normalizing cycle did not improve mechanical and impact properties. Low impact and ductile properties are results of Widmanstätten structure and continue to be present in the final product. Low impact and ductile properties of this structure might not be the best solution for dynamically loaded parts.

Case carburizing grade steel forgings are often normalized or iso-annealed to improve machinability. The aim here is to get a uniform ferrite-pearlite microstructure and controlled, uniform hardness. Since during forging material is above austenitizing temperature, controlled slow cooling after trimming can give similar results. In this work, the effect of forging temperature and cooling rate at different stages on microstructure is studied. Further the effect of this process on machinability and distortion behavior of gears during case carburizing is studied. It was observed that the controlled cooled gear blanks had coarse grain size resulting in superior machinability, and no change was observed in the distortion behavior of the gears during case carburizing.

The effect of forging temperature and temperature before quenching on microstructure is studied. This is related to the mechanical properties like tensile strength, yield strength and impact toughness. It was observed that martensitic needles in direct quenched parts were slightly longer than the normal hardened and tempered parts. This was attributed to the coarser prior austenite grain size, resulting in fewer nucleation sites in case of direct quenched parts.

Forgings traditionally undergo normalizing or iso-annealing processes to achieve consistent hardness within controlled bands and to improve machinability. The need for these heat treatments stems primarily from the uncontrolled cooling of forgings after trimming operations. This paper demonstrates that similar results can be achieved through controlled cooling rates after trimming, with only minor differences in specific properties. The microstructure obtained through controlled cooling is predominantly coarse-grained, consisting of pearlite and ferrite matrices, contributing to improved machinability. Notably, the controlled cooling process offers potential energy savings of approximately 20 kg of oil per metric ton of net forging weight, with corresponding reductions in CO₂ emissions of up to 250 kg per metric ton. Implementation requires a specially designed cooling tunnel to regulate cooling rates precisely. This paper details the mechanical properties achieved for a carburizing grade steel, discusses necessary refinements to steel specifications, and outlines the process controls required to replace conventional normalizing/iso-annealing with controlled cooling effectively. Additionally, the paper presents the established cycles and cooling rates that produce optimal results in production environments.