February 2022 Volume 4

FORGING RESEARCH

Forging trials were conducted at UAB to determine the minimum reduction ratio required to consolidate cast steel. This effort was to better understand the effect of steel chemistry, heat treatment, and strength on the required forging ratio. A low alloy high-performance steel used by the military was subjected to different experimental forging reduction ratios. Results from samples forged at UAB's lab were compared with the as-received condition of the cast material, as well as a commercially forged sample as an industry baseline for mechanical properties. In almost all cases, even the smallest forging ratio improved the ductility of the steel. All reduction ratios exceeded target values for yield strength and ultimate strength and the standard deviation of the strength values decreased after forging in comparison with as-received results, proving forging increases the consistency of the properties. The largest increase in properties due to the forging operation was observed in the ductility, as would be expected. The elongation values for all experimental ratios more than doubled after forging in comparison with a below

target value in the as-received cast steel. The standard deviation was also dramatically reduced. There was no baseline for reduction in area, however, similar to elongation, the mean and standard deviation significantly improved after forging. It was found that a forging reduction between 1.5:1 to 2:1 is sufficient to eliminate the majority of enclosed micro-porosity for a typical, well-risered casting. The relationship between maximum pore cluster size on the fracture surface and mechanical properties in this low alloy high- performance steel, removed from several castings and subjected to different forging reductions, is shown in Figure 1 and Figure 2. The corresponding reduction ratios for each data set are noted in the plot legend. The maximum pore cluster size is the measured total length of a cluster of pores that appears to be the longest on the fracture surface image taken from a stereomicroscope. A group of pores was considered a cluster if the distance between them was smaller than the largest of the adjacent pores.

Figure 2: %Elongation vs max pore cluster size of low alloy high performance Q&T steel. Round data points are as-cast properties, and diamond data points are taken from forged samples.

FIA MAGAZINE | FEBRUARY 2022 69