The Effects of Casting Porosity on the Tensile Behavior of Investment Cast 17-4PH Stainless Steel

Abstract

The effect of casting porosity on the mechanical behavior of investment cast 17-4PH stainless steel was studied as well as the effect of heat treatment on the alloyÕs sensitivity to casting defects. Interdendritic porosity, formed during solidification and shrinkage of the alloy, reduces the yield strength and ultimate tensile strength roughly in proportion to the reduction in load bearing cross-section. The effects of casting porosity on ductility (% strain, % reduction in area) are more severe, in agreement with research on other alloy systems. In this study, 10% porosity reduced the ductility of 17-4PH stainless steel by almost 80% for the high-strength H925 condition. Tensile testing at -10°C (263 K) further reduces the alloy ductility with and without pores present. In the lower strength H1100 condition, the ductility is higher than the H925 condition, as expected, and somewhat less sensitive to porosity. By measuring the area % porosity on the fracture surface of tensile specimens, the trend in failure strain versus area % porosity was obtained and analyzed using two methods: an empirical approach to determine an index of defect susceptibility with a logarithmic fit and an analytical approach based on the constitutive stress-strain behavior and critical strain concentration in the vicinity of the casting voids. The applicability of the second method depends on the amount of non-uniform strain (necking) and, as such, the softer H1100 material did not correlate well to the model. The behavior of 17-4PH was compared to previous work on cast Al alloys, Mg alloys, and other cast materials.

Effect of Hot Isostatic Pressing and Powder Feedstock on Porosity, Microstructure, and Mechanical Properties of Selective Laser Melted AlSi10Mg

“…This observation suggests that fracture preferentially traveled across pores rather than through the bulk metal. This corroborates works which suggest that the tensile behavior of porous parts depends on local porosity, rather than the bulk porosity of the material [13].…”

“…As a result, it is probable that these pores had a significant impact on the deformation mechanisms and mechanical properties of the tensile bars. Pores could reduce the strength of the material by providing a route of easy fracture [13]. These pores may be attributed to water uptake on the surface of the aluminum Fig.…”

“…Bulk porosity fraction greater than several percent has been found to detrimentally impact mechanical properties of metallic parts [11][12][13]. This is often attributed to the fracture path preferentially traveling along regions with high numbers of defects [14].…”

Effect of Layer Directions on Internal Structures and Tensile Properties of 17-4PH Stainless Steel Parts Fabricated by Fused Deposition of Metals

“…The as-sintered W- and T-specimens exhibited strengths of 840 and 880 MPa, respectively, and strains at break of 24% and 23%, respectively. These values meet the JMPA standards (tensile strength > 800 MPa, strain at break > 4%; JPMA S01:2014) [ 39 ]. The strength and strain at break were lower in the L-specimen (780 MPa and < 20%, respectively).…”

“…The strain at break of the W- and T-specimens was lower in the as-aged specimens (~13%) than in the as-sintered specimens (~16%). Although the strains met the JPMA standards (> 2%, JPMA S01:2014), the strengths were slightly below the standards (tensile strength > 1200 MPa, JPMA S01:2014) [ 39 ]. In general, the solution and aging treatment strengthened the tensile strength of 17-4PH SS by forming nanoscale Cu-rich spherical precipitates in the martensite matrix, which prevents dislocation movements.…”