Ten experimental 0.18 pct C-1.2 pct Mn-0.002 pct B steels with various Ti/N ratios were evaluated in this study. The hardenability of these steels was first determined using Jominy tests. Slab sections were then rolled to produce 12.5-mm-thick plates, and subsequently quenched and tempered for mechanical property evaluation. The volume fraction of coarse (greater than 1 m) TiN particles was measured in all steels using quantitative metallographic techniques. Scanning transmission electron microscopy was used to investigate fine precipitates, and scanning electron microscopy was used to examine the fracture surface of Charpy specimens. The results show that a complete boron (B) hardenability effect is obtained with Ti/N ratios ≥2.9, a value slightly below the stoichiometric Ti/N ratio of 3.4. Any excess Ti, above that which combines with N, provides an additional increase in hardenability on quenching (effect of Ti in solution) and an increase in strength on tempering (Ti (C,N) precipitation). Steels with a higher (Ti)(N) product develop a higher volume fraction of coarse TiN particles during solidification. These coarse TiN particles result in reduced toughness levels of the heat-treated plates evaluated in the present study.

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This study evaluated mechanical behavior of the intermetallic compounds (IMCs) formed at the interfaces between potential Pb-free solders (Sn-Ag-Cu and Sn-Zn) and the wires of Cu and Ag under different loading rates. Compared to Ag based IMCs, Cu based IMCs were harder and stiffer, but less strain rate sensitive. The morphology of the indent impression was found depending on the ratio of the modulus to hardness, and the crystal structure of the IMCs.

This study investigated the behavior of Cu-containing intermetallic compounds (IMCs) in liquid Sn–Ag and Sn–Zn solders. Experimental results show that for the intermetallics investigated, Cu–Sn and Cu–Zn compounds, the occurrence of settling was dominated by the crystalline temperature of IMCs, buoyancy due to difference in densities, and dissolution potential for the compounds into the liquid. The complete dissolution of Cu–Zn compounds, which took place in the Sn–Zn solders when the Cu content exceeded a critical value, might be ascribed to the depletion of Zn in the melt.