Easily Sinterable Low-Alloy Steel Powders for P/M Diamond Tools

The work presents the design and fabrication procedures used to manufacture inexpensive iron-base powders employed as a matrix in diamond-impregnated tool components. Three newly developed low alloy steel powders, containing from 94.4 to 99.4 wt.% Fe, have been formulated with the assistance of ThermoCalc software and produced by means of a proprietary process patented by AGH-UST. It has been shown that the powders are readily pressureless sintered to a closed porosity condition (>95% theoretical density) at a temperature range between 840 and 950 °C. All as-consolidated materials achieve the desired tool matrix hardness of more than 200 HV. One of the experimental powders has been designed to partly melt within the sintering window. This is particularly important in fabrication of wire saw beads by the conventional press and sinter route because sintering of a diamond-impregnated ring and its further brazing to a tubular steel holder can be combined into one operation.

Thermodynamics of nitrogen solutions in liquid nickel

The simplest model of the structure and interatomic interaction is applied to nitrogen solutions in liquid alloys of Fe – Ni system, which earlier (2019) was used by the authors for nitrogen solutions in alloys of Fe – Cr system. The principles of statistical mechanics are used in this model. Thus, three formulas were obtained. The first formula expresses the Sieverts law constant for the solubility of nitrogen in liquid nickel through a similar constant for the solubility of nitrogen in liquid iron and the Wagner interaction coefficient of nitrogen with nickel in low-concentration liquid iron-base alloys. The second formula expresses the partial enthalpy of dissolution of nitrogen in liquid nickel during the formation of an infinitely dilute solution through a similar value for dissolution of nitrogen in liquid iron and the Wagner interaction coefficient of nitrogen with nickel in iron-base liquid alloys. The third formula expresses the Wagner interaction coefficient of nitrogen with iron in low-concentration liquid nickel-base alloys through the Wagner interaction coefficient of nitrogen with nickel in liquid iron-base alloys. The constant of the Sieverts law for the solubility of nitrogen in liquid iron at T = 1873 K is assumed to be 0.044 mass. %. The partial enthalpy of dissolution of nitrogen in liquid iron assumed to be 5.0 kJ/mol. For Wagner interaction coefficient of nitrogen with nickel in iron-base liquid alloys at 1873 K three variants of values were studied: 2.4, 2.6, and 2.85. For the first option, theoretical value of the Sieverts law constant for solubility of nitrogen in liquid nickel at T = 1873 K, equal to 0.00195 mass. % was obtained. Theoretical value of the enthalpy of dissolution of nitrogen in liquid nickel is 52.7 kJ/mol. Theoretical value of the Wagner interaction coefficient of nitrogen with iron in nickel-base liquid alloys is –4.0. The agreement of theory with experiment seems to be satisfactory.