Effect of Alloying Additives and Microadditives on Hardenability Increase Caused by Action of Boron

The presented work was aimed at evaluating influence of boron on hardenability of steel quantitatively and evaluating this effect during complex use of boron with other alloying additives like chromium, vanadium and titanium. For this purpose, eight melts with variable chemical compositions were prepared. From the ingots, cylindrical specimens with normalized dimensions according to EN ISO 642:1999 were cut out and subjected to full annealing at 1200 °C and to normalizing at 900 °C. Such specimens were subjected to the hardenability Jominy test. In order to distinguish the influence of boron on hardenability of a given melt and thus to eliminate the differences resulting from its chemical composition, grain size and austenitizing temperature, the obtained ideal critical diameter was corrected and the boron effectiveness factor was determined. The performed examinations and analyses showed that inadequate quantities of microadditives result in losing the benefits coming from introduction of boron as the hardenability-improving element and can even result in a reduction of hardenability of the boron-containing steel.

Effect of Boron and Chromium on Hardenability in 0.33% C Cold Heading Steel

The effect of B and Cr on hardenability in 0.33% C cold heading steel was studied. The results show that the hardenability enhanced from adding 0.0020% B or 0.28% Cr. The length of high hardness stability region of the Jominy Curve obviously increased with adding B,and the hardness of low hardness stability region of the Jominy Curve increased significantly with adding Cr. The ideal critical diameter DI of the experimental steels was calculated, the DI is 20.0 mm of the base steel with 0.33% C and no other alloying element addition, but the DI becomes 29.5 mm with adding 0.28% Cr and 46.4mm with adding 0.0020% B. The hardenability of the test steels was calculated by the nonlinear equation and compared with the experimental results. The calculated Jominy curve did not reflect characteristics of 2# steel with B and needs to be further optimized.