Purpose: The paper presents the results of investigations on the effect of 0.003% boron
microaddition on the hardenability of new-developed HSLA-type steels. In order to prevent
the binding of the boron microaddition with nitrogen in BN nitrides, Ti microaddition at
concentrations of 0.033% and 0.028% was also added into the tested steels.
Design/methodology/approach: Evaluation of hardenability of the investigated steels
was carried out on the basis of the Jominy test and the analytical method, according to
the ASTM 255-89 standard, taking into account the effect of the boron microaddition.
Additionally, developed of the CCT-diagram of investigated steel. A DIL 805A/D dilatometer
with a LVDT-type measuring head was used to carry out the dilatometric test.
Findings: Microaddition of boron, introduced into steel in a concentration of 0.003% along
with Ti microaddition shielding (in concentration of 0.033% in steel A and 0.028% in steel B),
advantageously improves hardenability. This is reflected in calculated ideal critical diameter
DIB, which is equal 163 mm for steel A and 155 mm for steel B. The form of curves of phase
transformations of supercooled austenite is typical for steels with microaddition of boron,
with similar chemical composition.
Research limitations/implications: Due to similar chemical composition of investigated
steels, the kinetics of phase transformations of austenite, supercooled under continuous
cooling, was determined for steel B containing 0.28% C, 1.4% Mn, 0.3% Si, 0.26% Cr, 0.22%
Mo and Nb, Ti, V and B microadditions at 0.027%, 0.028%, 0.019% and 0.003% respectively.
Practical implications: Tested steels have high hardenability and show the full usability
for production of forged parts with the method of thermomechanical treatment, i.e., hot-
deformed in the temperature range adjusted to the type of microadditions added to steel,
with direct quenching of forgings from finishing forging temperature. The results of the tests
may be useful for developing the parameters of heat treatment and thermomechanical
treatment of investigated steels.
Originality/value: The hardenability of new-developed HSLA-type steels was determined.