Investigation of thermal residual stress of borided steel: finite-element simulation

Abstract

Although a technologically interesting characteristic of boriding is the production of a hard, wear-resistant layer on the treated steel parts, thermal residual stresses may lead to crack formation in both the iron boride (FeB) layer and the vicinity of the iron boride–diiron boride (Fe2B) interface. In this study, the thermal residual stress distribution in borided tool steel without temperature gradients was investigated systematically by using finite-element analysis. A transient analysis was performed to obtain the stress change with cooling time. The models were cooled down from 823 to 293 K under steady-state conditions. The maximum compressive residual stress is about 690 MPa and tends to decrease with increasing layer thickness. For the case of the double-layer model with 60 μm thick diiron boride, the tensile residual stress occurs on the surface of the iron boride layer and its value changes within the range of 1870–2025 MPa with the iron boride layer thickness. However, the magnitude of the shear stress at the steel–diiron boride interface is not crucial in the model with a single boride layer. The shear stress at the iron boride–diiron boride interface in the double-layer model increases dramatically with the iron boride layer and exceeds 1050 MPa for a high percentage of iron boride (52%) in the total layer thickness.