A micro-alloyed 1045 steel was commercially rolled into 54 mm diameter bars by conventional hot rolling at 1000 °C and by lower temperature thermomechanical rolling at 800 °C. The lower rolling temperature refined the ferrite-pearlite microstructure and influenced the microstructural response to rapid heating at 200 °C·s -1 , a rate that is commonly encountered during single shot induction heating for case hardening. Specimens of both materials were rapidly heated to increasing temperatures in a dilatometer to determine the A c1 and A c3 transformation temperatures. Microscopy was used to characterize the dissolution of ferrite and cementite. Continuous cooling transformation (CCT) diagrams were developed for rapid austenitizing temperatures 25 °C above the A c3 determined by dilatometry. Dilatometry and microstructure evaluation along with hardness tests showed that thermomechanical rolling reduced the austenite grain size and lowered the heating temperature needed to dissolve the ferrite. With complete austenitization at 25 °C above the A c3 there was little effect on the CCT behavior.

Microalloying of medium carbon bar steels is a common practice for a number of traditional components; however, use of vanadium microalloyed steels is expanding into applications beyond their original designed use as controlled cooled forged and hot rolled products and into heat treated components. As a result, there is uncertainty regarding the influence of vanadium on the properties of heat treated components, specifically the effect of rapid heat treating such as induction hardening. In the current study, the torsional fatigue behavior of hot rolled and scan induction hardened 1045 and 10V45 bars are examined and evaluated at effective case depths of 25, 32, and 44% of the radius. Torsional fatigue tests were conducted at a stress ratio of 0.1 and shear stress amplitudes of 550, 600, and 650 MPa. Cycles to failure are compared to an empirical model, which accounts for case depth as well as carbon content.

Due to their diverse microstructures, micro-alloyed steels are increasingly being adopted across various industries. While extensive literature exists on the processing routes of these steels, experimental data on their suitability for fracture mechanics-based design and manufacturing approaches is relatively scarce, particularly in two areas: (1) the alteration of fundamental fracture mechanics properties of micro-alloyed steels in the presence of structural restraints such as pre-stress and pre-strain, and (2) a comparative study of the effect of heat treatment practices on the fracture mechanics properties of micro-alloyed steels relative to their as-rolled conditions. This study addresses these gaps by experimentally determining the quasi-static initiation fracture toughness (J1c) of low carbon (0.19%) micro-alloyed steel in its as-rolled condition, following ASTM E-1820 standards, without any heat treatment. Additionally, the study examines the effects of normalizing, shot-peening, and cyaniding followed by shot-peening on the fracture toughness parameter. The results indicate that normalizing, shot-peening, and cyaniding, followed by shot-peening, positively influence the initiation fracture toughness of this micro-alloyed steel.