# Thermomechanical Processing of Medium-Carbon Boron-Bearing Microalloyed-Steel Forgings Targeting Normalized-like Structure and Properties

## TL;DR

This paper explores how to process a specific type of steel to achieve desired properties without traditional heat treatment, using direct cooling after forging.

## Contribution

The study introduces a novel thermomechanical processing route using direct cooling to achieve microstructures and properties comparable to conventional normalization.

## Key findings

- Direct cooling produced a microstructure of grain-boundary ferrite and pearlite with high tensile properties.
- The direct cooling method achieved Re ≈ 610 MPa, Rm ≈ 910 MPa, and elongation A5 ≥ 12%.
- The method offers energy-efficient alternatives to conventional normalizing for high-duty steel parts.

## Abstract

The paper presents designing thermomechanical processing routes for medium-carbon boron-bearing microalloyed steel and investigates their effect on microstructure–property characteristics obtained through controlled cooling directly from hot forging temperature. Direct cooling was carried out in situ within the industrial process of hot forging, replacing conventional heat treatment with slow and accelerated air cooling, realized with a fully automated fan-cooling laboratory conveyor which accommodates the desired cooling strategy. Comparative analysis of conventionally normalized and direct-cooled microstructure and mechanical properties obtained under varied thermo-mechanical conditions is presented to investigate the potential of medium-carbon microalloyed steel with boron addition for producing tailored properties comparable to those of the normalized condition. The obtained microstructure composed of grain-boundary ferrite and pearlite which resulted in tensile properties as good as Re ≈ 610 MPa, Rm ≈ 910 MPa, and elongation A5 ≥ 12%. Although the achieved microstructure–property parameters differ from those achieved through conventional normalizing (Rm ≤ 780 MPa, Re ≤ 460 MPa, and A ≥ 14%), they are considerable in terms of selected machinability aspects. The observed effect of the imposed treatment strategies on interlamellar spacing and morphology of ferrite showed possibilities regarding the control of mechanical properties and application of direct cooling as a beneficial alternative to conventional normalizing, where energy consumption is the main concern in manufacturing high-duty parts made of boron-bearing microalloyed steel 35MnTiB4.