Investigation of heat affected zone softening in armour steels Part 1 – Phase transformation kinetics

Abstract

Heat affected zone (HAZ) softening in two armour steels (high hard and flash processed) was investigated by monitoring phase transformations during simulated welding thermal cycles. The high hard steel was produced by conventional thermomechanical processing followed by quench and tempering. Flash processed steel was produced by rapid heating and cooling of a spheroidised steel to produce a mixed microstructure. Heat affected zone softening in high hard steel was observed on heating to a peak temperature below Ac 1 due to overtempering of the original microstructure. In flash processed steel, the softening was associated with allotriomorphic ferrite formation when heated to a peak temperature between Ac 1 and Ac 3 . The above results demonstrate the importance of initial microstructure on HAZ on phase transformation transients and associated softening in armour steels.

Toward Process-Based Quality through a Fundamental Understanding of Weld Microstructural Evolution

“…In another example, the role of initial microstructure (e.g., distribution of carbides and chemical segregation) in advanced high-strength steels (AHSS) and its response to welding was attributed to improved ballistic properties in comparison to welds made with homoge-neous materials (Refs. 35,36). Similarly, during spot welding a small change in the electrode curvature led to large changes in weld nugget development - Fig.…”

Techno-economic Feasibility of Modified Pulse Arc Deposition on Thick Section of Quenched and Tempered Steel

“…The heat affected zone (HAZ) exhibits softening due to tempering [1,10]. This softened zone often exhibits low creep and fatigue properties and poor ballistic performance [11,12] compromising the integrity of the structure. Additionally, like most high strength low alloy steels, Q&T steels are susceptible to hydrogen-assisted cold cracking.…”

High-hardness armor welded by CW-GMAW: economic, geometric and CGHAZ analysis

“…This classification distinguishes steels that have the isotropic mechanical and ballistic properties in the rolling direction and steels with anisotropy properties. The most commonly used steels are cast homogeneous armor (CHA), rolled homogeneous armor (RHA), high-hardness armor (HHA), dual hardness armor (DHA) and hardened face armor (HFA) [1]. Modenesi et al [2] showed a summary of the formation of heataffected zone (HAZ) in different base materials in welded joints, with variations in the thermal cycle, with four basic groups being solid hardened alloys, hardened alloys, precipitation hardened alloys and transformable alloys, each one forming different divisions in the microstructure of the HAZ.…”

“…In this case, the heat involved in welding processes changes their structure significantly, especially those that require high values of welding energy. The main problems occurring in steels with carbon percentages above 0.25% C is that of no tempered martensitic is formed with high hardness in the heat-affected zone (HAZ), nevertheless, with a great brittleness, as occurred in the HHA steel [1]. Indeed, microstructure is one of the most important factors to analyze in the HHA steel because changes in mechanical properties such as toughness, ductility and hardness directly affect the ballistic properties such as drilling resistance, spalling and fragmentation.…”

“…In almost all studies so far, the heat input affected directly the hardness and toughness in the HAZ. However, almost all these studies are focused in the softening zone because the ballistic performance is especially affected, reducing the mechanical properties, mainly its hardness [1,[7][8][9]. Nevertheless, the coarse-grained heat-affected zone (CGHAZ) has a higher importance in the mechanical properties of the welding joint because of the severe losses in toughness, ductility and crack formation despite having elevated hardness.…”