Investigation of heat affected zone softening in armour steels Part 2 – Mechanical and microstructure heterogeneity

Abstract

Flash processed (FP) steels have shown potential for armour applications based on the response to ballistic loading. In this research, weldability of these steels was studied and compared to commercial high hard (HH) armour steel. Simulated heat affected zone (HAZ) microstructures in these steels were investigated by comprehensive microscopy and hardness mapping. HAZ softening in HH steel was observed on heating to a peak temperature below Ac 1 due to overtempering of original microstructure. In FP steel, the softening was associated with allotriomorphic ferrite formation when heated to a peak temperature between Ac 1 and Ac 3 . The transformation kinetics, softening, and hardening characteristics are rationalised based on changes in prior austenite grain size, cooling rate and underlying chemical heterogeneity.

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.…”

Influence of solidification structure on austenite to martensite transformation in additively manufactured hot-work tool steels

“…To understand the implications of chemical heterogeneities and be able to control them are crucial for all manufacturing processes. In the case of conventionally manufactured armour and pressure-vessel steels, for example, banding occurs due to elemental segregation during casting [ 9 , 10 ]. This, in turn, may cause spatially different microstructure evolution upon heat treatments [ 9 ] or in the heat affected zones during welding [ 10 ], leading to mechanical heterogeneities and consequently inconsistent mechanical properties.…”

“…In the case of conventionally manufactured armour and pressure-vessel steels, for example, banding occurs due to elemental segregation during casting [ 9 , 10 ]. This, in turn, may cause spatially different microstructure evolution upon heat treatments [ 9 ] or in the heat affected zones during welding [ 10 ], leading to mechanical heterogeneities and consequently inconsistent mechanical properties. Elemental segregation, when controlled, can also be advantageous.…”

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.…”