Abstract
This paper focuses on the mechanical properties analysis of the high strength S700MC steel applied in welding joints. The research comprised mechanical tests for checking what the changes of tensile characteristics, mechanical parameters, resistance to impact, and fracture toughness look like in selected regions of the welding joint. Stress-strain curves have shown significant differences in the tensile characteristic shape and the values of Young’s modulus, yield stress, ultimate tensile strength, and ductility due to the welding process applied. In the case of Charpy tests, the courses of the accumulated energy, force, deflection, and project velocity are presented, indicating the maximum value of absorbed energy, the same level of force during the first contact of the projectile with the specimens, and the significant variation of the velocity for the impact energy ranging from 50 J up to 300 J. On the basis of the fracture toughness tests, the distributions of the CTOD (Crack Tip Opening Displacement) values are presented for the parent material, HAZ (Heat Affected Zone) and weld. Moreover, the characteristic features of the fatigue pre-crack, transient and crack propagation zones are identified and discussed.
Highlights
High strength steels belong to the modern engineering materials with attractive mechanical parameters from an engineering point of view
The welding joints produced from the S700MC steel were characterized using standard tensile tests, impact Charpy tests, and fracture toughness tests applying Crack Tip Opening Displacement (CTOD)
Contrary to the parent material fracture results that exhibited longitudinal cracks induced as an effect of the hot-rolling process of the S700MC steel (Figure 4b), the fracture region close to the weld was more uniform (Figure 4c)
Summary
High strength steels belong to the modern engineering materials with attractive mechanical parameters from an engineering point of view. The treatment process is designed to take carbon out at the baking stage, creating more formable steel during plastic work and strengthening it for the applications required [1] This stage creates a single or multi-phase microstructure represented by a ferritic single-phase or other phases such as martensite, bainite or austenite. The multi-phase microstructure enables the unique mechanical properties and beneficial behaviour of the steel under loading to be obtained as an effect of transformation hardening [4]. It can be attained by such treatment processes as ausforming or tempforming. Significant microstructural effects can be Materials 2020, 13, 5249; doi:10.3390/ma13225249 www.mdpi.com/journal/materials
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