Resistance spot welding of a thin 0.7 mm EN10130: DC04 material onto a thicker 2.4 mm 817M40 engineering steel

The effects of welding current, electrode force, and welding time in a resistance spot weld were studied to investigate the effectiveness of welded joints between a thin EN10130: DC04 material and a thicker 817M40 part, through analysis of the microstructural and mechanical properties. All welded specimens were subjected to tensile testing at room temperature (25°C) and sub-zero temperature (-46°C) to test the strength of the welded joints. No full button failure was observed at either room temperature or sub-zero temperature after optimization of the weldng parameters. The fusion zone was observed to consist mainly of martensitic phase, due to rapid quenching, while the HAZ was composed of clusters of martensite in a ferrite and bainite matrix. The base 817M40 metal remained fully ferritic after welding. The hardness was found to increase with increasing welding current. An increase in nugget size, indicating good fusion of the weld, was observed with an increase in the welding current.

Suitability of DIC and ESPI optical methods for monitoring fatigue damage development in X10CrMoVNb9-1 power engineering steel

The aim of this research was to compare the effectiveness of two different optical measurement techniques (digital image correlation—DIC and electronic speckle pattern interferometry—ESPI) during fatigue damage development monitoring in X10CrMoVNb9-1 (P91) power engineering steel for pipes. The specimens machined from the as-received pipe were subjected to fatigue loadings and monitored simultaneously using DIC and ESPI techniques. It was found that DIC technique, although characterised by lower resolution, was more effective than ESPI. DIC allows to monitor the fatigue behaviour of steel specimens and accurately indicate the area of potential failure even within the initial stage of fatigue damage development.

New Weldable Steel for Rebars

A new steel grade, developed at the CELSA steelworks in Ostrowiec Świętokrzyski and used in the production of rebars, contributes greatly to the development of industrial and civil engineering. Steel B600B is characterised by yield point fyk = 600 MPa and immediate tensile strength ftk = 700 MPa. Tests revealed that the steel satisfies all requirements of related standards, both in terms of strength and processing properties. The mechanical properties of the new steel grade are higher by 20% than those of currently produced steels characterised by the highest mechanical properties (characteristic yield point Re= 500 MPa). As a result, the application of the new steel provides notable technical and economic advantages. The new steel grade meets requirements concerning technical class C in accordance with PN-EN 1992-1-1, which indicates that the steel has a significant yield point margin (being an important advantage in terms of limit state design). Plastic steels are easier to weld and less susceptible to welding crack formation. Technological (research-related) tests revealed the favourable welding properties of the new steel. Welding tests were performed using the manual metal arc welding method, i.e. the most common welding process used when making structural reinforcements. The welding tests involved the making of butt, overlap and cruciform joints. The strength and technological tests revealed that the steel satisfied the requirements specified in the PN-EN ISO 17660-1 standard.

Defects and post-manufac- turing processes of additively manufactured steels: A Review (Part 2)

Design freedom, complex geometry fabrication capability, minimal parts assembly and excellent material utilization attributes of additive manufacturing processes have provided a leverage ground for the development of functional engineering steel parts in the manufacturing industries. Despite the good attributes of additive manufacturing technology, there are still some local and inherent defects of as-built steel parts that can jeopardize the overall integrity of structural steel components. This review paper provides the associated defects of as-built steel and summarizes the post-manufacturing strategies being deployed to mitigate the severity of as-built steel defects. The microstructural and mechanical responses of some specific as-built steel under different fabrication conditions or additive manufacturing techniques are also summarized in this paper.

Effect of Aging Time on Microstructure and Mechanical Properties in a Cu-Bearing Marine Engineering Steel

This study elucidated the structure–property relationship in a Cu-bearing marine engineering steel that was water cooled and then aged at 500 °C for 0.5–3 h. The microstructural features, tensile properties and impact properties were comparatively investigated as a function of aging time. When the aging period was increased, the Cu precipitates underwent coarsening, and a stable face-centered cubic (fcc) formation occurred. Additionally, the tensile properties were significantly improved at the expense of low temperature toughness, which can be attributed to the presence of nano-sized Cu precipitates. The increment of yield strength mainly derived from Cu precipitate–dislocation interaction strengthening effects (232 MPa for 1 h and 199 MPa for 3 h.) during aging process. Therefore, optimization of mechanical properties was achieved by controlling the parameters of aging process. The peak age hardening condition (i.e., at 500 °C for 1 h) resulted in the yield strength of 755 MPa, tensile strength of 812 MPa, elongation of 26.3% and impact energy of 78 J at −80 °C.