Toughness properties at multi-layer laser beam welding of high-strength steels

The material characteristics of high toughness and high strength in steel are usually not available at the same time. However, it would be an advantage if high-strength steels would show high impact toughness also at lower temperatures for applications in critical surroundings. In this paper, an approach of multi-layer welding of high-strength steel is presented in order to increase the weld-metal toughness using wire material in combination with thermal cycle modifications. Promising interlocking microstructures were found after multiple tempering of the previously applied structure at homogeneously distributed material in the weld seam. It was found that short thermal cycles during laser processing lead to insufficient time for carbon diffusion, which leads to remaining ferrite structures in contrast to the prediction of welding transformation diagrams. The additionally applied heating cycles during multi-layer laser welding induce the formation of interlocking microstructures that help to increase the weld seam toughness.

Effect of Multiple Tempering on Mechanical Properties and Microstructure of Ledeburitic Tool Steel AISI D3

The effects of multiple tempering on the mechanical properties and microstructure of ledeburitic tool steel AISI D3 were investigated. Austenized samples at: 940 °C and 970 °C were used The subsequent tempering was carried out in three stages with the same temperatures: 250-350-450-550 ° C; for 1 hr. The microstructure was revealed at optical (OM) and electronic (SEM) levels and then X-ray diffraction analysis (DRX) was made along with an X-ray scatter spectrometry (EDS) test. It was found that the yield stress (σf), the maximum tensile strength (σr) and ductility (ɛ) decrease with the number of temperings. The microstructures, in the three stages, show primary, massive and small carbides of type M7C3 , and Cr7C3 , accompanied by precipitated fine carbides of the same type, with the presence of the phases: Fe3C, Cr0.03 Fe0.97 and residual austenite (γr ), the latter phase is minimized with the third temper. These precipitates occur at each stage of tempering simultaneously or as the temperature increases. The variation of these properties is closely related to the microstructure obtained.

Examination of Heat Treatment on the Microstructure and Wear of Tool Steels

The microstructure of the investigated X153CrMoV12 grade tool steel in delivered condition consisted of spheroidal matrix and primary carbides. The primary carbides were not dissolved under austenitisation time on either 1030°C or 1070°C. The microstructure and abrasion resistance of the steel changed due to quenching from different austenitisation temperatures. After conventional quenching from the higher austenitising temperature, there is more residual austenite in the steel than at quenching from the lower austenitisation temperature, which decreased the wear resistance. As a result of quenching from 1070°C followed by a multiple tempering process around 500 to 540°C, the retained austenite content is reduced and finely dispersed carbides are precipitated in the matrix, resulting in a higher matrix hardness and an increased wear resistance. After cryogenic treatment, the residual austenite content decreases compared to the conventional process, which leads to an increase in hardness and wear resistance.

Effect of Chemical Composition and Heat Treatment Parameters on the Structure and Properties of Vanadis 23 and Vanadis 30 PM High-Speed Steels

The paper deals with the assessment of the effect of content of cobalt and cryogenic treatment on mechanical properties and structure of Vanadis 23 and Vanadis 30 PM high-speed steels. The studied characteristics are evaluated after conventional heat treatment (quenching and multiple tempering) and also when deep cryogenic treatment at -196°C/4 hours was inserted between quenching and tempering. The mechanical properties are assessed by a three-point bending flexural test and by measurement of the hardness. Metallographic analysis is performed using an energy dispersive spectrometer (EDS) and the scanning electron microscope (SEM).