Statistical Research of Stainless Austenitic Steel Grain Size Distribution after Screw Rolling

Screw rolling of austenitic stainless-steel billets was conducted in two- and three-high mills. Statistical research results showed that, compared to heated but not rolled conditions, both screw rolling techniques provided a decrease of grain size, variance, grain size distribution asymmetry, and excess in the billet cross-section at the stationary stage of screw rolling. At that stage, grain size distribution after two-high screw rolling is closer to normal in terms of asymmetry and excess values compared to grain-size distribution after three-high screw rolling. A strong negative correlation between strain effective values and grain-size values for the cross-section of the rolled billets at the stationary stage was revealed for both two- and three-high screw rolling.

Influence of Die Surface Topography and Lubrication on the Product Quality during Indirect Extrusion of Copper-Clad Aluminum Rods

Copper-clad aluminum rods are usually fabricated using hydrostatic extrusion, since during direct and indirect extrusion fracture of the copper sleeve is difficult to avoid. In this study, different die surface topographies and lubrication conditions were applied to improve the material flow during indirect extrusion of copper-clad aluminum rods. Thus, conic dies with different roughness (polished and sandblasted) and surfaces shapes (fine and coarse grooves) were tested. Additionally, the effects of a wax-graphite-based lubricant as well as a graphite-like carbon (GLC) coating of the die conic surfaces were investigated. The composite billets were made of aluminum EN AW-1080A cores and copper CW004A sleeves with an equivalent copper cross section of 0.24 of the total billet cross section. For all trials, an extrusion ratio of 14.8:1 and a conic die angle of 2α = 90° were chosen. Non-isothermal extrusion trials were carried out using a container at 330 °C and billet and tools at room temperature to reduce the flow stress ratio σCu/σAl. The extruded composite rods’ integrity, surface quality, interface integrity, and equivalent copper cross section were analyzed. In addition, a visual inspection of the sleeve-die contact surface was performed. The results showed that the GLC coating proved to be unsuitable due to a lack of lubrication, which causes accumulated sleeve fractures and longitudinal grooves on the extruded rods. The best results were achieved with the combination of the sandblasted die surface and the wax-graphite-based lubricant, observing a uniform material flow without sleeve fractures.

Consequences of microphysical segregation of chemical elements in welded steels

Defects of metallurgy-originated steel (sub-cored bubbles, impurities, macro- and micro-segregations of chemical elements, nonmetallic inclusions) to a large extent determines the faultiness of metal rolled products. The processes of chemical elements segregation in steel macro- and micro volumes considerably influence its quality. Reasons of microphysical dendrite segregation originating in steels of welding purpose of Св-09Г2С and Св-08ГНМ type considered. Mechanism of dendrites formation studied as well as the segregation degree of chemical elements along the continuously casted billet cross section. To estimate the segregation degree a criteria was used – the segregation coefficient, determined as relation of chemical elements mass shares in different micro-areas (dendrites, inter-dendrite gaps) of continuously casted billet cross section to those elements content by a ladle analysis of a heat or one another in different micro-areas. A heredity of segregation transfer from CC billet to finished wire rod of Св-08Г2С and Св-08ГНМ steels studied. It was determined, that decrease of the number of bainite-martensite areas as a result of decrease of dendrite segregation of chemical elements takes place by minimization within grade chemical composition of both main alloying element and impurities ones. Besides an additional alloying of steel by boron takes place based on boron to nitrogen relation at the level of B/N = 0,8±0,15. It was shown that to decrease the inter-dendrite segregation it is necessary to elaborate and implement effective steel modifying by calcium and REMs regimes as well as electro-magnetic stirring during continuous casting.

Distribution of Mechanical Properties by Volume in Titanium Billets Processed by Twist Extrusion

The influence of multipass processing by Twist Extrusion (TE) on distribution of mechanical properties by volume in commercially pure (CP) titanium billets is investigated. Experiments show that the mechanical properties are almost homogeneous in the billet cross-section already after the second pass of TE. This can be explained by mixing effect and saturation of properties as well. Warm TE leads to the formation of high strength properties in combination with high plasticity. Ultimate and yield stresses of the billet processed by two cycles of TE increased, in comparison with initial state, by 30% and 60% respectively. The value of the reduction in area remained at the initial value. This fact is indicating a high technological plasticity of the material, i.e. its ability for further shaping by metal forming methods.

Influences of Cross-Sectional Geometry and Surface Roughness on the Compression Stability in Upsetting High Aspect-Ratio Shaped Billets by FE Analysis

Metal forming for micro or mini-parts is a new developing trend in the metal forming application. The analysis of billet compression stability in upsetting is essential in selecting forming parameters and determining the size effect. The current study aims to explore the influence of billet geometry and surface roughness on the compression stability in upsetting high aspect-ratio shaped billets. 3D finite element simulation was employed to analyze the influence of surface roughness on the end faces of the billet and shapes profiles of the billet cross-section, on buckling in upsetting mini-size billets. Simulation results indicated that the rougher the contact surface, the lower was compression stability in upsetting the billets. In addition, the cross-sectional shape of the billet affected the compression stability in upsetting. Mini billets with larger shape factors would lead to higher compression stability.