Strain Hardening and Stretch Formability Behavior of Triple Phase (TP) Steel Strips

The current work explores the strain hardening and stretches formability behaviour of the developed Triple Phase (TP) steel. Double quenched TP steel strips posse three distinguished stages of strain hardening on tensile forming. 1st stage represents the highest n-value reflecting resistance to homogeneous deformation, where steel can be safely stretched. 2nd and 3rd stage reveals lower n-values, where localized thinning exist. On Erichsen testing, the relationship between punch forming force and punch stroke exhibits two forming regions. The 1st region is delineated by a straight line showing an ultra-high strain-hardening rate, which represents a reversible elastic stretch forming. The 2nd forming region continues to a higher Erichsen punch stroke than that of the 1st region and presents the permanent plastic stretch forming behaviour. It is found that bainite and martensite clusters created, by double quenching, in TP-steel exaggerated the elastic stretch forming limit 10 times higher than the as-hot rolled condition. 7 min. holding time of strips in the salt bath is considered the most effective for the creation of a useful volume fraction of the bainite phase. However, 21 min. holding time in salt bath grows martensite laths through the bainite aggregates, affecting negatively on stretch formability.

Effects of Aging on the Microstructure and Phase Transformation Behavior of Cu-Al-Mn Shape Memory Alloy

In the present work, the effects of artificial aging treatment on the transformation temperatures and hardness of Cu-Al-Mn shape memory alloy have been investigated. The aging processes have been performed on the one-time re-melted and 90% rolled samples. Differential scanning calorimetry reveals that reverse transformation is present for the re-melted sample which is aged at 400°C. However, in 90% rolled condition, this transformation takes place at 200°C and 300°C. Hardness examination shows that the aged specimens possess higher values in hardness in comparison to un-aged samples at all studied temperatures. Although, the peak-aged condition was demonstrated at 300°C for the re-melted sample, the rolled sample displayed increased hardness levels up to 500°C. Based on the DSC measurements and microstructural observations, it can be asserted that the thermo-mechanical processing including rolling plus aging at 300°C provides favorable transformation characteristics for shape memory behavior.

Steel Production Technology Development for the Manufacture of Pipes Used in the Extraction and Transportation of Petroleum Products

The technology has been developed for the production of low-carbon and microalloyed steel for the production of strips in order to manufacture small and medium-diameter pipes for the extraction and transportation of petroleum products. The developed technology allows to obtain stable corrosion properties, according to the NACE Standard TM 0284 technique, in a hot-rolled condition from slab with thickness more than 200 mm and with a content of more than 0.03% of carbon, which is very difficult in terms of ensuring the availability of inclusions and heterogeneity in the structure - as the main reasons for the reduced fracture toughness of steels working in acid media (in environments saturated with H2S). The obtained results allowed, with minimum costs, to prepare the previously developed integrated computer model (STAN 2000) for calculating the structure and mechanical properties. Calculations using the model made it possible to select such temperature-deformation regimes, which would be the minimum structural inhomogeneity over the section of the thickness of the hot-rolled strip. The results obtained: corrosion resistance repeatedly confirmed by the absence of cracks at the beginning after testing in accordance with the procedure Standard TM 0284.

Tensile Properties of AZX612 Magnesium Alloy Sheets Processed by Friction-Assisted Extrusion

Tensile properties at room and elevated temperatures of AZX612 alloy sheets processed by a kind of lateral extrusion method namely Friction-Assisted Extrusion (FAE) were investigated. The FAE was developed to control the texture, and carried out at temperatures ranging from 250 to 350°C with an extrusion ratio of 4 from the as-rolled condition. The results showed that FAE changes the basal texture of the as-rolled sheet into that inclined by about 15˚ against the extrusion direction and raises the intensity of the texture. It was observed that the significant microstructure refinement from as-rolled condition of 10.8μm to 4.7μm after FAE due to dynamic recrystallization at the extrusion temperature of 250°C. The 0.2% proof stress of the FAEed sheets at room temperature became significantly smaller than that of the as-rolled sheet in the extrusion direction but became larger in the transverse direction, resulting in the larger anisotropy. This can be understood by the activity of basal slip. The anisotropy of the tensile properties disappeared at a temperature of 300°C and an initial strain rate of 3.3×10-4s-1. In addition, the elongation was improved from 72% of the as-rolled sheet to 152% at maximum of the FAEed sheets in the extrusion direction. This improvement was attributable to superplastic flow based on grain boundary sliding.

Hot Deformation Behavior of Al-Cu-Li-Mg-Zn-Zr-Sc Alloy in As-Cast and Hot-Rolled Condition

The results of physical simulation of hot compression of semi-finished products, selected from a cast ingot and hot-rolled plate from aluminum-lithium alloy V-1461, in the temperature range of 400-460°C and strain rates of 1-60 s-1are presented. It is established that at a constant strain rate the flow stresses decrease with increasing test temperature, an increase in the strain rate leads to an increase in flow stresses at a constant temperature. The parameters of the hot deformation rheological model, including the Zener-Hollomon parameter and the hyperbolic sine law, are determined. It is established that the parameters of the rheological model for the cast and hot-rolled state differ insignificantly.

OVAKO CROMAX IH 482

Induction hardened Cromax IH 482 is based on a medium carbon, microalloyed steel, which is characterized by high strength in the as-rolled condition, i.e., without heat treatment. The alloy is used for the manufacture of piston rods, pistons, and eyes for hydraulic cylinders. This datasheet provides information on composition, hardness, and tensile properties as well as fracture toughness. It also includes information on corrosion resistance and surface qualities as well as forming, machining, and joining. Filing Code: SA-742. Producer or source: Ovako Cromax AB.

Friction Stir Welding of an Al-Mg-Sc-Zr Alloy with Ultra-Fined Grained Structure

Effect of friction stir welding (FSW) on mechanical properties and microstructure of Al-5.4Mg-0.2Sc-0.1Zr sheets with ultra-fined grained (UFG) structure was studied. The UFG-sheets were produced by equal-channel angular pressing (ECAP) followed either by cold or hot rolling. FSW was found to be very effective for retaining the UFG microstructure as well as constituent coherent nano-scale dispersoids in the welded material. Despite the preservation effect, however, the essential material softening was observed in the weld zone. This was attributed to the recrystallization occurring during FSW. The joint efficiency for yield strength of the obtained friction stir welds was found to be 81% in the hot rolled condition and only 55% in the cold rolled state. The relatively low joint efficiency was associated with the recrystallization softening as well as with the formation of a specific “kissing bond” defect in the stir zone. The joint efficiency is believed may be improved by adjusting of welding conditions and/or tool design.

Effect of Rolling on Microstructure and Room Temperature Tensile Properties of Newly Developed Mg-4Li-1Ca Alloy

Mg-30Ca and Mg-14Li (wt %) master alloys were melted successively in the induction furnace to obtain a Mg-Li-Ca ternary alloy containing 3.99 % Li and 1 % Ca. The as-cast material of thickness 4 mm was homogenised at 350° C for 120 mins and subsequently rolled to 62.5 % reduction in thickness at 300 °C to get 1.5 mm thick sheet. The microstructures of hot rolled samples were examined in as-rolled condition as well as after annealing at 350° C for various lengths of time. The presence of deformation twins was clearly seen in the as-rolled structure, whereas equiaxed twin-free grains were observed in the annealed condition. The average grain size was found to increase from 10 μm to 18 μm by annealing, according to the kinetics that follows a parabolic law. Tensile samples taken from rolled plate were deformed to failure at room temperature and a strain rate of 10-4 s-1. Ultimate tensile strength of as-rolled material increased to 213 MPa, while tensile elongation dropped to 6.5 % from the initial values of 134 MPa and 8.5 %, respectively. Annealing after rolling offered a good compromise between the enhanced tensile strength (160 MPa) and tensile ductility (9 %) suggesting viability of the proposed thermomechanical treatment as a means for enhancing both strength and ductility of Mg-4Li-1Ca alloy.

Fast Position and Accurate Segmentation Algorithms for Detecting Surface Defects of the Thermal-State Heavy Rail Based on Machine Vision

Color imaging in the hot rolled condition provides the better reaction of heavy rail on surface defects. In this paper, it proposes a series of novel algorithms of accurate position and segmentation of surface defects of heavy rail. An image acquisition device is designed on the adjustable camera bracket with the linear array CCD, and based on the correlation among pixels at the image level, a fast positioning method is developed for searching the Region Of Interesting (ROI) of the surface defects. Using the Mean-Shift image filtering algorithm which features multi-parameter kernel function, amendments to the sampling point weights and regional search with the nearest neighbor sampling points, accurate segmentation of the identification character is easily achieved by K-means clustering. Experiments show that this algorithm for the identification of the heavy rail surface defects is proven to be more rapid in testing the inclusions, cracks and oxide skin defects with a good promotional value.