Effect of Quenching Strategy and Nb-Mo Additions on Phase Transformations and Quenchability of High-Strength Boron Steels

The application of direct quenching after hot rolling of plates is being employed in the production of ultra-high-strength hot rolled plates. When heavy gauge plates are produced, the complexity involve in achieving high cooling rates in the plate core is increased and the formation of undesirable soft phases within martensite is common. In the current paper, both direct quenching and conventional quenching (DQ and CQ) processing routes were reproduced by dilatometry tests and continuous cooling transformation (CCT) diagrams were built for four different high-strength boron steels. The results indicate that the addition of Mo and Nb-Mo suppresses the ferritic region and considerably shifts the CCT diagram to lower transformation temperatures. The combination of DQ strategy and the Mo-alloying concept provides the best option to ensure hardenability and the formation of a fully martensitic microstructure, and to avoid the presence of soft phases in the center of thick plates.

Interrelation of CCM (Steel Billet Continuous Casting Machine) Tube Steel Casting Parameters and Hot-Rolled Plate Quality

The quality of the hot-rolled plate up to 36 mm thick was estimated by the percentage of rolled products, sorted due to the presence of a surface defect "Non-metallic inclusions", and internal defects, detected by ultrasonic plate control. The analysis of the data on the total sorting of hot-rolled plates demonstrated that the amount of sorting differs significantly on the melting from which each series of tubular metal casting commenced, compared to all the other melting in the series. The sorting of the sheets rolled from the metal of the first in a series of melting proved to be 1.9 times higher than that of the metal of all other melts. The main reason (in 68% of cases) of sorting is the presence of non-metallic inclusions on the surface of the plates. The effect of sorting of hot-rolled plates on non-metallic inclusions of various parameters has been studied: the duration of the intermediate ladle-heating; the length of time from the end of the heating of the intermediate ladle, prior to the beginning of the casting; lining temperatures of the intermediate ladle before the beginning of casting; duration of filling the intermediate ladle; the filling rate of the intermediate ladle with metal; mass of metal in the intermediate ladle before the beginning of casting into the crystallizer; chemical composition of metal; overheating of the metal over the liquidus point at the beginning, middle and end of the casting. On the sorting of flat products for non-metallic inclusions, of all the parameters considered, a statistically significant effect is due only to the overheating of the metal above the liquidus point, which varies in the range from 19 to 35 ° C. In order to obtain an acceptable quality of both the surface of slabs and the surface of hot-rolled plates for non-metallic inclusions, the first in a series of melts recommends overheating of the metal in the intermediate ladle above the liquidus temperature of 30-35 ° C.

Quantitative assessment of microstructural inhomogeneity by thickness of hot-rolled plates made of cold-resistant low-alloy steel for Arctic applications

A technique to assess microstructural anisotropy assessing by the thickness of the plate steel based on the texture analysis of the image has been developed. This technique provides for the anisotropy assessment at two dimensional levels: in the short-distance and long-distance neighborhoods, which characterize the elongation along the rolling direction of fine and coarse structural constituents, respectively. The practical approval results of this technique in the study of the microstructural heterogeneity of ferritic-bainitic steels over the thickness of 25–70 mm hot-rolled plates have been presented. It has been shown that the proposed anisotropy criteria in combination with the volume fraction of coarse packet-block regions of lath bainite as well as regions of bainite without an internal developed subgrain structure adequately estimate the microstructural heterogeneity over the thickness of plate steel and can be used for a detailed interpretation of the two-stage thermomechanical processing technology with accelerated cooling including taking into account the metallurgical inheritance of the slab.

Cutting Force during Surface Layer Milling of Selected Aluminium Alloys

This paper presents the analysis of cutting force during surface layer milling of selected aluminium alloys, which are widely used in the aviation industry. The cutting force is one of the most important parameters determining the machinability of the material and also provides important information about the course of the cutting. The study analysed the influence of the technological parameters, i.e., cutting speed vc and depth of cut ap as well as the relation between cutting tool feed direction and rolling direction on the value of cutting force during milling of selected aluminium alloys, i.e., EN AW-2017A T451 and EN AW-2024 T351. The material anisotropy is a very important issue, since the engineering industry faces enormous problems related to the cutting of the tested materials that are usually supplied in the form of rolled plates. The surface layer was cut due to the fact that it accumulates the greatest residual stresses. The measurement process of cutting force was performed by using 9257B Kistler piezoelectric dynamometer. As part of the analysis of the results, the measurement uncertainty was also estimated, which was determined on the basis of two components obtained by using the A and B methods, respectively.

Pre-Machining of Rolled Plates as an Element of Minimising the Post-Machining Deformations

The paper presents the influence of the milling strategy, the relation between the cutting tool feed direction and the rolling direction, as well as the pre-machining consisting of the removal of the textured surface layer of rolled plates in the rolling process on the thin-walled elements deformations made of the EN AW-2024 T351 wrought aluminium alloy, after milling. The research used strategies such as: high-performance cutting (HPC), high-speed cutting (HSC) and conventional milling (CM), as well as their combinations. Another tested variable was the relation between the tool feed direction and the rolling direction. In addition, the tests were carried out in the following versions: leaving the textured surface layer created after plastic working and with its removal with technological parameters corresponding to HSC and CM. Based on the obtained results, it was found that the post-machining deformation of thin-walled elements can be minimised owing to the use of a selected milling strategy and its combination with pre-machining (or lack thereof). It was also observed that larger deformations were obtained for samples after milling in the direction perpendicular to the rolling direction.