J.I. Verdeja

Microstructure selection criteria for cast irons with more than 10 wt.% chromium for wear applications

A series of wear-resistant irons was cast, and in some cases heat treated, to study and characterize their microstructure. These castings were especially designed to vary the type, size and proportion of the different carbides that might be present in the microstructure at room temperature, either as a primary constituent or associated with the matrix. All the microstructural constituents were rationalized in terms of binary and ternary diagrams. It is possible from this work to derive a rational criterion for the selection of the most adequate material for wear and erosion applications.

Metallographic Characterization of Hypoeutectic Martensitic White Cast Irons: Fe-C-Cr System

High wear resistance and low cost are among the most appreciated properties for the non-alloyed white cast irons. Their toughness levels, however, are poor. An attempt to optimize the compromise between abrasive wear resistance and impact toughness could be reached through the use of low-alloy Ni-Hard cast irons satisfying the majority of mining applications in mineral crushing, classification, and transportation. The present work, based on microstructural considerations, points out some of the limitations in the use of Ni-Hard martensitic cast irons, in contrast to the advantages brought about by the use of white cast irons of non-ledeburitic matrix with high chromium content with respect to the wear resistance and toughness level.

Ferritic steels: Optimization of hot-rolled textures through cold rolling and annealing

Abstract This paper describes the processes used in the production of tinplate, autobody and interstitial-free (IF) steels, and examines how the microstructure and the texture of the hot-rolled stock modify the cold formability properties ( n , r m and Δ r ) of the blanks through the subsequent cold-rolling and annealing processes. The process of fabrication of ferritic steel strip must comply with the specified drawing quality requirements: commercial quality (CQ), drawing quality (DQ), deep drawing quality (DDQ) or extra deep drawing quality (EDDQ). The quality level is determined by several factors, such as the chemical composition, microstructure and texture of the hot-rolled sheet, the percentage of cold reduction (CR) and the recrystallization treatment in the continuous annealing process or batch process. To a lesser degree, other parameters such as the coiling temperature in the hot strip workshop and the degree of reduction in the temper rolling (TR) mill also modify the cold workability of the strip.

Ultrafine Grained HSLA Steels for Cold Forming

The industrial level production of ultrafine grained (or ultrafine ferrite) ferrous alloys was investigated through three examples of steels that complied with the EN 10149-2 Euronorm and were produced by advanced controlled hot rolling techniques. The steel samples were tension tested and chemically analyzed, and the microstructure was evaluated through quantitative metallographic techniques to determine parameters such as yield stress, amount of microalloying elements, strain hardening coefficient, grain size, and grain size distribution. These steels were micro-alloyed with Ti, Nb, and Mn with ASTM grain sizes of approximately 13–15. The careful control of chemical composition and deformation during production, giving a specific attention to the deformation sequences, austenite non-recrystallization temperatures and allotropic transformations during cooling, are indispensable to obtain steels with an adequate strain hardening coefficient that allows cold working operations such as bending, stretching or drawing.

Interstitial free steel: Influence of α-phase hot-rolling and cold-rolling reduction to obtain extra-deep drawing quality

Abstract This paper shows the drawing properties of Ti-bearing interstitial free steel. The study was carried out on the basis of microstructure, mechanical properties and texture using X-ray diffraction techniques and orientation distribution function (ODF) analysis. The results obtained prove the influence of each stage of processing to achieve extra-deep drawing quality (EDDQ), focusing our attention on hot-rolling and cold-rolling reduction. It is demonstrated that the optimum cold-rolling reduction increases to 90% for both rm and Δr coefficients.

Annealing Textures for Drawability: Influence of the Degree of Cold Rolling Reduction for Low-Carbon and Extra Low-Carbon Ferritic Steels

Abstract This work considers the optimization of deep drawing properties by studying the influence of hot rolling conditions, cold reduction rate, and final annealing on the evolution of steel sheet textures. Two steels have been selected: a low-C steel used for enameling applications, and an extra-low-C steel of the interstitial-free type. Results show that the intensity of {111} component—and, consequently, drawability—is considerably higher in the textures of cold-rolled and annealed sheets than in hot-rolled sheets. It is suggested that drawability of sheets annealed after cold rolling improves if greater than conventional reduction rates are used during rolling. Finally, it is shown that, contrary to what has sometimes been claimed, improvements of the “r” coefficient are not accompanied by a “pancake” morphology of the ferrite grains.

Microstructure, a limiting parameter for determining the engineering range of compositions for light alloys : The Al-Cu-Si system

Twelve as-cast alloys of the Al-Cu-Si ternary system were investigated. In all the cases, the microstructural phases observed were: {alpha} solid solution of Cu and Si in Al, CuAl{sub 2} ({theta} phase), and silicon crystals. The morphology and distribution of the {theta} and Si brittle constituents limit the percentages of Cu and Si added in the composition ranges of these commercial alloys.

Mechanical behaviour of thermomechanically produced ultrafine grained dual-phase steels

Abstract Dual-phase (DP) steels are an excellent alternative in the production of automotive parts that require high mechanical resistance, high impact strength and elevated elongation. These materials are produced using low alloy steels as a basis, reducing costs and resulting in a combination of martensite and ferrite structures with ultrafine grain size. These characteristics are achieved through strict control of rolling conditions, strain rate, cooling rate and coiling temperature. This work presents the results of tension testing of two types of DP steels, along with microstructural characterisation, in order to understand the effect of the advanced thermomechanical controlled rolling processes on the formation of the microstructure and resulting mechanical properties. Les aciers biphasés sont une excellente substitution pour la production de composantes automobiles qui requièrent une résistance mécanique élevée, une haute résistance à l’impact et une grande élongation. Ces matériaux sont produits en utilisant des aciers faiblement alliés comme base, réduisant les coûts et engendrant des combinaisons de structures martensitiques et ferritiques à granularité ultrafine. On obtient ces caractéristiques grâce à un contrôle strict des conditions de laminage, de la vitesse de déformation, de la vitesse de refroidissement et de la température d’enroulement. Cet article présente les résultats des essais de traction de deux nuances d’acier biphasé, de même que la caractérisation de la microstructure, afin de comprendre l’effet des procédés avancés de laminage thermomécanique contrôlé sur la formation de la microstructure et les propriétés mécaniques qui en déroulent.

MACHINABILITY IMPROVEMENT THROUGH HEAT TREATMENT IN 8620 LOW-CARBON ALLOYED STEEL

The effect of different heat treatments is evaluated on SAE 8620 low-carbon alloyed steel by means of drilling tests. Improving machinability through prior heat treatment in steels used for nitro-carburizing surface treatments is very important in the manufacturing of large series of parts, due to its impact in production costs. This is the case for the commonly used SAE 8620 grade, in its carburized and quenched and tempered state, for the production of gears, shafts and other transmission box components for the automobile industry. The machinability of the steel, determined by simple drilling tests (which are typical in industry labs), is a function of microstructure, which is determined by the state in which the steel is received and/or heat treatments prior to carburizing. This work shows that by employing some inter-critic annealing treatments, followed by sub-critic isothermal ones, the machinability of 8620 steel can be improved by ∼16% over the typical as-received cold drawn state.

Multiphase Steels: Structure-Mechanical Properties Relationships in the Cold Rolled and Continuous Annealed Condition

The present work describes the correlation between the microstructure and the mechanical properties of multiphase steels processed through a Continuous Annealing Process Line (CAPL). The mechanical and microstructural properties of one of the former experimental steel compositions was also processed via Batch Annealing (BA) and the results have been included for comparison reasons.