Transformation induced plasticity (TRIP) steels are a promising solution for the production of cars with low body mass because of the combination of high strength and large uniform elongation that they offer. However, conventional CMnSi TRIP steels with more than 1 wt-%Si have the drawback of poor Zn coating quality after continuous galvanising. This problem is due to the presence of complex Si ± Mn oxides on the strip surface. The present research work therefore focused on the full substitution of Si by Al in TRIP steels and the detailed analysis of the galvanising behaviours of these Si free CMnAl TRIP steels. If the hot dipping is done after a combination of intercritical annealing and isothermal bainitic transformation in a furnace atmosphere with a high dewpoint, the wetting of the strip by the liquid Zn is improved signi® cantly. However, the improvement is limited and not enough to avoid bare spots and coating defects cannot be avoided on conventional CMnSi TRIP steel. In contrast, the Si free CMnAl TRIP steel has a much better wettability when annealed at a low dewpoint. The surface segregation of the elements, which have a high af® nity for oxygen, i.e. Si, Al, and Mn, was studied in detail and this revealed that Si was much more readily enriched on the surface than Al during the annealing in the low dewpoint atmosphere. The difference in the surface segregation between Si and Al resulted in a clear difference in the galvanisability. The limited presence of Al on the strip surface is due to the fact that Al can be oxidised internally during hot rolling. As a result, an Al depleted surface region is formed owing to selective internal oxidation of Al before the continuous galvanising.MST/5293
A high-strength interstitial-free (HS IF) steel, solution strengthened with P and Mn, was hot-dip galvanized and galvannealed in a laboratory hot-dip simulator. The dew point of the N 2 -H 2 annealing atmosphere during recrystallization was varied, and the effect of the dew-point changes on the galvannealing kinetics was studied. Annealing in a high-dew-point N 2 -H 2 atmosphere improved the wettability by the zinc and the galvannealing reactivity of the Mn-P-added IF steels considerably. Scanning electron microscopy (SEM) analysis and glow discharge optical emission spectroscopy (GDOES) depth profiles of the surface of the steel sheet and the subsurface region revealed clear differences in oxidation mode after recrystallization annealing. Plane-view SEM and transmission electron microscopy (TEM) analyses were done on the inhibition layer of the as-galvanized samples. Differences in the Mn and P contents were found. By analyzing the Mn and P contents in the coatings during galvannealing, a mechanism was proposed to explain the higher galvannealing reactivity which is observed when the dew point during recrystallization annealing is increased.
In this work, the influence of surface modification of titania and alumina particles with carbon on their codeposition behavior with nickel during electroplating is studied. The surface modification was done using a two step procedure where a carbon rich precursor was first deposited on the particle surface by hydrolysis which was subsequently pyrolyzed in an inert atmosphere. The effect of synthesis conditions and the properties of the carbon coating were studied using XPS and Raman spectroscopy and were linked to the contact angle measurements and electrical conductivity of the carbon coating. Modified and unmodified particles were codeposited with nickel from a sulphamate base electrolyte at several current densities. It was found that large contact angles between particles and electrolyte and high electrical conductivity of the carbon coating, led to the highest incorporation rates, as long as particle agglomeration was limited. Optimized carbon synthesis conditions doubled the Al 2 O 3 and tripled the TiO 2 content in the nickel coating compared to the unmodified particles.
We demonstrate how a limited number of ab initio calculations in combination with a simple Debye model can predict a concentration-and temperature-dependent mixing enthalpy for a binary system. Fe-Mo is taken as a test case, and our predictions are compared with phase diagram information and a recently measured heat of solution for Mo in Fe. Crystallographic and magnetic information is calculated for the λ and μ intermetallic phases in the Fe-Mo phase diagram as well. The present methodology can be useful for making a quick survey of mixing enthalpies in a large set of binary systems, in particular in the dilute concentration ranges where tabulated data are often lacking and where CALPHAD-style modeling is less reliable.
Many multiphase cold-rolled high-strength steels require complex thermal processing, including a (partial) austenitization to reach the desired microstructure. However, of importance for their galvanizability, the selective oxidation of these steels in the austenitic region has not been studied extensively. The present work aims at characterizing the selective oxidation of a CMnSi steel during heating up to 1030°C by X-ray photoelectron spectroscopy (XPS) surface analysis. A phenomenological description of the evolution of the surface composition during heating and soaking in a N 2 -5 pct H 2 atmosphere with a dew point of -50°C is presented. Four distinct stages of selective oxidation were identified during heating; manganese oxidation, SiO 2 film growth, a transition stage, and a steady state with boron nitride (BN) passivation. During the transition stage, the previously formed SiO 2 film disappears, resulting in increased iron concentration at the surface. Simultaneously, a BN film forms on the uncovered metallic iron, inhibiting any further oxidation of the surface. It is demonstrated that the SiO 2 oxidation is reversible and temperature controlled.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.