Enamel Firing Research Articles

Microstructure, Mechanical Properties, and Fish-Scaling Resistance of a Ti-Nb Microalloyed Hot-Rolled Enamel Steel

Currently, the fish-scaling resistance of most hot-rolled enamel steels is improved by adding Ti to form fine TiC carbides as hydrogen traps. Given that the hydrogen capture capacity of NbC is higher than that of TiC, the manufacture of hot-rolled enamel steels via Ti-Nb microalloying has a promising future. In the present study, a Ti-Nb microalloyed hot-rolled enamel steel was developed, and its microstructure, mechanical properties, and fish-scaling resistance were studied by optical microscopy, transmission electron microscopy, tensile test, and hydrogen permeation test. The results show that the microstructure of hot-rolled experimental steel is composed of ferrite and fine carbides, with a large number of fine precipitates uniformly distributed in the ferrite grains. After the first and second enamel firings, the average sizes of ferrite grain and precipitates gradually increase, the yield strength decreases from 711 ± 9 MPa to 471 ± 17 MPa and 409 ± 8 MPa, the tensile strength decreases from 761 ± 7 MPa to 524 ± 15 MPa and 490 ± 12 MPa, and the elongation increases from 21.0 ± 2.8% to 27.8 ± 1.8% and 33.9 ± 1.1%. The hydrogen permeation value (TH value) decreases from 35.9 min/mm2 to 6.8 min/mm2 and 3.9 min/mm2 after the first and second enamel firings. That is, the fish-scaling resistance of hot-rolled experimental steel is significantly reduced after enamel firing, which is caused by the coarsening of precipitates, resulting in a significant reduction in the density of irreversible hydrogen traps (from 1.21 × 1025 cm−3 to 6.50 × 1023 cm−3 and 4.27 × 1023 cm−3). A large amount of semi-coherent precipitates is the key to obtaining the good fish-scaling resistance of hot-rolled enamel steel.

Variations of microstructure and resistance to fish-scaling of a hot rolled enamel steel before and after enamel firing

Different temperature enamel firings were applied on a Ti-containing hot rolled enamel steel. The microstructure, mechanical properties and resistance to fish-scaling were characterized by optical microscopy, transmission electron microscopy, tensile test and hydrogen permeation test. The results show that both ferrite grain size and TiC particles size were increased after enamel firing. The yield strength, tensile strength and resistance to fish-scaling of experimental steel decrease with increasing firing temperature, which can be attributed to the increase in ferrite grain size and TiC particles size. TiC precipitates significantly affect the resistance to fish-scaling, and small sized TiC particles are beneficial for the high resistance to fish-scaling.

The Influence of Enamel Firing Process on Microstructure and Mechanical Properties of Steel Substrate

The as-rolled and enamel fired microstructure and mechanical properties of two low carbon steels with different compositions were analysed in the paper. The results show that the grains do not coarsen in lab firing process, and could be refined after industrial enamel firing process. The strength can keep stable in the firing process and the impact energy could be enhanced greatly under the industrial enamel firing process. The surface decarburized layer was occurred as a result of chemical reaction among the carbon in steel and water, oxides in the enamel frit.

Low-temperature covering enamels for steel and aluminum

The possibility of obtaining for steel white covering enamel with melting temperature 1000–1100°C and firing temperature 750–780°C and for aluminum white enamel with melting temperature 900–950°C and firing temperature 530–560°C is investigated. The physical and technological characteristics of the frits melted are measured and the temperature-time firing regimes with the enamel deposited in the form of slip are determined. It is established that introducing modifier oxides and glass-forming oxides makes it possible to lower the melting temperature by 15–20% and the enamel firing temperature by 20–30°C without introducing new components into the enamel composition.

Effect of the Enamel Firing Thermal Cycle on the Microstructure and the Hydrogen Permeability of Enamel-Grade Steels

Effect of the Enamel Firing Thermal Cycle on the Microstructure and the Hydrogen Permeability of Enamel-Grade Steels

Sol—gel coatings for the substitution of fluoride or lead containing white decorations on glass

A SiO 2-based sol was developed, which allows the deposition of thick (10 μm), crack free coatings on soda-lime glass. By homogeneous dispersion of TiO 2 particles (10 nm to 250 nm in radius) lead and fluorine free white paints are obtained, which can be applied by spray coating to as produced glass without any pretreatment. The coatings can be densified using rapid firing in a tunnel furnace at a temperature of about 560°C for about 30 min, which is typical for firing of enamels. After this densification step, the coatings show good adhesion on soda-lime glass (class 0 of cross hatch cut and tape test) and excellent chemical durability according to Kesternich-Tests.

Effect of protective vitreous enamel coatings on the mechanical properties of surface layers of 08sp steel

1. In the course of the application of the enamel coating to 08sp steel, a diffusion redistribution of elements takes place accompanied by the formation in the metal surface layers of a diffusion zone which lost some manganese and gained silicon, boron, and titanium. 2. The diffusion processes at the metal-enamel interface are accompanied by a change in the mechanical properties of surface layers of steel which can considerably affect its strength. 3. The mechanical properties of surface layers of steel depend on the number of enamel firing cycles.

A Radioisotope Study of the Nickel Dip

Radioisotope tracer studies of the deposition of nickel during nickel dipping of steel and of the effect of this nickel deposit on the reduction of cobalt ions to metallic cobalt during enamel firing showed the following: (1) The deposition of nickel on the metal surface during the dipping and the deposition of cobalt at the enamel‐metal interface during firing were both markedly affected by the type of cleaning given the steel and by the mechanical deformation of the metal surface. (2) The nickel from the nickel dip remained as metal at the interface during firing of the enamel. (3) The presence of the nickel deposit had little or no effect on the deposition of cobalt at the interface during firing.

CAUSE OF PINHOLES AND SOME RELATED DEFECTS IN ENAMEL COATINGS ON CAST IRON*

The confusion in identifying hydrogen as the predominating cause of certain defects in enamel on cast iron has been due largely to the close association of carbon and hydrogen in cast iron and steel. The principal relation of carbide and graphite to enameling defects is the release of hydrogen from the carbon during enamel firing. The much-discussed “chill layer” therefore is important chiefly because this layer often contains hydrogen that is bound to the carbon in the cementite. Experiments show that when hydrogen is absent, regardless of the depth or nature of the surface chill, no pinholing or blistering results during firing at 725°C. Sources of the hydrogen that causes the defacement are found chiefly in melting and in casting. The low oxygen pressure of molten cast iron favors hydrogen absorption. Moisture in the atmosphere, in the charge, or chemically combined in the rust on scrap provides the greatest quantities of the gas, and moisture and organic materials in the mold are also prolific sources of hydrogen for absorption by the iron. At ordinary temperatures, rusting is often harmful. Flushing the melt with a dry, hydrogen-free gas, such as nitrogen, removes the dissolved hydrogen, and defects during subsequent enameling will not occur unless hydrogen is obtained later from other sources. Chipping phenomena probably are caused chiefly by hydrogen effusion, just as are analogous defects in sheet-steel enameling.

MECHANICS OF ENAMEL ADHERENCE, VIII*

ABSTRACTThe desirability of firing enamels under accurately controlled conditions has, in general, been recognized. The author has made a study of enamel firing under varying pressures and atmospheres (oxidizing, reducing, and neutral) as well as with accurately controlled temperatures. A special apparatus, which is described, was developed for this purpose and soiiie results of these studies under reduced pressure are given and analyzed. This analysis reveals some basic causes of gas defects in enamels.