Defects and their removal stainless steel
Products made of stainless steels are designed to work in corrosive environments at ordinary or high temperatures. The main requirement for stainless steels is corrosion resistance, which depends on the composition of the alloy, its structural state, aggressiveness of the corrosive environment and the impact loads. Corrosion resistance is due to the formation, on the surface of the product, of a strong passivating film that prevents penetration of aggressive substance into the deeper layers of stainless steel.
It refers to the strongest passivating elements in oxidizing media. On the surface of the alloy, it forms the thinnest invisible film of chromium oxides several atomic layers thick. The film density and anticorrosive properties of stainless steel increase with an increase in the proportion of chromium. At 12−13% Cr, the steel becomes stainless, that is, resistant to the effects of atmospheric and soil moisture. Increasing the chromium content to 28−30% makes the alloy resistant in highly aggressive environments. Chromium is a ferrite-forming element, so steel with a high chromium content (16−30%) is referred to as a ferrite class. The strength of ferrite makes them resistant to hardening, so they are characterized by low strength properties, which limits the scope of their application. Purely ferritic steels based on 25−28% Cr (X25, X28, etc.) with small additions of titanium or nitrogen (for grinding grain) are used as heat-resistant, not carrying loads.
Strength and ductility
These qualities of metal depend on many factors: the crystal structure, the binding energy of atoms in the crystal lattice, the purity of the metal, the chemical composition, the purity of the boundaries, and other factors. According to modern ideas, the resistance of plastic deformation is determined mainly by the number of imperfections in the structure of the crystal lattice, primarily by dislocations. High strength can be obtained if we reduce or, conversely, significantly increase the number of dislocations.
The issue of creating defect-free materials in practical conditions has not yet been resolved, but hardening by increasing the number of dislocations and other imperfections is used very widely. The hardening of stainless steels, which are solid solutions, occurs as a result of the interaction of impurity atoms — not forming the lattice of the basic solid solution — with dislocations. However, steel hardens the blocking of shifts by highly disperse particles of the other phase, which result from alloying and appropriate heat treatment. The greatest hardening corresponds to a fine structure with the second phase precipitates measuring 20−50 nm (200−500 A), evenly distributed throughout the grain volume. The growth of emissions up to 100 nm (1000 A) or more leads to softening of the steel.
When corrosion resistance and high strength are simultaneously required, chromium steels of the martensitic class with a reduced chromium content (12−18%) are used. These steels can be hardened. Carbon content in them is usually 0.1−0.4% (steel 1X13−4X13). If it is necessary to obtain after hardening a high hardness, the carbon content can be increased to 1% (steel 9X18). Steel of this type is used for the manufacture of knives, scissors, surgical tools, molds for plastics, and steels with a high content of carbon for the production of ball bearings operating in corrosive environments. But they are all unsuitable for work at high temperatures.
As the temperature increases, the bond of atoms in the crystal lattice weakens, the diffusion mobility of the atoms increases, and the strengthening phase (mainly chromium carbides) degenerates-enlarges, spheroidizes, and redistributes the alloying elements between the solid solution and the strengthening phase. This leads to weakening of stainless steel. Long-term preservation of strength at high temperature is facilitated by inhibition of diffusion processes, achieved by optimal alloying.
To improve the quality of the ingot surface and reduce titanium porosity, stainless steel has to be poured at high speed, to protect the metal surface in the mold with a reducing atmosphere or slags, and the jet of the metal when pouring — with inert gases.
In the warehouse of Electrovek-Steel LLC there is a wide range of stainless steel products of standard and non-standard sizes. We value the time of our customers, so we are always ready to help with the best choice. At your service are experienced management consultants. Quality of production is guaranteed by strict observance of production standards. The lead times for orders are minimal. Wholesale buyers receive preferential discounts.