Typical applications of corrosion-resistant steels

The main difference between heat-resistant steels and stainless steels is their intended use. The primary operational characteristic of stainless steels is corrosion resistance. The use of this type of steel can occur both in ambient conditions and in environments with significantly subzero temperatures, up to about 500°C. Such conditions dictate requirements for high corrosion resistance of materials. Mechanical properties are of lesser importance in this regard. In the past, steels were divided into stainless steels and acid-resistant steels. Currently, the term stainless is understood to mean all steels that exhibit corrosion resistance and, at the same time, are not high-temperature (heat-resistant) steels.
In the case of heat-resistant steels, the basic characteristic of the material is considerable corrosion resistance at temperatures exceeding 500°C. Heat-resistant steels are required to have high mechanical properties at temperatures above 500°C. This is related to the material’s resistance to slow deformation under stresses lower than the material’s yield strength, the so-called creep resistance.
The group of corrosion-resistant steels includes acid-resistant stainless steels and heat-resistant steels. The designation of stainless steel grades ranges from 1.40.. to 1.45… Heat-resistant and high-temperature steels are designated with numbers from 1.47… to 1.48…
Summing up, stainless steels are used up to about 500°C. Above 500°C heat-resistant steels are used. In such conditions materials are exposed to oxidation and corrosion.
It should be remembered that heat-resistant steels 1.4749 (X18CrN28) and 1.4724 (X10CrAlSi13) are characterized by varied weldability. In general, the weldability of austenitic grades is higher than that of ferritic heat-resistant steels. The welding process of ferritic heat-resistant steels requires preheating (before welding) to temperatures of about 100 to 300 °C. Furthermore, after welding a heat treatment based on annealing at about 750-800 °C is necessary. The above requirements apply to grades such as: 1.4742 (X10CrAlSi18), 1.4762 and 1.4724 (X10CrAlSi13). The grade 1.4749 (AlSi446) has significantly better weldability. It does not require heat treatment immediately after welding. In the case of 1.4749 (AISI 446) only preheating to temperatures from 200 to 400 °C is necessary.
Stainless steels can also be joined with carbon steels by observing certain rules.
It is possible to join stainless steel with ordinary steel. For this purpose, the use of filler 309L (according to EN 1600 23 12 L R, according to AWS E309L) is recommended. This type of filler contains about 23% Cr, 13% Ni. It is intended for joining Cr-Ni stainless steels with low-alloy steels. In the welding of stainless steels without molybdenum (1.4301, OH18N9) with low-alloy (carbon) steels, wires of the type: 309L-Si, 309L, 309L-HF are used. These are high-alloy wires that ensure crack-resistant welds. The 309L wire model is most often chosen to join stainless steel type 304 and carbon steel.
Stainless steels can also be used in building structures, e.g. for reinforcing walls with concrete. Because concrete is a porous material it can be used to encase structures made of corrosion-resistant steels. It is important here to choose the appropriate steel grade for such an application. There are commonly specialized grades of corrosion-resistant steels recommended for use in reinforcing concrete. The most popular include: EN 1.4301, 1.4429, 1.4462, 1.4436, 1.4501. Steels with an austenitic structure: 1.4429, 1.4301, 1.4436. Steels of grades 1.4462, 1.4501 are characterized by a ferritic-austenitic (duplex) structure. Reinforcing bars are manufactured from the following stainless steel grades: EN 1.4436, 1.4429, 1.4301, 1.4462.