Stainless steel application technology for building structure(2)

04/giu/2018 03:23:38 stainless steel Contatta l'autore

3. Application of Cr stainless steel in construction

Austenitic  410 Stainless Steel Bar not only has good corrosion resistance, but also has good toughness and weldability of hot rolled plate, and is widely used as welded structural steel in industrial machinery and equipment. In the construction industry, according to the comprehensive characteristics of steel, various shapes of workability and actual use, the representative stainless steel SUS304 will become the target of stainless steel for building research. In addition to the harsh environment containing high concentrations of chloride, the correct use of SUS304 can suppress the occurrence of significant rust for a long period of time, and it also has sufficient performance as a structural steel. However, due to the high content of Ni, a rare metal element in SUS304 steel, there is a large price gap between general structural steels and structural steels (such as coated steels) that are subjected to anti-corrosion measures, and they are susceptible to changes in raw material costs. Although we must pay attention to LCC, due to the increase in initial project costs, there are certain obstacles to popularizing and promoting SUS304 steel in the current severe domestic economic situation.

The problems of the toughness and weldability of the Cr stainless steel in the welding zone (prevention of cracking at low temperatures) have also been well solved. Since the Cr content is small, the occurrence of pitting corrosion is unavoidable in an environment exposed to outdoor sea salt particles, but in a normal outdoor environment, the corrosion rate is small, and the long-term durability of the building can be ensured. There is no need for traditional anti-corrosion treatment such as coating or plating, and additional corrosion protection for the processing site and welding site.

YUS 410W-MS steel has passed the ministerial certification as stipulated in Article 37 of the Building Code. It can be used in general buildings and becomes a Class 3 (100-year durability) high-strength structural steel in accordance with relevant laws and regulations governing residential quality. . It can be expected that this type of steel can be used not only for the main structure of long-lived dwellings but also as a new type of structural stainless steel for use in the construction industry in order to reduce the amount of antiseptic handling during construction and maintenance.

4, using Cr stainless steel reinforcement to improve the durability of reinforced concrete structures

Improvements have also been made to the durability of reinforced concrete structures (RC structures). In the high-alkaline concrete, ordinary steel bars are in a passivated state without corrosion, but when chlorides penetrate from the outside, the steel bars are corroded due to the neutralization of the concrete, which is an important factor in deterioration of RC structures. the reason. After the corrosion of the steel bar, not only the strength of the steel bar itself is reduced, but also the cracking and spalling of the concrete due to the volume expansion caused by the rust causes a serious problem that the overall durability of the RC structure is reduced. In order to prevent the corrosion of the steel bar, the concrete can be modified and measures taken in the design, but there are also practices using highly corrosion-resistant steel bars, especially structures in severe chloride environments (such as marine structures, coastal bridges, and spraying Snow-melting salt highway viaducts, etc.) can be coated with epoxy resin, and stainless steel reinforcement is also used in countries other than Japan.

As far as the steel bar itself is concerned, the stainless steel bar is more expensive than the ordinary bar, but it is not necessary to use stainless steel reinforcement for the entire structure. Only stainless steel bars can be used in locations where corrosion damage is likely to occur (for example, near the surface of the concrete that is easily penetrated by chlorides). The overall durability of the structure is fundamentally improved. The limited use of stainless steel reinforcement can minimize the increase in construction costs, and the advantages of LCC become very large. At the same time, due to the improvement of the overall reliability of the RC structure, the asset value of the structure is increased, which is very favorable economically.

At present, three 347 Stainless Steel Bar, SUS410 (12% Cr), SUS304 (18% Cr-8%Ni), and SUS316 (17% Cr-8%Ni-2.5%Mo), have been standardized (JIS). According to the results of durability evaluation tests for reinforcing steel bars in concrete, Cr-free stainless steel SUS410 bars without Ni have the possibility of being widely used. Therefore, SUS410 steel bars (Nippon Steel trade name: NSSD 410) are widely used. High-strength steel bars are being vigorously promoted. So far, the NSSD 410 rebar has been used in seaside embankments, wharf bollards, and industrial water storage tanks. It is expected that in the future, it will be further used in harbor equipment, coastal bridges, road structure devices and tunnels that require high durability in salt-damaged environments.

In addition, it is also expected that SUS410 steel bars will be used in the outer structures and infrastructures of special buildings such as shrines and temples requiring super long-term durability, and coastal structures. With the Ministry of Land, Infrastructure, Transport and Tourism as the mainstay, in the model work for ultra-long-term residences (so-called 200-year residences) that began in 2008, plans have been made to build high-endurable homes with NSSD 410 rebar. After the construction of high-strength reinforced concrete ultra-long-term residences, it is estimated that within the next 200 years, LCC will be reduced by 35% and CO2 emissions will be reduced by 45%. In addition, in order to use stainless steel rebar for general buildings, SUS410 rebar produced by Nippon Steel passed the certification of the Ministry of Land, Infrastructure, Transport and Transportation as stipulated in Article 37(2) of the Japanese Construction Act.

It can be considered that stainless steel reinforcement will be applied to general reinforced concrete structures in the future. Stainless steel reinforcement is in the stage of development from trial to popularity.

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