Stainless steel for use under circumstance where organic acid and saline are present

Abstract

The present invention provides a stainless steel which is suitable for use in the food manufacturing plant, particularly a soy sauce manufacturing plant. A stainless steel to be used in the environment which contains organic acid and common salt comprising, C; 0.05 wt % or less, Si; 1.00 wt % or less, Mn; 1.00 wt % or less, P; 0.040 wt % or less, S; 0.03 wt % or less, Ni; 40.0 wt % or less, 16.0 wt %≦Cr≦26.0 wt %, 2.0 wt %≦Mo≦8.0 wt %, 0.05 wt %≦Al≦0.100 wt %, 0.10 wt %≦N≦0.30 wt %, Mg: 0.005 wt % or less, Ca; 0.0010 wt % or less and balance consisting of Fe and inevitable impurities, and satisfying equation (1), Cr+3.3Mo+20N≧38   (1) wherein, Cr, Mo and N show the content of each ingredients by weight %.

Description

FIELD OF THE INVENTION The present invention relates to a stainless steel which is superior in resistance to crevice corrosion and in resistance to stress corrosion cracking, and suited to the food manufacturing plant, preferably to the food manufacturing plant in the process of which organic acid such as amino acid, citric acid or acetic acid are generated and also the contents of common salt is high, in particular to the soy sauce manufacturing plant. DESCRIPTION OF THE PRIOR ART In general, for the food manufacturing plant, stainless steel, steel coated by inorganic or organic layer or FRP are used according to the contained ingredients in the foods to be handled, temperature or the operating conditions, especially, the use of stainless steel is increasing from the view point of the easy maintenance, low maintenance cost and excellent cleaning ability. In general, in the food manufacturing plant, such as soft drink, beer or milk, standard stainless steel, for example, SUS304 or...

AI Technical Summary

Benefits of technology

The inventors of the present invention have conducted intensive study to investigate the stainless which is suited for the food manufacturing plant, in particular for a seasoning manufacturing plant for such as soy sauce having a fermentation process which contains large amount of common salt. And they found that in the case of fermentation process which generate organic acid such as amino acid, citric acid or lactic acid, these organic acid accelerated the corrosion of the stainless steel, especially the crevice corrosion or the stress corrosion cracking.

(in the formula, Cr, Mo and N show the content of (wt %) each ingredient.) Further, the inventors of the present invention have found that when the amount of CaO and MgO contained in the inclusion of the stainless steel is reduced and the main components of the inclusion in stainless steel is altered to SiO2 or Al2O3, the corrosion resistance in the condition containing organic acid and large amount of common salt is improved. Namely, according to the experimental results, the inventors of the present invention have found that the generation of the crevice corrosion or the stress corrosion cracking, which is the main corrosion of the stainless steel, can be suppressed by satisfying following equation (2),

Problems solved by technology

And they found that in the case of fermentation process which generate organic acid such as amino acid, citric acid or lactic acid, these organic acid accelerated the corrosion of the stainless steel, especially the crevice corrosion or the stress corrosion cracking.

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