304 – 321 Products Features

304 Quality

304 quality stainless steel are available in stocks from 0.40mm to 80.00mm. This quality provides high oxidation resistance up to 600-650 ° C. It is preferred in chemistry, petro-chemistry, food, kitchen, automotive industry, all sanitary ware, medical industry and heat exchanger production. 304 quality stainless steel shiny, nylon, stones and designs are used in elevator cabin and all types of decorations.

321 Quality

316 quality stainless steel is available in our stocks up to 0,50mm-65,00mm. Resistant to oxidation at temperatures up to 850 ° C, high mechanical and tensile strength. It is used in steam boilers used in chemical industry, petrochemical and food industry, fruit juice and liquor production, textile machines and meat processing units. It is also used against sea water.

PHYSICAL PROPERTIES / 304-304H-304L-321

* It is not magnetic in principle, but when processed cold it is lightly magnetic .

** These figures are actual densities of the material, the theoretical mass for the purpose of costing is 8.07 kg / m² / mm

(where different tolerances are added to the account) .

MECHANICAL PROPERTIES Note: “Typical” features are not provided for design purposes.

MECHANICAL CHARACTERISTICS IN ROOM TEMPERATURE ACCORDING TO ASTM A240:

HIGH SPEED FEATURES /strong>

SHORT TERMINAL HIGH STRENGTH STRENGTH STRENGTH

10.000 HOUR POUR FRONT RATE RESISTANCE

RECOMMENDED MAXIMUM SERVICE TEMPERATURE (UNDER PASSIVE CONDITIONS)

FATIGUE STRENGTHTypical S-N curve for 304 stainless steel (lengthwise)

Graphics Copyright: Columbus Steel

TYPICAL CHARACTERISTICS AT ZERO SUB-TEMPERATURES FOR 304

CORROSION RESISTANCE

304 and 321 have excellent corrosion resistance in a wide variety of corrosive media, including foodstuffs, sterilising solutions, most organic chemicals and dyes and a wide variety of inorganic chemicals. Iso-Corrosion diagrams for 304 and 321 in sulphuric, nitric, acetic, hydrochloric and phosphoric acids are shown below. In service, acid corrosion may be either inhibited or accelerated by the presence of other chemicals or contaminants. The reaction of a material to all the possible service variables cannot be full assessed in the laboratory. Consequently, tests have been carried out in pure acid solutions and are intended only to provide a guide to general uniform corrosion in these media. In-situ testing will provide more reliable data for material selection.

Comparative data for standard grade stainless steels are presented in the form of iso-corrosion diagrams. These indicate the relationships between acid concentration, temperature and corrosion rate.

Graphics Copyright: Columbus Steel

ATMOSPHERIC CORROSION

The atmospheric corrosion resistance of austenitic stainless steels is unequalled by virtually all other uncoated engineering materials.Stainless steel develops maximum resistance to staining and pitting with the addition of molybdenum. For this reason, it is common practice to use the 316 molybdenum bearing grade in areas where the atmosphere is highly polluted with chlorides, sulphur compounds and solids, either singly or in combination.

304 is generally acceptable for most atmospheric applications..

PITTING CORROSION

Pitting resistance is important, mainly in applications involving contact with chloride solutions, particularly in the presence of oxidising media. These conditions may be condusive to localised penetration of the passive surface film on the steel and a single deep pit may well be more damaging than a muck greater number of relatively shallow pits. Where pitting corrosion is anticipated steels containing moly bdenum (such as 316) have a superior performance over the other grades.

INTERGRANULAR CORROSION

Sensitisation may occur when some austenitic stainless steels are welded or otherwise heated in the sensitising temperature range 480-760C, when a compositional change may occur at the grain boundaries. If a sensitised material is then subjected to a corrosive environment, some intergranular attack may be experienced.

When associated with welding, corrosion takes place preferentially in the heat affected zone on the parent material parallel to the weld. Susceptibility to this form of attack, often termed “weld decay”, may be assessed by the following standard tests:

a)    Boilling copper sulphate/sulphuric acid testsspecified in ASTM A262 – 70, Practice E..

b)    Bolling nitric acid test specified in ASTM A262 – 86, Practice C..

In the more severe nitric acid test, some weldments in plates of 304 quality may exhibit slight intergranular corrosion. For service in the as-welded condition in severe chemical environments, 304L would be recommended in preference to 304

STRESS CORROSION

Stress corrosion can occur in austenitic stainless steels when they are stressed in tension in chloride environments at temperatures in excess of about 60C. The stress may be applied, as in a pressure system or it may be residual arising from cold working operations or welding. Additionally, the chloride ion concentration need not be very high initially, if locations exist in which concentrations can occur. Assessment of these parameters and accurate prediction of the probability of stress corrosion accuring in service is therefore difficult. .

Where there is a likelihood of stress corrosion occuring, a beneficial increase in life can be easily obtained by a reduction in operating stress and temperature. Alternatively, specially designed alloys (such as duplex stainless steels) for applications where S.C.C. is likely to occur will have to be used.

FABRICATION

304 and 304L, being extremely tough and ductile, are easily cold formed. These grades of stainless steel also have excellent welding characteristics although care may have to be taken when welding 304 and 304H in heavy sections.

In order to avoid sensitisation in the weld metal when welding 321, it is necessary to use a stabilised filler metal such as type347 (Niobium stabilised). Titanium is not readily recovered during deposition and therefore type 321 fillers are generally not recommended.