Stainless Steel type SUS 304 - Their Advantages and Disadvantages

AISI 304 (SUS 304) Grade Stainless Steel Stainless steel types 1.4301 and 1.4307 are also known as grades 304 and 304L respectively. Type 304 is the most versatile and widely used stainless steel. It is still sometimes referred to by its old name 18/8 which is derived from the nominal composition of type 304 being 18% chromium and 8% nickel. Corrosion Resistance 304 has excellent corrosion resistance in a wide variety of environments and when in contact with different corrosive media. Pitting and crevice corrosion can occur in environments containing chlorides. Stress corrosion cracking can occur at temperatures over 60°C. Heat Resistance 304 has good resistance to oxidation in intermittent service up to 870°C and in continuous service to 925°C. However, continuous use at 425-860°C is not recommended if corrosion resistance in water is required. In this instance 304L is recommended due to its resistance to carbide precipitation. Where high strength is required at temperatures above 500°C and up to 800°C, grade 304H is recommended. This material will retain aqueous corrosion resistance. Fabrication Fabrication of all stainless steels should be done only with tools dedicated to stainless steel materials. Tooling and work surfaces must be thoroughly cleaned before use. These precautions are necessary to avoid cross contamination of stainless steel by easily corroded metals that may discolour the surface of the fabricated product. Type 304 stainless steel is an austenitic grade that can be severely deep drawn. This property has resulted in 304 being the dominant grade used in applications like sinks and saucepans. Type 304L is the low carbon version of 304. It is used in heavy gauge components for improved weldability. Some products such as plate and pipe may be available as “dual certified” material that meets the criteria for both 304 and 304L. 304H, a high carbon content variant, is also available for use at high temperatures. Applications 304 stainless steel is typically used in: ·         Sinks and splashbacks ·         Saucepans ·         Cutlery and flatware ·         Architectural panelling ·         Sanitaryware and troughs ·         Tubing ·         Brewery, dairy, food and pharmaceutical production equipment ·         Springs, nuts, bolts and screws ·         Medical implants Typical chemical composition % 304 304L 304H C 0.08 max 0.03 max 0.10 max Mn 2.0 2.0 2.0 Si 0.75 0.75 0.75 P 0.045 0.045 0.045 S 0.03 0.03 0.03 Cr 18-20 18-20 18-20 Ni 10.5 12 10.5 N 0.1 0.1 - Typical Mechanical Properties Grade 304 304L 304H Tensile strength 520 500 520 Compression Strength (MPa) 210 210 210 Proof Stress 0.2% (MPa) 210 200 210 Elongation A5 (%) 45 45 45 Hardness Rockwell B 92 92 92 Typical Physical Properties Property Value Density 8.00 g/cm3 Melting Point 1400-1450°C Modulus of Elasticity 193 GPa Electrical Resistivity 0.072x10-6 Ω.m Thermal Conductivity 16.2 W/m.K at 100°C Thermal Expansion 17.2x10-6 /K at 100°C Alloy Designations Stainless steel 304 also corresponds to the following standard designations and specifications: Euronorm UNS BS En Grade 1.4301 S30400 304S15 304S16 304S31 58E 304 1.4306 S30403 304S11 304L 1.4307 - 304S11 304L 1.4311 - 304S11 304L 1.4948 S30409 304S51 304H Cold Working 304 stainless steel readily work hardens. Fabrication methods involving cold working may require an intermediate annealing stage to alleviate work hardening and avoid tearing or cracking. At the completion of fabrication a full annealing operation should be employed to reduce internal stresses Hot Working Fabrication methods, like forging, that involve hot working should occur after uniform heating to 1149-1260°C. The fabricated components should then be rapidly cooled to ensure maximum corrosion resistance. Heat Treatment 304 stainless steel cannot be hardened by heat treatment. Solution treatment or annealing can be done by rapid cooling after heating to 1010-1120°C. Machinability 316 stainless steel has good machinability. Machining can be enhanced using the following rules: ·         Cutting edges must be kept sharp. Dull edges cause excess work hardening. ·         Cuts should be light but deep enough to prevent work hardening by riding on the surface of the material. ·         Chip breakers should be employed to assist in ensuring swarf remains clear of the work ·         Low thermal conductivity of austenitic alloys results in heat concentrating at the cutting edges. This means coolants and lubricants are necessary and must be used in large quantities. Welding Fusion welding performance for type 304 stainless steel is excellent both with and without fillers. Recommended filler rods and electrodes for stainless steel 304 is grade 308 stainless steel. For 304L the recommended filler is 308L. Heavy welded sections may require post-weld annealing. This step is not required for 304L. Grade 321 may be used if post-weld heat treatment is not possible. Supplied Forms 304 stainless steel is typically supplied by Tecni-Cable Ltd in the following forms: ·         Fittings ·         Cable tools & accessories Disclaimer This information is based on our present knowledge and is given in good faith. However, no liability will be accepted by the Company is respect of any action taken by any third party in reliance thereon As the products detailed may be used for a wide variety of purposes and as the Company has no control over their use; the Company specifically excludes all conditions or warranties expressed or implied by statute or otherwise as to dimensions, properties and/or fitness for  any particular purpose. Any advice given by the Company to any third party is given for that party’s assistance only and without liability on the part of the Company. Any contract between the Company and a customer will be subject to the Company’s Conditions of Sale. The extent of the Company’s liabilities to any customer is clearly set out in those Conditions; a copy of which is available on request. Credit to : http://www.tecni-cable.co.uk/