1. Mechanical Properties of Stainless Steel
Required mechanical properties are normally given in purchase specifications for stainless steel. Minimum mechanical properties are also given by the various standards relevant to the material and product form. Meeting these standard mechanical properties indicates that the material has been properly manufactured to an appropriate quality system. Engineers can then confidently utilise the material in structures that meet safe working loads and pressures.
Mechanical properties specified for flat rolled products are normally tensile strength, yield stress (or proof stress), elongation and Brinell or Rockwell hardness. Property requirements for bar, tube, pipe and fittings typically state tensile strength and yield stress.
2. Yield Strength of Stainless Steel
Unlike mild steels, the yield strength of annealed austenitic stainless steel is a very low proportion of the tensile strength. Mild steel yield strength is typically 65-70% of the tensile strength. This figure tends to only be 40-45% in the austenitic stainless family.
Cold working rapidly and greatly increases the yield strength. Some forms of stainless steel, like spring tempered wire, can be cold worked to lift the yield strength to 80-95% of the tensile strength.
3. Ductility of Stainless Steel
The combination of high work hardening rates and high elongation / ductility makes stainless steel very easy to fabricate. With this property combination, stainless steel can be severely deformed in operations like deep drawing.
Ductility is normally measured as the % elongation before fracture during tensile testing. Annealed austenitic stainless steels have exceptionally high elongations. Typical figures are 60-70%.
4. Hardness of Stainless Steel
Hardness is the resistance to penetration of the material surface. Hardness testers measure the depth that a very hard indenter can be pushed into the surface of a material. Brinell, Rockwell and Vickers machines are used. Each of these has a different shaped indenter and method of applying the known force. Conversions between the different scales are therefore only approximate.
Martensitic and precipitation hardening grades can be hardened by heat treatment. Other grades can be hardened through cold working.
5. Tensile Strength of Stainless Steel
Tensile strength is generally the only mechanical property required to define bar and wire products. Identical material grades may be used at various tensile strengths for completely different applications. The supplied tensile strength of bar and wire products directly relates to the final use after fabrication.
Spring wire tends to have the highest tensile strength after fabrication. The high strength is imparted by cold working into coiled springs. Without this high strength the wire would not function properly as a spring.
Such high tensile strengths are not required for wire to be used in forming or weaving processes. Wire or bar used as raw material for fasteners, like bolts and screws, needs to be soft enough for a head and thread to be formed but still strong enough to perform adequately in service.
The different families of stainless steel tend to have different tensile and yield strengths. These typical strengths for annealed material are outlined in Table 1.
Table 1. Typical strength for annealed stainless steel from different families
| Tensile Strength | Yield Strength | |
| Austenitic | 600 | 250 |
| Duplex | 700 | 450 |
| Ferritic | 500 | 280 |
| Martensitic | 650 | 350 |
| Precipitation Hardening | 1100 | 1000 |
6. Physical Properties of Stainless Steel
● Corrosion resistance
● High and low temperature resistance
● Ease of fabrication
● High Strength
● Aesthetic appeal
● Hygiene and ease of cleaning
● Long life cycle
● Recyclable
● Low magnetic permeability
7. Corrosion Resistance of Stainless Steel
Good corrosion resistance is a feature of all stainless steels. Low alloy grades can resist corrosion in normal conditions. Higher alloys resist corrosion by most acids, alkaline solutions and chloride environments.
The corrosion resistance of stainless steel is due to their chromium content. In general, stainless steel contain a minimum of around 10.5% chromium. The chromium in the alloy forms a self-healing protective clear oxide layer that forms spontaneously in air. The self healing nature of the oxide layer means the corrosion resistance remains intact regardless of fabrication methods. Even if the material surface is cut or damaged, it will self heal and corrosion resistance will be maintained.
8. Extreme Temperature Resistance
Some stainless steel grades can resist scaling and retain high strength at very high temperatures. Other grades maintain high mechanical properties at cryogenic temperatures.
High Strength of Stainless Steel
Component designs and fabrication methods can be altered to take advantage of the work hardening of stainless steels that occurs when they are cold worked. The resultant high strengths can allow the use of thinner material, leading to lower weights and costs.
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Post time: Dec-19-2022