I assume that you are familiar with stainless steel, as it is widely used in many electrical appliances in our daily lives.
For instance, the electric kettle that is commonly used.
Observant individuals may have noticed that there are groups of numbers on the inner wall of the electric kettle, some of which are 304 and others are 316.
So what do these numbers indicate and what distinguishes them?
Today, I will shed light on this mystery.
304 and 316 are codes for different types of stainless steel. Although they are both considered stainless steel, they have distinct differences.
Let’s examine the chemical composition, physical properties, mechanical properties, national brands, characteristics, and applications of these two types of stainless steel.
Comparison of chemical compositions of 304 and 316 stainless steel
Comparison of physical properties of 304 and 316 stainless steel
|Physical performance parameters||304||316|
|Density / (kg / dm3) 20 ℃||7.93||8.00|
|Baking point / ℃||1398-1454||1370-1397|
|Specific heat capacity / [kJ / (kg · K)] 0 ℃ ~ 100 ℃||0.50||0.50|
|Thermal conductivity / [w / (m·k)]||100℃||16.3||16.3|
|Linear expansion coefficient / (10–6 / k)||0℃~100℃||17.2||16.0|
|Resistivity / (Ω · mm2 / M) 20 ℃||0.73||0.74|
|Longitudinal elastic model / (KN / mm2) 20 ℃||193||193|
Comparison of 304 and 316 stainless steel grades in different countries
|Comparison of stainless steel grades of various countries:||304||316|
|ChinaGB / T20878-2007||Uniform numerical code||S30408||S31608|
IS0 / TS 15510:2003
The chemical composition, physical performance, and comparison of stainless steel grades across different countries are based on the national standard for stainless steel and heat-resistant steel grades and chemical compositions (GB/T 20878-2007).
Comparison of mechanical properties of 304 and 316 after solid solution treatment
|Mechanical properties after solution treatment||304||316|
|Specified plastic extension strength Rp0.2/MPa||≥205||≥205|
|Tensile strength Rm / MPa||≥515||≥515|
|Elongation after fracture A /%||≥40||≥40|
Comparison of mechanical properties of 304 and 316H 1/4 states
|Mechanical properties in H 1/2 state||304||316|
|Specified plastic extension strength Rp0.2/MPa||≥515||≥515|
|Tensile strength Rm / MPa||≥860||≥860|
|Elongation after fracture A /%||Thickness < 0.4mm||≥10||≥10|
|Thickness: 0.4mm ~ < 0.8mm||≥10||≥10|
|Thickness ≥ 0.8mm||≥12||≥10|
Comparison of mechanical properties of 304 and 316H 1/2 states
|Mechanical properties in H 1/2 State||304||316|
|Specified plastic extension strength Rp0.2/MPa||≥760||≥760|
|Tensile strength Rm / MPa||≥1035||≥1035|
|Elongation after fracture A /%||Thickness < 0.4mm||≥6||≥6|
|Thickness: 0.4mm ~ < 0.8mm||≥7||≥7|
|Thickness ≥ 0.8mm||≥7||≥7|
Characteristics and uses
304 stainless steel is a widely used and heat-resistant type of stainless steel that can be found in food equipment, general chemical equipment, and the atomic energy industry, among others.
On the other hand, 316 stainless steel boasts better resistance to corrosion compared to 06Cr19Ni0 in seawater and other environments. It is mainly used for applications that require resistance to pitting.
Heat treatment schedule
Both 304 and 316 stainless steel undergo the same heat treatment process.
The heat treatment temperature is ≥ 1040 ℃ and it is cooled using water or another rapid cooling method.
Note: The information on the mechanical property tables for solid solution treatment, H1/4, and H1/2, as well as the characteristics, applications, and heat treatment system, are all sourced from the national standard for cold rolled stainless steel plate and strip (GB/T 3280-2015).
Difference between 304 and 316
The primary difference between 304 and 316 stainless steel lies in their market applications.
304 stainless steel is generally more affordable than 316 stainless steel and is widely used in various applications such as kitchen utensils and tableware, building decoration, food industry, agriculture, ship parts, sanitary ware, and automobile parts, among others.
Although a small portion of 316 stainless steel is used in daily life, it is primarily utilized in equipment that is exposed to seawater and in production equipment that requires strong corrosion resistance.
This is due to the addition of 2-3% molybdenum, which strengthens the structure of 316 stainless steel, making it more resistant to wear and oxidation, and significantly improves its resistance to corrosion.
The difference between 304 and 316 stainless steel materials
304 stainless steel is primarily used in containers, tableware, furniture, railings, and medical equipment that require corrosion resistance. On the other hand, 316 stainless steel is mainly used in the food industry, watch accessories, the pharmaceutical industry, and surgical equipment.
Chloride Corrosion Resistance:
304 stainless steel is non-magnetic and its metallographic structure remains unchanged even after heat treatment.
However, the addition of the molybdenum element gives 316 stainless steel a unique corrosion-resistant structure, resulting in improved resistance to chloride corrosion. This type of stainless steel is also commonly referred to as “marine steel”.
316 stainless steel is an austenitic type of stainless steel that is characterized by its improved corrosion resistance and high-temperature strength, thanks to the addition of Mo. It has a high-temperature resistance of up to 1200-1300 degrees and is suitable for use in harsh conditions.
On the other hand, 304 stainless steel is a common type of stainless steel with a density of 7.93 g/cm3. It is also referred to as 18/8 stainless steel in the industry and is capable of withstanding high temperatures of up to 800 ℃. It boasts good processing performance and high toughness and is widely used in various industries, including furniture decoration, food and medical industries.
Stainless steel is a term used to describe both stainless and acid-resistant steel. Steel that is resistant to air, steam, water, and other weak corrosive media or rust is called stainless steel, while steel that is resistant to chemical corrosive media (such as acid, alkali, salt, etc.) is referred to as acid-resistant steel.
Stainless steel has excellent inherent corrosion resistance and can maintain its physical and mechanical properties even at high temperatures. It is also widely used in the field of 3D printing.