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A Comprehensive Guide to 316 Stainless Steel
In various industries, stainless steel has become indispensable due to its exceptional mechanical, corrosion resistance, and machinability properties. Among these alloys, 316 stainless steel has gained significant attention and widespread use.
The article provides a comprehensive overview of 316 stainless steel, including its properties, applications, and machining intricacies. It also showcases this alloy’s diverse range of applications and evaluates its advantages and disadvantages in manufacturing.
Definition of 316 Stainless Steel
316 stainless steel is widely recognized for its exceptional ability to resist corrosion in different environments. This type of austenitic stainless steel is composed of 16-18% chromium, 10-14% nickel, 2-3% molybdenum, 0.08% carbon, and small amounts of other elements. The addition of molybdenum sets it apart from the most commonly used 304 stainless steel and gives SS 316 much better corrosion resistance than SS 304. Its crystalline structure with a face-centered cubic (FCC) arrangement of atoms contributes to its high strength and toughness.
Producing Process of 316 Stainless Steel
Melting and Casting
The process of creating 316 stainless steel items involves melting together raw materials such as iron ore, chromium, nickel, and molybdenum in a large electric furnace for 8 to 12 hours. After the melting process is complete, the molten steel is cast into various semi-finished shapes, including slabs, blooms (rectangular shapes), billets (round or square), tube rounds and rods.
Forming
During the second stage, semi-finished steel shapes undergo a series of forming operations. For instance, aisi 316 is heated and passed through huge rolls in a process called hot rolling. Blooms and billets, as mentioned earlier, are transformed into bars and wires, while slabs are formed into plates, strips, or sheets. Bars are the most versatile form of stainless steel and are made in all grades and sizes. They come in round, square, octagonal, and hexagonal shapes, each suited for different applications.
Heat Treatment
The different forms of stainless steel undergo a meticulous process called annealing. Annealing involves heating and cooling stainless steel in a controlled environment to improve its properties. This heat treatment aims to eliminate any internal stress and make the material softer, making it more suitable for various applications. The personnel in charge of the annealing process must be vigilant about the conditions, as even the slightest changes in temperature, pressure, duration, or cooling rate could result in a defective product.
Descaling
When 316 stainless steel undergoes annealing, a scale layer develops on its surface. A group of processes known as descaling removes this scale. One of the most widely used methods of descaling is pickling.
Cutting
In this step, the semi-finished, heat-treated, and descaled 316 stainless steel forms are cut into specific shapes. Mechanical cutting can be achieved through the use of guillotine knives, blanking, nibbling, or high-speed blades.
Surface Finishing
316 stainless steel products undergo finishing to improve their aesthetic appeal and make them smoother and more accessible to clean for sanitary applications.
Chemical Composition of 316 Stainless Steel
The chemical composition of 316 stainless steel comprises various elements: 16-18% chromium, 10-14% nickel, and 2-3% molybdenum. Table 1 below details the composition.
| Element | Percentage |
| Sulfur | <= 0.030% |
| Phosphorus | <=0.045% |
| Carbon | <= 0.08% |
| Nitrogen | <= 0.10% |
| Silicon | <= 1.00% |
| Manganese | <= 2.00% |
| Molybdenum | 2-3% |
| Nickel | 10-14% |
| Chromium | 16-18% |
| Iron | Balance (69%) |
The Properties of 316 Stainless Steel
Physical Properties of 316 Stainless Steel
| Property | Value |
| Density（g/cm3） | 8 |
| Electrical ResistivityΩ .m （at 20ºC） | 0.74 x 10-6 |
| Embodied Energy（MJ/kg） | 53 |
| Calomel Potential | －50 mV |
| Magnetism | Nonmagnetic |
| Note: SS 316 is mostly non-magnetic; however, it can become slightly magnetic after certain manufacturing processes. | |
Mechanical Properties of 316 Stainless Steel
| Property | Value |
| Rockwell Hardness | 95 |
| Brinell Hardness | 219 |
| Tensile Strength, Ultimate | 550 MPa （79800 psi ） |
| Tensile Strength, Yield | 240 MPa（34800 psi ） |
| Elongation at Break | 60% |
| Modulus of Elasticity | 193 GPa （28000 ksi ） |
| Izod Impact | 129 J （95.1 ft-lb ） |
| Charpy Impact | 105 J （77.4 ft-lb ） |
Thermal Properties of 316 Stainless Steel
| Property | Value |
| CTE, linear, µm/m-°C（@Temperature 0.000 – 100 °C ） | 16 |
| CTE, linear,µm/m-°C（@Temperature 0.000 – 315 °C） | 16.2 |
| CTE, linear,µm/m-°C（@Temperature 0.000 – 540 °C ） | 17.5 |
| Specific Heat Capacity(J/g-°C) | 0.5 |
| Thermal Conductivity(W/m-K) | 16.3 |
| Thermal Expansion(/K) | 15.9 x 10-6 |
| Melting Point( °C) | 1370 – 1400 |
Some Other Properties of 316 stainless steel
Corrosion Resistance
This material is highly effective in various atmospheric conditions and can withstand many corrosive substances. It is generally stronger than the material known as 304 stainless steel. But, in warm chloride environments, there is a risk of pitting and crevice corrosion affecting it. In addition, stress corrosion cracking can occur above 60 °C. Nonetheless, it is considered resistant to potable water that contains up to 1000 mg/L of chlorides at room temperature. As the temperature rises to 60°C, the chloride concentration should be lowered to around 500 mg/L.
Many people consider SS 316 as the default “marine grade stainless steel”. However, it doesn’t hold up well to warm seawater. In most marine environments, the surface of 316 stainless steel corrodes, which typically appears as a brown stain. This is more likely to occur in cracks and on rough surfaces.
Heat Resistance
It is important to note that intermittent use of 316 stainless steel up to 870°C and continuous use up to 925°C has good oxidation resistance. However, if water corrosion resistance is a priority, it is not recommended to use SS 316 continuously at temperatures between 425-860°C. Instead, Grade 316L is a better option as it is less likely to form carbides and can be used in the aforementioned temperatures. For structural and pressure-containing applications that require more robust materials, Grade 316H can be used at temperatures above 500°C.
Heat Treatment
Heat treatment is a process that can alter or improve the properties of SS 316 steel, increasing its strength and hardness. The most common heat treatments for 316 stainless steel are annealing (heating it to 1010-1120°C and then cooling it rapidly) and tempering (quick cooling). Besides, heat treatments like stress relief and solution annealing can enhance durability.
Hot Working
All typical hot working processes can be performed on 316 stainless steel. However, hot working should not be performed below 927°C. The recommended temperature range for optimal hot working is 1149-1260°C. Post-work annealing is advised to ensure maximum corrosion resistance.
Cold Working
316 stainless steel can be easily rolled or broken into different shapes. Additionally, it is ideal for stamping, heading, and drawing. However, annealing the steel after these processes is recommended to release any internal stresses. Cold working can enhance the strength and hardness of 316 stainless steel.
Fabrication
When fabricating all stainless steels, it is important to use tools exclusively meant for stainless steel materials. The tooling and work surfaces should be cleaned thoroughly before use. This is necessary to prevent cross-contamination of stainless steel by easily corroded metals that may cause discoloration of the surface of the fabricated product.
Machinability
316 stainless steel is a material that is easy to machine. In order to improve the machining process, the following guidelines can be followed:
- It is essential to maintain the sharpness of cutting edges. Dull edges can lead to excessive work hardening, which can cause further problems.
- Cuts should be mild but deep enough to prevent work hardening without riding on the surface.
- It is recommended to use chip breakers to keep the swarf clear from the work area.
- Due to low thermal conductivity, austenitic alloys require large amounts of coolants and lubricants to prevent heat concentration at cutting edges.
Welding
The fusion welding performance of 316 stainless steel is excellent, whether using fillers or not. It is recommended that the same filler rods and electrodes for 316 and 316L be used for the base metal. However, heavy welded sections may require annealing after the welding process. In such cases, 316Ti may be used as an alternative to 316 stainless steel. Note that oxyacetylene welding is unsuitable for joining 316 stainless steel.
Equivalent Forms of 316 Stainless Steel
The following are equivalent forms of 316 stainless steel:
| Country | Equivalent Grade |
| EU | EN/DIN 1.4401, X5CrNiMo17-12-2 |
| CN | GB 0Cr17Ni12Mo2 |
| Russia | GOST 08X17H13M2T |
| Japan | JIS SUS 316, JIS SUS 316L |
| France | AFNOR Z6CND17.11 |
| UK | BS 316S31, BS 316S33 |
| Germany | DIN X5CrNiMo17-12-2 |
| USA | ASTM/UNS S31600 |
| Italy | UNI X5CrNiMo17-12 |
| Sweden | SS 2347 |
| Czechia | CSN 17346 |
| Austria | NORM X5CrNiMo17-12-2KW |
Common Forms of 316 Stainless Steel
316 stainless steel is available in various forms, including:
Sheet
Sheet metal is a type of metal that ranges in width from 0.5 to 6mm, and the width determines the thickness. Among the versatile options of sheet metal, 316 stainless steel sheet, also known as cold-rolled products, are especially useful. These sheets can be easily molded into various shapes, making them ideal for cookware applications such as grills, pots, and sinks. Additionally, they are commonly used as finishes for appliances like countertops, refrigerators, freezers, and dishwashers. Stainless steel sheet metal also finds utility in manufacturing light bulb bases and automobile license plates.
Bar
316 stainless steel bars are rods available in various sizes and shapes, including cylindrical and rectangular, depending on the application’s particular requirements. This type of stainless steel bar stock has the same properties and composition as sheets but is more rigid, making it able to support higher loads than sheet metal. Bar stock is commonly used in construction, architectural applications, shafts, fasteners, and marine hardware.
Plate
316 stainless plates are flat plates that are typically thicker than 6 mm. They offer the same properties as a sheet, but their additional thickness makes them suitable for heavy-duty applications. Common uses include structural components, pressure vessels, and chemical processing equipment.
Tube
For applications in high-pressure and harsh environments, 316 stainless steel tubes offer increased strength and corrosion resistance, meeting the requirements of your projects.
In addition, other forms of 316 stainless steel are available such as strips, tubes, fittings, and flanges.
Available Finishes
A variety of finishing techniques are available to customize the appearance of 316 stainless steel to specific design requirements. These techniques include mechanical finishes such as grinding and polishing, chemical processes like passivation and electropolishing, and coatings such as powder coating and PVD.
Finishes on stainless steel serve multiple purposes, including enhancing aesthetics, improving corrosion resistance, and simplifying maintenance. Two common finishes are passivation and electropolishing, and we will discuss each of them in detail:
Passivation:
Passivation is a chemical process that helps enhance the corrosion resistance of stainless steel. It does this by creating a passive oxide layer on the surface of the steel, which acts as a barrier against corrosion. As a result, stainless steel becomes more resistant to rusting, staining, and pitting. The passivation process involves a few steps, including:
- Cleaning: Before starting the passivation process, it is crucial to thoroughly clean the surface of stainless steel to eliminate contaminants such as oil and grease.
- Passivating: Next, stainless steel is pickled by treating it with an acid solution, such as nitric or citric acid, to remove any iron particles or contaminants on the surface. This step is also helpful in eliminating any present oxides from the surface.
Passivation is a common process for protecting stainless steel against harsh environments. Industries such as pharmaceutical, food processing, and aerospace use this process extensively.
Electropolishing:
Electropolishing is a non-contact electrochemical process that removes a thin layer of material from stainless steel surfaces. This process is utilized for polishing and deburring, and it provides numerous benefits over traditional methods:
- Surface Finish: Electropolishing produces a smoother surface finish that improves aesthetics, reduces surface roughness, and makes cleaning easier by preventing the accumulation of contaminants.
- Microfinishing: The process can effectively smooth out surface imperfections such as micro-irregularities and pits, which are often difficult to address using mechanical polishing.
- Passivation Effect: Electropolishing enhances the passivation effect, forming a uniform and dense passive oxide layer, which enhances the stainless steel’s corrosion resistance.
- Deburring: Electropolishing eliminates burrs, sharp edges, and unwanted material from surfaces, reducing injury risk and improving product safety.
Electropolishing is a process used in various industries, such as pharmaceuticals, food processing, medical devices, and semiconductor manufacturing, to achieve a high-quality and corrosion-resistant surface finish.
In conclusion, passivation and electropolishing are crucial for enhancing the corrosion resistance, appearance, and overall performance of 316 stainless steel in various industries. Although they have distinct roles, they are often used together to achieve the desired results and improve the material’s properties.
Applications of 316 Stainless Steel
316 ss is highly resistant to corrosion and can be easily shaped, welded, and machined using standard fusion methods. Because of its exceptional qualities, it is extensively utilized in various sectors:
- New Energy
- Medical devices and tools
- Aerospace engineerings
- Food processing equipment
- Automotive Industry
- Marine engineering and boat fittings
- Machine Tool Industry
Additional reasons why 316ss is used in the sectors above include:
- An aesthetically good appearance
- Easy for cleaning
- Relatively high-strength to weight ratio
- Relatively high availability in various forms
Advantages & Disadvantages
Advantages:
- SS316 stainless steel is a durable and robust choice for CNC machining, retaining good mechanical properties even under challenging conditions. It has excellent strength and toughness for structural applications.
- It has excellent resistance to corrosion, especially in harsh environments with exposure to chlorides, acids, and marine conditions. Additionally, it can maintain its resistance to corrosion and strength even at high temperatures.
- CNC machining is ideal for creating intricate and detailed designs on 316 stainless steel surfaces, making it perfect for applications that require both functionality and aesthetic appeal, such as architectural and decorative components.
- It can be easily fabricated, welded, and molded into different shapes and sizes.
- It is a non-toxic material that is easy to clean and resistant to bacterial growth. This makes it ideal for food processing and medical applications.
Disadvantages:
- Compared to other stainless steel grades, machining 316 stainless steel can be slower due to lower machinability and increased tool wear.
- The work-hardening behavior and abrasive nature of stainless steel accelerate tool wear during CNC machining, which results in frequent tool changes, increased downtime, and higher production costs.
- CNC machining can cause a work-hardening effect in stainless steel due to heat generation and dimensional inaccuracies, owing to the high coefficient of thermal expansion.
- 316 stainless steel has lower formability and machinability when compared to 304 stainless steel.
- The higher cost of SS 316 is due to its higher alloy content than other stainless steel grades.
CNC machining of 316 stainless steel has several advantages, such as its ability to resist corrosion, withstand high temperatures, and provide strength. However, some challenges must be considered, such as machinability, tool wear, heat generation, and post-machining. Mechanical engineers must balance material properties, machining techniques, and design requirements to produce high-quality machined components from 316 stainless steel.
Comparison of SS316 and Other Grade
316 Stainless Steel &304 Stainless Steel
The prime difference between 304 and 316 stainless steel is that 316 has 2-3% molybdenum, while 304 has none. Additionally, SS 316 has a higher nickel content and slightly less chromium than SS 304. These variations make SS 316 more resistant to corrosion in environments that contain chloride. On the other hand, SS 304 is less expensive than SS 316 and is commonly used in approximately 60% of austenitic stainless steel applications.
316 Stainless Steel & 316L Stainless Steel
316 and 316L stainless steel are suitable for marine environments but differ significantly. 316L is a type of stainless steel with a lower carbon content than 316. To be classified as aisi 316L, the carbon content cannot exceed 0.03%. This helps reducing the risk of carbon precipitation, making it a better choice for welding and ensuring maximum resistance to corrosion.
On the other hand, ss316 contains a mid-range level of carbon and between 2% and 3% molybdenum. The presence of molybdenum makes it more resistant to corrosion, acidic elements, and high temperatures.
Summary
Compared to other steel types available today, 316 stainless steel offers excellent mechanical properties and superior resistance to corrosion. Its diverse range of applications spans medical equipment to construction projects, where its durability and longevity are crucial requirements from a structural standpoint. Thanks to its good formability and weldability characteristics, combined with its excellent strength, toughness, and hardness capabilities, 316 stainless steel is an ideal choice for many different industries that demand reliable materials capable of withstanding extreme temperatures, pressures, loads, vibrations, impacts, and more.
Enze is a 316 stainless steel manufacturer, also, we are one of the famous 316l stainless steel suppliers in China. If you have any question, please feel free to contact us.
