The Complete Guide to Stainless Steel Machining
Stainless steel is one of the most commonly processed materials and plays an important role in modern industry. From prototyping to mass production, stainless steel machining creates products for every sector that meet the industry's applications.
Due to its high hardness and tensile strength, machining stainless steel is much more complex than machining wood, therefore, selecting the appropriate machining technology is crucial. This article will provide a detailed introduction to the definition, advantages, classification, and applications of stainless steel, enabling you to better understand its characteristics and facilitate the machining of stainless steel.
What is Stainless Steel?
Stainless steel is a stainless and corrosion-resistant high-alloy steel, with high chemical stability in corrosive media such as air, water, brine, acids and alkalis. It has a chromium content of at least 10.5% and a maximum carbon content of 1.2%.
Stainless steel is a general term for both stainless steel and acid-resistant steel. Stainless steel refers to steel that is resistant to weak corrosive media such as atmospheric air, steam, and water, while acid-resistant steel refers to steel that is resistant to corrosion by chemical corrosive media such as acids, alkalis, and salts. Stainless steel and acid-resistant steel have significant differences in alloy composition. While stainless steel is resistant to rust, it may not necessarily be acid-resistant. However, acid-resistant steel generally exhibits rust resistance.
What are the Benefits of Stainless Steel?
Corrosion Resistance: It can withstand corrosion from most chemical media, including acids, alkalis, and salts. This gives stainless steel excellent stability in humid and corrosive environments, extending its service life.
High Strength: By controlling the content of alloying elements and heat treatment, the strength of stainless steel can be adjusted to meet the needs of different applications, making it widely used in structural engineering.
Wear Resistance: Stainless steel is very strong and can maintain its surface integrity and durability under friction and wear conditions. This makes stainless steel important in the manufacture of wear-resistant parts and engineering structures.
Heat Resistance: Stainless steel can maintain its excellent physical and mechanical properties at high temperatures, making it heat-resistant.
Excellent Hygiene: Its smooth surface is not easily contaminated by bacteria or dirt, making it easy to clean and disinfect, meeting hygiene standards. Therefore, it is widely used in medical, food processing, pharmaceutical, and other fields.
Aesthetic Appearance: Stainless steel comes in a variety of colors, from cool and elegant metallic to vibrant colors, making it suitable for different settings. It has a modern and elegant appearance, making it attractive in architecture, home furnishings, and industrial design.
Recyclability: Scrap stainless steel can be recycled and reused, reducing resource waste and environmental pollution, aligning with the concept of sustainable development.
Types of Stainless Steel
Stainless steel can be classified in many different ways. Based on the main chemical composition, it can be divided into chromium stainless steel and chromium-nickel stainless steel. According to its use, it can be divided into nitric acid resistant stainless steel, sulfuric acid resistant stainless steel, seawater resistant stainless steel, etc. Next, let's delve into the classification based on microstructure after heat treatment.
Austenitic Stainless Steels
Austenitic stainless steel is the most popular and widely used stainless steel in the world. It contains more than 18% chromium, about 8% nickel, and small amounts of molybdenum, titanium, nitrogen, and other elements, also known as 18-8 austenitic stainless steel. It is essentially non-magnetic. This type of steel has excellent comprehensive properties and strong corrosion resistance. Common grades are indicated by numbers in the 200 and 300 series, such as 304.
301: It has good ductility and is used for forming products. It can also be hardened through processing. It has good weldability, wear resistance, and fatigue strength superior to 304 stainless steel.
304: As a widely used steel, it has good corrosion resistance, heat resistance, low-temperature strength, and mechanical properties.
304L: As a low-carbon 304 steel, its corrosion resistance is similar to that of 304 steel, but its corrosion resistance is more prominent after welding or stress relief.
316: With the addition of Mo, it has excellent high-temperature corrosion resistance. It is used in seawater equipment, chemicals, food processing, and papermaking industries.
316L: As a low-carbon 316 steel, the molybdenum content is slightly higher than that of 316 stainless steel, which can improve the corrosion resistance of stainless steel in acidic environments.
321: It contains Ti, which can prevent stainless steel from sensitization and improve the high-temperature service life of stainless steel. It has excellent high-temperature stress rupture performance and high-temperature creep resistance.
Ferritic Stainless Steels
Ferritic stainless steel is mainly composed of ferritic microstructure and contains 12% to 30% chromium. Its corrosion resistance, toughness, and weldability increase with the increase of chromium content. It has excellent resistance to chloride stress corrosion cracking compared to other types of stainless steel. The American Iron and Steel Institute uses 430 and 446 as its designation.
430: Contains at least 16% chromium, corrosion-resistant. It has heat fatigue resistance and a smaller coefficient of thermal expansion than austenitic stainless steel. It is used in household appliances and architectural decoration.
Martensitic Stainless Steels
Martensitic stainless steel is a hardenable stainless steel. Due to its higher carbon content, it has high strength, hardness, and wear resistance, as well as moderate corrosion resistance and low weldability. Its mechanical properties can be altered through heat treatment. It is currently mainly used in manufacturing steam turbine blades, surgical instrument parts, and other applications.
Duplex Stainless Steels
It has the advantages of both austenitic and ferritic stainless steels and has superplasticity. The matrix has both austenitic and ferritic two-phase structures, in which the content of the lesser phase matrix is generally greater than 15%, and it is magnetic and can be strengthened by cold working. 329 is a typical duplex stainless steel. Compared with austenitic stainless steel, duplex steel has higher strength and stronger corrosion resistance.
Precipitation Hardening Stainless Steels (PHSS)
For a base with austenitic or martensitic structure and high Cr content, mechanical properties are primarily enhanced through phase transformation and age precipitation hardening. The American Iron and Steel Institute designates these with a 600 series number, such as 630, which corresponds to 17-4PH.
17-4PH: This alloy exhibits excellent heat treatment performance. Its properties can be altered through various heat treatment methods, such as quenching and annealing, quench cooling, or aging quenching, allowing for the attainment of different mechanical properties and fatigue resistance.。
Can Stainless Steel Be Machined?
Yes, stainless steel can certainly be machined, and there are various methods for machining stainless steel. Next, let's explore 7 common stainless steel processing techniques together.
Stainless Steel Machining Processes
Milling: Is the most commonly used process for machining stainless steel, typically employing high-speed steel (HSS) milling cutters to machine fixed workpieces. Choosing the right tools is crucial for machining stainless steel. While end mills and some face mills can use carbide as the cutter material, other types of milling cutters generally use high-speed steel, which offers higher tool durability.
Turning: Is a common process for machining stainless steel. During this process, the cutting tool is fixed while the workpiece rotates around an axis to remove material. Machining stainless steel involves high cutting forces and difficulty in chip breaking, which can lead to tool sticking or the formation of built-up edges, affecting surface quality and accelerating tool wear. Therefore, YD-type, YN-type, and coated carbide tools should be used when turning high-strength steel.
Grinding: Improve the surface finish and precision of stainless steel parts. Ground stainless steel components exhibit enhanced wear resistance, corrosion resistance, and fatigue strength, thereby extending their service life.
EDM (Electrical Discharge Machining): Uses the high temperature generated by instantaneous spark discharge between the tool electrode and the workpiece electrode to erode material. The thickness of the metal limits the use of this process.
Drilling: Drilling stainless steel requires sharp drill bits. Low rotational speed, high cutting pressure (high feed rate), and plenty of coolant are needed to complete the secondary processing, enhancing performance and aesthetics.
Threading: Is an essential process for steel parts used for fastening or screw installation. It involves creating threads on a workpiece using forming tools or grinding tools.
Laser Cutting: Uses a high-energy density laser beam to precisely cut materials, making it suitable for cutting thin stainless steel sheets.
Tips of Machining Stainless Steel
Selecting the Right Material: Stainless steel comes in many different grades, each with varying alloy compositions that result in different properties. You need to choose the highest quality grade that meets the project requirements to help save significant costs.
Selecting the Right Tool: Choosing the correct tool is crucial for machining high-quality parts. Selecting tools based on specific needs can improve cutting efficiency and extend tool life. Common cutting tools for stainless steel are carbide and high-speed steel.
Using Cutting Fluids: Lubricants have multiple uses in machining stainless steel. They not only reduce wear between the cutting tool and the workpiece, extending tool life, but also effectively lower cutting temperature, reduce the formation of built-up edges, and minimize hardening.
Using Sharp Tools: Ensuring the use of sharp tools can reduce cutting forces and achieve consistent and precise machining. When machining stainless steel, it's essential to regularly check tool wear and replace tools as needed.
Stainless Steel Machining Applications
Stainless steel, as a widely used metal material in industrial manufacturing, holds significant economic and engineering value. Consequently, it has become a primary material in various industries. Next, let's explore the specific applications of stainless steel in different industries:
Automotive: Due to its high-temperature resistance, high toughness, and high strength, stainless steel is commonly used in exhaust systems, fuel tanks, and stainless steel components.
Aerospace: Machined stainless steel parts are often used in aircraft fuselages and engine components.
Medical: Stainless steel's excellent biocompatibility and corrosion resistance make it a common choice for manufacturing medical instruments and implants.
Food and Beverage: Stainless steel is widely used in food processing equipment and storage containers because of its hygiene, ease of cleaning, and durability.
Marine: Stainless steel's outstanding acid and corrosion resistance make it frequently used in marine applications.
Stainless Steel FAQs
Is Stainless Steel Difficult to Machine?
Although there are some problems that may not be encountered in other metal machining when machining stainless steel, many problems can be solved by combining the operator's experience and material characteristics, so processing stainless steel is not difficult.
When Machining, make corresponding preparations in advance, including: choosing the right tools, setting the correct cutting parameters, using cutting fluids and sharp tools, which will reduce the difficulty of machining stainless steel accordingly.
What is the Cheapest Stainless Steel for Machining?
SUS409 is the cheapest grade of stainless steel and is a ferritic stainless steel (chrome steel). 409 stainless steel has a lower alloying element content, so the cost is relatively low. Due to its high temperature stability and corrosion resistance, it is often used as an automotive exhaust pipe.
Which Stainless Steels are Difficult to Machine?
High carbon steel: Due to its high strength and hardness, it is easy to wear the tool
Low carbon steel: Because it is soft, it is easy to cause the steel chips from cutting to adhere to the tool, shortening the service life of the tool
304: Easy to work harden.
Are There Any Disadvantages to Stainless Steel for Machining?
Yes, stainless steel machining needs to consider the following disadvantages:
- High cost of stainless steel
- Poor weldability, easy to cause material waste
- Easy to dent
- Easy to scratch, affecting the appearance
What Surface Treatments Can Be Used to Machine Stainless Steel?
Stainless steel machining often uses polishing, electroplating, electrolytic polishing, bead blasting, surface coating and other surface treatments.
Conclusion
After studying this guide, I believe you have a more comprehensive understanding of stainless steel. Due to its corrosion resistance, strength and toughness, stainless steel machining parts are the preferred material in many industries. If you have a new stainless steel project, please contact DEK and let us take a deeper look at the world of stainless steel or other materials machining.
DEK is a top manufacturer in the field of stainless steel machining services. We have rich experience and advanced equipment to effectively speed up your project progress and provide you with one-stop quality services.
