It has become widely used in different applications in industries such as the automotive, aerospace, medical equipment, and food preparation industries, owing to its strength and non-corrosive nature. However, this type of material faces some of the greatest difficulties associated with machining, given its hardness, low thermal conductivity, and work-hardening tendency.
Stainless steel machining is associated with heat generation very rapidly. Besides, stainless steel machining is also characterized by the formation of built-up edges, making the task of chip evacuation and manufacturing of quality products difficult. Hence, selection of suitable carbide inserts is very important when undertaking any stainless steel machining operation.
Understanding ISO M-Group Classification
Material may be classified under six different colors based on its machinability property as per the ISO standard. The ISO M-Group is stainless steel, but ISO M-Group includes only one color, which is yellow. This is due to the reason that stainless steel cannot be categorized under one type of metal.
Austenitic Stainless Steel (304, 316) – High Sticky Nature
- Features: This is the most frequently found alloy among stainless steels, rich in chromium and nickel content, hence not magnetic.
- Problem with Machining: The alloy is very ductile and sticky; hence, there will be serious built-up edge as the material tends to bond to the insert. The alloy is also known for rapid work hardening.
- Inserts Needed: Inserts require sharp, positive rake geometry with thin PVD coatings.
Martensitic & Ferritic Steel (410, 430) – Abrasive and Hard
- Properties: Martensitic steel can be heat treated to make it hard steel. On the other hand, ferritic steel is a magnetic metal that lacks nickel.
- Problems during the Cutting Process: It is less sticky than austenitic steel but abrasive. It causes flank wear through the abrasion of cutting tool edges.
- Material for Tool: This material should possess high wear resistance properties. Therefore, hardened carbides with CVD coating would suit best.
Duplex Stainless Steel—Extremely Tough and Difficult to Machine
- Properties: It is a 50-50 blend of both austenitic and ferritic material, with properties of extreme tensile strength and high corrosion resistance.
- Machining Problem: Because of its extremely high structural strength, enormous machining forces occur along with extreme heat, causing fast plastic deformation and sudden insert breaking.
- Insert Needs: Needs tough carbide inserts (ISO M25-M35) in combination with special coatings for thermal protection from heavy machining load.
Core Carbide Substrate Types for Stainless Steel
It is the core material that influences the ability of the tool to cope with the mechanical forces associated with cutting operations. The critical properties that must be balanced for stainless steel are the hardness and toughness of the substratum. These can be controlled by varying the grain structure of the WC and the proportion of the Co binder.
Micrograin Carbide for Edge Sharpness and Toughness
- Composition: The composition of this substrate contains fine grains of tungsten carbide (usually ranging from 0.5 to 0.9 microns) with a slightly higher content of the binder material cobalt.
- Advantages: The fine grains give it good edge stability, thus ensuring that the cutter keeps a very sharp edge without breaking down.
- Application: It is very effective in machining the austenitic stainless steel (304/316), as its sharp edge will cut through the adhesive metal very easily, avoiding any form of work hardening and buildup edge (BUE).
- Application Best Suited For: Finish machining, light profiling, and interrupted machining conditions.
Sub-Micrograin Carbide for High-Hardness and Wear Resistance
- Composition: Contains ultra-fine grains (<0.5 microns) along with a carefully balanced lower cobalt composition for increased density.
- Key Advantages: Provides optimum hot hardness as well as excellent anti-plastic deformation at high temperatures. The dense construction protects the tool surface from being eroded by the hard particles in the steel.
- Recommended For Use: Ideal for martensitic, ferritic, and duplex stainless steels that place the tool under tough conditions due to severe abrasive and thermal stresses.
- Best Suited For Operation: Continuous turning and roughing operations, especially with long cycle times.
Top Carbide Insert Grades by Leading Brands
Various producers provide special grades designed specifically for stainless steel turning operations. Each grade is designed to be suitable for different operations, such as roughing, semi-finishing, and finishing.
Among the key features of good quality grades are:
- Thermal resistance
- High edge-holding ability
- Coating technology advancements
- Chip control capabilities
The grades table for the inserts chart, issued by producers, allows one to pick the most appropriate grade according to cutting speed, feed, and operation type.
Inserts a chart of high performance by well-known producers, providing increased productivity and minimizing downtime at high production volumes.
PVD vs. CVD Coating on Carbide Inserts
Coatings also play an important role in improving the efficiency of the tools. The two main types of coating include:
PVD—Physical Vapor Deposition
- Thin coating film
- Sharper edges
- Best suited for finishing operations and light machining
- Good anti-built-up edge characteristics
CVD—Chemical Vapor Deposition
- Thick coating film
- High wear-resistance
- Suitable for roughing and high-speed machining operations
Good thermal stability
Selection between PVD and CVD can be made based on machining needs. In most instances, PVD coatings are preferred for carbide inserts machining stainless steel because of better surface finish and low friction.
Grade Selection by Machining Operation
Choosing the right grade is determined by the nature of the operation to be done.
Roughing
- Use hard grades that offer high toughness
- CVD coatings are the best option for this application
- Heat resistance and chip control are key considerations here
Semi-finishing
- Balance grades with moderate levels of toughness and wear resistance
- Ideal for average cutting speeds
Finishing
- Choose fine-grain substrates
- PVD coatings work best in this operation
- Surface finish is very important
A properly set-up CNC tool machine coupled with the right insert grades guarantees effective machining operations.
Expert Tips to Extend Carbide Tool Life
Optimization of tool life is necessary for cost reduction and productivity enhancement. The following points are recommended by experts in order to increase tool life:
- Using appropriate cutting parameters including speed, feed rate, and depth of cut
- Applying coolant properly in order to avoid unnecessary heat generation
- Ensuring that tools are not overloaded or excessively vibrated
- Regular monitoring of tool wear
- Using high-quality Carbide inserts
Correct handling and storage of tools is equally important in ensuring their proper performance.
Conclusion
Selection of the most appropriate grade of inserts when machining stainless steel requires not only the choice of an optimal insert but the optimization of the entire process as well. Knowing the physical properties of stainless steels and choosing the most suitable substrate and coating will positively affect performance.
Proper usage of high-quality carbide inserts can help in obtaining a superior surface finish and increasing tool life and productivity.
Jaibros – Your Trusted Tool Partner
Jaibros is one of the key providers of premium-quality cutting tools and industrial services in India. Cutting tools are well known for their durability and efficiency. A comprehensive range of cutting tools has been designed to meet the demands of current machining applications. Whether you want CNC inserts or a complete cutting tool system, you can get the best product from us.
FAQs
1. Which insert grade will be suitable for stainless steel machining?
The best grades vary based on the process used; however, tough grades with PVD coating tend to excel in this situation.
2. Why does stainless steel create problems in machining operations?
Due to its tough nature and poor heat dissipation, it makes machining operations more challenging.
3. In what ways do PVD-coated inserts differ from CVD?
PVD coating creates a sharper edge than CVD coating. CVD coating ensures better wear resistance at heavy cuts.
4. How do I choose the suitable insert grade?
Consult the insert grade charts for choosing the suitable insert grade according to the material and operation.
5. Which are the best places to buy high-quality inserts in India?
Several good vendors are selling high-performing cutting tools. happens to be one such reliable source.