Comparing Alloy Steel and Stainless Steel Strength for Machining--cncmass.com( stainless steel cnc machining Wallis)
- source:FANYA CNC Machining
What Gives Alloy Steel Its Strength?
Alloy steel contains alloying elements like chromium, nickel, silicon, and vanadium added to iron. This improves specific properties like hardness, wear resistance, or toughness compared to regular carbon steel. The most common alloy steel is 4140 which has 1% chromium and 0.2% molybdenum added to the iron. The molybdenum in particular improves machining characteristics.
Other popular alloy steels include 4340 and H13. These contain additional alloying elements like tungsten, cobalt, and vanadium to make the steel even stronger than 4140. The tradeoff is these steels are more difficult to machine.
Alloy steel derives its strength from the bonds formed between the iron and alloying elements. This makes the atomic structure more rigid and resistant to shearing forces. Alloy steels typically have tensile strengths from 60,000 psi to over 300,000 psi depending on the alloy composition. Aircraft and structural parts are often made from high-strength alloy steels.
Why is Stainless Steel Strong?
Stainless steel gets its strength from the inclusion of chromium. Modern stainless steels usually have at least 10.5% chromium added to iron. The chromium forms a passive oxide layer on the surface that protects against corrosion. Nickel is also added to improve formability and resistance to corrosion.
The most common stainless steel is 304, also known as 18-8 for its composition of 18% chromium and 8% nickel. The corrosion resistance and high strength make it ideal for kitchenware, industrial equipment, and construction materials.
The addition of chromium and nickel increases the strength through solid solution strengthening. This alters the iron's crystal lattice structure to make it more rigid. Stainless steels typically have tensile strengths from 50,000 psi to over 200,000 psi. When higher strengths are needed, martensitic and precipitation hardening stainless steels are used.
Key Factors in Strength Comparison
When comparing the strength of alloy steel versus stainless steel, the following factors come into play:
- Alloy composition: Varying the percentages of chromium, nickel, molybdenum etc. significantly alters strength.
- Production method: How the steel is produced affects its hardness and grain structure. Quenched and tempered steels are stronger.
- Yield strength: The yield point where plastic deformation starts can differ between types.
- Tensile strength: The maximum stress sustained before failure varies based on alloying elements.
- Toughness: Resistance to fracture depends on composition and production. Stainless steel is often tougher.
- Fatigue strength: The endurance limit under cyclic stresses can favor alloy or stainless steel depending on alloy.
In general, the highest strength alloy steels exceed the strongest stainless steels. But stainless steels have an advantage in toughness and ductility in most cases. When selecting a steel for machining, both strength and machinability characteristics should be evaluated.
Removing Chrome from Steel
In some cases, chromium may need to be removed from stainless steel or reclaimed from scrap steel. Some key methods for removing the chrome layer include:
- Mechanical Removal: Manual grinding or media blasting removes chrome coating but is labor intensive.
- Electrolytic Processes: Requires submerging steel in electrolyte bath and applying electric current to dissolve chrome.
- Chemical Bath Stripping: Immerse steel in heated chemical bath using strong alkaline or acid solutions to react away chrome layer.
- Thermal Removal: Heating steel to high temperatures allows molten chrome to oxidize which can then be washed away.
- Laser Ablation: High power laser physically vaporizes and removes the chrome coating from the steel surface.
Mechanical removal works well for stripping chrome from coiled steel. Electrolytic and chemical bath stripping accommodate large steel parts and tools. Thermal and laser processes offer more precision removal.
Proper ventilation, protective equipment, and hazardous waste disposal are critical when using any chemical or thermal chrome removal methods. The spent chemicals used will contain dissolved chrome and require responsible handling.
Chrome is toxic in its pure form, but chrome-coated steels are perfectly safe for machining and use. Removing chrome is only necessary for refinishing or recycling the steel once an object reaches the end of its useful life. With proper precautions, the chrome layer can be removed to recover the bare steel.
The unique properties of alloy and stainless steels make both ideal choices for machined parts and components. Understanding their strength and makeup allows matching the correct type of steel to the intended application. Processes are available to safely remove chrome when required from end of life products. Careful design, material selection, machining, and finishing produces steel parts with the right combination of strength, durability, and corrosion resistance. CNC Milling CNC Machining