Machining and Decarb Limits

Effects Of Common Alloying Elements In Steel

By definition, steel is a combination of iron and carbon. Steel is alloyed with various elements to improve physical properties and to produce special properties such as resistance to corrosion or heat. Specific effects of the addition of such elements are outlined below.

Carbon (C) is the most important constituent of steel. It raises tensile strength, hardness, and resistance to wear and abrasion. It lowers ductility and toughness.

Manganese (Mn) is a deoxidizer and degasifier and reacts with sulfur to improve forgeability. It increase tensile strength, hardness, hardenability and resistance to wear. It decreases tendency toward scanling and distortion. It increases the rate of carbon-penetration in carburizing.

Phosphorus (P) increases strength and hardness and improves machinability. However, It adds marked brittleness or cold-shortness to steel.

Sulfur (S) improves machinability in free-cutting steels, but without sufficient manganese it produces brittleness at red heat. It decreases weldability, impact toughness and ductility.

Silicon ( Si ) is a deoxidiser and degasifier. It increases tensile and yield strength, hardness, forgeability and magnetic permeability.

Chromium ( Cr ) increases the tensile strength, hardness, hardenability, toughness, resistance to wear and abrasion, resistance to corrosion and scaling at elevated temperatures.

Nickel ( Ni ) increases strength and hardness without sacrificing ductility and toughness. It also increases resistance to corrosion and scaling at elevated temperatures when introduced in suitable quantities in high – chromium ( stainless ) steels.

Molybdenum ( Mo ) increases strength, hardness, hardenability, and toughness, as well as creep resistance and strength at elevated temperatures. It improves machineability and resistance to corrosion and it intensifies the effects of other alloying elements. In hot – work steels and high-speed steels, it increases red – hardness properties.

Tungsten (W) increases strength, wear resistance, hardness, and toughness. Tungsten steel has superior hot -working and greater efficiency at related temperatures.

Vanadium (V) increases strength, hardness, wear resistance and resistance to shock impact. It retards grain growth, permitting higher quenching temperatures. It also enhances red-hardness properties of high-speed metal cutting tools.

Cobalt ( Co ) increases strength, hardness permitting higher quenching temperatures. It also increases red-hardness properties of high-speed steel. It also intensifies the individual effects of other major elements in more complex steels.

Aluminium ( Al ) is a deoxidiser and degasifier. It retards grain growth and is used to control austenitic grain size. In nitriding steels, it aids producing a uniformly hard and strong nitrided case when used in amounts 1.00% – 1.25 %

Recommendation For Tool Designed To Avoid Failure

Tools and machine parts made from tool steels are often subjected to high stress in operation. These parts also have a certain amount of internal stress as a result of their fabrication and heat treatment. When these stresses, either singly or in combination, exceed the strength limits of the steel, cracking, breaking or warping of the part results. Many fully hardened tool steels, particularly highly alloyed types, can withstand relatively high compressive loading, but only limited tensile loading. Tool engineers should seek to minimize tensile stresses through proper design and use of support tooling so as to permit use of the highest performance die steels on crucial components. When required tooling designs must involve significant tensile stresses, then selection of tougher tool steel with reduced wear resistance, most likely one of those shock resisting grade, is advised.


  • User of sharp corners ; failure to use fillets or adequate radii.
  • Presence of non – uniform sections in tooling causing variation in stress distribution in service as well as variable quenching rates during hardening.
  • Use of improper clearance between punch and die edges.
  • Tools designs involving excessive unit stresses or overloading during operation. Tools should be redesigned to operate at a lower unit stress.


If sharp corners and variable sections cannot be avoided in the design of a part the use of an air hardening die steel is essential of greatest safety in hardening. Cracking and/or distortion are more apt to occur on such sensitive sections when liquid quenching is employed during hardening.


Tool clearance is the distance between adjacent punch and die edges. In general, the press load required for a given operation decreases as clearance increases, so tools are more highly stressed with a small degree of punch and die clearance. Enlarging clearance from 5 to 10% of stock thickness usually will improve tool life. Although the finish of the sheared edges of parts may improve with a small clearance, tool life will be shortened. Breakage due to misalignment may also result.

While acceptance clearance is often 10% of the stock thickness, this subject is debatable since many variables besides stock thickness influence clearance, including stock material, hardness and surface ( scale condition and finish ) and the required finish on the shear cut.

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