What Materials Are Commonly Used for Crankshaft Manufacturing?

What materials are used to manufacture crankshafts?  

Choosing materials for crankshafts is mostly a function of operating conditions and is largely an abstract analysis since they could be subjected to mechanical stress, high temperatures, friction, and/or several other extremes, and evaluation for operating performance, durability, and reliability is justified. There is an almost infinite number of measurable parameters that must be balanced, and as counter crankshaft materials are selected for optimum performance based on crankshaft design and prevailing crankshaft standards, so are counter crankshaft materials.

Building blocks out of Carbon Steel. 

For the manufacture of the primary crankshaft for entry level car engines and mid range engine systems, carbon steel has for many years been the material of choice for crankshaft manufacturing. Carbon Steel is admired for it’s machinable qualities and mechanical characteristics when heat treating is involved, and its cost effectiveness. When it comes to balance of strength and ductility, medium carbon steel is preferred, with carbon content of 0.30% to 0.50%. Though quenching and tempering it can enhance its hardness and toughness, it will be able to the cyclic loads during engine operations. Most of the carbon steel crankshafts that are sold in the market are produced for passenger vehicles and commercial vehicles weighing light. This is so they can be economically manufactured, while improving the most important performance characteristics. Many industries have mass produced carbon steel crankshafts, so there is a long history of automotive industry carbon steel that has been used in conformed engineering required for safe standard operating conditions.

Alloy Steel for Enhanced Performance

Alloy steel has recently become a preferred material for crankshafts that require for heavy duty and high performance applications. Manufacturers use a variety of alloying components to improve the steel’s matrix; with the addition of chromium, nickel, molybdenum, or vanadium the key improvement properties that can be attained include, tensile strength, fatigue resistance, and impact toughness. Alloying components also improve grain structure, overall hardenability and decrease the likelihood of wear or deformation under extreme conditions. Alloy steel crankshafts can be found in high performance sports cars and heavy duty trucks, and industrial diesel engines. Alloy steel crankshafts stand out due to their ability to endure higher torque outputs and withstand longer service periods, sustaining a wider spectrum of industrial operating conditions. Compared to carbon steel, industry studies show that alloy steel can withstand 30% more crankshaft fatigue cycles and make demanding operating environments more efficient. For their premium and commercial vehicles, leading automotive manufacturers also value engine reliability above all else and recognize alloy steel as an integral component.

Ductile iron also known as nodular cast iron, is a flexible and affordable substitute for steel in making crankshafts. It's also different from gray iron as ductile iron incorporates spherical graphite particles. These particles enhance its ductility, impact resistance, castability, and wear resistance. Aside from these properties, ductile iron has the ability to dampen vibrations, noises, and improve the overall smoothness of the engine. Balanced strength, durability, and cost efficiency in one is the reason ductile iron is common place in marine applications, agricultural machinery, and medium duty engines. Because of cutting-edge casting technology the consistency and quality of ductile iron components has improved greatly. Today's casting processes are achieving dimensional accuracy that is on par with steel forgings. Many engine manufacturers are settling for ductile iron crankshafts instead of higher cost components because most engines made today are only made for moderate power outputs.

Cutting-Edge Materials In Specialized Applications

Extreme performance demands the use of advanced materials in specialized applications engines. Although titanium alloys are pricey, they have an outstanding strength to weight ratio, making them ideal for high speed racing engines, and the aerospace industry. To meet weight criteria, titanium crankshafts reduce total mass and improve engine responsiveness and fuel consumption. Also, some specialized applications are using new composites, like titanium reinforced carbon fiber polymers, which have outstanding strength and resistance to corrosion. Advanced materials in crankshop technology are destined to become mainstream, but complexity of manufacturing, and high cost materials still keep them out of the high end, specialized equipment. Leading manufacturers and research institutions have been focusing on the utilization of these materials for various engine types in a cost effective manner.

Key Factors Affecting Material Choices

Materials selection for crankshafts is influenced by many factors such as, for example, engine and power output types. In the case of large power engines, the need for increasing tensile strength and fatigue resistance is critical. For smaller engines, cost and machinability might take priority. Other than contradictory demands of cost and machinability, other factors such as operating conditions, range of temperatures, and load cycles have to be considered. For example, engines used in harsh weather may need higher corrosion and heat resistance. The means of manufacturing such as forging, casting, heat treatment, are also determinants of the materials used as some materials function better with some production processes than with others. Cost is a practical constraint as the manufacturers look for a balance in performance and cost. In the end, the materials used should also comply with the industry standards and regulations. Doing this gives assurance to the manufacturers and end users that the materials used are safe and durable.

Crankshaft Materials Conclusion

Choosing the crankshaft materials is a process that requires understanding the requirements and goals as well as the limitations and tradeoffs involved. Each material such as carbon steel, alloy steel, ductile iron, and others, advanced as they may be, present advantages for a particular application and specific operating conditions for the engine. The advancement of engines is matched by the advancement of materials science, progressively paving the way for the higher performance and increased durability of components. Manufacturers fuse understanding of material properties with empirical testing and experience to make the evaluation that best balances the performance and reliability of the engine. Engine manufacturers who strive to offer a competitive and quality product should collaborate with material and component specialists to secure the most advanced tailored solutions that address the specific application requirements and constraints.