Question 1

Crankshaft Materials:

Accepted Answer

The steel alloys commonly used in high-strength crankshafts have been chosen in what each designer considers to be the most desirable combination of properties. The nominal chemistry of crankshaft alloys discussed here. Medium-carbon steel alloys are composed primarily of the element iron & contain smalls percentages of carbons 0.25% to 0.45%, describes as "25 to 45 point" of carbons, several A combination of alloying elements, a mixture of which has been carefully designed to produce specific properties in the target alloy, including hardness, surface, and core hardness, ultimate tensile strength, yield strength, endurance limit fatigue strength, ductility, impact resistance, corrosion resistance, temper-inflammatory resistance.

Commonly used alloying elements in these carbon steels are manganese, chromium, molybdenum, nickel, silicon, cobalt, vanadium, and sometimes aluminum and titanium. Each of those elements adds specific properties to a given material. The carbon contents are the main determinant of the ultimate strength & hardness to which such alloys can be heat treated.

Question 2

Crankshaft Heat Treating:

Accepted Answer

The typical heat-treatment process for carbon-steel alloys first alters the structure of the rough-machined part by heating the part to full temperature in an oven to convert it into a face-centered-cubic austenite crystalline structure ('austenitize'). The part stabilizes in a neighborhood of 1550°F to 1650°F, depending on the specific material. Thereafter, the part is removed from the heating oven and rapidly cooled ("quenched") to remove heat from the parts at rates sufficient to convert a large percentage of the austenitic composition into fine-grained martensite.

The desired martensitic post-quench crystalline structure of steel is a high strength, high hardness, the form of iron-carbon solutions. The rate of cooling required to achieve maximums change varies with the hardness of the material, which is determined by the combination of the alloying elements. Deformation and residual induced stress are the two biggest problems involved in heat treatment.

Less severe quenching methods reduce residual stress and deformation. Some alloys (EN-30B and some tool steels, for example) can reach full hardness by air quenching. Other alloys with lower hardness can be quenched in a 400°F molten salt bath. Still, others require polymer-based quenching in oil, and at least hard alloys requiring quenching in water.

Question 3

Forged Crankshafts of Materials:

Accepted Answer

If one was made for your engines, the most commons steel used is 1038. It is largely plain old clean steel with some carbon added for heat-treating purposes. A forged steel crankshaft is generally a good choice for its low cost and high power, especially when purchased. These forged crankshafts will remain in more demanding applications than cast crankshafts but still require some preparation work before they can be used in engine applications.

Again, the first thing we do is to make sure we don't spend time and money on a cracked crankshaft. Further, we remove the stress riser from the rod throw and cross drill the oil hole. Another option, especially attractive to circle tracks racers, is to drill rod throws parallel to the crank axis with the rod or 7/8 holes.

This makes the rod journal hollow and very light, with only minimal loss in strength, and can be done for less than $100. In the end, the forged crankshaft was shot before it could be revved. It also relieves the steel from stress and creates a more stable crankshaft. A forged crankshaft designed this way will survive in all but the most demanding racing environments. A racer can choose which degree of the crankshaft is best suited for their application and budget.

Question 4

Crankshaft Manufacturing Processes:

Accepted Answer

#1. Two-Plane V8 Crankshaft Raw Forging

Many high-performance crankshafts are made by the forging process, in which a billet of a suitable size is heated to a suitable forging temperature, typically in the range 1950 – 2250 °F, and then squeezed and stretched sequentially to the desired size. Or is pressed between the pairs, the billet dies under very high pressure.

These die sets have a concave negative form of the desired outer shape. Shaping complex shapes and/or excessive deformations often requires more than one set of dies. Originally, the two-plane V8 cranks were forged in a single plane, then main journals number two and four were reheated and rotated 90° to move crankpin numbers two and three in a vertical plane. Later developments in forging technologies allowed the forging of straight 2-plane "non-twist" cranks.

#2. Billet Crankshaft Machining

Courtesy of Bryant Racing:- Uppers end of the motorsports spectrum, the crankshafts are manufactured from billets of high-grade alloy steels. Billets crankshafts are fully machined from a round bar ("billet") of the selected material. This method of manufacturing provides extreme flexibility of design and allows rapid changes to a design in search of optimum performance characteristics.

In addition to fully machined surfaces, the billet process makes it easy to locate the counterweight and journal web exactly where the designer wants them to be. The process includes demanding machining operations, particularly with regard to counterweight shaping and undercutting, rifling-drilling main and rod journals, and drilling lubrication passages.

The availability of multi-axis, high-speed, high-precision CNC machining equipment has made the billet-to-billet method significantly cost-effective and enabled extremely precise fabrication combined with precise 3D-CAD and FEA design methodologies. Crankshafts often need little in the way of massaging the latter for balancing purposes.

#3. Built-Up Radial Engine Crank

There is an old argument that forged cranks are superior to billet cranks due to the supposedly smooth grain flow that can be achieved in the forging process. This may be true of some components, but with respect to the crankshaft, the argument fails due to the large dislocations in the material that are required to move the crankpin & counterweight material from the centers of the forging blanks to the outer edge of the part.

Chemistry of Crankshaft Alloys
Materials	AMS	C	Mn	Cr	Ni	Mo	Si	V
4340	6414	0.4	0.75	0.82	1.85	0.25
EN-30B		0.3	0.55	1.2	4.15	0.3	0.22
4330-M	6427	0.3	0.85	0.9	1.8	0.45	0.3	0.07
32-CrMoV-13	6481	0.34	0.55	3	<0.30	0.9	0.25	0.28
300 – M	6419	0.43	0.75	0.82	1.85	0.4	1.7	0.7

Crankshaft Materials | Crankshaft Heat Treating | Forged Crankshafts of Materials | Crankshaft Manufacturing Processes