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Technical Memo

Special Designs for Heavily Torqued or Loaded Components

There wouldn't be an HMC Difference if we didn't select the best materials for your Replacement Part Designs!

HMC has used Materials made of Special Alloys and or Special Alloy Combinations; Nickel, Chromium, Vanadium, and Molybdenum; since the middle 1980's. That is why our Heavy Torqued and Loaded Forged Steel Products always pass the True Test - The Test of Time.

Our Gears, Pinions, Shafting, and other Critical to Process Products are designed to offer increased Tensile and Yield and Surface Endurance without causing any sacrifice to the materials ability to Deform and Absorb Stress, (See Impact Value Chart below). We often select 4330 Vanadium Modified as a solution to problems and critical applications. 4330 VM provides 100% improved Impact Values over 4340 and 4350. 4330 VM has tested; time and time again at (25 ft-lb) Impact Values at temperatures of Minus 40 Degrees Fahrenheit when 4340 tested at 11 (ft-lbs.) and 4350 tested at (8 ft-lbs.).

4340 or 4350 are very poor material selections when heavy cross section and large diameter shafting components are required because of their candidature for segregation of carbon; caused by slow solidification rates. The below graph illustrates the actual carbon content across a thick cross sectioned forging as compared to the nominal (ladle) carbon content. Near the center of the forging, the carbon level can more than double due to segregation. Once the carbon level exceed 0.7% a condition known as hypereutectoid can occur. When hypereutectoid results; brittle carbides begin to form in the material which invites microcracking of the forging along with decreased mechanical property results. HMC chooses to limit the carbon content of their alloy steels to around 0.30 to 0.35% to prevent this phenomenon. Clearly 4350; at 0.50% carbon and 4340; at 0.40% carbon invites hypereutectoid in heavy cross section or large diameter components.

4330 Graph 1

Since tensile and yield strengths relate directly to surface hardness, the three materials exemplified are essentially equivalent; assuming surface hardnesses are comparable. The primary and distinguishing difference between 4340, 4350, and 4330 VM is ductility; (% of elongation, % of reduction, and toughness); the materials ability to deform and absorb stress; (Impact Values). The below table compares the tensile and impact properties of the three materials at the same hardness. The samples were tested in the transverse direction from a 30" thick disks. 4330 VM provided vastly superior properties.

4330 Graph 2

Open Gearing and other large critical to process mechanical components intended for heavy loading require design by Experience. HMC has that experience. And our Unsurpassed Warranties speak for themselves.



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