Torsion bar and method of forming the same

A method of forming a torsion bar having an outer case and a core from a steel alloy bar having a circular cross section and a medium carbon content or a steel bar having similar hardenability characteristics;

• comprising the steps of forming the bar into the desired size and shape with non-circular anchoring means on both end portions thereof, through hardening the bar to a predetermined hardness, case hardening the bar for transforming austenite in the case into martensite which expands inducing a high compressive stress near the surface of the bar with the compressive stresses diminishing radially inward of the surface, retaining the core at a temperature below the transformation temperature for resisting expansion of both the case and the core and for inducing hoop and axial compressive stresses and radial tensile stresses in the case, and presetting the hardened bar by cold working the bar at least twice by applying sufficient torsional stresses on the bar for twisting the bar beyond its initial yield strength causing a redistribution of stresses and inducing residual torsional stresses in the case and in the core in a direction opposite to the direction of the applied torque.

A torsion bar comprising;

• a steel bar having a hardenability characteristic similar to an alloy steel having a carbon content within the range of about 0.28% to 0.06%, said bar including an outer case and a core within the case, said case including a variable composition of martensite and austenite with a high percent of martensite being at the outer surface and diminishing to approximately 80% martensite at the interface between the case and the core, said case having an induced hardness at 0.01 inches below the surface of a minimum of Rockwell C46 and being subjected to induced hoop and axial compressive stresses and radial tensile stresses, said core having a hardness within the range of about Rockwell C20 to C45, said case and core having torsional stresses induced therein which act in a direction opposite to that of the torsional load to be applied to the bar during normal operation.

A torsion bar comprising;

• a steel bar having a body of circular cross section and hardenability characteristics similar to an alloy steel having a carbon content within the range of about 0.28% to 0.60%, said bar including an outer case and a core within the case, said case including a variable composition of martensite and austenite with a high percent of martensite being at the outer surface and diminishing to approximately 80% martensite at the interface between the case and the core, said case having an induced hardness at 0.01 inches below the surface of a minimum of Rockwell C46 and being subjected to induced hoop and axial compressive stresses and radial tensile stresses, said core having a hardness within the range of about Rockwell C20 to C45, said case and core having torsional stresses induced therein which act in a direction opposite to that of the torsional load to be applied to the bar during normal operation.

A torsion bar comprising;

• an alloy steel bar having a body of circular cross section and a carbon content within the range of about 0.28% to 0.60%, said bar including an outer case and a core with the case having a radial depth of between about 25% to 40% of the bar radius, said case including a variable composition of martensite and austenite with a high percent of the martensite being at the outer surface and diminishing to approximately 30% martensite at the interface between the case and the core, said case having an induced hardness at 0.005 inches below the surface of the minimum of Rockwell C52 and being subjected to induced hoop and axial compressive stresses and radial tensile stresses, said core having a hardness within the range of about Rockwell C25 to C40, said case and core having torsional stresses induced therein which act in a direction opposite to that of the torsional load to be applied to the bar during normal operation.