As-cast high strength nodular iron with favorable machinability

Abstract

The present invention provides as-cast high strength nodular iron with favorable machinability. The nodular iron alloy and automotive components, such as crankshafts, are provided. The nodular iron alloy may include iron, about 3.3-3.9 wt% carbon, about 0.2-0.5 wt% manganese, about 1.9-2.6 wt% silicon, about 0.15-0.30 wt% copper, about 0.03-0.06 wt% magnesium, about 0-0.02 wt% sulfur, about 0-0.1wt% chromium, about 0-0.05 wt% phosphorus, and / or about 0-0.01 wt% tin. The nodular iron alloy may include a number of graphite nodules, each having a diameter between 15 and 120 micrometers, and thegraphite nodules having a number density of at least 90 per square millimeter. Iron may surround the graphite nodules in an amount of 20-40% of a ferrite microstructure and 60-80% of a pearlite microstructure. The nodular iron alloy may have an ultimate tensile strength in the range of 550 MPa to 680 MPa as-cast and at least 80% nodularity.

Description

Technical field [0001] The present disclosure relates generally to ferroalloys, and more specifically to ductile iron alloys that have as-cast strength desired to obtain good workability, and components made therefrom, such as crankshafts, flywheels, and transmission shafts. Background technique [0002] The typical ductile cast iron used in the crankshaft is provided by a foundry and has an ultimate tensile strength of about 700 MPa to 800 MPa and a microstructured iron or iron alloy part including 5% to 10% ferrite and the remainder of pearlite. Such ductile iron or ductile iron alloy meets the strength requirements of crankshafts, but they are very difficult to machine, and any machining generates residual stress. To alleviate these problems, subcritical annealing is performed to reduce the ultimate tensile strength of ductile iron, resulting in a reduction of the ultimate tensile strength by approximately 17%. However, subcritical annealing adds extra time and cost, and brin...

AI Technical Summary

Problems solved by technology

Such ductile iron or ductile iron alloys meet the strength requirements for crankshafts, but they are very difficult to machine and any machining produces residual stresses

To alleviate these problems, subcritical annealing is performed to reduce the ultimate tensile strength of ductile iron, resulting in a decrease in ultimate tensile strength of approximately 17%

However, subcritical annealing adds additional time and cost, and poses potential material handling issues

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