Effect of cold drawing on microstructure and properties of the invar alloy strengthened by carbide-forming elements

Abstract

Invar alloys with both high strength and low coefficient of thermal expansion (CTE) are highly desirable in modern industry. In this paper, cold drawing was applied to wire rods of the invar alloy strengthened by carbide-forming elements for the first time. As a result, the mechanical strength of alloy significantly increased and its CTE value decreased with dramatic cross-section reduction (Z). The sample with the largest cross-section reduction of 89.6% exhibited the maximum tensile strength of 1166 MPa and the minimum CTE value of 4.85 × 10−6/oC in the temperature range of −50 to 100 °C. They are about one times larger and 16.4% lower than those without cold drawing, respectively. Further microstructure observation revealed that cold drawing resulted in an apparent increase in grain boundaries and dislocations and precipitation of the nano-scaled secondary phases like VC, Mo2C and TiN. It is thus the synthetic effect of these factors that improved the mechanical and physical properties of the invar alloy.

Keywords

• Invar alloy
• High-strength invar alloy
• Cold drawing
• Strengthening