# Vari Morph Cast Iron—A High IQ Material—Structure, Properties, Ultrasonic Control, Technology and Industrial Application

## TL;DR

Researchers developed a new type of cast iron called Vari-Morph, which has unique properties based on the shape and proportion of graphite precipitates, and they found strong correlations between ultrasonic wave velocity and material properties.

## Contribution

The paper introduces empirical relationships linking ultrasonic wave velocity to physical and mechanical properties of Vari-Morph cast iron, enabling non-destructive material assessment.

## Key findings

- A strong correlation (R > 0.90) was found between ultrasonic wave velocity (CL) and the graphite shape indicator (fK) in Vari-Morph cast iron.
- New empirical relationships were established between ultrasonic wave velocity and properties like thermal conductivity, strength, and fatigue resistance.
- These relationships allow non-destructive evaluation of Vari-Morph cast iron properties using ultrasonic measurements.

## Abstract

Cast iron, whose structure simultaneously contains graphite precipitates in various forms, with controlled proportions of individual forms, has been named “Vari-Morph” (VM) cast iron by the authors. The authors have been researching the properties of such cast iron for many years, and the results are being published successively. This new type of cast iron, not included in national (Polish) or European standards, is intended as a material for special-purpose castings. These castings have unique requirements for a set of properties: physical, mechanical, and functional. VM cast iron is characterized by a set of properties that cannot be achieved when the graphite is uniform in shape. The desired properties of VM cast iron are achieved by controlling the morphology of graphite precipitates and the proportion of individual forms in the structure, rather than by changing the matrix. To quantitatively describe graphite precipitates, a proprietary method for determining the graphite shape indicator (fK) was developed. Graphite precipitate analysis is performed by scanning a microscopic image of the metallographic specimen, and then using Tescan Imaging Software (Tescan ESSENCE™) Unified Control for Imaging and Analysis, each precipitate is described using surface metrology parameters. The final value of the graphite shape indicator (fK) is calculated as a weighted average of all precipitates present in the analysis field. Empirical relationships between the fK indicator and a selected group of physical, mechanical, and functional properties of VM cast iron were determined. Studies have demonstrated a very well-correlated relationship between the fK indicator in VM cast iron and ultrasonic wave velocity (CL). The relationship CL = f(fk) is characterized by a very high correlation coefficient of R > 0.90. In previous publications, the authors presented the relationships between the fK indicator and physical properties such as thermal conductivity (λ), specific density (ρ), strength (Rm), elongation (A5), index quality (IQ), and functional properties such as low-cycle mechanical fatigue resistance (Zc), thermal fatigue resistance (N), and cast iron tightness (H) as functions of the fK index. The study concerned VM cast iron with a ferritic matrix. This work contains new empirical relationships that extend previous studies. The newly developed relationships replace the fk shape indicator with the velocity of the ultrasonic wave determined in cast iron with a specific fK indicator value. This resulted in a number of practical dependencies, including: λ = f(CL); ρ = f(CL); ED = f(CL); Rm = f(CL); A5 = f(CL); IQ = f(CL); N = f(CL); Zc = f(CL); H = f(CL). These relationships allow us to measure the wave velocity in a Vari Morph iron casting (with various forms of graphite) and determine a number of characteristics and properties of the material/iron from which the casting was made. It is possible to assess the suitability of a casting with a specific structure for operation under selected conditions.