Casting answers & advice.

Q: our customers often ask if there are industry-recognized standards that define ductile iron casting quality. What are the common standards and specifications for ductile iron castings?

Background: Casting buyers and users often ask that foundries produce castings to precise specifications, but this isn't as easy as it sounds. In any one specification, there may be three or more grades of metal and two different U.S. organizations--ASTM and SAE--writing specifications. Additionally, many large casting users add their own criteria and create a unique specification. If foundries do business on an international level, they fall under international specifications and requirements.

With all the differences in ductile iron material specifications, it can be difficult to ensure compliance. This is even more evident when castings are manufactured to several different specifications--some being specific while others are general. Industry-recognized specifications are available from a number of sources (Table 1). Foreign specifications can be referenced to U.S. specifications by checking the ASM publication Worldwide Guide to Equivalent Irons and Steels.

Recommendations: A foundry can begin by determining its production capabilities and specialty. Most ductile iron foundries have the capability to produce several grades of the metal. In addition, each foundry has its own unique alloying requirements and nuances. Foundries must utilize them when producing castings to different specifications. A foundry may not be required to make changes in its operation to produce castings that meet a domestic or foreign specification.

Next, a foundry must decide which specification is required and obtain a copy of the national or international standard from the organization that developed it or the customer. The foundry can examine the specification in relation to its own capabilities and determine whether it can meet the requirements.

Table 1 provides an overview and evaluation of four widely used industry specifications for ductile iron castings. As these specifications are compared, subtle differences are evident. Each specification allows for working specifications to be developed between the casting producer and user. Many customers have their own specifications that may reference one or more of the major specifications.

The information in the column was supplied by the AFS Ductile Iron Research Committee (5-1).

Table 1

Four Industry Recognized Specifications for Ductile Iron

Specification  Summary and Evaluation

ASTM A536      A general specification for ductile
               iron castings. Its main emphasis is
               on the mechanical properties of
               the iron in a standard condition,
               not on the performance of the
               casting. It has no chemical or
               nodularity requirements. All that
               is stated in the standard is,
               "Nodular Iron that is described
               as cast iron with the graphite
               substantially in the spheroidal
               shape and free of other forms."
               ASTM A536 states that no precise
               correlation can be made between
               the properties of a casting and
               those of a test specimen.

JIS GS502      This Japanese specification is
               similar to ASTM in many ways.
               Its main emphasis is on mechanical
               properties, and uses hardness just
               as a reference. There are chemical
               limits only on carbon, sulfur,
               and two grades of silicon (if the
               customer requires additional
               chemical limits, those will be
               addressed in the inspection
               standard supplied by the customer.)
               The major difference with JIS is

               the nodularity requirement and
               calculation, which has a 70%
               minimum nodularity requirement.
               This is lower than that of most
               other specifications.

SAE J434       This specification is a good
               starting point. The scope
               states that this standard
               "covers the hardness and
               microstructural requirements for
               ductile iron used in automotive
               and related fields." The
               appendix provides some general
               information on the application
               of grades for particular service
               conditions.

DIN 1693       This is German specification that
               closley follows the JIS
               specification. Its major emphasis
               is on mechanical properties of the
               iron. The scope states, "Nodular
               iron in which the carbon exists
               almost exclusively in a nodular
               form." This specification also
               is open and leaves the manufacture
               and chemistry up the to supplier.
               Similarly, it contains references
               to test standards and procedures.
               One difference with DIN 1693 is
               that it isolates two ferritic
               grades with impact importance.
               These two grades are designated
               to reflect transition temperatures.
               DIN 1693 has been superseded by
               ISO EN 1563, which is accepted
               throughout Europe. The grades
               remain similar to those in DIN
               1693.