Ductile cast iron
Selecting nodular iron by grade, matrix, casting route and test basis, with bounded continuous-cast bar examples and finished-casting acceptance requirements.
Tags: materials, cast-iron, casting, specialty-metals
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Identity and material specification
ASTM A536 states that a test specimen gives no precise quantitative relationship to a casting's local properties, even when both come from the same iron. Agree whether acceptance uses a separate coupon, an attached coupon or a specimen from the casting, and record the sampling location and heat. ASTM A536 scope
Ductile cast iron, also called nodular or spheroidal-graphite iron, contains graphite substantially in spheroidal form. ASTM A536-26, scope
Matrix and grade selection
Dura-Bar describes its 65-45-12 continuous-cast product as nodular graphite in a predominantly ferritic matrix with some pearlite. Its 80-55-06 product uses ferrite and pearlite and is positioned for higher strength and wear resistance than its ferritic grade. These are named producer examples, not guarantees for every casting with a similar designation. Dura-Bar 65-45-12 · Dura-Bar 80-55-06
The producer's carbon-steel comparison brief gives these minimum tensile values and average hardness figures. The elongation basis is 2 inches; hardness is an average, rather than a stated acceptance interval in this comparison. Dura-Bar, ductile iron versus carbon steel technical brief
| Named bar grade | Minimum tensile strength | Minimum yield strength | Minimum elongation in 2 in | Average hardness |
|---|---|---|---|---|
| 65-45-12 | 65,000 psi | 45,000 psi | 12% | 180 BHN |
| 80-55-06 | 80,000 psi | 55,000 psi | 6% | 229 BHN |
The strength/elongation tradeoff matters more than selecting the largest first number. Confirm the actual product and test basis against the order; do not promote a marketing comparison's average hardness to a universal minimum.
Calculated conversion: 65,000 psi × 0.006894757 = 448.2 MPa, and 45,000 psi × 0.006894757 = 310.3 MPa. These are conversions of the named example's values. ASTM A536-26 specifies inch-pound values as standard and treats parenthetical SI conversions as informational; an independently rounded metric number should not silently replace the controlling requirement. ASTM A536-26, units clause
Test specimens and casting sections
A tensile result needs a specimen location and preparation basis. Specify whether acceptance uses a separately cast coupon, an attached coupon or material removed from the part, as required by the governing documents. Record the heat/lot relationship and any processing performed before testing. ASTM's explicit specimen-to-casting limitation is a reason to define this evidence, rather than assume a coupon proves every local section. ASTM A536-26, section 1.2
For a drawing, separate tensile acceptance from hardness, microstructure, soundness and dimensional requirements. If nodularity, matrix balance or carbide limits are functionally important, agree their measurement locations and acceptance criteria with the producer. Do not infer all of them from a satisfactory tensile number.
A housing with thick bosses and thin walls deserves attention to both regions; a machined bar component deserves attention to the stock and final geometry actually used. Neither case is fully described by a generic family property table. Where the design needs impact or fatigue evidence, request the relevant test and conditions rather than interpreting tensile elongation as an impact guarantee.
Heat treatment and ADI are separate decisions
Austempered ductile iron (ADI) has a separate specification, ASTM A897/A897M-22. It covers castings subsequently austempered and includes requirements involving microstructure and mechanical properties. Its scope also asks the purchaser to establish contractual responsibility where casting, machining and heat treatment are performed by different manufacturers. ASTM A897/A897M-22
Do not transfer an as-supplied bar's properties to a heat-treated component or call any hardened ductile iron ADI. Define the required final condition and qualification before selecting the stock, machining sequence and heat treater. Keep dimensional change and final inspection in the process plan.
Dura-Bar's 65-45-12 page notes that quench-hardening can produce different hardness at the outside and core. That illustrates why a surface reading alone cannot establish through-section properties after treatment. The page's process example is not a general heat-treatment instruction for arbitrary castings. Dura-Bar heat-treatment response
For welding or repair, obtain a procedure accepted for the actual casting and service. Define the affected area's inspection and acceptance requirements. A material's tensile grade does not establish that an unqualified repair preserves its local microstructure, dimensions or service performance.
Machining stock and finished-part release
Dura-Bar distinguishes round stock intended to clean up at nominal diameter, with added allowance, from rectangular/square stock cast to actual dimensions without the same added allowance. Verify the applicable stock-allowance table before placing finished geometry inside an as-cast envelope. Dura-Bar stock-size and allowance guidance
The carbon-steel comparison's relative tool-life results used 450 sfm, 0.010 in feed and 0.125 in depth of cut; it warns that process variables and actual size affect results. These comparison conditions are not a recommended universal machining recipe. Dura-Bar comparison brief
Develop machining parameters for the actual grade, stock condition, tool, machine and feature. For sealed or pressure-containing components, state the finished leak/proof-test requirement separately. For cyclic loads, assess the real notches, holes, surfaces and load spectrum. Similar tensile strength to steel does not establish equivalent stiffness, fatigue performance, joining behavior or corrosion resistance.
At release, connect the heat/lot, grade, condition and test record to the actual casting or bar used. Retain approved repair and heat-treatment history with the finished dimensions and required inspection. Resolve substitutions against those linked requirements before machining or assembly.
Source versions
ASTM's publisher pages identify A536-26 and A897/A897M-22; only their publicly available scopes/abstracts are used here. Dura-Bar's live product pages do not display technical revision dates. Its comparison brief prints the identifier 0119, retained as a document code rather than an inferred full revision date. Sources reviewed 2026-11-01, America/Los_Angeles.