Heat Treatment of Steel Castings – How to Improve Strength and Reliability

Table of contents

Why Heat Treatment Matters in Steel Castings

Steel castings leave the mold with internal stresses, non-uniform microstructures, and varying hardness levels. Without proper heat treatment, they may be brittle, prone to cracking, or unable to withstand demanding service conditions.

Heat treatment of steel castings is essential because it:

• Relieves residual stresses from solidification and machining
• Improves mechanical properties such as tensile strength, toughness, and fatigue resistance
• Enhances microstructural uniformity for better reliability
• Meets customer and industry standards (ASTM, ISO, EN)

TXmetal applies tailored heat treatment cycles to match the application—whether for heavy mining equipment, high-pressure pump housings, or energy industry components.

Main Heat Treatment Processes for Steel Castings

Different applications require different treatments. The choice depends on the steel grade, casting geometry, and service environment.

Annealing

• Purpose: Reduce hardness, improve machinability, relieve stresses.
• Typical cycle: Heat to 850–950°C (1560–1740°F), slow furnace cooling.
• Applications: Large housings, pump bodies, low-alloy steel castings.

Normalizing

• Purpose: Refine grain structure, improve strength and toughness.
• Typical cycle: Heat to 900–950°C (1650–1740°F), air cooling.
• Applications: Structural parts, gears, wear-resistant components.

Quenching and Tempering

• Purpose: Achieve high strength with balanced toughness.
• Cycle: Austenitize at 850–950°C → Quench in water/oil → Temper at 500–700°C.
• Applications: Pressure vessels, mining equipment, crane hooks.

Stress Relieving

• Purpose: Remove machining and welding stresses without major microstructural changes.
• Cycle: Heat to 550–650°C (1020–1200°F), hold, slow cool.
• Applications: Precision machined parts, welded assemblies.

Table 1: Common Heat Treatment Processes for Steel Castings

Strength and Toughness Improvements

Heat treatment modifies the microstructure of steel castings—converting coarse pearlite into fine ferrite-pearlite, martensite, or tempered martensite.

• Strength: Quenching and tempering can double the tensile strength compared to as-cast condition.
• Toughness: Normalizing reduces brittleness, providing higher impact energy absorption.
• Hardness: Tempering controls hardness for wear resistance while maintaining ductility.

Example data (ASTM A216 WCB cast steel):

• As-cast tensile strength: ~415 MPa (60 ksi)
• After normalize + temper: 485–620 MPa (70–90 ksi)
• Impact toughness: 20–27 J (Charpy V-notch at room temp)

Standards and Quality Testing

Buyers often require compliance with international standards:

• ASTM A216 – Steel castings for high-temperature service
• ASTM A487 – High-strength steel castings
• ISO 4990 – General requirements for steel castings
• EN 10213 – Technical delivery conditions for steel castings

TXmetal verifies heat treatment results with:

• Hardness testing (HB, HRC)
• Tensile testing (yield, ultimate strength, elongation)
• Impact testing (Charpy V-notch)
• Microstructure evaluation

👉 Reference standards:

ISO 4990 – Steel Castings General Requirements

ASTM A216/A216M – Standard Specification

Case Example – TXmetal Heat Treatment Project

A heavy-equipment manufacturer required high-strength steel castings for an excavator component. The challenge was balancing wear resistance with impact toughness.

Original Issue: The as-cast part had inconsistent hardness and failed impact testing.

TXmetal Solution:

• Applied quench and temper cycle
• Optimized tempering at 620°C (1148°F)
• Conducted full mechanical property verification

Result:

• Yield strength improved by 25%
• Hardness stabilized at 220–240 HB
• Impact toughness exceeded specification requirements

This case demonstrated how proper heat treatment transforms castings into safe, reliable components.

Best Practices for Buyers and Engineers

When evaluating suppliers, buyers should confirm whether the foundry can:

• Provide certified heat treatment furnaces with calibrated temperature controls
• Document treatment cycles with furnace charts
• Perform full mechanical testing (tensile, hardness, impact)
• Meet ASTM/ISO standards for specific grades
• Supply PPAP or FAI reports for critical applications

At TXmetal, we integrate heat treatment into the production line, ensuring that castings are delivered with the right properties for their intended application. Of course, heat treatment delivers the best results when combined with optimized geometry. For design best practices, see our steel casting design guide.