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Clean Steel Castings: Exploring the Dynamics

of Producing Clean Steel Castings with

Modern Technology

• Types of inclusion defects

• Cause of inclusion defects

• Effects of inclusion defects

• Defect prevention

Agenda

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Types of Inclusion Defects - The Origins of Inclusions

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• Refractory

• Slag

• Mould

• Products of De-oxidation

• Reoxidation

• Refractory

• Slag

• Mould

Effects of Inclusion Defects - Large Defects

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Poor surface finish

Scrap

Rework

Delayed despatch

Customer rejection

Effects of Inclusion Defects - Small Defects

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A carbon steel casting exhibiting wrinkles caused by

a solid, slightly rigid, oxide film on the liquid metal.

A Ni alloy test bar, showing a typical distribution of

bifilm cracks, opened up by the tensile test

Poor surface finish

Poor mechanical properties

Poor machinability

Customer rejection

Casting Cleanliness is Important

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ICE3 High Speed train

Rated for 330km/hr

2008 train departed Cologne

Drive axle collapses at low speed

Cause - Fatigue failure

Casting Cleanliness is Important

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Examples for non-metallic

inclusions found in the longitudinal

microsection (a/r-plane) close to

the crack initiation area at the

fracture

Chemical EDS analysis of the

inclusions found below the

surface of the broken axle

Mechanisms for controlling steel cleanliness

Molten Steel preparation - Before the steel

enters the mould

• Clean and dry charge

• Clean furnace technology

• Clean ladle and metal flow technology

• De oxidation practice

As the steel enters the mould

• Metal Stream control

• Running system design

• Swirl Gates

• Turbulence control

• Filtration

• Appropriate mould technology

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Clean Ladle Technology

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• Application

– All Silica Base

– Complete Reline 7 Tonne ladle 45 minutes

– Operators value simplicity

• Operation

– 2 Tonne Ladle – 6 fills

– 5 and 7 Tonne - 3 fills

– 15 and 25 Tonne 1 fill

Insulating Board System at Akdas Turkey

• Major Benefits

– Improvement in metal temperature control

• Reduced rate of temperature loss

• More moulds per ladle

– Improved casting cleanliness

• 27% reduction in welding rod consumption

• Reduced upgrading time

• Reduced machining costs

– Improved energy efficiency

• Avoiding ladle preheat (LPG) saved €168000 (2004)

• Other Benefits

– Ladle temperatures much lower

– No heat and noise from ladle preheaters

– No pneumatic hammers

Insulating Board System at Akdas

Indigenous Inclusions

Origins

• Products of De-oxidation

• Products of Re-Oxidation

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Argon Purging

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Benefits

• Separation and floatation of non metal

• Alloy homogenisation

• Temperature homogenisation

Argon has very low solubility in molten steel

De-Oxidation

Typical De-oxidants

• Silicon

• Aluminium

• Titanium

• Zirconium

• Calcium

Outcome

• All form oxides

• All form other compounds to some extent

(nitrides, sulphides etc)

• Non metallics formed will coalesce with sand

and slag to form bigger complex inclusions

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Undertaken in both furnace and ladle.

Actual practice depends on

• Alloy

• Casting Design

• Specification

• Foundry metallurgist

Re-Oxidation

When it occurs

• Furnace Tapping

• Mould Pouring

• Running System

• Mould Filling

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• Ladle Tapping

• Ladle Pouring

• Mould Filling

Re-Oxidation

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83% of inclusions in Steel Castings

arise from re-oxidation

How Filters Work - Flow Control

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The metal has to undertake a tortuous

path through the filter, the metal velocity is

reduced allowing time for inclusion

capture.

Energy is removed from the metal

resulting in turbulence reduction

Non Turbulent fill

enables the

production of

high surface

quality castings

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Real time X-Ray experiments

Plate size: 600x400x60mm

Casting weight: 112kg

How Filters Work - Flow Control

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Side Sprue – No Filter

How Filters Work - Flow Control

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How Filters Work - Flow Control

Side Sprue – With Filter

How Filters Work - Inclusion Removal

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Filters remove inclusions by 3 main mechanisms

• Particle Sieving

• Deep – Bed Filtration

• Cake filtration

How Filters Work - Inclusion Removal

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The front face of a filter after casting, showing

the “caking” effect which traps inclusions.

Sand and slag

Alumina Powder from de-oxidation

THANK YOU FOR YOUR ATTENTION

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