This document discusses various types of ferrous metals and alloys used in manufacturing, including different categories of advanced high-strength steels and their properties. It describes dual-phase steels that have a microstructure of ferrite and martensite, providing improved forming ability. Transformation-induced plasticity steels have a microstructure of ferrite, martensite and retained austenite, enabling high strength. The document also covers free-machining steels, precoated steel sheets, electrical steels, maraging steels used for high strength applications, and steels for high temperature service.

1. Chapter 07: Ferrous Metals
and Alloys
DeGarmo’s Materials and Processing in
Manufacturing

2. Classification of Common Ferrous Metals
and Alloys
Note:
Figure 6-1 Classification of common ferrous metals andalloys.
%Carbon > 2.11 - cast irons; %Carbon < 2.11 - steels

3. Advanced High-Strength Steels (AHSS)
AHSS replaces low carbon and HSLA steels in automotive applications
AHSS is primarily ferrite-phase, soft steels with varying amount of martensite,
bainite or retained austenite – which offer high strength with enhanced ductility
Improved formability
Enable the stamping or hydroforming of complex parts
Higher strength provides improved fatigue resistance
Possibility of weight reduction

4. Types of Advanced High-Strength Steels
(AHSS)
Dual-phase (DP) steels
microstructure of Ferrite and martensite
Improved forming characteristics and no loss in weldability (compared with
HSLA)
High strain-rate sensitivity
The faster the steel is crushed, the more energy it absorbs
A feature to enhance crash resistance in automotive applications
Transformation-induced plasticity (TRIP) steels
Microstructure of Ferrite , hard martensite or bainite and at least 5 vol% of
retained austenite
At higher strains, the retain austenite transforms progressively to martensite,
enabling high work-hardening to persist to greater levels of deformation
Excellent energy absorption during crash deformation

5. Types of Advanced High-Strength Steels
(AHSS)
Complex-phase (CP) steels and martensitic (Mart) steels
high strength with capacity for deformation and energy absorption
CP steels – microstructure of ferrite and bainite with small amount of
martensite, retained austenite and pearlite
Strengthened by grain refinement created by a fine precipitate of Niobium,
titanium or vanadium carbides or nitrides
Mart steels – almost entirely martensite
Other types
Ferritic-bainite (FB) steels
Twinning-induced plasticity (TWIP) steels - (17-24% Mn)
Nano steels - (replace hard phase with nano-size precipitates)

7. Free-Machining Steels
 Steels machine readily and form small chips when cut
 The smaller the chips reduce friction on the cutting tool which
reduces the amount of energy required
 Reduces tool wear
 Free-machining steels carry a cost of 15-20% over conventional
steels
 Carbon steel with addition of S, Pb, Bi, Se, Te or P
 Enhance machinability
 Additions provide built-in lubrications
 sulfur combines with manganese to form soft manganese sulfide inclusions
 Lead – as insoluble particle
 Bismuth - more environmentally friendly than lead
 Ductility and impact properties are reduced

8. Precoated Steel Sheet
 Typical sheet metal processes shape bare steel
followed by finishing (or coating)
 Expensive and time-consuming stages of manufacture
 Precoated steel sheets can also be formed
 Eliminates the post processing finishing operations
 Dipped, plated, vinyls, paints, primers and
polymer coatings can be used
 These coating are specially formulated to
endure the subsequent forming and bending

9. Steels for Electrical and Magnetic
Applications
 Soft magnetic materials can be magnetized by low-
strength magnetic fields
 Lose almost all of their magnetism when the field is removed
 Products such as solenoids, transformers, generators, and
motors
 Materials such as high-purity iron, low-carbon steel, iron-silicon
electrical steels, amorphous ferromagnetic alloys, iron-nickel
alloys and soft ferrite (ceramic material)
 Amorphous metals
 No crystal structure, grains, or grain boundaries
 Magnetic domains can move freely
 Properties are the same in all directions
 Corrosion resistance is improved

10. Special Steels
Maraging Steels
• The term maraging is derived from the strengthening
mechanism, which is transforming the alloy to
martensite with subsequent age hardening.
• Carbon free iron-nickel alloys with additions of
cobalt, molybdenum, titanium and aluminium.
• The common, non-stainless grades contain 17–19
wt.% nickel, 8–12 wt.% cobalt, 3–5 wt.%
molybdenum, and 0.2–1.6 wt.% titanium.

11. • Air cooling the alloy to room temperature from 820 °C
creates a soft iron nickel martensite, which contains
molybdenum and cobalt in supersaturated solid
solution.
• Tempering at 480 to 500 °C results in strong hardening
due to the precipitation of a number of intermetallic
phases, including, nickel-molybdenum, iron-
molybdenum and iron-nickel varieties.
• With yield strength between 1400 and 2400 MPa
maraging steels belong to the category of ultra-high-
strength materials.
• The high strength is combined with excellent toughness
properties and weldability.

12. Applications
• Maraging steel's strength and malleability in the
pre-aged stage allows it to be formed into thinner
rocket and missile skins than other steels, reducing
weight for a given strength.
• Aerospace, e.g. undercarriage parts and wing
fittings.
• Tooling & machinery, e.g. extrusion press rams
and mandrels in tube production, gears.
• Ordnance components and fasteners.

13. Long products for the aircraft industry (Courtesy of Boehler AG, Austria)

14. • Maraging steel production, import, and export
by certain states, such as the United States, is
monitored.
• It is particularly suited for use in gas
centrifuges for uranium enrichment
• Lack of maraging steel significantly hampers
this process. Older centrifuges used aluminum
tubes; modern ones, carbon fiber composite.

15. Special Steels
Maraging steels
Used when extremely high strength is required
Typically also have high toughness
Very-low-carbon steel with 15-20% Nickel and significant amount of Co, Mo, Ti
Steels for High-Temperature Service
Plain-carbon steels should not be used for temperatures in excess of 250°C
Tend to be low-carbon materials (< 0.1% carbon)

16. Summary
The processing of steels determines the final
material properties
Steel’s typically have high strength, rigidity, and
durability
Steel is recyclable
Different alloying elements may be added to
produce known effects to the material