Page 159 - Manufacturing Engineering and Technology - Kalpakjian, Serope : Schmid, Steven R.

Chapter 5 Ferrous Metals and Alloys: Production, General Properties, and Applications

Titanium improves hardenability; it deoxidizes steels.
Tungsten has the same effects as cobalt.
Vanadium improves strength, toughness, abrasion resistance, and hardness at
elevated temperatures; it inhibits grain growth during heat treatment.
Zirconium has the same effects as cerium.

5.5.2 Residual Elements in Steels
During steel production, refining, and processing, some residual elements (trace ele-
ments) may remain. Although the elements in the preceding list also can be considered
as residuals the followin g g enerall are considered unwanted residual elements:
> Y
Antimony and arsenic cause temper embrittlement.
Hydrogen severely embrittles steels; however, heating during processing drives
out most of the hydrogen.
Nitrogen improves strength, hardness, and machinability; in aluminum-
deoxidized steels, it controls the size of inclusions. Nitrogen can increase or
decrease strength, ductility, and toughness, depending on the presence of
other elements.
Oxygen slightly increases the strength of rimmed steels; it severely reduces
toughness.
Tin causes hot shortness and temper embrittlement.

5.5.3 Designations for Steels
Traditionally, the American Iron and Steel Institute (AISI) and the Society of
Automotive Engineers (SAE) have designated carbon and alloy steels by using four
digits. The first two digits indicate the alloying elements and their percentages, and
the last two digits indicate the carbon content by weight.
The American Society for Testing and Materials (ASTM) has another designa-
tion system, which incorporates the AISI and SAE designations and includes stan-
dard specifications for steel products. For ferrous metals, the designation consists of
the letter “A” followed by a few numbers (generally three). The present numbering
system is known as the Unified Numbering System (UNS) and has been adopted
widely by ferrous and nonferrous industries. It consists of a letter indicating the gen-
eral class of the alloy, followed by five digits designating its chemical composition.
Typical letter designations are as follows:
G-AISI and SAE carbon and alloy steels
]-cast steels
K-miscellaneous steels and ferrous alloys
S-stainless steels and superalloys
T-tool steels
Two examples are G413OO for AISI 4130 alloy steel and T30108 for AISI A-8 tool
steel.

5.5.4 Carbon Steels
Carbon steels generally are classified by their proportion (by weight) of carbon con-
tent. The general mechanical properties of carbon and alloy steels are shown in