Page 52 - Quick Guide to Welding and Weld Inspection by S.E. Hughes, Clifford Matthews

Materials and Their Weldability

Figure 4.1 Simplified carbon equivalency formula
each material thickness acts as a heat sink and can cool the
weld area more quickly, making it harder and therefore more
susceptible to cracking.
Figure 4.1 shows the formula used to determine the Cev
for a material. As a general guide the following Cev levels
determine the weldability of steels:
. up to 0.4%: good weldability;
. 0.4 to 0.5%: limited weldability;
. above 0.5%: poor weldability.
Classification of steels
Low carbon steel: contains 0.01–0.3% carbon
Medium carbon steel: contains 0.3–0.6% carbon
High carbon steel: contains 0.6–1.4% carbon

Plain carbon steels contain only iron and carbon as main
alloying elements. Traces of other elements such as Mn, Si,
Al, S and P may also be present. It can be seen from the
carbon diagram in Fig. 4.2 that an increase in carbon causes
the ductility of steel to decrease while the tensile strength and
hardness increase. Note also how the maximum tensile
strength of plain carbon steel is achieved at 0.83% carbon
content.
Alloy steels contain alloying elements such as Mn, Mo, Cr
and Ni and are divided into two groups:
. Low alloy steels contain < 7% total of other alloying
elements.
. High alloy steels contain > 7% total of other alloying
elements.

37

Woodhead Publishing Ltd – A Quick Guide to Welding and Weld Inspection
Data Standards Ltd, Frome, Somerset – 17/9/200904QG Welding chap4.3d Page 37 of 48