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SOLUTIONS: Unalloyed/low alloyed steel

Introduction

Steel can be generally classified as an alloy of Ferrum (Fe), better known as iron, and carbon (C). Iron is the main component in most types of steel. Steel is classified in three grades: – Unalloyed steel (containing up to 1% alloy elements). This type of steel is also termed mild steel, carbon steel and carbon manganese steel.

– Low alloy steel (containing 1–5% alloy elements).

– High alloy steel (containing more then 5% alloy elements). Alloy elements are metals such as manganese (Mn), silicon (Si), chrome (Cr), nickel (Ni), molybdenum (Mo). Carbon is not an alloy element.

Unalloyed steel

Often referred to as carbon steel, mild steel or black steel. On board a ship, unalloyed steel will usually be found in the superstructure.

Angle iron, flat iron and rod iron are usually in unalloyed steel. A common composition of this type of steel is as follows (%): Fe

C

Mn

Rest

0.18

0.60

Si

S

P

0.30

0.03

0.03

Use the following Unitor filler materials for welding unalloyed steel: GPO, GPR, LH, LHV, MS, IMS, SPECIAL

Low alloy steel

Low alloy steel includes construction steel, ship quality steel (sometimes referred to as high tensile steel), heat resistant steel, low temperature

steel, weather steel, and tool steel. On board a ship we find this type of steel in hullplates, frames, deck plates, deck beams and bulkheads. A common composition of this type of steel is (%): C

Mn

Si

0.18

1.30

0.40

Al

P

S

0.057

0.02

0.03

2.04

Higher strength filler materials must be used for welding low alloy steel. Use: SPECIAL, LH, LHV, LHT, LHL, LHR, ICROMO, TENSILE, GPS.

If there is doubt as to whether steel to be welded is unalloyed or low alloy, higher strength filler materials should always be used. They should always be used for welding the following components (including components in unalloyed steel): –Lifting equipment subject to heavy loads. Lifting lugs and other parts subject to sudden loads.

– Parts which are subject to heavy vibration (pipes, engine mountings, etc.)

– Welding deck equipment in position (winches, cranes, etc.). – Welding cast steel (important). To differentiate between cast steel and cast iron, see the section on identification of metals.

Heat resistant steel

Heat resistant steel is a low alloy steel, alloyed with a certain percentage of molybdenum (Mo) and sometimes also chromium (Cr). The addition of these alloying elements imparts heat resistant characteristics and the steel retains its strength at 53