**10. Molybdenum steels**

*Engineering Steels and High Entropy-Alloys*

**50**

**Nb micro-alloyed steels**

Addition of Nb in steels causes

formation of niobium carbide

and niobium nitride which

improves grain refinement, and

retardation of recrystallization

ultimately increases toughness,

strength, formability, and

weldability

**Table 2.** *Basic comparison of different types of micro-alloyed steels.*

**Ti micro-alloyed** 

**Ni micro-alloyed steels**

**Cr micro-alloyed** 

**Mn microalloyed steels**

**Mo micro-alloyed steels**

**W micro-alloyed steels**

**steels**

In the alloying

The presence of

Molybdenum is used

Tungsten is

mainly popular

for providing

high temperature

properties and

hardenability of

steels

in combination with

Ni or Cr or both. Plain

molybdenum steel is

carburized to improve

wear resistance

manganese in

the alloy steel

reduces the

prone to the hot

shortness

steels, chromium

containing more than

5% improves the

corrosion resistance

and high temperature

properties

**steels**

Addition of Ti in

Ni lowers the critical

temperature of steels and

retards the decomposition

of austenite. As a result at

low temperature or room

temperature, austenite

gets stable

steels passives to

acids and minerals

at low temperature

and improves

high temperature

properties

Molybdenum is a little expensive alloying element. It has limited solubility in austenite and ferrite. As a result of which, it is a strong carbide former. Molybdenum is used in combination with Ni or Cr or both. Plain molybdenum steel is carburized to improve wear resistance.

A lot of research has been done in the case of interphase precipitation. In matter molybdenum plays significant roles. Four steels were manufactured with identical composition, and Ti, V, Mo, and N content is added to investigate the effect of composition on interphase precipitation. Alloys were rapidly cooled from the single austenite phase field and isothermally transformed at 630°C and 650°C for 90 min. When Mo is added, then there is a significant reduction in the austenite to ferrite transformation kinetics, particularly in the case of V steels. Interphase precipitation was observed in all alloys at both transformation temperatures. In the case of the Ti-bearing steel, two types of precipitate were observed, namely, TiC (finer) and Ti2C (coarser), while for the V-bearing steels, VC (finer) and V4C3 (coarser) were observed. Where Mo was present in the alloy, it was found dissolved in all carbide types. The (Ti,Mo)C and (V,Mo)C were formed by classical planer interphase precipitation (PIP), while the (Ti,Mo)2C and (V,Mo)4C3, which had a much wider row spacing, were formed through curved interphase precipitation (CIP). Each adopted one variant of the Baker-Nutting orientation relationship. The Ti-micro-alloyed steels undergo the smallest precipitates of all the steels, which were approximately the same size irrespective of whether Mo was present in the alloy and irrespective of the transformation temperature. However, the addition of Mo to the V-bearing steels causes significant increase in precipitate volume fraction and a reduction in precipitate size.
