Water Hardened Steels

Question 1

What are hypereutectoid steels and why are they difficult to machine?

Answer 1

Brittle network of pearlite

Question 2

Describe spherization annealing, why is it applied?

Answer 2

Involves heating, then speaking and then cooling (very slowly).
Breaks up the hypereutectoid steel - Cementite and Pearlite

Question 3

What does the presence of Cr and V do within the steel?

Answer 3

Presence of Cr inhibits pearlite formation and therefor increases hardness and hardenability (the ability to form martensite).

Vanadium is often added to inhibit grain growth when austenitzing, this works by forming v4c3 which then pins the grain boundaries, increasing hardness and improving wear resistance.

Question 4

What are characteristics of water hardened tool steels?

Answer 4

High tensile strength and hardness levels.
Low ductility and toughness values.
Very poor hardenability.

Question 5

What is the typical heat testing process?

Answer 5

1. PREHEATING the annealed tool, typically at 670 C.
2. AUSTENITZING (Soaking at high heat).
3. QUENCHING - Quench to hard brittle (martensite) condition.
4. TEMPERING or ANNEALING (drawing to desired hardness).

Question 6

What are the aims of spheridization annealing?

Answer 6

Breaks up the Cementite and pearlite network.
Minimise hardness
Maximise ductility, machinability and softness

Question 7

What are applications of water hardened tool steels?

Answer 7

•Heavy forging hammers, hand hammers.
•Forging dies, bending dies, cutting dies.
•Large blanking tools, boring tools.
•Chisels, scissors, lathe centre
•Watch makers tools
•Engraving tools