High Speed Steels (HSS)/ tool steels and specialty alloy making 68-85

Question 1

69. What does HS2-10-1-8 stand for?

Answer 1

Chemical composition: 2wt% of W; 10wt% of Mo; 1 wt% of V; 8wt% of Co

Question 2

72. What challenges do the high Carbon contents in tools steels pose in terms of their solidification microstructures?

Answer 2

High carbon content leads to the formation of coarse primary carbide network (?) which is unwanted.

Question 3

73. How are coarse, primary carbides in a tool steel refined (more than one correct answer)?

Answer 3

Hot forming to crush the coarse primary carbide (often have linear distribution which might not ideal)
Remelting so that there is always only a small melt bath present in the system and hence less segregation occurs

Question 4

75. What happens at the microstructural level during austenitisation of a tool steel? What are the consequences of a too high or too low austenitisation temperature?

Answer 4

Austenitisation occurs at high temperature (1150-1200) to partially dissolve coarse primary carbide so solutes (carbide forming elements) can be put back in solid solution which later used to form nano-scaled secondary carbide during tempering.
Too high: we get larger grains and part of the microstructure might be melted which precipitates as unwanted coarse primary carbide upon cooling.
Too low: Get fine grains but do not have enough dissolution of primary carbides

Question 5

78. Why are tool steel makers seeking to develop new tool steels with little to no distortion during the final heat treatment?

Answer 5

After final heat treatment, the product is very hard and hence has a high machine cost if machining needs to be done.

Question 6

79. What are the main three advantages of re-melting on the microstructure of a specialty alloy?

Answer 6

better ductility properties, less anistropy –> better mechanical and technological properties