Tempering and precipitation hardening High speed toolsteels

[KrisHe]

Hello,

First post here so not sure if this is the right place but I'll ask it anyway.
I'm studying about the production of HSS steels. To make HSS steel you austenize the steel to dissolve the alloys (W, Cr, V, Mo) and then quench the steel to give it a martensite structure.
Next the steel goes through a precipitation treatment at ~600°C to give it the red hardness properties. Now in my course notes they say that the microstructure of HSS steel is 'tempered martensite with fine carbide precipitates'. I'm a bit confused between the difference in tempering and precipitation hardening. I know that tempering is to create a less brittle martensite structure by reducing inner stress and precipitation hardening is to let precipitates form in the microstructure for hardening. Now I get the different effect but don't see the difference in treatment? Aren't both heat treatments for prolonged time at a temperature below A1? So am I right if I say that tempering a structure which has alloying elements that are oversaturated and a martensite matrix it will grow precipitates and temper the martensite thus doing tempering and precipitation hardening in one heat treatment?

 

[EdStainless]

In some of the steels yes, you are tempering martensite and forming a secondary phase at the same time.
In some of the grades there are two separate treatments involved, it depends on what secondary phases(s) you are wanting to form.

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P.E. Metallurgy, Plymouth Tube

 

[blacksmith37]

The 600C is a temper and precipitation of carbides and then transformation of retained austenite.

 

[arunmrao]

High speed tool steels is very complex. During tempering, complex carbides are precipitated and a reduction in retained austenite occurs. Double tempering is followed to reduce retained austenite levels, so that there are no soft spots and also minimize risk of cracking. There is no harm if subzero treatment is adopted .

I have provided 2 excellent references below, other than ASM Handbook.



Heat Treatment, Selection, and Application of Tool Steels 2E Second Edition
by William E. Bryson (Author)

https://www.amazon.com/Heat-Treatment-Selection-Application-Steels/dp/156990376X

Tool Steels, 5th Edition

Front Cover
George Adam Roberts, Richard Kennedy, G. Krauss
ASM International, 1998 - TECHNOLOGY & ENGINEERING - 364 pages

https://books.google.com.ng/books/about/Tool_Steels_5th_Edition.html?id=ScphevR_eP8C&redir_esc=y

"Even,if you are a minority of one, truth is the truth."

Mahatma Gandhi.

 

[Maui]

The secondary hardening response that allows many high-speed steels to possess good red hardness is due to the precipitation of fine alloy carbides on tempering. However, this precipitation process requires that the alloying elements have been dissolved back into the austenite during the austenitization step. It is apparent that quite high austenitization temperatures are required to dissolve the Mo-W-V alloy carbides of high-speed steels. This relationship between alloy content and recommended austenitization temperature is illustrated in Table 11.6 on page 285 of Metallurgy for the Non-Metallurgist, Second Edition, which lists the recommended heat-treating practices for a variety of high-speed and tool steels. It can be seen that the austenitization temperatures increase from values typical of plain carbon and low-alloy steels, approximately 845 °C (1550 °F), all the way up to the extremely high temperatures—reaching 1230 °C (2250 °F)—recommended for the most highly alloyed steels, namely the high-speed steels.

Maui