Steels_ Metallurgy and Applications, Third Edition

Stainless steels 311

2. Improved tempering resistance and toughness via balanced additions of molyb-
   denum, vanadium and nickel.

Type 410 (12% Cr, 0.1% C) is probably the most popular grade in the marten-
sitic series and is used in a wide variety of general engineering applications in
both the wrought and cast condition. In Type 420, the carbon content is raised
to about 0.3% to provide increased hardness and is typical of the steels used
in cutlery. Type 416 and 416Se are free cutting versions of 12% Cr steel and
contain additions of 0.15% S min. and 0.15% Se min. respectively in order to
provide improved machining characteristics.
During the 1950s, a considerable amount of work was carried out on the devel-
opment of high-strength 12% Cr steels, particularly in relation to the requirements
of the power generation industry for improved steam turbine bolting and blading
materials. Two publications from that period by Irvine et al. 5 and Irvine and
Picketing ~ still serve as classic texts on the metallurgy of high-strength 12% Cr
steels. In the solution-treated condition (1050~ AC), a 12% Cr 0.1% C steel
develops a tensile strength of about 1300 N/ram 2 and must be tempered in order
to achieve a good combination of strength and toughness. Depending on the
strength requirement, 12% Cr steels are tempered at temperatures up to about
675~ and the above authors adopted the temperature-time parameter approach
to demonstrate the effects of alloying elements on the tempering behaviour. An
example is shown in Figure 4.8 for a 12% Cr 0.14% C steel, the tempering
parameter being T(20 + log t) x 10 -3 where T is the temperature in ~ and t the
time in hours. Detailed electron metaUographic studies revealed the following
changes during the tempering of the steel:

500

450

4OO

Z

13- 350

300

25o

200

150

.... .g,~ d~ -.. Init!alhardness --

3OO o C ~ ~ o300 C

• 350oc ~ ~ o 350~
  400oC ~ ~. 400oc
  450~ ~- a 450oc
  _ ~ v 500oc
  v~ .550oc
  v 600oc


• v~ 9 650~
  "~. 9 7oooc
  soooc oo,, soo ';:i c
  600~ = ................ ~


• 650oc -= ......... ~ .... :
  700oc : 9 ., =
  ,I .I , I. I I I I. I 750~C= |i:. i = .1
  11 12 13 14 15 16 17 18 19 20 21 22 23
  T (20 + Log t) x 10-3

Figure 4.8 Tempering curve for 0.14% C 12% Cr base steel (After Irvine et al. ~)