Steels_ Metallurgy and Applications, Third Edition

Stainless steels 371

provides good resistance to wear. Cook et al. 39 have reported on the performance
of austenitie steels in a number of installations handling coal, coke and ore
and, as well as providing long life compared with low-alloy steels or high-
density polythene, the authors also comment favourably on the flow-promoting
characteristics of Type 304 steel.
For many applications, a 12% Cr steel provides adequate corrosion resistance
and the high martensitic hardness of such material also offers comparable abrasion
resistance to the traditional quenched and tempered low-aUoy steels. Many of the
12% Cr steels used for this type of work are based on Type 420 steel (12% Cr
0.14-0.2%C) and provide hardness levels of 400-450 BHN in section sizes
up to 40 mm thick in the as-rolled condition. Hyflow 420R is an example of
a proprietary 12% Cr steel that is marketed as a corrosion/abrasion-resisting
material and provides the mechanical properties shown in Table 4.18 in the
as-rolled condition. Thus low-carbon material of this type can provide a good
combination of strength and toughness without resort to costly heat treatments.
Metcalfe et al. 4~ have described the development of 8-12% Cr steels for
corrosion/abrasion-resistant applications in South African gold mines. The rock
in which the gold-bearing ore is embedded is extremely hard and causes severe
abrasion problems. In addition, large quantities of water are used to allay dust
and cool machinery. In turn, the water becomes contaminated with acids and
salts from the working environment and, at air temperatures of about 30"C, this
leads to very humid and corrosive operating conditions. The compositions of the
steels developed for use in such situations are shown in Table 4.19.
After oil quenching from 1100*C and tempering at 200"C, the first three
steels in Table 4.19 develop microstructures that are predominantly martensitic
with hardness levels in the range 471-583 HV. Steel 1210 involves an entirely
different approach in that the high manganese and nitrogen contents produce an
austenitic microstructure. However, the austenite is unstable and transforms to
strain-induced martensite under mechanical action in service.

Table 4.18

TS

(N/ram 2)

Mechanical Properties of Hyflow 420R

0.2% PS El (%) 2 mm CVN (J)

(N/ram 2)

Long. Trans.

HV

1520 1050 16 55 16 450

Table 4.19
....
Code

Corrosion/abrasion resistant steels

DIN designation Composition %

C Mn Cr Ni Al N

825
102A
122
1210

X 25 CrNi 8.3 0.25

X 20 CrNiAI 10.1 0.2 1

X 20 CrMn 12.1 0.2 1

X 5 CrMnN 12.10 <0.05 10

8

lO

12

12

0.5

0.17