December 1947
Corrosion Corrosion resistance, m e c h a n i c a l properties, a n d some uses of a new h e a t - h a r d e n a b l e 18-8 stainless steel.
by Mars G. Fontana
Τ
HE austenitic stainless steel commonly designated as 18-8S nate from the corrosion standpoint, when or Type 304 is a relatively soft material in the annealed con one considers that Stainless W was de dition, and it can be hardened or strengthened only by cold work veloped primarily for high strength pur poses. ing methods. A steel, with approximately the corrosion resist ance of 18-8, that could be hardened by heat treatment alone Corrosion tests in sea water, salt spray, various atmospheres, hydrogen sulfide gas, would be very desirable, particularly in cases where high strength sulfur dioxide gas, and hot milk indi and hardness and/or resistance to wear, galling, or seizing are re cate no essential differences in cor quired. In addition, the fields of application of this type of ma rosion resistance between Stainless W terial could be greatly expanded because it could be used in and 18-8. The Stainless W did not show susceptibility to intershapes and equipment that are not readily amenable to cold work granular attack in a modified Strauss test (boiling solution of cop ing. In general, cold working is applied to only such shapes as per sulfate and sulfuric acid). Stainless W in the precipitationwire, sheets, tubing, and strip. hardened state is considerably inferior to annealed 18-8S in the Investigations of heat-hardenable or age-hardening 18-8 type boiling 65% nitric acid test; this means, of course, that Stainless steels was begun quite a few years ago, but it was not until re W should not be used in applications involving boiling 65% nitric cently that a material of this type became commercially avail acid. The boiling 65% nitric acid tost does not, however, indi able. The writer recalls obtaining a piece broken from an 18-8 cate the corrosion resistance or applicability of the material for high titanium ingot in 1939 and testing this piece in plant rayon service in other corrosive media, including nitric acid at lower coagulating bath (10% sulfuric acid). This sample practically concentrations and/or temperatures. dissolved, but regular 18-8S showed comparatively little attack. Stainless W is under investigation at the Corrosion Research Tremendous advancements have been made since that time, Laboratory at The Ohio State University. William E. Few however, and a commercial alloy designated Stainless W is being studied this material for his senior thesis in metallurgical engi produced by the Carnegie-Illinois Steel Corporation. This alloy neering, and other students have also investigated this alloy. is also tentatively identified as Type 322 stainless steel. We are interested in the corrosion resistance of Stainless W to The nominal composition of this alloy is as follows: 17% Cr, corrosives that are considered between mild and severe for 18-8— 7 % Ni, 0.7% Ti, 0.2% Al, 0.07% C, 0.5% Si, 0.5% Mn, 0.01% P, or, in other words, media that are in the medium range, more or and 0.01% S. I t could be described as a "starved" 18-8 con less. We are attempting to explore the field in order to find the taining titanium and aluminum with titanium as the principal conditions under which Stainless W and Type 304 could be conhardening agent. In the soft or solution-annealed state it shows a tensile strength of 120-150,000 pounds per square inch, an elongation of 8-14%, and a hardness of 235-270 TABLE I. CORROSION TESTS ON STAINLESS W AND 18-8S Brinell. The material is precipitationCorrosion R a t e for Each 48-Hr . Period, hardened or age-hardened by holding Mils/Year 1 s t at 950° F. or a little higher, and then Material Heat T r e a t m e n t Corrosive Media 2nd 3rd 4th 5 t h Cumulative Type 322 Aged a t 950° F. Boiling 7 5 % HAc 1 0 0 24 0 cooling in air. The hardened material Type 322 A.C. from 1700° F.» 1 0 0 105 0 shows a tensile of 195-255,000 pounds T y p e 304 W.Q. from 1950" F.!> 1 0 0 110 (1 T y p e 304 Air-cooled after 1 hr. 96, 0 .1 0 94 0 per square inch, an elongation of 8-14%, at 1200° F. (sensi tized) and a Brinell hardness of 370 to 460. T y p e 322 Aged at 950° F. 10%, 3 0 % , and 40% 0 0 Stainless W can be produced in cast T y p e 304 W.Q. from 1950° F. 0 HAc at 75° F. 0 or wrought form. The alloy parts could Tyce 322 Aged at 950° F. 10% H2SO4 a t 75° F. « 0 65 2 05 Type 322 Aged a t 950° F. 46 50 "t 2 75 55 Type 322 A.C. from 1700° F. 26 Hardened Stainless W is not as re 7 5 5 5 6 Type 304 W.Q. from 1950° F. 8 47 2 05 42 5 6 70 275 Type 304 Sensitized 13 sistant as annealed 18-8S to severe cor β Air-cooled. rosion conditions, but for the more 6 Water-quenched. c Tests for which only two periods are shown were run for one 48-hour period and a second 120-hour mild services the two materials can be period. considered equivalent as far as corrosion * Average of duplicate tests in 10% H2SO4. is concerned. This situation is fortu 91 A
Corrosion
v& Stokes Microvac Pumps produce and maintain high vacuum within die low micron range, economically and dependably in hard, continuous service. They combine high volumetric efficiency and low power requirements ; are simple in design, rugged in construc tion, fool-proof in opera tion. Six models, 10 to 500 cu. ft. displacement. Bulle tin No. 463.
