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I.

INTRODUCTION

H A R D E N A B L E low-carbon stainless steels with 16 pct Cr, 5 to 6 pct Ni, and 1 to 2 pct Mo are becoming increasingly popular for their combination of high yield strength and impact resistance and good corrosion resistance, including sulfide stress cracking resistance and easy weldability. ~-6 One of their most attractive properties is the yield strength which can be raised to about 900 MPa by employing appropriate heat treatment. The effect of heat treatment on the yield strength of these steels has been studied by several investigators, j'3'7-9 who employed heat treatments consisting of either normalizing or oil quenching, from 1000 to 1050 ~ followed by single or double tempering treatment. The effect of tempering temperature on yield strength, as documented in several publications, is illustrated by the data given in Figure 1. Although there is considerable scatter of the data points due to differences in composition, austenitizing temperature, and tempering time, a distinct minimum in the yield strength is obtained after tempering between 600 and 700 ~ This minimum is generally ascribed to correspond to the temperature of tempering that produces a maximum amount of austenite retained at room temperature. 3'4 Double tempering is often recommended for this type of steel, a treatment consisting of a first tempering at a temperature in the range of 600 to 700 ~ followed by a second tempering at 400 to 625 ~ The second tempering treatment in the lower temperature range (about 400 ~ further increases the yield strength of the steel to values of up to 1000 MPa, 3'8 presumably by carbide strengthening, while a second tempering in the higher temperature range (600 to 700 ~ reduces the yield strength. The phase reactions associated with various heat treatments of these steels are rather complex, and up to the present, not fully investigated. P. J. GROBNER is Senior Staff Metallurgist, Amax Materials Research Center, 1600 Huron Parkway, Ann Arbor, MI 48105. V. BISS, formerly with Amax Materials Research Center, is now with the Howmet Turbine Components Corporation, Technical Center, 699 Benston Road, Whitehall, MI 49461. Manuscript submitted January 17, 1983. METALLURGICAL TRANSACTIONS A

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TEMPERING TEMPERATURE, C

Fig. 1 - - Effect of tempering temperature on the yield strength of hardenable Cr-Mo-Ni steels. Ref. 1: 0.035C, 16.0Cr, 5.0Ni, l.OMo, normalized 1050 ~ (1925 ~ tempered 4 h. Ref. 3: 0.040C, 16.0Cr, 5.5Ni, 1.0Mo, normalizing temperature and tempering time not given. Ref. 7: 0.025C, 16.5Cr, 5.0Ni, 1.0Mo, oil-quenched from 1000 ~ (1830 ~ tempered 2 h . Ref. 4:

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