Weldability of High Strength Martensitic Stainless Steels

Abstract

Influences of the conditions of weld thermal cycle and postweld heat treatment on the notch toughness, tensile properties and crack sensitivity in the HAZ of two high strength (80 kg/mm2 type and 100 kg/ mm2 type) martensitic stainless steels containing Ni, Mo, Nb and Cu were investigated by means of welding thermal cycle simulating method and the slit type cracking test. The results of these tests are sum-marizsed as follows.(1) In the case of 80 kg/mm2 type steel (base metal A), the impact value steeply falls when thermal cycle above 1, 300°C peak temperature is experienced, and recovery of the impact value due to the postheating is little even with postheating at 650°C for 2 hours.(2) In case of the 100 kg, /mm2 type (base metal B; precipitation hardening) steel, the impact value does not almost decrease even though peak temperature of the thermal cycle is changed within the range of Ac1 point-1, 300°C. However, postweld aged at 500°C for 4 hours after exposure to the tehrmal cycle, the impact value drops remarkably when the peak temperature of the thermal cycle exceeds 950°C.(3) In the multipass weld joint tests on two test steels which was carried out under optimum welding procedure and postweld haet treatment as shown in Table 4, satisfactory notch toughness and tensile properties were obtained.(4) In the slit type cracking test, the HAZ cracking can be perfectly prevented when the preheating temperature was higher than 200°C for base metal A and 100°C for base metal B, and holding temperature after welding was at 100°C for each kinds of the test steels and then postheated at 600°C for 10 minutes.