EFFECT OF THERMAL TREATMENTS ON MECHANICAL PROPERTIES OF 13/4 STEEL WELDMENTS

Abstract

In the present study, investigations have been carried out on the effect of thermal treatments " on the structure, mechanical properties of 13/4 martensitic stainless steel (CA-6NM) of normal composition (%) : C:.0.06 max, Mn: 1.00 , Si :.1.00 max., P:0.04 max., S:0.03 max., Cr: 11.5-14.0, Ni: 3.5-4.5, Mo : 0.4 —1.0, Fe : Balance. This steel is used almost in all hydroelectric power projects in India for the fabrication of turbine parts especially its blades and runners. Due to high silt in the Himalayan region, there is rapid damage of these parts which leads to frequent_ shut downs of power projects. So, the repair welding of these blades are carried out quite often. The work involves development of effective repair welding of these components by studying the effect of various thermal treatments on the mechanical properties of 13/4 martensitic stainless steels. The cast plates of 13/4 martensitic stainless steel (as received from B.H.E.L., Hardwar) were welded by using fixed welding parameters and were given a different pre-and post welding heat treatments. 13/4 STEEL WELDMENTS(SMAW) was carried out on single V-groove of 60° included angle using citochrom 13/4 L 410 Ni Mo (Martensitic Stainless Steel) electrodes and 308 (austenitic stainless steel) electrodes. In the, study using citochrom 13/4 L410 Ni Mo electrodes, the three 13/4 martensitic stainless steel plates were welded. Out of these, two were welded without pre-heat but one is given .post weld heat treatment of 600°C for 4 hours followed by air cooling and other was insulated with asbestos sheet just after welding for 5 minutes, to complete the transformations at slower cooling rate and then P.W.H.T. at 600°C for 4 hours followed by air cooling. The third steel plate was welded with preheating the plate at 75°C for 20 minutes and after welding, P.W.H.T. of 600°C for 4 hours followed by air cooling to room temperature. Prospects of repair welding of under water parts (guide vanes) were also studied by using 308 (austenitic stainless steel) electrodes., baked at 350°C before welding. Electrode composition of 308 grade is Cr: 18-20%, Ni.:.11-12%. Using 308 electrode, multi-pass welding was done with three electrodes without pre-heating and post-heating. Only insulated the welded specimen just after welding with asbestos sheet all around and cool the welded plate upto room temperature. Mechanical properties such as (Hardness, U.T.S., (ductility) and (toughness) were determined and optical microscopy was carried out to study the formation and distribution of various phases. From the present investigations, it was showed that base metal have highest toughness in all the cases except specimen No. 4 in which H.A.Z. and base metal have same toughness. In case of sample No. 1, 2 and 3 the toughness of H.A.Z. was approximately 70% to 80% of the base metal. The percent elongation of specimen No. 1, 2 and 3 were found almost in the same range whereas the percentage elongation of specimen 4 was found highest among all the four samples. It was observed that in the sample No. 1, 2 and 3 there was lowest hardness at the fusion line zone, contrary to it there was highest hardness in the similar region for sample 4. (