Structure-Properties Correlation in Welded CA-6NM Stainless Steel

Various types of stainless steels are being used for many industrial applications. The martensitic stainless steel CA-6NM is specially used for pumps, impellers and water turbine components. This steel has a very good combination of mechanical as well as microstructural characteristics. However the weldability of this steel is not good. The pre-heating and post-weld treatment is necessary for better properties.

In this paper, the mechanical properties and microstructure of CA-6NM SS welded samples are studied. The correlation between structure and properties of weldments are discussed for SMAW and TIG welding processes. The following welding parameters were used: (1) Welding by SMAW: Filler material-martensitic grade, Current-110 Amp, Voltage-25 Volt, Polarity - DCRP, Speed- 1.2 mm/sec and PHT/IPT-350 ° C, PWHT-600° C/ 4hrs/ FC and (2) Welding by TIG: Filler material -martensitic grade, PHT/IPT-300° C, PWHT-650° C/10 hrs/AC, Retempering -620° C/5hrs/AC, Current-130 Amp, Voltage-12 Volt, Polarity-DCRP, Speed- 2.14 mm/sec and Ar gas pressure- 10 Kg/cm² .

The increase in toughness and ductility is observed in welded samples compared to as cast base metal whereas the hardness and tensile strength was observed lower The hardness in. SMA welded sample at PHT/IPT 350° C are observed 309 HV in parent metal, 348 HV in weld and 371 HV in HAZ after PWHT at 600° C.

The hardness observed in TIG welded samples are as 270 HV in parent, 309 HV in weld and 299 HV in HAZ. These hardness values show lower tensile strength in TIG welded samples than the SI\/IA welded samples. The microstructure shows ferrite in martensite matrix. The studies show that best optimisation of properties can be made by correlation of microstructure and mechanical properties.