HOT CRACKING SUSCEPTIBILITY OF BORON MODIFIED AISI-304 AUSTENITIC STAINLESS-STEEL WELDS

The hot cracking susceptibility of welds made on AISI 304 stainless steel modified with from 0.2 to 1.0 wt-%B has been investigated. Varestraint tests showed that the hot cracking susceptibility is high for boron additions of about 0.2%, but is decreased when the boron content is increased to greater-than-or-equal-to 0.5%. Steels containing about 0.2% B were found to have a wide solidification temperature range and their high temperature ductility was low compared with boron free AISI 304 steel and the other boron modified steels. Ferrite precipitation was inhibited in the 0.2%B steels and the formation of low melting point grain boundary films was thereby promoted. Increasing the boron content to greater-than-or-equal-to 0.6% reduces the coefficient of thermal expansion and narrows the solidification temperature range. In addition, crack refilling was observed, resulting in improved hot ductility and high resistance to hot cracking. It is concluded that in structures where weld restraint forces are not high, hot cracking is not likely to occur if boron additions of >0.6% are made to AISI 304 stainless steel. In T-type and Fisco weld cracking tests, in which the weld restraint forces are close to those experienced by actual structural welds, the boron modified stainless steels show a low hot cracking susceptibility which is not significantly different from that of boron free AISI 304 steel.