Influence of fill thickness on tensile perfomance of 300M high strength steel following laser metal deposition repair

Laser metal deposition (LMD) presents a novel method for the repair of high value aerospace components as cracked or wear damaged areas may be locally removed and replaced with fresh materials. To better understand the influence of the extent of repair on mechanical performance, tensile specimens of 300M high strength steel were repaired using LMD to account for 10%, 20%, and 40% of the total cross section depth, with 420SS used as the feed material. LMD repair provided significant improvements to strength compared to the grind-out condition, with greater benefit for larger fill thicknesses. The repaired ultimate tensile strength (UTS) decreased from 1900 to 1750 MPa as the fill thickness increased from 10% to 40%. This was in line with the increasing proportion of 420SS, as this steel has a lower UTS (1360 Mpa) compared to 300M (2000 MPa), with the repaired samples showing typical composite behavior. Brittle martensite in the upper layers of the deposit caused ductility to drop from 13% to below 3% following repair. In situ tempering eliminates untempered martensite in the heat-affected zone and lower layers of the deposit, with hardness in the tempered region ranging from 425 to 550 HV, compared to 600 HV in the substrate and 650 HV in the untempered region. The softest regions of the deposit have the greatest influence over the yield strength, while the UTS is governed by the average strength over the entire region.