EFFECTS OF COPPER, NICKEL AND BORON ON MECHANICAL-PROPERTIES OF LOW-ALLOY STEEL WELD METALS DEPOSITED AT HIGH HEAT INPUT

We studied the effects of copper, nickel and boron on the mechanical p roperties of low-alloy steel weld metals deposited at high heat input (4.8 kJ/mm) by the submerged arc process. The copper and nickel conten ts of the welds were systematically varied within the ranges of 0.03 t o 0.89 wt-% Cu and 0.01 to 1.54 wt-% Ni. In addition, several of these copper and nickel combinations were duplicated with welds containing 36 to 44 ppm B. Tensile testing revealed yield strengths, R(p0.2), in the range from 462 to 546 MPa, and ultimate tensile strengths, R(m), f rom 638 to 869 MPa. The weld metal Charpy V-notch (CVN) data showed a 35 J transition temperature, ITT35J, ranging from -28-degrees to 55-de grees-C. Upon adding boron, patches of intergranular fracture were pre sent on the CVN fracture surfaces. This was particularly true when bor on was added at the higher copper and nickel levels. Qualitative metal lographic examinations revealed the presence of extensive amounts of p articles at the prior austenite grain boundaries in boron containing w elds. Furthermore, adding boron at the higher copper and nickel levels promoted the formation of the MAC (martensite-austenite-carbide) micr oconstituent. Also nickel seemed to promote formation of MAC in reheat ed weld metal. At this high heat input (4.8 kj/mm), additions of coppe r, nickel and boron did not improve the mechanical properties.