Approved for public release; distribution is unlimited / The high strength low alloy (HSLA) steels which are being developed as replacements for the HY family of steels ire low carbon steels which derive their strength in part due to the precipitation of fine coherent copper particles formed during a quench and aging heat treatment. HSLA- 100 is being developed to meet the strength and oughness requirements of HY-100 but can be easily welded without preheat, thereby reducing fabrication costs. This investigation uses light and electron microscopy for microstructural characterization while tensile, Charpy, ind hardness tests are relied upon for the mechanical properties. The microstructure and mechanical characteristics }f HSLA- 100 after aging at several different temperatures was correlated. A high ductility and the minimum 100 csi yield strength was found after aging at 675 C, although this temperature was found to be close to the low jutectoid temperature displayed by HSLA- 100. Splitting was observed in the tensile fracture surfaces but the nechanical properties were not adversely affected. / http://archive.org/details/effectofagingtre00hein / Lieutenant, United States Navy

Approved for public release; distribution is unlimited / The US Navy is currently developing a new family of high-strength , low-alloy steels which derive a significant portion of their strength from copper precipitation. These highly weldable steels require little or no preheat. resulting in substantial cost savings. The first of these steels. HSLA-80, has been certified for ship construction, but recent studies have indicated some susceptibility to stress relief cracking in weldments. HSLA-100, a modification of HSLA-80, is now being considered for several higher-strength naval structures. Stress-relief cracking has not been studied previously in this steel and is the subject of investigation in this work. The steel weldments were loaded below their yield strength, heated to temperatures of 550°-650° C, and permitted to stress relieve for one hour. At all temperatures, the steel exhibited susceptibility to stress relief cracking in certain stress ranges. Optical and scanning electron microscopy exhibited intergranular cracking which always traversed the coarse-grained region of the heat-affected zone. Auger and transmission electron microscopy indicated high concentrations of alloying elements at the grain boundaries. Stress-relief cracking was associated with the diffusion of alloying elements to the prior austenite grain boundaries. / http://archive.org/details/stressreliefcrac00mcnu / Captain, Canadian Forces