The Influence of Reduction-ratio in the Hot Rolling on the Strength and Toughness of a Quenched and Tempered Steel

The influence oj the reduction-ratio in hot-rolling on the microstmctu re and mechanical /noperties oj quenched and tempered low C-3 ..5° a Ni steel was investigated and the Jollowing conclusions were ob tained.The average r grain size became finer with increasing reduction-ratio but the grains were more elongated in their shape in the rolling direction .With increasing reduction-ratio, the unit crack path (U.c.P .)observed in the fractured sUI/ace oj longitudinal Charpy V-notch s/Jecimell became shorter, while the V.C.P. ill the transverse s/Jecimen changed less evidenti)'.The Jracture appearance transition tem/Jerature in the longitudinal specimen behaved similar(v to that oj V .C. P .with increasing reduction-ratio.The difference in the unit crack path alld the sha/)e oj 'lOn -metaliic ineiusions between longitudinal and transverse directioll brought about the directional difference in the Chmjry transition temperature.Th e ujJ/Jer and lower yield point in the stress-strain curve se/Jarated more a/J/Jreciably with increasing reduction-ratio Jrom 1 to 8.This is due to the Jac t that the inhomogeneity in the cast structure such as micro-segregation was leveled out and consequently the difference oj tensile strength at various locations disappea red.B oth the columnar and equiaxed zones in the cast structure responded similarly to the reduction-ratio with res/Ject to the average r grain size and imjJact properties, but the quanti!.} oj nOll-metallic ineiusi0l7s was more in the equiaxed .:onewith the consequence oj somewhat inJerior ductility in this zone.The orientation oj the reduction with res/Ject 10 the columnar ax"is in the cast st ructure had no appreciable injluence 0' _ the various /) !"O-/)erties.