| Abstract: | Grain refinement improves not only strength but also toughness.Small reaustenized grains were discovered to form along the grain boundaries and lath boundaries in an as rolled high-strength low-alloy (HSLA) steel when heated to double phase region.The number and size of the small reaustenized grains were revealed to depend mainly on temperature in the range of 700 to 760℃.These small reaustenized grains were deduced to form by consuming precipitates.The mechanical property tests showed that they resulted in slight changes to tensile properties.However,the sample heated at 740℃ produced a peak Charpy V-notch (CVN) impact energy of 248J when tested at-30℃.Fractography showed that the facture surface of the 740℃ heated impact sample exhibited the smallest brittle zone away from the notch root and a large dimple zone lay ahead of the notch tip,which demonstrated the highest toughness. |
