Heat treatment for improving the toughness of high manganese ste

Details Heat treatment for improving the toughness of high manganese ste Heat treatment for improving the toughness of high manganese ste

1976-10-08

1977-09-13

Stallard, W.

Metal treatment

Compositions

Heat treating

148 12F, 148 124, 148 36, C21D 714, C22C 3804

Patent

active

040479790

ABSTRACT:
The potent hardenability effect of manganese and its relatively low cost and availability make it an attractive candidate for the production of high strength steels, especially in the range of about 2.0 to 6.0 percent manganese. The main deterent to the use of such high manganese steels has been their poor toughness. This can be improved by producing steels with high purity or with controlled low carbon contents. However, the requirements of high purity and very low carbon tend to offset, to a large extent, the cost advantage of manganese. The instant invention utilizes an intercritical anneal at a temperature just slightly above austenite start temperature (A.sub.s) in order to form retained austenite at the grain boundaries. The steel is heated at temperatures from the A.sub.s to about A.sub.s + 75.degree. C for time periods varying from as little as one minute to 16 hours, the time being generally inversely proportional to the temperature. While this annealing procedure will produce enhanced toughness for high purity steels containing controlled low carbon contents, it will also provide steels containing a combination of high strength (greater than 90 ksi) with a CVN energy absorption value at minus 50.degree. F of greater than 30 ft./lbs. even for steels containing normal impurity levels and conventional carbon contents.

REFERENCES:
patent: 2516125 (1950-07-01), Kramer et al.
patent: 3235413 (1966-02-01), Grange et al.
patent: 3250648 (1966-05-01), Grange et al.
patent: 3423252 (1969-01-01), Grange

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