PROPERTIES OF STRUCTURAL METALS. 39 



Effect of Heating. The changes produced in the physical 

 properties of steel through reheating and chilling by quench- 

 ing are radical ; little less so is the effect produced by anneal- 

 ing, or the tempering of steel by reheating as in shop-work, 

 where the metal, after being heated for rolling or bending, is 

 allowed to cool gradually. 



The average extent of the changes thus produced is shown 

 from the tests made by Mr. H. H. Campbell upon specimens 

 both of Bessemer and open-hearth steels, and recorded as 

 follows : 



" The decrease in ultimate strength by annealing the Bes- 

 semer bars averaged 4175 pounds per square inch in the 

 rounds and 5683 pounds in the flats, while the open-hearth 

 was lowered 5 1 34 pounds in the rounds and 7649 in the flats. 



" In this important and fundamental quality the two kinds 

 of steel are very similarly affected, but in other particulars 

 there seems to be a radical difference which is difficult to ex- 

 plain. The elongation of the Bessemer steel is increased by 

 annealing in every case except two, the average being 1.33 

 per cent., while the open-hearth metal shows a loss in three 

 cases, with an average loss for all cases of 0.21 per cent. This 

 is not very conclusive, but there is a more marked difference 

 in the reduction of area, for in the Bessemer steel there is an 

 increase in the annealed bar in every case varying from 7 to 

 15.18 per cent., while the open-hearth showed an increase in 

 only three cases, the maximum being 2.81 per cent., and a 

 decrease in five cases, the greatest loss being 7.20 per cent." 



The results arrived at by Mr. Campbell after exhaustive 

 tests, comparing the effect upon both Bessemer and open- 

 hearth steels, are as follows : * ' Annealing is useful in removing 

 the strains caused by distortion, for in such cases the gain in 

 safety more than counterbalances the loss of strength, but it 

 may be accepted as a general rule that steel is in its best con- 

 dition when it leaves the rolling-mill; that the shop treatment 



