Describe the behaviour of steel as it responds to increasing applied torque?

It would be same as in the case of a tensile stress, with increase in torque in the proportional limit, shear stress would be equal to the shear strain and then would lead to the yielding shear stress and then to the ultimate stress and then the fracture of the specimen.As in the case of brittle materials the would be a little complex than the ductile material.