I have a grade specific query. We are currently using 35 mm dia shaft of 1020 grade steel. We want to upgrade to 4140 steel of same diameter. Researching on google and this forum i found out the ultimate tensile strength of 1020 grade is 710 MPa and UTS of 4140 grade is 1080 MPa. But thats general Strength i want to calculate Torsional strength for 35 mm dia and length of 680 mm for both the grade. how do i make comparison ? Urgently required the solution so thanking all of you in advance....I also read Torsional strength is .6 of UTS but does it apply to all grade of steel ???