TECHNICAL INFORMATIONAnasayfa / Technical Information / Mechanical Properties In Steels
MECHANICAL PROPERTIES IN STEELS
Steel types show different characteristics from each other according to their chemical composition and annealing and heat treatment. These properties can be in electrical, physical, chemical fields. However, the most important feature of steel, which is valid for all types of steel, is the mechanical properties. The most important of these mechanical properties, which vary according to steel types, are tensile strength, yield limit, elongation, shrinkage (section narrowing), impact resistance and hardness.
1- TENSILE STRENGTH: It is the steel's resistance to being pulled apart. The highest tensile force applied to a drawbar of a certain cross-section until it breaks is subtracted from the section of the bar to the initial cross-section. The tensile force applied on the tension rods is accepted as Newton (N), not Kg and is 1kg/mm².
2- YILED POINT: It is the value obtained by dividing the applied force at the point where the elasticity is no longer present (yield point) to the initial cross-section of the drawbar. It is expressed in N/mm². The yield point is not evident in many steels. For this reason, a concept called 0.2 limit has been developed. Accordingly, at the point where the continuous elongation exceeding the elasticity limit reaches 0.2% of its initial length, the applied force divided by the bar cross-section is accepted as the yield limit and marked as Rp 0.2.
3- ELONGATION: The elongation is the ratio of the difference between the length of the drawbar measured at the moment it breaks and the initial length to the initial length and is indicated by %. The larger the length of the drawbar relative to its diameter, the lower the elongation. Therefore, the length of the tension rods to be used in the elongation test is generally accepted as (5 d) and the elongation is marked (A5).
4-CONTRACTION: The shrinkage is the ratio of the cross section of the drawbar at the time it breaks to the initial section and is expressed as %.
5-IMPACT RESISTANCE: Impact resistance is the power spent to break a notched bar with a single impact, which is bedded on both sides or bonded on one side. ISO; standardized the test rods, the notches to be drilled and the test method. Impact strength is measured in Joules (J) for pointed notched ISO rods (marked KCU). For round notched ISO rods, the measurement result is given in J/cm².
6-HARDNESS: The resistance of an object against the penetration of a harder object into its body is the hardness of that object. Many objects have created various hardness test methods because they are both elastic and plastic. It is not possible to compare the hardness of objects that are not of the same type with each other. Hardness testing methods are mainly as follows;
Brinel Hardness (HB): It is obtained by inserting a sphere of diameter D into an object with the force P applied uninterruptedly and without impact. Hardness is reached from the circle diameter of the trace made by the sphere. Sphere diameter and sphere material (steel or hard metal) are selected differently according to the hardness of the object to be inspected. The most commonly used sphere diameters are 10 and 5 mm. A feature of Brinel hardness is that the Brinel hardness number measured in steels multiplied by 0.35 gives approximately the tensile strength of that steel. It is spelled as HB.
Vickers Hardness (HV): Here, instead of a sphere, a four-sided diamond pyramid, whose opposite surfaces are 136° relative to each other, is used. From the pyramid entrance depth, the hardness degree is read according to its own tables and determined by HV.
Rockwell Hardness (HRc): It is a widely used method for determining the hardness degree of especially hard steels. In this method, instead of a sphere and a pyramid, a rounded diamond cone with an angle of 120°; 1/16, 1/8, ¼ diameter spheres are used in mild steels. The hardness is determined according to the entry depth of the cone or sphere and with the help of the tables at hand. Rockwell hardness is denoted by HR.
Shore Hardness (NS): Brinel, Vickers, Rockwell hardness measurements are static methods and are used to measure according to the plastic properties of objects. Shore Hardness examination, which is done by the rebound method, determines the elastic hardness more. In this method, a weight with a rounded diamond tip attached to its tip falls freely on the piece to be inspected from a certain height and bounces back. Rebound height provides a measure of stiffness.
Hardness testing is of great importance in practice. Without damaging the part to be inspected, it provides a very solid judgment on whether they are homogeneous and their possibilities of use.