EFFECT OF SOME ALLOYING ELEMENTS ON WELDABILITY OF LOW ALLOY STRUCTURAL STEELS

Abstract

Nickel, chromium or molybdenum was added singly to a base composition of C 0.14 (0.18 for Mo series only), Mn 1.10 and Si 0.35%. Eighteen heats of small ingots, about 3.5kg in weight, were melted in a high-frequency induction furnace and then rolled into bars of a diameter 16mm.
Tensile and V-Charpy impact tests as well as a simplified weld maximum hardness test
with a taper bar specimen, were made under conditions of both normalizing and water quenching followed by tempering at 650°C. From these test results, the following conclusions were summarized:
1. By Ni addition, the tensile strength was remarkably increased, while the yield strength only slightly, especially in quenched and tempered condition.
2. In the quenched and tempered condition, the addition of Cr was very effective to improve the mechanical properties, increasing the tensile strength and decreasing the reduction of area and elongation.
3. Mo increased tensile and yield strengths greatly both in normalized and quenched and tempered conditions.
4. The transition temperature in V-Charpy test was lowered by Ni addition up to about 1%, but raised slightly by addition of Ni more than 1%. Cr and Mo considerably increased the transition temperature. Generally, notch toughness was improved more by quenching and tempering than by normalizing.
5. The as-welded maximum hardness was increased only a little by nickel addition less than about 1%, however it was increased as remarkably as in case of Cr or Mo addition.
6. The allowable strength limit of the steels which showed satisfactory weldability, was found to be as follows, provided the element were added singly to the above base composition:
In the normalized condition: