The internal and external surface quality of galvanized flat bar is mainly determined by the surface quality and internal structure of the raw material and the production process of the steel strip. The quality of the outer surface of galvanized flat bar is closely related to the surface quality and grinding of the tube billet. The poor surface quality (defective) of the tube billet will eventually be reflected on the finished galvanized flat bar, making the surface quality of the galvanized flat bar poor. Defects on the outer surface of galvanized flat bar are sometimes caused during the pipemaking process. The inner surface defects of galvanized flat bar are either caused by steel quality or caused by improper pipe making process.
The three major factors affecting the cold and brittleness of galvanized flat bar:
1. Solid solution strengthening elements. Phosphorus increases the toughness-brittleness transition temperature, and there are molybdenum, titanium and vanadium; when the content is low, the effect is not large, but when the content is high, the elements that increase the toughness-brittleness transition temperature are silicon, chromium and copper; reduce the toughness-brittleness transition temperature Nickel is the one, and manganese is the one that first decreases and then increases the toughness-brittleness transition temperature.
2. Elements that form the second phase. With the second phase increase, the cold and brittle important element of cold-rolled precision bright steel pipe is carbon. With the increase of carbon content in cold-rolled precision bright steel pipe, the pearlite content in cold-rolled precision bright steel pipe increases, and the average pearlite volume increases by one percent , the ductile-brittle transition temperature increased by 2.2°C on average. Figure 2 shows the effect of carbon content on brittleness in ferritic-pearlitic steel. Microalloying elements such as titanium, niobium and vanadium are added to form dispersed nitrides or carbonitrides, which causes the toughness-brittleness transition temperature of cold-rolled precision bright steel pipes to rise.
3. The grain size affects the toughness-brittle transition temperature, and the toughness-brittle transition temperature increases with grain coarsening. Refining grains reduces the cold and brittle tendency of cold-rolled precision bright steel pipes, which is a widely used method.
