Hot rolled state
After hot rolling or forging, the steel is no longer subjected to special heat treatment, and it is delivered directly after cooling, which is called hot rolling or hot forging. Natural cooling, so the hot rolling (forging) state is equivalent to normalizing treatment. The difference is that the termination temperature of hot rolling (forging) varies from high to low, unlike the strict control of normalizing heating temperature, so the fluctuation of steel structure and performance is larger than that of normalizing. Many iron and steel enterprises adopt controlled rolling. Due to the strict control of the final rolling temperature and the forced cooling measures after the final rolling, the grains of the steel are refined, and the delivered steel has high comprehensive mechanical properties. This is the reason why the performance of non-twist-controlled cold and hot-rolled wire rods is superior to that of ordinary hot-rolled wire rods. The steel delivered in the hot-rolled (forging) state has a certain corrosion resistance because the surface is covered with a layer of oxide scale. The requirements are not as strict as those delivered in the cold-drawn (rolled) state. Large and medium-sized steel and medium-thick steel plates can be stored in the open yard or after being covered with thatch.
Cold drawn
State The state of steel products that have been cold-formed by cold drawing, cold rolling, etc., and delivered directly without any heat treatment, is called cold drawn or cold rolled state. Compared with the hot-rolled (forged) state, the steel in the cold-drawn (rolled) state has high dimensional accuracy, good surface quality, low surface roughness, and high mechanical properties. The surface is not covered by scale, and there is a large internal stress, which is very easy to be corroded or rusted. Therefore, the packaging, storage and transportation of cold-drawn (rolled) steel products have strict requirements, and generally need to be kept in the warehouse. And should pay attention to the temperature and humidity control in the warehouse.
Normalizing state
The steel is subjected to normalizing heat treatment before leaving the factory, and this delivery state is called normalizing state. Since the normalizing heating temperature (Ac3+30~50°C for hypoeutectoid steel, Accm+30~50°C for hypereutectoid steel) is strictly controlled than the hot rolling termination temperature, the structure and properties of the steel are uniform. Compared with the steel in the annealed state, due to the faster normalizing cooling rate, the number of pearlite in the steel structure increases, the pearlite layer and the grain of the steel are refined, so it has higher comprehensive mechanical properties and is conducive to improving The Widmanstatten structure of low carbon steel and the cementite network of hypereutectoid steel can prepare the structure for further heat treatment of finished products. Carbon structural steel and combined structural steel are often delivered in a normalized state. Some low-alloy high-strength steels such as 14MnMoVBRE and 14CrMnMoVB steels also require normalized delivery in order to obtain bainite structure.
Annealed state
The steel is annealed and heat-treated before leaving the factory. This delivery state is called the annealed state. The purpose of annealing is mainly to eliminate and improve the structural defects and internal stress left over from the previous process, and to prepare for the structure and performance of the subsequent process. Alloy structural steel, hardenable structural steel, cold heading steel, bearing Steel, tool steel, steel for steam turbine blades, and cable-shaped stainless heat-resistant steel are usually delivered in the annealed state.
High temperature tempering
State The steel has been heat treated by high temperature tempering before leaving the factory. This delivery state is called high temperature tempering state. High temperature tempering has a high tempering temperature, which is conducive to completely eliminating internal stress and improving plasticity and toughness. Carbon structures, alloy steels, and structural steels with guaranteed hardenability can all be delivered in a high-temperature tempering state. Some martensitic high-strength stainless steels, high-speed tool steels and high-strength alloy steels, due to their high hardenability and the strengthening effect of alloying elements, are often subjected to a high-temperature tempering after quenching (or tempering) to make the steel The medium carbides are properly aggregated to obtain a tempered sorbite structure with coarser carbide particles (similar to the spheroidized annealed structure). Therefore, the steel in this delivery state has good machinability.
Solution treatment
State Steel is solution treated before leaving the factory, and this delivery state is called solution treatment state. This state is mainly suitable for the treatment of austenitic stainless steel before leaving the factory. Through solution treatment, a single-phase austenite structure is obtained to improve the toughness and plasticity of the steel, to create conditions for further cold working (cold rolling or cold drawing), and to prepare for further precipitation hardening.