What are delivery status of steel
Steel used in the oil tubular goods will pass through a complex process before leaving factory. According to the different characteristics and use of steel, the final delivery state of the steel is different. Common delivery conditions are: hot rolling treatment, cold stretching treatment, normalizing treatment, annealing state, high tempering state and solid treatment.
Hot rolling treatment
It’s known as hot rolling treatment when steel deliver directly after cooling without special heat treatment. The terminal temperature of hot rolling treatment is between 800℃ and 900℃, after that, it’s generally refrigerated in the air. As a result, the hot rolling treatment is similar to normalizing treatment. The difference is due to the hot rolling termination temperature fluctuated, which is different from strict normalizing temperature, fluctuations in steel microstructure and properties are more than that of normalizing treatment.
Currently, many steel companies apply controlled hot rolling. Because of strict termination temperature and forced cooling measures, delivered steel has higher comprehensive mechanical properties. Covered with a layer of iron oxide, delivered steel with hot rolling treatment has a certain degree of corrosion resistance. The storage requirements of hot rolling steel are unlike to cold stretching, medium-sized steel and thick steel plate can be stored in the open air yard.
Cold stretching treatment
The steel by cold stretching, which is without any heat treatment and direct delivery, is called cold stretching treatment. Compared with hot rolling treatment, cold stretching treatment steel has the features of good surface quality, low surface roughness and higher mechanical properties. However, the surface of steel staying cold-drawn state is not covered with oxide skin and there is internal stress result in corrosion and rusty. What’s more, the packaging and storage of that has higher strict requirements, that it’s generally stored in the warehouse and the temperature and humidity in warehouse should be controlled.
Annealing state
Before leaving factory, the delivery status is called annealing state by annealing treatment. The main purpose of annealing is to improve the organization defects and eliminate internal stress, at the same time, prepare for the later process. Alloy steel, cold heading steel, bearing steel, tool steel, turbine blade steel are commonly used in annealing state to deliver.
Normalizing treatment
Through normalizing before leaving factory, the steel is staying normalizing treatment. Since the normalizing heating temperature is stricter than hot rolling terminated temperature, the performance and organization of steel has stable performance. Compared with steel annealed condition, because of faster speed of normalizing cooling, pearlite in the steel is increasing and lamellar, therefore it has a higher comprehensive cooperation properties and it’s profitable to improve Widmanstaten of low carbon steel and make preparation for further heat treatment.
High tempering state
The steel, which is through high tempering heating treatment before leaving factory, is known as high tempering state. It’s useful to eliminate the internal stress because of the high tempering temperature. Carbon structure and alloy steel can be used in high tempering state to deliver. Some high strength stainless steel, high speed tool steel and high-strength alloy steel, due to the strengthening effect of alloying elements, often carry out a high temperature tempering after quenching in order to assemble carbide and obtain the organization of tempered sorbite. Accordingly, this delivery status of steel has a good cutting performance.
Solid treatment
The delivery condition of the solid treatment is steel carry out solid solution treatment before leaving factory. This state is mainly suitable for the treatment of Austenitic stainless steel before leaving the factory. Usually by solution treatment to obtain single-phase Austenite and create conditions for the further cold working.
