All heat treatment processes for cold drawn seamless steel pipes

Heat treatment refers to a metal thermal processing process in which the material is in a solid state and obtained by heating, holding and cooling to obtain the expected structure and properties.

(1) Cold drawn seamless steel pipe annealing: refers to a heat treatment process in which metal materials are heated to an appropriate temperature, maintained for a certain period of time, and then slowly cooled. Common annealing processes include: recrystallization annealing, stress relief annealing, spheroidizing annealing, complete annealing, etc. The purpose of annealing: mainly to reduce the hardness of metal materials, improve plasticity, to facilitate cutting or pressure processing, reduce residual stress, improve the uniformity of the structure and composition, or prepare the structure for subsequent heat treatment, etc.

(2) Normalizing cold-drawn steel pipes: refers to a heat treatment process in which steel or steel parts are heated to 30 to 50°C above Ac3 or Acm (the upper critical point temperature of steel), maintained for an appropriate period of time, and then cooled in still air. The purpose of normalizing: mainly to improve the mechanical properties of low carbon steel, improve the machinability, refine the grains, eliminate structural defects, and prepare the structure for subsequent heat treatment.

(3) Quenching of seamless cold-drawn steel pipes: refers to heating steel parts to a temperature above Ac3 or Ac1 (lower critical point temperature of steel), maintaining it for a certain period of time, and then using an appropriate cooling rate to obtain martensite (or Bainite) structure heat treatment process. Common quenching processes include salt bath quenching, martensitic graded quenching, bainite isothermal quenching, surface quenching and partial quenching. The purpose of quenching is to obtain the required martensitic structure of the steel parts, improve the hardness, strength and wear resistance of the workpiece, and prepare the structure for subsequent heat treatment.

(4) Cold drawn steel pipe tempering: refers to the heat treatment process in which the steel parts are hardened, then heated to a temperature below Ac1, kept for a certain period of time, and then cooled to room temperature. Common tempering processes include: low temperature tempering, medium temperature tempering, high temperature tempering and multiple tempering. The purpose of tempering: mainly to eliminate the stress generated by the steel parts during quenching, so that the steel parts have high hardness and wear resistance, as well as the required plasticity and toughness.

(5) Cold drawn steel pipe quenching and tempering: refers to the composite heat treatment process of quenching and tempering steel or steel parts. Steel used for quenching and tempering treatment is called quenched and tempered steel. It generally refers to medium carbon structural steel and medium carbon alloy structural steel.

(6) Chemical heat treatment of cold-drawn steel pipe: refers to a heat treatment process in which metal or alloy workpieces are placed in an active medium at a certain temperature for insulation, so that one or several elements can penetrate into its surface layer to change its chemical composition, structure and properties. Common chemical heat treatment processes include: carburizing, nitriding, carbonitriding, aluminizing, boronizing, etc. The purpose of chemical heat treatment: mainly to improve the hardness, wear resistance, corrosion resistance, fatigue strength and oxidation resistance of the steel surface.

(7) Solid solution treatment of cold drawn steel pipe: refers to a heat treatment process in which the alloy is heated to a high temperature and maintained at a constant temperature in the single-phase zone, so that the excess phase is fully dissolved into the solid solution and then rapidly cooled to obtain a supersaturated solid solution. The purpose of solid solution treatment: mainly to improve the plasticity and toughness of steel and alloys, to prepare for precipitation hardening treatment, etc.

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