Question

What is the heat treatment of metals? what is the benefit of it? why and how it's useful?

Please answer in details, please do not write by hand.

Answer 1

Stainless steels are generally heat-treated based on the stainless steel type and reasons for carrying out the treatment. Heat treatment methods, such as stress relieving, hardening and annealing, strengthen the ductility and corrosion resistance properties of the metal that is modified during fabrication or generate hard structures capable of tolerating abrasion and high mechanical stresses.

Heat treatment of stainless steels is mostly carried out under controlled conditions to avoid carburization, decarburization and scaling on the metal surface.

Annealing

Annealing, or solution treatment, is employed for recrystallizing the work-hardened austenitic stainless steels and drawing chromium carbides, precipitated around the work-hardened stainless steels, into the solution. In addition, this treatment removes stresses occurred during cold-working, and homogenizes dendritic stainless steel welds.

Annealing of stainless steels is carried out at temperatures greater than 1040°C, but certain types of steel can be annealed at very controlled temperatures of below 1010°C while considering fine grain size. The process is maintained for a short interval, in order to prevent surface scaling and control grain growth.

Quench Annealing

Quench annealing of austenitic stainless steel is a process of rapidly cooling the metal by water quenching to overcome sensitization.

Stabilizing Anneal

A stabilizing anneal is often carried out following conventional annealing of grades 321 and 347. Carbon present in the composition of these grades is allowed to combine with titanium in grade 321, and niobium in grade 347, during annealing. Precipitation of carbon, in the form of niobium or titanium carbide, occurs by further annealing at temperatures of 870 to 900°C for 2 to 4 h, followed by rapid-cooling, thereby preventing precipitation of chromium carbide.

This treatment can be performed under rigorously corrosive operating conditions or conditions that involve temperatures ranging from 400 to 870°C.

Cleaning

The surface of austenitic stainless steels must be thoroughly cleaned, to eliminate carbonaceous residues, grease and oil, prior to heat treatment or annealing because the presence of residues results in carburization that, in turn, reduces corrosion resistance properties.

Process Annealing

All Ferritic and martensitic stainless steels can be process annealed by heating in the ferrite temperature range, or fully annealed by heating above the critical temperature in the austenite range. Sub-critical annealing can be carried out, usually in temperatures from 760 to 830°C. Soft structure of spheroids and ferrite carbides can be produced by cooling the material at 25°C from full annealing temperature for an hour or holding the material for an hour at the subcritical annealing temperature. Products that have been cold-worked following full annealing can be annealed at subcritical temperatures in less than 30 min.

The Ferritic steel grades retaining single-phase structures throughout the operating temperature range require nothing more than short recrystallization annealing at temperatures of 760 to 955°C.