3Cr13 (oil quenched at 1000°C, tempered at 580°C) metallographic diagram

MARTENSITE STRUCTURE OF AISI 420/3CR13 STEEL

AISI 420/3CR13 steel is a martensitic stainless steel alloy. It contains 0.3-0.5 Carbon, 13-14.5% Chromium and other minor elements. Martensite is a type of microstructure that forms when a steel is heated to a temperature above the critical temperature and then cooled rapidly. This cooling forms a very hard, brittle structure which is known as martensite.

AISI 420/3CR13 steel undergoes a process known as ‘oil quenching’, in which the steel is heated up to 1000°C and then cooled in oil. This process dramatically increases the hardness of the steel, making it an ideal choice for tools and knives. After oil quenching, the steel is typically then reheated to 580°C, to reduce any residual stresses in the material and also to allow for some additional hardening. This is known as ‘tempering’.

The microstructure of AISI 420/3CR13 steel after oil quenching and tempering is shown in the figure below. The main component of the microstructure is the martensite, which is the white region in the image. The blue regions are areas of soft, untempered, ferrite steel. The edge of the martensite (the black line in the image) marks the transition point between the hard martensite and the soft ferrite.

The martensite structure of this steel is a result of its low carbon concentration, while the presence of chromium and other alloying elements contributes to the overall strength and hardenability of the material. These characteristics make it well-suited to applications that require a high level of wear and corrosion resistance.

The microstructure of the AISI 420/3CR13 steel can be further improved by the addition of other elements, or by heat treatment at different temperatures. Magnetic particle inspection is also used to assess the microstructure, which can help to identify any potential flaws or imperfections in the steel.

Overall, AISI 420/3CR13 steel is a popular martensitic stainless steel alloy, due to its combination of good strength and corrosion resistance. The martensite microstructure produces an extremely hard and tough steel, making it an excellent choice for use in applications such as knives, cutting tools and other precision instruments. With proper heat treatment and observation, the microstructure of this steel can be further improved, resulting in even greater levels of hardness and strength.

AISI 420 (UNS S42000, 13Cr-S) is a martensitic stainless steel that has a relatively high hardenability with good wear resistance and corrosion resistance. It is generally machined with heat treatment and can be heat-treated with a 1000℃ oil quenching and 580℃ tempering. When heated properly and cooled slowly, it can achieve good hardness and impact resistance in various operating temperature ranges.

The AISI 420 (UNS S42000, 13Cr-S) microstructure consists of ferrite and some carbides in addition to free iron and chromium. It exhibits typical ferrite microstructure characteristics, with a grain boundary along the ferrite matrix and some small carbide particles. The ferrite matrix has a very large grain size, accounting for most of the microstructure of AISI 420.

The ultimate tensile strength of AISI 420 (UNS S42000, 13Cr-S) is 500 MPa and the yield strength is 190 MPa. It has an elongation at break of 20%, an Izod impact strength of 322 J/cm2, an HWB of 18~19 HRC, and a Rockwell hardness of 21-41 HRC. The fully heat-treated AISI 420 (UNS S42000, 13Cr-S) can achieve a hardness of about 50 HRC.

AISI 420 (UNS S42000, 13Cr-S) could be used in various industries. It is usually used to manufacture tools, dies and components that require high hardness and wear resistance. For example, it can be used as a cutting tool material, as a mould material and as a wear resistant material in the aerospace, automotive and petrochemical industries.

In conclusion, AISI 420 (UNS S42000, 13Cr-S) is an important martensitic stainless steel. It has a typical ferrite microstructure and can achieve high hardness, good wear resistance and corrosion resistance after heat treatment. Its applications are extensive and it is widely used in the aerospace, automotive and petrochemical industries.