Types and uses of iron-based materials

Strictly speaking, steel materials are also iron-based alloys, but engineering usually distinguishes between the two. Iron-based alloys are those in which metallic alloying elements are deliberately added to form a replacement solid solution, and all strengthening effects caused by non-metallic carbon are secondary.
The most typical age-hardening iron-based alloy is a martensitic ageing steel (type 18Ni). Its carbon mass fraction is very low, no more than 0.03%, adding a large amount of Ni, air-cooled to room temperature can obtain slatted martensite, because of the low mass fraction of carbon, martensite strength hardness is not high, but good toughness. In 450 ~ 500 ℃ aging treatment, the alloying elements first in the dislocation of the formation of "gas clusters", and then "gas clusters" as the core precipitation Ni2M, Ni3M (M represents other metal alloying elements) type intermetallic compounds, precipitation strengthening to make the steel Maraging steel has three strengthening mechanisms: precipitation strengthening, solid solution strengthening and phase transformation strengthening (martensite), of which the contribution of precipitation strengthening is the largest. The precipitation strengthening effect comes from: (1) solute atoms to dislocation bias; (2) a large number of small, diffusely distributed, high hardness intermetallic compounds.

Iron-based alloys can be divided into the following categories according to different metallographic organizations.
(1) Martensitic alloy steel
The main hardening element is Cr, there are Si, Mo, Mn, V, W and other strengthening elements, the total amount of alloying elements does not exceed 10%. Coating organization is low carbon martensite, good machinability, coating hardness HRc30?54, impact toughness is excellent, also has good stress fatigue and hot and cold fatigue resistance. Its material made of metal wire and tubular wire submerged arc overlay welding, welding performance is better, not easy to crack. Typical use is between the metal without lubrication rolling or sliding parts. Such as hot rolling work rolls, support rolls, continuous casting machine rolls, guide rolls, straightening rolls and excavator rolls, etc.
(2) High chromium cast iron
This kind of alloy has high hardness, HRc48?60, and has excellent anti-abrasive wear performance. Wear resistance at <200℃ is second only to tungsten carbide hard surface material, but the price is only 1/3 of tungsten carbide material.
High chromium cast iron contains 2% to 6% carbon and 20% to 35% chromium, the main wear-resistant hard phase Cr7C3 in the weld layer, and the matrix organization is martensite and austenite.
High chromium cast iron using electrode or tubular wire bright arc or submerged arc surfacing, surfacing process due to a large number of carbide precipitation, the weld layer produces cracking release the internal stress in the weld layer, and does not affect its use performance. Mainly used for agricultural machinery, mining, coal grinding machine rollers and other medium or severe abrasive wear parts.
High chromium cast iron type self-melting alloy powder, oxyacetylene flame (or plasma) spray welding, coating hardness (HRc50 or more), for non-strong impact of the abrasive wear parts. [2]
(3) Austenitic manganese steel
High manganese steel hard surface material can withstand high impact and slight to moderate abrasive wear, overlay layer non-magnetic, with high toughness, after welding hardness HRc16 ~ 20, after cold hardening can be increased to HRc4448, with different carbon content and change.
High manganese steel contains Mn12% ~ 15% and Cr, Ni, Mo, austenite organization is stabilized with manganese. Welding without gas welding only with electric welding to reduce the heat-affected zone to obtain a rapid cooling of the weld layer. Improper welding will appear martensite phase and lead to weld layer cell crack.
High manganese steel electrode and bright arc welding wire, for serious intermetallic impact and ore on the metal of the surfacing.
(4) martensitic stainless steel
Such combined metal low carbon high chromium martensitic steel. The main component contains C 0.2% carbon and chromium > 12%. Has good overall mechanical properties, hardness HRc50 or so, strength, toughness are very good, can resist the corrosion of the atmosphere and steam, and the ability to resist hot and cold fatigue. The products are available in metallic wire and tubular wire. It is mainly used in medium impact, medium intermetallic wear and medium abrasive wear applications.
Martensitic stainless steel type spray powder, oxyacetylene flame spraying, coating hardness (HB320 ~ 450), used for shaft, piston, plunger and other wear-resistant parts.
(5) light body steel
This alloy contains low carbon (0 ~ 25%) amount of other alloying elements, the organizational structure of pearlite, impact resistance, low hardness (HRc25 ~ 35), with excellent weldability, suitable for overlay welding, mainly used to restore the size of mechanical equipment parts. Such as rolling, sliding or impact load of heavy machinery and equipment rotating shaft, rollers and other parts. Another important use is as overlay welding transition layer